WI-LAN Inc. v. Alcatel-Lucent USA Inc. et al

Filing 481

MOTION for New Trial CONCERNING THE NON-INFRINGEMENT OF CERTAIN CLAIMS OF U.S. PATENT NOS. 6,088,326; 6,222,819; 6,195,327 AND 6,381,211 by WI-LAN Inc.. (Attachments: # 1 Exhibit A - Trial Transcript (July 9, 2013 Morning Session), # 2 Exhibit B - Trial Transcript (July 11, 2013 Morning Session), # 3 Exhibit C - Trial Transcript (July 11, 2013 Afternoon Session), # 4 Exhibit D - Trial Transcript (July 10, 2013 Afternoon Session), # 5 Exhibit E - PX-1 - U.S. Patent No. 6,088,326, # 6 Exhibit F - PX-2 - U.S. Patent No. 6,195,327, # 7 Text of Proposed Order)(Weaver, David)

WI-LAN Inc. v. Alcatel-Lucent USA Inc. et al

Doc. 481 Att. 6

Exhibit F

Dockets.Justia.com

PX-2

exhibitsticker.com

PLAINTIFF'S TRIAL
EXHIBIT
6:10-CV-521-LED

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u.s. Patent

Feh. 27, 2()()1

US 6,195,327 BI

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Feb. 27, 2(}()1

US 6,195,327 B1

Sheet 2 of 16

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Feh.27,2001

Sheet 3 of 16

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Feh. 27, 2m)1

US 6,195,327 Bl

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Feh. 27, 2001

US 6,195,327 Bl

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US 6,195,327 B1

1

2

CONTROLLING INTERFERENCE IN A CELL
OF A WIRELESS TELECOMMUNICATIONS
SYSTEM

subscriber terminals, communication between a central terminal and a subscriber terminal being arranged to occur over
a wireless link, a plurality of code division multiplexed
channels being provided within a single frequency channel
to enable data items pertaining to a plurality of wireless links
to be transmitted simultaneously within different code division multiplexed channels of said single frequency channel,
the interference controller comprising: an analyser for comparing with predetermined criteria parameters within the cell
indicative of whether the code division multiplexed channels
are subject to interference from signals generated by said
other cells; and a channel controller, responsive to the
analyser, to selectively prevent code division multiplexed
channels from being used in order to reduce the effect of the
interference from said other cells.
By using the above approach, the effects of interference
from other cells can be suppressed, since taking a code
division multiplexed channel out of cOlUmission enhances
the interference rejection of the remaining code division
multiplexed channels. Further, it is not just the effect of
interference from other cells which is reduced, but also the
effect of any internal interference within the cell, such as
multipath i;terference, will also be reduced. Taking a code
division multiplexed channel out of commission may affect
the number of calls that can be handled simultaneously by
the cell but will enable the cell to retain a satisfactory
quality ;vhere no calls are affected to an un'acceptable degree
by outside interference.
In preferred embodiments, a parameter provided to the
analyser is the bit error rate (BER) for signals transmitted
within said code division multiplexed channels, and the
predetermined criteria with which the analyser compares
said BER is a threshold BER valuc identifying a predetermined maximum acceptable BER, the channel controller
being responsive to the analyser indicating that the HER
exceeds the predetermined maximum acceptable BER to
remove a code division multiplexed channel from use. A
BER signal can be provided to the analyzer for each uplink
and downlink communication path, the BER signal giving
an indication of the errors introduced by interfe.rence during
the transmission of a data signal over the particular wireless
linle Hence, for each \vireless link, the analyser can be
provided with information about the interference levels
being experienced on those links.
Further, an additional parameter preferably provided to
the analyser is a grade of service (GOS) signal indicative of
the availability of the code division multiplexed channels,
and the predetermined criteria with which the analyser
compares said GOS signal is a threshold GOS value identifving a predetermined maximum grade of service, the
ch;nnel controller being responsive to the analyser indicating that the GOS signal has excetded the predtltrmined
maximum grade of service to remove a code division
multiplexed channel from use.
Preferably, each subscriber terminal and each modem on
a modem shelf within the central terminal will have a call
control function associated the.rewith. The call control function within an ST will collect information about how readily
the ST is able to acquire an uplink channel for incoming or
outgoing calls, whilst each call control functions within the
CT will monitor how rtadily tht modtms within the CT can
establish downlink channels. Hence, the analyser will in
prefl~rred embodiments receive information indicative of
bow readilv the modems within the CT and each ST is able
to acquire ~hanncls. If the GOS exceeds that which would be
considered acceptable (as indicated by the predetermined
maximum GOS), then the channel controllier can remove a

TECHNICAL FIELD OF THE INVENTION
TI1e present invention relates in general to \"lireless telecommunications systems and more particularly to techniques for controlling interference in a ceJJ of a wireless
telecommunications system.

10

BACKGROUND OF THE INVENTION
A wireless telecommunications system has been proposed
in which a geographical area is divided in to cells, each cell
having one or more central terminals (CTs) for communicating over wireless links ,'vith a number of subscriber
terminals (STs) in the cell. These wireless links are established over predetermined frequency channels, a frequency
channel typically consisting of one frequency for uplink
signals from a subscriber terminal to the central terminal,
and another frequency for downlink signals from the central
terminal to the subscriber terminal.
Due to bandwidth constraints, it is not practical for each
individual subscriber terminal to have its own dedicated
frequency channel for communicating with the central terminal. Hence, techniques need to be applied to enable data
items relating to different communications to be passed over
the same frequency channel without interfering "vith each
other. In current wireless telecommunications systems, this
can he achieved through the use of a 'Code Division
Multiple Access' (CDMA) technique, whereby a set of
orthogonal codes may be applied to the data items to be
transmitted on a particular frequency channel, data items
relating to different communications being combined with
different orthogonal codes from the set.
Signals to which an orthogonal code has been applied can
be considered as being transmitted over a corresponding
orthogonal channel within a particular frequency channel.
Hence, if a set of 16 orthogonal codes are lLsed, 16 orthogonal channels can be created within a single frequency
channel, and hence up to sixteen separate communiccttion
signals (corresponding to sixteen separate wireless links)
can be transmitted simultaneously over the single frequency
channel if different orthogonal codes are applied to each
communication signal.
This reduces interference between signals transmitted on
the same frequency channel in a particular cell, but does not
avoid the prospect of interference from signals generated by
nearby cells that happen to be using the same frequency
channel. This problem is alleviated somewhat by adopting a
deployment arrangement whereby adjacent cells all use
difftrtnl frtqutncy channds. Howtvtr, thtrt art only a
limited number of frequency channels that can be allocated
to the wireless telecommunications system. Hence it is
inevitable, particularly in densely populated areas where
there are many subscriber terminals and thus each cell only
covers a small geographical area, that signals from nearby
cells using the same frequency channel may interfere with
those generated within a cell.

15

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35

40

45

50

55

60

SUMMARY OF THE INVENTION
According to the present invention, there is provided an
interference controller for limiting in one cell the effect of
interference generated by other cells of a wireless telecommunications system, each cell of the wireless telecommunications system having a central terminal and a plurality of

65

WIL-0009825

US 0,195,327 B1

3

4

code division multiplexed channel from use with the aim of
In preferred embodiments, said code division multiplexed
channels are orthogonal channels, a set of orthogonal codes
reducing the effect of interference within the remaining code
being used to create said orthogonal channels.
division multiplexed channels.
In preferred embodiments of the present invention, an
Preferably, the channel controller, upon receipt of a signal
interference controller in accordance with the invention is
from the analyser indicating that a code division mUltiplexed
provided within a central terminal for a cell of a wireless
channel should be removed from use, is arranged to detertelecommunications system, the telecommunications system
mine which code division multiplexed channel is least
having a plurality of cells, and each cell having a central
heavily used, and to remove that code division multiplexed
terminal and a plurality of subscriber terminals, communichannel from use. This ensures that the least number of users
10 cation between the central terminal and a subscriber terminal
are affected bv the removal of the code division multiplexed
in said cell being arranged to occur over a wireless link, a
channel. Ho~ever, it will be apparent that other criteria
plurality of code division multiplexed channels being procould be used by the channel controller to decide which
vided within a single frequency channel to enable data items
channel to remove. For example, the least heavily used
pertaining to a plurality of wireless links to be transmitted
channel may be reserved for priority calls, and hence it may
15 simulLaneously within di.[erent code division multipkxed
not be appropriate to remove that channel from use. In such
channels of said single frequency channel. The provision of
cas\::s, 1ht channtl controlltr might bt arranged to remove
the interference controller within the central terminal
the least heavily used channel that is not handling, or
enables the CT to limit the effect of interference generated
reserved for handling, a priority call. As yet another
by other cells of said wireless telecommunications system.
alternative, it may be acceptable for the channel controller
In such embodiments, the central terminal would typically
not to react to the request from the analyser to remove a 20
further comprise: an orthogonal code generator for providchannel, until such time as a channel is completely free of
ing an orthogonal code from a set of orthogonal codes used
traffic, and to then remove that channel from use.
to create said code division multiplexed channels within the
In preferred embodiments, a plurality of the code division
singh: frequency channt1; a ilrst tncodtr for combining a
multiplexed channels are designated as traffic channels, the 25 data item to be transmitted on the single frequency channel
analyser is arranged to monitor the parameters relating to
with said orthogonal code from the orthogonal code
interference on those traffic channels, and the channel congenerator, the orthogonal code determining the code division
troller is arranged to selectively designate one or more of
multiplexed channel over which the data item is transmitted,
said traffic channels as locked channels which should not be
thereby enabling data items pertaining to different wireless
used in order to reduce the effect of the interference from 30 links to be transmitted simultaneously within different code
said other cells.
division multiplexed channels of said single frequency chanPreferably, if the analyser determines that the BER signal
nel.
is helmv a predetermined minimum HER value, the channel
Viewed from a further aspect, the present invention procontroller is arranged to designate one of said locked chanvides a wireless telecommunications system comprising a
nels as a free traffic channel which can subsequently be used 35 plurality of cells, each cell having a central terminal and a
for data traffic. Hence, if the effect of.interference on the
plurality of subscriber terminals, communication between a
channels is below what would be considered acceptable,
central terminal and a subscriber terminal within a cell being
then the channel controller can add another code division
arranged to occur over a wireless link, a plurality of code
mUltiplexed channel to the pool of traffic channels, thereby
division multiplexed channels being provided within a
improving the GOS.
40 single frequency channel to enable data items pertaining to
Similarly, if the analyser determines that the GOS signal
a plurality of wireless links to be transmitted simultaneollsly
has dropped below a second predetermined minimum GOS
within different code division multiplexed channels of said
value, the channel controller is arranged to designate one of
single frequency channel, at least one cell of the wireless
said locked channels as a free traffic channel which can
telecommunications system comprising an interference consubseqlJently be used for data traffic. If the GOS drops below 45 troller in accordance with the present invention for limiting
a minimum acceptable level, then it is preferable to increase
the effect of interference generated by other cells of said
the number of available channels if possible, but this will
wireless telecommunications system.
tend to adversely affect the BER, since each channel will
In preferred embodiments, the interference controller may
become more susceptible to interference. The analyser in
further comprise a transmission controller for processing
combination with the channel controller will aim to strike a 50 data items to be transmitted over a wireless link connecting
balance where there are sufficient channels to provide an
a central terminal and a subscriber terminal of a wireless
acceptable GOS, but not so many that the interference level
telecommunications system, a single frequency channel
becomes unacceptable on any of the channels.
being employed for transmitting data items pertaining to a
In preferred embodiments, the channel controller is proplurality of wireless links, the transmission controller comvided with a value indicating a maximum number of code 55 prising: an orthogonal code generator for providing an
division multiplexed channels that can be designated as
orthogonal code from a set of 'm' orthogonal codes used to
traffic channels, the channel controller only adding code
create 'm' orthogonal channels within the single frequency
division multiplexed channels upon request from the analychannel; a first encoder for combining a data item to be
ser if doing so would not exceed the maximum number of
transmitted on the single frequency channel with said
code division multiplexed channels.
60 orthogonal code from the orthogonal code generator, the
Prtferably, a number 01 the trallic channels are reservtd as
urthogonal code determining the orthogonal channtl. over
which the data item is transmitted, whereby data Items
call channels, and a number of the traffic channels are
pertaining to different wireless links may be transmitted
designated as free channels, and if a call channel is used to
simultaneously within different orthogonal channels of said
pass call data, the chaunel controller is arranged to designate
a free channel as a call channel if a free channel is available, 65 single frequency channel; an overlay code generator for
providing an overlay code from a first set of 'n' overlay
thereby improving the chance of a call channel being
codes which are orthogonal to each other; and a second
available for a subsequent call.

WIL-0009826

US 6,195,327 Bl

6

5

encoder arranged to apply the overlay code from the overlay
of the orthogonal channel, whereby a plurality of data items
code generator to said data item, whereby 'n' data items
relating to different wireless links may be transmitted within
pertaining to different wireless links may be transmitted
the same orthogonal channel during a predetennined frame
simultaneously within the same orthogonal channel.
period.
Additionally, or alternatively, the interference controller
Additionally, or alternatively, the interference controller
may further comprise a reception controller for processing
may further comprise a reception controller for processing
data items received over a wireless link connecting a central
data items received over a wireless link connecting a central
terminal and a subscriber terminal of a wireless telecomterminal and a subscriber terminal of a wireless telecommunications system, a single frequency channel being
munications system, a single frequency channel being
employed for transmitting data items pertaining 10 a plural- 10 employed for transmitting data items pertaining to a plurality of wireless links, and em' orthogonal channels being
ity of wireless links, the receiver controller comprising: an
provided within the single frequency channel, the receiver
orthogonal code generator for providing an orthogonal code
controller comprising: an orthogonal code generator for
from a set of 'm' orthogonal codes used to create 'm'
providing an orthogonal code from a set of 'm' orthogonal
orthogonal channels within the single frequency channel; a
first decoder for applying, to signals n:ceived on the single 15 codes used to create said 'm' orthogonal channels within the
single frequency channel; a first decoder for applying, to
frequency channel, the orthogonal code provided by the
signals received on the single frequency channel, the
orthogonal code generator, in order to isolate data items
orthogonal code provided by the orthogonal code generator,
transmitted within the corresponding orthogonal channel; an
in order to isolate data items transmitted within the correoverlay code generator for providing an overlay code from
a first set of 'n' overlay codes which are orthogonal to each 20 sponding orthogonal channel; and a TDM decoder arranged
to extract a data item from a predetermined time slot within
other, the set of 'n' overlay codes enabling 'n' data items
said orthogonal channel, a plurality of data items relating to
pertaining to different wireless links to be transmitted simuldifferent wireless links being transmittecil within the same
taneously within the same orthogonal channel; and a second
orthogonal channel during a predetermined frame period.
decoder for applying, to the data items of the orthogonal
By using TDM techniques in addition to a known set of
channel, the overlay code from the overlay code generator so 25
orthogonal codes, it is possible for selected orthogonal
as to isolate a particular data item transmitted using that
channels to be subdivided in the time dimension. For
overlay code.
examplt:, if TDM is used to divide one frame period in to
By using overlay codes in addition to a known set of
four sub frames, and each orthogonal channel is subject to
orthogonal codes, it is possible for selected orthogonal
channels to be subdivided to form additional orthogonal 30 the IDM technique, then up to 64 separate communication
signals can be transmitted on the sixteen orthogonal chanchannels. For example, if there are originally sixteen
nels during one frame period, albeit at a quarter of the rate
orthogonal channels and a set of four overlay codes are
that the communication signals could be transmitted if the
defined, each orthogonal channel being subject to overlay
IDM technique was not used.
codes, then up to 64 orthogonal channels can be defined. By
Such an approach has the advantage that it preserves
application of appropriate orthogonal codes and overlay 35
compatibility with current hardware and software equipment
codes, up to 64 separate communication signals could be
which use the set of orthogonal codes, but which do nol
sent simultaneously on the one frequency channel, albeit at
support the use of TDM techniques. By designating certain
a quarter of the rate that the communication signals could be
orthogonal channels as channels for which TDM is not used,
transmitted if the overlay codes were not used.
Such an approach has the advantage that it preserves 40 the current equipment can communicate over those channels
without any changes being required to the equipment.
compatibility with current hardware and software equipment
In preferred embodiments, the interference controller may
\vhich use the set of orthogonal codes, but which do not
further comprise a channel selection controller for establishsupport the use of overlay codes. By designating certain
ing a wireless link connecting a central terminal and a
orthogonal channels as channels for which overlay codes are
not used, the current equipment can communicate over those 45 subscriber terminal of a wireless telecommunications
system, at least two frequency channels being provided over
channels without any changes being required to the equipwhich said wireless link could be established, the channel
ment.
controller comprising: a storage for storing data identifying
1n another preferred embodiment, the interference conthe at least two frequency channels; a selector for selecting
troller may further comprise a transmission controller for
processing data items to be transmitted over a \vireless link 50 a frequency channel from those listed in said storage; link
acquisition logic for establishing a wireless link on the
connecting a central terminal and a subscriber terminal of a
frequency channel selected by the selector; the selector
wireless telecommunications system, a single frequency
being responsive to the link acquisition logic being unable to
channel being employed for transmitting data items pertainestablish said wireless link, to select an alternative frequency
ing to a plurality of wireless links, the transmission controller comprising: an orthogonal code generator for providing 55 channel from those listed in said storage.
By this approach, it is possible to increase the number of
an orthogonal code from a set of 'm' orthogonal codes used
subscriber terminals that can be supported by the wireless
to create 'm' orthogonal channels within the single fretelecommunications system, since if one frequency channel
quency channel; a first encoder for combining a data item to
is fully used at the time that a wireless link connecting a
be transmitted on the single frequency channel with said
orthogonal code from the orthogonal code generator, the 60 particular subscriber terminal with a central terminal is
required, then another frequency channel can be selected for
orthogonal code determining the orthogonal channel over
the establishment of that wireless link. Formerly this would
\vhich the data item is transmitted, 'whereby data items
not have heen possible, since the subscriher terminal would
pertaining to different wireless links may be transmitted
have: been arranged to only communicate with a central

simultaneously within different orthogonal channels of said

single frequency channel; and a TDM encoder arranged to
apply time division multiplexing (TDM) techniques to the
data item in order to insert the data item within a time slot

65

terminal using one predefined frequency channel.
Viewed from a further aspect, the present invention provides a method of limiting in one cell the effect of interfer-

WIL-0009827

US 6,195,327 Bl
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8

ence generated by other cells of a \-'lireless telecommunicaFIGS. 13A and 13B illustrate the structure of the frames
tions system, each cell of the wireless telecommunications
of information sent over the downlink and uplink paths.
system having a central terminal and a plurality of subFIGS. 14A and 14B illustrate the overhead frame strucscriber terminals, communication between a central terminal
ture for the downlink and uplink paths.
and a subscriber terminal being arranged to occur over a
FIGS. 15Aand 15B illustrate typical downlink and uplink
wireless link, a plurality of code division multiplexed chanchannel structures that might occur in a loaded system in
nels being provided within a single frequency channel to
accordance with preferred embodiments of the present
enable data items pertaining to a plurality of wireless links
invention.
to be transmitted simultaneously within different code diviFIG. 16 illustrates how the available traffic channels are
sion mUltiplexed channels of said single frequency channel, 10
classified in preferred embodiments of the present invention.
the method comprising the steps of: (a) employing an
FIG. 17 illustrates the elements used by the central
analyser to compare with predetermined criteria parameters
terminal to perform interference limiting.
within the cell indicative of whether the code division
multiplexed channels are subject to interference from signals
FIG. 18 illustrates possible antenna configurations that
generated by said other cell'>; and (b) responsive to the 15 can be employed in a wireless telecommunications system in
analyser, selectively preventing code division mUltiplexed
accordance with the preferred embodiment of the present
channels from being used in order to reduce the effect of the
invention.
interference from said other cells.
FIG. 19A and 19B is a block diagram illustrating how
By using the above approach, the effects of interference
channel switching is facilitated in preferred embodiments of
from other cells can be suppressed, since taking a code 20 the present invention.
division multiplexed channel out of commission enhances
DETAILED DESCRIPTION OF THE
the interference rejection of the remaining code division
INVENTION
multiplexed channels.
FIG. 1 is a schematic overview of an example of a
wireless telecommunications system. The telecommunications system includes one or more service areas 12, 14 and
An embodiment of the invention will be described
16, each of which is served by a respective central terminal
hereinafter, by way of example only, with reference to the
(CT) 10 which establishes a radio link with subscriber
accompanying drawings in which like reference signs are
30 terminals (ST) 20 within the area concerned. The area which
used for like features and in which:
is covered by a central terminal 10 can vary. For example,
FIG. 1 is a schematic overview of an example of a
in a rural area with a low density of subscribers, a service
wireless telecommunications system in which an example of
area 12 could cover an area with a radius of 15-20 Km. A
the present invention is included;
service area 14 in an urban environment where is there is a
FTG. 2 is a schematic illustration of an example of a
35 high density of subscriber terminals 20 might only cover an
subscriber terminal of the telecommunications system of
area with a radius of the order of 100 m. In a suburban area
FIG. 1;
with an intermediate density of subscriber terminals, a
FIG. 3 is a schematic illustration of an example of a
service area 16 might cover an area with a radius of the order
ce:ntral tt:rminal of the: tekcommunications system of FIG.
of 1 Km. It will be appreciated that the area covered by a
l'
40 particular central terminal 10 can be chosen to suit the local
FIG. 3Ais a schematic illustration of a modem shelf of a
re:quirements of e:xpe:cte:d or actual subscribe:r density, local
central terminal of the telecommunications system of FIG.
geographic considerations, etc, and is not limited to the
1;
examples illustrated in FI G. 1. Moreover, the coverage need
not be, and typically will not be circular in extent due to
FIG. 4 is an illustration of an example of a frequency plan
45 antenna design considerations, geographical factors, buildfor the telecommunications system of FIG. 1;
ings and so on, which will alIect the distribution of transFIGS. 5A and 5B are schematic diagrams illustrating
mitted signals.
possible configurations for cells for the telecommunications
The central terminals 10 for respective service areas 12,
system of FIG. 1;
14, 16 can be connected to each other by means of links 13,
FIG. 6 is a schematic diagram illustrating aspects of a
code division multiplex system for the telecommunications 50 15 and 17 which interface, for example, with a Pl1blic
switched telephone network (PSTN) 18. The links can
system of FIG. 1;
include conventional telecommunications technology using
FIGS. 7 A and 7B are a schematic diagram illustrating
copper wires, optical fibres, satellites, microwaves, etc.
signal transmission processing stages for the telecommuniThe \vi.reless telecommunications system of HG. 1 is
cations system of FI G. 1;
55 based on providing fixed microwave links between subFIG. 8A and 8B are schematic diagrams illustrating signal
scriber terminals 20 at fixed locations within a service area
reception processing stages for the telecommunications sys(e.g., 12,14,16) and the central terminal 10 for that service
tem of FIG. 1;
area. Each subscriber terminal 20 can be provided with a
FIG. 9A and 9B are diagrams illustrating the uplink and
permanent fixed access link to its central terminal 10, but in
downlink delivery methods when the system is fully loaded. 60 preferred embodiments demand-based access is provided, so
FIG. 10 illustrates the CDMAchannel hierarchy in accorthat the number of subscribers which can be supported
dance with preferred embodiment", of the present invention.
exceeds the number of available wireless links. The manner
in which demand-based access is implemented vi,rill be
FIG. 11 is a schematic diagram illustrating downlink and
uplink communication paths for the wireless communicadiscussed in detail later.
tions system.
65
FIG. 2 illustrates an example of a configuration for a
FIG. 12 is a schematic diagram illustrating the makeup of
subscriber terminal 20 for the telecommunications system of
a downlink signal transmitted by the central terminal.
FIG. 1. FIG. 2 includes a schematic representation of
BRIEF DESCRIPTION OF mE INVENTION

25

WIL-0009828

US 6,195,327 B1
9

10

customer premises 22. A customer radio unit (CRU) 24 is
mounted on the customer's premises. The customer radio
unit 24 includes a flat panel antenna or the like 23. The
customer radio unit is mounted at a location on the customer's premises, or on a mast, etc., and in an orientation such
that the flat panel antenna 23 within the customer radio unit
24 faces in the direction 26 of the central terminal10 for the
service area in which the customer radio unit 24 is located.
The customer radio unit 24 is connected via a drop line 28
to a power supply unit (PSU) 30 within the customer's
premises. The power supply unit 30 is connected to the local
power supply for providing power to the customer radio unit
24 and a network terminal unit (NTU) 32. The customer
radio unit 24 is also connected via the power supply unit 30
to the nelwork lemunal unit 32, which in Lum is connected
to telecommunications equipment in the customer's
premises, for example to one or more telephones 34, facsimile machines 36 and computers 38. The telecommunications equipment is represented as being within a single
customer's premises. However, this need not be the case, as
the subscriber termina120 preferably supports either a single
or a dual line, so that two subscriber lines could be supported
by a single subscriber terminal 20. The subscriber terminal
20 can also be arranged to support analogue and digital
telecommunications, for example analogue communications
at 16, 32 or 64khits/sec or digital communications in accordance with the ISDN BRA standard.
FIG. 3 is a schematic illustration of an example of a
central terminal of the telecommunications system of FIG. 1.
The common equipment rack 40 comprises a number of
equipment shelves 42, 44, 46, including a RF Combiner and
power amp shelf (RFC) 42, a Power Supply shelf (PS) 44
and a number of (in this example four) Modem Shelves
(MS) 46. The RF combiner shelf 42 allows the modem
shelves 46 to operate in parallel. If 'n' modem shelves are
provided, then the RF combiner shelf 42 combines and
amplifies the power of 'n' transmit signals, each transmit
signal being from a respective one of the 'n' modem shelves,
and amplifies and splits received signals 'n' way so that
separate signals may be passed to the respective modem
shelves. The power supply shelf 44 provides a connection to
the local power supply and fusing for the various components in the common equipment rack 40. A bidirectional
connection extends between the RF combiner shelf 42 and
the main central terminal antenna 52, such as an omnidirectional antenna, mounted Oll a central terminal mast 50.
This example of a central terminal 10 is connected via a
point-to-point micro\vave link to a location where an interface to the public switched telephone network 18, shown
schematically in FIG. 1, is made. As mentioned above, other
types of connections (e.g., copper wires or optical fibres) can
be used to link the centrallerminal10 to the public switched
telephone network 18. In this example the modem shelves
are connected via lines 47 to a microwave terminal (MT) 48.
A microwave link 49 extends from the microwave terminal
48 to a point-to-point microwave antenna 54 mounted on the
mast 50 for a host connection to the public switched telephone network 18.
A personal computer, workstation or the like can be
provided as a site controller (SC) 56 for supporting the
central terminal 10. The site controller 56 can be connected
to each modem shelf of the central terminal 10 via, for
example, RS232 connections 55. The site controller 56 can
then provide support functions such as the localisation of
faults, alarms and status and the configuring of the central
terminal 10. A site controller 56 will typically support a
single central terminal 10, although a plurality of site

controllers 56 could be networked for supporting a plurality
of eentral terminals 10.
As an alternative to the RS232 connections 55, which
extend to a site controller 56, data connections such as an
X.25 links 57 (shown with dashed lines in FIG. 3) could
instead be provided from a pad 228 to a switching node 60
of an element manager (EM) 58. An element manager 58 can
support a number of distributed central terminals 10 connected by respective connections to the switching node 60.
The element manager 58 enables a potentially large number
(e.g., up to, or more than 1000) of central terminals 10 to be
integrated into a management network. The element manager 58 is based around a powerful workstation 62 and can
include a number of computer terminals 64 for network
engineers and control personnel.
FIG. 3A illustrates various parts of a modem shelf 46. A
transmit/receive RF unit (RFU-for example implemented
on a card in the modem shelt) 66 generates the modulated
transmit RF signals at medium power levels and recovers
and amplifies the baseband RF signals for the subscriber
terminals. The RF unit 66 is connected to an analogue card
(AJ'Ir) 68 which performs A-D/D-A conversions, baseband
.filtering and the vector summation of 15 transmitted signals
[rom the modem cards (MCs) 70. The analogut unit 68 is
connected to a number of (typically 1-8) modem cards 70.
The modem cards perform the baseband signal processing of
the transmit and receive signals to/fro111 the subscriber
terminals 20. '111is may include Y2 rate convolution coding
and x 16 spreading with "Code Division Multiplexed
Access" (CDMA) codes on the transmit signals, and synchronisation recovery, de-spreading and error correction on
the receive signal". Each modem card 70 in the present
example has two modems, and in preferred embodiments
there are eight modem cards per shelf, and so sixteen
modems per shelf. However, in order to incorporate redundancy so that a modem maybe substituted in a subscriber
link when a fault occurs, only 15 modems on a single
modem shelf 46 are generally used. The 16th modem is then
used as a spare which can be switched in if a failure of one
of the other 15 modems occurs. The modem cards 70 are
connected to the tributary unit (TV) 74 which terminates the
connection to the host public switched telephone network 18
(e.g" vi.a one of the lines 47) and handles the signalling of
telephony information to the subscriber terminals via one of
15 of the 16 modems.
The wireless telecommunications between a central terminal10 and the subscriber terminals 20 could operate on
various frequencies. FIG. 4 illustrates one possible example
of the frequencies which could be used. In the present
example, the wireless telecommunication system is intended
to operate in the 1.5-2.5 GHz Band. In particular the present
example is intended to operate in the Band defined by ITU-R
(CCIR) Recommendation F.701 (2025-2110 MHz,
2200-2290 MHz). FIG. 4 illustrates the frequencies used for
the uplink from the subscriber terminals 20 to the central
terminal 10 and for the downlink from the central terminal
10 to the subscriber terminals 20. It will be noted that 12
uplink and 12 downlink radio channels of 3.5 MHz each are
provided centred about 2155 MHz. The spacing between the
rece,lve and transmit channels exceeds the required minimum spacing of 70 MIIz.
In the present example, each modem shelf supports I
frequency channel (i.e. one uplink frequency plus the corresponding downli.nk frequency). Currently, in a wireless
telecommunications system as described above, CDMA
encoding is used to support up to 15 subscriber links on one
frequency channel (one subscriber link on each modem).

10

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WIL-0009829

us

6,195,327 Bl

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12

Hence, if a central terminal has four modem shelves, it can
support 60 (15x4) subscriber links (ie. 6U S'ls can be
connected to one CT). However, it is becoming desirable for
more than 60 STs to be supported from one central terminal,
and, in preferred embodiments of the present invention,
enhancements to the CDMA encoding technique are provided to increase the number of subscriber links that can bc
supported by a central terminal. Both CDMA encoding, and
the enhancements made to the CDMA encoding in accordance with preferred embodiments, will be discussed in
more detail later.
Typically, the radio traffic from a particular central terminal10 will extend into the area covered by a neighbouring
central terminal 10. To avoid, or at least to reduce interference problems caused by adjoining areas, only a limited
numbtr of tht available fn:4utncits will bt: ustd by any
given central terminal 10.
PIG. 5A illustrates one cellular type arrangement of the
frequencies to mitigate interference problems between adjacent central terminals 10. Tn the arrangement illustrated in
FIG. SA, the hatch lines for the cells 76 illustrate a frequency
set (FS) for the cells. By selecting three frequency sets (e.g.,
where: FS1=Fl, F4, F7, FlO; FS2=F2, F5, F8, F11; FS3=F3,
F6, F9, F12), and arranging that immediately adjacent cells
do not use the same frequency set (see, for example, the
arrangement shown in FIG. SA), it is possible to provide an
array of fixed assignment omnidirectional cells where interference between nearby cells can be reduced. The transmitter power of each central terminal 10 is preferably set such
that transmissions do not extend as far as the nearest cell
which is using tht: samt frt:4ut:ncy st:l. Thus, in acconlance
with the arrangement illustrated in FIG. SA, each central
terminal 10 can use the four frequency pairs (for the uplink
and downlink, respectively) within its cell, each modem
shelf in the central terminal 10 being associated with a
respective RF channel (channel frequency pair).
FIG. 5B illustrates a cellular type arrangement employing
sectored cells to mitigate prohlems between adjacent central
terminals 10. As with FIG. 5A, the different type of hatch
lines in FIG. 5B illustrate different frequency sets. As in
FIG. SA, FIG. 5B represents three frequency sets (e.g.,
\vhere: FS1=F1, F4, F7, FlO; FS2=F2, FS, F8, F11; FS3=F3,
F6, F9, F12) However, in FIG. 5B the cells are sectored by
using a sectored central terminal (SCT) 13 which includes
three central terminals 10, one for each sector Sl, S2 and S3,
with lhe transmissions [or each of the three central terminals
10 being directed to the appropriate sector among SI, S2 and
S3. This enables the number of subscribers per cell to be
increased three fold, while still providing permanent fixed
access [or each subscriber terminal 20.
Arrangements such as those in FIGS. SA ilnd SD can help
reduce interference, but in order to ensure that cells oper-

ating all the same frequency don't inadvertently decode each
others data, a seven cell repeat pattern is used such that for
a cell operating on a given frequency, all six adjacent cells
operating on the same frequency are allocated a unique
pseudo random noise (PN) code. The use of PN codes will
be discussed in more detail later. The use of different PN
codes prevents nearby cells operating on the same frequency
from inadvertently decoding each others data.
As mentioned above, COMA techniques can be used in a
fixed assignment arrangement (ie. one where each ST is
assigned to a particular modem on a modem shelf) to enable
each channel frequency to support 15 suhscriber links. FTG.
6 gives a schematic overview of COMA encoding and
15 decoding.

10

In order to encode a COMA signal, base band signals, for
example the user signals for each respective subscriber link,
are encoded at 80-80N into a 160 ksymbols/sec baseband
signal where each symbol represents 2 data bits (see, for
20 example the signal represented at 81). This signal is then
spread by a factor of 16 using a spreading function 82-82N
to gent:raLe signals at an dItctivt chip ratt: of 2.56
Msymbols/sec in 3.5 MHz. The spreading function involves
applying a PN code (that is specified on a per CT basis) to
25 the Sigllal, and also applying a Rademacher-Walsh (RW)
code which ensures that the signals for respective subscriber
terminals will be orthogonal to each other. Once this spreading function has been applied, the signals for respective
subscriber links are then combined at step 84 and converted
30 to radio frequency (RF) to give multiple user channel signals
(e.g. 85) for transmission from the transmitting antenna 86.
Ouring transmission, a transmitted signal will be subjected to interference sources 88, including external interference 89 and interference from other channels 90.
35 Accordingly, by the time the COMA signal is received at the
receiving antenna 91, the multiple user channel signals may
be distorted as is represented at 93.
In order to decode the signals for a given subscriber link
from the received multiple user channel, a Walsh correlator
94-94N uses the same RW and PN codes that were used for
the encoding for each subscriber link to extract a signal(e.g.
as represented at 95) for the respective received baseband
signal 96-96N. It will b~ nottd that lht: rtcdvtd signal will
45
include some residual noise. However, unwanted noise can
be removed using a low pass filter and signal processing.

40

50

The key to CDMA is the application of the RW codes,
these being a mathematical set of sequences that have the
function of "orthonormality". In other words, if any RW
code is multiplied by any other RW code, the results are
zero. Aset of 16 RW codes that may be used is illustrated in
Table 1 below:
TABLE 1

RWO
RW1
RW2
RW3
RW4
RW5
R\V6

RW7
RW8
RW9
RWI0
RWIJ

J
-1
1
-1
1
-1
1
-1
1

1
-1
-1
1
-1
-1

-1
-1

-1
-1

-1
-1
1
1
-1
-1
1
1
-1

1
-1

-1
-1
-1

-1
1
-1
-1
1
-1
1
1

-1
-1
-1
-1

-]

-1

-1
1

-1

-1

1
-1

-1
1
-1
1
-1
1
-1
-1

-1
-1

1 -1
-1

-1

1

-1
-1

-1
1
1
-1
1
-1
-1

1

-1
-1

-1
-1
-1

-1
-1
1
1
-1
-1
1
-1
1

-1

1

-1
-1
-1
-1
-1
-1
-1

-J

-1
1
1 -1
-1 -1
-1 -1
1 -1
-1
1
1
-1 -1

-1
-1

1 -1
-1

1

-1

-1
-1

-1

WIL-0009830

US 6,195,327 B1

14

13
TABLE I-continued
RW12
RW13
RW14
RW15

1
-1
1
-1

1
1 -1
1 -1 -1
-1 -1 -1
-1
1 -1

-1
1
-1

-1
-1
1

-1

1
1
-1

-1
-1
-1
-1

-1
1

-1
-1

-1
1
]

-]

1

-1

1
-1
1 -1
-1 -1

1
-1
-J

The above set of RW codes are orthogonal codes that
Overlay codes are used extensively to provide variable
allow the multiple user signals to be transmitted and 10 rate uplink traffic channels. Overlay codes will also be used
received on the same frequency at the same rime. Once the
to implement downlink control channels, these control chanbit stream is orthogonally isolated using the RW codes, the
nels being discussed in more detail later. However, as
signals for respective subscriber links do not interfere with
mentioned earlier, a different approach is taken for providing
each other. Since RW codes are orthogonal, when perfectly
flexihle channelisations on the downlink traffic channel
aligned all codes have zero cross-correlation, thus making it 15 paths. Downlink traffic channels will operate in high rate,
possible to decode a signal while cancelling interference
160 kb/s, mode, with lower data rates of 80 and 40 kb/s
from users operating on other RW codes.
being supported by 'Time Division Multiplexing' (IDM)
the available bandv.ridth.
In preferred embodiments o[ the present invention, it is
In preferred embodiments, TUM timeslot bit numbering
desired to provide the central terminal with the ability to
support more than 15 subscriber links on each channel 20 win follow the CCITT G.732 convention with bits transmitted in the sequence bit 1, bit 2 bit 8. Byte orientation is
frequency, and to achieve this the above set of 16 RW codes
specified per channel as either most significant bit (MSB)
has been enhanced. In order to maintain compatibility with
first, least significant bit (LSB) first or N/A.
former products using the 16 RW codes, it was desirable that
any enhancements should retain the same set of 16 RW
The provision of a hybrid CDMA;TlDM approach for
codes.
25 downlink traffic channels retains the benefits of CDMA
access, ie. interference is reduced when traffic is reduced.
The manner in which the enhancements have been impleFurther, use o[ TDM ensures that the CDMA signal is
mented provides flexibility in the way the frequency chanlimited to a 256 'Quadrature Amplitude Modulation' (QAM)
nels are configured, with certain configurations allowing a
greater number of subscriber links to be supported, but at a 30 constellation which reduces receiver dynamic range requirements. QAM constellations will be familiar to those skilled
lower gross bit rate. In preferred embodiments, a channel
in the art.
can be selected to operate with the following gross bit rates:
On the uplink channels, the pure CDMA approach using
overlay codes eliminates the need to time synchronise STs to
35 a TDM frame reference. This has the advantage of elimi160 kb/s
Full rate (F1)
nating TDM delays and the' guard time' in between TDM
80 kb/s
Half rate (H1, H2)
frames. Another benefit is reduced peak power handling
40 kb/s
Quarter rate (Q1, Q2, Q3,
Q4)
requirements in the ST RF transmit chain which would
10 kb/s
Low rate CLl, L2, L3,
oth(:rwise be needed when transmitting bursty TDM data.
L4), for uplink acquisition
40 High dynamic range requirement is restricted to the CT
receiver.
The manner in which the transmitted and received signals
In preferred embodiments, the manner in which these
are processed in accordance with preferred embodiments of
channelisations are provided differs for the downlink (CT to
the present invention will be described "vith reference to
ST) and uplink CST to CT) communication paths. This is
because it has been realised that different performance 45 FIGS. '7 and 8. FIG. 7A is a schematic diagram illustrating
requirements exist for the downlink and uplink paths. On the
signal transmission processing stages as configured in a
subscriber terminal 20 in the telecommunications system of
downlink all signals emanate from a single source, namely
FIG. 1. In FIG. 7A, an analogue signal from a telephone is
the central terminal, and hence the signals will be synchropassed via an interface such as two-wire interface 102 to a
nised. However, on the uplink path, the signals will emanate
from a number of independent STs, and hence the signals 50 hybrid audio processing circuit 104 and th(:n via a codec 106
to produce a digital signal into which an overhead channel
will not be synchronised.
including control information is inserted at 108. If the
Given the above considerations, in preferred
subscriber terminal supports a number of telephones or other
embodiments, on the uplink path full rate (160 kb/s) operatelecommunications equipment, then elements 102, 104 and
tion is implemented using the basic set of RW codes
discussed earlier, but half and quarter rates are achieved 55 106 may be repeated for each piece of telecommunications
equipment.
through the use of 'Overlay Codes' which comprise RW
At the output of overhead insertion circuit 108, the signal
coded high rate symbol patterns that are transmitted for each
will have a bit rate of either 160,80 or 40 kbits!s, depending
intermediate rate data symbol. For half rate operation, two
on which channel has been selected for transmission of the
2-bit overlay codes are provide, whilst for quarter rate
operation, four 4-bit overlay codes are provided. When 60 signal.
generating a signal for transmission, one o[ the overlay
The resulting signal is then processed by a convolutional
codes, where appropriate, is applied to the signal in addition
encoder 110 to produce two signals with the same bit rate as
to the appropriate RW code. When the signal is received,
the input signal (collectively, these signals will have a
then at the CDMA demodulator the incoming signal is
symbol rate of 160, 80 or 40 KS/s). Next, the signals are
multiplied by the channel's PN, RWand Overlay codes. The 65 passed to a spreader 111 where, if a reduced bit rate channel
correia tor integration period is set to match the length of the
has been selected, an appropriate overlay eode provided by
Overlay code.
overlay code generator 113 is applied to the signals. At the

WIL-0009831

US 6,195,327 Bl

15

16

so as to produce the desired overlay code, in preferred
output of the spreader 111, the signals \v.ill be at 160 KSIs
embodiments, this control coming from the OAengine (ra be
irrespective of the bit rate of the input signal since the
discussed in more detail later).
overlay code will have increased the symbol rate by the
necessary amount.
FIG. 8A is a schematic diagram illustrating the signal
reception processing stages as configured in a subscriber
The signals output from spreader 111 are passed to a
terminal 20 in the telecommunications system of FIG. 1. In
spreader 116 where the Rademacher-Walsh and PN codes
FIG. 8A, signals received at a receiving antenna 150 are
are applied to the signals by a RW code generator 112 and
passed via a band pass filter 152 before being amplified in
PN Code generator 114, respectively. The resulting signals,
a low noise amplifier 154. The output of the amplifier 154 is
at 2.56 MC/s (2.56 Mega chips per second, where a chip is
the smallest data element in a spread sequence) are passed 10 then passed via a further band pass filter 156 before being
further amplified by a further low noise amplifier 158. The
via a digital to analogue converter 118. The digital to
output of the amplifier 158 is then passed to a mixer 164
analogue converter 118 shapes the digital samples into an
where it is mixed with a signal generated by a voltage
analogue waveform and provides a stage of baseband power
controlled oscillator 162 which is responsive to a synthesizer
control. The signals are then passed to a low pass filter 120
to be modulaLed in a modulator 122. Tht: modulatt:d signal 15 160. The output of the mixer 164 is then passed via the I1Q
de-modulator 166 and a low pass filter 168 before being
from the modulator 122 is mixed with a signal generated by
passed to an analogue to digital converter 170. The digital
a voltage controlled oscillator 126 which is responsive to a
output of the AID converter 170 at 2.56 MC/s is then passed
synthesizer 160. The output of the mixer 128 is then
to a correlator 178, to which the. same Rademacher-Walsh
amplified in a low noise amplifier 130 before being passed
via a band pass filter 132. The output of the band pass filter 20 and PN codes used during transmission are applied by a RW
code generator 172 (corresponding to the RW code genera132 is further amplified in a further low noise amplifier 134,
tor 112) and a PN code generator 174 (corresponding to PN
before being passed to power control circuitry 136. The
code generator 114), respectively. The output of the COffoutput of the power control circuitry is further amplified in
elator 178, at 160 KS/s, is then applied to correlator 179,
a power amplifier 138 before being passed via a further band
pass filter 140 and transmitted from the transmission antenna 25 where any overlay code used at the transmission stage to
encode the signal is applied to the signal by overlay code
142.
generator 181. The elements 170, 172, 174, 178, 179 and
FIG. 7B is a schematic diagram illustrating signal trans181 form a CDMA demodulator. The output from the
mission processing stages as configured in a central terminal
CDMA demodulator (at correlator 179) is then at a rate of
10 in the telecommunications system of FIG. 1. As will be
apparent, the central terminal is configured to perform 30 either 160, 80 or 40 KS/s, depending on the overlay code
applied by correlator 179.
similar signal transmission processing to the subscriber
The output from correlator 179 is then applied to a Viterbi
terminal 20 il111strated in FIG. 7A, but does not inchlde
decoder 180. The output of the Viterbi decoder 180 is then
elements 100, 102, 104 and 106 associated with telecompassed to an overhead extractor 182 for extracting the
munications equipment. Further, the central terminal
includes a TDM encoder 105 for performing time division 35 overhead channel information. If the signal relates to call
data, then the output of the overhead extractor 182 is then
multiplexing where required. The central terminal will have
passed through TDM decoder 183 to extract the call data
a network interface over which incoming calls destined for
from the particular time slot in which it was inserted by the
a subscriber terminal are received. When an incoming call is
CT TDM encoder 105. Then, the call data is passed ~ia a
received, the central terminal will contact the subscriber
terminal to which the call is directed and arrange a suitable 40 codec 184 and a hybrid circuit 188 to an interface such as
two wire interface 190, where the resulting analogue signals
channel over which the incoming call can be established
are passed to a telephone 192. As mentioned earlier in
with the subscriber terminal (in preferred embodiments, this
connection with the ST transmission processing stages,
is done using the call control channel discussed in more
elements 184, 188, 190 may be repeated for each piece of
detail later). The channel established for the call will determine the time slot to be used for call data passed from the 45 telecolllmunications equipment 192 at the ST.
If the data output by the overhead extraction circuit 182
CT to the ST and the TDM encoder 105 will be supplied with
is data on a downlink control channels, then instead of
this information.
passing that data to a piece of telecommunications
Hence, when incoming call data is passed from the
equipment, it is passed via switch 187 to a call control logic
network interface to the TDM encoder 105 over line 103, the
TDM encoder will apply appropriate TDM encoding to 50 185, where that data is interpreted by the ST.
At the subscriber terminal 20, a stage of automatic gain
enable the data to be inserted in the appropriate time slot.
control is incorporated at the IF stage. The control signal is
From then on, the processing of the signal is the same as the
derived from the digital portion of the CDMAreceiver using
equivalent processing performed in the ST and described
the output of a signal quality estimator.
with reference to FIG. 7A, the overlay code generator
FIG. 8B illustrates the signal reception processing stages
producing a single overlay code of value '1' so that the 55
as configured in a central terminal 10 in the telecommunisignal output from spreader 111 is the same as the signal
cations system of FIG. 1. As will be apparent from the figure,
input to the spreader 111.
the signal processing stages between the RX antenna 150
As mentioned earlier, in preferred embodiments, overlay
and the overhead extraction circuit 182 are the as those
codes, rather than TDM, are used to implement downlink
control channels, and data relating to such channels is passed 60 within the ST discussed in connection with FIG. SA.
However, in the case of the CT, call data output from the
from a demand assignment engine. (to be discussed in more
overhead extraction circuit is passed over line 189 to the
detail later) over line 107 through switch 109 to the overhead
network interface within the CT, whilst control channel data
insertion circuit 108, thereby bypassing the TOM encoder
is passed via switch 191 to the DA engine 380 for proeess105. The processing of the signal is then the same as the
equivalent processing performed in the ST, with the overlay 65 ing. The OA engine is discussed in more detail later.
Overlay codes and channelisation plans are selected to
code generator providing appropriate overlay codes to the
ensure signal orthogonality-i.e. in a properly synchronised
spreader 111. The overlay code generator will be controlled

WI L-0009832

US 0,195,327 B1

17

18

FIG. 11 is a block diagram of downlink and uplink
communication paths between central terminallOl and subscriber terminal 20. A downlink commUlllcation path is
established from transmitter 200 in central terminal 10 to
receiver 202 in subscriber terminal 20. iUI uplink communication path is established from transmitter Z04 in subscriber terminal 20 to receiver 206 in central terminal 10.
Once the downlink and the uplink communication paths
have been established in wireless telecommunication system
TABLE 2
10 1, telephone communication may occur between a user 208,
210 of subscriber terminal 20 and a user serviced through
STTx.
central terminal 10 over a downlink signal 212 and an uplink
power
Net Channel relative
CorrelatOI
signal 214. Downlink signal 212 is transmitted by transmitRate design- to F1-U
integration
Acquisition
ter 200 of central terminal 10 and received by receiver 20Z
Overlay Code
pedod (US)
overlay
(kb/s) ation
(dB)
of subscriher terminal ZO. Uplink signal 214 is transmitted
15 by transmitter 204 of subscriber terminal 20 and received by
160
-FI-U
6.25
L1
80
·HI-U
-3
12.5
1 1
L1
recdvtr 206 o[ ce.ntral terminal 10.
80
-H2-U
-3
1 -1
12.5
L3
Receiver 206 and transmitter 200 withi.n central terminal
-QI-U
40
-6
25
1
1
Ll
10 are synchronized to each other with respect to time and
40
-Q2-U
-6
-1
-1
25
L2
phase, and aligned as to information boundaries. In order to
40
-Q3-U
-6
1 -1 -1
25
L3
20 establish the downlink communication path, receiver 202 in
40
-Q4-U
-6
-1 -1 1
25
L4
subscriber terminal 20 should be synchronized to transmitter
200 in central terminal 10. Synchronization occurs by perIn preferred embodiments, a 10 kb/s acquisition mode is
forming an acquisition mode function and a tracking mode
provided which u~e~ concatenated overlays to form an
function on downlink signal 212. Initially, transmitter 200 of
acquisition overlay; this is illustrated in table 3 below:
25 central terminal 10 transmits downlink signal 212. FIG. 12
shows the contents of downlink signal 212. A frame information signal 218 is combined with an overlay code 217
TABLE 3
where appropriate, and the resultant signal 219 is combined
Acquisition
with a code sequence signal 216 for central terminal 10 to
Overlay
Equivalent high rate pattern
30 produce the downlink 212. Code sequence signal 216 is
derived from a combination of a pseudo-random noise code
Ll-U
111111111111111
1
signal.220 and a Rademacher-Walsh code signal 222.
L2-U
11 -1 -1 11 -1 -111 -1 -11 1 -1
Downlink signal 212 is received at receiver 202 of
-1
subscriber terminal 20. Receiver 202 compares its phase and
L3-U
1 -11 -11 -11 -11 -11 -11 -11
-1
35 code sequence to a phase and code sequence within code
l.4-lJ
1 -1 -1 1 1 -1 -1 1 1 -1 -11 1 -1 -1
sequence signal 216 of downlink signal 212. Central terminal 10 is considered to have a master code sequence and
subscriber terminal 20 is considered to have a slave code
sequence. Receiver 202 incrementally adjusts the phase of
FIGS. 9A and 9B are diagrams illustrating the uplink and
downlink delivery methods, respectively, when the system is 40 its slave code sequence to recognize a match to master code
sequence and place receiver 202 of subscriber terminal 20 in
fully loaded, and illustrate the difference between the use of
phase \Ol'ith transmitter 200 of central terminal 10. The slave
overlay codes illustrated in FIG. 9A and the use of IDM as
code sequence of receiver 202 is not initially synchronized
illustrated in FIG. 9B. When using overlay codes, an RW
to the master code sequence of transmitter 200 and central
code is split in the RW space domain to allow up to four sub
channels to operate at the same time. In contrast, when using 45 terminal 10 due to the path delay between central terminal
10 and subscriber terminal 20. This path delay is caused by
TDM, an RW code is split in the time domain, to allow up
the geographical separation between subscriber terminal 20
to four signals to he sent using one RW code, hut at different
and central terminal 10 and other environmental and techtimes during the 125 us frame. As illustrated in FIGS. 9A
nical factors affecting wireless transmission.
and 9B, the last two RW codes, RW14 and RW15, are not
Aiter acquiring and initiating tracking on the central
used for data traffic in preferred embodiments, since they are 50
terminal 10 master code sequence of code sequence signal
reserved for call control and acquisition functions; this will
216 within downlink. signal 212, receiver 202 enters a frame
be discussed in more detail later.
alignment mode in order to establish the downlink commuThe CDMAchannel hierarchy is as illustrated in FIG.lO.
nication path. Receiver 202 analyzes frame information
Using this hierarchy, the following CDMA channelisations
55 within frame information signal 218 of downlink signal 212
are possible:
to identify a beginning of frame position for downlink signal
Fl
212. Since receiver 202 does not know at what point in the
Hl+HZ
data stream of downlink signal 212 it has received
Hl+Q3+Q4
information, receiver 202 must search for the beginning of
H2+Ql+QZ
60 frame position in order to be able to process information
Ql+Q2+Q3+Q4
received from transmitter 200 of central terminal 10. Once
receiver 202 has identified one further beginning of frame
Having discussed how the CDMA codes are enhanced to
position, the downlink communication path has been estahenable flexible channelisations to be achieved, whereby the
lished from transmitter 200 of central terminal 10 to receiver
bit rates can be lowered to enable more subscriber links to
be managed per channel frequency, a general overview of 65 202 of subscriber terminal 20.
how the downlink and uplink paths are established will be
The structure of the radio frames of information sent over
provided with reference to FIGS. 11 and 12.
the downlink and uplink paths will now be discussed with
system, the contribution of all channels except the channel
being demodulated sum to zero over the correlator integration period. Further, uplink power is controlled to maintain
constant energy per bit. The exception to this is Low rate
which will be transmitted at the same power as a Quarter rate
signal. Table 2 below illustrates the overlay codes used for
full, half and quarter rate operations:

WIL-0009833

US 6,195,327 Bl

19

20

reference to FIGS. 13 and 14. In FIGS. 13 and 14, the
following terms are used:

TABLE 4
Rate Channel
(kb/s) designation

Bn
Customer payload, 1 x 32 to 2 x 64 Kb/s
Dn
Signalling Channel, 2 to 16 kb/s
OH
Radio Overhead Channel
16 kb/s Traffic Mode
10 kb/s Acquisition/Standby Mode

160

-Fl-D-T1/1

80

-FI-D-T2/l

80

-Fl-D-T2/2

40
40

-Fl-D-T4/1
-Fl-D-T4/2
-FI-D-T4/3
-Fl-D-T4/4

10

Both FIGS. 13A and 13B show a 12Sus subframe format,
which is repeated throughout an entire radio frame, a frame
typically lasting for 4 milliseconds (ms). FIG. 13Aillustrates
the radio frame structures that are used in preferred embodiments for the downlink path. Subframe (i) in FIG. 13A
shows the radio frame structure used for low rate, 10 Kb/s,
acquisition mode (Ln-D) during which only the overhead
channel is transmitted. Sub frame (ii) in FIG. 13Ashows the
radio frame structure employed for the call control channel
operating in quarter rate, 40 Kb/s, mode (On-D), whilst
subframe (iii) of FIG. 13A illustrates the radio frame structure used for traffic channels operating in full rate, 160 kb/s,
mode (FI-D).
Similarly, subframe (i) of FIG. 13B shows the radio frame
structure used for the uplink path when operating in low rate
acquisition or call control mode (Ln-V). Subframes (ii) to
(iv) show the radio frame structure used for traffic channels
when operating in quarter rate mode (Qn-V), half rate mode
(Hn-V), and full rate mode (F1-V) respectively.
Considering now the overhead channel in more detail,
FIGS. 14A and 14B show the overhead frame structure
employed for various data rates. The overhead channel may
include a llllmber of fields-a frame alignment word (FAW),
a code synchronization signal (CS), a power control signal
(PC), an operations and maintenance channel signal (OMC),
a mixed OMC/D-Channel (IIDLC) signal (OMCID), a channel identifier byte (Ch.IO), and some unused fields.
The frame alignment word identifies the beginning of
frame position for its corresponding frame of information.
The code synchronization signal provides information to
control synchronization of transmitter 204 in subscriber
terminal 20 to receiver 206 in central terminal 10. The power
control signal provides information to control transmitting
power of transmitter 204 in subscriber terminal 20. The
operations and maintenance channel signal provides status
information with respect to the downlink and uplink communication paths and a path from the central terminal to the
subscriber terminal on which the communication protocol
which operates on the modem shelf between the shelf
controller and the modem cards also extends. The OMC/D
signal is a combination of the OMC signal and a signalling
signal CD), whilst the Ch. ID signal is used to uniquely
identify an RW channel, this Ch. ID signal being used by the
subscriber terminal to ensure that the correct channel has
been acquired.
In preferred embodiments, the subscriber terminal will
receive downlink traffic channel data at a rate of 160 kb/s.
Depending on the B-channel rate, the ST will be allocated an
appropriate share of the radio overhead. The following TDM
mappings are created:

40
40

15

20

25

30

35

40

45

50

55

60

65

Bearer

CS

B1, B2, CS1,
B3,B4 CS3
Bl, B2 CS1,
CS3
B3, B4 CS2,
C54
131
CSl
B2
CS2
B3
CS3
B4
CS4

PC

OMC

Overhead
rate

PC1,
PC3
PC1,
PC3
PCZ,
PC4
PCl
PC2
PC3
PC4

OMC1,OMC3

4 ms

OMC1,OMC3

4 ms

OMC2,OMC4

4 ms

OMCI
OMC2
031C3
OMC4

8
8
8
8

ms
ms
ms
ms

In the above chart, the scheme used to identify a channel
is as follows. Rate code 'Fl' indicates full rate, 160kb/s, '0'
indicates that the channel is a downlink channel, and 'Tn/t'
indicates that the channel is time division mUltiplexed
between STs, 'n' indicating the total number of TDM
timeslots, and '1' indicating the selected traffic timeslot.
All ST's operating on a traffic channel will receive
O-channel information at the 16 kb/s rate. The D-channel
protocol includes an address field to specify which ST is to
process the contents of the message.
The channel structure was illustrated earlier in FIGS. 9A
and 9B. In preferred embodiments, the channel structure is
flexible but comprises:
At least one Link Acquisition Channel (LAC)
At least one Call Control Channel (CCC)
Typically one Priority Traffic Channels (PTC)
1 to 13 Traffic Channels eTC)
The manner in which the channelisation is provided
ensures that former fixed assignment arrangements using the
set of 16 RW codes discussed earlier are still supported, as
well as demand access services that are available when using
a system in accordance with the preferred embodiment.
FIGS. lSA and lSB illustrate typical downlink and uplink
channel structures that might occur in a loaded system in
accordance with preferred embodiments of the present
invention. As illustrated in FIG. lSA, on the dO\vnlink path,
some signals may be at 160 kb/s and milise an entire RW
channel. An example of such signals would be those sent
over fixed assignment links to products which do not support
the CDMA enhancements provided by systems in accordance with preferred embodiments of the present invention,
as illustrated for RWI and RW2 in FIG. 15A Alternatively,
a user may have authority to utilise a whole RW channel, for
example when sending a fax, as illustrated by RW12 in FIG.
lSA.
As illustrated by RW5 to RWll, TOM can be used on the
downlink traffic channels to enable more than one CT to ST
communication to take place on the same RW channel
during each frame. Further, as illustrated for RW3 and RW4,
in preferred embodiments, certain channels can be locked to
limit interference from other nearby cells, as wm be discussed in more detail later.
Similar channelisations can be achieved for the uplink
paths, but as illustrated in FIG. ISB, overlay codes are used
instead of TDM 10 enable more than one ST LO CT communication to take place on the same RW channel during
each frame (as shown in FIG. I5B for RW5 to RWll). It
should be noted that, in both FIGS. lSA and 1SB, the
channels RW14 and RW15 arc reserved as a call control
channel and an link acquisition channel, respecLively, and
overlay codes are employed on these channels, irrespective

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of whether the path is a downlink or an uplink path. TIlese
two channels will be discussed in more detail belO\v.
Acquisition/net entry will take place via the Link Acquisition Channel (LAC). Following power-up an ST will
automatically attempt downlink acquisition of the LAC on a
pre-determined 'home' RF channel. The LAC downlink
channel (eg. RW15 in preferred embodiments) will operate
at 10 kb/s, full single user power. Downlink acquisition will
be simultaneous for all STs.
Each CT Modem Shelf will maintain a database holding 10
the serial numbers of all STs that could possibly be supported by that CT. The state of each ST will recorded with
top level states as follows:
cold
15
idle
Transition states will also be defined. An ST is considered
cold if the ST is newly provisioned, the CT has lost
management communications with the ST or the CT has
been power cycled. Over the LAC, the CT broadcasts
individual ST serial numbers and offers an invitation to
acquire the LAC uplink. Cold uplink acquisition will be
carried out on the T,ink Acquisition Channel at low rate. The
CTwill invite specific ST's to cold start via the management
channel.
Assuming an uplink channel is available, the appropriate
acquisition overlay will be selected, and acquisition will be
initiated.
'Rapid' downlink RW channel switching may be supported at rates other than Ln-D. Rapid means that coherent
demodulation is maintained, and only convolutional decoding and frame synchronisation processes need be repeated.
On acquisition, management information will he
exchanged. The ST will be authenticated and allocated a
short ST_identifier (between 12 and 16 bits) which will be
used for subsequent addressing. The ST uplink will operate
for long enough for the uplink to be parametised by the ST
in terms of code phase and transmit power. These parameters
will be used by the ST for subsequent warm start acquisitions and will also be held by the CT to allow the CT to force
a cold ST to warm start. On successful completion of net
entry, the ST will be placed in the idle state and instructed
to cease uplink communications and move to the Call
Control Channel (CCe) (RW14 in preferred embodiments).
The time taken for net entry to be achieved can be
monitored, and the following techniques can be used to
decrease net entry time if desired:
(i) Prioritise so that high GOS (Grade Of Service) users are
offered net entry first.
(ii) Convert Traffic Channels to LACs.
( iii) In the event of a CT restart, invite STs to attempt
uplink warm start. A reduction in net entry time of a factor
of 4 could be achieved. This mechanism would need to be
safeguarded against possible deterioration of uplink warm
start parameters-i.e. it should only be allowed provided
no CT RF related parameters have been modified. The CT
would need to broadcast an ID to allow an 5T to validate
that the uplink warm start parameters were valid for this
CT.
(iv) ST restart-the CT will keep copies of the STwarm start
parameters so that a cold ST may have warm start

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parameters downloaded in the invitation to acquire and

then be instructed to warm start.
Following Net Entry, all STs listen to the CCc. This
channel broadcasts management and call control informa-

65

t.ion via a 32 kb/s HDLC channel. In order to maintaIn
management communication, the CT polls each ST in
sequence. Each poll comprises a broadcast invitation for an
addressed ST to acquire the CCC Uplink followed by an
exchange of management informat.ion ( authentication, ST
alarm update, warm start parameters, downlink radio performance data etc).
A Management Poll may fail for one of the following
reasons:
(i) The ST is or has been powered down. An EM alarm may
be flagged if this persists and the database for that ST
should be marked cold. The Net Entry process will follow.
(ii) The ST is either making a call or in the process of malcing
a cal1. The poll cycle may be suspended and management
communications effected on the appropriate traffic channel.
When a Management Poll fails it should be followed up
by a number of faster polls until either the ST responds or
it is marked cold. The CCC is required to transmit all copies
of the invitations to acquire the LAC so that an ST can be
forced to acquire the LAC uplink.
Traffic Channel Uplink Acquisition Procedure
The basic acquisition process from the ST side is as
follows;
(i) Switch the downlink (receiver) circuitry to 10 kb/s rate,
and select the appropriate Traffic Channel RW and Overla_y codes. Acquisition of the TC downlink is limited to
achieving frame alignment.
(ii) The downlink pe/CS channel will be decoded to create
a busy/idle flag. If PC/CS reports busy, then this means
that another ST is using that traffic channel and the ST
aborts the acquisition process.
(iii) Switch uplink to 10 kb/s rate, and select the appropriate
Traffic Channel RW and Overlay codes. Enable the ST
transmitter at a level of nominal full rate power minus 18
dlB. While PC/CS reports idle the ST will continue uplink
fast codesearch, stepping the uplink power level by +2 dB
at the end of each search. The uplink should acquire at
nominal full rate power minus 6 dB. Uplink acquisition is
aborted if maximum transmit level is reached and PC/CS
continues to report idle.
(iv) PC/CS reports busy. At this point the ST may have
genuinely acquired the traffic channel, or instead may be
observing PCjCS go busy because another ST has
acquired the traffic channel. The ST is sent an authentication request and responds with it's ST_identifer. The
cr grants uplink access by returning the ST_identifier.
TIle ST aborts the acquisition process if the returned
ST_identifier is not recognised (ie. is not the
ST_iden1ifer that it sent). This authentication process
arbitrates between two STs contending for outgoing
access and it also keeps STs from acquiring TCs that have
been reserved from incoming access.
Incoming Call
A number ofTCs will be reserved for incoming calls, and
incoming call processing is as follows:
(i) Check the CT database-if the ST is in the call_in
progress state the call is rejected.
(ii) Check that an uplink TC of the required bandwidth is
available. If there is bandwidth then a TC is reserved.
(iii) An incoming call setup message is broadcast over the
CCC to inform the addressed ST of the illcoming call and
specify the TC on which to receive the call. If no TC is
available but the CT forms part of a Service Domain, then
the: incoming call setup message is sent with a null TC
otherwise the call is rejected. Service domains will be
discussed in more detail later. The incoming call setup
message is repeated a number of times.

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(iii) If congestion tone is returned the customer is allowed to
(iv) The ST attempts uplink acquisition. The STlistens to the
downlink and keeps trying for uplink acquisition until the
dial the emergency number into the ST If the ST detects
CT sends a message to the ST to return the ST to the CCC.
an emergency DN sequence then uplink access via the
The ST will also run a timer to return it back to the CCC
Priority Traffic Channel (PTC) is attempted.
in the event of an incoming call failing to complete.
(iv) On PTC acquisition, the ST relays the dialled digit
(v) On successful uplink acquisition, the CT authenticates
sequence to the CT for dialling into the PSTN.
the ST.
(iv) The CT converts the PTC to a TC and reallocates
(vi) Rate switching is originated from the CT modem. A
another TC to become the PTC, dropping a normal call in
command is sent via the PC!CS to switch the downlink to
progress if necessary.
the required bandwidth. The ST returns the rate switch
10 Interference Limiting (Pool Sizing)
command via the uplink PCICS. The link is now of the
Across a large scale deployment of cells, optimum capacrequired bandwidth.
ity is achieved by minimising radio traffic while maintaining
Outgoing Call
an acceptable grade of service. Lowest possible radio traffic
Outgoing calls are supported by allowing slotted random
results in improved 'carrier to interference' (C/I) ratios for
access to the TC uplinks. The outgoing call processing is as
15 users within the cell of interest and to co-channel users in
follows:
nearby cells. The CII ratio is a measure (usually expressed
(i) Tht CT publishes a '[rte lisL' o[ available Traffic Chanin dB) of how high above interference the transmitted signal
nels and Priority Traffic Channels with their respective
needs to be to be decoded effectively. In preferred
handwidths. This list is published periodically (in preembodiments, the central terminal is provided with the
ferred embodiments, every 500 ms) and is used to mark
uplink acctss slots.
20 ability to tradt traffic [or C/I, thereby allowing network
planning to be carried out less rigidly. This feature can be
(ii) An off-hook condition is detected by the ST. The ST
realised by a system using CDMA as in preferred embodistarts a call setup timer.
(iii) The ST waits for the next free list to be received over
ments of the present invention, and is a benefit that CDMA
the CCc. If the Free list is empty the outgoing call is
offers over TDMA and FDMA systems.
25
blocked. The ST will generate a congestion tone.
In preferred embodiments, the CTwill control the number
(iv) If the Pree list has available channels, the ST picks a
of Traffic Channels to minimise access noise. TCs will be
channel from the free list at random. The algorithm that
classified as:
the ST lIses to pick a channel will need to be specified in
(i) Bllsy--carrying traffic;
(ii) Access, Incoming (Access_In)-rescrved for incoming
the free list. For example, the ST may be required to
always choose from a pool of minimum bandwidth chan- 30
access;
(iii) Access, Outgoing (Access_Out)-reserved for outgonels so that high bandwidth channels remain available for
high GOS users. Alternatively the ST may be allowed to
ing access-such TCs appear on the Free list;
choose any channel regardless of bandwidth for minimum
(iv) Priority-reserved for priority outgoing access-such
blocking. In preferred embodiments, STs will not choose
TCs appear in the Free list;
low bandwidth channels and negotiate the rate up.
35 (v) Free-available for any purpose; and
(vi) Locked-not available due to interference limiting.
(v) The ST attempts uplink acquisition on the specified TC,
This classification scheme is illustrated in FIG. 16. The
this process having been described earlier. If acquisition
CT will allocate traffic on the following basis:
is successful then the outgoing call is processed. Otherwise the ST returns to the CCC and waits for the next
(i) The CT will monitor incoming and outgoing call setupavailable free list. To avoid a number of STs repetitively 40
times and convert Access TCs from Free TCs in order to
achieve a required grade of service.
attempting to acquire the same TC, and blocking each
other, a suitable protocol can be employed to govern how
(ii) ·When a call is setup, an Access TC is converted to a Busy
individual STs will act upon receipt of the free list.
TC. If a Free TC is available, it is converted to a new
Access TC. If there are no Free TCs then the Access TC
(vi) The ST may be unable to acquire a TC by the time the
call setup timer expires. The ST may in such cases cease 45
is lost until a call clears.
(iii) When a call clears the Busy TC is converted to a Free
attempting outgoing access and generate congestion tone.
TC. If a previous call setup resulted in a lost Access TC
Outgoing Priority Call
then the Busy TC is converted back into an Access TC.
It is recognised that the random access protocol used to
(iv) When the PTC is accessed, a new PTC is created by
setup normal outgoing calls could lead to blocking. In
converting a Free, Access or Busy (normal call) Te.
preferred embodiments, access to a largely non-blocking 50
(v) The CT will monitor the Busy TC dO'wnlink and uplink
Priority Traffic Channel will be allowed. Priority calling is
soft error counts in an attempt to establish link quality. If
complicated because the ST must:
the CT records a lower than average soft error count and
(i) Capture and decode dialled digits.
long call setup times are being recorded, a Locked TC
(ii) Regenerate digits when a blocking condition occurs.
may be converted to a Free TC. Conversely, if the CT
(iii) Allow transparent network access in a non-blocking 55
records a higher than average soft error count, a Free or
condition.
Access TC may be converted to a Locked TC.
(iv) Categorise all outgoing calls as priority or normal so that
FIG. 17 illustrates how the central terminal performs the
normal calls are dropped in favour of priority calls.
above interference limiting function. When incoming call
The priority call procedure in preferred embodiments is as
60 data arrives at a central terminal modem 320, encoder 325
follows:
encodes the data [or transmission owr the wireless link 300
(i) Tht CT will publish Direclory Numbers (DNs) for a
to the subscriber terminal 20. At the subscriber terminal 20,
number of emergency services over the CCc.
the decoder 326 decodes the data, and passes the decoded
(ii) The ST will attempt uplink access according to the
user data over line 328 to the subscriber telecommunications
normal algorithms. If the outgoing access is successful
then the customer is able to dial as normal. All dialled 65 equipment. As the decoder 326 decodes the data, it is able to
establish a bit error rate (BER) estimate 330 associated with
digits are check against the emergency DN list so that
the signal transmission over the wireless link 300, which can
calls may be categorised normal or priority at the CT.

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be passed to the multiplexer 332 for combining with other
signals, such as those from a call control function 336 or user
data on line 338, before being passed to an encoder 334.
Here, the BER estimate is encoded and passed on the OMC
channel over the wireless link 310 to the decoder 340 within
the central terminal modem 320. Once decoded by the
decoder 340, the signal passes to the multiplexer 345, where
the BER estimate from the subscriber terminal is detected
and passed over line 355 to the dynamic pool sizing function
360.
Further, as at the subscriber terminal 20, the decoder 340
within the central terminal modem 320 is able to establish a
bit error rate estimate 350 associated with the signal transmission over the wireless link 310. This BER estimate 350
is also passed over line 355 to the dynamic pool sizing
function 360. The dynamic pool sizing function 360 is
provided on the CT modem shelf 302, and receives BER
estimates from each of the modems on that shelf indicated
by the lines entering the bottom of the dynamic pool sizing
function 360.
In addition to BER estimates, grade of service (GOS) data
is obtained from two sources. Firstly, at each subscriber
terminal 20, the call control function 336 will note how
readily it is able to establish traffic channels for transmitting
and receiving data, and from this can provide a GOS
estimate to the multiplexer 332 for encoding by the encoder
334 for subsequent transmission over the wireless link 310
to the central terminal modem 320. Here, the GOS estimate
is decoded by decoder 340, passed through multiplexer 345,
and then the GOS estimate is passed over line 355 to the
dynamic pool sizing function 360.
Additionally, incoming call information to the central
terminal, other than call information from the subscriber
terminals 20 connected to the central termina1, is provided
over the concentrated network interface 390 to the DA
engine 380. The DA engine 380 includes a call control
function, similar to the call control function 336 in each of
the subscriber terminals 20, for each of the modems on the
modem shelf. Hence, in a similar fashion to the call control
function 336 at the subscriber terminals 20, the call control
functions within the DA engine 380 are also able to provide
GOS estimates for incoming calls, and these GOS estimates
are passed over line 395 to the dynamic pool sizing function
360.
At set up, the management system 370 within the element
manager will have connected to the central terminal, and
provided the dynamic pool sizing function 360 within the
modem shelf with data identifying a TIER goal, a GOS goal,
and a pool size limit (i.e. the number of channels that can be
used for data traffic). The dynamic pool sizing function 360
then compares this data from the management system with
the actual BER, actual GOS, and the actual pool size
information that it receives. A suitable algorithm can be
provided within the dynamic pool sizing function 360 to
determine, based on this information, whether pool sizing is
appropriate. For example, if the actual bit error rate exceeds
the BER goal provided by the management system 370, then
the dynamic pool sizing function 360 may be arranged to
send a pool sizing request to the demand assignment engine
380.
The demand assignment engine 380 provides modem
enable signals over lines 400 to each of the modems on the
CT modem shelf. If the dynamic pool sizing function 360
bas requested that the DA engine 380 perform pool sizing,
then the DA engine 3~U can disable one or more of the
modems, this causing the interference, and hence the actual
BER, to be reduced. Apart from being used for interference

limiting, the DA engine is also responsible, in preferred
embodiments, for providing the encoders 325 with instructions on which set of overlay codes or how many IDM slots
to be used for signals to be transmitted to the STs 20.
The dynamic pool sizing function can store the BER and
GOS information received in the storage 365, and periodically may pass that data to the management system 370 for
analysis. Further, if the system is unable to attain the BER
or GOS goal with the allocated pool size, the dynamic pool
sizing function can be arranged to raise an alarm to the
management system. The receipt of this a.larm will indicate
to personnel using the management system that manual
intervention may be required to remedy the situation, eg by
the provision of more central terminal hardware to support
the S'TI,.
The COMA approach used in preferred embodiments
exhibits the property that the removal of any of the orthogonal channels (by disabling the modem) will improve the
resistance of the other channels to interference. Hence, a
suitable approach for the demand assignment engine 380,
upon receipt of pool sizing request from the dynamic pool
sizing function 360, is to disable the modem that has the
least traffic passing through it.
RF Channel Switching
In preferred embodiments, it has been realised that if an
ST is allowed to operate from more than one CT Modem
Shelf;RP Channel then the following benefits may be realised:
(i) Fault lOlerance-sh01~ld a CT Modem Shelf sub-system
fault occur, an ST may switch to an alternative frequency
for service.
(ii) Call blocking-an ST denied service from one CT shelf
may choose to switch to an alternative frequency for
service.
(iii) Traffic load balancing-the Element Manager mayan
the basis of call blocking statistics choose to move STs
between CT shelves.
(iv) Frequency diversity-in the presence of channel selective fading (slo\v multipath) an ST may operate on the
frequency channel offering highest signal strength and
lowest soft error count.
RF channel s\vitching is only possible where there are two
or more co-located CT shelves serving the same geograpllical area on different RF frequency channels within the same
RF band. A deployment that meets this criterion may be
configured as a 'Service Domain'. Possible deployment
scenarios are illustrated in FIG. 18. FIG. 18(i) shows an
arrangement where omni antennae are used to provide the
entire ce1l with four frequency channels, eg PI, P4, P7, PI0.
FIG. 18(ii) shows an arrangement where sectored antennae
are used to provide six separate sectors within a cell, each
sector being covered by two frequency channels. FIG. 18(iii)
shows an alternative arrangement where three sectored
antennae are used to divide the cell in to three sectors, each
sector being covered by a separate frequency channel, and
then an omni antenna is used to provide an 'umbrella'
coverage for the entire cell, this coverage employing a
frequency channel different to the three fn~quency channels
used by the sectored antennae.
For the system to work effectively, the STs must be able
to switch channels quickly, and fast channel switching
necessitales that CTshelf synchronisation be provided at the
following levels:
(i) CDMAPN code. This preserves uplink code phase across
RF channels during warm start; and
(ii) RF carrier frequency. This eliminates the need for the
coarse frequency search on a downlink RF channel
switch.

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On installation, an ST will be programmed with an RF
channel and PN code, these codes specifying the ST's initial
home channel.
The manner in which channel switching is facilitated in
preferred embodiments will be described with reference to
FIGS. 19A and 19B. A service domain controller 400 is
preferably provided to act as an interface between the
exchange connected to the service domain controller over
path 405 and a number of central terminals 10 connected to
the service domain controller over paths 410. The central
terminals connected to the service domain controller form a
'service domain' of central terminals that may be used by a
subscriber terminal 20 for handling communications.
In preferred embodiments, the service domain controller
400 is used to provide each CT 10 with appropriate information about the other CTs within the service domain. Each
CT can then broadcast a 'Service Domain' message comprising a list of RF frequencies and CT Identifiers that form
a Service Domain to be used by the STs for subsequent RF
switching [unctions. The ST then stores this information for
future reference when establishing a link with one of the
CTs. It is preferable for each CT to broadcast the service
domain message since an ST may be listening to any of the
CIs at the time that the message is broadcast.
Each CT database will hold an entry for every ST located
within the Service Domain. Each database entry describes
how the CT views it's relationship with the ST and may be
marked as:
(i) Primary service provider-the CT is the ST's home
channel. All management communication with an ST is
via it's home CT.
(ii) Supplying backup service-the CT is providing service
to the ST.
(iii) Available for backup service-the CT will provide
service to the ST if required.
It should be noted that the ST need not switch to an
entirely different CT, but can instead switch to a different CT
shelf (and hence different RF frequency channel) within the
same CT. However, in preferred embodiments, the ST will
typically switch to a different CT, since some errors experienced by one CTshelfmay also affect other shelves within
the same CT, and so for fault tolerance (described in IIlore
detail below), it is preferable for the ST to switch to a
separate CT.
Database consistency across CT shelves is preferably
supported through the service domain controller 400. Database consistency needs to be real-time so that an ST entering
the network is allowed full Service Domain access immediately (the Service Domain message is broadcast to all STs,
and so a new ST will expect access across the full Service
Domain).
Incoming access via backup CTs requires some function
to be provided to broadcast duplicate incoming call setup
messages to all CTs that form a Service Domain. Preferably
this is handled by the service domain controller 400, which
forwards incoming call setup messages to each CT operating
in the service domain. All CTs will allocate Access_In
Traffic Channels and relay the incoming call setup message
via the Call Control Channel. On successful uplink access,
one CT will respond to the service domain controller with a
call accepted message, the other CTs will eventually respond
with call setup failed messages. Outgoing access via a
backup CT is similar to normal outgoing access.
Another job which can be performed by the service
domain controller is to assist the element manager 58 in
reconfiguring equipment in the event of a fault. For example,
if one CT is taken out of commission because of a fault, a

different CT can be brought 'on-line', and the service
domain controller can provide that new Cf with the necessary information about the other CTs in the service domain.
FIG. 19B illustrates those elements of the subscriber
terminal used to implement RF channel switching. The radio
subsystem 420, which incorporates the transmission and
reception signal processing stages, will pass any data
received on the call control channel over line 425 to the
mes.~age decoder 430. T the decoder 430 determines th at the
f
data on the call control channel forms a service domain
message, then this is passed over line 435 to the channel
selection controller 440, where the information within the
service domain message is stored in storage 445.
Similarly, if the message decoder identifies the data as a
'free list' identifying the available traffic channels on a
particular RF frequency, then this data is passed to the call
control function 336 and the channel selection controller 440
over path 450. The call control function 336 stores the free
list in the storage 445 for subsequent use by the call control
[unction 336 and the channel selection controller 440.
If the message decoder 430 determines that the data forms
an incoming call setup message, then that information is
supplied over line 455 to the call control function 336 and
the channel selection controller 440 for processing. The
incoming call setup message will typically specify a TC on
the current frequency channel which should be used to
access the incoming call, and the channel selection controller will a ttempt to establish a link on that TC. The channel
selection controller will in such cases instruct the radio
sub-system 420 over line 465 to use the current frequency
channel to establish the required link. If, on the other hand,
the traffic channel specified in the call setup message is
'null', the channel selection controller has the option to
change RF frequency using the information stored in storage
445 about the other CTs in the service domain.
To enable the channel selection controller 440 to receive
information about the status of links, a link operating status
signal can be supplied over line 470 from the radio subsystem. This signal will give an indication of the radio link
quality, and may be a simple 'OK' or 'failed' indication, or
alternatively may include extra information such as BER
values for the link. This information can be used by the
channel selection controller to determine whether a particular frequency channel should be used or not.
To enable the call control function to specify a specific
Access-Out channel for outgoing calls, a line 460 is provided between the call control function 336 and the channel
selection controller 440. The call control function 336 may
choose an access-out channel from the free list in storage
445, and instruct the channel selection controller over line
460 to attempt acquisition of that channel.
The following examples indicate how the above described
structure may be used to perform channel switching in
particular circumstances.
RF Channel Switching for Fault Tolerance
Should one RF channel suffer complete loss of downlink,
the following process takes place in preferred embodiments:
(i) The ST will attempt downlink re-acquisition for a period
of time, say 20 seconds.
(ii) If acquisition fails, the channel selection controller 440
of the ST will selectlhe next available channel from lhe
Service Domain information in storage 445 and attempt
downlink acquisition. This process will be repeated until
a downlink signal is acquired.
(iii) Once a backup RF channel is located, the STwill 'camp'
on lhe Call Control Channel and may subsequently be
granted traffic access.

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(iv) If the cr fault persists, the EM 58 may use the service
quency channel to enable data items perta.tning to a plurality
of wireless links to be transmitted simultaneouslv within
domain controller 400 to reconfigure the Service Domain
different code division multiplexed channels of said single
so that the functioning CT shelves become primary serfrequency channel, the interference controller comprising:
vice providers for the pool of 'homeless' SIs.
a channel controller arranged to allocate a number of said
A fault that does not result in complete loss of downlink
plurality of code division mUltiplexed channels as a
signal will not result in RF channel switching 'en mass'.
channel pool of code division multiplexed channels
Rather, a fault may result in excessive or total call blocking,
available for the establishment of said wireless links;
as discussed below.
an analyzer for receiving parameters pertaining to a
RF Channel Switching for Call Blocking
wireless link within the cell indicative of whether that
If Incoming access traffic channels are being blocked, the 10
wireless link is subject to interference froIll signals
following process is employed in preferred embodiments:
generated by said other cells, the analyzer being
(i) The call setup message sent over the Call Control
arranged to compare those parameters with predeterChannel will specify a TC on which to access the call.
mined criteria and to generate an output signal depen(ii) In the case of incoming access being blocked, the CT
dent on the comparison;
will specify a null TC. The channel selection controller 15
440 of the ST will in such cases switch to the next RF
a channel controller being responsive to the output signal
channel from the Service Domain information in storage
from the analyser, to selectively reduce the number of
445 and monitor the Call Control ChanneL
code division multiplexed channels in the channel pool
in order to reduce the effect of the interference from
(iii) If the ST receives a call setup message with a valid TC,
then the call is processed as normal.
said other cells.
20
(iv) When the call clears, the ST downlink preferably
2. An interference controller as claimed in claim 1,
switches back to the home CT.
wherein a parameter provided to the analyser is the bit error
If Outgoing access traffic channels are being blocked, the
rate (BER) for signals transmitted within said code division
following process is employed in preferred embodiments:
multiplexed channels, and the predetermined criteria with
(i) The ST registers an off-hook. The Free List in storage 445 25 which the analyser compares said BER is a threshold BER
is checked and if a traffic channel is available, then the call
value identifying a predetermined maximum acceptable
control function 336 asserts a channel request on line 460
BER, the channel controller being responsive to the analyser
to the channel selection controller 440 and normal uplink
indicating that the BER exceeds the predetermined maxiaccess is attempted.
mum acceptable BER to remove a code division multiplexed
(ii) If the Free List shows no Access_Out channels are 30 channel from the channel pooL
available on the current frequency channel, then the
3. An interference controller as claimed in claim 1,
channel selection controller will be used to switch the ST
wherein a parameter provided to the analyser is a grade of
to the next RF channel in the Service Domain, whereupon
service (GOS) signal indicative of the availability of the
the ST will wait for the next Free List.
code division multiplexed channels, and the predetermined
(iii) When the ST finds a Free List with an available 35 criteria with which the analyser compares said GOS signal
Access_Out channel, then uplink access is attempted and
is a threshold GOS value identifying a predetermined maxithe call is processed as normal.
mum grade of service, the channel controller being respon(iv) When the call clears, the ST downlink preferably
sive to the analyser indicating that the GOS signal has
switches back to the home CT.
exceeded the predetermined maximum grade of service to
RF Channel Switching for Traffic Load Balancing
40 remove a code division multiplexed channel from the chanTraffic load balancing is, in preferred embodiments, pronel pool.
vided by static configuration via the EM 58. Call blocking
4. An interference controller as claimed in claim 1,
and setup time statistics may be forwarded to the EM where
wherein the channel controller, upon receipt of a signal from
an operator may decide to move an ST to another RF
the analyser indicating that a code division multiplexed
channel.
45 channel should be removed from use, is arranged to deterRF Channel Switching for Frequency Diversity Frequency
mine which code division multiplexed channel is least
diversity is, in preferred embodiments, provided by static
heavily used, and to remove that code division multiplexed
configuration via the EM 58. Radio link statistics may be
channel from the channel pooL
forwarded to the EM where an operator may decide to
5. An interference controller as claimed in claim 1,
move an ST to another RF channel.
50 wherein a plurality of the code division multiplexed chanAlthough a particular embodiment has been described
nels arc designated as traffic channels, the analyser is
herein, it will be appreciated that the invention is not limited
arranged to monitor the parameters relating to interference
thereto and that many modifications and additions thereto
on those traffic channels, and the channel controller is
may be made within the scope of the invention. For example,
arranged to selectively designate one or more of said traffic
various combinations of the features of the following depen- 55 channels as locked channels which should not be included in
dent claims could be made with the features of the indepenthe channel pool so as to reduce the effect of the interference
dent claims without departing from the scope of the present
from said other cells.
invention.
6. An interference controller as claimed in claim 5,
What is claimed is:
wherein if the analyser determines that a BER signal is
1. An interference controller for limiting in one cell the 60 below a predetermined minimum BER value, the channel
elIed of interference generated by other cells of a wireless
controller is arranged to designate one o[ said locked chantelecommunications system, each cell of the wireless telenels as a free traffic channel and to include that traffic
communications system having a central terminal and a
channel in the channel pool so that it can subsequently be
plurality of subscriber terminals, communication between a
used for clata traffic.
central terminal and a subscriber terminal being arranged to 65
7. An interference controller as claimed in claim 5,
occur over a wireless link, a plurality of code division
wherein if the analyser determines that a GOS signal has
multiplexed channels being provided within a single fredropped below a second predetermined minimum GOS

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32

value, the channel controller is arranged to designate one of
wireless links to be transmitted simultaneously within
different code division multiplexed channels of said
said locked channels as a free traffic channel and to include
single frequency channel.
that traffic channel in the channel pool so that it can
13. An interference controller as claimed in claim 1,
subsequently be used for data traffic.
further comprising a transmission controller for processing
8. An interference controller as claimed in claim 5,
data items to be transmitted over a wireless link connecting
wherein the channel controller is provided with a value
a central terminal and a subscriber terminal of a wireless
indicating a maximum number of code division multiplexed
telecommunications system, a single frequency channel
channels that can be designated as traffic channels, the
being employed for transmitting data items pertaining to a
channel controller only adding code division multiplexed
channels upon request from the analyser if doing so would 10 plurality of wireless links, the transmission controller comprising:
not exceed the maximum number of code division multian orthogonal code generator for providing an orthogonal
plexed channels.
code from a set of 'm' orthogonal codes used to create
9. An interference controller as claimed in claim 5,
'm' orthogonal channels within the single frequency
wherein a number of the traffic channels are reserved as call
channel;
channels, and a number of the traffic channels are designated 15
a first t:ncodt:r for combining a data itt:m to bt: transmilLt:d
as free channels, and if a call channel is used to pass call
on the single frequency channel with said orthogonal
data, the channel controller is arranged to designate a free
code from the orthogonal code generator, the orthogochannel as a call channel if a free channel is available,
nal code determining the orthogonal channel over
thereby improving the chance of a call channel being
which the data iLt:m is transmiUed, whereby daLa items
available [or a subseyuenL call.
20
pertaining to different wireless links may be transmitted
10. An interference controller as claimed in claim 1,
simlJltaneollsly within different orthogonal channels of
wherein said code division multiplexed channels are
said single frequency channel;
orthogonal channels, a set of orthogonal codes being used to
an overlay code generator for providing an overlay code
create said orthogonal channels.
from a first set of 'n' overlay codes which are orthogo11. A central terminal for a cell of a wireless telecommu- 25
nal to each other; and
nications system, the telecommunications system having a
a second t:ncoder arranged Lo apply tht: ovt:rlay c.:ode [rom
plurality of cells, and each cell having a central terminal and
the overlay code generator to said data item, whereby
a plurality of subscriber terminals, communication between
'n' data items pertaining to different wireless links may
be transmitted simultaneously within the same orthogothe central terminal and a subscriber terminal in said cell
nal channel.
being arranged to occur over a wireless link, a plurality of 30
14. An interference controller as claimed in claim 1,
code division multiplexed channels being provided within a
further comprising a reception controller for processing data
single frequency channel to enable data items pertaining to
items received over a wireless link connecting a central
a plurality of wireless links to be transmitted simultaneously
terminal and a subscriber terminal of a wireless telecomwithin different code division multiplexed channels of said
single frequency channel, the central terminal comprising an 35 munications system, a single frequency channel being
employed for transmitting data items pertaining to a pluralinterference controller for limiting the effect of interference
ity of wireless links, the receiver controller comprising:
generated by other cells of said wireless telecommunications
an orthogonal code generator for providing an orthogonal
system, the interference controller having;
code from a set of 'm' orthogonal codes used to create
a channel controller arranged to allocate a number of said
'm' orthogonal channels within the single frequency
plurality of code division multiplexed channels as a 40
channel;
channel pool of code division multiplexed channels
a first decoder for applying, to signals received on the
available for the establishment of said wireless links;
single frequency channel, the orthogonal code provided
an analyzer for receiving parameters pertaining to a
by the orthogonal code generator, in order to isolate
data items transmitted within the corresponding
wireless link within the cell indicative of whether that
orthogonal channel;
wireless link is subject to interference from signals 45
an overlay code generator for providing an overlay code
generated by said other cells, the analyzer being
from a first set of '[)' overlay codes which are orthogoarranged to compare those parameters with predeternal to each other, the set of 'n', overlay codes enabling
mined criteria and to generate an output signal depen'n' data items pertaining to different wireless links to be
dent on the comparison,
transmitted simultaneously within the same orthogonal
a channel controller being responsive to the output signal 50
channel; and
from the analyser, to selectively reduce the number of
a second decoder for applying, to the data items of the
code division multiplexed channels in the channel pool
orthogonal channel, the overlay code from the overlay
in order to reduce the effect of the interference from
code generator so as to isolate a particular data item
said other cells.
transmitted using that overlay code.
55
12. A central terminal as claimed in claim 11, further
15. An interference controller as claimed in claim L
compnsmg:
further comprising a transmission controller for processing
an orthogonal code generator for providing an orthogonal
data items to be transmitted over a wireless link connecting
code from a set of orthogonal codes used to create said
a central terminal and a subscriber terminal of a wireless
code division multiplexed channels within the single 60 telecommunications system, a single frequency channel
frequency channel;
being employed for transmitting data items pertaining to a
plurality of wireless links, the transmission controller coma first encoder for combining a data item to be transmitted
prising:
on the single frequency channel with said orthogonal
code from the orthogonal code generator, the orthogoan orthogonal code generator for providing an orthogonal
nal code determining the code division mUltiplexed 65
code from a set of 'm' orthogonal codes used to create
channel over which the data item is transmitted,
'm' orthogonal channels within the single frequency
thereby enabling data items pertaining to different
channel;

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a first encoder for combining, a data item to be transmitted
l.ink acquisition logic for establishing a wireless link on
on the single frequency channel with said orthogonal
the frequency channel selected by the selector;
code from the orthogonal code generator, the orthogothe selector being responsive to the link acquisition logic
nal code determining the orthogonal channel over
being unable to establish said wireless link, to select an
which the data item is transmitted, whereby data items
alternative frequency channel from those listed in said
pertaining to difterent wireless links may be transmitted
storage.
simultaneously within different orthogonal channels of
19. An interference controller as claimed in claim 15,
said single frequency channel; and
further comprising a channel selection controller for estaba TDIvI encoder arranged to apply time division multilishing a wireless link connecting a central terminal and a
plexing (TOM) techniques to the data item in order to
insert the data item within a time slot of the orthogonal 10 subscriber terminal of a wireless telecommunications
system, at least two frequency channels being provided over
channel, whereby a plurality of data items relating to
which said wireless link could be established, the channel
different wireless links may be transmitted within the
controller comprising:
same orthogonal channel during a predetermined frame
a storage for storing data identifying the at least two
period.
16. An interference controller as claimed in claim 1, 15
frequency channels;
further comprising a reception controller for processing data
a selector for selecting a frequency channel from those
items received over a wireless link connecting a central
listed in said storage;
terminal and a subscriber terminal of a wireless telecomlink acquisition logic for establishing 3. wireless link on
munications system, a single frequency channel being
the frequency channel selected by the selector;
employed for transmitting data items pertaining to a plural- 20
the selector being responsive to the link acquisition logic
ity of wireless links, and 'm' orthogonal channels being
being unable to establish said wireless link, to select an
provided within the single frequency channel, the receiver
alternative frequency channel from those listed in said
controller comprising:
storage.
an orthogonal code generator for providing an orthogonal
20. An interference controller as claimed in claim 16,
code from a set of 'm' orthogonal codes used to create 25
further comprising a channel selection controller for estabsaid 'm' orthogonal channels within the single frelishing a wireless link connecting a central terminal and a
quency channel;
subscriber terminal of a wireless telecommunications
a first decoder for applying, to signals received 011 the
system, at least two frequency channels bcing provided over
single frequency channel, the orthogonal code provided
by the orthogonal code generator, in order to isolate 30 which said wireless link could be established, the channel
controller comprising:
data items transmitted within the corresponding
a storage for storing data identifying the at least two
orthogonal channel; and
frequency channels;
a TDM decoder arranged to extract a data item from a
predetermined time slot within said orthogonal
a selector for selecting a frequency channel from those
channel, a plurality of data items relating to different 35
listed in said storage;
wireless links being transmitted within the same
link acquisition logic for establishing a wireless link on
orthogonal channel during a predetermined frame
the frequency channel selected by the selector;
period.
the selector being responsive to the link acquisition logic
17. An interference controller as claimed in claim 13,
being unable to establish said wireless link, to select an
further comprising a channel selection controller for estab- 40
alternative frequency channel from those listed in said
lishing a wireless link connecting a central terminal and a
storage.
subscriber terminal of a wireless telecommunications
21. A wireless telecommunications system comprising a
system, at least two frequency channels being provided over
plurality of cells, each cell having a central terminal and a
which said wireless link could be established, the channel
plurality of subscriber terminal,>, communication between a
45
controller comprising:
central terminal and a subscriber terminal within a cell being
a storage for storing data identifying the at least two
arranged to occur over a wireless link, a plurality of code
frequency channels;
division multiplexed channels being provided within a
a selector for selecting a frequency channel from those
single frequency channel to enable data items pertaining to
listed ill said storage;
50 a plurality of wireless links to be transmilted simultaneously
link acquisition logic for establishing a wireless link on
within different code division multiplexed channels of said
the frequency channel selected by the selector;
single frequency channel, at least one eell of the wireless
telecommunications system comprising an interference conthe selector being responsive to the link acquisition logic
troller for limiting the effect of interference generated by
being 1111able to establish said wireless link, to select an
alternative frequency channel from those listed in said 55 other cells of said wireless telecommunications system, the
interference controller including:
storage.
18. An interference controller as claimed in claim 14,
a channel controller arranged to allocate a number of said
further comprising a channel selection controller for estabplurality of code division multiplexed channels as a
lishing a wireless link connecting a central terminal and a
channel pool of code division multiplexed channels
subscriber terminal of a wireless telecommunications 60
available for the establishment of said wireless links;
system, at least two frequency channels being provided over
an analyzer [or receiving parameters pertaining to a
which said wireless link could be established, the channel
wireless link within the cell indicative of whether that
controller comprising:
wireless link is subject to interference from signals
a storage for storing data identifying the at least two
gelli~rated by said other cells, the analyzer being
frequency channels;
65
arranged to compare those parameters with predetera selector for selecting a frequency channel from those
mined criteria and to generate an output signal depenlisted in said storage;
dent on the comparison,

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a channel controller being responsive to the output signal
responsive to the generated output signal, selectjvely
from the analyser, to selectively reduce the number of
reducing the number of code division multiplexed
code division multiplexed channels in the channel pool
channels in the channel pool in order to reduce the
in order to reduce the effect of the interference from
effect of the interference from said other cells.
said other cells;
23. A method as claimed in claim 22, further comprising
wherein a parameter provided to the analyser is the bit
the steps of:
error rate (BER) for signals transmitted within said
providing the analyser with a parameter identifying the bit
code division multiplexed channels, and the predetererror rate (BER) for signals transmitted within said
mined criteria with which the analyser compares said
code division multiplexed channels;
HER is a threshold HER value identifying a predeter- 10
supplying as the predetermined criteria with which the
mined maximum acceptable BER, the channel controlanalyser compares said BER a threshold BER value
Itr being responsive to the analyser indicating that the
identifying a predetermined maximum acceptable
BER exceeds the predetermined maximum acceptable
BER; and
HER to remove a code division multiplexed channel
from the channel pool;
if the gentrated output signal indicates that the BER
15
wherein a parameter provided to the analyser is a grade of
exceeds the predetermined maximum acceptable BER,
service (GOS) signal indicative of the availahility of
then at said selectively reducing step removing a code
the code division multiplexed channels, and the prededivision multiplexed channel from the channel pool.
Lermined criteria with which the analyser compares said
24. A method as claimed in claim 22, further comprising
GOS signal is a threshold GOS value identifying a
the steps of:
predetermined maximum grade of service, the channel 20
providing the analyser with a parameter identifying a
controller being responsive to the analyser indicating
grade of service (GOS) signal indicative of the availLhat the GOS signal has exceeded the predetermined
ability of the code division multiplexed channels;
maximum grade of service to remove a code division
multiplexed channel from the channel pool;
supplying as the predetermined criteria with which the
analyser compares said GOS signal a threshold GOS
wherein a plurality of the code division multiplexed 25
value identifying a predetermined minimum grade of
channels are designated as traffic channels, the analyser
is arranged to monitor the parameters relating to interservice; and
ference on those traffic channels, and the channel
if the generated output signal indicates that the GOS
controller is arranged to selectively designate one or
signal has dropped below the predetermined minimum
more of said traffic channels as locked channels which 30
grade of service, then at said selectively reducing step
should not be included in the channel pool so as to
removing a code division multiplexed channel [rom the
reduce the effect of the interference from said other
channel pool.
cells
25. A method as claimed in claim 22, wherein, if the
wherein if the analyser determines that a BER signal is 35 generated output signal indicates that a code division mulbelow a predetermined minimum BER value, the chantiplexed channel should be removed from use, then at said
nel controller is arranged to designate one of said
selectively reducing step it is determined which code divilocked channels as a free traffic channel which can
sion multiplexed channel is least heavily used, and that code
subsequently be used for data traffic; and
division multiplexed channelis removed from the channel
wherein if the analyser determines that a GOS signal has
dropped below a second predetermined minimum GOS 40 pool.
26. A method as claimed in claim 24, wherein, if the
value, the channel controller is arranged to designate
generated output signal indicates that a code division mulone of said locked channels as a frec traffic channel and
tiplexed channel should be removed from use, then at said
to include that traffic channel in the channel pool so that
selectively reducing step it is determined which code diviit can subsequently be used for data traffic.
22. A method of limiting in one cell the effect of inter- 45 sian multiplexed channel is least heavily used, and that code
division multiplexed channel is removed from the channel
ference generated by other cells of a wireless telecommupool.
nications system, each cell of the wireless telecommunica27. A method as claimed in claim 22, wherein a plurality
tions SYSTem having a central terminal and a plurality of
of the code division multiplexed channels are designated as
subscriber terminals, communication between a central terminal and a subscriber terminal being arranged to occur over 50 traffic channels, the analyser being arranged to monitor the
parameters relating to interference on those traffic channels,
a wireless link, a plurality of code division multiplexed
and at said selectively reducing step the method comprising
channels being provided within a single frequency channel
the steps of selectively designating one or more of said
to enable data items pertaining to a plurality of wireless links
traffic channels as locked channels which should not be
to be transmitted simultaneously within different code division multiplexed channels of said single frequency channel, 55 included in the channel pool so as to reduce the effect of the
interference from said other cells.
the method comprising the steps of:
28. A method as claimed in claim 27, further comprising
allocating a number of said plurality of said code division
the steps of:
multiplexed channels as a channel pool of code division
reserving a number of the traffic channels as call channels;
multiplexed channels available for the establishment of
said wireless links;
designating a number of the traffic channels as free
60
channels; and
employing an analyzer to receive parameters pertaining to
a wireless link within the cell indicative of whether that
if a call channel is used to pass call data, designating a free
wireless link is subject to interference from signals
channel as a call channel if a free channel is available,
generated by said other cells and to compare these
thereby improving the chance of a call channel being
parameters with predetemlined criteria;
available for a subsequent call.
65
generating an output signal dependent on the comparison;
and
* * *
*

WI L-0009842