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

Filing 491

RESPONSE to Motion re 482 MOTION for Judgment as a Matter of Law [RENEWED] OF NO INVALIDITY OR, ALTERNATIVELY, MOTION FOR NEW TRIAL ON INVALIDITY filed by Alcatel-Lucent USA Inc., Ericsson Inc., Exedea INC., HTC America, Inc., HTC Corporation, Sony Mobile Communications (USA) Inc., Sony Mobile Communications AB, Telefonaktiebolaget LM Ericsson. (Attachments: # 1 Exhibit A: Trial Transcript, # 2 Exhibit B: Trial Transcript, # 3 Exhibit C: Trial Transcript, # 4 Exhibit D: Trial Transcript, # 5 Exhibit E: Trial Transcript, # 6 Exhibit F: Trial Transcript, # 7 Exhibit G: Trial Transcript, # 8 Exhibit H: DDX 13-19, # 9 Exhibit I: DDX 13-31, # 10 Exhibit J: DX 124, # 11 Exhibit K: DX 148, # 12 Exhibit L: PX 1, # 13 Text of Proposed Order)(Heinlen, James)

EXHIBIT L

111111111111111111111111111111111111111111111111111111111111111111111111111·
US006088326A

United States Patent
Lys~jko

[11]

et al.

[54]

Inventors: Martin Lysejko, Bagshot, United
Kingdom; Paul F. Struhsaker, Plano,
Tex.

[73]

Assignee: Airspan Cummunicatiuns
Corporation, Wilmington, Del.

6,088,326

Date of Patent:

Jul. 11, 2000

PROCESSING DATA TRANSMITTED AND
RECEIVED OVER A WIRELESS LINK
CONNECTING A CENTRAL TERMINAL AND
A SUBSCRIDER TERMINAL OF A WIRELESS
TELECOMMUNICATIONS SYSTEM

[75]

Patent Number:

[45]

[19]

f21l

Filed:

[30]

Nov. 26, 1997

Foreign Application Priority Data

Dec. 20, 199n

[51]

l52j
[58]

[GR]
7

United Kingdom ................... 902()507

H04J 11/00; H04J 13/00;
II04D 7/216
U.S. CJ ........................... 370/209; 370/342; 370/345;
370/441; 370/442; 370/479
Field of Search ..................................... 370/328, 329,
370/330, 335, 336, 337, 340, 341, 342,
343,345,347,441,442,465,468,479,
498, 203, 208, 209

Int. Cl.

.............. .. ...... .... . ..

References Cited

[56]

U.S. PA1ENT DOCUMENTS
4,688,210 8/1987 Eizenhoffer eta!. ................... 370/342
4,799,252 1/1989 Eizenhoffer et a!. ................... 370/342
5,373,502 12/1994 Turban ...................................... 370/18
5,592,469
li1997 Szabo .... ... .. .... .... ... ......... ... .... .. 370/342
6,005,854 12/1999 Xu et al. ................................. 370/335

FOREIGN PATENT DOCUMENTS
0652650

5/1995

European PaL Off. .. ........ H04L 1/00
United Kingdom .. ....... .... H04Q 7/32
WTPO .. ............................ H04N 1 /00
WIPO .. ........................... H04J 13/00
WIPO .. .. .. ...... ...... ... .... .. .. .. H04J 3/22

Primary Examiner-Ricky Ngo
Attorney, Agent, or Firm-Baker Botts L.L.P.
ABSTRACT

l57J

Appl. No .: 08/979,408

[22]

0730356
9/1996
2301744 12/1996
9::114590 7/'1993
9315573 8/1993
9523464 8/1995

The present invention provides a transmission controller and
method for processing data items to be transmitted over a
wireless link connecting a central terminal and a subscriber
terminal of a wireless telecommunications system, a single
frequency channel being employed for transmitting data
items pertaining to a plurality of wireless links. The transmission controller comprises an orthogonal code generator
for providing an orthogonal code from a set of 'm' orthogonal codes used to create 'm' orthogonal channels within the
single frequency channel, and a first encoder for combining
a data item to be transmitted on the single frequency channel
with said orthogonal code from the orthogonal code
generator, the orthogonal code determining the orthogonal
channel over which the data item ·is transmitted, whereby
data items pertaining to diiTen:nt wireless links may be
transmitted simultaneously within different orthogonal
channels of said single frequency channeL Further, the
transmission controller comprises a IDM encoder arranged
to apply time division multiplexing (TDM) techniques to the
data item in order to insert the data item within a time slot
of the orthogonal channel, whereby a plurality of data items
relating to difl::erent wireless links may be transmitted within
the same orthogonal channel during a predetermined frame
period. The invention also provides a reception controller
and method for processing data items received over a
wireless link.
15 Claims, 1li Orawing Sheets

European Pat. Off..... ...... H04B 7i26

113

126

140

1.38

136

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PLAINTIFF'S TRIAL
EXHIBIT
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Jul. 11, 2000

6,088,326

Sheet 1 of 16

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6,088,326

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Jul. 11, 2000

6,088,326

Sheet 4 of 16

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6,088,326

Sheet 11 of 16

Jul. 11, 2000

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Jul. 11, 2000

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6,088,326

Sheet 12 of 16

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Sheet 16 of 16

Jul. 11, 2000

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WIL-0009791

o,OR8,326
1

2

PROCESSING DATA TRANSMITTED AND
RECEIVED OVER A WIRELESS LINK
CONNECTING A CENTRAL TERMINAL AND
A SUBSCRIBER TERMINAL OF A WIRELJESS
TELECOMMUNICATIONS SYSTEM

communications system, and as it is desirable for neighbouring cells to use different frequency channels so as to
reduce interference, the demand cannot be met by merely
adding more modem shelves to each central terminal.
SUMMARY OF TI-lE INVENTION

TECHNICAL FIELD OF THE INVENTION

According to the present invention, there is provided a
transmission controller for processing data items to be
transmitted over a wireless tink connecting a central termi10 nal and a subscriber terminal of a wireless telecommunications system, a single frequency channel being employed for
transmitting data items pertaining to a plurality of wireless
links, the transmission controller comprising: an orthogonal
BACKGROUND OF THE INVENTION
code generator for providing an orthogonal code from a set
15
A wirdess telecommunications system has been proposed
of ·'m' orthogonal codes used to create 'm' orthogonal
channels within the single frequency channel; a first 1;ncoder
in which a geographical area is divided in to cells, each cell
having one or more central terminals (CTs) for communifor combining a data item to be transmitted on the single
frequency channel with said orthogonal code from the
cating over wireless links with a number of subscriber
orthogonal code generator, the orthogonal code determining
terminals (S'ls) in the cell. These wireless links are estab20
lished over pr~determined frequency channels, a frequency
the orthogonal channel over which the data item is
channel typically consisting of one frequency for uplink
transmitted, whereby data items pertaining to different wiresignals from a subscriber terminal to the central terminal,
less links may be transmitted simultaneously within different
and another frequency for downlink signals from the central
orthogonal channels of said single frequency channel; and a
terminal to the subscriber terminal.
TDM encoder arranged to apply time division multiplexing
25
(TDM) techniques to the data item in order to insert the data
Due to bandwidth constraints, it is not practical for each
item \vithin a time slot of the orthogonal channel, wherehy
individual subscriber terminal to have its own dedicated
a plurality of data items relating to different wireless links
frequency channel for communicating with the central termay be transmitted within the same orthogonal channel
minal. Hence, techniques need to be applied to enable data
items relating to different wireless links to be passed over the 30 during a predetermined frame period.
same frequency channel without interfering with each other.
Viewed from a second aspect, the present invention
In current wireless telecommunications systems, this can be
provides a reception controller for processing data items
achieved through the use of a 'Code Division Multiple
received over a wireless link connecting a central terminal
Access' (CDMA) technique. One way to implement CDMA
and a subscriber terminal of a wireless telecommunications
is through the application of a set of orthogonal codes to the 35 system, a single frequency channel being employed for
data items to be transmitted on a particular frequency
transmitting data items pertaining to a plurality of wireless
channel, data items relating to different wireless links being
links, and 'm' orthogonal channels being provided within the
combined with different orthogonal codes from the set. A
single frequency channel, the receiver controller comprissuitable set of orthogonal codes is a "Rademacher-Walsh"
ing: an orthogonal code generator for providing an orthogo(RW) set of sixteen 16-bit codes. Orthogonal codes have the
nal code from a set of 'm' orthogonal codes used to create
40
property that, when perfectly aligned, all codes crosssaid 'm' orthogonal channels within the single frequency
correlate to zero, thus making it possible to decode a signal
channel; a first decoder for applying, to signals received on
to which one orthogonal code has been applied while
the single frequency channel, the orthogonal code provided
cancelling interference from signals to which different
by the orthogonal code generator, in order to isolate data
orthogonal codes have been applied.
items transmitted within the corresponding orthogonal chan45
nel; and a TDM decoder arranged to extract a data item from
Signals to which an orthogonal code has been applied can
a predetermined time slot within said orthogonal channel, a
be considered as being transmitted over a corresponding
plurality of data items relating to different wireless links
orthogonal channel within a particular frequency charmel.
being transmitted within the same orthogonal channel during
Hence, considering the example of a set of 16 RW codes, 16
orthogonal channels can be created within a single fre- 50 a predetermined frame period.
quency channel, and hence up to sixteen separate commuBy using TDM techniques in addition to the known set of
nication signals (corresponding to sixteen separate wireless
orthogonal codes, it is possible for selected orthogonal
links) can be transmitted simultaneously over the single
channels to be subdivided in the time dimension. For
frequency channel if different RW codes are applied to each
example, if TDM is used to divide one frame period in to
communication signal.
55 four subframes, and each orthogonal channel is subject to
the TDM technique, then up to 64 separate communication
It is known to provide a number of modem shelves within
signals can be transmitted on the sixteen orthogona] chanone central terminal, and for each modem shelf to employ a
nels during one frame period, albeit at a quarter of the rate
different frequency channel. Hence, if a central terminal has
that the communication signals could be transmitted if the
four modem shelves, and the set of 16 RW codes is
employed for each frequency channel, one central terminal 60 TOM technique was not used.
would be able to support wireless links with up to 60
Such an approach has the advantage that it preserves
subscriber terminals simultaneously.
compatibility with current hardware and software equipment
However, as more subscribers subscribe to the wireless
which use the set of orthogonal codes, but which do not
tdecummunicatiuns ne!wurk, it is becoming desirablt: tu
~upport tht u~t uf TDM ttdmiyue::;. By designating '.;trtain
support more and more subscriber terminals from each 65 orthogonal channels as channels for which TDM is not used,
central terminal. There are only a limited number of frethe current equipment can communicate over those channels
quency channels that can be allocated to the wireless telewithout any changes being required to the equipment.
The present invention relates in general to wireless telecommunications systems and more particularly to techniques for processing data transmitted and received over a
wireless link connecting a central terminal and a subscriber
terminal of a wireless telecommunications system.

WIL-0009792

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3
In preferred embodiments, the transnuss1on controller
further comprises: an overlay code generator for providing
an overlay code from a first set of 'n' overlay codes which
are orthogonal to each other; and a second encoder, selectively operable instead of the TDM encoder, to apply the
overlay code from the overlay code generator to said data
item, whereby 'n' data items pertaining to different wireless
links may be transmitted simultaneously within the same
orthogonal channeL
Similarly, the reception controller may further comprise:
an overlay code generator for providing an overlay code
from a first set of 'n' overlay codes which are orthogonal to
each other, the set of 'n' overlay codes enabling 'n' data
items pertaining to different wireless links to be transmitted
simultaneously within the same orthogonal channel; and a
second decoder, selectively operable instead of the TDM
decoder, to apply to the data items of the orthogonal channel,
the overlay code from the overlay code generator so as to
isolate a particular data item transmitted using that overlay
code.
By such an approach, data items transmitted within certain orthogonal channels can be encoded using TDM techniques whilst data items transmitted within other orthogonal
channels can be encoded using overlay codes, the reception
controllers including the necessary decoders to decode either
type of encoded data item. A preferred arrangement, where
certain orthogonal channels are subject to TDM techniques
whilst others are subject to overlay codes, will be discussed
in more detail later.
The orthogonal code generator may be arranged to generate orthogonal codes 'on the fly' using predetermined
algorithms. However, alternatively, the orthogonal code
generator may be provided as a storage arranged to store the
set of orthogonal codes. Appropriate orthogonal codes can
then he read out to the encoder or decoder from the storage
as required.
In preferred embodiments, the set of orthogonal codes
comprise a set of Rademacher-Walsh (RW) codes, in preferred embodiments the set comprising a 16x16 matrix of
RW codes.
The transmission controller in accordance with the
present invention may be provided within the central terminal of a wireless telecommunications system. In preferred
embodiments, the central terminal would further comprise
channelisation means for determining which of the orthogonal channels will be subject to TDM techniques, and for
transmitting that information to a plurality of subscriber
terminals within the wireless telecommunications system.
This is useful since, for example, certain orthogonal channels can hence be designated as being reserved for communications with STs that do not incoqJOrate the features
necessary to support TDM techniques, and which hence
require the full orthogonal channel for the whole frame
period.
In preferred embodiments, the channelisation means also
determines, for those orthogonal channels subject to TDM
techniques, how many time slots will be provided within
each orthogonal channel. This gives a great deal of flexibility in how channels are used, since some can be subdivided
in the time dimension whilst others are not, and those which
are subdivided can be subdivided differently to yield differing numbers of time slots per frame period. For instance, if
an orthogonal channel operates at 160 kb/s, and [our Lime
slots are provided within that orthogonal channel in order to
carry data items pertaining to four different wireless links
during one frame period, then each ST receiving data from

said orthogonal channel will receive data at a rate of 40 kb/s
(since each ST will only read a quarter of the data transmitted on the orthogonal channel during each frame period).
If, alternatively, two time slots are provided within the
orthogonal channel, then data items pertaining to only two
different wireless links will be transmitted per frame period,
and the two STs receiving data will do so at a rate of 80 kb/s
(since each ST will read half of the data transmitted on the
orthogonal channel during one frame period). This flexihil10 ity is useful, since for some communications, eg. fax, a rate
of 40 kb/s may not be acceptable, and hence the use of four
time slots would not be suitable.
In preferred embodiments, a number of said orthogonal
channels are designated as traffic channels for the transmis15 sion of data items relating to communication content, and
the TDM encoder is employed to apply time division multiplexing (TDM) techniques to data items to be sent over a
traffic channel from said central terminal to said subscriber
terminal. The use of this CDMA!fDM hybrid approach for
zo downlink traffic channels retains the benefit of CDMA
access, i.e. interference is reduced when traffic is reduced,
and also reduces receiver dynamic range requirements.
However, a first of the orthogonal channels is preferably
reserved for the transmission of signals relating to the
25
acquisition of wireless links, and the second encoder is used
instead of the TDM encoder to enable overlay codes to be
applied to data items to be sent within said first orthogonal
channel from the central terminal to one of said subscriber
30

~er:~e~a~~~ ;::~~Yfoar ~~~~;n~!1~~:i~~t~~:i~~: 1:~e~~~:l~ f~
1

the control of calls, and the second encoder is used instead
of the TDM encoder to enable overlay codes to be applied
to data items to be sent within said second orthogonal
channel from the central terminal to one of said subscriber
35
terminals.
In preferred embodiments, at least one of the subscriber
terminals of a \vireless telecommunications system comprises a reception controller in accordance with the present
invention. However, for transmission of data from sub40
scriber terminals, it is preferable for the ST to have a
transmission controller which employs overlay codes for all
types of orthogonal channels, whether they be traffic channels or otherwise. On these uplink channels, the pure CDMA
approach using overlay codes eliminates the need to time
45
synchronise STs to a TDM frame reference, and reduces the
peak power handling requirements in the ST RF transmit
chain.
Viewed from a third aspect, the present invention provides
so a wireless telecommunications system comprising a central
terminal and a plurality of subscriber terminals, wherein the
central terminal comprises a transmission controller in
accordance with the present invention, and at least one of the
subscriber terminal comprises a reception controller in
55 accordance with the present invention.
Viewed from a fourth aspect, the present invention provides a method of processing data items to be transmitted
over a wireless link connecting a central terminal and a
subscriber terminal of a wireless telecommunications
60 system, a single frequency channel being employed for
transmitdng data items pertaining to a plurality of wireless
links, the method comprising the steps of: (a) providing an
orthogonal code from a set of 'm' orthogonal codes used to
create 'm' orthogonal charmels within the sirrgk frequency
65 channel; (b) combining a data item to be transmitted on the
single frequency channel with said orthogonal code, the
orthogonal code determining the orthogonal channel over

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6

which the data item is transmitted, whereby data items
FIG.10 illustrates the CDMAchannel hierarchy in accorpertaining to different wireless links may be transmitted
dance with preferred embodiments of the present invention;
simultaneously within different orthogonal channels of said
FIG. 11 is a schematic diagram illustrating downlink and
single frequency channel; and (c) applying time division
uplink communication paths for the wireless telecommunimultiplexing (TDM) techniques to the data item in order to
cations system;
insert the data item within a time slot of the orthogonal
FIG.l2 is a schematic diagram illustrating the makeup of
channel, whereby a plurality of data items relating to difa downlink signal transmitted by the central terminal;
ferent wireless links may be transmitted within the same
FIGS. 13A and 13B illustrate the structure of the frames
orthogonal channel during a predetermined frame period.
of information sent over the downlink and uplink paths;
Viewed from a fifth aspect, the present invention provides 10
FIGS. 14A and 14B illustrate the overhead frame struca method of processing data items received over a wireless
ture for the downlink and uplink paths;
link connecting a central terminal and a subscriber terminal
FIGS. 15Aand 15B illustrate typical downlink and uplink
of a wireless telecommunications system, a single frequency
channel structures that might occur in a loaded system in
channel being employed for transmitting data items pertaining to a plurality of wireless links, and 'm' orthogonal 15 accordance with preferred embodiments of the present
invention;
channels being provided within the single frequency
channel, the method comprising the steps of: (a) providing
FIG. 16 illustrates how the available traffic channels are
an orthogonal code from a set of 'm' orthogonal codes used
classified in preferred embodiments of the present invention;
to create said 'm' orthogonal channels within the single
FIG. 17 illustrates the elements used by the central
frequency channel; (b) applying, to signals received on the zo terminal to perform interference limiting;
single freq11ency channel, the orthogonal code in order to
FIG. 18 illustrates possible antenna configurations that
isolate data items transmitted vvithin the corresponding
can be employed in a wireless telecommunications system in
orthogonal channel; and (c) extracting a data item from a
accordance with the preferred embodiment of the present
predetermined time slot within said orthogonal channel, a
invention; and
plurality of data items relating to different wireless links 25
FIGS. 19A and 19B illustrate how channel switching is
being transmitted within the same orthogonal channel during
facilitated in preferred embodiments of the present invena predetermined frame period. By using TDM techniques in
tion .
addition to the known set of orthogonal codes, it is possible
for selected orthogonal channels to be subdivided in the time
DETAILED DESCRIPTION OF THE
dimension, thereby making it possible to support more 30
INVENTION
wireless links on one frequency channel.
FlfG. 1l is a schematic overview of an example of a
BRIEF DESCRIPTION OF THE INVENTION
wireless telecommunications system. The telecommunications system includes one or more service areas 12, 14 and
An embodiment of the invention will be described
hereinafter, by way of example only, with reference to the 35 ll6, each of which is served by a respective central terminal
(CT) 10 which establishes a radio link with subscriber
accompanying drawings in which like reference signs are
terminals (S1) 20 within the area concerned. The area which
used for like features and in which:
is covered by a central terminal10 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
40 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
FIG. 2 is a schematic representation of a premises; FIGS.
high density of subscriber terminals 20 might only cover an
2A and 2B are schematic illustrations of an example of a
area with a radius of tht order of 100 m. In a suburban area
subscriber terminal of the telecommunications system of
with an intermediate density of subscriber terminals, a
FIG.1;
service area 16 might cover an area with a radius of the order
FIG. 3 is a schematic illustration of an example of a 45
of 1 Km. It will be appreciated that the area covered by a
central terminal of the telecommunications system of FIG.
particular central terminal10 can be chosen to suit the local
1;
requirements of expected or achtal subscriber density, local
FIG. 3A is a schematic illustration of a modem shelf of a
geographic considerations, etc., and is not limited to the
central terminal of the telecommunications system of FIG.
50 examples illustrated in FIG.l. Moreover, the coverage need
1;
not be, and typically will not be circular in extent clue to
FIG. 4 is an illustration of an example of a frequency plan
antenna design considerations, geographical factors, buildfor the telecommunications system of FIG. 1;
ings and so on, which will affect the distribution of transFIGS. 5A and 5B are schematic diagrams illustrating
mitted signals.
possible configurations for cells for the telecommunications
The central terminals :n.o fur respective service areas 12,
55
system of FIG. 1;
ll4, 16 can be connected to each other by means of links 13,
FIG. 6 is a schematic diagram illustrating aspects of a
15 and 17 which interface, for example, with a public
code division multiplex system for the telecommunications
switched telephone network (PSTN) 18. The links can
system of FIG. 1;
include conventional telecommunications technology using
FIGS. 7A and 7B are schematic diagrams illustrating 60 copper wires, optical fibres, satellites, microwaves, etc.
signal transmission processing stages for the telecommuniThe wireless telecommunications system of FIG. 1 is
cations system of FIG. 1;
based on providing fixed microwave links between subFIGS. SA and 8B are schematic diagrams illustrating
scriber terminals 20 at fixed locations within a service area
signal reception processing stages for the telecommunica(t:.g.,. 12, 14, 16) amltht: <.:entral termina110 Lor Lhal ~.ervi<.:<;
tions system of FIG. 1;
65 area. Each subscriber terminal 20 can be provided with a
FIGS. 9A and 9B are diagrams :illustrating the uplink and
permanent fixed access link to its central terminallO, but in
preferred embodiments demand-based access is provided, so
downlink delivery methods when the system :is fully loaded;

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8

central terminal10. Tbe site controller 56 can be connected
that the number of subscribers which can be supported
exceeds the number of available wireless links. The manner
to each modem shelf of the central terminal 10 via, for
example, RS232 connections 55. The site controller 56 can
in which demand-based access is implemented will be
then provide support functions such as the localisation of
discussed in detail later.
faults, alarms and status and the configuring of the central
FIGS. 2A and 2B illustrate an example of a configuration
terminal 10. A site controller 56 will typically support a
for a subscriber terminal 20 for the telecommunications
single central terminal 10, although a plurality of site
system of FIG. 1. FIG. 2 includes a schematic representation
controllers 56 could be networked for supporting a plurality
of customer premises 22. A customer radio unit (CRU) 24 is
of central terminals
mounted on the customer's premises. The customer radio
unit 24 includes a fiat panel antenna or the like 23. The 10
As an alternative to the RS232 connections 55, which
extend to a site controller 56, data connections such as an
customer radio unit is mounted at a location on the customX.25 links 57 (shown with dashed lines in FIG. 3) could
er's premises, or on a mast, etc., and in an orientation such
instead be provided from a pad 228 to a switching node 60
that the fiat panel antenna 23 within the customer radio unit
of an element manager (EM) 58. An element manager 58 can
24 faces in the direction 26 of the central terminal10 for the
support a number of distributed central terminals 10 conservice area in which the customer radio unit 24 is located.
The customer radio unit 24 is connected via a drop line 28 15 nectcd by respective connections to the switching node 60.
The element manager 58 enables a potentially large number
to a power supply unit (PSU) 30 within the customer's
(e.g., up to, or more than 1000) of central terminals 10 to be
premises. The power supply unit 30 is connected to the local
integrated into a management network. The element manpower supply for providing power to the customer radio unit
ager 58 is based around a powerful workstation 62 and can
24 and a network terminal unit (NTU) 32. The customer
20 include a number of computer terminals 64 for network
radio unit 24 is also connected via the power supply unit 30
engineers and control personneL
to the network terminal unit 32, which in turn is connected
FIG. 3A illustrates various parts of a modem shelf 46. A
to telecommunications equipment in the customer's
transmit/receive RF unit (RFU-for example implemented
premises, for example to one or more telephones 34, facon a card in the modem shel±) 66 generates the modulated
simile machines 36 and computers 38. The telecommunica- 25 transmit RF signals at medium power levels and recovers
tions equipment is represented as heing within a single
and amplifies the baseband RF signals for the subscriber
customer's premises. However, this need not be the case, as
terminals. The RF unit 66 is connected to an analogue card
the subscriber termina120 preferably supports either a single
(AN) 68 which performs A-DID-A conversions, baseband
or a dual line, so that two subscriber lines could be supported
filtering and the vector summation of 15 transmitted signals
by a single subscriber terminal 20. The subscriber terminal 30 from the modem cards (MCs) 70. The analogue unit 68 is
20 can also be arranged to support analogue and digital
connected to a number of (typically 1-8) modem cards 70.
telecommunications, for example analogue communications
The modem cards perform the baseband signal processing of
at 16, 32 or 64 kbits/sec or digital communications in
the transmit and receive signals to/from the subscriber
accordance with the ISDN BRA standard.
terminals 20. This may include Y2 rate convolution coding
FIG. 3 is a schematic illustration of an example of a 35 and x16 spreading with "Code Division Multiplexed
central terminal of the telecommunications system of FIG. 1.
Access" (CDMA) codes on the transmit signals, and synThe common equipment rack 40 comprises a number of
chronisation recovery, de-spreading and error correction on
equipment shelves 42, 44, 46, including a RF Combiner and
the receive signals. Each modem card 70 in the present
power amp shelf (RFC) 42, a Power Supply shelf (PS) 44
example has two modems, and in preferred embodiments
and a number of (in this example four) Modem Shelves 40 there are eight modem cards per shelf, and so sixteen
(MS) 46. The RF combiner shelf 42 allows the modem
modems per shelf. However, in order to incorporate redunshelves 46 to operate in paralleL If 'n' modem shelves are
dancy so that a modem may be substituted in a subscriber
provided, then the RF combiner shelf 42 combines and
link -when a fault occurs, only 15 modems on a single
amplifies the power of 'n' transmit signals, each transmit
modem shelf 46 are generally used. The 16th modem is then
signal being from a respective one of the 'n' modem shelves, 45 used as a spare which can be switched in if a failure of one
and amplifies and splits received signals 'n' way so that
of the other 15 modems occurs. The modem cards 70 are
separate signals may be passed to the respective modem
connected to the tributary unit (TU) 74 which terminates the
shelves. The power supply shelf 44 provides a connection to
connection to the host public switched telephone network 18
the local power supply and fusing for the various compo(e.g., via one of the lines 47) and handles the signalling of
nents in the common equipment rack 40. A bidirectional so telephony information to the subscriber terminals via one of
connection extends between the RF combiner shelf 42 and
15 of the 16 modems.
the main central terminal antenna 52, such as an omnidiThe wireless telecommunications between a central terrectional antenna, mounted on a central terminal mast 50.
minal 10 and the subscriber terminals 20 could operate on
This example of a central terminal10 is connected via a
various frequencies. FIG. 4 illustrates one possible example
point-to-point microwave link to a location where an inter- 55 of the frequencies which could be used. In the present
face to the public switched telephone network 18, shown
example, the wireless telecommunication system is intended
schematically in FIG. 1, is made. As mentioned above, other
to operate in the 1.5-2.5 GHz Band. In particular the present
types of connections (e.g., copper wires or optical fibres) can
example is intended to operate in the Band defined by ITU-R
be used to link the central terminal10 to the public switched
(CCIR) Recommendation F.701 (2025-2110 MHz,
telephone network 18. In this example the modem shelves 60 2200-2290 MHz). FIG. 4 illustrates the frequencies used for
are connected via lines 47 to a microwave terminal (MT) 48.
the uplink from the subscriber terminals 20 to the central
A microwave link 49 extends from the microwave terminal
terminal10 and for the downlink from the central terminal
48 to a point-to-point microwave antenna 54 mounted on the
10 to the subscriber terminals 20. It will be noted that 12
mast 50 for a host connection to the public switched teleuplink aml12 downlink radio channels o[ 3.5 MHz each are
phone network 18.
65 provided centred about 2155 MHz. The spacing between the
A personal computer, workstation or the like can be
receive and transmit channels exceeds the required miniprovided as a site controller (SC) 56 for supporting the
mum spacing of 70 MHz.

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9

In the present example, each modem shelf supports 1
increased three fold, while still providing permanent fixed
frequency channel (i.e. one uplink frequency plus the coraccess for each subscriber terminal 20.
responding downlink frequency). Currently, in a wireless
Arrangements such as those in FIGS. SA and SB can help
telecommunications system as described above, CDMA
reduce interference, but in order to ensure that cells operencoding is used to support up to 15 subscriber links on one
ating on the same frequency don't inadvertently decode each
frequency channel (one subscriber link on each modem).
others data, a seven cell repeat pattern is used such that for
Hence, if a central terminal has four modem shelves, it can
a cell operating on a given frequency, all six adjacent cells
support 60 (15x4) subscriber links (i.e. 60 STs can be
operating on the same frequency are allocated a unique
connected to one C:T). However, it is becoming desirable for
pseudo random noise (PN) code. The use of PN codes will
more than 60 STs to be supported from one central terminal, 10 be discussed in more detail later. The use of different PN
and, in preferred embodiments of the present invention,
codes prevents nearby cells operating on the same frequency
enhancements to the COMA encoding technique are profrom inadvertently decoding each others data.
vided to increase the number of subscriber links that can be
.As mentioned above, CDMA techniques can be used in a
supported by a central terminal. Both CDMA encoding, and
fixed assignment arrangement (ie. one where each ST is
the enhancements made to the CDMA encoding in accor- 15 assigned to a particular modem on a modem shelf) to enable
dance with preferred embodiments, will be discussed in
each channd fn:qutncy to support 15 subscriber links. FIG.
more detail later.
6 gives a schematic overview of CDMA encoding and
Typically, the radio traffic from a particular central terdecoding.
minallO will extend into the area covered by a neighbouring
In order to encode a CDMA signal, base band signals, for
central termina110. 'lb avoid, or at least to reduce interfer- 20 example the user signals for each respective subscriber link,
ence problems caused by adjoining areas, only a limited
are encoded at 80-SON into a 160 ksymbols/sec baseband
number of the available frequencies will be used by any
signal where tach symbol represents 2 data bits (see, for
given central terminal 10.
example the signal represented at 81). This signal is then
spread by a factor of 16 using a spreading function 82-82N
FIG. SA illustrates one cellular type arrangement of the
frequencies to mitigate interference problems between adja- 25 to generate signals at an effective chip rate of 2.56
Msymbols/sec in 3.5 MHz. The spreading function involves
cent central terminals 10. In the arrangement illustrated in
applying a PN code (that is specified on a per CT basis) to
FIG. SA, the hatch lines for the cells 76 illustrate a frequency
the signal, and also applying a Rademacher-Walsh (RW)
set (FS) for the cells. By selecting three frequency sets (e.g.,
code which ensures that the signals for respective subscriber
where: FS1=F1, F4, F7, FlO; FS2=F2, F5, F8, Fll; FS3=F3,
F6, F9, F12), and arranging that immediately adjacent cells 30 terminals will be orthogonal to each other. Once this spreading function has been applied, the signals for respective
do not use the same frequency set (see, for example, the
subscriber links are then combined at step 84 and converted
arrangement shown in FIG. SA), it is possible to provide an
to radio frequency (RF) to give multiple user channel signals
array of fixed assignment omnidirectional cells where inter(e.g. 85) for transmission from the transmitting antenna 86.
ference between nearby cells can be reduced. The transmitDuring transmission, a transmitted signal will be subter power of each central terminal10 is preferably set such 35
that transmissions do not extend as far as the nearest cell
jected to interference sources 88, including external interwhich is using the same frequency set. Thus, in accordance
ference 89 and interference from other channels 90.
Accordingly, by the time the CDMAsignal is received at the
with the arrangement illustrated in .FIG. SA, each central
receiving antenna 91, the multiple user channel signals may
terminallO can use the four frequency pairs (for the uplink
and downlink, respectively) within its cell, each modem 40 be distorted as is represented at 93.
shelf in the central terminal 10 being associated with a
In order to decode the signals for a given subscriber link
respective RF channel (channel frequency pair).
from the received multiple user channel, a Walsh correlator
94-94N ust:s the samt: RV( and PN codes lhat wt:re ust:d for
FIG. 5B illustrates a cellular type arrangement employing
sectored cells to mitigate problems between adjacent central 45 the encoding for each subscriber link to extract a signal (e.g,
as represented at 95) for the respective received baseband
terminals 10. As with FIG. SA, the different type of hatch
signal 96-96N. It will be noted that the received signal will
lines in FIG. 5B illustrate different frequency sets. As in
include some residual noise. However, unwanted noise can
FIG. SA, FIG. SB represents three frequency sets (e.g.,
be removed using a low pass filter and signal processing.
where: FS1=F1, F4, F7, FlO; FS2=F2, F5, F8, Fll; FS3=F3,
F6, F9, F12). Howevt:r, in FIG. SB the cdls are st:ctored by 50
Tht: kty to CDMA i& the application of lhe RW codes,
using a sectored central terminal (SCT) 13 which includes
these being a mathematical set of sequences that have the
three central terminals 10, one for each sector S1, S2 and S3,
function of "orthonormality". In other words, if any RW
with the transmissions for each of the three central terminals
code is multiplied by any other RW code, the results are
zero. A set of 16 RW codes that may be used is illustrated in
10 being directed to the appropriate sector among S1, S2 and
S3. This enables he number of subscribers per cell to be
Table 1 below:
TABLE 1
RWO
RW1
KW2

RW3
RW4
RWS
RW6
RW7
RW8
RW9

-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

-1

1
1
-1
-1
1
-1

1
-1

1

-1

WIL-0009796

6,0R8,326

12

11
TABLE 1-continued
RW10
RW11
RW12
RW13
RW14
RW15

1 -l
-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
-1
-1

-1

-1

-1
1

-1
l

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

10

Overlay codes are used extensively to provide variable
rate uplink traffic channels. Overlay codes will also be used
to implemerrt downlink control channels, these control channels being discussed in more detail later. However, as
15 mentioned earlier, a different approach is taken for providing
flexible channelisations on the dmvnlink traffic channel
paths. Downlink traffic channels will operate in high rate,
160 kb/s, mode, with lower data rates of 80 and 40 kb/s
being supported by 'Time Division Multiplexing' (IDM)
20 the available bandvvi.dth.
In preferred embodiments, TDM timeslot bit numbering
will follow the CCITT G.732 convention with bits transmitted in the sequence bit 1, bit 2 ... bit 8. Byte orientation
is specified per channel as either most significant bit (MSB)
25 first, least significant bit (LSB) first or N/A
The provision of a hybrid CD1tiA!TDM approach for
downlink traffic channels retains the benefits of CDMA
access, ie. interference is reduced when traffic is reduced.
Further, use of TDM ensures that the CDMA signal is
30 limited to a256 'Quadrature Amplitude Modulation' (QAM)
constellation which reduces receiver dynamic range requirements. QAM constellations will be familiar to those skilled
in the art.
On the uplink channels, the pure CDMA approach using
35
overlay codes eliminates the need to time synchronise STs to
a TDM frame reference. This has the advantage ofelimi160 kbis
Full rate (F1)
nating TDM delays and the 'guard time' in between TDM
80 kb/s
Half rate (H1, H2)
Quarter rate (Q1, Q2. Q3, Q4)
40 kbis
frames. Another benefit is reduced peak power handling
10 kbis
Low rate (Ll, L2, L3, L4), for uplink acquisition
requirements in the ST RF transmit chain which would
40
otherwise be needed when transmitting bursty TDM data.
High dynamic range requirement is restricted to the CT
In preferred embodiments, the manner in which these
receiver.
channelisations are provided differs for the downlink (CT to
The manner in which the transmitted and received signals
ST) and uplink (ST to CT) communication paths. This is
because it has been realised that different performance 45 are processed in accordance with preferred embodiments of
the present invention will be described with refe.rence to
requirements exist for the downlink and uplink paths. On the
FIGS. 7 and 8. FIG. 7A is a schematic diagram illustrating
downlink all signals emanate from a single source, namely
signal transmission processing stages as configured in a
the central terminal, and hence the signals will be synchrosubscriber tcrminal20 in the telecommunications system of
nised. However, on the uplink path, the signals will emanate
from a number of independent STs, and hence the signals so FIG. 1. In FIG. 7A, an analogue signal from a telephone is
passed via an interface such as two-wire interface 102 to a
will not be synchronised.
hybrid audio processing circuit 104 and then via a codec 106
Given the above considerations, in preferred
to produce a digital signal into which an overhead channel
embodiments, on the uplink path fu11 rate (160 kh/s) operaincluding control information is inserted at 108. If the
tion is implemented using the basic set of RW codes
discussed earlier, but half and quarter rates are achieved 55 subscriber terminal supports a number of telephones or other
telecommunications equipment, then elements 102, 104 and
through the use of 'Overlay Codes' which comprise RW
106 may be repeated for each piece of telecommunications
coded high rate symbol patterns that are transmitted for each
equipment.
intermediate rate data symbol. For half rate operation, two
At the output of overhead insertion circuit 108, the signal
2-bit overlay codes are provide, whilst for quarter rate
operation, four 4-bit overlay codes are provided. When 60 wi11 have a bit rate of either 160, RO or 40 kbits/s, depending
on which channel has been selected for transmission of the
generating a signal for transmission, one of the overlay
signal.
codes, where appropriate, is applied to the signal in addition
The resulting signal is then processed by a convolutional
to the appropriate RW code. When the signal is received,
encoder 110 to produce lwo signals with tht: same bil rale as
then at the CDMA demodulator the incomirrg signal is
multiplied by the channel's PN, RW and Overlay codes. The 65 the input signal (collectively, these signals will have a
symbol rate of 160, 80 or 40 KS/s). Next, the signals are
correlator integration period is set to match the lerrgth of the
passed to a spreader 111 where, if a reduced bit rate channel
Overlay code.
TI1e above set of RW codes are orthogonal codes that
allow the multiple user signals to be transmitted and
received on the same frequency at the same time. Once the
bit stream is orthogonally isolated using the RW codes, the
signals for respective subscriber links do not interfere with
each other. Since RW codes are orthogonal, when perfectly
aligned all codes have zero cross-correlation, thus making it
possible to decode a signal while cancelling interference
from users operating on other RW codes.
In preferred embodiments of the present invention, it is
desired to provide the central terminal with the ability to
support more than 15 subscriber links on each channel
frequency, and to achieve this the above set of 16 RW codes
has been enhanced. In order to maintain compatibility with
former products using the 16 RW codes, it was desirable that
any enhancements should retain the same set o[ 16 RW
codes.
TI1e manner in which the enhancement-s have been implemented provides flexibility in the way the frequency channels are configured, with certain configurations allowing a
greater number of subscriber links to be supported, but at a
lower gross bit rate. In preferred embodiments, a channel
can be selected to operate with the following gross bit rates:

WIL-0009797

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13

14

bas been selected, an appropriate overlay code provided by
code generator providing appropriate overlay codes to the
overlay code generator 113 is applied to the signals. At the
spreader 111. The overlay code generator will be controlled
output of the spreader 111, the signals will be at 160 KS/s
so as to produce the desired overlay code, in preferred
irrespective of the bit rate of the input signal since the
embodiments, this control coming from the DAengine (to be
discussed in more detail later).
overlay code will have increased the symbol rate by the
necessary amount.
FIG. SA 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
tcrminal20 in the telecommunications system of FIG. 1. In
spreader 116 where the Rademacher-Walsh and PN codes
are applied to the signals by a RW code generator 112 and
FIG. SA, signals received at a receiving antenna 150 are
PN Code generator 114, respectively. The resulting signals, 10 passed via a band pass filter 152 before being amplified in
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
then passed via a further band pass filter 156 before being
the smallest data element in a spread sequence) are passed
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
analogue wavdorm and provides a stage of baseband power 15 where it is mixed with a signal generated by a voltage
controlled oscillator 162 which is responsive to a synthesizer
control. The signals are then passed to a low pass filter 120
160. The output of the mixer 164 is then passed via the T/Q
to be modulated in a modulator 122. The modulated signal
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
synthesizer 160. The output of the mixer 128 is then 20 output of the A;D converter 170 at 2.56 MC/s is then passed
to a correlator 178, to which the same Rademacher-Walsh
amplified in a low noise amplifier 130 before being passed
and PN codes used during transmission are applied by a RW
via a band pass filter 132. The output of the band pass iilter
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
output of the power control circuitry is further amplified in 25 code generator 114), respectively. The output of the correlator 178, at 160 KS/s, is then applied to correlator 179,
a power amplifier 13S before being passed via a further hand
where any overlay code used at the transmission stage to
pass filter 140 and transmitted from the transmission antenna
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 transmission processing stages as configured in a central terminal 30 181 form a CDMA demodulator. The output from the
CDMA demodulator (at correlator 179) is then at a rate of
10 in the telecommunications system of FIG. 1. As will be
either 160, 80 or 40 KS/s, depending on the overlay code
apparent, the central terminal is configured to perform
applied by correlator 179.
similar signal transmission processing to the subscriber
The output from correlator 179 is then a]pplied to a Viterbi
terminal 20 illustrated in FIG. 7A, but does not include
elements 100, 102, 104 and 106 associated with telecom- 35 decoder 180. The output of the Viterbi decoder 180 is then
passed to an overhead extractor 182 for extracting the
munications equipment. Further, the central terminal
overhead channel information. If the signal relates to call
includes a TDM encoder 105 for performing time division
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
a subscriber terminal are received. When an incoming call is 40 from the particular time slot in which it was inserted by the
CT TDM encoder 105. Then, the call data is passed via a
received, the central terminal will contact the subscriber
codec 184 and a hybrid circuit 188 to an interface such as
terminal to which the call is directed and arrange a suitable
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
is done using the call control channel discussed in more 45 connection with the ST transmission processing stages,
elements 184, 188, 190 may be repeated for each piece of
detail later). The channel established for the call will dett:rtelecommunications equipment 192 at the ST.
mine the time slot to be used for call data passed from the
If the data output by the overhead extraction circuit 182
CT to the STand the TDM encoder 105 will be supplied \Vith
is data on a downlink control channels, then instead of
this information.
Hence, when incoming call data is passed from the so passing that data to a piece of telecommunications
equipment, it is passed via switch 187 to a call control logic
network interface to the TDM encoder 105 over line 103, the
185, where that data is interpreted by the ST.
TDM encoder will apply appropriate TDM encoding to
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
e4uivalent processing performed in the ST and described 55 derived from the digital portion of the COMA receiver using
with reference to FIG. 7A, the overlay code generator
the output of a signal quality estimator.
producing a single overlay code of value '1' so that the
FIG. SB illustrates the signal reception processing stages
signal output from spreader 111 is the same as the signal
as configured in a central terminal 10 in the telecommuniinput to the spreader 111.
cations system ofFIG.l. As will be apparent from the figure,
As mentioned earlier, in preferred embodiments, overlay 60 the signal processing stages between the RX antenna 150
and the overhead extraction circuit 182 are the as those
codes, rather than TDM, are used to implement downlink
within the ST discussed in connection with FIG. SA
control channels, and data relating to such chmmels is passed
However, in the case of the CT, call data output from the
from a demand assignment engine (to be discussed in more
uverht:ad extraction circuit is passed over line 189 to the
detail later) over line 107 through switch 109 lo the overhead
insertion circuit 108, thereby bypassing the TOM encoder 65 network interface within the CT, whilst control channel data
is passed via switch 191 to the DA engine 380 for process105. The processing of the signal is then the same as the
ing. The DA engine is discussed in more detail later.
equivalent processing performed in the ST, with the overlay

WIL-0009798

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16

15

scriber terminal 20. A downlink communication path is
established from transmitter 200 in central terminal 10 to
receiver 202 in subscriber terminal 20. An uplink communication path is established from transmitter 204 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
1, telephone communication may occur between a user 208,
210 of subscriber terminal 20 and a user serviced through
10 central terminal10 over a downlink signa1212 and an uplink
signal214. Downlink signal212 is transmitted by transmitTABLE 2
ter 200 of central terminal 10 and received by receiver 202
STTx.
of suhscriher terminal 20. Uplink signal 214 is transmitted
power
by transmitter 204 of subscriber terminal20 and received by
Net Channel relative
C:orrelator
Rate designa- to Fl-U
integration
Acquisition 15 receiver 206 of central terminallO.
Receiver 206 and transmitter 200 within central terminal
tion
Overlay Code
(kb/s)
(dB)
period (us)
overlay
10 are synchronized to each other with respect to time and
-Fl-U
160
6.25
L1
1
phase, and aligned as to information boundaries. In order to
80
-Hl-U
-3
1
12.5
L1
establish the downlink communication path, receiver 202 in
80
-H2-U
-3
1 -1
12.5
L3
·Ql-U
-6
40
1
25
L1
20 subscriber terminal20 should be synchronized to transmitter
-Q2-U
-6
-1
40
25
1 -1
L2
200 in central terminal10. Synchronization occurs by per-Q3-U
-6
40
1 -1 -1
25
L3
forming an acquisition mode function and a tracking mode
-Q4-U
-G
40
1 -1 -1
25
L4
function on downlink signal212. Initially, transmitter 200 of
c~::ntral t~::rminal10 transmits downlink signal 212. FIG. 12
In preferred embodiments, a 10 kb/s acquisition mode is 25 shows the contents of downlink signal 212. A frame inforprovided which uses concatenated overlays to form an
mation signal 218 is combined with an overlay code 217
acquisition overlay; this is illustrated in table 3 below:
where appropriate, and the resultant signal219 is combined
Overlay codes and channelisation plans are selected to
ensure signal orthogonality-i.e. in a properly synchronised
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:

TABLE 3
Acquisition overlay

Ll-U
L2-U
13-U
IA-U

Equivalent high rate pattern

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

FIGS. 9A and 9B are diagrams illustrating the uplink and
downlink delivery methods, respectively, when the system is
fully loaded, and illustrate the difference hetween the use of
overlay codes illustrated in FIG. 9A and the use of IDM as
illustratt:d in FIG. 9B. When using overlay codes, an RW
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
TDM, an RW code is split in the time domain, to allow up
to four signals to be sent using one RW code, but at dille rent
times during the 125 us frame. As illustrated in FIGS. 9A
and 9R, the last two RW codes, RW14 and RW15, are not
used for data traffic in preferred embodiments, since they are
reservt:cl for call control and acquisition functions; this will
be discussed in more detail later.
The CDMAchannel hierarchy is as illustrated in FIG. 10.
Using this hierarchy, the following CDMA chan:nelisations
are possible:
Fl

with a code sequence signal 216 for central terminal 10 to
produce the downlink 212. Code sequence signal 216 is
40 derived from a com hi nation of a pseudo-random noise code
signal 220 and a Rademacher-Walsh code signal 222.
Downlink signal 212 is receivtd at receiver 202 of
subscriber terminal20. Receiver 202 compares its phase and
code sequence to a phase and code sequence within code
45 sequence signal 216 of downlink signal 212. Central tenninal 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
its slave code sequence to recognize a match to master code
50 sequence and place receiver 202 of subscriber terminal 20 in
phase with transmitter 200 of central terminal10. The slave
code sequence of receiver 202 is not initially synchronized
to the master code sequence of transmitter 200 and central
terminal10 due to the path delay between central terminal
55 10 and subscriber terminal 20. This path delay is caused by
Hl+H2
the geographical separation between subscriber terminal 20
H1+03+Q4
and central terminal 10 and other environmental and techH2+Ql+Q2
nical factors affecting wireless transmission.
After acquiring and initiating tracking on the central
01+02+03+04
Having discussed how the CDMA codes are enhanced to 60 terminal10 master code sequence of code sequence signal
enable flexible channelisations to be achieved, whereby the
216 within downlink signal212, receiver 202 enters a frame
bit rates can be lowered to enable more subscriber links to
alignment mode in order to establish the downlink commube managed per channel frequency, a general overview of
nication path. Receiver 202 analyzes frame information
how the downlink aml uplink paths art: tstablisht:cl will be
within frame information signal218 of downlink signal 212
provided with reference to FIGS. 11 and 12.
65 to identify a beginning of frame position for downlink signal
FIG. 11 is a block diagram of downlink and uplink
212. Since receiver 202 does not know at what point in the
communication paths between central terminal10 and subdata stream of downlink signal 212 it has received

WIL-0009799

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17

18

information, receiver 202 must search for the beginning of
frame position in order to be able to process information
received from transmitter 200 of central terminal 10. Once
receiver 202 has identified one further beginning of frame
position, the downlink communication path has been established from transmitter 200 of central terminallO to receiver
202 of subscriber terminal 20.
The structure of the radio frames of information sent over
the downlink and uplink paths will now be discussed with
reference to FIGS. 13 and 14. In FIGS. 13 and 14, the
following terms are used:
Bn Customer payload, lx32 to 2x64 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

munication 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 (D), 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.

10

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:
TABLE 4

Ralt Channd
(kb/s) designation
1GO

-Fl-0-Tl/1

80

-Fl-D-T2/l

~0

-F1-JJ--T2/2

40
40
40
40

-F1-D-T4/2
-F1-D-T4/3
-F1-D-T4/4

-F1~D-T4/1

Bearer

cs

Bl, B2, B3, B4 CS1,
CS3
Bl, B2
CSl,
CS3
H3, .1:54
CS2,
CS4
Bl
CS1
B2
CS2
CS3
B3
B4
CS4

Overhead rate

PC

OMC

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

OMCl, OMC3

4

OMCl, OMC3

4 ms

OMC2, OMC4

4 ms

OMC1
OMC2
OMC3
OMC4

8
8
8
8

IllS

ms
ms
ms
ms

Both FIGS. 13A and 13B show a 125 us subframe format,
In the above chart, the scheme used to identify a channel
which is repeated throughout an entire radio frame, a frame
is as follows. Rate code 'F1' indicates full rate, 160 kb 'D'
typically lasting for 4 milliseconds (ms). FIG. 13A illustrates 35 indicates that the channel is a downlink channel, and 'Tn/t'
the radio frame structures that are used in preferred embodiindicates that the channel is time division multiplexed
ments for the downlink path. Subframe (i) in FIG. 13A
between STs, 'n' indicating the total number of TDM
shows the radio frame structure used for low rate, 10 Kb/s,
time:slots, and 't' indicating the selected traffic timeslot.
acquisition mode (Ln-D) during which only the overhead
All ST's operating on a traffic channel will receive
channel is transmitted. Suhframe (ii) in FIG. 13A shows the
D-channel information at the 16 kb/s rate. The D-channcl
radio frame structure employed for the call control channel 40 protocol includes an address field to specify which ST is to
operating in quarter rate, 40 Kb/s, mode (Qn-D) , whilst
process the contents of the message.
subframe (iii) of FIG. 13A illustrates the radio frame strucThe channel structure was illustrated earlier in FIGS. 9A
ture used for trilffic cbilnnels operilting in full rate, 160 kb/s,
and 9B. In preferred embodiments, the channel structure is
mode (F1-D).
flexible but comprises:
Similarly, sub frame (i) of FIG. 13B shows the radio frame 45
At least one Link Acquisition Channel (LAC)
structure used for the uplink path when operating in low rate
At least one Call Control Channel (CCC)
acquisition or call control mode (Ln-U). Sub-frames (ii) to
Typically one Priority Traffic Channels (PTC)
(iv) show the radio frame structure used for traffic channels
\Vhen operating in quarter rate mode (Qn-U), half rate mode
1 to 13 Traffic Channels (TC)
The manner in which the channelisation is provided
(Hn-U), and full rate mode (Fl-U), respectively.
50
Considering now the overhead channel in more detail,
ensures that former fixed assignment arrangements using the
FIGS. 14A and 14B show the overhead frame structure
set of 16 RW codes discussed earlier are still supported, as
employed for various data rates. The overhead channel may
we11 as demand access services that are available when using
include a number of fields-a frame alignment word (PAW),
a system in accordance with the preferred embodiment.
a code synchronization signal (CS), a power control signal ss FIGS. 15A and 15B illustrate typical downlink and uplink
(PC), an operations and maintenance channel signal (OM C),
channel structures that might occur in a loaded system in
a mi.'l:ed OMC/D-Channel (HDLC) signal (OMC/D), a chanaccordance with preferred embodiments of the present
nel identifier byte (Ch.ID), and some unused fields.
invention. As illustrated in FIG. 15A, on the downlink path,
The frame alignment word identifies the beginning of
some signals may be at 160 kb!s and utilise an entire RW
frame position for its corresponding frame of information. 60 channel. An example of such signals would be those sent
The code synchronization signal provides information to
over fixed assignment links to products which do not support
control synchronization of transmitter 204 in subscriber
the CDMA enhancements provided by systems in accorterminal20 to receiver 206 in central termina110. The power
dance with preferred embodiments of the present invention,
cunlrol signal pruvidt:s infunnaliun lu L:unlrul transmitting
as illu:siraltu fur RW1 <mu RW2 in FIG. 15A. Al!trnalivdy,
power of transmitter 204 in subscriber terminal 20. The 65 a user may have authority to utilise a whole RW channel, for
operations and maintenance channel signal provides status
example when sending a fax, as illustrated by RW12 in FIG.
information with respect to the downlink and uplink com15A.

WI L-0009800

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19

20

As .illustrated by RW5 to RWll, TDM can be used on the
(iii) In the event of a CT restart, invite STs to attempt
downlink traffic channels to enable more than one CT to ST
uplink warm start. A reduction in net entry time of a
communication to take place on the same RW channel
factor of 4 could be achieved. This mechanism would
during each frame. Further, as illustrated for RW3 and RW4,
need to be safeguarded against possible deterioration of
in preferred embodiments, certain channels can be locked to
uplink warm start parameters-i.e. it should only be
limit interference from other nearby cells, as will be disallowed provided no CT RF related parameters have
cussed in more detail later.
been modified. The CT would need to broadcast an ID
Similar channelisations can be achieved for the uplink
to allow an ST to validate that the uplink warm start
paths, hut as illustrated in FIG. 15R, overlay codes are used
parameters were valid for this C::T.
instead of TDM to enable more than one ST to CT com- 10
(iv) ST n:start-tht CT will ktt:p copies of tht: ST warm
munication to take place on the same RW channel during
start parameters so that a cold ST may have warm start
each frame (as shown in FIG. 15B for RW5 to RWll). It
parameters downloaded in the invitation to acquire and
should be noted that, in both FIGS. 15A and 15B, the
then be instructed to warm start.
channels RW14 and RW15 are reserved as a call control
Following Net Entry, all STs listen to the CCC. This
channel and an link acquisition channel, respectively, and 15 channel broadcasts management and call control informaoverlay codes are employed on these channels, irrespective
tion via a 32 kb/s HDLC channel. In order to maintain
of whether the path is a downlink or an uplink path. These
management communication, the CT polls each ST in
two channels will be discussed in more detail below.
sequence. Each poll comprises a broadcast invitation for an
Acquisition/net entry will take place via the Link Acquiaddressed ST to acquire the CCC Uplink followed by an
sition Channd (LAC). Following power-up an ST will zo exchange of management information (authentication, ST
automatically attempt downlink acquisition of the LAC on a
alarm update, warm start parameters, downlink radio perpre-determined 'home' RF channel. The LAC downlink
formance data etc.).
channel (eg. RW15 in preferred embodiments) will operate
A Management Poll may fail for one of the following
at 10 kb/s, full single user power. Downlink acquisition will
reasons:
be simultaneous for all STs.
25
(i) The ST is or has been powered down. An EM alarm
Each CT Modem Shelf will maintain a database holding
may be tlagged if this persists and the database for that
the serial numbers of all STs that could possibly be supST should be marked cold. The Net Entry process will
ported by that CT. The state of each ST will recorded with
follow.
top level states as follows:
(ii) The ST is either making a call or in the process of
30
cold
making a call. The poll cycle rna y be suspended and
idle
management communications effected on the appropriate traffic channel.
call_in_proogress
When a Management Poll fails it should be followed up
Transition states will also be defined. An ST is considered
cold if the ST is newly provisioned, the CT has lost 35 by a number of faster polls until either the ST responds or
it is marked cold. The CCC is required to transmit all copies
management communications with the ST or the CT has
of the invitations to acquire the LAC so that an ST can be
been power cycled. Over the LAC, the CT broadcasts
forcetl to acquire the LAC uplink.
individual ST serial numbers and offers an invitation to
Traffic Channel Uplink Acquisition Procedure
acquire the LAC uplink. Cold uplink acquisition will be
The basic acquisition process from the ST side is as
carried out on the Link Acquisition Channel at low rate. The 40
follows;
CTwill invite specific ST's to cold start via the management
channel.
(i) Switch the downlink (receiver) circuitry to 10 kh/s rate,
and select the appropriate Traffic Channel RW and
Assuming an uplink channel is available, the appropriate
acquisition overlay will be selected, and acquisition will be
Overlay codes. Acquisition of the TC downlink is
limited to achieving frame alignment.
initiated.
s
4
'Rapid' downlink RW channel switching may be sup(ii) The downlink PC/CS channel will be decoded to
ported at rates other than Ln-D. Rapid means that coherent
create a busy/idle tlag. lf PC/CS reports busy, then this
demodulation is maintained, and only convolutional decodmeans that another ST is using that traffic channel and
ing and frame synchronisation processes need be repeated.
the ST aborts the acquisition process.
On acquisition, managc:mt:nt information will bt 50
(iii) Switch uplink to 10 kb/s rate, and select the approexchanged. The ST will be authenticated and allocated a
priate Traffic Channel RW and Overlay codes. Enable
short ST_identifier (between 12 and 16 bits) which will be
the ST transmitter at a level of nominal full rate power
used for subsequent addressing. The ST uplink will operate
minus 18 dB. While PC/CS reports idle the ST will
for long enough for the uplink to be parametised by the ST
continue uplink fast codesearch, stepping the uplink
in terms of code phase and transmit power. These parameters 55
powc:r ltvd by +2 dB at the c:nd of each search. The
will be used by the ST for subsequent warm start acquisiuplink should acquire at nominal full rate power minus
tions and will also be held by the CT to allow the CT to force
6 dB. Uplink acquisition is aborted if maximum transa cold ST to warm start. On successful completion of net
mit level is reached and PC/CS continues to report idle.
entry, the ST will be placed in the idle state and instructed
(iv) PC/CS reports busy. At this point the ST may have
to cease uplink communications and move to the Call 60
genuinely acquired the traffic channel, or instead may
Control Channel (CCC) (RW14 in preferred embodiments).
be observing PC/CS go busy because another ST has
The time taken for net entry to be achieved can be
acquired the traffic channel. The ST is sent an authenmonitored, and the following techniques can be used to
tication request and responds with it's ST_identifer.
decrease net entry time if desired:
Tht: CT grants uplink access by returning tht
(i) Prioritise so that high GOS (Grade Of Service) users 65
ST_identifier. The ST aborts the acquisition process if
are offered net entry first.
the returned ST_identifier is not recognised (i.e. is not
the ST_identifer that it sent). This authentication pro(ii) Convert Traffic Channels to LACs.

WIL-0009801

o,ORR,326

21

22

~ess

arbitrates between two STs contending for outgo(vi) The ST may be unable to acquire a TC by tbe time the
mg access and it also keeps STs from acquiring TCs
call setup timer expires. The ST may in such cases
that have been reserved from incoming access.
c.ease attempting outgoing access and generate congestiOn tone.
Incoming Call
Outgoing Priority Call
A number of TCs will be reserved for incoming calls, and
It is recognised that the random access protocol used to
incoming call processing is as follows:
setup normal outgoing calls could lead to blocking. In
(i) Check the CT database-if the ST is in the call in
preferred embodiments, access to a largely non-blocking
progress state the call is rejected.
- Priority Traffic Channel will be allowed. Priority calling is
(ii) Check that an uplink TC ~f the required bandwidth is
complicated because the ST must:
available. If there is bandwidth then a TC is reserved. 10
(i) Capture and decode dialed digits.
(iii) An incoming call setup message is broadcast over the
(ii) Rt:gt:neratt: digits wht:n a bloc..:king condition occurs.
CCC to inform the addressed ST of the incomincr call
(iii) Allow transparent network access in a non-blockina
and specify the TC on which to receive the call. If no
· condition.
""
TC is available but the CT forms part of a Service
(iv) Categorise all outgoing calls as priority or normal so
Domain, then the incoming call setup message is sent 15
that normal calls are dropped in favor of priority calls.
with a null TC otht:rwise the c.;all is rt:jt:c.:led. St:rvic.;e
1be priority call procedure in preferred embodiments is as
domains will be discussed in more detail later. The
follows:
incoming call setup message is repeated a number of
(:i) The CT will p11blish Directory Numbers (DNs) for a
times.
number of emergency services over the CCC.
(iv) The ST attempts uplink acquisition. The ST listens to 20
(ili) The ST will attempt uplink access according to the
the downlink and keeps trying for uplink acquisition
normal algorithms. If the outgoing access is successful
until tht: CT s~:::nds a mt:ssagt: to tht: ST to rdurn the ST
then the customer is able to dial as normal. All dialed
to the CCC. The ST will also run a timer to return it
digits are check against the emergency DN list so that
back to the CCC in the event of an incoming call failing
calls may be categorised normal or priority at the CT.
25
to complete.
(iii) J[f congt:slion tone is returned Lhe c.;ustornt:r is allowt:d
(v) On successful uplink acquisition, the CT authenticates
to dial the emergency number into the ST. If the ST ·
the ST.
detects an emergency DN sequence then uplink access
(vi) Rate switching is originated from the CT modem. A
via the Priority Traffic Channel (PTC) is attempted.
command is sent via the PC/CS to switch the downlink
30
(iv) On PTC acquisition, the ST relays the dialed digit
to the required bandwidth. The ST returns the rate
sequence to the CT for dialling into the PSTN.
switch command via the uplink PC/CS. The link is now
(iv) The CT converts the PTC to a TC and reallocates
of the required bandwidth.
another TC to become the PTC, dropping a normal call
Outgoing Call
in progress if necessary.
Outgoing calls are supported by allowing slotted random
35 Interference Limiting (Pool Sizing)
access to the TC uplinks. The outgoing call processing is as
Across a large scale deployment of cells, optimum capacfollows:
ity is achieved by minimising radio traffic while maintaining
(i) The CT publishes a 'free list' of available Traffic
an acceptable grade of service. Lowest possible radio traffic
Channels and Priority Traffic Channels with their
respective bandwidths. This list is published periodi- 40 results in improved 'carrier to interference' (C./I) ratios for
users within the cell of interest and to co-channel users in
cally (in preferred embodiments, every 500 ms) and is
nearby cells. The C/I ratio is a measure (usually expressed
used to mark uplink access slots.
in dB) of how high above interference the transmitted signal
(ii) An off-hook condition is detected by the ST. The ST
needs to be to be decoded effectively. In preferred
starts a call setup timer.
·
embodiments, the central terminal is provided with the
(iii) The ST waits for the next free list to be received over 45
ability to trade traffic for C;I, thereby allowing network
the CCC. If Lhe Fret: list is t:mply the outu-oinu- c.;all is
planning to be carried out less rigidly. This fe.ature can be
blocked. The ST will generate a ·congesti;'n to~e.
realist:d by a system using CDMA as in prt:ferred embodi(iv) If the Free list has available channels, the ST picks a
ments of the present invention, and is a benefit that CDMA
channel from the free list at random. The algorithm that
offers over TDMA and FDMA systems.
the ST uses to pick a channel will need to be specified 50
In preferred embodiments, the CT will control the number
in the free list. For example, the ST may be required to
of Traffic Channels to minimise access noise. TCs will be
always choose from a pool of minimum bandwidth
classified as:
channels so that high bandwidth channels remain avail(i} Busy-carrying traffic;
able for high GOS users. Alternatively the ST may be
(ii) Access, Incoming (Access_ln)-reserved for :incomallowt:d to choost any channd rt:gardkss of bandwidth 55
ing access;
for minimum blocking. In preferred embodiments, STs
(iii) Access, Outgoing (Access_Out)-reserved for outwill not choose low bandwidth channels and negotiate
going access-such TCs appear on the Free list;
the rate up.
(iv) Priority-reserwd for priority outgoing acc..:t:ss-suc.;h
(v) The ST attempts uplink acquisition on the specified
TCs appear in the Free list;
TC, this process having been described earlier. If 60
(v) Free-available for any purpose; and
acquisition is successful then the outgoing call is pro(vi) Locked-not available due to interference limiting.
cessed. Otherwise the ST returns to the CCC and waits
This classification scheme is illustrated in FIG. 16. The
for the next available free list. To avoid a number of STs
CT will allocate traffic on the following basis:
rt:pelilivdy attempting Lo acquire the same TC, and
blocking each other, a suitable protocol can be 65
(i) The CT will monitor incoming and outgoing call
employed to govern how individual STs will act upon
setup-times and convert Access TCs from Free TCs in
receipt of the free list.
order to achieve a required grade of service.

WIL-0009802

6,088,326

23

24

(ii) When a call is setup, an Access TC is converted to a
Busy TC. If a Free TC is available, it is converted to a
new Access TC. H there are no Free TCs then the
Access TC is lost until a call clears.
(iii) When a call clears the Busy TC is converted to a Free
TC. If a previous call setup resulted in a lost Access TC
then the Busy TC is converted back into an Access TC.
(iv) When the PTC is accessed, a new PTC is created by
converting a Free, Access or Busy (normal call) TC.
(v) The CTwill monitor the Busy TC downlink and uplink
soft error counts in an attempt to establish link quality.
If the CT records a lower than average soft error count
and long call setup times are being recorded, a Locked
TC may be converted to a Free TC. Conversely, if the
C:T records a higher than average soft error count, a
Free or Access TC may be converted to a Locked TC.
FIG. 17 illustrates how the central terminal performs the
above interference limiting function. When incoming call
data arrives at a central terminal modem 320, encoder 325
encodes the data for transmission over the wireless link 300
to the subscriber terminal 20. At the subscriber terminal 20
the decoder 326 decodes the data, and passes the decoded
user data over line 328 to the subscriber telecommunications
equipment. As the decoder 326 decodes the data, it is able to
establish a bit error rate (BER) estimate 330 associated with
the signal transmission over the wireless link 300, which can
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 terminal20, 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 al~o passed over line 355 to the dynamic pool sizing
function 360. The dynamic pool sizing function 360 is
provided on the CT modern 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 ad.dition to BER estimates, grade of service (GOS) data
IS obtamed from two sources. Firstly, at each subscriber
terminal 20, the call control function 336 will note bow
readily it is able to establish traffic channels for transmittinoand 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 modern 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 terminal, 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 tem1inals 20, the call control
functions within the DA engine 380 are also able to provide

GOS estimates for incoming calls, and r.hese 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 withi~ the
modem shelf with data identifvino- a BER o-oal a GOS goal
and a pool size limit (i.e. the n~1mber of ch~nn~ls that can b~
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
determi~e, based on this information, whether pool sizing is
appropnate. 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 encine

10

15

380.
20

25

30

35

40

45

so

55

60

65

b

The demand assignment engine 380 provides modern
enable signals over lines 400 to each of the modems on the
CT modem shelf. If the dynamic pool sizing function 360
has requested that the DA engine 380 perform pool sizing,
then the DA engine 380 can disable one or more of the
modems, this causing the interference, and hence the actual
BER, to be n:duced. 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 TDM slots
to he 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 alarm 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 ST.<>.
The CDMA 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 Modern
Shelf/RI' Channel then the following benefits may be realised:
(i) Fault tolerance-should a CT Modem Shelf subsystem fault occur, an ST may switch to an alternative
frequency for service.
(ii) Call blocking-an ST denied servkt: from one CT
shelf may choose to switch to an alternative frequency
for service.
(iii) Traffic load balancing-the Element Manager may on
the basis of call blocking statistics choose to move STs
between CT shelves.
(iv) Frequency diversity-in the presence of channel
selective fading (slow rnultipath) an ST may operate on
the frequency channel offering highest signal strength
and lowest soft error count.

WIL-0009803

6,mm,326

25

26

RF channel switching is only possible where there are two
typically switch to a different CT, since some errors e),"Peor more co-located cr shelves serving the same geographirienced by one CT shelf may also affect other shelves within
cal area on different RF frequency channels within the same
the same CT, and so for fault tolerance (described in more
RF band. A deployment that meets this criterion may be
detail below), it is preferable for the ST to switch to a
configured as a 'Service Domain'. Possible deployment
separate CT.
scenarios are illustrated in FIG. 18. FIG. 18(i) shows an
Database consistency across CT shelves is preferably
arrangement where omni antennae arc used to provide the
supported through the service domain controller 400. Dataentire cell with four frequency channels, eg Fl, F4, F7, FlO.
base consistency needs to be real-time so that an ST entering
FIG. lR(ii) shows an arrangement where sectored antennae
the network is allowed full Service Domain access immeare used to provide six separate sectors within a cell, each 10 diately (the Service Domain message is broadcast to all STs,
sector being covered by two frequency channels. FIG. 18(iii)
and so a new ST will expect access across the full Service
shows an alternative arrangement where three sectored
Domain).
antennae are used to divide the cell in to three sectors, each
Incoming access via backup CTs requires some f-unction
sector being covered by a separate frequency channel, and
to be provided to broadcast duplicate incoming call setup
then an omni antenna is used to provide an 'umbrella' 15 messages to all CT.o:; that form a Service Domain. Preferably
coverage for the entire cell, this coverage employing a
this is handled by the service domain controller 40(]1, which
frequency channel different to the three frequency channels
forwards incoming call setup messages to each CT operating
used by the sectored antennae.
in the service domain. All CTs will allocate Access_In
For the system to work effectively, the STs must be able
Traffic Channels and relay the incoming call setup message
to switch channels quickly, and fast channel switching 20 via the Call Control Channel. On successful uplink access,
necessitates that CT shelf synchronisation be provided at the
one CT will respond to the service domain controller with a
following levels:
call accepted message, the other CTs will eventually respond
with call setup failed messages. Outgoing access via a
(i) CDMA PN code. This preserves uplink code phase
backup CT is similar to normal outgoing access.
across RF channels during warm start; and
.Another job which can be performed by the service
(ii) RF carrier frequency. This eliminates the need for the 25
domain controller is to assist the element manager 58 in
coarse frequency search on a downlink RF channel
reconfiguring equipment in the event of a fault. For example,
switch.
if one CT is taken out of commission because of a fault, a
On installation, an ST will be programmed with an RF
different CT can be brought 'on-line', and the service
channel and PN code, these codes specifying the ST' s initial
home channel.
30 domain controller can provide that new CT with the necessary information ahout the other CTs in the service domain.
The manner in which channel switching is facilitated in
FIG. 19B illustrates those clements of the subscriber
preferred embodiments will be described with reference to
terminal used to implement RF channel switching. The radio
FIGS. 19A and 19B. A service domain controller 400 is
subsystem 420, which incorporates the transmission and
preferably provided to act as an interface between the
exchange connected to the service domain controller over 35 reception signal processing stages, will pass any data
received on the call control channel over line 425 to the
path 405 and a number of central terminals 10 connected to
message decoder 430. If the decoder 430 determines that the
the service domain controller over paths 410. The central
data on the call control channel forms a service domain
terminals connected to the service domain controller form a
message, then this is passed over line 435 to the channel
'service domain' of central terminals that may be used by a
40 selection controller 440, where the information within the
subscriber terminal 20 for handling communications.
service domain message is stored in storage 445.
In preferred embodiments, the service domain controller
Similarly, if the message decoder identifies the data as a
400 is used to provide each CT 10 with appropriate infor'free list' identifying the available traffic channels on a
mation about the other CTs within the service domain. Each
particular RF frequency, then this data is passed to the call
CT can then broadcast a 'Service Domain' message comprising a list of RF frequencies and CT Identifiers that form 45 control function 336 and the channel selection controHer 440
over path 450. The call control function 336 stores the free
a Service Domain to be used by the ST.o:; for subsequent RF
list in the storage 445 for subsequent use by the call control
switching functions. The ST then stores this information for
function 336 and the channel selection controller 440.
future reference when establishing a link with one of the
If the message decoder 430 determines that the data forms
CTs. It is preferable for each CT to broadcast the ~ervice
domain message since an ST may be listening to any of the so an incoming call setup message, then that information is
supplied over line 455 to the call control function 336 and
CT..;; at the time that the message is broadcast.
the channel selection controller 440 for processing. The
Each CT database will hold an entry for every ST located
incoming call setup message will typically specify a TC on
within the Service Domain. Each database entry describes
the current frequency channel which should be used to
how the CT views it's relationship with the STand may be
ss access the incoming call, and the channel selection controlmarked as:
ler will attempt to establish a link on that TC. The channel
(i) Primary service provider-the CT is the ST's home
seleetion controller will in such cases instruct the radio
channel. All management communication with an ST is
sub-system 420 over line 465 to use the current frequency
via it's home CT.
channel to establish the required link. If, on the other hand,
(ii) Supplying backup service-the CT is providing ser- 60 the traffic channel specified in the call setup message is
vice to the ST.
'null', the channel selection controller has the option to
(iii) Available for backup service-the CT will provide
change RF frequency using the information stored in storage
service to the ST if required.
445 about the other CT.<; in the service domain.
It should be noted Lhal lht: ST nt:t:d nol ~witl:h to an
To t:nablt: !ht: channd ~dtl:tion controlkr 440 to rt:ct:ivt:
entirely different CT, but can instead switch to a different CT 65 information about the status of links, a link operating status
shelf (and hence different RF frequency channel) within the
signal can be supplied over line 470 from the radio subsame CT. However, in preferred embodiments, the ST will
system. This signal will give an indication of the radio link

WIL-0009804

6,0RR,32o
27

28

(iv) When the call clears, the ST downlink preferably
quality, and may be a simple 'OK' or 'faikd' indication, or
alternatively may include e:ll..1:ra information such as BER
switches back to the home CT.
RF Channel Switching for Traffic Load Balancing
values for the link. This information can be used by the
Traffic load balancing is, in preferred embodiments, prochannel selection controller to determine whether a particuvided by static configuration via the EM 58. Call blocking
lar frequency channel should be used or not.
and setup time statistics may be forvvarded to the EM where
To enable the call control function to specify a specific
an operator may decide to move an ST to another RF
Access-Out channel for outgoing calls, a line 460 is prochannel.
vided between the call control function 336 and the channel
selection controller 440. The call control function 336 may
RF Channel Switching for Frequency Diversity
choose an access-out channel from the free list in storage
Frequency diversity is, in preferred embodiments, pro10
vided by static configuration via the EM 58. Radio link
445, and instruct the channel selection controller over line
statistics may be forwarded to the EM where an operator
460 to attempt acquisition of that channel.
may decide to move an ST to another RF channel.
The following examples indicate how the above described
structure may be used to perform channel switching in
Although a particular embodiment has been described
particular circumstances.
herein, it will he appreciated that the invention is not limited
15 thereto and that many modifications and additions thereto
RF Channel Switching for Fault Tolerance
Should one RF channel su.lier complete loss of downlink,
may be made within the scope of the invention. For example,
the following process takes place in preferred embodiments:
various combinations of the features of the following dependent claims could he made with the features of the indepen(i) The ST will attempt downlink re-acquisition for a
dent claims without departing from the scope of the present
period of time, say 20 seconds.
(ii) If acquisition fails, the channel selection controller zo invenLion.
What is claimed is:
440 of the ST will select the next available channel
1. A transmission controller for processing data items to
from the Service Domain information in storage 445
be transmitted over a wireless link connecting a central
and attempt downlink acquisition.
terminal and a subscriber terminal of a wireless telecoi:nThis process will be repeated until a downlink signal is
25 munications system, a single frequency channel being
acquired.
employed for transmitting data items pertaining to a plural(iii) Once a backup RF channel is located, the ST will
ity of wireless links, the transmission controller comprising:
'camp' on the Call Control Channel and may subsean orthogonal code generator for providing an orthogonal
quently be granted traffic access.
code from a set of 'm' orthogonal codes used to create
(iv) If the CT fault persists, the EM 58 may use the service
'm' orthogonal channels within the single frequency
30
domain controller 400 to reconfigure the Service
channel;
Domain so that the functioning CT shelves become
a first encoder for combining a data item to be transmitted
primary service providers for the pool of 'homeless'
on the single freq11ency channel with said orthogonal
STs.
code from the orthogonal code generator, the orthogoA fault that docs not result in complete loss of downlink
nal code determining the orthogonal channel over
signal will not result in RF channel switching 'en mass'. 35
which the data item is transmitted, whereby data items
Rather, a fault may result in excessive or total call blocking,
pertaining to different wireless links may be transmitted
simultaneously within different orthogonal channels of
as discussed below.
said single frequency channel; and
RF Channel Switching for Call Blocking
a TDM encoder arranged to apply time division multiIf Incoming access traffic channels are being blocked, the
plexing (TDM) techniques to the data item in order to
following process is employed in preferred embodiments: 40
insert the data item within a time slot of the orthogonal
(i) The call setup message sent over the Call Control
channel, whereby a plurality of data items relating to
Channel will specify a TC on which to access the call.
different wireless links may be transmitted within the
(ii) In the cas~;; of incoming a<.:cess b~;;ing blocked, the CT
same orthogonal channel during a predetermined frame
will specify a null TC. The channel selection controller
45
period.
440 of the ST will in such cases switch to the next RF
2. A transmission controller as claimed in claim 1, further
channel from the Service Domain information in storcomprising:
age 445 and monitor the Call Control Channel.
an overlay code generator for providing an overlay code
(iii) If the ST receives a call setup message with a valid
from a first set of 'n' overlay codes which are orthogoTC, th~;;n the call is processed as normaL
nal to each other; and
50
(iv) When the call clears, the ST downlink preferably
a second encoder, selectively operable instead of the TDM
switches back to the home CT.
encoder, to apply the overlay code from the overlay
If Outgoing access traffic channels are being blocked, the
code generator to said data item, whereby 'n' data items
following process is employed in preferred embodiments:
pertaining to different wireless links may be transmitted
(i) The ST registers an off-hook. The Pree List in storage 55
simultaneously within the same orthogonal channel.
445 is checked and if a traffic channel is available, then
3. A transmission controller as claimed in claim 1,
the call control f1mction 336 asserts a channel request
wherein the orthogonal code generator is a storage arranged
on line 460 to the channel selection controller 440 and
to store the set of orthogonal codes.
normal uplink access is attempted.
4. A transmission controller as claimed in claim 1,
(ii) If the Free List shows no Access_Out channels are 60 wherein the set of orthogonal codes comprise a set of
Rademacher-Walsh (RW) codes.
available on the current frequency channel, then the
channel selection controller will be used to switch the
5. A central terminal of a wireless telecommunications
ST to the next RF channel in the Service Domain,
system, comprising a transmis.<>ion controller having:
whereupon the ST will wait for the next f<ree List.
an orthogonal code generator [or providing an orthogonal
code from a set of 'm' orthogonal codes used to create
(iii) When the ST finds a Free List with an available 65
'm' orthogonal channels within the single frequency
Access_Out channel, then uplink access is attempted
channel;
and the call is processed as normal.

WI L-0009805

o,mm,326
29

30

a first encoder for combining a data item to be transmitted
code from the orthogonal code generator, the orthogoon the single frequency channel with said orthogonal
nal code determining the orthogonal channel over
code from the orthogonal code generator, the orthogowhich the data item is transmitted, whereby data items
nal code determining the orthogonal channel over
pertaining to different wireless links may be transmitted
which the data item is transmitted, whereby data items
simultaneously within different orthogonal channels of
pertaining to different wireless links may be transmitted
said single frequency channel; and
simultaneously within different orthogonal channels of
a TOM encoder arranged to apply time division multisaid single frequency channel;
plexing (TOM) techniques to the data item in order to
a TDM encoder arranged to apply time division multiinsert the data item within a time slot of the orthogonal
plexing (TOM) techniques to the data item in order to 10
channel, whereby a plurality of data items relating to
insert the data item within a time slot of the orthogonal
different wireless links may be transmitted within the
channel, whereby a plurality of data items relating to
same orthogonal channel during a predetermined frame
different wireless links may be transmitted within the
period;
same orthogonal channel during a predetermined frame
period;
an overlay code generator for providing an overlay code
from a first set of 'n' overlay codes which are orthogoan overlay code generator for providing an overlay code 15
nal to each other;
from a first set of 'n' overlay codes which are orthogonal to each other;
a second encoder, selectively operable instead of the TOM
a second encoder, selectively operable instead of the TOM
encoder, to apply the overlay code from the overlay
encoder, to apply the overlay code from the overlay
code generator to said data item, whereby 'n' data items
20
code generator to said data item, whereby 'n' data items
pertaining to different wireless links may be transmitted
pertaining to different wireless links may be transmitted
simultaneously within the same orthogonal channel,
simultaneously within the same orthogonal channel,
wherein the orthogonal code generator is a storage
wherein the orthogonal code generator is a storage
arranged to store the set of orthogonal codes and
arranged to store the set of orthogonal codes and
wherein the set of orthogonal codes comprise a set of
wherein the set of orthogonal codes comprise a set of 25
Rademacher-Walsh (RW) codes;
Rademacher-Walsh (RW) codes.
and wherein at least one subscriber terminal comprises a
6. A central terminal as claimed in claim 5, further
reception controller having:
comprising channelisation means for determining which of
an orthogonal code generator for providing an orthogothe orthogonal channels will be subject to TOM techniques,
nal code from a set of 'm' orthogonal codes llsed to
and for transmitting that information to a plurality of sub- 30
scriber terminals within the wireless telecommunications
create said 'm' orthogonal channels within the single
system.
frequency channel;
7. A central terminal as claimed in claim 6, wherein the
a first decoder for applying, to signals received on
channelisation means also determines, for those orthogonal
the single frequency channel, the orthogonal code
provided by the orthogonal code generator, in
channels subject to TOM techniq11es, how many time slots 35
order to isolate data items transmitted within the
will be provided within each orthogonal channel.
8. A central terminal as claimed in claim 7, wherein a
corresponding orthogonal channel; and
number of said orthogonal channels are designated as traffic
a TOM decoder arranged to extract a data item from a
channels for the transmission of data items relating to
predetermined time slot within said orthogonal
channel, a plurality of data items relating to different
communication content, and the TOM encoder is employed 40
to apply time division multiplexing (TOM) techniques to
wireless links being transmitted within the same
data items to be sent over a traffic channel from said central
orthogonal channel during a predetermined frame
period;
terminal to said subscriber terminal.
9. A central terminal as claimed in claim 5, wherein a first
an overlay code generator for providing an overlay
of the orthogonal channels is reserved for the transmission 45
code from a first set of 'n' overlay codes which are
of signals relating to the; acquisition of wireless links, and
orthogonal to each other, the set of 'n' ovt:rlay codes
enabling 'n' data items pertaining to different wirethe second encoder is used instead of the TOM encoder to
enable overlay codes to be applied to data items to be sent
less links to be transmitted simultaneously within the
\>,ritbin said first orthogonal channel from the central terminal
same orthogonal channel;
to one of said subscriber terminals.
a second decoder, selectively operable instead of the
50
10. A central terminal as claimed in claim 5, wherein a
TOM decoder, to apply to the data items of the
second of the orthogonal channels is reserved for the transorthogonal channel, the overlay code from the overmission of signals relating to the control of calls, and the
lay code generator so as to isolate a particular data
second encoder is used instead of the TDM encoder to
item transmitted using that overlay code, wherein the
enable overlay codes to be applied to data items to be sent 55
orthogonal code generator is a storage arranged to
within said second orthogonal channel from the central
store the set of orthogonal codes and wherein the set
terminal to one of said subscriber terminals.
of orthogonal codes comprise a set of Rademacher11. A wireless telecommunications system comprising a
Walsh (RW) codes.
central terminal and a plurality of subscriber terminals,
12. A method of processing data items to be transmitted
wherein the central terminal comprises a transmission con- 60 over a wireless link connecting a central terminal and a
troller having:
subscriber terminal of a wireless telecommunications
system, a single frequency channel being employed for
an orthogonal code generator for providing an orthogonal
transmitting data items pertaining to a plurality of wireless
code from a set of 'm' orthogonal codes used to create
links,. the method comprising steps of:
'm' orthogonal channels within the single frequency
channel;
65
providing an orthogonal code from a set of 'm' orthogonal
a first encoder for combining a data item to be transmitted
codes used to create 'm' orthogonal channels within the
single frequency channel;
on the single frequency channel with said orthogonal

WI L-0009806

6,088,326

31

32

comb.in.ing a data item to be transmitted on the s.ingle
applying the overlay code to said data item, whereby 'n'
data items pertaining to different wireless links may be
frequency channel with said orthogonal code, the
transmitted simultaneously within the same orthogonal
orthogonal code determining the orthogonal channel
channel.
over which the data item is transmitted, whereby data
14. A method as claimed in claim 12, further comprising
items pertaining to different wireless links may be
steps of:
transmitted simultaneously within different orthogonal
determining which of the orthogonal channels will be
channels of said single frequency channel; and
subject to TDM techniques; and
applying time division multiplexing (TDM) techniques to
transmitting that information to a plurality of subscriber
the data item in order to insert the data item within a
terminals within the wireless telecommunications syslime slot of the orthogonal channel, whereby a plurality 10
tem.
of data items relating to different wireless links may be
15. A method as claimed in claim 14, further comprising
transmitted within the same orthogonal channel during
a step of:
a predetermined frame period.
determining, for those orthogonal channels subject to
13. A method as claimed in claim 12, wherein said
TDM techniques, how many time slots will be provided
applying step is selectively replaced by steps of:
15
within each orthogonal channel.
providing an overlay code from a first set of 'n' overlay
codes which are orthogonal to each other; and

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WIL-0009807