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

Filing 492

RESPONSE to Motion re 481 MOTION for New Trial CONCERNING THE NON-INFRINGEMENT OF CERTAIN CLAIMS OF U.S. PATENT NOS. 6,088,326; 6,222,819; 6,195,327 AND 6,381,211 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: Markman Transcript, # 2 Exhibit B: Trial Transcript, # 3 Exhibit C: Trial Transcript, # 4 Exhibit D: Trial Transcript, # 5 Exhibit E: Trial Transcript, # 6 Exhibit F: PX 1, # 7 Exhibit G: PX 2, # 8 Exhibit H: PX 3, # 9 Text of Proposed Order)(Heinlen, James)

EXHIBIT H

111111111111111111111111111111111111111111111111111111111111111111111111111
US006222819Bl

United States Patent

(10)

Lysejko et al.

(12)

(45)

(54)

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

(75)

Inventors: Martin Lysejko, Bagshot (GB); Paul F.
Struhsakcr, Plano, TX (US)

(73)

Assignee: Airspan Networks, lnc., Seattle, WA
(US)

( *)

Notice:

Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 0 days.

(21)

Appl. No.: 08/978,970

(22)

Filed:

Nov. 26, 1997

Foreign Application Priority Data

(30)

Dec. 20, 1996

(51)
(52)
(58)

(GB) .................................................. 9626566

Int. Cl? ...................................................... H04J 11/00
U.S. CI. ............................................. 370/209; 370/342
Field of Search ..................................... 370/203, 208,
370i209, 320, 335, 342, 343, 441, 479;
375/130, 146, 147

(56)

References Cited
U.S. PATENT DOCUMENTS
5,373,502
5,414,728
5,764,630 *
5,793,759 *
5,956,345 *

12/1994
5/1995
6/1998
8/1998
9/1999

Turban ..... ... .... .... .. .. .. .. ... .... ... . 370/18
Zehavi ................................. 375/200
Natali et al. ......................... 370/320
Rakib et al. ......................... 370/342
Allpress et al. ..................... 370/480

FOREIGN PATENT DOCUMENTS
0633676
0652650
0730356

1/1995 (EP) ............................... H04J/13/00
5/1995 (EP) ................................ H04B!7/26
9/1996 (EP) ................................ H04L/l/OO

Patent No.:
US 6,222,819 Bl
Date of Patent:
Apr. 24, 2001

12/1993
12/1996
7/1993
2/1995
11/1996

2267627
2301744
9314588
9503652
9637066

(GB) ............................... H04BI7/00
(GB) ............................... H04QI7/32
(WO).
(WO) .............................. H04B/7/26
(WO) ............................ H04L/27/30

* cited by examiner
Primary Examiner-Wellington Chin
Assistant Examiner-Kwang B. Yao
(74) Allorney) Agent) or Firm-Baker Bulls L.L.P.

(57)

ABSTRACT

The present invention provides a transmission controller and
method for processing data items to be transmitted over a
wirtl~;;ss link conm:cting a c~;;ntral 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, wherehy
data items pertaining to different wireless links may be
transmitted simultaneously within different orthogonal
channels of said single frequency channel. Further, the
transmission controller 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 arranged to apply the overlay code from the overlay
coc.k g~;;n~;;rator to said data item, whereby 'n', data ilems
pertaining to different wireless links may be transmitted
simultaneously within the same orthogonal channel. The
invention also provides a reception controller and method
for processing data items received over a wireless link.
32 Claims, 16 Drawing Sheets
113

126

124

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US 6,222,819 Bl

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Apr. 24, 2001

US 6,222,819 Bl

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Sheet 16 of 16

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1

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PROCESSING DATA TRANSMITTED AND
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CONNECTING A CENTRAL TERMINAL AND
A SUBSCRIBER TERMINAL OF A WIRELESS
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 THE INVENTION

TECHNICAL FIELD OF THE INVENTION

According to the present invention, there is provided a
The present invention relates in general to wireless teletransmission controller for processing data items to be
communications systems and more particularly to techtransmitted over a wireless link connecting a central terminiques for processing data transmitted and received over a 10 nal and a subscriber terminal of a wireless telecommunicawireless link connecting !l central terminill and a subscriber
tions system, a single frequency channel being employed for
terminal of a wireless telecommunications system.
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 wireless telecommunications system has been proposed
of 'm' orthogonal codes used to create 'rn' orthogonal
in which a geographical area is divided in to cells, each cell
channels within the single frequency channel; a first encoder
having one or more central terminals (CTs) for communifor combining a data item to be transmitted on the single
cating over wireless links \'vith a number of subscriber
frequency channel with said orthogonal code frmn the
terminals (S'ls) in the cell. These wireless links are estaborthogonal code generator, the orthogonal code determining
lished over predetermined frequency channels, a frequency 20 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; an
terminal to the subscriber terminal.
overlay code generator for providing an overlay code from
25
a first set of 'n' overlay codes which are orthogonal to each
Due to band\vidth constraints, it is not practical for each
other; and a second encoder arranged to apply the overlay
individual subscriber terminal to have its own dedicated
code from the overlay code generator to said data item,
frequency channd for communicating with the central terwhereby 'n' data items pertaining to different wireless links
minal. Hence, techniques need to be applied to enable data
may be transmitted simultaneously within the same orthogoitems relating to different wireless links to be passed over the
same frequency channel without interfering with each other. 30 nal channel.
In current wireless telecommunications systems, this can be
Vie~red from a second aspect, the present invention
achieved through the use of a 'Code Division Multiple
provides a reception controller for processing data items
Access' (CDMA) technique. One way to implement CDMA
received over a wireless link connecting a central terminal
is through the application of a set of orthogonal codes to the 35 and a subscriber terminal of a wireless telecommunications
data items to be transmitted on a particular frequency
system, a single frequency channel being employed for
channel, data items relating to different wireless links being
transmitting data items pertaining to a plurality of wireless
combined with different orthogonal codes from the set. A
links, the receiver controller comprising: an orthogonal code
suitable set of orthogonal codes is a "Rademacher-Walsh"
generator for providing an orthogonal code from a set of 'm'
(RW) set of sixteen 16-bit codes. Orthogonal codes hav<~ the
orthogonal codes used to create 'm' orthogonal channels
40
property that, when perfectly aligned, all codes crosswithin the single frequency channel; a first decoder for
correlate to zero, thus making it possible to decode a signal
appl ying, to signals received on the single frequency
to which one orthogonal code has been applied while
channel, the orthogonal code provided by the orthogonal
cancelling interference from signals to which different
code generator, in order to isolate data items transmitted
orthogonal codes have been applied.
within the corresponding orthogonal channel; an overlay
45
code generator for providing an overlay code from a :first set
Signals to which an orthogonal code has been applied can
of 'n' overlay codes which are orthogonal to each other, the
be considered as being transmitted over a corresponding
set of 'n' overlay codes enabling 'n' data items pertaining to
orthogonal channel within a particular frequency channel.
different wireless links to be transmitted simultaneously
lienee, considering the example of a set of 16 RW codes, 16
orthogonal channels can be created within a single fre- 50 within the same orthogonal channel; and a second decoder
for applying, to the data items of the orthogonal channel, the
quency channel, and hence up to sixteen separate commuoverlay code from the overlay code generator so as to isolate
nication signals (corresponding to sixteen separate wireless
a particular data item transmiltt:d using that overlay code.
links) can be transmitted simultaneously over the single
frequency channel if different RW codes are applied to each
By using overlay codes in addition to the known set of
communication signal.
55 orthogonal codes, it is possible for selected orthogonal
channels to be subdivided to form additional orthogonal
It is known to provide a number of modern shelves within
channels. For example, if there are originally sixteen
one central terminal, and for each modern shelf to employ a
orthogonal channels and a set of four overlay codes arc
different frequency channel. Hence, if a central terminal has
four modem shelves, and the set of 16 RW codes is
defined, each orthogonal channel being subject to overlay
employed for each frequency channel, one central terminal 60 codes, then up to 64 orthogonal channels can be defined. By
application of appropriate orthogonal codes and overlay
\Yould be able to support wireless links with up to 60
codes, up to 64 separate communication signals could be
subscriber terminals simultaneously.
sent simultaneously on the one frequency channel, albeit at
However, as more subscribers subscribe to the wireless
a quarter of the rate that the communication signals could be
telecommunications network, it is becoming desirable to
support more and more subscriber terminals from each 6s transmitted if the overlay codes were not used.
central terminal. There are only a limited number of freSuch an approach has the advantage that it preserves
quency channels that can be allocated to the wireless telecompatibility with current hardware and software equipment
1

WIL-0009860

US 6,222,R19 Bl

3

4

which use the set of orthogonal codes, but which do not
reception controller in accordance with the present invensupport the use of overlay codes. By designating certain
tion. Further, the central terminal preferably includes cbanorthogonal channels as channels for which overlay codes are
nelisation means for determining which of the orthogonal
not used, the current equipment can communicate over those
channels will be subject to overlay codes, and for transmitchannels without any changes being required to the equipting that information to a plurality of subscriber terminals
ment.
within the telecommunications system. This is usdul since,
In preferred embodiments, the overlay code generator is
for example, certain orthogonal channels can hence be
arranged to store one or more further sets of overlay codes
designated as being reserved for communications with STs
having different numbers of overlay codes to the first set of
that do not incorporate the features necessary to support
overlay codes. This enables the orthogonal channels to be 10 overlay codes, and which hence require a full 160 kb/s
subdivided differently, depending on which set of overlay
orthogonal channel.
codes is selected. For instance, if an orthogonal channel
In preferred embodiments, the channelisation means also
operates at 160 kb/s, and a set of four overlay codes is used
determines, for those orthogonal channels subject to overlay
to subdivide that orthogonal channel, then four 40 kb/s
codes, which set of overlay codes will apply to each
orthogonal channels can be created from the one original
orthogonal channel. If, alternatively, a set of two overlay 15 orthogonal channel. This gives a great deal of flexibility in
how the channels art: ust:d, since: some can bt: subdividt:d
codes is used, then two SO kb/s orthogonal channels can be
whilst others are not, and those which are subdivided can be
created from the one orthogonal channel. This flexibility is
subdivided differently to yield differing numbers of differing
useful, since for some communications, eg. fax, a rate of 40
rate channels.
kb/s may not be acceptable, and hence a set of four overlay
20
codes would not be suitable.
As with the central terminal, a subscriber terminal of the
wireless telecommunications system may comprise a transThe orthogonal code generator and overlay code generamission controller and/or a reception controller in accortor may generate orthogonal codes and overlay codes 'on the
dance with the present invention. Unlike the central
fly' using predetermined algorithms. However, alternatively,
terminal, it is preferable for the subscriber terminal to use
the orthogonal code generator may be provided as a storage
25
overlay codes for all types of channels, whether they be
arranged to store the set of orthogonal codes, and the overlay
traffic channels or otherwise. On these uplink traffic
code generator may be provided as a storage arranged to
channels, the pure COMA approach using overlay codes
store the set of overlay codes. Appropriate orthogonal codes
eliminates the need to time synchronise STs to a TDM frame
and overlay codes could then be read out to the encoders or
reference, and reduces the peak power handling requiredecoders as required.
In preferred embodiments, the set of orthogonal codes 30 ments in the ST RF transmit chain.
Viewed from a third aspect, the present invention provides
comprise a set of Rademacher-Walsh (RW) codes, in prea wireless telecommunications system comprising a central
ferred embodiments the set comprising a 16x16 matrix of
terminal and a plurality of subscriber terminals, wherein the
RW codes. Further, the set of overlay codes are preferably
derived from RW codes, each set of 'n' overlay codes 35 central terminal comprises a transmission controller in
accordance with the present invention, and at least one of the
preferably comprising an nxn matrix of RW codes.
subscriber terminal comprises a reception controller in
The: transmission controller in accordance with the
accordance with the present invention. Alternatively, or
present invention may be provided within the central termiadditionally, within the wireless telecommunications
nal of a wireless telecommunications system. In preferred
embodiments, a first of the orthogonal channels is reserved 40 system, at least one of the subscriber terminals may comprise a transmission controller in accordance with the
for the transmission of signals relating to the acquisition of
present invention, and the central terminal may comprise a
wireless links, and the transmission controller is provided in
reception controller in accordance with the present inventhe central terminal to enable overlay codes to be applied to
tion.
data items to be sent within said first orthogonal channel
from the central terminal to one of said subscriber terminals. 45
Viewed from a fourth aspect, the present invention proSimilarly, a second of the orthogonal channels is preferably
vides a method of processing data items to be transmitted
reserved for the transmission of signals relating to the
over a wireless link connecting a central terminal and a
control of calls, and the transmission controller in the central
subscriber terminal of a wireless telecommunications
terminal also enables overlay codes to be applied to data
system, a single frequency channel being employed for
items to be sent within said second orthogonal channel from 50 transmitting data items pertaining to a plurality of wireless
the central terminal to one of said subscriber terminals.
links, the method comprising the steps of: providing an
However, a number of said orthogonal channels are
orthogonal code from a set of 'm' orthogonal codes used to
designated as traffic channels for the transmission of data
create 'm' orthogonal channels within the single frequency
items relating to communication content, and in preferred
channel; combining a data item to be transmitted on the
embodiments a TDM encoder is provided within the central 55 single frequency channel with said orthogonal code, the
terminal arranged to apply time division multiplexing
orthogonal code determining the orthogonal channel over
(TDM) techniques to data items to be sent over a traffic
which the data item is transmitted, whereby data items
channel from said central terminal to said subscriber
pertaining to different wireless links may be transmitted
terminal, so as to enable a plurality of data items pertaining
simultaneously within different orthogonal channels of said
to different wireless links to be sent within one orthogonal 60 single frequency channel; providing an overlay code from a
traffic channel during a predetermined frame petiod.
first set of 'n' overlay codes \vhich are orthogonal to each
other; and applying the overlay code to said data item,
The use of a CDMA/TDM hybrid approach for downlink
whereby 'n' data items pertaining to different wireless link>
traffic channels retains the benefits of CDMA access, ie.
may be transmitted simultaneously within the same orthogointerference is reduced when traffic is reduced, and also
65 nal channt:I.
reduces receiver dynamic range requirements.
Viewed from a fifth aspect, the present invention provides
In addition to, or as an alternative to, having a transmisa method of processing data items received over a wireless
sion controller, the central terminal may also comprise a

WI L-0009861

US 6,222,R19 Bl
5

6

FIGS. 14A and 14B illustrate the overhead frame struclink connecting a central terminal and a subscriber terminal
ture for the downlink and uplink paths;
of a wireless telecommunications system, a single frequency
channel being employed for transmitting data items pertainFIGS. 15Aanc115B illustrate typical downlink and uplink
ing to a plurality of wireless links, the method comprising
channel structures that might occur in a loaded system in
the steps of: providing an orthogonal code from a set of 'm'
accordance with preferred embodiments of the present
orthogonal codes used to create 'm' orthogonal channels
invention;
within the single frequency channel; applying, to signals
FIG. 16 illustrates how the available traffic channels are
received on the single frequency channel, the orthogonal
classified in preferred embodiments of the present invention;
code in order to isolate data items transmitted within the
FIG. 17 illustrates the elements used by the central
corresponding orthogonal channel; providing an overlay 10
terminal to perform interference limiting;
code from a first set of' n' overlay codes which are orthogoFIG. 18 illustrates possible antenna confignrations that
nal to each other, the set of 'n' overlay codes enabling 'n'
can he employed in a wireless telecommunications system in
data items pertaining to different wireless links to be transaccordance vvith the preferred embodiment of the present
mitted simultaneously within the same orthogonal channel;
and applying, to the data items of the orthogonal channel, the 15 invention; and
overlay code so as to isolate a particular data item transFIGS. 19A and 19B illustrate how channel switching is
mitted using that overlay code.
facilitated in preferred embodiments of the present invention.
By using overlay codes in addition to the known set of
orthogonal codes, it is possible for selected orthogonal
DETAILED DESCRIPTION OP TilE
channels to be subdivided to form additional orthogonal 20
INVENTION
channels, thereby making it possible to support more wireless links on one frequency channel.
FIG. 1 is a schematic overview of an example of a
wireless telecommunications system. The telecommunicaBRIEF DESCRIPTION OF THE INVENTION
25 tions system includes one or more service areas 12, 14 and
An embodiment of the invention will be described
16, each of which is served by a respective central terminal
hereinafter, by way of example only, with reference to the
(C1) 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 30 area 12 could cover an area with a radius of 15-20 Km. A
the present invention is included;
service area 14 in an nrban environment where is there is a
FIG. 2 is a schematic illustration of an example of a
high density of subscriber terminals 20 might only cover an
subscriber terminal of the telecommunications system of
area with a radius of the order of 100 m. In a suburban area
FIG.1;
with an intermediate density of subscriber terminals, a
35
serv'ice area 16 might cover an area with a radius of the order
FIG. 3 is a schematic illustration of an example of a
of 1 Km. It will be appreciated that the area covered by a
central terminal of the telecommunications system of PIG.
particular central terminal10 can be chosen to suit the local
1;
requirements of expected or actual subscriber density, local
FIG. 3Ais a schematic illustration of a modem shelf of a
ctntral terminal of the telecommunications system of FIG. 40 geographic considerations, etc, and is not limited to the
examples illustrated in FIG.l. Moreover, the coverage need
1;
not be, and typically will not be circular in extent due 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. SA and SB are schematic diagrams illustrating
45 mitted signals.
possible configurations for cells for the telecommunications
The central terminals 10 for respective service areas 12,
system of FIG. 1;
14, 16 can be connected to each other by means of links 13,
FIG. 6 is a schematic diagram illustrating aspects of a
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. 7 A and 7B are schematic diagrams illustrating 50 copper wires, optical fibres, satellites, microwaves, etc.
signal transmission processing stages for the telecommuniTb.e wireless telecommunications system of FIG. 1 is
cations system of FIG. 1;
based on providing fixed microwave links between subFIGS. SA and SB are schematic diagrams illustrating
scriber terminals 20 at fixed locations within a service area
signal reception processing stages for the telecommunica55 (e.g., 12, 14, 16) and the central terminallO for that service
tions system of FIG. 1;
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 terminal10, but in
downlink delivery methods when the system is fully loaded;
preferred embodiments demand-based access is provided, so
FIG.10 illustrates the CDMAchannel hierarchy in accorthat the number of subscribers which can be supported
dance with preferred embodiments of the present invention; 60 exceeds the number of available wireless links. The manner
FIG. 11 is a schematic diagram illustrating downlink and
in which demand-based access is implemented vv-ill be
uplink communication paths for the wireless telecommunidiscussed in detail later.
cations system;
FIG. 2 illustrates an example of a configuration for a
FIG. 12 is a schematic diagram illustrating the makeup of
subscriber terminal20 for the telecommunications system of
a downlink signal transmitted by the central terminal;
65 FIG. 1. FIG. 2 includes a schematic representation of
FIGS. 13A and 13B illustrate the structure of the frames
customer premises 22. A customer radio unit (CRU) 24 is
of information sent over the downlink and uplink paths;
mounted on the customer's premises. The customer radio

WI L-0009862

US 6,222)H 9 B1
7

8

unit 24 includes a fiat panel antenna or the like 23. The
A;:, an alternative to the RS232 connections 55, which
customer radio unit is mmmtecl at a location on the customextend to a site controller 56, data connections such as an
er's premises, or on a mast, etc., and in an orientation such
X.25 links 57 (shown with dashed lines in FIG. 3) could
that the fiat panel antenna 23 within the customer radio unit
instead be provided from a pad 228 to a switching node 60
of an element manager (EM) 58. An element manager 58 can
24 faces in the direction 26 of the central tcrminal10 for the
service area in which the customer radio unit 24 is located.
support a number of distributed central terminals 10 connected by respective connections to the switching node 60.
The customer radio unit 24 is connected via a drop line 28
The element manager 58 enables a potentially large number
to a power supply unit (PSU) 30 within the customer's
premises. The power supply unit 30 is connected to the local
(e.g., up to, or more than 1000) of central terminals 10 to be
power supply for providing power to the customer radio unit 10 integrated into a management network. The element man24 and a network terminal unit (NTU) 32. The customer
ager 58 is based around a powerful workstation 62 and can
radio unit 24 is also connected via the power supply unit 30
include a number of computer terminals 64 for network
engineers and control personnel.
·
to the network terminal unit 32, which in tum is connected
to telecommunications equipment in the customer's
FIG. 3A illustrates various parts of a modem shelf 46. A
premises, for exampk to one or more telephom:s 34, fac- 15 transmit/receive RF unit (RFU-for example implemented
simile machines 36 and computers 38. The telecommunicaon a card in the modem shelt) 66 generates the modulated
tions equipment is represented as being within a single
transmit RF signals at medium power levels and recovers
customer's premises. However, this need not be the case, as
and amplifies the baseband RF signals for the subscriber
the subscriber terminal20 preferably supports either a single
terminals. The RF unit 66 is connected to an analogue card
or a dual line, so that two subscriber lines could be supported 20 (AN) 68 which performs A-DID-A conversions, baseband
by a single subscriber terminal 20. The subscriber terminal
filtering and the vector summation of 15 transmitted signals
20 can also be arranged to support analogue and digital
from the modem cards (MCs) 70. The analogue unit 68 is
telecommunications, for example analogue communications
connected to a number of (typically 1-8) modem cards 70.
at 16, 32 or 64 kbits/sec or digital communications in
Tht: mmkm carcls perform the bast:baml signal proct:ssing of
accordance with the ISDN BRA standard.
25 the transmit and receive signals toifrom the subscriber
FIG. 3 is a schematic illustration of an example of a
tenninals 20. This may include lh rate convolution coding
central terminal of the telecommunications system of FIG.1.
and x16 spreading with "Code Division Multiplexed
The common equipment rack 40 comprises a number of
Access" (CDMA) codes on the transmit signals, and synequipment shelves 42, 44, 46, including a RF Combiner and
chronisation recovery, de-spreading and error correction on
power amp shelf (RFC) 42, a Power Supply shelf (PS) 44 30 the receive signals. Each modem card 70 in the present
and a number of (in this example four) Modem Shelves
example has two modems, and in preferred embodiments
there are eight modem cards per shelf, and so sixteen
(MS) 46. The RF combiner shelf 42 allows the modem
shelves 46 to operate in parallel. If 'n' modem shelves arc
modems per shelf. However, in order to incorporate redunprovided, then the RF combiner shelf 42 combines and
dancy so that a modem may be substituted in a subscriber
amplifies the power of 'n' transmit signals, each transmit 35 link when a fault occurs, only 15 modems on a single
signal being from a respective one of the 'n' modem shelves,
modem shelf 46 are generally used. The 16th modem is then
and amplifies and splits received signals 'n' way so that
used as a spare which can be switched in if a failure of one
of the other 15 modems occurs. The modem cards 70 are
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
the local power supply and fusing for the various compo- 40 connection to the host public switched telephone network 18
(e.g., via one of the lines 47) and handles the signalling of
nents in the common equipment rack 40 .. A bidirectional
connection extends between the RF combiner shelf 42 and
telephony information to the subscriber terminals via one of
the main central terminal antenna 52, such as an omnidi15 of the 16 modems.
rectional antenna, mounted on a central terminal mast 50.
The wireless telecommunications between a central terThis example of a central terminallO is connected via a 45 minal 10 and the subscriber terminals 20 could operate on
various frequencies. FIG. 4 illustrates one possible example
point-to-point microwave link to a location where an interface to the public switched telephone network 18, shown
of the frequencies which could be used. In the present
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
be used to link the central terminal10 to the public switched so example is intended to operate in the Band defined by ITU-R
(CCIR) Recommendation F.701 (2025-2110 MHz,
telephone network 18. In this example the modem shelves
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
terminal 10 and for the downlink from the central terminal
48 to a point-to-point microwave antenna 54 mounted on the
mast 50 for a host connection to the public switched tele- 55 10 to the subscriber terminals 20. It will be noted that 12
uplink and 12 downlink radio channels of 3.5 MHz each are
phone network 18.
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.
central terminal10. The site controller 56 can be connected
In the present example, each modem shelf supports 1
to each modem shelf of the central terminal 10 via, for 60
frequency channel (i.e. one uplink frequency plus the corexample, RS232 connections 55. The site controller 56 can
responding downlink frequency). Currently, in a wireless
then provide support functions such as the localisation of
telecommunications system as described above, CDMA
faults, alarms and status and the configuring of the central
encoding is used to support up to 15 subscriber links on one
terminal 10. A site controller 56 will typically support a
single central terminal 10, although a plurality of site GS frequency channel (one subscriber link on each modem).
Hence, if a central terminal has four modem shelves, it can
controllers 56 could be networked for supporting a plurality
support 60 (15x4) subscriber links (ie. 60 STs can be
of central terminals 10.

WIL-0009863

US 6,222,Rl9 Bl

10

9

connected to one CT). However, it is becoming desirable for
ating on the same frequency don't inadvertently decode each
more than 60 STs to be supported from one central terminal,
others data, a seven cell repeat pattern is used such that for
and, in preferred embodiments of the present invention,
a cell operating on a given frequency, all six adjacent cells
enhancements to the COMA encoding technique are prooperating on the same frequency are allocated a unique
vided to increase the number of subscriber links that can be
pseudo random noise (PN) code. The use of PN codes w.ill
supported by a central terminal. Both COMA encoding, and
be discussed in more detail later. The use of different PN
codes prevents nearby cells operating on the same frequency
the enhancements made to the COMA encoding in accordance with preferred embodiments, will be discussed in
from inadvertently decoding each others data.
more detail later.
As mentioned above, CDYIA techniques can be used in a
Typically, the radio traffic from a particular central ter- 10 fixed assignment arrangement (ie. one where each ST is
minal10 will extend into the area covered by a neighbouring
assigned to a particular modem on a modem shelf) to enable
l:tntral ltrminal 10. To avoid, or at ltast to rtuuct intr;:rftr~::ach channel frequency to support 15 subscriber links. FIG.
ence problems caused by adjoining areas, only a limited
6 gives a schematic overview of CDMA encoding and
numher of the available frequencies \vill he used by any
decoding.
given central terminal 10.
In order to encode a COMA signal, base band signals, for
15
example the user signals for each respective subscriber link,
.FIG. SA illustrates one cellular type arrangement of the
are encoded at 80-80N into a 160 ksymbols/sec baseband
frequencies to mitigate interference problems between adjasignal where each symbol represents 2 data bits (see, for
cent central terminals 10. In the arrangement illustrated in
FIG. SA, the hatch lines (or tht cells 76 illustrate a frtquency
example the signal represented at 81). ll1is signal is then
spread by a factor of 16 using a spreading function 82-82N
set (FS) for the cells. By selecting three frequency sets (e.g.,
20
to generate signals at an effective chip rate of 2.56
where: FS 1 =F1, F4, F7, F1 0; FS2=F2, F5, FR, F11; FS3=F3,
Msymbols/sec in 3.5 MHz. The spreading function involves
F6, F9, F12), and arranging that immediately adjacent cells
applying a PN code (that is specified on a per CT basis) to
do not use the same fn:qutm:y set (stt, (or examplt, the
the signal, and also applying a Rademacher-Walsh (RW)
arrangement shown in FIG. SA), it is possible to provide an
code which ensures that the signals for respective subscriber
array of fixed assignment omnidirectional cells where interference between nearby cells can be reduced. The transmit- 25 terminals will be orthogonal to each other. Once this spreading function has been applied, the signals for respective
ter powtr of each <..:entralterminal10 is prtferably set such
subscriber links are then combined at step 84 and converted
that transmissions do not extend as far as the nearest cell
to radio frequency (RF) to give multiple user channel signals
which is using the same frequency set. Tlms, in accordance
(e.g:. 85) for transmission from the transmitting antenna 86.
with the arrangement illustrated in FIG. SA, each central
terminal10 can use the four frequency pairs (for the uplink 30
During transmission, a transmitted signal will be suband dmvnlink, respectively) within its cell, each modem
jected to interference sources 88, including external intershelf in the central terminal 10 being associated with a
ference 89 and interference from other channels 90.
respective RF channel (channel frequency pair).
Accordingly, by the time the COMA signal is received at the
receiving antenna 91, the multiple user channel signals may
Figure SB illustrates a cellular type arrangement employing sectored cells to mitigate problems between adjacent 35 be distorted as is represented at 93.
central terminals 10. As with FIG. SA, the different type of
In order to decode the signals for a given subscriber link
hatch lines in FIG. SB illustrate different frequency sets. As
from the received multiple user channel, a Walsh correlator
in FIG. 5A, FIG. SB represents three frequency sets (e.g.,
94-94N uses the same RW and PN codes that were used for
where: FSl=Fl, F4, F7, FlO; FS2=F2, F5, F8, Fll; FS3=F3,
the encoding for each subscriber link to extract a signal (e.g,
F6, F9, F12) However, in FIG. 5B the cells are sectored by 40 as represented at 95) for the respective received baseband
using a sectored central terminal (SCT) 13 which includes
signal 96-96N. It will be noted that the received signal will
three central terminals 10, one for each sector Sl, S2 and S3,
include some residual noise. However, unwanted noise can
with the transmissions for each of the three central terminals
be removed using a low pass filter and signal processing.
10 being directed to the appropriate sector among S1, S2: and
The key to COMA is the application of the RW codes,
S3. This enables the number of subscribers per cell to be
these being a mathematical set of sequences that have the
45
increased three fold, while still providing permanent fixed
function of "orthonormality". In other words, if any RW
access for each subscriber terminal 20.
code is multiplied by any other RW code, the results are
Arrangements such as those in FIGS. SA and SB can help
zero. A set of 16 RW codes that may be used is illustrated in
reduce interference, but in order to ensure that cells operTable 1 below:
TABLE 1
RWO
RW1
RW2
RW3
RW4

RW5
RW6
RW7

RW8
RW9
RW10
RW11

RW12
RWJ3
RW14
RW15

-1
1
-1
1
-1
1

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

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-1

-]

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

-1
-1

1

1
-1

-J
1
-1
-1
-1

-1
-1

-]

-1
-1

1
-1
-1

1
1
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1

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-1

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-]

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1
-1

1

-1
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-J

-1

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

-1
-1
-1

-1
1
-1
-1
1

-1

-]

1
1

-1

-1
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-1

1
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WI L-0009864

US 6,222,R19 Bl

11

12

In preferred embodiments, TDM timeslot bit numbering
The above set of RW codes are orthogonal codes that
will follow the CCl'lT G. 732 convention with bits transallow the multiple user signals to be transmitted and
received on the same frequency at the same time. Once the
mitted in the sequence bit 1, bit 2 ... bit 8. Byte orientation
bit stream is orthogonally isolated using the RW codes, the
is specified per channel as either most significant bit (MSB)
signals for respective subscriber links do not interfere with
first, least significant bit (LSB) first or N/A.
each other. Since RW codes are orthogonal, when perfectly
The provision of a hybrid CDMA;TDM approach for
aligned all codes have zero cross-correlation, thus making it
downlink traffic channels retains the benefits of CDMA
possible to decode a signal while cancelling interference
access, ie. interference is reduced when traffic is reduced.
from users operating on other RW codes.
Further, use of TDM ensures that the CDMA signal is
In preferred embodiments of the present invention, it is 10
limited to a 256 'Quadrature Amplitude Modulation' (QAM)
desired to provide the central terminal with the ability to
constellation which reduces receiver dynamic range requiresupport more than 15 subscriber links on each channel
ments. QAM constellations will be familiar to those skilled
frequency, and to achieve this the above set of 16 RW codes
in the art.
has been enhanced. In order to maintain compatibility with
On the uplink channels, the pure CDMA approach using
former products using the 16 RW codes, it was desirable that
any enhancements should retain the same set of 16 RW 15 overlay codes eliminates the need to time synchronise STs to
a TUM frame reference. This has the advantage of elimicodes.
nating TOM delays and the 'guard time' in between TOM
The manner in which the enhancements have been impleframes. Another benefit is reduced peak power handling
mented provides flexibility in the way the frequem:y chanrequirements in the ST RF transmit chain which would
nels are configured, with certain configurations allowing a
20 otherwise be needed when transmitting bursty TDM data.
greater number of subscriber links to be supported, but at a
High dynamic range requirement is restricted to the CT
lower gross bit rate. In preferred embodiments, a channel
receiver.
can be selected to operate with the following gross bit rates:
The manner in which the transmitted and received signals
are processed in accordance with preferred embodiments of
25
the present invention will be described \vith reference to
Full rate (Fl)
160 kb/s
FIGS. 7 and 8. FIG. 7A is a schematic diagram illustrating
Half rate (Hl, H2)
80 kb/s
signal transmission processing stages as configured in a
Quarter rate (Ql, Q2, Q3, Q4)
40 kb/s
Low rate (Ll, L2, L3, L4), for uplink
subscriber terminal20 in the telecommunications system of
10 kb/s
acquisition
FIG. 1. In FIG. 7A, an analogue signal from a telephone is
30
passed via an interface such as two-wire interface 102 to a
hybrid audio processing circuit 104 and then via a codec 106
In preferred embodiments, the manner in which these
to produce a digital signal into which an overhead channel
channclisations arc provided differs for the downlink (CT to
including control information is inserted at 108. If the
ST) and uplink (ST to CT) communication paths. This is
hecause it has heen realised that different performance 35 subscriber terminal supports a number of telephones or other
telecommunications equipment, then elements 102, 104 and
requirements exist for the downlink and uplink paths. On the
106 may be repeated for each piece of telecommunications
downlink all signals emanate from a single source, namely
equipment.
the central terminal, and hence the signals will be synchroAt the output of overhead insertion circuit 108, the signal
nised. However, on the uplink path, the signals will emanate
from a number of independent STs, and hence the signals 40 will have a bit rate of either 160, 80 or 40 kbits/s, depending
on which channel has been selected for transmission of the
will not be synchronised.
signal.
Given the above considerations, in preferred
The resulting signal is then processed by a convolutional
embodiments, on the uplink path full rate (160 kb/s) operaencoder 110 to produce two signals with the same bit rate as
tion is implemented using the basic set of RW codes
discussed earlier, but half and quarter rates are achieved 45 the input signal (collectively, these signals will have a
symbol rate of 160, 80 or 40 KS/s). Next, the signals are
through the use of 'Overlay Codes' which comprise RW
passed to a spreader 111 where, if a reduced bit rate channel
coded high rate symbol patterns that are transmitted for each
has been selected, an appropriate overlay code provided by
intermediate rate data symbol. For half rate operation, two
overlay code generator 113 is applied to the signals. At the
2-bit overlay codes are provide, whilst for quarter rate
operation, four 4-bit overlay codes are provided. WEn so output of the spreader 111, the signals will be at 160 KS/s
irrespective of the bit rate of the input signal since the
generating a signal for transmission, one of the overlay
overlay code will have increased the symbol rate by the
codes, where appropriate, is applied to the signal in addition
necessary amount.
to the appropriate RW code. When the signal is received,
then at the CDMA demodulator the incoming signal is
The signals output from spreader 111 are passed to a
multiplied by the channel's PN, RW and Overlay codes. The 55 spreader 116 where the Rademacher-Walsh and PN codes
correlator integration period is set to match the length of the
are applied to the signals by a RW code generator 112 and
PN Code generator 114, respectively. The resulting signals,
Overlay code.
at 2.56 MC/s (2.56 Mega chips per second, where a chip is
Overlay codes are used extensively to provide variable
the smallest data element in a spread sequence) are passed
rate uplink traffic channels. Overlay codes will also be used
to implement downlink control channels, these control chan- 60 via a digital to analogue converter 118. The digital to
analogue converter 118 shapes the digital samples into an
nels being discussed in more detail later. However, as
analogue waveform and provides a stage of baseband power
mentioned earlier, a different approach is taken for providing
control. The signals are then passed to a low pass filter 120
flexible channelisations on the downlink traffic channel
to be modulated in a modulator 122. The modulated signal
paths. Downlink traffic channels will operate in high rate,
160 kb/s, mode, with lower data rates of 80 and 40 kb/s 65 from the modulator 122 is mixed with a signal generated by
a voltage controlled oscillator 126 which is responsive to a
being supported by 'Time Division Multiplexing' (TDM)
synthesizer 160. The output of the mixer 128 is then
the available bandwidth.

WIL-0009865

US 6,222,R19 Bl

13

14

amplified .in a low noise amplifier 130 before being passed
tor 112) and a PN code generator 174 (corresponding to PN
via a band pass filter 132. The output of the band pass filter
code generator 114), respectively. The output of the corr132 is further amplified in a further low noise amplifier 134,
elator 178, at 160 KS/s, is then applied to correlator 179,
where any overlay code used at the transmission stage to
before being passed to power control circuitry 136. The
output of the power control circuitry is further amplified .in
encode the signal is applied to the signal by overlay code
a power amplifier 138 before being passed via a further band
generator 181. The elements 170, 172, JL 74, 178, 179 and
pass filter 140 and transmitted from the transmission antenna
181 form a CDMA demodulator. The output from the
142.
CDMA demodulator (at correlator 179) is then at a rate of
either 160, 80 or 40 KS/s, depending on the overlay code
FIG. 7B is a schematic diagram illustrating signal transmission processing stages as configured in a central terminal 10 applied by correlator 179.
10 in the telecommunications system of FIG. 1. As will be
The output from corrclator 179 is then applied to a Vitcrbi
apparent, the central terminal is configured to perform
decoder 180. The output of the Viterbi decoder 1801 is then
similar signal transmission processing to the subscriber
passed to an overhead extractor 182 for extracting the
terminal 20 illustrated in FIG. 7A, but does not include
ove.rhead channel information. If the signal relates to call
elements 100, 102, 104 and 106 associated with telecomdata, then the output of the overhead extractor 182 is then
munications equipment. Further, the central terminal 15 passed through TDM decoder 183 to extract the call data
includes a TDM encoder 105 for performing time division
from the particular time slot in which it was inserted by the
multiplexing where required. The central terminal will have
CT TDM encoder 105. Then, the call data is passed via a
a network interface over which incoming calls destined for
codec 184 and a hybrid circuit 188 to an interface such as
a subscriber terminal are received. When an incoming call is
two wire interface 190, where the resulting analogue signals
received, the central terminal will contact the subscriber 20 are passed to a telephone 192. As mentioned earlier in
terminal to which the call is directed and arrange a suitable
connection with the ST transmission processing stages,
channel over which the incoming call can be established
elements 184, 188, 190 may be repeated for each piece of
with the subscriber terminal (in preferred embodiments, this
telecommunications equipment 192 at the ST.
is done using the call control channel discussed in more
If the data output by the overhead extraction circuit 182
detail later). The channel established for the call will deter- 25
is data on a downlink control channels, then instead of
mine the time slot to be used for call data passed from the
passing that data to a piece of telecommunications
CT to the STand the TDM encoder 105 will be supplied with
eq11ipment, it is passed via switch 187 to a call control logic
this information.
185, where that data is interpreted by the ST.
Hence, when incoming call data is passed from the
At the subscriber terminal 20, a stage of automatic gain
network interface to the TDM encoder 105 over line 103, the 30
control is incorporated at the IF stage. The control signal is
TDM encoder will apply appropriate TDM encoding to
derived from the digital portion of the CDMAreceiver using
enable the data to be inserted in the appropriate time slot.
the output of a signal quality estimator.
From then on, the processing of the signal is the same as the
equivalent processing performed in the ST and described
FIG. 8B illustrates the signal reception processing stages
as configured in a central terminal10 in the telecommuni35
cations system of FIG. 1. As will be apparent from the figure,
signal output from spreader 111 is the same as the signal
the signal processing stages between the RX antenna 150
input to the spreader 111.
and the overhead extraction circuit 182 are the as those
As mentioned earlier, in preferred embodiments, overlay
within the ST discussed in connection with FIG. 8A.
codes, rather than TDM, are used to implement downlink
However, in the case of the CT, call data output from the
control channels, and data relating to such channels is passed 40 overhead extraction circuit is passed over line 189 to the
from a demand assignment engine (to be discussed in more
network interface within the CT, whilst control channel data
detail later) over line 107 through switch 109 to the overhead
is passed via switch 191 to the DA engine 380 for processinsertion circuit 108, thereby bypassing the TOM encoder
ing. The OA engine is discussed in more detai1 later.
105. The processing of the signal is then the same as the
Overlay codes and channelisation plans are selected to
equivalent processing performed in the ST, with the overlay 45 ensure signal orthogonality-i.e. in a properly synchronised
code generator providing appropriate overlay codes to the
system, the contribution of all channels except the channel
spreader 111. The overlay code generator will be controlled
being demodulated sum to zero over the correlator integraso as to produce the desired overlay code, in preferred
tion period. Further, uplink power is controlled to maintain
embodiments, this control coming from the DAengine (to be
constant energy per bit. The exception to this is Low rate
discussed in more detail later).
so which will be transmitted at the same power as a Quarter rate
FIG. SA is a schematic diagram illustrating the signal
signal. Table 2 below illustrates the overlay codes used for
reception processing stages as configured in a subscriber
full, half and quarter rate operations:
terminal 20 in the telecommunications system of FIG. l. In
FIG. SA, signals received at a receiving antenna 150 are
TABLE 2
passed via a band pass filter 152 before being amplified in 55
a low noise amplifier 154. The output of the amplifier 154 is
STTx.
power
then passed via a further band pass filter 156 before being
Net
relative
Correlator
further amplified by a further low noise ampliiier 158. The
Rate
Channel
to Fl-U
integration Acquisition
output of the amplifier 158 is then passed to a mixer 164
(kb/s) d,_e_sl.:.
g_na_tl_·
o_n_...;(d_B..;.)__o_v_e_rl_a~;_'_c_od_e__;p_e_ri_od_(u_s)__o_verlay
where it is mixed with a signal generated by a voltage
controlled oscillator 162 which is responsive to a synthesizer 60 160
-Fl-U
6.25
L1
-Hl-U
-3
1 1
12.5
80
L1
160. The output of the mixer 164 is then passed via the 1/Q
-.J
-H2-U
1 -1
L3
12.5
80
de-modulator 166 and a low pass filter 168 before being
-Q1-U
-6
40
25
1 1 1
L1
passed to an analogue to digital converter 1'70. The digital
40
-02-U
1 -1 1 -1
25
L2
-6
output of the AID converter 170 at 2.56 MC/s is then passed
-Q3-U
40
-6
25
L3
1 1 -1 -1
to a correlator 178, to which the same Rademacher-Walsh 65 40
-Q4-lJ
1 -1 -1 1
25
L4
-6
and PN codes used during transmission are applied by a RW
code generator 172 (corresponding to the RVv code genera-

;~~u~~~~e~c;in~~e ~~~1~~\~~: ~;~r~~e ~~~esog~~~[at~~

WIL-0009866

US 6,222,R19 Bl

15

16

In preferred embodiments, a 10 kb/s acquisition mode is
provided which uses concatenated overlays to form an
acquisition overlay; this is illustrated in table 3 below:

central terminallO transmits downlink si2.nal 212. FIG. 12
shows the contents of downlink signal 212. A frame information signal 218 is combined with an overlay code 217
where appropriate, and the resultant signal 219 is combined
with a code sequence signal 216 for central terminal 10 to
TABLE 3
produce the downlink 212. Code sequence signal 216 is
Acqui~ition
derived from a combination of a pseudo-random noise code
overlay
Equivalent high rate pattern
signal 220 and a Rademacher-Walsh code signal 222.
Downlink signal 212 is received at receiver 202 of
L1-U
1 1 1 1 1 1 1 1
1 1 1 1 1 1 1
L2-U
1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1
10 subscriber terminal20. Receiver 202 compares its phase and
13-U
1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1
code sequence to a phase and code sequence within code
L4-U
1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1
sequence signal216 of downlink signal212. Central terminal 10 is considered to have a master code sequence and
subscriber terminal 20 is considered to have a slave code
FIGS. 9A and 9B are diagrams illustrating the uplink and
downlink delivery methods, respectively, when the system is 15 seyuenct:. Receiver 202 incrementally adjusts the phase of
its slave code sequence to recognize a match to master code
fully loaded, and illustrate the difference between the use of
sequence and place receiver 202 of subscriber terminal 20 in
overlay codes illustrated in FIG. 9A and the use of IDM as
phase with transmitter 200 of central terminal10. The slave
illustrated in FIG. 9B. When using overlay codes, an RW
code sequence of receiver 202 is not initially synchronized
code is split in the RW space domain to allow up to four sub
channt:ls lo opt:rale at tht: samt: time. In contrast, when using 20 to the master code sequence of transmitter 200 and central
terminal10 due to the path delay between central terminal
TDM, an RW code is split in the time domain, to allow up
10 and subscriber terminal 20. This path delay is caused by
to four signals to be sent using one RW code, but at different
the geographical separation between subscriber terminal 20
times during the 125 us frame. As illustrated in FIGS. 9A
and central terminal 10 and other environmental and techand 9B, the last two RW codes, RW14 and RW15, are not
used for data traffic in preferred embodiments, since they are 25 nical factors affecting wireless transmission.
After acquiring and initiating tracking on the central
reserved for call control and acquisition functions; this will
terminal 10 master code sequence of code sequence signal
be discussed in more detail later.
216 within downlink signal212, receiver 202 enters a frame
The CDMAchannel hierarchy is as illustrated in FIG. 10.
alignment mode in order to establish the downlink commuUsing this hierarchy, the following CDMA channelisations
30 nication path. Receiver 202 analyzes frame information
are possible:
within frame information signal218 of downlink signal 212
Fl
to identify a beginning of frame position for downlink signal
H1+H2
212. Since receiver 202 does not know at what point in the
H1+Q3+Q4
data stream of downlink signal 212 it has received
H2+Q1+Q2
35 information, receiver 202 must search for the beginning of
frame position in order to be able to process information
Q1+Q2+Q3+Q4
rect:ived from transmitter 200 of central terminal 10. Once
Having discussed how the CDMA codes are enhanced to
receiver 202 has identified one further beginning of frame
enable flexible channelisations to be achieved, wherebv the
position, the downlink communication path has been estabbit rates can be lowered to enable more subscriber links to
be managed per channel frequency, a general overview of 40 lished from transmitter 200 of central terminal10 to receiver
202 of subscriber terminal 20.
how the downlink and uplink paths are established will be
The structure of the radio frames of information sent over
provided with reference to FIGS. 11 and 12.
the downlink and uplink paths will now be discussed with
FIG. 11 is a block diagram of downlink and uplink
reference to FIGS. 13 and 14. In FIGS. 13 and 14, the
communication paths between central terminal 10 and subscriber terminal 20. A downlink communication path is 45 following terms are used:
Bn Customer payload, 1x32 to 2x64 Kb/s
established from transmitter 200 in central terminal 10 to
Dn Signalling Channel, 2 to 16 kb/s
receiver 202 in subscriber terminal 20. An uplink communication path is established from transmitter 204 in subOil Radio Overhead Channel
scriber terminal 20 to receiver 206 in central terminal 10.
16 kb/s Traffic Mode
Once the downlink and the uplink communication paths 50
10 kb/s Acq11isition/Standby Mode
Both FIGS. 13A and 13B show a 125 us subframe format,
have been established in wireless telecommunication system
1, telephone communication may occur between a user 208,
which is repeated throughout an entire radio frame, a frame
210 of subscriber terminal 20 and a user serviced through
typically lasting for 4 milliseconds (ms). FIG. 13Aillustrates
central terminal10 over a downlink signal212 and an uplink
the radio frame structures that are used in preferred embodisignal214. Downlink signal212 is transmitted by transmit- 55 ments for the downlink path. Subframe (i) in FIG. 13A
ter 200 of central terminal 10 and received bv receiver 202
shows the radio frame structure used for low rate, 10 Kb/s,
of subscriber terminal 20. Uplink signal 214. is transmitted
acquisition mode (Ln-D) during which only the overhead
by transmitter 204 of subscriber terminal20 and received by
channel is transmitted. Subframe (ii) in FIG.13Ashows the
receiver 206 of central terminal 10.
radio frame structure employed for the call control channel
Receiver 206 and transmitter 200 within central terminal 60 operating in quarter rate, 40 Kb/s, mode (Qn-D), whilst
subframe (iii) of FIG. 13A illustrates the radio frame struc10 are synchronized to each otht:r with respect to Lime and
phase, and aligned as to information boundaries. In order to
ture used for traffic channels operating in full rate, 160 kb/s,
establish the dO\vnlink communication path, receiver 202 in
mode (Fl-D).
Similarly, subframe (i) of FIG. 13B shows the radio frame
subscriber terminal20 should be synchronized to transmitter
200 in central terminal 10. Synchronization occurs by per- 65 structure used for the uplink path when operating in low rate
forming an acquisition mode function and a tracking mode
acquisition or call control mode (Ln-U). Sub-frames (ii) to
(iv) show the radio frame structure used for traffic channels
function on downlink signal212. Initially, transmitter 200 of

WIL-0009867

US 6,222,R19 Bl

17

18

\Vhen operating .in quarter rate mode ( Qn- U), half rate mode
(Hn-U), and full rate mode (Fl-U), respectively.
Considering now the overhead channel in more detail,
FIGS. 14A and 14B show the overhead frame structure
employed for various data rates. The overhead channel may
include a number of fields-a frame alignment word (FAW),
a code synchronization signal (CS), a power control signal
(PC), an operations and maintenance channel signal (OM C),
a mixed OMC/D-Channel (HDLC) signal (OMC/D), a channel identifier byte (Ch.ID), and some unused fields.
The frame alignment word identifies the beginning of
frame position for its corresponding frame of information.
The code synchronization signal provides .information to
control synchronization of transmitter 204 in subscriber
terminal20 to receiver 206 in central terminal10. The pm,ver
control signal provides information to control transmitting
powt:r of transmiUtr 204 in subscribtr tt:rminal 20. The
operations and maintenance channel signal provides status
information with respect to the downlink and uplink communication paths and a path from the central terminal to the
subscriber terminal on which the communication protocol
which operates on the modem shelf between the shelf
controller and the modem cards also extends. The OMC/D
signal is a combination of the OMC signal and a signalling
signal (D), whilst the C:h. TD signal is used to uniquely
identify an RW channel, this Ch. ID signal being used by the
subscriber terminal to ensure that the correct channe:l has
been acquired.
In preferred embodiments, the subscriber terminal will
receive downlink traffic channel data at a rate of 160 kb/s.
Depending on the B-channel rate, the ST will be allocated an
appropriate share of the radio overhead. The following TDM
mappings are created:

assignment arrangements using the set of 16 RW codes
discussed earlier are still supported, as well as demand
access services that are available when using a system
in accordance with the preferred embodiment. FIGS.
15A and 15B .illustrate typical downlink and uplink
channel structures that might occur in a loaded system
in accordance with preferred embodiments of the
present invention. As illustrated in FIG. 15A, on the
downlink path, some signals may be at 160 kb/s and
utilise an entire RW channel. An example of such
signals would be those sent over fixed assignment links
to products which do not support the CDMA enhancements provided by systems in accordance with preferred embodiments of the present invention, as illustrated for RW1 and RW2 in FIG. 15A. Alternatively, a
user may have authority to utilise a whole RW channel,
for example whtn sending a fax, as illustrated by RW12
in FIG. 15A
As illustrated by RW5 to RW11, TDM can he used on the
dow"Olink traffic channels to enable more than one CT to ST
communication to take plact on the sam<:: RW channd
during each frame. Further, as illustrated for RW3 and RW4,
in preferred embodiments, certain channels can be locked to
limit interference from other nearby cells, as will be discusstd in mort dttaillater.
Similar channelisations can be achieved for the uplink
paths, hm as illustrated in FIG. 15R, overlay codes are used
inst·ead of TOM to enable more than one ST to CT communication to take place on the same RW channel during
each frame (as shown in FIG. 15B for RWS to RWll). It
should be noted that, in both FIGS. lSA and 15B, the
channels RW14 and RW15 are reserved as a call control
channel and an link acquisition channel, respectively, and
overlay codes are employed on these channels, irrespective
of whether the path is a downlink or an uplink path. These
two channels will be discussed in more detail below.
Acquisition/net entry will take place via the Link Acquisition Channel (LAC). Following power-up an ST will
automatically attempt downlink acquisition of the U1.C on a
pre-determined 'home' RF channel. The LAC downlink
channel (eg. RW15 in prefen·ed embodiments) will operate
at 10 kb/s, i'ull single user power. Downlink acquisition will
be simultaneous for all STs.
Each CT Modem Shelf will maintain a database holding
the serial numbers of all STs that could possibly be supported by that CT. The state of each ST will recorded with
top level states as follows:
cold
idle
call__in_progress
Transition states will also be defined. An ST is considered
cold if the ST is newly provisioned, the CT has lost
management communications with the ST or the CT has
been power cycled. Over the LAC, the CT broadcasts
individual ST serial numbers and offers an invitation to
acquire the LAC uplink. Cold uplink acquisition will be
carried out on the Link Acquisition Channel at low rate. The
CT will invite specific ST's to cold start via the management
channel.
Assuming an uplink channel is available:, the appropriate
acquisition overlay will be selected, and acquisition will be
initiated.
'Rapid' downEnk RW channel switching may be supported at rates other than Ln-D. Rapid means that coherent
demodulation is maintained, and only convolutional decoding and frame synchronisation processes need be repeated.
On acquisition, management information will be
exchanged. The ST will be authenticated and allocated a

10

15

20

25

30

TABLE 4
35
Rate

Channel

(kb/s) designation
160
80

Bearer

-Fl-D-Tl/1 Bl, B2, B3,
B4
-Fl-D-TI/1 Bl,B2

80

-Fl-D-TI/2 B3,B4

40
40
40
40

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

Bl
B2
B3
B4

cs

PC

OMC

Overhead
rate

CS1,
CS3
CSl,
CS3
CS2,
CS4
CS1
CS2
CS3
CS4

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

OMC1,0MC3

4 ms

OMCl, OMC3

4 ms

OMC2,0MC4

4 ms

OMCl
OMC2
OMC3
OMC4

8 ms
8 ms
8 IllS
8 ms

40

45

In the above chart, the scheme used to identify a channel
.is as follows. Rate code 'Fl' .indicates full rate, lGO kb/s, 'D'
50
indicates that the channel is a downlink channel, and 'Tn/t'
indicates that the channel is time division multiplexed
between STs,
'n' indicating the total number of TDM timeslots, and 't'
indicating the selected traffic timeslot.
55
All ST's operating on a traffic channel will receive
D-channel information at the 16 kb/s rate. The D-channel
protocol inch1des an address field to specify which ST is to
process the contents of the message.
The channel structure was illustrated earlier in FIGS. 9A
60
and 9R. Tn preferred embodiments, the channel stmcture is
flexible but comprises:
At least one Link Acquisition Channel (LAC)
At least one Call Control Channel (CCC)
Typically one Priority Traffic Channels (FTC)
65
1 to 13 Traffic Channels (TC) The manner in which the
channelisation is provided ensures that former fixed

WIL-0009868

US 6,222,R19 Bl

19

20

short ST_.identifier (between 12 and lG bits) which will be
used for subsequent addressing. The ST uplink will operate
for long enough for the uplink to be parametised by the ST
in terms of code phase and transmit power. These parameters
will be used by the ST for subsequent warm start acquisitions and will also be held by the CT to allow the CT to force
a cold ST to warm start. On successful completion of net
entry, the ST will be placed in the idle state and instructed
to cease uplink communications and move to the C::all
Control Channel (CCC) (RW14 in preferred embodiments).
The time taken for net entry to be achieved can be
monitored, and the following techniques can be used to
decrease net entry time if desired:
(i) Prioritise so that high GOS (Grade Of Service) users
are offered net entry first.
(ii) Convert Traffic Channels to LACs.
(iii) In the event of a CT restart, invite STs to attempt
uplink warm start. A reduction in net entry time of a
factor of 4 could be achieved. This mechanism would
need to be safeguarded against possible deterioration of
uplink warm start parameters-i.e. it should only be
allowed provided no CT RF related parameters have
been modified. The CT would need to broadcast an ID
to allow an ST to validate that the uplink warm start
parameters were valid for this CT.
(iv) ST restart-the CT will keep copies of the ST warm
start parameters so that a cold ST may have warm start
parameters downloaded in the invitation to acquire and
then be instmcted to warm start.
Following Net Entry, all STs listen to the CCC. This
channel broadcasts management and call control information via a 32 kb/s HDLC channel. In order to maintain
management communication, the CT polls each ST in

Enable the ST transmitter at a level of nominal full rate
power minus lS dB. While PC/CS report<; idle the ST will
continue uplink fast codesearch, stepping the uplink power
level by +2 dB at the end of each search. The uplink should
acquire at nominal full rate power minus 6 dB. Uplink
acquisition is aborted if maximum transmit level is reached
and PC/CS continues to report idle.
(iv) PC/CS reports busy. At this point the ST may have
genuinely acquired the traffic channel, or instead may
10
be observing PC/CS go busy because another ST has
acquired the traffic channel. The ST is sent an authentication request and responds with it's ST_identifer.
The CT grants uplink access by returning the
ST_identifier. The ST aborts the acquisition process if
15
the returned ST_identifier is not recognised (ie. is not
the ST_itkntifer that it sent). This authentication process arbitrates between two STs contending for outgoing access and it also keeps STs from acquiring TCs
that have been reserved from incoming access.
20 Incoming Call
A number of TCs will be reserved for incoming calls, and
incoming call processing is as follows:
(i) Check the CT database-if the ST is in the call_in_
progress state the call is rejected.
25
(ii) Check that an uplink TC of the required bandwidth is
available. If there is bandwidth then a TC is reserved.
(iii) An incoming call setup message is broadcast over the
CCC to inform the addressed ST of the incoming call
and specify the TC on which to receive the call. If no
30
TC is available but the CT forms part of a Service
Domain, then the incoming call setup message is sent
with a null TC otherwise the call is rejected. Service
domains will be discussed in more detail later. The
incoming call setup message is repeated a number of
35
times.
exchange of management information (authentication, ST
(iv) The ST attempts uplink acquisition. The ST listens to
alarm update, warm start parameters, downlink radio perthe downlink and keeps trying for uplink acquisition
formance data etc).
until the CT sends a message to the ST to return the ST
A Management Poll may fail for one of the follmving
to the CCC. The ST will also run a timer to return it
40
reasons:
back to the CCC in the event of an incoming call failing
(i) The ST is or has been powered down. An EM alarm
to complete.
may be flagged if this persists and the database for that
(v) On successful uplink acquisition, the CT authenticates
ST should be marked cold. The 1\et Entry process will
the ST.
follow.
45
(vi) Rate switching is originated from the CT modem. A
(ii) The ST is either making a call or in the process of
command is sent via the PC/CS to switch the downlink
making a call. The poll cycle may be suspended and
to the required bandwidth. The ST returns the rate
management communications effected on the appropriswitch command via the uplink PC/CS. The lin1c is now
ate traffic channel.
of the required bandwidth.
When a Management Poll fails it should be followed up 50
Outgoing Call
by a number of faster polls until either the ST responds or
Outgoing calls are supported by allowing slotted random
it is marked cold. The CCC is required to transmit all copies
access to the TC uplinks. The outgoing call processing is as
of the invitations to acquire the LAC so that an ST can be
follows:
forced to acquire the LAC uplink.
(i) The C::T publishes a 'free list' of availahle Traffic
Traffic Channel Uplink Acquisition Procedure
55
Channels and Priority Traffic Channels with their
The basic acquisition process from the ST side is as
respective bandwidths. This list is published periodifollows;
cally (in preferred embodiments, every 500 ms) and is
(i) Switch the downlink (receiver) circuitry to 10 kb/s rate,
used to mark uplink access slots.
and select the appropriate Traffic Channel RW and
(ii) An olf-hook condition is detected by the ST. The ST
Overlay codes. Acquisition of the TC downlink is 60
starts a call setup timer.
limited to achieving frame alignment.
(iii) The ST waits for the next free list to be received over
(ii) The downlink PC;'CS channel will be decoded to
the CCC. If the Free list is empty the outgoing call is
create a busy/idle flag. Tf PC/C::S reports busy, then this
blocked. The ST \Vill generate a congestion tone.
means that another ST is using that traffic channel and
the ST aborts the acquisition process.
(iv) If the Free list has available channels, the ST picks a
65
(iii) Switch uplink to 10 kb/s rate, and select the approchannel from the free list at random. The algorithm that
priate Traffic Channel RW and Overlay codes.
the ST uses to pick a channel will need to be specified

!~d~:~~ed ~~~!~~q~~~P[~e~~~o~~~i~~~ if0~~~~~~ ~o; :~

WI L-0009869

US 6,222,R 19 B 1

21

22

In preferred embodiments, the CTw.ill control the number
in the free list. For example, the ST may be required to
always choose from a pool of minimum bandwidth
of Traffic Channels to minimise access noise. TCs will be
channels so that high bandwidth channels remain availclassified as:
able for high GOS users. Alternatively the ST may be
(i) Busy-carrying traffic;
allowed to choose any channel regardless of bandwidth
(ii) Access, Incoming (Access_In)-reserved for incomfor minimum blocking. In preferred embodiments, STs
ing access;
will not choose low bandwidth channels and negotiate
(iii) Access, Outgoing (Access_Out)-reserved for outthe rate up.
going access-such TCs appear on the Free list;
(v) The ST attempts uplink acquisition on the specified
(iv) Priority-reserved for priority outgoing access-such
TC, this process having been described earlier. If 10
TCs appear in the Free list;
acquisition is successful then the outgoing call is pro(v) Free-available for any purpose; and
cessed. Otherwise the ST returns to the CCC and waits
for the next available free list. To avoid a number of STs
(vi) Locked-not available due to interference limiting.
repetitively attempting to acquire the same TC, and
This classification scheme is illustrated in FIG. 16. The
blocking each other, a suitable protocol can be 15 CT will allocate traffic on the following !basis:
employed to govern how individual STs vvill act upon
(i) The cr will monitor incoming and outgoing call
receipt of the free list.
sehtp-times and convert Access TCs from Free TCs in
(vi) The ST may be unable to acquire a TC hy the time the
order to achieve a required grade of service.
call setup timer expires. The ST may in such cases
(ii) When a call is setup, an Access TC is converted to a
cease attempting outgoing access and generate conges- zo
Busy TC. If a Free TC is available, it is converted to a
tion tone.
new" Access TC. If there are no Free TC'~ then the
Outgoing Priority Call
Access TC is lost until a call clears.
It is recognised that the random access protocol used to
(iii) When a call clears the Dusy TC is converted to a Pree
setup normal outgoing calls could lead to blocking. In
TC. If a previous call setup resulted in a lost Access TC
preferred embodiments, access to a largely non-blocking 25
then the Rusy TC is converted hack into an Access TC
Priority Traffic Channel will be allowed. Priority calling is
(iv) When the PTC is accessed, a new JPTC is created by
complicated because the ST must:
converting a Free, Access or Busy (normal call) TC.
(i) Capture and decode dialled digits.
(v) The CTwill monitor the Busy TC downlink and uplink
(ii) Regenerate digits when a blocking condition occurs.
soft error counts in an attempt to establish link quality.
(iii) Allow transparent network access in a non-blocking 30
If the CT records a lower than average soft error count
condition.
and long call setup times are being recorded, a Locked
(iv) Categorise all outgoing calls as priority or normal so
TC may be converted to a Free TC. Conversely, if the
that normal calls are dropped in favour of priority calls.
CT records a higher than average soft error count, a
The priority call procedure in preferred embodiments is as
Free or Access TC may be converted to a Locked TC.
35
follows:
FJ[ G. 17 illustrates how the central terminal performs the
(i) The CT will publish Directory Numbers (DNs) for a
above interference limiting function. When incoming call
number of emergency services over the CCC.
data arrives at a central terminal modem .320, encoder 325
(ii) The ST will attempt uplink access according to the
encodes the data for transmission over the wireless link 300
normal algorithms. If the outgoing access is successful 40 to the subscriber terminal 20. At the subscriber terminal20,
then the customer is able to dial as normal. All dialled
the decoder 326 decodes the data, and passes the decoded
digits are check against the emergency DN list so that
user data over line 328 to the subscriber teleconunun.icat.ions
calls may be categorised normal or priority at the CT.
equipment. As the decoder 326 decodes the data, it is able to
(iii) If congestion tone is returned the customer is allowed
establish a bit error rate (BER) estimate 330 associated with
to dial the emergency number into the ST. If the ST 45 the signal transmission over the wireless link 300, which can
detects an emergency DN sequence then uplink access
be passed to the multiplexer 332 for combining with other
via the Priority Traffic Channel (PTC) is attempted.
signals, such as those from a call control function 336 or user
(iv) On PTC acquisition, the ST relays the dialled digit
data on line 338, before being passed to an encoder 334.
sequence to the CT for dialling into the PSTN.
Here, the BER estimate is encoded and passed on the OMC
(iv) The CT converts the PTC to a TC and reallocates so channel over the wireless link 310 to the decoder 340 within
the central terminal modem 320. Once decoded by the
another TC to become the PTC, dropping a normal call
decoder 340, the signal passes to the multiplexer 345, where
in progress if necessary.
the BER estimate from the subscriber terminal is detected
Interference Limiting (Pool Sizing)
and passed over line 355 to the dynamic pool sizing function
Across a large scale deployment of cells, optimum capacity is achieved by minimising radio traffic while maintaining 55 360.
Further, as at the subscriber terminal 20, the decoder 340
an acceptable grade of service. Lowest possible radio traffic
within the central terminal modem 320 is able to establish a
results in improved 'carrier to interference' (C/I) ratios for
bit error rate estimate 350 associated with the signal transusers within the cell of interest and to co-channel users in
mission over the wireless link 310. This BER estimate 350
nearby cells. The C/I ratio is a measure (usually expressed
in dB) of how high above interference the transmitted signal 60 is also passed over line 355 to the dynamic pool sizing
function 360. The dynamic pool sizing function 360 is
needs to be lo be decoded e!Iectively. In preferred
embodiments, the central terminal is provided with the
provided on the CT modem shelf 302, and receives BER
estimates from each of the modems on that shelf indicated
ability to trade traffic for C;1, thereby allowing network
by the lines entering the bottom of the dynamic pool sizing
planning to be carried out less rigidly. This feature can be
realised by a system using CDMA as in preferred embodi- GS function 360.
In addition to BER estimates, grade of service (GOS) data
ments of the present invention, and is a benefit that CDI\!IA
is obtained from two sources. Firstly, at each subscriber
offers over TDMA and FDMA systems.

WIL-0009870

US 6,222,R19 Bl

23

24

RF Channel Switching
terminal 20, the call control function 336 wlll note how
ln preferred embodiments, it has been realised that if an
readily it is able to establish traffic channels for transmitting
and receiving data, and from this can provide a GOS
ST is allowed to operate from more than one CT Modem
estimate to the multiplexer 332 for encoding by the encoder
Shelf!RF Channel then the following benefits may be rea334 for subsequent transmission over the wireless link 310
lised:
to the central terminal modem 320. Here, the GOS estimate
(i) Fault tolerance-should a CT Modem Shelf subis decoded by decoder 340, passed through multiplexer 345,
system fault occur, an ST may switch to an alternative
and then the GOS estimate is passed over line 355 to the
frequency for service.
dynamic pool sizing function 360.
(ii) Call blocking-an ST denied service from one CT
Additionally, incoming call information to the central
10
shelf may choose to switch to an alternative frequency
terminal, other than call information from the subscriber
for service.
terminals 20 connected to the central terminal, is provided
over the concentrated network interface 390 to the DA
(iii) Traffic load balancing~the Element Manager may on
engine 380. The DA engine 380 includes a call control
the hasis of call blocking statistics choose to move STs
function, similar to the call control function 336 in each of
between CT shelves.
the subscriber terminals 20, for each of the modems on the 15
(iv) Frequency diversity-in the presence of channel
modem shelf. Hence., in a similar fashion to the. call control
selective fading (slow multipath) an ST may operate on
function 336 at the subscriber terminals 20, the call control
the frequency channel offering highest signal strength
functions within the DA engine 380 are also ahle to provide
and lowest soft error count.
GOS estimates for incoming calls, and these GOS estimates
RF channel switching is only possible where there are two
are passed ove-r line 395 to the dynamic pool sizing function 20
or more co-located CT shelves serving the same geographi360.
cal area on different RF frequency channels within the same
At set up, the management system 370 within the element
RF band. A deployment that meets this criterion may be
manager will have connected to the central terminal, and
configured as a 'Service Domain'. Possible deployment
provided the dynamic pool sizing function 360 within the
modem shelf with data identifying a BER goal, a GOS goal, 25 scenarios are illustrated in FIG. 18. FIG. 18(i) shows an
arrangement where omni antennae are used to provide the
and a pool size limit (i.e. the number of channels that can be
entire cell with four frequency channels, eg Fl, F4, F7, FlO.
used for data traffic). The dynamic pool sizing function 360
FIG. 18(ii) shows an arrangement where sectored antennae
then compares this data from the management system with
are used to provide six separate sectors within a cell, each
the actual BER, actual GOS, and the actual pool size
information that it receives. A suitable algorithm can be 30 sector being covered by two frequency channels. FIG.18(iii)
shows an alternative arrangement where three sectored
provided within the dynamic pool sizing function 360 to
antennae are used to divide the cell in to three sectors, each
determine, based on this information, whether pool sizing is
sector being covered by a separate frequency channel, and
appropriate. For example, if the actual bit error rate exceeds
then an omni antenna is used to provide an 'umbrella'
the BER goal provided by the management system 370, then
the dynamic pool sizing function 360 may be arranged to 35 coverage for the entire cell, this coverage employing a
frequency channel different to the three frequency channels
send a pool sizing request to the demand assignment engine
used by the st:ctored antennae.
380.
For the system to work effectively, the STs must be able
The demand assignment engine 380 provides modem
to switch channels quickly, and fast channel switching
enable signals over lines 400 to each of the modems on the
CT modem shelf. If the dynamic pool sizing function 360 40 necessitates that CT shelf synchronisation be provided at the
following levels:
has requested that the DA engine 380 perform pool sizing,
(i) CDMA PN code. This preserves uplink code phase
then the DA engine 380 can disable one or more of the
across RF channels during warm start; and
modems, this causing the interference, and hence the actual
BER, to be reduced. Apart from being used for interference
(ii) RF carrier frequency. This eliminates the need for the
limiting, the DA engine is also responsible, in preferred 45
coarse frequency search on a downlink RF channel
embodiments, for providing the encoders 325 with instrucswitch.
On installation, an ST will be programmed with an RF
tions on which set of overlay codes or how many TDM slots
to be used for signals to be transmitted to the STs 20.
channel and PN code, these codes specifying the ST' s initial
The dynamic pool sizing function can store the BER and
home channel.
GOS information received in the storage 365, and periodi- so
The manner in which channel switching is facilitated in
cally may pass that data to the management system 370 for
preferred embodiments will be described with reference to
FIGS. 19A and 19B. A service domain controller 400 is
analysis. Further, if the system is unable to attain the BER
or GOS goal with the allocated pool size, the dynamic pool
preferably provided to act as an interface between the
sizing function can be arranged to raise an alarm .to the
exchange connected to the service domain controller over
management system. The receipt of this alarm will indicate 55 path 405 and a number of central terminals 10 connected to
to personnel using the management system that manual
the service domain controller over paths 410. The central
terminals connected to the service domain controller form a
intervention may be required to remedy the situation, eg by
'service domain' of central terminals that may be used by a
the provision of more central terminal hardware to support
the STs.
subscriber terminal 20 for handling communications.
In preferred embodiments, the service domain controller
The CDMA approach used in preferred embodiments 60
exhibits the properly that tht: removal of any of the orthogo400 is used to provide each CT 10 with appropriate information about the other CTs within the service domain. Each
nal channels (by disabling the modem) will improve the
resistance of the other channels to interference. Hence, a
CT can then broadcast a 'Service Domain' message comprising a list of RF frequencies and CT Identifiers that form
suitable approach for the demand assignment engine 380,
upon receipt of pool sizing request from the dynamic pool 65 a Service Domain to be used by the STs for subsequent RF
switching functions. The ST then stores this information for
sizing function 360, is to disable the modem that has the
future reference when establishing a link with one of the
least traffic passing through it.

WIL-0009871

US 6,222,R19 Bl

25

26

CTs. It is preferable for each CT to broadcast the service
supplied over line 455 to the call control function 336 and
domain mes~age since an ST may .be listening to any of the
!he ch.annel selection controller 440 for processing. The
CTs at the time that the message 1s broadcast.
mcommg call setup message will typically specify a TC on
Each CT database will hold an entry for every ST located
the current frequency channel which should be used to
\'Vithin the Service Domain. Each database entry describes
access the incoming call, and the channel selection controlhow the CT views it's relationship with the STand may be
ler will attempt to establish a link on that TC. The channel
marked as:
selection controller will in such cases instruct the radio
sub-system 420 over line 465 to use the current frequency
(i) Primary service provider-the CT is the ST's home
channel to establish the required link. If, on the other hand,
channel. All management communication with an ST is
the traffic channel specified in the call setup messao-e is
via it's home CT.
10
'null', the channel selection controller has the opti;n to
(ii) Supplying backup service the CT is providing service
change RF frequency using the information stored in storage
Lo the ST.
445 about the other CTs in the service domain.
(iii) Available for backup service-the CT will provide
To enable the channel selection controller 440 to receive
service to the ST if required.
information about the status of links, a link operating status
It should be noted that the ST need not switch to an
15 signal can be supplied over line 470 from the radio subentirely different CT, but can instead switch to a different CT
system. This signal will give: an indication of the radio link
shelf (and hence different RF frequency channel) within the
quality, and may be a simple 'OK' or 'failed' indication, or
same CT. However, in preferred embodiments, the ST will
alternatively may include extra information such as BER
t~pically switch to a different CT, since some errors expevalues for the link. This information can be used by the
nenced by one CT shelf may also affect other shelves within
the same CT, and so for fault tolerance (described in more zo channel selection controller to determine whether a particular frequency channel should be used or not.
detail below), it is preferable for the ST to switch to a
To enable the call control function to specify a specific
separate CT.
Access-Out channel for outgoing calls, a. line 460 is proDatabase consistency across CT shelves is preferably
vidt:d between the call control function 336 and the channel
supported through the service domain controller 400. Database consistency needs to be real-time so that an ST entering 25 selection controller 440. The call control function 336 may
choose an access-out channel from the free list in storao-e
the network is allowed full Service Domain access imme445, and instruct the channel selection controller over li~e
diately (the Service Domain message is broadcast to all STs,
460 to attempt acquisition of that channel.
and so a new ST will expect access across the full Service
The following examples indicate how the above described
Domain).
structure may be used to perform channel switching in
Incoming access via backup CTs requires some function 30
particular circumstances.
to be provided to broadcast dupbcate incoming call setup
RF Channel Switching for Faull Tolerance
m~s~ages to all CTs that form a Service Domain. Preferably
Should one RF channel suffer complete loss of downlink,
tins IS handled by the service domain controller 400, which
the following process takes place in preferred embodiments:
forwards incoming call setup messages to each CT operating
(i) The ST will attempt downlink re-acquisition for a
in the service domain. All CTs will allocate Access In 35
period of time, say 20 seconds.
Traffic Channels and relay the incoming call setup mes~ge
(ii) If acquisition fails, the channel selection controller
via the Call Control Channel. On successful uplink access,
440 of the ST will select the next available channel
one CT will respond to the service domain controller with a
from the Service Domain information in storage 445
call accepted message, the other CTs will eventually respond
and attempt downlink acquisition. This process will be
\Vith call setup failed messages. Outgoing access via a 40
repeated until a downlink signal is acquired.
backup CT is similar to normal outgoing access.
(uii) Once a backup RF channel is located, the ST will
Another job which can be performed by the service
'camp' on the Call Control Channel and may subsedomain controller is to assist the element manager 58 in
quently be granted traffic access.
reconfiguring equipment in the event of a fault. For example,
(iv) If the CT fault persists, the EM 58 may use the service
if one CT is taken out of commission because of a fault a 45
domain controller 400 to reconfigure the Service
different CT can be brought 'on-line', and the service
Domain so that the functioning CT shelves become
domain controller can provide that new CT vvith the necesprimary service providers for the pool of 'homeless'
sary information about the other CTs in the service domain.
STs.
FIG. 19B illustrates those elements of the subscriber
A fault that does not result in complete loss of downlink
terminal used to implement RF channel switching. The radio so
signal \Vill not result in RF channel switching 'en mass'.
subsystem 420, which incorporates the transmission and
Rather, a fault may result in excessive or total call blockinoreception signal processing stages, will pass anv data
as discussed below.
'=''
received on the call control channel over line 425 ·to the
RF Channel Switching for Call Blocking
message decoder 430. If the decoder 430 determines that the
If Incoming access traffic channels are being blocked, the
data on the call control channel forms a service domain 55
following process is employed in preferred embodiments:
message, then this is passed over line 435 to the channel
(i) The call setup message sent over the Call Control
selection controller 440, where the information within the
Channel will specify a TC on which to access the call.
service domain message is stored in storage 445.
(ii) In the case of incoming access being blocked, the CT
Similarly, if the message decoder identifies the data as a
will specify a null TC. The channel selection controller
'free list' identifying the available traffic channels on a 60
440 of the ST will in such cases switch to the next RF
particular RF frequency, then this data is passed to the call
channel from the Service Domain information in storcontrol function 336 and the channel selection controller 440
age 445 and monitor the Call Control Channel.
over path 450. The call control function 336 stores the free
(ii:i) If the ST receives a call setup message with a valid
list .in the storage 445 for subsequent use by the call control
TC, then the call is processed as normal.
65
function 336 and the channel selection controller 440.
(iv) When the call clears, the ST downlink preferably
If the message decoder 430 determines that the data forms
switches back to the home CT.
an incoming call setup message, then that information is

WIL-0009872

US 6,222,R19 Bl
27

28

If Outgoing access traffic channels are being blocked, the
following process is employed in preferred embodiments:
(i) The ST registers an off-hook. The Free List in storage
445 is checked and if a traffic channel is available, then
the call control function 336 asserts a channel request
on line 460 to the channel selection controller 440 and
normal uplink access is attempted.
(ii) If the Free List shows no Access_Out channels are
available on the current frequency channel, then the
channel selection controller will he used to switch the 10
ST to the next RF channel in the Service Domain,
whereupon the ST will wait fur the next Free List.
(iii) When the ST finds a Free List with an available
Access_Out channel, then uplink access is attempted
and the call is processed as normal.
15
(iv) When the call clears, the ST downlink preferably
switches hack to the home CT.
RF Channel Switching for Traffic Load Balancing
Traffic load balancing is, in prderred embodiments, pro-

3. A transmission controller as claimed in claim 1,
wherein the orthogonal code generator is a storage arranged
to store the set of orthogonal codes.
4. A transmission controller as claimed in claim 1,
wherein the overlay code generator is a storage arranged to
store the set of overlay codes.
5. A transmission controller as claimed in claim 1,
wherein the set of orthogonal codes comprise a set of
Rademacher-Walsh (RW) codes.
6. A transmission controller as claimed in claim 5,
wherein the set of overlay codes are derived from RW codes,
each set of 'n' overlay codes comprising an nxn matrix of
RW codes.
7. A central terminal of a wireless telecommunications
system, comprising:
a transmission controller having:
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
20
channel, wherein 'm' is a positive integer;
an operator may decide to move an ST to another RF
a first encoder for combining a data item to be transmitted
channel.
on the single frequency channel with said orthogonal
RF Channel Switching for Frequency Diversity
code from the orthogonal code generator, the orthogoFrequency diversity is, in preferred emhodiments, pronal code determining the orthogonal channel over
vided by static configuration via the EM 58. Radio link 25
which the data item is transmitted, whereby data items
statistics may be forwarded to the EM where an operator
pertaining to different wireless links may be transmitted
may decide to move an ST to another RF channel.
simultaneously within diiTerent orthogonal channels of
Although a particular embodiment has been described
said single frequency channel;
herein, it will be appreciated that the invention is not limited
an overlay code generator for providing an overlay code
thereto and that many modifications and additions thereto 30
from a first set of 'n' overlay codes which are orthogomay be made within the scope ofthe invention. For example,
various combinations ofthe features of the following depennal to each other, wherein 'n' is a positive integer;
dent claims could be made with the features of the indepena second encoder arranged to apply the overlay code from
dent claims without departing from the scope of the present
the overlay code generator to said data item, whereby
invention.
35
'n' data items pertaining to different wireless links may
What is claimed is:
be transmitted simultaneously within the same orthogo1. A transmission controller for processing data items to
nal channel, wherein the overlay code generator is
be transmitted over a wireless link connecting a central
arranged to provide overlay codes from one or more
terminal and a suhscriher terminal of a wireless telecomfurther sets of overlay codes having different numbers
munications system, a single frequency channel being 40
of overlay codes to said first set of overlay codes,
employed for transmitting data items pertaining to a pluralwherein the orthogonal code generator is a storage
ity of wireless links, the transmission controller comprising:
arranged to store the set of orthogonal codes, wherein
an orthogonal code generator for providing an orthogonal
the overlay code generator is a storage arranged to store
code from a set of 'm' orthogonal codes used to create
the set of overlay codes, wherein the set of orthogonal
'm' orthogonal channels within the single frequency 45
codes comprise a set of Rademacher-Walsh (RW)
channel, wherein 'm' is a positive integer;
codes, and wherein the set of overlay codes are derived
a first encoder for combining a data item to be transmitted
from RW codes, each set of 'n' overlay codes comprison the single frequency channel with said orthogonal
ing an nxn matrix of RW codes.
code from the orthogonal code generator, the orthogo8. A central terminal as claimed in claim 7, wherein a first
nal code determining the orthogonal channel over so of the orthogonal channels is reserved for the transmission
which the data item is transmitted, whereby data items
of signals relating to the acquisition of wireless links, aod
pertaining to different wireless links may be transmitted
the transmission controller is provided in the central termisimultaneously within different orthogonal channels of
nal to enable overlay codes to be applied to data items to be
said single frequency channel;
sent within said first orthogonal channel from the central
an overlay code generator for providing an overlay code ss terminal to one of said subscriber terminals.
from a first set of 'n' overlay codes which are orthogo9. A central terminal as claimed in claim 8, wherein a
nal to each other, wherein 'n' is a positive integer; and
second of the orthogonal channels is reserved for the transa second encoder arranged to apply the overlay code from
mission of signals relating to the control of calls, and the
the overlay code generator to said data item, whereby
transmission controller is provided in the central terminal to
'n' data items pertaining to different wireless links may 60 enable overlay codes to be applied to data items to be sent
be transmitted simultaneously within the same orthogowithin said second orthogonal channel from the central
nal channel.
terminal to one of said subscriber terminals.
2. A transmission controller as claimed in claim 1,
10. A central terminal as claimed in claim 7, further
wherein the overlay code generator is arranged to provide
comprising channelisation means for determining which of
overlay codes from one or more further sets of overlay codes 65 the orthogonal channels will be subject to overlay codes, and
having different numbers of overlay codes to said first set of
for transmitting that information to a plurality of subscriber
overlay codes.
terminals within the wireless telecommunications system.

~~~e~e~p ~~~~ s~~~~tk:~i~; ~~:~~~a~reds~ t~~~~o~~e~~

WIL-0009873

US 6,222,Rl9 Bl
29

30

11. A central terminal as claimed in claim 7, wherein a
an overlay code generator for providing an overlay code
number of said orthogonal channels are designated as traffic
from a first set of 'n' overlay codes which are orthogochannels for the transmission of data items relating to
nal to each other, the set of 'n' overlay codes enabling
communication content, said central terminal further com'n' data items pertaining to different wireless links to be
prising:
transmitted simultaneously within the same orthogonal
channel, wherein 'n' is a positive integer; and
a TDM encoder arranged to apply time division multia second decoder for applying, to the data items of the
plexing (TDM) techniques to data items to be sent over
a traffic channel from said central terminal to said
orthogonal channel, the overlay code from the overlay
code generator so as to isolate a particular data item
subscriber terminal, so as to enable a plurality of data
itt:ms pc:rtaining to dilic:rc:nl wirdc:ss links to be: sml 10
transmiUt:d using that ovc:rlay code:.
within one orthogonal traffic channel during a prede19. A central terminal as claimed in claim 18, further
termined frame period.
comprising channelisation means for determining which of
the orthogonal channels will be subject to overlay codes, and
12. A reception controller for processing data items
for transmitting that information to a plurality of subscriber
received over a wireless link connecting a central terminal
and a subscriber terminal of a wireless telecommunications 15 terminals within the wireless telecommunications system.
20. A central terminal as claimed in claim19, wherein the
system, a single frequency channel being employed for
channelisation means also determines, for those orthogonal
transmitting data items pertaining to a plurality of wireless
links, the receiver controller comprising:
channels subject to overlay codes, which set of overlay
codes will apply to each orthogonal channel.
an orthogonal code generator for providing an orthogonal
21. A subscriber terminal of a wireless telecommunicacode from a set of 'm' orthogonal codes used to create 20
tions system, comprising:
'm' orthogonal channels within the single frequency
a transmission controller having:
channel, wherein 'm' is a positive: inlt:gc:r;
an orthogonal code generator for providing an orthogonal
a first encoder for applying, to signals received on the
code from a set of 'm' orthogonal codes used to create
25
'm' orthogonal channels within the single frequency
channel, wherein 'm' is a positive integer;
data items transmitted within the corresponding
orthogonal code;
a first encoder for combining a data item to be transmitted
on the single frequency channel with said orthogonal
an overlay code generator for providing an overlay code
code from the orthogonal code generator, the orthogofrom a first set of 'n' overlay codes which are orthogo- 30
nal code determining the orthogonal channel over
nal to each other, the set of 'n' overlay codes enabling
which the data item is transmitted, whereby data items
'n' data items pertaining to different wireless links to be
pertaining to different wireless links may be transmitted
transmitted simultaneously within the same orthogonal
simultaneously within different orthogonal channels of
channel, wherein 'n' is a positive integer; and
said single frequency channel;
a second encoder for applying, to the data items of the 35
an overlay code generator for providing an overlay code
orthogonal channel, the overlay code from the overlay
from a first set of 'n' overlay codes which are mihogocode generator so as to isolate a particular data itc:m
nal to each other, wherein 'm' is a positive integer;
transmitted using that overlay code.
13. A reception controller as claimed in claim 12, wherein
a second encoder arranged to apply the overlay code from
the overlay code generator is arranged to provide overlay 40
the overlay code generator to said data item, whereby
'n' data items pertaining to different wireless links may
codes from one or more further sets of overlay codes having
be transmitted simultaneously within the same orthogodifferent numbers of overlay codes to said first set of overlay
nal channel, wherein the overlay code generator is
codes.
arranged to provide overlay codes from one or more
14. A reception controller as claimed in claim 12, wherein
further sets of overlay codes having different numbers
the orthogonal code generator is a storage arranged to store 45
the set of orthogonal codes.
of overlay codes to said first set of overlay codes,
15. A reception controller as claimed in claim 12, wherein
wherein the orthogonal code generator is a storage
the overlay code generator is a storage arranged to store the
arranged to store the set of orthogonal codes, wherein
set of overlay codes.
the set of orthogonal codes comprise a set of
16. A reception controller as claimed in claim 12, wherein 50
Rademacher-Walsh (RW) codes, and wherein the set of
the set of orthogonal codes comprise a set of Rademacheroverlay codes are derived from RW codes, each set of
Walsh (RW) codes.
'n' overlay codes comprising an nxn matrix of RW
17. A controller as claimed in claim 12, wherein the set of
codes; the transmission controller operable to enable
overlay codes to be applied to data items sent from the
overlay codes are derived from RW codes, each set of 'n'
overlay codes comprising an nxn matrix of RW codes.
subscriber terminals to the central terminal.
55
18. A central terminal of a wireless telecommunications
22. A subscriber terminal of a wireless telecommunicasystem, comprising:
tions system, comprising:
a reception controller having:
a reception controller having:
an orthogonal code generator for providing an orthogonal
an orthogonal code generator for providing an orthogonal
code from a set of 'm' orthogonal codes used to create
code from a set of 'm' orthogonal codes used to create 60
'm' orthogonal channels within the single frequency
'm' orthogonal channels within the single frequency
channel, wherein 'm' is a positive integer;
channel, wherein 'm' is a positive integer;
a first decoder for applying, to signals received on the
a first decoder for applying, to signals received on the
single frequency channel, the orthogonal code provided
single frequency channel, the orthogonal code provided
by the orthogonal code generator, in order to isolate
by the orthogonal code generator, in order to isolate 65
data items transmitted within the corresponding
data items transmitted within the corresponding
orthogonal channel;
orthogonal channel;

~i;~~ef~rf~~;~~~f~:~l,~~~e~:~~~,g~:a~r~~~et~r~;~~~~

WIL-0009874

US 6,222,R19 Bl

31

32

an overlay code generator for providing an overlay code
24. A wireless telecommunications system comprising a
from a first set of 'n' overlay codes which are orthogocentral terminal and a plurality of subscriber terminals,
nal to each other, the set of 'n' overlay codes enabling
wherein at least one of the subscriber terminals comprises:
'n' data items pertaining to different wireless links to be
a transmission controller having:
transmitted simultaneously within the same orthogonal
an orthogonal code generator for providing an orthogonal
channel, wherein 'n' is a positive integer;
code from a set of 'm' orthogonal codes used to create
a second decoder for applying, to the data items of the
'm' orthogonal channels within the single frequency
orthogonal channel, the overlay code from the overlay
channel, wherein 'm' is a positive integer;
code generator so as to isolate a particular data item
a first encoder for combining a data item to be transmitted
transmitted using that overlay code, wherein the over- 10
on the single frequency channel with said orthogonal
lay code generator is arranged to provide overlay codes
code from the orthogonal code generator, the orthogofrom one or more further sets of overlay codes having
nal code determining the orthogonal channel over
different numbers of overlay codes to said first set of
which the data item is transmitted, whereby data items
overlay codes, wherein the orthogonal code generator
pertaining to different wireless links may be transmitted
is a storage arranged to store the set of orthogonal 15
simultaneously within different orthogonal channels of
codes, wherein the overlay code generator is a storage
said single frequency channel;
arranged to store the set of overlay codes, wherein the
an overlay code generator for providing an overlay code
set of orthogonal codes comprise a set of Rademacher[rom a first set of 'n' overlay codes which are orthogoWalsh (RW) codes, and wherein the set of overlay
nal to each other, wherein 'n' is a positive integer; and
codes are derived from RW codes, each set of 'n' 20
a second encoder arranged to apply the overlay code from
overlay codes comprising an nxn matrix of RW codes.
the overlay code generator to said data item, whereby
23. A wireless telecommunications system comprising a
'n' data items pertaining to different wireless links may
central terminal and a plurality of subscriber terminals,
be transmitted simultaneously within the same orthogowherein the central terminal comprises:
nal channel; and
a transmission controller having:
25
the central terminal comprises:
an orthogonal code gtmerator [or providing an orthogonal
a reception controller having:
code from a set of 'm' orthogonal codes used to create
'm' orthogonal channels within the single frequency
an orthogonal code generator for providing an orthogonal
channel, wherein 'm' is a positive integer;
code from a set of 'm' orthogonal codes used to create
'm' orthogonal channels within the single frequency
a first encoder for combining a data item to be transmitted 30
channel;
on the single frequency channel with said orthogonal
code from the orthogonal code generator, the orthogoa first decoder for applying, to signals received on the
nal code determining the orthogonal channel over
single frequency channel, the orthogonal code provided
which the data item is transmitted, whereby data items
by the orthogonal code generator, in order to isolate
pertaining to different wireless links may be transmitted 35
data items transmitted within the corresponding
simultaneously within different orthogonal channels of
orthogonal channel;
said single frequency channel;
an overlay code generator for providing an overlay code
an overlay code generator for providing an overlay code
from a first set of 'n' overlay codes which are orthogofrom a first set of 'n' overlay codes which are orthogonal to each other, the set of 'n' overlay codes enabling
40
nal to each other, wherein 'n' is a positive integer; and
'n' data items pertaining to different wireless links to be
a second encoder arranged to apply the overlay code from
transmitted simultaneously within the same orthogonal
the overlay code generator to said data item, whereby
channel; and
'n' data items pertaining to different wireless links may
a second decoder for applying, to the data items of the
be transmitted simultaneously within the same orthogoorthogonal channel, the overlay code from the overlay
nal channel; and
45
code generator so as to isolate a particular data item
at least one of the subscriber terminal comprises:
transmitted using that overlay code.
a reception controller having:
25. A method of processing data items to be transmitted
over a wireless link connecting a central terminal and a
an orthogonal code generator for providing an orthogonal
code from a set of 'm' orthogonal codes used to create 50 subscriber terminal of a wireless telecommunications
system, a single frequency channel being employed for
'm' orthogonal channels within the single frequency
transmit6ng data items pertaining to a plurality of wireless
channel;
links, the method comprising steps of:
a first decoder for applying, to signals received on the
providing an orthogonal code from a set of 'm' orthogonal
single frequency channel, the orthogonal code provided
codes used to create 'm' orthogonal channels within the
by the orthogonal code generator, in order to isolate 55
single frequency channel, wherein 'm' is a positive
data items transmitted within the corresponding
integer;
orthogonal channel;
combining a data item to be transmitted on the single
an overlay code generator for providing an overlay code
frequency channel with said orthogonal code, the
from a first set of 'n' overlay codes which are orthogoorthogonal code determining the orthogonal channel
nal to each other, the set of 'n' overlay codes enabling 60
over vvhich the data item is transmitted, whereby data
'n' data items pertaining to different wireless links to be
items pertaining to different wireless links may be
transmitted simultaneously within the same orthogonal
transmitted simultaneously within different orthogonal
channel; and
channels of said single frequency channel;
a second decoder for applying, to the data items of the
providing an overlay code from a first set of 'n' overlay
orthogonal channel, the overlay code from the overlay 65
codes which are orthogonal to each other, wherein 'n'
code generator so as to isolate a particular data item
transmitted using that overlay code.
is a positive integer; and

WIL-0009875

US 6,222,Rl9 Bl

33

34

providing an overlay code from a first set of 'n' overlay
applying the overlay code to said data item, whereby · n'
data items pertaining to different wireless links may be
codes which are orthogonal to each other, the set of 'n'
transmitted simultaneously within the same orthogonal
overlay codes enabling 'n' data items pertaining to
channel.
different wireless links to be transmitted simulta26. A method as claimed in claim 25, further comprising 5
neously within the same orthogonal channel, wherein
a step of:
'n' is a positive integer; and
providing one or more further sets of overlay codes
having different numbers of overlay codes to said first
applying, to the data items of the orthogonal channel, the
set of overlay codes.
overlay code so as to isolate a particular data item
27. A method as claimed in claims 25, further comprising 10
transmitted using that overlay code.
steps of:
30. A method as claimed in claim 29, further comprising
dt:lermining which of the orthogonal channels will be
a step of:
subject to overlay codes; and
transmitting that information to a plurality of subscriber
providing one or more further sets of overlay codes
terminals within the wireless telecommunications sys15
having different numbers of overlay codes to said first
tern.
set of overlay codes.
28. A method as claimed in claim 27, further comprising
a step of:
31. A method as claimed in claim 29, further comprising
determining, for those orthogonal channels subject to
steps of:
overlay codes, which set of overlay codes will apply to
20
determining which of the orthogonal channels will be
each orthogonal channel.
subject to overlay codes; and
29. A method of processing data items received over a
wirelt:ss link wnnecting a central terminal and a subscriber
transmitting that information to a plurality of subscriber
terminal of a wireless telecommunications system, a single
terminals within the wireless telecommunications sysfrequency channel heing employed for transmitting data
tem.
items pertaining to a plurality of wireless links, the method 25
comprising the steps of providing an orthogonal code from
32. A method as claimed in claim 31, ±iurther comprising
a set of 'm' orthogonal codes used to create 'm' orthogonal
a step of:
channels within the single frequency channel, wherein 'm' is
determining, for those orthogonal channels subject to
a positive integer;
overlay codes, which set of overlay codes will apply to
applying, to signals received on the single frequency 30
each orthogonal channel.
channel, the orthogonal code in order to isolate data
items transmitted within the corresponding orthogonal
channel;
*
* * *

WIL-0009876