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

Filing 174

MOTION for Partial Summary Judgment that Patent Claims Are Indefinite by Alcatel-Lucent USA Inc., Ericsson Inc., Telefonaktiebolaget LM Ericsson. Responses due by 4/13/2012 (Attachments: # 1 Exhibit A, # 2 Exhibit B, # 3 Text of Proposed Order)(Sostek, Bruce)

EXHIBIT A

US006088326A

United States Patent

[I91

[ill

Lysejko et al.

[45]

Appl. No.: 081979,408

Nov. 26, 1997

Filed:

Foreign Application Priority Data
20, 1996 [GB]

United Kingdom

................... 9626567

Int. CL7 ............................. H04J 11/00; H04J 13100;
H04B 71216
U.S. C1. .......................... 3701209; 3701342; 3701345;
3701441; 3701442; 3701479
Field of Search ..................................... 3701328, 329,
3701330, 335, 336, 337, 340, 341, 342,
343, 345, 347, 441, 442, 465, 468, 479,
498, 203, 208, 209
References Cited
U.S. PATENT DOCUMENTS
4,688,210 811987 Eizenhoffer et al. ................... 3701342
4,799,252 111989 Eizenhoffer et al. ................... 3701342
5,373,502 1211994 Turban ...................................... 370118
5,592,469 111997 Szabo ...................................... 3701342
6,005,854 1211999 Xu et al. ................................. 3701335

FOREIGN PATENT DOCUMENTS
0652650

511995

European Pat. Off.

HYBRID

2 WIRE
l/i -

\

15 Claims, 16 Drawing Sheets

CONVOLUTIONAL
ENCODER

OVERLAY CODE
GENERATOR

118

OVERHEAD

-fhJ
- INSERTION - /
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104

ANTENNA

ABSTRACT

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

.......... H04B 7126

COOEC
--

Jul. 11,2000

Primary Examiner4icky
Ngo
Attorney, Agent, or F i r m a a k e r Botts L.L.P.

[571

Assignee: Airspan Communications
Corporation, Wilmington, Del.

6,088,326

0730356 911996 European Pat. Off. .......... H04L 1/00
2301744 1211996 United Kingdom ............. H04Q 7/32
9314590 711993 WIPO .............................. H04N 1/00
9315573 811993 WIPO ............................. H04J 13/00
9523464 811995 WIPO ............................... H04J 3/22

[54] PROCESSING DATA TRANSMITTED AND
RECEIVED OVER A WIRELESS LINK
CONNECTING A CENTRAL TERMINAL AND
A SUBSCRIBER TERMINAL OF A WIRELESS
TELECOMMUNICATIONS SYSTEM
[75] Inventors: Martin Lysejko, Bagshot, United
Kingdom; Paul F. Struhsaker, Plano,
Tex.

Patent Number:
Date of Patent:

-

106

108

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110

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142
8PF

-

MIXER

LPF

U.S. Patent

Jul. 11,2000

Sheet 1 of 16

U.S. Patent

Jul. 11,2000

Sheet 2 of 16

FIG. 3

U.S. Patent

Jul. 11,2000

Sheet 3 of 16

U.S. Patent

Jul. 11,2000

Sheet 4 of 16

U.S. Patent

Jul. 11,2000

Sheet 5 of 16

U.S. Patent

Jul. 11,2000

Sheet 6 of 16

U.S. Patent

Jul. 11,2000

Sheet 7 of 16

RX
ANTENNA

LNA

BPF

A

1501

192

190

1 88

154

184

f'

156

170

MIXER

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CORRELATOR

187
TDM
DECODER

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OVERHEAD
EXTRACTION

CODEC

-

R= 1/2, K=7

VITERBI

181

CONTROL

FIG. 8 A

174

4

GENERATOR
PN

p

U.S. Patent

Jul. 11,2000

Sheet 9 of 16

U.S. Patent

Jul. 11,2000

Sheet 10 of 16

U.S. Patent

Jul. 11,2000

Sheet 11 of 16

FIG. 70

I SUBSCRIBER TERMINAL

CENTRAL TERMINAL

FIG. 7 7

CODE SEQUENCE

PN CODE

!
R/W
CODE
OVERLAY
CODE

FIG. 7 2

FRAME
INFORMATION

DOWNLINK

U.S. Patent

Jul. 11,2000

Sheet 12 of 16

I

1oous

FIG. 73A

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75us

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125us

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CS

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(Ill)

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CH.ID*

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OMC4

FIG. 74A

I

U.S. Patent

I

Sheet 13 of 16

Jul. 11,2000

FAW

CS

D

PC

FAW

CS

PC

OMC/D

FAW
FAW

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D

CS

PC

OMC

PC

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CHAD

UNUSED UNUSED UNUSED

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FIG. 14B

TOTAL TRAFFIC CHANNEL

4

INTERFERENCE LIMITED TRAFFIC CHANNEL POOL

4

LTC

D

FTC
LTC
FTC
AOTC
AlTC
BTC
PTC

AOTC

AlTC

BTC

= LOCKED TRAFFIC CHANNEL
= FREE TRAFFIC CHANNEL

= ACCESS OUTGOING TRAFFIC CHANNEL
= ACCESS INCOMING TRAFFIC CHANNEL
= BUSY TRAFFlC CHANNEL

= PRIORITY TRAFFIC CHANNEL

FIG. 76

D

PTC

-

LOCKED CHANNELS
TURNED OFF

RWI

RW2

RW3

RW4

RW5

W
CDMA R SPACE
RW6

RW7

RW8

RW9

RWlO

RW11

+

RW12

RW13

RW14

RW15

TIME

FIXED ASSIGNMENT
LINKS, 160kb/s

7
4Okb/s

FIG. 1 5 A

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CDMA R SPACE W
+
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RW4

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RW6

RW7

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LINKS, 16Okb/s

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FOR UPLINK ACQUISITION

FREE Ln SLOT: AVAILALE
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FIG. 15B

PRIORITY UPLINK
ACQUISITION, 1Okb/s

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U.S. Patent

Sheet 15 of 16

Jul. 11,2000

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11,2000

6,088,326

Sheet 16 of 16

FIG. 18

405

20

DOMAl N
CONTROLLER

FIG. 19A

SUBSYSTEM

7 CHANNEL /
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FIG. 19B

6,088,326

1

2

PROCESSING DATA TRANSMITTED AND
RECEIVED OVER A WIRELESS LINK
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.
s
SUMMARY OF THE INVENTION

TECHNICAL FIELD OF THE INVENTION

According to the present invention, there is provided a
transmission controller for processing data items to be
transmitted over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, a single frequency channel being employed for
transmitting data items pertaining to a plurality of wireless
links, the transmission controller comprising: an orthogonal
BACKGROUND OF THE INVENTION
. - code generator for providing an orthogonal code from a set
orthogonal codes used to create 'm' orthogonal
Awireless telecommunications system has been proposed l5 of
in which a geographical area is divided in to cells, each cell
channels within the single frequency channel; a first encoder
for combining a data item to be transmitted on the single
having one or more central terminals (CTs) for communicatinn over wireless links with a number of subscriber
freauencv channel with said orthononal code from the
u
u
terminals (STs) 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; and a
terminal to the subscriber terminal.
TDM encoder arranged to apply time division multiplexing
Due to bandwidth constraints, it is not practical for each 25 (TDM) techniques to the data item in order to insert the data
item within a time slot of the orthogonal channel, whereby
individual subscriber terminal to have its own dedicated
a plurality of data items relating to different wireless links
frequency channel for communicating with the central termay be transmitted within the same orthogonal channel
minal. Hence, techniques need to be applied to enable data
items relating to different wireless links to be passed over the 30 during a predetermined frame period.
same frequency channel without interfering with each other.
Viewed from a second aspect, the present invention
In current wireless telecommunications systems, this can be
provides a reception controller for processing data items
achieved through the use of a 'Code Division Multiple
received over a wireless link connecting a central terminal
Access' (CDMA) technique. One way to implement CDMA
and a subscriber terminal of a wireless telecommunications
is through the application of a set of orthogonal codes to the 35 system, a single frequency channel being employed for
data items to be transmitted on a particular frequency
transmitting data items pertaining to a plurality of wireless
channel, data items relating to different wireless links being
links, and 'm' orthogonal channels being provided within the
combined with different orthogonal codes from the set. A
single frequency channel, the receiver controller comprissuitable set of orthogonal codes is a "Rademacher-Walsh
ing: an orthogonal code generator for providing an orthogo(RW) set of sixteen 16-bit codes. Orthogonal codes have the 40 nal code from a set of 'm' orthogonal codes used to create
property that, when perfectly aligned, all codes crosssaid 'm' orthogonal channels within the single frequency
correlate to zero, thus making it possible to decode a signal
channel; a first decoder for applying, to signals received on
to which one orthogonal code has been applied while
the single frequency channel, the orthogonal code provided
cancelling interference from signals to which different
by the orthogonal code generator, in order to isolate data
orthogonal codes have been applied.
45 items transmitted within the corresponding orthogonal chanSignals to which an orthogonal code has been applied can
nel; and a TDM decoder arranged to extract a data item from
be considered as being transmitted over a corresponding
a predetermined time slot within said orthogonal channel, a
orthogonal channel within a particular frequency channel.
plurality of data items relating to different wireless links
Hence, considering the example of a set of 16 RW codes, 16
being transmitted within the same orthogonal channel during
a predetermined frame period.
orthogonal channels can be created within a single frequency channel, and hence up to sixteen separate commuBy using TDM techniques in addition to the known set of
nication signals (corresponding to sixteen separate wireless
orthogonal codes, it is possible for selected orthogonal
links) can be transmitted simultaneously over the single
channels to be subdivided in the time dimension. For
frequency channel if different RW codes are applied to each
example, if TDM is used to divide one frame period in to
communication signal.
55 four subframes, and each orthogonal channel is subject to
the TDM technique, then up to 64 separate communication
It is known to provide a number of modem shelves within
signals can be transmitted on the sixteen orthogonal chanone central terminal, and for each modem shelf to employ a
nels during one frame period, albeit at a quarter of the rate
different frequency channel. Hence, if a central terminal has
that the communication signals could be transmitted if the
four modem shelves, and the set of 16 RW codes is
employed for each frequency channel, one central terminal 60 TDM technique was not used.
would be able to support wireless links with up to 60
Such an approach has the advantage that it preserves
subscriber terminals simultaneously.
compatibility with current hardware and software equipment
However, as more subscribers subscribe to the wireless
which use the set of orthogonal codes, but which do not
telecommunications network, it is becoming desirable to
support the use of TDM techniques. By designating certain
support more and more subscriber terminals from each 65 orthogonal channels as channels for which TDM is not used,
central terminal. There are only a limited number of frethe current equipment can communicate over those channels
quency channels that can be allocated to the wireless telewithout any changes being required to the equipment.
The present invention relates in general to wireless tele~~mmunications
systems and more particularly to techniques for processing data transmitted and received over a
wireless link connecting a central terminal and a subscriber
terminal of a wireless telecommunications system.

'm'

.

a

6,088,326

3

4

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

said orthogonal channel will receive data at a rate of 40 kbls
(since each ST will only read a quarter of the data transmitted on the orthogonal channel during each frame period).
If, alternatively, two time slots are provided within the
orthogonal channel, then data items pertaining to only two
different wireless links will be transmitted per frame period,
and the two STs receiving data will do so at a rate of 80 kbls
(since each ST will read half of the data transmitted on the
orthogonal channel during one frame period). This flexibility is useful, since for some communications, eg. fax, a rate
of 40 kbls may not be acceptable, and hence the use of four
time slots would not be suitable.
In preferred embodiments, a number of said orthogonal
channels are designated as traffic channels for the transmission of data items relating to communication content, and
the TDM encoder is employed to apply time division multiplexing (TDM) techniques to data items to be sent over a
traffic channel from said central terminal to said subscriber
terminal. The use of this CDMAITDM hybrid approach for
downlink traffic channels retains the benefit of CDMA
access, i.e. interference is reduced when traffic is reduced,
and also reduces receiver dynamic range requirements.
However, a first of the orthogonal channels is preferably
reserved for the transmission of signals relating to the
acquisition of wireless links, and the second encoder is used
instead of the TDM encoder to enable overlay codes to be
applied to data items to be sent within said first orthogonal
channel from the central terminal to one of said subscriber
terminals. Similarly, a second of the orthogonal channels is
preferably reserved for the transmission of signals relating to
the control of calls, and the second encoder is used instead
of the TDM encoder to enable overlay codes to be applied
to data items to be sent within said second orthogonal
channel from the central terminal to one of said subscriber
terminals.
In preferred embodiments, at least one of the subscriber
terminals of a wireless telecommunications system comprises a reception controller in accordance with the present
invention. However, for transmission of data from subscriber terminals, it is preferable for the ST to have a
transmission controller which employs overlay codes for all
types of orthogonal channels, whether they be traffic thanriels or otherwise. On these uplink channels, the Pure CDMA
approach using overlay codes eliminates the need to time
synchronise STs to a TDM frame reference, and reduces the
peak Power handling requirements in the ST RF transmit
chain.
Viewed from a third aspect, the present invention provides
a wireless telecommunications system comprising a central
terminal and a plurality of subscriber terminals, wherein the
central terminal comprises a transmission controller in
accordance with the present invention, and at least one of the
subscriber terminal comprises a reception controller in
accordance with the present invention.
Viewed from a fourth aspect, the present invention provides a method of processing data items to be transmitted
over a wireless link connecting a central terminal and a
subscriber terminal of a wireless telecommunications
system, a single frequency channel being employed for
transmitting data items pertaining to a plurality of wireless
links, the method comprising the steps of: (a) providing an
orthogonal code from a set of 'm' orthogonal codes used to
create 'm' orthogonal channels within the single frequency
channel; (b) combining a data item to be transmitted on the
single frequency channel with said orthogonal code, the
orthogonal code determining the orthogonal channel over

s

10

15

20

25

30

35

40

45

so

55

60

65

6,088,326
5

6

which the data item is transmitted, whereby data items
FIG. 10 illustrates the CDMAchannel hierarchy in accorpertaining to different wireless links may be transmitted
dance with preferred embodiments of the present invention;
simultaneously within different orthogonal channels of said
FIG, 1 is a schematic diagram illustrating downlink and
1
single frequency channel; and (c) applying time division
uplink communication paths for the wireless telecommunimultiplexing (TDM) techniques to the data item in order to s cations svstem:,
,
insert the data item within a time slot of the orthogonal
FIG, 12 is a schematic diagram illustrating the makeup of
channel, whereby a plurality of data items relating to difa downlink signal transmitted by the central terminal;
ferent wireless links may be transmitted within the same
FIGS. 13A and 13B illustrate the structure of the frames
orthogonal channel during a predetermined frame period.
lo of information sent over the downlink and uplink paths;
Viewed from a fifth aspect, the present invention provides
14A and 14B
the overhead frame stmca method of processing data items received over a wireless
hrefor the
and up1ink paths;
link connecting a central terminal and a subscriber terminal
FIGS. 15 and 15B illustrate typical downlink and uplink
.4
of a wireless telecommunications system, a single frequency
channel stmctures that might occur in a loaded system in
channel being employed for transmitting data items pertaining to a plurality of wireless links, and 'm' orthogonal 1s accordance with preferred embodiments of the present
invention;
channels being provided within the single frequency
channel, the method comprising the steps of: (a) providing
FIG. 16 illustrates how the available trafic channels are
an orthogonal code from a set of 'm' orthogonal codes used
classified in preferred embodiments of the present invention;
to create said 'm' orthogonal channels within the single
FIG, 1 7 illustrates the elements used by the central
frequency channel; (b) applying, to signals received on the 20 terminal to perform interference limiting;
sing1e
the
in
FIG. 18 illustrates possible antenna configurations that
isolate data items transmitted within the corresponding
,,,be employed in a wireless te~ecommun~cat~ons in
system
and (c) extracting a data item
a
accordance with the preferred embodiment of the present
predetermined time slot within said orthogonal channel, a
invention; and
plurality of data items relating to different wireless links 25
FIGS, 19A and 19B illustrate how channel switching is
being transmitted within the same orthogonal channel during
facilitated in preferred embodiments of the present invena predetermined frame period. By using TDM techniques in
tion,
addition to the known set of orthogonal codes, it is possible
for selected orthogonal channels to be subdivided in the time
DETAILED DESCRIPTION OF THE
dimension, thereby making it possible to support more 30
INVENTION
wireless links on one frequency channel.
FIG. 1 is a schematic overview of an example of a
BRIEF DESCRIPTION OF THE INVENTION
wireless telecommunications system. The telecommunications system includes one or more service areas 12,14 and
embodiment of the invention will be described
hereinafter, by way of example only, with reference to the 35 163 each of which is served by a respective central terminal
accompanying drawings in which like reference signs are
(CT) 10 which establishes a radio link with subscriber
terminals (ST) 20 within the area concerned. The area which
used for like features and in which:
FIG, 1 is a schematic overview of an example of a
is covered by a central terminal 10 can vary. For example,
wireless telecommunications system in which an example of
in a rural area with a low density of subscribers, a service
40 area 12 could cover an area with a radius of 15-20 Km. A
the present invention is included;
service area 14 in an urban environment where is there is a
FIG. 2 is a schematic representation of a premises; FIGS.
high density of subscriber terminals 20 might only cover an
2A and 2B are schematic illustrations of an example of a
area with a radius of the order of 100 m. In a suburban area
subscriber terminal of the telecommunications system of
with an intermediate density of subscriber terminals, a
FIG. 1;
service area 16 might cover an area with a radius of the order
FIG. 3 is a schematic illustration of an example of a 4s of Km, It will be appreciated that the area covered by a
central terminal of the telecommunications system of FIG.
particular central terminal 10 can be chosen to suit the local
1;
requirements of expected or actual subscriber density, local
FIG. 3A is a schematic illustration of a modem shelf of a
geographic considerations, etc,, and is not limited to the
of the
'ystem of
examples illustrated in FIG, 1,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. 5A and 5B are schematic diagrams illustrating
mitted signals.
possible configurations for cells for the telecommunications 55
~h~ central terminals 10 for respective
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, ~h~ links can
system of FIG. 1;
include conventional telecommunications technology using
FIGS. 7A and 7B are schematic diagrams illustrating 60 copper wires, optical fibres, satellites, microwaves, etc.
signal transmission processing stages for the telecommuni~ h ,ireless te~ecommunicationssystem of FIG, 1 is
,
cations system of FIG. 1;
based on providing fixed microwave links between subFIGS. 8A and 8B are schematic diagrams illustrating
scriber terminals 20 at fixed locations within a service area
signal reception processing stages for the telecommunica(e.g., 12,14,16) and the central terminal 10 for that service
tions system of FIG. 1;
65 area. Each subscriber terminal 20 can be provided with a
FIGS. 9A and 9B are diagrams illustrating the uplink and
permanent fixed access link to its central terminal 10, but in
downlink delivery methods when the system is fully loaded;
preferred embodiments demand-based access is provided, so

6,088,326

7

8

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

6,088,326

9

10

In the present example, each modem shelf supports 1
frequency channel (i.e. one uplink frequency plus the corresponding downlink frequency). Currently, in a wireless
telecommunications system as described above, CDMA
encoding is used to support up to 15 subscriber links on one
frequency channel (one subscriber link on each modem).
Hence, if a central terminal has four modem shelves, it can
support 60 (15x4) subscriber links (i.e. 60 STs can be
connected to one CT). However, it is becoming desirable for
more than 60 STs to be supported from one central terminal,
and, in preferred embodiments of the present invention,
enhancements to the CDMA encoding technique are provided to increase the number of subscriber links that can be
s u ~ ~ o r t e a central terminal. Both CDMAencoding, and
db~
the enhancements made to the CDMA encoding in accordance with preferred embodiments, will be discussed in
more detail later.
Typically, the radio traffic from a particular central terminallo will extend into the area covered by a neighbouring
central terminal 10. To avoid, or at least to reduce interference problems caused by adjoining areas, only a limited
number of the available frequencies will be used by any
given central terminal 10.
FIG. S A illustrates one cellular type arrangement of the
frequencies to mitigate interference problems between adjacent central terminals 10. In the arrangement illustrated in
FIG. 5A, the hatch lines for the cells 76 illustrate a frequency
set (FS) for the cells. By selecting three frequency sets (e.g.,
where: FSl=Fl, F4, F7, F10; FS2=F2, F5, F8, F11; FS3=F3,
F6, F9, F12), and arranging that immediately adjacent cells
do not use the same frequency set (see, for example, the
arrangement shown in FIG. 5A), it is possible to provide an
array of fixed assignment omnidirectional cells where interference between nearby cells can be reduced. The transmitter power of each central terminal 1 0 is preferably set such
that transmissions do not extend as far as the nearest cell
which is using the same frequency set. Thus, in accordance
with the arrangement illustrated in FIG. 5A, each central
terminal 1 0 can use the four frequency pairs (for the uplink
and downlink, respectively) within its cell, each modem
shelf in the central terminal 10 being associated with a
respective RF channel (channel frequency pair).
FIG. 5B illustrates a cellular type arrangement employing
sectored cells to mitigate problems between adjacent central
terminals 10. As with FIG. 5A, the different type of hatch
lines in FIG. 5B illustrate different frequency sets. As in
FIG. 5A, FIG. 5B represents three frequency sets (e.g.,
where: FSl=Fl, F4, F7, F10; FS2=F2, F5, F8, F11; FS3=F3,
F6, F9, F12). However, in FIG. 5B the cells are sectored by
using a sectored central terminal (SCT) 13 which includes
three central terminals 10, one for each sector S1, S2 and S3,
with the transmissions for each of the three central terminals
1 0 being directed to the appropriate sector among S1, S2 and
S3. This enables he number of subscribers per cell to be

increased three fold, while still providing permanent fixed
access for each subscriber terminal 20.
Arrangements such as those in FIGS. 5A and 5B can help
reduce interference, but in order to ensure that cells operating on the same frequency don't inadvertently decode each
others data, a seven cell repeat pattern is used such that for
a cell operating on a given frequency, all six adjacent cells
operating on the same frequency are allocated a unique
pseudo random noise (PN) code. The use of PN codes will
be discussed in more detail later. The use of different pN
codes prevents nearby cells operating on the same frequency
from inadvertently decoding each others data.
A, mentioned above, CDMA techniques can be used in a
fixed assignment arrangement (ie. one where each ST is
assigned to a particular modem on a modem shelf) to enable
each channel frequency to support 15 subscriber links. FIG.
6 gives a schematic overview of CDMA encoding and
decoding.
In order to encode a CDMA signal, base band signals, for
example the user signals for each respective subscriber link,
are encoded at 80-80N into a 160 ksymbols/sec baseband
signal where each symbol represents 2 data bits (see, for
example the signal represented at 81). This signal is then
spread by a factor of 16 using a spreading function 82-82N
to generate signals at an effective chip rate of 2.56
Msymbolslsec in 3.5 MHz. The spreading function involves
applying a PN code (that is specified on a per CT basis) to
the signal, and also applying a Rademacher-Walsh (RW)
code which ensures that the signals for respective subscriber
terminals will be orthogonal to each other. Once this spreading function has been applied, the signals for respective
subscriber links are then combined at step 84 and converted
to radio frequency (RF) to give multiple user channel signals
(e.g. 85) for transmission from the transmitting antenna 86.
During transmission, a transmitted signal will be subjected to interference sources 88, including external interference 89 and interference from other channels 90.
Accordingly, by the time the CDMAsignal is received at the
receiving antenna 91, the multiple user channel signals may
be distorted as is represented at 93.
In order to decode the signals for a given subscriber link
from the received multiple user channel, a Walsh correlator
94-94N uses the same RW and PN codes that were used for
the encoding for each subscriber link to extract a signal (e.g,
as represented at 95) for the respective received baseband
signal 96-96N. It will be noted that the received signal will
include some residual noise. However, unwanted noise can
be removed using a low pass filter and signal processing.
The key to CDMA is the application of the RW codes,
these being a mathematical set of sequences that have the
function of "orthonormality". In other words, if any RW
code is multiplied by any other RW code, the results are
zero. Aset of 16 RW codes that may be used is illustrated in
Table 1 below:

s

10

1s

20

2s

30

3s

40

4s

TABLE 1
RWO
RW1
RW2
RW3
RW4
RWS
RW6
RW7
RW8
RW9

11
TABLE 1-continued
RWlO
RWll
RW12
RW13
RW14
RW15

1
1
1
1
1
1

1
-1
1
-1
1
-1

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

-1
-1
-1
-1
1
1

-1
1
-1
1
1
-1

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

1
-1
1
-1
-1
1

10

The above set of RW codes are orthogonal codes that
Overlay codes are used extensively to provide variable
allow the multiple user signals to be transmitted and
rate uplink traffic channels. Overlay codes will also be used
received on the same frequency at the same time. Once the
to implement downlink control channels, these control chanbit stream is orthogonally isolated using the RW codes, the
nels being discussed in more detail later. However, as
signals for respective subscriber links do not interfere with 1s mentioned earlier, a different approach is taken for providing
each other. Since RW codes are orthogonal, when perfectly
flexible channelisations on the downlink traffic channel
aligned all codes have zero cross-correlation, thus making it
paths. Downlink traffic channels will operate in high rate,
possible to decode a signal while cancelling interference
160 kbls, mode, with lower data rates of 80 and 40 kbls
from users operating on other RW codes.
being supported by 'Time Division Multiplexing' (TDM)
In preferred embodiments of the present invention, it is 20 the available bandwidth.
desired to provide the central terminal with the ability to
In preferred embodiments, TDM timeslot bit numbering
support more than 15 subscriber links on each channel
will follow the CCITT G.732 convention with bits transfrequency, and to achieve this the above set of 16 RW codes
mitted in the sequence bit 1, bit 2. . . bit 8. Byte orientation
has been enhanced. In order to maintain compatibility with
is specified per channel as either most significant bit (MSB)
former products using the 16 RW codes, it was desirable that 25 first, least significant bit (LSB) first or NIA.
any enhancements should retain the same set of 16 RW
~ h provision of a hybrid C D M ~ D M
,
approach for
codes.
downlink traffic channels retains the benefits of CDMA
The manner in which the enhancements have been impleaccess, ie. interference is reduced when traffic is reduced.
mented provides flexibility in the way the frequency chanFurther, use of TDM ensures that the CDMA signal is
nels are configured, with certain configurations allowing a 30 limited to a 256 'Quadrature Amplitude Modulation' (QAM)
greater number of subscriber links to be supported, but at a
constellation which reduces receiver dynamic range requirelower u
nross bit rate. In vreferred embodiments. a channel
ments. OAM constellations will be familiar to those skilled
can be selected to operate with the following gross bit rates:
in the art.
On the uplink channels, the pure CDMA approach using
35
overlay codes eliminates the need to time synchronise STs to
a TDM frame reference. This has the ad;antage of elimi160 kbls
Full rate (Fl)
nating TDM delays and the 'guard time' in between TDM
80 kbls
Half rate (HI, HZ)
40 kbls
Quarter rate (Ql, Q2, Q3, Q4)
frames. Another benefit is reduced peak power handling
10 kbls
Low rate (L1, L2, L3, L4), for uplink acquisition
requirements in the ST RF transmit chain which would
40
otherwise be needed when transmitting bursty TDM data.
High dynamic range requirement is restricted to the CT
In preferred embodiments, the manner in which these
receiver.
channelisations are provided differs for the downlink (CT to
The manner in which the transmitted and received signals
ST) and
(ST to CT) communication paths, This is
because it has been realised that different performance 45 are processed in accordance with preferred embodiments of
requirements exist for the downlink and uplink paths, On the
the present invention will be described with reference to
downlink all signals emanate from a single source, namely
FIGS. 7 and 8. FIG. 7A is a schematic diagram illustrating
signal transmission processing stages as configured in a
the central terminal, and hence the signals will be synchronised, However, on the uplink path, the signals will emanate
subscriber terminal 20 in the telecommunications system of
from a number of independent STs, and hence the signals so FIG. 1. In FIG. 7A, an analogue signal from a telephone is
passed via an interface such as two-wire interface 102 to a
will not be synchronised.
hybrid audio processing circuit 104 and then via a codec 106
~i~~~ the above considerations, in preferred
to produce a digital signal into which an overhead channel
embodiments, on the
path full rate (160 kbIs) operaincluding control information is inserted at 108. If the
tion is implemented using the basic set of RW codes
a number
Or
discussed earlier, but half and quarter rates are achieved 55 subscriber
telecommunications equipment, then elements 102,104 and
through the use of 'overlay codes' which comprise RW
lo6
may be repeated for each piece
coded high rate symbol patterns that are transmitted for each
equipment.
intermediate rate data symbol. For half rate operation, two
At the output of overhead insertion circuit 108, the signal
2-bit overlay codes are provide, whilst for quarter rate
operation, four 4-bit overlay codes are provided, When 60 will have a bit rate of either 160,80 or 40 kbitsls, depending
generating a signal for transmission, one of the overlay
on which channel has been selected for transmission of the
signal.
codes, where appropriate, is applied to the signal in addition
to the appropriate RW code. When the signal is received,
The resulting signal is then processed by a convolutional
then at the CDMA demodulator the incoming signal is
encoder 110 to produce two signals with the same bit rate as
multiplied by the channel's PN, RW and Overlay codes. The 65 the input signal (collectively, these signals will have a
correlator integration period is set to match the length of the
symbol rate of 160, 80 or 40 KSls). Next, the signals are
Overlay code.
passed to a spreader 111 where, if a reduced bit rate channel

6,088,326

13

14

has been selected, an appropriate overlay code provided by
code generator providing appropriate overlay codes to the
spreader 111. The overlay code generator will be controlled
overlay code generator 113 is applied to the signals. At the
output of the spreader 111, the signals will be at 160 KSIs
so as to produce the desired overlay code, in preferred
irrespective of the bit rate of the input signal since the
embodiments, this control coming from the DAengine (to be
overlay code will have increased the symbol rate by the 5 discussed in more detail later).
necessary amount.
FIG. 8A is a schematic diagram illustrating the signal
The signals output from spreader 111 are passed to a
reception processing stages as configured in a subscriber
terminal 20 in the telecommunications system of FIG. 1. In
spreader 116 where the Rademacher-Walsh and PN codes
are applied to the signals by a RW code generator 112 and
FIG. 8A, signals received at a receiving antenna 150 are
PN Code generator 114, respectively. The resulting signals, lo passed via a band pass filter 152 before being amplified in
at 2.56 MC/s (2.56 Mega chips per second, where a chip is
a low noise amplifier 154. The output of the amplifier 154 is
the smallest data element in a spread sequence) are passed
then passed via a further band pass filter 156 before being
via a digital to analogue converter 118. The digital to
further amplified by a further low noise amplifier 158. The
output of the amplifier 158 is then passed to a mixer 164
analogue converter 118 shapes the digital samples into an
analogue waveform and provides a stage of baseband power
where it is mixed with a signal generated by a voltage
controlled oscillator 162 which is responsive to a synthesizer
control. The signals are then passed to a low pass filter 120
160. The output of the mixer 164 is then passed via the IIQ
to be modulated in a modulator 122. The modulated signal
de-modulator 166 and a low pass filter 168 before being
from the modulator 122 is mixed with a signal generated by
passed to an analogue to digital converter 170. The digital
a voltage controlled oscillator 126 which is responsive to a
synthesizer 160. The output of the mixer 128 is then 20 output of the A/D converter 170 at 2.56 MCls is then passed
to a correlator 178, to which the same Rademacher-Walsh
amplified in a low noise amplifier 130 before being passed
and PN codes used during transmission are applied by a RW
via a band pass filter 132. The output of the band pass filter
code generator 172 (corresponding to the RW code genera132 is further amplified in a further low noise amplifier 134,
tor 112) and a PN code generator 174 (corresponding to PN
before being passed to power control circuitry 136. The
output of the power control circuitry is further amplified in 25 code generator 114), respectively. The output of the corra power amplifier 138 before being passed via a further band
elator 178, at 160 KSIs, is then applied to correlator 179,
pass filter 140 and transmitted from the transmission antenna
where any overlay code used at the transmission stage to
encode the signal is applied to the signal by overlay code
142.
generator 181. The elements 170, 172, 174, 178, 179 and
FIG. 7B is a schematic diagram illustrating signal transmission processing stages as configured in a central terminal 30 181 form a CDMA demodulator. The output from the
CDMA demodulator (at correlator 179) is then at a rate of
10 in the te~ecommunications
system of FIG, 1,
will be
either 160, 80 or 40 KSls, depending on the overlay code
apparent, the central terminal is configured to perform
applied by correlator 179.
similar signal transmission processing to the subscriber
The output from correlator 179 is then applied to a Viterbi
terminal 20 illustrated in FIG. 7A, but does not include
elements 100, 102, 104 and 106 associated with telecom- 35 decoder 180. The output of the Viterbi decoder 180 is then
passed to an overhead extractor 182 for extracting the
munications equipment. Further, the central terminal
overhead channel information. If the signal relates to call
includes a TDM encoder 105 for performing time division
data, then the output of the overhead extractor 182 is then
multiplexing where required. The central terminal will have
passed through TDM decoder 183 to extract the call data
a network interface over which incoming calls destined for
a subscriber terminal are received. When an incoming call is 40 from the particular time slot in which it was inserted by the
CT TDM encoder 105. Then, the call data is passed via a
received, the central terminal will contact the subscriber
codec 184 and a hybrid circuit 188 to an interface such as
terminal to which the call is directed and arrange a suitable
two wire interface 190, where the resulting analogue signals
channel over which the incoming call can be established
are passed to a telephone 192. As mentioned earlier in
with the subscriber terminal (in preferred embodiments, this
is done using the call control channel discussed in more 45 connection with the ST transmission processing stages,
detail later). The channel established for the call will deterelements 184, 188, 190 may be repeated for each piece of
mine the time slot to be used for call data passed from the
telecommunications equipment 192 at the ST.
CT to the ST and the TDM encoder 105 will be supplied with
If the data output by the overhead extraction circuit 182
this information.
is data on a downlink control channels, then instead of
Hence, when incoming call data is passed from the so passing that data to a piece of telecommunications
equipment, it is passed via switch 187 to a call control logic
network interface to the TDM encoder 105 over line 103, the
185, where that data is interpreted by the ST.
TDM encoder will apply appropriate TDM encoding to
enable the data to be inserted in the appropriate time slot.
At the subscriber terminal 20, a stage of automatic gain
From then on, the processing of the signal is the same as the
control is incorporated at the IF stage. The control signal is
equivalent processing performed in the ST and described 5s derived from the digital portion of the CDMAreceiver using
with reference to FIG. 7A, the overlay code generator
the output of a signal quality estimator.
producing a single overlay code of value '1' so that the
FIG. 8B illustrates the signal reception processing stages
signal output from spreader 111 is the same as the signal
as configured in a central terminal 10 in the telecommuniinput to the spreader 111.
cations system of FIG. 1.As will be apparent from the figure,
As mentioned earlier, in preferred embodiments, overlay 60 the signal processing stages between the RX antenna 150
codes, rather than TDM, are used to implement downlink
and the overhead extraction circuit 182 are the as those
control channels, and data relating to such channels is passed
within the ST discussed in connection with FIG. 8A.
from a demand assignment engine (to be discussed in more
However, in the case of the CT, call data output from the
overhead extraction circuit is passed over line 189 to the
detail later) over line 107 through switch 109 to the overhead
insertion circuit 108, thereby bypassing the TDM encoder 65 network interface within the CT, whilst control channel data
105. The processing of the signal is then the same as the
is passed via switch 191 to the DA engine 380 for processequivalent processing performed in the ST, with the overlay
ing. The DA engine is discussed in more detail later.

6,088,326

16

15

Overlay codes and channelisation plans are selected to
scriber terminal 20. A downlink communication path is
established from transmitter 200 in central terminal 10 to
ensure signal orthogonality-i.e. in a properly synchronised
receiver 202 in subscriber terminal 20. An uplink commusystem, the contribution of all channels except the channel
nication path is established from transmitter 204 in subbeing demodulated sum to zero over the correlator integration period, ~ ~ ~ t h ~ is controlled to maintain s scriber terminal 20 to receiver 206 in central terminal 10.
uplink power ~ ,
Once the downlink and the uplink communication paths
constant energy per bit, ~h~ exception to this is L~~ rate
have been established in wireless telecommunication system
which will be transmitted at the same power as a ~~~~t~~
rate
1 telephone ~~mmunication occur between a user 208,
3
may
signal. Table 2 below illustrates the overlay codes used for
210 of subscriber terminal 20 and a user serviced through
full, half and quarter rate operations:
lo central terminal 10 over a downlink signal 212 and an uplink
signal 214. Downlink signal 212 is transmitted by transmitTABLE 2
ter 200 of central terminal 10 and received by receiver 202
ST TX.
of subscriber terminal 20. Uplink signal 214 is transmitted
power
by transmitter 204 of subscriber termTnal20 and received by
Net Channel relative
Correlator
integration
Acquisition
15 receiver 206 of central terminal 10.
Rate designa- to FI-u
[dB)
Overlav Code
period [US)
overlav
Receiver 206 and transmitter 200 within central terminal
Ikbls)
tion
,
,
,
,
, ,
10 are synchronized to each other with respect to time and
160
-F1-U
0
1
6.25
L1
phase, and aligned as to information boundaries. In order to
80
-HI-U
-3
1 1
12.5
L1
80
-HZ-u
-3
1 -1
12.5
~3
establish the downlink communication path, receiver 202 in
40
-QI-u
-6
1
1 1 1
25
LI
20 subscriber terminal 20 should be synchronized to transmitter
40
-Q2-U
-6
1 -1
1 -1
25
L2
200 in central terminal 10. Synchronization occurs by per40
-Q3-U
-6
1
1 -1 -1
25
L3
forming an acquisition mode function and a tracking mode
40
-Q4-U
-6
1 -1 -1
1
25
L4
function on downlink signal 212. Initially, transmitter 200 of
central terminal 10 transmits downlink signal 212. FIG. 12
In preferred embodiments, a 10 kbls acquisition mode is 25 shows the contents of downlink signal 212. A frame inforprovided which uses concatenated overlays to form an
mation signal 218 is combined with an overlay code 217
acquisition overlay; this is illustrated in table 3 below:
where appropriate, and the resultant signal 219 is combined
TABLE 3
Acquisition overlay

Equivalent high rate pattern

FIGS. 9A and 9B are diagrams illustrating the uplink and
with a code sequence signal 216 for central terminal 10 to
downlink delivery methods, respectively, when the system is
produce the downlink 212. Code sequence signal 216 is
fully loaded, and illustrate the difference between the use of 40 derived from a combination of a pseudo-random noise code
signal 220 and a Rademacher-Walsh code signal 222.
overlay codes illustrated in FIG. 9A and the use of TDM as
illustrated in FIG. 9B. When using overlay codes, an RW
Downlink signal 212 is received at receiver 202 of
code is split in the RW space domain to allow up to four sub
subscriber terminal 20. Receiver 202 compares its phase and
channels to operate at the same time. In contrast, when using
code sequence to a phase and code sequence within code
TDM, an RW code is split in the time domain, to allow up 45 sequence signal 216 of downlink signal 212. Central termito four signals to be sent using one RW code, but at different
nal 10 is considered to have a master code sequence and
times during the 125 us frame. As illustrated in FIGS. 9A
subscriber terminal 20 is considered to have a slave code
and
the last
RW codes, RW14 and
are
sequence. Receiver 202 incrementally adjusts the phase of
used for data tra£€ic in preferred embodiments, since they are
its slave code sequence to recognize a match to master code
reserved for call control and acquisition functions; this will so sequence and place receiver 202 of subscriber terminal 20 in
be discussed in more detail later.
phase with transmitter 200 of central terminal 10. The slave
The CDMAchannel hierarchy is as illustrated in FIG. 10.
code sequence of receiver 202 is not initially synchronized
Using this
the
CDMA
to the master code sequence of transmitter 200 and central
are possible:
terminal 10 due to the path delay between central terminal
F1
55 10 and subscriber terminal 20. This path delay is caused by
Hl+H2
the geographical separation between subscriber terminal 20
Hl+Q3+Q4
and central terminal 10 and other environmental and techH2+Ql+Q2
nical factors affecting wireless transmission.
Ql+Q2+Q3+Q4
After acquiring and initiating tracking on the central
Having discussed how the CDMA codes are enhanced to 60 terminal 10 master code sequence of code sequence signal
216 within downlink signal 212, receiver 202 enters a frame
enable flexible channelisations to be achieved, whereby the
bit rates can be lowered to enable more subscriber links to
alignment mode in order to establish the downlink commube managed per channel frequency, a general overview of
nication path. Receiver 202 analyzes frame information
how the downlink and uplink paths are established will be
within frame information signal 218 of downlink signal 212
provided with reference to FIGS. 11 and 12.
65 to identify a beginning of frame position for downlink signal
212. Since receiver 202 does not know at what point in the
FIG. 11 is a block diagram of downlink and uplink
data stream of downlink signal 212 it has received
communication paths between central terminal 10 and sub9B3

RW153

6,088,326

17

18

information, receiver 202 must search for the beginning of
munication paths and a path from the central terminal to the
frame position in order to be able to process information
subscriber terminal on which the communication protocol
received from transmitter 200 of central terminal 10. Once
which operates on the modem shelf between the shelf
receiver 202 has identified one further beginning of frame
controller and the modem cards also extends, The OMC/D
position, the downlink communication path has been estab- 5
is a
the OMC
and a
lished from transmitter 200 of central terminal 1 0 to receiver
signal (D), whilst the Ch.ID signal is used to uniquely
202 of subscriber terminal 20.
identify an RW channel, this Ch.ID signal being used by the
The structure of the radio frames of information sent over
the downlink and uplink paths will now be discussed with
subscriber terminal to ensure that the correct channel has
reference to FIGS. 13 and 14. In FIGS. 13 and 14, the lo been acquired,
following terms are used:
In preferred embodiments, the subscriber terminal will
Bn Customer payload, 1x32 to 2x64 Kbls
receive downlink traffic channel data at a rate of 160 kbls.
Dn Signalling Channel, 2 to 16 kbls
Depending on the B-channel rate, the ST will be allocated an
OH Radio Overhead Channel
appropriate share of the radio overhead. The following TDM
16 kbls Traffic Mode
mappings are created:
10 kbls AcquisitionlStandby Mode
TABLE 4
Rate Channel
(kbls) designation
160

-F1-D-TI11

80

-F1-D-T2I1

80

-F1-D-T212

40
40
40
40

-F1-D-T411
-F1-D-T412
-F1-D-T413
-F1-D-T414

Bearer

CS

PC

OMC

Overhead rate

B1, B2, B3, B4 CS1,
CS3
B1, B2
CS1,
CS3
B3, B4
CS2,
CS4
B1
CS1
B2
CS2
B3
CS3
B4
CS4

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

OMC1, OMC3

4 ms

OMC1, OMC3

4 ms

OMC2, OMC4

4 ms

OMCl
OMC2
OMC3
OMC4

8
8
8
8

ms
ms
ms
ms

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

h

~

6,088,326

19

20

As illustrated by RW5 to RW11, TDM can be used on the
(iii) In the event of a CT restart, invite STs to attempt
downlink traffic channels to enable more than one CT to ST
uplink warm start. A reduction in net entry time of a
communication to take place on the same RW channel
factor of 4 could be achieved. This mechanism would
during each frame. Further, as illustrated for RW3 and RW4,
need to be safeguarded against possible deterioration of
in preferred embodiments, certain channels can be locked to s
uplink warm start parameters-i.e. it should only be
limit interference from other nearby cells, as will be disallowed provided no CT RF related parameters have
cussed in more detail later.
been modified. The CT would need to broadcast an ID
Similar channelisations can be achieved for the uplink
to allow an ST to validate that the uplink warm start
paths, but as illustrated in FIG. 15B, overlay codes are used
parameters were valid for this CT.
instead of TDM to enable more than one ST to CT com- 10
(iv) ST restart-the CT will keep copies of the ST warm
munication to take place on the same RW channel during
start parameters so that a cold ST may have warm start
each frame (as shown in FIG. 15B for RW5 to RW11). It
parameters downloaded in the invitation to acquire and
should be noted that, in both FIGS. 15A and 15B, the
then be instructed to warm start.
channels RW14 and RW15 are reserved as a call control
Following Net Entry, all STs listen to the CCC, This
channel and an link acquisition channel, respectively, and 1s channel broadcasts management and call control informaoverlay codes are employed on these channels, irrespective
tion via a 32 kbIs HDLC channel, In order to maintain
of whether the path is a downlink or an uplink path. These
management communication, the CT polls each ST in
two channels will be discussed in more detail below.
sequence. Each poll comprises a broadcast invitation for an
Acquisitionlnet entry will take place via the Link Acquiaddressed ST to acquire the CCC Uplink followed by an
sition Chnnel (LAC). Following Power-up an ST will 20 exchange of management information (authentication, ST
automatically attempt downlink acquisition of the LAC on a
alarm update, warm start parameters, downlink radio perpre-determined 'home' RF channel. The LAC downlink
formance data etc,),
channel (eg. RW15 in preferred embodiments) will operate
A Management poll may fail for one of the following
at 10 kbls, full single user power. Downlink acquisition will
reasons:
be simultaneous for all STs.
25
(i) The ST is or has been powered down. An EM alarm
Each CT Modem Shelf will maintain a database holding
may be flagged if this persists and the database for that
the serial numbers of all STs that could possibly be supST should be marked cold. The Net Entry process will
ported by that CT. The state of each ST will recorded with
follow.
top level states as follows:
(ii) The ST is either making a call or in the process of
30
cold
making a call. The poll cycle may be suspended and
idle
management communications effected on the appropricallin_proogress
ate traffic channel.
When a Management Poll fails it should be followed up
Transition states will also be defined. An ST is considered
cold if the ST is newly provisioned, the CT has lost 35 by a number of faster polls until either the ST responds or
management communications with the ST or the CT has
lt IS marked cold. The CCC is required to transmit all copies
of the invitations to acquire the LAC SO that an ST can be
been power cycled, Over the LAC, the CT broadcasts
forced to acquire the LAC uplink.
individual ST serial numbers and offers an invitation to
Traffic Chnnel Uplink Acquisition Procedure
acquire the LAC uplink. Cold uplink acquisition will be
The basic acquisition Process from the ST side is as
carried out on the Link Acquisition Channel at low rate. The
CT will invite specific ST'S to cold start via the management 40 follows;
channel.
(i) Switch the downlink (receiver) circuitry to 10 kbls rate,
Assuming an uplink channel is available, the appropriate
and select the appropriate Traffic Channel RW and
acquisition overlay will be selected, and acquisition will be
Overlay codes. Acquisition of the TC downlink is
initiated.
45
limited to achieving frame alignment.
'Rapid' downlink RW channel switching may be SUP(ii) The downlink PCICS channel will be decoded to
ported at rates other than Ln-D. Rapid means that coherent
create a busylidle flag. If PCICS reports busy, then this
demodulation is maintained, and only convolutional decodmeans that another ST is using that traffic channel and
ing and frame synchronisation processes need be repeated.
the ST aborts the acquisition process.
On
management
be 50
(iii) Switch uplink to 10 kb/s rate, and select the approexchanged. The ST will be authenticated and allocated a
priate Traffic Channel RW and Overlay codes. Enable
short ST-identifier (between 12 and 16 bits) which will be
the ST transmitter at a level of nominal full rate power
used for subsequent addressing. The ST uplink will operate
minus 18 dB. While PCICS reports idle the ST will
for long enough for the uplink to be parametised by the ST
continue uplink fast codesearch, stepping the uplink
in terms of code phase and transmit power. These parameters 55
power level by +2 d~ at the end of each search, ~h~
will be used by the ST for subsequent warm start acquisiuplink should acquire at nominal full rate power minus
tions and will also be held by the CT to allow the CT to force
6 dB. Uplink acquisition is aborted if maximum transa cold ST to warm start. On successful completion of net
mit level is reached and PCICS continues to report idle.
entry, the ST will be placed in the idle state and instructed
reports busy, At this point the ST may have
(iv)
to cease
communications and move to the
60
genuinely acquired the traffic channel, or instead may
Control Channel (CCC) (RW14 in preferred embodiments).
be observing PCICS go busy because another ST has
The time taken for net entry to be achieved can be
acquired the traffic channel. The ST is sent an authenmonitored, and the following techniques can be used to
tication request and responds with it's ST-identifer.
decrease net entry time if desired:
The CT grants uplink access by returning the
6 ) Prioritise so that high GOS (Grade Of Service) users 65
ST-identifier. The ST aborts the acquisition process if
are offered net entry first.
the returned ST-identifier is not recognised (i.e. is not
the ST-identifer that it sent). This authentication pro(ii) Convert Traffic Channels to LACS.

6,088,326

21

22

cess arbitrates between two STs contending for outgo(vi) The ST may be unable to acquire a TC by the time the
call setup timer expires. The ST may in such cases
ing access and it also keeps STs from acquiring TCs
that have been reserved from incoming access.
cease attempting outgoing access and generate congesIncoming Call
tion tone.
A number of TCs will be reserved for incoming calls, and 5 Outgoing Priority Call
It is recognised that the random access protocol used to
incoming call processing is as follows:
setup normal outgoing calls could lead to blocking. In
(i) check the CT database-if the ST is in the c a l l p i n
preferred embodiments, access to a largely non-blocking
progress state the call is rejected.
Priority Traffic Channel will be allowed. Priority calling is
(ii) Check that an uplink TC of the required bandwidth is
complicated because the ST must:
available. If there is bandwidth then a TC is reserved. l o
(i) Capture and decode dialed digits.
(iii) An incoming call setup message is broadcast over the
(ii) Regenerate digits when a blocking condition occurs.
CCC to inform the addressed ST of the incoming call
(iii) Allow transparent network access in a non-blocking
and specify the TC on which to receive the call. If no
condition.
TC is available but the CT forms part of a Service
(iv) Categorise
as priority Or
Domain, then the incoming call setup message is sent 15
that normal calls are dropped in favor of priority calls.
with a null TC otherwise the call is rejected. Service
The priority call procedure in preferred embodiments is as
domains will be discussed in more detail later, The
follows:
incoming call setup message is repeated a number of
(i) The CT will publish Directory Numbers (DNs) for a
times.
of emergency services Over the CCC.
(iv) The ST attempts uplink acquisition. The ST listens to 20
(ii) The ST will attempt uplink access according to the
the downlink and keeps trying for uplink acquisition
normal algorithms. If the outgoing access is successful
until the CT sends a message to the ST to return the ST
then the customer is able to dial as normal. All dialed
to the CCC. The ST will also run a timer to return it
digits are check against the emergency DN list so that
back to the CCC in the event of an incoming call failing
25
calls may be categorised normal or priority at the CT.
to complete.
(iii) If congestion tone is returned the customer is allowed
(v) onsuccessful uplink acquisition, the CT authenticates
to dial the emergency number into the ST. If the ST
the ST.
detects an emergency DN sequence then uplink access
(vi) Rate switching is originated from the CT modem. A
via the Priority Traffic Channel (PTC) is attempted.
command is sent via the PCICS to switch the downlink
(iv) On PTC acquisition, the ST relays the dialed digit
to the required bandwidth, ~h~ ST returns the rate 30
sequence to the CT for dialling into the PSTN.
switch command via the uplink PCICS. The link is now
(iv) The CT converts the PTC to a TC and reallocates
of the reauired bandwidth.
another TC to become the PTC, dropping a normal call
Outgoing Call
in progress if necessary.
Outgoing calls are supported by allowing slotted random
access to the TC uplinks. The outgoing call processing is as 35 Interference Limiting (Pool Sizing)
Across a large scale deployment of cells, optimum capacfollows:
(i) ~h~ CT publishes a 'free list' of available ~ ~ ~ f ity isi achieved by minimising radio traffic while maintaining
f
~
an acceptable grade of service. Lowest possible radio traffic
channels and priority ~ ~ ~ channels with their
f f i ~
results in improved 'carrier to interference' (C/I) ratios for
respective bandwidths, m i s list is published periodically (in preferred embodiments, every 500 ms) and is 40 users within the cell of interest and to co-channel users in
nearby cells. The C/I ratio is a measure (usually expressed
used to mark uplink access slots.
in dB) of how high above interference the transmitted signal
(ii) An off-hook condition is detected by the ST, The ST
needs to be to be decoded effectively. In preferred
starts a call setup timer.
embodiments, the central terminal is provided with the
(iii) The ST waits for the next free list to be received over 45 ability to trade traffic for C/I, thereby allowing network
the CCC. If the Free list is empty the outgoing call is
planning to be carried out less rigidly. This feature can be
blocked. The ST will generate a congestion tone.
realised by a system using CDMA as in preferred embodi(iv) If the Free list has
the ST picks a
ments of the present invention, and is a benefit that CDMA
channel from the free list at random. The algorithm that
offers over TDMA and FDMA systems,
the ST
pick a
need be
so
In preferred embodiments, the CT will control the number
in the free list. For
the ST may be required to
of Traffic Channels to rninimise access noise, TCs will be
always choose from a pool of minimum bandwidth
classified as:
channels so that high bandwidth channels remain avail(i) Busydarrying traffic;
able for high GOS users. Alternatively the ST may be
( 4 Access, Incoming (Access-In)-reserved
for iKomallowed to choose any channel regardless of bandwidth 55
ing access;
for minimum blocking. In preferred embodiments, STs
(iii) Access, Outgoing (Access-Out)-reserved
for Outwill not choose low bandwidth channels and negotiate
going access-such TCs appear on the Free list;
the rate up.
(iv) Priority-reserved for priority outgoing access-such
(v) ~h~ ST attempts uplink acquisition on the specified
TCs appear in the Free list;
TC, this process having been described earlier. If 60
(v) Free-available for any Purpose; and
acquisition is successful then the outgoing call is pro(vi) Locked-not available due to interference limiting.
cessed. Otherwise the ST returns to the CCC and waits
This classification scheme is illustrated in FIG. 16. The
for the next available free list. To avoid a number of STs
CT will allocate traffic on the following basis:
repetitively attempting to acquire the same TC, and
(i) The CT will monitor incoming and outgoing call
blocking each other, a suitable protocol can be 65
setup-times and convert Access TCs from Free TCs in
employed to govern how individual STs will act upon
receipt of the free list.
order to achieve a required grade of service.

6,088,326

23

24

(ii) When a call is setup, an Access TC is converted to a
GOS estimates for incoming calls, and these GOS estimates
Busy TC. If a Free TC is available, it is converted to a
are passed over line 395 to the dynamic pool sizing function
new Access TC. If there are no Free TCs then the
360.
Access TC is lost until a call clears.
At set up, the management system 370 within the element
(iii) When a call clears the Busy TC is converted to a Free s manager will have connected to the central terminal, and
provided the dynamic pool sizing function 360 within the
TC. If a previous call setup resulted in a lost Access TC
modem shelf with data identifying a BER goal, a GOS goal,
then the Busy TC is converted back into an Access TC.
and a pool size limit (i.e. the number of channels that can be
(iv) when the PTC is accessed, a new PTC is created by
used for data traffic). The dynamic pool sizing function 360
converting a F ~A~~~~~ B~~~ (normal call) TC,
~ ~ ,
or
TC downlink and uplink l o then COmPares this data from the management system with
(v) he CT will monitor the
soft error counts in an attempt to establish link quality.
the
BER,
and the
pool size
If the CT records a lower than average soft error count
information that it receives. A suitable algorithm can be
and long call setup times are being recorded, a Locked
provided within the dynamic pool sizing function 360 to
TC may be converted to a Free TC, Conversely, if the
determine, based on this information, whether pool sizing is
CT records a higher than average soft error count, a ls appropriate. For example, if the actual bit error rate exceeds
the BER goal provided
the management system 370, then
Free or Access TC may be converted to a Locked TC,
the
pool sizing function 360 may be arranged to
FIG, 17 illustrates how the central terminal performs the
send a pool sizing request to the demand assignment engine
above interference limiting function, When incoming call
380.
data arrives at a central terminal modem 320, encoder 325
The demand assignment engine 380 provides modem
encodes the data for transmission over the wireless link 300 20
Over lines 400 to each Of the modems On the
to the subscriber terminal 20. At the subscriber terminal 20,
CT modem
If the
pool sizing function 360
the decoder 326 decodes the data, and passes the decoded
has requested that the DA engine 380 perform pool sizing,
user data over line 328 to the subscriber telecommunications
then the DA engine 380 can
One Or more Of the
equipment. As the decoder 326 decodes the data, it is able to
establish a bit error rate (BER) estimate 330 associated with 2s modems, this causing the interference, and hence the
BER, to be reduced.
from being
for interference
the signal transmission over the wireless link 300, which can
limiting, the DA engine is also responsible, in preferred
be passed to the multiplexer 332 for combining with other
embodiments, for providing the encoders 325 with instmcsignals, such as those from a call control function 336 or user
On which set Of Overlay 'Odes
Or how many TDM
data on line 338, before being passed to an encoder 334,
for
to be transmitted to the
20.
Here, the BER estimate is encoded and passed on the OMC 30 to be
The
pool sizing function can store the BER and
channel over the wireless link 310 to the decoder 340 within
GOS information received in the storage 365, and periodithe central terminal modem 320, Once decoded by the
c a l ' ~may pass that data to the management 'ystem 370 for
decoder 340, the signal passes to the multiplexer 345, where
analysis. Further, if the system is unable to attain the BER
the BER estimate from the subscriber terminal is detected
goal with the
pool size, the
pool
and passed over line 355 to the dynamic pool sizing function 35 Or
sizing function can be arranged to raise an alarm to the
360.
management system. The
Of this
indicate
Further, as at the subscriber terminal 20, the decoder 340
to personnel
the management 'ystem that
within the central terminal modem 320 is able to establish a
intervention may be required to
the situation, eg
bit error rate estimate 350 associated with the signal transthe provision of more central terminal hardware to support
mission over the wireless link 310, This BER estimate 350
the
is also passed over line 355 to the dynamic pool sizing
The CDMA
in preferred embodiments
function 360, The dynamic pool sizing function 360 is
exhibits the property that the removal of any of the orthogoprovided on the CT modem shelf 302, and receives BER
estimates from each of the modems on that shelf indicated
nal
the modem)
the
by the lines entering the bottom of the dynamic pool sizing 4s resistance of the other channels to interference. Hence, a
suitable approach for the demand assignment engine 380,
function 360.
In addition to BER estimates, grade of
(GOS) data
'POn
Of pool sizing request from the
pool
sizing function 360, is to disable the modem that has the
is obtained from two sources, Firstly, at each subscriber
least traffic passing through it.
terminal 20, the call control function 336 will note how
Switching
readily it is able to establish traffic channels for transmitting so RF
In preferred embodiments, it has been realised that if an
and receiving data, and from this can provide a GOS
ST is
to 'perate from
than One CT Modem
estimate to the multiplexer 332 for encoding by the encoder
then the
benefits may be rea334 for subsequent transmission over the wireless link 310
lised:
to the central terminal modem 320. Here, the GOS estimate
is decoded by decoder 340, passed through multiplexer 345, ss
(i)
a CT Modem
suband then the GOS estimate is passed over line 355 to the
system fault occur, an ST may switch to an alternative
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
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 60
(iii) Trafficload balancing-the Element Manager may on
over the concentrated network interface 390 to the DA
the basis of call blocking statistics choose to move STs
engine 380. The DA engine 380 includes a call control
between CT shelves.
function, similar to the call control function 336 in each of
the subscriber terminals 20, for each of the modems on the
(iv) Frequency diversity-in the presence of channel
modem shelf. Hence, in a similar fashion to the call control 65
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 able to provide
and lowest soft error count.

6,088,326

25

26

RF channel switching is only possible where there are two
typically switch to a different CT, since some errors expeor more co-located CT shelves serving the same geographirienced by one CT shelf may also affect other shelves within
cal area on different RF frequency channels within the same
the same CT, and so for fault tolerance (described in more
RF band. A deployment that meets this criterion may be
detail below), it is preferable for the ST to switch to a
configured as a 'Service Domain'. Possible deployment s separate CT.
Database consistency across CT shelves is preferably
scenarios are illustrated in FIG. 18. FIG. 18(i) shows an
arrangement where omni antennae are used to provide the
supported through the service domain controller 400. Database consistency needs to be real-time so that an ST entering
entire cell with four frequency channels, eg F1, F4, F7, F10.
the network is allowed full Service Domain access immeFIG. 18(ii) shows an arrangement where sectored antennae
are used to provide six separate sectors within a cell, each 10 diately (the Service Domain message is broadcast to all STs,
sector being covered by two frequency channels. FIG. 18(iii)
and so a new ST will expect access across the full Service
shows an alternative arrangement where three sectored
Domain).
antennae are used to divide the cell in to three sectors, each
Incoming access via backup CTs requires some function
sector being covered by a separate frequency channel, and
to be provided to broadcast duplicate incoming call setup
then an omni antenna is used to provide an 'umbrella' IS messages to all CTs that form a Service Domain. Preferably
coverage for the entire cell, this coverage employing a
this is handled by the service domain controller 400, which
frequency channel different to the three frequency channels
forwards incoming call setup messages to each CT operating
used by the sectored antennae.
in the service domain. All CTs will allocate A c c e s s l n
For the system to work effectively, the STs must be able
Traffic Channels and relay the incoming call setup message
to switch channels quickly, and fast channel switching 20 via the Call Control Channel. On successful uplink access,
necessitates that CT shelf synchronisation be provided at the
one CT will respond to the service domain controller with a
following levels:
call accepted message, the other CTs will eventually respond
(i) CDMA p~ code, m i s preserves uplink code phase
with call setup failed messages. Outgoing access via a
backup CT is similar to normal outgoing access.
across RF channels during warm start; and
/mother job which can be performed by the service
(ii) RF carrier frequency. This eliminates the need for the 25
domain controller is to assist the element manager 58 in
coarse frequency search on a downlink RF channel
reconfiguring equipment in the event of a fault. For example,
switch.
if one CT is taken out of commission because of a fault, a
On installation, an ST will be programmed with an RF
different CT can be
and the service
channel and PN code, these codes specifying the ST's initial
30 domain controller can provide that new CT with the neceshome channel.
sary information about the other CTs in the service domain.
The manner in which channel switching is facilitated in
FIG. 19B illustrates those elements of the subscriber
preferred embodiments will be described with reference to
terminal used to implement RF channel switching. The radio
FIGS, 19A and 19B, A service domain controller 400 is
preferably provided to act as an interface between the
420, which
the
and
processing stages,
pass any data
exchange connected to the service domain controller over 35
received on the call control channel over line 425 to the
path 405 and a number of central terminals
connected to
message decoder 430. If the decoder 430 determines that the
the
domain controller over paths 410, The central
data On the
forms a
domain
terminals connected to the service domain controller form a
message, then this is passed over line 435 to the channel
domain, of central terminals that may be used by a
40 selection controller 440, where the information within the
subscriber terminal 20 for handling communications,
Service domain message is stored in
445.
In preferred embodiments, the service domain controller
Similarly, if the message decoder identifies the data as a
400 is used to provide each CT
with appropriate infor'free list' identifying the available traffic channels on a
mation about the other CTs within the service domain, Each
particular RF frequency, then this data is passed to the call
CT can then broadcast a 'Service Domain, message
prising a list of RF frequencies and CT Identifiers that form 45 control function 336 and the channel selection controller 440
a Service Domain to be used by the STs for subsequent RF
over path 450. The call control function 336 stores the free
list in the
445 for subsequent
the
switching functions, The ST then stores this information for
function 336 and the channel selection controller 440.
future reference when establishing a link with one of the
If the message decoder 430 determines that the data forms
CTs, It is preferable for each CT to broadcast the service
domain message since an ST may be listening to any of the SO an incoming call setup message, then that information is
CTs at the time that the message is broadcast.
supplied over line 455 to the call control function 336 and
the channel selection controller 440 for processing. The
Each CT database will hold an entry for every ST located
within the Sewice Domain, Each database entry describes
incoming
setup message
a TC On
the current frequency channel which should be used to
how the CT views it,s relationship with the ST and may be
ss access the incoming call, and the channel selection controlmarked as:
ler will attempt to establish a link on that TC. The channel
service providerpthe CT is the ST's
selection controller will in such cases instmct the radio
channel.All managementcommunication with an ST is
sub-system 420 over line 465 to use the current frequency
via it's home CT.
channel to establish the required link. If, on the other hand,
6 ) Supplying backup service-the CT is providing ser- 60 the traffic channel specified in the call setup message is
vice to the ST.
'null', the channel selection controller has the option to
(iii) Available for backup service-the CT will provide
change RF frequency using the information stored in storage
445 about the other CTs in the service domain.
service to the ST if required.
It should be noted that the ST need not switch to an
To enable the channel selection controller 440 to receive
entirely different CT, but can instead switch to a different CT 65 information about the status of links, a link operating status
shelf (and hence different RF frequency channel) within the
signal can be supplied over line 470 from the radio subsame CT. However, in preferred embodiments, the ST will
system. This signal will give an indication of the radio link

6,088,326

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28

quality, and may be a simple 'OK' or 'failed' indication, or
alternatively may include extra information such as BER
values for the link. This information can be used by the
channel selection controller to determine whether a particular frequency channel should be used or not.
To enable the call control function to specify a specific
Access-Out channel for outgoing calls, a line 460 is provided between the call control function 336 and the channel
selection controller 440. The call control function 336 may
choose an access-out channel from the free list in storage
445, and instruct the channel selection controller over line
460 to attempt acquisition of that channel.
The following examples indicate how the above described
structure may be used to perform channel switching in
particular circumstances.
RF Channel Switching for Fault Tolerance
Should one RF channel suffer complete loss of downlink,
the following process takes place in preferred embodiments:
(i) The ST will attempt downlink re-acquisition for a
period of time, say 20 seconds.
(ii) If acquisition fails, the channel selection controller
440 of the ST will select the next available channel
from the service ~~~~i~ information in storage 445
and attempt downlink acquisition.
m i s process will be repeated until a downlink signal is
acquired.
(iii) Once a
RF
is located, the ST
'camp' on the Call Control Channel and may subsequently be granted traffic access.
(iv) If the CT fault persists, the EM 58 may use the service
domain controller 400 to reconfigure the Service
so that the
CT
primary service providers for the pool of 'homeless'
STs.
A fault that does not result in complete loss of downlink
signal will not result in RF channel switching 'en mass'.
Rather, a fault may result in excessive or total call blocking,
as discussed below.
RF Channel Switching for Call Blocking
If Incoming access traffic channels are being blocked, the
following process is employed in preferred embodiments:
(i) The call setup message sent over the Call Control
Channel will specify a TC on which to access the call.
(ii) In the case of incoming access being blocked, the CT
will specify a null TC. The channel selection controller
440 of the ST
in
cases switch to the next RF
channel from the Service Domain information in storage 445 and monitor the Call Control Channel.
(iii) If the ST receives a call setup message with a valid
TC, then the call is processed as normal.
(iv) When the call clears, the ST downlink preferably
switches back to the home CT.
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 be used to switch the
ST to the next RF channel in the Service Domain,
whereupon the ST will wait for 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.

(iv) When the call clears, the ST downlink preferably
switches back to the home CT.
RF Channel Switching for Traffic Load Balancing
Traffic load balancing is, in preferred embodiments, provided by static configuration via the EM 58. Call blocking
and setup time statistics may be forwarded to the EM where
an operator may decide to move an ST to another RF
channel.
RF Channel Switching for Frequency Diversity
Frequency diversity is, in preferred embodiments, provided by static configuration via the EM 58. Radio link
statistics may be forwarded to the EM where an operator
may decide to move an ST to another RF channel.
Although a particular embodiment has been described
herein, it will be appreciated that the invention is not limited
thereto and that many modifications and additions thereto
may be made within the scope of the invention. For example,
various combinations of the features of the following dependent claims could be made with the features of the independent claims without departing from the scope of the present
invention.
What is claimed is:
1.A transmission controller for processing data items to
be transmitted over a wireless link connecting a central
terminal and a subscriber terminal of a wireless telecommunications system, a single frequency channel being
employed for transmitting data items pertaining to a plurality of wireless links, the transmission controller comprising:
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;
a first encoder for combining a data item to be transmitted
on the single frequency channel with said orthogonal
code from the orthogonal code generator, the orthogonal code determining the orthogonal channel over
which the data item is transmitted, whereby data items
pertaining to different wireless links may be transmitted
simultaneously within different orthogonal channels of
said single frequency channel; and
a TDM encoder arranged to apply time division multiplexing (TDM) techniques to the data item in order to
insert the data item within a time slot of the orthogonal
channel, whereby a plurality of data items relating to
different wireless links may be transmitted within the
same orthogonal channel during a predetermined frame
period.
2. A transmission controller as claimed in claim 1,further
comprising:
an overlay code generator for providing an overlay code
from a first set of 'n' overlay codes which are orthogonal to each other; and
a second encoder, selectively operable instead of the TDM
encoder, to apply the overlay code from the overlay
code generator to said data item, whereby 'n' data items
pertaining to different wireless links may be transmitted
simultaneously within the same orthogonal channel.
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 set of orthogonal codes comprise a set of
Rademacher-Walsh (RW) codes.
5. 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
channel;

5

10

20

25

30

35

40

45

so

55

60

65

a first encoder for combining a data item to be transmitted
code from the orthogonal code generator, the orthogoon the single frequency channel with said orthogonal
nal code determining the orthogonal channel over
code from the orthogonal code generator, the orthogowhich the data item is transmitted, whereby data items
nal code determining the orthogonal channel over
pertaining to different wireless links may be transmitted
which the data item is transmitted, whereby data items 5
simultaneously within different orthogonal channels of
pertaining to different wireless links may be transmitted
said single frequency channel; and
simultaneously within different orthogonal channels of
a TDM encoder arranged to apply time division multisaid single frequency channel;
plexing (TDM) techniques to the data item in order to
a TDM encoder arranged to apply time division multiinsert the data item within a time slot of the orthogonal
plexing (TDM) techniques to the data item in order to lo
channel, whereby a plurality of data items relating to
insert the data item within a time slot of the orthogonal
different wireless links may be transmitted within the
channel, whereby a plurality of data items relating to
same orthogonal channel during a predetermined frame
different wireless links may be transmitted within the
period;
same orthogonal channel during a predetermined frame
period;
an overlay code generator for providing an overlay code
15
from a first set of 'n' overlay codes which are orthogoan overlay code generator for providing an overlay code
nal to each other;
from a first set of 'n' overlay codes which are orthogonal to each other;
a second encoder, selectively operable instead of the TDM
a second encoder, selectively operable instead of the TDM
encoder, to apply the overlay code from the overlay
encoder, to apply the overlay code from the overlay
code generator to said data item, whereby 'n' data items
code generator to said data item, whereby 'n' data items 20
pertaining to different wireless links may be transmitted
pertaining to different wireless links may be transmitted
simultaneously within the same orthogonal channel,
simultaneously within the same orthogonal channel,
wherein the orthogonal code generator is a storage
wherein the orthogonal code generator is a storage
arranged to store the set of orthogonal codes and
arranged to store the set of orthogonal codes and
wherein the set of orthogonal codes comprise a set of
wherein the set of orthogonal codes comprise a set of 25
Rademacher-Walsh (RW) codes;
Rademacher-Walsh (RW) codes.
and wherein at least one subscriber terminal comprises a
6. A central terminal as claimed in claim 5, further
reception controller having:
comprising channelisation means for determining which of
an orthogonal code generator for providing an orthogothe orthogonal channels will be subject to TDM techniques,
nal code from a set of 'm' orthogonal codes used to
and for transmitting that information to a plurality of sub- 30
create said 'm' orthogonal channels within the single
scriber terminals within the wireless telecommunications
frequency channel;
system.
7. A central terminal as claimed in claim 6, wherein the
a first decoder for applying, to signals received on
the single frequency channel, the orthogonal code
channelisation means also determines, for those orthogonal
provided by the orthogonal code generator, in
channels subject to TDM techniques, how many time slots 35
order to isolate data items transmitted within the
will be provided within each orthogonal channel.
8. A central terminal as claimed in claim 7, wherein a
corresponding orthogonal channel; and
number of said orthogonal channels are designated as traffic
a TDM decoder arranged to extract a data item from a
channels for the transmission of data items relating to
predetermined time slot within said orthogonal
communication content, and the TDM encoder is employed 40
channel, a plurality of data items relating to different
to apply time division multiplexing (TDM) techniques to
wireless links being transmitted within the same
data items to be sent over a traffic channel from said central
orthogonal channel during a predetermined frame
terminal to said subscriber terminal.
period;
9. A central terminal as claimed in claim 5, wherein a first
an overlay code generator for providing an overlay
of the orthogonal channels is reserved for the transmission 45
code from a first set of 'n' overlay codes which are
of signals relating to the acquisition of wireless links, and
orthogonal to each other, the set of 'n' overlay codes
the second encoder is used instead of the TDM encoder to
enabling 'n' data items pertaining to different wireenable overlay codes to be applied to data items to be sent
less links to be transmitted simultaneously within the
within said first orthogonal channel from the central terminal
same orthogonal channel;
to one of said subscriber terminals.
a second decoder, selectively operable instead of the
SO
10. A central terminal as claimed in claim 5, wherein a
TDM decoder, to apply to the data items of the
second of the orthogonal channels is reserved for the transorthogonal channel, the overlay code from the overmission of signals relating to the control of calls, and the
lay code generator so as to isolate a particular data
second encoder is used instead of the TDM encoder to
item transmitted using that overlay code, wherein the
enable overlay codes to be applied to data items to be sent 55
orthogonal code generator is a storage arranged to
within said second orthogonal channel from the central
store the set of orthogonal codes and wherein the set
terminal to one of said subscriber terminals.
of orthogonal codes comprise a set of Rademacher1 .A wireless telecommunications system comprising a
1
Walsh (RW) codes.
central terminal and a plurality of subscriber terminals,
12. A method of processing data items to be transmitted
wherein the central terminal comprises a transmission con- 60 over a wireless link connecting a central terminal and a
troller having:
subscriber terminal of a wireless telecommunications
system, a single frequency channel being employed for
an orthogonal code generator for providing an orthogonal
transmitting data items pertaining to a plurality of wireless
code from a set of 'm' orthogonal codes used to create
links, the method comprising steps of:
'm' orthogonal channels within the single frequency
65
channel;
providing an orthogonal code from a set of 'm' orthogonal
a first encoder for combining a data item to be transmitted
codes used to create 'm' orthogonal channels within the
on the single frequency channel with said orthogonal
single frequency channel;

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combining a data item to be transmitted on the single
frequency channel with said orthogonal code, the
orthogonal code determining the orthogonal channel
over which the data item is transmitted, whereby data
items pertaining to different wireless links may be
transmitted simultaneously within different orthogonal
channels of said single frequency channel; and
applying time division multiplexing (TDM) techniques to
the data item in order to insert the data item within a
time slot of the orthogonal channel, whereby a plurality
of data items relating to different wireless links may be
transmitted within the same orthogonal channel during
a predetermined frame period.
13. A method as claimed in claim 12, wherein said
applying step is selectively replaced by steps of:
providing an overlay code from a first set of 'n' overlay
codes which are orthogonal to each other; and

applying the overlay code to said data item, whereby 'n'
data items pertaining to different wireless links may be
transmitted simultaneously within the same orthogonal
channel.
14. A method as claimed in claim 12, further comprising
StepS of:
determining which of the orthogonal channels will be
subject to TDM techniques; and
transmitting that information to a plurality of subscriber
terminals within the wireless telecommunications system.
15, A method as claimed in claim 14, further comprising
a step of:
determining, for those orthogonal channels subject to
TDM techniques, how many time slots will be provided
within each orthogonal channel.

10

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