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 B

US006222819Bl

United States Patent

(10)

Lysejko et al.

(12)

(45)

(54) PROCESSING DATA TRANSMITTED AND
RECEIVED OVER A WIRELESS LINK
CONNECTING A CENTRAL TERMINAL AND
A SUBSCRIBER TERMINAL OF A WIRELESS
TELECOMMUNICATIONS SYSTEM
(75) Inventors: Martin Lysejko, Bagshot (GB); Paul F.
Struhsaker, Plano, TX (US)
(73) Assignee: Airspan Networks, Inc., Seattle, WA
(US)

( * ) Notice:

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

(21) Appl. No.: 081978,970

Nov. 26, 1997

(22) Filed:

Foreign Application Priority Data
Dec. 20, 1996 (GB) .................................................. 9626566

(30)

(51) Int. CL7 ...................................................... H04J 11/00
(52) U.S. C1. ........................................ 3701209; 3701342
(58) Field of Search ..................................... 3701203, 208,
3701209, 320, 335, 342, 343, 441, 479;
3751130, 146, 147

References Cited

(56)

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

*
*
*

1211994
511995
611998
811998
911999

Turban ................................... 370118
Zehavi ................................. 3751200
Natali et al. ......................... 3701320
Rakib et al. ......................... 3701342
Allpress et al. ..................... 3701480

FOREIGN PATENT DOCUMENTS
0633676
0652650
0730356

111995 (EP)
511995 (EP)
911996 (EP)

............................... H04Jl13100
................................ H04Bl7126
................................ H04Ll1100

Patent NO.:
US 6,222,819 ~1
Date of Patent:
Apr. 24,2001

2267627
2301744
9314588
9503652
9637066

1211993
1211996
711993
211995
1111996

(GB)
(GB)
(WO)
(WO)
(WO)

............................... H04Bl7100
............................... H04Ql7132
.
.............................. H04Bl7126
............................ H04Ll27130

* cited by examiner
Primary Examiner-Wellington Chin
Assistant ExaminerXwang B. Yao
(74) Attorney, Agent, or F i r m a a k e r Botts L.L.P

ABSTRACT

(57)

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 an overlay code generator
for providing an overlay code from a first set of 'n' overlay
codes which are orthogonal to each other, and a second
encoder arranged to apply the overlay code from the overlay
code generator to said data item, whereby 'n', data items
pertaining to different wireless links may be transmitted
simultaneously within the same orthogonal channel. The
invention also provides a reception controller and method
for processing data items received over a wireless link.
32 Claims, 16 Drawing Sheets

OVERLAY COOF

-

JAl
.-

4 Hh
m
HYBRID

COOEC

ENCODER

2 WIRE
/
NF

/

/

GENERATOR

TX
ANTENNA

140

138

{

142J+t0H
BPF

PA

136

134

132

130

H H nH
a
J

AE;~ a

BPF

120

@
MIXER

I-DUMTORH

t

I
LPF

U.S. Patent

Apr. 24,2001

Sheet 1 of 16

US 6,222,819 B1

U.S. Patent

Apr. 24,2001

Sheet 2 of 16

FIG. 3

1
I
I
I
I
I
I

55

I
I
I
I

I
I
I
I
I
I
I

L-,,----,--,,-,-------,--J

U.S. Patent

Apr. 24,2001

Sheet 3 of 16

US 6,222,819 B1

U.S. Patent

Apr. 24,2001

Sheet 4 of 16

FIG. 5 A

U.S. Patent

Apr. 24,2001

Sheet 5 of 16

U.S. Patent

Apr. 24,2001

Sheet 6 of 16

U.S. Patent

Apr. 24,2001

Sheet 7 of 16

U.S. Patent

Sheet 8 of 16

Apr. 24,2001

I

F

a3
-

U.S. Patent

Apr. 24,2001

Sheet 9 of 16

CDMA R SPACE ---,
W
RW1

RW2

RW3

RW4

RW5

RW6

RW7

RW8

RW9

RWlO

RW11

RW12

RW13

RW14

RW15

u

TlME

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

1

1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1

1

\

\

4Okb/s

10kb/s

FIG. 9A

A

125.00~s

10kb/s

CDMA RW SPACE ---,
RWI
RW2
RW3
RW4
RW5
RW6
RW7
RW8
RW9
RWlO RW11 RW12
RW13
RWl4
TIME F1-T4/1 F1-T4/1 F1-T4/1 F1-T4/1 F1-T4/1 F1-T4/1 F1-T4/1 F1-T4/1 F1-~4/1 F1-T4/1 F1-T4/1 F1-T4/1 F1-~4/1
F l -T4/2 F1-T4/2 F1-T4/2 F1-T4/2 F1-T4/2 21 -T4/2 F l - ~ 4 / 2 F l -T4/2 F l -T4/2 F1-T4/2 FI -T4/2 F1-T4/2 F1-T4/2
F1-T4/3 F1-T4/3

F1 -T4/3 F1-T4/3 F1-T4/3 31-TI13 FI -~413

RW15
31.25~s

Q

L

F1-T4/3 F1-T4/3 F l -T4/3 F1-T4/3 31 - ~ 4 / 3 F1-T4/3 1

1

93.75~~

F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-~4/4 F1-T4/4 ~1-T4/4 F1-T4/4 F1-T4/4

J

FIG. 9B

62.50~s

J

125.0011s

U.S. Patent

Apr. 24,2001

US 6,222,819 B1

Sheet 11 of 16

FIG. I0

UPLINK
USER 2

I SUBSCRIBER TERMINAL I

CENTRAL TERMINAL

FIG. I I

CODE SEQUENCE

PN CODE

I

R/W
CODE

CODE
OVERLAY

FIG. I2

-7-3
FRAME
INFORMATION

DOWNLINK

210

US. Patent

Sheet 12 of 16

Apr. 24,2001

I

1oous

FIG. 1 3 A

I

1oous

FIG. 13B

FAW

PC

CS

FAW

OMC

CS

CH.ID

PC

CH.ID

FAW

CS 1

PC1

OMC1

CH.ID

CS2

PC2

OMC2

FAW

CS3

PC3

OMC3

CHAD*

CS4

PC4

OMC4

FIG. 1 4 A

1
I

U.S. Patent

Sheet 13 of 16

Apr. 24,2001

FAW

CS

D

D

PC

FAW

PC

OMC/O

FAW
FAW

CS
CS

PC

OMC

PC

CS

OMC

CH.ID

I

UNUSED UNUSED UNUSED

I

Oms

FIG. 14B

TOTAL TRAFFIC CHANNEL POOL
INTERFERENCE LIMITED TRAFFIC CHANNEL POOL

*
LTC

FTC
LTC
FTC
AOTC
AITC
BTC
PTC

AOTC

AITC

BTC

= LOCKED TRAFFIC CHANNEL
= FREE TRAFFIC CHANNEL

= ACCESS OUTGOING TRAFFIC CHANNEL
= ACCESS INCOMING TRAFFIC CHANNEL

= BUSY TRAFFIC CHANNEL
= PRIORITY TRAFFIC CHANNEL

FIG. 16

e

PTC

LOCKED CHANNELS
TURNED OFF

RW1

RW2

TIME

RW3

RW4

RW5

COMA RW SPACE +
RW6

FIXED ASSIGNMENT
LINKS, 16Okb/s

RW7

RW8

RW9

RWlO

RW11

RW12

RW14

RW15

RW14

RW13

RW15

FIG. 7 5 A
CDMA RW SPACE +

RWI

RW2

RW3

RW4

RW5

RW6

RW7

RW8

RW9

RWlO

RWII

RW12

H H

F1

RW13

TIME

F1

F1

FIXED ASSIGNMENT
LINKS, 160kb/s

Q
1

QQQ
412

FREE Ln SLOTS AVAILABLE
FOR UPLINK ACQUISITION

QQLQ
4123

H

1

Q H QQ H
4 1 3 4 1

A E E L SLOTS AVAILABCE s8
;
b
/;
FOR UPLINK ACQUISITION

UPLINK ACQUISITION,
10kb/s

1

2

160kb/s

L
1

L
I

bl
s
;
/

PRIORITY UPLINK
ACQUISITION, 10kb/s

L
1

12b/s

U.S. Patent

Apr. 24,2001

Sheet 15 of 16

U.S. Patent

Apr. 24,2001

US 6,222,819 B1

Sheet 16 of 16

FIG. 78

405

CONTROLLER

FIG. 7 9 A

RADIO
SUBSYSTEM

425 \
'
I

MESSAGE
DECODER

I

430

I

f

CHANNEL
SELECTION
CONTROLLER

t

A

465

A

A

435
r/

+

6

A

460

=

4 L 450

FIG. 19B

:

CALL
CONTROL

336

US 6,222,819 B1

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; an
terminal to the subscriber terminal.
overlay code generator for providing an overlay code from
Due to bandwidth constraints, it is not practical for each 25 a first set of 'n' overlay codes which are orthogonal to each
other; and a second encoder arranged to apply the overlay
individual subscriber terminal to have its own dedicated
code from the overlay code generator to said data item,
frequency channel for communicating with the central terwhereby 'n' data items pertaining to different wireless links
rninal, Hence, techniques need to be applied to enable data
may be transmitted simultaneously within the same orthogoitems relating to different wireless links to be passed over the
same frequency channel without interfering with each other. 30 nal channel.
In current wireless telecommunications systems, this can be
Viewed from a second aspect, the present invention
achieved through the use of a 'Code Division Multiple
provides a reception controller for processing data items
Access' (CDMA) technique. One way to implement CDMA
received over a wireless link connecting a central terminal
is through the application of a set of orthogonal codes to the 35 and a subscriber terminal of a wireless telecommunications
data items to be transmitted on a particular frequency
system, a single frequency channel being employed for
channel, data items relating to different wireless links being
transmitting data items pertaining to a plurality of wireless
combined with different orthogonal codes from the set. A
links, the receiver controller comprising: an orthogonal code
suitable set of orthogonal codes is a "Rademacher-Walsh
generator for providing an orthogonal code from a set of 'm'
(RW) set of sixteen 16-bit codes. Orthogonal codes have the 40 orthogonal codes used to create 'm' orthogonal channels
property that, when perfectly aligned, all codes crosswithin the single frequency channel; a first decoder for
correlate to zero, thus making it possible to decode a signal
applying, to signals received on the single frequency
to which one orthogonal code has been applied while
channel, the orthogonal code provided by the orthogonal
cancelling interference from signals to which different
code generator, in order to isolate data items transmitted
orthogonal codes have been applied.
45 within the corresponding orthogonal channel; an overlay
Signals to which an orthogonal code has been applied can
code generator for providing an overlay code from a first set
of 'n' overlay codes which are orthogonal to each other, the
be considered as being transmitted over a corresponding
orthogonal channel within a particular frequency channel.
set of 'n' overlay codes enabling 'n' data items pertaining to
Hence, considering the example of a set of 16 RW codes, 16
different wireless links to be transmitted simultaneously
orthogonal channels can be created within a single frewithin the same orthogonal channel; and a second decoder
for applying, to the data items of the orthogonal channel, the
quency channel, and hence up to sixteen separate commuoverlay code from the overlay code generator so as to isolate
nication signals (corresponding to sixteen separate wireless
a particular data item transmitted using that overlay code.
links) can be transmitted simultaneously over the single
frequency channel if different RW codes are applied to each
By using overlay codes in addition to the known set of
communication signal.
55 orthogonal codes, it is possible for selected orthogonal
channels to be subdivided to form additional orthogonal
It is known to provide a number of modem shelves within
channels. For example, if there are originally sixteen
one central terminal, and for each modem shelf to employ a
orthogonal channels and a set of four overlay codes are
different frequency channel. Hence, if a central terminal has
defined, each orthogonal channel being subject to overlay
four modem shelves, and the set of 16 RW codes is
employed for each frequency channel, one central terminal 60 codes, then up to 64 orthogonal channels can be defined. By
would be able to support wireless links with up to 60
application of appropriate orthogonal codes and overlay
codes, up to 64 separate communication signals could be
subscriber terminals simultaneously.
sent simultaneously on the one frequency channel, albeit at
However, as more subscribers subscribe to the wireless
a quarter of the rate that the communication signals could be
telecommunications network, it is becoming desirable to
support more and more subscriber terminals from each 65 transmitted if the overlay codes were not used.
central terminal. There are only a limited number of freSuch an approach has the advantage that it preserves
quency channels that can be allocated to the wireless telecompatibility with current hardware and software equipment
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

US 6,222,819 B1

3

4

which use the set of orthogonal codes, but which do not
reception controller in accordance with the present invensupport the use of overlay codes. By designating certain
tion. Further, the central terminal preferably includes chanorthogonal channels as channels for which overlay codes are
nelisation means for determining which of the orthogonal
not used, the current equipment can communicate over those
channels will be subject to overlay codes, and for transmitchannels without any changes being required to the equip- s ting that information to a plurality of subscriber terminals
ment.
within the telecommunications system. This is useful since,
In preferred embodiments, the overlay code generator is
for example, certain orthogonal channels can hence be
arranged to store one or more further sets of overlay codes
designated as being reserved for communications with ST^
having different numbers of overlay codes to the first set of
that do not incorporate the features necessary to support
overlay codes. This enables the orthogonal channels to be lo overlay codes, and which hence require a full 160 kbls
subdivided differently, depending on which set of overlay
orthogonal channel,
codes is selected. For instance, if an orthogonal channel
1" preferred embodiments, the channelisation means also
operates at 160 kbIs, and a set of four overlay codes is used
determines, for those orthogonal channels subject to overlay
to subdivide that orthogonal channel, then four 40 kbls
codes, which set of overlay codes will apply to each
orthogonal channels can be created from the one original
orthogonal channel. If, alternatively, a set of two overlay lS orthogonal channel. This gives a great deal of flexibility in
codes is used, then two 80 kb/s orthogonal channels can be
how the channels are used, since some can be subdivided
created from the one orthogonal channel, hi^ flexibility is
whilst others are not, and those which are subdivided can be
since for some communications, eg, fax, a rate of 40
subdivided differently to yield differing numbers of differing
kbls may not be acceptable, and hence a set of four overlay
rate channels.
20
codes would not be suitable.
As with the central terminal, a subscriber terminal of the
wireless telecommunications system may comprise a transThe orthogonal code generator and overlay code generamission controller andlor a reception controller in accortor may generate orthogonal codes and overlay codes 'on the
dance with the present invention. Unlike the central
fly' using predetermined algorithms. However, alternatively,
terminal, it is preferable for the subscriber terminal to use
the orthogonal code generator may be provided as a storage
arranged to store the set of orthogonal codes, and the overlay 2s overlay codes for all types of channels, whether they be
code generator may be provided as a storage arranged to
traffic channels or otherwise. On these uplink traffic
store the set of overlay codes. Appropriate orthogonal codes
channels, the pure CDMA approach using overlay codes
and overlay codes could then be read out to the encoders or
eliminates the need to time synchronise STs to a TDM frame
reference, and reduces the peak power handling requiredecoders as required.
In preferred embodiments, the set of orthogonal codes 30 ments in the ST RF transmit chain.
comprise a set of Rademacher-Walsh (RW) codes, in preViewed from a third aspect, the present invention provides
ferred embodiments the set comprising a 16x16 matrix of
a wireless telecommunications system comprising a central
RW codes. Further, the set of overlay codes are preferably
terminal and a plurality of subscriber terminals, wherein the
derived from RW codes, each set of 'n' overlay codes 3s central terminal comprises a transmission controller in
preferably comprising an nxn matrix of RW codes.
accordance with the present invention, and at least one of the
The transmission controller in accordance with the
subscriber terminal comprises a reception controller in
present invention may be provided within the central termiaccordance with the present invention. Alternatively, or
rial of a wireless telecommunications system. In preferred
additionally, within the wireless telecommunications
embodiments, a first of the orthogonal channels is reserved 40 system, at least one of the subscriber terminals may comprise a transmission controller in accordance with the
for the transmission of signals relating to the acquisition of
present invention, and the central terminal may comprise a
wireless links, and the transmission controller is provided in
reception controller in accordance with the present inventhe central terminal to enable overlay codes to be applied to
tion.
data items to be sent within said first orthogonal channel
from the central terminal to one of said subscriber terminals. 4s
Viewed from a fourth aspect, the present invention proSimilarly, a second of the orthogonal channels is preferably
vides a method of processing data items to be transmitted
reserved for the transmission of signals relating to the
over a wireless link connecting a central terminal and a
control of calls, and the transmission controller in the central
subscriber terminal of a wireless telecommunications
terminal also enables overlay codes to be applied to data
system, a single frequency channel being employed for
items to be sent within said second orthogonal channel from
transmitting data items pertaining to a plurality of wireless
the central terminal to one of said subscriber terminals.
links, the method comprising the steps of: providing an
However, a number of said orthogonal channels are
orthogonal code from a set of 'm' orthogonal codes used to
designated as traffic channels for the transmission of data
create 'm' orthogonal channels within the single frequency
items relating to communication content, and in preferred
channel; combining a data item to be transmitted on the
embodiments a TDM encoder is provided within the central 5s single frequency channel with said orthogonal code, the
terminal arranged to apply time division multiplexing
orthogonal code determining the orthogonal channel over
(TDM) techniques to data items to be sent over a traffic
which the data item is transmitted, whereby data items
channel from said central terminal to said subscriber
pertaining to different wireless links may be transmitted
terminal, so as to enable a plurality of data items pertaining
simultaneously within different orthogonal channels of said
to different wireless links to be sent within one orthogonal 60 single frequency channel; providing an overlay code from a
traffic channel during a predetermined frame period.
first set of 'n' overlay codes which are orthogonal to each
other; and applying the overlay code to said data item,
The use of a CDMNTDM hybrid approach for downlink
whereby 'n' data items pertaining to different wireless links
traffic channels retains the benefits of CDMA access, ie.
may be transmitted simultaneously within the same orthogointerference is reduced when traffic is reduced, and also
65 nal channel.
reduces receiver dynamic range requirements.
In addition to, or as an alternative to, having a transmisViewed from a fifth aspect, the present invention provides
sion controller, the central terminal may also comprise a
a method of processing data items received over a wireless

US 6,222,819 B1
5

6

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: providing an orthogonal code from a set of 'm'
orthogonal codes used to create 'm' orthogonal channels
within the sing1e
to
received On the sing1e
the
code in order to isolate data items transmitted within the
corresponding orthogonal channel; 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 applying, to the data items of the orthogonal channel, the
overlay code so as to isolate a particular data item transmitted using that overlay code.
By using overlay codes in addition to the known set of
orthogonal codes, it is possible for selected orthogonal
channels to be subdivided to form additional orthogonal
channels, thereby making it possible to support more wireless links on one frequency channel.

FIGS. 14A and 14B illustrate the overhead frame structure for the downlink and uplink paths;
FIGS, 1 5 ~ 1513 illustrate typical downlink and uplink
~ ~ d
channel structures that might occur in a loaded system in
accordance with preferred embodiments of the present
invention;
FIG, 16 illustrates how the available trafic channels are
classified in preferred embodiments of the present invention;

5

10

IS

20

BRIEF DESCRIPTION OF THE INVENTION
An embodiment of the invention will be described
hereinafter, by way of example only, with reference to the
drawings in which like reference signs are
used for like features and in which:
FIG. 1 is a schematic overview of an example of a
wireless telecommunications system in which an example of
the present invention is included;
FIG. 2 is a schematic illustration of an example of a
subscriber terminal of the telecommunications system of
FIG. 1;
FIG. 3 is a schematic illustration of an example of a
central terminal of the telecommunications system of FIG.
1;
FIG, 3A is a schematic illustration of a modem
of a
central terminal of the telecommunications system of FIG,
1;
FIG, 4 is an illustration of an example of a frequency plan
for the telecommunications system of FIG. 1;
FIGS. 5A and 5B are schematic diagrams illustrating
possible configurations for cells for the telecommunications
system of FIG. 1;
FIG. 6 is a schematic diagram illustrating aspects of a
code division multiplex system for the telecommunications
system of FIG. 1;
FIGS. 7A and 7B are schematic diagrams illustrating
signal transmission processing stages for the telecommunications system of FIG. 1;
and 8B are schematic diagrams
signal reception processing stages for the telecommunications system of FIG. 1;
FIGS. 9A and 9B are diagrams illustrating the uplink and
downlink delivery methods when the system is fully loaded;
FIG. 10 illustrates the CDMA channel hierarchy in accordance with preferred embodiments of the Present invention;
FIG. 1 is a schematic diagram illustrating downlink and
1
uplink communication paths for the wireless telecommunications system;
FIG. 12 is a schematic diagram illustrating the makeup of
a downlink signal transmitted by the central terminal;
FIGS. 13A and 13B illustrate the structure of the frames
of information sent over the downlink and uplink paths;

25

30

35

40

45

55

60

65

l7
the
used by the
to perform interference limiting;
FIG. 18 illustrates possible antenna configurations that
can be employed in a wireless telecommunications system in
accordance with the preferred embodiment of the Present
invention; and
FIGS. 19A and 19B illustrate how channel switching is
facilitated in preferred embodiments of the present invention.
DETAILED DESCRIPTION OF THE
INVENTION
FIG. 1 is a schematic overview of an example of a
wireless telecommunications system. The telecommunications system includes one or more service areas 12,14 and
16, each of which is served by a respective central terminal
(CT) 10 which establishes a radio link with subscriber
terminals (ST) 20 within the area concerned. The area which
is covered by a central terminal 10 can vary. For example,
in a rural area with a low density of subscribers, a service
area 12 could cover an area with a radius of 15-20 k.
A
service area 14 in an urban environment where is there is a
high density of subscriber terminals 20 might only cover an
area with a radius of the order of 100 m. In a suburban area
with an intermediate density of subscriber terminals, a
service area 16 might cover an area with a radius of the order
of 1 k. will be appreciated that the area covered by a
It
particular central terminal 10 can be chosen to suit the local
requirements of expected or actual subscriber density, local
geographic considerations, etc, and is not limited to the
examples illustrated in FIG. 1. Moreover, the coverage need
not be
in extent due to
"Ot be, and
antenna design considerations, geographical factors, buildings and so on, which will affect the distribution of transmitted signals,
The central terminals 10 for respective service areas 12,
14,16 can be connected to each other by means of links 13,
and 17 which interface, for example, with a public
switched telephone network (PSTN) 18. The links can
include conventional telecommunications technology using
copper wires, optical fibres, satellites, microwaves, etc.
The wireless telecommunications system of FIG. 1 is
based on providing fixed microwave links between subscriber terminals 20 at fixed locations within a
area
(e.g., 12,14,16) and the central terminal 10 for that service
area. Each subscriber terminal 20 can be provided with a
permanent fixed access link to its central terminal 10, but in
preferred embodiments demand-based access is provided, so
that the number of subscribers which can be supported
exceeds the number of available wireless links. The manner
in which demand-based access is implemented will be
discussed in detail later.
FIG. 2 illustrates an example of a configuration for a
subscriber terminal 20 for the telecommunications system of
FIG. 1. FIG. 2 includes a schematic representation of
customer premises 22. A customer radio unit (CRU) 24 is
mounted on the customer's premises. The customer radio

US 6,222,819 B1

7

8

unit 24 includes a flat panel antenna or the like 23. The
As an alternative to the RS232 connections 55, which
customer radio unit is mounted at a location on the customextend to a site controller 56, data connections such as an
er's premises, or on a mast, etc., and in an orientation such
X.25 links 57 (shown with dashed lines in FIG. 3) could
instead be provided from a pad 228 to a switching node 60
that the flat panel antenna 23 within the customer radio unit
24 faces in the direction 26 of the central terminal 10 for the 5 of an element manager (EM) 58. An element manager 58 can
service area in which the customer radio unit 24 is located.
support a number of distributed central terminals 10 connected by respective connections to the switching node 60.
The customer radio unit 24 is connected via a drop line 28
The element manager 58 enables a potentially large number
to a power supply unit (PSU) 30 within the customer's
(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
power supply for providing power to the customer radio unit lo integrated into a management network. The element man24 and a network terminal unit (NTU) 32. The customer
ager 58 is based around a powerful workstation 62 and can
include a number of computer terminals 64 for network
radio unit 24 is also connected via the power supply unit 30
to the network terminal unit 32, which in turn is connected
engineers and control personnel.
to telecommunications equipment in the customer's
FIG. 3A illustrates various parts of a modem shelf 46. A
premises, for example to one or more telephones 34, factransmitireceive RF unit (RFU-for example implemented
on a card in the modem shelf) 66 generates the modulated
simile machines 36 and computers 38. The telecommunications equipment is represented as being within a single
transmit RF signals at medium power levels and recovers
customer's premises. However, this need not be the case, as
and amplifies the baseband RF signals for the subscriber
the subscriber terminal 20 preferably supports either a single
terminals. The RF unit 66 is connected to an analogue card
or a dual line, so that two subscriber lines could be supported 20 (AN) 68 which performs A-DID-A conversions, baseband
by a single subscriber terminal 20. The subscriber terminal
filtering and the vector summation of 15 transmitted signals
20 can also be arranged to support analogue and digital
from the modem cards (MCs) 70. The analogue unit 68 is
telecommunications, for example analogue communications
connected to a number of (typically 1-8) modem cards 70.
at 16, 32 or 64 kbitsisec or digital communications in
The modem cards perform the baseband signal processing of
accordance with the ISDN BRA standard.
25 the transmit and receive signals toifrom the subscriber
terminals 20. This may include YZ rate convolution coding
FIG. 3 is a schematic illustration of an example of a
central terminal of the telecommunications system of FIG. 1.
and x16 spreading with "Code Division Multiplexed
Access" (CDMA) codes on the transmit signals, and synThe common equipment rack 40 comprises a number of
equipment shelves 42,44,46, including a RF Combiner and
chronisation recovery, de-spreading and error correction on
power amp shelf (RFC) 42, a Power Supply shelf (PS) 44 30 the receive signals. Each modem card 70 in the present
and a number of (in this example four) Modem Shelves
example has two modems, and in preferred embodiments
(MS) 46. The RF combiner shelf 42 allows the modem
there are eight modem cards per shelf, and so sixteen
modems per shelf. However, in order to incorporate redunshelves 46 to operate in parallel. If 'n' modem shelves are
provided, then the RF combiner shelf 42 combines and
dancy so that a modem may be substituted in a subscriber
amplifies the power of 'n' transmit signals, each transmit 35 link when a fault occurs, only 15 modems on a single
signal being from a respective one of the 'n' modem shelves,
modem shelf 46 are generally used. The 16th modem is then
and amplifies and splits received signals 'n' way so that
used as a spare which can be switched in if a failure of one
separate signals may be passed to the respective modem
of the other 15 modems occurs. The modem cards 70 are
shelves. The power supply shelf 44 provides a connection to
connected to the tributary unit (TU) 74 which terminates the
the local power supply and fusing for the various compo- 40 connection to the host public switched telephone network 18
nents in the common equipment rack 40. A bidirectional
(e.g., via one of the lines 47) and handles the signalling of
telephony information to the subscriber terminals via one of
connection extends between the RF combiner shelf 42 and
15 of the 16 modems.
the main central terminal antenna 52, such as an omnidirectional antenna, mounted on a central terminal mast 50.
The wireless telecommunications between a central terThis example of a central terminal 10 is connected via a 45 minal 10 and the subscriber terminals 20 could operate on
point-to-point microwave link to a location where an intervarious frequencies. FIG. 4 illustrates one possible example
face to the public switched telephone network 18, shown
of the frequencies which could be used. In the present
example, the wireless telecommunication system is intended
schematically in FIG. 1, is made. As mentioned above, other
types of connections (e.g., copper wires or optical fibres) can
to operate in the 1.5-2.5 GHz Band. In particular the present
be used to link the central terminal 10 to the public switched so example is intended to operate in the Band defined by ITU-R
telephone network 18. In this example the modem shelves
(CCIR) Recommendation F.701 (2025-2110 MHz,
2200-2290 MHz). FIG. 4 illustrates the frequencies used for
are connected via lines 47 to a microwave terminal (MT) 48.
the uplink from the subscriber terminals 20 to the central
A microwave link 49 extends from the microwave terminal
48 to a point-to-point microwave antenna 54 mounted on the
terminal 10 and for the downlink from the central terminal
mast 50 for a host connection to the public switched tele- 5s 10 to the subscriber terminals 20. It will be noted that 12
phone network 18.
uplink and 12 downlink radio channels of 3.5 MHz each are
A personal computer, workstation or the like can be
provided centred about 2155 MHz. The spacing between the
provided as a site controller (SC) 56 for supporting the
receive and transmit channels exceeds the required minicentral terminal 10. The site controller 56 can be connected
mum spacing of 70 MHz.
to each modem shelf of the central terminal 10 via, for 60
In the present example, each modem shelf supports 1
example, RS232 connections 55. The site controller 56 can
frequency channel (i.e. one uplink frequency plus the corthen provide support functions such as the localisation of
responding downlink frequency). Currently, in a wireless
faults, alarms and status and the configuring of the central
telecommunications system as described above, CDMA
encoding is used to support up to 15 subscriber links on one
terminal 10. A site controller 56 will typically support a
single central terminal 10, although a plurality of site 65 frequency channel (one subscriber link on each modem).
controllers 56 could be networked for supporting a plurality
Hence, if a central terminal has four modem shelves, it can
support 60 (15x4) subscriber links (ie. 60 STs can be
of central terminals 10.

US 6,222,819 B1

9

10

connected to one CT). However, it is becoming desirable for
ating on the same frequency don't inadvertently decode each
others data, a seven cell repeat pattern is used such that for
more than 60 STs to be supported from one central terminal,
and, in preferred embodiments of the present invention,
a cell operating on a given frequency, all six adjacent cells
enhancements to the CDMA encoding technique are prooperating on the same frequency are allocated a unique
vided to increase the number of subscriber links that can be 5 pseudo random noise (PN) code. The use of PN codes will
supported by a central terminal. Both CDMA encoding, and
be discussed in more detail later. The use of different PN
codes prevents nearby cells operating on the same frequency
the enhancements made to the CDMA encoding in accordance with preferred embodiments, will be discussed in
from inadvertently decoding each others data.
more detail later.
As mentioned above, CDMA techniques can be used in a
Typically, the radio traffic from a particular central ter- lo fixed assignment arrangement (ie. one where each ST is
minal10 will extend into the area covered by a neighbouring
assigned to a particular modem on a modem shelf) to enable
central terminal 10. To avoid, or at least to reduce interfereach channel frequency to support 1 5 subscriber links. FIG.
ence problems caused by adjoining areas, only a limited
6 gives a schematic overview of CDMA encoding and
number of the available frequencies will be used by any
decoding.
given central terminal 10.
In order to encode a CDMA signal, base band signals, for
example the user signals for each respective subscriber link,
FIG. 5A illustrates one cellular type arrangement of the
are encoded at 8&80N into a 160 ksymbols/sec baseband
frequencies to mitigate interference problems between adjasignal where each symbol represents 2 data bits (see, for
cent central terminals 10. In the arrangement illustrated in
example the signal represented at 81). This signal is then
FIG. 5A, the hatch lines for the cells 76 illustrate a frequency
spread by a factor of 16 using a spreading function 82-82N
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, 20 to generate signals at an effective chip rate of 2.56
Msymbols/sec in 3.5 MHz. The spreading function involves
F6, F9, F12), and arranging that immediately adjacent cells
do not use the same frequency set (see, for example, the
applying a PN code (that is specified on a per CT basis) to
the signal, and also applying a Rademacher-Walsh (RW)
arrangement shown in FIG. 5A), it is possible to provide an
array of fixed assignment omnidirectional cells where intercode which ensures that the signals for respective subscriber
ference between nearby cells can be reduced. The transmit- 2s terminals will be orthogonal to each other. Once this spreadter power of each central terminal 1 0 is preferably set such
ing function has been applied, the signals for respective
that transmissions do not extend as far as the nearest cell
subscriber links are then combined at step 84 and converted
which is using the same frequency set. Thus, in accordance
to radio frequency (RF) to give multiple user channel signals
(e.g. 85) for transmission from the transmitting antenna 86.
with the arrangement illustrated in FIG. 5A, each central
During transmission, a transmitted signal will be subterminal 1 0 can use the four frequency pairs (for the uplink 30
and downlink, respectively) within its cell, each modem
jected to interference sources 88, including external intershelf in the central terminal 10 being associated with a
ference 89 and interference from other channels 90.
respective RF channel (channel frequency pair).
Accordingly, by the time the CDMAsignal is received at the
receiving antenna 91, the multiple user channel signals may
Figure SB illustrates a cellular type arrangement employing sectored cells to mitigate problems between adjacent 35 be distorted as is represented at 93.
central terminals 10. As with FIG. 5A, the different type of
In order to decode the signals for a given subscriber link
hatch lines in FIG. 5B illustrate different frequency sets. As
from the received multiple user channel, a Walsh correlator
in FIG. 5A, FIG. 5B represents three frequency sets (e.g.,
94-94N uses the same RW and PN codes that were used for
where: FSl=Fl, F4, F7, F10; FS2=F2, F5, F8, F11; FS3=F3,
the encoding for each subscriber link to extract a signal (e.g,
F6, F9, F12) However, in FIG. 5B the cells are sectored by 40 as represented at 95) for the respective received baseband
using a sectored central terminal (SCT) 13 which includes
signal 96-96N. It will be noted that the received signal will
three central terminals 10, one for each sector S1, S2 and S3,
include some residual noise. However, unwanted noise can
with the transmissions for each of the three central terminals
be removed using a low pass filter and signal processing.
1 0 being directed to the appropriate sector among S1, S2 and
~ h key to CDMA is the application of the RW codes,
,
S3. This enables the number of subscribers Per cell to be
these being a mathematical set of sequences that have the
,
increased three fold, while still providing permanent fixed 4s function of u o r t ~ o n o r m a ~ i t y ~other words, if any RW
access for each subscriber terminal 20.
code is multiplied by any other RW code, the results are
Arrangements such as those in FIGS. 5A and 5B can help
zero. Aset of 16 RW codes that may be used is illustrated in
reduce interference, but in order to ensure that cells operTable 1 below:
TABLE 1
RWO
RW1
RW2
RW3
RW4
RWS
RW6
RW7
RW8
RW9
RWlO
RWll
RW12
RW13
RW14
RWlS

US 6,222,819 B1

11

12

The above set of RW codes are orthogonal codes that
allow the multiple user signals to be transmitted and
received on the same frequency at the same time. Once the
bit stream is orthogonally isolated using the RW codes, the
signals for respective subscriber links do not interfere with
each other. Since RW codes are orthogonal, when perfectly
aligned all codes have zero cross-correlation, thus making it
possible to decode a signal while cancelling interference
from users operating on other RW codes.
In preferred embodiments of the present invention, it is
desired to provide the central terminal with the ability to
support more than 15 subscriber links on each channel
frequency, and to achieve this the above set of 16 RW codes
has been enhanced. In order to maintain compatibility with
former products using the 16 RW codes, it was desirable that
any enhancements should retain the same set of 16 RW
codes.
The manner in which the enhancements have been implemented provides flexibility in the way the frequency channels are configured, with certain configurations allowing a
greater number of subscriber links to be supported, but at a
lower gross bit rate. In preferred embodiments, a channel
can be selected to operate with the following gross bit rates:

In preferred embodiments, TDM timeslot bit numbering
will follow the CCITT G. 732 convention with bits transmitted in the sequence bit 1, bit 2 . . . bit 8. Byte orientation
is specified per channel as either most significant bit (MSB)
first, least significant bit (LSB) first or NIA,
The provision of a hybrid CDMAiTDM approach for
downlink traffic channels retains the benefits of CDMA
access, ie. interference is reduced when traffic is reduced.
Further, use of TDM ensures that the CDMA signal is
limited to a 256 'Quadrature Amplitude Modulation' (QAM)
constellation which reduces receiver dynamic range requirements. QAM constellations will be familiar to those skilled
in the art.
On the uplink channels, the pure CDMA approach using
overlay codes eliminates the need to time synchronise STs to
a TDM frame reference. This has the advantage of eliminating TDM delays and the 'guard time' in between TDM
frames. Another benefit is reduced peak power handling
requirements in the ST RF transmit chain which would
otherwise be needed when transmitting bursty TDM data.
High dynamic range requirement is restricted to the CT
receiver.
The manner in which the transmitted and received signals
are vrocessed in accordance with vreferred embodiments of
the present invention will be described with reference to
FIGS. 7 and 8. FIG. 7A is a schematic diagram illustrating
signal transmission processing stages as configured in a
subscriber terminal 20 in the telecommunications system of
FIG. 1. In FIG. 7A, an analogue signal from a telephone is
passed via an interface such as two-wire interface 102 to a
hybrid audio processing circuit 104 and then via a codec 106
to produce a digital signal into which an overhead channel
including control information is inserted at 108. If the
subscriber terminal supports a number of telephones or other
telecommunications equipment, then elements 102, 104 and
106 may be repeated for each piece of telecommunications

5

10

20

-

23

160 kbls
80 kbls
40 kbls
10kbls

Full rate (Fl)
Half rate (HI. HZ)
Quarter rate (Ql, Q2, Q3, Q4)
Low rate (Ll, L2, ~ 3 ~, 4 ) for uplink
,
acquisition

30

preferred embodiments, the manner in which these
channelisations are provided differs for the downlink (CT to
ST) and uplink (ST to CT) communication paths, hi^ is
because it has been realised that different performance 3s
requirements exist for the downlink and uplinkpaths. On the
downlink all signals emanate from a single source, namely
the central terminal, and hence the signals will be synchronised. However, on the uplink path, the signals will emanate
At the output of overhead insertion circuit 108, the signal
from a number of independent STs, and hence the signals 40 will have a bit rate of either 160,80 or 40 kbitsls, depending
on which channel has been selected for transmission of the
will not be synchronised.
Given the above considerations, in preferred
signal.
The resulting signal is then processed by a convolutional
embodiments, on the uplink path full rate (160 kbls) operaencoder 110 to produce two signals with the same bit rate as
tion is implemented using the basic set of RW codes
discussed earlier, but half and quarter rates are achieved 45 the input signal (collectively, these signals will have a
through the use of 'Overlay Codes' which comprise RW
symbol rate of 160, 80 or 40 KSls). Next, the signals are
coded high rate symbol patterns that are transmitted for each
passed to a spreader 111 where, if a reduced bit rate channel
intermediate rate data symbol. For half rate operation, two
has been selected, an appropriate overlay code provided by
2-bit overlay codes are provide, whilst for quarter rate
overlay code generator 113 is applied to the signals. At the
operation, four 4-bit overlay codes are provided. WEn so output of the spreader 111, the signals will be at 160 KSIs
generating a signal for transmission, one of the overlay
irrespective of the bit rate of the input signal since the
codes, where appropriate, is applied to the signal in addition
overlay code will have increased the symbol rate by the
to the appropriate RW code. When the signal is received,
necessary amount.
then at the CDMA demodulator the incoming signal is
The signals output from spreader 111 are passed to a
multiplied by the channel's PN, RW and Overlay codes. The ss spreader 116 where the Rademacher-Walsh and PN codes
correlator integration period is set to match the length of the
are applied to the signals by a RW code generator 112 and
Overlay code.
PN Code generator 114, respectively. The resulting signals,
Overlay codes are used extensively to provide variable
at 2.56 MCIs (2.56 Mega chips per second, where a chip is
rate uplink traffic channels. Overlay codes will also be used
the smallest data element in a spread sequence) are passed
to implement downlink control channels, these control chan- 60 via a digital to analogue converter 118. The digital to
nels being discussed in more detail later. However, as
analogue converter 118 shapes the digital samples into an
mentioned earlier, a different approach is taken for providing
analogue waveform and provides a stage of baseband power
flexible channelisations on the downlink traffic channel
control. The signals are then passed to a low pass filter 120
paths. Downlink traffic channels will operate in high rate,
to be modulated in a modulator 122. The modulated signal
160 kbls, mode, with lower data rates of 80 and 40 kbls 65 from the modulator 122 is mixed with a signal generated by
being supported by 'Time Division Multiplexing' (TDM)
a voltage controlled oscillator 126 which is responsive to a
the available bandwidth.
synthesizer 160. The output of the mixer 128 is then

US 6,222,819 B1

13

14

amplified in a low noise amplifier 130 before being passed
tor 112) and a PN code generator 174 (corresponding to PN
via a band pass filter 132. The output of the band pass filter
code generator 114), respectively. The output of the corr132 is further amplified in a further low noise amplifier 134,
elator 178, at 160 KS/s, is then applied to correlator 179,
before being passed to power control circuitry 136. The
where any overlay code used at the transmission stage to
output of the power control circuitry is further amplified in 5 encode the signal is applied to the signal by overlay code
generator 181. The elements 170, 172, 174, 178, 179 and
a power amplifier 138 before being passed via a further band
181 form a CDMA demodulator. The output from the
pass filter 140 and transmitted from the transmission antenna
142.
CDMA demodulator (at correlator 179) is then at a rate of
either 160, 80 or 40 KSls, depending on the overlay code
FIG. 7B is a schematic diagram illustrating signal transmission processing stages as configured in a central terminal lo applied by correlator 179.
10 in the telecommunications system of FIG. 1. As will be
The output from correlator 179 is then applied to a Viterbi
apparent, the central terminal is configured to perform
decoder 180. The output of the Viterbi decoder 180 is then
similar signal transmission processing to the subscriber
passed to an overhead extractor 182 for extracting the
terminal 20 illustrated in FIG. 7A, but does not include
overhead channel information. If the signal relates to call
elements 100, 102, 104 and 106 associated with telecomdata, then the output of the overhead extractor 182 is then
munications equipment. Further, the central terminal
passed through TDM decoder 183 to extract the call data
includes a TDM encoder 105 for performing time division
from the particular time slot in which it was inserted by the
multiplexing where required. The central terminal will have
CT TDM encoder 105. Then, the call data is passed via a
a network interface over which incoming calls destined for
codec 184 and a hybrid circuit 188 to an interface such as
a subscriber terminal are received. When an incoming call is
two wire interface 190, where the resulting analogue signals
received, the central terminal will contact the subscriber 20 are passed to a telephone 192. As mentioned earlier in
terminal to which the call is directed and arrange a suitable
connection with the ST transmission processing stages,
channel over which the incoming call can be established
elements 184, 188, 190 may be repeated for each piece of
with the subscriber terminal (in preferred embodiments, this
telecommunications equipment 192 at the ST,
is done using the call control channel discussed in more
If the data output by the overhead extraction circuit 182
detail later). The channel established for the call will deter- 25 is data on a downlink control channels, then instead of
mine the time slot to be used for call data passed from the
passing that data to a piece of telecommunications
CT to the ST and the TDM encoder lo5 be
with
equipment, it is passed via switch 187 to a call control logic
this information.
185, where that data is interpreted by the ST.
Hence, when incoming call data is passed from the
At the subscriber terminal 20, a stage of automatic gain
network interface to the TDM encoder 105 over line 103, the 30
control is incorporated at the IF stage. The control signal is
TDM encoder will apply appropriate TDM encoding to
derived from the digital portion of the CDMAreceiver using
enable the data to be inserted in the appropriate time slot,
the Output a
quality
From then on, the processing of the signal is the same as the
equivalent processing performed in the ST and described
FIG. 8B illustrates the signal reception processing stages
with reference to FIG. 7-4, the overlay code generator 35 as configured in a central terminal 10 in the telecommuniproducing a single overlay code of value '1' so that the
cations system of FIG. 1.As will be apparent from the figure,
the signal processing stages between the RX antenna 150
signal output from spreader 111 is the same as the signal
input to the spreader 111.
and the overhead extraction circuit 182 are the as those
As mentioned earlier, in preferred embodiments, overlay
within the ST discussed in connection with FIG. 8A.
codes, rather than TDM, are used to implement downlink
However, in the case of the CT, call data output from the
control channels, and data relating to such channels is passed 40 overhead extraction circuit is passed over line 189 to the
from a demand assignment engine (to be discussed in more
network interface within the CT, whilst control channel data
is passed via switch 191 to the DA engine 380 for processdetail later) over line 107 through switch 109 to the overhead
insertion circuit 108, thereby bypassing the TDM encoder
ing. The DA engine is discussed in more detail later.
lo5. processing
The
the
is then the same as the
Overlay codes and channelisation plans are selected to
processing performed in the ST, with the
45 ensure signal orthogonality-i,e, in a properly synchronised
generator providing
the
system, the contribution of all channels except the channel
The
generator
be
being demodulated sum to zero over the correlator integraas
produce the desired
in preferred
tion period. Further, uplink power is controlled to maintain
embodiments, this control coming from the DAengine (to be
,,t,t
energy per bit, The exception to this is Low rate
discussed in more detail later).
50 which will be transmitted at the same power as a Quarter rate
FIG. 8A is a schematic diagram illustrating the signal
signal. Table 2 below illustrates the overlay codes used for
reception processing stages as configured in a subscriber
full, half and quarter rate operations:
terminal 20 in the telecommunications system of FIG. 1. In
FIG. 8A, signals received at a receiving antenna 150 are
TABLE 2
passed via a band pass filter 152 before being amplified in 55
a low noise amplifier 154. The output of the amplifier 154 is
ST TX.
power
then passed via a further band pass filter 156 before being
further amplified by a further low noise amplifier 158. The
Net
relative
Correlator
Rate
to F1-u
integration Acquisition
output of the amplifier 158 is then passed to a mixer 164
(kbls) designation
(dB)
Overlay Code period (us)
overlay
where it is mixed with a signal generated by a voltage
controlled oscillator 162 which is responsive to a synthesizer 60 160
-FI-u
o
1
6.25
LI
160. The output of the mixer 164 is then passed via the I/Q
80
-HI-U
-3
1 1
12.5
LI
de-modulator 166 and a low pass filter 168 before being
-3
1-1
12.5
~2
L1
passed to an analogue to digital converter 170. The digital
1
1;
L2
output of the AID converter 170 at 2.56 MC/s is then passed
40
-Q3-U
-6
25
~2
to a correlator 178, to which the same Rademacher-Walsh 65 40
-~4-u
-6
1-1 -1 1
2s
LA
and PN codes used during transmission are applied by a RW
code generator 172 (corresponding to the RW code genera-

-;;-;

;z

US 6,222,819 B1

16

15
In preferred embodiments, a 10 kbls acquisition mode is
provided which uses concatenated overlays to form an
acquisition overlay; this is illustrated in table 3 below:
TABLE 3
Acquisition
overlay

LI-u

LZ-u

~3-u
LA-u

Equivalent high rate pattern
I I I I I I I I I I I I I I I I
1 1 -1 -1 1 1 -1 -1 1 1 -1 -1 1 1 -1 -1
1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1 1 -1

FIGS, 9A and 9B are diagrams illustrating the uplink and
downlink delivery methods, respectively, when the system is
fully loaded, and illustrate the difference between the use of
overlay codes illustrated in FIG, 9A and the use of TDM as
illustrated in FIG, 9 ~when using overlay codes, an RW
.
code is split in the RW space domain to allow up to four sub
channels to operate at the same time. In contrast, when using
TDM, an RW code is split in the time domain, to allow up
to four signals to be sent using one RW code, but at different
times during the 125 us frame,
illustrated in FIGS, 9A
and 9B, the last two RW codes, ~
~ and1 ~4 1are not
~
5 ,
used for data traffic in preferred embodiments, since they are
reserved for call control and acquisition functions; this will
be discussed in more detail later.
The CDMAchannel hierarchy is as illustrated in FIG. 10.
Using this hierarchy, the following CDMA channelisations
are possible:
F1
Hl+H2
Hl+Q3+Q4
H2+Ql+Q2
Ql+Q2+Q3+Q4
~~~i~~ discussed how the CDMA codes are enhanced to
enable flexible channelisations to be achieved, whereby the
bit rates can be lowered to enable more subscriber links to
be managed per channel frequency, a general overview of
how the downlink and uplink paths are established will be
provided with reference to FIGS. 1 and 12.
1
FIG, 1 is a block diagram of downlink and uplink
1
communication paths between central terminal 10 and subscriber terminal 20. A downlink communication path is
established from transmitter 200 in central terminal 10 to
receiver 202 in subscriber terminal 20. An uplink communication path is established from transmitter 204 in subscriber terminal 20 to receiver 206 in central terminal 10.
Once the downlink and the uplink communication paths
have been established in wireless telecommunication system
1, telephone communication may occur between a user 208,
210 of subscriber terminal 20 and a user serviced through
central terminal 10 over a downlink signal 212 and an uplink
signal 214. Downlink signal 212 is transmitted by transmitter 200 of central terminal 10 and received by receiver 202
of subscriber terminal 20. Uplink signal 214 is transmitted
by transmitter 204 of subscriber terminal 20 and received by
receiver 206 of central terminal 10.
Receiver 206 and transmitter 200 within central terminal
10 are synchronized to each other with respect to time and
phase, and aligned as to information boundaries. In order to
establish the downlink communication path, receiver 202 in
subscriber terminal 20 should be synchronized to transmitter
200 in central terminal 10. Synchronization occurs by performing an acquisition mode function and a tracking mode
function on downlink signal 212. Initially, transmitter 200 of

central terminal 10 transmits downlink signal 212. FIG. 12
shows the contents of downlink signal 212. A frame information signal 218 is combined with an overlay code 217
where appropriate, and the resultant signal 219 is combined
5 with a code sequence signal 216 for central terminal 10 to
produce the downlink 212. Code sequence signal 216 is
derived from a combination of a pseudo-random noise code
signal 220 and a Rademacher-Walsh code signal 222.
a
a
Downlink signal 212 is received at receiver 202 of
,,, subscriber terminal 20. Receiver 202 compares its phase and
code sequence to a phase and code sequence within code
sequence signal 216 of downlink signal 212. Central terminal 10 is considered to have a master code sequence and
subscriber terminal 20 is considered to have a slave code
adjusts the phase
1s Sequence. Receiver 202
its
sequence
a match master
sequence and place receiver 202 of subscriber terminal 20 in
phase with transmitter 200 of central terminal 10. The slave
code sequence of receiver 202 is not initially synchronized
the master code sequence of transmitter 200 and
20
terminal 10 due to the path delay between central terminal
loand subscriber
20. This path
is caused
the geographical separation between subscriber terminal 20
and central terminal 10 and other environmental and techtransmission.
25 nical factors affecting
After acquiring and initiating tracking on the central
terminal 10 master code sequence of code sequence signal
216 within downlink signal 212, receiver 202 enters a frame
alignment mode in order to establish the downlink cornmu30 nication path. Receiver 202 analyzes frame information
within frame information signal 218 of downlink signal 212
to identify a beginning of frame position for downlink signal
212. Since receiver 202 does not know at what point in the
data stream of downlink signal 212 it has received
35 information, receiver 202 must search for the beginning of
frame position in order to be able to process information
received from transmitter 200 of central terminal 10. Once
receiver 202 has identified one further beginning of frame
position, the downlink communication path has been estab40 lished from transmitter 200 of central terminal 10 to receiver
20.
202 of subscriber
The structure of the radio frames of information sent over
the downlink and uplink paths will now be discussed with
l3 and 14. In
l3 and 1 4 3 the
reference
terms are wed:
45
Bn Customer payload, 1x32 to 2x64 Kbls
Dn Signalling Channel, 2 to 16 kbls
OH Radio Overhead Channel
16 kbls Traffic Mode
so
10 kbls AcquisitionIStandby Mode
Both FIGS. 13A and 13B show a 125 us subframe format,
which is repeated throughout an entire radio frame, a frame
typically lasting for 4 milliseconds (ms). FIG. 13Aillustrates
the radio frame structures that are used in preferred embodiss ments for the downlink path. Subframe (i) in FIG. 13A
shows the radio frame structure used for low rate, 10 Kbls,
acquisition mode (Ln-D) during which only the overhead
channel is transmitted. Subframe (ii) in FIG. 13A shows the
radio frame structure employed for the call control channel
60 operating in quarter rate, 40 Kbls, mode (Qn-D), whilst
subframe (iii) of FIG. 13A illustrates the radio frame structure used for traffic channels operating in full rate, 160 kbls,
mode (Fl-D).
Similarly, subframe (i) of FIG. 13B shows the radio frame
65 structure used for the uplink path when operating in low rate
acquisition or call control mode (Ln-U). Sub-frames (ii) to
(iv) show the radio frame structure used for traffic channels
A"

US 6,222,819 B1

17

18

when operating in quarter rate mode (Qn-U), half rate mode
(Hn-U), and full rate mode (Fl-U), respectively.
Considering now the overhead channel in more detail,
FIGS. 14A and 14B show the overhead frame structure
employed for various data rates. The overhead channel may
include a number of fields-a frame alignment word (FAW),
a code synchronization signal (CS), a power control signal
(PC), an operations and maintenance channel signal (OMC),
a mixed OMCID-Channel (HDLC) signal (OMCD), a channel identifier byte (Ch.ID), and some unused fields.
The frame alignment word identifies the beginning of
frame position for its corresponding frame of information.
The code synchronization signal provides information to
control synchronization of transmitter 204 in subscriber
terminal 20 to receiver 206 in central terminal 10. The power
control signal provides information to control transmitting
power of transmitter 204 in subscriber terminal 20. The
operations and maintenance channel signal provides status
information with respect to the downlink and uplink communication paths and a path from the central terminal to the
subscriber terminal on which the communication protocol
which operates on the modem
between the
controller and the modem cards also extends, ~h~ OMCD
signal is a
of the OMC signal and a signalling
signal (D), whilst the Ch. ID signal is used to uniquely
identify an RW channel, this Ch, ID signal being used by the
subscriber terminal to ensure that the correct channel has
been acquired.
In preferred embodiments, the subscriber terminal will
receive downlink traffic channel data at a rate of 160 kbls.
Depending on the B-channel rate, the ST will be allocated an
appropriate share of the radio overhead. The following TDM
mappings are created:

assignment arrangements using the set of 16 RW codes
discussed earlier are still supported, as well as demand
access services that are available when using a system
in accordance with the preferred embodiment. FIGS.
15A and 15B illustrate typical downlink and uplink
channel structures that might occur in a loaded system
in accordance with preferred embodiments of the
present invention. As illustrated in FIG. 15A, on the
downlink path, some signals may be at 160 kbls and
utilise an entire RW channel. An example of such
signals would be those sent over fixed assignment links
to products which do not support the CDMA enhancements provided by systems in accordance with preferred embodiments of the present invention, as illustrated for RW1 and RW2 in FIG. 15A. Alternatively, a
user may have authority to utilise a whole RW channel,
for example when sending a fax, as illustrated by RW12
in FIG. 15A.
As illustrated by RW5 to RW11, TDM can be used on the
downlink traffic channels to enable more than one CT to ST
communication to take place on the same RW channel
during each frame. Further, as illustrated for RW3 and RW4,
in preferred embodiments, certain channels can be locked to
limit interference from other nearby cells, as will be discussed in
later.
Similar channelisations can be achieved for the uplink
paths, but as illustrated in FIG. 15B, overlay codes are used
instead of TDM to enable more than one ST to CT communication to take place on the same RW channel during
each frame (as shown in FIG. 15B for RW5 to RW11). It
should be noted that, in both FIGS. 15A and 15B, the
channels RW14 and RW15 are reserved as a call control
channel and an link acquisition channel, respectively, and
overlay codes are employed on these channels, irrespective
of whether the path is a downlink or an uplink path. These
two channels will be discussed in more detail below.
Acquisitionlnet entry will take place via the Link Acquisition Channel (LAC). Following power-up an ST will
automaticallv attemat downlink acauisition of the LAC on a

TABLE 4
Rate Channel
(kbls) designation
160

-Fl-D-T1/1

5

10

20

25

30

35

Bearer

CS

PC

OMC

Overhead
rate

CS1,
cs3
CS1,
CS3
CS2,
cs4
CSI
cs2
CS3
CS4

PC1,
pc3
PC1,
PC3
PC2,
pc4
PCI
PCZ
PC3
PC4

OMC1, OMC3

4 ms

80

-Fl-D-T211

B1, B2, B3,
B4
B1, B2

80

-F1-D-T212

B3, B4

40
40
40
40

-FI-D-~411
-FI-D-~412
-F1-D-T413
-F1-D-T414

BI
B2
B3
B4

40

OMCLOMC3

4 ms

OMC2, OMC4

4 ms

OMC~
OMC2
OMC3
OMC4

8 ms
8 ms
ms
8 ms

In the above chart, the scheme used to identify a channel
is as follows. Rate code 'Fl' indicates full rate, 160 kbls, 'D'
indicates that the channel is a downlink channel, and 'Tnlt'
indicates that the channel is time division multiplexed
between STs,
'n' indicating the total number of TDM timeslots, and 't'
indicating the selected traffic timeslot.
All ST's operating on a traffic channel will receive
D-channel information at the 16 kbls rate. The D-channel
protocol includes an address field to specify which ST is to
process the contents of the message.
The channel structure was illustrated earlier in FIGS. 9A
and 9B. In preferred embodiments, the channel structure is
flexible but comprises:
At least one Link Acquisition Channel (LAC)
At least one Call Control Channel (CCC)
Typically one Priority Traffic Channels (PTC)
1 to 13 Traffic Channels (TC) The manner in which the
channelisation is provided ensures that former fixed

45

P
~ 'home' RF ~
The -LAC
~
channel (eg. RW15 in preferred embodiments) will operate
at 10 kbls, full single user power. Downlink acquisition will
be simultaneous for all STs.
Each CT Modem Shelf will maintain a database holding
the serial numbers of all STs that could possibly be supported by that CT. The state of each ST will recorded with
top level states as follows:
cold
idle
call_in_progress
Transition states will also be defined. An ST is considered
cold if the ST is newly provisioned, the CT has lost
management communications with the ST or the CT has
been power cycled. Over the LAC, the CT broadcasts
individual ST serial numbers and offers an invitation to
acquire the LAC uplink. Cold uplink acquisition will be
carried out on the Link Acquisition Channel at low rate. The
CT will invite specific ST's to cold start via the management
channel.
Assuming an uplink channel is available, the appropriate
acquisition overlay will be selected, and acquisition will be
initiated.
'Rapid' downlink RW channel switching may be supported at rates other than Ln-D. Rapid means that coherent
demodulation is maintained, and only convolutional decoding and frame synchronisation processes need be repeated.
On acquisition, management information will be
exchanged. The ST will be authenticated and allocated a

~

US 6,222,819 B1

19

20

short STLidentifier (between 12 and 16 bits) which will be
Enable the ST transmitter at a level of nominal full rate
used for subsequent addressing. The ST uplink will operate
power 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 power
in terms of code phase and transmit power. These parameters
level by +2 dB at the end of each search. The uplink should
will be used by the ST for subsequent warm start acquisi- s acquire at nominal full rate power minus 6 dB. Uplink
tions and will also be held by the CT to allow the CT to force
acquisition is aborted if maximum transmit level is reached
a cold ST to warm start. On successful completion of net
and PCICS continues to report idle.
entry, the ST will be placed in the idle state and instructed
(iv) PCICS reports busy, ~t this point the ST may have
to cease uplink communications and move to the Call
genuinely acquired the traffic channel, or instead may
Control Channel (CCC) (RW14 in preferred embodiments). 10
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
(i) Prioritise so that high GOS (Grade Of Service) users
STLidentifier. The ST aborts the acquisition process if
15
are offered net entry first.
the returned STLidentifier is not recognised (ie. is not
the STLidentifer that it sent). This authentication pro(ii) Convert Traffic Channels to LACS.
cess arbitrates between two STs contending for outgo(iii) In the event of a CT restart, invite STs to attempt
ing access and it also keeps STs from acquiring TCs
uplink warm start. A reduction in net entry time of a
that have been reserved from incoming access.
factor of 4 could be achieved. This mechanism would
need to be safeguarded against possible deterioration of 20 Incoming Call
Anumber of TCs will be reserved for incoming calls, and
uplink warm start parameters-i,e, it should only be
incoming call processing is as follows:
allowed provided no CT RF related parameters have
been modified. The CT would need to broadcast an ID
(i) Check the CT database-if the ST is in the c a l l i n to allow an ST to validate that the uplink warm start
progress state the call is rejected.
25
parameters were valid for this CT.
(ii) Check that an uplink TC of the required bandwidth is
(iv) ST restart-the CT will keep copies of the ST warm
available. If there is bandwidth then a TC is reserved.
start parameters so that a cold ST may have warm start
(iii) An incoming call setup message is broadcast over the
parameters downloaded in the invitation to acquire and
CCC to inform the addressed ST of the incoming call
then be instructed to warm start.
and specify the TC on which to receive the call. If no
30
Following Net Entry, all STs listen to the CCC. This
TC is available but the CT forms part of a Service
channel broadcasts management and call control informaDomain, then the incoming call setup message is sent
tion via a 32 kbls HDLC channel. In order to maintain
with a null TC otherwise the call is rejected. Service
management communication, the CT polls each ST in
domains will be discussed in more detail later. The
sequence. Each poll comprises a broadcast invitation for an 35
incoming call setup message is repeated a number of
addressed ST to acquire the CCC Uplink followed by an
times.
exchange of management information (authentication, ST
(iv) The ST attempts uplink acquisition. The ST listens to
alarm update, warm start parameters, downlink radio perthe downlink and keeps trying for uplink acquisition
formance data etc).
until the CT sends a message to the ST to return the ST
A Management Poll may fail for one of the following
40
to the CCC. The ST will also run a timer to return it
reasons:
back to the CCC in the event of an incoming call failing
(i) The ST is or has been powered down. An EM alarm
to complete.
may be flagged if this persists and the database for that
(v) On s~ccessful
uplink acquisition, the CT authenticates
ST should be marked cold, The Net Entry process will
the ST.
follow.
(vi) Rate switching is originated from the CT modem. A
(ii) ~h~ ST is either m k i n g a call or in the process of 45
command is sent via the PCICS to switch the downlink
making a call. The poll cycle may be suspended and
to the required bandwidth. The ST returns the rate
management communications effected on the appropriswitch command via the uplink PCICS. The link is now
ate traffic channel.
of the required bandwidth.
When a Management Poll fails it should be followed up
Outgoing
by a number of faster polls until either the ST responds or
Outgoing
are
it is marked cold. The CCC is required to transmit all copies
the TC
The
processing is as
of the invitations to acquire the LAC so that an ST can be
follows:
forced to acquire the LAC uplink.
Traffic Channel Uplink Acquisition Procedure
ss (i) The CT publishes a 'free list' of available Traffic
Channels and Priority Traffic Channels with their
The basic acquisition process from the ST side is as
respective bandwidths. This list is published periodifollows;
cally (in preferred embodiments, every 500 ms) and is
(i) Switch the downlink (receiver) circuitry to 10 kbls rate,
used to mark uplink access slots.
and select the appropriate Traffic Channel RW and
(ii) An off-hook condition is detected by the ST. The ST
Overlay codes. Acquisition of the TC downlink is 60
starts a call setup timer.
limited to achieving frame alignment.
(iii) The ST waits for the next free list to be received over
(ii) The downlink PCICS channel will be decoded to
the CCC. If the Free list is empty the outgoing call is
create a busylidle flag. If PCICS reports busy, then this
blocked. The ST will generate a congestion tone.
means that another ST is using that traffic channel and
the ST aborts the acquisition process.
65
(iv) If the Free list has available channels, the ST picks a
(iii) Switch uplink to 10 kbls rate, and select the approchannel from the free list at random. The algorithm that
priate Traffic Channel RW and Overlay codes.
the ST uses to pick a channel will need to be specified

US 6,222,819 B1

23

24

terminal 20, the call control function 336 will note how
readily it is able to establish traffic channels for transmitting
and receiving data, and from this can provide a GOS
estimate to the multiplexer 332 for encoding by the encoder
334 for subsequent transmission over the wireless link 310
to the central terminal modem 320. Here, the GOS estimate
is decoded by decoder 340, passed through multiplexer 345,
and then the GOS estimate is passed over line 355 to the
dynamic pool sizing function 360.
Additionally, incoming call information to the central
terminal, other than call information from the subscriber
terminals 20 connected to the central terminal, is provided
over the concentrated network interface 390 to the DA
engine 380. The DA engine 380 includes a call control
function, similar to the call control function 336 in each of
the subscriber terminals 20, for each of the modems on the
modem shelf. Hence, in a similar fashion to the call control
function 336 at the subscriber terminals 20, the call control
functions within the DA engine 380 are also able to provide
GOS estimates for incoming calls, and these GOS estimates
are passed over line 395 to the dynamic pool sizing function
360.
set up, the management system 370 within the element
manager will have connected to the central terminal, and
provided the dynamic pool sizing function 360 within the
modem shelf with data identifying a BER goal, a GOS goal,
and a pool size limit (i.e. the number of channels that can be
used for data traffic),The dynamic pool sizing function 360
then compares this data from the management system with
the actual BER, actual GOS, and the actual pool size
information that it receives. A suitable algorithm can be
provided within the dynamic pool sizing function 360 to
determine, based on this information, whether pool sizing is
appropriate. For example, if the actual bit error rate exceeds
the BER goal provided by the management system 370, then
the dynamic pool sizing function 360 may be arranged to
send a pool sizing request to the demand assignment engine
380.
me demand assignment engine 380 provides modem
enable signals over lines 400 to each of the modems on the
CT modem shelf, ~f the dynamic pool sizing function 360
has requested that the DA engine 380 perform pool sizing,
then the DA engine 380 can disable one or more of the
modems, this causing the interference, and hence the actual
BER, to be reduced. Apart from being used for interference
limiting, the DA engine is also responsible, in preferred
embodiments, for providing the encoders 325 with instructions on which set of overlay codes or how many TDM slots
to be used for signals to be transmitted to the STs 20.
The dynamic pool sizing function can store the BER and
GOS information received in the storage 365, and periodically may pass that data to the management system 370 for
analysis. Further, if the system is unable to attain the BER
or GOS goal with the allocated pool size, the dynamic pool
sizing function can be arranged to raise an alarm to the
management system. The receipt of this alarm will indicate
to personnel using the management system that manual
intervention may be required to remedy the situation, eg by
the provision of more central terminal hardware to support
the STs.
The CDMA approach used in preferred embodiments
exhibits the property that the removal of any of the orthogonal channels (by disabling the modem) will improve the
resistance of the other channels to interference. Hence, a
suitable approach for the demand assignment engine 380,
upon receipt of pool sizing request from the dynamic pool
sizing function 360, is to disable the modem that has the
least traffic passing through it.

RF Channel Switching
In preferred embodiments, it has been realised that if an
ST is allowed to operate from more than one CT Modem
Shelf/RF Channel then the following benefits may be realised:
(i) Fault tolerance~should a CT Modem Shelf subsystem fault occur, an ST may switch to an alternative
frequency for service.
(ii) Call blocking-an ST denied service from one CT
shelf may choose to switch to an alternative frequency
for service.
(iii) Traffic load balancing-the Element Manager may on
the basis of call blocking statistics choose to move STs
between CT shelves.
(iv) Frequency diversity-in
the presence of channel
selective fading (slow multipath) an ST may operate on
the frequency channel offering highest signal strength
and lowest soft error count.
RF
switching is
possible where there are
or more co-located CT shelves serving the same geographical area on different RF frequency channels within the same
RF band. A deployment that meets this criterion may be
configured as a 'Service Domain'. Possible deployment
scenarios are illustrated in FIG. 18. FIG. 18(i) shows an
arrangement where omni antennae are used to provide the
entire cell with four frequency channels, eg F1, F4, F7, F10.
FIG. 18(ii) shows an arrangement where sectored antennae
are used to provide six separate sectors within a cell, each
being
shows an alternative arrangement where three sectored
antennae are used to divide the cell in to three sectors, each
being
by a separate frequency
and
then an omni
is used
provide an
coverage for the entire cell, this coverage employing a
different the three
used by the sectored antennae.
For the system to work effectively, the STs must be able
switch
quickly, and fast
switching
necessitates that CT shelf synchronisation be provided at the
levels:
(i) CDMA PN code. This Preserves uplink code phase
across RF channels during warm start; and
(ii) RF carrier frequency. This eliminates the need for the
coarse frequency search on a downlink RF channel
switch.
On installation, an ST will be programmed with an RF
channel and PN code, these codes specifying the ST'S initial
home channel.
The manner in which channel switching is facilitated in
preferred embodiments will be described with reference to
FIGS. 19A and 19B. A service domain controller 400 is
preferably provided to act as an interface between the
exchange connected to the service domain controller over
path 405 and a number of central terminals 10 connected to
the service domain controller over paths 410. The central
terminals connected to the service domain controller form a
'service domain' of central terminals that may be used by a
subscriber terminal 20 for handling communications.
In preferred embodiments, the service domain controller
400 is used to provide each CT 10 with appropriate information about the other CTs within the service domain. Each
CT can then broadcast a 'Service Domain' message comprising a list of RF frequencies and CT Identifiers that form
a Service Domain to be used by the STs for subsequent RF
switching functions. The ST then stores this information for
future reference when establishing a link with one of the

5

lo

l5

20

25

30

35

40

45

so

ss

60

65

US 6,222,819 B1

26

25
CTs. It is preferable for each CT to broadcast the service
domain message since an ST may be listening to any of the
CTs at the time that the message is broadcast.
Each CT database will hold an entry for every ST located
within the Service Domain. Each database entry describes
how the CT views it's relationship with the ST and may be
marked as:
(i) Primary service provider-the CT is the ST'S home
channel. All management communication with an ST is
via it's home CT.
(ii) supplying backup
the CT is providing service
to the ST.
(iii) ~ ~ ~ iforl backup l ~
~ b service-the CT will provide
service to the ST if required.
should be noted that the ST need not switch to an
entirely different CT, but can instead switch to a different CT
(and hence different RF frequency channel) within the
same CT, However, in preferred embodiments, the ST will
typically switch to a different CT, since some errors experienced by one CT shelf may also affect other shelves within
the same CT, and so for fault tolerance (described in more
detail below), it is preferable for the ST to switch to a
separate CT.
Database consistency across CT shelves is preferably
supported through the
domain controller 400, D ~
base consistency needs to be real-time so that an ST entering
the network is allowed full service ~~~~i~ access immediately (the Service Domain message is broadcast to all STs,
and so a new ST will expect access across the full Service
Domain).
Incoming access via backup CTs requires some function
to be provided to broadcast duplicate incoming call setup
messages to all CTs that form a Service Domain. Preferably
this is handled by the service domain controller 400, which
forwards incoming call setup messages to each CT operating
in the service domain. All CTs will allocate Access-In
Traffic
and
the
setup message
via the Call Control Channel. On successful uplink access,
one CT will respond to the service domain controller with a
call accepted message, the other CTs will eventually respond
with call setup failed messages. Outgoing access via a
backup CT is similar to normal outgoing access.
Another job which can be performed by the service
domain controller is to assist the element manager 58 in
reconfiguring equipment in the event of a fault. For example,
if one CT is taken out of commission because of a fault, a
different CT can be brought 'on-line', and the service
domain controller can provide that new CT with the necessary information about the other CTs in the service domain.
FIG. 19B illustrates those elements of the subscriber
terminal used to implement RF channel switching. The radio
subsystem 420, which incorporates the transmission and
reception signal processing stages, will pass any data
received on the call control channel over line 425 to the
message decoder 430. If the decoder 430 determines that the
data on the call control channel forms a service domain
message, then this is passed over line 435 to the channel
selection controller 440, where the information within the
service domain message is stored in storage 445.
Similarly, if the message decoder identifies the data as a
'free list' identifying the available traffic channels on a
particular RF frequency, then this data is passed to the call
control function 336 and the channel selection controller 440
over path 450. The call control function 336 stores the free
list in the storage 445 for subsequent use by the call control
function 336 and the channel selection controller 440.
If the message decoder 430 determines that the data forms
an incoming call setup message, then that information is

supplied over line 455 to the call control function 336 and
the channel selection controller 440 for processing. The
incoming call setup message will typically specify a TC on
the current frequency channel which should be used to
5 access the incoming call, and the channel selection controller will attempt to establish a link on that TC. The channel
selection controller will in such cases instruct the radio
sub-system 420 over line 465 to use the current frequency
channel to establish the required link. If, on the other hand,
the traffic channel specified in the call setup message is
10
'null" the channel selection controller has the option to
change RF frequency using the information stored in storage
445 about the other CTs in the service domain.
To enable the channel selection controller 440 to receive
information about the status of links, a link operating status
can be
Over line 470
the
subsystem. This signal will give an indication of the radio link
quality, and may be a simple 'OK' or 'failed' indication, or
alternatively may include extra information such as BER
values for the link. This information can be used by the
20 channel selection controller to determine whether a particular frequency
be wed Or
To enable the call control function to specify a specific
Access-0ut
for
a line 460 is pro~vided between the call control function 336 and the channel
~ 25 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
The following examples indicate how the above described
structure may be used to perform channel switching in
30
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
35
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 Domain information in storage 445
and attempt downlink acquisition. This process will be
40
repeated until a downlink signal is acquired,
(iii) Once a backup RF channel is located, the ST will
'camp' on the Call Control Channel and may subsequently be granted traffic access.
(iv) If the CT
persists, the EM may
the service
45
domain controller 400 to reconfigure the Service
Domain so that the functioning CT shelves become
primary service providers for the pool of 'homeless'
STs.

A
that does not
in
loss of
signal will not result in RF channel switching 'en mass'.
Rather, a fault may result in excessive or total call blocking,
discussed
RF
Switching for
If Incoming access traffic
are being
the
5s
process is
in preferred
The
setup message sent Over the
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
60
440 of the ST will in such 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.
6s
(iv) When the call clears, the ST downlink preferably
switches back to the home CT.
so

US 6,222,819 B1

27

28

If Outgoing access traffic channels are being blocked, the
3. A transmission controller as claimed in claim 1,
following process is employed in preferred embodiments:
wherein the orthogonal code generator is a storage arranged
(i) The ST registers an off-hook. The Free List in storage
to store the set of orthogonal codes.
445 is checked and if a traffic channel is available, then
4. A transmission controller as claimed in claim 1,
the call control function 336 asserts a channel request s wherein the overlay code generator is a storage arranged to
on line 460 to the channel selection controller 440 and
store the set of overlay codes,
normal uplink access is attempted.
5. A transmission controller as claimed in claim 1,
(ii) If the Free List shows no Access_Out channels are
wherein the set of orthogonal codes comprise a set of
available on the current frequency channel, then the
~ ~ d ~ ~ ~ codes, h ~ ~ - ~ ~
(RW) ~
channel selection controller will be used to switch the lo
6, A transmission controller as claimed in claim 5,
ST
the next RF
in the
Domain,
wherein the set of overlay codes are derived from RW codes,
whereupon the ST will wait for the next Free List.
each set of 'n' overlay codes comprising an nxn matrix of
(iii) When the ST finds a Free List with an available
RW codes,
Access-Out channel, then uplink access is attempted
7,A central terminal of a wireless telecommunications
and the call is processed as normal.
IS system, comprising:
(iv) When the call clears, the ST downlink preferably
a transmission controller having:
switches back to the home CT.
an orthogonal code generator for providing an orthogonal
RF Channel Switching for Traffic Load Balancing
code from a set of 'm' orthogonal codes used to create
Traffic load balancing is, in preferred embodiments, pro'm' orthogonal channels within the single frequency
vided by static configuration via the EM 58. Call blocking
channel, wherein 'm' is a positive integer;
and setup time statistics may be forwarded to the EM where 20
an Operator
decide
an ST
RF
a first encoder for combining a data item to be transmitted
channel.
on the single frequency channel with said orthogonal
RF Channel Switching for Frequency Diversity
code from the orthogonal code generator, the orthogoFrequency diversity is, in preferred embodiments, pronal code determining the orthogonal channel over
vided by static configuration via the EM 58. Radio link 25
which the data item is transmitted, whereby data items
statistics may be forwarded to the EM where an operator
pertaining to different wireless links may be transmitted
may decide to move an ST to another RF channel.
simultaneously within different orthogonal channels of
Although a particular embodiment has been described
said single frequency channel;
herein, it will be appreciated that the invention is not limited
an overlay code generator for providing an overlay code
thereto and that many modifications and additions thereto 30
from a first set of 'n' overlay codes which are orthogomay be made within the scope of the invention. For example,
various combinations of the features of the following depennal to each other, wherein 'n' is a positive integer;
dent claims could be made with the features of the indepena second encoder arranged to apply the overlay code from
dent claims without departing from the scope of the present
the overlay code generator to said data item, whereby
invention.
35
'n' data items pertaining to different wireless links may
What is claimed is:
be transmitted simultaneously within the same orthogo1. A transmission controller for processing data items to
nal channel, wherein the overlay code generator is
be transmitted over a wireless link connecting a central
arranged to provide overlay codes from one or more
terminal and a subscriber terminal of a wireless telecomfurther sets of overlay codes having different numbers
munications 'ystem3 a sing1e
being 40
of overlay codes to said first set of overlay codes,
employed for transmitting data items pertaining to a pluralwherein the orthogonal code generator is a storage
ity of wireless links, the transmission controller comprising:
arranged to store the set of orthogonal codes, wherein
an orthogonal code generator for providing an orthogonal
the overlay code generator is a storage arranged to store
code from a set of 'm' orthogonal codes used to create
the set of overlay codes, wherein the set of orthogonal
'm' orthogonal channels within the single frequency 45
codes comprise a set of Radernacher-walsh (RW)
channel, wherein 'm' is a positive integer;
codes, and wherein the set of overlay codes are derived
a first encoder for combining a data item to be transmitted
from RW codes, each set of 'n' overlay codes comprison the single frequency channel with said orthogonal
ing an nxn matrix of RW codes.
code from the orthogonal code generator, the orthogo8. A central terminal as claimed in claim 7, wherein a first
rial, code determining the o!thogonal channel ,over SO of the orthogonal channels is reserved for the transmission
which the data Item 1s transmitted, whereby data Items
of signals relating to the acquisition of wireless links, and
pertaining to different wireless links may be transmitted
the transmission controller is provided in the central termisimultaneously within different orthogonal channels of
nal to enable overlay codes to be applied to data items to be
said single frequency channel;
sent within said first orthogonal channel from the central
an overlay code generator for providing an overlay code 5 s terminal to one of said subscriber terminals.
from a first set of 'n' overlay codes which are orthogo9. A central terminal as claimed in claim 8, wherein a
nal to each other, wherein 'n' is a positive integer; and
second of the orthogonal channels is reserved for the transa second encoder arranged to apply the overlay code from
mission of signals relating to the control of calls, and the
the overlay code generator to said data item, whereby
transmission controller is provided in the central terminal to
'n' data items pertaining to different wireless links may 60 enable overlay codes to be applied to data items to be sent
within said second orthogonal channel from the central
be transmitted simultaneously within the same orthogonal channel.
terminal to one of said subscriber terminals.
2. A transmission controller as claimed in claim 1,
10. A central terminal as claimed in claim 7, further
wherein the overlay code generator is arranged to provide
comprising channelisation means for determining which of
overlay codes from one or more further sets of overlay codes 65 the orthogonal channels will be subject to overlay codes, and
having different numbers of overlay codes to said first set of
for transmitting that information to a plurality of subscriber
overlay codes.
terminals within the wireless telecommunications system.

l

~

h

11. A central terminal as claimed in claim 7, wherein a
number of said orthogonal channels are designated as traffic
channels for the transmission of data items relating to
communication content, said central terminal further comprising:
a TDM encoder arranged 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, so as to enable a plurality of data
items pertaining to different wireless links to be sent
within one orthogonal traffic channel during a predetermined frame period.
12. A reception controller for processing data items
received 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 receiver 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, wherein 'm' is a positive integer;
a first encoder for applying, to signals received on the
single frequency channel, the orthogonal code provided
by the orthogonal code generator, in order to isolate
data items transmitted within the corresponding
orthogonal code;
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, wherein 'n' is a positive integer; and
a second encoder for applying, 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.
13. Areception controller as claimed in claim 12, wherein
the overlay code generator is arranged to provide overlay
codes from one or more further sets of overlay codes having
different numbers of overlay codes to said first set of overlay
codes.
14. Areception controller as claimed in claim 12, wherein
the orthogonal code generator is a storage arranged to store
the set of orthogonal codes.
15. Areception controller as claimed in claim 12, wherein
the overlay code generator is a storage arranged to store the
set of overlay codes.
16. Areception controller as claimed in claim 12, wherein
the set of orthogonal codes comprise a set of RademacherWalsh (RW) codes.
17. A controller as claimed in claim 12, wherein the set of
overlay codes are derived from RW codes, each set of 'n'
overlay codes comprising an nxn matrix of RW codes.
18. A central terminal of a wireless telecommunications
system, comprising:
a reception 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, wherein 'm' is a positive integer;
a first decoder for applying, to signals received on the
single frequency channel, the orthogonal code provided
by the orthogonal code generator, in order to isolate
data items transmitted within the corresponding
orthogonal channel;

s

10

1s

20

25

30

35

40

45

55

60

65

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, wherein 'n' is a positive integer; and
a second decoder for applying, 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.
19. A central terminal as claimed in claim 18. further
comprising channelisation means for determining which of
the orthogonal channels will be subject to overlay codes, and
for transmitting that information to a plurality of subscriber
terminals within the wireless telecommunications system.
20. Acentral terminal as claimed in claim 19. wherein the
channelisation means also determines, for those orthogonal
channels subject to overlay codes, which set of overlay
codes will apply to each orthogonal channel.
21. A subscriber 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, wherein 'm' is a positive integer;
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;
an overlay code generator for providing an overlay code
from a first set of 'n' overlay codes which are orthogonal to each other, wherein 'm' is a positive integer;
a second encoder arranged 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, wherein the overlay code generator is
arranged to provide overlay codes from one or more
further sets of overlay codes having different numbers
of overlay codes to said first set of overlay codes,
wherein the orthogonal code generator is a storage
arranged to store the set of orthogonal codes, wherein
the set of orthogonal codes comprise a set of
Rademacher-Walsh (RW) codes, and wherein the set of
overlay codes are derived from RW codes, each set of
'n' overlay codes comprising an nxn matrix of RW
codes: the transmission controller overable to enable
overlay codes to be applied to data items sent from the
subscriber terminals to the central terminal.
22. A subscriber terminal of a wireless telecommunications system, comprising:
a reception 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, wherein 'm' is a positive integer;
a first decoder for applying, to signals received on the
single frequency channel, the orthogonal code provided
by the orthogonal code generator, in order to isolate
data items transmitted within the corresponding
orthogonal channel;

US 6,222,819 B1

31

32

an overlay code generator for providing an overlay code
24. A wireless telecommunications system comprising a
from a first set of 'n' overlay codes which are orthogocentral terminal and a plurality of subscriber terminals,
nal to each other, the set of 'n' overlay codes enabling
wherein at least one of the subscriber terminals comprises:
'n' data items pertaining to different wireless links to be
a transmission controller having:
transmitted
within the same
5
an orthogonal code generator for providing an orthogonal
channel, wherein 'n' is a positive integer;
code from a set of 'm' orthogonal codes used to create
a second decoder for applying, to the data items of the
'm' orthogonal channels within the single frequency
orthogonal channel, the overlay code from the overlay
channel, wherein 'm' is a positive integer;
code generator so as to isolate a particular data item
a first encoder for combining a data item to be transmitted
transmitted using that overlay code, wherein the over- 10
on the single frequency channel with said orthogonal
lay code generator is arranged to provide overlay codes
code from the orthogonal code generator, the orthogofrom one or more further sets of overlay codes having
nal code determining the orthogonal channel over
different numbers of overlay codes to said first set of
which the data item is transmitted, whereby data items
overlay codes, wherein the orthogonal code generator
pertaining to different wireless links may be transmitted
is a
arranged to store the set of
1s
simultaneously within different orthogonal channels of
codes, wherein the overlay code generator is a storage
said single frequency channel;
arranged to store the set of overlay codes, wherein the
an
generator for providing an
set of orthogonal codes comprise a set of Rademacherfrom a first set of 'n' overlay codes which are orthogoWalsh (RW) codes, and wherein the set of overlay
nal to each other, wherein 'n' is a positive integer; and
codes are derived from RW codes, each set of 'n, 20
a second encoder arranged to apply the overlay code from
overlay codes comprising an nxn matrix of RW codes.
the overlay code generator to said data item, whereby
23. A wireless telecommunications system comprising a
'n' data items pertaining to different wireless links may
central terminal and a plurality of subscriber terminals,
be transmitted simultaneously within the same orthogowherein the central terminal comprises:
25
nal channel; and
a transmission controller having:
the
an orthogonal code generator for providing an orthogonal
a reception controller having:
code from a set of 'm' orthogonal codes used to create
'm' orthogonal channels within the single frequency
an orthogonal code generator for providing an orthogonal
channel, wherein 'm' is a positive integer;
code from a set of 'm' orthogonal codes used to create
'm' orthogonal channels within the single frequency
a first encoder for combining a data item to be transmitted 30
channel;
on the single frequency channel with said orthogonal
code from the orthogonal code generator, the orthogoa first decoder for applying, to signals received on the
nal code determining the orthogonal channel over
single frequency channel, the orthogonal code provided
which the data item is transmitted, whereby data items
by the orthogonal code generator, in order to isolate
pertaining to different wireless links may be transmitted 35
data items transmitted within the corresponding
simultaneously within different orthogonal channels of
orthogonal channel;
said single frequency channel;
an overlay code generator for providing an overlay code
an overlay code generator for providing an overlay code
from a first set of 'n' overlay codes which are orthogofrom a first set of 'n' overlay codes which are orthogonal to each other, the set of 'n' overlay codes enabling
nal to each other, wherein 'n' is a positive integer; and 40
'n' data items pertaining to different wireless links to be
a second encoder arranged to apply the overlay code from
transmitted simultaneously within the same orthogonal
the overlay code generator to said data item, whereby
channel; and
'n' data items pertaining to different wireless links may
a second decoder for applying, to the data items of the
be transmitted simultaneously within the same orthogoorthogonal channel, the overlay code from the overlay
45
nal channel; and
code generator so as to isolate a particular data item
at least one of the subscriber terminal comprises:
transmitted using that overlay code.
25. A method of processing data items to be transmitted
a reception controller having:
over a wireless link connecting a central terminal and a
an orthogonal code generator for providing an orthogonal
subscriber terminal of a wireless telecommunications
code from a set of 'rn' orthogonal codes used to create
system, a single frequency channel being employed for
'm' orthogonal channels within the single frequency
transmitting data items pertaining to a plurality of wireless
channel;
links, the
a first decoder for applying, to signals received on the
providing an orthogonal code from a set of 'm' orthogonal
single frequency channel, the orthogonal code provided
codes used to create 'm' orthogonal channels within the
by the orthogonal code generator, in order to isolate 55
single frequency channel, wherein 'm' is a positive
data items transmitted within the corresponding
orthogonal channel;
integer;
combining a data item to be transmitted on the single
an overlay code generator for providing an overlay code
frequency channel with said orthogonal code, the
from a first set of 'n' overlay codes which are orthogoorthogonal code determining the orthogonal channel
nal to each other, the set of 'n' overlay codes enabling 60
over which the data item is transmitted, whereby data
'n' data items pertaining to different wireless links to be
items pertaining to different wireless links may be
transmitted simultaneously within the same orthogonal
transmitted simultaneously within different orthogonal
channel; and
channels of said single frequency channel;
a second decoder for applying, to the data items of the
providing an overlay code from a first set of 'n' overlay
orthogonal channel, the overlay code from the overlay 65
code generator so as to isolate a particular data item
codes which are orthogonal to each other, wherein 'n'
transmitted using that overlay code.
is a positive integer; and

US 6,222,819 B1

33

34

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

-