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

Filing 182

REPLY to 167 Claim Construction Brief,,,,, filed by WI-LAN Inc.. (Attachments: # 1 Affidavit Declaration of Jeffrey T. Han, # 2 Exhibit I - true and correct copy of U.S. Patent No. 5,603,095, # 3 Exhibit II - true and correct copy of U.S. Patent No. 5,239,682, # 4 Exhibit III - true and correct copy of U.S. Patent No. 5,659,598., # 5 Exhibit IV - true and correct copy of WO 96/37054., # 6 Exhibit V - true and correct copy of Sanford Bingham, Multiplexers, Computerworld, Nov. 27, 1989, at 61., # 7 Exhibit VI - true and correct copy of David J. Stang, Network)(Weaver, David)

EXHIBIT II

111111111111111111111111111111111111111111111111111111111111111111111111111

United States Patent

USOO5239682A
[19]

[11]

Strawcynski et al.
[54]

[75]

[45]

INTER·CELL CALL HAND·OVER IN RADIO
COMMUNICATION SYSTEMS WITH
DYNAMIC CHANNEL ALLOCATION
Inventors: Leo Strawcynski; Howard M.
Sandler, both of Ottawa; Gregory L.
Plett, North Gower; Dand G. Steer,
Nepean, all of Canada

[73]

Assignee:

[21]

Appl. No.: 710,867

[22]

Filed:

[30]

Northern Telecom Limited, Montreal,
Canada

Jun. 6, 1991

Foreign Application Priority Data

Dec. 5, 1990 [CAl

Canada ................................. 2031551

[51]
[52]

Int. Cl.l ......................... A04B 7/00; H04B 17/00
U.S. Cl................................... 455/54.1; 455/56.1;

[58]

455/62; 379/59
Field of Search .................... 455/33.1,33.2, 33.4,
455/54.1,54.2,56.1,62; 379/58, 59, 60

[56]

References Cited
U.S. PATENT DOCUMENTS

5,239,682
Aug. 24, 1993

5,093,926 3/1992 Sasufa ................................... 455/62
Primary Examiner-Reinhard J. Eisenzopf
Assistant Examiner-Lisa Charouel
Attorney, Agent, or Firm-Jean·Pierre Fortin
[57]

ABSTRACI'

The call hand-over technique of this invention is characterized by the use of channel information from both
the target base station and subscriber terminal in determining which radio traffic channel will be used to hand
over a call in progress from a serving base station to a
target base station. Calls are handed over to the radio
channel which, of a set of channels under consideration
by the subscriber terminal, contains the least amount of
interference as measured by the subscriber terminal.
The set of channels under consideration by the subscriber terminal is a subset of the entire set of channels
allocated to the service. This subset is comprised of
those channels having little interference, as measured
by the target base station. The hand-over technique
thereby assures that calls proceed on channels containing little interference from the viewpoints of both the
target base station and subscriber terminal.

4,475,010 10/1984 Huensch et al. ................... 455156.1
5,038,399 8/1991 Bruckert ............................... 455/62
SERVING
BASE STATION

SUBSCRIBER TERMINAL

Patent Number:
Date of Patent:

7 Claims, 6 Drawing Sheets
TARGET
BASE STATION

SEL A GP. OF
CANDIDATE
TRAFFIC CH.
WITH LOW

r----I

WITH LOW
INTERFR.

SEND GROUP OF
TRAFF I C CH. TO
SUB. TER.

SEND GROUP OF
TRAFF I C CH. TO
SERVING BASE
STATION

SEND
CANDIDATE
TRAFFIC CH. T o r - - - - - ,
TARGET
ASE STATION

WIL-0192815

u.s. Patent

Aug. 24, 1993

Sheet 1 of 6

5,239,682

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WIL-0192816

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Sheet 2 of 6

Aug. 24, 1993

5,239,682

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WIL-0192817

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Aug. 24, 1993

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WIL-0192818

u.s. Patent

Aug. 24, 1993

SUBSCRIBER TERMINAL

SERVING
BASE STATION

Sheet 4 of 6

5,239,682

TARGET
- BASE ST ATION

SEl. A GP. OF
CANDIDATE
TRAFFIC CH.
WITH LOW
INTERFR

SCAN EACH
CANDIDATE
TRAFFIC CH.
IN GP.

SEND GROUP OF
SEND GROUP OF
TRAFFIC CH. TO
TRAFFIC CH. TO
14------1
SUB. TER
...-~ SERVING BASE
STATION

SELECT &
SEND A
SEND
CANDIDATE
CANDIDATE
TRAFFIC CH. t---~TRAFFIC CH. TO
WITH LOW
TARGET
INTERFR.
BASE STATION

FIG.4a

WIL-0192819

u.s. Patent

Aug. 24, 1993

SUBSCRIBER TERMINAL

*

r--__

Sheet 5 of 6

SERVING
BASE ST ATION

5,239,682

TARGET
BASE STATION

ONITOR CHANNEL
FOR
INTERFERENCE

SEND
RECEIVE
RECEIVE
REQUEST
REQUEST
REQUEST
FOR NEW ~---4~ FOR NEW t------t~ FOR NEW
CHANNEL
CHANNEL
CHANNEL

DO INTER-CELL
CALL
HANDOVER TO
CANDIDATE
TRAFF I C CH ANNEL

DO INTER-CELL
CALL
HANDOVER TO
CANDIDATE
TRAFFIC CHANNEL

DO INTER-CELL
CALL
HANDOVER TO
CANDIDATE
TRAFFIC CHANNEL

FIG.4b

WIL-0192820

u.s.

Patent

Aug. 24, 1993

SUBSCRIBER TERMINAL

Sheet 6 of 6

SERVING
BASE STATION

....

...---

5,239,682

TARGET
BASE STATION

MONITOR CHANNEL
FOR
INTERFERENCE

YES

RECEIVE
REQUEST
FROM
SERVING
STATION

SEND

RECEIVE
REQUEST

REQUEST I-----~
FROM
FOR NEW
SERVING
CHANNEL
ST ATION

DO INTER-CELL
CALL HAND-O VER
TO CANDIDATE
TRAFFIC
CHANNEL

DO INTER-CELL
CALL HANO-O VER
TO CANDIDATE
TRAFFIC
CHANNEL

DO INTER-CELL
CALL HAND-OVER
TO CANDIDATE
TRAFFIC
CHANNEL

FIG.4c

WIL-0192821

1

5,239,682

2

As indicated above, when this is done without changing
INTER-CELL CALL HAND-OVER IN RADIO
the base station that communicates with the subscriber,
COMMUNICATION SYSTEMS WITH DYNAMIC
it is known as an "intra-ceU" hand-over, i.e., within a
CHANNEL ALLOCATION
cell.
5
When either an intra- or inter-cell hand-over is perFIELD OF THE INVENTION
formed in a DCA system, a suitable radio channel must
be selected to continue the call. In present systems inThis invention relates to radio communication systems which use dynamic channel allocation, especially,
corporating DCA, the determination of which channel
but not restricted to, cellular radio systems.
is used for a call set-up or hand-over is made according
10 to channel information from the base station or the
DESCRIPTION OF THE PRIOR ART
subscriber terminal. The disadvantage with this apA duplex radio link conveying user analogue and/or
proach is that appreciable interference may be present
on the selected channel from the viewpoint of the other
digital information shall henceforth be referred to as a
"call". An example is a telephone call over a wireless
end of the link. For example, a traffic channel may have
15 little appreciable interference, as monitored by the servchanne1.
Cellular radio communication systems are able to
ing base station. However, the same traffic channel may
have unacceptable interference at the subscriber termiservice a high volume of traffic with a limited amount
of radio spectrum by re-using the same radio channels in
na1 or at the target base station if a inter-cell handover
is attempted. Therefore, the presence of interference
sufficiently separated cells. In conventional city-wide
mobile cellular systems, such as the North American 20
Advanced Mobile Phone System, the frequency allocamay reduce the quality of the link and also make it more
susceptible to any further channel impairments which
tions for a specific cell are fixed; Le., each cell can make
might arise.
.
use of only a specified subset of channels of those allocated to the entire service. The allocations of channels
Accordingly, it is an object of the present invention
require careful engineering analyses of radio propaga- 25 to provide an improved method of performing inter-cell
tion conditions and traffic patterns within and between
hand-over in radio systems with DCA, characterized by
the cells. Fixed allocation cellular radio systems are
the use of channel information from both the target base
engineered so that harmful levels of interference from
station and subscriber terminal in determining which
signals used in neighbouring cells are unlikely to be
traffic channel to use.
30
encountered.
SUMMARY OF THE INVENTION
When the communication link is changed without
The hand-over procedures of this invention require
changing the base station that communicates with the
that there be a means of communicating call supervisubscriber, it is known as an "intra-cell" hand-over, i.e.,
sory information between a base station and a subscriber
within a cell. A description of an intra-cell handover is
disclosed in a co-pending application entitled "Im- 35 terminal. A suitable means is an in-band signalling chanproved Intra-cell Call Handover in Radio Communicanel associated with each traffic channel. When a subtion Systems with Dynamic Channel Allocation" filed
scriber moves away from a serving cell towards or into
on Jun. 6, 1991 and having Ser. No. 07/710,866. On the
an adjacent cell, or moves within range of another base
other hand, when a subscriber terminal moves out of the
station, an inter-cell handover maybe necessary. In adcoverage area of one base station and into that of an- 40 vance of an inter-cell hand-over, the target, i.e., proother, the call may be maintained by switching the
spective new base station, compiles a list of candidate
communication link to the closer base station. This is
traffic channels which have low interference from its
known as an "inter-cell" hand-over, i.e., between cells.
perspective (and are not otherwise undesirable due to
Micro-cellular radio systems tend to use dynamic,
additional information known to the base stati~m). This
rather than fixed, channel allocation. With dynamic 45 list is passed via a wired link to the original base station.
channel allocation (DCA) each cell can potentially use
The original base station conveys the information over
any traffic channel for a given call of those allocated to
the inband or associated signalling channel to the subthe entire service. The decision as to which channel to
scriber terminal. The subscriber terminal checks these
use is made dynamically. i.e. based on channel usage
candidates, chooses the traffic channel which has the
conditions experienced at the time of call set-up. The 50
lowest interference from its perspective, and reports
decision is also made in a decentralized manner, i.e. by
this choice to the original base station over the associthe base station or subscriber terminal in question, withated signalling channel. The original base station conout any centralized coordination with other cells. This
veys this information to the target base station via the
has the advantages that no detailed engineering analyses
are required for each cell site, cell sites can easily be 55 wired link. If an inter-cell hand-over becomes necessary, the call proceeds on the agreed-upon traffic chanadded or moved, and more traffic can be handled than
nel to the target base station.
with fixed allocation, because channels unused in neighAccordingly, an aspect of the present invention is to
bouring cells can be "borrowed". Examples of radio
provide a method of performing a radio channel handsystems which use DCA are the digital U.K. CT2 system, and some models of analogue North American 60 over in a radio system with dynamic channel allocation,
from a serving base station in communication with a
46/49 MHz cordless telephones.
subscriber terminal to a target base station, comprising
A disadvantage of DCA, however, is that interferthe steps of:
ence may suddenly arise in an existing call if another
selecting, from a plurality of traffic channels, a numcall is set up on the same or an adjacent channel in a
nearby cell. Without fixed channel assignments, free- 65 ber of suitable traffic channels, as measured at the target
base station;
dom from interference is not assured. To escape from
forwarding, from the target base station to the servinterference, an existing call may need to be handed
over to a radio channel which is free from interference.
ing base station, a message indicative of which traffic

WIL-0192822

3

5,239,682

4

channels were determined suitable at the target base
station 24b, the call is handed over from the serving
base station 240 to the target base station 24b.
station;
sending the message to the subscriber terminal along
Referring now to FIGS. 2 and 40, the base station
a signalling channel linking the serving base station and
24b, which has been selected to be the target base staS tion, would scan all available traffic channels, and select
the subscriber terminal;
traffic channels that are useable or free of interference
receiving the message at the subscriber terminal;
at the base station's end of the link. It is to be noted that
selecting, from the traffic channels indicated by the
the base stations could also be configured such that all
message, a traffic channel that is also suitable at the
traffic channels are prescanned. That is, the base stasubscriber terminal;
forwarding, to the serving base station, a response 10 tions could scan the traffic channels continuously or on
a regular interval and thereby maintain a list of useable
message indicative of a selected traffic channel;
traffic channels. A list of frequencies or traffic channels
sending the response message to the target base station; and
is made and forwarded to serving base station 240 via an
switching to the selected radio channel at the subinter base station link or trunk. 26a and 26b linking the
scriber terminal and the target base station.
15 serving base station 240, the target base station 24b and
PBX 20. In the preferred embodiment, only a certain
BRIEF DESCRIPTION OF THE DRAWINGS
number of traffic channels would be selected as useable.
FIG. 1 is an illustration of a typical low power radio
For example, the base station could be configured to
system embodying the invention;
select the first 3 traffic channels with interference levels
FIG. 2 illustrates how a call hand over can be imple- 20 below a threshold. Similarly, the base station could also
mented in a low power radio system such as shown in
be configured to select the 3 traffic channels which
FIG. 1;
have the lowest interference levels. If there are no suffiFIG. 3 illustrates the frame structure ofa traffic chancient traffic channels with interference below the
nel; and
threshold, then, additional channels with interference
FIGS. 40 to 4c are flow diagrams illustrating the 25 levels above the threshold may be selected as well. The
inter-cell hand-over technique of the present invention.
traffic channels selected would be those that have the
lowest interference levels even though the levels are
DESCRIPTION OF THE PREFERRED
above the threshold. It will of course be understood that
EMBODIMENT
if some of the latter traffic channels are considered to
In the illustration of FIG. 1, a low-power wireless 30 otTer inadequate communication between the base stacommunication system is shown. A typical network can
tion and the subscriber terminal, they would be exeluded from the selection. The serving base station 240
consist of one or more small base stations, such as
shown at reference numeral 11. In FIG. 1, base station
then forwards the list of traffic channels to the sub11 is connected to the Public Switched Telephone Netscriber terminal 22 via the inband or associated signalwork (PSTN) 12. Base stations are basically used as 35 ling channel. Once received, the list of useable frequenradio transceivers. These can be deployed in offices,
cies or traffic channels, is scanned by subscriber termiresidences, and public areas, such as airports, gas stanal 22. The subscriber terminal can then select frequentions and shopping malls, etc. Base stations form the
cies or traffic channels of those indicated in the list
interface between a number of subscriber terminals such
which are also free of interference at the subscriber end
as portable handsets 13a and 13b and PSTN 12. Simi- 40 of the link. In the preferred embodiment, the traffic
larly, several base stations, such as those shown at referchannel determined to contain the least interference
ence numerals 140 and 14b can also be linked to a host,
level of those scanned is selected by the subscriber tersuch as a private branch exchange PBX 15 to provide
minal.
coverage of larger areas, in say, a private business or
Once the traffic channel containing the least interferoffice building. A subscriber terminal 16 could there- 45 ence is selected, the subscriber terminal sends a message
fore operate in an office building via base station 140 or
to the serving base station 240 on the inband or associ14b and outside thereof, via base station 11. Such a
ated signalling channel providing an indication of
wireless PBX system is disclosed in U.S. Pat. No.
which traffic channel was selected. The serving base
4,771,448.
station then forwards the selection to the target base
Referring now to FlO. 2, we have shown a low 50 station 24b. As shown in FIGS. 4b and 4c, if an inter-cell
power wireless communication system which can be
hand-over becomes necessary, the subscriber terminal
installed in a private business or office building. A PBX
22 and the target base station 24b are switched over to
20 is used by POTS (Plain Old Telephone Service) 21
the selected channel and the call continues. If none of
and a wireless subscriber terminal 22 to establish call
the traffic channels in the list were determined to be
connections to PSTN 23. Base stations 240 and 24b can 55 adequate, a message can be sent to the base station indibe placed at various locations in the office building to
eating that the call hand-over between the subscriber
allow the use of a wireless subscriber terminal 22 where
terminal and the target base station cannot proceed.
required. In the illustration, subscriber terminal 22 is
The hand-over Can then be initiated, by instructing
being served by base station 240. In the event that interboth the target base station and the subscriber terminal
ference arises on the communication channel linking the 60 to switch to the selected channel. The serving base
base station and the subscriber terminal, an intracell
station would then release the channel once the handhandover may be necessary. That is, another channel
over is complete.
without interference would be selected. A description
The signalling and traffic channels of the wireless
of an intra-cell handover is disclosed in a co-pending
communication system may be used in time-division
application entitled "Improved Intra-cell Call Hand- 65 duplex mode. That is, base station and subscriber termiover in Radio Communication Systems with Dynamic
nal alternately transmit so that their transmissions do
Channel Allocation". In the event that the subscriber
not overlap. This technique is commonly referred to as
terminal moves to an area which is better served by base
"pingpong". This is shown in FIG. 3.

WIL-0192823

5

5,239,682
6

2, A method as derIDed in claim 1, wherein said group
As is shown, the frame structure is comprised of one
of candidate traffic channels are selected at the target
slot 42 used for communication between the base station
base station by:
and the subscriber terminal and another slot 43 for comscanning each traffic channel in said plurality of trafmunication between the subscriber terminal and the
fic channels;
detecting the interference level on the scanned traffic
base station, Each slot contains a voice or data portion
44 and an inband or associated signalling channel comchannels,and
selecting the scanned traffic channel as the candidate
prised of two sets of bits 45a and 4Sb, In the preferred
embodiment, the voice or data portion contains 64 bits
traffic channel if the interference level is below a
of information per frame and the inband or associated Hi
first predetermined threshold,
3, A method as defIDed in claim 2, wherein additional
signalling channel contain four bits of information per
frame,
candidate traffic channels are selected from the plurality of traffic channels available for service if an inadeWhat is claimed is:
I, A method of performing a radio channel hand-over
quate number of the candidate traffic channels were
in a radio system with dynamic channel allocation, from 15 found to have interference levels below the fIrSt predetermined threshold,
4, A method as defined in claim 5, wherein if addia serving base station in communication with a subscriber terminal to a target base station, comprising the
tional candidate traffic channels are selected, a traffic
steps of:
channel of the additional candidate traffic channels
selecting, at said target base station, from a plurality 20 having the lowest mterference level above the fIrst
of traffic channels, a group of candidate traffic
predetermined threshold will be selected,
5, A method as defIDed in claim 4, wherein if any
channels, with low interference levels as measured
at the target base station;
remaining traffic channels in said plurality have an exforwarding, from the target base station to the servcessive level of interference offering inadequate coming base station, a message indicative of the candi- 25 munication between the target base station and the subdate traffic channels in said group;
scriber terminal, they will be excluded from the selec'
'b
'
tion, A
6
thod d fi d' l' 2 h '
'd
sen dIDg th e message f rom t h e servmg ase station to
'be
' I al
'11'
h I ' me
as e me m c 81m , W erem sat mest,he ,subscn r t~rmIDa on~ a signa IDg c ~ne
sage is sent to the serving base station by:
grouping as a list, each candidate traffic channel idenlmking the servmg base station and the subscnber 30
terminal;
tifled as having low interference levels at the target
receiving the message at the subscriber terminal;
base station; and
scanning each candidate traffic channel in said group
forwarding to the serving base station the list of the
indicated by the message;
candidate traffic channels, along an inter base staselecting, the candidate traffic channel from said 35
tion connection link,
,
group having a lowest interference level, as mea7, A method as defIned ~ c1,aim 6, w~erein the candisured at the subscriber terminal'
date traffic channel on the Itst IS detemuned to have low
,
"
,
interference levels at the subscriber terminal by:
forwardmg,' to the servIDg base statIOn, , a response
' eac
'd 'fi
, ,
scanrungh cand'date tramIC ch anne1 I ent! Ied on
I
message mdlcattve of the selected candIdate traffic 40
the list,
channel;
detecting'the interference level on each scanned cansending the response message to the target base stadidate traffic channel' and
tion; and
selecting the candidate traffic channel with the lowswitching to the selected candidate traffic channel at
est interference level.
• • • • •
the subscriber terminal and the target base station, 45

50

55

60

65

WIL-0192824