METHOD AND ARRANGEMENT FOR CHANNEL ALLOCATION IN A RADIO COMMUNICATIONS SYSTEM

METHODE ET DISPOSITIF D'ATTRIBUTION DE CANAL DANS UN SYSTEME DE COMMUNICATIONS RADIO

English Abstract

The present invention relates to a method and an
arrangement for channel allocation in a radio communication
system in which data is transmitted between two stations over
two or more radio channels (SPDCH3-SPDCH7). Data is
communicated as packets which are divided into blocks (b1-bm)
while the transmission follows a protocol for automatic
re-transmission of data that have been erroneously transmitted.
In accordance with the proposed method, channels for
re-transmission (SPDCH5, SPDCH6) are allocated with respect to a
transmission parameter (TP), which has been created at a
previous transmission and which is based upon information of
the result (Nack) of said previous transmission. The
transmission parameter (TP) is aimed to ensure that
re-transmission is performed via those channels (SPDCH5, SPDCH6)
which have the highest probability of transmitting data
correctly. The channels (SPDCG5, SPDCH6) which had the
highest transmission quality in said previous transmission
are expected to have the highest transmission quality also by
re-transmission.

French Abstract

Méthode et dispositif d'attribution de canal dans un système de communications radio dans lequel des données sont transmises entre deux stations sur deux ou plus de deux canaux radio (SPDCH3-SPDCH7). Les données sont communiquées sous forme de paquets qui sont divisés en blocs (b1-bm) tandis que la transmission suit un protocole de retransmission automatique de données ayant été transmises de manière erronée. Selon la méthode envisagée, les canaux de retransmission (SPDCH5, SPDCH6) sont attribués par rapport à un paramètre de transmission (TP) qui a été élaboré lors d'une transmission antérieure et qui est basé sur les informations concernant le résultat (accusé de réception) de la transmission précédente. Le paramètre de transmission (TP) a pour but de garantir que la retransmission s'effectue par les canaux (SPDCH5, SPDCH6) qui ont le plus de chance de transmettre correctement les données. Les canaux (SPDCH5, SPDCH6) qui offraient la meilleure qualité de transmission lors des transmissions précédentes doivent, selon toute probabilité, présenter également la plus haute qualité de transmission pour la retransmission.

Claims

31
The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A method of channel allocation in a radio
communication system comprising a primary station and a
secondary station adapted to communicate data over two or
more channels in accordance with a protocol for automatic
re-transmission of erroneously transmitted data, the method
comprising the steps of:
deriving for a given transmission a transmission
parameter associated with each of the two or more channels,
wherein said transmission parameter is related to channel
quality; and
allocating for transmission, in accordance with the
transmission parameter created from a previous
transmission, at least one preceding channel used for
previously transmitting data when data is transmitted
erroneously over a given channel.
2. A method according to claim 1, wherein said previous
transmission of data is a nearest preceding data
transmission.
3. A method according to claim 1 or 2, wherein the
transmission parameter is based on information relating to
which channel was used for transmitting each given data
between the primary station and the secondary station.
4. A method according to claim 3, further comprising the
step of allocating for transmission at maximum one channel
of the previous channels use for earlier transmitted data
on which the number of errors occurrent in previous data

32
transmission was greater than a predetermined number n F,
when data is transmitted erroneously over the given
channel.
5. A method according to claim 4, wherein n F =0.
6. A method according to claim 4, wherein when each of
all channels that were used in the previous transmission,
transmitted data having more errors than n F, allocating for
re-transmission of the data at least one further channel
that was not used in the previously transmission, provided
that such a channel is available.
7. A method according to claim 3, further comprising the
step of for each used channel, calculating a quality
measurement, Q z, according to
<IMG>
where N tot represents a total number of blocks transmitted
on said channel where N Nack denotes a number of blocks
transmitted erroneously on said channel by the previous
channels used for earlier data transmission for which the
quality measurement, Q z, is below a predetermined quality
limit Q1.
8. A method according to claim 7, wherein Q1 =0.9.
9. A method according to claim 7, further comprising the
step of when the quality measurement, Q z, for all channels
that were used in the previous transmission is below Q1,
allocating for transmission at least one further channel

33
that was not used in the previous transmission, provided
that one such channel is available.
10. A method according to any one of claims 1 to 9,
wherein said channels are time divided.
11. A method according to any one of claims 1 to 9,
wherein said channels are frequency divided.
12. A method according to any one of claims 1 to 9,
wherein said channels are divided by a spreading code
unique for each channel.
13. An arrangement for allocating channels in a radio
communications system, the arrangement comprising:
a primary station and a secondary station adapted to
communicate data over two or more channels in accordance
with a protocol for automatic re-transmission of
erroneously transmitted data, wherein the primary station
includes a control unit,
the control unit including:
means for deriving a transmission parameter relating
to channel quality for each of the two or more
channels; and
channel allocating means for allocating, in an event
of erroneously transmitted data over a given channel,
at least one of the previous channels used for earlier
data transmission in accordance with the transmission
parameter created from a previous transmission.
14. An arrangement according to claim 13, wherein said
previous transmission is a nearest preceding data
transmission.

34
15. An arrangement according to claim 13, wherein the
transmission parameter is based on information relating to
the channel that was used for transmitting each given data
between the primary station and the second station.
16. An arrangement according to claim 15, wherein the
control unit calculates a quality measurement, Q z, according
to
<IMG>
for each used channel where N tot represents a total number
of blocks that have been transmitted on said channel and
where N Nack denotes a number of blocks transmitted
erroneously on said channel where at maximum one channel of
previous channels for earlier transmitted data for which
the quality measurement, Q z, is below a predetermined
quality limit, Q1, is allocated for retransmission.
17. An arrangement according to claim 16, wherein Q1 =0.9.
18. An arrangement according to claim 16, wherein when the
quality measurement, Q z, for all channels that were used in
a previous transmission is beneath Q1, the control unit
allocates for re-transmission at least one further channel
that was not used in the previous transmission, provided
that such a channel is available.
19. An arrangement according to claim 15, wherein in the
event of erroneously transmitted data over a given channel,
the control unit allocates for re-transmission at maximum

35
one channel from the previous channels used for earlier
data transmission on which a number of errors in said
previous transmission was greater than a predetermined
number n F.
20. An arrangement according to claim 19, wherein n F =0.
21. An arrangement according to claim 19, wherein when all
channels used in a previous transmission have each
transmitted data with more errors than n F, the control unit
allocates for re-transmission at least one further channel
that was not used in said previous transmission, provided
that such a channel is available.
22. An arrangement according to any one of claims 13 to
21, wherein the channel allocating means includes a
processor and a memory unit; and the processor creates said
transmission parameter for each transmission of data
between the primary station and the secondary station and
stores the transmission parameter in the memory unit.
23. An arrangement according to any one of claims 13 to
22, wherein the arrangement is included in the primary
station.
24. An arrangement according to any one of claims 13 to
23, wherein the primary station is comprised of a base
station system; and the secondary station is a mobile
station.
25. An arrangement according to any one of claims 13 to
23, wherein the primary station is a base station; and the
secondary station is a mobile station.

36
26. An arrangement for channel allocation in a radio
communication system, the arrangement comprising:
a primary station and a secondary station adapted to
communicate data over two or more channels in accordance
with a protocol for automatic re-transmission of
erroneously transmitted data, where a status of transmitted
data is given through a reception acknowledgment, which
data is divided into one or more packets, each of which
comprises one or more blocks, the primary station including
a control unit for deriving for a given transmission a
transmission parameter, associated with each of said two or
more channels, wherein the transmission parameter is
related to channel quality, the control unit including:
channel allocation means for allocating in an event
of erroneously transmitted data over a given channel
at least one previous channel for earlier transmitted
data in accordance with the transmission parameter
created from a previous transmission; and the
transmission parameter is based on information
relating to which channel was used for the
transmission of each given data between the primary
station and the secondary station.
27. An arrangement according to claim 26, wherein said
channel allocation means includes a processor and a memory
unit; and the processor creates said transmission parameter
for each transmission of data between the primary station
and the secondary station and stores this parameter in the
memory unit.

37
28. An arrangement according to claim 27, the transmission
parameter is created by the processor with the aid of
information relating to the previous channels for earlier
transmitted data and a reception acknowledgement; and the
transmission parameter contains information relating to
those channels that can be used for re-transmission of
erroneously transmitted data.
29. An arrangement according to claim 27, wherein the
memory unit functions to store the transmission parameter
at least until a reception acknowledgement has been
received informing that an entire packet in which the
blocks are included has been transmitted correctly.
30. An arrangement according to claim 27, wherein in the
event of data being transmitted erroneously over a given
channel, the channel allocation means allocates for re-
transmission at maximum one channel of the at least one
previous channel used for the previous transmission of data
on which a number of errors occurring in said previous
transmission was greater than a predetermined number n F.
31. An arrangement according to claim 30, wherein n F =0.
32. An arrangement according to claim 30, wherein when
each of the channels used in a previous transmission
transmitted data with more errors than n F, the control unit
functions to allocate for re-transmission at least one
further channel that was not used in the previous
transmission, provided that one such channel is available.

38
33. An arrangement according to claim 27, wherein the
channel allocation means calculates for each used channel a
quality measurement, Q z, according to
<IMG>
where N tot represents a total number of blocks that have
been transmitted on said channel and where N Nack denotes a
number of erroneously transmitted blocks on the channel;
and wherein for re-transmission there is allocated at
maximum one channel of the previous channels used for
previous data transmission for which the quality
measurement, Q z, is below a predetermined quality limit, Q1.
34. An arrangement according to claim 33, wherein Q1 =0.9.
35. An arrangement according to claim 33, wherein when the
quality measurement, Q z, for all channels used in a previous
transmission is beneath Q1, the channel allocation means
allocates for re-transmission at least one further channel
which was not used in the previous transmission, provided
that one such channel is available.
36. A base station controller adapted to communicate data
with at least one mobile station via at least one base
station and over two or more channels in accordance with a
protocol for automatic re-transmission of erroneously
transmitted data, wherein the base station controller
includes a control unit for creating a transmission
parameter that is derived with the aid of information

39
relating to channel quality for each transmission of said
data between the base station and the mobile station,
wherein the control unit includes channel allocation means
for allocating in an event of erroneously transmitted data
over a given channel at least one previous channel for
earlier transmitted data in accordance with the
transmission parameter created from a previous
transmission.
37. A base station controller according to claim 36,
wherein said previous transmission is a nearest preceding
data transmission.
38. A base station controller according to claim 36,
wherein the transmission parameter is based on information
relating to the channel that was used for transmitting each
given data between the base station and the mobile station.
39. A base station controller according to claim 38,
wherein in the event of erroneously transmitted data over a
given channel, the control unit allocates for re-
transmission at maximum one channel from the previous
channels used for the earlier transmission of data in which
a number of occurrent errors was greater than a
predetermined number n F.
40. A base station controller according to claim 39, N F =0.
41. A base station controller according to claim 39,
wherein all channels that were used in a previous
transmission, each transmitted data with more errors than
n F, the control unit allocates for re-transmission at least

40
one further channel that was not used in the previous
transmission, provided that one such channel is available.
42. A base station controller according to claim 38,
wherein the control unit calculates for each used channel a
quality measurement, Q Z, according to
<IMG>
where N tot represents a total number of blocks that were
transmitted on said channel and where N Nack denotes a number
of blocks transmitted erroneously on said channel; there is
allocated for re-transmission at maximum one channel of the
at least one previous channel used for previous transmitted
data for which the quality measurement, Q Z, is below a
predetermined quality limit, Q1.
43. A base station controller according to claim 42,
wherein Q1 =0.9.
44. A base station controller according to claim 42,
wherein when the quality measurement, Q Z, for all channels
that were used in a previous transmission is below Q1, the
control unit allocates for re-transmission at least one
further channel that was not used in a previous
transmission, provided that one such channel is available.
45. A base station controller according to any one of
claims 36 to 44, wherein said channel allocation means
includes a processor and a memory unit; and the processor
for each transmission of data between the base station and

41
the mobile station creates said transmission parameter and
stores said parameter in the memory unit.
46. In a radio communication system, a method for channel
allocation, the method comprising the steps of:
transmitting data over a plurality of channels from a
primary station to a secondary station;
deriving a channel quality estimation for each of said
plurality of channels; and
selecting one of the plurality of channels, based upon
said channel quality estimation, for retransmission of data
that was erroneously transmitted, if a data transmission
error occurs while transmitting said data over one of the
plurality of channels.

Description

CA 02245881 1998-08-13
WO 97/30563 PCT/SE97/002I8
1
METHOD AND ARRANGEMENT FOR CHANNEL ALLOCATION
~ IN A RADIO COMMUNICATIONS SYSTEM
~ FIELD OF INVENTION
The present invention relates to a method fox channel allocation
in a radio communications system in which data is transmitted as
packets in accordance with a protocol for the automatic retran-
smission of erroneously transmitted data. More specifically, the
invention relates to a method for channel allocation in the
transmission of erroneously transmitted data. Packet transmission
of data over radio channels is applied in a GSM system (GSM -
Global System for Mobile communication) for instance. The radio
channels may be frequency division multiple access channels
25 (FDMA), time division multiple access channels (TDMA) or code
division multiple access channels (CDMA).
The invention also relates to an arrangement and to a base
station controller for carrying out the method.
DESCRIPTION OF THE PRIOR ART
In a mobile radio communications system for data package trans-
mission, a base station is able to communicate with one or more
mobile stations through the medium of one or more time-divided
channels between the base station and the mobile station. A time-
divided channel is divided into time slots. A data burst compris-
i-ng-a--~riiisa3:3.ty of--information-bits--caW he transmitted in each
time slot. Data that is transmitted in a packet switching radio
communications system is divided into one or more packets, which
' in turn comprise one or more blocks . Depending on the application
and system concerned, the blocks may be the smallest data unit
° that are transmitted via the radio interface.
In data transmission, where, in contradistinction to speech

CA 02245881 1998-08-13
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2
transmission, no errors can be tolerated in the transmitted
messages there can be used a protocol for the automatic re-
transmission of erroneously transmitted data. The most common
solution involves the use of an ARQ protocol (ARQ - Automatic
Repeat reQuest). This protocol implicates a return channel on
which information concerning the status of a transmitted message
can be transmitted. The receiver discloses via the return channel
whether or not a given message has been transmitted correctly.
When certain blocks in a packet have been transmitted erroneous-
ly, so-called selective ARQ enables solely the erroneous blocks
to be retransmitted without needing to retransmit the remaining
blocks in the packet.
Increasing requirements on high bit rates and short delays have
resulted in a greater need for communications systems of large
bandwidth. This need can either be satisfied with one single
channel of very large bandwidth or by combining a plurality of
narrowband channels such that the channels together provide the
desired bit rate and delay. One example of this latter solution
is the general packet radio service (GPRS) which ETSI SMG (ETSI
- European Technical Standards Institute; SMG = Special Mobile
Group) is in the process of specifying as a part of GSM phase 2+.
Those channels that are used for data transmission within such a
radio communications system, e.g. the cellular GSM system, will
very probably have highly varying qualities.
GB-A-2 279.205 teaches a packet data transmission radio system in
which a mobile terminal monitors a parameter which discloses an
anticipated communications quality for each channel. The parame-
ter is based on statistical measurements of the signal strength
of the desired signal C in relation, C/I, to the signal strength
of an interfering signal, I, preferably in those time slots in
which data is transmitted. The parameter is utilized when a
mobile terminal initially informs a base station of those time
_slots in which the mobile terminal wishes to communicate data,

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3
when establishing a radio connection with said base station. The
~ base station then reserves these time slots for communication
with the mobile terminal, provided that the desired time slots
are available at that time.
Patent Specification WO-A1-93/14579 discloses an algorithm
according to which channels are allocated in a radio communica-
tions system. The algorithm utilizes earlier registered events on
the channels concerned for generating a list in which the chan-
nels are ranked in a descending order of quality. When allocating
a new channel for communication between a base station and a
mobile station, the base station chooses the top available
channel on the list. Examples of events that are recorded during
a given time period are the number of interrupted calls, the
25 number of completed calls and the number of blocked requests for
a call setup. When allocating channels, the algorithm also takes
into account whether or not a certain channel is heavily loaded
locally.
SUMMARY OF THE INVENTION
The present invention provides a solution to those problems
caused by the aforesaid greatly varying channel qualities, and
also constitutes an improvement in relation to the aforesaid
known techniques. In a radio communications system for transmit-
ting data between two stations that communicate data over two or
more channels in accordance with a protocol for the automatic re-
transmission of erroneously transmitted data, the invention
attacks the problem of allocating the most effective channels for
the automatic re-transmission of erroneously transmitted data, in
other words those channels on which there is the greatest proba-
bility of re-transmitting the data correctly.
The channels utilized in the radio communications system may be
frequency divided, such as in an FDMA system ( FDMA - Frequency

CA 02245881 1998-08-13
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4
Division Multiple Access), for instance NMT (NMT = Nordic Mobile
Telephone), or may be time divided, such as in pure TDMA (TDMA = '
Time Division Multiple Access). One example of combined TDMA and
FDMA is GSM, in which a given channel is characterized by a '
specific time slot on a separate carrier frequency. The channels
may also be separated with the aid of a spread code sprectrum
which is unique for each channel, such as in a CDMA system (CDMA
- Code Division Multiple Access), for instance IS-95.
According to GB-A-2 279 205, the mobile terminal states in its
access request to the base station those channels that are
preferred by the mobile terminal. The present-day TDMA system is
unable to handle an access request of the length that this would
require. For instance, the access request in GSM is comprised
solely of eight bits. Thus, in order -to apply the solution
proposed by GB-A-2 279 205 in a GSM system, it would be necessary
to lengthen the access request, which would, in turn, result in
greater delays. According to GB-A-2 279 205, the mobile terminal
determines the quality of solely the downlink of the channel,
i.e. when data is transmitted from the base station to the mobile
terminal. Consequently, the measurements do not provide suffi-
cient basis on which the channel quality on the uplink can be
estimated, i.e. when data is transmitted from the mobile terminal
to the base station.
The algorithm described in WO-Al-93/i4579 is based on events
recorded during a given time period and provides a mean value
quality measurement. In the transmission of data when relatively
large volumes of information are transmitted in a relatively
short time, it is essential to choose precisely that channel or
that set of channels which will give the highest transmission
quality at that moment in time. Because the algorithm described
in WO-A1-93/14579 gives a mean value of the historic quality of
the radio channels, the algorithm does not provide a suitable
solution for allocating channels for the re-transmission of data

CA 02245881 2005-09-O1
which were erroneously transmitted in a previous data transmis-
sion.
Accordingly, one object of the present invention is to provide
methods and arrangements for finding that channel or that set of
channels which will, at that moment in time, provide the highest
transmission quality in the re-transmission of erroneously trans-
mitted data.
This object is achieved in accordance with the proposed method,
by selecting a transmission parameter with each transmission. The
transmission parameter is derived with the aid of information
relating to the channel used for transmitting each given data.
At least one of the preceding channels for earlier transmitted
data is used in the. re-transmission of data.
Accordingly, in one aspect, the invention provides a method
of channel allocation in a radio communication system
comprising a primary station and a secondary station
adapted to communicate data over two or more channels in
accordance with a protocol for automatic re-transmission of
erroneously transmitted data, the method comprising the
steps of deriving for a given transmission a transmission
parameter associated with each of the two or more channels,
wherein the transmission parameter is related to channel
quality, and allocating for transmission, in accordance
with the transmission parameter created from a previous
transmission, at least one preceding channel used for
previously transmitting data when data is transmitted
erroneously over a given channel.
The proposed arrangement creates a transmission parameter in a
control unit for each transmission, this parameter being derived
with the aid of information relating to the channel used for
transmitting each given data. The channel allocating means in the

CA 02245881 2005-09-O1
' Sa
control unit allocates at least one of the preceding channels
used for earlier transmitted data for the re-transmission of
erroneously transmitted data, in accordance with the transmission
parameter.
In another aspect; then, the invention provides an arrangement
for allocating channels in a radio communications system,
the arrangement comprising a primary station and a
secondary station adapted to communicate data over two or
more channels in accordance with a protocol for automatic
re-transmission of erroneously transmitted data, wherein
the primary station includes a control unit, the control
unit including means for deriving a transmission parameter
relating to channel quality for each of the two or more
channels, and channel allocating means for allocating, in
an event of erroneously transmitted data over. a given
channel, at least one of the previous channels used for
earlier data transmission in accordance with the
transmission parameter created from a previous
transmission.
In the case of erroneously transmitted data, channels are allo-
cated for re-transmission of data in accordance with the trans-
mission garameter that has been created in a previous transmis-
sion. According to one preferred.embodiment of the first. method
according to the invention, the transmission parameter discloses
those channels whose quality has exceeded a predetermined limit
value in the transmission of data between a primary station and

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6
a specific secondary station.
According to one advantageous embodiment, the aforementioned
previous transmission may be the immediately preceding transmis- '
sion of data between the primary station and the secondary
station.
According to another preferred embodiment, data is re-transmitted
primarily on those channels whose transmission quality has
exceeded a predetermined value. This value can be given as the
highest number of errors, nF, that may be accepted on a given
channel in order for this channel to be allocated for the possi-
ble re-transmission of erroneously transmitted data. When all of
the previously used channels have transmitted data containing
more errors than nF, at most one of these channels is allocated
for re-transmission of the data. The channel that has transmitted
data with the lowest number of errors is preferably a7.located. In
addition, at least one further channel that has not been used in
an earlier transmission is allocated, provided that such a
channel is available.
According to an alternative embodiment, there can be calculated
for each channel used in a previous transmission a quality
measurement, Q, calculated in accordance with Q= Ntot-~1''a~x
Nto t
where nto~ represents the total number of blocks that have been
transmitted on the channel, and where nHack denotes the number of
erroneously transmitted blocks on the channel. When retransmit-
ting erroneous data, there is allocated at most one of the
previous channels whose quality measurements Q are below a
predetermined quality Limit Qi. If the Q value of all the channels -
used in a previous transmission are below Q, there is allocated
for re-transmission at Least one further channel which has not

CA 02245881 2005-09-O1
7
been used in a previous transmission, provided that such a
channel is available,
The invention also relates to a base station switching centre in
a radio communications system, which utilizes the method and the
arrangement according to the invention. Data is transmitted
between a primary and a secondary station in the radio communica-
tions system via two or more channels and the data is transmitted
in accordance with a protocol for the automatic re-transmission
of erroneously transmitted data.
One embodiment of the inventive arrangement presumes that each
data message is divided into one or more packets, each of which
includes one or more blocks. In this case, the re-transmission of
erroneously transmitted data is effected in each block, so as to
avoid those channels on which an excessive number of blocks or an
excessively high percentage of blocks have been transmitted
erroneously.
According to a further embodiment of the inventive arrangement,
the arrangement includes a control unit in which the transmission
parameter is created. The control unit includes channel allocat-
ing means in the form of a processor and a memory unit. The
processor is used when creating the transmission.parameter, this
parameter then being stored in the memory unit at least until a
receipt acknowledgement has been received to the effect that the
whole packet in which the relevant blocks are included has been
transmitted correctly.
Accordingly, the invention also provides a base station
controller adapted to communicate data with at least one
mobile station via at least one base station and over two
or more channels in accordance with a protocol for
automatic re-transmission of erroneously transmitted data,
wherein the base station controller includes a control unit

CA 02245881 2005-09-O1
7a
for creating a transmission parameter. that is derived with
the aid of information relating to channel quality for each
transmission of the data between the base station and the
mobile station, wherein the control unit includes channel
allocation means for allocating in an event of erroneously
transmitted data over a given channel at least one previous
channel for earlier transmitted data in accordance with the
transmission parameter created from a previous
transmission.
gy re_transmitting erroneously transmitted data solely on those
channels of good quality, it is possible to reduce the total data
message transmission time and to therewith enhance the capacity

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8
of the data transmission system.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure Z illustrates a known mobile radio communications
system with associated nodes and connecting a
packet-switching telecommunications network;
Figure 2 illustrates a known method of dividing a message
into packets, blocks and data bursts;
Figure 3 illustrates a known method of dividing the radio
spectrum into different frequencies (FDMA);
Figure 4 illustrates a known method of dividing the radio
spectrum into different time slots (TDMA);
Figure 5 illustrates a known method of dividing the radio
spectrum with the aid of spread codes (CDMA);
Figure 6 illustrates a known method of defining a specific
channel in a time-divided system, such as time
slots on a given frequency;
-Figure 7 illustrates how channels in a time-divided radio
communications system are related to TDMA frame
numbers in a known manner;
Figure 8 illustrates generally the manner in which a prima-
ry station in the radio communications system
according to Figure 1 transmits a message to a
secondary station in the same system;
Figures 9a-d illustrate the signalling procedure prior to and
during the transmission of a message from a prima-

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9
ry station to a given secondary station, in accor-
dance with the inventive method;
Figure 10 illustrates generally the manner in which a sec-
ondary station in the radio communications system
according to Figure 1 transmits a message to a
primary station in the same system;
Figures 11a-c illustrate the signalling procedure prior to and
during the transmission of a message from a given
secondary station to a primary station, in accor-
dance with the inventive method;
Figure I2 is a flowchart illustrating an inventive method
for application when data transmission is termi-
nated in a mnhi7P ~fatinn~
______ ___ _ ________ ___._____,
Figure 13 is a flowchart illustrating an alternative method
to the method illustrated in Figure 12;
Figure 14 is a flowchart illustrating an inventive method
for application when data transmission is origi-
nated from a mobile station;
Figure 15 is a flowchart illustrating an alternative method
to the method illustrated in Figure 14;
Figure 16 illustrates an example of creating the inventive
transmission parameter;
Figure 17 illustrates a control unit for creating the pro-
posed transmission parameter;
Figure 18 illustrates a memory unit for storing channel
numbers relating to block numbers in accordance

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with the inventive method;
Figure I9 illustrates a memory unit for storing a number of
erroneous blocks related to channel numbers in
5 accordance with the inventive method;
Figure 20 illustrates the inventive control unit connected
to a base station; and
10 Figure 21 illustrates the inventive control unit connected
to a base station controller.
The invention will now be described in more detail with reference
to preferred exemplifying embodiments thereof and also with
I5 reference to the accompanying drawings.
DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 illustrates a public packet switched data transmission
network PSPDN and a mobile radio communications system for GPRS
{GPRS - General Packet Radio Service), in which the inventive
method is applied. GPRS couples the radio communications system
to the packet switched public data network PSPDN through the
medium of a support node N1 designated GGSN (GGSN = Gateway GPRS
Support Node). The mobile radio communications system GPRS also
includes serving support nodes N2 and N3, designated SGSN (SGSN
- Serving GPRS Support Node). Each of the serving support nodes
N2 and N3 connects together a plurality of base station control-
lers BSC1 and BSC2_ Each respective base station controller BSC1
and BSC2 controls one or more base transceivers BTS, B1-B3. Each
base transceiver BTS is responsible for radio communication with
mobile stations MS1-MS5 within at least one cell C1-C3. For
instance, the base station B2 communicates with the mobile
stations MS2 and MS3 in the cell C2. A base station controller
BSC1 including base stations Bl-B3 connected thereto is designat-

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11
ed base station system BSS and it is through the base station
- system BSS that the mobile stations MS1-MS5 communicate data via
the general packet radio service GPRS.
Prior to the transmission of data messages switched between the
radio communications system and a mobile station MS, the messages
are divided into one or more packets whose lengths may vary from
case to case, among other things in accordance with the load on
the transmission network at that moment in time. Figure 2 illus-
trates the division of a message into packets pl-pn. Figure 2
also shows the division of each packet into blocks bl-bm, each
block including a specific number of information bits, e.g. 240
bits. If information space is left in the last block bm when
dividing the blocks, this space is filled with dummy bits. In the
physical transmission of data between the base station and the
mobile station, each block is divided into four data bursts sl-s4
of equal size and each containing sixty information bits, for
instance. When the radio communications system is a TDMA system,
the data bursts can be transmitted bit-interleaved in four
consecutive time slots on a time divided channel. Since the
blocks are the smallest data units that are transmitted via the
radio interface, it is necessary to allocate four new time slots
on a time divided channel when re-transmitting an erroneously
transmitted block.
However, the aforesaid two or more channels can be separated in
the available radio spectrum in a manner different to what is the
case in a TDMA system. The channels can be separated by one of
the three methods described below, or by combining two or more of
these methods, as illustrated respectively in Figures 3, 4 and 5.
4
The available radio spectrum has a frequency spread f, a time
. spread t and a spread in a dimension c, which is characterized by
coding information signals in a particular manner.
The available radio spectrum can be frequency divided in the

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12
manner shown in Figure 3. In this division, different channels
are separated by allocating to each channel a specific frequency '
space Bi , BZ and B3 around a respective carrier frequency fl, f2
and f3 which is unique for each channel. In an FDMA system (Fre- -
quency Division Multiple Access system), such as a Nordic mobile
telephone (NMT) system, the radio spectrum is divided in accor-
dance with the aforesaid principle, wherein information signals
from different channels are modulated on different carrier
frequencies fl-f3.
Figure 4 illustrates an alternative division of the radio spec-
trum, according to which a specific channel is characterized by
a specific time slot TL1, TL2 or TL3. Tn this case, a first
channel TL1 is comprised of the time space in a time frame
between the time t - 0 and t - I, a second channel TL2 is
comprised of the time space between the time t = 1 and t = 2, and
a third channel TL3 is comprised of the time space between the
time t = 2 and t = 3. After channel TL3, channel TL1 is repeated
in the next frame. The TDMA system constitutes an example of this
type of radio spectrum division. GSM represents a combination of
the radio spectrum division described in Figures 3 and 4, since
a given channel in GSM is characterized both by a specific time
slot and a special carrier frequency.
Figure 5 illustrates another alternative division of the radio
spectrum. In this case, all channels constantly utilize the
available spectrum. Thus, the channels are neither separated in
time nor in frequency, but by a spreading sequence C1, C2 or C3
which is unique for each channel. In modulation, a digital
information signal corresponding to a given channel is multi-
plied, spread, with a spreading sequence unique to said channel.
In demodulation, the modulated signal is multiplied by the same
spreading sequence as that used in modulation and the original
signal is recreated. In the CDMA system (Code Division Multiple
Access system), such as a system according to the American

CA 02245881 1998-08-13
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13
standard IS-95, the radio spectrum is divided in accordance with
this principle.
- The invention will be described in the following with reference
to a TDMA system, such as a GSM system, for instance. However, it
will be understood that the invention can be applied to both FDMA
and CDMA systems either as combinations of the systems or combi-
nations of said systems and the TDMA system.
Figure 6 illustrates the manner in which a specific channel in a
TDMA system is defined as time slots on a given frequency in a
manner known per se. In GSM, a so-called TDMA frame is comprised
of eight time slots numbered from zero to seven. These time slots
form eight so-called physical channels. For instance, twenty-six
TDMA frames, numbered from zero to twenty-five, together form a
multi-frame. Multi-frames are used in GSM as carriers of the so-
called logic channels, for instance the packet data channels. One
such logic channel is comprised of a specific time slot in each
TDMA frame on a separate carrier frequency. For instance, the
packet data channel SPDCH2 may be comprised of time slot 2 on the
carrier frequency f. The Figure illustrates the manner in which
time slot 2 in a multi-frame corresponding to a packet data
channel SPDCH2 is created from TDMA frame 0, 1 and 2 respectively
on the carrier frequency f.
Figure 7 illustrates haw the available channels on a given
carrier frequency in a TDMA system are related to TDMA frame
numbers in a known manner. Each TDMA frame in a multi-frame
includes information from all channels on a specific carrier
frequency. For instance, TDM~1 frame 0 contains information from
all channels SPDCHO-SPDCH7. Correspondingly, TDMA frame 1 con-
tains information from all channels SPDCHO-SPDCH7, as illustrated
in Figure 7. Remaining TDMA frames in the mufti-frame are filled
in an analogous manner. When TDMA frame 25 has finally been
filled with information from all channels SPDCHO-SPDCH7, TDMA

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14
frame 0 is commenced in the next following mufti-frame and the
same procedure is repeated for this mufti-frame. -
Figure 8 provides a general picture of how data is transmitted
from a primary station BTS to a secondary station MS via time-
divided radio channels in a known manner. In this example, it is
assumed that the primary station is a base transceiver BTS,
although the station may equally as well be comprised of other
units in the base station system BSS, such as a base station
controller. It is also assumed in the illustrated case that the
secondary station is a mobile station MS_ However, the secondary
station may equally as well be any station capable of communicat-
ing packet data via time-divided radio channels. Data transmis-
sion is effected via time-divided slave packet data channels
I5 SPDCH on which the information stream is controlled by a specific
control and return channel MPDCH hereinafter referred to as a
Master Packet Data CHannel. Information consisting of the data
messages is divided in the base transceiver into packets p1-pn,
which are then transmitted to the mobile station as blocks, via
two or more time-divided slave packet data channels SPDCH. The
mobile station MS reveals the result of the transmission via the
master packet data channel MPDCH, or via an arbitrary slave
packet data channel SPDCH, i.e. discloses whether or not the
transmission has taken place correctly. A slave packet data
channel SPDCH is used primarily to reveal the result of the
transmission. This is because all utilized slave packet data
channels SPDCH normally lie on one and the same carrier frequency
and the master packet data channel MPDCH normally lies on another
carrier frequency. This means that it is unnecessary for the
mobile station to change carrier frequency from -the carrier
frequency used in the preceding reception when one of the slave
packet data channels SPDCH is used to disclose the result of the
transmission instead of the master packet data channel MPDCH.
Since this minimizes the number of frequency switches, the total
transmission time is also shortened.

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When the mobile station MS indicates to the base transceiver
station BTS that a specific block has been transmitted erroneous-
ly, this block is re-transmitted on an appropriate slave packet
data channel SPDCH. The slave packet data channel SPDCH that is
5 appropriate for use to re-transmit the block is decided by the
proposed control unit CU in the base transceiver station BTS.
Figures 9a-9d are intended to illustrate the inventive method in
signalling and message-transmitting procedures, wherein data pl,
10 consisting of blocks bl-b5, is transmitted from a base station 1
to a mobile station 2. Figure 9a illustrates how the base station
1 first localizes the mobile station 2, by sending to the mobile
station 2 an alert message, Page, on the downlink NL of a master
packet data channel MPDCH. By downlink NL is meant the transmis-
15 sion direction of a given duplex channel from a base station to
a mobile station. Correspondingly, by uplink UL is meant the
transmission direction of a given duplex channel to a base
station from a mobile station. In the illustrated example, the
alert message Page is sent in TDMA frames 4-7. The mobile station
2 then sends a gage response PR in TDMA frame 10, via the uplink
UL of the master packet data channel MPDCH. The mobile station 2
reports that the alert message Page has been received, through
the medium of the page response message PR.
When the page response message PR is received by the base station
1, the station reserves in TDMA frames 16-19 a plurality of slave
packet data channels SPDCH4-SPDCH6 for transmission of the data
b1-b5, via a channel reservation message ChRes on the downlink NL
of the master packet data channel MPDCH. This is illustrated in
Figure 9b.
Figure 9c illustrates the manner in which the base station 1
transfers block or blocks bl-b5 in the packet p1 in the next
stage, via the reserved slave packet data channels SPDCH4, SPDCH5
and SPDCH6. The blocks are preferably distributed circularly over

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16
the allotted slave packet data channels SPDCH4-SPDCH6, so that
these channels will be filled as uniformly as possible. Thus, the '
first block is transmitted via the first allocated slave packet
data channel SPDCH4, the second block is transmitted via the -
second allocated slave packet data channel SPDCHS, and so on.
Thus, in the illustrated case, the blocks bl and b4 are transmit-
ted on the slave packet data channel SPDCH4. This takes place in
TDMA frames 20-27. The blocks b2 and b5 are transmitted via slave
packet channel SPDCH5 in the same TDMA frames and block b3 is
transmitted via slave packet data channel SPDCH6 in TDMA frames
20-23. An error occurs, however, in the second block b2 of the
packet pl in the transmission. The error is discovered in an
error check carried out in the mobile station 2 and is registered
in an error vector F. The discovery of the error may be effected
in accordance with the following procedure, for instance. The
transmitting station creates a block check sequence prior to
transmitting a block. This block check sequence is created on the
basis of the information contained in the block and is transmit-
ted together with the block concerned. The receiving station
determines whether or not the block has been transmitted errone-
ously, for instance by counting the number of bits in the re-
ceived block, including its block check sequence. It is necessary
for the block check sequence to include only one parity bit to
discover a single bit error. When wishing to discover mufti-bit
errors, the block check sequence must be made longer, i.e. the
sequence must include several parity bits. An account of how this
is resolved is given, for instance, in a book entitled "Digital
Communications" by Simon Haykin, John Wiley & Sons, Inc., New
York, 1988, pp. 365-393. The mobile station 2 discloses that the
second block b2 of the packet has been transmitted erroneously by
a negative receipt acknowledgement, Nack (hack = Not acknowl-
edged) on the uplink UL of the slave packet data channel SPDCH6
in TDMA frames 30-33.
The control unit CU in the base station 2 allocates a slave

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17
packet data channel SPDCH4 for re-transmission of the erroneously
' transmitted block b2, in accordance with a transmission parameter
created in the transmission of the packet blocks bl-b5. The
transmission parameter is based on information as to which
channel was used for transmitting each block, and when re-trans
mitting blocks that have been transmitted erroneously, the
control unit CU ensures that those channels that have transmitted
blocks erroneously are avoided. Figure 9d illustrates how the
base station 1 re-transmits the erroneously transmitted block b2
on the downlink NL of the slave packet data channel SPDCH4 in
TDMA frames 36-39. This slave packet data channel is chosen by
the control unit CU, because it was the first channel of the
preceding channels on which no errors occurred in the previous
transmission. In principle, the control unit CU may equally as
well have allocated slave packet data channel SPDCH6, since no
errors occurred on this channel in the previous transmission
either. The mobile station 2 carries out an error check on the
block b2 when the block is received. Because the error check
discovers no errors, the mobile station 2 reports that the block
b2 has been received correctly, by sending a positive receipt
acknowledgement Ack (Ack = Acknowledged) to the base station I on
the uplink UL of the slave packet data channel SPDCH4 in TDMA
frames 44-47.
Figure 10 illustrates a general picture of haw data a.s transmit-
ted from a secondary station MS to a primary transceiver station
BTS in a known manner, i.e. the reverse condition to that de-
scribed with reference to Figure 8. In other respects, the same
conditions as those illustrated in Figure 8 apply. Thus, it is
also assumed in this example that the primary station is a base
transceiver station and that the secondary station is a mobile
station MS. Data is transmitted via time-divided slave packet
data channels SPDCHs on which the information stream is con-
trolled by a specific master packet data channel MPDCH. The
information, consisting of data messages, is divided in the

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18
mobile station MS into packets p1-pn, which are then transmitted
as blocks to the base transceiver station BTS, via two or more
time-divided slave packet data channels SPDCH. The base trans-
ceiver station BTS reveals whether or not the transmission has
taken place correctly, via the master packet data channel MPDCH
or via any selected slave packet data channel SPDCH.
Tf the base transceiver station BTS indicates that a specific
block has been transmitted erroneously, this block is re-trans-
mitted on an appropriate slave packet data channel SPDCH. The
control unit CU in the base transceiver station BTS decides which
slave packet data channel SPDCH is suitable for re-transmission
of the block.
-Figures 11a-31c are intended to illustrate the inventive method
when signalling and transmitting messages, wherein data p1,
consisting of blocks b1-b5, is sent from the mobile station 2 to
the base station I. Figure lla illustrates the manner in which
the mobile station 2 announces a channel requirement for trans-
mission of data pl, by sending an access request RA (RA = Random
Access) to the base station 1 in TDMA frame 2, on the uplink UL
of the master packet data channel MPDCH. The base station 1 meets
the channel request made by the mobile station 2, by sending in
TDMA frames 5-8 a channel reservation message ChRes to the mobile
station 2 on the downlink NL of the master packet data channel
MPDCH, in which a number of slave packet data channels SPDCH4-
SPDCH6 are reserved for the transmission.
Figure 11b shows how the mobile station 2 in the next stage
transmits blocks b1-b5 in the packet pI via the reserved slave
packet data channels SPDCH4, SPDCH5 and SPDCH6. The blocks are
- preferably distributed circularly over the allocated slave packet
data channels, so that these channels will be filled as uniformly
as possible. Thus, the first block is transmitted via the first
allocated slave packet data channel SPDCH4, the second block is

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19
transmitted via the second allocated slave packet data channel
SPDCH5, and so on. Thus, in the illustrated example, the blocks
b1 and b4 are transmitted on slave packet data channel SPDCH4.
This takes place in TDMA frames 16-23. The blocks b2 and b5 are
sent via slave packet data channel SPDCHS in the same frames, and
block b3 is sent via slave packet data channel SPDCH6 in TDMA
frames 16-19. However, an error occurs in the fourth block b4 of
the packet p1 in the transmission. The error is discovered in an
error check carried out in the base station 1, and is registered
in an error vector F. The base station I announces that block b4
has been transmitted erroneously, by a negative acknowledgement
Nack on the downlink NL of the slave packet data channel SPDCH6
in TDMA frames 28-31. Parallel with the negative acknowledgement
Nack, there is also transmitted a channel reservation ChRes
through which slave packet data channel SPDCH5 is reserved for
re-transmission of the erroneously transmitted block b4. The
slave packet data channel SPDCH5 was chosen by the control unit
CU in the base station 1, because this was the first channel of
the previous transmissions on which no errors occurred. In
principle, the control unit CU could equally as well have allo-
cated slave packet data channel SPDCH6, since no errors occurred
on this channel either in the previous transmission.
Figure 11c illustrates how the mobile station 2 re-transmits the
erroneously transmitted block b4 on the uplink UL of the slave
packet data channel SPDCH5 in TDMA frames 40-43. The base station
I carries out an error check on the block b4 when the block is
received. Since the error check is unable to discover any errors,
the base station 1 announces that the block b4 has been received
correctly, by sending a positive acknowledgement Ack to the
mobile station 2 on the downlink NL of the slave packet data
channel STDCH5 in TDMA frames 48-51.
There now follows a description, with reference to the flowchart
shown in Figure 12, of how the aforesaid transmission parameter,

CA 02245881 1998-08-13
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here designated TP(SPDCHz) is created when a given data message
is transmitted from a base station to a specific mobile station,
i.e. in a transmission which terminates in a mobile station.
Compare Figures 9a-9d. The processor of the control unit CU
5 includes a variable n and a counter variable k which can be
stepped from 0 to n.
In step 100, the variable n is made equal to the number of
packets into which the data message has been divided, and the
10 counter variable k is set to zero. In step 110, it is ascertained
whether or not the counter variable k is equal to n; when such is
the case, this means that the transmission of the data message is
ready and the flowchart is ended in step 300. If the counter
variable k is different from n, in other words the counter-
15 variable k is smaller than n, the next packet in the data message
is transmitted in step 120. In step 130, the control unit CU
registers which respective channel, SPDCHz, of the allotted
channels SPDCHl-SPDCHq was used for transmitting each individual
block bi, where 1 = i, 2,..., m, of the m blocks included in the
20 packet concerned. In step 140, it is ascertained whether an
acknowledgement, Ack, or a negative acknowledgement, Nack, has
been received, and if such is the case it is ascertained in step
150 whether or not the acknowledgement is a positive acknowledge-
ment, Ack. Otherwise, the flowchart waits in step 240 until a
receipt acknowledgement, Ack or Nack, has been obtained. If the
receipt acknowledgement is a positive Ack, the counter variable
k is counted up by one in step 200 and a return is made to step
110 in the flowchart for possible transmission of the next
packet. In another case, i.e. when the receipt acknowledgement is
negative Nack, it is ascertained in step 160 on which channels
SPDCHyI-SPDCHy~ of the channels used in a previous transmission on
which more than nF of the erroneously transmitted blocks b~l-bai
have been transmitted, these blocks having been given as errone-
ously transmitted in the negative reception acknowledgement Nack.
=n step 170, it a.s ascertained whether or not all channels

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21
SPDCH1-SPDCHq that were used in a previous transmission have each
transmitted more than a predetermined number, nF, blocks errone-
ously. If such is the case, the blocks are re transmitted in step
190 on the channel that has transmitted the least number of
blocks erroneously and on at least one further channel SPDCHqtl
which has not been used in the previous transmission, provided
that such a channel is available, and a return is made to step
150 in the flowchart and a new reception acknowledgement Ack or
Nack is awaited. Otherwise, the erroneously transmitted blocks
bgl-bgi are re-transmitted in accordance with the inventive trans-
mission parameter TP(SPDCHz) in step 180, on those channels of
the previous channels on which the number of errors occurring in
previous transmission was not greater than nF. If the transmission
parameter TP(SPDCHz) reveals that the number of channels avail-
able for re-transmission is greater than that required for the
re-transmission in question, the blocks are re-transmitted solely
on a least necessary number of the very best channels, i.e. on
those channels an which the least number of blocks have been
erroneously transmitted. A return is then made to step 150 and a
new reception acknowledgement Ack or Nack awaited.
The number of erroneously transmitted blocks on a given channel
corresponding to an acceptable channel quality for retransmis-
sion can be shown by selection of nF. Naturally, nF can be set to
any positive integer value whatsoever, although nF is zero in the
preferred embodiment.
Figure 13 describes alternative steps corresponding to the steps
contained in the broken line square Q in Figure 12. In step 460,
there is calculated for each used channel, SPDCHz; z = 1,..., q,
z z - Ntot-~rrack ~ where ntot
a quality measurement, Q , according to Q - -
fro t

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22
represents the total number of blocks transmitted on the channel
SPDCHz and where ngack denotes the number of blocks transmitted
erroneously on the channel SPDCHz. In step 470, a check is made
to ascertain whether or not all of the QZ values of the used
channels lie beneath a predetermined quality value Qi. If such is
the case, the erroneously transmitted blocks b$1-b$i are retrans-
mitted in step 490 on the channel that has the highest QZ, and on
at least one further channel SPDCH~+1 which was not used in the
previous transmission, provided that such a channel is available,
and a return to step 150 is made in the flowchart in waiting for
a new reception acknowledgement Ack or Nack. Otherwise, the
erroneously transmitted blocks b~~-bRi are transmitted on those
channels SPDCHz whose Q~ value is greater than or equal to Q1, in
accordance with the inventive transmission parameter TP(SPDCHz).
If the transmission parameter TP(SPDCHz} reveals that more
channels are available for re-transmission than are required for
the re-transmission concerned, the blocks are re-transmitted
solely on a smallest necessary number of the very best channels,
i . a . on the channels which have the highest QZ value . A return to
step 150 is then made in waiting for a new reception acknowledge-
ment Ack or Nack.
Figure 14 is a flowchart which illustrates how the aforesaid
transmission parameter TP(SPDCHz) is created in accordance with
the inventive method when a given data message is transmitted
from a specific mobile to a base station, i.e. in the case of a
transmission which originates from a mobile station. C.f. Figures
11a-11c. The processor of the control unit CU includes a variable
n and a counter-variable k, which can be stepped from 0 to n.
In step 500, the variable n is set to a value equal to the number
of packets into which the data message has been divided, and the
counter-variable k is set to zero. The base station is informed
of the number of packets in the data message, via the access
request from the mobile station. In step 510, it is ascertained

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23
whether or not the counter variable k is equal to n, and if such
is the case then the data message transmission is finished and
the flowchart terminated in step 700. When the counter variable
- k differs from n, i.e. is smaller than n, the next packet in the
data message is received in step 520. In step 530, the control
unit CU computes the number of blocks aZ that will be transmitted
on each of the allotted channels SPDCHz, where z = 1, 2,..., q.
In step 540, it is ascertained whether or not the packet has been
received, and if the packet has been received it is then ascer
tamed in step 550 whether or not the packet was received without
error, i.e. whether or not a positive reception acknowledgement
Ack has been sent to the mobile station. Otherwise, the flowchart
waits in step 540 until the packet has been received. If the
packet has been received with no error, the counter variable k is
counted up one increment in step 600 and a return is made in the
flowchart to step 510 for receiving a possible next packet in the
data message. Otherwise, i.e. when the reception acknowledgement
is negative Nack, those blocks bgl-bxi that have been transmitted
erroneously are registered in step 560, and the number of errone-
ously transmitted blocks bZ for each channel SPDCHz, which z = l,
2,..., q are also registered. In step 570, it is ascertained
whether or not all channels SPDCH1-SPDCHq that have been used in
a previous transmission have each transmitted more than a prede-
termined number of blocks, nF, erroneously. If such is the case,
there is allocated in step 590 for re-transmission that channel
which has transmitted the least number of blocks erroneously and
at least one further channel SPDCHQ+1 which was not used in the
previous transmission, provided that such a channel is available,
and a return is made to step 550 in the flowchart in expectation
of the re-transmission of the erroneously transmitted blocks bgl-
bzi. Otherwise, re-transmission of the erroneously transmitted
blocks bxl-bgi is requested in step 580 in accordance with the
inventive transmission parameter TP(SPDCHz) on those channels of
the previous channels on which the number of errors in the
previous transmission was not greater than nF. If the transmission

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24
parameter TP(SPDCHz) reveals that the number of channels avail-
able for re-transmission is greater than that required for the
re-transmission concerned, only a least necessary number of the
very best channels are allocated, i.e. those channels which have -
transmitted the smallest number of blocks erroneously. The
flowchart then returns to step 550 and waits for the retransmis-
sion of the erroneously transmitted blocks bal-bai.
The number of erroneously transmitted blocks on a given channel
corresponding to acceptable channel quality for transmission is
shown by selection of nF. Naturally, ng can be set to any positive
integer value whatsoever, although nF is zero in the preferred
embodiment.
Figure 15 describes alternative steps corresponding to the steps
within the broken line square Q in Figure 14. In step 660, there
is calculated for each used channel, SPDCHz; z - 1,..., q, a
quality measurement, QZ, in accordance with Qz - ~t~t NNack
Ntot
where ntot represents the total number of blocks that have been
transmitted on channel SPDCHz, and where nHack shows the number of
blocks transmitted erroneously on the channel SPDCHz. In step
670, it is ascertained whether or not the QZ value of ali used
channels lies beneath a predetermined quality value Ql. If such
is the case, a request is made in step 690 for the re-transmis-
sion of those erroneously transmitted blocks bal-bai on that
channel which has the highest QZ, and on at least on one further
channel SPDCHq+1 which was not used in the previous transmission,
provided that such a channel is available, and a return is made
to step 550 while awaiting the re-transmission of the erroneously
transmitted blocks bai-bai. Otherwise, it is requested in step 680 .
that the blocks bal-bai are transmitted on those channels SPDCHz
whose QZ value is greater than or equal to Ql , in accordance with

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the inventive transmission parameter TP(SPDCHz). If the transmis-
sion parameter TP(SPDCHz) discloses that the number of channels
available for re-transmission is greater than that required for
- the re-transmission concerned, only the least necessary number of
5 the very best channels are allocated, i.e. those channels that
have the highest QZ value. The flowchart then returns to step 550
and waits for re-transmission of the erroneously transmitted
blocks bgl-bxi .
10 Figure 16 illustrates an example of a result that can be obtained
When the method according to the flowchart in Figure I2 is run
through and when the parameter nF is set to zero. The diagram in
Figure 16 shows channel resources along the horizontal axis and
illustrates the time order of different events on the vertical
15 axis. In this example, the slave packet data channels SPDCH3-
SPDCH7 are allocated for transmission of the blocks b1-bl~_ ~rhP
blocks are distributed circularly over the allocated slave packet
data channels SPDCH3-SPDCH7. Thus, the first block bl is trans-
mitted via the first allocated slave packet data channel SPDCH3,
20 the second block b2 is transmitted via the second allocated slave
packet data channel SPDCH4, and so on in accordance with Figure
16. Errors occurred in blocks b2, b6, b7 and b10 in the transmis-
sion. These errors are detected in error checks carried out in
the receiving station, which reports that these blocks have been
25 transmitted erroneously by sending a negative acknowledgement
Nack. Figure 16 illustrates how the erroneously transmitted
blocks b6; b2, b7 and b20 are related to the used slave packet
data channels SPDCH3, SPDCH4 and SPDCH7 respectively. Since n~ is
zero, according to the transmission parameter TP, only slave
packet data channel SPDCH5 and SPDCH6 can be allocated for re-
transmission, since these channels are the only channels that
have not transmitted blocks erroneously. The blocks are also
distributed circularly over the allocated slave packet data
channels in the re-transmission of said blocks, such that blocks
b2 and b7 are re-transmitted via slave packet data channel SPDCHS

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26
and blocks b6 and b10 are transmitted via slave packet data
channel SPDCH6.
Shown in Figure 17 is the inventive control unit CU which con-
s trots the steps described in the aforegoing with reference to
Figures 12-15. The control unit CU includes a processor PU and a
memory unit M. The processor PU receives information relating to
used slave packet data channels SPDCH, status s for the data
transmitted on these channels, and information M relating to the
total number of blocks transmitted. This information is processed
in the processor PU and stored in a memory module M1 in the
memory unit M when the blocks are transmitted from the base
station system BSS to the mobile station MS, i.e. when transmis-
sion is terminated in the mobile station MS. If the blocks are
transmitted to the base station system BSS from 'the mobile
station MS, i.e. if transmission is originated in the mobile
station MS, the processed information A and B is stored in a
second memory module M2 in the memory unit M instead. A third
memory module M3 is used to store the proposed transmission
parameter TP, which is created in the processor PU in accordance
with one of the methods described in Figures 12-15, with the aid
of the information taken from memory module MI or M2. The trans-
mission parameter TP includes a list of those slave packet data
channels SPDCHs which should be used for any re-transmission and
is created subsequent to the control unit CU having received a
reception acknowledgement Ack, Nack, from the receiving station.
The reception acknowledgement is represented by a status vector
s in the illustrated case, this status vector denoting the status
of each transmitted block, i.e. whether a given block has been
transmitted correctly, Ack, or erroneously, Nack. Also stored in
the memory module M3 are the aforesaid quality parameters nF and
Ql. nF may be chosen as zero and QZ set to 0.9, although it is
evident that nF may be any positive integer and QZ may take any
value whatsoever between zero and one. A control signal CS
indicates the slave packet data channels SPDCHs that shall be

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27
used to transmit the erroneously transmitted blocks bgl-bgi . The
control signal CS is produced by the processor PU on the basis of
the created transmission parameter TP. Only the very best slave
packet data channel of those channels which have sufficiently
good transmission quality according to the transmission parameter
TP are primarily used for re-transmission.
Figure 18 illustrates how information z relating to used slave
packet data channels SPDCH1-SPDCHq is stored in the memory module
M1 in Figure 17 for each transmitted block 1, where 1 = 1, 2,...,
m in data transmission that terminates in the mobile station MS.
A vector SPDCH delivered from a transmitter unit via the proces-
sor PU, includes information as to which slave packet data
channels SPDCH1-SPDCHq were used far the transmission. Transmis-
sion status, i.e. information relating to the result of the
transmission of each individual block, is delivered in the form
of a vector s from the processor PU. The vector s includes status
information s~-sm for each transmitted block. An output signal in
the form of a matrix (s, SPDCH) relates to information concerning
transmission status sl-sm to the used slave packet data channels
SPDCH1-SPDCHq. The matrix (s, SPDCH) constitutes a basis for the
aforesaid transmission vector TB and is created in the following
manner. Channel number z, where z - l, 2,..., q, is stored for
each transmitted block number 1, where 1 - 1, 2,..., m, in
respective memory cells, as shown in Figure 18. In column 1, n
denotes the highest number of blocks that can be included in a
packet in the packet switching radio communications system. When
a reception acknowledgement in the form of vector s has been
received for the transmission concerned, there is stored in
respective memory cells s, as shown in Figure 18, for each block
1, where 1 = 1, 2,..., m, a corresponding status si, where i = 1,
2,..., m; si - 0 with respect to Ack and si - 1 with respect to
Nack. The matrix {s, SPDCH) is obtained by reading status sZ-s~
and slave packet data channels SPDCH1-SPDCHq for each block 1,
where 1 - 1, 2,..., m. The processor PU then creates the trans-

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28
mission vector TP by comparing information relating to status si
with one of the predetermined quality parameters nF or Q1 for each
slave packet data channel SPDCH1-SPDCHq. The processor PU can
either ascertain for each slave packet data channel whether the -
sum EsZ of status sZ is greater than or equal to a first predeter-
mined value nF stored in the memory module M3, or the processor
PU can calculate for each slave packet data channel SPDCHz a
value, QZ , according to QZ _ Q2- nz n sz ; where nZ denotes the
2
number of status elements for slave packet data channel SPDCHz
and EsZ constitutes said sum of status s~, and ascertain whether
QZ is greater than or equal to a second predetermined value Q~,
which is also stored in the memory module M3.
Figure 19 illustrates the manner in which the memory module M2
stores information relating to the total number of transmitted
blocks ntot and the number of erroneously transmitted blocks npa~k
for each of the used slave packet data channels SPDCHI-SPDCHq in
data transmission that originates from the mobile station MS. A
vector A created in the processor PU includes information al-aq
relating to the number of blocks a~ transmitted on respective
slaved packet data channels SPDCHz of the allocated slave packet
data channels SPDCHl-SPDCHq. A vector B includes information
relating to the result of the transmission and revealing the
number of blocks bZ transmitted erroneously on respective slave
packet data channels SPDCHz. The vector B is also created in the
processor PU. An output signal in the form of a matrix (A, B)
relates to information concerning the transmission status of the
used slave packet data channels SPDCH1-SPDCHq. The matrix (A, B)
forms a basis for the transmission vector TP and is created in
the following manner. With the aid of information relating to the
total number of blocks m that shall be transmitted on the re-
served slave packet data channels SPDCH1-SPDCHq, the processor PU

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29
in the control unit CU calculates how many blocks aZ which will
be transmitted on each slave packet data channel SPDCHz. The
number of blocks m is given in the mobile station access request
RA and the number of blocks aZ that will be transmitted on
respective allocated slave packet data channels SPDCHz can be
readily calculated, since the blocks bl, where 1 - 1, 2,..., m,
are distributed circularly over the allocated slave packet data
channels SPDCH1-SPDCHq, from the lowest channel number to the
highest. It can be mentioned by way of example that when trans-
mitting a packet which comprises twenty-three blocks on five
slave packet data channels SPDCHI-SPDCH5, five blocks will be
transmitted on each of the three slave packet data channels that
have the lowest channel numbers SPDCHl-SPDCH3 and four blocks on
the remaining two slave packet data channels SPDCH4 and SPDCH5.
I5 The control unit CU receives from a receiver unit information
relating to status block B of the received blocks bl, where 1 -
l, 2,._., m, and registers the number of erroneously transmitted
blocks bZ for each used slave packet data channel SPDCHz in the
memory module M2. In column z, p represents the greatest number
of slave packet data channels SPDCHs that can be allocated in the
packet switching radio communications system. The numbers aZ and
bZ are then used by the processor PU to decide whether or not a
specific slave packet data channel SPDCHz is suitable for use in
re-transmission of the blocks, this decision being made with the
aid of one of the quality parameters nF or Q1. The processor PU
can either ascertain whether b~ is smaller than or equal to a
first predetermined value nF stored in the memory module M3, or
can calculate for each channel SPDCHz a value, QZ, according to
QZ - a a ba and ascertain whether or not QZ is greater than or
E
equal to a second predetermined value Q1, which is also stored in

CA 02245881 1998-08-13
WO 97/30563 PCT/SE971002I8
the memory module M3.
Figure 20 illustrates the manner in which the inventive control
unit CU is connected to remaining units in a base station BI. The -
5 base station B1 includes at least one transmitter and receiver
unit TRX. The control unit CU is arranged in the transmitter and
receiver unit TRX, so that all information arriving at and
departing from the unit TRX will pass via the control unit CU.
This enables the control unit CU to register information relating
IO to data received in the base station B1 from a specific mobile
station MS1, and controlling the slave packet data channels
SPDCHs on which data is transmitted from the base station BI to
the mobile station MS1 when re-transmission terminates in the
mobile station MSI. In the case of re-transmission that origi-
15 nates from the mobile station MSI, the control unit CU is also
able to disclose, via the master packet data channel MPDCH, on
which slave packet data channels SPDCHs re-transmission from the
mobile station MS1 to the base station BI shall take place.
20 Alternatively, the control unit CU may be arranged between the
transmitter and receiver units TRX of the base station B1 and the
antenna unit A, so as to provide a common resource for two or
more transmitter and receiver units TRX.
25 -As before mentioned, the inventive control unit CU may also be
connected to a base station controller BSCI. This enables the
control unit CU to control channel allocation in re-transmission
for a number of base stations B1-B3 that communicate data with
mobile stations MS1-MS5 in a manner analogous to when the control
30 unit is placed in a base station B1 as before described. Figure
21 illustrates this situation.

Representative Drawing