Note: Descriptions are shown in the official language in which they were submitted.
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Interleaving For Multiplexed Data
Field of the Invention
The present invention relates to a mobile communication system.
Background to the Invention
The concept of transport channels is known from UTRAN (Universal mobile
Telecommunications System Radio Access Network). Each of these transport
channels can carry a bit class having a different quality of service (QoS)
requirement. A plurality of transport channels can be multiplexed and sent in
the
same physical channel.
Summary of the Invention
It is an object of the present invention to improve upon the prior art
communications systems employing transport channels.
According to the present invention, there is provided a radio transmitting
device
comprising radio transmitter circuitry and processing means for processing
digital
signals to produce a modulating signal fox the radio transmitter circuitry,
wherein
the processing means is configured to implement a protocol stack having a
physical
layer and a medium access control layer, above the physical layer, providing a
plurality of transport channels which are combined and then interleaved to
produce
said modulating signal.
Preferably, the device is adapted for TDMA communication and said interleaving
is
performed on blocks of data constituting a plurality of TDMA bursts.
Preferably, the processing means performs interleaving of said transport
channels
before they are combined.
Brief Description of the Drawings
Figure 1 shows a mobile communication system according to the present
invention;
Figure 2 is a block diagram of a mobile station;
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Figure 3 is a block diagram of a base transceiver station;
Figure 4 illustrates the frame structure used in an embodiment of the present
invention;
Figure 5 illustrates a packet data channel in an embodiment of the present
invention;
Figure 6 illustrates the sharing of a radio channel between two half-rate
packet
channels in an embodiment of the present invention;
Figure 7 illustrates the lower levels of a protocol stack used in an
embodiment of
the present invention;
Figure 8 illustrates the generation of a radio signal by a first embodiment of
the
present invention;
Figure 9 illustrates a data burst generated by a first embodiment of the
present
invention;
Figure 10 illustrates the generation of a radio signal by a second embodiment
of the
present invention; and
Figure 11 illustrates part of a reception process adapted for receiving
signals
produced by the second embodiment of the present invention.
Detailed Description of the Preferred Embodiment
A preferred embodiment of the present invention will now be described, by way
of
example, with reference to the accompanying drawings.
Referring to Figure 1, a mobile phone network 1 comprises a plurality of
switching
centres including first and second switching centres Za, 2b. The first
switching
centre 2a is connected to a plurality of base station controllers including
first and
second base station controllers 3a, 3b. The second switching centre 2b is
similarly
connected to a plurality of base station controllers (not shown).
The first base station controller 3a is connected to and controls a base
transceiver
station 4 and a plurality of other base transceiver stations. The second base
station
controller 3b is similarly connected to and controls a plurality of base
transceiver
stations (not shown).
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In the present example, each base transceiver station services a respective
cell.
Thus, the base transceiver station 4 services a cell 5. However, a plurality
of cells
may be serviced by one base transceiver station by means of directional
antennas. A
plurality of mobile stations 6a, 6b are located in the cell 5. It will be
appreciated
what the number and identities of mobile stations in any given cell will vary
with
time.
The mobile phone network 1 is connected to a public switched telephone network
7
by a gateway switching centre 8.
A packet service aspect of the network includes a plurality of packet service
support
nodes (one shown) 9 which axe connected to respective pluralities of base
station
controllers 3a, 3b. At least one packet service support gateway node 10
connects
the or each packet service support node 10 to the Internet 11.
The switching centres 3a, 3b and the packet service support nodes 9 have
access to
a home location register 12.
Communication between the mobile stations 6a, 6b and the base transceiver
station
4 employs a time-division multiple access (TDMA) scheme.
Referring to Figure 2, the first mobile station 6a comprises an antenna 101,
an rf
subsystem 102, a baseband DSP (digital signal processing) subsystem 103, an
analogue audio subsystem 104, a loudspeaker 105, a microphone 106, a
controller
107, a liquid crystal display 108, a keypad 109, memory 110, a battery 111 and
a
power supply circuit 112.
The rf subsystem 102 contains if and rf circuits of the mobile telephone's
transmitter and receiver and a frequency synthesizer for tuning the mobile
station's
transmitter and receiver. The antenna 101 is coupled to the rf subsystem 102
for
the reception and transmission of radio waves.
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The baseband DSP subsystem 103 is coupled to the rf subsystem 102 to receive
baseband signals therefrom and for sending baseband modulation signals
thereto.
The baseband DSP subsystems 103 includes codec functions which are well-known
in the art.
The analogue audio subsystem 104 is coupled to the baseband DSP subsystem 103
and receives demodulated audio therefrom. The analogue audio subsystem 104
amplifies the demodulated audio and applies it to the loudspeaker 105.
Acoustic
signals, detected by the microphone 106, are pre-amplified by the analogue
audio
subsystem 104 and sent to the baseband DSP subsystem 4 for coding.
The controller 107 controls the operation of the mobile telephone. It is
coupled to
the rf subsystem 102 for supplying tuning instructions to the frequency
synthesizer
and to the baseband DSP subsystem 103 for supplying control data and
management data for transmission. The controller 107 operates according to a
program stored in the memory 110. The memory 110 is shown separately from the
controller 107. However, it may be integrated with the controller 107.
The display device 108 is connected to the controller 107 for receiving
control data
and the keypad 109 is connected to the controller 107 for supplying user input
data
signals thereto.
The battery 111 is connected to the power supply circuit 112 which provides
regulated power at the various voltages used by the components of the mobile
telephone.
The controller 107 is programmed to control the mobile station for speech and
data
communication and with application programs, e.g. a WAP browser, which make
use of the mobile station's data communication capabilities.
The second mobile station 6b is similarly configured.
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Referring to Figure 3, greatly simplified, the base transceiver station 4
comprises an
antenna 201, an rf subsystem 202, a baseband DSP (digital signal processing)
subsystem 203, a base station controller interface 204 and a controller 207.
The rf subsystem 202 contains the if and rf circuits of the base transceiver
station's
transmitter and receiver and a frequency synthesizer for tuning the base
transceiver
station's transmitter and receiver. The antenna 201 is coupled to the xf
subsystem
202 for the reception and transmission of radio waves.
The baseband DSP subsystem 203 is coupled to the rf subsystem 202 to receive
baseband signals therefrom and for sending baseband modulation signals
thereto.
The baseband DSP subsystems 203 includes codec functions which are well-known
in the art.
The base station controller interface 204 interfaces the base transceiver
station 4 to
its controlling base station controller 3a.
The controller 207 controls the operation of the base transceiver station 4.
It is
coupled to the xf subsystem 202 fox supplying tuning instructions to the
frequency
synthesizer and to the baseband DSP subsystem for supplying control data and
management data for transmission. The controller 207 operates according to a
program stored in the memory 210.
Referring to Figure 4, each TDMA frame, used fox communication between the
mobile stations 6a, 6b and the base transceiver stations 4, comprises eight
0.577ms
tim__e slots. A "26 multiframe" comprises 26 frames and a "51 multiframe"
comprises 51 frames. Fifty one "26 multiframes" or twenty six "51 multiframes"
make up one superframe. Finally, a hypexframe comprises 2048 superfxames.
The data format within the tune slots varies according to the function of a
time slot.
A normal burst, i.e. time slot, comprises three tail bits, followed by 58
encrypted
data bits, a 26-bit training sequence, another sequence of 58 encrypted data
bits and
a further three tail bits. A guard period of eight and a quarter bit durations
is
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provided at the end of the burst. A frequency correction burst has the same
tail bits
and guard period. However, its payload comprises a fixed 142 bit sequence. A
synchronization burst is similar to the normal burst except that the encrypted
data is
reduced to two clocks of 39 bits and the training sequence is replaced by a 64-
bit
synchronization sequence. Finally, an access burst comprises eight initial
tail bits,
followed by a 41-bit synchronization sequence, 36 bits of encrypted data and
three
more tail bits. In this case, the guard period is 68.25 bits long.
~Ihen used for circuit-switched speech traffic, the channelisation scheme is
as
employed in GSM.
Referring to Figure 5, full rate packet switched channels make use of 12 4-
slot radio
blocks spread over a "51 multiframe". Idle slots follow the third, sixth,
ninth and
twelfth radio blocks.
Referring to Figure 6, for half rate, packet switched channels, both dedicated
and
shared, slots are allocated alternately to two sub-channels.
The baseband DSP subsystems 103, 203 and controllers 107, 207 of the mobile
stations 6a, 6b and the base transceiver stations 4 are configured to
implement two
protocol stacks. The first protocol stack is for circuit switched traffic and
is
substantially the same as employed in conventional GSM systems. The second
protocol stack is for packet switched traffic.
Referring to Figure 7, the layers relevant to the radio link between a mobile
station
6a, 6b and a base station controller 4 are the radio link control layer 401,
the
medium access control layer 402 and the physical layer 403.
The radio link control layer 401 has two modes: transparent and non-
transparent.
In transparent mode, data is merely passed up or down through the radio link
control layer without modification.
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In non-transparent mode, the radio link control layer 401 provides link
adaptation
and constructs data blocks from data units received from higher levels by
segmenting or concatenating the data units as necessary and performs the
reciprocal
process for data being passed up the stack. It is also responsible for
detecting lost
data blocks or reordering data block for upward transfer of their contents,
depending on whether acknowledged mode is being used. This layer may also
provide backward error correction in acknowledged mode.
The medium access control layer 402 is responsible for allocating data blocks
from
the radio link control layer 401 to appropriate transport channels and passing
received radio blocks from transport channels to the radio link control layer
403.
The physical layer 403 is responsible to creating transmitted radio signals
from the
data passing through the transport channels and passing received data up
through
the correct transport channel to the medium access control layer 402.
Referring to Figure 8, data produced by applications 404x, 404b, 404c
propagates
down the protocol stack to the medium access control layer 402. The data from
the
applications 404a, 404b, 404c can belong to any of a plurality of classes for
which
different qualities of service are required. Data belonging to a plurality of
classes
may be produced by a single application. The medium access control layer 402
directs data from the applications 404a, 404b, 404c to different transport
channels
405, 406, 407 according to class to which it belongs.
Each transport channel 405, 40G, 407 can be configured to process signals
according
to a plurality of processing schemes 405a, 405b, 405c, 406x, 406b, 406c, 407a,
407b,
407c. The configuration of the transport channels 405, 406, 407 is established
during call setup on the basis of the capabilities of the mobile station 6a,
6b and the
network and the nature of the application or applications 404a, 404b, 404c
being
run.
The processing schemes 405a, 405b, 405c, 406a, 406b, 406c, 407a, 407b, 407c
are
unique combinations of cyclic redundancy check 405a, 406a, 407a , channel
coding
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405b, 406b, 407b and rate matching 405c, 406c, 407c. These unique processing
schemes will be referred to as "transport formats". An interleaving scheme
405d,
406d, 407d may be selected for each transport channel 405, 406, 407. Thus,
different transport channels may use different interleaving schemes and, in
alternative embodiments, different interleaving schemes may be used at
different
times by the same transport channel.
The combined data rate produced for the transport channels 405, 406, 407 must
not
exceed that of physical channel or channels allocated to the mobile station
6a, 6b.
This places a limit on the transport format combinations that can be
permitted. For
instance, if there are three transport formats TF1, TF2, TF3 for each
transport
channel, the following combinations might be valid:-
TF1 TF1 TF2
TF1 TF3 TF3
but not
TF1 TF2 TF2
TF1 TF1 TF3
The data output by the transport channel interleaving processes are
multiplexed by a
multiplexing process 410 and then subject to further interleaving 411.
A transport format combination indicators is generated by a transport format
combination indicator generating process 412 from information from the medium
access control layer and coded by a coding process 413. The transport format
combination indicator is inserted into the data stream by a transport format
combination indicator insertion process after the further interleaving 411.
The
transport format combination indicator is spread across one radio block with
portions placed in fixed positions in each burst, on either side of the
training
symbols (Figure 9) in this example. The complete transport format combination
indicator therefore occurs at fixed intervals, i.e. the block length 20ms.
This makes
it possible to ensure transport format combination indicator detection when
different interleaving types are used e.g. g burst diagonal and 4 burst
rectangular
interleaving. Since the transport format combination indicator is not subject
to
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variable interleaving, it can be readily located by the receiving station and
used to
control processing of the received data.
The location of data for each transport channel within the multiplexed bit
stream
can be determined by a received station from the transport format combination
indicator and knowledge of the multiplexing process which is deterministic.
In the foregoing, the physical channel or subchannel is dedicated to a
particular
mobile station for a particular call. When physical channels and subchannels
are
shared, it is necessary for a mobile stations to know when it has access to
the
uplink. For this purpose, in shared channel operation, uplink state flags are
included in each downlink radio block. This flag indicates to the receiving
mobile
station whether it may start sending data in the next uplink radio block. For
compatibility with GPRS and EGPRS mobile stations, the uplink status flags
preferably occupy the same bit positions as are specified for EGPRS, e.g. data
bits
150, 151, 168, 169, 171, 172 174, 175, 177, 178 and 195 of each 348-data-bit
burst
when 8PSK modulation is used. When GMSK modulation is used the situation is
more complicated in that different bit positions axe used in different burst,
albeit in
an overall cyclical manner. More particularly, in a four burst cycle, bits 0,
51, 56,
57, 58 and 100 are used in the first burst, bits 35, 56, 57, 58, 84 and 98 are
used in
the second burst, bits 19, 56, 57, 58, 68 and 82 are used in the third burst
and bits 3,
52, 56, 57, 58 and 66 are used in the fourth burst.
Similarly, downlink status flags are included in downlink radio bursts to
indicate
which mobile station a burst is intended fox.. These flags always have the
same
position within bursts so that a receiving mobile station can easily locate
them. In
the preferred embodiment, the uplink and downlink flags have the same mapping
onto mobile stations 6a, 6b.
A mobile station 6a, 6b using a shared subchannel includes its identifier,
which is
used for the above-described uplink and downlink access control, in its own
transmission. Again, this identifier is located in a predetermined position
within
each burst. Although the network will generally know the identity of the
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transmitting mobile station 6a, 6b because it scheduled the transmission,
corruption
of transmissions from the base transceiver station could result in the wrong
mobile
station transmitting. Including the identifier in this way enables the base
transceiver
station to identify the transmitting mobile station from the received signal
and then
decode the current block, starting by reading the transport format combination
indicator and then selecting the correct transport channel decoding processes
in
dependence on the identity of the transmitting mobile station 6a, 6b and the
decoded transport format combination indicator.
Referring to Figure 10,. in another embodiment, the medium access control
layer
402 can support a plurality of active transport format combination sets 501,
502.
Each transport format combination set 501, 502 is applicable to transmission
according to a different modulation technique, e.g. GMSK and 8PSK. All of the
active transport format combination sets 501, 502 are established at call set
up.
Signals in a control channel from the network to a mobile station 6a, 6b cause
the
mobile station 6a, 6b to switch modulation techniques and, consequently,
transport
format combination sets 501, 502. The control signals can be generated in
response
to path quality or congestion levels. The mobile station 6a, 6b may also
unilaterally
decide which modulation technique to employ.
Referring to Figure 11, at a receiving station, be it a mobile station 6a, 6b
or a base
transceiver station 4, a received signal is applied to demodulating processes
601, 602
for each modulation type. The results of the demodulating processes 601, 602
are
analysed 603, 604 to determine which modulation technique is being employed
and
then the transport format combination indicator is extracted 605 from the
output of
the appropriate demodulated signal and used to control further processing of
the
signal.
It will be appreciated that the above-described embodiments may be modified in
many ways without departing from the spirit and scope of the claims appended
hereto.
