Abstract:
In a TDMA packet mobile communication system employing the concept of transport channels in a medium access control layer, an downlink access control signal, for identifying a destination mobile station, is inserted into each burst in a predetermined manner.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to downlink access control in a mobile communication system.  
         BACKGROUND TO THE INVENTION  
         [0002]    In the general packet radio service (GPRS) of GSM (Global System for Mobile communications) networks, downlink multiplexing of radio blocks destined for different mobile stations, sharing a basic physical subchannel, is enabled with an identifier called the temporary flow indicator (TFI) included in each radio block. A temporary block flow (TBF) is a physical connection used by to RR (Radio Resource) entities to support the unidirectional transfer of LLC PDUs (Low Layer Compatibility Packet Data Units) on shared basic physical subchannels. Each TBF is assigned a TFI, which is unique among concurrent TBFs, by the network.  
           [0003]    The TFI is encoded in the RLC/MAC header in such a way that every mobile station that can receive the radio block can decode the TFI.  
           [0004]    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 for the same user can be multiplexed and sent in the same physical subchannel. In such a system, each radio block may carry one or more TBFs which means that including TFIs in RLC/MAC headers is not a practical way of identifying the mobile station to which a radio block is destined.  
         SUMMARY OF THE INVENTION  
         [0005]    According to the present invention, there is provided a method of wirelessly transmitting data signals to one of a plurality of mobile stations, each of which can sense the transmitted signal, the method comprising:  
           [0006]    allocating a locally unique code to a destination mobile station; and  
           [0007]    transmitting a radio block, comprising a plurality of bursts and conveying data belonging to a plurality of data streams, to said mobile station,  
           [0008]    wherein said code is included in each of said bursts at a predetermined location therein.  
           [0009]    Preferably, said location is static.  
           [0010]    Preferably, a method according to the present invention includes transmitting a further radio block, comprising a plurality of bursts and conveying data belonging to a plurality of data streams, to said mobile station, wherein said code is included in each of said bursts at another predetermined location therein to indicate that said mobile station may transmit in the next uplink radio block.  
           [0011]    According to the present invention, there is also provided a method of operating a mobile station for the reception of data signals, the method comprising:  
           [0012]    receiving a locally unique code;  
           [0013]    receiving a burst of a radio block, the radio block comprising a plurality of bursts and conveying data belonging to a plurality of data streams, to said mobile station; and  
           [0014]    extracting a code from a predetermined location in said burst and decoding said radio block if the extracted code matches said locally unique code.  
           [0015]    According to the present invention, there is method of operating a mobile station comprising performing a data reception method according to the present invention, and transmitting a radio block comprising a plurality of bursts, each burst containing said extracted code in a predetermined location.  
           [0016]    According to the present invention, there is further provided a mobile station including receiving means and processing means, wherein the processing means is configured for controlling the mobile station to perform a method according to the present invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 shows a mobile communication system according to the present invention;  
         [0018]    [0018]FIG. 2 is a block diagram of a mobile station;  
         [0019]    [0019]FIG. 3 is a block diagram of a base transceiver station;  
         [0020]    [0020]FIG. 4 illustrates the frame structure used in an embodiment of the present invention;  
         [0021]    [0021]FIG. 5 illustrates a packet data channel in an embodiment of the present invention;  
         [0022]    [0022]FIG. 6 illustrates the sharing of a radio channel between two half-rate packet channels in an embodiment of the present invention;  
         [0023]    [0023]FIG. 7 illustrates the lower levels of a protocol stack used in an embodiment of the present invention;  
         [0024]    [0024]FIG. 8 illustrates the generation of a radio signal by a first embodiment of the present invention;  
         [0025]    [0025]FIG. 9 illustrates a data burst generated by a first embodiment of the present invention;  
         [0026]    [0026]FIG. 10 illustrates the generation of a radio signal by a second embodiment of the present invention; and  
         [0027]    [0027]FIG. 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  
       [0028]    A preferred embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings.  
         [0029]    Referring to FIG. 1, a mobile phone network  1  comprises a plurality of switching centres including first and second switching centres  2   a ,  2   b . The first switching centre  2   a  is connected to a plurality of base station controllers including first and second base station controllers  3   a ,  3   b . The second switching centre  2   b  is similarly connected to a plurality of base station controllers (not shown).  
         [0030]    The first base station controller  3   a  is connected to and controls a base transceiver station  4  and a plurality of other base transceiver stations. The second base station controller  3   b  is similarly connected to and controls a plurality of base transceiver stations (not shown).  
         [0031]    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  6   a ,  6   b  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.  
         [0032]    The mobile phone network  1  is connected to a public switched telephone network  7  by a gateway switching centre  8 .  
         [0033]    A packet service aspect of the network includes a plurality of packet service support nodes (one shown)  9  which are connected to respective pluralities of base station controllers  3   a ,  3   b . At least one packet service support gateway node  10  connects the or each packet service support node  10  to the Internet  11 .  
         [0034]    The switching centres  3   a ,  3   b  and the packet service support nodes  9  have access to a home location register  12 .  
         [0035]    Communication between the mobile stations  6   a ,  6   b  and the base transceiver station  4  employs a time-division multiple access (TDMA) scheme.  
         [0036]    Referring to FIG. 2, the first mobile station  6   a  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 .  
         [0037]    The rf subsystem  102  contains if and rf circuits of the mobile telephone&#39;s transmitter and receiver and a frequency synthesizer for tuning the mobile station&#39;s transmitter and receiver. The antenna  101  is coupled to the rf subsystem  102  for the reception and transmission of radio waves.  
         [0038]    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.  
         [0039]    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.  
         [0040]    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 .  
         [0041]    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.  
         [0042]    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.  
         [0043]    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&#39;s data communication capabilities.  
         [0044]    The second mobile station  6   b  is similarly configured.  
         [0045]    Referring to FIG. 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 .  
         [0046]    The rf subsystem  202  contains the if and rf circuits of the base transceiver station&#39;s transmitter and receiver and a frequency synthesizer for tuning the base transceiver station&#39;s transmitter and receiver. The antenna  201  is coupled to the rf subsystem  202  for the reception and transmission of radio waves.  
         [0047]    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.  
         [0048]    The base station controller interface  204  interfaces the base transceiver station  4  to its controlling base station controller  3   a.    
         [0049]    The controller  207  controls the operation of the base transceiver station  4 . It is coupled to the rf subsystem  202  for 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 .  
         [0050]    Referring to FIG. 4, each TDMA frame, used for communication between the mobile stations  6   a ,  6   b  and the base transceiver stations  4 , comprises eight 0.577 ms time 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 hyperframe comprises 2048 superframes.  
         [0051]    The data format within the time 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 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.  
         [0052]    When used for circuit-switched speech traffic, the channelisation scheme is as employed in GSM.  
         [0053]    Referring to FIG. 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.  
         [0054]    Referring to FIG. 6, for half rate, packet switched channels, both dedicated and shared, slots are allocated alternately to two sub-channels.  
         [0055]    The baseband DSP subsystems  103 ,  203  and controllers  107 ,  207  of the mobile stations  6   a ,  6   b  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.  
         [0056]    Referring to FIG. 7, the layers relevant to the radio link between a mobile station  6   a ,  6   b  and a base station controller  4  are the radio link control layer  401 , the medium access control layer  402  and the physical layer  403 .  
         [0057]    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.  
         [0058]    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.  
         [0059]    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 .  
         [0060]    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 .  
         [0061]    Referring to FIG. 8, data produced by applications  404   a ,  404   b ,  404   c  propagates down the protocol stack to the medium access control layer  402 . The data from the applications  404   a ,  404   b ,  404   c  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  404   a ,  404   b ,  404   c  to different transport channels  405 ,  406 ,  407  according to class to which it belongs.  
         [0062]    Each transport channel  405 ,  406 ,  407  can be configured to process signals according to a plurality of processing schemes  405   a ,  405   b ,  405   c ,  406   a ,  406   b ,  406   c ,  407   a ,  407   b ,  407   c . The configuration of the transport channels  405 ,  406 ,  407  is established during call setup on the basis of the capabilities of the mobile station  6   a ,  6   b  and the network and the nature of the application or applications  404   a ,  404   b ,  404   c  being run.  
         [0063]    The processing schemes  405   a ,  405   b ,  405   c ,  406   a ,  406   b ,  406   c ,  407   a ,  407   b ,  407   c  are unique combinations of cyclic redundancy check  405   a ,  406   a ,  407   a , channel coding  405   b ,  406   b ,  407   b  and rate matching  405   c ,  406   c ,  407   c . These unique processing schemes will be referred to as “transport formats”. An interleaving scheme  405   d ,  406   d ,  407   d  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.  
         [0064]    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  6   a ,  6   b . 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:  
         [0065]    TF1 TF1 TF2  
         [0066]    TF1 TF3 TF3  
         [0067]    but not  
         [0068]    TF1 TF2 TF2  
         [0069]    TF1 TF1 TF3  
         [0070]    The data output by the transport channel interleaving processes are multiplexed by a multiplexing process  410  and then subject to further interleaving  411 .  
         [0071]    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 (FIG. 9) in this example. The complete transport format combination indicator therefore occurs at fixed intervals, i.e. the block length 20 ms. This makes it possible to ensure transport format combination indicator detection when different interleaving types are used e.g. 8 burst diagonal and 4 burst rectangular interleaving. Since the transport format combination indicator is not subject to variable interleaving, it can be readily located by the receiving station and used to control processing of the received data.  
         [0072]    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.  
         [0073]    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 8 PSK modulation is used. When GMSK modulation is used the situation is more complicated in that different bit positions are 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.  
         [0074]    Similarly, downlink status flags are included in downlink radio bursts to indicate which mobile station a burst is intended for. 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  6   a ,  6   b.    
         [0075]    A mobile station  6   a ,  6   b  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 transmitting mobile station  6   a ,  6   b  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  6   a ,  6   b  and the decoded transport format combination indicator.  
         [0076]    Referring to FIG. 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 8 PSK. All of the active transport format combination sets  501 ,  502  are established at call set up.  
         [0077]    Signals in a control channel from the network to a mobile station  6   a ,  6   b  cause the mobile station  6   a ,  6   b  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  6   a ,  6   b  may also unilaterally decide which modulation technique to employ.  
         [0078]    Referring to FIG. 11, at a receiving station, be it a mobile station  6   a ,  6   b  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.  
         [0079]    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.