Patent Abstract:
A method of generating a received signal quality signal in a communication system, the method comprising: receiving a signal from a physical channel, extracting a transport channel format combination indicator from the received signal, processing one or more transport channel signals, contained in the received signal, in accordance with the extracted transport channel format combination indicator, said processing including at least channel decoding, and generating a received signal quality signal in dependence on the quality of the or each transport channel signal prior to channel decoding.

Full Description:
FIELD OF THE INVENTION 
   The present invention relates to the determination of received signal quality in a radio communication system. 
   BACKGROUND TO THE INVENTION 
   In a radio communication network, such as a mobile phone network, mobile stations monitor the quality of received signals and report the received signal quality back to a base station, typically in a control channel. 
   It has been proposed that a mobile station report received signal quality in a slow associated control channel (SACCH) using a three bit code. The signal quality is determined as the bit error rate (BER) of the received signal before channel decoding and is averaged over one SACCH multiframe, for example 480 ms. 
   The BER is only used if the a block is correctly received, i.e. it passes a CRC (cyclic redundancy code) check. If a block is not correctly received, a default notional BER of, for example 50%, is assumed. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention, there is provided a method of generating a received signal quality signal in a communication system, the method comprising:
         receiving a signal from a physical channel;   extracting a transport channel format combination indicator from the received signal;   processing one or more transport channel signals, contained in the received signal, in accordance with the extracted transport channel format combination indicator; said processing including at least channel decoding; and   generating a received signal quality signal in dependence on the quality of the or each transport channel signal prior to channel decoding.       

   According to the first aspect of the present invention, there is also provided a communication device comprising:
         a receiver for receiving a signal from a physical channel;   processing means configured for:
           extracting a transport channel format combination indicator from the received signal;   processing one or more transport channel signals, contained in the received signal, in accordance with the extracted transport channel format combination indicator; said processing including at least channel decoding; and   generating a received signal quality signal in dependence on the quality of the or each transport channel signal prior to channel decoding.   
               

   The or each transport channel signal may comprise a sequence of data blocks. The quality of the or each transport channel signal may be represented by a block bit error rate determined prior to channel decoding. The determined bit error rate of a transport channel signal may be averaged over period comprising a plurality of data blocks. In the case of there being a plurality of transport channel signals, the bit error rates of each transport channel signal may be averaged over the same period. An average bit error rate may be calculated across the transport channel signals with the averaging being weighted in dependence on the transport formats used for said transport signals. 
   The received signal quality signal may be transmitted in a control channel. 
   According to a second aspect of the present invention, there is provided a method of generating a received signal quality signal in a communication system, the method comprising:
         receiving a signal from a physical channel, the signal comprising one or more transport channels;   extracting a transport channel format combination indicator from the received signal and determining the bit error rate therefore; and   generating a received signal quality signal in dependence on the bit error rate of the extracted transport channel format combination indicator.       

   According to the second aspect of the present invention, there is also provided a communication device comprising:
         a receiver for receiving a signal from a physical channel, the signal comprising one or more transport channels; and   processing means configured for:
           extracting a transport channel format combination indicator from a received signal and determining the bit error rate therefore; and   generating a received signal quality signal in dependence on the bit error rate of the extracted transport channel format combination indicator.   
               

   The determined bit error rates of a plurality of transport channel format combination indicator instances may be averaged. 
   The received signal quality signal may be transmitted in a control channel. 
   According to a third aspect of the present invention, there is provided a method of generating a received signal quality signal in a communication system, the method comprising:
         receiving a signal from a physical channel, the signal comprising a plurality of bursts each including a training sequence; and   generating a received signal quality signal in dependence on the bit error rate of the training sequence of a received burst.       

   According to the third aspect of the present invention, there is also provided a communication device comprising:
         a receiver for receiving a signal from a physical channel, the signal comprising a plurality of bursts each including a training sequence; and   processing means configured for generating a received signal quality signal in dependence on the bit error rate of the training sequence of a received burst.       

   The determined bit error rates of the training sequences of a plurality of bursts may be averaged. 
   The bit error rate of a training sequence may be produced by comparing a received training sequence with a reference training sequence. 
   The received signal quality signal may be transmitted in a control channel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a mobile communication system according to the present invention; 
       FIG. 2  is a block diagram of a mobile station; 
       FIG. 3  is a block diagram of a base transceiver station; 
       FIG. 4  illustrates the frame structure; 
       FIG. 5  illustrates a packet data channel; 
       FIG. 6  illustrates the sharing of a radio channel between two half-rate packet channels; 
       FIG. 7  illustrates the lower levels of a protocol stack; 
       FIG. 8  is a block diagram illustrating the processing of the transport channels of a received physical layer signal; 
       FIG. 9  is a block diagram illustrating received signal quality determination; 
       FIG. 10  is a flowchart of a first part of a received signal quality determination process; 
       FIG. 11  is a flowchart of a second part of a received signal quality determination process; 
       FIG. 12  is a block diagram illustrating another approach to signal quality determination; 
       FIG. 13  is a flowchart illustrating another received signal quality determination process; 
       FIG. 14  is a block diagram illustrating yet another approach to signal quality determination; and 
       FIG. 15  is a flowchart illustrating yet another received signal quality determination process. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
   Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings. 
   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). 
   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). 
   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. 
   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 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 . 
   The switching centres  3   a ,  3   b  and the packet service support nodes  9  have access to a home location register  12 . 
   Communication between the mobile stations  6   a ,  6   b  and the base transceiver station  4  employs a time-division multiple access (TD MA) scheme. 
   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 . 
   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. 
   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&#39;s data communication capabilities. 
   The second mobile station  6   b  is similarly configured. 
   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 . 
   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. 
   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  3   a.    
   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 . 
   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. 
   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. 
   When used for circuit-switched speech traffic, the channelization scheme is as employed in GSM. 
   Referring to  FIG. 5 , full rate packet switched channels make use of 12 4-slot radio packets spread over a “51 multiframe”. Idle slots follow the third, sixth, ninth and twelfth radio packet. 
   Referring to  FIG. 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  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. 
   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 . 
   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. 
   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 packets 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  FIG. 8 , data produced for applications  404   a ,  404   b ,  404   c  propagates up the protocol stack from 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 required by a single application. The medium access control layer  402  directs data to the applications  404   a ,  404   b ,  404   c  from different transport channels  405 ,  406 ,  407  according to class to which it belongs. 
   Each receive transport channel  405 ,  406 ,  407  can be configured to process received 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. 
   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 decoding  405   b ,  406   b ,  407   b  and rate matching  405   c ,  406   c ,  407   c . These unique processing schemes are the reciprocals of transmitter processing schemes which define different “transport formats”. An interleaving scheme may be selected for each transport channel  405 ,  406 ,  407  and require corresponding de-interleaving  405   d ,  406   d ,  407   d . 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  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 TF 1 , TF 2 , TF 3  for each transport channel, the following combinations might be valid:
         TF 1  TF 1  TF 2     TF 1  TF 3  TF 3 
 
but not
   TF 1  TF 2  TF 2     TF 1  TF 1  TF 3         

   The received signal is de-interleaved  411  and then demultiplexed by a demultiplexing process  410 , which outputs transport channel signals to respective transport channel de-interleaving processes  405   d ,  406   d ,  407   d.    
   A transport format combination indicator is spread across one radio packet 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. 
   The transport format combination indicator is extracted from the received data stream by a transport format combination indicator extraction process  414  after the deinterleaving process  411 . 
   The transport format combination indicator from the transport format combination indicator extraction process  414  is decoded by a decoding process  413 . The decoded transport format combination indicator is then processed by a transport format combination detecting process  412  which provides information on the current transport format combination to the medium access control layer  402 . This information is then used in the medium access control layer  402  to select the appropriate decoding and de-interleaving process for the transport formats used in the received signal. 
     FIG. 9  illustrates received signal quality determination in the case where the received physical layer signal carries a data stream comprising three transport channels using respective formats. Of course, the data stream may comprise more or fewer transport channels and the same transport format may be used by more than one of the transport channels. 
   Referring to  FIG. 9 , first, second and third transport channel quality determiners  501 ,  502 ,  503  receive the cyclic redundancy check results from respective cyclic redundancy check processes  405   a ,  406   a ,  407   a  and a bit error rate estimate from respective channel decoding processes  405   b ,  406   b ,  407   b.    
   The operation of the first transport channel quality determiner  501  will now be described with reference to  FIG. 10 . 
   Referring to  FIG. 10 , at the start of a SACCH multiframe period (also known as the SACCH reporting period), the CRC result for a first transport block is received from the first cyclic redundancy check process  405   a  (step s 1 ). If the result is determined to be true, i.e. the CRC is correct, (step s 2 ), the BER for the first transport block is obtained from the first channel decoder  405   b  (step s 3 ) and stored (step s 4 ). A block counter is then incremented (step s 5 ). It is then determined whether the current SACCH multiframe period has come to an end (step s 6 ). 
   If the current SACCH multiframe period has not come to an end (step s 6 ), the program flow returns to step s 1  where the CRC for the next block is obtained. 
   If, at step s 2 , it is determined that the cyclic redundancy check result is determined to be false, steps s 3  to s 5  are skipped. 
   When all of the blocks of the current the current SACCH multiframe period have been processed (step s 6 ), the BER is averaged over a period corresponding to the product of the block period and the number of correctly received transport blocks, i.e. the value accumulated by the step s 5 . 
   The second and third transport channel quality determiners  502 ,  503  operate in the same way as the first transport channel quality determiners  501  except that the cyclic redundancy check result and the BER estimates are obtained from the corresponding cyclic redundancy check process  406   a ,  407   a  and channel decoders  406   b ,  407   b.    
   The transport channel quality determiners  501 ,  502 ,  503  output their average BERs and transport block counts to a physical channel quality determiner  504 . 
   The operation of the physical channel quality determiner  504  will now be described with reference to  FIG. 11 . 
   Referring to  FIG. 11 , the physical channel quality determiner  504  obtains the TFCI applicable to the most recent transport channel quality determinations (step s 11 ) and then receives the transport block counts from the transport channel quality determiners  501 ,  502 ,  503  (step s 12 ). 
   The TFCI information determines what percentage of each radio packet is used by each transport channel. This information is used to convert the transport block counts into the percentage of the data in the transmitted data stream that was correctly received in one SACCH multiframe, according to: 
           P   =       ∑     c   =   1     n     ⁢         b   ⁡     (   c   )       ·     p   ⁡     (   c   )             b   T     ⁡     (   c   )                 
where c is the transport channel number, n is the number of transport channels, b is the number of correctly received bits in the transport block, b t  is the number of bits in the transport block in the transmitted signal and p is the percentage of the data stream used by a particular transport channel.
 
   If the result P is greater than or equal to 50%, the BERs are obtained from the transport channel quality determiners  501 ,  502 ,  503  (step s 15 ). The BERs are then averaged (step s 16 ). In the present embodiment, the BERs are averaged in accordance with the following: 
           B   =         ∑     c   =   1     n     ⁢       b   ⁡     (   c   )       ·     p   ⁡     (   c   )               ∑     c   =   1     n     ⁢     p   ⁡     (   c   )                 
where B is the average BER.
 
   If, however, the percentage of the data in the transmitted data stream that was incorrectly received is greater than 50% (step s 14 ), the average bit error rate B is set arbitrarily to 50%. 
   The average bit error rate B is then quantized and encoded into 3 bits which are made available for transmission to a base transceiver station  4  by the mobile station  6   a  in the SACCH as a received signal quality report. 
   It will be appreciated that the formulae given above are examples of the effect required and that the value ranges and scaling factors actual used may vary. 
   A second embodiment of the present invention will now be described. 
   A mobile station is as described above with the exception of the generation of the received signal quality report. In this embodiment, the report is based on the quality of the TFCI signal. 
   Referring to  FIG. 12 , TFCI BERs are fed from the TFCI decoder  413  ( FIG. 8 ) to a received signal quality determiner  601 . The received signal quality determiner  601  generates a received signal quality signal in dependence on the TFCI BERs from the TFCI decoder  413  and outputs it for transmission in the SACCH. 
   Referring to  FIG. 13 , the received signal quality determiner  601  obtains a first TFCI BER for the first TFCI transmitted in a SACCH multiframe period (step s 31 ) and stores it (step s 32 ). Successive TFCI BERs are then obtained (step s 31 ) and stored (step s 32 ) until the BER for the last TCFI of the current SACCH multiframe period ends (step s 33 ). 
   When the last BER has been obtained and stored, the stored BERs are averaged (step s 34 ) and then the average quantized and encoded (step s 35 ) and output (step s 36 ) for transmission to a base transceiver station  4  by the mobile station  6   a  in the SACCH as a received signal quality report. 
   A third embodiment of the present invention will now be described. 
   A mobile station is as described above with the exception of the generation of the received signal quality report. In this embodiment, the report is based on the quality of the received training sequences. 
   As shown in  FIG. 4 , each burst comprises a training sequence sandwiched between two blocks of data bits. The training sequences are predetermined. 
   Referring to Referring to  FIG. 14 , received training sequences are fed to a received signal quality determiner  701 . The received signal quality determiner  701  generates a received signal quality signal in dependence on the received training sequences and outputs it for transmission in the SACCH. 
   Referring to  FIG. 12 , TFCI BERs are fed from the TFCI decoder  413  ( FIG. 8 ) to a received signal quality determiner  601 . The received signal quality determiner  601  generates a received signal quality signal in dependence on the TFCI BERs from the TFCI decoder  413  and outputs it for transmission in the SACCH. 
   Referring to  FIG. 15 , the received signal quality determiner  701  obtains a first training sequence in a SACCH multiframe period (step s 41 ) and compares it with a reference copy (step s 42 ). The number of differences between the received training sequence and the reference is added to a record of the errors for the current SACCH multiframe period (step  43 ). The errors in successive training sequences are then obtained (step s 42 ) and added to the error record (step s 43 ) until the training sequence of the last burst in the current SACCH multiframe period has been processed (step s 44 ). 
   When the last training sequence has been processed, the accumulated error count is quantized (step s 45 ) and output (step s 46 ) for transmission to a base transceiver station  4  by the mobile station  6   a  in the SACCH as a received signal quality report. The three embodiments described above may be combined to produce additional embodiments. For instance, bit error rates obtained by two or three techniques may be averaged to produce a bit error rate that is then quantized, encoded and transmitted to a base transceiver station  4  by the mobile station  6   a  in the SACCH as a received signal quality report. 
   It is to be understood that the foregoing embodiments are merely examples and that many modifications are possible without departing from the spirit and scope of the appended claims.

Technology Classification (CPC): 7