Abstract:
In a TDMA communication system, mobile stations ( 6   a   , 6   b ) are given slot allocations and output power levels by base stations. This can lead to situations where the combination of slot allocation size and output power level demanded exceeds the capability of the mobile station ( 6   a   , 6   b ). To solve this problem, mobile stations ( 6   a   , 6   b ) are given the ability to unilateraly reduce their average output powers by reducing their peak output powers or reducing their take up of allocated slots.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method of operating a mobile station in a TDMA network.  
       BACKGROUND TO THE INVENTION  
       [0002]     The provision of high-speed data services to mobile stations such as mobile telephones and communicators in TDMA networks has resulted in the need for mobile stations to transmit in more than one slot in each TDMA frame. A difficulty with this is that the base station needs to know the maximum power capability of the mobile station.  
         [0003]     It has been proposed to allow a mobile station to change its power class through a is classmark change procedure or a routing area update but these procedures are found to be too slow and also not properly supported by several network implementations.  
       SUMMARY OF THE INVENTION  
       [0004]     According to the present invention, there is provided a method of operating a mobile station in a TDMA network, the method comprising receiving a peak output power setting command from a base station and receiving a transmit slot allocation from the base station, characterised by:  
         [0005]     detecting, at the mobile station, a parameter of the rf system of the mobile station meeting a predetermined criterion; 
        responding to said detection by modifying the average rf output power of the mobile station over a plurality of slots such that it falls below what would have been the average output power level had the peak output power setting command been complied with in all of the allocated slots.        
 
         [0007]     The criterion may comprise an increase in slot allocation. A increase in slot allocation occurs when additional bandwidth is required. Another usable criterion is the temperature of the rf output power amplifier. The plurality of slots may or may not be consecutive.  
         [0008]     The response may comprise reducing the average rf output power by reducing the instantaneous rf output power during each transmit slot and/or reducing the average rf output power by reducing the take up of the allocated slots. In the case of slot allocation changes, it is preferable that there is a predetermined time delay between said detection and said response.  
         [0009]     According to the present invention, there is also provided a mobile station for a TDMA network, the mobile station comprising a controller and an rf output power amplifier, characterised in that the controller is configured to control the operation of the mobile station so as to perform a method according to the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows a mobile communication system according to the present invention;  
         [0011]      FIG. 2  is a block diagram of a mobile station;  
         [0012]      FIG. 3  is a block diagram of a base transceiver station;  
         [0013]      FIG. 4  illustrates the frame structure used in an embodiment of the present invention;  
         [0014]      FIG. 5  illustrates a packet data channel in an embodiment of the present invention;  
         [0015]      FIG. 6  illustrates the sharing of a radio channel between two half-rate packet channels in an embodiment of the present invention;  
         [0016]      FIG. 7  illustrates the lower levels of a protocol stack used in an embodiment of the present invention;  
         [0017]      FIG. 8  is a flowchart illustrating a first embodiment of the present invention;  
         [0018]      FIG. 9  is a flowchart illustrating a second embodiment of the present invention;  
         [0019]      FIGS. 10 and 11  are flowcharts illustrating a third embodiment of the present invention;  
         [0020]      FIG. 12  is a flowchart illustrating a fourth embodiment of the present invention;  
         [0021]      FIG. 13  is a flowchart illustrating a fifth embodiment of the present invention; and  
         [0022]      FIGS. 14 and 15  are flowcharts illustrating a sixth embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Preferred embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings.  
         [0024]     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).  
         [0025]     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).  
         [0026]     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.  
         [0027]     The mobile phone network  1  is connected to a public switched telephone network  7  by a gateway switching centre  8 .  
         [0028]     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 .  
         [0029]     The switching centres  3   a ,  3   b  and the packet service support nodes  9  have access to a home location register  12 .  
         [0030]     Communication between the mobile stations  6   a ,  6   b  and the base transceiver station  4  employs a time-division multiple access (TDMA) scheme.  
         [0031]     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 .  
         [0032]     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.  
         [0033]     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.  
         [0034]     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.  
         [0035]     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 .  
         [0036]     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.  
         [0037]     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.  
         [0038]     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.  
         [0039]     The second mobile station  6   b  is similarly configured.  
         [0040]     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 .  
         [0041]     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.  
         [0042]     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.  
         [0043]     The base station controller interface  204  interfaces the base transceiver station  4  to its controlling base station controllers  3   a.    
         [0044]     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 .  
         [0045]     The base station controllers  3   a ,  3   b  are responsible for allocating radio link resources to mobile stations and cause the base transceiver stations  4  to transmit power command signals to the mobile stations  6   a ,  6   b . Under normal circumstances, the mobile stations  6   a ,  6   b  transmit with the power level which accord with these command signals. However, according to the present invention, this is not always the case as will be explained below.  
         [0046]     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.  
         [0047]     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.  
         [0048]     When used for circuit-switched speech traffic, the channelisation scheme is as employed in GSM.  
         [0049]     Referring to  FIG. 5 , full rate packet switched channels make use of 12 4-slot radio blocks spread over a “52 multiframe”. Idle slots follow the third, sixth, ninth and twelfth radio blocks.  
         [0050]     Referring to  FIG. 6 , for half rate, packet switched channels, both dedicated and shared, slots are allocated alternately to two sub-channels.  
         [0051]     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.  
         [0052]     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 .  
         [0053]     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.  
         [0054]     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.  
         [0055]     The medium access control layer  402  is responsible for allocating data blocks from the radio link control layer  401  to appropriate transport or logical channels and passing received radio blocks from transport or logical channels to the radio link control layer  403 .  
         [0056]     The physical layer  403  is responsible to creating transmitted radio signals from the data passing through the transport or logical channels and passing received data up through the correct transport or logical channel to the medium access control layer  402 .  
         [0057]     Blocks are exchanged between the medium access control layer  402  and the physical layer  403  in synchronism with the radio block timing, i.e. block is passed to the physical layer at each radio block interval.  
         [0058]     As the demand for bandwidth increases to support increasing transport or logical channel throughput, more slots are required. Increased slot usage can result in overheating of the mobile station&#39;s power amplifier and an unsupportable current demand.  
         [0059]     In a first embodiment, the mobile station immediately changes its output power according to threshold slot usage/power combinations.  
         [0060]     Referring to  FIG. 8 , when the demand for slots changes, the controller  107  of a mobile station  6   a ,  6   b  determines whether the current instantaneous power amplifier output power level exceeds a first threshold set for the number of slots to be used after change (step s 1 ). The first threshold is the instantaneous output power level that gives an acceptable average output power level. If the first threshold is exceeded, the controller  107  determines the power reduction required and compares this with a second threshold set at the power level, demanded of the mobile station  6   a ,  6   b  by the serving base station controller  3   a ,  3   b , less an “allowable reduction” margin, for example 3 dB. If this reduced power level falls below the second threshold, the controller  107  notifies the application that the service requiring the extra slots cannot be provided (step s 3 ). If the power reduction does not take the power amplifier output power level below the second threshold, the controller  107  reduces the output power accordingly (step s 4 ). The process is left after steps s 3  and s 4 .  
         [0061]     If the first threshold is not exceeded (step s 1 ), the controller  107  determines whether the current power amplifier output power level is less than the current power level demanded of the mobile station  6   a ,  6   b  by its serving base station controller  3   a ,  3   b  (step s 5 ). This situation may arise where the slot usage is being reduced. If the current output power level is not less than the demanded level, the process is exited. However, if the current power level is below demanded level, the current power amplifier output power level is increased as dose to the demanded level as possible without exceeding the second threshold (step s 6 ) and then the process is exited.  
         [0062]     In a second embodiment, the mobile station changes its output power according to the temperature of its rf power amplifier, which is sensed by monitoring a convenient DC voltage in the amplifier or a temperature sensor (not shown) provided for the purpose. In this case the peak output power is kept on all slots at the level requested by the BSS until the temperature exceeds a threshold level, after which the output power will be reduced within specified limits.  
         [0063]     Referring to  FIG. 9 , the controller  107  regularly compares the temperature of the mobile station&#39;s if power amplifier with a first threshold, corresponding to a maximum allowable operating temperature (step s 101 ). If the first threshold is exceeded, the controller  107 , the power is reduced (step s 102 ). The process is left after step s 102 .  
         [0064]     If the first threshold is not exceeded (step s 101 ), the temperature is compared with a second lower threshold (s 103 ). The second lower threshold is used to introduce some hysteresis into the power control. If the temperature is not below the second threshold, the process is exited. However, if the temperature is below the second threshold, the controller  107  determines whether the current power is below the level demanded by the serving base station controller  3   a ,  3   b  (step s 104 ) and, if so, increases the output power level of the mobile station, for example by one 2 dB step s 105 , and the process is exited. Otherwise the procedure is simply exited without the output power of the mobile station being changed.  
         [0065]     In a third embodiment, relatively high average power levels are allowed. However, such high power levels are adjusted down after a delay to avoid overheating while allowing short period of high bandwidth use.  
         [0066]     Referring to  FIG. 10 , when the demand for slots changes, the controller  107  of the mobile station  6   a ,  6   b  determines whether the current instantaneous power amplifier output power level exceeds a first threshold (step s 201 ). The first threshold is the instantaneous output power level that gives an acceptable average output power level. If the first threshold is exceeded, the controller  107  determines whether a cooling flag is set (step s 202 ) and, if not, sets a timer (step s 203 ), unless the timer is already running, increases the output power level (step  204 ) and exits the process. Otherwise the application is alerted that the service requiring the extra slots cannot be provided (step s 205 ) and then the process is exited.  
         [0067]     If the first threshold is not exceeded (step s 201 ), the controller  107  determines whether the current instantaneous power amplifier output power level is less than the current power level demanded of the mobile station  6   a ,  6   b  by its serving base station controller  3   a ,  3   b  (step s 206 ). This situation may arise where the slot allocation is being reduced. If the current instantaneous output power level is not less than the demanded level the process is exited. However, if the current power level is below demanded level it is increased as close to the demanded level as possible without exceeding the second threshold (step s 204 ) and then the process is exited.  
         [0068]     Referring to  FIG. 11 , when the timer expires, the controller  107  determines the power reduction required and compares this with a second threshold set at the power level demanded of the mobile station  6   a ,  6   b  by the serving base transceiver station  4  less an “allowable reduction” margin, for example 6 dB, step s 207 . If the reduced power falls below the second threshold, the controller  107  notifies the application that the service requiring the extra slots cannot be provided (step s 208 ). If the power reduction does not take the power amplifier output power below the second threshold, the controller  107  reduces the output power accordingly (step s 209 ). The cooling flag is also set when the timer expires (step s 210 ).  
         [0069]     An alternative to reducing the instantaneous output power is to reduce the average output power by not using all of the slots allocated to the mobile station by the serving base station controller  3   a ,  3   b.    
         [0070]     In a fourth embodiment, the mobile station immediately changes its actual slot usage according to threshold granted slot usage/power combinations.  
         [0071]     Referring to  FIG. 12 , when the demand for slots changes, the controller  107  of a mobile station  6   a ,  6   b  determines whether the new average power amplifier output power level would exceed a first threshold set for the number of slots to be used after change (step s 301 ). If the first threshold is exceeded, the controller  107  determines the allocated slot take up reduction required to reduce the average power level below the first threshold. The new slot take up value is compared with a second threshold, i.e. the minimum number of slots required to support the current service level (step s 302 ). If the reduced allocated slot take up falls below the second threshold, the controller  107  notifies the application that the service requiring the extra slots cannot be provided (step s 303 ). If the slot take up reduction does not take the slot take up below the second threshold, the controller  107  reduces the proportion of the allocated slots used (step s 304 ). The process is left after steps s 303  and s 304 .  
         [0072]     If the first threshold is not exceeded (step s 301 ), the controller  107  determines whether the new average power amplifier output power would be less than the average corresponding to the current power level demanded of the mobile station  6   a ,  6   b  by its serving base station controller  3   a ,  3   b  (step s 305 ). This situation may arise where the slot usage is being reduced. If the new average output power level would not be less than that corresponding to the demanded level, the process is exited. However, if the new average power level would be below that corresponding to the demanded instantaneous power level, the slot take up is increased as close to the allocated level as possible without the first threshold being exceeded (step s 306 ) and then the process is exited.  
         [0073]     In a fifth embodiment, the mobile station changes its allocated slot take up according to the temperature of its rf power amplifier, which is sensed by monitoring a convenient DC voltage in the amplifier or a sensor provided specifically for this purpose.  
         [0074]     Referring to  FIG. 13 , the controller  107  regularly compares the temperature of the mobile station&#39;s rf power amplifier with a first threshold corresponding to a maximum allowable operating temperature (step s 401 ). If the first threshold is exceeded, the controller  107  determines whether a reduction in the allocated slot take up is possible without abandoning a service (step s 402 ). If the allocated slot take up would fall below the minimum acceptable level, a service or services can be lost due to insufficient resources and the application is notified of the lack of resources (step s 403 ). Otherwise, the slot take up reduction is made (step s 404 ). The process is left after steps s 403  and s 404 .  
         [0075]     If the first threshold is not exceeded (step s 401 ), the temperature is compared with a second lower threshold (s 402 ). The second lower threshold is used to introduce some hysteresis into the slot take up control. If the temperature is not below the second threshold, the process is exited. However, if the temperature is below the second threshold, the controller determines whether the current average rf amplifier output power level is below that corresponding to the demanded power level from the serving base station controller  3   a ,  3   b  (step s 406 ) and, if so, increases the allocated slot take up of the mobile station (step s 407 ) and the process is exited. Otherwise the procedure is simply exited without the allocated slot take being changed.  
         [0076]     In a sixth embodiment, the allocated slot take up is adjusted down after a delay to avoid overheating while allowing short period of high bandwidth used.  
         [0077]     Referring to  FIG. 14 , when the demand for slots changes, the controller  107  of a mobile station  6   a ,  6   b  determines whether the new average power amplifier output power level exceeds a first threshold (step s 501 ). The first threshold is the instantaneous output power level that gives an acceptable average output power level. If the first threshold is exceeded, the controller  107  determines whether a cooling flag is set (step s 502 ) and, if not, sets a timer (step s 503 ), unless the timer is already running, increases the output power level (step  504 ) and exits the process. Otherwise the application is alerted that the service requiring the extra slots cannot be provided (step s 505 ) and then the process is exited.  
         [0078]     If the first threshold is not exceeded (step s 501 ), the controller  107  determines whether the new average power amplifier output power level is less than that corresponding to the current power level demanded of the mobile station  6   a ,  6   b  by its serving base station controller  3   a ,  3   b  (step s 506 ). This situation may arise where the slot allocation is being reduced. If the new average output power level would not be less than that corresponding to the demanded level, the process is exited. However, if the new average power level is below that corresponding to the demanded level the allocated slot take up is increased so that the average output power level is as close to that corresponding to the demanded level as possible without exceeding the second threshold (step s 504 ) and then the process is exited.  
         [0079]     Referring to  FIG. 15 , when the timer expires, the controller  107  determines the allocated slot take up reduction required and compares this with a second threshold set at the minimum usable slot take up for supporting the current services, step s 507 . If the reduced slot take up falls below the second threshold, the controller  107  notifies the application that the service requiring the extra slots cannot be provided (step s 508 ). If the power reduction does not take the power amplifier output power below the second threshold, the controller  107  reduces the output power accordingly (step s 509 ). The cooling flag is also set when the timer expires (step s 510 ).  
         [0080]     The power averages referred to above are calculated from the instantaneous power power levels in a moving window. The length of the window will depend on the thermal characteristics of the rf power amplifier and the durations of slots and frames and the numbers of slots in a frame.