Abstract:
A method of and a mobile terminal for transmitting data over an uplink from a mobile terminal to a base station, the data being transmitted over radio bursts, the method comprising and the mobile terminal being suitable for: assessing radio propagation conditions between the mobile terminal and the base station; determining if the radio propagation conditions fulfil a predetermined condition; wherein if it is determined that the radio propagation conditions fulfil the predetermined condition the transmission energy parameters of the signal bursts are adapted to reduce the energy used to transmit the data.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of International App. No. PCT/EP2011/053516, filed Mar. 9, 2011 which claims priority to European Patent App. No. 10305249.4, both of which are hereby incorporated by reference as if fully set forth herein. 
     FIELD OF THE INVENTION 
     The present invention relates in general to a method and apparatus of communication between a mobile station and a base station. Particularly but not exclusively, the invention relates to a method of voice communication in GSM 2G. 
     BACKGROUND OF THE INVENTION 
     With the development of faster and more powerful processors in many electronic devices power consumption has become an issue of increasing importance, in particular with regard to mobile electronic devices with limited power sources. Mobile devices such as, but not limited to, mobile telephones, personal data appliances, personal digital assistants (PDAs), lap top computers and the like, are sometimes required to operate for long periods of time before their power source can be recharged. 
     Power consumption of a mobile station is determined by the amount of energy used to transmit data, such as audio data, over an uplink to a base station (BS), as well as receive data from the base station over a downlink. 
     In transmission, data is grouped in blocks with each block being transmitted over a number of radio bursts. During a voice call on a mobile telephone the amount of power consumed depends on the amount of power needed to transmit audio data blocks on the uplink to the base station BS such that the base station correctly receives the information sent by the mobile telephone. The amount of power used to transmit the information over the uplink is configured by the base station with the Power Control Level (PCL) value, the channel coding parameters, modulation and source coding parameters. The total amount of transmission energy is dependent on the consumption of each component of the mobile to transmit the information and the amount of power per burst and the duration of each audio block encoded in frames. One block is encoded on S bursts and the amount of power is directly proportional to S*PCL. 
     In reception power consumption of a mobile station in communication with a base station will depend on the period of time during which the radio frequency sub-system of the mobile telephone phone is open to receive an audio block on the downlink and the operating parameters of the receiver. One audio block is encoded on S bursts. 
     Consequently an important issue for the manufacturer of a mobile station is to reduce as much as possible the power needed to transmit audio data while still enabling the BS station to decode the audio data and to reduce the time window for decoding audio blocks sent by the BS. 
     SUMMARY OF THE INVENTION 
     The present invention has been devised with the foregoing in mind. 
     Accordingly, a first aspect of the invention provides a method of transmitting data over an uplink from a mobile terminal to a base station, the data being transmitted over radio bursts, the method comprising: assessing radio propagation conditions between the mobile terminal and the base station; determining if the radio propagation conditions fulfil a predetermined condition; wherein if it is determined that the radio propagation conditions fulfil the predetermined condition the transmission energy parameters of the signal bursts are adapted to reduce the energy used to transmit the data. 
     A second aspect of the invention provides a method of receiving data at a mobile terminal over a downlink from a base station, the data being transmitted over radio bursts, the method comprising: assessing radio propagation conditions between the mobile terminal and the base station; determining if the radio propagation conditions fulfil a predetermined condition; wherein if it is determined that the radio propagation conditions fulfil the predetermined condition the reception parameters of a receiving means of the mobile terminal are degraded to reduce the energy used to receive the data. 
     A third aspect of the invention provides a mobile terminal for transmitting data to a base station, the mobile terminal comprising: a transmitter for transmitting data over radio bursts; a radio environment analyzer for assessing radio propagation conditions between the mobile terminal and the base station; a processor for determining if the radio propagation conditions fulfil a predetermined condition; a transmission controller for adapting the transmission energy parameters of the signal bursts to reduce the energy used by the transmitter to transmit the data when it is determined that the radio propagation conditions fulfil the predetermined condition. 
     A fourth aspect of the invention provides a mobile terminal for receiving data from a base station, the mobile terminal comprising: a receiver for receiving data over radio bursts; a radio environment analyzer for assessing radio propagation conditions between the mobile terminal and the base station; a processor for determining if the radio propagation conditions fulfil a predetermined condition the processor being operable a reception controller for adapting the reception parameters of the receiver to reduce the energy used to receive the data when it is determined that the radio propagation conditions fulfil the predetermined condition. 
     In embodiments of the invention:
         the level of reception at the base station of a signal transmitted from the mobile station may be determined by determining signal power attenuation between the mobile terminal and the base station   assessing radio propagation conditions may comprise analysing an RxQual quality measurement parameter   adapting the transmission energy parameters may comprise at least one of suppressing one or more signal bursts, reducing the transmission power of one or more signal bursts and reducing the power control level;   the processor of the mobile terminal may be operable to determine the level of reception at the base station of a signal transmitted from the mobile station by determining signal power attenuation between the mobile terminal and the base station   the radio environment analyzer of the mobile terminal may be operable to analyse an RxQual quality measurement parameter   the transmission controller is operable to perform at least one of the following: suppress one or more signal bursts, reduce the transmission power of one or more signal bursts, and reduce the power control level.   the processor is operable to determine the level of reception at the base station of a signal transmitted from the mobile station by determining signal power attenuation between the base station and the mobile terminal.   the radio environment analyzer is operable to analyse an RxQual quality measurement parameter       

     Parts of the methods according to the invention may be computer implemented. The methods may be implemented in software on a programmable apparatus. They may also be implemented solely in hardware or in software, or in a combination thereof. 
     Since parts of the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which: — 
         FIG. 1  is a schematic diagram illustrating communication between a base station and a mobile station 
         FIG. 2A  is a block diagram illustrating a transmission chain of a mobile station which can be used in the context of embodiments of the present invention 
         FIG. 2B  is a block diagram illustrating a reception chain of a mobile station which can be used in the context of embodiments of the present invention 
         FIGS. 3A and 3B  are block diagrams illustrating modules of a mobile station according to an embodiment of the invention; 
         FIG. 4  is a block illustrating sub-components of a decision making module according to the embodiment of the invention; 
         FIGS. 5A and 5B  illustrate transmission configuration of bursts according to embodiments of the invention; 
         FIG. 6  is a flow chart outlining the steps of a method of communication between a mobile station and a base station according to en embodiment of the invention; and 
         FIG. 7  is a block chart illustrating components a mobile station for adapting reception of incoming signals according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     A first embodiment of a method of, of the invention will be described with reference to  FIGS. 1 to 6 . 
       FIG. 1  illustrates communication between a mobile station and a base station in GSM 2G (Global Systems for Mobile Communications 2 nd  Generation) during, for example, a voice call. The mobile station transmits audio data to the base station via an uplink UL while the base station transmits audio data to the mobile station via a downlink DL. In TCH FR (traffic channel full rate) which is the OSI (open system interconnection) model Layer 1 name for a type of GSM voice call one block of audio data after channel coding is transmitted over 4 radio bursts. 
     With reference to  FIG. 2A  the transmission chain of a mobile station  100  supporting 2G radio access comprises an audio data encoder ( 101 ) for receiving analogue data from an audio source coder such as a micro-phone and encoding the analogue data according to the Audio codec type, for example Adaptive Multi-Rate (AMR) as described in the 3GPP specification. The codec type is provided by the network during the service negotiation according to the quality of service to be attained and the capabilities of the mobile station. The Audio data encoder ( 101 ) delivers blocks of data whereby the amount of data per blocks depends on the Audio codec. One block of data may be composed of several types of data. The different types of data are defined according to their importance, which determines their number and the associated level of encoding in order to protect them. 
     The next block on the transmission chain of the mobile station  100  is a channel encoder/interleaver  102  for receiving coded audio data and for applying a channel coding with a parameter of redundancy R. All the data of the Audio block may not have the same redundancy rate. Important data will have a higher redundancy rate while less important data will have a lower redundancy rate. In the standard the redundancy coefficient R is equal to 1, 2, 3 or 4. For R superior to 1, the used channel coder is convolutional code. This parameter is provided by the network in function of the quality of service to be attained. Once channel coded, in order to make the transmission more robust to fading i.e. loss of data over the air interface, the data are interleaved. This operation is described in technical specification TS 45.01. At the output of the channel encoder, the amount of data that will be mapped on burst is equally divided into S frames. 
     The next block on the transmission chain of the mobile station  100  is a burst builder  103  for collecting a data block from the channel encoder ( 102 ), dividing the data block into S sub-blocks of equal size and mapping them to the data part of the TCH burst. S is dependent on the traffic channel (TCH(type (FR, EFR, . . . ). The mapping of channel coded blocks to TCH burst is described in TS 45.008. 
     The transmission chain further comprises a modulator  104  for receiving TCH type bursts of data of in bits and for transforming these bits into an analogue signal. This modulation operation is described in TS 45.01. The modulator  104  introduces a notion of time. One burst is transmitted every GSM frame, i.e. every 4.615 ms. One audio block is fully transmitted after S frames, i.e. after S*4.615 ms. 
     The last block of the transmission chain is an RF/antenna  105 . Modulated data, analogue signal, are then amplified at the PCL level and modulated on the desired frequency before being broadcast over the air by an antenna. PCL (power control level) is provided by the pair Base Station in function of the level of reception, the quality of service to reach, the negotiated audio codec, the TCH plus some infrastructure manufacturer proprietary algorithms. 
     It can be noted that at the output of the channel encoder, the amount of data that will be mapped on burst is equally divided into S frames. 
       FIG. 2B  schematically illustrates the 2G reception and decoding chain of the mobile station  100 . The reception chain comprises a RF antenna r 105  for receiving RF signals over the air interface, a demodulator R 104  for demodulating the received signals, a data collector R 103 , a channel decoder/de-interleaver R 102  and an audio data decoder R 101 . The functional blocks r 101  to r 105  perform the inverse operation of the corresponding blocks of the mobile station transmission chain as described above. In the reception chain instead of the PCL being provided by the network the mobile station  100  amplifies the signal at the output of the antenna r 105  so that it can be decoded. 
       FIGS. 3A and 3B  illustrate the different sub-components involved in the first embodiment of the invention and their related information flow for the reduction of the power consumption of the Transmission of Audio blocks. 
     With reference to  FIGS. 3A and 3B  the mobile station  100  further comprises a radio environment type analyser  110  for analysing the radio wave propagation conditions such as quality and path loss etc, between the mobile station  100  and the base station  200 . This component can be used to determine the type of propagation channel between the mobile station  100  and the base station  200  and to analyse the fade types and size present in the propagation channel. In one embodiment of the invention the quality measurement functions Rx_Qual of 2G communications can be used to provide this information. The average value of RxQual provides the level of Noise to Interference ratio. The second level order esperance i.e. variance provides the insight on radio propagation variation. 
     While RxQual is used as an example in this embodiment of the invention to provide information on the radio propagation environment it will be appreciated that in alternative embodiments of the invention any other appropriate Signal to noise processing and post processing could also be used to assess the radio propagation environment. 
     The mobile station  100  further includes an uplink parameter module  120  for providing to a power adaption decision module  150  data parameters required for determining how to adapt the power level for audio data transmission in order to obtain an optimized level of power consumption. 
     The mobile station  100  is not aware of the level of reception at the base station  200  of the radio signal transmitted by the mobile station  100 . In order to determine an indicator of the margin between a requested PCL and the power level effectively received by the base station the mobile station  100  may use a time advance processing module  121  which applies timing advance, required in a 2G MS, and the Friis formula to provide an attenuation parameter att as follows:
 
 att=− 20 log 10 ( c★d /(4 ★Pi★F )  (1)
 
     where att is the attenuation in dB, c denotes the speed of light, d denotes the distance in metres between the mobile station  100  and the base station  200 , and F denotes the frequency in Hz of the GSM carrier 
     On the other side, we have:
 
 d=c ★(timing_advance)  (2)
 
where
 
     Timing _advance corresponds to the length of time a signal from the mobile station  100  takes to reach the base station  200 . Technical Specifications 3GPP TS 05.10 and TS 45.010 describe the time advance (TA) value adjustment procedures. Any other procedure providing this distance could also be applied e.g. AGPS,. . . 
     Consequently the margin between the requested PCL and power effectively received at the base station antenna can be written
 
 RxLev   —   BS= PCL− att   (3)
 
where:
 
     RxLev_BS is the level of reception of mobile station signal at the base station antenna connector and PCL is the Power Control Level applied by the mobile station and provided to it by the base station. The parameter RxLev_BS is provided by the RxLev_BS processing module  122  which receives a PCL parameter input and an att parameter input from the time advance processing module  121 . 
     The level of reception of the BS signal at the MS antenna connector is a component already exists in a 2G MS. It provides an RxLev value as described in 3GPP TS45.01 specification. 
     With reference to  FIG. 4 , as well as receiving the radio environment characterization parameter RxQual and an indication RxLev_BS of the level of reception of the MS signal at BS side, the power adaption decision module  150  also receives audio service characteristics including the type of TCH channel and the Audio Codec; and internal characteristics of the mobile station including the power consumption of an audio block per burst and per PCL in order to determine how the transmission power may be adapted to optimize power consumption. 
     A Target RxQual processing module  151  includes an array containing the different levels of quality to be ensured according to the type of TCH and to the Audio codec applied. As examples of realization this array can be obtained by measurement on a different network (NW) or by simulation. A Target RxQual parameter RxQual_target is provided to a comparator  153 . 
     A Margin on Tx quality module  152  provides an offset for the comparator  153  according to the RxLev_BS input. This offset Offset_TxSupp is proportional to the margin of power received at the input of BS antenna i.e. to RxLev_BS. 
     The comparator  153  determines a parameter TxSupp representative of the Uplink amount of power that can be suppressed from the total budgeted power initially needed by applying the following expression:
 
 TxSupp =min(0,floor( RxQual _target− RxQual +Offset —   TxSupp ))  (4)
 
     if (RxQual_target−RxQual+Offset_TxSupp) is negative, it is determined that no power can be suppressed. 
     A mapping component  154  determines the quantity of UL power and the way this power will be suppressed according to the TxSupp parameter received from the comparator  153  and such that the gain of power will be the biggest as well as taking into account other proprietary implementation constraints. 
     For example a decision may be made to transmit every burst of the audio data block as illustrated in  FIG. 5A  in which one radio block is transmitted over four bursts on the UL, or to suppress one burst of the audio data block as illustrated in  FIG. 5B  where only three bursts are transmitted. In alternative embodiments more than one burst of audio data may be suppressed. 
     The power control level which ranges from 5 to 19 where 5 represents the highest level of power and 19 represents the lowest level of power can be modified. A power level of one or more bursts may be modified to reduce the power consumption. In particular embodiments of the invention while the level of one or more bursts is reduced the level of one or more of the remaining bursts may be increased 
     An Error code correction ECC module can be used to compensate for a suppressed burst or a reduction in power without compromising the quality of the voice call. ECC can be used by the base station to determine if a protected block of data of the audio block has been corrupted and is lost. 
     Table 1 is an example according to one embodiment of the invention in which the suppression of power according to the TxSupp parameter range is outlined 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 TxSupp range 
                 Amount of power to be suppressed 
               
               
                   
                   
               
             
             
               
                   
                 0 
                 No power reduction 
               
               
                   
                 [1; PCL[ 
                 The reduction of power applied on 1 st . 
               
               
                   
                   
                 Tx burst is equal to PCL − TxSupp 
               
               
                   
                 PCL 
                 1 st  burst is suppressed 
               
               
                   
                 ]PCL; 2xPCL[ 
                 1 st  burst is suppressed and the reduction 
               
               
                   
                   
                 of power on the 2 nd  Tx burst is equal to 
               
               
                   
                   
                 PCL − TxSupp 
               
               
                   
                 . . . 
                 . . . 
               
               
                   
                   
               
             
          
         
       
     
     Table 2 is an example according to another embodiment of the invention in which the suppression of power according to the TxSupp parameter range is outlined 
     
       
         
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 TxSupp range 
                 Amount of power to be suppressed 
               
               
                   
               
             
             
               
                 0 
                 No power reduction 
               
               
                 [1; PCL[ 
                 TxSuppBurst = TxSupp/S 
               
               
                   
                 TxSuppBurst amount of power can be 
               
               
                   
                 removed from each burst of the Audio block. 
               
               
                 PCL 
                 1 st  burst of the block is suppressed. 
               
               
                 ]PCL; 2xPCL[ 
                 TxSuppBurst = (TxSupp − PCL)/(S − 1) 
               
               
                   
                 1 st  burst of the block is suppressed and 
               
               
                   
                 TxSuppBurst amount of power can be removed 
               
               
                   
                 from each of remaining burst of the Audio block. 
               
               
                 . . . 
                 . . . 
               
               
                   
               
             
          
         
       
     
     The transmission burst generation module  160  receives orders from the decision module as to how to generate the transmission bursts of blocks received from transmission block generation module  170 . 
     A method of communication between the mobile station  100  and the base station  200  for reducing power consumption will be described with reference to  FIG. 6 . In this example, the communication is established between the mobile station  100  and the base station  200  to make a voice call. The communication may be initiated by the mobile station  100  in the case where the user of the mobile station  100  makes the call, or by the base station  200  in the case where the mobile station  100  receives the call from another user. 
     In step S 101  the radio propagation environment between the mobile station  100  and the base station  200  is assessed by radio environment analyzer module  110  as described above in order to determine parameters such as transmission quality, path loss, fading etc. A RxQual parameter is provided to Decision module  150 . 
     In step S 102  the decision module  150  processes radio environment characterization parameter RxQual, the level of reception indicator of the mobile station signal at the base station RxLev_BS, the transmission power consumption characteristics of the mobile station, the TCH type and the Audio codec in order to determine the amount of power TxSupp that can be suppressed from the total power initially set. In step S 103  according to the range of TxSupp it is determined if and how the transmission power level or number of transmission bursts may be adapted to optimize the power consumption level. In step S 104  the audio data blocks are transmitted to the base station according to the determined transmission configuration. 
       FIG. 7  illustrates sub-components used to reduce power consumption when receiving audio data. Decision module r 150  receives radio environment characterisation parameters RxQual from a radio environment analyser module r 110 , traffic channel type and audio codec parameters, a RxLev parameter and mobile station reception power consumption parameters from a module r 123  in order to  25  determine how incoming audio data bursts on a downlink channel from the base station  200  should be received in order to optimise the power consumption. The decision module r 150  can then command RF antenna r 105  and demodulator r 104  whether or not to receive an incoming burst or whether the reception characteristics of the Rf antenna can be degraded in order to reduce the reception  30  power consumption. 
     In embodiments of the invention data lost by suppression can be compensated by channel encoding. Channel encoding performed by the channel encoder block  102  of  FIG. 2A  introduces some redundancy on the important data. This redundancy plus the interleaving helps to enable data lost by fading to be recovered by channel coding. 
     Convolution codes, used for transporting audio blocks, do not require that the entire audio block to be transmitted in UL or received in DL. In addition, audio codec handles some losses of blocks within a certain tolerance. As an example for illustration purposes, 3GPP defines some requirements according to the Audio codec, the TCH types and propagation channels. 
     Consequently in embodiments of the invention if radio propagation conditions permit, the quality of transmission/reception and/or the amount of data received/transmitted can be reduced in such a way that the audio quality is not impacted. 
     The methods according to the embodiments of the invention reduces the power consumption of a mobile phone during voice calls in GSM 2G by suppressing a determined amount of power on the UL or DL, by reducing the used power for each burst or by suppressing one part of a burst, one complete burst or several bursts constituting a block. The robustness of convolution coder enables methods according to embodiments of the invention to be implemented for decreasing total amount of energy needed to transmit or receive data blocks. 
     Since the energy configured for transmission of channel coded information is often over estimated for the required audio performance leading to over consumption of energy by a mobile telephone operating in 2G during a voice call, embodiments of the invention which reduce the transmission energy reduces power consumption of the mobile phone without compromising the quality of the communication. 
     Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention, that being determined solely by the appended claims. In particular the different features from different embodiments may be interchanged, where appropriate. 
     In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. Any reference signs in the claims should not be construed as limiting the scope of the invention.