Abstract:
The invention concerns a method for boosting data transmission in a telecommunications system and a mobile communications system. The invention is characterised in that the telecommunications network uses at least on a part of the transmission path between the fixed station, e.g. a base transceiver station, and the transcoder unit speech coding at a lower transmission rate than the transmission rate of the speech coding used on the transmission path between the fixed station and the terminal equipment. The speech parameters received from the terminal equipment are converted for the speech coding method used on the transmission connection between the fixed station and the transcoder unit and vice versa. In the network transcoder unit it is possible to reconvert speech parameters received from the direction of the terminal equipment e.g. into speech parameters of the speech coding used on the transmission path between the terminal equipment and the fixed station.

Description:
This application is a continuation of international application serial number PCT/FI99/01070, filed 22 Dec. 1999. 

   FIELD OF THE INVENTION 
   This invention concerns a method of boosting data transmission in a telecommunications network. 
   BACKGROUND OF THE INVENTION 
   In  FIG. 1  of the appended drawing a simplified Global System for Mobile communications, a GSM system for short, is shown as a block diagram. The Network Subsystem, NSS, includes a mobile services switching centre MSC  2  which is connected to other mobile services switching centres, and directly or through a Gateway Mobile Services Switching Centre, a GMSC system interface the mobile network is connected to other networks, such as a Public Switched Telephone Network, PSTN  4 , an Integrated Services Digital Network, ISDN  6 , other Public Land Mobile Networks, PLMN  10 , and packet switched public data networks, PSPDN  12 , and circuit switched public data networks, CSPDN  14 . In the mobile services switching centre MSC  2  there are Network Interworking Functions, IWF  16 , for matching the GSM network with the other networks. Through an A-interface the NSS network subsystem is connected to a Base Station Subsystem, BSS, which includes base station controllers BSC  20 , each one of which controls the base transceiver stations BTS  22  connected to them. The interface between the base station controller BSC and the base transceiver stations BTS connected to it is an A bis interface. The base transceiver stations BTS  22  for their part are connected over a radio path with mobile stations MS  24  across the radio interface. The operation of the whole system is monitored by an Operation and Maintenance Centre, OMC. 
   The mobile station MS  24  sends speech or user data across the radio interface on a radio channel at standard rates of e.g. 13 kbit&#39;s or 5.6 kbit/s. Speech coding is used in the speech transmission to achieve a lower transmission rate than typically in telephone networks, whereby the band width needed by the radio link on the radio path is reduced. The base transceiver station BTS  22  receives the data of the traffic channel and transmits it into the 64 kbit/s time slot of the PCM line. Into the same time slot, that is, channel, are also placed three other full-rate traffic channels of the same carrier wave, so the transmission rate per connection will be 16 kbit/s. For half-rate traffic channels the transmission rate is 8 kbit/s per connection. A transcoder/rate adapting unit TRAU  26  converts the coded 16 kbit/s or 8 kbit/s digital information to the 64 kbit/s channel, and on this channel the data is transmitted to an IWF  16  unit which is located in the mobile services switching centre MSC  2  and which performs the required modulation and rate conversion, whereupon the data is transmitted to some other network. Thus, the user data is transmitted over fixed connections in the uplink direction from base transceiver station BTS  22  to base station controller BSC  20  and to mobile services switching centre MSC  2  and, correspondingly, the data to be relayed to mobile station MS  24  is transmitted in the downlink direction from mobile services switching centre MSC  2  through base station controller BSC  20  to base transceiver station BTS  22  and from there further over the radio path to mobile station MS  24 . 
   In the GSM system, a Channel Codec Unit, CCU, of the base transceiver station performs a conversion of the signal received on the radio channel to the PCM time slot channel of the trunk line running over the A bis interface and a conversion of the frame structure of the signal received over the A bis interface into a form which can be transmitted on the radio channel. The transcoder unit TRAU  26  performs the conversion operations on the signals to be transmitted across the A-interface. The transcoder/rate adapting unit TRAU  26  is often located far from the base transceiver station  22 , e.g. in connection with the base station controller BSC  20 . 
   In a digital mobile system, speech is generally coded into a digital form by using low rate speech coding. Nowadays the SM system uses Full Rate FR  30  coding at a transmission rate of 13 kbit/s, Half Rate HR  32  coding at a transmission rate of 5.6 kbit/s, Enhanced Full Rate EFR  30 ′ coding at a transmission rate of 12.2 kbit/s and Enhanced Half Rate EHR  32 ′ coding. The enhanced speech codings  30 ′,  32 ′ are so advanced that the quality of speech is not significantly reduced in them. 
   Thus, speech coding is performed in the mobile station and on the mobile network side in the transcoder unit TRAU  26 . The speech information to be transmitted is one of the parameters of the speech coding method. In modern GSM systems the TRAU  26  transcoders are of several different types of coding, e.g. full rate, half rate or double acting, which is able to change from one rate to another. The transcoders convert the speech from a digital format into another, e.g. they convert 64 kbit/s A-law PCM arriving from the exchange over the A interface into 13 kbit/s full rate FR  30  coded speech for transmission to the base transceiver station line, and vice versa. In a call between two mobile stations PCM speech samples are transmitted from one transcoder to another, which codes them by a speech coding method which is used on the radio path. Repeated coding and decoding of the speech signal during the transmission will distort the speech signal, for which reason this coding-decoding chain, which is called tandem coding, is usually avoided. 
   The Finnish Patent Application FI-951807 presents transmission of speech frames, which have not been decoded, between transcoders and thus barring of tandem coding in the transcoder, when the call is one between two mobile stations, that is, a Mobile to Mobile Call, MMC. In the solution according to the application, the coded speech parameters are sent on the PCM time slot sub-channel without any decoding and coding in the TRAU transcoders of the mobile station network. Tandem coding is avoided by relaying with minor changes the frames coming from one base transceiver station BTS  22  through these tandem connected TRAU  26  transcoders to another base transceiver station BTS  22 ′. The receiving transcoder will perceive from these minor changes in the frame that coding need not be done, and it will relay further the received speech parameters of the frame as such. 
   The Finnish Patent Application FI-960590 presents a transmission adaptation for a connection between exchanges. In the solution according to the application, a speech signal is transmitted coded by a speech coding method on a sub-channel of a PCM channel. The speech coding for the connection between exchanges is chosen according to the speech coding of the TRAU frames of the A-interface, except if the speech coding of the TRAU frames received from the A-interface is different from the speech coding of TRAU frames received from other transmission equipment, that is, if the parties to the call are using different speech codings.  FIGS. 2   a – 2   c  illustrate this adaptation of the transmission for a connection between exchanges in a few cases shown as examples. The speech coding used in each part of the transmission path is marked in the figures, in this example they are full rate FR  30  and half rate HR  32  speech coding. In  FIG. 2   a  both mobile stations MS 1   24  and MS 2   24 ′ use the full rate FR  30  speech coding method. Hereby the speech parameters are transmitted through the mobile station network as unchanged full rate speech parameters. In  FIG. 2   b  both mobile stations MS 1  and MS 2  use a half rate HR  32  speech coding method. Hereby the speech parameters are transmitted through the mobile station network as half rate speech parameters. In the case shown in  FIG. 2   c , mobile station MS 1  uses half rate HR speech coding while mobile station MS 2  uses full rate FR  30  speech coding. In this situation, a change is made at the mobile services switching centre MSC 1  end to full rate speech coding and the necessary decoding and speech coding are performed. 
   A problem with the presented transmission situations is the need of transmission capacity, especially on the transmission connection between the base transceiver station and the network transcoder. The transmission in the mobile station network of speech parameters of the mobile station using full rate speech codec requires a full rate channel, which cannot be transmitted, if on the transmission connection e.g. only a half of that transmission capacity is available, which is required by a full rate signal. 
   BRIEF SUMMARY OF THE INVENTION 
   The purpose of this invention is to boost data transmission especially in transmission connections on the network side of a mobile communications system. 
   This objective is achieved with the method and arrangement according to the invention, which are characterised by the features stated in the independent claims. Advantageous embodiments of the invention are presented in the dependent claims. 
   The invention is based on the idea that the data communications network uses at least in a part of the transmission path between a fixed station, e.g. a base transceiver station, and a transcoder unit a lower transmission rate speech coding than the transmission rate of the speech coding used on the transmission path between the fixed station and the terminal equipment. The speech parameters received from the terminal equipment are converted to the speech coding method used in the transmission connection between the fixed station and the transcoder unit, and vice versa. In the transcoder unit of the network it is possible to convert speech parameters received from the terminal equipment back to e.g. the speech parameters of the speech coding used on the transmission path between the terminal equipment and the fixed station. 
   It is an advantage of such boosting of data transmission that less transmission capacity is needed per speech connection at least in a part of the transmission connection between the base transceiver station and the transcoder unit of the network. 
   It is another advantage of the data communications system according to the invention that it allows trafficking between terminal equipment using different speech coding methods, at best with only one speech coding during the transmission. 

   
     LIST OF FIGURES 
     The invention will now be described in greater detail in connection with advantageous embodiments and referring to the examples in accordance with  FIGS. 3–6   b  in the appended drawings, wherein: 
       FIG. 1  shows such parts of a mobile communications network which are essential to the invention; 
       FIGS. 2   a – 2   c  show examples of state-of-the-art speech transmission situations; 
       FIG. 3  is a speech transmission diagram of data transmission boosting according to the invention; 
       FIGS. 4   a  and  4   b  show speech transmission situations according to a first embodiment of the invention as examples; 
       FIGS. 5   a  and  5   b  show speech transmission situations according to another embodiment of the invention as examples; and 
       FIGS. 6   a  and  6   b  show flow charts of data transmission boosting according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention may be applied in connection with any telecommunications system. The invention will be described hereinafter by way of example and mainly in connection with a digital GSM mobile communications system.  FIG. 1  shows the simplified structure of the GSM network described above. The interested reader will find background information as regards a more detailed description of the GSM system from GSM recommendations and from the book “The GSM System for mobile Communications”, M. Mouly &amp; M. Pautet, Palaiseau, France, 1992, ISBN:2-9507190-0-7. 
     FIG. 3  shows boosting of data transmission in a mobile communications system in accordance with the invention. In the case shown as an example in  FIG. 3 , the mobile station MS  24  uses full rate speech coding  30 . Hereby speech parameters of full rate FR  30  speech coding are transmitted between base transceiver station BTS  22  and mobile station MS  24 . According to the invention, the speech parameters are converted for a transmission connection between base transceiver station BTS  22  and the network transcoder unit TRAU  26  into speech parameters of speech coding of a lower transmission rate, in the case shown in  FIG. 3  into speech parameters of half rate speech coding  32 . Thus, the speech parameters received from the mobile station are decoded at the end of base transceiver station BTS  22  and a new speech coding is carried out by a speech coding method of a lower transmission rate, in the case shown in  FIG. 3  by half rate speech coding  32 . The new speech parameters thus obtained are transmitted over the transmission connection to the transcoder unit TRAU  26 . Correspondingly, the speech parameters received from transcoder unit TRAU  26  are decoded at the end of base transceiver station BTS  22  and a new speech coding is performed by a speech coding method available on the radio path, in the case shown in  FIG. 3  by full rate speech coding  30 . The resulting speech parameters are transmitted to mobile station MS  24  over the radio path. When required, a corresponding conversion of the speech parameters is performed at the end of transcoder unit TRAU  26  to transmit speech elsewhere in the network and from elsewhere in the network to the base transceiver station connection. From transcoder unit TRAU  26  the speech is transmitted elsewhere in the network in some state-of-the-art manner. Instead of the speech codings  30 ,  32  shown in  FIG. 3  other speech codings may also be used, however, so that the speech coding in use in the connection between the base transceiver station  22  and the transcoder unit  26  is a speech coding of a lower transmission rate than the speech coding used on the radio path. 
   In the following the invention will be described in greater detail in the light of a first embodiment of the invention and referring to  FIGS. 4   a  and  4   b . In the first embodiment of the invention, a speech coder  45  according to the invention is located when required in connection with base transceiver station BTS  22  to decode and recode the call to be relayed so that the speech parameters to be transmitted are converted between a first and a second speech coding method.  FIG. 4   a  shows a call transmission connection between two mobile stations MS 1   24  and MS 2   24 ′ as an example. Mobile station MS 1   24  uses enhanced full rate speech coding EFR  30 ′ and mobile station MS 2  uses enhanced half rate speech coding EHR  32 ′. Base transceiver station BTS 1  receives the EFR  30 ′ speech parameters from mobile station MS 1   24 . The speech coder according to the invention decodes them and recodes by enhanced half rate speech coding HER  32 ′. These EHR  32 ′ speech parameters are transmitted through base station controller BSC 1   20  to transcoder unit TRAU 1   26  and from there further by using state-of-the-art barring of tandem coding as EHR  32 ′ speech parameters by way of exchanges MSC 1   2  and MSC 2   2 ′ to transcoder unit TRAU 2   26 ′, which transmits the EHR  32 ′ speech parameters further through base station controller BSC 2   20 ′ to base transceiver station BTS 2   22 ′. At the end of base transceiver station BTS 2   22 ′ the EHR  32 ′ speech parameters are transmitted over the radio path to mobile station MS 2   24 ′, where enhanced half rate speech coding EHR  32 ′ is used. Thus, in the speech transmission described above, only one decoding and recoding of speech coding is performed on the mobile station network side. Correspondingly, the EHR  32 ′ speech parameters received from mobile station MS 2   24 ′ are transmitted unchanged over the transmission network to the end of base transceiver station BTS 1   22 , where a speech coder according to the invention decodes them and carries out recoding by enhanced full rate speech coding  30 ′. These EFR  30 ′ speech parameters are transmitted from base transceiver station BTS 1   22  over the radio path to mobile station MS 1   24 . 
     FIG. 4   b  is an example of another situation showing a call transmission connection between two mobile stations MS 1   24  and MS 2   24 ′ where both mobile stations MS 1   24  and MS 2   24 ′ use enhanced full rate speech coding EFR  30 ′. Base transceiver station BTS 1   22  receives the EFR  30 ′ speech parameters sent by mobile station MS 1   24 . In order to boost the data transmission on the connection between the base transceiver station and the network transcoder unit, the speech coder according to the invention decodes the speech parameters received at base transceiver station BTS 1   22  and recodes the speech by enhanced half rate speech coding  32 ′. The resulting EHR  32 ′ speech parameters are transmitted to transcoder unit TRAU 1   26 , which again transmits the EHR  32 ′ speech parameters unchanged through exchanges MSC 1   2  and MSC 2   2 ′ to transcoder unit TRAU 2   26 ′. TRAU 2   26 ′ sends the EHR  32 ′ speech parameters to base transceiver station BTS 2   22 ′. Before being transmitted onto the radio path, the received EHR  32 ′ speech parameters are decoded in a speech coder according to the invention and they are recoded by the enhanced full rate speech coding available on the radio path. The EFR  30 ′ parameters are transmitted to mobile station MS 2   24 ′. Correspondingly, the same procedure is used for the EFR  30 ′ speech parameters of mobile station MS 2   24 ′ which are received at base transceiver station BTS 2   22 ′. 
     FIGS. 5   a  and  5   b  show examples of situations in accordance with another embodiment of the invention. In this second embodiment of the invention a first speech coder  45  is located in connection with the base transceiver station, besides which another speech coder  55  is located in connection with transcoder TRAU  26  also to decode and recode the speech to be relayed so that the speech parameters are converted between a first and a second speech coding method.  FIG. 5   a  shows a speech transmission connection between two mobile stations MS 1   24  and MS 2   24 ′, when both mobile stations use enhanced full rate speech coding  30 ′. The EFR  30 ′ speech parameters received by base transceiver station BTS 1   22  from mobile station MS 1   24  are converted in accordance with the invention into EHR  32 ′ parameters and they are transmitted to transcoder unit TRAU 1   26  in the same manner as was described above in connection with the first embodiment of the invention. The EHR  32 ′ speech parameters received in transcoder unit TRAU 1   26  are converted in a speech coder in accordance with the invention for a transmission rate of enhanced full rate speech coding. When required, the speech parameters may also be converted into PCM samples. At the transmission rate of enhanced full rate speech coding the speech is transmitted from transcoder unit TRAU 1   26  through exchanges MSC 1   2  and MSC 2   2 ′ to transcoder unit TRAU 2   26 ′. The speech received in transcoder unit TRAU 2   26 ′ is converted in a speech coder  55 ′ according to the invention back to EHR  32 ′ speech parameters, which are transmitted to base transceiver station BTS 2   22 ′. Before being transmitted onto the radio path, the EHR  32 ′ speech parameters are converted in accordance with the invention into EFR  30 ′ speech parameters, as was described above in connection with a first embodiment of the invention. 
     FIG. 5   b  shows an example of another situation where mobile station MS 1   24  uses enhanced full rate speech coding EFR  30 ′ and mobile station MS 2   24 ′ uses enhanced half rate speech coding EHR  32 ′. The EFR  30 ′ speech parameters received at base transceiver station BTS 1   22  are converted in accordance with the invention into EHR  32 ′ speech parameters and they are transmitted to transcoder unit TRAU 1   26  in the same manner as was presented above in connection with the description of  FIG. 4   a . The EHR  32 ′ speech parameters received in transcoder unit TRAU 1   26  are converted in a speech coder  55  according to the invention into a transmission rate of enhanced full rate speech coding  30 ′. When required, the speech parameters may also be converted into PCM samples. At the transmission rate of enhanced full rate speech coding  30 ′ the speech is transmitted from transcoder unit TRAU 1   26  through exchanges MSC 1   2  and MSC 2   2 ′ to transcoder unit TRAU 2   26 ′. The speech received in transcoder unit TRAU 2   26 ′ is again converted in a speech coder according to the invention into EHR  32 ′ speech parameters, which are transmitted to base transceiver station BTS 2   22 ′ and from there further over the radio path to mobile station MS 2   24 ′. The EHR  32 ′ speech parameters received from mobile station MS 2   24 ′ are converted correspondingly in a reversed order when transmitting the speech in the network from base transceiver station BTS 2   22 ′ to base transceiver station BTS 1   22 . 
     FIG. 6   a  shows boosting of data transmission in accordance with the invention in a mobile communications system in the uplink direction. At point  602  the transmission rate is determined which is to be used on the transmission path between the base transceiver station and the transcoder unit, and at point  604  the transmission rate of speech parameters received from mobile station MS at the base transceiver station is determined, that is, the transmission rate used on the radio path. At point  606  the transmission rates determined above are compared with one another. If the radio path transmission rate is higher than the transmission rate of the transmission path between the base transceiver station and the transcoder unit, the speech parameters are decoded (point  608 ) and they are recoded by the second speech coding, which is used on the transmission path between the base transceiver station and the transcoder unit (point  610 ). The speech parameters thus processed are transmitted from the base transceiver station to the transcoder unit over the transmission path (point  612 ). If in the check at point  606  the radio path transmission rate is not higher than the transmission rate of the transmission path, then the speech parameters are processed in a state-of-the-art manner and they are transmitted further in the network. 
     FIG. 6   b  shows boosting of data transmission in accordance with the invention in a mobile communications system in the downlink direction. At point  622  the transmission rate used on the radio path is determined, while at point  624  the transmission rate of speech parameters received from the transcoder unit at the base transceiver station are determined. At point  626  a comparison is made between the transmission rates determined above. If the transmission rate used on the transmission path between the base transceiver station and the transcoder unit is lower than the transmission rate of the radio path, then the received speech parameters are decoded (point  628 ) and they are recoded by a first speech coding, which is used on the radio path (point  630 ). The reprocessed speech parameters are transmitted from the base transceiver station to the mobile station over the radio path (point  632 ). If it is found in the check at point  626  that the transmission rate of the transmission path is not lower than the transmission rate of the radio path, then the speech parameters are transmitted to the mobile station in a state-of-the-art manner. 
   The speech coder in accordance with the invention supports two or more speech coding methods, which are used in a telecommunications system, preferably in a mobile communications system. The speech coder according to the invention may also be used in other situations than those shown in the preceding examples to implement the functionality according to the invention. 
   In mobile station MS speech coding and decoding are performed in a state-of-the-art manner, which is why it is not described in greater detail in this connection. 
   The drawings and the related explanation are intended only to illustrate the inventive idea. As regards its details the boosting of data transmission in accordance with the invention may vary within the scope of the claims. Even though the invention was described above mainly in connection with a mobile communications system, the boosting of data transmission may be used also for a telecommunications system of some other kind, when the telecommunications system uses a low transmission rate speech coding on the transmission path between the fixed station and the terminal equipment. Thus, in the present application a base transceiver station means any such unit in a telecommunications network which is in connection with pieces of terminal equipment, whereas a mobile station means both mobile and fixed pieces of terminal equipment which are in connection with a telecommunications network. The functionality according to the invention may be implemented in the network for all connections or for some connections only.