Abstract:
Provided is a method and system for a radio system including at least one base station and terminal equipment including a receiver and a transmitter. The transmitter is structured and arranged to independently adjust a symbol rate of at least two signals and combine the two signals after adjusting the symbol rate. The transmitter then transmits the combined signal along one physical path. By adjusting the signal rate before combining the two signals, the transmitter optimizes the signal qualities of each of the signals.

Description:
This application is the national phase of international application PCT/FI99/00248 filed Mar. 25, 1999 which designated the U.S. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a data transmission method, which is used in a radio system comprising at least one base station and terminal equipment comprising a receiver and a transmitter and communicating with each other over at least one physical channel. 
     The invention further relates to a radio system, particularly a radio system comprising at least one base station and terminal equipment comprising a receiver and a transmitter and communicating with each other over at least one physical channel. 
     BACKGROUND OF THE INVENTION 
     Present mobile telephone systems attempt to provide the user with increasingly versatile services. This goal is shared by IMT-2000 (International Mobile Telecommunications for the Year 2000) services which aim to offer high-quality speech/audio signal transmission, high-rate data transfer, photograph transmission and video image transmission. In addition, the IMT-2000 service encompasses interactivity, multimedia electric mail, video conferences and target location determination, for example. 
     Transferring different data requires different symbol rate and signal transmission power. In the present radio systems the symbol rate is not optimized for the changing channel conditions since the symbol rate of several signals cannot be adapted in one physical channel. If, for example, two service signals transmitted over the same physical channel have differing quality requirements when received and the signals act differently when the delay profile of the channel changes, problems affecting the power level of the two signals occur. Such a problem typically arises when Reed-Solomon coding and convolution coding are used together. When the channel delay profile changes, a situation may arise when the first signal in accordance with the example is barely acceptable in terms of quality, while the other signal is of unnecessarily high quality. The situation is particularly critical when a service signal only requiring a low symbol rate forces a service signal requiring a high symbol rate to use extra transmission power. The prior art solutions fail to resolve this disparity. Unresolved, the disparity will cause interference over the whole area of the radio system. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An object of the invention is thus to provide a method and a radio system implementing the method so as to solve the above problems and balance the signal quality. This is achieved by a method of the type described in the introduction, the method being characterized by the transmitter transmitting at least over one physical channel at least two signals having differing quality requirements when received, and the transmitter changing, if necessary, signal-specifically the symbol rates of the signals used over the physical channel in order to meet the quality requirements. 
     The radio system of the invention is characterized by the transmitter being arranged to transmit over one physical channel at least two signals having differing quality requirements when received, the transmitter therefore comprising at least means for changing the symbol rate of the signals signal-specifically in order to meet the quality requirements, and combination means for combining the signals in the same physical channel. 
     A plurality of advantages can be achieved with the method and system of the invention. The desired quality requirements of a signal to be received can be balanced, which enables optimized transmission power be used. The result is less interference in the radio system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is now described in closer detail in connection with the preferred embodiments with reference to the accompanying drawings, in which 
     FIG. 1 shows a prior art transmitter, 
     FIG. 2 shows a transmitter of the invention, and 
     FIG. 3 shows a transceiver of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The solution of the invention is suited particularly for WCDMA (Wideband Code Division Multiple Access), UMTS (Universal Mobile Telephone System) and IMT-2000 radio systems. Hence, the invention is suitable for at least TDMA-based (Time Division Multiple Access) and CDMA-based radio systems. 
     Examine first by means of FIG. 1 how data is transmitted in accordance with the prior art. In the present example, a transmitter  90  only transmits a signal  1  and a signal  2  over the same physical channel, but the same principle applies also to three or more signals to be transmitted. The signals typically have differing quality standards when received. A carrier-to-interference ratio or for instance a bit error rate BER can be used as the quality standard. The BER of the signal  1  is for example BER1=e −3  and the BER of the signal  2  is BER2=e −6 . Since the quality requirements are signal-specific, the signals should be transmitted at different transmission powers/symbol rates. The signal  2  to be transmitted is first encoded by for example Reed-Solomon coding at means  100 . This coding can also be some other coding. Next, at means  102 , the signal  2  is interleaved, in other words the bits or symbols of the signal are rearranged such that the signal  2  becomes more tolerant of fadings. The signal  1  and the signal  2  are combined into a combined signal at a combination means  104 , which can be a multiplexer. Next, the combined signal is convolution-coded at a coder  106 . The symbol rate and thus also the transmission power—of the combined signal is changed by removal coding or repetition coding, if necessary, at means  108 . The removal coding or repetition coding increases or decreases the number of bits to be transmitted, affecting the two signals in a similar manner. The signal is further interleaved at means  110 . Eventually, the signal is modulated into a radiofrequency signal at radio frequency means  114  in a manner obvious to one skilled in the art, and the radio-frequency signal is transmitted by an antenna  116 . The fact that only one shared unit  108  is provided to adapt the symbol rate prevents the signal power levels from being optimized. 
     Examine now a solution of the invention by means of FIG. 2. A transmitter  190  transmits a total of P signals having differing quality requirements. The number P of the signals to be transmitted is two or more. Before being combined, a signal  1  is encoded by a coder  200 , the symbol rate is adapted at means  202  and interleaved at means  204 . Other signals are processed in a similar manner; a signal P is thus encoded at a coder  206 , the symbol rate is adapted at means  208  and interleaved at means  210 . Although being typically employed in a radio system transmitter, the coders  200 ,  206  and the interleaving means  204 ,  210  are irrelevant to the invention. Hence, in addition to or instead of the coders  200 ,  206  and the interleaving means  204 ,  210 , the solution of the invention can further comprise other signal processing means. Essential in the inventive solution is that the signals in this embodiment at least have the unique means  208  and  210  affecting the symbol rate which change the symbol rate by removal coding and/or repetition coding, if necessary. Changing the symbol rate also changes the signal transmission power; changing the symbol rate is thus equivalent to changing signal transmission power. The signals are combined at a combination means  212 , which is a multiplexer. In the solution of the invention, the symbol rate of the combined signal can be further changed at means  214 , if necessary. The means  214  also performs removal coding and/or repetition coding. In the solution of the invention, it is not, however, necessary to change the symbol rate at this point. The subsequent operation of the transmitter  190  is irrelevant to the inventive solution. Typically, however, the signal is interleaved at means  206 , spreading-coded and modulated in one or more manners at means  218 , modulated into a radio-frequency signal at means  220 , and transmitted via an antenna  222 . Hence, at least two different signals that are usually associated with different services are transmitted over the same physical channel. A physical channel is here defined as a channel based on the use of one or more spreading codes. 
     In a preferred embodiment of the invention the symbol rate of the transmitter  190  can be controlled by a receiver. In such a case, a control signal (CONTROL SIGNAL FROM RECEIVER) is supplied from the receiver to a control unit  224  of the transmitter, the control unit controlling the blocks  202 ,  208  changing the symbol rate as instructed by the control signal. The control block  224  can also control the block  214  changing the symbol rate if such a block is in use at the transmitter  190 . The signals  1  to P are also supplied to the control block  224 , whereby the control block  224  knows the required symbol rate. Removal coding and/or repetition coding changing the symbol rate and the transmission power is performed both for the transmitter and the receiver in a known manner. Consequently, the change does not otherwise affect the data transmission. 
     FIG. 3 shows the features of the inventive solution in greater detail. The base stations and terminal equipment of the radio system are transceivers, the block diagram of FIG. 3 showing such a transceiver in general. The transceiver transmits P signals, which a transmitter  290  first encodes at means  300 ,  306 , adapts the symbol rates at means  302 ,  308 , and interleaves at means  304 ,  310  as in FIG.  2 . Henceforth, the signal processing also proceeds in accordance with FIG. 2, in other words the signals are combined by a combination means  312 , the symbol rate of the combined signal is further adapted at means  314 , and the combined signal is interleaved at means  316 . Next, at a typical transmitter part  290 , control data is added to the signal to be transmitted at means  318 , preferably being a multiplexer. Next, the signal is spreading-coded, which is performed in such a manner that the signal is multiplied at a multiplier  322  by a spreading code supplied from a spreading code generator  320 . The spreading-coded signal is modulated into a radiofrequency signal by multiplying at a multiplier  326  the signal by a carrier supplied from an RF oscillator  324  and by filtering the signal at a filter  328 . The radio-frequency signal is amplified at an RF power amplifier  330  and transferred via a duplex-filter  332  to an antenna  334  to be transmitted. 
     In the solution of the invention, a receiver  280  operates in the following manner. The antenna  334  receives the signal, which is a combination signal consisting of several signals. The received signal propagates via the duplex-filter  332  to a filter  336 , which only allows the desired band to pass. The filtered signal is demodulated by multiplying the signal at a multiplier  340  by the signal of a local oscillator  342 , and low-pass-filtering the signal at a filter  344 . Next, the aim is to keep the power level of the received signal unchanged with an AGC amplifier  346 . The signal is changed to digital by an analogue/digital converter  348 . Since the signal is a multipath-propagated signal, the aim is to combine the signal components propagated via different paths in a block  350  which, in accordance with the prior art, comprises a plurality of RAKE branches. The signal components received by the RAKE branches at different delays are searched by correlating the received signal with the spreading codes used, which are delayed by predetermined delays. When the signal component delays are found out, signal components belonging to the same signal are combined. Simultaneously, the spreading coding of the signal components is decoded. Next, the control signals and data signals included in the received signal are separated by demultiplexing at means  352 . The signal part containing data is conveyed to be deinterleaved at means  354 . Here, the interleaving of the block corresponding to the interleaving means  316  is thus deinterleaved. Next, at means  356 , the signal undergoes an inverse operation of the symbol rate change corresponding to the transmitter block  314 . Hence, if the transmitter block  314  has performed removal coding, the block  356  performs repetition coding of a corresponding extent. Next, the combination signal is divided into P signals at demultiplexing means  358 . The interleaving of the first signal is deinterleaved at deinterleaving means  360 , the symbol rate is inversely adapted in relation to the adaptation of the transmitter block  302  at means  362  and the signal coding is decoded at the means  362 , in which case the signal  1  is available to the receiver. A similar procedure is repeated in connection with other demultiplexed signals; similarly, the interleaving of the signal P is deinterleaved at means  366 , removal coding or repetition coding is performed at means  368 , and the signal is decoded at means  370 . The means  300 ,  306  of the transmitter usually perform convolution coding, the convolution coding being decoded by the means  364 ,  370  of the receiver. 
     The receiver  280  further comprises a block  372  measuring the signal quality. If any of the received signals does not meet the quality requirements or exceeds the quality requirements too dramatically, in other words deviates too much from a predetermined quality requirement, a signal controlling the symbol rate is supplied from the block  372  to the block  318  of the transmitter part for the control channel. 
     The solution of the invention is also suited for radio systems wherein the physical channel is based on bursts instead of spreading code(s), as is the case with the TDMA-based transmissions for example in a GSM radio system. In such a case, a plurality of service signals can be transmitted at an optimal power level in the same burst. The advantage of this is that the receiver does not need to receive separate signals from each service. This also applies to the TDMA/CDMA radio system wherein spreading coding is used within the burst. Hence, several different services can be simultaneously placed for the code or group of codes to be used in the burst. FIGS. 1 to  3  show transmitters and receivers using spreading coding. Truly TDMA-based transmitters and receivers are similar to the ones shown in FIGS. 1 to  3  as regards the rest of the blocks, but spreading coding is naturally ignored at the blocks  112 ,  218 , the means  320  and  322  also being unnecessary. Furthermore, neither are the delays of the received signal caused by multipath-propagation searched on the basis of the spreading code at the block  350  in such a case. In the TDMA receiver, the block  350  performs equalization wherein the received signal is multiplied by an estimate of the impulse response of the channel. The impulse response estimate is formed, in turn, by means of a training sequence or another known sequence in a manner obvious to one skilled in the art. Both transmission and reception modes are employed in the TDMA/CDMA transceivers. 
     Although the invention is described above with reference to the example in accordance with the accompanying drawings, it is obvious that the invention is not restricted thereto but can be modified in various ways within the scope of the inventive idea disclosed in the attached claims.