Patent Publication Number: US-2005123005-A1

Title: Rate matching method and apparatus for multiplexing channels having different transmission time intervals in a mobile communcation system

Description:
PRIORITY  
      This application claims priority under 35 U.S.C. § 119 to an application entitled “Rate Matching Method and Apparatus for Multiplexing Channels Having Different Transmission Time Intervals in a Mobile Communication System” filed in the Korean Intellectual Property Office on Dec. 4, 2003 and assigned Serial No. 2003-87779, the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to rate matching of channel-coded signals in a mobile communication system, and in particular, to a rate matching method and apparatus for multiplexing channels having different Transmission Time Intervals (TTIs).  
      2. Description of the Related Art  
      Generally, in wireless communication systems such as Integrated Services Digital Network (ISDN) system, digital cellular system, Wideband Code Division Multiple Access (W-CDMA) system, and CDMA2000 system, source user data is channel-coded with error correction codes before being transmitted in order to improve reliability of transmission data. Typical codes used for channel coding include convolutional codes, and linear block codes for which a single decoder is used. Recently, in addition to the foregoing typical codes, turbo codes are popularly used.  
      In order to match the number of coded data bits to the number of bits actually output with a radio frame, puncturing and repetition are performed on specific bits among the coded data bits. The puncturing and repetition is called “rate matching.” 
       FIG. 1  is a block diagram illustrating a structure of a UMTS (Universal Mobile Telecommunication System) uplink transmitter. Referring to  FIG. 1 , transmission data is input to a channel coder  110 , 111  on a TTI-by-TTI basis. The TTI can be determined according to quality-of-service (QoS) of the transmission data. A data rate or a TTI can be determined according to the QoS, and the TTI can be set to 10 ms, 20 ms, 40 ms and 80 ms. The channel coder  110 , 111  receives data on a frame-by-frame basis, codes the received data according to a predetermined coding rate, and outputs coded bits. A radio frame equalizer  120 , 121  generates F i  consecutive radio frames each having the same number of bits as the number of the output coded bits. The number of bits allocable to one frame is expressed as 
   T   i   =F   i   *N   i     N   i =floor{ E   i   /F   i }  (1) 
 where ‘i’ denotes a unique transport channel number, F i  denotes the number of radio frames that can be generated for one TTI in an i th  transport channel, N i  denotes the number of bits included in each of radio frames generated for one TTI in an i th  transport channel, and E i  denotes the number of bits included in one TTI in an i th  transport channel. A first interleaver  130 , 131  interleaves the bits output from the radio frame equalizer  120 , 121 , and an output of the first interleaver  130 , 131  is input to a radio frame segmentation block  140 , 141 . The radio frame segmentation block  140 , 141  allocates the interleaved bits to F i  radio frames. If a transport channel over which the bits are transmitted has a TTI of 10 ms or longer, the radio frame segmentation block  140 , 141  segments the radio frame according to the TTI. When the number of bits allocated to the segmented radio frame is smaller than the number of bits allocable in the TTI, a rate matcher  150 , 151  performs repetition to match the bits in number. In contrast, when the number of bits allocated to the radio frame is larger than the number of bits allocable in the TTI, the rate matcher  150 , 151  punctures specific bits to match the bits in number. That is, for rate matching, the rate matcher  150 , 151  performs puncturing or repetition to the number of bits that can be transmitted for one TTI. The foregoing elements can be separately provided for each service, as shown by dotted-line blocks. 
 
      A multiplexer (MUX)  160  receives radio frames finally rate-matched for respective services, and multiplexes the radio frames. The multiplexed radio frames are transmitted over a physical channel in a physical channel processing process.  
       FIG. 2  is a diagram illustrating a process of performing rate matching according to the prior art. With reference to  FIG. 2 , a description will be made of a process in which a service A and a service B are multiplexed with one transport channel. It is assumed herein that the service A is provided on a 10-ms TTI basis, and the service B is provided on a 20-ms TTI basis. For example, the service A transmits 100-bit data for an initial 10-ms TTI and transmits no data for the next 10-ms TTI, and the service B transmits 199-bit data for a 20-ms TTI. The 100 bits and the 199 bits for respective TTIs are obtained by counting the numbers of bits output from the channel coders. Therefore, when the 10-ms TTI-based service A and the 20-ms TTI-based service B are multiplexed and transmitted over a physical channel, the total number of bits per 10 ms is 150 bits.  
      When a 10-ms TTI transport channel and a 20-ms TTI transport channel are multiplexed as described above, 10 ms which is the minimum TTI is defined as a unit frame, and the 20-ms TTI transport channel is segmented by the 10 ms which is the unit frame, and transmitted twice. That is, the 20-ms TTI transport channel is multiplexed with the 10-ms TTI transport channel before being transmitted.  
      A description will now be made of a method for multiplexing the service A and the service B in a first 10-ms frame.  
      For the service A, the channel coder  110  codes received transmission data according to a predetermined coding rate, and outputs the coded bits to the radio frame equalizer  120 . The radio frame equalizer  120  compares a 10-ms TTI for transmitting data for the service A with the defined unit frame. Here, a TTI for the service A is equal to the unit frame, i.e., 10-ms TTI. Because the number of bits allocable for one TTI is 100, additional bit padding is not performed. The first interleaver  130  interleaves the received 100-bit data. The radio frame segmentation block  140  allocates the interleaved 100-bit data to a 10-ms frame. The rate matcher  150  performs Rate Matching Attribute (RMA) on the 100-bit data allocated to the 10-ms frame. That is, the rate matcher  150  performs puncturing and repetition on the received data in order to match the total number of bits allocable to one frame, as the service A and the service B are multiplexed before being transmitted. A detailed description of the rate matching operation will be given below.  
      For the service B, a channel coder  111  codes 199-bit transmission data received for a 20-ms TTI. A radio frame equalizer  121  compares a TTI for the service B with the defined unit frame. Because the TTI for the service B is not equal to the unit frame, the radio frame equalizer  121  generates a frame for supporting the service B with the unit frame considering Equation (1). That is, the radio frame equalizer  121  segments the 20-ms TTI into 10-ms unit frames. Therefore, according to Equation (1), the number E i  of bits included in the 20-ms TTI is 199, F i  is 2, and N i  is 100. In order to equally include 100 bits in the unit frames, the radio frame equalizer  121  additionally pads 1 bit. The 200-bit data obtained by performing the 1-bit padding is output to the first interleaver  131 . The first interleaver  131  interleaves the 200-bit data. A radio frame segmentation block  141  segments the 20-ms TTI into 100-bit unit frames, i.e., 10-ms unit radio frames, and sequentially outputs 200-bit data. A rate matcher  151  performs puncturing and repetition on the 100-bit data received by the 10-ms unit frame, using Rate Matching Attribute. That is, the rate matcher  151  performs puncturing and repetition on the received data in order to match the total number of bits allocable to one frame, as the service A and the service B are multiplexed before being transmitted.  
      In other words, the total number of bits output from the rate matcher  150  and the rate matcher  151  is 200. However, the total number of bits that should be transmitted for the 10-ms unit frame is 150. Therefore, the rate matchers  150  and  151  should puncture 25 bits, respectively. That is, the rate matcher  150  punctures 25 bits in the 100-bit data for the service A and outputs the result to the multiplexer  160 , and the rate matcher  151  punctures 25 bits in the 100-bit data of a first radio frame for the service B and outputs the result to the multiplexer  160 .  
      The multiplexer  160  receives 75-bit data for the service A and a 75-bit first radio frame for the service B, multiplexes the 150-bit data for the 10-ms unit frame, and transmits the multiplexing result over a physical channel.  
      Next, a description will be made of a method for multiplexing the service A and the service B in a second 10-ms frame.  
      For the service A, because there is no input data for a second 10-ms TTI, the channel coder  110  to the rate matcher  150  perform no operation for the second 10-ms TTI.  
      However, for the service B, the channel coder  111  to the radio frame segmentation block  141  perform the same signal processing as that performed on the first frame.  
      The rate matcher  151  performs rate matching on 100 bits in the second 10-ms frame. Because the total number of bits received for the 10-ms unit frame is 100 and the total number of bits that should be transmitted over a 10-ms physical channel is  150 , the rate matcher  151  repeats 50 bits according to Rate Matching Attribute, outputting 150-bit data.  
      That is, for the second 10-ms TTI, the multiplexer  160  outputs the 0-bit data for the service A and the 150-bit data for the service B.  
      When a plurality of transport channels having different TTIs are multiplexed as described above, a minimum TTI is defined as a unit frame and, in the case of a transport channel having a TTI longer than the unit frame, a data sequence is segmented into unit frames. The segmented radio frames are adjusted through a padding process such that they have the same number of bits. The radio frames segmented in this manner are sequentially subjected to rate matching. However, the foregoing rate matching method has the following problems.  
      Referring to  FIG. 2 , the service A transmits only 75 (=100−25+0) bits in 100-bit data for a total of 20 ms, and the service B transmits only 174 (=75+99) bits in 199-bit data for 20 ms. That is, the service B should additionally transmit 1 data bit padded by the radio frame equalizer  121  and 50 data bits repeated for a second 10-ms TTI.  
      Therefore, for the service A and the service B, 50 data bits are punctured and 51 data bits are repeated unnecessarily for a total of 20 ms before being transmitted.  
      It is generally known that to improve performance of a mobile communication system it is desirable that the system receives as many information bits as possible and decodes the received information bits. However, the conventional rate matching method punctures an unnecessarily large number of information bits and pads unnecessary bits. That is, the conventional rate matching method punctures effective data and repeats the same data, causing a reduction in system performance.  
     SUMMARY OF THE INVENTION  
      It is, therefore, an object of the present invention to provide an apparatus and method for multiplexing channels having different Transmission Time Intervals (TTIs) before transmission.  
      It is another object of the present invention to provide a rate matching apparatus and method for supporting services having different TTIs using a predetermined bandwidth in a mobile communication system.  
      To achieve the above and other objects, an embodiment of the invention provides a method for multiplexing a first channel and a second channel having different Transmission Time Intervals (TTIs) for a first service and a second service and transmitting the multiplexed channels through one frame in a mobile communication system providing the first service and the second service. The method comprises the steps of comparing a TTI for the first service with a TTI for the second service, defining a minimum TTI as a unit frame for which the first channel and the second channel are multiplexed and transmitted, and matching symbols for the first service and symbols for the second service according to the maximum number of symbols allocatable to the unit frame.  
      To achieve the above and other objects, another embodiment of the invention provides an apparatus for multiplexing a first channel and a second channel having different Transmission Time Intervals (TTIs) for a first service and a second service and transmitting a plurality of symbols in a mobile communication system providing the first service and the second service. The apparatus comprises channel coders for performing coding on the first service and the second service based on TTIs for corresponding services, channel interleavers for performing interleaving based on TTIs of the respective services, rate matchers for sequentially transmitting the channel-interleaved symbols for the first service and the channel-interleaved symbols for the second service, considering the number of symbols to be transmitted through one frame, and a multiplexer for multiplexing the first channel for the first service and the second channel for the second service on a unit frame basis. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
       FIG. 1  is a block diagram schematically illustrating a structure of an uplink transmitter in a mobile communication system;  
       FIG. 2  is a diagram illustrating a process of performing rate matching on a frame-by-frame basis according to the prior art;  
       FIG. 3  is a block diagram schematically illustrating a structure of an uplink transmitter in a mobile communication system according to an embodiment of the present invention; and  
       FIG. 4  is a diagram illustrating a process of performing rate matching on a frame-by-frame basis according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION  
      An embodiment of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for conciseness.  
      A 3 generation mobile communication system supporting a high-speed multimedia service uses a scheme of multiplexing channels having different Transmission Time Intervals (TTIs) and transmitting the multiplexed channels over a single physical channel. The TTI corresponds to a channel coding or channel interleaving unit, and this corresponds to a multiple of a frame which is a data transmission unit.  
      Therefore, exemplary embodiments of the present invention propose an efficient rate matching (RM) apparatus and method for multiplexing and transmitting channels having different TTIs in a mobile communication system. That is, according to exemplary embodiments of the present invention, efficient rate transmission, especially when several transport channels having different TTIs are multiplexed before being transmitted, may be performed, which may thereby facilitate optimization of channel decoding performance at a receiver.  
       FIG. 3  is a block diagram schematically illustrating a structure of an uplink transmitter in a mobile communication system according to an embodiment of the present invention.  FIG. 4  is a diagram illustrating a process of performing rate matching on a frame-by-frame basis according to an embodiment of the present invention.  
      With reference to  FIGS. 3 and 4 , a description will be made of a process of multiplexing a service A and a service B with a single transport channel according to an embodiment of the present invention. For illustrative purposes, it is assumed herein that the service A is provided on a 10-ms TTI basis, and the service B is provided on a 20-ms TTI basis. Also, it is assumed that the service A transmits 100-bit data for an initial 10-ms TTI and transmits no data for the next 10-ms TTI, and that the service B transmits 199-bit data for a 20-ms TTI. The 100 bits and the 199 bits for respective TTIs are obtained by counting the numbers of bits output from corresponding channel coders. In addition, it is assumed that when the 10-ms TTI-based service A and the 20-ms TTI-based service B are multiplexed and transmitted over a physical channel, the total number of bits per 10 ms is 150 bits.  
      When a 10-ms TTI transport channel and a 20-ms TTI transport channel are multiplexed as described above, the 10-ms transport channel which is the minimum TTI is defined as a unit frame, and the 20-ms TTI transport channel is segmented by the 10 ms which is the unit frame, and then multiplexed with the 10-ms TTI transport channel.  
     FIRST EMBODIMENT  
      A description will now be made of a method for multiplexing the service A and the service B in a first 10-ms TTI.  
      For the service A, a channel coder  310  codes receives 100-bit data, and outputs the coded data to a first interleaver  320 . The first interleaver  320  interleaves the coded 100-bit data. A radio frame segmentation block  330  generates radio frames in the defined unit frame in order to transmit 100-bit data for 100-ms TTI. Because a TTI for the service A is equal to the 10-ms unit frame, the radio frame segmentation block  330  outputs the interleaved 100-bit data to a rate matcher  340  without performing any separate operation. The rate matcher  340  performs puncturing and repetition on the 100-bit data received by the unit frame using Rate Matching Attribute (RMA). A detailed description of the rate matching operation will be given below.  
      For the service B, a channel coder  311  codes 199-bit transmission data for a 20-ms TTI. A first interleaver  321  interleaves the 199-bit data. A radio frame segmentation block  331  segments the 20-ms TTI into 10-ms unit frames. That is, the radio frame segmentation block  331  generates two 10-ms radio frames and sequentially outputs the 199-bit data using the generated 10-ms radio frames. The number E i  of bits included in the 20-ms TTI for the service B is 199, and when the 20-ms TTI is segmented into 10-ms unit frames, F i  becomes 2. N i  is determined according to a method proposed in an embodiment of the present invention, and the number N i  of bits included in each of the segmented 2 radio frames can be different according to radio frame. A rate matcher  341  performs puncturing and repetition on the sequentially input radio frames using Rate Matching Attribute. A detailed description will now be made of operations of the radio frame segmentation blocks  330  and  331  and the rate matchers  340  and  341  according to an embodiment of the present invention.  
      For first 10 ms, for the service A, because a TTI for the service A is equal to the unit frame, the radio frame segmentation block  330  outputs the received 100-bit data to the rate matcher  340  without performing any separate operation. The rate matcher  340  receives the 100-bit data.  
      For first 10 ms, for the service B, 199-bit data interleaved by the 20 ms through the first interleaver  321  is input to the radio frame segmentation block  331 . The radio frame segmentation block  331  segments the interleaved 199-bit data into 10-ms unit frames.  
      In order to determine the number of bits to be output for the service B for first 10 ms, the radio frame segmentation block  331  estimates a rate matching result for the case where 199 bits are segmented in the size of N i =floor{199/2} in accordance with N i =floor{E i /F i}  of Equation (1). That is, the sum of output bits of the rate matcher  340  and the output bits of the rate matcher  341  should be 150 bits. Therefore, the rate matcher  340  and the rate matcher  341  should puncture 25 bits, respectively. Depending on the decision result, the radio frame segmentation block  331  outputs only 75 bits to the rate matcher  341  for rate matching for first 10 ms.  
      In other words, the rate matcher  340  for the service A punctures 25 bits in 100-bit data, and the rate matcher  341  for the service B outputs received 75 bits without performing any separate operation.  
      However, in a second 10-ms frame, because the service A has no data, the channel coder  310  to the rate matcher  340  are disabled. That is, the rate matcher  340  receives 0-bit data and outputs 0-bit data.  
      However, for second 10 ms, for the service B, the radio frame segmentation block  331  outputs the remaining 124 bits to the rate matcher  341 . In this case, 0 bit is input to the rate matcher  340 , and 124 bits are input to the rate matcher  341 , so that the total number of bits allocated to one physical channel is 124 bits. However, because the total number of bits that should be output from the rate matchers  340  and  341  is 150, the rate matcher  340  for the service A outputs 0 bit and the rate matcher  341  for the service B repeats 26 bits among the received 124 bits and outputs a total of 150 bits.  
      As described above, according to an embodiment of the present invention, data for respective services is punctured considering the number of bits allocable to one unit frame, thereby preventing unnecessary puncturing. In addition, according to an embodiment of the present invention prevents meaningless data repetition related to the puncturing may be prevented.  
     SECOND EMBODIMENT  
      A description will now be made of another embodiment of the present invention. In order to determine the number of bits to be output for the service B for first 10 ms, the radio frame segmentation block  331  segments the 199 bits in the size of N i =floor{199/2} in accordance with N i =floor{E i /F i } of Equation (1). That is, 100 bits are input to the rate matcher  340  and 100 bits are input to the rate matcher  341 , so that a total of 200 bits are input to the rate matchers  340  and  341 . Because the total number of bits that should be output from the rate matchers  340  and  341  is 150, the rate matchers  340  and  341  should puncture 25 bits, respectively. For this, the rate matcher  340  punctures 25 bits and outputs 75 bits, and the rate matcher  341  outputs only 75 bits of a 1 st  bit to a 75 th  bit in a 100-bit sequence and does not output the remaining 25 bits of a 76 th  bit to 100 th  bit. That is, the rate matcher  341  outputs first 75 symbols instead of conventionally puncturing 25 bits among 100 bits. This operation is called “TTI shortening.” 
      For a second 10-ms frame, because the service A has no data, the channel coder  310  to the rate matcher  340  are disabled. That is, the rate matcher  340  receives 0-bit data and outputs 0-bit data.  
      For the second 10-ms frame, for the service B, the 199 bits interleaved by the 20 ms through the first interleaver  321  are input to the radio frame segmentation block  331 . The radio frame segmentation block  331  segments the interleaved 199 bits.  
      Because the radio frame segmentation block  331  has output 100 bits for the service B for the first 10 ms, the radio frame segmentation block  331  outputs the remaining 99 bits to the rate matcher  341  for the service B for the second 10 ms. In this case, it can be considered that 0 bit is input to the rate matcher  340  and a total of 124 bits are input to the rate matcher  341 . Because the total number of bits that should be output from the rate matchers is 150, the rate matcher  340  outputs 0 bit and the rate matcher  341  repeats 26 bits among received 124 bits and outputs a total of 150 bits. That is, the rate matcher  341  performs rate matching on a total of 124 bits of 76 th  bit to 198 th  bits following the remaining bits transmitted for the previous 10 ms among the 199 bits, by sequentially accessing the bits to be transmitted for respective frames, considering the Rate Matching Attribute. For the service B that transmits 199 bits for a 20-ms TTI, the rate matcher  341  performs rate matching the data bits following the bits transmitted for the previous 10-ms TTI. Such an operation is called “TTI extension.” 
      For reference, when repetition should be used in rate matching, an embodiment of the present invention proposes a method for performing rate matching by performing repetition on 26 bits of a 1 st  bit to a 26 th  bit among a total of 199 bits in the 20-ms TTI.  
      As described above, for channels having different TTIs, a channel coder performs coding according to a TTI for a corresponding service and delivers coded symbols to a channel interleaver. The channel interleaver performs interleaving according to the TTI for the corresponding service. Therefore, the rate matcher sequentially transmits the interleaved symbols considering the number of symbols that can be transmitted through a predetermined frame. That is, the rate matcher sequentially cyclically outputs the interleaved symbols according to the number of bits that can be transmitted through the Rate Matching Attribute.  
      That is, an embodiment of the present invention proposes a method for sequentially transmitting as many channel-coded symbols that were channel-interleaved according to the TTI as the number of symbols required for respective frames. Therefore, an embodiment of the present invention determines whether the number of symbols to be output through the channel coder is large or small at an end point of the TTI, to minimize unnecessary puncturing or repetition which may occur, thereby contributing to an increase in channel decoding performance.  
      As can be understood from the foregoing description, exemplary embodiments of the present invention may have the following possible, but not required advantages. When multiplexing channels having different TTIs, according to exemplary embodiments of the present invention rate matching is performed on a TTI basis so that punctured or repeated symbols are uniformly distributed over the TTI, thereby improving channel decoding performance. The improvement of channel decoding performance reduces transmission power required for achieving the same QoS, thereby improving performance of the mobile communication system.  
      While the invention has been shown and described with reference to a certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.