Patent Publication Number: US-2010110959-A1

Title: Mobile communication system, terminal device, base station device and data communication method

Description:
TECHNICAL FIELD 
     The present invention relates to a downstream data communication in a mobile communication system, and more particularly, to a data communication for distributing the same data to a plurality of terminals. 
     BACKGROUND ART 
     Recently, a next generation mobile communication system has been studied extensively as a 3 GPP (3rd Generation Partnership Project)-LTE (Long Term Evolution). An OFDM (Orthogonal Frequency Division Multiplexing) system is determined as a common downlink communication scheme of a 3 GPP-LTE system. 
     In an OFDM scheme, a band of the system is split into several subcarriers, and a base station transmits independent data on each subcarrier to terminals. Allocation of subcarriers to each terminal is performed by the unit of the resource block in which a plurality of subcarriers are grouped into clusters. 
     The resource block to be used in the transmission of data transmitted individually to each terminal from a base station is determined on the basis of reception quality measured at each terminal. In detail, terminals feedback the base station with a CQI (Channel Quality Indicator) including information of the reception quality of pilot sequence transmitted from the base station. The resource block to be used in the transmission of data transmitted individually to each terminal is selected on the basis of reception quality based on CQI. 
     However, 3 GPP-LTE includes MBMS (Multimedia Broadcast/Multicast Service) which distributes the same data to a number of terminals from a base station. MBMS distributes the same data simultaneously to a plurality of terminals by using the same resource block. 
     DISCLOSURE 
     Technical Problem 
     In MBMS, it is impossible to select a resource block on the basis of the reception quality of each terminal, since, as mentioned previously, data is simultaneously distributed to a number of terminals by the same resource block. The downlink receiving condition varies in each terminal, and therefore, a certain terminal has high reception quality while another terminal has low reception quality. Moreover, even through a terminal outputs low reception quality, the resource block allocated to MBMS is continuously used. As a result, a low reception quality state caused due to the terminal with low reception quality is continued. 
     A method is disclosed in that reception quality is improved by adopting a point-to-point transmission mode in a terminal in which the reception quality is low (see Japanese Patent Application Laid-open No. 2006-135956). However, this method has failed to show efficient use of resources. 
     It is an object of the present invention to provide a mobile communication system and a data communication system capable of improving reception quality at terminals in a service for simultaneously distributing same data to a number of terminals while utilizing resources with high efficiency, and a terminal thereof and a base station. 
     Technical Solution 
     To accomplish the above object of the present invention, there is provided according to an exemplary embodiment a mobile communication system for performing data communication of multimedia broadcast/multicast service by using a resource block obtained by dividing a radio resource of a downlink, 
     wherein the mobile communication system includes 
     a plurality of terminals for selecting a resource block allocated to a multimedia broadcast/multicast service from among the resource blocks contained in a radio received signal, extracting multimedia broadcast/multicast service data from the selected resource block, measuring reception quality of the selected resource block, and extracting auxiliary data for enhancing reception quality of the multimedia broadcast/multicast service data from another resource block contained in the radio received signal and synthesizing the extracted auxiliary data to the multimedia broadcast/multicast service data when the reception quality has deteriorated, and 
     a base station for selecting a resource block allocated to the multimedia broadcast/multicast service, transmitting the multimedia broadcast/multicast service data on the selected source block to the terminals via a radio transmitting system, and transmitting the auxiliary data on another resource block when the reception quality of the resource block allocated to the multimedia broadcast/multicast service has deteriorated in any of the terminals. 
     According to one exemplary embodiment of the present invention, there is provided a terminal for use in a mobile communication system, wherein the mobile communication system 
     uses a resource block obtained by dividing a radio resource of a downlink in a multimedia broadcast/multicast service, 
     allows a base station to transmit multimedia broadcast/multicast service data carried on the resource block allocated to multimedia broadcast/multicast service to a plurality of terminals through a radio transmitting system, 
     allows the terminals to extract the multimedia broadcast/multicast service data from the resource block allocated to the multimedia broadcast/multicast service from among the resource blocks contained in a radio received signal sent from the base station, and estimate reception quality of the resource block, 
     transmits auxiliary data carried on another resource block for improving reception quality of the multimedia broadcast/multicast service data from the base station when the reception quality of the resource block allocated to the multimedia broadcast/multicast service has deteriorated in any of the terminals, and 
     allows the terminal with the deteriorated reception quality to extract the auxiliary data from another resource block contained in the received signal and synthesize the auxiliary data with the multimedia broadcast/multicast service data, 
     wherein the terminal includes 
     first receiving means for extracting multimedia broadcast/multicast service data from the resource block allocated to a multimedia broadcast/multimedia service from among resource blocks contained in a radio received signal sent from the base station, 
     quality estimation means for measuring reception quality of the resource block allocated to the multimedia broadcast/multicast service, 
     second receiving means for extracting auxiliary data for improving reception quality of the multimedia broadcast/multicast service from another resource block contained in the received signal when the reception quality measured by the quality estimation means has deteriorated, and 
     synthesizing means for synthesizing the auxiliary data extracted by the second to receiving means with the multimedia broadcast/multicast service data extracted by the first receiving means. 
     According to one exemplary embodiment of the present invention, there is provided a base station for use in a mobile communication system, wherein the mobile communication system 
     uses a resource block obtained by dividing a radio resource of a downlink in a multimedia broadcast/multicast service, 
     allows a base station to transmit multimedia broadcast/multicast service data carried on the resource block allocated to multimedia broadcast/multicast service to a plurality of terminals through a radio transmitting system, 
     allows the terminals to extract the multimedia broadcast/multicast service data from the resource block allocated to the multimedia broadcast/multicast service from among the resource blocks contained in a radio received signal sent from the base station, and estimate reception quality of the resource block, 
     transmits auxiliary data carried on another resource block for improving reception quality of the multimedia broadcast/multicast service data from the base station when the reception quality of the resource block allocated to the multimedia broadcast/multicast service has deteriorated in any of the terminals, and 
     allows the terminal with the deteriorated reception quality to extract the auxiliary data from another resource block contained in the received signal and synthesize the auxiliary data with the multimedia broadcast/multicast service data, 
     wherein the base station includes 
     transmission deciding means for deciding whether to transmit the auxiliary data for improving reception quality of the multimedia broadcast/multicast service data, on the basis of the deterioration of reception quality in any of terminals of the resource block allocated to the multimedia broadcast/multicast service, and 
     mapping means for permitting the resource block allocated to the multimedia broadcast/multicast service data to carry multimedia broadcast/multicast service data, and additionally permitting the resource block allocated to the auxiliary data to carry the auxiliary data if it is decided, by the transmission deciding means, to transmit the auxiliary data, and transmitting the multimedia broadcast/multicast service data and the auxiliary data to a plurality of terminals via a radio transmission system. 
     According to one exemplary embodiment of the present invention, there is provided a data communication method in a mobile communication system for performing a multimedia broadcast/multicast service by using a resource block obtained by dividing a radio resource of a downlink, wherein the data communication method 
     allows a base station to transmit multimedia broadcast/multicast service data carried on the resource block allocated to multimedia broadcast/multicast service to a plurality of terminals through a radio transmitting system, 
     allows the terminals to extract the multimedia broadcast/multicast service data from the resource block allocated to the multimedia broadcast/multicast service from among the resource blocks contained in a radio received signal sent from the base station, and estimate reception quality of the resource block, 
     transmits auxiliary data carried on another resource block for improving reception quality of the multimedia broadcast/multicast service data from the base station when the reception quality of the resource block allocated to the multimedia broadcast/multicast service has deteriorated in any of the terminals, and 
     allows the terminal with the deteriorated reception quality to extract the auxiliary data from another resource block contained in the received signal and synthesize the auxiliary data with the multimedia broadcast/multicast service data. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing the configuration of 3 GPP-LTE mobile communication system according to an exemplary embodiment of the present invention; 
         FIG. 2  illustrates the configuration of a resource block in a downlink resource; 
         FIG. 3  is a block diagram showing the arrangement of devices in 3 GPP-LTE mobile communication system according to an exemplary embodiment of the present invention; and 
         FIG. 4  is a flowchart showing the operation of 3 GPP-LTE mobile communication system according to an exemplary embodiment of the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     An exemplary embodiment of the present invention will be explained hereinafter with reference to the accompanying drawings. 
       FIG. 1  is a block diagram showing the configuration of a 3 GPP-LTE mobile communication system according to an exemplary embodiment of the present invention. Referring to  FIG. 1 , 3 GPP-LTE mobile communication system includes base station  11  and terminals  12   1  to  12   3 . 
     Base station  11  communicates with the terminals in cells thereof over a wireless channel. An MBMS distributes the same MBMS data to a number of terminals. Base station  11  may transmit, as auxiliary data, a part of MBMS data to the terminals if needed. 
     Terminals  12   1  to  12   3  existing within the cells of base station  11  receive MBMS data from base station  11 . In addition, Terminals  12   1  to  12   3  may receive both MBMS data and auxiliary data from base station  11  and synthesize the received data if needed. 
     In the system shown in  FIG. 1 , base station  11  transmits MBMS data by the resource block allocated to MBMS. Terminals  12   1  to  12   3  monitor a pilot sequence to estimate reception quality of the resource block of MBMS, and request base station  11  to transmit auxiliary data when the reception quality has deteriorated. The judgment on the deterioration of the reception quality is made through a comparison with a predetermined threshold value. For example, if the received power level is lower than the threshold value, the received power can be judged as having deteriorated. 
     Base station  11  transmits auxiliary data by another resource block while continuing to transmit MBMS data by the resource block allocated to MBMS when a request for transmission of auxiliary data is made from any of the terminals  12 . It is desirable to select a resource block with high reception quality for transmitting auxiliary data to terminal  12  which has made a request for transmission of auxiliary data. The judgment on the reception quality of the resource block is made through the comparison between the reception quality and a predetermined threshold value. The auxiliary data is a part of MBMS data. Terminal  12  which has made a request for transmission of auxiliary data receives both MBMS data and auxiliary data, and synthesizes the received data. 
       FIG. 2  illustrates the configuration of a resource block in a downlink resource, in which an example of the relationship between a resource block for MBMS and a resource block for individual data is shown. 
     Referring to  FIG. 2 , a band of the system is divided into subcarriers, and a plurality of resource blocks obtained by dividing a time axis by TTI (Transmission Timing Interval) of 0.5 milliseconds are shown. In data communication, resources are allocated by the unit of resource block. 
     Resource block  101  is one allocated to MBMS. Regardless of the reception quality at each of terminals  12   1  to  12   3 , the same resource block is used consistently. 
     Resource blocks  102  and  103  are those having high reception quality selected in accordance with the CQI information notified from terminal  12 , and used in the data to be transmitted individually to terminal  12 . In the exemplary embodiment of the present invention, if terminal  12  shows low reception quality in receiving data by the resource block for MBMS, base station  11  transmits, for terminal  12 , auxiliary data in the resource blocks for individual transmission, for example, resource blocks  102  and  103 . 
       FIG. 3  is a block diagram showing the arrangement of devices in a 3 GPP-LTE mobile communication system according to an exemplary embodiment of the present invention. Referring to  FIG. 3 , transmitter  20  and receiver  21  are opposite to each other. Transmitter  20  transmits data in an OFDM scheme, and is contained in base station  11  of 3 GPP-LTE mobile communication system. Receiver  21  receives data in an OFDM scheme, and is contained in terminal  12  of a 3 GPP-LTE mobile communication system. 
     Transmitter  20  includes channel coding unit  201 , first HARQ (Hybrid Automatic Repeat Request) unit  202 , first modulation unit  203 , second HARQ unit  204 , second modulation unit  205 , subcarrier mapping unit  206 , inverse FFT (Fast Fourier Transform) unit  207 , and transmission deciding unit  208 . 
     Channel coding unit  201  performs channel coding on the data to be transmitted. In detail, channel coding unit  201  performs turbo coding with a coding rate of 1/3. 
     First and second HARQ units  202  and  204  perform a HARQ (Hybrid Automatic Repeat Request) re-transmission and rate match process on the data coded by channel coding unit  201 . In detail, as a rate match process, first and second HARQ units  202  and  204  adjust coded bits so as to be received in the allocated resource block. During adjustment, a puncture or repetition process is properly carried out on the coded data. The puncture process aims to delete parity bits, and the repetition process repeatedly outputs the same bit. 
     In addition, it is desirable that, through an incremental redundancy process, the output of the rate match process carried out by second HARQ unit  204  contains, if possible, bits punctured in the rate match process performed by first HARQ unit  202 . 
     First and second modulation units  203  and  205  modulate outputs of first and second HARQ units  202  and  204 . In detail, first and second modulation units  203  and  205  carry out modulation processes in any modulation scheme of QPSK, 16QAM and 64QAM. 
     Subcarrier mapping unit  206  maps data modulated by the first and second modulation units  203  and  205  to an allocated resource block. 
     Inverse FFT unit  207  collectively transforms symbol data mapped on a frequency axis by subcarrier mapping unit  206  into symbols on a time axis through IFFT (Inverse Fast Fourier Transform) process. 
     Transmission deciding unit  208  decides whether to actually transmit auxiliary data when a request for transmission of auxiliary data is made from terminal  12 . 
     For example, let&#39;s assume that a terminal has three classes of A, B and C which is priority-ranked in accordance with a subscription contract. The classes can be prioritized by subscription fees or the like. Then, when a request for transmission of auxiliary data is made from terminal  12  of class A, transmission deciding unit  208  performs a transmission scheduling process on another terminal in the priority level (e.g., medium) identical with that of individual data. In addition, when a request for transmission of auxiliary data is made from terminal  12  of class B, transmission deciding unit  208  performs a transmission scheduling process in the priority level (e.g., low) which is lower than that of individual data. Further, transmission deciding unit  208  performs no transmission process when a request for transmission of auxiliary data is made from the terminal of class C. 
     Referring back to  FIG. 3 , receiver  21  includes FFT unit  211 , first demodulation unit  212 , second demodulation unit  213 , HARQ unit  214 , channel decoding unit  215  and quality estimation unit  216 . 
     FFT unit  211  transforms sample data received from transmitter  20  into symbol data on a frequency axis through FFT process. 
     First and second demodulation units  212  and  213  extract symbols of an allocated resource block from symbol data output from FFT  211  and demodulate the extracted symbols to produce a bit sequence. First demodulation unit  212  demodulates MBMS data, and second demodulation unit  213  demodulates auxiliary data. Only first demodulation unit  212  operate while only MBMS data is being transmitted from transmitter  20 , and both first demodulation unit  212  and second demodulation unit  213  operates while MBMS data and auxiliary data are being transmitted from transmitter  20 . 
     HARQ unit  214  performs a HARQ re-transmission and rate de-match process on the data sequence produced by first demodulation unit  212  when only first demodulation unit  212  is in operation. The rate de-match process results in restoration of the data to the state before it is rate-matched by transmitter  20 . 
     Further, when both first and second demodulation units  212  and  213  are being operated, HARQ unit  214  performs a rate de-match process on both of the bit sequence produced by first demodulation unit  212  and the bit sequence produced by second demodulation unit  213 , and synthesizes data by a HARQ buffer (not shown) to restore data to the state before it is rate-matched. 
     Channel decoding unit  215  performs a channel decoding process on the data restored by HARQ unit  214 . 
     Quality estimation unit  216  measures reception quality of the resource block for MBMS, and makes a request for transmission of auxiliary data to base station  11  when the measured reception quality of the resource block is lower than a predetermined threshold value. 
       FIG. 4  is a flowchart showing the operation of a 3 GPP-LTE mobile communication system according to an exemplary embodiment of the present invention. Referring to  FIG. 4 , MBMS data transmitted from base station  11  is received in terminals  12   1  to  12   3  (step  31 ). Subsequently, terminals  12   1  to  12   3  monitor the pilot sequence being transmitted from base station  11  to estimate reception quality of the resource block, and judge whether the reception quality of the resource block being used in the transmission of MBMS data has deteriorated (step  33 ). If it is judged that the reception quality of the resource block for MBMS has not deteriorated, the process returns to step  31  to be repeated. If it is judged that the reception quality of the resource block for MBMS has deteriorated, terminal  12  makes a request for transmission of auxiliary data to base station  11  (step  33 ). 
     Upon receipt of the request for transmission of auxiliary data from terminal  12 , base station  11  investigates the class of terminal  12  and determines whether to start transmission of auxiliary data in accordance with the class (step  34 ). In the previously discussed example, base station  11  starts transmission of auxiliary data in the priority level of medium when a request is made from terminal  12  of class A. In addition, base station  11  starts transmission of auxiliary data in the priority level of low when a request is made from terminal  12  of class B. Further, upon receipt of a request from the terminal of class C, base station  11  destroys the request and performs no transmission of auxiliary data, and the process returns to step  31 . 
     When transmission of auxiliary data starts, terminal  12  which has made the request for transmission receives both MBMS data and auxiliary data, synthesizes the data, and carries out a decoding process (step  35 ). 
     Terminal  12  which has made the request for transmission of auxiliary data monitors enhancement of reception quality of the resource block for MBMS (step  36 ). If the reception quality shows no enhancement, the process returns to step  35  to repeat the process. If the reception quality is enhanced, terminal  12  makes a request for stoppage of transmission of auxiliary data to base station  11  (step  37 ). Upon receipt of the request for stoppage of transmission, base station  11  stops transmission of auxiliary data. The process returns to the state in which terminal  12  receives only MBMS data, when base station  11  has stopped transmission of auxiliary data. 
     As described so far, in the exemplary embodiment of the present invention, terminals  12   1  to  12   3  makes a request for transmission of auxiliary data to base station  11  when reception quality of MBMS data sent from base station  11  has deteriorated. Upon receipt of the request for transmission of auxiliary data from any of terminals  12 , base station  11  transmits, as auxiliary data, a part of MBMS data by using a resource block showing high reception quality at terminal  12 , while transmitting MBMS data by the resource block for MBMS. Terminal  12  synthesizes and decodes MBMS data and auxiliary data sent from base station  11 . In MBMS which distributes the same data simultaneously to a plurality of terminals  12   1  to  12   3  by a common resource block for MBMS, base station  11  transmits auxiliary data for terminal  12  with low reception quality, and terminal  12  synthesizes auxiliary data to MBMS data to improve reception quality. As a result, resources can be utilized in an efficient manner while improving reception quality at each terminal  12   1  to  12   3 . 
     While the present invention has been described with reference to the exemplary embodiment in which the number of resource blocks for MBMS is larger than that of resource blocks for auxiliary data, the invention is not restricted to such exemplary embodiment only. As another example, the number of resource blocks for MBMS can be the same as that of resource blocks for auxiliary data. 
     In addition, the present invention has been described with reference to the exemplary embodiment in which auxiliary data is transmitted to a single terminal  12 , however, the invention is not restricted only to such exemplary embodiment. As another example, auxiliary data can be transmitted commonly to a number of terminals. In detail, auxiliary data can be transmitted commonly to a number of terminals belonging to the same class. 
     In addition, the present invention has been described with reference to the exemplary embodiment in which whether to transmit auxiliary data is determined in accordance with the class of terminal  12  which has made a request for transmission of auxiliary data, however, the invention is not restricted only to such an exemplary embodiment. 
     As another example, it may be possible to decide whether to transmit auxiliary data on the basis of the points given to each of terminals  121  to  123  according to class levels. In this case, upon receipt of request for transmission of auxiliary data from terminal  12  of a certain class, base station  11  adds up points of that class. When the value of the added points exceeds a predetermined threshold value, base station  11  starts the transmission of auxiliary data. For instance, under the assumption that class A has 10 points, class B has 5 points, and class C has 1 point, it is preferable to start transmission of auxiliary data when the sum of values obtained by multiplying the number of terminals  12  of each class which have made requests for transmission of auxiliary data and points of those classes exceeds a threshold value. In addition, it would be preferable to adaptively vary the threshold value in accordance with the degree of congestion of a downlink resource. This may overcome drawbacks in which the congestion of the downlink resource increases due to control for enhancing the reception quality of a terminal, since the resource to be used in enhancing the reception quality of the terminal varies in accordance with the degree of congestion. In detail, it may be possible to lower the threshold value for judging the deterioration of reception quality when the downlink resource is congested. As a result, transmission of auxiliary data is suppressed during the congestion period of the downlink resource. 
     In addition, the present invention has been described with reference to the exemplary embodiment in which turbo coding with a coding rate of 1/3 is employed in the channel coding process, however, the invention is not restricted only to such an exemplary embodiment, and a coding method which allows HARQ would be preferable. 
     In addition, the present invention has been described with reference to the exemplary embodiment in which terminal  12  makes a request for starting and stoppage of transmission of auxiliary data to base station  11 , however, the invention is not restricted only to such an exemplary embodiment. As another example, base station  11  may decide starting and stoppage of transmission of auxiliary data on the basis of the CQI periodically notified from terminals  12   1  to  12   3 . 
     In addition, the present invention has been described with reference to the exemplary embodiment in which the bit punctured in the MBMS data rate match process performed by second HARQ unit  204  for auxiliary data transmission has remained unpunctured by using the incremental redundancy process. However, the invention is not restricted only to such an exemplary embodiment. As another example, it may be possible to use, in the rate match process performed by second HARQ unit  204 , a parameter completely identical with that in the rate match process performed by first HARQ unit  202 , and the bit string which is completely identical with that transmitted by the resource block for MBMS can be transmitted by the resource block for auxiliary data. 
     While the present invention has been described with reference to particular embodiments thereof, it is not limited to the specially described exemplary embodiments. It will be understood by those skilled in the art that various changes in the claimed constitution or details of the invention may be made without departing from the scope of the invention. 
     This application claims priority based on Japanese Patent Application No. 2007-016643 filed on Jan. 26, 2007, the disclosure of which is incorporated herein by reference.