Data communication method and mobile communication system

Abstract

Since OFDM (Orthogonal Frequency Division Multiplexing), which is a downlink access scheme used for an LTE (Long Term Evolution) communication system, is weak at interference, it is preferable that the number of base stations for transmitting the same E-MBMS (Evolved Multimedia Broadcast Multicast Service) data be not excessive. Thus, the mobile terminal performs: processing of obtaining measurement quality values by measuring reception quality of each base station; processing of deciding on whether the measurement quality value of a serving base station exceeds a certain receiving level; processing of adding measurement quality values of other base stations to the measurement quality value of the serving base station until the sum exceeds the certain receiving level; and processing of notifying the serving base station of the serving base station and other base stations as candidates for an active set for E-MBMS. This makes it possible to select as the active set for E-MBMS an appropriate number of base stations that make it compatible to maintain good reception quality and to prevent interference.

1 . A data communication method executed in a communication system including base stations for carrying out broadcast data transmission for providing point-to-multipoint broadcast communication service using an OFDM (Orthogonal Frequency Division Multiplexing) scheme as a downlink access scheme, and a mobile terminal for receiving and combining the broadcast data transmitted from the plurality of base stations, said data communication method comprising:
 selecting processing of selecting one or more base stations for transmitting the broadcast data to said mobile terminal, and of creating a set of said base stations for transmitting the broadcast data, said selecting processing being executed by a serving base station that arranges a transmission and reception schedule of said mobile terminal; and   receiving processing of receiving the broadcast data transmitted from said one or more base stations selected by the selecting processing.   
     
     
         2 . The data communication method according to  claim 1 , including candidate base station selecting processing executed by said mobile terminal, said candidate base station selecting processing comprising:
 processing of obtaining measurement quality values by measuring reception qualities of said one or more base stations from which said mobile terminal receives the broadcast data;   processing of making a decision on whether the measurement quality value of said serving base station is higher than a threshold notified by said serving base station;   processing of obtaining a sum measurement quality value by adding measurement quality values of other base stations to the measurement quality value of said serving base station until the sum measurement quality value satisfies reception quality defined by the threshold; and   processing of notifying, when the sum measurement quality value satisfies the reception quality defined by the threshold, said serving base station of the one or more base stations, whose signals are combined with a signal received from said serving base station, as candidate base stations.   
     
     
         3 . The data communication method according to  claim 2 , wherein
 said mobile terminal is notified of a first threshold and a second threshold, said first threshold defining an upper limit reception quality of a combined received signal obtained by combining signals received from one or more base stations by said mobile terminal, and said second threshold defining a lowest limit reception quality of the combined received signal; and   the candidate base station selecting processing is executed when reception quality of the combined received signal is higher than the first threshold, or when the reception quality of the combined received signal does not satisfy the reception quality the second threshold requires.   
     
     
         4 . The data communication method according to  claim 2 , wherein the candidate base station selecting processing is executed at least at a handover that changes the serving base station for arranging a schedule of said mobile terminal. 
     
     
         5 . The data communication method according to  claim 1 , wherein
 said mobile terminal is notified of a first threshold and a second threshold, said first threshold defining an upper limit reception quality of a combined received signal obtained by combining signals received from one or more base stations by said mobile terminal, and said second threshold defining a lowest limit reception quality of the combined received signal; and   said mobile terminal performs notification processing in which when the reception quality of the combined received signal is higher than the first threshold, said mobile terminal notifies said serving base station that the reception quality is too high, and when the reception quality of the combined received signal does not satisfy reception quality the second threshold requires, said mobile terminal notifies said serving base station that the reception quality is insufficient.   
     
     
         6 . The data communication method according to  claim 1  or  5 , wherein said one or more base stations for transmitting the broadcast data to said mobile terminal are determined in advance concerning said serving base station, and said selecting processing selects one or more corresponding base stations in accordance with said serving base station. 
     
     
         7 . A mobile communication system including base stations for carrying out broadcast data transmission for providing point-to-multipoint broadcast communication service using an OFDM (Orthogonal Frequency Division Multiplexing) scheme as a downlink access scheme, and a mobile terminal for receiving and combining the broadcast data transmitted from the plurality of base stations, said mobile communication system being characterized by that:
 said mobile terminal performs candidate base station selecting processing comprising: processing of obtaining measurement quality values by measuring reception qualities of said one or more base stations from which said mobile terminal receives the broadcast data; processing of making a decision on whether the measurement quality value of said serving base station is higher than a threshold notified by said serving base station; processing of obtaining a sum measurement quality value by adding measurement quality values of other base stations to the measurement quality value of said serving base station until the sum measurement quality value satisfies reception quality defined by the threshold; and processing of notifying, when the sum measurement quality value satisfies the reception quality defined by the threshold, said serving base station of the one or more base stations, whose signals are combined with a signal received from said serving base station, as candidate base stations; and   said base station selects from said candidate base stations notified by said mobile terminal one or more base stations for transmitting the broadcast data to said mobile terminal.