Band control method and communication apparatus

A communication apparatus for performing data transmission by controlling frequency bandwidth when data communication is performed with an other communication apparatus with full duplex by using two or more divided frequency bandwidths within a previously allocated whole frequency bandwidth, wherein

• frequency bandwidths which said communication apparatus and said other communication apparatus use at data transmission are different frequency bandwidths, the communication apparatus comprising:
• bandwidth presumption means for presuming a first bandwidth which is required by said communication apparatus at data transmission;
• bandwidth acquisition means for acquiring a second bandwidth from said other communication apparatus which is required by said other communication apparatus at data transmission;
• bandwidth comparison means for comparing said first bandwidth with a first bandwidth used which said first communication apparatus currently uses, and comparing said second bandwidth with a second bandwidth used which said second communication apparatus currently uses;
• and
• bandwidth used determination means for determining a third bandwidth used by said first communication apparatus at data transmission and a fourth bandwidth used by said second communication apparatus at data transmission according to comparison results obtained by said bandwidth comparison means, wherein said third bandwidth and said fourth bandwidth are determined such that:
• if said first bandwidth is less than said first bandwidth used and said second bandwidth is greater than said second bandwidth used, said third bandwidth is determined to be equal to said first bandwidth and said fourth bandwidth is determined to be equal to said whole frequency bandwidth less said third bandwidth,
• if said first bandwidth is greater than said first bandwidth used and said second bandwidth is less than said second bandwidth used, said fourth bandwidth is determined to be equal to said second bandwidth and said third bandwidth is determined to be equal to said whole frequency bandwidth less said fourth bandwidth,
• if said first bandwidth is greater than said first bandwidth used and said second bandwidth is greater than said second bandwidth used, said third bandwidth and said fourth bandwidth are determined such that a ratio of said first bandwidth to said second bandwidth is the same as a ratio of said third bandwidth to said fourth bandwidth, and
• if said first bandwidth is less than or equal to said first bandwidth used and said second bandwidth is less than or equal to said second bandwidth used, said third bandwidth is determined to be equal to said first bandwidth used and said fourth bandwidth is determined to be equal to said second bandwidth used,
• wherein said communication apparatus transmits data by using said third bandwidth and receives data by using said fourth bandwidth and said other communication apparatus transmits data by using said fourth bandwidth and receives data by using said third bandwidth.