In an LTE (Long Term Evolution) system, which is one of the next generation mobile communication systems of which specifications are being finalized by the 3GPP standardization group and of which commercialization is expected in 2010 to 2011 and later, the radio transmission bandwidth in the downlink direction is divided into sub-bands having a same width (for example, Non-patent Document 1). User data for each terminal apparatus is transmitted using one or a plurality of sub-bands. If user data for a terminal apparatus is assigned to a plurality of sub-bands, these sub-bands are arranged continuously or discontinuously on the frequency axis.
In an LTE system, information on association of user data and a sub-band used for the user data is expressed as a bit map. FIG. 10A illustrates a configuration example of a sub-frame, and FIG. 10B is an example of a bit map. In the example of FIG. 10A and FIG. 10B, there are ten sub-bands in total, and the third and fourth sub-bands from the left (“Y” in FIG. 10A) are used for a terminal apparatus. A bit map is included in a control signal, and a resource thereof is assigned to the control channel area of the sub-frame (e.g. “X” in FIG. 10A).
FIG. 11A and FIG. 11B illustrate a relationship between a radio transmission bandwidth and sub-bands. If the radio transmission bandwidth becomes wider than the case of FIG. 11A, the total number of sub-bands increases. If the total number of sub-bands increases, a bit map length increases, and the information volume of the control signal increases compared with the case of FIG. 11A. To solve this problem, in the LTE system, if the radio transmission bandwidth increases, the bandwidth of each sub-band is increased accordingly so that the bit map length does not increase. FIG. 12A to FIG. 12C illustrate an example when the bandwidth of each sub-band increases as the radio transmission bandwidth increases, with keeping the bit map length constant. Non-patent Document 1: 3GPP TS36.213V8.3.0