Signaling Overhead for ASBA in an MC-CDMA System

OFDM-based multi-carrier systems combined with a hybrid multiple access scheme, MC-CDMA/FDMA, are able to provide high flexibility and granularity for the synchronized downlink transmission. In combination with a new resource allocation scheme, referred to as adaptive sub-band allocation (ASBA), the sub-carriers are assigned to the users in order to maximise the overall system capacity based on the channel knowledge. In a time-variant channel the channel knowledge for ASBA should be updated and an estimate of the channel is supposed to be obtained by measuring the pilots periodically inserted in the uplink (UL) under the assumption of TDD (Time Division Duplex) operation mode. This paper analyzes different channel estimation methods and the signalling overhead due to pilot transmission. An optimized updating period for ASBA is derived based on the simulation results such that the performance in terms of system throughput is maximized. It is shown that when a proper updating period is selected, ASBA has a considerable gain even at a velocity of 200 km/h.