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To support the increasing requirement for additional services demanding very high bit rates and higher system capacity, high speed downlink packet access (HSDPA) is provided in the UMTS standard. Orthogonal frequency division multiplexing (OFDM) is a technology that has been shown to be well suited to HSDPA for high data rate transmission. Selective transmit diversity is a well-known technique to combat the detrimental effects of multipath fading and obtain diversity gain from multiple antennas. We consider transmit selection diversity applied to the OFDM-HSDPA system. The proposed OFDM architecture adopts antenna selection diversity and a novel groupwise subcarrier allocation algorithm in closed-loop mode. In the conventional closed-loop mode, user equipment (UE) should feed back channel quality information (CQI) bits for each associated subcarrier, and there may be a lot of feedback information. We try to reduce the feedback bandwidth compared to previous allocation methods while the system performance should not be degraded by grouping adjacent subcarriers. Through simulation results, we found that the throughput, capacity, coverage and reliability can be dramatically increased by employing the proposed scheme.