Adaptive Channel Allocation for OFDM-Based Smart Antenna Systems with Limited Transceiver Resources

Smart antennas constitute perhaps the most promising means of increasing capacity in wireless systems by allowing intra-cell channel reuse by several users. The employment of smart antennas at the physical layer raises significant issues in medium access control (MAC) layer. In this paper, we study the impact of smart antennas on MAC layer channel allocation in the presence of limited transceiver resources, where a transceiver is a communication unit that is used to set up a distinct beam. The problem is addressed in the context of Orthogonal Frequency Division Multiplexing (OFDM), which is the predominantly proposed signaling scheme for wireless broadband access. Since a beam can only serve users in different subcarriers, the problems of subcarrier and transceiver assignment are coupled. We propose heuristic algorithms to allocate channels to users, adjust beamforming vectors and assign users and channels in beams, with the objective to increase system throughput and provide QoS to users in the form of minimum rate guarantees. Our criteria for resource assignment and beam formation are based on spatial separability properties of users, beam vector cross-correlations and induced interference to the system. This unified cross-layer approach is shown to yield significant throughput benefits