Adaptive algorithms for OFDMA wireless ad hoc networks with multiple antennas

The design of higher-layer protocols is an active area of research for ad hoc networks that operate on multiple channels. In orthogonal frequency-division multiplexing (OFDM), symbols are transmitted on orthogonal subcarriers which can be viewed as separate transmission channels. In an orthogonal frequency-division multiple-access (OFDMA) ad hoc network, adjacent nodes operate on different sets of subcarriers. As the number of users increases in such a network, the throughput drops due to the availability of fewer subcarriers for each user and because of the increased cochannel interference between users. Multiple antenna receivers have been proposed for ad hoc networks to reduce power consumption and enhance the range of each node in the network. In this paper, we extend a frequency-domain subcarrier adaptive beamformer to an OFDMA ad hoc network that beamforms in the direction of a desired node and nulls interferers from cochannel nodes. A blind time-domain subcarrier adaptive beamformer and signal canceler are proposed that satisfy a constant-modulus criterion. Since each group of nodes in an ad hoc network communicates on a unique set of subcarriers, the optimal beamformer should ideally place nulls in the directions of the interferers only on those subcarriers and independently of other subcarriers.