Adaptive interference suppression in multiuser OFDM

Orthogonal frequency-division multiplexing (OFDM) with multiple access has been proposed for future wireless networks because of its resistance to channel multipath effects and narrowband interference. In a multiuser OFDM (MU-OFDM) network employing frequency-division multiple-access (FDMA), users of a base station operate on different subcarriers. As the number of users increases in such a network, the cochannel interference caused by users from other base stations also increases, and thus the receiver might require multiple antennas to reject this interference. We present a blind interference suppression system for MU-OFDM that is based on the blind constant modulus (CM) array. The subcarriers of each antenna element have independent weights, so that s can be placed in the directions of the interference affecting each subcarrier. Thus, using an M-element CM array, the receiver can more than M-1 partially overlapping cochannel interferers of different power levels and modulation formats. A constrained CM array that keeps the blind algorithm from capturing an interferer instead of the signal of interest is also described.