Adaptive beamforming for interference rejection in an OFDM system

Orthogonal frequency-division multiplexing (OFDM) has been utilized in various communication systems because of its ability to compensate for multipath channels using simple low-complexity equalizers. However, the performance of OFDM systems can still be compromised due to adjacent channel and cochannel interference. In this paper, we investigate the performance of an adaptive beamforming algorithm for an OFDM system based on the constant modulus (CM) array. We consider this blind technique for a wireless local area network such as the IEEE 802.11a standard. The algorithm exploits the constant modulus property of the low-rate OFDM data carriers, and we show that it can also be used for the nonconstant modulus constellations at higher data rates. We consider the case where cochannel users become active part way into the transmitted packet such that new beamformer weights should be computed to these interfering signals.