Interference cancellation using antenna arrays

A limiting factor for the performance of the conventional CDMA receiver is the near-far effect. Practical CDMA systems use power control to overcome this problem, which requires additional circuitry at the mobile. On the other hand, optimal and suboptimal multiuser detectors have been proposed which are shown to be near-far resistant and thus increase the capacity of the system significantly. The major drawback of these detectors is their computational complexity which makes them less attractive for implementation. This paper describes a simple detector which is a spatio-temporal interference canceller. The receiver employs an array of M antennas which allows it to discriminate between the users based on their spatial diversity. The received signal goes through a bank of K beamformers each matched to one user, followed by a bank of matched filters. The K outputs are compared to rank the users in the order of their strength. Multiple access interference from each user is cancelled successively from the received signal based on this order. This detector is compared with a single antenna interference canceller and also the conventional detector and it is shown that using multiple antennas improves the performance of the interference canceller and compensates for nonzero crosscorrelations between the users´ signature waveforms