Co-channel interference cancellation: a prefiltering approach

In this paper, a prefiltering approach is taken in order to suppress co-channel interference signals in a frequency selective fading environment. A complex time-variant prefilter results. It rotates the signal space to place the interferer on the axis orthogonal to the detection axis. After the equalizer, a projection on the detection axis is done and a maximum likelihood sequence estimation (MLSE) is performed. Up to 3 totally asynchronous users are considered. The simulation results indicate that the suggested technique outperforms a conventional maximum likelihood sequence estimation (MLSE) for the bit error rate (BER) region of interest in practical systems. The technique works with signal spaces of the desired signals that have their signal points on an straight line in the signal space. With Laurent´s decomposition, also GMSK signals can be treated. This approach of practical interest is taken here. As an application, the interference canceller is applied to a receiver following the Global System for Mobile Communications (GSM) standard.