Multiuser soft interference canceler via iterative decoding for DSL applications

This paper presents a method to mitigate interference on a transmission system by another system with an overlapping frequency band. The systems are uncoordinated so that they cannot be made to transmit in orthogonal coding space. The transmission environment is an interference channel rather than the multiaccess channel often considered in other multiuser detection problems, for instance at the base station of a CDMA wireless system. Using the fact that the inputs are all from discrete constellations, it is possible to perform a multi-user maximum likelihood (ML) detector to decode the signals from the system of interest with low probability of error. However, the ML detector often requires impractical computation. A soft linear canceler is instead used to reduce the interference with a small loss of bandwidth in the system of interest. The method has much lower complexity than a full-blown Maximum Likelihood detector, and the soft canceler performance is close to a ML detector. The method is demonstrated on a VDSL system with a home LAN interference. The system of interest is using a Multi-carrier modulation transmission scheme such as Discrete Multi-tone (DMT), while the interfering system transmits using Quadrature Amplitude Modulation (QAM). Index: Multiuser detection, Digital Subscriber Line (DSL), soft interference canceler, iterative decoding, interference channel. i