MLD INTERFERENCE CANCELER FOR M-ARRAY QAM SIGNALS APPLIED TO FWA SYSTEMS

We propose a maximum likelihood detection (MLD) interference canceler applied to fixed wireless access (FWA) systems. There are two major degradation factors associated with a conventional MLD canceler. One is the decision error caused by constellation ambiguity when distinguishing between desired and interference signal components for M-array QAM signals. The novelty of our interference canceler is its use of our antenna switching technique to reduce constellation ambiguity. The phase difference between the desired and interference signals received by the main and sub antennas depends on the path gap between desired and interference signal transmitters to the two receiving antennas. Cancelation performance is improved by using the phase difference that maximizes the separation of the received signal points. Two key points of the proposed technique are the path gap and the threshold for antenna switching. The second degradation factor is the degradation in interference signal replica accuracy caused by the phase rotation of the interference signals. An automatic phase control (APC) circuit estimates and compensates for this phase rotation, enabling the interference canceler with APC to achieve excellent bit error rate (BER) performance. Computer simulations show that our interference canceler improves the BER performance.