Suppression of constant modulus interference in multimode transceivers by closed-loop tuning of a nonlinear circuit

In multimode transceivers, the transmitter for one communication standard may induce a large interferer in the receiver for another standard. To linearly suppress this interferer, which can be several orders of magnitude larger than the desired received signal, the receiver should have a very large linear dynamic range, resulting in excessive power consumption. Many of potential interferers have a constant modulus modulation. Baier and Friederichs introduced a tuneable nonlinear circuit which can suppress a constant modulus interferer without excessive power consumption. Since an open- loop tuning method is used, the worst- case interference suppression was strongly limited by inaccuracy of circuit components. To alleviate this limitation, we propose a closed- loop tuning method that exploits the locally available interference as side information. Our analysis shows that the proposed method can strongly suppress the interferer while a symbol error rate performance close to that of an exactly linear receiver is achieved. Simulation results for a practical scenario confirm this analysis, and promise much smaller power consumption than for linear interference suppression approaches.