Parameter Estimation and Tracking in Physical Layer Network Coding

In this paper, we present an algorithm for joint decoding of the modulo-2 sum of the bits transmitted from two unsynchronized transmitters using Physical Layer Network Coding (PLNC). We address the problems that arise when the boundaries of the signals do not align with each other and when the channel parameters are slowly varying and are not known to the receiver at the relay node. Our approach first estimates jointly the timing and fading gains of both the signals, and uses a state-based Viterbi decoding scheme that takes into account the timing offsets between the interfering signals. We also track the amplitude and phase of the channel which may be slowly varying. Simulation results demonstrate the sensitivity of the detection performance at the relay node to the relative offset of the timings of the two user´s signals as well as the advantage of our algorithm over previously published algorithms.