Estimation of Symbol Timing in Physical-Layer Network Coding With Arrival Time Differences

Abstract

Network coding on physical-layer shows much interest due to its well-known ability to double the throughput in relay-aided networks. In an asynchronous PNC system, when the nodes are not equally distant from the relay, the path lengths from the nodes to the relay can vary sufficiently to cause the superimposed waveforms to be evidently offset in time. These arrival time differences, also influenced by the discrepancy of node-clocks, can lead to severe performance degradation and must be estimated in practice. To deal with this problem, a novel symbol timing estimator with baud-rate sampling is proposed in this letter, which is based on the a priori knowledge of the pulse-shaping function. Compared with the known techniques with high oversampling factor, the proposed scheme shows the lower complexity advantage with the unit oversampling factor and better mean square error performance when the excess bandwidth factor of the pulse-shaping function is at 0.3.