Noncoherent Physical-Layer Network Coding with Frequency-Shift Keying Modulation

摘要

The rapid growth of wireless communication technology has motivated novel approaches into improving performance. A major avenue of research investigates the benefit of relaying, where wireless devices outside radio range of each other communicate by passing information through a device in between. Traditionally, devices communicating through a relay transmit at separate times to avoid interfering with each other. Physical-layer network coding is a recent technique that improves throughput by allowing devices to transmit at the same time to the relay, deliberately interfering. This dissertation develops a system performing physical-layer network coding in the topology where two devices exchange information through a single relay. Many signaling techniques require synchronized carrier phases and frequencies for all three devices, which can be challenging to achieve in some scenarios. To alleviate the need for synchronization, this work develops a noncoherent system that requires only frame and symbol synchronization and relaxes the need for carrier synchronization. To combat the degrading effects of the wireless channel, the system utilizes bit-interleaved coded modulation (BICM) along with powerful iterative LDPC and turbo coding. The modulation considered, M-ary frequency-shift keying, is suitable for noncoherent reception and has constant envelope and high energy efficiency. Two formulations of demodulation are developed, one that requires knowledge of the fading amplitudes, and the other that requires only knowledge of the average power. The LDPC codes are optimized for the particular scheme by using extrinsic information transfer (EXIT) charts to identify promising variable-node degree distributions. Simulation results illustrate the efficacy of the proposed demodulator when it is combined with the optimized LDPC codes. The simulation results agree with the coded modulation (CM) capacities, which are also developed. Throughout this work, the capacity and error rate performance of the developed receiver is compared against conventional network coding where the end nodes avoid interfering by transmitting in different times or bands.