Receiver design for noncoherent digital network coding

Physical-layer network coding is considered for the two-way relay network with realistic assumptions on the coherence of the channel. In contrast to analog network coding, which relays received analog signals plus noise, our system relays digital network codewords, obtained by digital demodulation and channel decoding. By using binary frequency-shift keying and noncoherent reception, the relay may operate without knowledge of the phases of the signals transmitted simultaneously by the two sources. The channels between the end nodes and the relay are modeled as noncoherent block fading channels, and an outer turbo code is used. A noncoherent receiver is formulated for the relay, which estimates the fading amplitudes but not the phases. Several block sizes are considered, and the effect of block size on error-rate performance is investigated. As a baseline for performance comparison, the system is also simulated using perfect knowledge of the fading amplitudes, and it is observed that the performance lost to channel estimation is negligible for sufficiently large blocks. An example realization of the proposed system demonstrates a 32.4% throughput improvement compared to a similar system that performs network coding at the link layer.