Polynomial-complexity GLRT-optimal noncoherent PNC

摘要

Noncoherent two-way relay (TWR) systems with physical-layer network coding (PNC) usually operate with differential or orthogonal modulation. In either case, due to channel-induced memory, the optimal receiver at both the relay and source nodes takes the form of a sequence detector. Such a receiver has exponential (in the sequence length) complexity, when implemented through an exhaustive search among all possible sequences. Hence, many works in the literature consider single-symbol or short-block noncoherent PNC. In this work, we consider transmission of frequency-shift keying (FSK) signals in a TWR system and present an algorithm that performs generalized-likelihood-ratio-test (GLRT) optimal noncoherent PNC with polynomial (in the sequence length) complexity. Although presented in the context of FSK, our developments hold for other orthogonal modulation techniques as well. As a low-cost alternative, we also present a quadratic-complexity suboptimal detector that attains near-optimal performance. Simulation studies indicate that the proposed GLRT-optimal and suboptimal noncoherent PNC attains near-coherent-PNC performance with affordable complexity when the sequence length is on the order of 64, offering a 2-4dB gain over conventional noncoherent PNC approaches that can handle only short values of the sequence length.