Noncoherent digital network coding using multi-tone CPFSK modulation

Digital network coding is a relaying technique that increases throughput in two-way relay networks. In contrast with analog network coding, which relays received analog signals plus noise, digital network coding relays digital codewords. The digital codewords are created by demodulation, channel decoding, and re-encoding at the relay. By using FSK and noncoherent reception, the relay may operate without knowledge of the phases of the signals transmitted by the two source terminals. In this paper, previous work on binary FSK is extended to multi-tone FSK, where the number of tones may be any power of 2. The relay receiver is formulated for any number of tones that is a power of two. Binary FSK is compared against quaternary FSK, which requires no expansion of bandwidth compared with binary FSK. The comparison is made using two metrics: the simulated bit-error rate (both with and without an outer turbo code), and the binary information rate between the sources and relay. The results illustrate that the energy-efficiency advantage of quaternary FSK on a point-to-point link is magnified when it is applied to digital network coding.