Abstract

This paper investigates the performance of a two-way relay network (TWRN) for wireless sensor networks (WSNs) that combines fountain coding (FC) and digital network coding (DNC) in the presence of co
channel interference (CCI).
A three-phase FC–DNC transmission protocol (SM-3P-FC) is considered and compared with the conventional four-phase fountain-coded protocol (SM-4P-FC). To isolate the contribution of fountain coding, an additional same-budget three-phase uncoded fixed-repetition benchmark (SM-3P-NoFC) is introduced, in which the Q transmission opportunities are distributed among H distinct uncoded packets. Under inde
pendent block-Rayleigh fading, closed-form analytical expressions for the outage probabilities at the two terminal nodes are derived by accounting for CCI at both the relay and the source nodes. Based on the
derived outage probabilities, a bandwidth-normalized sum-throughput expression is further developed to characterize the tradeoff between the target spectral efficiency and the probability of successful message
recovery.
Monte Carlo simulations based on 10^6 independently generated channel realizations per plotted point show close agreement with the derived analytical expressions over the evaluated parameter settings. The
numerical results show that the proposed SM-3P-FC scheme achieves lower outage probabilities and higher bidirectional sum throughput than both the SM-3P-NoFC and SM-4P-FC benchmarks under the consid
ered system settings. The additional CCI-power comparison further shows that the outage probabilities continue to decrease when interference is absent or when its power remains fixed, whereas proportional
desired/interference power scaling produces nonzero outage floors.

Key words: Fountain Coding; Digital Network Coding; Two-Way Relay Network; Three-Phase Transmission; Co-Channel Interference; Outage Probability; Sum Throughput; Rayleigh Fading.