Selective Soft-Message-Forward Cooperation With Threshold Decision Detection in Two-Way Physical-Layer Network-Coded MIMO IoT Systems

A selective soft-message-forward (SSMF) cooperation with new threshold decision (TD)-based detection is presented to improve the bit error ratio (BER) performance and power efficiency in two-way physical-layer network-coded multiple-input-multiple-output (MIMO) Internet of Things (IoT) systems. First, the SSMF-based physical-layer network coding (PNC) is proposed by selecting appropriate received signals for soft decoding at relay nodes for better BER performance and low complexity. The signals least affected by noises after zero forcing detection are mapped into log-likelihood ratio metrics for most reservation of the soft messages. Second, a new TD-based detection is obtained by classifying the amplified received signals into different processing regions to reduce false decoding for better performance. Finally, an adaptive power allocation (APA) for the SSMF-based PNC is given to further improve power efficiency. By adaptively allocating the transmitting power in source nodes, the amplitudes of two received signals are similar at the relay and thus efficiently eliminate the near-far effect. Simulation results indicate that the SSMF-based PNC surpasses the existing PNC with a binary phase-shift keying (BPSK) modulation. At BER of $10^{-3}$ , the SSMF-based PNC outperforms the selective decode-and-forward (DF), SMF, and DF schemes by approximately 0.6, 1.0, and 1.7 dB, respectively. At BER of $10^{-3}$ , the APA scheme outperforms the equal power allocation one by about 2 dB. Therefore, it can be efficiently used in two-way integrated satellite and ground wireless MIMO IoT systems.