A Full-Duplex Decode-and-Forward Relaying Approach Based on QAM Constellation Suitable for Small-Size Devices

The explosive growth of the Internet of Things (IoT) is putting higher requirements for the performance of co-time co-frequency full-duplex relaying (CCFD-R) due to small-size devices appearing in abundance. In this paper, we present a novel CCFD-R approach with very low complexity to deal with the issue above. Based on the orthogonality of its two components, a distributed usage mode of quadrature amplitude modulation (QAM) constellation is proposed to perform self-interference cancellation (SIC) without the complicated processing modules, as used widely in traditional full-duplex techniques. Instead of the conventional practice of assigning the entire QAM constellation to only one communication node, our scheme (termed as QAM-R) splits the constellation into two parts and further assigns them to different communication nodes, respectively. With the principle above, the mapping pattern and the frame format are carefully designed. Then, the corresponding signal model is established and the approximation of end-to-end bit error probability (BEP) is derived. Finally, numerical simulations validate the theoretical analysis and show that QAM-R can balance spectrum effectiveness and transmission reliability very well and, especially, performs even better in the low range of signal noise ratio (SNR) when adopting higher-order QAM constellations.