Improving Two-Way Selective Decode-and-forward Wireless Relaying with Energy-Efficient One-bit Soft Forwarding

Inspired by the application scenarios such as battery-operated wireless sensor networks (WSN), we investigate the design of an easy-to-implement energy-efficient two-way relaying scheme in which two source nodes exchange their messages with the help of an intermediate relay node. Due to their efficient decoder hardware implementation, block codes, such as Hamming and BCH codes, instead of convolutional and other sophisticated codes, are adopted in WSN-related standards, such as Bluetooth and IEEE802.15.6. At the network level, cooperative relaying with network coding can help reduce overall energy consumption. Motivated by these considerations, we address the challenge of improving the standard two-way selective decode-and-forward protocol (TW-SDF) with minor additional complexity and energy consumption. By following the principle of soft relaying, our solution is the two-way one-bit soft forwarding (TW-1bSF) protocol in which the relay forwards the one-bit quantization of a posterior information about the transmitted bits, associated with an appropriately designed reliability parameter. As the second main contribution, we derive tight upper bounds on the BLER performance for both the TW-SDF protocol and the TW-1bSF protocol, provided that the two-way relaying network applies block codes and hard decoding. The error probability analysis confirms the superiority of the TW-1bSF protocol over the TW-SDF protocol. In addition, our further derived asymptotic performance gain by TW-1bSF over TW-SDF suggests that the proposed protocol offers higher gain when longer block codes are used. Wai Ho Mow is with the Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay Hong Kong S.A.R., China. Qing F. Zhou was with the Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, now is with the Department of Electronic Engineering, City University of Hong Kong. This work was supported by the AoE grant E-02/08 from the University Grants Committee of the Hong Kong S.A.R., China. 1