Recovering Multiplexing Loss Through Successive Relaying Using Repetition Coding (0705.3261v1)

Abstract: In this paper, a transmission protocol is studied for a two relay wireless network in which simple repetition coding is applied at the relays. Information-theoretic achievable rates for this transmission scheme are given, and a space-time V-BLAST signalling and detection method that can approach them is developed. It is shown through the diversity multiplexing tradeoff analysis that this transmission scheme can recover the multiplexing loss of the half-duplex relay network, while retaining some diversity gain. This scheme is also compared with conventional transmission protocols that exploit only the diversity of the network at the cost of a multiplexing loss. It is shown that the new transmission protocol offers significant performance advantages over conventional protocols, especially when the interference between the two relays is sufficiently strong.

• The paper proposes a successive relaying strategy that mitigates multiplexing loss in half-duplex relay networks using repetition coding.
• Achievable rate analyses reveal superior performance over classical TDMA strategies, with the network emulating MIMO behavior under strong interference.
• Space-time V-BLAST detection is integrated to enhance diversity gains and achieve a favorable diversity-multiplexing tradeoff in dense relay environments.

Overview of Successive Relaying Protocol with Repetition Coding in Wireless Networks

The paper "Recovering Multiplexing Loss Through Successive Relaying Using Repetition Coding" by Yijia Fan, Chao Wang, John Thompson, and H. Vincent Poor, presents an innovative approach to address multiplexing losses in half-duplex relay networks. By employing successive relaying and repetition coding, the authors focus on enhancing the achievable rates in a two-relay wireless network context. They provide a comprehensive analysis of the diversity-multiplexing tradeoff and propose a practical implementation of space-time V-BLAST detection techniques to approach theoretical limits.

Key Contributions and Results

1. Protocol Design: The proposed protocol introduces a successive relaying strategy whereby relays transmit alternatively. This approach aims to mitigate the multiplexing losses encountered in traditional half-duplex relay systems, where relays operate in fixed slots. By allowing continuous transmission from the source and implementing joint decoding at the destination over $L+1$ time slots, the protocol ensures $L$ wireless transmissions with improved spectral efficiency.
2. Achievable Rates: Through rigorous analysis, the authors derive achievable rate expressions under two CSI scenarios: when CSI is known to both the receiver and transmitter, and when it is limited to the receiver. The protocol demonstrates significant advantages over classical TDMA strategies under strong relay-to-relay interference, effectively making the network behave like a $L \times (L+1)$ MIMO system under certain conditions.
3. Interference and Space-Time Processing: A critical aspect is the handling of interference in the relay-to-relay channel. The authors devise methods for interference cancellation using a decoding criterion that dynamically adapts based on channel conditions. The integration of a space-time V-BLAST decoding algorithm is highlighted for its potential to capture considerable diversity gains in slow fading scenarios.
4. Performance Analysis: A comparative paper with classical relay protocols, specifically analyzing scenarios with strong relay-to-relay interference, demonstrates that the proposed method achieves a favorable diversity-multiplexing balance. The protocol provides maximal diversity compatible with only minimal multiplexing reductions, achieving almost optimal performances similar to MIMO settings.
5. Diversity-Multiplexing Tradeoff: The authors extend the investigation to deduce the diversity-multiplexing tradeoff curve, revealing a tradeoff that is markedly superior to established half-duplex schemes, particularly in dense relay environments where high interference prevails.

Theoretical and Practical Implications

The analysis conducted in this paper offers essential insights into adaptive protocol design in multi-relay communications. The potential to adaptively select relay pairs based on channel conditions introduces possibilities for notably enhanced throughput in dense relay networks. The emphasis on leveraging interference effectively in favor of capacity growth lays a foundation for future relay system designs, especially those leveraging cognitive awareness and cooperation.

Furthermore, this research expands on theoretical foundations of relaying strategies, contextualizing their practical applications in scenarios where reliable CSI is not always feasible. This adaptability is poised to influence relay-based communications under various network conditions, aligning with growing demands for efficient spectrum usage in wireless networks.

Future Directions

The paper points to several future directions, notably extending the protocol analysis to larger relay arrays and further refining strategies for effective interference alignment and cancellation. Additionally, translating the proposed V-BLAST decoding adjustments into rapid-fading environments remains a key frontier for achieving continual advancements in cooperative communication frameworks.

In conclusion, the protocol explored in this paper serves as a compelling advancement in the field of relay-aided wireless communications, promising improved data rates and reliability through intelligent use of existing network potentials.