Multipair Full-Duplex Relaying with Massive Arrays and Linear Processing (1405.1063v1)

Abstract: We consider a multipair decode-and-forward relay channel, where multiple sources transmit simultaneously their signals to multiple destinations with the help of a full-duplex relay station. We assume that the relay station is equipped with massive arrays, while all sources and destinations have a single antenna. The relay station uses channel estimates obtained from received pilots and zero-forcing (ZF) or maximum-ratio combining/maximum-ratio transmission (MRC/MRT) to process the signals. To reduce significantly the loop interference effect, we propose two techniques: i) using a massive receive antenna array; or ii) using a massive transmit antenna array together with very low transmit power at the relay station. We derive an exact achievable rate in closed-form for MRC/MRT processing and an analytical approximation of the achievable rate for ZF processing. This approximation is very tight, especially for large number of relay station antennas. These closed-form expressions enable us to determine the regions where the full-duplex mode outperforms the half-duplex mode, as well as, to design an optimal power allocation scheme. This optimal power allocation scheme aims to maximize the energy efficiency for a given sum spectral efficiency and under peak power constraints at the relay station and sources. Numerical results verify the effectiveness of the optimal power allocation scheme. Furthermore, we show that, by doubling the number of transmit/receive antennas at the relay station, the transmit power of each source and of the relay station can be reduced by 1.5dB if the pilot power is equal to the signal power, and by 3dB if the pilot power is kept fixed, while maintaining a given quality-of-service.

• The paper proposes novel techniques to reduce loop interference using massive receive and large transmit antenna arrays, enhancing full-duplex performance.
• The paper derives closed-form and approximate achievable rate expressions for MRC/MRT and ZF processing, highlighting full-duplex advantages over half-duplex.
• The paper develops an optimal power allocation strategy via geometric programming to maximize energy efficiency while maintaining spectral efficiency.

An Analysis of Multipair Full-Duplex Relaying with Massive Arrays and Linear Processing

The paper "Multipair Full-Duplex Relaying with Massive Arrays and Linear Processing" investigates the potential of combining massive MIMO systems with full-duplex relaying to significantly improve communications in multipair relay networks. This research is pivotal in advancing the understanding of full-duplex systems in massive MIMO settings, particularly focusing on the interplay between loop interference and spectral efficiency.

The considered system consists of multiple sources and destinations communicating through a full-duplex relay equipped with massive antenna arrays. The relay employs linear processing techniques such as zero-forcing (ZF) and maximum-ratio combining (MRC)/maximum-ratio transmission (MRT). These methods are crucial for managing interpair interference and enhancing signal quality.

Key Contributions

1. Loop Interference Reduction: The paper proposes two techniques for mitigating loop interference which arises in full-duplex systems. Firstly, by leveraging a massive receive antenna array, the orthogonality of the signal spaces reduces interference. Alternatively, a large transmit antenna array can be used in conjunction with low transmit power, maintaining signal quality while diminishing interference.
2. Achievable Rate Analysis: The paper derives closed-form expressions for the achievable rates. For MRC/MRT processing, it provides exact rate expressions, while for ZF processing, it offers an approximate analysis. These findings help delineate scenarios where full-duplex outperforms half-duplex setups, offering insights into optimal operational settings.
3. Optimal Power Allocation: An optimal power allocation strategy is developed to maximize energy efficiency under a fixed spectral efficiency. This is achieved using geometric programming, which adjusts power levels at the relay and sources based on channel conditions and interference levels.
4. Performance Comparison: The research thoroughly compares the performance of full-duplex and half-duplex modes. Results demonstrate that full-duplex offers substantial gains in spectral efficiency, provided that loop interference can be effectively managed through large antenna arrays and power control.
5. Massive MIMO Benefits: The paper underscores the benefits of massive MIMO in the relay system, showing a potential 2K increase in spectral efficiency with power reductions achievable by scaling the number of antennas. Specifically, numerical results indicate that doubling the number of antennas allows for a 3 dB power reduction with fixed pilot power.

Implications and Future Directions

This research highlights the viability of merging full-duplex technologies with massive MIMO arrays to enhance wireless communications, particularly in terms of spectral efficiency and interference management. The results suggest that, with adequate loop interference control, full-duplex systems can surpass traditional half-duplex approaches, paving the way for more efficient and capable networks.

The paper opens several avenues for future exploration, including the development of more sophisticated interference cancellation techniques and the examination of real-world deployment challenges. Further research could explore the implementation of these systems in emerging wireless standards such as 5G and beyond, where the demands for higher efficiency and capacity are ever-growing.

In conclusion, this paper contributes significantly to the field by providing detailed analytical results and insights that can inform the design and optimization of full-duplex relay systems in massive MIMO contexts. The fusion of full-duplex operations with massive arrays represents a promising strategy for meeting future communication needs.