Full-duplex MIMO Relay Research Articles

Optimal Transmission Using a Self-Sustained Relay in a Full-Duplex MIMO System

This paper investigates wireless information and power transfer in a full-duplex MIMO relay channel where the self-sustained relay harvests energy from both source transmit signal and self-interference signal to decode and forward source information to a destination. We formulate a new problem to jointly optimize power splitting at the relay and precoding design for both the source and relay transmissions. Using duality theory, we establish closed-form optimal primal solutions in terms of the dual variables, based on which we then design a customized and efficient primal-dual algorithm to maximize the achievable throughput. Numerical results demonstrate the rate gains from using multiple transmit and receive antennas in both information decoding and energy harvesting, and the significant benefit of harvesting energy from self-interference signals. We also extend our analysis to the case when channel state information is only available at receiving nodes and show how our algorithm can optimize the power splitting at the relay for it to remain self-sustained. Through analysis and simulation, we demonstrate that an optimal combination of non-uniform power splitting, variable power allocation, and self-interference power harvesting can effectively exploit a full-duplex MIMO system to achieve significant performance gains over existing uniform power splitting and half-duplex transmissions.

Nonlinear Transceiver Designs for Full-Duplex MIMO Relay Systems

This paper investigates nonlinear transceiver design for full-duplex multiple-input multiple-output (FD-MIMO) relay systems. A dual-hop amplify-and-forward relaying protocol is considered. At the destination, nonlinear successive-interference-cancellation (SIC) is used for signal detection. The goal is to find the source and relay precoders such that the symbol-vector error rate (SVER) can be minimized. Due to the loop interference (LI), optimizing the relay precoder in FD systems is much more involved. In this paper, we propose novel designs to solve this problem. Starting from the QR-SIC receiver, we theoretically show that the relay precoder can be solved with a closed-form expression even when the system incurs LI. Then, we consider the system with a minimum mean-squared-error SIC receiver, where the relay precoder design entails a different problem formulation and introduces new challenges. We propose a novel iterative method, with closed-form solutions in each iteration, to solve this problem. Simulations show that our designs can significantly improve the SVER performance for FD-MIMO relay systems.

MMSE Transceiver Design for Full-Duplex MIMO Relay Systems

Full-duplex (FD) multiple-input multiple-output relaying has been considered an effective scheme to increase the spectral efficiency for wireless communications. As known, the main problem for the FD system is the cancellation of loop interference (LI). In this paper, we propose using the joint source/relay precoding to reduce the influence of LI. Therein, linear precoders are used at the source and relay, while the minimum mean-squared-error receiver is adopted at the destination. The joint precoder design is complicated when spatial multiplexing is exploited for signal transmission. To solve the problem, we propose an iterative method in which the original problem is split into two subproblems. With some matrix properties, we then show that each subproblem can be formulated as a convex optimization. Finally, a closed-form solution can be obtained with the Karush–Kuhn–Tucker conditions. Using a mean-squared-error upper bound, we also propose a low-complexity method to reduce the computational complexity. The proposed precoders have closed-form expressions, which is a great advantage in real-world implementation. Simulation results show that the proposed methods significantly outperform existing ones.

Linear Transceiver Design for Full-Duplex MIMO Relay Systems: A Non-Iterative Approach

Full-duplex (FD) multiple-input multiple-output relaying can significantly increase the spectral efficiency of cooperative systems. As known, the loop interference (LI) is a main factor affecting the performance of FD systems. The joint source/relay precoding has been considered a promising technique to reduce the influence of LI. Unfortunately, existing methods are developed as iterative, which is not desirable from the implementation point of view. In this letter, we propose a novel design to solve the problem. The proposed scheme not only gives closed-form solutions but avoids iterative operations. Simulation results show that our design can provide comparable performance to iterative schemes; meanwhile the required computational complexity is lower.

Outage analysis of TAS/MRC in dual hop full-duplex MIMO relay networks with co-channel interferences

In this paper, we investigate the outage performance of transmit antenna selection (TAS) and maximal-ratio combining (MRC) in dual hop full-duplex (FD) amplify-and-forward (AF) relay network over Rayleigh fading channels. In the analysis, Rayleigh faded multiple co-channel interferers (CCIs) are also taken into account at the relay. In the network, source and destination are equipped with multiple antennas, and relay is equipped with one receive and one transmit antennas, respectively and source-destination link is not available. While the TAS is applied at the source without considering residual self-interference (RSI) effect, received signals at the destination are combined based on the MRC technique. For the analysis, we consider three approaches at the relay. In the first, we consider the received signal at the relay is corrupted by faded RSI and noise, in the second one, the RSI is considered as non-fading. In the last one, the noise is neglected. In all cases, the relay suffers from multiple Rayleigh faded CCIs. Outage probability (OP) expression related to all the cases is derived and obtained in single integral forms in case of the faded/non-fading RSI and in closed form in case of the noise neglected approach. Moreover, we also find asymptotic OPs and conduct effective diversity order analysis. The analytical results are verified by the Monte Carlo simulations. Results show that TAS decreases error floor at high signal-to-noise ratio (SNR) region and MRC provides diversity gain at low SNR region. In addition, approaches II and III are good approximations to approach I at low and high SNR regions, respectively.

Joint Transceiver Beamforming Design for End-to-End Optimization in Full-Duplex MIMO Relay System With Self-Interference

In this letter, a novel transceiver beamforming design is proposed for improving the end-to-end performance of a full-duplex amplify-and-forward relay system. Different from previous schemes based on nulling out residual self-interference (RSI), our proposed schemes can capture a balance between useful signal improvement and RSI suppression for further achievable rate improvement. To solve the nonconvex optimization problem, an iterative algorithm with proven convergence is developed. Specifically, at each iteration, an optimal solution derived by reformulating the optimization problem as a fractional program problem and an efficient sub-optimal closed-form solution are presented, respectively. The simulation results show that the proposed design outperforms the traditional schemes in all signal-to-noise ratio regime.

Wideband full-duplex MIMO relays with blind adaptive self-interference cancellation

We develop adaptive self-interference cancellation algorithms for both filter-and-forward and decode-and-forward multiple-input multiple-output relays. The algorithms are blind in the sense that they only exploit the spectral properties of the transmitted signal to identify the self-interference channel, while dealing with frequency-selective channels and arbitrary signal spectra. Our approach is non-intrusive in the sense that the algorithms can successfully identify, track, and cancel the self-interference distortion while the relay is operating in its normal mode. We study the stationary points of the algorithms and analyze under which conditions they achieve perfect cancellation of the self-interference. Simulation results show that the algorithms provide residual self-interference levels below the noise floor by using the time samples of only a few OFDM symbols.

The Degrees of Freedom of Full-Duplex Bidirectional Interference Networks With and Without a MIMO Relay

In a full-duplex bidirectional interference network with $2K$ transceivers, there are $K$ communication pairs: each user transmits a message to and receives a message from one intended user and interferes with and experiences interference from all other users. All nodes may interact, or adapt inputs to past received signals, and may thus co-operate with each other. We derive a new outer bound, and use interference alignment to demonstrate that the optimal degrees of freedom (DoF, also known as the multiplexing gain) is $K$ : full-duplex operation doubles the DoF, but interaction and co-operation does not further increase the DoF. We next characterize the DoF of a full-duplex bidirectional interference network with a MIMO full-duplex relay. If the relay is noncausal/instantaneous (at time $k$ forwards a function of its received signals up to time $k$ ) and has $2K$ antennas, we demonstrate a one-shot scheme where the relay mitigates all interference to achieve the interference-free $2K$ DoF. In contrast, if the relay is causal (at time $k$ forwards a function of its received signals up to time $k-1$ ), we show that a full-duplex MIMO relay cannot increase the DoF of the full-duplex bidirectional interference network beyond $K$ , as if no relay or interaction is present.

Recent advances in antenna design and interference cancellation algorithms for in-band full duplex relays

In-band full-duplex relays transmit and receive simultaneously at the same center frequency, hence offering enhanced spectral efficiency for relay deployment. In order to deploy such full-duplex relays, it is necessary to efficiently mitigate the inherent self-interference stemming from the strong transmit signal coupling to the sensitive receive chain. In this article, we present novel state-of-the-art antenna solutions as well as digital self-interference cancellation algorithms for compact MIMO fullduplex relays, specifically targeted for reduced-cost deployments in local area networks. The presented antenna design builds on resonant wavetraps and is shown to provide passive isolations on the order of 60–70 dB. We also discuss and present advanced digital cancellation solutions, beyond classical linear processing, specifically tailored against nonlinear distortion of the power amplifier when operating close to saturation. Measured results from a complete demonstrator system, integrating antennas, RF cancellation, and nonlinear digital cancellation, are also presented, evidencing close to 100 dB of overall self-interference suppression. The reported results indicate that building and deploying compact full-duplex MIMO relays is already technologically feasible.

Precoding and Power Allocation for Full-Duplex MIMO Relays

Precoding and Power Allocation for Full-Duplex MIMO Relays