Non-regenerative MIMO Relay System Research Articles

Joint Transceiver Optimization for Wireless Information and Energy Transfer in Nonregenerative MIMO Relay Systems

In this paper, a two-hop nonregenerative multiple-input multiple-output relay system is investigated, where the relay node relies on harvesting the radio frequency energy transferred from the source node to forward information from source to destination. We consider the time switching (TS) protocol between wireless information and energy transfer. In particular, we propose a more general energy consumption constraint at the source node during the information and energy transfer, which includes the constant power constraints used in existing works as special cases. We study the joint optimization of the source precoding matrices, the relay amplifying matrix, and the TS factor to maximize the source–destination mutual information (MI). The optimal structure of the source and relay matrices is derived, which reduces the original transceiver optimization problem to a simpler power allocation problem. We propose a primal decomposition based algorithm and an upper bound based approach to efficiently solve the power allocation problem. The first algorithm achieves the global optimum, whereas the latter one has a lower computational complexity. Numerical simulations show that both proposed algorithms yield much higher system MI and better rate-energy tradeoff than existing approaches.

Optimum Linear Precoding Design for Non-Regenerative MIMO Relay System with Direct Link

This paper designs the closed-form precoding matrices for non-regenerative MIMO relay system with the direct link. A multiple power constrained non-convex optimization problem is formulated by using the minimum-mean-squared error (MMSE) criterion. We decompose the original problem into two sub-problems. The relay transceiver Wiener filter structure is first rigorously derived, then the source transmit and destination receive matrices are jointly designed by solving an equivalent dual problem. Through our proposed joint iterative algorithm, the closed-form solutions can be finally obtained. The effectiveness of our proposed scheme is validated by simulations with comparison to some of the existing schemes.

Optimal Design of Source and Relay Pilots for MIMO Relay Channel Estimation

In this paper, we consider a channel estimation scheme for a two-hop nonregenerative MIMO relay system without the direct link between source and destination. This scheme has two phases. In the first phase, the source does not transmit while the relay transmits and the destination receives. In the second phase, the source transmits, the relay amplifies and forwards, and the destination receives. At the destination, the data received in the first phase are used to estimate the relay-to-destination channel, and the data received in the second phase are used to estimate the source-to-relay channel. The linear minimum mean-square error estimation (LMMSE) is used for channel estimation, which allows the use of prior knowledge of channel correlations. For phase 1, an algorithm is developed to compute the optimal source pilot matrix for use at the relay. For phase 2, an algorithm is developed to compute the optimal source pilot matrix for use at the source and the optimal relay pilot matrix for use at the relay.

Optimal Design of Spatial Source-and-Relay Matrices for a Non-Regenerative Two-Way MIMO Relay System

This paper considers a system where two users exchange information via a non-regenerative half-duplex two-way MIMO relay and each of the two users and the relay is equipped with multiple antennas. We study the design of the spatial source covariance matrices (or source matrices) at the two users and the spatial transformation matrix (or relay matrix) at the relay to maximize the achievable weighted sum rate of the system. The source matrices and the relay matrix are optimized alternately until convergence. If the relay matrix is given, we show that the optimal design of the source matrices (for uniformly weighted sum rate) follows a generalized water filling (GWF) algorithm. If the source matrices are given, we show two search algorithms to optimize the relay matrix. The first algorithm is a hybrid gradient method which adaptively switches between the (steepest) gradient descent and the Newton's search. The second is an iterative weighted minimum mean square error (WMMSE) method which alternately refines the MMSE equalizers at the users and the relay matrix. We compare the convergence behaviors of the two algorithms and demonstrate their advantage over prior algorithms. We also show an optimal structure of the relay matrix, which is useful to reduce the search complexity.

Joint Linear MMSE Processing for Closed-Loop Multi-User Non-regenerative MIMO-Relay Systems

This letter addresses linear processing issues for the downlink of closed-loop multi-user non-regenerative MIMO-relay systems with arbitrary number of antennas at each node. First three precoding design schemes at BS are presented. Then given the fixed BS linear processing matrix, we propose a joint iterative linear processing scheme for the relay station and mobile stations, aiming to minimize the total mean squared error (MSE). Finally Simulation results are provided to show the performance gain of joint linear processing at the multi-antenna nodes.

Precoder design for non-regenerative MIMO relay systems

This paper studies the precoder design for a 3-node non-generative MIMO relay channel, taking the direct link transmission into consideration. We first look into the scenario where precoding is only performed at the relay. Our analytical approach enables a relay precoding design to achieve better ergodic capacity than the precoding design to achieve a lower bound of the capacity reported in earlier works. We next propose an iterative algorithm to perform joint precoding design at both the source and the relay. To reduce the computation complexity of the iterative algorithm, a two-step algorithm is then developed. Our numerical results show that under some circumstances, capacity gain can be achieved by performing precoding at both the source and the relay compared to the case where precoding is performed at the relay only. The efficiency of the proposed two-step algorithm is verified since it achieves roughly identical capacity as the iterative joint precoding scheme.

Joint Linear Filter Design in Multiuser Cooperative Nonregenerative MIMO Relay Systems

This paper addresses the filter design issues for multiuser cooperative nonregenerative MIMO relay systems in both downlink and uplink scenarios. Based on the formulated signal model, the filter matrix optimization is first performed for direct path and relay path respectively, aiming to minimize the mean squared error (MSE). To be more specific, for the relay path, we derive the local optimal filter scheme at the base station and the relay station jointly in the downlink scenario along with a more practical suboptimal scheme, and then a closed-form joint local optimal solution in the uplink scenario is exploited. Furthermore, the optimal filter for the direct path is also presented by using the exiting results of conventional MIMO link. After that, several schemes are proposed for cooperative scenario to combine the signals from both paths. Numerical results show that the proposed schemes can reduce the bit error rate (BER) significantly.

Joint linear transceiver design for non-regenerative MIMO relay systems

The problem of designing the linear transmitters and receiver jointly in a non-regenerative MIMO relay system is considered, where linear processing is applied at the source, relay and destination node, using the minimum mean square error criterion. Under average power constraint at both the source and the relay node, the transmitters and receiver could be realised through a joint iterative algorithm. Simulation results are also provided to demonstrate the performance of this new method.

Joint MMSE Transceiver Design in Non-Regenerative MIMO Relay Systems

In this letter, we address the problem of transceiver design in a non-regenerative MIMO relay system, where linear processing is applied at both the relay and destination to jointly minimize the mean-squared error (MSE) of symbol estimations. Under average power constraint at the relay station, we show that the optimal relay-precoder always loads power across channel eigenvectors and then decomposes the equivalent MIMO channel into a set of parallel SISO channels. Simulation results demonstrate that our method outperforms other relaying schemes in terms of both BER and MSE.