Multi-pair Two-way Relay Networks Research Articles

Joint beamforming optimisation for NOMA‐based wireless powered multi‐pair two‐way AF and DF relaying networks

Joint beamforming optimisation for a wireless-powered multi-pair two-way relay network (MP-TWRN) is studied. Different from the existing works, the authors investigate relay beamforming and power-domain non-orthogonal multiple access for the wireless powered MP-TWRN. The authors' goal is to optimise the energy-transfer beamforming matrix and the relaying beamforming matrix in the sense of maximising the minimum of the achievable rates among all the users with the power constraint at the relay. Further, they explore the above issue under two relaying schemes: amplify-and-forward and decode-and-forward. The formulated problems are highly non-convex, and thus, it is challenging to solve. To address these, they propose two iterative algorithms to solve those two problems based on the difference of convex programming transformation and the successive convex approximation. Simulations demonstrate that the proposed schemes outperform the orthogonal multiple access schemes.

Segment Training Based Individual Channel Estimation for Multi-pair Two-Way Relay Network with Power Allocation

In this paper, we design a segment training based individual channel estimation (STICE) scheme for the classical two-way relay network (TWRN) with multi-pair sources (MPS) and amplify-and-forward (AF). We adopt the linear minimum mean square error (LMMSE) channel estimator to minimize the mean square error (MSE) without channel estimation error, where the optimal power allocation strategy from the relay for different sources is obtained. Then the MSE gains are given with different source pairs among the proposed power allocation scheme and the existing power allocation schemes. Numerical results show that the proposed method outperforms the existing ones.

Wireless Power Transfer-Based Multi-Pair Two-Way Relaying With Massive Antennas

In this paper, we study a multi-pair two-way relay network consisting of two groups of user equipments (UEs), who want to exchange information through a common relay equipped with massive antennas. In the multiple access phase, the UEs transmit information to the relay using the energy harvested in the last time block, and the relay decodes information using zero-forcing (ZF) or maximal ratio combining (MRC) technique. In the broadcasting phase, the relay performs simultaneous wireless information and power transfer (SWIPT), and each UE receives energy and information using the power-splitting scheme. Due to the channel hardening effect of the large-scale antenna array, the harvested energy of each UE in each time block is asymptotically constant. Based on the derived achievable rates of UEs, a multi-objective optimization problem (MOOP) is formulated to maximize the achievable rates of all the pairs. Through solving the MOOP, the power-splitting ratios of UEs can be determined in closed-form for the ZF-based relaying. For the MRC-based relaying, a two-stage iterative Pareto improvement algorithm is proposed to achieve the Pareto optimality. Simulation results are presented to validate our theoretical analysis and verify the efficiency of our proposed algorithm in improving the system rate.

NOMA-Based Multi-Pair Two-Way Relay Networks With Rate Splitting and Group Decoding

In this paper, we develop a non-orthogonal multiple access (NOMA)-based multi-pair two-way relay (TWR) network, in which a rate splitting scheme and a successive group decoding strategy are employed. By exploiting the interference signals received from neighbor users with the leverage of the full-duplex technique, we enhance the decoding ability of each user and further achieve an effective multiuser interference management for the network. We propose different decoding strategies for different types of nodes by processing the received signals with only local incoming channel state information in different manners. Moreover, under the limited group decoding size, each individual node decodes its own desired messages along with a fraction of the interference successively. We further investigate the joint uplink and downlink fair rate allocation problem based on the max–min criterion, and the solution to which also contains the optimal group decoding schedule. Simulation results in terms of ergodic rate and outrage probability corroborate the superiority of our NOMA-based multi-pair TWR network over the OMA-based counterpart.

Adaptive robust beamformer formulti-pair two-way relay networks with imperfect channel state information

In wideband multi-pair two-way relay networks, the performance of beamforming at a relay station (RS) is intimately related to the accuracy of the channel state information (CSI) available. The accuracy of CSI is determined by Doppler spread, delay between beamforming and channel estimation, and density of pilot symbols, including transmit power of pilot symbols. The coefficient of the Gaussian-Markov CSI error model is modeled as a function of CSI delay, Doppler spread, and signal-to-noise ratio, and can be estimated in real time. In accordance with the real-time estimated coefficients of the error model, an adaptive robust maximum signal-to-interferenceand- noise ratio (Max-SINR) plus maximum signal-to-leakage-and-noise ratio (Max-SLNR) beamformer at an RS is proposed to track the variation of the CSI error. From simulation results and analysis, it is shown that: compared to existing non-adaptive beamformers, the proposed adaptive beamformer is more robust and performs much better in the sense of bit error rate (BER); with increase in the density of transmit pilot symbols, its BER and sum-rate performances tend to those of the beamformer of Max-SINR plus Max-SLNR with ideal CSI.

Transceiver Design for Multi-User Cellular Two-Way Relay Networks

In this paper, we consider a general cellular two-way relay network, where a common multi-antenna relay station (RS) helps multiple base stations (BSs) to exchange messages with their served users simultaneously. This network model includes the thoroughly studied two-way relay (TWR) networks, multi-pair TWR networks and multi-user TWR cellular networks as special cases. We first develop a transceiver design for such a network under interference free constraints. The power allocation at the RS, BSs and users is then investigated to maximize the system sum rate. The performance of the proposed algorithm is evaluated through numerical examples. The results show that the proposed design outperforms the existing ones for those special TWR networks, and the sum rate is improved significantly through the proposed power allocation method compared to equal power allocation.

Low-complexity optimal spatial channel pairing for AF-based multi-pair two-way relay networks

This paper considers a multi-pair two-way relay system with multi-antenna users and proposes a low-complexity optimal spatial channel pairing (SCP) strategy at the relay station (RS) for such a system. The proposed SCP scheme, following the BD-like beamformer at RS, pairs the uplink spatial subchannels of each user pair with the corresponding downlink spatial subchannels by maximizing sum-rate (Max-SR). Furthermore, a new mathematical inequality (arrangement inequalities of a product) is developed and applied to obtain sufficient and necessary conditions for achieving Max-SR-SCP. This also yields a simple low-complexity implementation of the proposed SCP in contrast to the NP-hard complexity of the original Max-SR-SCP problem. Simulation results illustrate that the proposed Max-SR-SCP achieves substantial sum-rate gains over other pairing schemes.

High-sum-rate beamformers for multi-pair two-way relay networks with amplify-and-forward relaying strategy

In multi-pair two-way relay networks, the control over inter-pair-interference is a challenging problem. When mobile stations (MSs) cooperate fully, to achieve the sum capacity of networks and at the same time completely remove the inter-pair-interference, a singular value decomposition (SVD) based beamforming scheme at relay station (RS) is established where SVD beamformers are applied over both uplink and downlink channels, respectively. To avoid any cooperation among users, an efficient beamforming scheme is proposed. This scheme uses the Max-SINR based receive beamformer at RS in uplink channel and the Max-SLNR based transmit precoder at RS in downlink channel. It omits interference (uplink) and leakage (donwlink) inside each pair of users due to their abilities of self-interference cancellation. This beamforming scheme provides an analytical solution like some well-known linear beamformers such as zero-forcing, block diagonalization, etc. From simulation, we find: the proposed SVD shows an excellent sum-rate performance at the expense of a large cooperation overhead at MSs and can be used as a tighter upper bound of sum-rate; the proposed scheme of Max-SINR beamformer plus Max-SLNR precoder performs much better on sum-rate than the ZF-based and the BD-based schemes by using almost the same computational amount.

Transceiver Design for Multi-Pair Two-Way Relay Networks with Analogue Network Coding

In this letter, we consider multi-pair two-way relay networks where multiple user pairs simultaneously exchange information via a common multi-antenna relay station. We develop a relaying protocol based on analogue network coding to avoid inter-pair interference in such networks. The user pair selection and power allocation for active user pairs are developed and integrated in the design to enhance the system sum rate. Numerical results show that our proposed design can significantly increase the sum rate compared with the existing scheme.

Large-Scale Multipair Two-Way Relay Networks with Distributed AF Beamforming

We consider a multipair two-way relay network where multiple communication pairs simultaneously exchange information with the help of multiple relay nodes. All nodes are equipped with a single antenna and channel state information is available at the relay nodes. Each relay uses very simple signal processing in a distributed manner, called distributed amplify-and-forward (AF) relaying. A closed-form expression for the achievable rate is derived. We show that the distributed AF scheme outperforms conventional orthogonal relaying. When the number of relays is large, the distributed AF relaying scheme can achieve the capacity scaling given by the cut-set upper bound. Furthermore, when the number of relays grows large, the transmit powers of each terminal and of the relay can be made inversely proportional to the number of relays while maintaining a given quality-of-service. If the transmit power of each terminal is kept fixed, the transmit power of each relay can be scaled down inversely proportional to the square of the number of relays.