A Distributed Iterative Transceiver Beamforming Algorithm for Multipair Two-Way Relay Networks

The transceiver beamforming design problem is studied in this paper for a multi-pair two-way distributed relay network, where multi-antenna users in one user group communicate with their partners in the other user group via distributed single-antenna relay nodes. An iterative algorithm is proposed where transmit and receive beamformings are performed at user nodes, and relay nodes have their own simple strategies for deciding the weights. The computation tasks are distributed among each user and relay node, through which high computation efficiency can be ensured. By coordinating them together, satisfactory performance is obtained when relay number is low and significant performance enhancement is also achieved for a large relay number

Iterative Transceiver Beamformer Design for Multi-Pair Two-Way Distributed Relay Networks

In this paper the transceiver beamforming design problem for multipair two-way distributed relay networks is studied, where each multi-antenna user in one user group communicate with its partner in the other user group via distributed single-antenna relay nodes. To achieve a satisfactory performance while relieving relay nodes of the usual computation task, two iteration-based transceiver beamforming schemes are proposed to coordinate the operation of the users from the two user groups, where the beamforming vectors are determined at the user nodes through an iterative process. Simulation results indicate that both schemes can achieve considerable SINR improvement after only a few iterations compared to the existing zero-forcing scheme

Impact of Relay Cooperation on the Performance of Large-scale Multipair Two-way Relay Networks

We consider a multipair two-way relay communication network, where pairs of user devices exchange information via a relay system. The communication between users employs time division duplex, with all users transmitting simultaneously to relays in one time slot and relays sending the processed information to all users in the next time slot. The relay system consists of a large number of single antenna units that can form groups. Within each group, relays exchange channel state information (CSI), signals received in the uplink and signals intended for downlink transmission. On the other hand, per-group CSI and uplink/downlink signals (data) are not exchanged between groups, which perform the data processing completely independently. Assuming that the groups perform zero-forcing in both uplink and downlink, we derive a lower bound for the ergodic sumrate of the described system as a function of the relay group size. By close observation of this lower bound, it is concluded that the sumrate is essentially independent of group size when the group size is much larger than the number of user pairs. This indicates that a very large group of cooperating relays can be substituted by a number of smaller groups, without incurring any significant performance reduction. Moreover, this result implies that relay cooperation is more efficient (in terms of resources spent on cooperation) when several smaller relay groups are used in contrast to a single, large group.Comment: Accepted to Globecom 2018. Copyright 2018 IEE

A Novel User Pairing Scheme for Functional Decode-and-Forward Multi-way Relay Network

In this paper, we consider a functional decode and forward (FDF) multi-way relay network (MWRN) where a common user facilitates each user in the network to obtain messages from all other users. We propose a novel user pairing scheme, which is based on the principle of selecting a common user with the best average channel gain. This allows the user with the best channel conditions to contribute to the overall system performance. Assuming lattice code based transmissions, we derive upper bounds on the average common rate and the average sum rate with the proposed pairing scheme. Considering M-ary quadrature amplitude modulation with square constellation as a special case of lattice code transmission, we derive asymptotic average symbol error rate (SER) of the MWRN. We show that in terms of the achievable rates, the proposed pairing scheme outperforms the existing pairing schemes under a wide range of channel scenarios. The proposed pairing scheme also has lower average SER compared to existing schemes. We show that overall, the MWRN performance with the proposed pairing scheme is more robust, compared to existing pairing schemes, especially under worst case channel conditions when majority of users have poor average channel gains.Comment: 30 pages, 6 figures, submitted for journal publicatio

Multipair Two-Way DF Relaying with Cell-Free Massive MIMO

We consider a two-way half-duplex decode-and-forward (DF) relaying system with multiple pairs of single-antenna users assisted by a cell-free (CF) massive multiple-input multiple-output (mMIMO) architecture with multiple-antenna access points (APs). Under the practical constraint of imperfect channel state information (CSI), we derive the achievable sum spectral efficiency (SE) for a finite number of APs with maximum ratio (MR) linear processing for both reception and transmission in closed-form. Notably, the proposed CF mMIMO relaying architecture, exploiting the spatial diversity, and providing better coverage, outperforms the conventional collocated mMIMO deployment. Moreover, we shed light on the power-scaling laws maintaining a specific SE as the number of APs grows. A thorough examination of the interplay between the transmit powers per pilot symbol and user/APs takes place, and useful conclusions are extracted. Finally, differently to the common approach for power control in CF mMIMO systems, we design a power allocation scheme maximizing the sum SE.Comment: 15 pages, 8 figures, This work was accepted in IEEE Trans. Green Commun. Net. Copyright may be transferred without notice, after which this version may no longer be accessibl