Linear Precoders for Non-Regenerative Asymmetric Two-way Relaying in Cellular Systems

TL;DR

This paper proposes a structured precoding scheme for non-regenerative asymmetric two-way relaying in cellular systems, improving spectral efficiency by effectively managing interference and channel triangulation with MIMO nodes.

Contribution

It introduces a novel transmission protocol and a structured precoder at the relay to cancel interference and optimize channel triangulation in asymmetric TWR cellular systems.

Findings

The proposed precoder effectively cancels back-propagating interference.

Channel triangulation simplifies the sum-rate optimization to power allocation.

Simulation results show improved spectral efficiency over conventional methods.

Abstract

Two-way relaying (TWR) reduces the spectral-efficiency loss caused in conventional half-duplex relaying. TWR is possible when two nodes exchange data simultaneously through a relay. In cellular systems, data exchange between base station (BS) and users is usually not simultaneous e.g., a user (TUE) has uplink data to transmit during multiple access (MAC) phase, but does not have downlink data to receive during broadcast (BC) phase. This non-simultaneous data exchange will reduce TWR to spectrally-inefficient conventional half-duplex relaying. With infrastructure relays, where multiple users communicate through a relay, a new transmission protocol is proposed to recover the spectral loss. The BC phase following the MAC phase of TUE is now used by the relay to transmit downlink data to another user (RUE). RUE will not be able to cancel the back-propagating interference. A structured precoder is designed at the multi-antenna relay to cancel this interference. With multiple-input multiple-output (MIMO) nodes, the proposed precoder also triangulates the compound MAC and BC phase MIMO channels. The channel triangulation reduces the weighted sum-rate optimization to power allocation problem, which is then cast as a geometric program. Simulation results illustrate the effectiveness of the proposed protocol over conventional solutions.