Noncoherent Relaying in Energy Harvesting Communication Systems

TL;DR

This paper introduces two noncoherent energy harvesting relay protocols, PS-NcAF and TS-NcAF, that do not require channel state information, offering improved performance and lower complexity in SWIPT systems.

Contribution

The paper develops a unified noncoherent framework for EH relay networks, deriving optimal detectors and proposing a low-complexity approximation, with insights into protocol performance.

Findings

Proposed noncoherent EH relaying protocols outperform grid-powered systems under the same power.

The closed-form detector achieves near-optimal performance with lower complexity.

PS-NcAF is better in single-relay, TS-NcAF in multi-relay scenarios.

Abstract

In energy harvesting (EH) relay networks, the coherent communication requires accurate estima- tion/tracking of the instantaneous channel state information (CSI) which consumes extra power. As a remedy, we propose two noncoherent EH relaying protocols based on the amplify-and-forward (AF) relaying, namely, power splitting noncoherent AF (PS-NcAF) and time switching noncoherent AF (TS-NcAF), which do not require any instantaneous CSI. We develop a noncoherent framework of simultaneous wireless information and power transfer (SWIPT), embracing PS-NcAF and TS-NcAF in a unified form. For arbitrary M-ary noncoherent frequency-shift keying (FSK) and differential phase- shift keying (DPSK), we derive maximum-likelihood detectors (MLDs) for PS-NcAF and TS-NcAF in a unified form, which involves integral evaluations yet serves as the optimum performance benchmark. To avoid expensive integral computations, we propose a closed-form detector using the Gauss-Legendre approximation, which achieves almost identical performance as the MLD but at substantially lower complexity. These EH-based noncoherent detectors achieve full diversity in Rayleigh fading. Numerical results demonstrate that our proposed PS-NcAF and TS-NcAF may outperform the conventional grid- powered relay system under the same total power constraint. Various insights which are useful for the design of practical SWIPT relaying systems are obtained. Interestingly, PS-NcAF outperforms TS-NcAF in the single-relay case, whereas TS-NcAF outperforms PS-NcAF in the multi-relay case.