Joint Design of Transmit Beamforming, IRS Platform, and Power Splitting SWIPT Receivers for Downlink Cellular Multiuser MISO

TL;DR

This paper proposes a joint design framework for transmit beamforming, IRS configuration, and power splitting in a multiuser MISO SWIPT system, demonstrating significant power savings and performance improvements with IRS deployment.

Contribution

It introduces a joint optimization approach for beamforming, IRS phase shifts, and power splitting ratios, including a guaranteed convergence algorithm and low-complexity sub-optimal methods.

Findings

IRS deployment reduces BS power by 10-20 dBw.

Proposed algorithms outperform non-IRS solutions in power efficiency.

Passive IRS can maintain QoS with lower transmit power.

Abstract

A multiple antenna base station (BS) with an intelligent reflecting surface (IRS) platform, and several single antenna users are considered in the downlink mode. Simultaneous wireless information and power transfer (SWIPT) is utilized by the BS via transmit beamforming to convey information and power to all devices. Each device applies power splitting (PS) to dedicate separate parts of received power to information decoding and energy harvesting. We formulate a total transmit power minimization problem to jointly design the BS beamforming vectors, IRS phase shifts, and PS ratios at the receivers subject to minimum rate and harvested energy quality of service (QoS) constraints at all the receivers. First, we develop a block coordinate descent algorithm, also known as alternating optimization that can decrease the objective function with every iteration with guaranteed convergence. Afterwards, two low-complexity sub-optimal algorithms that rely on well-known maximum ratio transmission and zero-forcing beamforming techniques are introduced. These algorithms are beneficial when the number of BS antennas and/or number of users are large, or coherence times of channels are small. Simulations corroborate the expectation that by deploying a passive IRS, BS power can be reduced by $10-20$ dBw while maintaining similar guaranteed QoS. Furthermore, even the proposed sub-optimal algorithms outperform the globally optimal SWIPT solution without IRS for a modest number of IRS elements.