Multiuser MISO Beamforming for Simultaneous Wireless Information and Power Transfer (1303.1911v4)

Abstract: Simultaneous wireless information and power transfer (SWIPT) is anticipated to have abundant applications in future machine or sensor based wireless networks by providing wireless data and energy access at the same time. In this paper, we study a multiuser multiple-input single-output (MISO) broadcast SWIPT system, where a multi-antenna access point (AP) sends information and energy simultaneously via spatial multiplexing to multiple single-antenna receivers each of which implements information decoding (ID) or energy harvesting (EH). Since EH receivers in practice operate with considerably higher received power than ID receivers, we propose a receiver location based transmission scheduling, where receivers that are close to the AP are scheduled for EH while those more distant from the AP for ID. We aim to maximize the weighted sum-power transferred to all EH receivers subject to a given set of minimum signal-to-interference-and-noise ratio (SINR) constraints at different ID receivers. In particular, we consider two types of ID receivers (referred to as Type I and Type II, respectively) without or with the capability of cancelling the interference from (a priori known) energy signals. For each type of ID receivers, we formulate the joint information and energy transmit beamforming design as a non-convex quadratically constrained quadratic program (QCQP). First, we obtain the globally optimal solutions for our formulated QCQPs by applying an optimization technique so-called semidefinite relaxation (SDR). It is shown via SDR that no dedicated energy beam is needed for Type I ID receivers to achieve the optimal solution; while for Type II ID receivers, employing no more than one energy beam is optimal. Next, we establish a new form of the celebrated uplink-downlink duality to develop alternative algorithms to obtain the same optimal solutions as SDR.

• The paper introduces optimal beamforming designs for SWIPT that maximize energy delivery while satisfying SINR requirements at ID receivers.
• It employs semidefinite relaxation to transform challenging non-convex QCQP problems into convex ones, achieving globally optimal solutions.
• The results highlight that Type II ID receivers, capable of interference cancellation, significantly improve energy harvest efficiency compared to Type I receivers.

Multiuser MISO Beamforming for Simultaneous Wireless Information and Power Transfer

This paper explores the intricacies of simultaneous wireless information and power transfer (SWIPT) within a multiuser multiple-input single-output (MISO) broadcast system. The authors, Jie Xu, Liang Liu, and Rui Zhang, tackle the complex challenge of designing beamforming strategies that optimize energy transfer while maintaining the quality of information decoding for multiple single-antenna receivers.

System Model and Problem Formulation

The research considers a multi-antenna access point (AP) that transmits both information and energy to multiple single-antenna receivers. These receivers are either engaged in information decoding (ID) or energy harvesting (EH). The primary objective is to maximize the weighted sum of power delivered to EH receivers while satisfying specific signal-to-interference-and-noise ratio (SINR) constraints at ID receivers.

Two types of ID receivers are explored: Type I, which cannot cancel interference from energy signals, and Type II, which can cancel known energy signals' interference. For each type, the beamforming design is framed as a non-convex quadratically constrained quadratic program (QCQP), a classically challenging optimization problem.

Approach and Methods

The authors propose using semidefinite relaxation (SDR) to obtain globally optimal solutions for these QCQPs. This method allows for an effective and practical way to relax the non-convex problems into convex ones, enabling the use of standard optimization tools.

Key findings include:

• For Type I ID receivers, no dedicated energy beams are required to achieve optimal solutions under independently distributed user channels.
• For Type II ID receivers, employing at most one energy beam is optimal.

Additionally, they introduce an alternative algorithm leveraging uplink-downlink duality, which offers further insights into the optimal beamforming design. This approach reformulates the downlink beamforming problem to an equivalent uplink scenario, providing an iterative method to achieve optimal solutions.

Numerical Results and Implications

Numerical evaluations illustrate the superiority of the proposed beamforming designs over heuristic schemes, particularly in terms of the weighted sum-power harvested by EH receivers. The results highlight the practical benefits of using Type II ID receivers due to their ability to handle energy beam interference, indicating notable gains over Type I scenarios.

Implications and Future Work

This research has notable implications for future wireless networks aiming to integrate SWIPT technology. By efficiently managing beamforming designs, the paper ensures robust information delivery alongside effective power transfer, paving the way for advancements in energy-constrained wireless systems like IoT networks and sensor deployments.

Looking forward, exploring systems with even more complex receiver capabilities or varying network constraints may further enhance SWIPT efficiency. Additionally, addressing imperfect channel state information and real-world constraints remains an open avenue for future investigation.

This paper's contribution lies in its rigorous exploration of SWIPT beamforming optimization, providing a foundational understanding that underscores both theoretical and practical advancements in wireless network design.