Multi-Antenna Aided Secrecy Beamforming Optimization for Wirelessly Powered HetNets

TL;DR

This paper investigates secrecy beamforming in wirelessly powered HetNets with multiple CSI scenarios, optimizing energy and information transmission to maximize secrecy rates and enhance security against eavesdroppers.

Contribution

It introduces a comprehensive secrecy beamforming framework for wirelessly powered HetNets under perfect, imperfect, and unknown eavesdropper CSI conditions, including closed-form solutions.

Findings

Optimal beamforming solutions are rank-1 for all cases.

Closed-form solutions are available when cross-tier interference is inactive.

Proposed designs outperform baseline algorithms in secrecy performance.

Abstract

The new paradigm of wirelessly powered two-tier heterogeneous networks (HetNets) is considered in this paper. Specifically, the femtocell base station (FBS) is powered by a power beacon (PB) and transmits confidential information to a legitimate femtocell user (FU) in the presence of a potential eavesdropper (EVE) and a macro base station (MBS). In this scenario, we investigate the secrecy beamforming design under three different levels of FBS-EVE channel state information (CSI), namely, the perfect, imperfect and completely unknown FBS-EVE CSI. Firstly, given the perfect global CSI at the FBS, the PB energy covariance matrix, the FBS information covariance matrix and the time splitting factor are jointly optimized aiming for perfect secrecy rate maximization. Upon assuming the imperfect FBS-EVE CSI, the worst-case and outage-constrained SRM problems corresponding to deterministic and statistical CSI errors are investigated, respectively. Furthermore, considering the more realistic case of unknown FBS-EVE CSI, the artificial noise (AN) aided secrecy beamforming design is studied. Our analysis reveals that for all the above cases both the optimal PB energy and FBS information secrecy beamformings are of rank-1. Moreover, for all considered cases of FBS-EVE CSI, the closed-form PB energy beamforming solutions are available when the cross-tier interference constraint is inactive. Numerical simulation results demonstrate the secrecy performance advantages of all proposed secrecy beamforming designs compared to the adopted baseline algorithms.