Achieving Covert Communication in Uplink NOMA Systems via Energy Harvesting Jammer

This letter investigates covert communication in uplink NOMA systems assisted by an energy harvesting jammer (EHJ), where a reliability-required user (RRU) and a covertness-required user (CRU) are paired to perform NOMA to transmit messages to Bob, in the presence of a warden (Willie) who tries to detect CRU’s transmission behavior. In particular, the EHJ with time switching (TS) scheme has been employed for the purpose of confusing Willie and compensating for the energy supply. We derive the closed-form expressions of expected minimum detection error probability (EMDEP) and connection outage probabilities (COPs) at RRU and CRU, then we analyse the maximum effective covert rate (ECR) under the covertness and RRU’s quality of service (QoS) constraints. Our analysis indicates that there exist an optimal transmit power at Bob and time switching factor to maximize the maximum ECR, and RRU’s QoS constraint has a remarkable effect on the maximum ECR as the transmit power at Bob or time switching factor increases.

I. Introduction

Non-orthogonal multiple access (NOMA) systems are facing serious security threats due to the broadcast and openness of wireless channels. To address security problems of NOMA systems, the existing research mainly focuses on physical layer security (PLS) technology [1]. However, PLS only protects security of communication content, which will expose the communication behavior and cause the attack from adversary. Against this background, covert communication as a promising approach has gradually attracted people’s attention [2], which aims to hide the existence of wireless transmissions.