Abstract
In this paper, a novel approach is introduced to study the achievable delay-guaranteed secrecy rate, by introducing the concept of the effective secrecy rate (ESR). This study focuses on the downlink of a non-orthogonal multiple access (NOMA) network with one base station, multiple single-antenna NOMA users and an eavesdropper. Two possible eavesdropping scenarios are considered: 1) an internal, unknown, eavesdropper in a purely antagonistic network; and 2) an external eavesdropper in a network with trustworthy peers. For a purely antagonistic network with an internal eavesdropper, the only receiver with a guaranteed positive ESR is the one with the highest channel gain. A closed-form expression is obtained for the ESR at high signal-to-noise ratio (SNR) values, showing that the strongest user’s ESR in the high SNR regime approaches a constant value irrespective of the power coefficients. Furthermore, it is shown the strongest user can achieve higher ESR if it has a distinctive advantage in terms of channel gain with respect to the second strongest user. For a trustworthy NOMA network with an external eavesdropper, a lower bound and an upper bound on the ESR are proposed and investigated for an arbitrary legitimate user. For the lower bound, a closed-form expression is derived in the high SNR regime. For the upper bound, the analysis shows that if the external eavesdropper cannot attain any channel state information (CSI), the legitimate NOMA user at high SNRs can always achieve positive ESR, and the value of it depends on the power coefficients. Simulation results numerically validate the accuracy of the derived closed-form expressions and verify the analytical results given in the theorems and lemmas.
Highlights
N ON-ORTHOGONAL multiple access (NOMA) is considered to be a promising multiple access (MA) technique for fifth generation (5G) and beyond (B5G) networks, because of its advantages over conventional orthogonal multiple access (OMA) schemes, in terms of spectral efficiency [1], cell-edge throughput [2], and energy efficiency [3]
The analysis shows that if the external eavesdropper cannot attain any channel state information (CSI), the legitimate NOMA user in the high signal-to-noise ratio (SNR) regime can always achieve positive delay-guaranteed secrecy rate, and the value of it depends on the power coefficients
The accuracy of the derived analytical closed-forms and the theoretical analysis given in Section III will be numerically validated
Summary
N ON-ORTHOGONAL multiple access (NOMA) is considered to be a promising multiple access (MA) technique for fifth generation (5G) and beyond (B5G) networks, because of its advantages over conventional orthogonal multiple access (OMA) schemes, in terms of spectral efficiency [1], cell-edge throughput [2], and energy efficiency [3]. The obtained prior information can be utilized to help the weaker users to decode their messages [2], but as mentioned in [8], this can cause security issues. Based on the concept of perfect secrecy proposed by Shannon [12], Wyner introduced the wiretap channel model, in which two legitimate users can communicate reliably through a main channel while keeping the exchanged messages confidential from an eavesdropper. Considering Gaussian wiretap channels, the secrecy capacity, i.e., the maximum achievable rate which guarantees reliable communication while the eavesdropper cannot decode any confidential message, is equal to the difference between the main channel’s Shannon capacity and the adversary channel’s Shannon capacity [9], [13].
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