Secure Communication in Uplink Transmissions: User Selection and Multiuser Secrecy Gain

TL;DR

This paper analyzes secure uplink communication strategies with multiple users and antennas, deriving formulas for secrecy rates, proposing user selection schemes, and examining how multiuser gains depend on system configurations and user count.

Contribution

It introduces two low-complexity user selection schemes for uplink secrecy, providing closed-form expressions for ergodic secrecy sum rates in various regimes, and explores multiuser secrecy gains.

Findings

Multiuser secrecy gain increases with more users.

Serving a single strongest user can be optimal when eavesdropper has many antennas.

Secrecy sum rate scales with the square root of 2 log K.

Abstract

In this paper, we investigate secure communications in uplink transmissions, where there are a base station (BS) with M receive antennas, K mobile users each with a single antenna, and an eavesdropper with N receive antennas. The closed-form expressions of the achievable ergodic secrecy sumrates (ESSR) for a random k users selection scheme in the high and low SNR regimes are presented. It is shown that the scaling behavior of ESSR with respect to the number of served users k can be quite different under different system configurations, determined by the numbers of the BS antennas and that of the eavesdropper antennas. In order to achieve a multiuser gain, two low-complexity user selection schemes are proposed under different assumptions on the eavesdropper's channel state information (CSI). The closed-form expressions of the achievable ESSRs and the multiuser secrecy gains of the two schemes are also presented in both low and high SNR regimes. We observe that, as k increases, the multiuser secrecy gain increases, while the ESSR may decrease. Therefore, when N is much larger than M, serving one user with the strongest channel (TDMA-like) is a favourable secrecy scheme, where the ESSR scales with root square of 2 log K.