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

摘要

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 sum rates (ESSRs) for a random $k$ users selection scheme in the high and low signal-to-noise ratio 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. 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 (Time Division Multiple Address-like) is a favorable secrecy scheme, where the ESSR scales with $sqrt {2log K}$ .