Enhancing Physical Layer Security Under Imperfect Quantized Feedback

In this paper, we propose and analytically evaluate two distinct transmit antenna selection (TAS) schemes, tailored for wiretap communication systems with orthogonal space-time block codes (OSTBC), utilizing quantized feedback. The first strategy, denoted as error-tolerant-weighting best 2 TAS (E-B2TAS), elects the optimal two antennas from $N$ available transmit antennas. The second method, termed error-tolerant-weighting cluster-based best 2 TAS (EC-B2TAS), partitions the transmit antennas into two clusters, selecting the superior antenna from each subset. Furthermore, an adaptive precoder matrix facilitating optimal power allocation across transmit antennas is devised for both schemes. A thorough examination is undertaken to elucidate the trade-off between feedback overhead and the system's secrecy performance, where optimal weights are determined by minimizing the secrecy outage probability (SOP). Numerical results validate that both schemes maintain full diversity, even under the presence of imperfect feedback. Additionally, the EC-B2TAS scheme demonstrates a reduction in feedback requirements without significant deterioration of the secrecy coding gain relative to E-B2TAS.