ENHANCING PHYSICAL LAYER SECURITY UNDER IMPERFECT QUANTIZED FEEDBACK

Abstract

In this work, two schemes based on transmit antenna selection (TAS) under imperfect quantized feedback are proposed for a N × 1 multiple-input single-output (MISO) wireless communication system using M-quadrature amplitude modulation (QAM). In the first scheme, the two most robust transmit antennas information are found from all available N antennas, and based on that, an optimum power allocation is done across the antennas. In the second scheme, two clusters are formed from all available N transmit antennas using the adjacent antennas; one robust antenna from each cluster is found and based on that, an optimum power allocation is done across the antennas. In this thesis, the communication links are considered Quasi-static Rayleigh distributed to characterize wireless channels. The system’s performance is irreparably harmed by erroneous feedback information. As a result, error-tolerant weighting schemes using diagonal precoders have been used to mitigate the effect of erroneous feedback information. With the use of a diagonal precoder, optimum power allocation (OPA) improves secrecy performance. Orthogonal space-time block code (OSTBC) is also employed to enhance the proposed system’s security. Firstly, with order statistics, a closed-form expression of the 4×1 MISO system’s secrecy outage probability (SOP) is derived under imperfect feedback for both proposed schemes. The most optimal transmit weights for the diagonal precoder matrix (based on feedback bits) are obtained by minimizing the derived SOP. Later, a closed-form expression of average symbol-errorrate (SER) with erroneous feedback bits is derived for the schemes investigated. Under erroneous feedback information, the error-tolerant weighting methods achieve a significant performance gain compared to existing precoding techniques and uniform power allocation, as per simulated and analytical results for all the derived performance metrics.