On the Trade-off between Output SNR and Secret Key Generation Rate in Switch-and-Stay Combining

Switch-and-Stay Combining (SSC) is a widely used switched diversity technique that reduces receiver complexity and provides improvement in fading conditions. Until now, the main objective of SSC, was to provide favorable decoding performance. Current work proposes to augment this objective with the main goal of Wireless Physical Layer Security (WPLS) - fast and secure key generation. In a typical practical scenario for consumer electronics, where only one of the two participants employs switched diversity in the form of SSC, we consider a communication protocol where one correspondent always sends a request, while another responds. We show that under this assumption manipulating a switching threshold has a tremendous effect on the upper bound of Key Generation Rate (KGR). Thus, KGR improvement can reach up to 12%. More importantly, we show that maximizing the output SNR does not lead to the highest KGR, meaning that optimizing for both requires resolving a trade-off. If KGR is of priority, the loss in output SNR is approximately 0.4 dB.