On the target secrecy rate for SISOME wiretap channels

We propose a new framework for optimizing the target secrecy rate for SISOME wiretap channels when the instantaneous capacity of the eavesdropper's channel is not available at the transmitter. In our framework we introduce the effective secrecy throughput, a new optimization metric that implicitly captures the two key features of wiretap channels, namely, reliability and secrecy. We derive target secrecy rates which maximize the effective secrecy throughput for two different schemes, an on-off transmission scheme and an adaptive transmission scheme. Our analysis demonstrates that the adaptive transmission scheme outperforms the on-off transmission scheme and that the difference in the effective secrecy throughput between the two schemes increases with the SNR of the main channel. The work reported here solves the important problem of how to optimally set the target secrecy rate of wiretap codes for an important class of channels. Notably, our solution for the target secrecy rate does not require us to set a priori any reliability or secrecy constraint for the channel.