On–Off-Based Secure Transmission Design With Outdated Channel State Information

We design new secure on-off transmission schemes in wiretap channels with outdated channel state information (CSI). In our design, we consider not only the outdated CSI from the legitimate receiver but two distinct scenarios as well, depending on whether the outdated CSI from the eavesdropper is known at the transmitter. Under this consideration, our schemes exploit useful knowledge contained in the available outdated CSI, and based on this, the transmitter decides on whether to transmit or not. We derive new closed-form expressions for the transmission probability, the connection outage probability, the secrecy outage probability, and the reliable and secure transmission probability to characterize the achievable performance. Based on these results, we present the optimal solutions that maximize the secrecy throughput under dual connection and secrecy outage constraints. Our analytical and numerical results offer detailed insights into the design of the wiretap coding parameters and the imposed outage constraints. We further show that allowing more freedom on the codeword transmission rate enables a larger feasible region of the dual outage constraints by exploiting the tradeoff between reliability and security.