Towards achieving full secrecy rate in wireless networks: A control theoretic approach

In this paper, we consider a single-user secure data communication system. Data packets arriving at the transmitter are enqueued at a data queue to be transmitted to the receiver over a block fading channel, securely from an eavesdropper that listens to the transmitter over another independent block fading channel. We address two separate problems, both of which involve the maximization of a long-term average utility, defined as a function of the number of secure packets transmitted in each time slot. We propose a transmission controller and an admission controller based on simple index policies that do not rely on any prior statistical information on the data arrival process. The former chooses a random key generation (and transmission) rate as well as the secure data transmission rate in each time slot. Part of the data is secured by the available secrecy rate while the other part is encrypted by the key bits, enqueued at both the transmitter and the receiver. The latter chooses the amount of data admitted by the transmitter to be enqueued in the data queue. We show that our controller pair has a provably efficient performance. Also, we illustrate via simulations that the use of a key queue reduces the queuing delay for the data packets, while serving packets that are admitted at the maximum admissible rate. To our best knowledge, this is the first work that addresses the queuing delay in the context of secrecy.