# Secure Communications Over Wireless Broadcast Networks Stability and Utility Maximization

A wireless broadcast network model with secrecy constraints is investigated, in which a source node broadcasts K confidential message flows to K user nodes, with each message intended to be decoded accurately by one user and to be kept secret from all other users (who are thus considered to be eavesdroppers with regard to all other messages but their own). The source maintains a queue for each message flow if it is not served immediately. The channel from the source to the K users is modeled as a fading broadcast channel, and the channel state information is assumed to be known to the source and the corresponding receivers. Two eavesdropping models are considered. For a collaborative eavesdropping model, in which the eavesdroppers exchange their outputs, the secrecy capacity region is obtained, within which each rate vector is achieved by using a time-division scheme and a source power control policy over channel states. A throughput optimal queue-length-based rate scheduling algorithm is further derived that stabilizes all arrival rate vectors contained in the secrecy capacity region. Moreover, the network utility function is maximized via joint design of rate control, rate scheduling, power control, and secure coding. More precisely, a source controls the message arrival rate according to its message queue, the rate scheduling selects a transmission rate based the queue length vector, and the rate vector is achieved by power control and secure coding. These components work jointly to solve the network utility maximization problem. For a noncollaborative eavesdropping model, in which eavesdroppers do not exchange their outputs, an achievable secrecy rate region is derived based on a time-division scheme, and the queue-length-based rate scheduling algorithm and the corresponding power control policy are obtained that stabilize all arrival rate vectors in this region. The network utility maximizing rate control vector is also obtained.