Committee: 

Dr. Bloch, Advisor        

Dr. Barry, Chair

Dr. Weitnauer

Abstract:

The objective of the proposed research is to characterize the maximum rate at which information can be transmitted reliably to a legitimate receiver over certain multi-user channels while simultaneously escaping detection from an adversary. Specifically, we investigate the fundamental limits of covert communication over two channel models — a K-user discrete memoryless multiple-access channel (MAC) and a discrete memoryless broadcast channel. In the first channel model, we characterize the covert capacity region and show that, asymptotically, all sum-rate constraints are inactive unlike the traditional MAC capacity region. In the second channel model, we embed covert messages in an innocuous codebook and identify the exact asymptotic behavior of the number of reliable and covert bits when the rate of the innocuous codebook is close to the channel capacity of the adversary. In both models, we observe that the covert throughput is subject to the square-root law.