On secrecy capacity per unit cost

The concept of channel capacity per unit cost was introduced by Verdu in 1990 to study the limits of wideband communication. It was shown that an orthogonal coding scheme achieves the channel capacity per unit cost of memoryless stationary channels with a zero-cost input letter. This paper introduces the concept of secrecy capacity per unit cost to study wideband secrecy communications. For degraded memoryless stationary wiretap channels, it is shown that an orthogonal coding scheme achieves the secrecy capacity per unit cost with a zero-cost input letter. For general memoryless stationary wiretap channels, the performance of orthogonal codes is studied and lower and upper bounds on the secrecy capacity per unit cost are provided.