Physical layer security of hybrid spread spectrum systems

Physical layer security puts a limit on the information content an eavesdropper can obtain when observing a signal. In hybrid spread spectrum systems, there are two distinct components of the physical layer- the frequency hopping portion and the direct sequence portion, each of which uses different mechanisms to spread the signal in frequency. We examine the ability of an eavesdropper to perform a chip-by-chip attack on hybrid systems, as well as some of the direct sequence components. We offer suggestions for parameters that would increase the physical layer security of hybrid spread spectrum systems.