Sub-space Hopped Orthogonal Communication (SHOC)

DARPA wishes to develop an orthogonal communication system that is impervious to interference. This system must provide covert communication capabilities for tactical environments in the L and S bands. To this end, Barron Associates, Inc. (BAI) proposes to investigate Sub-Space Hopped Orthogonal Communication (SHOC). Different orthogonal techniques and wireless standards that are prominent in the L and S RF bands (e.g., IS-95, GSM, IEEE 802.11) allow multiple users to share the same RF resource by subdividing it into sub-spaces according to time, frequency, waveform, polarization, and combinations thereof. Each user operates in their own sub-space, unaffected by other users. With such sub-space based techniques, it is rare that all of the available sub-spaces will be occupied. The unused degrees of freedom comprise a larger sub-space of the RF resource that may be exploited by another, outside user without being subject to interference from (or causing interference to) the original users. BAI will develop and demonstrate a technique for covert wireless communication within the unoccupied sub-space of an existing orthogonal communication system. SHOC uses a detection step to determine the vacant sub-space of an existing communication system, then communicates covertly by hopping over (time-varying) basis functions spanning the unoccupied sub-space.