Concurrent Code Spread Spectrum: Theory and Performance Analysis of Jam Resistant Communication Without Shared Secrets

As commercial and military reliance on wireless communications grows, jam resistance becomes increasingly important. Jam resistance in omnidirectional radio communications relies on spread spectrum techniques that employ symmetric keys (i.e., shared secrets). Key management is a challenging problem in scaling up critical networks such as the Global Information Grid (GIG). While alternatives to symmetric keys utilizing asymmetric cryptography and a Public Key Infrastructure (PKI) exist for the Traffic Encryption Keys (TEK) used to encrypt, decrypt, and authenticate transmissions, the same cannot be said for the Transmission Security Keys (TSK) that protect the waveform from hostile jamming.;An unstated, but widespread, assumption exists that spread spectrum systems require symmetric keys to achieve jam resistance. While such shared-secret schemes are workable in small networks, the scale and nature of theater-wide, mobile, ad hoc wireless networks will quickly overwhelm any practical key management strategy. The problem could be alleviated if an asymmetric system for the physical layer were developed, but little attention has been directed at this problem and no such solution exists. Making matters worse is that public-access systems---such as the civilian side of the Global Positioning System (GPS)---preclude reliance on secret keys since every person is an authorized user. Yet while these systems are recognized as having little to no jam resistance, they are becoming increasingly critical to activities such as civilian aviation operations.;Presented here is a new form of spread spectrum based on a new coding theory---the theory of concurrent codes---that permits the construction of jam-resistant physical layers that not only do not rely on shared secret keys, but rely on no keys at all. One particular unkeyed concurrent algorithm, the BBC algorithm, is explored in depth. Then the performance of BBC pulse-based concurrent code spread spectrum (CCSS) is also analyzed for the case of additive white Gaussian noise (AWGN) barrage jamming and compared to similar frequency hop (FHSS) and direct sequence (DSSS) systems. Finally, prototype systems that demonstrate the capabilities of concurrent codecs using audio, image, and radio frequency transmission channels will be discussed.