In hostile jamming, the jammer intends to disable the legitimate transmission by saturating the receiver with noise or false information through deliberate radiation of radio signals. Comparing to passive attacks such as unauthorized detection and eavesdropping, hostile jamming is an active attack and is much more destructive. Along with the wide spread of advanced wireless devices, especially with the advent of user configurable intelligent devices, jamming attack is no longer limited to battlefield or military related events, but has become an urgent and serious threat to civilian communications as well.

This project was focused on secure and efficient anti-jamming system design for civilian applications. In communication system design, security is often achieved with a sacrifice on efficiency. Unlike in military applications where rich spectral diversity is generally available, civilian applications are often highly limited in both bandwidth and power. As can be seen, the biggest challenge here lies in how to design secure anti-jamming systems which are robust, reliable and yet possess high spectral and power efficiency. For practical applications, the anti-jamming systems need to be feasible, cost effective, and ideally, can be implemented through smooth upgrades of existing systems. These are the major criterions and guidelines in our study and research on anti-jamming system design.

In this project, we revisited existing jamming patterns, and introduce new jamming patterns. We analyzed the limitations of existing communication systems and anti-jamming techniques. We found  that existing communication systems do not possess sufficient security features and are generally very fragile under disguised jamming. Most communication systems, such as EDGE and OFDM, are designed for efficient and accurate information transmission from the source to destination, and do not have inherent security features. When attacked by disguised jamming, the deterministic capacity of these systems will be reduced to zero. Existing work on anti-jamming system design or jamming mitigation is mainly based on spread spectrum techniques, including CDMA and frequency hopping (FH). Both CDMA and FH systems possess anti-jamming features by exploiting frequency diversity over large spectrum. However, while these systems work reasonably well for voice-centric communication, their security feature and information capacity are far from adequate and acceptable for today’s high speed multimedia wireless services.

We presented a whole family of innovative and feasible anti-jamming techniques, which can strengthen the inherent security of the 3G, 4G and the upcoming 5G systems with minimal and inexpensive changes to the existing CDMA, frequency hopping, TDMA and OFDM schemes. We enhanced the security of CDMA systems through secure scrambling, in addition to its robustness to narrow-band jamming, CDMA with secure scrambling is proved to be secure and efficient under disguised jamming. We developed innovative frequency hopping techniques, known as messagedriven frequency hopping (MDFH), and collision-free frequency hopping (CFFH). In MDFH, part of the encrypted message stream acts as the PN sequence, and transmitted through hopping frequency control. Transmission through hopping frequency control essentially introduces another dimension to the signal space, and the corresponding coding gain can increase the system efficiency by multiple times. On the other hand, CFFH is developed to resolve the self-collision problem in conventional frequency hopping. CFFH can ensure that each user hops in a pseudo-random manner, and different users always transmit on non-overlapping sets of subcarriers. CFFH can be directly applied to any mutliband multiaccess systems to achieve secure and dynamic spectral access control. CFFH is proved to be particulary effective in mitigating partial band jamming and follower jamming. When applied to OFDMA system, the resulted CFFH-OFDM has the same spectral efficiency as the original OFDM system. We developed an innovative secure precoding scheme which can achieve constellation randomization, break the symmetricity between the authorized signal and jamming, and hence achieve secure and efficient transmission under disguised jamming.We applied it to the OFDM system, and come up with the securely precoded OFDM (SP-OFDM). While achieving strong resistance against disguised jamming, SP-OFDM has the same high spectral efficiency as the traditional OFDM system.The innovative techniques developed in this project can serve as benchmarks for the design of next generation secure and efficient wireless communication systems under intentional interference,