| In wireless networks, one of the most commonly used techniques for limiting the effectiveness of an opponent's communication is referred to as jamming, in which the legitimate user's signal is deliberately interfered by the adversary. Along with the wide spread of various wireless devices, especially with the advent of user reconfigurable intelligent devices, jamming attack is no longer limited to military applications, but has become an urgent and serious threat to civilian communications as well. Motivated by this observation, in this dissertation, we consider hostile jamming modeling, classification, and spectrally efficient anti-jamming system design and analysis.;First, we investigate the cognitive jamming modeling and classification in wireless communications. Instead of using existing jamming models that assume the jamming remains invariant during the signal transmission period, we focus on time-varying jamming and its classification based on time-frequency analysis and the relative correlation between the signal and the jamming interference: (i) We introduce the general concepts of time-varying jamming coherence time and time-frequency jamming coherence bandwidth, and propose a new jamming classification scheme based on these parameters; (ii) We introduce the concept of disguised jamming, where the jamming is highly correlated with the signal, and has a power level close or equal to the signal power; (iii) Based on time-frequency analysis and approximation theory, we propose algorithms to estimate the time-varying coherence time and the time-frequency coherence bandwidth for both stationary and locally stationary jamming.;Next, we break new ground on anti-jamming system design in wireless networks based on message-driven frequency hopping (MDFH). MDFH is a highly efficient spread spectrum technique that is particularly robust under strong jamming. However, it experiences considerable performance losses under disguised jamming. To overcome this drawback, we propose an anti-jamming MDFH (AJ-MDFH) system. The main idea is to transmit a secure ID sequence along with the information stream. The ID sequence is generated through a cryptographic algorithm using the shared secret between the transmitter and receiver, it is then exploited by the receiver for signal extraction. It is shown that AJ-MDFH can effectively reduce the performance degradation caused by disguised jamming while remains robust under strong jamming. We investigate ID constellation design and its impact on the performance of AJ-MDFH under both noise jamming and disguised jamming. In addition, we extend AJ-MDFH to a multi-carrier scheme, which can increase the system efficiency and jamming resistance significantly through jamming randomization and frequency diversity, and can readily be used as a collision-free multiple access system. Our analysis indicates that: while AJ-MDFH has strong anti-jamming property, its spectral efficiency is very close to that of MDFH, which is several times higher than that of the conventional FH.;Finally, we analyze the capacity of MDFH and AJ-MDFH under disguised jamming using the arbitrarily varying channel (AVC) model. We show that under the worst case disguised jamming, as long as the secure ID sequence is unavailable to jammer (which is ensured by AES), the AVC corresponding to AJ-MDFH is nonsymmetrizable. This implies that the deterministic code capacity of AJ-MDFH with respect to the average probability of error is positive. On the other hand, due to lack of shared randomness, the AVC corresponding to MDFH is symmetric, resulting in zero deterministic code capacity. We further calculate the capacity of AJ-MDFH and show that it converges as the ID constellation size goes to infinity, which echoes with convergence result for the probability of error of AJ-MDFH. We also extend the capacity analysis to multiuser AJ-MDFH system (MC-AJ-MDFH) and show that it outperforms the multiple access scheme for conventional FH (FHMA).;Future research will be conducted on adaptive transceiver design under cognitive jamming scenario. |
