Wireless communications have recently gained much popularity in various commercial applications. Because of the peculiar characteristic of radio channels, the ability for communicators to stand various kinds of interference in the open air is one of the most important issues in wireless communications. The focus of this dissertation is on the analysis and cancellation of narrowband interference (NBI) which is one very detrimental form of interference. To facilitate the analysis of SFH/DPSK under tone interfere, an analytical framework is developed for determination of the probability distribution of a corrupted differential phase. The concept of the phase characteristic function is introduced and its characterizations such as factorization are investigated. Based on it, expressions are derived for the general probability distribution of a received differential phase corrupted by signal tone interference and Gaussian noise under non-fading as well as different fading environments. Furthermore, we also derive the probability distribution of a received differential phase perturbed by multiple tone interference. Subsequently, an extensive analysis of SFH/DPSK is carried out in terms of bit error rate performance given different signalling schemes, fading environments and jamming strategies using band multitone and frequency jitter. Finally, we propose a new technique for rejection of narrowband interference based on multiple symbol detection of coherent or differential phase shift keying. We first show that the direct use of multiple symbol detection offers poor performance when narrowband interference is dominant. Our proposed technique employs a special signalling or coding scheme which is shown to be robust against narrowband interference. Our evaluation of bit error rate shows significant performance improvement in narrowband interference vis-a-vis direct multiple symbol detection. When viewed as a coding scheme, the proposed signalling scheme is significantly simpler for achieving the same coding gain than conventional error correction codes. / Graduate