Communication over fading channels with frequency offsets

Abstract

Mobile communication systems are usually maligned by the presence of Doppler frequencies as there exists a relative motion between the tranmitter and the receiver. Modulation schemes that have potential immunity to frequency offsets have been a topic of interest since the development of mobile technology. Double differential phase shift keying (DDPSK) is one among such schemes and has the advantage of being simple. In this thesis, DDPSK is analyzed over fading channels taking into effect the presence of frequency offsets, as fading and Doppler frequencies characterize a mobile channel. Though the scheme is simple, analysis show that the performance of DDPSK is poor when compared to the conventional differential phase shift keying (DPSK). In order to overcome this shortcoming, a receiver structure has been proposed in the present work. By utilizing the proposed receiver model, it has been found that the probability of error obtained is less than that of the conventional DPSK. All analytical results showed good agreement with the Monte-Carlo simulations.