Abstract
The advent of high data rate (broadband) applications and user mobility into modern wireless communications presents new challenges for synchronization in digital receivers. These include low operating signal-to-noise ratios, wideband channel effects, Doppler effects and local oscillator instabilities. In this thesis, we investigate robust synchronization for DVB-S2 (Digital Video Broadcasting via Satellite) and OFDM (Orthogonal Frequency Division Multiplexing) systems, as these technologies are well-suited for the provision of broadband services in the satellite and terrestrial channels respectively. DVB-S2 systems have a stringent frequency synchronization accuracy requirement and are expected to tolerate large carrier frequency offsets. Consequently, the existing techniques make use of a coarse acquisition and a fine-tracking stage. However, the use of two stages introduces extra synchronization delays. Therefore, we propose an improved technique for DVB-S2 frequency synchronization based on a novel method also proposed for single frequency estimation. The proposed method is single-stage, feed-forward, of practical complexity and has a wide estimation range. Consequently, a significant reduction in synchronization delays and a wider estimation range is achievable for DVB-S2 fixed and mobile systems. On the other hand, OFDM systems are quite sensitive to symbol timing offsets and very sensitive to earner frequency offsets due to orthogonality requirements. The existing techniques for timing and frequency synchronization suffer from various drawbacks in terms of overhead efficiency, computational complexity, accuracy and estimation range. Therefore, in this thesis, we propose two novel low-complexity techniques for timing and time-frequency synchronization in OFDM respectively. Both use only one training symbol with a simple and conventional structure to achieve a similar bit-error-rate (BER) performance to that of an ideal synchronized system and also a wide frequency estimation range. The improvement achieved translates into reduced overhead, higher power efficiency, lower hardware costs and higher reliability in OFDM receivers.