Robert Heaton

OFDM timing synchronisation under multi-path channels

Wireless OFDM signals typically have a prefixed guard interval. The FFT timing synchronisation at the receiver is traditionally based on the peak point of correlation output between the guard interval and its corresponding duplicate at the OFDM symbols tail. This approach does not in general find the optimum timing position for the FFT when the channel contains more than one path. This is particularly true when the first arriving replica of the signal is not the strongest, potentially resulting in the timing position that is outside the acceptable range, causing ISI. In this paper, the OFDM FFT timing synchronisation problem under multi-path channel conditions is studied. Algorithms that produce improved FFT timing synchronisation are developed, which exploit either the channel information obtained, say, through scattered pilots or the characteristics exhibited by combining a modified correlation scheme with a special filtering process. Results from simulation study are presented which have shown a noticeable performance improvement.

A fine frequency and fine sample clock estimation technique for OFDM systems

This paper describes a low complexity method of calculating the estimate of fine frequency offset and fine sample clock offset in an OFDM receiver. Fine frequency offsets of less than one subcarrier spacing, and fine sample clock offsets cause loss of orthogonality in an OFDM receiver, leading to loss of noise margin. The described technique uses a short DFT to estimate frequency error. Since it does not require pilot carriers, it is efficient to implement, it is tolerant of multipath, relatively low in complexity and can achieve comparable performance to other schemes, according to software simulations.

Low-complexity antenna diversity receiver for ISDB-T system

This paper explores two antenna diversity schemes suitable for orthogonal frequency division multiplexing (OFDM) based terrestrial integrated services digital broadcasting (ISDB-T) system. A novel switched antenna diversity scheme and antenna wideband phase combining scheme are proposed for handheld terminal implementation. Computer simulation is used to verify these schemes and methods to improve the two diversity techniques are discussed.