This paper presents a frequency offset estimation scheme for Orthogonal Frequency Division Multiplex (OFDM) direct conversion receivers. The key idea is to use a differential filter for reduction of DC offset. Frequency offset is estimated in the presence of time-varying DC offset. In order to overcome the varying DC levels under automatic gain control (AGC) circuits, a threshold level is set for the output of the differential filter. The proposed compensation scheme offers superior frequency offset estimation when compared with a conventional scheme with a high pass filter.

In this paper, a new fractional sample rate conversion (SRC) scheme based on a direct insertion/cancellation scheme is proposed. This scheme is suitable for signals that are sampled at a high sample rate and converted to a lower sample rate. The direct insertion/cancellation scheme may achieve low-complexity and lower power consumption as compared to the other SRC techniques. However, the direct insertion/cancellation technique suffers from large aliasing and distortion. The aliasing from an adjacent channel interferes the desired signal and degrades the performance. Therefore, a modified direct insertion/cancellation scheme is proposed in order to realize high performance resampling.