A new frequency offset estimation algorithm for DBO-CSS in multipath channels

In this paper, we propose a new frequency offset estimation algorithm for differentially bi-orthogonal chirp- spread-spectrum (DBO-CSS) which is a standard for wireless personal area network (WPAN). Because of both the long time difference between the samples of differential relations and the high permissible frequency offset and the high permissible frequency offset of the crystal oscillators between the transmitter and the receiver, there can be several integer multiples of 2pi in the phase rotation caused by the frequency offset. The integer part of the phase rotation can not be determined by the usual estimation methods based on auto-correlation. In this paper, we propose an estimation algorithm by using the relationships of each sub-chirp signals to find the integer part without the phase ambiguity. The proposed method is based on the matched filter in order to maximize the received signal-to-noise ratio (SNR) before differential demodulation. As a result, we can estimate the frequency offset without the phase ambiguity and reduce the estimation error in above constant SNR compared with the methods based on the auto-correlation in multipath channels.