Method and apparatus for partial and course frequency offset estimation in a digital audio broadcasting (DAB) system

Abstract

A method and apparatus are disclosed for frequency offset estimation in a hybrid in-band on-channel (HIBOC) digital audio broadcasting (DAB) system. The frequency offset estimation algorithm first determines the coarse frequency offset, in terms of integer number of OFDM bin separations between an actual and measured location of a correlated peak, followed by estimation and tracking of the partial (residual) offset in a continuous fashion. A frame is correlated at a first frequency, and then the frequency is shifted by a predefined amount, such as half of the inter-bin frequency amount, Δf, before correlating again. The measurement with the highest peak of the plurality of frequency values is utilized to obtain the course frequency offset estimate. The partial frequency offset estimation algorithm utilizes phase information contained in reference frequency points in the frequency domain. The phase rotation of the reference vector is proportional to the frequency error, and the frequency error is extracted and filtered in the time domain. The initial partial frequency offset estimation is corrected and used for continuous frequency tracking. Following the course frequency offset estimation, the unmodulated pilot bins (and all other bins), are within at least half the of the OFDM bin separation. In the presence of a frequency offset, the complex bins start rotating. The rate of the rotation is a function of the extent of the partial frequency offset. The change in phase from one frame to the next is proportional to the rate of rotation, and the sign of the rotation indicates the direction of the shift.

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