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Abstract

A carrier signal acquisition technique is disclosed that improves the reliability of the generated carrier frequency offset. An improved course carrier frequency offset algorithm is employed in conjunction with a conventional fine carrier frequency offset algorithm. The course carrier frequency offset algorithm associated with the present invention estimates large offsets that are multiples of the carrier spacing that may occur at system startup. A spectral null is placed in the center of the transmit spectrum and is thereafter located in a received signal. The position of the spectral null provides an estimate of the local oscillator carrier offset. A frequency finite state machine (FSM) is disclosed that processes a number of metrics to ensure the reliability of the course carrier frequency offset and of transitions between acquisition and tracking modes. The frequency FSM will utilize the frequency offset (modin) generated by a MODSC algorithm provided one or more predefined thresholds are satisfied. A first metric value, c2adj, is the normalized ratio of average power (excluding null carrier power) of carriers to the null carrier power. A second metric, p2av, is the normalized ratio of average power (excluding minimum carrier power) of carriers to the minimum carrier power. If the average difference of the ratios of the powers of the carriers (p2av and c2adj) is less than a predefined threshold, then frequency acquisition is completed. Similarly, while in tracking mode, if the differences are consistently greater than the threshold, then loss of track is achieved and the frequency FSM process will switch operation to the acquisition mode.

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First Claim