Correcting carrier wave frequency shift in direct sequence band spread communication system

摘要

Received signals are matched with a spread code whose middle frequency is present in whole number multiples of the reciprocal value of the period for the code. The matched results are then scanned to search for the value with the highest amplitude in order to obtain the whole number part of the carrier wave frequency shift, which will be a whole number multiple of the reciprocal value for the period in the code. A directional flag is determined by comparing the searched value with the earlier value and the value with the closest match. A phase angle difference is calculated between two successive matched values in accordance with the flag, and this difference is used to calculate the fraction part of the frequency shift. Finally, both the whole number and fraction parts of the frequency shift are corrected. Independent claims are also included for (a) the above correction method, including an additional step for correcting the time shift in the spread code using the amplitudes from the matched values, and (b) a receiver for a direct sequence band spread communication system, which utilises this carrier wave frequency shift correction method.