Acquisition of a Spread Spectrum Signal with Frequency Offset

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In this research, initial acquisition of a Spread Spectrum (SS) signal under large frequency offset is investigated. The following two schemes are proposed and evaluated. The schemes and main results are as follows.1.Divide Matched Filter MethodIn this method, the spreading sequence is divied into a set of sub-sequences and a bank of matched filters, which are corresponding to the sub-sequences, are prepared in the initial acquisition circuit. The circuit then stores the output of the matched filters, and by searching the outputs, it finds the timing, or the phase, of the spreading sequence of the received signal. The results of performance evaluation show that this proposed scheme outperform conventional scheme with a non-divided filter in mean acquisition time under large frequency offset.2. Frequency-Time Domains MethodWhen the frequency offset is very large, even the scheme proposed above can not provide quick synchronization. For this condition, the employment of a set of FFT after the bank of spreading codes with different time-offset is proposed. In this method, the frequency and timing of the received SS signal at the same time. As the results, the advantage of this scheme is shown with the selection of some parameters.