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Code Synchronization

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A spread-spectrum receiver requires code synchronization to generate a spreading sequence or frequency-hopping pattern that is synchronized with the received sequence or pattern. After code synchronization, the received and receiver-generated chips or dwell intervals must precisely or nearly coincide. Any misalignment causes the signal amplitude at the demodulator output to fall in accordance with the autocorrelation or partial autocorrelation function. A practical implementation of code synchronization is greatly facilitated by dividing synchronization into two operations: acquisition and tracking. Code acquisition Acquisition provides coarse synchronization by limiting the possible timing offsets of the receiver-generated chips or dwell intervals to a finite number of quantized candidates. Code acquisition is almost always the dominant design issue and most expensive component of a complete spread-spectrum system. Following the code acquisition, code tracking is activated to provide fine synchronization by which synchronization errors are further reduced or at least maintained within certain bounds. Symbol synchronization, which is needed to provide timing pulses for symbol detection to the decoder, is derived from the code-synchronization system. Although the use of precision clocks in both the transmitter and the receiver limits the timing uncertainty of sequences or patterns in the receiver, clock drifts, range uncertainty, and the Doppler shift may cause synchronization problems. The methods of code acquisition and code tracking for both direct-sequence and frequency-hopping systems are presented in this chapter.

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  • DOI: 10.1007/978-3-319-70569-9_4
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Torrieri, D. (2018). Code Synchronization. In: Principles of Spread-Spectrum Communication Systems. Springer, Cham.

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