A Demodulation Method for Incoherent Spread Spectrum Communication System

Abstract

The invention discloses a demodulation method for an incoherent spread spectrum communication system and belongs to the technical field of satellite relay communication. The method comprises the following steps of carrying out intermediate frequency down-conversion and low-pass filtering on a receiving signal; carrying out de-spreading on signals after down-conversion by utilizing local pseudo codes; carrying out delay conjugate multiplication on the de-spreading signals and carrying out accumulation operation and modulo operation in one pseudo code period to obtain a pseudo code predicted value; de-spreading through a pseudo code phase and carrying out delay multiplication on a de-spreading value, and carrying out fast Fourier transform on a result to obtain a Doppler frequency estimated value; after the Doppler frequency estimated value is obtained, removing the influence of Doppler frequency shift and utilizing the obtained pseudo code predicted value to carry out de-spreading on the down-conversion signals; constructing two ways of local mobile windows; and adopting the two ways of local mobile windows to search initial phases of data bits to complete bit synchronization. The method is simple to realize and is insensitive to a jump time of a data bit and has accurate and reliable bit synchronization and short capture time, and furthermore, the method is suitable for engineering realization.

Description

technical field [0001] The invention belongs to the technical field of satellite relay communication, and more specifically relates to a demodulation method of a non-coherent spread spectrum communication system. Background technique [0002] The conventional direct spread (direct sequence spread spectrum) communication system currently used is usually a coherent spread spectrum system, that is, the relationship between the spread spectrum code period and the data symbol time width is an integer multiple. The conventional spread spectrum system has a certain processing gain, so that the receiver itself has strong anti-interference ability, and with the increase of the processing gain of the spreading code, the anti-interference ability is also enhanced. However, the conventional spread spectrum system has the defect of relatively weak anti-interception ability in information security. Once the spread spectrum sequence is detected by malicious users, the data symbols of norma...

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Problems solved by technology

[0004] Aiming at the above defects or improvement needs of the prior art, the present invention provides a demodulation method of a non-coherent spread spectrum communication system. Calculate the time-domain correlation between the received signal and the local spreading code, that is, the pseudo code, complete the parallel capture of the pseudo code phase, that is, the synchronization of the spreading code, and use the fast Fourier transform spectrum analysis to complete the estimation and compensation of the Doppler frequency, and then use two channels The local moving window searches for the initial phase of the data bit to complete the bit synchronization, thereby solving the defects of incomplete demodulation scheme and high data symbol miscapture in the non-coherent spread spectrum communication system in the prior art

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