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Research on Improvement of DSSS Receiver Based on Phase Domain

Author: ZhuKai
Tutor: ShaXueJun
School: Harbin Institute of Technology
Course: Information and Communication Engineering
Keywords: DSSS Fourier transform phase directly dispreading and demodulating
CLC: TN914.42
Type: Master's thesis
Year: 2008
Downloads: 42
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Abstract


According to the classic signal processing theories, signals in the time domain are uniquely specified by the magnitude and phase of their Fourier transform. In the traditional theories of wireless communication, people mainly focuse on the magnitude while usually pay less attention to the phase of a signal in the frequency domain. Recently, as the special qualities of phase frequency funcition are widely applicated in some signal processing fields such as the voice and image processing, people have got a conclusion that usually, phase contains more information than magnitude. Specially, for direct-sequence spread-spectrum signals, no matter the bit of information is ’1’ or ’0’, the magnitude of its Fourier transform will surely be the same. And all the informations need in the judgement of despreading come from its phase equivalently. For the signals with noise into a receiver, the magnitude only contains the information of the noise power in different frequencies. The phase frequency function has a intrinsical property of assembling the narrow-band interferences, that is a arbitrary kind of narrow-band interference, no matter how strong, will only show in the few points in the phase frequency domain and will not interrupt most of the spectrum. For this special property, a DSSS receiver in the frequency domain can be constructed, and its performance is expected to be different with the tranditional receiver.In this paper, a mathematic model describing the interruption in the phase frequency domain caused by the noise is first given. then basic on this model, deduce the distribution of interference in each frequency sample point in white noise. And after this, a best phase frequency domain receiver model for the base band DSSS signals and DS-2PSK signals in mid frequency. that is in the case only the phase is known, the best receiver according to the maximum likelihood probability criteria.According to the simulation of this new kind of receiver, the result shows that in only white noise background, the performence of this phase-frequency-domain receiver is slightly worse than the performence of traditional correlation receivers. And with the SNR descends, the performence of this two receivers is closely near. But when facing the narrow-band interferences they are significantly different, the phase-frequency-domain receiver can well resist the narrow-band interference and it is adaptive. That is the receiver can resist the interference adaptively without the acknowledgement of the strength and frequency, which is same as the conclusions of theoretical analysis.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Communicate > Communication systems ( transmission system) > Frequency hopping spread spectrum communication system > Spread spectrum communication
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