Coherent spread spectrum communication system

Abstract

The invention discloses a coherent spread spectrum communication system. The system is composed of a spread spectrum transmitter and a spread spectrum receiver. The spread spectrum transmitter uses an orthogonal spread spectrum code to modulate a data code. Another orthogonal spread spectrum code is further added. Baseband signals after the addition are modulated to a medium-frequency carrier wave and further radiated out through an up-conversion channel and a transmitting antenna. The spread spectrum receiver uses an antenna to receive a radiofrequency signal which undergoes down conversion through a down conversion channel and is converted into a medium frequency one. The medium-frequency signal passes through two matching filters. The impulse responses of the two matching filters are respectively the arithmetic products of the opposite sequence of each orthogonal spread spectrum code and the medium-frequency carrier wave. After output signals of the two filters are multiplied, the signals then pass through a low pass filter. Absolute value taking operations and symbol taking operations are respectively performed on an output signal of the low pass filter. An absolute value taking operation output signal undergoes threshold decision. When a threshold value is exceeded, it shows that a pseudo code is captured. A symbol taking operation output signal is then a data signal after a demodulation process.

Description

technical field [0001] The invention belongs to the technical field of spread spectrum communication, and in particular relates to a coherent spread spectrum communication system. Background technique [0002] Direct Sequence Spread Spectrum (DSSS) communication is a communication technology that uses spreading codes to broaden the spectrum of the transmitted data signal so that the bandwidth it occupies is much larger than the bandwidth required to transmit information. Direct-sequence spread spectrum communication has strong anti-interference ability, less interference to other communication systems, difficult to intercept, and multiple access multiplexing, etc. It is widely used in mobile communication, satellite communication, electronic countermeasures and other fields. [0003] In a spread spectrum communication system, in order to demodulate the data, the receiver usually needs two tracking loops, namely the code synchronization loop and the carrier tracking loop, so ...

AI Technical Summary

Problems solved by technology

When the code synchronization loop and the carrier tracking loop are out of lock, the spread spectrum communication system cannot work normally

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