Method for simulating frequency dynamic of radio frequency signal at intermediate frequency by using two DDSs

Abstract

The invention relates to a method for simulating the frequency dynamic of a radio frequency signal at an intermediate frequency by using two direct digital synthesizers (DDSs). The method comprises the following steps of: simplifying the Doppler frequency characteristics of a pseudo code and a carrier in a satellite transmitted signal to form a linear proportional relationship between the output signal frequency of a first DDS for producing a clock signal of a code clock of the pseudo code and the output signal frequency of a second DDS for producing a clock signal of a modulated carrier; performing synchronization control on the output signal frequency of the first DDS and the output signal frequency of the second DDS through frequency control words to dynamically simulate the frequency Doppler of the code clock of the pseudo code and the carrier of an application object; sending an output signal of the first DDS to a spread spectrum transmitter to produce a transmitted pseudo code, and performing spread spectrum modulation on information data by using the transmitted pseudo code to acquire a baseband spread spectrum signal; performing frequency multiplication on an output signalof the second DDS to produce an intermediate frequency carrier signal; and directly modulating the baseband spread spectrum signal by using the intermediate frequency carrier signal to acquire an intermediate frequency signal which contains the required pseudo code and carrier frequency dynamic.

Description

technical field [0001] The invention belongs to the field of aerospace measurement and control communication, and relates to a method for simultaneously simulating a pseudo-code code clock and a carrier Doppler frequency deviation by using double DDS. Background technique [0002] The important equipment of the aerospace measurement and control communication system based on spread spectrum technology is the intermediate frequency digital receiver. The radio frequency signal of the satellite is received by the antenna, passed through the low-noise preamplifier, and the local oscillator signal synthesized by the local oscillator is down-converted to an intermediate frequency. After the frequency mixing process, the Doppler frequency offset and pseudo code information of the signal are retained, but the carrier frequency is reduced, and the Doppler frequency offset is still based on the Doppler frequency offset on the original radio frequency signal. The intermediate frequency...

AI Technical Summary

Problems solved by technology

The frequency of the intermediate frequency signal and the pseudo code rate in this device are fixed values, and it is impossible to flexibly generate pseudo code signals and intermediate frequency modulation signals of other frequencies, and it is also impossible to simulate the frequency dynamics of any RF frequency / pseudo code rate combination conditions of the application object

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