Research On Frequency Calibration Technology Of Low Speed Transmission In Scatter Channel

Firstly, this thesis introduces the principle and transmission characteristics oftroposcatter communication channels, including radiate loss, multi-path fading (fastfading and slow fading), and available bandwidth; and then builds up a troposcatterchannel simulation model basing on theoretical analysis.Usually, phased lock loop(i.e. PLL) and other auxiliary methods are adopted incarrier recovery technology, but its frequency tracking range is seriously restricted,which means it could be easily out of lock. Therefore, PLL is usually not effective forlow bit rate troposphere scatter communication.In order to solve the above problem, a maximum likelihood estimation aboutcarrier frequency error based on CORDIC algorithm and rectifying algorithm arepresented, whose anti-noise performance is simulated completely with Matlab. Thefrequency error estimation and rectifying algorithm is implemented in AlteraEP1C20F324I7, and the test results are presented.It is the first time to achieve dynamic frequency calibration by using such atechnique in a scatter communication system; its realization involves such aspects asfollows: implementation of linear frequency based digital modulation by means ofwaveform storage method, maximum likelihood carrier frequency error estimationbased on CORDIC algorithm, the principle and implementation of digitalfrequency-locked loop, digital comb filter, matching filter and bit synchronizationextraction circuit. At last, the performance of the frequency calibration system is testtedand the result appears to be satisfactory.