The Effects Of Phase Noise On BER Of QAM Digital Microwave Communication System

The BER (bite error rate) is the most important performance of a communication system. This paper studies how the phase noise of local oscillator in system affects theBER in QAM (quadrature amplitude modulation) digital microwave radio. The paper introduces the concept of phase noise at first, analyzes its creation mechanism. The definitions of phase noise based on all kinds of power spectral density function are studied in detail , and the measuring methods in digital microwave radio system are presented. After discussing the basic theory of digital microwave communication system, the paper analyzes the reasons caused error bits, introduces the concept of residual BER. Based on the project, the paper studies the effect of phase noise on BER. Especially in high order QAM system, like that 16~ 512QAM ,the relationship expression between phase noise and BER is educed. The practical calculation program is writed using EXCEL. Last the paper gives a simulation and analysis the effect of phase noise on BER, taking the SIMULINK of MATLAB as a software platform. The resulting answer indicates that the phase noise will effect the bit error rate performance of a high order QAM digital microwave radio system seriously. In the threshold, phase noise arouses increasing of error bits. In the normal receiving level, phase noise is the most reason of residual BER.