A Research And Application Of Adaptive Equalizer On High-speed Troposcatter Communication

In recent years,high speed transmission has become an important direction in the development of troposcatter communication.It will generate inter symbol interference(ISI)because of the multipath effect existing in the scattering channel,and simultaneously due to its limited bandwidth and nonideal response.Severe ISI will bring performance degradation,and even to the extent that communication system cannot work normally.Accordingly,eliminating ISI influence is the critical and difficult point in high speed troposcatter communication.In general,we can adopt adaptive equalization technique in receiving terminal to achieve this aim.Adaptive equalizer can enhance the adaptability of communication equipment,effectively eliminate ISI effect and reduce cost.In this thesis,on the basis of researching the troposcatter channel characteristics,it analyzes and simulates several kinds of equalizer structure,then elaborates the LMS algorithm which is one of adaptive equalization algorithms,especially the relationship between convergence characteristics and step length u.According to the feature of scatter communication,it proposes a digital interpolation timing algorithm;moreover,it realizes 34Mbps digital QPSK modem using large capacity FPGA.The major research contents include:1.Discrete time channel model used in describing multipath effect is introduced.Based on this channel model,firstly it conducts theoretical analysis by formula derivation on these two equalizer,then through simulation by matlab,compares their performance;finally,it discusses the steady-state and convergence characteristics of LMS algorithm.2.It analyzes and simulates the output mean square error performance of fractionally spaced equalizer and integer spaced equalizer in the condition of existing timing deviation,then through studying center tap tracking algorithm which is a conventional timing extraction combined with equalization algorithm,it derives and discusses its characteristics of phase error adjustment function.Considering traditional center tap tracking algorithm needs the support of external hardware,it proposes a digital interpolation timing algorithm in this thesis.3.It introduces the hardware implementation block diagram of 34Mbps troposcatter modem,and also points out its critical technique.Meanwhile,it provides performance testing result of this modem,which includes the two different channel condition of Gauss white noise and multipath channels,besides,it measures the system timing synchronization.