Design And Research On Digital Speech Communication System Under The Strong Interference

The strong noise would destroy the integrity and effectiveness of thespeech signal, and may even seriously reduce the performance of the speechcommunication system, and destroy the quality of the voice call. Therefore, the moreeffective and reliable speech communication in high noise, high electromagneticinterference, high-risk operation zone environment (such as: mines, civilian blastingspaceport and so on), the greater need for effective anti-interference, denoise digitalcommunication technology to extract the available speech signal from the noiseenvironments.In harsh transmission environments such as mines where has serious noiseinterference, and old transmission line, and also the wireless communicationtransmission could not be realized normally. This paper combine the effectiveanti-jamming technologies with making full use of the existing transmission line andsaving the economic point to achieve designing and researching on the effectivecommunication in the strong interference environment. The PCM(Paulse-codemodulation) transmission technology as for the high-speed speech signaltransmission rate, and the characteristics of nonlinear quantization, can improve thespeech signal noise rate effectively is used in this paper. The DPSK modulation anddemodulation technology, which have relative advantage in the anti-interferenceability, as well as the FIR filter and adaptive filter technology which especially in thegetting rid of the noise interference are been used in the paper. Somesynchronization techniques (such as bit synchronization, frame synchronization) andTime division multiplexing technology are added into the PCM transmission systemto ensure the reliability and validity of the digital speech signal transmission,meanwhile each technique is been realized as a separate circuit module in this paper.The Digital Signal Processor (DSP) and FPGA technology which are high-speed andvalidity are taken to assist to accomplish some modules in this paper, in order toimprove the low reliability and reduce the large power consumption during the logicgate circuit. The frame synchronization signal of the receiving part is finished with the QuartusⅡsoftware platform,by the description mode of graphics and text, andalso it is implemented by loading into the FPGA(Field－Programmable Gate Array)chip(EPM7128SLC84) in this paper.Meanwhile for the strong background noise andconstant frequency interference noise in the strong interference environment of thispaper, the MATLAB software is taken to aid design to determine the optimalparameter of the filter and also to verify the performance of the filter, finally the80-order FIR low pass filter is finished in the DSP(TMS320C5509) hardwareplatform to filter out the high-frequency and interference signal mixed in thevoice.Then the performance of the fixed step LMS algorithm adaptive filter and thevariable step LMS algorithm adaptive filter based on the sample function arecompared by the MATLAB software platform and DSP platform.The variable stepLMS algorithm adaptive noise canceller based on the sample function with the betterdenoise ability and voice-enhance ability completed by the DSP platform is taken asthe last noise reduction module to extract the available signal and enhance the voicesignal in the paper.Finally, considering saving the hardware resources and economiccost, the converter circuit of two-four line is realized in the platform of DSP.The idea of software simulation and hardware design is taken to implement thedesign of digital speech communication system under strong interferenceenvironment in this paper, and also the performance of some modules is realized byoptimal researching. The final simulation test result shows that the system designedin this paper meets the expected goals.The actual test result shows that individualindicator of the system designed in the paper improved slightly than some exsistingcommunication equipments’.