Modulation In Multi-mode Digital Communications Radio Despreading Demodulation Module

This article research content is a part of multi-mode software radio transmission broadcasting station. This broadcasting station based on the software radio structure,integtate modulation, spread, demodulation technologies of various different modes, rates of spread in a common platform,it has many modulate and demodulae ways such as DS/DQPSK, DS/FH/DQPSK,DS/D8PSK, DS/OQPSK and so on . On the modulation side, it uses different PN code to spread and divide the voice and data information separately,modulate information which has no correlation on a same frequency carrier wave,and lunch. On the demodulation side, it uses corresponding PN code to match the signal, made a distinction between data and voice information. This allows the radio a big transmit capacity, high utilization of the spectrum, strong antijamming ability, and good confidentiality performance.In chapter 1, first introduced the basic concepts of software radio, characteristics, structure and type of software radio assessment methods.Then brief introduced the principle, type, as well as advantages of spread spectrum communication technology which we adopted.In the second chapter, made a brief summary with pseudo-random code the key element of spread spectrum communication technology.Introduced the characteristics and generate metheds of m sequence, gold sequence, big/small Kasami sequence as well as chaotic sequence.In the third chapter, the pattern and algorithm of modulation, despreading, demodulation of this broadcasting station is given in detail. Mathematical derivation and simulation results with matlab of the key steps are also presented.In the 4th chapter, first discussed the advantage of using FPGA to implement DSP function, then introduced FPGA development tools we used, finally realized the algorithm of modulation, despreading, demodulation mainly with FPGA, presented the simulated waveform in modelsim and actual data waveform data produced by FPGA.In the 5th chapter, introduced entire broadcasting station's each module and overall diagram, introduced the modulation demodulation module hardware design as well as the components we uesd, in detail described the PCB board layout wiring principle and the consideration.In the 6th chapter, physical picture of the whole system, as well as equipment test results were given.In the 7th chapter, a conclusion of the whole paper is drawn, reviewed resolved problems and pointed out the aspect to improve.