扩频通信系统毕业论文

Abstract: Since wide frequency correspondence concept starts maturely after the 50s, hereafter more than 20 year wide frequency communication still obtained the very big development, but is only the partial development, like hardware's improvement and application domain development. yizhi dao the early 80s, the wide frequency correspondence's concept was only obtains the application in the military channels, this kind of condition to only then obtained the change in the mid-80s. The spread spectrum technology develops the present, the CDMA technology becomes in the present spread spectrum technology to study most objects, the civil correspondence's direct sequence spread spectrum technology applies widely. the m sequence, the Gold code, the WalSh code and the OVSF code are in the wide frequency communications system the commonly used several kind of wide frequency sequence, the Walsh code use in the edma2000 system, but the OVSF code is the use in W-CDMA and in the TD-SCDMA system. but in the 3G mainstream standard, China proposed the TD-SCDMA standard has the huge domestic market. And, the TD-SCDMA wide frequency communications system has strong anti-characteristics and so on jamming, mitigation disturbance, anti-multi-diameter disturbance ability and information hiding, multiple access privacy communication. Present paper's goal is makes the wide frequency sequence by the OVSF code to realize one based on the MATLAB TD-SCDMA direct sequence spread spectrum communications system wide frequency part. This goal realizes involves the wide frequency communications system's related knowledge, the key point is the OVSF code generator, harasses the code generator as well as the root rises the cosine to roll falls filter's realization. the present paper has completed the following prime task:①Data Canada harasses as well as the string/and transforms this design uses Xie Raoshi does not need complex synchronized self-synchronizing Canada to harass the technology, the scrambler by the fifth-order linear feedback shift register constitution. Carries on the string the data signal and transforms.②Differential coding the differential coding causes the PSK signal to turn the DPSK signal, overcomes “the phase ambiguity” the question. The differential coding plan is decided in the modulation system is BPSK or QPSK. When selects the BPSK method, the code operation is quite simple: Outputs bit(k) by to input bit(k) different or outputs bit (k l) to obtain; When selects the QpSK method, because four kind of possibility's preceding output states and four kind of possibility's current input state may determine 16 kind of output states, therefore the difference interpretative version compared to uses BPSK complex many.③The frequency spectrum expansion as well as the pulse take shape this design to select the autocorrelation characteristic very good OVSF code achievement wide frequency code, carries on mold two Canada after the OVSF code and the code output data to realize the wide frequency modulation. To suit the request which transmits in the channel, after needs to undergo the wave shaping, reduces the frequency band, reduces the intersymbol interference, simultaneously causes the signal energy to be more centralized, enhancement signal-to-noise ratio. This design uses one to roll step-down ratio a= the root to rise the cosine FIR digit filter to complete the I/Q road signal the formation, escorts to the exterior modulator after the formation I/Q road data as the baseband processor transmitting end's output data to carry on the next step processing.④TD-SCDMA direct sequence spread spectrum communications system wide frequency part's system simulation compiles TD-SCDMA the direct sequence spread spectrum communications system wide frequency part the MATLAB procedure, and carries on the MATLAB simulation, obtains the TD-SCDMA direct sequence spread spectrum communications system wide frequency part simulation profile and a= root rises the cosine to roll falls filter's phase response and the frequency response simulation profile, has carried on the corresponding simulation analysis to the simulation profile. key word: OVSF; Direct sequence spread spectrum; TD-SCDMA; MATLAB