Design Of CDMA Multiple Access Code On FPGA And Implementation Of Up-conversion Module

Distributed measurement system is widely used in environmental monitoring, earthquake prediction and so on. Distributed measurement system control many factors such as transmission rate,transmission range, safety and reliability, between the control center and the test nodes directly determine whether the system can adapt to the complex work environment. In view of the above problems, this paper design a CDMA RF front-end analog up-conversion module. The module can improve the reliability of data transmission, increase the speed of data transmission, and broaden the scope of data transmission.All of this will make the distributed measurement system widely used in every complex test environment.It analyses principle of CDMA in this paper and proposed a scheme of IF analog up-conversion based on double IF mixing. It introduces the main parameters, technology indexes and realization method, it designs CDMA multiple access code module based on FPGA and the mixing module based on PLL technology.In CDMA multiple access code module, it discusses what the ideal spread spectrum code and address code should be. Moreover, m sequence and Walsh sequence is chosen respectively as the spread spectrum code and address code, and then it generates m sequence and Walsh sequence, codes and decodes based on FPGA. Finally, the scheme will be verified feasible though Modelsim and the hardware, experiments show that all parameters achieve16.In up conversion module, it designs mixing circuit on ADF4106and HMC175MS8. Test shows that the frequency point of oscillator circuit is2.4GHz, phase noise achieves <-90dBc/Hz@10KHz, and the whole circuit has low phase noise and wide-band characteristics, which is applicable to use in wireless communication part of distributed measurement system.