Design Of Digital Baseband In Wireless Monitering Network Based On Software Radio

Software radio is a new technique that is used in the development of communication system. It can give the communication system high adapting ability and broad expansibility. TDOA network positioning is a popular positioning system now. For the mass production and miniaturization of mobile station of positioning network, this paper makes a deep research of digital baseband technology based on software radio and gives the design and implementation of some key module.The digital baseband of mobile platform includes transmitting and receiveing modules. Transmitting module uses direct spread spectrum and BPSK modulation technology, and the receive part uses software-based digital frequency down conversion technology to achieve quadrature demodulation.This artical focused on various parts of receiving module, first, detailed the design of nco and cic module in the digital down conversion process, and gave the relization of these module under QUARTUSII using verilogHDL, at the same time, gave the analysis and simlation models of carrier synchronization and symbol synchronization based on nco under the environment of matlab and QUARTUSII, got satisfactory results.Secondly, this paper discussed the key technology of transmiting module, including the generation of PN sequence as well as BPSK modulation, at the same time, introduced the channel decoding technology of POCSAG, and gave the relization of software decoding of BCH(31,21) under QUARTUSII.Finally, this paper analyses the relation between system bit error rate and signal to noise ratio,as well as part of base-band front-end circuit,including the choice of AD-chip and the power supply. And also analyses another popular IF receive scheme based on digital down conversion chip HSP50214B, and gives a simple comparison of the two schemes.