Key Technologies Of Broadband Data Transmission Modem

With the more and more demand for the data transmission, wideband wirelss access has been the access technique that is developing the most quickly now. Making full use of the frequency resource, choosing high-efficient modulation mode and transmiting data at higher rate, are all the key techniques .This paper investigated several key problems of modulation and demodulation. It investigated two important modulation model, then a wireless data transmission scheme was presented on the basis of studying the data transmission of radar system. And the main scheme was presented for digital modulation on intermediate frequency for data rate as high as 20 Mbps. In this scheme, a wideband programmable modulator-HSP50415 was used to support quadrature modulation , and a SCM was utilized for control. On the basal theory of piont to piont communication, the design of shaping FIR filters was studied , and the parameters which suit this scheme and can make the system performance optimization were gained through simulation. Then this paper introduced the techniques on carrier synchronization and symbol synchronization which were commomly used in the process of demodulation. Finally , this paper introduced two representative algorithms for symbol timing recovery in digital synchronous data receivers , and two methods to improve the accuracy of estimated data were investigated. It could be seen that the two methods were effective.