Study On The Key Techniques Of Spread Spectrum Transmission About Multimedia

Spread spectrum communication is an excellent system, the transmission of multimedia will be necessary in the development of mobile communication. The multimedia spread spectrum transmission will be realized in the third generation mobile communication system. The mobile multimedia communication system need to support the transmission of high-speed data and variable speed data compared with the ordinary spread spectrum communication. The data rate ranges from several Kbps to hundred Kbps for wide up to 2Mbps.In order to assure different data rate to transmission in the same spread spectrum bandwidth, we need to use different lengths and orthogonal PN codes. The lengths , numbers and orthogonality of the PN codes are important technologies.In the thesis we analyze the methods of spread spectrum transmission of WCDMA. Two multi-rate transmission schemes are discussed and compared. And in OVSF-CDMA transmission scheme, we analyze the relationship of high velocity and low velocity users.WCDMA use OVSF code as channel spread spectrum code. OVSF play an important role in. WCDMA which offers flexible traffics. In the up link of WCDMA the spread factor ranges from 4-256 and ranges from 4-512 in the down link of WCDMA. OVSF code is important resource, we need to assign them rightly and efficiently. We study the assignment of OVSF code in the downlink of WCDMAJn order to assure the real time traffic, the dynamic allocation method based on priority is proposed and simulated.In the end we compare the two key technologies of the multimedia transmission. The conclusion indicates the adaptive rate technologies are better than adaptive power technologies on some issues.