Diversity Receivers in a Fast Fading Multipath Channel

摘要

Some radio channels are fast fading in the sense that they are randomly time-variant and the Doppler spread is in the order of or larger than the symbol rate of the digital signal. Such channels can be found in land-mobile, aircraft, and satellite communications, especially when the symbol rate is small, the velocity of the mobile station is large, and the carrier frequency is large. With small symbol rates, a Doppler barrier exists, below which the complexity of the optimal receiver is increased. The Doppler barrier is the time-frequency dual of the ISI barrier with large symbol rates. In the thesis, the history of digital communications in fading multipath channels is first summarized. The ML sequence detector, consisting of a correlator and an estimator, is derived in a WSSUS fast Rayleigh fading channel. In the system model, each symbol is divided into several short segments and ideal symbol synchronization is assumed.