Research On The Technology Of Middle Capacity Communication With A Low Ricean Factor

In this dissertation, the design and hardware emulation is presented in a three-frequency diversity QPSK modem in the Ricean channel. Some important components of this modem are discussed as follows in detail.Through the study about the principles of radio wave's transmitting and the analysis of huge lots of testing data in ground-to-air communication model. The channel can be regarded as a Ricean channel which means a Rayleigh channel with a low Ricean factor. But as a result of the multi-path transmit in the Rayleigh channel, fading and ISI (inter-symbol interference) will occur in the received signals.With an aim at overcoming fading and ISI, the system I structured uses diversity technology and coherent detection technology. It is the first time that a system of modem which using three-frequency diversity QPSK communication technology and coherent detection technology realizes a fading-overcoming ground-to-air communication.The system which will be discussed in detail mainly includes five parts, three-frequency diversity QPSK modulator, coherent detection demodulator, digital feedback reproduction loop, digital comb filter, digital integrated and dump filter. The excellent performances of this system are tested in chapter five .And ultimately ideal results just as my estimation are gotten.