Research On Channel Estimation For Wireless Relay Networks

With the fast development of wireless communication technology, relay technology hasbecome one of the key technologies of the next generation in wireless communication field.Radio relay network can bring to the system diversity gain, improve the information capacityof the system and improve the quality of communications relying on its special networkstructure and communication mode. So relay technology is the hot technology in the future of4G communication era. As a key technology to assist to communication, channel estimationcan help the receiver to extract useful data from the received signal more accurately, reducethe bit error rate and improve the communication quality of the system. At present, althoughthere are many of the researches about relay technology, the researches on relay networkchannel estimation are less, in order to take advantages of the relay technology better. Thetheme of this paper is to research the wireless relay network channel estimation in depth.This paper studies the characteristics of the wireless channels firstly and then analyzesthe various factors in depth, which influence the wireless channel in the wirelesscommunication environment. This paper describes the channel selective decline caused by theDoppler frequency, multipath delay and the different incidence angle of the signal. Based onthis, this paper introduces two wireless channel models in the wireless communication field,one is Rice channel model and the other is Rayleigh channel model. Then this paper analyzeseach model and chooses Rayleigh channel model as the study model.This paper studies the different kinds of wireless relay network, which areAmply-and-Forward, Decode-and-Forward and Demodulate-and-Forward relays. Theresearch of this paper is based on Amply-and-Forward relay network. Then this paperresearches the least square (LS), maximum likelihood (ML) and linear minimum mean squareerror (LMMSE) channel estimations. After researching the shortcomings of traditionalchannel estimations, this paper puts forward the dynamic LMMSE channel estimation anddesign the dynamic LMMSE channel estimator. Compared to traditional channel estimationmethods, the LMMSE channel estimator is able to adapt to the time-varying channelenvironment and estimates the channel more accurately. The simulation results show theeffectiveness of the estimator and the influence of estimator parameters on channelestimation.Finally, this paper expand the relay technology, it combine the relay technology with theorthogonal frequency division multiplexing (OFDM) technology, which is the OFDM relay network. This paper studies the channel of OFDM relay, improves the shortcomings of thetraditional OFDM channel model and puts forward a new kind of channel model applicable toOFDM relay system. Then this paper researches the methods of OFDM relay channelestimation and proposes a new channel estimation method called the OFDM relay LMMSEfrequency channel estimation algorithm based on the time domain correlation of the channel.Simulation results show the effectiveness and accuracy of this method and the influence ofchannel model and Doppler frequency on channel estimation.