Study And Implementation Of SNR Estimation And Adaptive Transmission Technique On OFDM System

In the wireless communication,the channel is time varying due to the movement of objects or some other reasons.If the parameter design of the system is based on the worst environment,the channel capacity can not be made full use of when the channel is good;Reversely if the design is based on the best one,the reliability of system may be decreased on account of a bad channel condition. It is a quite important problem to employ limited frequency band resource effectively,when the wireless frequency resource is more and more sparse day and day.How to select the way of adaptive modulation and power allocation efficiently is the key to solving the problem.Our system is based on the technique of Orthogonal frequency division multiplexing(OFDM).It develops from Multi-Carriers Modulation.Each subcarrier corresponds to a separated channel,which provides the foundation for the realization of adaptive transmission technique.Meanwhile,the adaptive algorithm and channel estimation techniques are usually complementary.The more accurate the estimation of channel state information is,the better performance the adaptive transmission technique will play.This article mainly aims on the research and implementation of SNR estimation algorithm and the subband adaptive transmission technique.Firstly,SNR estimation technique is introduced.We discuss some typical algorithms applied both in the environment of AWGN and wireless channel.Then some adaptive modulation techniques used in the single-user OFDM system are discussed.We put emphasis on the analysis of Fischer algorithm.Next,we study the subband adaptive transmission technique.At last, we select Boumard's algorithm and simple block loading algorithm(SBLA) as the basis of the hardware implementation,fmish the design of receiving section in FPGA and construct a simple system based on the subband adaptive transmission technique.Finally, with the reference of wireless local area network protocol standard IEEE 802.11g and the system characteristics of adaptive transmission based on the subband,we improve the implementation scheme about frame format,communication processes and functional modules,which can be treated as the perfect objective for the next-step work.