Research Of Adaptive Modulation Technology On Broadband Wireless Multimedia Communication System

Adaptive modulation technology is one of the crucial techniques for the mobile broadband systems. Its ideal is that modulation mode can be adaptively adjusted by estimating such wireless parameters as fading degree,channel traffic and etc. Channel capacity will achieve a maximum and system performance will be best anytime. By this way,although mobile wireless channel broadband is more and more congesting today,adaptive modulation can be provided preferable spectral efficiency and can be increased the information transmission rate. So the transmission system broadband will be effectively improved. Adaptive modulation technology is based on the rapidly development of computer technology and digital signal processing technology. Studying algorithm and implementation of the adaptive modulation technology have a signification for studying personal communications,satellite communications,multimedia communications,high wireless local area network and metro area network. At the present,wireless LAN and wireless MAN is the most of the wireless communications field in America,Europe and Japan. Following the third-generation mobile communication,it is a high wireless multimedia communication network. It has extensively application foreground. Adaptive modulation technology is one of the key techniques that must be deal with.Adaptive modulation mainly include several problem for example signal shape,channel estimation,all digital receiver and so on. Since the channel referring to adaptive modulation is very hostile in wireless transmission channel,its algorithms and architectures used for the modulation and demodulation should be carefully devised and considered. Designing appropriate algorithms and architectures of the adaptive modulation are main research goal of this paper to meet the need of flat fading channel and selective fading channel.This paper,special research object is the QAM constellation controllable adaptive modulation system,symbol rate and modulation level controllable adaptive modulation system.After introducing the ideals of the slow adaptive modulation and fast adaptive modulation,we demonstrated the need applying adaptive modulation from the aspects of broadband wireless multimedia communications. We have introduced the practice application of the adaptive modulation technology in many protocols nowadays. And we have briefly showed research background and developing trend of the adaptive modulation technology. Afterwards we theoretically analyze and conclude the model of the adaptive modulation system. We find out three kinds of channel model appropriated for actual cannels and draw out pulse response matrix equations. And then facing the problem of the channel estimation of the adaptive modulation system,we conclude out the channel estimation algorithms on maximum likelihood (ML) estimation and maximum a posteriori (MAP) estimation under the condition of flat fading channel and selective fading channel in detail. To meet flat fading channel,we simulate the relationship of the ratio between the error covariance in MAP estimation and ML estimation and pilot symbolmessage length. The conclusion can be drawn from these results. The error covariance can mainly be affected on Doppler spectrum. And considering the practical adaptive modulation,when the value of pilot symbol message length is more than twenty symbol message length,MAP channel estimation is obviously superior to ML channel estimation.Facing the QAM constellation controllable adaptive modulation system,we go deep into the models,frame architecture,the constellation select for star QAM and square QAM,architecture implementation and so on. We elaborate on the slice decision of the square QAM. And we present the simulation result of the slice decision. We mainly stress the channel estimator that effect on the performance of adaptive modulation systems. Utilizing the MAP channel estimated algorithm we draw out from the third chapter,we put forward to the special implementation architecture for the pilot intensive estimator a...