The Research And Implementation Of Channel Estimation Based On OFDM Systems

Wireless communication technology is one of the most vibrant fields in scientific researches,it breaks the restriction of the physical aspects in wired communication.Thus,everyone can communicate with others all hours in areas where radio could be radiated,it brings greatly expands of communication on the temporal and spatial scales.Channel estimation,as a key technology in wireless communication,has been required more and more demanding since a huge increase of data volume and faster transmission speed in the communication systems.The main content of this paper is to study how the performing is within different pilot patterns or different channel estimation algorithms,then puts emphasis on building up a channel estimation platform for OFDM base band system which bases on Field Programmable Gate Array with a selected low complexity algorithm.Firstly this paper describes the background and current situation of the research.Brief analysis on the property of fading channel in the wireless mobile communication system,including large-scale fading and small-scale fading channel.The two commonly using channel models are analyzed by mathematics,they are model and complex exponential basis expansion model.In this paper,the channel estimation algorithm based on computer simulation is described performance of LS,DFT and MMSE channel estimation algorithm.In addition,three pilot patterns,such as block,comb and diamond,are analyzed to compare the performance of channel estimation under different speeds.Another focus on this paper is the implementation of channel estimation is based on FPGA.LS channel estimation algorithm and linear interpolation are adopted for its better performance and lower complexity.Compared to the most of Base-band processing as the FPGA DSP architecture,the implementation of channel estimation algorithm in this paper that using FPGA instead of DSP can reduce the efficiency of the two data communication and design difficulty.The design based on FPGA has the advantage of variable estimation in the paper,for example,it could change pilot patterns above three and satisfy interval with both time domain and frequency domain for different moving scene.The study mainly focuses on the basic framework of OFDM system.The first chapter describes the background and current situation of research briefly.In the second chapter,we mainly discuss the characteristics of wireless channel and the common wireless channel model.And then we explore Jakes model and CE-BEM model briefly.In the third chapter,we start with our analysis on the principle of OFDM system,and then we research the pilot pattern and discuss different applicability.It is discovered that the comb pilot is the most suitable for high speed mobile environment while the grid pilot has higher spectrum efficiency.The influence of the pilot interval within diamond pilot pattern on the performance of channel estimation is also involved in this research.Based on the above chapters,the fourth chapter aims at implementation of channel estimation based on LS and linear interpolation.In the design scheme,it is given the design idea of the top level file and timing planning.Then we discuss the design principles and waveform simulation of each module.It is variable of system' s parameter,users could define the system's parameter they want,such as CP length,the first position of pilot,pilot number,time-frequency interval if pilot and so on.It has good portability and universal applicability.