Pilots-Based OFDM Channel Estimation Schemes Research And Application

OFDM (orthogonal frequency division multiplexing) is a Parallel transmission scheme of Multi-Carriers Modulation. It transmits information through orthogonal multiple sub-carriers and has high utilization off frequency spectrum, good capability of countering multi-Path interference. It is also adaptive to high-rate data transmission and Multimedia data transmission. This technology has been regarded as the core technology of 4G wireless communications system in the future. Channel estimation is an important part for OFDM systems performing coherent detection. In this thesis, we study channel estimation methods in OFDM systems, then apply them to IEEE 802.16e OFDM downlink systems, seeking estimators with better performance and lower complexity.This paper mainly researches on the channel estimation based on pilots. Firstly, introduces the basic principle and realization of OFDM systems, describes the system construction and system model, discusses some key problems in OFDM systems, summarizes multi-path and time -variety statistic properties of general wireless channel, analysis the properties of channel ,especially Circulate Prefix and Doppler shift's influence to system under different sub-carrier bandwidth. Based on these analyses, the paper investigates principles and performances of the existing channel estimation methods in block-type, comb-type and star-type pilot arrangements. To block-type pilot arrangement, the performance of channel estimation is discussed with least square criterion, minimum mean squared error estimation criterion and mend linear minimum mean squared error estimation criterion; To comb-type pilot arrangement, the paper introduces three interpolation methods including linear interpolation; To star-type pilot arrangement, the paper puts the pilots to the least square criterion to estimate the channel frequency domain response by using different interpolation methods. After that, 802.16e is introduced; software simulation platform is also set up according to parameters defined in protocol. We apply such channel estimation methods as LS,LMMSE and Wiener filter to 802.16e OFDM downlink systems of different symbol modulations and channel coding rates under PB and VA channel models, compare and analyse their block error rate (BLER) performance, then draw some advice.