Theoretical Research And Algorithm Realization Of Delay Spread Estimation And Channel Estimation In OFDM Systems

In wireless digital mobile communication, Inter-Symbol Interference (ISI) caused by time disperse of radio channel is one of main factors that limit bandwidth of communicated information and system performance of communication. In receiver, Orthogonal Frequency Division Multiplexing (OFDM) system can easily cancel ISI and equalize frequency-selective fading that are both caused by time disperse of radio channel. It is also adaptive to high-rate data transmission and multimedia data transmission. For this, This technology has been regarded as the core technology of 4G wireless communications system in the future.Channel estimation is one of research hotspot, and many related algorithms are presented these years all over the world. Channel estimation based on pilot-aided can obtains the channel impulse response for all subcarriers by pilot subcarrier. It can tracks the variety of channel, and obtain high accuracy with low complexity. So it's a practical channel estimation method. The conventional channel estimator in OFDM system was designed to cope with the worst-case channel condition, thus performance degradation can be induced due to the imperfect channel estimation. The new generation of OFDM system must have the estimator for the channel status, in order to select the near optimal algorithm and interpolation coefficients for different channel conditions in different wireless transmission environments. Channel parameters detecting methods including maximum multi-path delay and Doppler frequency based on the time and frequency correlation functions were proposed.The time spread estimation as a basic parameter in the parameter estimation is a fundamental problem in wireless mobile communications; this estimation method has a wide range of applications. This paper mainly researches on the time spread estimation based on pilot-aided, summarizes multi-Path and time-variety statistic properties of general wireless channel. We have analyzed the relationship between delay spread and Cyclic Prefix (CP), the number of pilot in OFDM system.The two-dimensional pilot pattern is a unique model of the OFDM system, the proposed algorithms in this paper estimate the power delay profile (PDP), which utilize the frequency-domain correlation of pilot. According to the PDP, the two important dispersion parameters, namely root-mean-squared (RMS) delay spread and maximum excess delay of the channel, are estimated. At last we can real time track the channel parameters and adaptive adjust them in OFDM system. Simulation shows that we can obtain the approximately statistical information of channel model's delay parameters. Adaptive channel estimation algorithm can also improve the transmission efficiency and achieve the optimization for system redundancy information.