Research Of Channel Estimation With Pilot In OFDM System

In wireless communications,high quality and high speed communication services are objectives of communication.OFDM system has high spectral efficiency and the unique ability of confronting frequency selective fading,which is paid more attention to by people.The transmitted signal is attenuated severely by variational wireless channel. In order to demodulate the baseband information correctly, it is important to estimate channel information correctly. So channel estimation is a key technology of wireless communication.There are there channel estimation methods for OFDM system:channel estimation with pilot,semi-blind channel estimation and blind channel estimation,in which channel estimation with pilot is widely used in the actual system.The channel estimation algorithm with pilot was researched mainly. Firstly,the pilot selection and inserted modes were discussed,then channel estimation algorithms were studied,such as least square algorithm,minimum mean square algorithm,singular value decomposition algorithm and transform-domain filtering algorithms,which were used to estimate only sub-carrier channel state of pilot.The interpolation algorithms were studied in order to estimate the sub-carrier channel state of data,such as constant interpolation,linear interpolation,gauss interpolation,and time-domain interpolation algorithm,and so on.A detailed comparison of least square algorithm, minimum mean square algorithm and singular value decomposition algorithm was done by simulation.Meanwhile,various interpolation algorithms were simulated.According to the characteristic of block pilot and comb pilot,joint pilot was brought forward, and simulation results showed that joint pilot could accurately estimate the data channel state near pilot block,could also track the channel changes.The paper focused on the channel estimation algorithm of transform-domain filter. When the pilot information changed fast,then the pilot information could not be concentrated in low frequency region in transform-domain, low pass filter would bring heavy losses of pilot information. In order to moderate changes of pilot information in the transform-domain, the presented algorithm joint interpolation filter and transform- domain filter,simulation results showed that the new algorithm could improve channel estimation performance with little additional complexity.