OFDM Channel Estimation Based On Comb Pilot

The development of wireless communication has made great change in people's living. But the present mobile network is designed just for the oral communication and low rate data communication . By the people's requirement in more aspect communication and more high rate data communication the present technology can not satisfy it. So OFDM (orthogonal frequency division multiplexing) as the technology that can support the high rate communication attracts the attention of peoples. Now some communication scientist have done a lot of research in it.The OFDM technology has a history about 40 years. But it's application in high rate double direction data communication is in recent years. Because of the development in the technology it is widely used in the video and audio field .Now it is used in the ADSL(asymmetric digital subscriber line), WLL( wireless local loop)DAB(digital audio broadcast),HDTV(high-definition television), WLAN(wireless local area network).OFDM can also reduce the effect of ISI so it will play a key role in the forth generation wireless communication. The main virtues of OFDM are listed below:1) Because it transform the high rate signal from serial to parallel so the duration of one signal became longer. It also add a cyclic prefix before the signal block . all of these can efficiently reduce the ISI of multipath channel.2) OFDM technology allow the overlap of frequency because of it's orthogonal among it's subcarries . This can increase the utilization rate of the frequency.3) The orthogonal modulation and demodulation is performed by FFT. By the development of DSP technology it is easy to realize.In this paper we will discuss the realization of the channel estimation based on the OFDM base band module. The channel estimation and tracking is realized by transmitting the known pilot signal in given poison of the signal block .For fast varying fading multipath wireless channel ,the change of the channel gains is notgegligible between consecutive OFDM symbols. So if you want to get the get a accurate estimation, pilot subcarries must been placed in every OFDM symbols. Here we use the comb pilot pattern arrangement show in part 3.2. This pilot pattern not only satisfy the channel estimation accuracy but also the channel capacity. In this framework,The traditional approach is divided into two parts: first the LS estimation is obtained over the pilot position. Then the entire estimation is obtained by the interpolation of the estimation of the pilot subcarries. Here according to the character of the multipath channel that each path of it is parametrized by a fast varying amplitude and a constant delay during a large number of OFDM symbols, the estimation presented here is based on the tracking of the delay subspace and it will improve the performance of the estimation of the OFDM channel just need a little more computation complexity. The estimation method in this paper is simulated by Matlab.