The Research And Implementation Of Channel Estimation For802.16d OFDM System

The standard IEEE802.16d is developed and published by IEEE802.16group to realizethe Broadband Wireless Access(BWA). OFDM(Orthogonal frequency division multiplexing)is one of the key techniques in the IEEE802.16d due to its high spectrum utilization. Thedoppler shift phenomenon will occur on the carrier which is used for modulating signals, thiswill lead to the inter-carrier interference between the sub-carriers in OFDM system. In thiscase,the channel estimation technique has become an integral part of the OFDM system.In this paper, we proposed a new channel estimation algorithm in time-varyingenvironment by using the special preamble and pilot in IEEE802.16d OFDM system. Thisalgorithm include two steps. The first step process is a rough channel estimation based on thepreamble sequence, and the equalization based on the first step of channel estimation canroughly compensate the channel fading in the OFDM system. The second step of channelestimation based on the pilot can track the time-varying characteristics of the wireless channel.This process needs the weighted average processing for the three adjacent OFDM symbols,and this process is used to inhibit the effects of phase noise.Compared with the traditional channel estimation algorithm, the proposed channelestimation algorithm in this paper with low computational complexity and better performancehas obvious advantage, especially in the environment with high Doppler shift(the high speedtrain, for example).In addition,we have implemented the existing channel estimation algorithm for the slowtime-varying channel environment in the hardware. This design include the asynchronousinterface and the algorithm implementation process in the DSP chip. Finally we verify thecorrectness of this design by analyzing the data collected in the hardware.