We prefer OFDM technique to achieve high data rates in mobile environment. The task of estimating the frequency response of the radio channel which the transmitted signal travels before reaching the receiver antenna is known as Channel Estimation. A dynamic estimation of channel is necessary before the demodulation of OFDM signals since the radio channel is frequency selective and time-variant for wideband mobile communication systems. In this article the channel estimation techniques for OFDM systems based on pilot arrangements are investigated. The channel estimation based on comb type pilot arrangement is studied through different algorithms for both estimating channel at pilot frequencies and interpolating the channel. The estimation of channel at pilot frequencies is based on LS and LMS while the channel interpolation is linear interpolation, second order interpolation, low-pass interpolation, spline cubic interpolation, and time domain interpolation. Time-domain interpolation [18] is obtained by passing to time domain through IDFT, zero padding and going back to frequency domain through DFT. In addition, the channel estimation based on block type pilot arrangement is performed by sending pilots at every sub-channel and using this estimation for a specific number of symbols like BPSK, QPSK and 16 QAM has been carried out. The Performance comparison of all schemes by measuring bit error rate using different modulation techniques like 16QAM, QPSK, and BPSK has been discussed. Simulation results shows that comb-type pilot based channel estimation with DFT interpolation [16] performs the best among all other comb based channel estimation algorithms. This is again expected since the comb type channel estimation allows the tracking of fast fading channels and low pass interpolation does the interpolation in such a way that mean square error is minimized. For fast varying channels, performance of comb arrangement with low pass interpolation is much better than other. It has been concluded that block type of arrangement performs better when the channel is changing slowly and the comb type channel estimation allows the tracking of fast fading channels.

Author Name: Keshav Kumar, Amit Grover

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Keywords: IJSER,2229-5518,22295518,Keshav Kumar, Amit Grover

ISSN: 22295518

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