International Journal of Engineering and Advanced Technology (IJEAT) ISSN: 2249 – 8958, Volume-2 Issue-3, February 2013 26 Published By: Blue Eyes Intelligence Engineering & Sciences Publication Retrieval Number: C0982022313/2013©BEIESP Abstract– This paper investigate and compare the various channel estimation techniques based on pilot arrangement with the communication system that uses QPSK and 16-QAM to transmit information using OFDM over multipath Rayleigh fading channel. Bit Error Rate (BER) has been considered as the performance index in all analysis. In the block type pilot arrangement, the performance of channel estimation is analyzed with three different algorithms: LS, LMMSE and SVD algorithm. In comb type pilot arrangement, the paper introduces three method of interpolation: linear interpolation, second order interpolation and cubic spline interpolation for channel estimation. The analysis has been carried out with simulation studies under MATLAB environment. Index Terms- Channel Estimation, OFDM, Pilot Symbol, Rayleigh Fading channel I. INTRODUCTION For high-volume and high-speed wireless mobile communication systems, Orthogonal Frequency Division Multiplexing (OFDM) is a promising modulation scheme, and will play an increasingly important role in the future development of wireless mobile communication network due to its high data rate transmission capability with high bandwidth efficiency and its robustness to multi-path delay and no Inter Symbol Interference (ISI). It has been used in wireless LAN standards such as American IEEE802.11a and the European equivalent HIPERLAN/2 and in multimedia wireless services such as Japanese Multimedia Mobile Access Communications. The channel estimation plays a very important role in OFDM system. For better performance, dynamic estimation of channel is necessary before the demodulation of OFDM signals since the radio channel is frequency selective and time-varying for wideband mobile communication systems [1]. As a research hotpot, many related algorithms have been presented these years, which can be generally separated into two methods, pilot-based channel estimation and blind channel estimation. Pilot-based channel estimation estimates the channel information by obtaining the impulse response from all sub-carriers by pilot. Compared with blind channel estimation, which uses statistical information of the received Manuscript Received on February, 2013. Sanjay khadagade, Electronics and communication, RGPV/ O.I.S.T./ Bhopal,India. N.K.Mittal, Electronics and communication, RGPV/O.I.S.T./ Bhopal, India. signals, pilot-based channel estimation is a practical and an effective method. The pilot based channel estimation can be performed by either inserting pilot tones into all of the subcarriers of OFDM symbols with a specific period or inserting pilot tones into each OFDM symbol. The first one, block type pilot channel estimation, has been developed under the assumption of slow fading channel. Even with decision feedback equalizer, this assumes that the channel transfer function is not changing very rapidly. The estimation of the channel for this block-type pilot arrangement can be based on Least Square (LS) or Minimum Mean-Square-Error (MMSE). The MMSE estimate has been shown to give 10–15 dB gain in signal-to-noise ratio (SNR) for the same mean square error of channel estimation over LS estimate [2]. In [3], a low-rank approximation is applied to linear MMSE by using the frequency correlation of the channel to eliminate the major drawback of MMSE, which is complexity. The later, the comb-type pilot channel estimation has been introduced to satisfy the need for equalizing when the channel changes even in one OFDM block. The comb-type pilot channel estimation consists of algorithms to estimate the channel at pilot frequencies and to interpolate the channel. MMSE has been shown to perform much better than LS. In [4], the complexity of MMSE is reduced by deriving an optimal low-rank estimator with singular-value decomposition (SVD). The interpolation of the channel for comb-type based channel estimation can depend on linear interpolation, second order interpolation and spline cubic interpolation. In [4], second-order interpolation has been shown to perform better than the linear interpolation. In [5], cubic spline interpolation has been proven to give lower BER compared to second order interpolation. In this paper, our aim is to compare the performance of all of the above schemes by applying 16QAM (16 Quadrature Amplitude Modulation), QPSK (Quadrature Phase Shift Keying), as modulation schemes with multipath Rayleigh fading and Doppler frequency shift channels with Additive White Gaussian Noise (AWGN) as channel models. In Section II, the description of the OFDM transceiver based on pilot channel estimation, channel modal and QPSK, 16QAM is given. In Section III, the estimation of the channel based on block-type pilot arrangement is discussed. In Section IV, the estimation of the channel at pilot frequencies is presented. In Section VI, the simulation environment and results are described. Section VI concludes the paper. Comparison of BER of OFDM System using QPSK and 16QAM over Multipath Rayleigh Fading Channel using Pilot-Based Channel Estimation Sanjay Kumar Khadagade, N.K. Mittal