Comparison and Analysis of Channel Estimation Algorithms in Ofdm Systems
Comparison And Analysis Of Channel Estimation Algorithms In OFDM Systems
Vineetha Mathai
Dept. of Electronics Engineering, Madras Institute of Technology, Chennai-600044, India. e-mail: vineethamathai@yahoo.in
Abstract—The channel estimation can be performed for analyzing effect of channel on signal 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 block type pilot channel estimation has been developed under the assumption of slow fading channel. When the data is transmitted at high bit rates, the channel impulse response can extend over many symbol periods, it leads to inter symbol interference. Orthogonal Frequency Division Multiplexing is one of the promising candidate to mitigate the ISI. This work improved various channel performance measures based on the comparison of various channel estimation algorithms and suggest a new technique which provides better performance. Keywords-OFDM, Block Pilot symbols, Channel estimation, Linear minimum mean square error (LMMSE), Mean square error (MSE), Bit error rate (BER)
based estimation came into our preference. In this method, the transmitted signal is known at the receiver. There are two modes: the block pilot mode and the comb pilot mode. In the block pilot mode, all the subcarriers of an OFDM symbol are dedicated to the known pilots. In the comb pilot mode, only a few subcarriers are used for the initial estimation process. II. CHANNEL ESTIMATION
I.
INTRODUCTION
Orthogonal Frequency Division Multiplexing is a very attractive technique for high bit-rate transmission in 4G wireless communication systems, where bandwidth is very precious, and service providers are continuously met with the challenges of including more number of users with in a limited allocated bandwidth. OFDM is a multicarrier modulation technique which provides an efficient means to handle high speed data streams on a multipath fading
Vineetha Mathai
Dept. of Electronics Engineering, Madras Institute of Technology, Chennai-600044, India. e-mail: vineethamathai@yahoo.in
Abstract—The channel estimation can be performed for analyzing effect of channel on signal 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 block type pilot channel estimation has been developed under the assumption of slow fading channel. When the data is transmitted at high bit rates, the channel impulse response can extend over many symbol periods, it leads to inter symbol interference. Orthogonal Frequency Division Multiplexing is one of the promising candidate to mitigate the ISI. This work improved various channel performance measures based on the comparison of various channel estimation algorithms and suggest a new technique which provides better performance. Keywords-OFDM, Block Pilot symbols, Channel estimation, Linear minimum mean square error (LMMSE), Mean square error (MSE), Bit error rate (BER)
based estimation came into our preference. In this method, the transmitted signal is known at the receiver. There are two modes: the block pilot mode and the comb pilot mode. In the block pilot mode, all the subcarriers of an OFDM symbol are dedicated to the known pilots. In the comb pilot mode, only a few subcarriers are used for the initial estimation process. II. CHANNEL ESTIMATION
I.
INTRODUCTION
Orthogonal Frequency Division Multiplexing is a very attractive technique for high bit-rate transmission in 4G wireless communication systems, where bandwidth is very precious, and service providers are continuously met with the challenges of including more number of users with in a limited allocated bandwidth. OFDM is a multicarrier modulation technique which provides an efficient means to handle high speed data streams on a multipath fading
References: [1] Geng Nian, Xiaojun Yuan and Li Ping, "DualDiagonal LMMSE Channel Estimation for OFDM Systems”, IEEE Trans.on Communication, pp.1420, November 2011. [2] Aida Zaier and Ridha Bouallègue,"Channel Estimation Study For Block-Pilot Insertion In OFDM Systems Under Slowly Time Varying Conditions”, International Journal of Computer Networks & Communications (IJCNC) Vol.3, No.6, November 2011. [3] Lie Ma, Hua Yu and Shouyin Liu, "The MMSE Channel Estimation Based on DFT for OFDM System", IEEE Trans.on Communication, pp. 1-4, October 2009. [4] M. Faulkner, "The effect of filtering on the performance of OFDM systems", IEEE Trans. on Vehicular Technology, vol. 49, September 2000. [5] Y. Qiao, S. Yu, P. Su, and L. Zhang, "Research on an interative algorithm of Is channel estimation in MIMO OFDM systems", IEEE Trans., Broadcast., vol. 51, pp. 149-153, March 2005. [6] S. Coleri, M. Ergen, A. Puri, and A. Bahai, “Channel estimation techniques based on pilot arrangement in OFDM systems”, IEEE Transactions on Broadcasting, vol.48, pp. 223-229, Sept. 2002. [7] J.-C. Lin, “Least-squares channel estimation for mobile OFDM communication on time-varying frequency- selective fading channels”, IEEE Transactions on Vehicular Technology, vol. 57, pp. 3538–3550, 2008. [8] M. Noh, Y. Lee and H. Park,” Low complexity LMMSE channel estimation for OFDM”, IEEE Proc. Commun., Vol. 153, October 2006. Figure 4. MSE curve for various estimation algorithms Figure 5. BER curve for various estimation algorithms CONCLUSION The channel is estimated using least square (LS), minimum mean-square error (MMSE), DFT based channel estimation, linear minimum mean square error (LMMSE), dual diagonal linear minimum mean square error (DDLMMSE), Proposed Method. The performance of the proposed method is closed to the ideal LMMSE estimation and better than the LS and DFT based CE, because it uses the channel autocorrelation matrix and the noise variance which was estimated in the LMMSE algorithm. At high SNR, the performance of the proposed method is much better. Since the effect of the noise is also small, hence the In