Abstract_1.6_2
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Timing and frequency synchronization for OFDM systems Dheerajkumar C* and Vighnesh S Bhat † Department of Electrical Engineering, Indian Institute of Technology Kanpur Kanpur, Uttar Pradesh, India 208016 Email: *[email protected] and † [email protected] Abstract—Performance of an Orthogonal Frequency Division Multiplexing (OFDM) system is found to deteriorate because of timing and frequency synchronization errors (offsets) at the receiver. TO at receiver results in capture of wrong Fast Transform (FFT) window causing distortion. Frequency offset at the receiver results in loss of orthogonality of OFDM sub carriers causing Inter Carrier Interference (ICI). Thus the effects of these offsets have to be studied and compensated at the receiver. Here different timing offset (TO) and frequency offset (FO) estimation techniques are analyzed. Maximum Likelihood (ML) method for estimation of TO where, redundancy in cyclic prefix and pilots used for channel estimation are exploited is studied. A timing synchronization method for OFDM in the cases of continuous or burst transmissions where a training symbol is transmitted which aids in estimation is studied. Integer FO estimation for OFDM systems with residual TO over frequency selective fading channel using cross ambiguity function (CAF) based optimization is studied. Fractional FO over mobile radio channels using cost function based optimization is studied. Keywords : Cross ambiguity function (CAF), Maximum like- lihood (ML), Inter Carrier Interference (ICI), Orthogonal fre- quency division multiplexing (OFDM), synchronization, Timing offset (TO), Frequency offset (FO). REFERENCES [1] Daniel Landstrm, Sarah Kate Wilson, Jan-Jaap van de Beek, Per dling, and Per Ola Brjesson, “Symbol Time Offset Estimation in Coherent OFDM Systems”, IEEE Trans. on Communications., vol. 50, No. 4, April. 2002. [2] Timothy M. Schmidl and Donald C. Cox, “Robust Frequency and Timing Synchronization for OFDM”, IEEE Trans. on Communications., vol. 45, No. 12, Dec. 1997. [3] H. Minn, M. Zeng and V. K. Bhargava, “On Timing Offset Estimation for OFDM Systems”, IEEE Communications Letters., vol. 4, No. 7, July. 2000. [4] Byungjoon Park, Hyunsoo Cheon, Changeon Kang and Daesik Hong “A Novel Timing Estimation Method for OFDM Systems”, IEEE Communi- cations Letters., vol. 7, No. 5, May. 2003. [5] Danping Li, Yongzhao Li, Hailin Zhang, Leonard J. Cimini and Yuguang Fang “Integer Frequency Offset Estimation for OFDM Systems With Residual Timing Offset Over Frequency Selective Fading Channels”, IEEE Trans. on Vehicular Technology., vol. 61, No. 6, July. 2012. [6] A. Al-Dweik, A. Hazmi, S. Younis, B. Sharif and C. Tsimenidis “Carrier Frequency Offset Estimation for OFDM Systems Over Mobile Radio Channels”, IEEE Trans. on Vehicular Technology., vol. 59, No. 2, Feb. 2010.
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Timing and frequency synchronization for OFDMsystems
Dheerajkumar C* and Vighnesh S Bhat†Department of Electrical Engineering, Indian Institute of Technology Kanpur
Kanpur, Uttar Pradesh, India 208016Email: *[email protected] and †[email protected]
Abstract—Performance of an Orthogonal Frequency DivisionMultiplexing (OFDM) system is found to deteriorate becauseof timing and frequency synchronization errors (offsets) atthe receiver. TO at receiver results in capture of wrong FastTransform (FFT) window causing distortion. Frequency offset atthe receiver results in loss of orthogonality of OFDM sub carrierscausing Inter Carrier Interference (ICI). Thus the effects of theseoffsets have to be studied and compensated at the receiver. Heredifferent timing offset (TO) and frequency offset (FO) estimationtechniques are analyzed. Maximum Likelihood (ML) method forestimation of TO where, redundancy in cyclic prefix and pilotsused for channel estimation are exploited is studied. A timingsynchronization method for OFDM in the cases of continuousor burst transmissions where a training symbol is transmittedwhich aids in estimation is studied. Integer FO estimation forOFDM systems with residual TO over frequency selective fadingchannel using cross ambiguity function (CAF) based optimizationis studied. Fractional FO over mobile radio channels using costfunction based optimization is studied.
Keywords : Cross ambiguity function (CAF), Maximum like-lihood (ML), Inter Carrier Interference (ICI), Orthogonal fre-quency division multiplexing (OFDM), synchronization, Timingoffset (TO), Frequency offset (FO).
REFERENCES
[1] Daniel Landstrm, Sarah Kate Wilson, Jan-Jaap van de Beek, Per dling,and Per Ola Brjesson, “Symbol Time Offset Estimation in CoherentOFDM Systems”, IEEE Trans. on Communications., vol. 50, No. 4, April.2002.
[2] Timothy M. Schmidl and Donald C. Cox, “Robust Frequency and TimingSynchronization for OFDM”, IEEE Trans. on Communications., vol. 45,No. 12, Dec. 1997.
[3] H. Minn, M. Zeng and V. K. Bhargava, “On Timing Offset Estimationfor OFDM Systems”, IEEE Communications Letters., vol. 4, No. 7, July.2000.
[4] Byungjoon Park, Hyunsoo Cheon, Changeon Kang and Daesik Hong “ANovel Timing Estimation Method for OFDM Systems”, IEEE Communi-cations Letters., vol. 7, No. 5, May. 2003.
[5] Danping Li, Yongzhao Li, Hailin Zhang, Leonard J. Cimini and YuguangFang “Integer Frequency Offset Estimation for OFDM Systems WithResidual Timing Offset Over Frequency Selective Fading Channels”,IEEE Trans. on Vehicular Technology., vol. 61, No. 6, July. 2012.
[6] A. Al-Dweik, A. Hazmi, S. Younis, B. Sharif and C. Tsimenidis “CarrierFrequency Offset Estimation for OFDM Systems Over Mobile RadioChannels”, IEEE Trans. on Vehicular Technology., vol. 59, No. 2, Feb.2010.
