An Iterative Maximum Likelihood Synchronization Method for OFDM System

Chi-Min Li, Wei-Tse Sun

Department of Communications, Navigation and Control Engineering, National Taiwan Ocean University, Keelung, Chinese Taipei.

DOI: 10.4236/cn.2013.52B008                

Abstract

OFDM system divides a wideband transmission bandwidth into several overlapped narrowband subcarriers to avoid the serious frequency selective fading problem. However, if Timing Offset (TO) and Carrier Frequency Offset (CFO) exist between the Transmitter (Tx) and Receiver (Rx), OFDM system will suffer the Inter-Symbol Interference (ISI) and Inter-Carrier Interference (ICI) that degrade the system performance dramatically. In this paper, we propose an iterative maximum likelihood method for synchronization. We also adopt the overlap concept to reduce the plateau problem. Simulation results show that the proposed method can predict the time delay and frequency offset correctly even under the multipath fading scenarios.

Keywords

Synchronization; Maximum Likelihood; OFDM

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	T. M. Schmidl and D. C. Cox, “Robust Frequency and Timing Synchronization for OFDM,” IEEE Transactions on Communication, Vol. 45, No. 12, 1997, pp.1613-1621. doi:10.1109/26.650240
[2]	Z. S. Pang and X. M. Li, “A Novel Synchronization Algorithm for OFDM System Based on Training Sequence Added Scramble Code,” IEEE Communications Technology and Applications (ICCTA), 2009
[3]	J. J. van de Beek, M. Sandell and P. O. Borjesson, “ML Estimation of Time and Frequency Offset in OFDM Systems,” IEEE Transactions on Signal Processing, Vol. 45, No.7, 1997, pp.1800-1805. doi;10.1109/78.599949
[4]	H. Minn, M. Zeng and V. K. Bhargava, “On Timing Offset Estimation for OFDM Systems,” IEEE Communications on Letters, Vol. 4, No. 7, 2000, pp. 242-244. doi;10.1109/4234.852929
[5]	S. D. Ma, X. Y. Pan, G. H. Yang and T. S. Ng, “Blind Symbol Synchroniza-tion Based on Cyclic Prefix for OFDM Systems,” IEEE Trans-actions on Vehicular Technology ,Vol. 58, No. 4, 2009, pp. 1746-1751. doi;10.1109/TVT.2008.2004031
[6]	Z. Q. He, Y. Han and X. Fu, “Frequency Synchronization Algorithm Based on PN Sequence,”4th International Conference on Wireless Communications, Networking and Mobile Computing, 2008.
[7]	H. Hwang and H. Park, “A Timing Synchronization Design In OFDM Systems,” IEEE International Workshop on Satellite and Space Communications, 2008, pp.290-293. doi;10.1109/IWSSC.2008.4656815
[8]	3GPP TS 25.101 V5.12.0, “Technical Specification Group Radio Access Network User Equipment (UE) Radio Transmission and Reception (FDD),” 2004.
[9]	C. M. Li, H. C. Chen, P. J. Wang, J. C. Wu and I. T. Tang, ”Timing Synchronization and Channel Estimation of a Constant Pilot Padding OFDM System,” The 14th Asia-Pacific Conference on Communications (APCC2008) Tokyo, Japan.