Robust OFDMA Uplink Synchronization by Exploiting the Variance of Carrier Frequency Offsets

In this paper, the uplink frequency offset estimation for orthogonal frequency-division multiplexing access (OFDMA) is discussed. We consider a general subcarrier allocation scheme where each user subcarrier group need not be contiguous. For an OFDMA uplink, we model the frequency offset for each user as an independent and identically distributed (i.i.d.) random variable with mean zero and variance sigma epsiv 2. An analysis of multiple access interference (MAI) is performed, and the Cramer-Rao lower bound (CRLB) for the estimation of variance of each user is derived. The signal-to-interference-plus-noise ratio (SINR) is derived as a function of the variance of the frequency offset. The variance of the frequency offset estimation error is lower bounded as a function of the signal-to-noise ratio (SNR). Successive interference cancellation (SIC) and iterative frequency offset estimation are considered. An estimate of the variance of the frequency offset is derived as a function of SINR and SNR. An estimate of the range of frequency offsets is derived using the assumption of uniformly distributed frequency offsets. Based on this estimate of the range of frequency offsets, the accuracy of any existing algorithm can be improved. Thus, new versions of the SIC-based frequency offset estimation and differential estimation algorithms are derived. Extensive simulation results are provided for a 16-user, 256-subcarrier OFDMA system over a multipath fading channel.

[1]  S. Kay.  Fundamentals of statistical signal processing: estimation theory , 1993 .

[2]  Vijay K. Bhargava,et al.  Optimal periodic training signal for frequency offset estimation in frequency selective fading channels , 2004, 2004 IEEE International Conference on Communications (IEEE Cat. No.04CH37577).

[3]  Yuanan Liu,et al.  High accuracy frequency offset correction with adjustable acquisition range in OFDM systems , 2005, IEEE Transactions on Wireless Communications.

[4]  Paul H. Moose,et al.  A technique for orthogonal frequency division multiplexing frequency offset correction , 1994, IEEE Trans. Commun..

[5]  Chintha Tellambura,et al.  Joint channel and frequency offset estimation and training sequence design for MIMO systems over frequency selective channels , 2004, IEEE Global Telecommunications Conference, 2004. GLOBECOM '04..

[6]  C.-C. Jay Kuo,et al.  Maximum-likelihood synchronization and channel estimation for OFDMA uplink transmissions , 2006, IEEE Transactions on Communications.

[7]  Ami Wiesel,et al.  SNR estimation in time-varying fading channels , 2006, IEEE Transactions on Communications.

[8]  H. Bolcskei.  Blind high-resolution uplink synchronization of OFDM-based multiple access schemes , 1999, 1999 2nd IEEE Workshop on Signal Processing Advances in Wireless Communications (Cat. No.99EX304).

[9]  Yuanan Liu,et al.  Frequency offset estimation with fast acquisition in OFDM system , 2004, IEEE Communications Letters.

[10]  Per Ödling,et al.  A time and frequency synchronization scheme for multiuser OFDM , 1999, IEEE J. Sel. Areas Commun..

[11]  Michele Morelli,et al.  Timing and frequency synchronization for the uplink of an OFDMA system , 2004, IEEE Transactions on Communications.

[12]  Yu-Dong Yao,et al.  Deterministic multiuser carrier-frequency offset estimation for interleaved OFDMA uplink , 2004, IEEE Transactions on Communications.

[13]  Norman C. Beaulieu,et al.  A comparison of SNR estimation techniques for the AWGN channel , 2000, IEEE Trans. Commun..

[14]  S. Haykin,et al.  Adaptive Filter Theory , 1986 .

[15]  Khaled Ben Letaief,et al.  An interference-cancellation scheme for carrier frequency offsets correction in OFDMA systems , 2005, IEEE Transactions on Communications.

[16]  Khaled Ben Letaief,et al.  Enhanced carrier frequency offset estimation for OFDM using channel side information , 2006, IEEE Transactions on Wireless Communications.

[17]  Sergio Barbarossa,et al.  Channel-independent synchronization of orthogonal frequency division multiple access systems , 2002, IEEE J. Sel. Areas Commun..

[18]  Jong-Ho Lee,et al.  Time and Frequency Synchronization for OFDMA Uplink System using the SAGE Algorithm , 2007, IEEE Transactions on Wireless Communications.

[19]  Ilan Ziskind,et al.  Maximum likelihood localization of multiple sources by alternating projection , 1988, IEEE Trans. Acoust. Speech Signal Process..

[20]  Umberto Mengali,et al.  An improved frequency offset estimator for OFDM applications , 1999, IEEE Communications Letters.

[21]  Cihan Tepedelenlioglu,et al.  SNR estimation for nonconstant modulus constellations , 2005, IEEE Transactions on Signal Processing.