Timing Synchronization and Frequency Offset Estimation for OFDMA/TDD Mode in Downlink of IEEE 802.16-2004 (original) (raw)
Related papers
1st International Symposium onWireless Communication Systems, 2004., 2004
This paper develops a novel and simple algorithm to perform joint carrier frequency offset and channel estimation in Orthogonal Frequency Division Multiplexing (OFDM) systems. Carrier frequency offset of upto several frequency subcarrier spacings has to be estimated and compensated in order to enhance the OFDM system performance. The time domain synchronization algorithms using the preamble structure provided for fixed broadband wireless OFDM uplink access (IEEE 802.16 LAN/MAN standards) can only measure a frequency offset with an ambiguity equal to an even number of subcarrier spacings, in case of the actual offset being more than a subcarrier spacing. Our proposed algorithm uses the received preamble to jointly estimate this remaining integer part of the frequency offset and the initial channel impulse response using a least squares criterion in an iterative manner. Computer simulations show that the proposed estimator is very robust at low signal to noise ratios (SNRs) and operate near the Cramer-Rao bound for the variance of the frequency offset estimate.
A Novel Timing Synchronization Method for OFDM Systems
IEEE Communications Letters, 2000
In this letter, a novel timing offset estimation method is presented for orthogonal frequency division multiplexing (OFDM) systems. The proposed method is developed on the basis of the cyclic structure of OFDM symbol and uses a new noise subspace based metric to estimate the timing offset. Simulation results show that the proposed method has a significantly higher probability of correct estimation of the timing offset than the other methods in multipath channels.
A Frame Synchronization and Frequency Offset Estimation Algorithm for OFDM System and its Analysis
EURASIP Journal on Wireless Communications and Networking, 2006
Orthogonal frequency division multiplexing (OFDM) is a parallel transmission scheme for transmitting data at very high rates over time dispersive radio channels. In an OFDM system, frame synchronization and frequency offset estimation are extremely important for maintaining orthogonality among the subcarriers. In this paper, for a preamble having two identical halves in time, a timing metric is proposed for OFDM frame synchronization. The timing metric is analyzed and its mean values at the preamble boundary and in its neighborhood are evaluated, for AWGN and for frequency selective channels with specified mean power profile of the channel taps, and the variance expression is derived for AWGN case. Since the derivation of the variance expression for frequency selective channel case is tedious, we used simulations to estimate the same. Based on the theoretical value of the mean and estimate of the variance, we suggest a threshold for detection of the preamble boundary and evaluating the probability of false and correct detections. We also suggest a method for a threshold selection and the preamble boundary detection in practical applications. A simple and computationally efficient method for estimating fractional and integer frequency offset, using the same preamble, is also described. Simulations are used to corroborate the results of the analysis. The proposed method of frame synchronization and frequency offset estimation is applied to the downlink synchronization in OFDM mode of wireless metropolitan area network (WMAN) standard IEEE 802.16-2004, and its performance is studied through simulations.
A New OFDM Synchronization Symbol for Carrier Frequency Offset Estimation
IEEE Signal Processing Letters, 2007
This letter proposes a new data-aided carrier frequency offset (CFO) estimation scheme for orthogonal frequency division multiplexing (OFDM) communications suitable for frequency-selective channels. The proposed method is based on the transmission of a specially designed synchronization symbol that generates a particular signal structure between the received observation samples at the receiver. This structure is exploited to derive a closed-form expression of the CFO. The proposed solution offers a wide acquisition range with reduced computational load. Simulations over frequency-selective channels confirm the superiority of the proposed method compared to recent data-aided synchronization algorithms.
New joint frame synchronisation and carrier frequency offset estimation method for OFDM systems
European Transactions on Telecommunications, 2009
We propose a new joint frame synchronisation and carrier frequency offset estimation scheme for burst transmission mode OFDM systems. This scheme uses a central-symmetric and comb-like (CSCL) training sequence, which eases the power detection at the receiver without increasing the total training sequence power. Fine frame synchronisation as well as carrier frequency offset acquisition with a maximum acquisition range of ± N 4×SF times the sub-carrier spacing can also be performed based on the proposed CSCL training sequence, where N is the discrete Fourier transform (DFT) length and SF is an integer-valued spreading factor used to generate CSCL. The post-acquisition residual carrier frequency offset can be further estimated and corrected via a fine adjustment algorithm. In order to reduce performance loss due to the high peakto-average power ratio (PAPR) of the CSCL training sequence, a time-domain constant-envelope (CE) training sequence is also proposed. The superior estimation accuracy of the proposed algorithm over that of the Moose algorithm and the SS (Shi and Serpedin) algorithm is proved by computer simulation. † Part of this paper has been presented at IEEE GLOBECOM2006.
A reduced complexity scheme for carrier frequency synchronization in uplink 802.16e OFDMA
EURASIP Journal on Advances in Signal Processing, 2012
Synchronization of the carrier frequency offset (CFO) in the uplink of OFDMA systems is a complex task because each user presents a different CFO. It is performed in two stages: estimation and compensation. Although a few existing schemes already achieve good performance in terms of bit error rate (BER), all of them perform huge amounts of operations, specially during estimation, thus leading to very costly, if not impractical, hardware implementations. In addition, if estimation is performed in the time domain, a preamble is required. Since the IEEE 802.16e standard for OFDMA has no preamble at the beginning of the uplink frame, optional midambles must be used at the cost of reducing the system throughput. This article proposes a combined CFO estimation and compensation technique that uses the pilot subcarriers of the 802.16e frame. It achieves similar BER performance than previous approaches without any throughput penalty, while reducing the number of required computations by several orders of magnitude. This reduction is the result of a simpler estimation algorithm and two techniques that improve its accuracy: an iterative process integrated with the compensation stage and the delayed correction of the phase shifts.
Joint symbol timing and frequency offset estimation for wireless OFDM systems
2008
This work presents a new technique for blind and joint estimation of symbol timing and carrier frequency offset in wireless orthogonal frequency division multiplexing (OFDM) systems. The joint estimation is achieved by sensing the interference introduced at the fast Fourier transform (FFT) output when a carrier frequency or timing offsets exist. The synchronization parameters are selected such that the interference is minimized. The proposed joint estimator is highly efficient because it does not require any overhead or channel state information. Simulation results show that the system is effective and robust even at low signal-to-noise ratios.
Estimation of Time Offset in OFDM Systems in the Presence of CFO
Orthogonal frequency-division multiplexing (OFDM) has been adopted by many broadband wireless communication systems for the simplicity of the receiver design to support high data rates and user mobility. However, studies also show that the advantage of OFDM over the single-carrier modulation schemes could be substantially compromised by timing or frequency estimation errors at the receiver. The time synchronization problem for OFDM systems is most common in the downlink of wireless communication systems, in this paper a novel timing synchronization algorithm which minimizes false alarm probability and indirectly improves correct detection probability. We then introduce a universal fractional carrier frequency offset (CFO) estimator that outperforms conventional methods at low signal to noise ratio with lower complexity. More accurate timing and frequency estimates can be obtained by our proposed algorithms, presenting a successive timing estimation algorithm to solve the timing ambiguity. Both analytical and simulation results are presented to confirm the performance of the proposed methods in various realistic channel conditions.
Time and Frequency Synchronization in OFDM System
2014
Orthogonal frequency division multiplexing (OFDM) is one of the multicarrier modulation techniques, which transmits data in very high rate and efficiently mitigates the effects of multipath distortions as well as loss in bandwidth efficiency. However, OFDM systems are very sensitive towards synchronization error. Synchronization of an OFDM signal is required to find the symbol timing and carrier frequency offset (CFO). Before demodulation of subcarriers, either from explicit training data or using cyclic prefix of the OFDM signal we can get synchronization at receiver. After demodulation of the OFDM subcarriers, information about the synchronization can be obtained from training symbols embedded into the regular data symbol pattern. The estimation of synchronization error can be performed depending on the type of the training data. In this paper, it is focused on preamble based training data following IEEE802.11a preamble structure of the WLAN system and cyclic prefix based training...
Carrier frequency offset estimation in OFDM systems
2013 IEEE CONFERENCE ON INFORMATION AND COMMUNICATION TECHNOLOGIES, 2013
This paper presents a basic useful technique for carrier frequency offset (CFO) estimation in orthogonal frequency division multiplexing (OFDM) over frequency selective fading channel. The performance of OFDM system is very sensitive to CFO, which introduces inter-carrier interference (ICI). In cyclic prefix (CP) based estimation, the CFO can be found from the phase angle of the product of CP and corresponding rear part of the OFDM symbol. In CFO estimation using training symbol, the CFO estimation range can be increased by reducing the distance between two blocks of samples for correlation. This was made possible by using training symbol that are repetitive with shorter period. An analytic expression in form of mean square error(MSE) of frequency offset synchronization is reported, and simulation results verify theoretical analysis.