Effect of OFDM Transmission Mode on Frequency Synchronization Performance (original) (raw)

Frequency Synchronization in OFDM System

An accurate frequency synchronization method using the zadoff-chu (ZC) constant envelop preamble is analyzed, and a new preamble weighted by pseudo-noise sequence is used for orthogonal frequency division multiplexing (OFDM) systems. Using this method, frequency offset estimator range is greatly enlarged with no loss in accuracy. The range of the frequency estimation is ±30 of subcarrier spacing using ZC sequence as preamble. Simulations in the MATLAB for an AWGN channel show that the proposed method achieves superior performance to existing techniques in terms of frequency accuracy and range.

A Novel Timing and Frequency Synchronization Technology for OFDM System

Due to its high spectrum efficiency and good ability in coping with multi-path fading, orthogonal frequency division multiplexing (OFDM) technology has attracted considerable attention from researchers. However, OFDM system is very sensitive to symbol timing offset and carrier frequency offset, so accurate timing synchronization and frequency synchronization are necessary to OFDM system. This paper discusses on OFDM synchronization technology based on training symbol. OFDM synchronization algorithms based on training symbol are investigated, and two algorithms are proposed. An improved algorithm is proposed aimed at resolving training symbol redundancy and timing metric plateau in Schmidl algorithm. The training symbol in this algorithm is conjugated symmetrical and repeated. The timing metric has a sharp peak and eliminates the plateau. Both integral and fractional frequency offset estimation employ the same training symbol, and therefore the system overhead is saved and the complexity is degraded. The second algorithm proposed in this paper does not just improve symbol timing method or frequency offset estimation method. It is a complete set of solution project of OFDM synchronization. A new training symbol with special structure is designed, and a new joint symbol timing and frequency synchronization algorithm is presented based on this symbol. New frequency offset estimation algorithms are characteristic of large estimation range and high accuracy. At the same time, timing synchronization can produce a sharp peak, through which we can find where the OFDM symbol starts. The simulation results show that the performance of the synchronization algorithms proposed here is better than that of conventional methods.

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...

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 Novel Time and Frequency Synchronization Scheme for OFDM Systems

A new training symbol is designed and a novel time and frequency synchronization scheme for orthogonal frequency division multiplexing systems is proposed. The time synchronization is accomplished by using the symmetric conjugate of the training symbol in time domain and the frequency synchronization is finished by utilizing the good autocorrelation of the training symbol in frequency domain. The simulation results show that compared with conventional schemes, the proposed scheme gives a more accurate estimate of symbol timing and carrier frequency offset and provides a wider acquisition range for the carrier frequency offset. 1

Efficient frequency synchronization and channel estimation method for OFDM wireless systems

2010

Very efficient and robust frequency synchronization and channel estimation method based on pilot tone usage, for OFDM systems in the case of slow time varying channels is proposed. The presented method uses preamble consisting of just one OFDM symbol, for channel and frequency offset estimation and additional two pilot tones embedded in each data symbol, for the neutralization of the cumulative effect of frequency offset in the slow time varying channels. This method enables accurate estimation and correction of all frequency offset values, even those larger than subcarrier spacing. Simulation results show that OFDM system with the proposed frequency synchronization method keeps the BER performance close to the performance of the ideally synchronized system.

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 Sample Clock Frequency Synchronization Technique for OFDM Wireless Systems

A new sampling clock frequency offset (SFO) synchronization technique for OFDM systems based on pilot symbol tracking has been proposed. This technique significantly reduces the complexity of traditional OFDM receivers by eliminating the need to have two separate algorithms for coarse estimation (pre FFT synchronization) and fine tracking (post FFT synchronization). The proposed algorithm updates the error estimate at every sample of the input signal compared to the update available only at OFDM symbol rate by the traditional algorithms. This feature allows rapid sample clock frequency correction.

On the Synchronization Techniques for Wireless OFDM Systems

IEEE Transactions on Broadcasting, 2006

The latest research works on the synchronization scheme for either continuous transmission mode or burst packet transmission mode for the wireless OFDM communications are overviewed in this paper. The typical algorithms dealing with the symbol timing synchronization, the carrier frequency synchronization as well as the sampling clock synchronization are briefly introduced and analyzed. Three improved methods for the fine symbol timing synchronization in frequency domain are also proposed, with several key issues on the synchronization for the OFDM systems discussed.

A Review on Timing & Synchronization Technique in OFDM

International Journal of Science and Research (IJSR), 2017

The aim of this paper is to survey and compare previous methods for Data-aided timing and frequency synchronization of OFDM System.Synchronization has been one of the crucial research topics in orthogonal frequency division multiplexing (OFDM) system because of its sensitivity to the timing and frequency errors [1]. To guarantee the fast and accurate data transmission, the Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) caused in the transmission have to be eliminated as much as possible.ORTHOGONAL frequency-division multiplexing(OFDM) has been of major interest for both wireline-based and wireless applications [1]-[3] due to its highdata rate transmission capability and its robustness to multipathdelay spread. However, OFDM systems are much more sensitive to synchronization errors than single carrier systems [4],[5]. This paper summarizes various methods to cater this synchronization problem.