Symbol Timing Offset Estimation Research Articles

STO Estimation for OFDM System Using CDM

In this letter, we propose a novel scheme for symbol timing offset (STO) estimation by using a convolutional neural network (CNN)-deep neural network (DNN) model (CDM) architecture for the orthogonal frequency division multiplexing (OFDM) system over different fading channel models. The proposed scheme estimates STO in the presence of carrier frequency offset (CFO) and without prior knowledge of the channel, modulation format, and transmitted OFDM signal parameters. The CDM architecture achieves better estimation accuracy gain compared to that of statistical-based and pilot-assisted CNN-based methods. Finally, the proposed CDM is validated over a radio frequency testbed, and the desired constellation diagram is obtained.

Joint STO and DFO Estimation for SEFDM in Low-Earth-Orbit Satellite Communications

In this article, a joint symbol timing offset (STO) and Doppler frequency offset (DFO) estimation algorithm is proposed for spectrally efficient frequency division multiplexing (SEFDM) system in the downlink of low-earth-orbit (LEO) satellite communications. Considering the nonorthogonality of SEFDM, the proposed algorithm is derived by maximizing likelihood function. To reduce computation complexity of STO estimator, all unnecessary terms in likelihood function are ignored. Further, the proposed CFO estimator is simplified by replacing the inverse trigonometric function with polynomial approximation. According to relevant standards issued by the International Telecommunications Union and the 3rd Generation Partnership Project, simulation parameters are set to evaluate the estimation performance. Simulation results show that the proposed algorithm is robust to different packing factors of SEFDM, and outperforms traditional estimation methods.

Efficient Timing Offset Estimation Method Tailored for ACO-OFDM VLC Systems

The asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM)-based visible light communication (VLC) system has received widespread attention due to its capability to support high spectrum efficiency as well as high power efficiency. The accuracy of symbol timing offset estimation is a critical factor limiting the performance of ACO-OFDM. In order to cope with this challenge, a training symbol-aided symbol timing synchronization method tailored for ACO-OFDM is put forward. The influence of the design of training symbol structure and timing metric on the synchronization accuracy is investigated, and three timing metrics are presented to supply simple and efficient timing offset estimation by utilizing the structure of odd-even mirror-symmetric and complementary symmetric of the newly designed training symbol. In addition, the system bit error rate (BER) penalty induced by timing synchronization error is analyzed, and the approximate relationship between BER performance loss and timing estimation error probability and ideal BER performance is presented. Simulation is used to assess the performance of the three proposed timing metric methods in different channel environments, and they are compared with the two existing timing synchronization algorithms in ACO-OFDM, namely the modified Park method and the Tian method. The results show that the new synchronization method is superior to the comparison methods concerning achievable synchronization accuracy and system BER penalty.

ML-Based Forward Symbol Timing Offset Estimation for Burst Signals

In order to ensure the performance of burst signal demodulation, forward symbol timing offset estimation algorithm is usually used for symbol timing recovery. Aiming at the shortcomings of common forward symbol timing estimation algorithms, a new algorithm based on maximum likelihood estimation joint trigonometric polynomial interpolation is proposed in this article, which is suitable for the data of four samples per symbol and can resist large frequency offset. Hereafter, in order to make it more suitable for engineering practice, optimize it into an improved data-aided (DA) forward symbol timing offset estimation algorithm with multiple characteristics, e.g., moderate frequency offset capture range, insensitive to shaping coefficient, relatively low complexity, excellent estimation performance, flexible algorithm structure and less sample data required for calculation. The simulation results show that the performance of the improved algorithm in this article can approach the modified cramer-rao bound (MCRB) within the frequency offset capture range, under the conditions of low signal to noise ratio (SNR) and small shaping coefficient.

Joint Estimation of Symbol Timing and Sampling Frequency Offset for CDD-OFDM-Based DRM Systems

In this paper, an efficient symbol timing offset (STO) and sampling frequency offset (SFO) estimation scheme is proposed in an orthogonal frequency division multiplexing-based digital radio mondiale system using cyclic delay diversity. By using a periodic nature of channel transfer function, cyclic delay and pilot pattern with a maximum channel power are chosen, which aids to enable a robust estimation of STO and SFO against frequency selectivity of the channel. As a performance measure, the mean squared error of the proposed scheme is theoretically derived and is verified through simulations. By simulation results, the proposed estimation scheme is proved to profit from properly selected cyclic delay and pilot pattern, with a superior performance over the conventional estimation scheme.

Preamble Based Timing Offset Estimation and Correction in OFDM Assisted Massive MIMO Systems in the Presence of Inter-User-Interference

This paper presents a new preamble design for correct timing synchronization and symbol time offset (STO) estimation in orthogonal frequency division multiplexing (OFDM) based massive multi input multi output (M-MIMO) systems. The proposed preamble design is more robust and accurate than conventional designs at low signal to noise ratio (SNR). This paper further analyses the effect of inter user interference (IUI) on the estimation and correction. Simulations are performed for single and multi-user cases considering Rayleigh multipath channel model. Mean and standard deviation of the evaluated STO and probability of the correct timing synchronization are considered as the performance parameters. Considering the effect of fading and IUI, result shows that the proposed preamble gives better performance at low SNR.

An Analysis of the Performance of ML Blind OFDM Symbol Timing Estimation

Symbol timing offset (STO) estimation constitutes an important part in orthogonal frequency-division multiplexing (OFDM) signal synchronization, and many blind methods based on the maximum likelihood (ML) principle have been proposed. A theoretical analysis of the estimation performance, however, is very difficult, due in part to the discrete nature of the STO. As a result, most studies on OFDM STO estimation have relied only on computer simulation for performance evaluation. This paper presents a theoretical performance analysis for ML-based blind OFDM STO estimation. We start with a review of the formulation of ML blind STO estimation problem and its solution. We then conduct the said performance analysis. The analysis turns out to involve a study of the eigenvalues of some matrix functions of the autocorrelation of the received signal. As the general case leads to highly complicated mathematics, we treat the case of full-band OFDM in additive white Gaussian noise in more detail. In this case, we are able to obtain mathematically tractable bounds and approximation to the estimation error probability and the corresponding mean-square error. In high signal-to-noise ratio (SNR), these bounds and approximation show inverse power-law dependence on the SNR. We also compare the bounds with simulation results and with an existing approximation in the literature.

A Joint Low-Power Cell Search and Frequency Tracking Scheme in NB-IoT Systems for Green Internet of Things.

As a dedicated communication protocol for Internet-of-Things, narrowband internet of things (NB-IoT) needs to establish the communication link rapidly and reduce retransmissions as much as possible to achieve low power consumption and stable performance. To achieve these targets, the low-power scheme of the initial cell search and frequency tracking is investigated in this paper. The cell search process can be subdivided into narrowband primary synchronization signal (NPSS) detection and narrowband secondary synchronization signal (NSSS) detection. We present an NPSS detection method whose timing metric is composed of symbol-wise autocorrelation and a dedicated normalization factor. After the detection of NPSS, the symbol timing and fractional frequency offset estimation is implemented in a resource-efficient way. NSSS detection is conducted in the frequency domain with a calculation-reduced algorithm based on the features of NSSS sequences. To compensate the accumulated frequency offset during uplink transmission, a pilot-aided rapid frequency tracking algorithm is proposed. The simulation results of the proposed cell search scheme are outstanding in both normal coverage and extended coverage NB-IoT scenarios, and the accumulated frequency offset can be estimated with high efficiency.

A Hardware-Efficient Synchronization in L-DACS1 for Aeronautical Communications

L-band digital aeronautical communication system type-1 (L-DACS1) is an emerging standard that aims at enhancing air traffic management by transitioning the traditional analog aeronautical communication systems to the superior and highly efficient digital domain. L-DACS1 employs modern and efficient orthogonal frequency-division multiplexing (OFDM) modulation technique to achieve more efficient and higher data rate in comparison to the existing aeronautical communication systems. However, the performance of OFDM systems is very sensitive to synchronization errors such as symbol timing offset (STO) and carrier frequency offset (CFO). STO and CFO estimations are extremely important for maintaining orthogonality among the subcarriers for the retrieval of information. This paper proposes a novel efficient hardware synchronizer for L-DACS1 systems that offers robust performance at low power and low hardware resource usage. Monte Carlo simulations show that the proposed synchronization algorithm provides accurate STO estimation as well as fractional CFO estimation. Implementation of the proposed synchronizer on a widely used field-programmable gate array (FPGA) (Xilinx xc7z020clg484-1) results in a very low hardware usage which consumed 6.5%, 3.7%, and 6.4% of the total number of lookup tables, flip-flops, and digital signal processing blocks, respectively. The dynamic power of the proposed synchronizer is below 1 mW.

Non-data aided joint estimation of symbol timing offset and carrier frequency offset for OFDM/OQAM systems

This paper deals with the problem of blind synchronization for orthogonal frequency division multiplexing based on offset quadrature amplitude (OFDM/OQAM) systems without the prior information of the channel response and transmitting signals power. A novel non-data aided (NDA) joint estimation method of symbol timing offset (STO) and carrier frequency offset (CFO) for OFDM/OQAM is conceived in multipath fading channels condition. The multipath fading channels are equivalent to multiple parallel sub-channels with flat Rayleigh fading characteristics firstly, and then STO and CFO are estimated by the second-order cyclic-cumulant with different cycle frequency values and time delay values. Moreover, the modified Cramer-Rao Bound (MCRB) of NDA joint STO and CFO estimation is presented. The simulation results demonstrate that the proposed method is effective and feasible over frequency selective fading channels.

Performance Evaluation of Timing Estimation Technique Using Extended Cyclic Prefix for Correlation Sequence for OFDM Systems

This paper presents an analysis of symbol timing offset (STO) estimation method for orthogonal frequency division multiplexing systems. The proposed method does not require any preamble and with the use of available cyclic prefix (CP) samples we have proposed an extended CP. The extended CP is used to exploit more number of correlation products in correlation sequence so that a more accurate starting point of any symbol can be estimated. A simplified maximum likelihood estimation process for proposed timing estimation technique is given which enables us much more accurate timing estimate due to decreased error variance. The performance of the proposed method is evaluated in terms of mean square error of timing estimator against different signal to noise ratio values and in terms of error distribution of the estimators with and without the effect of carrier frequency offset in various channel scenarios such as AWGN, HIPERLAN/2A and HIPERLAN/2E. Simulation results shows that proposed method has significantly better performance compared to the CP based method for STO estimation.

New Algorithm for Time and Frequency Synchronization in MIMO-OFDM Systems

This paper addresses the problem of time and frequency synchronization in MIMO-OFDM systems, which are extremely sensitive to these errors. A preamble based algorithm is proposed for the estimation of synchronization errors. Product of autocorrelation function and cross correlation function is used for symbol timing offset estimation which reduces the uncertainty in timing estimation due to timing metric plateau. Phase difference between two identical parts of the preamble is used for carrier frequency offset estimation. Simulation results are presented to validate the performance of the algorithm.

A Joint Timing Offset and Channel Estimation Using Fractional Fourier Transform and Cazac Sequences

This paper deals with symbol timing offset and channel estimation in OFDM (orthogonal frequency division multiplexing) system in fast varying channel. Symbol timing offset (STO) estimation is a major task in OFDM. Most of existing methods for estimating STO used cyclic prefix or training sequences. In this paper, we consider a new system for STO estimation using constant amplitude zero autocorrelation (CAZAC) sequences as pilot sequences in conjunction with fractional Fourier transform (FRFT). After STO estimation is done, timing compensation is made. Thereafter, channel is estimated to well recover the original transmitted signal. This method gives good results in terms of MSE in comparison with other known techniques, it estimated well the channel and it is important for fast varying channel. MATLAB Monte-Carlo simulations are used to evaluate the performance of the proposed estimator.

Analyse Performance of Fractional Fourier Transform on Timing and Carrier Frequency Offsets Estimation

This paper deals with the performance of the use of fractional Fourier transform (FRFT) instead of conventional Fourier transform (FFT) in either symbol timing offset (STO) and carrier frequency offset (CFO) estimation. Orthogonal frequency division multiplexing is widely used in many systems due to advantages of theses technique compared with mono-carrier systems. In spite of his advantages, OFDM presents drawbacks such as sensitivity to timing and frequency offsets. Many techniques are used in the literature to estimate these two parameters in order to compensate them (synchronization task). These techniques used conventional Fourier transform. In this paper, we are interested in estimating STO and CFO using fractional Fourier transform. Monte Carlo simulation demonstrates the performance of the use of FRFT instead of FFT.

QoS enhancement in OFDM based systems under transceiver impairments

Broadband wireless systems generally use orthogonal frequency division multiplexing (OFDM) with link adaptation (LA) to achieve high throughput while meeting bit error rate (BER) constraint. OFDM systems are known to be affected by non-linearity of high power amplifier (HPA) at transmitter, carrier frequency offset (CFO), symbol timing offset (STO) and channel estimation error at the receiver. The delay in feedback of channel state information (CSI) further affects the performance of LA procedures. The focus of this work is on performance analysis in presence of simultaneous affect of all these impairments on LA based OFDM systems. The results are found to be useful for threshold readjustment which is essential for successful implementation of LA scheme to counter the effects of change in operating conditions from ideal to as listed above.

Signal detection technique for asynchronous filtered multi‐tone modulation‐based mesh systems

In this study, the authors propose a signal detection technique of successive interference cancellation to reduce the effect of inter-symbol interference (ISI), which is caused by the time difference of arrivals among distributed nodes in an asynchronous wireless mesh network based on filtered multi-tone modulation. The proposed signal detection technique uses partial matrices of a transmission gain matrix to mitigate the ISI effect from the adjacent symbols. Under the assumption of perfect symbol time offset and channel estimation at each node, it is shown by simulation that the proposed technique can improve the bit error rate performance with lower complexity compared with the conventional technique.

Joint timing and frequency synchronization based on weighted CAZAC sequences for reduced-guard-interval CO-OFDM systems.

A novel joint symbol timing and carrier frequency offset (CFO) estimation algorithm is proposed for reduced-guard-interval coherent optical orthogonal frequency-division multiplexing (RGI-CO-OFDM) systems. The proposed algorithm is based on a constant amplitude zero autocorrelation (CAZAC) sequence weighted by a pseudo-random noise (PN) sequence. The symbol timing is accomplished by using only one training symbol of two identical halves, with the weighting applied to the second half. The special structure of the training symbol is also utilized in estimating the CFO. The performance of the proposed algorithm is demonstrated by means of numerical simulations in a 115.8-Gb/s 16-QAM RGI-CO-OFDM system.

Preamble-based frequency-domain joint CFO and STO estimation for OQAM-based filter bank multicarrier

Abstract Filter bank multicarrier systems, similarly to orthogonal frequency division multiplexing (OFDM), are very sensitive to carrier frequency offset (CFO) and symbol timing offset (STO). In this paper, a low-complexity preamble-based joint CFO and STO technique is presented. It is based on a relatively long preamble in order to improve the CFO estimation performance as well as avoid interference coming from the data following this preamble. After CFO and STO correction, the preamble can be reused to estimate the channel. Unlike most current techniques, the CFO and STO estimation occurs in the frequency domain. This allows for a low-complexity estimation with respect to time-domain techniques and, as will be shown by simulations, provide even better performance in a reasonable range. The drawback however is that the estimation range is shorter. Specifically, for large STOs (and to a smaller extent large CFOs), the performance decreases below time-domain estimations. Two versions of the STO estimation technique will be presented, the second one being an approximation of the first one, making it less complex yet also less precise. The performance is assessed by means of computer simulations, testing for both large and small STOs, and compared with existing techniques.

Robust and Efficient OFDM Synchronization for FPGA-Based Radios

Orthogonal frequency division multiplexing (OFDM) is a popular modulation technique that can combat impulsive noise, is robust to multipath fading, is spectrally efficient, and can allow flexible allocation of spectrum. It has become a key standard in cognitive radio systems as well as an enabling technology for mobile data access systems. An OFDM receiver's performance is heavily impacted by the accuracy of its symbol timing offset (STO) and carrier frequency offset (CFO) estimation. This paper proposes a novel OFDM synchronization method that combines robust performance with computational efficiency. FPGA prototyping is used to explore the trade-off between the number of computations to be performed and computation word length with respect to both synchronization performance and power consumption. Through simulation, the proposed method is shown to provide accurate fractional CFO estimation as well as STO estimation in a range of channels. In particular, it can yield excellent synchronization performance in the face of a CFO that is larger than many state-of-the-art synchronization implementations can handle. The system implementation demonstrates efficient resource usage and reduced power consumption compared with existing methods, and this is explored as a fine-grained trade-off between performance and power consumption. The result is a robust method suitable for use in low-power radios, enabling less precise analog front ends to be used.

Simple Joint Symbol Timing and Carrier Frequency Offset Estimation for Wireless Body Area Networks

In this letter, we propose a simple algorithm to jointly estimate the symbol timing offset (STO) and carrier frequency offset (CFO) of wireless body area network (WBAN) signals. The preamble specified in IEEE 802.15.6 WBAN is used to achieve an accurate timing and frequency estimation based on the differential correlation. Simulations demonstrate that the proposed joint estimation scheme can be effectively employed to get accurate STO and CFO estimate with less complexity.