Timing Offset Estimation Research Articles

Joint Timing Offset and Channel Estimation for Multi-User UFMC Uplink

The universal filtered multi-carrier (UFMC) system, which groups and filters subcarriers before transmission, is a potential multi-carrier modulation technique for the emerging Machine-Type Communications. Given the relaxed time synchronization requirement of UFMC, we design a novel joint timing offset and channel estimation method for multi-user UFMC uplink transmission. The joint estimation problem is formulated based on atomic norm minimization (ANM) that enhances the sparsity of timing offsets in the continuous frequency domain. Simulation results show that the proposed method can achieve considerable performance gain, as compared with existing approaches.

Timing Offset Correction and Channel Tap Estimation of OFDM Systems Over Frequency Selective Fading Channels

In OFDM systems we need to perfectly time synchronize the receiver to the transmitter to maximize its BER performance. In the absence of timing synchronization the channel estimation can never be optimum. Both timing synchronization and optimum channel estimation are the essential requirements to maximize the performance. We present an algorithm that uses the cyclic prefix to determine the timing offset of the system. The same algorithm can be used to determine the number of channel taps and their variances also. Determination of number of channel taps helps us in minimizing the length of the cyclic prefix to be added and also in the channel estimation, to minimize the variance of the estimation error. The knowledge of the variances of the channel taps helps us in further reducing the estimation error. We present in this paper the timing offset corrected MMSE channel estimation and show by simulations the effectiveness of the method presented.

Implementation of Seven Finger RAKE Receiver using MRC Technique

The radio receiver that counters the effects of the multipath fading is known as a rake receiver. Rake receiver used to combine the multipath signals by number of ‘sub receivers’ known as ‘fingers’. Rake receiver uses a multipath diversity principle; it rakes the energy from the multipath propagated signal components. This paper gives the review on implementation of MRC (Maximal Ratio Combining) for the seven fingers rake receiver. It gives the same information to receiver as transmitter, it eliminates the multipath fading and the time offset estimation to seven fingers of rake receiver. In the simulation results we observed that both the signals that is input and output signal resembles the same with the help of MRC.

Estimation of Crystal Timing Properties and Efficiencies for the Improvement of (Joint) Maximum-Likelihood Reconstructions in TOF-PET.

With increasing improvements in the time of flight (TOF) resolution of positron emission tomography (PET) scanners, an accurate model of the TOF measurements is becoming increasingly important. This work considers two parameters of the TOF kernel; the relative positioning of the timing data-bins and the timing resolution along each line of response (LOR). Similar to an existing data-driven method, we assume that any shifts of data-bins along lines of response can be modelled as differences between crystal timing offsets. Inspired by this, timing resolutions of all LORs are modelled as the hypotenuse of timing resolutions of the crystal-pairs in coincidence. Furthermore, in order to mitigate the influence of potential inaccuracies of detector-pair sensitivities on crystal timing resolutions, relative LOR sensitivities are modelled as the product of efficiency factors for the two crystals in coincidence. We validate estimating maps of crystal timing offsets, timing resolutions and efficiencies from the emission data using noisy simulations of a brain phantom. Results are shown for phantom and patient data scanned on clinically available TOF-PET scanners. We find that the estimation of crystal timing resolutions is more sensitive to the data statistics than the estimation of crystal timing offsets. As a result, estimation of crystal timing properties could either be limited to high count emission data, or be obtained utilizing additional regularizations on the estimates. Using a more accurate model of the TOF acquisition, improvements are observed in standard activity reconstructions as well as joint reconstructions of activity and attenuation.

Timing Estimation Based on Higher Order Cyclostationarity for Faster-Than-Nyquist Signals

Faster-than-Nyquist (FTN) transmission is a promising technique to increase the spectral efficiency at a fixed constellation size. However, traditional timing synchronization algorithms mostly rely on the eye diagram opening after matched-filtering (e.g., Gardner and zero-crossing). Such approaches are, thus, unsuitable in the presence of the FTN-induced intersymbol interference. In this letter, we first show that FTN signals exhibit cyclostationarity at the $l$ th order ( $l > 2$ ) according to their bandwidth and symbol period. Then, we derive non-data-aided timing offset estimators from the cyclic temporal cumulant function. Besides its relevance for strong FTN scenarios, the proposed solution is also robust to frequency and phase offsets.

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.

Joint timing and frequency synchronization in coherent optical OFDM systems

In this paper, we review our joint timing and frequency synchronization algorithms in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. We first present a timing estimation method by designing the pattern of the training symbol, whose timing metric has a sharp and clear peak, to ensure accurate timing offset (TO) estimation performance. Then we provide both data-aided (DA) and blind (BL) approaches to estimate the carrier frequency offset (CFO). For the DA algorithm, we utilize the same training symbol structure as the timing estimation does, while for the BL algorithm, we utilize the zero-subcarrier power (ZSP) to achieve full-range CFO estimation. Note that our joint timing and frequency synchronization approaches require only one OFDM symbol, which ensure not only the data transmission efficiency, but also the TO and CFO estimation performance. A modified BL ZSP algorithm is proposed to further improve the CFO estimation performance by taking the power average over a series of OFDM symbols. The effectiveness of the TO estimation algorithm, and both the DA and BL CFO estimation algorithms are verified and demonstrated in both simulations and experiments.

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.

Near Optimal Timing and Frequency Offset Estimation for 5G Integrated LEO Satellite Communication System

The integration of satellite and terrestrial 5G networks aims to provide ubiquitous coverage, improve service reliability, and enable the network scalability. However, the inherent characteristics of satellite channels bring challenges on the air interface design of integrated terrestrial-satellite networks. For example, for low earth orbits (LEO) mobile satellite communication (SatCom) system, it is unclear so far whether the 5G new radio (5G-NR) synchronization signals could meet the requirement of timing and frequency offset estimation in the presence of large Doppler shifts. In this paper, we investigate time and frequency synchronization for the downlink transmission of 5G-NR signals over LEO satellite channels. Starting from the maximum log-likelihood criterion for timing offset estimation given the observation of the received primary synchronization signals (PSS), we derive an upper bound of the objective function for simplicity. With a priori information that the maximum Doppler shift of LEO satellite-ground link is within a specific range, we construct the local synchronization sequence via using the modulated discrete prolate spheroidal sequences (DPSS) vectors. Then the timing offset estimation can be recast into a one-dimensional peak search problem. Moreover, the cyclic prefix (CP) structure of orthogonal frequency division multiplexing (OFDM) can be utilized to improve the estimation performance further. Once the timing and frequency offset are captured in the above initial synchronization phase, the tracking synchronization can be much simplified as the variation of both the timing and frequency offset is very small between two adjacent synchronization blocks. Simulation results show that by using the proposed algorithms, the 5G-NR signals can achieve near optimal downlink time and frequency synchronization in typical LEO SatCom systems.

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.

Joint Time/Frequency Synchronization and Chromatic Dispersion Estimation With Low Complexity Based on a Superimposed FrFT Training Sequence

We design a new kind of fractional Fourier transform superimposed training sequence (TS) to simultaneously estimate linear distortions including chromatic dispersion (CD), timing offset (TO), and frequency offset (FO), etc. Without sacrificing additional spectrum efficiency, the scheme can reduce the computational complexity sharply compared to a regular estimation method. The feasibility of the proposed scheme is verified by simulations of 28 GBaud dual polarization quadrature phase-shift keying (DP-QSPK) and 16-ary quadrature amplitude modulation (DP-16 QAM) system. Simulation results show that the superimposed TS has negligible negative effects on the transmission performance considering 7% forward error correction while the TO, FO, and rough CD estimation perform well after a long distance transmission. The max TO estimation (TOE) errors are, respectively, eight samples and 12 samples for QPSK and 16 QAM, and the max FO estimation errors are, respectively, 5.7 and 3.6 MHz for QPSK and 16 QAM. The rough CD estimation (CDE) error is below 946 ps/nm. The TOE and rough CDE separately decrease the complexity of frame synchronization and CDE. In total, the computation complexity of the estimations decreases by 91.8% compared to a regular blind estimation method.

NavIC receiver clock offsets estimation with common view master clock method

The current manuscript proposes a new methodology for receiver clock offset estimation in IRNSS (Indian Regional Navigation Satellite System) which is also known as NavIC (Navigation Indian Constellation). This new methodology has been designed by clubbing the master clock concept with the traditional common view time transfer method and therefore it has been named as Common View Master Clock Method (CVMCM). The proposed methodology is intended to share the reference time uniformly and precisely across all the receiver clocks of IRNSS. The IRNSS receivers equipped at IRIMS (IRNSS Range and Integrity Monitoring Stations) acquire IRNSS satellite signals and generate code and carrier phase measurements on L5 and S frequencies. For ease of convenience, this range measurements and broadcast navigation messages are converted to standard RINEX (Receiver Independent Exchange) format in the form of RINEX observation files and RINEX navigation files respectively. As IRNWT1 (IRNSS Network Time Facility Bangalore) has been directly fetched to IRIMS Bangalore we have chosen IRIMS Bangalore as the master (reference) station. This is followed by time offset estimation of all IRIMS with respect to IRIMS Bangalore using the CVMCM method. This proposed methodology reduces all the error sources in IRNSS signals and produces very accurate time offsets results for all IRIMS. This helps in maintaining IRNSS reference time very precisely across all IRIMS with a proper time steering, thereby revamping the process of time synchronization in NavIC. Analyses were performed which establishes the stability and credibility of our results. In the process, it also corrects almost all the error sources in NavIC signals.

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.

Timing and Carrier Frequency Offset Estimation Using Selective Extended Cyclic Prefix for Correlation Sequence for OFDM Systems

In this paper a novel technique for timing and carrier frequency offset (CFO) estimation for orthogonal frequency division multiplexing (OFDM) systems is presented. This technique is a modification of extended cyclic prefix for correlation sequence (ECPCS) based technique, called as selective extended cyclic prefix for correlation sequence (SECPCS) based technique. In cyclic prefix (CP) based technique, magnitude of timing metric near the exact starting point of CP is quite similar which causes problem in timing estimation. SECPCS is utilized in order to increase the difference between magnitudes of timing metric at the exact starting point of time of CP and its adjacent timing instants. In SECPCS technique, first of all correlation length of CP is extended using available CP samples and then those sequences which enlarge the difference in the magnitude of timing metric is selected. In the proposed technique the difference between magnitude of timing metric at exact starting point and its adjacent timing instants is significantly large compared to the previous techniques. The performance of different techniques is evaluated in terms of mean square error (MSE) in estimation of timing and CFO estimate. Further signal-to-interference-plus-noise ratio (SINR) loss of different techniques in different channel conditions is also estimated. From the simulation results it is observed that under different channel conditions, performance of the proposed SECPCS based technique is significantly better than previous techniques.

Timing and Integer Frequency Offset Estimation for DLMT System over Time-Varying Rayleigh Fading Channel

In this paper, we study the timing and integer carrier frequency offset (ICFO) estimation problem for dynamic lattice multicarrier transmission (DLMT) system over time-varying Rayleigh fading channel. Firstly, a novel preamble structure based on two constant amplitude zero auto-correlation (CAZAC) sequences is designed for DLMT system. Then, by using the designed dual-CAZAC preamble, a discrete cross ambiguity function (DCAF) based timing and ICFO estimation algorithm is proposed. Simulation results show that the proposed DCAF based timing and ICFO estimation algorithm can mitigate the impact of time-varying multipath Rayleigh fading channel and outperforms traditional estimators on the correct estimation probability performance.

Synchronisation algorithm for OFDM/OQAM systems based on zero autocorrelation code

In this study, the authors first propose a sequence with the impulse-like autocorrelation property named zero autocorrelation code (ZAC) for orthogonal frequency division multiplexing (OFDM) based on offset quadrature amplitude modulation (OQAM) systems. The ZAC sequence can be generated by many prototype filters such as physical layer for dynamic spectrum access and cognitive radio and isotropic orthogonal transform algorithm filters. Thus, it has a wide application range. The authors then propose a synchronisation algorithm based on the ZAC. The proposed algorithm only needs two symbols to compose the preamble while existing algorithms need at least four symbols. They further assess the synchronisation performances via computer simulation. The simulation results show that the proposed algorithm can achieve better performance in terms of root mean square error of the timing and frequency offset estimation, with a 10 dB improvement on timing offset estimation performance over Saeedi-Sourck's algorithm when signal-to-noise ratio is 0 dB.

Joint Estimation of Timing and Carrier Phase Offsets for MSK Signals in Alpha-Stable Noise

Impulsive noise modeled as symmetric α-stable (SαS) distribution is commonly seen in many practical communication scenarios. In this letter, we focus on the joint timing and carrier phase synchronization of minimum shift keying signals in SαS noise. We first derive the Cramér-Rao lower bound (CRLB) of joint timing and carrier phase offsets estimation. Then, an optimal synchronization training sequence is designed to minimize the CRLB. As the corresponding maximum likelihood estimator is hard to implement in SαS noise, we further propose a pragmatic synchronization parameters estimation algorithm based on explicit myriad cost function and a global optimization method. Extensive simulation results show that our proposed algorithm works well and is robust to the estimation errors of received signal-to-noise ratio and SαS noise parameter.

A MMSE-based joint timing synchronization and channel estimation scheme for two-way amplify-and-forward relay networks

In the two-way relay networks, the receive nodes are difficult to retrieve the mixture of signals transmitted from different terminal nodes with unknown timing offsets and unknown channel information. This paper presents a joint timing synchronization and channel estimation scheme for two-way amplify-and-forward relay networks to solve this problem. Based on a well-designed training sequence arrangement, delayed timing offset and cascaded channel impulse responses (CIR) in different transmit-relay-receive links can be obtained. The proposed approach utilizes three procedures to acquire timing offsets, inter-terminal delay (ITD), and cascaded CIRs at each terminal node. First, a coarse timing offset (CTO) estimation algorithm is applied to find CTO and ITD. Then, the generalized maximum-likelihood estimation algorithm with an observation vector is exploited to obtain relative timing indices and the corresponding cascaded CIR estimates in all transmit-relay-receive links. Finally, the fine time adjustment based on the minimum mean squared error criterion is performed to reacquire timing offsets, revise the ITD estimate, and reconstruct cascaded CIR estimates. From the simulation results, the proposed approach has excellent timing synchronization and channel estimation performance under multipath fading channels with line-of-sight and non-line-of-sight propagation.

An efficient and hybrid timing offset estimation approach for universal-filtered multi-carrier based systems over multipath Rayleigh fading channel

For next generation (i.e., 5G) wireless communication, universal-filtered multi-carrier (UFMC) is a novel multi-carrier modulation technique, which is suitable for short packet and low latency transmissions. Although UFMC has lower sensitivity to synchronization errors compared with orthogonal frequency division multiplexing (OFDM), synchronization is still an important and open problem for UFMC-based systems. In this paper, in order to efficiently address the timing offset (TO) estimation issue of UFMC-based systems over multipath fading channels, a new preamble structure containing the pseudo-random noise (PN) sequences is devised in this paper. And that a robust and hybrid TO estimation approach is also proposed. This approach primarily consists of two steps. According to the devised preamble pattern, an improved timing metric is firstly developed for estimating the symbol TO coarsely. Moreover, a fine timing adjustable range is also offered. Secondly, the accurate estimation of the residual symbol TO is achieved within this adjustable range by utilizing both the threshold criterion and the cross-correlation operation between received signals and the local PN sequence. Finally, numerical simulations and comparisons are presented to confirm the practicability of the proposed algorithm under the condition of Rayleigh 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.