Sampling Frequency Offset Research Articles

Sampling Frequency Offset Estimation Methods for DVB-T/H Systems

A precise estimation and compensation of SFO (Sampling Frequency Offset) is an important issue in OFDM (Orthogonal Frequency Division Multiplexing) system, because sampling frequency mismatch between the transmitter and the receiver dramatically degrades the system performance due to the loss of orthogonality between the subcarriers. However, the conventional method causes serious performance degradation of SFO estimation in low SNR (Signal to Noise Ratio) or large Doppler frequency environment. Therefore, in this paper, we propose two SFO estimation methods which can achieve stable operation in low SNR and large Doppler frequency environment. The proposals for SFO estimation / compensation are mainly specialized on DVB (Digital Video Broadcasting) system, and we verified that the proposed method has good performance and stable operation through extensive simulation.

A Composite PN-Correlation Based Synchronizer for TDS-OFDM Receiver

In this paper, we presents a novel synchronizer dealing with carrier frequency offset (CFO), sampling frequency offset (SFO), as well as frame timing offset (FTO) in TDS-OFDM receiver. The proposed schemes are based on tracking the output waveform of a composite PN-correlator (CPC), which provides sufficient correlative gains to detect its peaks even in the presence of large CFOs. From the correlation peaks, we can extract useful information for estimating the synchronization offsets. CFO is recovered by a multi-stage CPC scheme, of which the parameters are adjustable for meeting the system's demands on the tracking range and accuracy. According to the inter-frame variations of correlation waveform, we estimate SFO for a large scale and correct SFO through an interpolator. Meanwhile, frame timing is investigated in this paper, and the analysis indicates a very fast and robust timing scheme is possible for TDS-OFDM receiver. The developed synchronizer is quite robust against a large CFO even in very adverse fading channels, and it is shown by computer simulation that the residual synchronization error has little effect on the performance of TDS-OFDM receiver.

Estimation of residual carrier and sampling frequency offsets in OFDM-SDMA uplink transmissions

This paper investigates the estimation of multiple residual carrier frequency offsets (RCFOs) and sampling frequency offsets (SFOs) in the uplink of a multiuser OFDM network with space division multiple access (SDMA). The proposed solutions are based on the presence of some dedicated pilot tones within the signal spectrum, which are traditionally employed in OFDM systems to track channel variations and residual frequency errors. The main obstacle is the large number of parameters involved in the estimation process, which makes the uplink synchronization a rather challenging task. A practical solution to this problem relies on the separation of the received signals before the estimation procedure is started. This way, the RCFOs and SFOs of different users are estimated independently with affordable complexity. We propose two alternative approaches for users' separation. The former is based on the use of orthogonal pilot sequences, while the latter exploits the distinct spatial signatures of the uplink signals. Computer simulations and theoretical analysis are employed to assess the performance of the proposed schemes and to make comparison with existing alternatives.

Efficient Phase-Error Suppression for Multiband OFDM-Based UWB Systems

This paper proposes an efficient phase-error suppression scheme for multiband (MB) orthogonal frequency-division multiplexing (OFDM)-based ultrawideband (UWB) communication systems. The proposed scheme consists of a clock-recovery loop and a common phase-error (CPE) tracking loop. The clock-recovery loop performs estimation of the sampling frequency offset (SFO) and its 2-D (time and frequency) compensation, while the CPE tracking loop estimates and corrects the phase errors caused by residual carrier frequency offset (CFO), residual SFO, and phase noise (PHN). The SFO and CPE estimators employ pilot-tone-based and channel-frequency-response (CFR)-weighted low-complexity approaches, each of which uses a robust error-reduction scheme without using angle calculations or divisions. Analytical results and numerical examples show the effectiveness of the proposed scheme in different multipath fading scenarios and signal-to-noise ratio (SNR) regimes.

Fine frequency synchronization in the uplink of multiuser OFDM systems

This contribution considers the estimation and compensation of residual multiple carrier frequency offsets (CFOs) and sampling frequency offsets (SFOs) in the uplink of multiuser OFDM systems. Based on the observation of a user-dependent phase rotation, an approximate maximum-likelihood (ML) estimator is proposed in order to estimate the CFOs and SFOs and to track the phase in a post-synchronization step. By using a Taylor approximation, the estimation complexity is reduced. Bit error-ratio (BER) simulations show that the system performance degradation due to (small) frequency mismatches is negligible if the proposed method is applied.

Intercarrier Interference in OFDM: A General Model for Transmissions in Mobile Environments with Imperfect Synchronization

Intercarrier Interference (ICI) is an impairment well known to degrade performance of Orthogonal Frequency Division Multiplexing (OFDM) transmissions. It arises from carrier frequency offsets (CFOs), from the Doppler spread due to channel time-variation and, to a lesser extent, from sampling frequency offsets (SFOs). Literature reports several models of ICI due to each kind of impairment. Some studies describe ICI due to two of the three impairments, but so far no general model exists to describe the joint effect of all three impairments together. Furthermore, most available models involve some level of approximation, and the diversity of approaches makes it cumbersome to compare power levels of the different kinds of ICI. In this work, we present a general and mathematically exact model for the ICI stemming from the joint effect of the three impairments mentioned. The model allows for a vis-a-vis comparison of signal-to-ICI ratios (SIRs) caused by each impairment. Our result was validated by simulations. An analysis of ICI in IEEE-802.16e-type transmissions shows that during steady-state tracking and at speeds below 150 km/h, SIR due to CFO is typically in the range between 25 dB and 35 dB, SIR due to Doppler spread is larger than 25 dB, and ICI due to SFO is negligible.

A scattered pilot synchronization scheme by partial correlation for DVB-H systems

This paper presents an improved, scattered pilot synchronization (SPS) scheme in digital video broadcasting-handheld (DVB-H) systems, which detect the pilot pattern of the currently received orthogonal frequency division multiplexing (OFDM) symbol. To reduce the SPS time, and to mitigate the influence of the sampling frequency offset (SFO), the proposed SPS method is based on the conventional correlation-based SPS, and adopts a partial correlation. By using computer simulations, the synchronization performances of the traditional SPS and the new proposed SPS algorithms are evaluated in terms of their probabilities of synchronization failure.

Joint Channel Estimation and Synchronization for MIMO–OFDM in the Presence of Carrier and Sampling Frequency Offsets

A pilot-aided scheme is proposed for the joint estimation and tracking of channel impulse response (CIR), carrier frequency offset (CFO) and sampling frequency offset (SFO) in burst mode, multiple-input-multiple-output (MIMO), and orthogonal frequency division multiplexing(OFDM) systems. First, a received signal model that takes into account nonlinear CFO/SFO effects is formulated. Then, based on the derived signal model and the received multicarrier signal samples containing the pilot tones in the frequency domain, an objective function that includes MIMO CIR, CFO, and SFO is introduced to develop a vector recursive-least-square (RLS)-based joint channel estimation and synchronization algorithm. The analysis and simulation results show that, over the large ranges of the CFO and SFO values, the proposed estimation and tracking scheme offers fast convergence, high stability, and a near-optimum receiver performance that is remarkably close to the ideal performance in the case of perfect channel estimation and synchronization over quasi-static Rayleigh multipath fading channels.

Carrier and Sampling Frequency Offset Estimation and Tracking in OFDM Systems

In This paper presents the proposition of the tracking algorithm of the carrier frequency and sampling frequency offsets. The algorithm uses a phase difference between channel transfer function estimates computed for the same subcarrier of two successive OFDM symbols. Proposed solution was compared, by means of computer simulation, with similar non-data aided algorithm introduced in [1]. Both schemes were tested by transmitting OFDM symbols over the Rayleigh fading channel.

Time and Frequency Synchronisation in 4G OFDM Systems

This paper presents a complete synchronisation scheme of a baseband OFDM receiver for the currently designed 4G mobile communication system. Since the OFDM transmission is vulnerable to time and frequency offsets, accurate estimation of these parameters is one of the most important tasks of the OFDM receiver. In this paper, the design of a single OFDM synchronisation pilot symbol is introduced. The pilot is used for coarse timing offset and fractional frequency offset estimation. However, it can be applied for fine timing synchronisation and integer frequency offset estimation algorithms as well. A new timing metric that improves the performance of the coarse timing synchronisation is presented. Time domain synchronisation is completed after receiving this single OFDM pilot symbol. During the tracking phase, carrier frequency and sampling frequency offsets are tracked and corrected by means of the nondata-aided algorithm developed by the author. The proposed concept was tested by means of computer simulations, where the OFDM signal was transmitted over a multipath Rayleigh fading channel characterised by the WINNER channel models with Doppler shift and additive white Gaussian noise.

RLS-Based Joint Estimation and Tracking of Channel Response, Sampling, and Carrier Frequency Offsets for OFDM

This paper proposes a pilot-aided joint channel estimation and synchronization scheme for burst-mode orthogonal frequency division multiplexing (OFDM) systems. Based on the received signal samples containing pilot tones in the frequency domain, a cost function that includes the carrier frequency offset (CFO), sampling clock frequency offset (SFO) and channel impulse response (CIR) coefficients is formulated and used to develop an accompanying recursive least-squares (RLS) estimation and tracking algorithm. By estimating the channel <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CIR</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">coefficients</i> instead of the channel frequency response in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">frequency</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">domain</i> , the proposed scheme eliminates the need for an IFFT block while reducing the number of parameters to be estimated, leading to lower complexity without sacrificing performance and convergence speed. Furthermore, a simple maximum-likelihood (ML) scheme based on the use of two long training symbols (in the preamble) is developed for the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">coarse</i> estimation of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">initial</i> CFO and SFO to suppress dominant ICI effects introduced by CFO and SFO and to enhance the performance and convergence of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fine</i> RLS estimation and tracking. Simulation results demonstrate that, over large ranges of CFO and SFO values, the proposed pilot-aided joint channel estimation and synchronization scheme provides a receiver performance that is remarkably close to the ideal case of perfect channel estimation and synchronization in both AWGN and Rayleigh multipath fading channels.

Turbo Processing for Joint Channel Estimation, Synchronization, and Decoding in Coded MIMO-OFDM Systems

This paper proposes a turbo joint channel estimation, synchronization, and decoding scheme for coded multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems. The effects of carrier frequency offset (CFO), sampling frequency offset (SFO), and channel impulse responses (CIRs) on the received samples are analyzed and explored to develop the turbo decoding process and vector recursive least squares (RLSs) algorithm for joint CIR, CFO, and SFO tracking. For burst transmission, with initial estimates derived from the preamble, the proposed scheme can operate without the need of pilot tones during the data segment. Simulation results show that the proposed turbo joint channel estimation, synchronization, and decoding scheme offers fast convergence and low mean squared error (MSE) performance over quasistatic Rayleigh multipath fading channels. The proposed scheme can be used in a coded MIMO-OFDM transceiver in the presence of multipath fading, carrier frequency offset, and sampling frequency offset to provide a bit error rate (BER) performance comparable to that in an ideal case of perfect synchronization and channel estimation over a wide range of SFO values.

Computationally Efficient Joint Frequency Synchronization for OFDM-Based DVB-T

This letter proposes a computationally efficient way of jointly estimating the residual frequency offset (RFO) and sampling frequency offset (SFO) by using a continual pilot (CP) defined in OFDM-based DVB-T system. In order to devise an unbiased joint frequency estimator in the current DVB-T system, a CP subset is selected to offset the effects of RFO and SFO simultaneously.

A Robust Sampling Frequency Offset Estimator for WLAN-OFDM

This letter presents a noise-robust sampling frequency offset (SFO) estimation scheme for OFDM-based WLAN systems. Mean square error of the proposed estimation scheme is derived and simulation results are provided to verify our analysis. The proposed SFO estimator has an improved performance over the existing schemes with a reduction of the estimation range.

Joint Estimation of Carrier-Frequency and Sampling-Frequency Offsets for SC-FDE Systems on Multipath Fading Channels

With single-carrier frequency-domain equalization, the carrier-frequency and sampling-frequency offsets are embedded in the phases of complex frequency-domain signal components. This paper proposes a sub-block processing to extract the phases and applies the least-squares regression to jointly estimate the offsets. The effectiveness of the proposed SC-FDE receiver is demonstrated on multipath fading channels.

A Robust Symbol Synchronization Method for Terrestrial-DMB Receivers in the Hierarchical Modulation Mode

Recently, hierarchical modulation has been considered as a way to increase the payload data in terrestrial digital multimedia broadcasting (T-DMB) transmission systems. This paper proposes a robust symbol synchronization method for T- DMB receivers working in the hierarchical modulation mode. The proposed method employs a timing error detector (TED) which produces a timing phase error at OFDM symbol rate instead of the frame rate. This method thus results in the robust synchronization of symbol timing in the presence of a sampling frequency offset (SFO). Simulation results show that the proposed method outperforms the conventional one especially at a large SFO .

Low-overhead Sampling Frequency Synchronization Scheme for UWB-OFDM

This paper proposes a computationally efficient approach of estimating a sampling frequency offset (SFO) in multi-band ultra wideband orthogonal frequency division multiplexing systems. In order to devise the post-FFT based SFO estimator with low complexity, the partial pilot subset is chosen such that it provides an equivalent estimation performance to the conventional SFO estimator using the full pilot symbols. Mean square error of the low-overhead frequency estimation scheme is derived and simulation results are provided to verify our analysis.

A Fine Frequency Synchronization and Tracking for Mobile WiMAX Broadcasting Systems

In this paper, we suggest a synchronization receiver for MIMO-OFDM based mobile broadcasting system. A MIMO-OFDM receiver with algorithms for tracking of residual frequency offset (RFO) and sampling frequency offset (SFO) is designed and simulated. The proposed synchronization and compensation schemes are applied to IEEE 802.16e WiMAX and its performance is investigated by computer simulations in terms of mean square error (MSE) and bit error rate (BER). The proposed RFO and SFO estimator has a fast convergence and a small residual degradation even for high speed mobile station.

ML-based Tracking Algorithms for MIMO-OFDM

This article addresses the problem of tracking the carrier frequency offset (CFO) and sampling frequency offset (SFO) in burst MIMO-OFDM systems. The goal is to accomplish those tasks with the smallest possible piloting overhead (highest spectral efficiency). For that, we derive a precise mathematical model that describes the joint effect of a CFO and SFO on the received MIMO-OFDM subcarriers. The model unifies simpler, well-known results found in the literature. We use it for deriving maximum likelihood (ML) estimators for both impairments based on observations of received pilot subcarriers at the output of the FFTs of the receiver branches. This approach yields estimators that are independent of the type of MIMO decoder, located further downstreams. At the same time, the estimators are the ML-optimal processors of pilot information at the MIMO channel's output. A pair of corresponding tracking algorithms based on the estimators is proposed and evaluated by simulation. The results show that the variance of our estimators decreases with larger MIMO configurations, allowing for increased synchronization accuracy at low SNR, or for reducing the number of pilot subcarriers to maintain equal estimator variance. We also show that the proposed tracking algorithms operate robustly under imperfect channel state information and with modulation sizes ranging from 4-QAM to 64-QAM. The SNR loss of the proposed algorithms is below 0.1 dB in all the cases, while a conventional tracking approach is shown to have an SNR loss between 0.8 dB and 1.2 dB.