Fractional Frequency Offset Research Articles

Dataset Augmentation and Fractional Frequency Offset Compensation Based Radio Frequency Fingerprint Identification in Drone Communications

Dataset Augmentation and Fractional Frequency Offset Compensation Based Radio Frequency Fingerprint Identification in Drone Communications

GNSS time and frequency transfers through national positioning, navigation and timing infrastructure

Abstract GNSS signals have been a practical time transfer tool to realise a Coordinated Universal Time (UTC) and set civilian clocks around the world with respect to this atomic time standard. UTC time scale is maintained by the International Bureau of Weights and Measurements (BIPM) adjusted to be close to a time scale based on the Earth’s rotation. In Thailand, the official atomic time clocks are maintained by the National Institute of Metrology Thailand (NIMT) to produce UTC(NIMT) and Thailand standard time which is always 7 hours ahead of UTC(NIMT) because of the time zone differences between Greenwich and Bangkok. National Positioning, Navigation and Timing (PNT) infrastructure comprises of GNSS geodetic receivers uniformly distributed to continually observe GNSS signals, mainly for geodetic survey applications both real-time and post-processing services. NIMT is involved in order to provide time link to UTC and to determine the characteristics of GNSS receiver internal clocks; namely, fractional frequency offset and frequency stabilities by applying the GNSS time transfer techniques of common-view algorithms. Monitored time differences with respect to UTC(NIMT) are achieved from selected 4 ground stations in different parts of the country with observations of 21 days in order to determine the frequency stability at 1-day and 7-day modes. GNSS standard log files; in RINEX format, at these receivers are transformed into a time transfer standard format; CGGTTS, used to compute the time differences between two stations, the fractional frequency offset and the frequency stability. Averaged fractional frequency offsets are 2.8 × 10 − 13 Hertz/Hertz 2.8\times {10^{-13}}\hspace{2.38387pt}\text{Hertz/Hertz} and computed Allan deviation is around 1.5 × 10 − 13 Hertz/Hertz 1.5\times {10^{-13}}\hspace{2.38387pt}\text{Hertz/Hertz} for an averaging time of 1 day. The comparison of the national time scale and receiver clock offsets of every receivers in this national GNSS PNT infrastructure could be accomplished through common-view time transfer using GNSS satellites to maintain the time link of geodetic active control points to UTC as well as to determine receiver internal clock characteristics.

A Low Complexity joint synchronization algorithm based on CAZAC sequence for OFDM system

To solve the problem of timing ambiguity and reduce the complexity of integer frequency offsets (IFO) estimation for OFDM system, this paper proposes a novel synchronization algorithm based on CAZAC sequence in time domain. The algorithm constructs a training sequence with conjugate and symmetry properties. Firstly, timing synchronization and IFO estimation are completed simultaneously by utilizing the cross-correlating of the training sequence and local signal based on the analysis of the impact of IFO on the timing of meric peak positions. Then the fractional frequency offsets (FFO) estimation is done using the repeatability of the symmetrical training sequence. Compared with the existing representative algorithms, the proposed algorithm achieves better synchronous performances with lower computational complexity and acceptable transmission efficiency.

A novel joint timing/frequency synchronization scheme based on Radon–Wigner transform of LFM signals in CO-OFDM systems

A joint timing and frequency synchronization method has been proposed for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) system in this paper. The timing offset (TO), integer frequency offset (FO) and the fractional FO can be realized by only one training symbol, which consists of two linear frequency modulation (LFM) signals with opposite chirp rates. By detecting the peak of LFM signals after Radon–Wigner transform (RWT), the TO and the integer FO can be estimated at the same time, moreover, the fractional FO can be acquired correspondingly through the self-correlation characteristic of the same training symbol. Simulation results show that the proposed method can give a more accurate TO estimation than the existing methods, especially at poor OSNR conditions; for the FO estimation, both the fractional and the integer FO can be estimated through the proposed training symbol with no extra overhead, a more accurate estimation and a large FO estimation range of [−5 GHz, 5GHz] can be acquired.

Fractional frequency offset estimation for OFDM systems in non-cooperative communication

The traditional fractional frequency offset (FFO) estimation schemes for orthogonal frequency division multiplexing (OFDM) in non-cooperative communication have the problems of susceptible performance with the frequency offset values and the number of OFDM symbols, a novel fractional frequency offset blind estimation scheme based on EKF for OFDM systems is conceived. The nonlinear function of the frequency offset is calculated by employing the correlation. And then the frequency offset is estimated by means of the iterative algorithm of EKF. The finally fractional frequency offset is estimated by adopting repeated the above process. Simulation results demonstrate that the proposed scheme is robust to the frequency offset values without any requirements of a prior knowledge.

Blind Estimation for OFDM Fractional Frequency Offset Over Multipath Channels

To solve the problem of low estimation accuracy for orthogonal frequency division multiplexing (OFDM) fractional frequency offset (FFO) over multipath channels in non-cooperation communication syst...

Frequency synchronization for TD-LTE-A downlink receiver

A high accuracy frequency synchronization method is proposed for the 3rd generation partnership project (3GPP) long term evolution advanced (LTE-A) downlink receiver in time division duplexing (TDD) mode. In general, cyclic prefix (CP) correlation based fractional frequency offset (FFO) estimation method and primary synchronization signal (PSS) differential correlation based integer frequency offset (IFO) estimation method are applied for LTE-A frequency synchronization. However, the polarity of CP based FFO estimation result may get reversed when system FFO is closer to the edge of frequency estimation range on account of noise interference; PSS based IFO estimation has performance degradation in low signal noise ratio (SNR). We propose polarity detection aided CP based FFO estimation and frequency domain enhanced differential correlation based IFO estimation to obtain higher accuracy of frequency synchronization. Computer simulation shows that the proposed method greatly outperforms the conventional methods, especially in low SNR scenario.

Twin-Cell Detection (TCD): A Code Acquisition Scheme in the Presence of Fractional Doppler Frequency Offset

As a novel code-acquisition scheme, the twin-cell detection (TCD) is proposed for the acquisition in time of spread-spectrum codes in the presence of fractional Doppler frequency offset (FDFO). When the FDFO exists, the correlation peak that is used for detection during the acquisition process is split into two neighboring peaks with smaller magnitudes, which results in a considerable degradation in the overall acquisition performance of conventional schemes. In the TCD, the decision variable for detection is formed by combining two consecutive correlator outputs so that the influence of the reduction in the correlation peak due to the FDFO can be alleviated. The numerical results show that the TCD can offer a better mean-time-to-synchronization performance than the conventional scheme based on the cell-by-cell detection.

Comment and further results on paper “Carrier Frequency Recovery Technique in OFDM systems”

This comment points out some inaccurate formulae, and shows some irrelevant comparison of different estimators. Moreover, the correct formulae are provided and the modification to the fractional frequency offset (FFO) estimator is indicated. On the other hand, Our analysis have shown that the integer frequency offset (IFO) estimator of Ai is of serious theoretic problem.

A new frequency synchronization scheme for OFDM

In this paper, we propose a new carrier frequency offset (CFO) estimation algorithm and a new CFO correction structure in the multi-stage synchronization strategy in time and frequency domain for OFDM. The new CFO estimation algorithm uses all pilots including continual pilots (CP) and scattered pilots (SP) to estimate the CFO in frequency domain, and it can acquire more accurate estimation results than the conventional algorithm only using CP. The new CFO correction structure is a double-loop structure, and in the double-loop synchronization structure, fractional frequency offset (FFO) is corrected using a long loop as conventional method, however, integral frequency offset (IFO) does not go back to the time domain, and it is recovered using a short loop in frequency domain, which can shorten the convergence time of frequency synchronization. The analysis and simulations show the improved performance of the proposed CFO estimation algorithm and the double-loop correction structure.