Integer Frequency Offset Research Articles

W-band photonic-aided mm-wave ISAC system enabled by a shared OFDM signal waveform and a two-stage carrier frequency recovery algorithm.

Integrated sensing and communication (ISAC) systems will play a potential role in the upcoming six-generation (6G) networks. The reason is that ISAC systems can effectively solve the spectrum resource shortage problem and decrease the cost of deploying hardware equipment for simultaneously realizing communication and sensing. In this Letter, we successfully realize a W-band photonic-aided millimeter-wave (mm-wave) ISAC system enabled by a shared orthogonal-frequency-division-multiplexing (OFDM) signal waveform and two-stage carrier frequency recovery (CFR) algorithm. The digital-signal-processing (DSP)-based two-stage CFR algorithm includes the first-stage fractional frequency offset (FFO) estimation and compensation as well as the second-stage integer frequency offset (IFO) estimation and compensation. We experimentally analyze and verify that, with the introduction of the two-stage CFR algorithm, the system robustness to carrier frequency offset can be significantly enhanced. We also experimentally demonstrate, based on the ISAC system and our receiver DSP, a net data rate of up to 47.54 Gbit/s with a total signal bandwidth of 16 GHz over a 5.2 m wireless link at 94.5 GHz. Moreover, the sensing results indicate that the ISAC system can realize the detection of one target 2 m away from the transmitter with a ranging resolution of 0.98 cm and a ranging error of 4 mm. The system is anticipated to facilitate diverse potential applications in future 6G networks.

Complexity-Effective Joint Detection of Physical Cell Identity and Integer Frequency Offset in 5G New Radio Communication Systems

This paper presents a simplified joint synchronization scheme for the integer carrier frequency offset and physical cell identity using a primary synchronization signal (PSS) in 5G new radio (NR) communication systems. We demonstrate the efficiency of our proposed NR-PSS synchronization scheme by deriving its simplified implementation, which exploits the near-zero autocorrelation feature between cyclically shifted NR-PSS symbols. As a figure of merit, we compute the probability of detection failure of the proposed NR-PSS synchronization scheme and validate its accuracy via simulations. To illustrate the benefits and limitations of the proposed NR-PSS synchronization scheme, we compare it with the conventional NR-PSS synchronization scheme, considering factors such as detection performance and computation complexity. Numerical results indicate that, regardless of the channel environment, the proposed NR-PSS synchronization scheme achieves a significant reduction in arithmetic complexity while maintaining the same detection capability as existing NR-PSS synchronization schemes.

A Neural Network based Integer Frequency Offset Estimation and PSS Detection in 5G NR Systems

A Neural Network based Integer Frequency Offset Estimation and PSS Detection in 5G NR Systems

The impact of PSS autocorrelation on cell search based on robust maximum likelihood scheme in LTE system

Robust Maximum Likelihood scheme for primary synchronization signal (PSS) detection and integer frequency offset (IFO) in Long Term Evolution (LTE) system has the best performance of cell search [5]. This scheme provides good synchronization performance based on correlation properties of Zadoff-Chu (ZC) sequences and reduced-rank representation of channel frequency response in multi-path propagation fading environment. The three ZC sequences used for PSS in LTE system cannot be said to have sufficient correlation properties in considering impact of symbol timing error. In this paper, we evaluate impact of the autocorrelation of PSS on PSS detection and IFO estimation and raise an issue of using other ZC sequence with better correlation properties. The simulation results show that PSS detection and IFO estimation performances are improved by using proposed ZC sequence.

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.

Robust Blind Detection of Integer Carrier Frequency Offset for Terrestrial Broadcasting Systems Using Band Segmented Transmission

In the integrated services digital broadcasting-terrestrial (ISDB-T) system, the combination of digital terrestrial transmission and MPEG-4 advanced video coding (MPEG-4 AVC) has offered ways to provide a variety of digital high-definition television (HDTV) programs. Using band segmented transmission orthogonal frequency division multiplexing (BST-OFDM), the delivery of innovative video-on-demand and HDTV services is supported. To take full advantage of the attractive benefits of BST-OFDM, it is important to estimate integer frequency offset (IFO) without a priori knowledge on the segment type that is transmitted over transmission and the multiplexing configuration control (TMCC) signal. To address this issue, an efficient IFO detection method is proposed for the ISDB-T system employing BST-OFDM. To enable IFO detection independent of the segment type, information-bearing TMCC signals that are asymmetrically distributed in the frequency domain are used as pilot symbols. Numerical analysis is performed to present the relationship between error probability and design parameter. We show via the numerical results that the multiple transmitted TMCC information is efficiently used for blind estimation of the IFO, achieving robust estimation in the presence of the fractional frequency offset.

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.

Experimental demonstration of a 16.9 Gb/s link for coherent OFDM PON robust to frequency offset and timing error

Due to its merits of flexible bandwidth allocation and robustness towards fiber transmission impairments, coherent optical orthogonal frequency division multiplexing (CO-OFDM) technology draws a lot of attention for passive optical networks (PON). However, a CO-OFDM system is vulnerable to frequency offsets between modulated optical signals and optical local oscillators (OLO). This is particularly serious for low cost PONs where low cost lasers are used. Thus, it is of great interest to develop efficient algorithms for frequency synchronization in CO-OFDM systems. Usually frequency synchronization proposed in CO-OFDM systems are done by detecting the phase shift in time domain. In such a way, there is a trade-off between estimation accuracy and range. Considering that the integer frequency offset (IFO) contributes to the major frequency offset, a more efficient method to estimate IFO is of demand. By detecting IFO induced circular channel rotation (CCR), the frequency offset can be directly estimated after fast Fourier transforming (FFT). In this paper, circular acquisition offset frequency and timing synchronization (CAO-FTS) scheme is proposed. A specially-designed frequency domain pseudo noise (PN) sequence is used for CCR detection and timing synchronization. Full-range frequency offset compensation and non-plateau timing synchronization are experimentally demonstrated in presence of fiber dispersion. Based on CAO-FTS, 16.9 Gb/s CO-OFDM signal is successfully delivered over a span of 80-km single mode fiber.

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.

A complete cell search and synchronization in LTE

The initial process of identifying any available base station (BS) by a user equipment (UE) that wants to communicate is termed as cell search. To ensure a reliable communication, any UE has to be synchronized with the BS both in time and frequency domains. Cell search process is said to be complete once cell ID associated with long-term evolution (LTE) BS is decoded successfully. This paper presents a series of cell search and synchronization algorithms, which efficiently estimated time and frequency offsets as well as cell ID. The synchronization signals present in LTE, namely, primary synchronization signal (PSS) and secondary synchronization signal, that carry cell ID are critically exploited in the algorithms. The aforementioned algorithms are classified into two modules, namely, module I and module II, based on their computation complexity.In module I, a cyclic prefix (CP)-based maximum likelihood (ML) estimator is employed to obtain a coarse estimate of time and fractional frequency offset; however, the estimates are refined using synchronization signals. A joint estimation of timing, integer frequency offset (IFO), and PSS ID (sector ID) is carried out in module II. Both the modules operate on the cross-correlation approach of PSS with the received signal for obtaining timing and sector ID. IFO as a part of module II is detected from a finite hypotheses set using synchronization signals. Extensive simulations are carried out on a time-varying frequency-selective channel to analyze the performance of the algorithms.

Efficient Integer Frequency Offset Estimation Architecture for Enhanced OFDM Synchronization

In orthogonal frequency-division multiplexing (OFDM) systems, integer frequency offset (IFO) causes a circular shift of the subcarrier indices in the frequency domain. The IFO can be mitigated through strict RF front-end design, which tends to be expensive, or by strictly limiting mobility and channel agility, which constrains operating scenarios. The IFO is, therefore, often estimated and removed at baseband, allowing implementations to benefit from the relaxed RF front-end specifications and to be tolerant to both Doppler shift and multistandard channel selection. This paper proposes a novel architecture for the IFO estimation which achieves reduced power consumption and lower computational cost than contemporary methods, while achieving excellent estimation performance, close to theoretically achievable bounds. A pilot subsampling technique enables fourfold resource sharing to reduce the computational cost, while multiplierless computation yields further power reduction. Performance exceeds that of the conventional techniques, while being much more efficient. When implemented on field-programmable gate array for IEEE 802.16-2009, the dynamic power reductions of 78% are achieved. The architecture and method is applicable to other OFDM standards including IEEE 802.11 and IEEE 802.22.

A Robust Maximum Likelihood Scheme for PSS Detection and Integer Frequency Offset Recovery in LTE Systems

Before establishing a communication link in a cellular network, the user terminal must activate a synchronization procedure called initial cell search in order to acquire specific information about the serving base station. To accomplish this task, the primary synchronization signal (PSS) and secondary synchronization signal (SSS) are periodically transmitted in the downlink of a Long Term Evolution (LTE) network. Since SSS detection can be performed only after successful identification of the primary signal, in this work we present a robust scheme for joint PSS detection, sector index identification and integer frequency offset (IFO) recovery in an LTE system. The proposed algorithm relies on the maximum likelihood (ML) estimation criterion and exploits a suitable reduced-rank representation of the channel frequency response to take multipath distortions into account. We show that some PSS detection methods that were originally introduced through heuristic reasoning can be derived from our ML framework by selecting an appropriate model for the channel gains over the PSS subcarriers. Numerical simulations indicate that the proposed scheme can be effectively applied in the presence of severe multipath propagation, where existing alternatives provide unsatisfactory performance.

A Low-Complexity Integer Frequency Offset Estimation Scheme Using Combined Training Symbols for OFDM Systems

In orthogonal frequency division multiplexing (OFDM) systems, an integer part of a frequency offset (IFO) that causesambiguity in data demodulation is estimated generally by comparing correlations between the received and local signalsfor IFO candidates. In this paper, we propose an IFO estimation scheme that provides a tradeoff between the estimationperformance and the computational complexity including a conventional scheme as a special case. In the proposedscheme, template signals are formed by combining frequency-shifted training symbols, allowing the receiver to reducethe number of IFO candidates in the estimation process. Numerical results illustrate the tradeoff of the proposed scheme:The proposed scheme exhibits a tradeoff between the correct estimation probability and the computational complexitytaking the number of the training symbols used to construct the template signal as a parameter.

Complexity Effective Integer Frequency Offset and Sector Cell Detection Scheme for LTE Downlink System

This paper proposes a low-complexity integer frequency offset (IFO) and sector cell index (CID) detection scheme in a long term evolution downlink system. In the proposed detection scheme, the IFO and CID are estimated in a decoupled manner. In doing so, the detection scheme is designed to first estimate IFO without a priori knowledge of cell-specific reference signals and then detect the CID consecutively. We show via simulations that such a design achieves not only a low computational load but also comparable performance, when compared to the conventional detection scheme.

Integer Frequency Offset Estimation for OFDM Systems With Residual Timing Offset Over Frequency Selective Fading Channels

Accurate integer frequency offset (IFO) estimation is crucial for orthogonal frequency-division multiplexing (OFDM) systems, particularly in the presence of frequency-selective fading and residual timing offset (RTO). For existing algorithms, however, it is still a challenge to obtain a good tradeoff among the estimation performance, complexity, and spectrum overhead. In this paper, we propose a novel cross ambiguity function (CAF)-based IFO estimator using only one training sequence. By designing the training sequence, which has only a single sharp peak on its ambiguity function surface, a highly accurate and full acquisition range estimation of the IFO can be obtained in the presence of frequency-selective fading and RTO. Moreover, the adoption of the CAF expression in terms of time-domain signals ensures that the complexity of the proposed algorithm is relatively low. Simulation results verify its superior accuracy in frequency-selective fading channels and in the presence of RTO.

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.

An efficient two-step approach to integer frequency offset detection for OFDM systems

An efficient preamble structure for OFDM systems is proposed which inserts a short embedded repetition pattern (SERP) into conventional preamble structures allowing a two-step detection of the integer frequency offset (IFO). A coarse estimate of the IFO using the SERP is performed in the time domain prior to performing fine IFO detection in the frequency domain based on the original preamble structure. The complexity of the overall IFO detection procedure can be significantly reduced at a price of slight loss in SNR.

Pilot Subset Partitioning Based Integer Frequency Offset Estimation for OFDM Systems With Cyclic Delay Diversity

Cyclic delay diversity (CDD) is a simple transmit diversity technique for coded OFDM systems with multiple transmit antennas. However, high frequency selectivity caused by CDD degrades the performance of post- FFT estimation, i.e., integer frequency offset (IFO). This paper suggests a simple way of improving the performance of the IFO estimator based on the pilot subset partitioning which is designed to reduce the effect of frequency selective fading by adopting the CDD. By partitioning uncorrelated pilot subcarriers into subsets to satisfy high correlation, and performing frequency estimation for each pilot subset, a robust IFO estimation scheme is derived. The simulation results show that the proposed method can provide benefit to the overall system performance .

Low-cost integer frequency offset estimation for OFDM-based DRM receiver

In this paper, we propose an improved and low-cost integer frequency offset (IFO) estimation method by partitioning pilot symbols effectively in an orthogonal frequency division multiplexing based digital radio mondiale (DRM) system. To this end, the time reference cell (TRC) symbol for frequency estimation is grouped into a number of pilot clusters, so that the TRC subcarriers in each cluster are closely spaced to show approximately frequency-nonselective characteristics. The performance of the proposed IFO estimator is compared with that of the conventional estimator, and shows that the proposed technique can effectively achieve lower estimation errors in frequency offset estimation as well as can be implemented with reduced computational complexity.

Multiplication-Free Estimation of Integer Frequency Offset for OFDM-Based DRM Systems

This letter proposes a low complexity integer frequency offset (IFO) estimation scheme in an orthogonal frequency division multiplexing (OFDM) based digital radio mondiale plus (DRM+) system with nonuniform phased pilot symbols. To reduce the computational complexity, the pilot symbols used for frequency estimation in the DRM+ system are partitioned into a number of pilot subsets, and pilots in each subset are phase-rotated to have a unique phase so that the estimator is made computationally efficient.