Integer Carrier Frequency Offset Research Articles

Efficient Maximum Likelihood Algorithm for Estimating Carrier Frequency Offset of Generalized Frequency Division Multiplexing Systems

This study presents a computationally efficient maximum likelihood (ML) algorithm for estimating the carrier frequency offset (CFO) of generalized frequency division multiplexing systems. The proposed algorithm uses repetitive subsymbols and virtual carriers to estimate the fractional and integer CFOs, respectively. Through the use of repetitive subsymbols, this study first calculates the ML estimate of the fractional CFO in the time domain and then, accordingly, compensates for it from the received signal. The integer CFO can then be estimated through a virtual-carrier-mapping process in the frequency domain. In addition to improving performance in terms of estimation accuracy and computational complexity, the proposed non-data-aided algorithm is spectrally efficient relative to traditional algorithms.

Throughput analysis of frequency-domain contention under realistic conditions for hyperautomation

ABSTRACT Internet of Things (IoT) has widely been deployed in various industrial fields. To achieve hyperautomation in IoT-based applications, it calls for high-efficient wireless transmission technologies to improve the response speed of IoT nodes. Frequency-domain contention (FDC) is a promising contention-based channel access mechanism to meet this requirement. However, the nature of FDC’s multiple-transmission-multiple-reception and the limit of IoT chip’s synchronization accuracy will lead to carrier frequency offset (CFO) and hence frequent transmission collisions and null transmissions. Considering integer and fractional CFO, this paper theoretically analyzes the FDC throughput and verifies the accuracy of our model via extensive simulations.

Design of a Blind Estimation Technique of Carrier Frequency Offset for a Universal-Filtered Multi-Carrier System Over Rayleigh Fading

This letter proposes a blind and simple estimation technique of carrier frequency offset (CFO) for a universal-filtered multi-carrier (UFMC) system under specified carrier assignment. The estimation design is divided into a fractional part and an integer part. In particular, by utilizing the characteristic of auto-correlation functions, the proposed scheme only needs a single UFMC symbol and a few complex multiplications to achieve fractional CFO estimation. Furthermore, the integer CFO is selected from the admissible candidates that minimize the frequency response of the frequency-compensated signal corresponding to the specified null subcarriers. The proposed CFO estimation does not require the aid of pilot symbols, and is easy to implement. Its achievable performance is quantified by our derived closed-form expression of the mean-square error of the proposed fractional CFO estimation. The computer simulation results verify the effectiveness and reliability of the proposed approach that does not require an exhaustive frequency search method.

Reduced Complexity Frequency Ambiguity Resolution and Synchronization Signal Detection for 5G NR-V2X Communication Systems

This article presents a reduced-complexity sequential integer carrier frequency offset (ICFO) and sidelink primary synchronization signal (S-PSS) detection scheme in the 5G new radio vehicle-to-everything system. To perform the ICFO detection without information about S-PSS, a two-dimensional detection problem of the ICFO and S-PSS is reduced to two one-dimensional subproblems. Such a design allows us to sequentially detect them and relieves the computational burden of the proposed joint detection scheme. We use both analytical and numerical examples to validate the usefulness of the proposed sequential detector. The simulation results show that the proposed method attains target detection performance with significantly reduced complexity at the cost of increased processing time, as compared to the conventional methods.

Efficient Sequential Detection of Carrier Frequency Offset and Primary Synchronization Signal for 5G NR Systems

In this paper, a complexity-effective integer carrier frequency offset (IFO) and primary synchronization signal (PSS) detection scheme is proposed for 5G new radio systems. To estimate the IFO without any prior information about the PSS, the proposed detector uses the fact that three PSS sequences are cyclic-shifted versions of each other, which enables sequential detection of IFO and PSS. Both theoretical and simulation results are presented to verify the effectiveness of the proposed synchronization scheme. It is shown that the proposed scheme achieves a considerable complexity reduction while suffering from only slight degradation in the detection performance, compared to the conventional scheme.

Efficient carrier frequency offset estimation algorithm for generalized frequency division multiplexing systems

This paper presents an efficient carrier frequency offset (CFO) estimation algorithm for generalized frequency division multiplexing (GFDM) systems. The proposed algorithm formats the preamble into multiple identical subsymbols, and then decimates the received signal in the time domain to estimate the fractional CFO through array signal processing. After compensating for the fractional CFO, the proposed algorithm uses a low-complexity searching process to estimate the integer CFO in a maximum likelihood. The proposed algorithm presents some distinctive features: (1) it provides the full range of frequency acquisition region (FAR), which was considerably larger than that provided by many existing algorithms whose FAR was limited to one subcarrier spacing; (2) the proposed algorithm can use a single subsymbol to estimate the integer CFO by using the searching process of stepsize 1, significantly reducing its computational complexity; and (3) the decimation of the received signal ensures the proposed algorithm a power gain in fractional CFO estimation, resulting in an improved estimation accuracy compared with conventional algorithms.

A Robust Joint Cell Identification and Frequency Recovery Scheme for LTE Machine-Type Communications

The main features for future machine-type communication (MTC) cellular networks are to support low-power consumption, low-bandwidth, and long-range communication. One of the most challenging issues to meet these goals in the MTC cellular network is a low-complexity and reliable initial synchronization. To address this issue, in this article an efficient joint detection of integer carrier frequency offset (IFO) and cell identity (CID) is proposed for MTC in a long-term evolution (LTE) system. Unlike the conventional approach, the primary synchronization signal (PSS) and secondary synchronization signal (SSS) transmitted in the LTE-MTC system are used together to remove the effect of channel fading and symbol timing offset (STO). This design facilitates robust detection of the IFO and CID in the presence of residual STO without priori information on the SSS. The grouping of PSS subcarriers is integrated for joint detection, which plays an important role on reducing computational load. Both analytical and simulation results are provided to corroborate the feasibility of the proposed method. It has been demonstrated that the unique characteristics of the PSS and SSS sequences are effectively used for robust cell search in the presence of residual STO, compared to existing methods.

Improved Joint Estimation of Set Information and Frequency Offset for LTE Device-to-Device Communications

Device-to-device (D2D) communication is a key enabler to facilitate the realization of the Internet of Things in which direct communication between mobile users is allowed without the intervention of the base station. One of the most challenging issues in the D2D cellular network is a low-complexity and reliable initial synchronization. To solve this issue, an efficient joint detection of integer carrier frequency offset (IFO) and set information (SI) is proposed for D2D communication in a long term evolution (LTE) system. Unlike the conventional approach, the primary sidelink synchronization signal (PSSS) and secondary sidelink synchronization signal (SSSS) transmitted in the LTE-D2D system are used together to remove the effect of channel fading and symbol timing offset (STO). In addition, the conjugate property between two PSSS sequences is utilized. This design facilitates robust sequential detection of the IFO and SI without priori information on two synchronization signals when residual STO is present. It has been demonstrated that the inherent properties of the PSSS and SSSS sequences are effectively used for efficient cell search in the presence of residual STO, compared to existing methods.

Low-Complexity Detection of Integer Carrier Frequency Offset and Sidelink Identity for LTE-D2D Communications

This letter proposes a computationally efficient sequential estimation of integer carrier frequency offset (IFO) and sidelink identity (SID) in the long term evolution-device-to-device system. To detect the IFO without a priori knowledge on the SID information, the proposed detection method utilizes the conjugate property between two primary sidelink synchronization sequences. This design facilitates joint detection of the IFO and SID so that it can be detected sequentially. Simulation results indicate that the proposed sequential detection scheme has good performance and reduces computational complexity significantly compared to existing detection methods.

Suboptimal Maximum Likelihood Detection of Integer Carrier Frequency Offset for Digital Terrestrial Television Broadcasting System

The integrated services digital broadcasting-terrestrial (ISDB-T) system adopts band segmented transmission orthogonal frequency division multiplexing (BST-OFDM) to support different services using hierarchical transmission. In the ISDB-T system, in particular, a hierarchical configuration depends on modulation type used in OFDM segment, which has to be decoded at the receiver. Therefore, it is necessary to detect integer carrier frequency offset (IFO) before decoding the modulation type carried through transmission and multiplexing configuration control (TMCC) signal. To address this issue, an effective IFO estimation scheme is presented for the ISDB-T system, considering information-carrying TMCC signal as pilot symbol without any need of additional pilots. In order to verify the performance of the proposed estimation scheme, theoretical detection error rate is derived. It is shown from simulation results that the redundantly transmitted TMCC signal can be efficiently utilized for IFO detection, offering an approximate performance of maximum likelihood detection.

Effective Estimation of Integer Carrier Frequency Offset in LTE Downlink Systems With Symbol Timing Error

An effective integer carrier frequency offset (IFO) detection scheme is proposed in the long-term evolution downlink system without relying on the knowledge of the cell ID (CID) that is carried through the synchronization signal. To enable IFO detection without relying on the CID, the proposed IFO detection method utilizes the symmetric property of the synchronization signal, such as the primary synchronization signal (PSS) and the secondary synchronization signal (SSS). This design avoids the need to retrieve the CID that is carried by the PSS and the SSS at the IFO-matching stage. In addition to investigating the usefulness of the proposed IFO detection method, the probability of detection failure is theoretically calculated. The simulation results demonstrate that both the synchronization signals are effectively exploited for the robust detection of the IFO in the presence of non-negligible symbol timing error, where the conventional approaches show unsatisfactory performance.

Maximum‐likelihood synchronization and channel estimation with multiuser detection in GFDMA

AbstractAccurate estimation and correction of channel distortions and carrier frequency offset (CFO) are of a great importance in any multicarrier communication system. Hence, in this paper, we propose data‐aided CFO and channel estimation techniques for both multiuser uplink and downlink of the generalized frequency division multiple access (GFDMA). Our proposed solutions jointly estimate the CFO and channel responses based on the maximum‐likelihood criterion. To simplify the implementation of the proposed estimation algorithms, we suggest a preamble composed of two similar Zadoff‐Chu training sequences in a generalized frequency division multiplexing block. It is worth mentioning that our proposed technique can estimate both integer and fractional CFO values without any limitation on the acquisition range of CFO. In the uplink phase, each user aligns its carrier frequency with the base station using the estimated CFO in the downlink. However, the CFO estimates may get outdated for the uplink transmission. Thus, residual CFOs may still remain in the received signal at the base station. While being trivial in the downlink, CFO correction is a challenging task in the uplink. Thus, we also propose a joint CFO correction and channel equalization technique for the uplink of GFDMA systems. Finally, we evaluate our proposed estimation and correction algorithms in terms of estimation mean square error and bit error rate performance through simulations.

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.

Efficient Sequential Integer CFO and Sector Identity Detection for LTE Cell Search

In this letter, we propose an efficient algorithm for the detection of the integer carrier frequency offset (CFO) and sector identity used in the LTE cell search. For the conventional LTE cell search, the integer CFO and sector identity are jointly detected by utilizing the primary synchronization signal (PSS). By exploiting the symmetric property of the PSS, the integer CFO can be solely detected without the knowledge of sector identity, and thus, the joint detection of the integer CFO and sector identity is decoupled. Additionally, the proposed sequential integer CFO and sector identity detection (SISID) removes the effect of the channel frequency responses such that the detection accuracy is enhanced. We also design the SISID hardware architecture where the parts of the signals are processed in the polar coordinate so that all the multiplications are realized by additions/subtractions. The simulation results demonstrate that the proposed SISID achieves better detection accuracy than the conventional methods with only one third of the computational complexity.

Baseband Transceiver Design of a High Definition Radio FM System Using Joint Theoretical Analysis and FPGA Implementation

Advances in wireless communications have enabled various technologies for wireless digital communication. In the field of digital radio broadcasting, several specifications have been proposed, such as Eureka-147 and digital radio mondiale (DRM). These systems require a new spectrum assignment, which incurs heavy cost due to the depletion of the available spectrum. Therefore, the in-band on-channel (IBOC) system has been developed to work in the same band with the conventional analog radio and to provide digital broadcasting services. This paper discusses the function and algorithm of the high definition (HD) radio frequency modulation (FM) digital radio broadcasting system. Content includes data format allocation, constellation mapping, orthogonal frequency division multiplexing (OFDM) modulation of the transmitter, timing synchronization, OFDM demodulation, integer and fraction carrier frequency (integer carrier frequency offset (ICFO) and fractional CFO (FCFO)) estimation, and channel estimation of the receiver. When we implement this system to the field programmable gate array (FPGA) based on a hardware platform, both theoretical and practical aspects have been considered to accommodate the available hardware resources.

Time and Frequency Synchronization for Multicarrier Transmission on Hexagonal Time-Frequency Lattice

In this paper, a novel synchronization acquisition approach, including preamble structure, time and frequency synchronization algorithms, is proposed for hexagonal multicarrier transmission (HMCT) system. Specifically, a novel signal acquisition scheme based on time-frequency subspace projection (TFSP) and its simplified form are proposed for reliable signal acquisition. Time and frequency synchronization is divided into three steps: 1) the coarse time offset (TO) and coarse fractional carrier frequency offset (CFO) estimation; 2) fine TO and integer CFO estimation; and 3) fine fractional CFO estimation. The closed-form Cramér-Rao lower bound of the proposed CFO estimation scheme is given. Theoretical analyses and simulation results show that the proposed preamble structure, time and frequency synchronization algorithms for HMCT system can obtain robust performance over doubly dispersive (DD) channel, and the simulation results show excellent agreement with theoretical analyses.

Multiple Invariance MUSIC-Based Blind Carrier Frequency Offset Estimation for OFDM System with Multi-Antenna Receiver

In this paper, we address the problem of carrier frequency offset (CFO) estimation for orthogonal frequency division multiplexing (OFDM) systems with multi-antenna receiver. The received signal can be reconstructed to form data model with multi-invariance property, and then a multi-invariance MUSIC algorithm for CFO estimation is proposed. This algorithm has better performance of CFO estimation than ESPRIT method, multi-invariance ESPRIT method and trilinear decomposition algorithm, and also qualifies the estimation for both integer CFO and fractional CFO. Simulation results illustrate validity of this algorithm.

Blind Integer Carrier Frequency Offset Estimation for OFDM Systems with Constant Modulus Signaling

This paper presents a blind integer carrier frequency offset (IFO) estimator for the constant modulus (CM) signaling based OFDM systems. The key idea behind this method is a power reallocation technique which modifies the power of data in some predefined subcarriers over two consecutive OFDM symbols, thus the IFO can be estimated in the receiver via analyzing the distribution of these subcarriers. Instead of the exhaustive search, a low-complexity algorithm is proposed. The selection criterions of these predefined subcarriers are carefully designed and more than two OFDM symbols are employed to improve the robustness of this method to the multipath effect. Furthermore, this method can be applicable in multiple-input multiple-output (MIMO) OFDM systems with the orthogonal space-time block coding (OSTBC).

Integer Frequency Offset Estimator by Frequency Domain Spreading for UWB Multiband-OFDM

In this letter, we propose an integer carrier frequency offset (IFO) estimator in the presence of symbol timing error for an ultra-wideband multi-band orthogonal frequency division multiplexing (UWB MB-OFDM) system. The proposed IFO estimator uses frequency-domain spreaded data symbol which is provided in the MB-OFDM system. To demonstrate the accuracy of the proposed IFO estimator, comparisons are made with conventional estimators via computer simulation.

A Practical Scheme for Frequency Offset Estimation in MIMO-OFDM Systems

This paper deals with training-assisted carrier frequency offset (CFO) estimation in multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. The exact maximum likelihood (ML) solution to this problem is computationally demanding as it involves a line search over the CFO uncertainty range. To reduce the system complexity, we divide the CFO into an integer part plus a fractional part and select the pilot subcarriers such that the training sequences have a repetitive structure in the time domain. In this way, the fractional CFO is efficiently computed through a correlation-based approach, while ML methods are employed to estimate the integer CFO. Simulations indicate that the proposed scheme is superior to the existing alternatives in terms of both estimation accuracy and processing load.