Large Carrier Frequency Offset Research Articles

Novel Wide-Range Frequency Offset Estimation and Compensation for Burst-mode CPFSK Upstream Signaling in TDM-Based Digital Coherent PON

The burst-mode continuous phase frequency shift-keying (CPFSK) transmitter that combines a directly modulated laser diode, an electro absorption modulator and a semiconductor optical amplifier is attractive as a cost-effective transmitter for phase modulation formats for digital signal processing (DSP)-based coherent passive optical network (PON) upstream signaling. However, since highly accurate wavelength controllers for the transmitters in optical network units (ONUs) create excessive cost burdens, large carrier frequency offsets (CFOs) must be expected. Thus, a CFO compensation method with wide compensation range is required. This paper proposes a novel CFO estimation and compensation method for burst-mode CPFSK signals in upstream PON signaling. The proposed method is based on a simple blind algorithm and does not require any training symbols. We demonstrate wide CFO compensation range, from −12 to 14 GHz, with high receiver sensitivity, less than −42.5 dBm for 10 Gbit/s binary CPFSK signals. This range far exceeds that of the conventional CFO compensation method using a blind algorithm. Moreover, the proposed method can enhance the convergence of finite impulse response (FIR) filters. The feasibility of the proposed CFO compensation technique is successfully demonstrated for burst-mode CPFSK signals.

PRACH in Self-Powered Satellite Internet of Things: Low-Cubic Metric Preamble Design and Detection

This paper focuses on the energy-efficient physical random access channel (PRACH) design for self-powered sensors integrated satellite internet of things (S-IoT), where two novel preamble design schemes are proposed by jointly considering cubic metric (CM) reduction, coverage enhancement, resistance to carrier frequency offset (CFO), and low-complexity detection. Specifically, both of schemes possess a uniform preamble format by repeatedly cascading a series of conjugate Zadoff-Chu sequence pairs in the frequency domain, which can effectively mitigate the adverse effect of large CFO under the premise of ensuring PRACH coverage. Furthermore, phase rotation optimization and inverse discrete Fourier transform scaling are respectively leveraged in the two schemes to cope with the problem of CM performance degradation caused by sequence repetitions. We also develop corresponding preamble detection mechanisms that are capable of performing joint timing advance and CFO estimation, and conduct mathematical analysis in terms of CM and maximum coupling loss. Simulation results verify the feasibility of our schemes in self-powered S-IoT, and demonstrate that with the increment of the number of sequence repetitions, the proposed schemes can maintain relatively lower CM values in comparison to the state-of-the-art ones, while having significantly enhanced PRACH coverage and detection performance.

Combining IST-Based CFO Compensation and Neural Network-Based Demodulation for Eigenvalue-Modulated Signal

Eigenvalue-based communication technologies using inverse scattering transform (IST) have gained attention as a new transmission strategy in optical fiber communications. In recent years, several studies on artificial neural network (ANN)-based equalization and demodulation schemes for eigenvalue-modulated signal have been conducted to enhance the receiver sensitivity. However, in the case of a presence of a carrier frequency offset (CFO) at receiver, the effects of the CFO on ANN receiver of eigenvalue-modulated signal is yet to be reported. In this study, we numerically and experimentally investigated the generalization performances of eigenvalue domain ANN-based demodulator on CFO. Furthermore, we propose to combine an ANN-based demodulator with a CFO compensation method based on IST and a relation between frequency and eigenvalue shifts. The proposed method, based on an appropriate soliton pulse, achieves a high CFO estimation accuracy of submegahertz order even if the CFO reaches <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 2.5 GHz under the noiseless condition. In the presence of noise and a large CFO of 2.5 GHz, the method attains a CFO estimation accuracy below 60 MHz for OSNR = 10 dB with a low pilot pulse rate, such as 0.064%. We show the simulation results obtained after applying the proposed CFO compensation to the ANN demodulator, which is valid for 2.5 GHz CFO and long-haul transmission over 5000 km. Experiments performed in this study demonstrate successful demodulation of an eigenvalue-modulated signal with OSNR penalty <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 1 dB in the presence of CFO within 1 GHz at 2.5 Gb/s.

New Satellite Random Access Preamble Design Based on Pruned DFT-Spread FBMC

Next generation satellite payload technology is expected to provide digital processing capabilities. This will pave the way to regard satellites as flying base stations. However, the initial access procedure must be improved. In this work we focus on non-geostationary earth orbit (NGEO) satellite networks. In this scenario, the random access preamble signal and the detection must be robust to large carrier frequency offsets (CFOs). Towards this end, we investigate the adoption of the pruned discrete Fourier transform spread filter bank multicarrier waveform. The proposed design is suitable for the access scheme of forthcoming 5G-based NGEO satellite communications. The reason is twofold. First, it improves the spectral confinement with respect to the standard single-carrier frequency-division multiplexing (SC-FDM) waveform. Second, it achieves a high level of commonality with 5G new radio, by keeping unchanged the subcarrier spacing, the slot duration and the preamble sequence. Remarkably, the new design allows the straightforward application of non-coherent post detection integration (NCPDI) techniques, which divide the correlation in blocks. Numerical results show that the proposed solution reduces out-of-band emissions and the missed detection probability in presence of CFO, with respect to the conventional approach based on SC-FDM and preamble detection with full-length correlation.

Improved LTE like initial uplink synchronization via reduced problem dimension

Initial uplink synchronization (IUS) is a random access process in LTE that enables the eNodeB to detect, and uplink synchronize new user equipment. In future networks with huge number of devices, the number of simultaneous IUS users will increase significantly. In addition, it is desirable to serve users moving at high speed. We exploit the structure of the physical random access channel (PRACH) in LTE to reduce the dimension of the underlying data model. This reduction gives a very compact representation of channel impulse response (CIR). We utilize this representation to develop an efficient algorithm which can work in presence of large multiple access interference (MAI) and high carrier frequency offsets (CFO). When compared with the state of the art methods, the proposed method is capable of detecting a significantly higher number of IUS users and can allow high values of CFO. In addition, it produces very reliable estimates of both CIR and CFO of the detected users.

CFO compensation method using optical feedback path for coherent optical OFDM system

Abstract We investigate feasibility of carrier frequency offset (CFO) compensation method using optical feedback path for coherent optical orthogonal frequency division multiplexing (CO-OFDM) system. Recently proposed CFO compensation algorithms provide wide CFO estimation range in electrical domain. However, their practical compensation range is limited by sampling rate of an analog-to-digital converter (ADC). This limitation has not drawn attention, since the ADC sampling rate was high enough comparing to the data bandwidth and CFO in the wireless OFDM system. For CO-OFDM, the limitation is becoming visible because of increased data bandwidth, laser instability (i.e. large CFO) and insufficient ADC sampling rate owing to high cost. To solve the problem and extend practical CFO compensation range, we propose a CFO compensation method having optical feedback path. By adding simple wavelength control for local oscillator, the practical CFO compensation range can be extended to the sampling frequency range. The feasibility of the proposed method is experimentally investigated.

Sparse Blind Carrier-Frequency Offset Estimation for OFDMA Uplink

Carrier-frequency offset (CFO) estimation for uplink orthogonal frequency-division multiplexing access (OFDMA) systems is very challenging as it requires the estimation of multiple CFOs. In this paper, we propose a new framework referred to as sparse blind CFO estimation for interleaved uplink OFDMA. The proposed framework first discretizes the potential frequency offset ranges into discrete grid points, and formulates the original CFO estimation into a sparse signal recovery problem. Then, a novel two-stage matrix Bayesian compressive sensing-based CFO estimation method is proposed to solve the formulated problem. In the first stage, we employ a relatively large grid interval, and iteratively reconstruct a hyperparameter vector to generate a coarse estimation of multiple CFOs. The second stage reduces the grid interval, and the refined CFOs are estimated one by one through a novel low-complexity one-dimension searching algorithm. Numerical results show that the proposed method significantly outperforms conventional ones in terms of estimation accuracy, especially in the scenarios, such as low signal-to-noise ratios, large CFOs, and a large number of users.

Frame timing estimation based on statistical analysis for orthogonal frequency division multiplexing systems in multipath fading channels

This study investigates the problem of frame timing estimation in orthogonal frequency division multiplexing systems. Conventional timing estimation methods, which take advantage of the correlation property of a given preamble, always experience performance degradation in multipath fading channels with severe channel dispersion. To achieve accurate timing estimation, the authors propose a robust threshold-based timing detection method independent of the preamble structure. Based on the autocorrelation and cross-correlation, a novel timing metric with an extended correlation length is proposed to mitigate noise and resist large carrier frequency offsets. Due to the superior statistical property of the proposed timing metric, the threshold can be easily determined with no need for the process of noise variance estimation. Simulation results under different multipath fading channels demonstrate that the proposed method achieves a remarkably improved timing accuracy compared to the existing methods.

Carrier-interleaved orthogonal multi-electrode multi-carrier resistivity-measurement tool

This paper proposes a new carrier-interleaved orthogonal multi-electrode multi-carrier resistivity-measurement tool used in a cylindrical borehole environment during oil-based mud drilling processes. The new tool is an orthogonal frequency division multiplexing access-based contactless multi-measurand detection tool. The tool can measure formation resistivity in different azimuthal angles and elevational depths. It can measure many more measurands simultaneously in a specified bandwidth than the legacy frequency division multiplexing multi-measurand tool without a channel-select filter while avoiding inter-carrier interference. The paper also shows that formation resistivity is not sensitive to frequency in certain frequency bands. The average resistivity collected from N subcarriers can increase the measurement of the signal-to-noise ratio (SNR) by N times given no amplitude clipping in the current-injection electrode. If the clipping limit is taken into account, with the phase rotation of each single carrier, the amplitude peak-to-average ratio can be reduced by 3 times, and the SNR can achieve a 9/N times gain over the single-carrier system. The carrier-interleaving technique is also introduced to counter the carrier frequency offset (CFO) effect, where the CFO will cause inter-pad interference. A qualitative analysis and simulations demonstrate that block-interleaving performs better than tone-interleaving when coping with a large CFO. The theoretical analysis also suggests that increasing the subcarrier number can increase the measurement speed or enhance elevational resolution without sacrificing receiver performance. The complex orthogonal multi-pad multi-carrier resistivity logging tool, in which all subcarriers are complex signals, can provide a larger available subcarrier pool than other types of transceivers.

Joint CFO and SFO Estimator for OFDM Receiver Using Common Reference Frequency

In this paper, we propose a maximum likelihood method for jointly estimating carrier frequency offset (CFO) and sampling frequency offset (SFO) in receivers for orthogonal frequency division multiplexing signals. The proposed estimator exploits the fact that a single source (such as a crystal oscillator or voltage controlled oscillator) is typically used in modern wireless receivers to provide a reference frequency for both the sampling clock and the radio frequency synthesizers. The proposed CFO estimator is capable of a large CFO estimation range (i.e., more than half of intercarrier spacing) without extending the length of the training sequence. The Cramer–Rao lower bound (CRLB) of the variance of the estimated joint CFO and SFO is derived and compared to the CRLBs of the CFO and SFO estimators in the literature. More importantly, the proposed method is validated on a real-time wireless test bed.

CFO estimation based on Taylor MVDR approach using particle swarm optimization for interleaved OFDMA uplink systems

The problem of carrier frequency offset (CFO) estimation based on the Taylor minimum variance distortionless response (MVDR) criterion in interleaved orthogonal frequency division multiple access uplink systems was investigated. However, in the presence of large CFOs, more iteration is required for the iterative search technique. Therefore, a new CFO vector, based on the Taylor series expansion of the vector initially given, is proposed. The problem of finding the new CFO vector is formulated as the closed form of a generalized eigenvalue problem, which is readily solved. A two-stage method for increasing the accuracy of the residual CFO estimation featuring a low computational load is presented in this paper. A proper initial CFO estimate is required for the Taylor MVDR estimator. First, an initial CFO estimate is determined using a particle swarm optimization estimator. The predominant CFO estimate is then sent to the Taylor MVDR estimator to form an estimate. The proposed estimator can estimate CFOs with a lower computational load. Several computer simulation results are provided to illustrate the effectiveness of the proposed estimation approach.

Preamble-based frequency-domain joint CFO and STO estimation for OQAM-based filter bank multicarrier

Abstract Filter bank multicarrier systems, similarly to orthogonal frequency division multiplexing (OFDM), are very sensitive to carrier frequency offset (CFO) and symbol timing offset (STO). In this paper, a low-complexity preamble-based joint CFO and STO technique is presented. It is based on a relatively long preamble in order to improve the CFO estimation performance as well as avoid interference coming from the data following this preamble. After CFO and STO correction, the preamble can be reused to estimate the channel. Unlike most current techniques, the CFO and STO estimation occurs in the frequency domain. This allows for a low-complexity estimation with respect to time-domain techniques and, as will be shown by simulations, provide even better performance in a reasonable range. The drawback however is that the estimation range is shorter. Specifically, for large STOs (and to a smaller extent large CFOs), the performance decreases below time-domain estimations. Two versions of the STO estimation technique will be presented, the second one being an approximation of the first one, making it less complex yet also less precise. The performance is assessed by means of computer simulations, testing for both large and small STOs, and compared with existing techniques.

Carrier recovery for M-QAM signals based on a block estimation process with Kalman filter.

A novel carrier recovery scheme for demodulating optical M-ary quadrature amplitude modulation (M-QAM) signals is proposed and demonstrated. The proposed scheme treats a certain number of consecutive symbols as a processing block for which linear evolution of the carrier phases in time is assumed. The Kalman filter algorithm is employed to simultaneously estimate the carrier-frequency offset and carrier phases of the symbols in each block from the observation result. Consequently, an optimal carrier recovery operation with minimum mean squared error can be obtained, and large phase errors due to optical noise and large carrier-frequency offsets can be tolerated. We experimentally demonstrate the proposed scheme in demodulating optical 16- and 64-QAM signals, confirming its stable operation for carrier-frequency offsets even larger than 10% of the symbol rate of the signal. We also demonstrate 160-km transmission of a single-channel, single-polarization 64-QAM signal by using the proposed scheme in the demodulation process.

Multiple carrier frequency offsets tracking in co‐operative space‐frequency block‐coded orthogonal frequency division multiplexing systems

This study addresses the problem of carrier frequency offset (CFO) tracking in co-operative space-frequency block-coded orthogonal frequency division multiplexing (OFDM) systems with multiple CFOs. Considering that the inserted pilot tones are decayed by data subcarriers in the presence of multiple CFOs, a novel recursive residual CFO tracking (R-RCFOTr) algorithm is proposed. This method first removes CFO-induced inter-carrier interference from data subcarriers, and then updates the residual CFO (RCFO) estimation of each OFDM block recursively. When used in conjunction with a multiple CFOs estimator, the proposed R-RCFOTr can effectively mitigate the impacts from the multiple RCFOs with affordable complexity. Finally, simulation results are provided to validate the effectiveness of our proposed R-RCFOTr algorithm, which has performance close to that of perfect CFO estimation at moderate and high signal-to-noise ratio, and significantly outperforms conventional CFO tracking algorithm for large CFOs.

Multiple CFO Mitigation in Amplify-and-Forward Cooperative OFDM Transmission

In cooperative orthogonal frequency division multiplexing (OFDM) systems, accurate frequency synchronization is critical to achieving any potential gains brought by the cooperative operation. The carrier frequency offsets (CFOs) present among multiple nodes (source, relays and destination) are more difficult to tackle than the single CFO problem in point-to-point systems. Multiple CFOs cause phase drift, inter-carrier interference (ICI) and inter-block interference (IBI) in the received signal. This paper deals with the CFO induced interference mitigation problem in distributed space time block coded (STBC) amplify-and-forward (AF) cooperative OFDM systems. We propose a two step approach to recover the phase distortion and suppress the ICI and IBI using low complexity methods to achieve high performance. The first step is time domain (TD) compensation and the second step is frequency domain (FD) decoding. Two TD compensation schemes are proposed, i.e., IBI-removal and ICI-removal. The IBI-removal scheme decouples the two blocks of one STBC codeword completely and then decodes the ICI degraded blocks individually. The ICI-removal scheme removes ICI first and the subsequent decoding requires joint decoding of the two blocks. Simulation results show that the IBI-removal scheme which is of lower complexity performs well with small CFO. For large CFO, the ICI-removal with modified iterative joint maximum likelihood decoding (MIJMLD) outperforms other schemes.

Iterative Detection and ICI Cancellation for MISO-mode DVB-T2 System with Dual Carrier Frequency Offsets

In the DVB-T2 system with a multiple-input single-output (MISO) transmission mode, Alamouti coded orthogonal frequency division multiplexing (OFDM) signals are transmitted simultaneously from two spatially separated transmitters in a single frequency network (SFN). In such systems, each transmit-receive link may have a distinct carrier frequency offset (CFO) due to the Doppler shift and/or frequency mismatch between the local oscillators. Thus, the received signal experiences dual CFOs. This not only causes dual phase errors in desired data but also introduces inter-carrier interference (ICI), which cannot be removed completely by simply performing a CFO compensation. To overcome this problem, this paper proposes an iterative detection with dual phase errors compensation technique. In addition, we propose a successive-iterative ICI cancellation technique. This technique successively eliminates ICI in the initial iteration by exploiting pre-detected data pairs. Then, in subsequent iterations, it performs a fine interference cancellation using a priori information, iteratively fed back from the channel decoder. In contrast to previous works, the proposed techniques do not require estimates of dual CFOs. Their performances are evaluated via a full DVB-T2 simulator. Simulation results show that the DVB-T2 receiver equipped with the proposed dual phase errors compensation and the successive-iterative ICI cancellation techniques achieves almost the same performance as ideal dual CFOs-free systems, even for large dual CFOs.

A novel CFO estimator with joint bisection-searching and complexity-reduction technique for uplink MC-CDMA systems

This paper presents a simple scheme, which speeds the estimation of carrier frequency offset (CFO) as well as reducing the estimation complexity for multicarrier code-division multiple-access (MC-CDMA) uplink. Based on the concept of bisection method, the CFO is efficiently estimated by way of locating the peak value in the output power spectrum of the minimum output energy (MOE) detector. Complexity reduction results from the proposed data vector partition associated with an innovative data processing technique for the MOE detector. Simulation results show that the expected advantage of the proposed scheme can be achieved at the expense of a reasonable performance loss even in the presence of a large CFO.

Frequency shift filter‐based multi‐carrier transceiver

ABSTRACTIt is well known that orthogonal frequency division multiplexing (OFDM) is sensitive to carrier frequency offset (CFO) and suffers from a high peak‐to‐average ratio. In addition, the performance of OFDM is severely affected by strong co‐channel interference and strong narrowband interference. To mitigate the limitations of OFDM, we propose a new multi‐carrier transceiver based on frequency‐shift filter. A frequency‐shift filter can separate spectrally overlapping sub‐carrier signals by exploiting the spectral correlation inherent in the cyclostationary modulated signals. To increase spectral efficiency, we increase the percentage of spectral overlap between two adjacent sub‐channels. We derive an upper bound and a lower bound on the bit error rate performance of the proposed multi‐carrier transceiver in additive white Gaussian noise channel and frequency‐nonselective Rayleigh fading channel, respectively. Compared with OFDM, our simulation results show that the proposed multi‐carrier transceiver is much less sensitive to CFO and has a lower peak‐to‐average ratio; moreover, without any additional interference suppression technique, the proposed transceiver has the advantage of being able to mitigate strong co‐channel interference with CFO from the intended multi‐carrier signal and mitigate strong narrowband interference in additive white Gaussian noise channel and in Rayleigh fading channel in which a large CFO between the transmitted signal and the received signal often occurs. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Bounds and Algorithms for Multiple Frequency Offset Estimation in Cooperative Networks

The distributed nature of cooperative networks may result in multiple carrier frequency offsets (CFOs), which make the channels time varying and overshadow the diversity gains promised by collaborative communications. This paper seeks to address multiple CFO estimation using training sequences in space-division multiple access (SDMA) cooperative networks. The system model and CFO estimation problem for cases of both decode-and-forward (DF) and amplify-and-forward (AF) relaying are formulated and new closed-form expressions for the Cramer-Rao lower bound (CRLB) for both protocols are derived. The CRLBs are then applied in a novel way to formulate training sequence design guidelines and determine the effect of network protocol and topology on CFO estimation. Next, two computationally efficient iterative estimators are proposed that determine the CFOs from multiple simultaneously relaying nodes. The proposed algorithms reduce multiple CFO estimation complexity without sacrificing bandwidth and training performance. Unlike existing multiple CFO estimators, the proposed estimators are also accurate for both large and small CFO values. Numerical results show that the new methods outperform existing algorithms and reach or approach the CRLB at mid-to-high signal-to-noise ratio (SNR). When applied to system compensation, simulation results show that the proposed estimators significantly reduce average-bit-error-rate (ABER).

Synchronization for TDS-OFDM over multipath fading channels

Time domain synchronous orthogonal frequency division multiplex (TDS-OFDM) is an effective multi-carrier modulation scheme to improve the spectrum efficiency. However, conventional synchronization algorithm based on the correlation property of the time-domain pseudo-noise (PN) sequence may not work well over severe multipath fading channels when large carrier frequency offset (CFO) exits. In this paper, a robust synchronization algorithm is proposed where the PN sequence in the frame head is considered as a cyclic prefix (CP) OFDM training symbol. The time-domain slide auto-correlation based on the cyclic structure of the PN sequence is adopted for timing and fine CFO estimation, while in the frequency domain, a differential correlation is applied for large CFO estimation. Simulations demonstrate that the proposed method could achieve the satisfactory performance over multipath fading channels. In addition, to reduce the implementation complexity, the frame head of the TDS-OFDM system is preferred to be binary PN sequences in the frequency domain with cyclic structure in the time domain.