Carrier Frequency Offset Compensation Research Articles

A novel method for reducing the effect of doppler frequency shift in high-speed railway mobile communication using machine learning

Currently, high-speed railway systems are rapidly expanding worldwide, necessitating reliable and efficient mobile communication solutions. However, the Doppler frequency shift caused by the high speeds of trains presents significant challenges to communication systems, particularly those using OFDM in LTE. This paper presents a novel for Doppler frequency compensation in high-speed railway communication based on the results of estimating the train's velocity using machine learning algorithms. By leveraging advanced algorithm such as neural networks, our method dynamically predicts and compensates for Doppler shifts in real-time. In this proposed novel, the Doppler frequency value is calculated based on the actual train’s velocity and the scenario of a high-speed railway, then the Doppler frequency is used to compensate the carrier frequency offset (CFO) directly at the Access Point (AP) device on the train. We conduct simulations to evaluate the effectiveness of our proposed solution in a high-speed railway scenario. The results demonstrate a marked improvement in communication reliability and data integrity, highlighting the potential of machine learning to enhance the performance of mobile communication systems in high-speed railways. The results of the proposed model are evaluated based on the system’s bit error rate BER after the CFO compensation decreases and the ratio of average energy per bit (Eb) to noise power density (N0) (Eb/N0) increases. This shows that the proposed solution works effectively and reduces the system’s bit errors while improving the communication performance. This study opens new avenues for integrating intelligent systems in transportation networks, ensuring seamless connectivity, and improving passenger experience

Performance Analysis of Filtered OFDM using MLE for Wireless Communication Networks

Introduction: OFDM has evolved as an effective modulation format for 4G mobile network technologies, Long-Term Evolution, and Worldwide Interoperability for Microwave Access. OFDM is the modulation technique adopted for communication standards such as DSL, wireless LAN, DVB, and DAB. However, because CP-OFDM has considerable out-of-band emission that may interfere with transmissions in adjacent bands and applies a single set of parameters to the whole band to fulfill a given service, it is unable to accommodate the diversity of services. The objective of the research is to develop a novel waveform with better adaptability than CP-OFDM that employs filters to increase spectrum containment. In this view, an FIR filter that uses the Blackman window function to lessen the OOBE is proposed in this manuscript. Filtered OFDM is sensitive to carrier frequency offset (CFO). CFO increases the Inter-Carrier Interference (ICI) in F-OFDM systems. However, research work that combines the CFO compensation technique with filtered OFDM has not been listed in the literature so far. Methods: In this paper, Maximum likelihood estimation is used to cancel the ICI caused by the CFO. The high PAPR of filtered OFDM is one of its drawbacks. The amplitude clipping method is used to reduce the PAPR. The distortion caused by amplitude clipping is prevented by filters used in the FOFDM system. Highlights: • A novel waveform addressing OOBE issues in OFDM is developed for 4G wireless communication networks. • An innovative solution using MLE is proposed to address the challenges faced by the filtered OFDM system due to the CFO. • Article addresses the high PAPR problem of filtered OFDM. Results: The performance of filtered OFDM with amplitude clipping is analyzed in terms of BER, PSD, and PAPR over the AWGN channel. Conclusion: Simulation results show that, when compared to the traditional OFDM system, such a combined method effectively suppresses PAPR while maintaining good BER (Bit Error Rate) and OOBE performance.

On the performance of OFDM-IM systems in the presence of CFO effects

This study presents a comprehensive analysis of the performance degradation effects of carrier frequency offset (CFO) on orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems operating over frequency-selective multipath fading channels. CFO is an impairing factor that degrades the signal-to-noise ratio (SNR) through signal attenuation and inter-carrier interference (ICI). We derive a closed-form expression to quantify the SNR degradation under CFO for OFDM-IM systems. Additionally, we formulate a very tight upper bound for the bit error rate (BER), accounting for index modulation errors, CFO distortion, and multipath fading.The presented analytical formulations capture the unique characteristics of OFDM-IM systems and facilitate precise performance evaluation. The findings yield valuable insights into mitigating CFO-induced BER degradation through appropriate system parameter selection and CFO compensation techniques. Moreover, this investigation makes significant contributions towards designing reliable OFDM-IM communication links resilient to the combined effects of index modulation, frequency offsets, and dispersive channel conditions.

OFDM Modulation Classification Using Cross-SKNet With Blind IQ Imbalance and Carrier Frequency Offset Compensation

OFDM Modulation Classification Using Cross-SKNet With Blind IQ Imbalance and Carrier Frequency Offset Compensation

Real-Time Wide-Range Carrier Frequency Offset Compensation by Multi-Thread PADE for Fully Softwarized Access Networks

Real-Time Wide-Range Carrier Frequency Offset Compensation by Multi-Thread PADE for Fully Softwarized Access Networks

Design of satellite mobile synchronization system based on OFDM code

In the 5G era, satellite communication has been widely applied in more scenarios. Orthogonal Frequency Division Multiplexing (OFDM) has been adopted to the 3GPP standard and is the primary sync encoding method for satellite communication. However, the OFDM-based system is extremely susceptible to carrier frequency offset (CFO), and Doppler shift make a major impact on the CFO. Therefore, the traditional methods of synchronization based on OFDM cannot meet the requirement of satellite communication with large frequency offset and delay. There are many studies focus on improving the methods of CFO estimation and compensation to adapt the technologies of synchronization based on OFDM to the satellite communication system. In this paper, ZC based and matrix-vector multiplication method, multi-symbol merging method and preamble and PSS symbols based and filter frequency locked loop-based method of synchronization of OFDM-based satellite communication will be introduced. The accuracy and complexity of these methods both meet the requirement of 5G satellite communication system. Future researchers may focus on reducing complexity and expanding application scenarios.

Low‐complexity joint equalization and CFO compensation in uplink SC‐FDMA NOMA system under different power allocation strategies

AbstractIn current wireless systems, the claim for rapid data services has become unavoidable in broadband communication. Single carrier frequency division multiple access (SC‐FDMA) has remained a multiple access (MA) technique with low peak‐to‐average power ratio (PAPR) in 4G systems. Non‐orthogonal multiple access (NOMA) is a complimentary MA technique in the fifth generation (5G) new radio with the capability of using similar frequency elements for multiuser communication within a single cellular system. In SC‐FDMA NOMA systems the carrier frequency offsets (CFO) destroy the orthogonal behavior in multiple carriers during transmission leading to inter‐carrier interference (ICI) and multiple access interference (MAI). Furthermore, the power allocated for each user in the NOMA cluster exhibits a noticeable part in enhancing the performance of the system. In this article, we propose a joint low‐complexity linear regularized zero forcing (JLC‐LRZF) for SC‐FDMA NOMA system and investigate its performance using discrete Fourier transform (DFT) and discrete cosine transform (DCT). The proposed JLC‐LRZF equalization algorithm is capable of performing equalization and CFO compensation with low‐complexity with banded‐matrix approximation (BMA). Additionally, we investigate the effectiveness of SC‐FDMA NOMA system in achieving improved performance with different values of CFO and power allocation policies in uniform random multipath channels.

A Carrier-Based Gardner Timing Synchronization Algorithm for BPSK Signal in Maritime Communication

Wireless communication at sea is an essential way to establish a smart ocean. In the communication system, however, signals are affected by the carrier frequency offset (CFO), which results from the Doppler effect and crystal frequency offset. The offset deteriorates the demodulation performance of the communication system. The conventional Gardner bit-synchronization algorithm performs timing synchronization on the baseband, but it fails to solve the problem of carrier frequency offset. In this paper, a carrier-based timing-synchronization Gardner algorithm was proposed. The algorithm performed error detection in the carrier signal to estimate the synchronization error in real time and the time-domain expansion in the passband signal. Based on the estimated expansion factor, the algorithm located the sampling points of the ideal signal and re-interpolated all the sampling points on the passband to recover the passband signal without Doppler. This algorithm can solve both the frequency shift and time-domain expansion caused by the Doppler effect without further CFO estimation and compensation, thus reducing the overall computational complexity of the system. The simulations showed that the proposed algorithm greatly improves the ability of the communication system to combat Doppler compared to the conventional Gardner algorithm. The algorithm is primarily designed for binary phase-shift keying (BPSK)-modulated signals under the additive white Gaussian noise (AWGN) channel and can be applied to various maritime communication scenarios.

Evaluation of orthogonal frequency‐division multiple‐access systems in the presence of carrier frequency offset using wireless images transmission

AbstractOrthogonal Frequency‐Division Multiple‐Access (OFDMA) is used in different recent wireless communication systems. However, it is susceptible to carrier frequency offset (CFO) which effects the orthogonality between subcarriers and causes inter‐carrier interference (ICI) and multiple access interference (MAI). The aim of this paper is to analyze the impact of the CFOs on the performance of Discrete Sine Transform (DST) DST‐OFDMA, Discrete Cosine Transform (DCT) DCT‐OFDMA and Discrete Fourier Transform (DFT) DFT‐OFDMA systems and to evaluate them with different modulation schemes and different subcarriers mapping schemes over vehicular A and Stanford University Interim (SUI) 3 channels. Transmission of image over the wireless system is performed to analyze and investigate the performance in terms of the Peak Signal‐to‐Noise Ratio (PSNR), and the Mean Square Error (MSE). Through the evaluation, with CFO compensation, without CFO, and without CFO compensation cases are considered. In this work, Joint Minimum Mean Square Error (JMMSE) equalization and CFO compensation technique is used. It is noted that when the QPSK scheme and the SUI3 channel model are used then the DCT‐OFDMA system provides better MSE and PSNR performances than other systems for the JMMSE compensation technique.

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.

A turbo‐based encryption and coding scheme for multiple‐input multiple‐output orthogonal frequency division multiplexing wireless communication systems affected by Doppler frequency offset

AbstractMultiple‐Input Multiple‐Output Orthogonal Frequency Division Multiplexing (MIMO‐OFDM) is an essential technology in the wireless communication system. However, its performance is significantly affected by Carrier Frequency Offset (CFO), which leads to inter‐carrier interference (ICI). The CFO estimation and compensation techniques are used to mitigate the Doppler effect. In addition, the confidentiality of data is a key factor of the system. This paper proposes a Turbo‐based encryption and coding scheme to improve reliability and security for the MIMO‐OFDM wireless communication systems affected by the Doppler frequency offset. In our proposed scheme, the secret key is produced from channel parameters between legitimate users and it is used as a seed for generating a pseudo‐random bit sequence using an Advanced Encryption Standard (AES) generator with variable key lengths. The Turbo code's puncturing mechanism is controlled by this pseudo‐random bit sequence. The proposed method is applied to the system with different modulation schemes through the Rayleigh channel. The simulation results show that the system affected by the Doppler effect would obtain the best performance when using the highest key length of the AES generator, the BPSK, and a great number of receive antennas. Furthermore, the proposed solution outperforms several previous approaches for the MIMO‐OFDM systems.

Novel Data-Aided Carrier Frequency Offset Compensation Methods Using Asymmetric-Shape Constellations for Burst-Mode Coherent Reception

This paper introduces a novel data-aided carrier frequency offset (CFO) estimation and compensation method for m-array phase shift keying (m-PSK) signals in burst-mode digital coherent reception. Its key advances are as follows; the use of newly designed training symbols (TS) that exhibit asymmetric distributed constellations after differential decoding and a vector summation based feed-forward CFO estimation algorithm. These offer short response time and strong robustness to training symbols (TS) timing detection error with wide CFO estimation range of ±B/2, where B is signal baudrate. We evaluate the feasibility of the proposal by simulations of and experiments on 12.5-Gbaud SP-QPSK signals that target optical budget enhancement of 25-Gbps/λ-class PONs to realize long-reach and high splitting ratio optical access. The 100-km burst-mode transmission experiments confirm the proposal offers high sensitivity detection of better than −43 dBm with much wider CFO range of above ±10 GHz.

Efficient Equalization and Carrier Frequency Offset Compensation for Underwater Wireless Communication Systems

Efficient Equalization and Carrier Frequency Offset Compensation for Underwater Wireless Communication Systems

Joint CFO and channel estimation using pilot aided interpolation for high performance MIMO-OFDM

ABSTRACT Multiple Input Multiple Output (MIMO) system with orthogonal frequency division multiplexing (OFDM) is a promising physical layer candidate for the current and future wireless standards. MIMO increases system throughput while OFDM maximizes spectrum efficiency. To reduce the impacts of frequency selective fading and increase the capacity, MIMO requires precise channel state information (CSI). The presence of carrier frequency offset (CFO) introduces intercarrier interference (ICI) among the subcarriers which degrades the system performance. MIMO channel estimation is done under the assumption of perfect frequency synchronisation between the transmitter and receiver, or zero CFO. However, such an assumption is incorrect for time-varying and frequency-selective wireless channels, and the presence of CFO has an impact on channel estimation accuracy. In the existing methods, CFO and channel estimations are carried out independently using separate training sequences which reduces the spectral efficiency. As a result, the pilot aided interpolation approach is proposed in this paper for the joint estimate and compensation of CFO and channel effects using the same set of pilot tones. Theresults show that the proposed method offers precise CFO and channel estimation which improves the bit error rate performance and carrier to interference power ratio (CIR) of MIMO-OFDM system.

Joint DFT Precoding and Discrete Wavelet Transform in SC-FDMA NOMA System with Carrier Frequency Offset Compensation

Joint DFT Precoding and Discrete Wavelet Transform in SC-FDMA NOMA System with Carrier Frequency Offset Compensation

Blind CFO Compensation for Next Gen WLAN Systems

With the next Gen Wireless Local Area Networks (WLANs) all geared up to enhance the network wireless capacity in gigabits with utmost reliability for mixed environments utilizing the MIMO OFDM/OFDMA technique with reduced subcarrier spacing and denser modulation schemes. These stern requirements make the system to be highly susceptible to Carrier Frequency Offset (CFO) and the IEEE standard specifies a very stringent frequency offset limit to be well within ±20ppm which is a demanding ask to be met to keep all the WiFi stations to operate within their specified channels with minimum spectral leakage. The current article proposes a novel blind carrier frequency offset compensation method which efficiently computes the CFO. The simulation results prove that the performance of the proposed algorithm not only satisfies the prescribed limits of ±20ppm but it is also robust to even higher offsets like ±25ppm. The proposed algorithm can be utilized in WiFi standards such as IEEE 802.11 n/ax. Rayleigh interference with additive white Gaussian noise (AWGN) channel was applied to analyze the algorithm’s performance. This technique offers better synchronization and reliable communication.

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.

Radio Frequency Fingerprint Identification for LoRa Using Deep Learning

Radio frequency fingerprint identification (RFFI) is an emerging device authentication technique that relies on the intrinsic hardware characteristics of wireless devices. This paper designs a deep learning-based RFFI scheme for Long Range (LoRa) systems. Firstly, the instantaneous carrier frequency offset (CFO) is found to drift, which could result in misclassification and significantly compromise the stability of the deep learning-based RFFI system. CFO compensation is demonstrated to be effective mitigation. Secondly, three signal representations for deep learning-based RFFI are investigated in time, frequency, and time-frequency domains, namely in-phase and quadrature (IQ) samples, fast Fourier transform (FFT) results and spectrograms, respectively. For these signal representations, three deep learning models are implemented, i.e., multilayer perceptron (MLP), long short-term memory (LSTM) network and convolutional neural network (CNN), in order to explore an optimal framework. Finally, a hybrid classifier that can adjust the prediction of deep learning models with the estimated CFO is designed to further increase the classification accuracy. The CFO will not change dramatically over several continuous days, hence it can be used to correct predictions when the estimated CFO is much different from the reference one. Experimental evaluation is performed in real wireless environments involving 25 LoRa devices and a Universal Software Radio Peripheral (USRP) N210 platform. The spectrogram-CNN model is found to be optimal for classifying LoRa devices which can reach an accuracy of 96.40% with the least complexity and training time.

Equalization and CFO compensation for SISO-OFDM communication systems with chaotic interleaving

ABSTRACT The conventional Orthogonal Frequency Division Multiplexing (OFDM) can be simply implemented using Inverse Discrete Fourier Transform (IDFT), and DFT instead of bank of modulator and bank of demodulator, respectively. However, the OFDM can be modified using chaotic interleaving that reduces the 1-Dimension (1-D), and 2-Dimension (2-D) burst errors, and improve the Bit-Error-Rate (BER) performance. In fact, the OFDM system suffers from high sensitivity to Carrier Frequency Offset (CFO). This paper presents a Joint Low-Complexity Regularised Zero Forcing (JLCRZF) equaliser for OFDM system based chaotic interleaving. The proposed JLCRZF jointly performs the equalisation and CFO compensation processes using banded-matrix approximation concept. Simulation results show that the proposed JLCRZF equaliser acts well especially in case of estimation errors.

ICA based estimation and compensation of carrier frequency offset for MBOFDM based UWB systems

A carrier frequency offset (CFO) is addressed as a main type of wireless communication system imperfections in this paper. Carrier frequency offset (CFO) severely deteriorates the performance of OFDM receiver. Here an effective time domain CFO estimation and compensation method using symmetric subcarrier allocation (SCA) for multiband orthogonal frequency division multiplexing (MBOFDM) based ultra-wideband system is proposed. A data supported CFO estimation technique, which is robust to a larger offset, is presented as a novel method in compensation of CFO. An effective separation matrix scheme of OFDM signal with CFO is obtained. Subsequently, independent component analysis (ICA) based CFO estimation is stated. On fully exploiting the ECMA-368 preamble symbols, the proposed technique is capable for carrier frequency offset of 100 ppm, and the result is confirmed through simulations.