Carrier Synchronization Research Articles

Design of SSB Communication System based on Carrier Synchronization Extraction

Design of SSB Communication System based on Carrier Synchronization Extraction

OF-FSE: An Efficient Adaptive Equalization for QAM-Based UAV Modulation Systems

Quadrature amplitude modulation (QAM) is one of the essential components of unmanned 1 aerial vehicle (UAV) communications. However, the output signal accuracy of QAM deteriorates dramatically and even collapses in the case of UAVs in a harsh channel environment. This is due to the fractionally spaced equalization based on the multi-modulus blind equalization algorithm being implemented prior to carrier synchronization in QAM-based UAV modulation systems. The carrier frequency offset from the harsh channel signal thus contributes to the significantly degraded performance of MMA by suffering the fractionally spaced equalization. Therefore, in this paper, a novel offset feedback fractionally spaced equalization architecture for UAVs to eliminate the carrier frequency offset is first proposed. In this architecture, the carrier frequency offset allows estimated and incorporation into the input signal of fractionally spaced equalization to compensate for the offset. Moreover, a new multi-modulus decision-directed algorithm is presented for the novel architecture to improve the received signal accuracy of UAVs further. It enables adaptive optimization of the convergence process in accordance with the dynamic UAV communication environment employing the multi-modulus blind equalization algorithm and decision-directed blind equalization algorithm (MDD). Simulation results demonstrate the effectiveness of the OF-FSE framework in enabling the QAM-based UAV modulation systems operation in harsh channel scenarios. Moreover, the performance of the presented new MDD algorithm compared with baseline approaches is also confirmed.

Enhanced Synchronization Algorithms for BOC Signals Based on Reconstructed Sub-Correlation Functions

Aiming at the ambiguous synchronization of binary offset carrier (BOC) and composite binary offset carrier (CBOC) modulation signals due to secondary peaks for Global Navigation Satellite System (GNSS), a reconstructed sub-correlation function synchronization algorithm (RSSA) for BOC and CBOC is proposed. The general autocorrelation subfunctions of BOC and CBOC are obtained by deriving the subfunctions of the cross-correlation function between BOC signals with different modulation orders. According to the characteristics of the subfunctions, the corresponding reconstruction rules are set to obtain the unambiguous correlation functions. To further reduce the complexity of the local auxiliary signal, a local auxiliary signal optimization algorithm (LASOA) is proposed based on RSSA, which only needs to generate a local two-level signal compared to the conventional CBOC local four-level signal. The simulations show that the two algorithms proposed in this paper reduce the amplitude of the side peaks of the normalized correlation peaks of BOC by at least 0.09 compared with the autocorrelation side-peak cancellation technique (ASPeCT), maintain a high detection probability, and the multipath error is smaller than that of the autocorrelation side-peak cancellation technique (ASPeCT) and other traditional algorithms. The phase discrimination curves show that the linear region slope gains of the two algorithms in this paper are above 2 dB compared with the ASPeCT and other conventional algorithms.

Carrier synchronisation in multiband carrierless amplitude and phase modulation for visible light communication‐based IoT systems

AbstractThe technical feasibility of developing an Internet of Things multi‐user communication system is evaluated based on a central digital multiband carrierless amplitude and phase transmitter, which broadcasts data on multiple channels for a number of low‐cost/low‐power devices. It addresses the issue of carrier synchronisation, which is critical in real‐world implementations because of imperfections of devices and the delays of the system. A simulation model for the traditional Costas Loop is presented, along with performance results, which demonstrate the system's ability to synchronise with pull‐in and lock ranges of ±800 and ±900 Hz, respectively. The loop requires 1.194 ms to be in the locked state, allowing the system to lock within 6 symbols period. In addition, the authors measured the performance of the system in the presence of noise and interference from other modulated bands. The results showed that noise and interference did not degrade the system's performance. Although the system was unable to lock when energy was present in adjacent bands, alternative options such as a high order phase‐locked loop and hybrid frequency‐division multiple access and time‐division multiple access, can improve system performance without significantly increasing the cost and complexity of the devices.

Impact and compensation of carrier synchronization errors in OFDM signals with very large QAM constellations

AbstractLow cost video sensors used for streaming video signals to help firefighters, require high bit rate due to uncompressed images. To increase spectral efficiency given a limited bandwidth, very high order constellations in high signal to noise ratio regimes can be used. However, noise is not the only factor effecting the high order constellations. These constellations are also sensitive to hardware impairments and system non‐linearities. Therefore, in this paper, the effect of carrier frequency offset (CFO) on the performance of an orthogonal frequency division multiplexing (OFDM) system with high order quadrature amplitude modulation (QAM) is studied. A closed form expression is derived for the maximum normalized residual CFO that an OFDM system with M‐QAM constellation can resist to have an error free symbol detection. Finally, the suitability of common previous CFO estimation techniques such as the cyclic prefix based technique and the Moose technique in these systems are investigate. The results show that the maximum residual CFO that an OFDM system with M‐QAM constellation can resist is proportional to the inverse of . The results also show that very large order QAM constellations such as 4096‐QAM are very sensitive to even small residual CFO values and their performance degrades, significantly. However, the bit error rate analysis indicate that the Moose CFO estimation technique can be used in these systems to compensate the CFO effect, accurately.

Blind symbol and carrier synchronization with carrier frequency offset estimation for space–time line coded systems

In this study, utilizing the structure of the space–time line code (STLC) signals, a blind symbol and carrier synchronization method considering the carrier frequency offset (CFO) is developed. The proposed method can achieve almost perfect synchronization performance with more than three transmit antennas, irrespective of the CFO values. Based on the results, the proposed blind symbol and carrier synchronization method is expected to accelerate the practical deployment and operation of the low-complexity STLC systems that achieve full spatial diversity gain with partial or no channel state information at the receiver.

Joint Physical Layer Frame Optimization and Carrier Synchronization for Satellite Communications

In this paper, we discuss general data-framing and optimization, parallel frequency-phase estimation, and powerful frequency estimator for satellite communications. Based on the standard pilot-symbol-assisted-modulation (S-PSAM) frame, we design a general PSAM (G-PSAM) frame, whose corresponding data-aided & non-data-aided Cramér-Rao bound (DA&NDA CRB) is derived with respect to carrier frequency offset, time delay and phase offset, followed by its approximate form. Also, we provide a simple solution to the G-PSAM frame optimization by means of the approximate DA&NDA CRB and the control-variate method. With an unbiased auto-correlation (AC) value, we then propose a frequency-phase decoupler and develop a parallel frequency-phase estimation (PFPE) mode in terms of the serial frequency-phase estimation (SFPE) mode, where a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">serial-to-parallel</i> estimation conversion can be implemented. Furthermore, we extend the AC frequency estimator in the PFPE mode as a powerful stepwise correlation-based one aiming at the target performance. Theoretical analysis and numerical results are provided to show the superiority of the optimized frames, the robustness of the PFPE mode, and the adaptability of the proposed frequency estimator with the optimized frames under different transmission systems.

Ionospheric Scintillation Mitigation With Kalman PLLs Employing Radial Basis Function Networks

We investigate two adaptive Kalman phase locked loop (PLL) structures for ionospheric scintillation mitigation for global navigation satellite systems (GNSS) receivers, employing radial basis function (RBF) networks to model the scintillation phase and amplitude, instead of the typically employed autoregressive (AR) models. In the first structure, the Kalman filter innovations are computed by the arctangent phase discriminator, and the state estimates are directly employed in the carrier replica generation. In the second structure, the Kalman filter measurements are the prompt correlator outputs, and the error states are computed and used by a state feedback controller to provide a control signal to drive the carrier replica generation. The nonlinear RBFs provide more flexibility to capture nonlinear dynamics evolving with time, possibly present in the scintillation phase and amplitude. The weights of the RBF networks and the covariance matrices of the process and measurement noise of the Kalman filters are estimated online, in the adaptive Kalman PLL structures. Simulations with synthetic severe scintillation data show the capability of the proposed Kalman PLLs to improve robustness to scintillation effects in carrier synchronization, with performance similar to the corresponding structures employing AR scintillation models. Simulations using recorded scintillation data collected by a commercial receiver highlight the learning and generalization capability of the RBF networks to cope with evolving scintillation characteristics over time with possibly nonlinear effects. The Kalman PLL structures employing the RBF networks present reduced errors compared to the structures using AR models.

A Carrier Synchronization Lock Detector Based on Weighted Detection Statistics for APSK Signals

To solve the application limitations of conventional detectors caused by discrete phase distribution of high-order APSK signals, and the problem that the detection performance will degrade when the automatic control gain is unideal, a carrier synchronization lock detector based on weighted detection statistics is proposed for APSK signals. Based on the detection statistics of the Linn detector, the proposed detector calculates a weighted factor according to the amplitude difference of the signal on the APSK constellation to adjust the weight of detection statistics for different rings. The proposed detector solves the detection performance degradation problem of the Linn detector caused by uneven phase distribution. In order to further improve detection performance, the detection threshold and statistical signal length are reasonably designed. The expectation and variance properties are derived, and the lock detection probability is analyzed. The performance of the proposed detector is verified through simulations. Simulation results show that the proposed carrier synchronization lock detector has better performance than the Linn detector.

Channel synchronization based on deep learning

AbstractAiming at the difficulty of the deep neural network (DNN) adapting to channel changes in communication systems, a channel synchronization deep neural network (CSDNN) based on deep learning (DL) is designed for realizing carrier synchronization, bit timing synchronization, and automatic gain control (AGC). By introducing a frequency‐domain cyclic convolution (FDCC) layer, the network transformed the time‐domain triangle activation into frequency domain linear activation taking FFT and IFFT matrixes as the activation function, solved the reverse gradient transmission‐blocking problems in training the time‐domain carrier synchronization neural network, effectively overcome the FFT inherent “fence” effect, and accurately compensated carrier frequency offset; By introducing a time‐domain cyclic convolution (TDCC) layer and the special frame structure design containing repetitive training sequence, the network training was completed to realize bit timing synchronization under the condition of the uncertain corresponding relationship between training data and labels. Combining phase inverse rotation dense (PIRD) layer, the network can be trained with very little training data to complete fast carrier synchronization and timing synchronization, at the same time adjust the received signal gain and suppress the jamming, which makes it is possible to train the channel synchronization deep neural network online under jamming environment, and provide a feasible way of realizing the intelligent communication system.

Secure optical communication based on M-ary signals masked by optical chaos

We propose a secure optical communication scheme by employing optical chaos to mask the M-ary signals. In this scheme, the key is obtained by injecting the chaotic source into the system parameters with different initial conditions from the receiver. The M-ary signal is generated by the digital analog converter using binary signals and the keys. And the neighboring level of M-ary signals is hidden so deeply in chaotic noise that it cannot be detected by eavesdroppers. Furthermore, the closed-loop synchronization scheme for optical chaos is used to ensure high-quality carrier synchronization between transmitter and receiver. In addition, we propose an algorithm to calculate the effect of chaotic masking by calculating the similarity between the original and the decoded signals to determine whether the signal is effectively masked. The secure transmission of 1.25 Gbps, 1024-ary signal is demonstrated by using the chaotic intensity concealment method, and the system masking performance is evaluated by analyzing different masking coefficients, signal level discernibility, parameter mismatch, and different modulation orders.

An Improved Phase Deviation Discriminator for Carrier Synchronization of APSK Signal in Satellite-to-Ground Communication Systems

The conventional phase deviation discriminator used in the decision feedback loop for carrier synchronization of APSK signal requires symbol decision for every constellation symbol. When the number of constellation symbols used for coherent integration becomes larger, the complexity would increase greatly. To solve this problem, this work proposes an improved phase deviation discriminator based on symbol decisions. It firstly executes doubling frequency on the APSK signal to reduce the modulation order and eliminate the modulation phase of the received signal. Then, it rotates the constellation clockwise and selects the constellation symbols that on the X-axis to execute coherent integration and phase deviation extraction. Compared to the conventional discriminator in the decision feedback loop, the proposed discriminator can reduce the symbol decision times and steps. Therefore, when a large number of constellation symbols are used for coherent integration, it can reduce the computational complexity significantly. Moreover, with a large number of constellation symbols, the proposed discriminator achieves better BER and RMSE performance than other existing feedback loops.

A Full-Digital M-CAP Receiver With Synchronisation and Adaptive Blind Equalisation for Visible Light Communications

With an emphasis on the real-time implementation of a practical carrier-less amplitude and phase (CAP) receiver for visible light communication (VLC), this paper proposes a full-digital architecture for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$M$</tex-math></inline-formula> -CAP receiver with synchronisation and adaptive blind equalisation. The architecture is mainly based on the observation that a CAP signal can be demodulated using a quadrature and amplitude (QAM) receiver with an added counterclockwise rotation operation. The proposed CAP receiver employs two digital phase-locked loops (DPLL) to realise the symbol timing and carrier synchronisation, which are the most critical issues in practical systems. With the constant-modulus algorithm (CMA) offering the benefit of decoupling carrier and symbol timing synchronisation, the receiver can blindly equalise the distorted signal at the output of symbol timing synchronisation. Finally, the performance of 4/16/64-CAP receivers, which are designed using this architecture and operates at 80/160/240 Mbit/s through a low-pass light-emitting diode (LED) with a 3-dB bandwidth of 7 MHz cascaded with three measured optical wireless channels, is evaluated by Monte Carlo simulations. Results show that the receiver architecture can successfully solve the symbol timing and carrier synchronisation problems and mitigate inter-symbol interference caused by LED and/or wireless channels. The design framework for a full-digital CAP receiver has been laid out in this paper.

Datasets design of gate diffusion input based pipeline architecture for numerically controlled oscillator

&lt;span lang="EN-US"&gt;Gate diffusion input (GDI) is a technique, which enables reducing power consumption, area and delay in the digital circuits significantly, at the same time maintains low complexity of the logical design. This paper focuses on the analysis and interpretation of the design and implementation of GDI-based pipeline architecture for numerically controlled oscillator (NCO) using look up table (LUT). Based on the input signal and the alternate signal, this phase separation will separate the phase difference signal. The NCO generates a frequency and phase harmonized output signal with an antecedence fixed frequency clock. The 32-bit counter then compares the current count to the value stored in the compare register. Here the Coherent control comes into picture. It controls the carrier synchronizer by employing data from the 32-bit counter and the obtained data will be saved. It is updated and advanced using the third peer group of frequency synthesis technology. The test outcomes are accompanied with the theoretical concept and reproduced the results. The main objective of GDI-based pipeline architecture for NCO using LUT is to reduce the usage of metal oxide semiconductor field effect transistors (MOSFET’s). NCO is an indispensable component in many digital communication systems linked to modems, software-defined radios, and digital radio, digital down/upconverters for cellular and personal communications service base stations.&lt;/span&gt;

ЧУВСТВИТЕЛЬНОСТЬ ПРИЕМНИКОВ ГНСС

Introduction. The article is devoted to determining the minimum (threshold) SNRthr values at which GNSS receivers can operate in high-precision phase mode and in less accurate code mode. These minimum (threshold) values of SNRthr are determined primarily by the GNSS receivers' carrier synchronization systems (CCH – carrier synchronization systems) and code delay (CVS – delay tracking schemes). The article considers two types of SSN (PLS and FAP) and two types of SSS – coherent (CSSS) and non-coherent (NSSS) – depending on the sensitivity of the SSS to the carrier phase. Any of these CVDs can be autonomous or guided by target designations from the SSN. Objective. The systems of synchronization of GNSS receivers in phase (frequency) of the carrier (PLL, FAP) and in code delay (CVD) are considered, taking into account their interaction with each other in a high-precision phase mode (with centimeter accuracy) and in a coarser, but more noise-resistant code mode. (with meter accuracy). Satellite signals can be of two types: data – inversely modulated a priori unknown binary symbols (μ=+1), or pilot – without such modulation, as well as with different types of modulation (BPSK, BOC, etc.). Tracking errors and minimum SNR (Signal-to-Noise density Ratio) values are estimated at which these systems (and, consequently, the entire receiver as a whole) can still work normally. Two traditional combinations of synchronization systems by carrier and by code are considered, namely: PLL + coherent CVD; FAP+incoherent CVD; as well as non-traditional FAP + non-coherent CVD. According to the results of the studies, it is the last link (PLL + non-coherent CVD) that is recommended for synchronizing GNSS receivers to ensure their best sensitivity. It is shown that the dynamic properties of FAP and FAP from the point of view of their CVD are equivalent in the linear mode, however, FAP provides much greater dynamic stability than FAP at high SNR.

Communication Performance vs. Implementation Trade-offs of Interpolation Techniques for FFT-Based Carrier Synchronization exemplified on DVB-RCS2

Abstract. Carrier synchronization is a crucial part of any wireless receiver, which is required due to frequency and phase offset. In case of transmission in a Time Division Multiple Access system the carrier synchronization has to be carried out for every burst separately. The DVB-RCS2 standard specifies a large variety of reference burst types with very limited known symbols. For each of these types a thorough exploration of different synchronization algorithms is required to find a trade-off between a good communication performance at very low Signal to Noise Ratio (SNR) and an efficient hardware implementation. A state-of-the-art algorithm for carrier synchronization is based on the so called Fast Fourier Transformation (FFT). An inherit limitation for the precision of frequency estimation is given by the FFT point size. To counteract this limitation, the FFT point size must be increased. In this paper we extensively compare two possible interpolation techniques for FFT results in three FFT-based carrier synchronization methods. These are applied to various reference burst types specified in the DVB-RCS2 standard. The trade-offs of these combinations are identified with a special focus on hardware implementation efficiency. Furthermore, we present a flexible IP core which can process the three synchronization methods in an efficient way and analyze its implementation complexity and throughput on a Xilinx Kintex FPGA.

An Efficient Carrier Synchronization Scheme for Demodulation Systems

A simple data-aided carrier synchronization scheme is proposed for variable modulation (VM) communication systems under the initial conditions of a low signal-to-noise ratio (SNR) and normalized carrier frequency offset (CFO) symbol rate of 20%. The proposed carrier synchronization scheme is simplified into two steps; a reconfigurable L&amp;R (RLR) algorithm and pilot-aided (PA) phase linear interpolation algorithm is applied for carrier frequency recovery (CFR) and carrier phase recovery (CPR), respectively. Furthermore, the autocorrelation values of multi-pilot blocks are superimposed to improve the accuracy of the CFR algorithm, and the algorithm formulas are decomposed and modularized to simplify the implementation complexity of the RLR algorithm. Simulation results show that the RLR algorithm can track and lock the CFO up to a 33.2% symbol rate and reduce the CFO to 0.024%. The bit error rate (BER) performance of the carrier synchronization scheme almost coincides with the theoretical curve results. Comparison of hardware complexity shows that the multiplication resource consumption can be reduced by at least 72.47%.

Carrier synchronization for continuous-variable measurement-device-independent quantum key distribution with a real local oscillator

We propose a carrier synchronization scheme for continuous-variable measurement-device-independent quantum key distribution (CV-MDI-QKD) with a real local oscillator (LO). The middle node Charlie evaluates carrier frequency offsets and phase drift values based on the pilot signal sent by the legal parties Alice and Bob and a part of their public data. Alice and Bob then calibrate their modulation data according to the evaluation parameters to achieve carrier synchronization. We simulate the entire CV-MDI-QKD protocol and verify the feasibility of this scheme. The influences of pilot segment size and public data size on the excess noise are also analyzed. Besides, we experiment to measure the actual frequency offsets and phase drifts in the channel, which gives guidance on the actual implementation. This solution can ensure the implementation of CV-MDI-QKD with a real LO, paving the way for the practical application of this high-rate QKD protocol.

Distributed transmit array multi-tone carrier synchronization

An open-loop (OL) method to enable distributed transmit beamforming is presented in this paper. The approach eliminates the need for feedback to distant receive nodes by using multiple tones to set a coherent phase across the distributed array. This arrangement is able to constantly keep the array synchronized to avoid the frequency drifting of the local oscillators (LOs) equipped by distributed communication nodes, even while transmit beamforming is taking place. This is made possible because the synchronization is achieved through radio frequency (RF) carriers at frequencies other than the beamforming frequency. This enables uninterrupted beamforming, which is not possible in previous carrier synchronization algorithms due to half-duplex limitation. The noise performance of the proposed scheme is also presented.

High Rate CV-QKD Secured Mobile WDM Fronthaul for Dense 5G Radio Networks

A coherent transmission methodology for a continuous-variable quantum key distribution (CV-QKD) system based on quantum-heterodyne measurement through a coherent intradyne receiver is experimentally demonstrated in the framework of 5G mobile fronthaul links. Continuous optical carrier synchronization is obtained through training information, which is multiplexing to the quantum signal as pilot tone in both, frequency and polarization. Spectral tailoring by means of optical carrier suppression and single-sideband modulation is adopted to simultaneously mitigate crosstalk into the quantum channel and self-interference for the pilot tone, thus allowing for a high signal-to-noise ratio for this training signal. Frequency offset correction and optical phase estimation for the free-running local oscillator of the receiver is accurately performed and guarantees low-noise quantum signal reception at high symbol rates of 250 MHz and 500 MHz with additional Nyquist pulse shaping. A low excess noise in the order of 0.1% to 0.5% of shot-noise units is obtained for fiber-based transmission over a fronthaul link reach of 13.2 km. Moreover, co-existence with 11 carrier-grade classical signals is experimentally investigated. Joint signal transmission in the C-band of both, quantum signal and classical signals, is successfully demonstrated. Secure-key rates of 18 and 10 Mb/s are obtained under strict security assumptions, where Eve has control of the receiver noise, for a dark and a lit fiber link, respectively. Moreover, rates of 85 and 72 Mb/s are resulting for a trusted receiver scenario. These secure-key rates are well addressing the requirements for time-shared CV-QKD system in densified 5G radio access networks with cloud-based processing.