Phase Synchronization Error Research Articles

A modified dispersed frequency and phase consensus algorithm based on differential evolution and credibility weighting matrix

In distributed antenna array systems, accurate synchronization of the frequency and phase of the transmission signals among subarrays is a premise for beamforming. To solve this problem, a modified dispersed frequency and phase consensus (MDFPC) algorithm, which is based on differential evolution (DE) and the credibility weighting matrix, is proposed in this paper. DE algorithm is adopted to optimize the mixing matrix of MDFPC algorithm, and the convergence speed of consensus algorithm can be improved. Moreover, Lanczos method is adopted to calculate the fitness of individuals during optimization, thus the computation amount of the eigenvalue decomposition of the large-scale, sparse and symmetric mixing matrix can be effectively reduced. In addition, the influence of the transmission distance between subarrays on the received Signal-to-Noise Ratio (SNR) is considered, and the credibility weighting matrix can be obtained. Then the contribution of low-credible frequency and phase messages to the iterative updated values can be decreased by the credibility weighting matrix, thus more accurate frequency and phase updated values can be obtained in each iteration. It is shown from simulation results that the proposed algorithm can further reduce the phase synchronization error by at least 8% and achieve at least 18% convergence speed improvement compared to dispersed frequency and phase consensus (DFPC) algorithm.

Unmanned Airborne Bistatic Interferometric Synthetic Aperture Radar Data Processing Method Using Bi-Directional Synchronization Chain Signals

The bistatic Interferometric Synthetic Aperture Radar (InSAR) system can overcome the physical limitations imposed by the baseline of monostatic dual-antenna InSAR. It provides greater flexibility and can enhance elevation measurement accuracy through a well-designed baseline configuration. Unmanned aerial vehicles (UAVs) equipped with bistatic InSAR, having relatively low cost and high flexibility, are useful for mapping and land resource exploration. However, due to challenges including spatiotemporal synchronization and motion errors, there are limited reports on UAV-borne bistatic InSAR. This paper proposes a comprehensive method for processing data from small UAV-borne bistatic InSAR by integrating two-way synchronization chain signals. The proposed method includes compensation for time and phase synchronization errors, trajectory refinement with synchronized chain and Position and Orientation System (POS) data, high-precision bistatic InSAR imaging, and interferometric processing. Height inversion results based on the proposed method are also provided, which demonstrate the effectiveness of the proposed method in improving the accuracy of interferometric measurement at calibration points from 0.66 m to 0.42 m.

Effect of synchronization system errors on the reception noise immunity of amplitude-phase shift keyed signals

Objectives. An urgent task in the context of modern radio and television systems is to improve the quality and quantity of transmitted information. For example, the use of multiple amplitude-phase shift keyed (APSK) signals—16-APSK and 32-APSK—in digital satellite television systems of the Digital Video Broadcasting-Satellite2 (DVB-S2) standard made it possible to transmit 30% more data in the same frequency bands in comparison with the previous DVB-S standard. Such increases in information transmission rates impose more stringent requirements on hardware. An important role in the reception of APSK signals, as well as the signals of other coherent signal processing systems, is played by the stability of synchronization systems. The presence of operational errors can significantly reduce the quality of information reception. The aim of the present work was to analyze the effect of phase and clock synchronization errors on the reception noise immunity of APSK signals with a ring signal constellation structure.Methods. The study used statistical radio engineering methods informed by optimal signal reception theory.Results. The effect of phase and clock synchronization errors on the reception noise immunity of APSK signals having a signal constellation ring structure is analyzed. The dependencies of the bit error probability on the magnitude of the phase shift and the clock offset were characterized. The effect of synchronization errors on reception quality were compared with the known results for quadrature amplitude modulation (QAM) signals.Conclusions. At an acceptable energy loss of no more than 1 dB, the critical phase error can be considered as 2°-3°, while the critical clock error is 3-4%. A coherent receiver of APSK signals is more sensitive to the phase error of reference oscillations than a similar receiver of QAM signals, whereas clock errors have the same effect on the reception quality of these signals.

Synchronization for mini‐UAV‐based high‐resolution BiSAR systems: Lost direct signal estimation based on Hampel filtering

In mini-unmanned aerial vehicle-based high-resolution bistatic synthetic aperture radar systems, the rotation of the unmanned aerial vehicle platforms will cause direct signal loss, resulting in the reduction of synchronization error compensation accuracy. Here, a synchronization algorithm is proposed to estimate the lost direct signal. First, bistatic time and phase synchronization signal models are established. Then, Hampel filtering is used to estimate the time delay of the lost direct signal, and the time and phase synchronization errors are estimated based on third-order polynomial fitting. A high-resolution synthetic aperture radar image is used to demonstrate the validity of the proposed algorithm in mini-unmanned aerial vehicle-based high-resolution bistatic synthetic aperture radar systems.

Phase synchronization sensitivity for widely separated MIMO radar in CES disturbance

This paper investigates the sensitivity to phase synchronization errors through the Hybrid Cramér–Rao Lower Bounds (HCRLB) for joint estimation of target location and velocity in coherent Multiple-Input Multiple-Output (MIMO) radars with distributed antennas. In particular, we derived the HCRLB of range and velocity of a target embedded in Complex Elliptically Symmetric (CES) distributed clutter when the phase error on each receiver and transmitter is modeled as a Gaussian random variable. Closed-form expressions of the HCRLBs are derived and evaluated as a function of the phase error variance.

First Demonstration of Single-Pass Distributed SAR Tomographic Imaging With a P-Band UAV SAR Prototype

A distributed configuration is a promising realization of tomographic synthetic aperture radar (TomoSAR) 3-D imaging. It is able to implement single-pass tomographic imaging in a very short time and, hence, outperforms the traditional time-consuming multipass TomoSAR. It also outperforms the traditional single-platform TomoSAR by achieving a higher resolution in elevation by forming a much larger spatial baseline. However, there has been little research reported on the distributed TomoSAR so far. In this article, we, for the first time, experimentally demonstrate the great potential of the single-pass distributed TomoSAR 3-D imaging. The main contributions are threefold. First, a new distributed TomoSAR 3-D imaging model is built, characterized by using both inner monostatic and bistatic spatial configurations. Second, a new multistatic synchronization scheme is developed for accurately correcting both multistatic time and phase synchronization errors. Finally, a P-band distributed unmanned-aerial-vehicle (UAV) TomoSAR prototype with four separate stations is built with an elaborately designed time-division waveform for full data acquisition. To the best of our knowledge, this is the first distributed TomoSAR system. We have also implemented the first single-pass TomoSAR 3-D imaging experiment and successfully achieved a meter-level 3-D image in Pinggu, Beijing, China.

Influence of phase and clock synchronization errors on the noise immunity of coherent reception of signals with quadrature amplitude modulation

Signals with quadrature amplitude modulation (QAM) is widely used for high-speed transmission of information in many radio systems and, in particular, in digital television systems. In the receiver, which is part of the transceiver equipment of such systems, there is a block for the formation of reference oscillations and a clock synchronization block. Due to hardware instabilities and propagation conditions, phase and clock errors may occur, which cause additional errors during demodulation of the received signal, and which can significantly impair the noise immunity of the reception. The paper investigates the effect of phase and clock synchronization errors on the noise immunity of coherent reception of QAM signals. Using the methods of statistical radio engineering, the parameters of the distributions of processes in the receiver are obtained and the probability of bit error is estimated. The dependences of the probability of bit error on the magnitude of the phase error in the formation of the reference oscillations and on the relative displacement of the clock moments, as well as on the signal-to-noise ratio, are obtained. It is shown that these errors can greatly reduce the noise immunity of the reception, and with an increase in the positioning of the signals, this effect increases. If we assume that the admissible reception energy loss is 0.5 dB due to each of these errors, then the allowable phase error is from ~3° at M = 4 to ~1° at M = 64, and the allowable clock synchronization error, respectively, is from ~5% at M = 4 to ~2% at M = 64. To provide more stringent requirements for the magnitude of losses, the requirements for the indicated errors increase significantly.

Airborne Distributed Coherent Aperture Radar Synchronization Error Calibration Method Based on Prominent Points

Airborne Distributed Coherent Aperture Radar (DCAR) has the advantages of wide observation range, high maneuverability and flexible deployment. However, airborne DCAR is confronted with more stringent time, space and phase synchronization requirements. Therefore, an airborne DCAR signal model and its matrix representation based on Slow-Time Code Division Multiple Access (ST-CDMA) waveform are established successively. Moreover, the influence on target coherence synthesis resulted from time, space and phase synchronization errors is analyzed in detail, and a novel airborne DCAR synchronization error calibration method based on prominent points is proposed. This method utilizes the target parameter search strategy to eliminate the grid mismatch filtering firstly. Then, with the utilization of estimation approaches based on target model or repeater station model, the unit platform position error is calibrated. Finally, equivalent amplitude and phase errors are calibrated by Eigen structure methods. The validity of the proposed method to calibrate the airborne DCAR synchronization error is demonstrated by simulation experiments.

On the unified error performance of PSK modulation schemes over mm‐wave wireless channels affected by carrier phase synchronization errors

SummaryThe performance of radio‐frequency (RF) networks where channels are modeled by an extended‐generalized‐K (EGK) distribution and consider significant phase errors during coherent detection at the receiver due to carrier‐phase‐synchronization‐mismatch is investigated in this work. The performance is evaluated for a single‐hop link and two‐hop amplify‐and‐forward (AF) and decode‐and‐forward (DF) relay‐assisted RF links. The EGK is a generalized distribution, which can model various fading conditions in millimeter (mm)‐wave wireless channels where transmission frequency is 60 GHz and above and takes into account non‐homogeneous propagation, interference effects in a multiuser transmission environment, multipath fading and shadowing effects. The average symbol error probability (ASEP) performance is evaluated for a single‐hop link when carrier is modulated using multilevel PSK modulation scheme. Based on the analytical results obtained for a single‐hop link, the mathematical analysis for the error performance in widely employed AF and DF relay‐assisted RF two‐hop networks is developed and ASEP is derived. To quantify the degradation in system performance introduced by phase errors, the reference‐carrier phase estimation loss for a single‐hop RF link is also evaluated. The obtained analytical results are also verified by numerical plots and depict the effects of various channel conditions existing over the RF link and phase synchronization errors.

Microwave Photonic Wideband Distributed Coherent Aperture Radar With High Robustness to Time Synchronization Error

In this article, we firstly analyze the specific effect of time and phase synchronization errors on the coherent gain of microwave photonic wideband distributed coherent aperture radar (DCAR), and further propose a robust design based on bandwidth segmentation. In our design, the intermediate-frequency narrowband linear frequency modulated waveform (LFMW) sub-pulses are mixed with the stepped-frequency local oscillator signals at the transmitter, generating the stepped-frequency LFMW. To ensure the waveform purity, a photonics-based single-sideband up-converter is proposed as the mixer. At the receiver side, the echo wave is processed by a photonics-based down-converter combined with the matched-filtering processing. The relatively low-resolution range profiles with low coherent gain loss can be achieved by the narrowband sub-pulses, and the high-resolution range profile with low coherent gain loss can be synthesized from these low-resolution range profiles. The coherent gain of the proposed system is less sensitive to time synchronization error comparing to the system where the wideband LFMW is transmitted. Higher level of robustness also enables easier implementation of such system. To show the effectiveness of our design, we conduct simulations and further establish an X-band (8–12 GHz) microwave photonic system with two transmitters and one receiver. The coherent gain under different time synchronization errors are measured. Both the simulation and experimental results confirm that the proposed system achieves a higher robustness to time synchronization error. For instance, to keep the coherent gain loss less than 0.3 dB, the required time synchronization accuracy can be relaxed from 35 ps to 127 ps.

A High Accuracy Positioning Method for Single Base Station in Indoor Emergency Environment

Objectives In recent years, the demand of indoor and outdoor emergency location service is growing rapidly. Affected by indoor space environment, signal types, sensor performance and other factors, the existing positioning methods of single signal source, single sensor source, integrated navigation, fusion positioning are not perfect in accuracy, stability, reliability, rapidity and other aspects. The main objective of this study is to propose a high precision wireless location method for single base station in emergency positioning environment. Methods A method of angle measurement with high precision was proposed to eliminate redundant phase caused by modulated signal and sequential sampling. Firstly, a circular antenna array was constructed which sampling received signal on one channel by switching the dual polarized antenna array element in turn, and on the second channel by comparison antenna. Then, the echo signal mathematical model of dual channel antenna was established. Finally, the super-resolution angle estimation algorithm of Capon spectral and polarization decoupling was given for multipath indoor environment. In order to reduce the computational complexity of four-dimensional search, the steering vector was rewritten by hardard product, and target angle estimation was obtained by solving the minimum eigenvalue to minimize the cost function. Results From the comparison results of array phases between single channel and dual channel, it can be seen that the proposed two channel antenna has better phase stability. Experimental results on several fixed location points demonstrate that the root mean square(RMS) positioning error in X direction and Z direction is better than 0.5 m. Both static and dynamic tests show that the influence of source signal phase and frequency synchronization error to switch-antenna array can be effectively eliminated. Conclusions The proposed method can achieve two-dimensional accurate localization with a single base station, which has wider application than the single channel switch-antenna array and is easy to rapid deployment in emergency positioning environment.

Shorebase-Shipborne bistatic ISAR robustness analysis

ABSTRACTIn this article, the robustness of Shorebase-Shipborne bistatic Inverse Synthetic Aperture Radar (ISAR) is tested when phase synchronization errors and nonstationary three-dimensional rotational motions occur. Mathematically, the point spread function is derived and distortions are analysed. It is shown that, the proposed image formation method in combination with range-instantaneous-Doppler technique is able to form focused images, even considering the poorest performance oscillators. The simulated results are provided to demonstrate the theoretical results.

Efficient Integration of Magnetic Positioning and Stable Communications

A promising integration method for high-precision positioning and stable communications by utilizing magnetic induction signals is proposed. In-phase and quadrature components are assigned to the positioning and communications, respectively. A pilot signal is used for identification of the in-phase and quadrature components, which leads to mutual interference of the two components caused by carrier phase synchronization error. Simulation and experiment confirm that the mutual interference and signal-to-noise ratio (SNR) loss are acceptable in our proposed scheme, i.e., the interference is weak and the SNR loss is about 1.6 dB as the carrier phase synchronization error less than ${5^\circ }$ . For instance, it is demonstrated that the root-mean-square error of positioning is less than 1.5 m and the transmission rate of communications is about 3000 bits per second when the distance is about 150 m, which is practical for applications such as the magnetic navigation, as well as compressed voice and message communications underground or underwater.

SIR Analysis of OFDM and GFDM Waveforms With Timing Offset, CFO, and Phase Noise

In this paper, we analyze the impacts of timing offset (TO), carrier frequency offset (CFO), and phase noise in orthogonal frequency division multiplexing (OFDM) and generalized frequency division multiplexing (GFDM) waveforms. As TO can be classified into four cases depending on the direction of offset, we provide the analysis of signal-to-interference ratio (SIR) for each of the cases when phase noise and synchronization errors of the desired user occur in frequency selective channel. We also propose the receiver filter for GFDM systems that is optimized to maximize SIR with CFO in additive white Gaussian noise channel. Simulation results show that GFDM is more sensitive to CFO than OFDM. We also confirm that GFDM systems using proposed receiver filter are robust against CFO compared with conventional systems.

基于相位同步的分布式全相参雷达参数估计及相参性能

For distributed aperture coherent radar with a general architecture, a signal model for coherent parameter estimation and coherent processing based on system phase synchronization is proposed in this paper, and the sensitivity of parameter estimation and coherent processing performance to synchronization errors is analyzed in detail. A closed-form hybrid Cramer-Rao bound (HCRB) of the estimation of time delay difference is first derived in multiple-input and multiple output (MIMO) work mode. Following this, in fully coherent work mode, the analytical formula of output signal-to-noise ratio gain (oSNRg) is addressed, and a numerical solution of the analytical formula is obtained by using high-order polynomial fitting. The principle of antenna configuration is then studied. It is concluded that the estimation accuracy of time delay difference or coherent processing performance is determined by both synchronization error and input SNR. Compared with existing methods, the method based on phase synchronization can yield higher estimation accuracy of time delay differences and better coherent processing performance, given the assumption that the phase synchronization error is small and the input SNR is low.

Estimation of Spatially-Correlated Random Fields With Compressed Observations

In this paper, we focus on the use of wireless sensor networks for the estimation of spatially-correlated random fields. We explicitly take communication aspects into account and propose a number of distributed pre-coding (beamforming) schemes allowing for an over-the-air compressed representation of the set of spatially correlated observations. Those observations are then encoded in a number of consecutive sensor-to-Fusion Center (FC) transmissions. The ultimate goal is to minimize the distortion in the reconstructed random field and, simultaneously, keep the number of transmissions low (i.e., the compression ratio high). Specifically, we first propose a family of distributed pre-coding schemes based on the Karhunen-Loève (KL) and partial KL transforms and we derive closed form expressions of the optimal power allocation strategies. Aspects such as residual phase synchronization errors or the fact that some sensors might be idle (inactive) are specifically taken into account in the analysis. Next, we propose an iterative and greedy scheme by which the pre-coder design and power allocation problems can be jointly solved for the general case. We assess the performance of the proposed pre-coding schemes by means of computer simulations. Other uncompressed transmission schemes are used as a benchmark.

Cramer-Rao bound and signal-to-noise ratio gain in distributed coherent aperture radar

This paper studies the estimation performance of the coherent processing parameter (CPP), including time delay differences and phase synchronization errors among different apertures of the distributed coherent aperture radar (DCAR). Firstly, three architectures of signal processing in the DCAR are introduced. Secondly, the closed-form Cramer-Rao bound (CRB) of the CPP estimation is derived and compared. Then, the closed-form CRB is verified by numerical simulations. Finally, when the next generation radar works in a fully coherent mode, the closed-form signal-to-noise ratio (SNR) gain of the three architectures is presented.

Doppler Centroid Estimation for Space-Surface BiSAR

Phase synchronization is a crucial problem in Bistatic Synthetic Aperture Radar (BiSAR). As phase synchronization error and Doppler phase have nearly the same form, Doppler Centroid (DC) cannot be estimated with traditional method in BiSAR. A DC estimation method is proposed through phase-interferometry of Dual-channel direct signal. Through phase interferometry, phase synchronization error can be counteracted while Doppler phase is reserved and DC can be estimated from the reserved phase.

Analysis of DS-CDMA System with Phase Synchronization Errors for Selection Diversity Scheme

Wireless communication is currently the most dynamic field with the invention of new technologies. Presently one of the main challenges in the wireless communication field is to combat fading. At the receiver, the signal may be lost completely due to destructive addition of multi paths signal components. Generally effect of fading is analyzed with channel compensation using different diversity combining schemes such as selection diversity, equal gain combining and maximal ratio combining techniques. Selection diversity is one of the preferred schemes due to its simplest implementation process. However, often channel estimation may not be perfect because of changing nature and other factors like correlation between the signals etc. The main aim of this paper is to observe the effect of imperfect channel estimation on the performance of the receiver. Analysis has been done for channel estimation along with selection diversity combining. Also, receiver may not be synchronized always with transmitter giving some phase errors. Such error is also incorporated along with selection diversity for performance evaluation of the system.

Phase Synchronization for Coherent MIMO Radar: Algorithms and Their Analysis

Multiple-input multiple-output (MIMO) radar can achieve improved localization performance by employing a coherent processing approach with proper antenna positioning. Coherent processing, however, entails the challenge of ensuring phase coherence of the carrier signals from different distributed radar elements. In this work, we aim to address such a challenge by providing a systematic treatment of the phase synchronization problem in coherent MIMO radar systems. We propose and study three different approaches for reaching a common notion of phase in coherent MIMO radar, namely, the master-slave closed-loop algorithm, the round-trip algorithm and the broadcast consensus based algorithm. These algorithms range from centralized to distributed types, and include both noniterative and iterative approaches. They do not require a priori establishment of the time synchronization, and thus are all time asynchronous in nature. Under a similar analytical framework, we mathematically characterize each of these algorithms, and further derive and study the statistical properties of a few relevant figures of merit including the resulting phase synchronization error. Simulation results are presented to validate our theoretical analysis.