Carrier Tracking Research Articles

All-Digital Galvanically-Coupled BCC Receiver Resilient to Frequency Misalignment.

It is promising for wearable devices to go to a miniature size to alleviate the load of human body. One way to miniaturize the communication nodes on human body is to remove the bulky components such as antenna and crystal. Galvanically-coupled body channel communication (GC-BCC) has a great advantage over conventional wireless communications in reducing the size of wearable devices because it reuses the monitoring electrodes for signal transmission in place of antennas. To remove the crystal as well, the receiver must be immune to different types of frequency misalignments. This paper presents a GC-BCC receiver based on low power all-digital Gaussian frequency shift keying (GFSK) demodulation and clock-data recovery (CDR). A carrier tracking technique is proposed to detect and automatically adapt to the misalignment of carrier frequency. In addition, we also propose a circle-index CDR circuit to deal with the inaccuracy or drift of the clock frequency. The proposed circuit is implemented with 0.18 μm CMOS technology, and it operates at 200 kHz with a BFSK/GFSK modulation index of 1.0. Measured results show that the chip consumes 0.53 mA at a data rate of 100 kb/s. At a 10 cm body channel length, the GC-BCC receiver can tolerate a carrier misalignment up to [Formula: see text] and a clock error up to [Formula: see text], while keeping the bit error rate (BER) below 0.1%.

Influence of Time-Varying Plasma Sheath on the Lock Condition of Phase-Locked Loop for TT&C Carrier Tracking System

Time-varying plasma sheath likely causes a parasitic phase modulation effect on communication signals. It is essential to understand the effect of plasma sheath on the tracking telemetry and command (TT&C) systems for blackout mitigation. This paper comprehensively investigates the impact of parasitic phase modulation effect on the TT&C tracking system of Ka band signals, especially single-frequency and phase-modulated signals. A fluctuant electron density model in the space-time domain is initially established. The phase noise caused by the time-varying plasma sheath is then obtained through wave impedance numerical calculation method. The effect of the time-varying plasma sheath with different fluctuant intensities on the carrier tracking performance is investigated and quantitatively analyzed by imposing phase noise on a phase-locked loop model. Simulation results show that a large fluctuant intensity corresponds to a great impact on the lockout threshold. A critical fluctuant intensity is observed in the three typical TT&C signals. The effect of the time-varying plasma sheath on phase-modulated signals is more severe than that on single-frequency signals. The maximum tolerable fluctuant intensities are 12%, 10%, and 6% for single-frequency signals, binary phase shift keying signals, and quadrature phase shift keying signals, respectively. With the critical fluctuant intensity, their lockout thresholds are increased to 0, 6, and 4 dB, respectively.

A power reduction method for pilot channel of LEO satellite based on dynamic compensation

Since the lower power requirement of code division multiple access (CDMA) than that of other multiple access, the CDMA technology is suitable to be used in low earth orbit (LEO) satellite communication system whose space power is limited due to the small size of satellite. The pilot channel of CDMA technology is very important for earth mobile station (EMS) in LEO system to recover carrier and code, but the power requirement of pilot channel is very higher than that of other channels. In this paper, a power reduction method for pilot channel is proposed. By the new method, the power of pilot channel transmitted from LEO satellite is reduced to a lower level. For improving the signal to noise ratio (SNR) of pilot channel with lower power, coherent integration is employed in EMS at the pre-processing stage. Considering the high dynamic situation of LEO satellite, the long period of time for integration will deteriorate the receiving performance of EMS, therefore, a dynamic compensation module is added to carrier tracking loop against the high dynamic. Meanwhile, the transfer function of the new tracking loop and the condition for steady-state zero error are deduced. Numerical examples are provided to demonstrate effectiveness of the proposed approach.

Wavelet de‐noising Kalman filter‐based Global Navigation Satellite System carrier tracking in the presence of ionospheric scintillation

Ionospheric scintillation can cause rapid changes in the phase and amplitude of Global Navigation Satellite System (GNSS) signals, resulting in degraded accuracy and robustness of signal tracking loops. Owing to the non-stationarity and non-linearity of carrier tracking under scintillation conditions, the conventional methods used to enhance the robustness of tracking loops are less effective. To overcome this problem, this study presents a wavelet de-noising adaptive Kalman filter (AKF)-based GNSS carrier tracking algorithm. Since the traditional wavelet de-noising cannot be conducted iteratively, the authors provide a sliding window-based online wavelet de-noising method to mitigate non-stationary and non-Gaussian noise caused by scintillation. After that, taking the de-noised integration as input, they employ the phase lock indicator-based AKF carrier phase estimation to avoid the nonlinearity of conventional discriminator. On this basis, the joint wavelet de-noising AKF algorithm is applied to the carrier tracking in the presence of ionospheric scintillation. Numerical results show that the proposed algorithm can improve the accuracy and robustness significantly, especially in the case of practical carrier-to-noise ratio (40 dB Hz) in moderate scintillation, the phase jitter and probability of loss-of-lock decrease about 7.5° (46%) and 73%, respectively.

GNSS Carrier Phase Tracking With Discrete Wavelet Transform Filtering Under Ionospheric Scintillation

In this letter, we propose the phase-locked loop with discrete wavelet transform filtering and redesigned Kalman filters (KFs) to enhance the global navigation satellite system signal carrier tracking robustness under ionospheric scintillation, being of the paramount importance in safety critical applications and advanced receivers. By normalizing the discriminator in the loop using the signal amplitude estimated with the discrete wavelet transform filtering, the phase variation due to scintillation is well estimated. The adaptive KF is modified with an additional amplitude state to copy with the scintillation-induced disturbance so as to stably track the fluctuated phases. Simulations are offered to verify the performance improvement of the proposed method versus the previous ones in the case of ionospheric scintillation.

Carrier Tracking Estimation Analysis by Using the Extended Strong Tracking Filtering

When the extended strong tracking filter (ESTF) is used to improve the carrier tracking estimation instead of the extended Kalman filter (EKF), it is found to be difficult to effectively and consistently evaluate superiority of the ESTF than the EKF. The primary cause is that the basic properties of the traditional Kalman filter are broken due to the subjective fading factor. The superiority of the ESTF is customarily shown by simulations and experiments in previous work only and the corresponding mechanism analysis is very lacking. Motivated by this, we study the performance comparison of the ESTF and EKF. First, the statistical parameters such as the prediction mean-squared error (MSE), the MSE, and the gain matrix are analytically and systematically compared in theory. Second, the inconsistency of estimation performances is explicitly revealed based on the comparison results. Third, mismatching analysis of estimation performance expressions, which are the root-mean-squared error and MSE, is briefly presented for the ESTF. The presented results state clearly that the usability of the conventional Kalman filtering theory is seriously limited and its structure is easy to be destroyed. It is a challenge and a good chance to study new performance evaluation methods on the class of strong tracking filters for engineering application.

Tuning a Kalman filter carrier tracking algorithm in the presence of ionospheric scintillation

Strong ionospheric electron content gradients may lead to fast and unpredictable fluctuations in the phase and amplitude of the signals from Global Navigation Satellite Systems (GNSS). This phenomenon, known as ionospheric scintillation, is capable of deteriorating the tracking performance of a GNSS receiver, leading to increased phase and Doppler errors, cycle slips and also to complete losses of signal lock. In order to mitigate scintillation effects at receiver level, the robustness of the carrier tracking loop, the receiver weakest link under scintillation, must be enhanced. Kalman filter (KF)-based tracking algorithms are particularly suitable to cope with the variable working conditions imposed by scintillation. However, the effectiveness of this tracking approach strongly depends on the accuracy of the assumed dynamic model, which can quickly become inaccurate under randomly variable situations. This study first shows how inaccurate dynamic models can lead to a KF suboptimum solution or divergence, when both strong phase and amplitude scintillation are present. Then, to overcome this issue, it proposes two self-tuning KF-based carrier tracking algorithms, which self-tune their dynamic models by exploiting the knowledge about scintillation that can be achieved through scintillation monitoring. The algorithms have been assessed with live equatorial data affected by strong scintillation. Results show that the algorithms are able to maintain the signal lock and provide reliable scintillation indices when classical architectures and commercial ionospheric scintillation monitoring receivers fail.

An approved frequency tracking method in connected element interferometry

Carrier tracking loop is a basic method of frequency tracking in CEI (connected element interferometry), but the tracking error is very large or even worse at high dynamic. To solve this problem, a frequency tracking method assisted by open loop frequency estimation is proposed in this paper. First, an open-loop frequency estimation algorithm is used to estimate the frequency of signals at different moments, then, the least squares fitting method is used to estimate the corresponding dynamic parameters of different orders. Next, a local signal is generated to compensate the received signal. After eliminating most of the dynamic characteristics, the signal is fed into PLL (Frequency locked loop) and high-precision frequency tracking results can be obtained. Simulation results show that, in the condition of low SNR, the new method has higher accuracy than the method assisted by FLL (Frequency locked loop), and the processing time is shorter. When there is a two order Doppler frequency change, the open-loop assisted method can overcome the steady phase error of the PLL, and is of great significance in the applications of connected elements interferometry.

Carrier tracking algorithm based on joint acquisition of frequency locked loop and phase locked loop

Aiming at the problem of frequency step in the frequency lock loop (FLL) - phase lock loop (PLL) carrier tracking algorithm’s conversion state, presenting an improved algorithm: PLL and FLL joint acquisition to replace the single FLL acquires frequency, and deduce the loop state transition threshold. The simulation results show that the improved algorithm is more stable in the conversion process, and the loop performance is optimized. When the SNR is -10dB, and has the acceleration rate, the tracking loop does not have a frequency step at the time of conversion, achieving the design purpose.

Adaptive wavelet denoising unscented Kalman filter for BeiDou signal carrier tracking under ionospheric scintillation conditions

Ionospheric scintillation can cause BeiDou system (BDS) signal amplitude fading and phase variation as the radio frequency (RF) signals pass through the ionosphere. With the accidental, sudden, and regional characteristics of ionospheric scintillation, it is difficult to effectively mitigate the impacts of ionospheric scintillation from a system perspective. To overcome this problem, this work addresses the mitigation of scintillation for the BDS signal. We propose an adaptive wavelet denoising unscented Kalman filter (WDUKF)-based carrier tracking algorithm to mitigate the adverse impacts of ionospheric scintillation. First, as WD can better characterize the nonstationary of signal, the non-Gaussian noise caused by scintillation can be filtered by designing a sliding window-based online WD filter. Second, taking the denoised integrations as an input, we employ the phase lock indicator (PLI)-based adaptive UKF carrier phase estimator to reduce the linearization approximate error of conventional KF-based algorithms. Through adjusting the measurement vector of UKF with different scintillation scenarios adaptively, the divergence problem of UKF can be mitigated. Simulation and real data experimental results demonstrate the validity of the proposed method, especially in the case of 36 dB-Hz in moderate scintillation, the phase jitter and probability of loss-of-lock decrease about 6 deg (40%) and 71%, respectively.

Time–frequency image‐based carrier tracking method for Global Navigation Satellite System signal with ultra‐high dynamics

Uncertainty principle has made the inevitable trade-off between achieving better frequency resolution and better time resolution in signal parameter estimation. High dynamics could make this problem even more challenging. In this study, the authors propose a novel tracking method for Global Navigation Satellite System (GNSS) signal carrier. Different from the single-domain tracking methods or Strapdown Inertial Navigation System, the presented method works in the time–frequency (TF) image generated by Wigner–Ville distribution. It has the ability to restrict the TF uncertainty to a small number of pixels around instantaneous frequency (IF) curve, which almost completely avoids the effect of high dynamics in its time/frequency estimation. The clear curve of the IF in TF image makes it possible to accurately estimate the instantaneous Doppler frequency and acceleration. Moreover, this estimation can be improved by image enhancement technique and image space transforms. Its ability of GNSS signal tracking is proved by the real signal static experiments. Simulation results show that the authors’ method has the ability to track GNSS signal under at least 400 g dynamic stress in standard outdoor carrier-to-noise ratio.

Sliding discrete Fourier transform based frequency‐locked loop for adaptive carrier tracking of bi‐phase signals

For bi-phase signals, an adaptive carrier tracking method based on sliding discrete Fourier transform (SDFT) frequency-locked loop (FLL) is proposed. Magnitude and phase spectra of closed-loop SDFT filter provide almost flat response around the centre frequency. However, the small magnitude and phase errors observed at the SDFT in-phase and quadrature components are corrected by adaptive sampling frequency control. The carrier frequency is estimated by computing the frequency error. Hence, the input frequency variation due to Doppler shift could be estimated for the bi-phase signal. Experimental investigations with digital implementation demonstrate the suitability of the FLL for bi-phase signals.

The Ionospheric Scintillation Effects on the BeiDou Signal Receiver.

Irregularities in the Earth’s ionosphere can make the amplitude and phase of radio signals fluctuate rapidly, which is known as ionospheric scintillation. Severe ionospheric scintillation could affect the performance of the Global Navigation Satellite System (GNSS). Currently, the Multiple Phase Screen (MPS) technique is widely used in solving problems caused by weak and strong scintillations. Considering that Southern China is mainly located in the area where moderate and intense scintillation occur frequently, this paper built a model based on the MPS technique and discussed the scintillation impacts on China’s BeiDou navigation system. By using the BeiDou B1I signal, this paper analyzed the scintillation effects on the receiver, which includes the acquisition and tracking process. For acquisition process, this paper focused on the correlation peak and acquisition probability. For the tracking process, this paper focused on the carrier tracking loop and the code tracking loop. Simulation results show that under high scintillation intensity, the phase fluctuation could be −1.13 ± 0.087 rad to 1.40 ± 0.087 rad and the relative amplitude fluctuation could be −10 dB to 8 dB. As the scintillation intensity increased, the average correlation peak would decrease more than 8%, which could thus degrade acquisition performance. On the other hand, when the signal-to-noise ratio (SNR) is comparatively lower, the influence of strong scintillation on the phase locked loop (PLL) is much higher than that of weak scintillation. As the scintillation becomes more intense, PLL variance could consequently results in an error of more than 2.02 cm in carrier-phase based ranging. In addition, the delay locked loop (DLL) simulation results indicated that the pseudo-range error caused by strong scintillation could be more than 4 m and the consequent impact on positioning accuracy could be more than 6 m.

A Residual Carrier Tolerant QAM Receiver Architecture Based on Time‐Varying Blind Source Separation

In case of Quadrature amplitude modulated (QAM) transmission, the residual carrier affects the quality of the received signal. We show that the carrier tracking problem is equivalent to a time-varying Blind source separation (BSS) problem if there exists a residual carrier. This motivates us to propose a new receiver architecture, that is tolerant to residual carrier, based on a Recursive least squares (RLS) BSS algorithm. Simulations are provided to show the promising performance of the proposed algorithm for tracking the residual carrier and for improving the quality of the received signal.

Increase of Carrier-to-Noise Ratio in GPS Receivers Caused by Continuous-Wave Interference

The increased use of personal private devices (PPDs) is drawing greater attention to the effects of continuous-wave interference (CWI) on the performance of global positioning system (GPS) receivers. The effective carrier-to-noise density ratio (C/N0), an essential index of GNSS receiver performance, is studied in this paper. Receiver tracking performance deteriorates in the presence of interference. Hence, the effective C/N0, which measures tracking performance, decreases. However, simulations and bench tests have shown that the effective C/N0 may increase in the presence of CWI. The reason is that a sinusoidal signal is induced by the CWI in the correlator and may be tracked by the carrier tracking loop. Thus, the effective carrier power depends on the power of the signal induced by the CWI, and the effective C/N0 increases with the power of the CWI. The filtering of the CWI in the carrier tracking loop correlator and its effect on the phase locked loop (PLL) tracking performance are analyzed. A mathematical model of the effect of the CWI on the effective C/N0 is derived. Simulation results show that the proposed model is more accurate than existing models, especially when the jam-to-signal ratio (JSR) is greater than 30 dBc.

Implementation of Advanced Carrier Tracking Algorithm Using Adaptive-Extended Kalman Filter for GNSS Receivers

Use of Global Navigation Satellite Systems (GNSS) receivers for real-time applications has improved significantly all over the world. The main problem with the designed receivers is their failure to function under harsh environmental conditions because of the structured phase-locked loop (PLL) architecture. One of the most critical phenomena that cause signal degradation in GNSS receiver is ionospheric scintillations, which create disturbances in amplitude and phase of the received signal. The problem in signal acquisition and tracking, even in the severe canonical fades (deep amplitude fading correlated with reference to half cycle phase jumps), can be mitigated using robust and adaptive carrier tracking algorithms. The autoregressive exogenous modeling parameters are useful in estimating the amplitude and phase scintillations. The proposed adaptive-extended Kalman filter (AEKF) approach works as an effective carrier tracking algorithm maintaining a balance in dual problems faced by PLL-based receivers, i.e., (estimation versus mitigation) and (dynamics versus noise reduction) tradeoff. The developed AEKF algorithm performed well for synthetic Cornell scintillation monitor data and for Global Positioning System L1 PRN 12 data collected around 21.30 H (local time) on October 24, 2012, in Rio de Janeiro, Brazil, with GNSS Software Navigation Receiver.

Decimation Double-Phase Estimator: An Efficient and Unambiguous High-Order Binary Offset Carrier Tracking Algorithm

Traditional binary offset carrier (BOC) tracking algorithms process the upper and lower sideband signals together, and thus, the sampling frequency and computational requirements are much higher than that required for binary phase-shift keying tracking algorithms, especially for high-order BOC signals. Addressing existing limitations, this letter proposes a decimation double-phase estimator (DDPE) tracking algorithm for BOC signals. The algorithm uses a normal carrier and a subcarrier with a constant frequency to shift the upper and lower sideband signals of BOC to the zero frequency and decimates the signal before processing by the correlator. The residual carrier and the subcarrier are then tracked by the double-phase estimator algorithm. Decimating the signals significantly reduces the computational complexity, and for a BOC(6 n , n ) signal, the DDPE is found to reduce 86% of correlator operations with a signal-to-noise ratio loss of 0.5 dB.

Initial frequency refining algorithm for pull‐in process with an auxiliary DLL in pseudolite receiver

Pulsed time division multiple access is recommended for psedudolite satellite signal to eliminate the near-far effect, which is different from global navigation satellite system signal design. However, in this case, the initial frequency bias obtained from acquisition is not precise enough for the carrier tracking loop to converge due to the signal's pulse modulation, as the rolling-off of auto-correlation function is insensitive to slight frequency changes. This Letter proposes an approach to narrowing the initial frequency error by mapping from code Doppler to carrier Doppler, in which the former one can be obtained from a delay lock loop (DLL). Simulation results demonstrate the validity of the proposed method in the initialisation of frequency pull-in process owing to the fixed proportion existed in the code and carrier Doppler.

Tracking Architecture Based on Dual-Filter with State Feedback and Its Application in Ultra-Tight GPS/INS Integration.

If a Kalman Filter (KF) is applied to Global Positioning System (GPS) baseband signal preprocessing, the estimates of signal phase and frequency can have low variance, even in highly dynamic situations. This paper presents a novel preprocessing scheme based on a dual-filter structure. Compared with the traditional model utilizing a single KF, this structure avoids carrier tracking being subjected to code tracking errors. Meanwhile, as the loop filters are completely removed, state feedback values are adopted to generate local carrier and code. Although local carrier frequency has a wide fluctuation, the accuracy of Doppler shift estimation is improved. In the ultra-tight GPS/Inertial Navigation System (INS) integration, the carrier frequency derived from the external navigation information is not viewed as the local carrier frequency directly. That facilitates retaining the design principle of state feedback. However, under harsh conditions, the GPS outputs may still bear large errors which can destroy the estimation of INS errors. Thus, an innovative integrated navigation filter is constructed by modeling the non-negligible errors in the estimated Doppler shifts, to ensure INS is properly calibrated. Finally, field test and semi-physical simulation based on telemetered missile trajectory validate the effectiveness of methods proposed in this paper.

A Robust NDA Carrier Tracking Method for LDPC-Coded Systems With Symbol Rate Sampling

In this letter, a robust nondata-aided (NDA) carrier tracking method is proposed for low-density parity-check (LDPC) coded systems with symbol rate sampling. The proposed method has a novel and hybrid carrier tracking loop combined with the frequency-locked loop (FLL), increasing/decreasing sampling rate blocks, phase-locked loop (PLL), and modified symbol decision method, which is capable of improving estimation accuracy of the frequency offsets and phase offsets at low signal-to-noise ratios (SNRs). When applied to the $(4096,3072)$ LDPC coded system, numerical simulations and comparisons are provided to validate the effectiveness of the proposed carrier tracking method in the case of relatively low SNRs.