Carrier Phase Variations Research Articles

Simultaneous measurement of temperature and water concentration using a novel laser dispersion spectrum extraction method immune to carrier phase variation

Quantitative measurement of temperature and concentration is of wide interest in combustion diagnostics. In this paper, simultaneous temperature and water concentration measurements in a combustion flame were realized by using a novel laser dispersion spectrum extraction method immune to carrier phase variation. The laser dispersion phase signal obtained in the frequency domain was converted into the molecular free induction decay (FID) signal in the time domain by inverse Fourier transform. Then the FID signals of the dispersion phase and the carrier phase were separated in the time domain. The optimal temperature and concentration values were efficiently searched by an improved simulated annealing algorithm through the FID signal in the window function. Numerical simulations verified the noise immunity of the proposed method at different noise levels. Experiments were implemented on a methane-air laminar premixed flame, and the results showed that the proposed method performed better in measurement stability and accuracy than laser absorption spectrometry, especially in the presence of incident laser power fluctuations. This method is proven promising in the field of combustion diagnosis.

Continuous estimation of coseismic and early postseismic slip phenomena via the GNSS carrier phase to fault slip approach: a case study of the 2011 Tohoku-Oki sequence

The transition process from coseismic to early postseismic phenomena within a half-day remains a significant topic for understanding the slip budget and friction properties of the fault. However, the investigation of this phase has undergone limited advancement. This is mainly due to the lack of precision pertaining to the Global Navigation Satellite System (GNSS) analysis caused by difficulty of separation between fault slip and other unknown parameters such as tropospheric delay. Therefore, we propose an alternative approach (phase-to-slip; PTS) that detects fault slip directly from GNSS carrier phase variation without conventional positioning. Since the PTS simultaneously estimates fault slip and other unknowns, we can quantitatively evaluate their separation accuracy and contribution in the estimation. This study attempts to continuously estimate the coseismic and early postseismic slip of the 2011 Tohoku-Oki sequence using the PTS method. We analyzed 1-Hz carrier phase data for approximately 2 h before and after the mainshock origin (2011/03/11/05:46UTC). As a result, we successfully obtained the coseismic slip of the Mw9.0 mainshock and two major aftershocks in the off-Ibaraki (Mw7.8) and off Iwate (Mw7.4) regions. For all three events, the estimated slip distribution, equivalent moment magnitude, and calculated displacement field well agreed with those from the conventional positioning. Additionally, our results suggest postseismic slip mainly in the downdip area adjacent to the mainshock rupture. We obtained three major slip areas around the downdip region near Aomori, Iwate, and Miyagi. The estimated slip amount reaches approximately 0.1–0.2 m in 34 min immediately after the mainshock. The equivalent seismic moment of the slip areas near Iwate and Miyagi were approximately Mw7.4. This amount is similar or slightly greater than the estimations based on conventional positioning. Significant overlap is observed in the locations of the slip areas. In this manner, PTS continuously detected a series of coseismic and early postseismic slips with timescale ranging from a few minutes to an hour. Our results demonstrate the capability of the PTS method for broadband fault slip monitoring and its potential contribution to the investigation of early postseismic phenomena.

On the Occurrence of GPS Signal Amplitude Degradation for Receivers on Board LEO Satellites

AbstractTransient signal loss of the global positioning system (GPS) has been frequently observed by receivers on board the European Space Agency's Swarm mission when the satellites encounter ionospheric plasma irregularities. In this study we provided the first comparison of the GPS signal amplitude degradations from receivers on board low Earth orbiting satellites at different altitudes. Intense carrier phase variations but almost no amplitude fades (less than 2 dB Hz) are observed when the spaceborne receiver lies right inside the ionospheric plasma irregularities, like the case for the Swarm and CHAMP satellites flying at about 400–500 km. This indicates that the strong phase variation, but not the amplitude fades, causes the receivers to stop tracking the GPS signals. When the receiver is located 100–200 km below the slab of plasma irregularities, like the case for the GOCE satellite flying at about 250 km, signal amplitude fades exceeding 10 dB Hz are observed, in addition to strong phase variation. Our results suggest that a considerable distance of the receiver to the plasma irregularity slab is needed to affect the Fresnel diffractive process and further causes GPS signal amplitude fades.

Ground-to-satellite time and frequency synchronization link with active carrier phase compensation.

In this paper, a synchronization link between one ground station and one geostationary satellite is established. The ground station receives retransmitted signals from the satellite, measures phase delay along the propagation route, and actively compensates back to its sending signals, realizing real-time phase fluctuation compensation. The transmitted signal contains two frequencies to eliminate common-mode phase noise. The difference between their carrier phase delays is measured. Different modes of carrier phase variation are separated and compensated, achieving a remaining time jitter of ±200 ps. Major sources of error are analyzed, and potential methods for improvement are discussed. The proposed ground-to-satellite link and active compensation method has potential applications in frequency standard dissemination to remote receivers (including ground stations or satellites). These potential applications justify further study of this system.

A Semi-Open Loop GNSS Carrier Tracking Algorithm for Monitoring Strong Equatorial Scintillation

Strong equatorial ionospheric scintillation of radio signals is often associated with simultaneous deep amplitude fading and rapid random carrier phase fluctuations. It poses a challenge for satellite navigation receiver carrier phase tracking loop operation. This paper presents a semi-open loop algorithm that utilizes the known position of a stationary receiver and satellite orbit information to estimate carrier phase variations during deep signal fading. Strong GPS scintillation data collected on Ascension Island in March 2013 are processed to reveal fast phase changes of half and full cycles over tens of milliseconds on all three GPS frequencies. Simulated signals are used to validate the algorithm and confirm that the fast phase changes are true scintillation effects rather than receiver processing artifacts. The algorithm performance is demonstrated through comparison with several closed-loop implementations. Potential errors associated with receiver clock bias and other environmental factors are also analyzed. A statistical summary of the concurrent fast phase changes and deep fades based on the processing results of the Ascension Island data is presented.

New Results on Ionospheric Irregularity Drift Velocity Estimation Using Multi‐GNSS Spaced‐Receiver Array During High‐Latitude Phase Scintillation

AbstractThe spaced‐receiver technique using Global Navigation Satellite Systems (GNSS) receivers offers an inexpensive approach for estimating ionospheric irregularity velocity during ionospheric scintillations. Our previous work has demonstrated that correlative studies of the GNSS carrier phase variations can be used to derive irregularity drift velocity at high latitudes. This study expanded upon our previous projects by incorporating Global Navigation Satellite System (GLONASS) signals, investigation on ionospheric irregularity height assumption, and all‐sky imager measurements into the methodology. A case study is presented based on Global Positioning System, Galileo, and GLONASS measurements during a geomagnetic storm event on 20 December 2015, obtained from a closely spaced receiver array at Poker Flat Research Range near Fairbanks, Alaska. The GNSS‐estimated irregularity drift velocities are in general agreement with the measurements from the Poker Flat Incoherent Scatter Radar and the Poker Flat all‐sky imager. The study also shows that the irregularity altitude assumption will not lead to significant variations in the irregularity drift velocity estimates, especially for satellites with relatively high elevations. The techniques presented in this paper demonstrate that GNSS receiver arrays can be used as powerful means to monitor the ionospheric plasma dynamics during space weather events.

Local Nusselt number enhancements in liquid–liquid Taylor flows

Abstract Thermal management has emerged as a critical requirement to ensure the performance and reliability of electronic devices and systems. System level heat fluxes are approaching the limits of conventional forced air cooling, and there is a need to develop alternative cooling techniques for devices such as processors, power amplifiers and laser arrays. This paper examines the potential heat transfer enhancements of a two phase liquid–liquid Taylor flow regime. The primary focus of the work was to examine the influence of slug length and carrier phase variations on the local Nusselt numbers. An experimental facility was designed and commissioned to subject the flow to a constant heat flux boundary condition, a boundary condition commonly encountered in thermal management applications. Local temperature measurements were acquired using a high resolution infrared thermography system. Experiments were carried out over slug length, Capillary and Prandtl numbers that spanned several orders of magnitude in a minichannel geometry. Reductions in carrier slug length and increases in dispersed slug length were found to augment the heat transfer rates, with the greatest enhancements observed in flows with carrier slug lengths approaching the channel diameter. The thickness of the liquid film separating the dispersed slugs from the heated capillary walls was found to play a significant role in the removal of heat, with increases in film thickness resulting in a reduction in the heat transfer rates. Based on the characteristics identified, a novel correlation is proposed to model the flow in the thermally developing and fully-developed regions.

GNSS 신호를 이용한 회전체의 롤 회전 속도 추정 기법

This paper proposes a roll rate estimation method for spinning vehicles. The carrier phase and frequency variations caused by spinning of vehicles are observed and the roll rate estimator is designed on the observation. The roll rate estimator consists of phase detector and zero crossing counter. The phase detector computes phase variation using in-phase and quadrature value from the correlator. By using zero crossing counter, the roll rate can be estimated since the output of phase detector is changed in proportion to the roll rate. Experiment a results show that estimated roll rate error is smaller than 0.0578Hz.

Frequency Estimation in Iterative Interference Cancellation Applied to Multibeam Satellite Systems

This paper deals with interference cancellation techniques to mitigate cochannel interference on the reverse link of multibeam satellite communication systems. The considered system takes as a starting point the DVB-RCS standard with the use of convolutional coding. The considered algorithm consists of an iterative parallel interference cancellation scheme which includes estimation of beamforming coefficients. This algorithm is first derived in the case of a symbol asynchronous channel with time-invariant carrier phases. The aim of this article is then to study possible extensions of this algorithm to the case of frequency offsets affecting user terminals. The two main approaches evaluated and discussed here are based on (1) the use of block processing for estimation of beamforming coefficients in order to follow carrier phase variations and (2) the use of single-user frequency offset estimations.

Differential spatial multiplexing

In this paper, we present a novel differential space-time (DST) architecture which is well suited for high data-rate applications but requires only a linear decoding complexity. Multiple transmit antennas are divided into groups and DST encoding is applied individually to each group. Instead of using the optimum joint-group decoding approach, the proposed receiver combines group interference suppression (GIS) and decision-feedback differential detection (DF-DD) to reduce the decoding complexity. By taking advantage of the differential encoding at the transmitter, the GIS filters can be calculated without explicit knowledge of channel state information. Since the optimization of the GIS filters requires a generalized eigendecomposition of two correlation matrices, we also devise efficient adaptive algorithms for recursive filter optimization. It is shown that both the GIS filter computation and the detection scheme are robust against carrier phase variations

Comment on "Fringe projection profilometry with nonparallel illumination: a least-squares approach"

We comment on the recent Letter by Chen and Quan [Opt. Lett.30, 2101 (2005)] in which a least-squares approach was proposed to cope with the nonparallel illumination in fringe projection profilometry. It is noted that the previous mathematical derivations of the fringe pitch and carrier phase functions on the reference plane were incorrect. In addition, we suggest that the variation of carrier phase along the vertical direction should be considered.

Noncoherent adaptive channel identification algorithms for noncoherent sequence estimation

In this letter, two novel noncoherent adaptive algorithms for channel identification are introduced. The proposed noncoherent least-mean-square (LMS) and noncoherent recursive least squares (RLS) algorithms can be combined easily with noncoherent sequence estimation (NSE) for M-ary differential phase-shift keying signals transmitted over intersymbol interference (ISI) channels. It is shown that the resulting adaptive noncoherent receivers are very robust against carrier phase variations. For zero frequency offset, the convergence speed and the steady-state error of the noncoherent adaptive algorithms are similar to those of conventional LMS and RLS algorithms. However, the conventional algorithms diverge even for relatively small frequency offsets, whereas the proposed noncoherent algorithms converge for relatively large frequency offsets. Simulations confirm the good performance of NSE combined with noncoherent adaptive channel estimation in time-variant (fading) ISI channels.

Noncoherent adaptive linear MMSE equalisation for16DAPSK signals

A novel adaptive noncoherent linear minimum mean squared error equaliser for 16-level differential amplitude/phase shift keying signals is proposed. A novel modified least mean square algorithm is derived which allows an efficient equaliser adaptation. Simulations confirm the high performance of the proposed noncoherent equaliser and its robustness against carrier phase variations.

A nonlinear filtering approach to estimation and detection in mobile communications

The paper develops an open-loop digital receiver suitable for operation with frequency flat-fading channels disturbed by fast-fading conditions and large carrier phase variations. The receiver consists of a bank of matched stochastic nonlinear filters (NLFs) and a maximum a posteriori probability (MAP) decision processor driven by the filters' innovations processes. This structure is able to perform symbol-by-symbol detection while keeping track of multiplicative distortion (carrier amplitude and phase) within the symbol interval. The NLF propagates probability densities represented as products of Tikhonov and Gaussian functions, whose parameters are computed according to a minimum Kullback (1959) distance criterion, i,e,. we adopt an information preserving strategy. This filter is hangup free and outperforms the extended Kalman-Bucy (1972, 1973) filter (EKBF), especially in terms of phase acquisition. These characteristics explain why the NLF-based receiver may exhibit much lower error probabilities than those obtained with an equivalent EKBF-based receiver. Simulations show that the proposed detection/estimation scheme is robust against mistuning of the receiver parameters, being appropriate for all-digital modems in mobile radio communications.

Direct sequence/code‐division multiple‐access adaptive interference canceller on differential detection for fast fading channel

AbstractThis paper proposes the differential detection type direct sequence/code‐division multiple‐access (DS/ CDMA) adaptive interference canceller (AIC) that can track the fast fading. The proposed AIC is composed of the fractionally chip‐spaced code‐orthogonalizing filter (COF) with tap length corresponding to several bit periods and the differential detector. The COF makes adaptively the tap weight orthogonal to all spreading codes of other users as a despreading code of the desired user so that the interferences from other users are cancelled and the signal component of the desired user is extracted. The differential detector compensates the carrier phase variation due to fading in the desired user's signal at the COF output. By such a structure, the tracking performance of AIC to the channel variation can be improved to the limit of the tracking performance of the differential detector.This paper evaluates the basic ability of the proposed AIC in the fast‐fading channel. The AIC is especially expected to be utilized in the DS/CDMA mobile communications since the receiver is of the single‐user type, where no information concerning other users is needed.

Block demodulation method for psk signal by sequential regression estimator

AbstractThis paper considers the block demodulation method with carrier phase synchronization without preamble, and presents a proposal and evaluation for the new carrier phase synchronization method based on the sequential regression estimator. The block demodulation has a feature in that the traditional way of real‐time demodulation is not adhered to, and the preamble is not required. This improves greatly the throughput especially in a short packet communication.The traditional system is based on the least‐square scheme, noting that the cumulative carrier phase variation between data symbols is represented in a linear form. It has a problem in that the linearity is lost due to noise in deriving the cumulative value for the phase variation, which may greatly deteriorate the demodulation performance.The sequential regression estimator proposed in this paper is based essentially on the least‐square principle. However, the cumulative value is not determined for each time as in the traditional method but the estimation is updated based on the difference between the observed value and the value estimated from the data up to the previous sample. Consequently, the problem in the traditional system essentially is eliminated.Because of this elaboration, the computation in the proposed system is very small compared with traditional systems. It is seen as a result of simulation that the tolerable noise margin for 80 percent synchronizing probability, which has been used as the evaluation criterion, is improved by 11 dB for BPSK.In the satellite packet communications network such as VSAT (very small aperture terminal), the throughput is improved remarkably. Applying the proposed principle to the design of the present link, the time‐ratio, where the burst synchronization error is 1 percent or less in the Ku band, is 0.03 percent. In VSAT, a random access scheme is employed. Considering the burst collision probability of the access, it follows that the burst synchronization error probability of 1 percent does not affect the overall performance, and the proposal in this paper can be considered as sufficiently practical.

Compression of transmitted pulses in plasmas

The compression of frequency-modulated RF pulses is discussed when the dispersive property of a lossless, isotropic, and homogeneous plasma is used to enhance the resolution of transmitted pulses at the receiver. Using the basic concept of group velocity, an expression is obtained for the carrier phase variation of a rectangular envelope pulse so that the pulse collapses on itself at the receiver. Unlike the chirp radar pulse, the frequency variation is not linear and the optimum detection of transmitted pulses depends on both the plasma frequency and the distance between the transmitter and the receiver. The method of convolution was used to obtain numerical results, which indicate that the formulation given results in compression for short propagation distances.