Different Types Of Receivers Research Articles

Influence of Inter-System Biases on Combined Single-Frequency BDS-2 and BDS-3 Pseudorange Positioning of Different Types of Receivers

The BeiDou Navigation Satellite System (BDS) has developed rapidly, and the combination of BDS Phase II (BDS-2) and BDS Phase III (BDS-3) has attracted wide attention. It is found that there are code ISBs between BDS-2 and BDS-3, which may have a certain impact on the BDS-2 and BDS-3 combined positioning. This paper focuses on the performance of BDS-2/BDS-3 combined B1I single-frequency pseudorange positioning and investigates the positioning performance with and without code ISBs correction for different types of receivers, include geodetic GNSS receivers and low-cost receivers. The results show the following: (1) For geodetic GNSS receivers, the code ISBs of each receiver is about −0.3 m to −0.8 m, and the position deviation is reduced by 7% after correcting code ISBs. The code ISBs in the baseline with homogeneous receivers has a little influence on the positioning result, which can be ignored. The code ISBs in the baseline with heterogeneous receivers is about −0.5 m, and the position deviation is reduced by 4% after correcting code ISBs. (2) The code ISBs in the low-cost receivers are significantly larger than those in the geodetic GNSS receivers, and the impact on the positioning performance of the low-cost receivers is significantly greater than that on the geodetic GNSS receivers. After correcting the code ISBs, the position deviation of low-cost receivers can be reduced by around 12% for both undifferenced and differenced modes. (3) For low-cost receivers, correcting the code ISBs can increase the number of epochs successfully solved, which effectively improves the low-cost navigation and positioning performance. (4) The carrier-phase-smoothing method can effectively reduce the distribution dispersion of code ISBs and make the estimation of ISBs more accurate. The STD values of estimated code ISBs in geodetic GNSS receivers are reduced by about 40% after carrier-phase smoothing, while the corresponding values are reduced by about 7% in low-cost receivers due to their poor carrier-phase observation quality.

Usability analysis of the amplitude scintillation index S4c derived from BDS-3 observations

The third phase of BDS (BDS-3) began to provide fully global positioning service. To investigate the performance of BDS observations in ionospheric scintillation index establishment, this study focuses on the construction of amplitude scintillation index S4c using the carrier-to-noise ratio data of BDS-3. Based on the newly installed ionospheric scintillation monitoring receiver (ISMR) data at the Ledong station in Hainan from July 2021 to December in 2022, the relationship between the amplitude scintillation indexes S4c and S4 is analyzed and compared. Statistical results indicate the correlation coefficient between S4c and S4 can reach 0.95. To analyze the magnitude difference of S4c derived from different geodetic GNSS receivers, six groups of collocated stations at various latitudes are employed to calculate the S4c from January to December in 2022. The values of S4c processed by different types of receivers are slightly different, sorted by the processed values in descending order as TRIMBLE > LEICA > SEPTENTRIO, where the mean value of difference between TRIMBLE and SEPTENTRIO is about 0.05, and the mean value of difference between LEICA and SEPTENTRIO is about 0.03. The six collocated groups of stations showed a significant increase in the difference in S4c values within the season of the year when scintillation occurred, with the increased values moving up and down in the range of one-fifth of the mean values. Finally, the S4c is applied in detecting ionospheric irregularities during the Tonga volcanic eruption on January 15, 2022. It is found that the ionospheric irregularities start at 11:00 UT and drift westward from the eruption center region, gradually shifting to the Southeast Asia region with obvious scintillation.

Performance analysis of rectangular and double-D transmitters with various receivers for electric vehicle static charging

The inductive charging stations of the future should be able to charge any car, regardless of the type of coil configuration attached to it. In this study the performance of different configurations of coils is investigated. Where the principle of interoperability is studied between the most common types of coils in the IPT system (rectangular and double-D) recommended by Society of Automotive Engineering (SAE) J2954. This interoperability analysis is done at a power level of 11.1 kVA and Z3-class ground clearance using the two types of coils on the side of the car, while double D (DD) is used as a general transmitter in one case, and in the other case, a rectangle (R) is used as a general transmitter. Four 3D finite-element models (FEMs), along with compensation circuits, are built to perform the interoperability tests. The circuit models are utilized to determine the frequency of operation and the parameters of compensation circuit that realize the rated power at highest efficiency. The concept of interoperability has been verified through multiple performance indicators, namely coupling coefficient, transmitted power, and transmission efficiency. These indicators were calculated at ideal alignment and the different cases of misalignment, whether lateral or angular. The findings prove that the two different types of receivers (R and DD) can work efficiently and smoothly with the general transmitter, whether DD pad or rectangular pad are used. At the same time, the nominal power can be transmitted at high efficiency, above the limits permitted by SAE j2954 (>85 % at alignment conditions and >80 % at misalignment conditions).

Research on performance improvement method of BDSBAS multi-GNSS service with DFMC protocol

BDSBAS refers to the DFMC protocol to broadcast long-term corrections and integrity messages in real-time to meet the high integrity requirements of civil aviation users. Based on the measured data of the BDSBAS monitoring station, the long-term corrections and integrity messages of BDS/GPS/GAL are calculated, and from the user's perspective verifies the service capability of the above information which mainly including positioning accuracy, pseudorange bias and Protection Level (PL). The test results show that the accuracy of multi-GNSS long-term corrections is better than 0.14 m; when the user uses the long-term corrections, the positioning accuracy can be improved by 27% in the horizontal direction and 31% in the vertical direction compared with the level of the single BDS. In addition, the results show that the BDSBAS DFMC service can satisfy the LPV-200 availability contour in Mainland China except western China and satisfy the Cat-I availability contour only in the central region of China depend on only BDS constellation. When all the messages of BDSBAS DFMC service based on BDS/GPS/GAL constellations are used, it can reach the availability of 100% which satisfy the LPV-200 index in China and surrounding areas, and the availability of 99.4% which satisfy the Cat-I index in Mainland China. Finally, the effect of pseudorange bias errors on positioning accuracy of different types of receivers are analyzed. Results show that pesudorange bias of BDS and GPS is about 0.2 m ∼ 0.3 m, and for Galileo is about 0.05 m. With multi-GNSS corrections and integrity information, the level of service availability and coverage for LPV-200 and CAT-I of BDSBAS DFMC service could be effectively improved.

BDS-2/BDS-3 uncalibrated phase delay estimation considering the intra-system bias

Intra-system biases (ISBs) between BDS-2 and BDS-3 are of critical importance when combining observations from the BDS-2 and BDS-3 systems, which is meaningful to fully take advantage of the BDS positioning capability. Meanwhile, ISBs should also be considered in the estimation of BDS uncalibrated phase delays (UPDs). In this research, we present a BDS-2/BDS-3 joint-processing scheme, as well as a method for estimating BDS UPDs. The characteristics of ISBs and the quality of BDS UPDs are analyzed based on 30-day data from 130 multi-GNSS experimental (MGEX) stations. Our results indicate that the ISBs are related to the type and version of the receiver. The ISBs can be regarded as constant across the course of a given day, and the mean standard deviation (STD) values of ISBs over one month for different types of receivers are generally within 0.2 m. Moreover, to assess the quality of UPD products, the residuals of the estimated UPDs and the utilization rates of the observation data are computed. The results show that the quality of BDS UPDs can be improved by correcting the satellite-induced pseudo-range variations, and by estimating the wide-lane (WL) UPD difference between BDS-2 and BDS-3. The average RMS values of the estimated residuals of WL UPD and narrow-lane (NL) UPD are 0.07 and 0.09 cycles, respectively; moreover, the utilization rate of the observation data of WL UPD and NL UPD can reach above 90 %. The performance of BDS precise point positioning (PPP) and PPP ambiguity resolution (PPP-AR) is analyzed in terms of positioning accuracy and convergence performance in both the static and kinematic modes. Compared with PPP ambiguity-float solutions, the positioning accuracy of PPP-AR is significantly improved, especially in the east direction. The impact of ISBs on PPP and PPP-AR is also analyzed, and the results indicate that ISBs can improve the convergence speed of float PPP, but can be disregarded in PPP-AR.

Fundamental SNR Limits Imposed by ASE in Frequency-Shifting Loops

Recirculating frequency-shifting loops (FSLs) are a simple source of optical frequency combs with bandwidth compatible with microwave technologies. As such, they have demonstrated promising capabilities for telecommunications, remote sensing, and microwave photonics. In these systems, the coherent frequency comb is produced by recirculation of a single frequency laser in a fiber loop containing a frequency shifter. Due to the insertion of an optical amplifier in the loop to compensate for the losses, amplified spontaneous emission (ASE) is inevitably emitted and superimposes to the coherent output. In this paper, we quantify theoretically the contribution of the ASE background to the FSL output for different types of receivers used in FSL-based techniques: direct, self-heterodyne, and dual-comb detection. In particular, we focus on two important practical applications of FSL: coherent optical reflectometry and real-time Fourier transforms of radio-frequency signals. We provide for each of them numerical estimations of the signal-to-noise ratio and dynamic range. This work constitutes a compact framework for the general evaluation of techniques based on FSLs.

Comparative performance evaluation of candidate receivers for an etendue-conserving compact linear Fresnel mirror field

While several studies of multitube and monotube linear Fresnel receivers exist in the literature, comparative studies on different types of receivers are limited. This paper therefore aims to address this gap within literature by comparing the optical and thermal performance of four different receivers: an adapted compound parabolic concentrator (CPC)-type monotube receiver, an adapted tailored edge ray concentrator (TERC)-type monotube receiver, a trapezoidal multitube receiver and an adapted TERC-type multitube receiver. Existing literature was used to determine the design elements limiting heat loss, which were then incorporated into the receiver design and optical optimisation of the four receivers. Once the geometry was determined through a series of Monte Carlo ray tracing (MCRT) simulations, a validated two-dimensional computational fluid dynamic (CFD) model was used to determine the heat loss of each receiver for the same thermal conditions. Given that these heat loss studies were decoupled from the optical study, they are valid for any type of mirror field. While both adapted TERC-type receivers performed well optically (with daily optical efficiencies of 56.93% and 56.6% for the monotube and multitube receivers, respectively), the adapted TERC-type multitube receiver had the highest thermal loss of all the receivers, increasing the heat loss of the TERC-type monotube receiver by a factor of 2.5. In contrast, the adapted CPC-type monotube receiver had a lower daily optical efficiency of 51.29% when paired with an etendue-conserving compact linear Fresnel mirror field, but had low thermal loss, second only to the lower heat loss of the adapted TERC-type monotube receiver by a factor of 1.26. The standard trapezoidal receiver had a relatively low daily optical efficiency of 53.69% and relatively high heat losses, higher than the adapted CPC- and TERC-type monotube receivers by a factor of 1.5 and 1.9, respectively. The adapted TERC-type monotube receiver was therefore determined to be the best candidate receiver for an etendue-conserving compact linear Fresnel field.

Речевое поведение русских писателей XIX века в жанрах «дружеское письмо» и «роман»

The purpose of the study is to compare writers’ speech behaviour when they actualise the accentuation strategy in the genres of informal letter writing and the novel while addressing different types of receivers (the individual one and the group one). Scientific originality of the study lies in applying comparative analysis elements to the texts of novels and informal letters within the framework of a pragmalinguistic approach. In the course of the study, the researcher has identified nuances of writers’ speech behaviour, taking into account how actively they actualise speech signals of accentuation in different genres. The attained results have demonstrated that writers’ speech behaviour in the genres of the novel and letter writing is similar, which is accounted for by the influence of authors’ professional speech preferences on their everyday speech.

Calibrating receiver-type-dependent wide-lane uncalibrated phase delay biases for PPP integer ambiguity resolution

Wide-lane (WL) uncalibrated phase delay (UPD) is usually derived from Melbourne–Wübbena (MW) linear combination and is a prerequisite in Global Navigation Satellite Systems (GNSS) precise point positioning (PPP) ambiguity resolution (AR). MW is a linear combination of pseudorange and phase, and the accuracy is limited by the larger pseudorange noise which is about one hundred times of the carrier phase noise. However, there exist inconsistent pseudorange biases which may have detrimental effect on the WL UPD estimation, and further degrade user-side ambiguity fixing. Currently, only the large part of pseudorange biases, e.g., the differential code bias (DCB), are available and corrected in PPP-AR, while the receiver-type-dependent biases have not yet been considered. Ignoring such kind of bias, which could be up to 20 cm, will cause the ambiguity fixing failure, or even worse, the incorrect ambiguity fixing. In this study, we demonstrate the receiver-type-dependent WL UPD biases and investigate their temporal and spatial stability, and further propose the method to precisely estimate these biases and apply the corrections to improve the user-side PPP-AR. Using a large data set of 1560 GNSS stations during a 30-day period, we demonstrate that the WL UPD deviations among different types of receivers can reach ± 0.3 cycles. It is also shown that such kind of deviations can be calibrated with a precision of about 0.03 cycles for all Global Positioning System (GPS) satellites. On the user side, ignoring the receiver-dependent UPD deviation can cause significant positioning error up to 10 cm. By correcting the deviations, the positioning performance can be improved by up to 50%, and the fixing rate can also be improved by 10%. This study demonstrates that for the precise and reliable PPP-AR, the receiver-dependent UPD deviations cannot be ignored and have to be handled.

“Who should I grant access to my post?”: Identifying the most suitable privacy decisions on online social networks

PurposeOnline social networks (OSNs) provide users with mechanisms such as social circles and individual selection to define the audiences (i.e., privacy policy) of the shared information. This privacy decision-making process is a hard and tedious task for users because they have to assess the cost-benefit in a complex environment. Moreover, little is known about how users assess the cost-benefit of matching the elements of online communication and their interests. Therefore, the purpose of this paper is to develop and test a research model to understand the impact that the types of receivers and the sensitivity of messages have on privacy decisions.Design/methodology/approachA study was conducted to understand how users evaluate the cost-benefit of the disclosure action in online social networks for the different types of receivers identified and the sensitivity of the message. Data from 400 respondents was collected and analyzed using partial least squares modeling.FindingsThe findings of this study demonstrated a trade-off variance between the perceived cost-benefit and the disclosure of sensitive information with different receiver types. Disclosing personal information with trusted receivers, influencer receivers and receivers from the circle of coworkers had a positive significant effect on social capital building. Conversely, disclosing personal information with receivers from the circle of family or unknown receivers had a significant negative effect on social capital building and even a significant positive effect on privacy concerns.Originality/valueRecent literature has documented the increasing interest of the research community in understanding users' concerns and interests in making the most suitable privacy decisions. However, most researchers have worked on understanding the disclosure action from a user-centered perspective and have not considered all of the elements of online communication. This study puts the focus on all of the elements of communication during disclosure actions, taking into account the properties of the message and receivers and the impact on users' cost benefit value.

EGNOS Performance Along Finnish Coast

The purpose of this article is to demonstrate the benefits of EGNOS (European Geostationary Navigation Overlay Service / SBAS in Europe) for the community and inform about the activities that are ongoing for the provision of EGNOS L1 maritime service. EC (European Commission) and GSA (European GNSS Agency) are assessing an EGNOS L1 maritime service with the objective to complement the existing maritime radio-navigation systems (e.g. DGNSS). community is interested in using SBAS for ocean waters, coastal waters and harbour entrances/approaches considering operational needs (IMO Res. 1046), especially where there is no back-up infrastructure or in poorly covered environments. EGNOS L1 Service aims at providing pseudo-range corrections and alert information to the GPS L1 signals for maritime navigation, obtaining enhanced accuracy and ranging integrity information over Europe. In order to ensure a safe use of SBAS by all shipborne receivers, an IEC 61108 standard for SBAS receiver equipment should be published. IEC 61108 is a collection of IEC standards for Maritime navigation and radio-communication equipment and systems - Global navigation satellite systems (GNSS). In consequence, EC, GSA, ESA and ESSP are developing guidelines for manufacturers for the implementation of SBAS in shipborne receivers to be compliant with the operational requirements defined in International Organization (IMO) Resolution A.1046. These guidelines, together with a set of test specifications, intend to support the integration of SBAS in the standardisation process for maritime navigation and radio-communication equipment and systems within IEC framework. One GNSS campaign will be performed along the Finnish coast in order to analyse the EGNOS performance in the border of Northeast EGNOS coverage area. Different types of receivers configured to use SBAS will be on board the vessel to analyse the results. The set of receivers to be used would include maritime receivers, high-end receivers and also new receivers aligned with the future SBAS guidelines. On one side, the EGNOS navigation errors will be obtained with respect to a reference PPP post-processed trajectory. On the other side, the EGNOS availability will be obtained, taking especial attention at the border service coverage area. The EGNOS performance results will be compared with respect to the GPS standalone solution, to verify EGNOS provides an enhanced navigation position. The performance obtained with the receivers will be compared with the operational requirements defined in the IMO Resolution A.1046 (27) to assess the feasibility of EGNOS for some maritime applications. Finally, a deep performance analysis will be done in the Northeast border of EGNOS coverage area for ocean waters, coastal waters and harbour entrances/approaches. Based on the results obtained from a receiver, it will be shown a reliable EGNOS navigation solution with better accuracy than GPS standalone solution. The results aim at confirming that EGNOS L1 service is compliant with the operational requirements defined in the IMO Res. A.1046 (27) for ocean waters, coastal waters and harbour entrances/approaches, being beneficial for maritime community.

A modified estimation method of GLONASS inter-frequency bias for RTK based on short baseline

Different from other satellite systems, GLONASS adopts frequency-division multiple access (FCMA) technology to distinguish satellites, which directly leads to frequency deviation during signal receiving. Additionally, carrier phase inter-frequency bias (IFB) between different types of receivers are usually not zero, hindering the ambiguity resolution and thus limits the positioning accuracy. To solve this problem, a new estimating method of GLONASS ambiguity is proposed in this paper. According to the variation range of frequency deviation rate, the influence of phase IFB on ambiguity was removed by using searching method and quadratic linear model, thus reducing phase IFB estimating problem to an optimizing one. Feasibility of the method was verified using zero baseline data. Results show that the method can guarantee the reliability of RTK solution effectively.

Pseudorange-bias characteristics and the weakening method of BDS satellites

The nonideal characteristics of a navigation satellite signal will cause a pseudorange bias, which is manifested by the same type of receiver with the same pseudorange biases and different types of receivers with different pseudorange biases. When the technical state of receivers providing the navigation product is inconsistent with that of the users, the pseudorange bias will cause degradation of navigation and positioning service performance. In this paper, the pseudorange bias of BDS (Beidou Satellite Navigation System) is calculated using the ultrashort baseline pseudorange double-difference O−C (Observation Minus Computation) method. A large bias of B1I is obtained between two different juxtapositional receivers in the early stage of the experimental satellites. Thereafter, three methods, including the adjustment of the parameters of the loop of the receiver, a change in the multipath reduction algorithm, and an adjustment of the filter parameter of the predistortion of the satellite, are designed to reduce the bias. Experimental results indicate that the adjustment of parameters of the loop of the receiver can significantly reduce the pseudorange bias between the satellites, and the standard deviation of the pseudorange bias of B1I can be reduced from 0.63 to 0.36 m. Compared with the antimultipath observation, the observation of a narrow correlation can significantly reduce the pseudorange bias, and the standard deviation of the pseudorange bias of BII can be reduced from 0.36 to 0.18 m. Further, an adjustment of the filter parameters of the predistortion of the satellite can reduce the pseudorange bias of a single satellite by 0.3–0.4 m. There is no fixed reference satellite to evaluate the pseudorange biases of BDS satellites. A non-real-time double-difference O−C method that is based on the same external time and frequency controls of different receivers is designed to calculate the pseudorange bias. Employing this method, the characteristics of the pseudorange biases of BDS and GPS (Global Positioning System) satellites are compared. It is confirmed that (1) pseudorange biases exist in both BDS and GPS satellites, (2) the pseudorange bias of the L2C signal of GPS satellites is equivalent to that of the B1C data branch of BDS satellites, (3) the pseudorange bias of L1CA of GPS satellites is equivalent to the interoperable B1C pilot branch of BDS satellites, and (4) the pseudorange bias of L5C of GPS satellites is larger than that of the interoperable B2a signal of BDS satellites.

Fast Time Synchronization on Tens of Picoseconds Level Using Uncombined GNSS Carrier Phase of Zero/Short Baseline.

Since the observation precision of the Global Navigation Satellite System (GNSS) carrier phase is on the order of millimeters, if the phase ambiguity is correctly solved, while calibrating the receiver inter-frequency bias, time synchronization on the order of tens of picoseconds is expected. In this contribution, a method that considers the prior constraints of the between-receiver inter-frequency bias (IFB) and its random variation characteristics is proposed for the estimation of the between-receiver clock difference, based on the uncombined GNSS carrier phase and pseudorange observations of the zero and short baselines. The proposed method can rapidly achieve the single-difference ambiguity resolution of the zero and short baselines, and then obtain the high-precision relative clock offset, by using only the carrier phase observations, along with the between-receiver IFBs being simultaneously determined. Our numerical tests, carried out using GNSS observations sampled every 30 s by a dedicatedly selected set of zero and short baselines, show that the method can fix the between-receiver single-difference ambiguity successfully within an average of fewer than 2 epochs (interval 30 s). Then, a clock difference between two receivers with millimeter precision is obtained, achieving time synchronization on tens of picoseconds level, and deriving a frequency stability of 5 × 10−14 for averaging times of 30,000 s. Furthermore, the proposed approach is compared with the precise point positioning (PPP) time transfer method. The results show that, for different types of receivers, the agreement between the two methods is between −6.7 ns and 0.2 ns.

Site-specific real-time GPS multipath mitigation based on coordinate time series window matching

Multipath effect is one of the main errors in precise global navigation satellite system (GNSS) positioning. Although there are many GNSS multipath mitigation models available, each model has some limitations. We discuss the problem of mitigating low-frequency multipath in a specific site from the coordinate domain. At present, sidereal filtering is one of the most commonly used methods, in which the repetition period of multipath has to be estimated before multipath mitigation. However, in such a method, the maneuver of the satellite orbit and the long ephemeris update interval will cause inaccurate estimation of the repetition period. We propose a variation of the sidereal filtering method based on window matching. In that method, the window of coordinate time series formed by the current epoch and several previous epochs is used as the query window, and the matched window is searched in the time series of the previous day. The degree of similarity between windows is evaluated by similarity measures. Based on the coordinate point pairs in the matching window, multipath mitigation of the current epoch is performed by an affine transformation. The effects of different similarity measures in window matching are explored, and an early and late matching algorithm is proposed to solve the ambiguous problem of multiple matching sequences in integer-valued similarity metrics. Two sets of short baseline data were collected by different types of receivers in harsh environments to validate the method. The results show the feasibility and effectiveness of the proposed method for site-specific real-time multipath mitigation.

Assessing the Security of TEMPEST Fonts against Electromagnetic Eavesdropping by Using Different Specialized Receivers

The main topic of the present paper is the printed text protection against electromagnetic infiltration. There are many solutions to protect such data. One of these methods is the one that uses computer fonts that are characterized by special shapes. The suitability of the solution has to be confirmed by many tests and analyses. An important element of such researches is the class of receiving devices used. In the case of measurements of the valuable emissions arising from electronic data processing of the printed text, typical receivers that are used for measurements of electromagnetic compatibility cannot be used. They have to be dedicated devices for measuring the very low level of signal that arises unintentionally. The sensitivity of the receiver must be very high in wide measuring bands. In addition, in order to assess the method of preventing electromagnetic infiltration, it is important to verify it by independent institutions. An additional advantage is the use of different receivers in the assessment process. This paper presents the results of studies made regarding the suitability of two sets of fonts with special shapes (secure symmetrical and secure asymmetrical) in secure information processing. The analysis of the fonts was based on visual examination, a basic method of preliminary assessment of electromagnetic emissions correlated with processed text information, of the images reproduced from unwanted emissions. The tests were carried out at two independent institutions, Military Communication Institute—Poland, Special Telecommunications Services—Romania, using three different types of receivers: Tempest Test System DSI-1550A, Rohde & Schwarz FSET22 and Rohde & Schwarz FSWT. The images obtained in the two independent laboratories with different setup and test equipment confirmed thus without doubt the possibility of using special fonts as the solution against an effectiveness of electromagnetic infiltration. The above assessment is correct, regardless of the used receiver and the environment of implementation of the secure fonts.

Assessment and improvement of optical properties of particles for solid particle receiver

Particle receiver technology is an increasing research field. Researchers are investigating various different types of receivers, such as falling particle receivers, obstructed flow particle receivers, beam down fluidized bed systems, dense particle receivers, or the centrifugal receiver (Ho, 2016).This paper describes the assessment of three samples of commercial available particles (“proppants”) by microscopy and by X-ray diffraction phase analysis: Sintered Bauxite from Saint Gobain (mean diameter 1.2 mm and 0.45 mm), and Carboprop HD from Carbo Ceramics. Analyzed proppants consist of alpha-Al2O3, a glassy phase, and minor amounts of FeAlTiO5 and mullite.Particle samples have been prepared, to measure the reflectivity by a Lambda 950 spectrometer and evaluate the solar absorptance. As-received Bauxite proppants of a reference batch (Saint Gobain) showed a solar absorptance of 87%.To enhance solar absorptance, the particles were coated by inorganic pigments using sol-gel methods, diffusion of coloring ions. Furthermore, a modification of the proppant́s raw material was investigated, such as bauxite power mixed with commercial inorganic pigments and a natural mixture of mainly quartz and clay.

Multiple GNSS inter-system biases in precise time transfer

Inter-system bias (ISB) is important for the fusion of multiple global navigation satellite system data. They should be estimated or corrected for precise position, navigation, and timing solutions. In this study, ISB estimation models are developed for the global positioning system, GLONASS, BeiDou Navigation Satellite System, and Galileo systems. Six stations, with three different types of receivers, are used to analyze the ISB characteristics of different systems. A pair of time-link stations, which have a short baseline and are connected to a common external time frequency from the laboratory, are used to analyze the performance of three different estimation strategies (epoch-wise variable, 30 min piece-wise constant, and daily constant). These stations are also used to evaluate the influence of ISB constrains on the precise estimation of time transfer, coordinates, and the troposphere. The results illustrate: (a) ISBs variation exists between different systems, and the same types of receivers also exhibit large differences between the different stations due to the receiver hardware delay; (b) the precision of the different measurements and their related errors, the estimated ISBs that exhibit large differences between pseudorange and carrier phase observations, and the different ISB estimation strategies can also cause differences in the final fusion results; and (c) using the estimated ISB as constraints can improve the precise estimation of time transfer, coordinates, and the troposphere in the real-time solution mode.

Effective self‐backhaul scheme for massive MIMO–enabled full‐duplex heterogeneous networks by exploiting NOMA

AbstractBy integrating full‐duplex (FD) and nonorthogonal multiple‐access (NOMA) techniques for wireless self‐backhaul at small‐cell base stations (SBSs), a novel multitier heterogeneous network (HetNet) is proposed. In the HetNet, NOMA is used at SBSs for combing backhaul and downlink (DL) signals. As a result, at each SBS, the backhaul, uplink transmission, and DL transmission are executed simultaneously, whereas the FD macro base stations (MBSs) communicate with mobile users (MUs) and transceive backhaul signals from associated SBSs by using massive‐MIMO antennas. The simple time‐division duplex is performed for the communications between MBSs and MUs so that a round of communications consists of MBS‐MU‐DL and MBS‐MU‐UL phases. This work particularly focuses on the MBS‐MU‐DL phase. By assuming the HetNet to be fully loaded, this paper first models the distribution of active SBSs and those of the interference received at the different types of receivers. Then, by formulating the received signal‐to‐interference ratios, this paper obtains the coverage probabilities of the MU‐SBS‐MBS uplink backhaul and MU DLs as well as the spectrum and energy efficiencies. The presented simulations and numerical results show that the integration of FD and NOMA at SBSs is an effective solution for creating the backhaul between FD‐SBS and FD‐MBS. It is obtained that when the power‐sharing coefficient allocated for a small‐cell DL is small, the coverage probability of SBS DL transmission increases; otherwise, it decreases. However, the coverage probabilities of the MBS DL and MU‐SBS‐MBS backhaul link monotonically vary with the power‐sharing coefficient. It is also achieved that the power‐sharing coefficient imposes the effect on the energy efficiencies of the MU‐SBS‐MBS backhaul link and MU DL in inverse directions. At the same time, it is found that the achieved energy efficiency gain depends greatly on the resolution of massive‐MIMO antennas.

Characteristics of BeiDou Navigation Satellite System (BDS) Code Observations for Different Receiver Types and Their Influence on Wide-Lane Ambiguity Resolution.

The Chinese BeiDou Navigation Satellite System (BDS) has been an important constitute of the Global Navigation Satellite System (GNSS), and the combination of GPS and BDS shows significant improvements when compared with single GPS system for real-time kinematic (RTK) positioning, and improves on availability and fixing rates, especially in the East Asian area. While network RTK might have different types of receivers, both for global and regional networks, different types of receiver may adopt different internal multipath mitigation methods and other techniques that result in different pseudorange characteristics, especially for a multipath. Then, the performance of wide-lane ambiguity resolution (WL AR) is affected. In this study, we first analyze and compare the characteristics of BDS dual-frequency observations for different types of receivers, including Trimble, Leica, Javad, and Septentrio, based on multipath (MP) observables, and then we assess their influence on double-differenced (DD) WL AR. The numerical results show that an obvious low-frequency component exists in MP observables of BDS geostationary earth-orbit satellites (GEOs) for Leica receivers, while its high-frequency measurement noise is very small. For geosynchronous orbit satellites (IGSOs) and medium earth-orbit satellites (MEOs), a slight fluctuation can also be observed that is similar to that of GPS satellites, except for the satellite-included code bias. In Trimble, Javad, and Septentrio receivers, the MP series are dominated by high-frequency measurement noise, both for GEOs and non-GEOs, except for satellite-included code bias. Furthermore, the characteristic of Leica receivers for BDS GEOs seriously affects WL AR and, even for a short baseline, it takes a long time for WL ambiguities to converge, or not converge for many GEO-related DD WL ambiguities, while Trimble, Javad, and Septentrio receivers perform well for short and medium baselines. Then, a time-difference method is proposed to mitigate the multipath of BDS GEOs for a Leica receiver. After applying the proposed method, WL ambiguity fixing rates of GEO-related satellite pairs are improved significantly and the convergence time is shortened from several hours to ten minutes.