Station Receiver Research Articles

Optimal sensor placement for multi‐source AOA localisation with distance‐dependent noise model

In this study, the optimal sensor placement problem for multi-source angle of arrival localisation is investigated. The authors adopt the A-optimality criterion, maximising the trace of Fisher information matrix, to determine the optimal sensor-target geometry under distance-dependent Gaussian noise model. A recursive representation of the Cramer-Rao lower bound is derived to recast the sensor placement problem into a sequential method, obtaining the optimal sensor geometries in a step by step manner. Note that the state-of-the-art methods are highly sensitive to the source location changes such that they should be relocated by any later changes in target geometries, which is practically impossible in systems with stationary receivers (such as radars). The proposed sequential method can circumvent this drawback by changing only one flexible sensor position rather than the whole geometry of the sensors. Numerical simulations are included to corroborate the theoretical results and determine the cost of such flexibility and robustness on the localisation performance.

Partial dam removal restores passage for a threatened salmonid

AbstractDams represent one of the major forms of river alteration. As these structures reach the end of their lifespan, they often require extensive refurbishments or removal. A small‐scale water supply dam in Banff National Park (Alberta, Canada) was partially removed, creating a breach that allowed water to scour a new passage resembling a nature‐like fishway. We investigated the permeability of the partially removed dam as a means of validating the conservation benefits of the partial dam removal. We quantified the proportion of bull trout (Salvelinus confluentus), a threatened species in Canada, that approached and passed the fishway using radio telemetry receiver stations. The proportion of bull trout that approached the fishway was low (37.0%; N = 27 of 73), but was consistent with upstream reference sites (33%; N = 20 of 60). For those that did approach, the proportion of bull trout that passed yielded a high passage efficiency (77.8%; N = 21 of 27 that approached). The probability that a fish passed the fishway was related to water depth and time of day. Bull trout were more likely to pass when water depths were high (>0.40 m), and at night. Passage duration ranged from 5‐mins to 13‐days, suggesting that this resident species used the fishway for a variety of purposes (e.g., station holding and foraging) and not just transiting. Some individuals underwent large‐scale movements 2‐km upstream (15.1%; N = 11 of 73), or 2‐km downstream (2.7%; N = 2 of 73) following a successful passage event. This study provides new insight on how, in some instances, a breach in a dam can function as a nature‐like fishway, accommodating year‐round stream flows and providing hydraulic conditions suitable for fish passage without costly engineering or construction.

Linear and nonlinear earthquake location approaches in a case study overview

Several seismic events are calculated by an iterative, linear algorithm relocated in a nonlinear, grid-search with a maximum-likelihood hypocenter method. The same simultaneous events separately registered by regional and local seismological networks have also been used. A verified 1D (one dimensional) velocity crustal structure model is used in both methods and in all datasets for better comparisons. Some rock quarry blasts registered by the local receiver stations as ground truths are examined by both methods. This study's main objectives were: (i) to carry out a comparative examination of the error estimates in both techniques and (ii) to generalize location assessment of the permanent low-density regional network in Central Alborz. The regional network operates under Iranian Seismological Center and its seismic data are massively applied. To reach the research goals, the dataset–method correlation matrix and the location variables were statistically processed. It was shown that the estimated earthquake epicenters by the linear and nonlinear methods are approximately similar for well-located events in each network. For dense-proper distribution of the seismic stations, the elliptical error estimates have lower amounts and consequently the seismicity pattern is more reliable. The difference between subsurface seismicity patterns resulting from the above-mentioned approaches in the studied area is presented. Some depth calculation errors for the same recorded events are higher in the regional network. The correlation comparisons demonstrated that the nonlinear approach and the locally-constrained data may be closer to reality and more convincing. The nonlinear application is more plausible due to all of the possible solutions and less elliptical error estimates under the Gaussian distribution assumption. Subsequently, the combination of the nonlinear method, proper location criteria, and appropriate crustal velocity structure can effectively improve some of the earthquake location estimates in the regional catalogue. As a result, this procedure can be useful in seismicity concept evaluations.

A Fractional Variable Partial Update Least Mean Square Algorithm (FVPULMS) for communication channel estimation

The study presents a study on communication channel estimation algorithms. Fractional Variable Partial Update Least Mean Square algorithm (FVPULMS) is proposed. The model consists of input signal, unknown channel, an adaptive filter and an adaptation algorithm. The adaptive filter is a finite impulse response transversal adaptive filter. The adaptation algorithm is a FVPULMS algorithm and the filter update uses coefficient with index factors of three and five. The proposed algorithm was compared with Variable Partial Update Least Mean Square (VPULMS) and Full Update Least Mean Square (FULMS) algorithms. The simulation was carried out using fixed step sizes and variable step sizes of ( ). The result showed that FVPULMS algorithm has enhanced average performance efficiency in terms of estimated signal error reduction at the receiver station compared with VPULMS and FULMS algorithms, and can help to achieve improved signal error at the receiver station. KEYWORDS: Adaptation, Channel, step size, convergence speed, computational complexity, error state.

Identifying Environmental Cues for Atlantic Sturgeon and Shortnose Sturgeon Spawning Migrations in the Savannah River

AbstractWe investigated environmental cues for spawning migration behavior of Atlantic Sturgeon Acipenser oxyrinchus and Shortnose Sturgeon A. brevirostrum in the lower Savannah River, South Carolina and Georgia, from January 2013 to May 2018. Sturgeon were implanted with acoustic transmitters and detected on an array of 45 stationary receivers located every 5–10 km between Savannah Harbor and the upstream‐most barrier to movement (301 fluvial kilometers). Throughout the study period, we observed six Atlantic Sturgeon attempting nine fall migrations (n = 918 records), four Atlantic Sturgeon attempting eight spring migrations (n = 257 records), and 15 Shortnose Sturgeon attempting 29 spring migrations (n = 3,542 records). Cues for the initiation of migration and upriver movement were species‐specific. We observed significance in the main effects of water temperature, 3‐d lagged temperature, maximum discharge, and 3‐d lagged discharge, as well as in the interaction effect of 3‐d lagged temperature × 3‐d lagged discharge. Water temperature was the primary predictor of sturgeon migrations, which can be used to determine spawning season, but discharge also played a significant role in predicting upriver movement, particularly when high flows began to diminish. Directed flow regulation (e.g., intermittent flood pulsing) during key temperature thresholds may better facilitate the upriver movement of sturgeons and aid in the conservation of these imperiled species.

Construction and Algorithms of the Onboard System for Measuring the Helicopter Air Data and State of the Atmosphere with a Stationary Receiver, Ion-Mark and Aerometric Measurement Channels

The problem is considered of measuring the air parameters and state of the atmosphere on board the helicopter under the aerodynamic disturbances of the main rotor vortex column. The functional scheme, design features of the air parameter sensor and algorithms of information processing at the parking, starting, takeoff and landing and other modes of helicopter of the onboard system with a fixed receiver, ion-mark and aerometric measurement channels are revealed.

Monopulse antenna‐pointing system modelling and simulation

Mahdasht Satellite Receiving Station (MSRS) has been using 10 m reflector antenna to communicate with LEO satellite at S-band (2.2–2.3 GHz) and X-band (8–8.4 GHz). Presently, antenna pointing operates in program tracking. Pointing accuracy under program tracking conditions is in the neighbourhood of 0.2°. This is acceptable at S-band, but not enough at X-band. Due to the narrow beamwidth at X-band, it is important to improve pointing accuracy significantly (0.05°). Monopulse antenna tracking is one approach that provides tracking accuracy at high-frequency bands. This study presents mathematical model and simulation of monopulse pointing system using a novel analytic approach. Monopulse error signals are calculated using the proposed model while considering the kinematic equations with the assumption of the Gaussian radiation pattern for reflector antenna. The simulation results are verified by using a real (MSRS antenna) monopulse tracking system in X-band frequency (8.2 GHz). The measurement and simulation results demonstrated the azimuth and elevation pointing errors are valid in 3 dB beamwidth.

A two-stage flow-shop scheme for the multi-satellite observation and data-downlink scheduling problem considering weather uncertainties

An Earth observation satellite (EOS) is a sort of low earth orbit (LEO) satellite that is equipped with high resolution cameras for observing various types of target objects scattered across the surface of the Earth. The available time windows of multiple EOSs for observing a given target object and for downloading the acquired image/video data from satellites to ground receiver stations are scarce resources that should to be utilized efficiently. This problem is hereby named as the multi-satellite observation and data-downlink scheduling problem (MSODSP). We developed a two-stage flow shop scheme for the MSODSP in order to optimize the observation scheduling (at stage 1) and data-downlink scheduling (at stage 2) concurrently and get truly optimized results. A mixed-integer linear programming (MILP) model is developed for the MSODSP with three objective functions. The effects of weather uncertainties on the tasks' success are considered in the MILP model, which allow us to conduct a reliability-maximized task arrangement of EOSs. Computational experiments were conducted on the simulated data of a real LEO satellite to verify the proposed MILP model. The results showed that it was able to solve real-world instances of the MSODSP for up to 20 tasks over 8 days.

Highlights about the performances of storm-time TEC modelling techniques for low/equatorial and mid-latitude locations

A statistical evaluation of storm-time total electron content (TEC) modelling techniques over various latitudes of the African sector and surrounding areas is presented. The source of observational TEC data used in this study is the Global Navigation Satellite Systems (GNSS), specifically the Global Positioning Systems (GPS) receiver networks. For each selected receiver station, three different storm-time models based on empirical orthogonal functions (EOF) analysis, non-linear regression analysis (NLRA) and Artificial neural networks (ANN), were implemented. Storm-time GPS TEC data used for both development and validation of the models was selected based on the storm criterion of Dst⩽-50 nT or Kp⩾4 to take into account both coronal mass ejections (CMEs) and co-rotating interaction regions (CIRs) driven storms, respectively. To make an independent test of the models, storm periods considered for validation were excluded from datasets used during the implementation of the models and results are compared with observations, monthly median values, and International Reference Ionosphere (IRI-2016) predictions. Considering GPS TEC as reference, a statistical analysis performed over six storm periods reserved for validation revealed that ANN model is about 10%, 26%, and 58% more accurate than EOF, NLRA, and IRI models, respectively. It was further found that, EOF model performs 15%, and 44% better than NLRA, and IRI models, respectively, while NLRA is 25% better than IRI. On the other hand, results are also discussed referring to the background ionosphere represented by monthly median TEC (MM TEC) and statistics are provided. Moreover, strengths and weaknesses of each model are highlighted.

Nursing management of gestational diabetes mellitus in Ghana: Perspectives of nurse-midwives and women

BackgroundGestational diabetes mellitus (GDM) is defined as any degree of glucose intolerance that is observed in the beginning of, or first acknowledged during pregnancy. The prevalence of GDM is estimated to be approximately 15% globally and is expected to increase due to growing numbers of overweight and obesity in women in their reproductive age. The nursing management of GDM in terms of lifestyle modifications (exercise, diet and nutrition) and the taking of diabetes medication, if required, and adherence thereto is crucial to prevent maternal and neonatal-perinatal complications. This qualitative study therefore aimed to explore and describe the experiences of women regarding the nursing management they received after being diagnosed with GDM; and the perceptions of nurse-midwives on their nursing management of GDM in Ghana. SettingThis study was conducted in the military health institutions in Ghana, which includes one hospital and nine satellite clinics referred to as Medical Reception Stations providing antenatal and postnatal care to both military as well as civilian patients. Research on GDM in Ghana is extremely limited. DesignWe used a descriptive phenomenological approach to conduct 15 unstructured individual interviews with women that have been diagnosed with GDM (n = 7) and nurse-midwives (n = 8) providing nursing management of GDM during a six months period (December 2014 to May 2015). Audio-recorded data was transcribed, coded and analyzed using an adapted version of Tesch's eight steps for coding. ParticipantsSeven (n = 7) women between 28 and 45 years of age, with 1 to 3 offspring each, participated. Most women (n = 5) did not have a family history of diabetes. The eight (n = 8) nurse-midwives that participated were between 32 and 50 years old with between 2 and 12 years of experience. FindingsParticipants in this study reported similar issues that could assist in better management of GDM. The majority of participants indicated the need for education on GDM, but both women and nurse-midwives acknowledged that this education is hugely lacking. Participants generally felt that emotional support for women is critical and it was included in the nursing management of GDM. Both groups of participants acknowledged that involving women and their significant others in the nursing management of GDM is important. Cultural and socio-economic issues, such as cultural beliefs that clashed with diabetic diets, lack of financial and social grants and limited nurse-midwifery staff were mentioned by both groups to affect the nursing management of GDM. Key conclusionsThe results demonstrate that, despite the reported challenges experienced by nurse-midwives and women, it was evident that the aim of nurse-midwives was to manage GDM as optimally as possible for women diagnosed with GDM, while considering the constraints established in the results. The challenges identified, specifically in terms of lack of education and cultural and socio-economic issues that affect the quality of and adherence to the nursing management of GDM, need to be addressed in order to optimize care for women diagnosed with GDM in Ghana. Implications for practiceBased on our findings, recommendations are provided that can assist nurse-midwives and other health practitioners to provide comprehensive nursing management to women that have been diagnosed with GDM.

Healthcare Delivery System Security: the orchestration of automated and organizational solutions

Many studies from around the world enhance awareness of medication errors in hospitals. A French national study on Adverse Events (AE) revealed that 60 000 to 130 000 AE per year appear to be consequences of medication errors, and 15 000 to 60 000 AE are preventable. Furthermore, hospital spending represents 37% of the French healthcare costs. Enhancing medication system quality and efficiency by reducing medication errors and costs are then considered as important public health issues. Medication management is a complex socio-technical system involving multiple people and numerous steps. Automated dispensing systems have been reported to be key components of strategies to prevent medication errors and create a better workflow. Few hospital pharmacies are implementing automated nominative dispensing robot that increase secure treatment preparation as well as dispensing safety and performance. Automated storage systems and medication delivery devices also reduce hidden costs related to pharmaceutical products stock control and remove professional agent time from non-value-added tasks for a more efficient redeployment tasks.Nevertheless, our results from auditing hospital pharmacies that are investing in automated systems revealed risks and hidden costs related to reception station, dispensing and care unit orders that should be settled by computerization and organizational actions. Our study shows that hospital pharmacy organizations require the implementation of specific actions settling software interface problems and enhancing coordination skills among health care actors in order to secure medication delivery system and prevent from hidden costs related to organizational factors. Then, automation does not seem a self-sustaining option to handle pharmacy’s activity dysfunctions. Many other parameters intervene.This paper presents a pharmacy’s automation project. It takes example at a French Hospital Center in Lens in the north of France (CHL). We present a human centered automation approach that includes an identification of tasks eligible for automation and tasks that need to be supervised, controlled or operated by a human agent.

Monitoring Earth's ionosphere by means of hardware-software complex using the GPS/GLONASS satellite systems

Near real-time one-dimensional vertical electron density profiles are determined from GPS-derived total electron content (TEC) data by means of the iterative conjugate gradient projection method (CGP). Electron density profiles are determined in near realtime (within minutes of the time of measurement) from short time series of slant TEC (STEC) approximately 5 minutes. Measured STEC values are obtained from dual frequency data from a single GPS satellite at a single dual frequency receiver station. Both code-based TEC derived from the P-observable (Ptec) and phase-based TEC derived from the carrier phase observable (Ltec) are used in the solution. The CGP method addresses the ill-posed inverse problem of determining the electron density profiles from TEC measurements through the application of a side constraint to the acceptable solution. This is an iterative method which approximates the solution of a least squares problem through a converging sequence of solutions. The accuracy of the results is verified by comparison to electron density determined from the ionograms measured with Digisondes (Pushkov Institute of Terrestrial Magnetizm, Ionosphere and Radio Wave Propagation, Russian Academy of Science) located at Troizk, Moscow region (55.5N, 37.3E). The results of a hardware-software complex intended for monitoring the Earth's ionosphere according to navigation satellite systems are presented. The anomalous behavior of the critical frequency of the F2-layer ionosphere at latitudes 57-59 degrees observed in December 2014 is detected.

Examining movement patterns of yellowtail snapper, Ocyurus chrysurus, in the Dry Tortugas, Florida

Yellowtail snapper, Ocyurus chrysurus (Bloch, 1970), is an important fisheries species in the Florida Keys. In 2008–2009, yellowtail snapper were tagged with acoustic transmitters and tracked through an array of 86 stationary receivers in the Dry Tortugas' network of marine reserves in Florida to determine site fidelity, home range, and temporal patterns of habitat use. Fifteen yellowtail snapper were tracked for 1–427 d [x = 188 (SE 39)]. A multistep method for data validation ensured that only the fish with high-quality detection data were selected for data analyses. Brownian bridge models were used to estimate home range rather than more traditional methods because they incorporate not only detection location, but also time between detections, the path between successive detections, and location error. For a species typically described as transient, six of the tagged yellowtail snapper had high site fidelity [x = 58.4% (SE 8.4%)], and Brownian bridge models estimated relatively small minimum home ranges [x = 5.45 km2 (SE 1.79)]. Movements were highly variable, but analyses showed that fish displayed diel and seasonal trends, and in general, were more likely to be absent during summer months or during dusk and at night. Tagged yellowtail snapper showed a preference for reef edge habitat, swimming in and out of the marine reserve where the boundary intersected this type of habitat. The knowledge that yellowtail snapper is less transient than previously believed and understanding the habitat preference and temporal movements of this species can help with its future management.

ADS-BI: Compressed Indexing of ADS-B Data

The introduction of ADS-B, a satellite-based aircraft tracking technology, and the increasing installation of ADS-B receiver stations around the globe eases the tracking of aircraft, compared with traditional solutions using secondary radar. Given the large scale of ADS-B implementation and the high frequency of data collection, storing and managing ADS-B induced data has become increasingly difficult: The worldwide ADS-B data easily aggregates to several hundreds of terabyte per year, depending on the spatial coverage and temporal resolution. Standard data management solutions do not work well for ADS-B data, since they either require a large uncompressed index structure or cannot be queried efficiently. In this paper, we propose a novel compressed index structure for managing ADS-B data, called ADS-BI. The essential building blocks are spatio-temporal reference partitioning, reordering, and compression. On top of the partitioned, compressed representation, metadata is stored effectively, and exploited during query answering for typical ATM related task such as trajectory adherence evaluation, as well as complexity and safety metrics assessment by only accessing parts of the compressed data as necessary. Our novel index structure is evaluated on worldwide ADS-B data for a week in November 2016. For comparison, we implemented ten standard compression/indexing methods. The experiments reveal that none of these traditional methods can target the sweet spot between a small storage and efficient query answering. Our novel technique provides fast query answering at smallest storage costs. This paper contributes toward efficient handling of the increasing amount of traffic data in air traffic management, and eventually, toward more efficient and safer air transportation.

Measuring System of Air Parameters of the Helicopter with a Stationary Receiver a Flow, Ion-Label and Aerometric Measurement Channels

It is shown that the known limitations on the measurement of air parameters on board the helicopter due to significant aerodynamic disturbances introduced by inductive flows of vortex column of main rotor. This determines the need to create the means of measurement, taking into account the aerodynamics and dynamics of the helicopter flight. The known direction of overcoming these limitations is the use for measuring the information of aerodynamic field of vortex column of main rotor and its perception by means of the stationary multi-functional aerometric receiver. However, the need to protect a large number of full-pressure tubes installed in the flow channel of the multifunctional aerometric receiver, strict requirements for the identity and stability of the characteristics of the large number aerometric channels, complicate the design, reduce reliability, increase cost, inhibit the use of the air parameters measurement system on helicopters of various classes and purposes. Principles of construction, functional scheme, features of perception of primary information of measuring system of air parameters of the helicopter with the stationary receiver of a stream, ion-label and aerometric measuring channels are showed. Algorithms for processing primary information at various stages and flight modes, including: in the parking lot before the launch of the power plant and when rotating the rotor, when taxiing and maneuvering on the earth’s surface, on takeoff and landing modes and when flying at low speeds, at flight speeds, when the stationary receiver of primary information leaves the zone of the vortex column of the rotor using ion-label and aerometric measuring channels, are presented. It is shown that the proposed approaches to the construction, models and algorithms for processing the primary information of the measuring system air parameters of helicopter with ion-label and aerometric measurement channels allow to determine the speed and direction of the wind vector, altitude-velocity parameters of motion relative to the environment and atmospheric parameters in a wide range of helicopter operation, which determines its competitive advantages in solving problems of piloting and provide the flight safety of helicopters of different classes and purposes.

Reconstruction of Storm‐Time Total Electron Content Using Ionospheric Tomography and Artificial Neural Networks: A Comparative Study Over the African Region

AbstractThe work presented here aims to evaluate the capabilities of Multi‐Instrument Data Analysis System (MIDAS) compared with artificial neural networks (ANNs) to reconstruct storm‐time total electron content (TEC) over the African low‐latitude and midlatitude regions. For MIDAS, the inversion was done based on the Global Positioning System (GPS) measurements from receiver stations extending from −30∘ to 36∘ in latitude and 30∘ to 44∘ in longitude while for ANNs, individual storm‐time models based on historical GPS data from receivers within the same region covered by MIDAS were used. Based on the minimum Dst index reached during the storm period, moderate (−50 nT −100 nT), strong (−100 nT 200 nT), and severe (−200 nT 350 nT) storms were used for validation. MIDAS and ANNs results were compared with IRI‐2016 predictions and validated with real GPS TEC observations. A statistical analysis revealed that MIDAS and ANNs provide comparable results in storm‐time TEC reconstruction with average mean absolute errors of 4.81 and 4.18 TECU respectively. However, MIDAS performed better compared to ANNs in following TEC enhancements and depletions as well as short‐term features observed during the selected storm periods. In terms of latitude, it was found that on average, MIDAS performs 13% better than ANNs in the African midlatitude, while ANN model performs 24% better than MIDAS in low latitudes. Furthermore, comparisons with IRI predictions showed that both MIDAS and ANNs produce more accurate estimations of the storm‐time TEC than IRI model.

Capability of low-temperature SQUID for transient electromagnetics under anthropogenic noise conditions

Transient electromagnetics (TEM) is a well-established method for mineral, groundwater, and geothermal exploration. Superconducting quantum interference device (SQUID)-based magnetic-field receivers used for TEM have quantitative advantages and higher sensitivity compared with commonly used induction coils. Special applications are deep soundings with target depths [Formula: see text] and settings with conductive overburden. However, SQUIDs have rarely been applied for TEM measurements in environments with significant anthropogenic noise. We compared a low-temperature SQUID with a commercially available induction coil in an area affected by anthropogenic noise. We acquired four fixed-loop data sets with totally 61 receiver stations close to Bad Frankenhausen, Germany. The high sensitivity of the SQUID enables low noise levels, which lead to longer high-quality transient data compared with the induction coil. The effect of anthropogenic and natural noise sources is more critical for the coil than for the SQUID data. In the vicinity of the transmitter loop, systematic distortion of the coil signals occurs at early times, most probably caused by sferic interferences. We have developed 1D inversion results of both receivers that matched well in general. However, the SQUID-based models were more consistent and showed greater depths of investigation. This led to a superior resolution of deeper layers and even enabled a potential detection of thin conducting targets at up to a 500 m depth. Moreover, we find that the SQUID data inversion revealed multidimensional effects within the conductive overburden. In this regard, we applied forward modeling to analyze systematic differences between inversion results of SQUID and coil data. We determine that low-temperature SQUIDs have the potential to significantly improve the reliability of subsurface models in suburban environments. Nevertheless, we recommend combined application of both types of receivers.

Acoustic telemetry array evolution: From species- and project-specific designs to large-scale, multispecies, cooperative networks

Acoustic telemetry is a powerful tool for investigating the movement ecology of aquatic animals. As the number of studies using passive acoustic telemetry technology has grown in recent years, so has membership in regional collaborative networks in which methodologies and detection data are shared among researchers. These networks can significantly augment research projects by increasing the geographic coverage of detection data beyond the initial monitored area, and encourage the development of research collaborations with the goal of improving aquatic research management. As tags expire and projects end, researchers must decide whether to maintain their receiver stations, adjust the configuration to accommodate a new scope of research, or remove the stations. We assessed telemetry data from two projects designed to monitor fishes in nearshore and offshore habitats of the eastern Gulf of Mexico to determine the configuration of receiver stations most informative for network scale monitoring. Modeled on the Index of Relative Importance commonly used to analyze fish diets, the Receiver Efficiency Index (REI) allowed us to reduce the size of the two arrays from 59 to 24 and 33 to 21 stations, reductions of 59% and 27%, while retaining more than 75% of all detections. The application of this method has general relevance to understanding the spatial dynamics of these arrays while providing researchers with a quantitative tool to guide decision making that can maximize spatial coverage at the lowest maintenance cost.

Tropospheric Scintillation with Rain Attenuation of Ku Band at Tropical Region

Tropospheric scintillation can become a significant impairment in satellite communication systems, especially in tropical regions with frequencies higher than 10 GHz, the attenuation is dramatically affecting the scintillation. This work concentrates on those aspects in equatorial Johor Bahru, Malaysia, based on a one-year Ku-band propagation measurement campaign, utilizing the equipment of Direct Broadcast Receiver (DBR) and Automatic Weather Station (AWS). This study investigates the relationship between wet scintillation and rain attenuation using experimental measurement and concentrate on the probability density function (PDF) of different scintillation parameters. From the results, it is concluded that wet scintillation intensity increases with rain attenuation. Thus, the relationship can be phrased by linear equations or power-law. The PDFs of wet scintillation intensity, adapted to a given rain attenuation level, are found lognormally distributed, leading to selection of method for determining the relation between conditional PDFs and rain attenuation.

Position Estimation Bias Analysis of a Multilateration System with a Reference Station Selection Technique

Multilateration (MLAT) system estimates the position of an aircraft using Time Difference of Arrival (TDOA) measurements estimated at spatially located Ground Receiving Station (GRS) pairs with a lateration algorithm. The Position Estimation (PE) accuracy of an MLAT system depends on several factors, one of which is the choice of reference station used to generate the TDOA estimations for use with the lateration algorithm. Furthermore, the closed-form lateration algorithm is known to introduce bias in the PE process. Thus, a bias analysis and improvement in the PE accuracy of an MLAT system with a reference selection technique is presented in the paper. The analysis is carried out for a square GRS configuration with each GRS equipped with a receiver whose Time of Reception (TOR) error Standard Deviation (SD) is assumed 1 nsec. Monte Carlo simulation result of lateration algorithm with reference selection technique shows a reduction of at least 75% in both the overall PE Mean Square Error (MSE) and bias. Furthermore, the PE Root Mean Square Error (RMSE) obtained by the lateration algorithm is reduced by at least 50% out of which 36% of the reduced PE RMSE is contributed only by the TOR estimation error.