Accurate GPS Research Articles

Measuring the response of variable bulk solid fertiliser application by computer-controlled delivery from aircraft

ABSTRACT This work measures the effectiveness of boundary delivery from a new computer-controlled aircraft bulk solid delivery system (Intellispread+). Computer controlled delivery of solid fertilisers by aircraft has been practised commercially in New Zealand since 2014. Aircraft position is determined in relation to a rate change polygon, aircraft ground speed, spread material characteristics, and control system parameters, and the hopper opening is altered to provide the correct rate. All these systems working simultaneously are computationally intense. Effective variable rate application depends on the response to boundary rate changes, aircraft GPS accuracy and update frequency, wind direction and speed, and particle ballistics that determine the deposition of fertiliser. Rapid responses to boundary rate changes improve fertiliser placement accuracy and mitigates off-target application near environmental sensitive areas. The system was tested on a block 200 m long by 18 m wide with 126, 0.5 m2 diameter collector cones, spaced 10 m apart longitudinally and 3 m laterally. A PAL Cresco 600 was flown at 64 ms−1 (130 knots) on three tests to measure performance, shutting off and opening at a boundary and changing rate halfway along the block. For all tests initiation of rate change and completion was achieved within 30 m.

A method for correcting discharge of boat-mounted ADCP measurements

GPS data are usually used to measure boat velocity during boat-mounted acoustic Doppler current profiler (ADCP) measurements when bottom tracking is biased by moving bed. GPS cannot provide consistently accurate boat velocity reference because of multipath errors, satellite signal reception problems, and heading errors. In addition, the computation of water velocity from an ADCP mounted onto a moving boat is a vector-algebra problem, thus the discharge calculation is subject to the compass error when GPS is used for boat velocity reference. This paper proposes a method for correcting discharge based on the idea that the discharge calculation is independent of the boat path. The processing of two sets of boat-mounted ADCP measurements integrated with differential GPS and non-differential GPS was simulated to verify the method. The results show that the proposed method performs well in both differential and non-differential GPS conditions. The relative errors range from 0.1% to 1.5% for all measurements with the mean relative errors of 0.7%. Analytical assessment of the GPS errors shows the proposed method is insensitive to the positioning accuracy of GPS, but positioning error of non-differential GPS may induce relative discharge error of more than 1% when the river or stream is narrow. On the contrary, a relatively small compass or heading error can cause a significant error in water velocity and discharge when using GPS as the boat velocity reference. Therefore, integrating a differential GPS and maintaining a slow boat speed are best practices for discharge measurement, especially for narrow streams or short boat paths.

Accuracy of GPS positioning concerning Köppen-Geiger climate classification

Recent studies revealed the effect of meteorological seasons on the accuracy of GPS positioning. The existing accuracy model is weak because it is derived from a climate classification in which the earth is divided into latitudinal zones, and each climate zone in the classification does not have sufficient number of International GNSS Service (IGS) sites as representative. Furthermore, the prediction is biased due to the loading effects and tectonic motion. Here, we will derive a new accuracy model using the climate zone classification of Köppen and Geiger, which is based on actual meteorological measurements. Fifty IGS stations almost homogenously covering the Köppen-Geiger geographical regions and the globe have been selected, and the data has been analyzed using Gipsy-X software. Using the new model, the average improvement in the accuracy prediction of the north, east, and up components is 50%, 68%, and 94%, respectively.

Low Cost and Centimeter-Level Global Positioning System Accuracy Using Real-Time Kinematic Library and Real-Time Kinematic GPSA

Introduction: Accuracy and total design and implementation cost of the GPS framework determine the viability of GPS based projects. As the greater part of the advanced framework including telemetry, IoT, Cloud, and AUTOSAR frameworks use GPS to get exact outcomes, finding a software-controlled error correction becomes important. The execution of open source library such as RTKLIB will help in controlling and revising GPS blunders. Methods: The project utilizes the RTKLIB along with two stations for better accuracy. The RTKGPS framework works under Linux environment, which is embedded in the Beagleboard. The communication between the GPS system is set up utilizing both serial communication protocol and TCP/IP suite. Results: To get high precision inside the network, two GPS modules are utilized. One of them will be mounted on the rover and another GPS is the base station of the setup. Both the GPS will have a double radio wire setup to increase the reception level to reduce the noise and obtain centimeterlevel precision. For long-range communication, rover utilizes Wi-Fi with TCP/IP stack protocol. In this research paper, setup is intended to accomplish the centimeter level precision through libraries in a Linux environment. Conclusion: The design will be set up and tried on a college campus under various conditions with different error parameters to acquire a low cost and centimeter level GPS accuracy.

TO THE ISSUE OF CREATING MODELS OF PRECISE SOIL COMPACTION DETECTION FOR PRODUCTION SCALE USE

Typical approaches to test soil compaction, along with technical possibilities are assessed with a purpose of scaling best approaches in production. Modern soil works related technologies, GPS accuracy aspirations for precision agriculture are addressed. Two most popular technologies in Ukraine to measure soil compaction are «The Top Soil Mapper» and «CTS-1000», although they function differently, most commonly are used independently. Simple mathematical calculations bringing together timing needed to gather reliable data to form variable depth soil ripping machinery and scale of Ukrainian production demonstrate irrelevance of applying typical mechanical methods. At the same time, sensor technologies have their own limitations. Thus, this article introduces the benefits of the mutual use of «The Top Soil Mapper» and «CTS-1000». Soil compaction models presented in the article include: 1. Smallest possible grid approach of soil compaction data presentation and interpolation for further use to create variable depth soil works assignment proves to provide a very good set of results and can be used as a standard, but at the same time it consumes so much time that production scaling is not achievable. As an example we can state that a grower with 1000 fields would need about 3 years to test all the fields, when production needs are to test all the fields within two or three months (depending on weather and crop rotation). 2. Small, midsize and large grid approach of soil compaction data presentation and interpolation for further use to create variable depth soil works assignment proves to vary from being still time inefficient to having gaps to gather enough data as main approach of any data processing for further interpolation makes an unproven assumption that the sample location is a center of a zone. In case with a smallest possible grid, that difference would be minimal, with a larger distance difference can be significant. 3. Depending on detecting zones to test compaction based other parameters does not prove to work and lacks scientific background. Thus it has been suggested to combine use of «Top Soil Mapper» and «CTS-1000».

Augmented Reality Application using Dynamic Location-Based Tracking of Taman Ayun Temple

Taman Ayun Temple is a world cultural heritage in Bali. Based on observations, information regarding the location at Taman Ayun Temple is still not optimal. This study aims to design an application that displays location information using markerless augmented reality. Markerless AR is a technology that displays virtual objects into the real world using GPS, digital compass, and accelerometer. The application is designed using the Wikitude SDK platform and displays information on location, description, image, distance from the user, and location direction. Data is stored in a database server and managed using the web server. Applications are in Indonesian and English. The testing compares the actual distance with the distance displayed in the application using devices with different OS and RAM. Application speed is less than 1 second depending on RAM and internet speed, while location accuracy depends on smartphone GPS accuracy with a difference of less than 10 meters from the actual distance.

LOCATION BASED FIRE DETECTION, WITH NEAREST FIRE FIGHTER FINDER

The lack of fire department makes it hard for most people to contact where the nearest fire department to the scene. Furethermore, when the fire department location was founded it is still a challenge for the fire fighters to find exact location of the fire. For this reason, we used sensitive sensors of fire to the flame. The project used arduino uno microcontrollers, fire sensors, Neo-7m Ublox GPS, ESP8266, and wavecom. As soon as the flame sensor detects the flame, ESP8266 will send the gps data from the home location to the web server www.thingspeak.com which then data from thingspeak is taken to do the nearest distance search using the method of Haversine Formula then send the sms using wavecom sms gammu gameway to the firefighter the nearest fire. The final result of this project shows that the flame sensor can detect a flame of about 75 cm, the GPS accuracy level approaches 100%, ESP8266 can transmit data to Thingspeak by about 20 seconds, accuracy method of accurate formula accuracy calculates Distance near 100% SMS Gateway Wavecom sends sms less than 10 seconds.

Combining modern tracking data and historical records improves understanding of the summer habitats of the Eastern Lesser White-fronted Goose Anser erythropus.

The Lesser White‐fronted Goose (Anser erythropus), smallest of the “gray” geese, is listed as Vulnerable on the IUCN Red List and protected in all range states. There are three populations, with the least studied being the Eastern population, shared between Russia and China. The extreme remoteness of breeding enclaves makes them largely inaccessible to researchers. As a substitute for visitation, remotely tracking birds from wintering grounds allows exploration of their summer range. Over a period of three years, and using highly accurate GPS tracking devices, eleven individuals of A. erythropus were tracked from the key wintering site of China, to summering, and staging sites in northeastern Russia. Data obtained from that tracking, bolstered by ground survey and literature records, were used to model the summer distribution of A. erythropus. Although earlier literature describes a patchy summer range, the model suggests a contiguous summer habitat range is possible, although observations to date cannot confirm A. erythropus is present throughout the modeled range. The most suitable habitats are located along the coasts of the Laptev Sea, primarily the Lena Delta, in the Yana‐Kolyma Lowland, and smaller lowlands of Chukotka with narrow riparian extensions upstream along major rivers such as the Lena, Indigirka, and Kolyma. The probability of A. erythropus presence is related to areas with altitude less than 500 m with abundant wetlands, especially riparian habitat, and a climate with precipitation of the warmest quarter around 55 mm and mean temperature around 14°C during June‐August. Human disturbance also affects site suitability, with a gradual decrease in species presence starting around 160 km from human settlements. Remote tracking of animal species can bridge the knowledge gap required for robust estimation of species distribution patterns in remote areas. Better knowledge of species' distribution is important in understanding the large‐scale ecological consequences of rapid global change and establishing conservation management strategies.

In vivo diagnosis of skin cancer with a portable Raman spectroscopic device.

In this study, we performed in vivo diagnosis of skin cancer based on implementation of a portable low-cost spectroscopy setup combining analysis of Raman and autofluorescence spectra in the near-infrared region (800-915nm). We studied 617 cases of skin neoplasms (615 patients, 70 melanomas, 122 basal cell carcinomas, 12 squamous cell carcinomas and 413 benign tumors) in vivo with a portable setup. The studies considered the patients examined by GPs in local clinics and directed to a specialized Oncology Dispensary with suspected skin cancer. Each sample was histologically examined after excisional biopsy. The spectra were classified with a projection on latent structures and discriminant analysis. To check the classification models stability, a 10-fold cross-validation was performed. We obtained ROC AUCs of 0.75 (0.71-0.79; 95% CI), 0.69 (0.63-0.76; 95% CI) and 0.81 (0.74-0.87; 95% CI) for classification of a) malignant and benign tumors, b) melanomas and pigmented tumors and c) melanomas and seborrhoeic keratosis, respectively. The positive and negative predictive values ranged from 20% to 52% and from 73% to 99%, respectively. The biopsy ratio varied from 0.92:1 to 4.08:1 (at sensitivity levels from 90% to 99%). The accuracy of automatic analysis with the proposed system is higher than the accuracy of GPs and trainees, and is comparable or less to the accuracy of trained dermatologists. The proposed approach may be combined with other optical techniques of skin lesion analysis, such as dermoscopy- and spectroscopy-based computer-assisted diagnosis systems to increase accuracy of neoplasms classification.

The effect of GPS refresh rate on measuring police patrol in micro-places

With the increasing prevalence of police interventions implemented in micro hot-spots of crime, the accuracy with which officer foot patrols can be measured is increasingly important for the robust evaluation of such strategies. However, it is currently unknown how the accuracy of GPS traces impact upon our understanding of where officers are at a given time and how this varies for different GPS refresh rates. Most existing studies that use GPS data fail to acknowledge this. This study uses GPS data from police officer radios and ground truth data to estimate how accurate GPS data are for different GPS refresh rates. The similarity of the assumed paths are quantitatively evaluated and the analysis shows that different refresh rates lead to diverging estimations of where officers have patrolled. These results have significant implications for the measurement of police patrols in micro-places and evaluations of micro-place based interventions.

The effect of GPS refresh rate on measuring police patrol in micro-places

With the increasing prevalence of police interventions implemented in micro hot-spots of crime, the accuracy with which officer foot patrols can be measured is increasingly important for the robust evaluation of such strategies. However, it is currently unknown how the accuracy of GPS traces impact upon our understanding of where officers are at a given time and how this varies for different GPS refresh rates. Most existing studies that use GPS data fail to acknowledge this. This study uses GPS data from police officer radios and ground truth data to estimate how accurate GPS data are for different GPS refresh rates. The similarity of the assumed paths are quantitatively evaluated and the analysis shows that different refresh rates lead to diverging estimations of where officers have patrolled. These results have significant implications for the measurement of police patrols in micro-places and evaluations of micro-place based interventions.

“Frame Wobbling” Causing Crustal Deformation Around the Ordos Block

AbstractAn accurate and dense GPS velocity field across the Ordos block is presented based on extensive observations. We utilized velocities from evenly distributed GPS stations within the block to estimate the parameters of rigid block motion and internal strain. Our results indicate that the Ordos block behaves rigidly, with a negligible anticlockwise rotation. The velocity profiles, strain, and block motion suggest that: the interior of the block undergoes no differential motion and internal strain is insignificant; relative to the Ordos, the adjacent blocks move in different directions and at different rates, and exert varying forces on it; the adjacent blocks deform the Ordos block along its boundaries of grabens and fold‐thrust fault zones. The Ordos block accommodates the forces exerted by the adjacent blocks through strain and deformation across its boundaries, which should be high strain or strain gradient zones. This pattern of deformation is illustrated by frame wobbling.

Performance improvement of real-time PPP ambiguity resolution using a regional integer clock

Obtaining reliable GNSS uncalibrated phase delay (UPD) or integer clock products is the key to achieving ambiguity-fixed solutions for real-time (RT) precise point positioning (PPP) users. However, due to the influence of RT orbit errors, the quality of UPD/integer clock products estimated with a globally distributed GNSS network is difficult to ensure, thereby affecting the ambiguity resolution (AR) performance of RT-PPP. In this contribution, by fully utilising the consistency of orbital errors in regional GNSS network coverage areas, a method is proposed for estimating regional integer clock products to compensate for RT orbit errors. Based on Centre National d’Études Spatiales (CNES) RT precise products, the regional GPS/BDS integer clock was estimated with a CORS network in the west of China. Results showed that the difference between the estimated regional and CNES global integer clock/bias products was generally less than 5 cm for GPS, whereas clock differences of greater than 10 cm were observed for BDS due to the large RT orbit error. Compared with PPP using global integer clock/bias products, the AR performance of PPP using the regional integer clock was obviously improved for four rover stations. For single GPS, the horizontal and vertical accuracies of ambiguity-fixed PPP solutions were improved by 56.2% and 45.3% on average, respectively, whereas improvements of 67.5% and 50.5% in the horizontal and vertical directions, respectively, were observed for the combined GPS/BDS situation. Based on a regional integer clock, the RMS error of a kinematic ambiguity-fixed PPP solution in the horizontal direction could reach 0.5 cm. In terms of initialisation time, the average time to first fix (TTFF) in combined GPS/BDS PPP was shortened from 18.2 min to 12.7 min. In view of the high AR performance realised with the use of regional integer clocks, this method can be applied to scenarios that require high positioning accuracy, such as deformation monitoring.

Recent GPS results on the geodynamics of the area around Sofia (Central-Western Bulgaria)

The paper outlines recent results from estimation of 23 years GPS measurements on the geodynamic network around Sofia. The obtained result, clearly provide new more accurate GPS geodynamic data on the considered area. All velocities clearly exceed 1.5–2 mm/y reaching up to 3–4 mm/y. As a general tendency the velocities tend to increase from North to South. According to the new results analysis of geological processes is given. The newly acquired velocities from three campaigns 1997, 2000 and 2020 years confirm that the general tendency of movement of the stations in the region of Central West Bulgaria is in the south direction with respect to stable Eurasia. The velocities tend to increase from north to south. This pattern is in agreement with the extensive movement of southern Bulgaria and northern Greece. The new results provide much better accuracy, reliability and local details.

Survival of the critically endangered Ditrichum cornubicum and dependence on conservation management intervention

ABSTRACT Introduction. Ditrichum cornubicum is one of the world's rarest bryophytes and is undergoing a long-term decline as its habitat is gradually lost to vegetation succession in derelict mining areas. This study investigates short-term changes in abundance of the species at two sites in Cornwall (UK), including within trial management plots where turf-stripping occurred in September 2015. Methods. A detailed survey of D. cornubicum was undertaken in January 2020, and locations recorded using high accuracy GPS. Results. The species has declined dramatically in trial management plots since January 2018, illustrated by a 93% loss in occupied 0.1 m grid cells. Outside trial management plots, such a decline did not occur over the same period. Conclusions. Within trial management plots, D. cornubicum underwent an initial dramatic increase soon after turf-stripping in September 2015, quickly followed by a rapid decline. Initial colonisation likely arose from germination of rhizoidal gemmae in the diaspore bank, exposed by turf-stripping. The subsequent decline is at least partly due to competitive exclusion by other colonists of exposed mine spoil, especially Ceratodon purpureus, and perhaps also changes in chemistry at the spoil surface, for example due to leaching. The life-strategy of D. cornubicum is poorly suited to the undisturbed conditions of derelict mining areas, and the species is critically dependent on conservation management interventions that re-expose areas of metalliferous substrate. Without such management, the long-term survival of the species is in serious jeopardy.

Algorithm-Based Online Software for Patients' Self-Referral to Breast Clinic as an Alternative to General Practitioner Referral Pathway.

IntroductionThe study aimed to assess the accuracy of online software in the use of self-referral to breast surgery clinics for patients with new signs and symptoms. The study also evaluated the appropriateness of GP referrals to breast clinics and evaluated patients' perceptions of an online self-referral portal to the breast clinic for the assessment of breast signs and symptoms. Design and methodsThe pilot study was divided into two phases. In the first phase, prospective questionnaire-based data was collected from patients who were referred by a GP and presented to the regional breast unit with new signs and symptoms for breast conditions, Princess Alexandra Hospital NHS Trust (May - October 2018). The questionnaire assessed the time at each stage required by the patient to have a visit at the breast unit. It also asked the patient's opinion about an online self-referral portal to the surgical clinic. They were given hypothetical scenarios to evaluate their understanding of breast conditions. In the second phase, the patients presenting to symptomatic breast clinics were provided with the iPad to fill in their medical information in the online software. The data was collected between July and October 2019. The software algorithm was based on the National Institute of Clinical Health and Excellence (NICE) guidelines for breast conditions (2015). Breast surgeons’ recommendations acted as a standard to evaluate the accuracy of GPs' referrals and software outcome for each patient. ResultsThere were 80 patients (mean age 49.1 [SD: 17.7], all females) included in the first phase of the study. The most common clinical presentation was a breast lump (47.6%), followed by breast pain (26.9%) and nipple changes (7.9%). Breast surgeons considered appropriate 75.6% of the referrals made by the GP. Seventy-two percent of the patients got an urgent appointment to see their GP, and 94.8% of the patients were urgently referred by their GP to see the breast surgeon. Only 37.8% of the urgent referrals were correctly referred as urgent. Having a direct online referral system for breast conditions will be beneficial for patients was agreed by 78.4%. The majority (98.1%) of the participants answered correctly for the hypothetical questions requiring breast surgeon review. In the second phase, there were a total of 86 patients with a mean age of 43.9 (SD: 13.3). The most common presentation was breast lump (n=68, 79.1%) and other presentations included breast pain, nipple changes, and discharge. The GPs' accuracy of correct referral was 69.1%. One third (30.9%) of the referrals could have been managed in the community or as a routine review by the breast surgeon. In comparison, the online software's accuracy was 85.1% accurate (p=0.001). The accuracy for detecting patients who needed urgent breast clinic review was 100% for online software. ConclusionA large proportion of referrals could have been dealt with in the community or referred routinely. Patients would prefer a direct online referral system to the breast clinic. They understand red flag signs and symptoms. Online software has the potential to streamline patients for symptomatic breast clinics. It can reduce the burden on the GPs who are constantly under pressure to diagnose patients accurately and refer to the correct specialty appropriately within a short time.

Simultaneous estimation of GPS P1-P2 differential code biases using low earth orbit satellites data from two different orbit heights

Global navigation satellite system (GNSS) differential code bias (DCB) is a significant error source in ionosphere modeling that uses GNSS observation data. Given that the orbit altitudes of low earth orbit (LEO) satellites are above the F layer of ionosphere, ionized electrons come from the upper ionosphere or plasmasphere, so observations suffer from small signal delays. DCBs can be estimated using LEO data instead of that from ground stations. In most studies, LEO-based DCB estimation employs onboard data from either a single LEO or from two that are at the same orbit height. In our study, we applied four LEO satellites data from two different orbit heights to estimate GPS satellite DCBs, receiver DCBs and LEO-based vertical total electron content (VTEC) parameters simultaneously. Before DCB estimation, a data preprocessing strategy suitable for LEO onboard data was applied to obtain clear pseudorange data. We developed a processing method for the upper ionosphere using LEO onboard data from different orbit heights, by introducing LEO-based VTEC models in advance to remove its effects; two introduced VTEC models were derived from modeling results using paired data from the same orbital height, respectively. We draw some conclusions as follows. For the LEO satellites at different orbit heights, the more the number of LEO satellites involved, the more stable estimation results achieved. We also noted that the GPS satellite DCBs stability and accuracy with established LEO-based VTEC models, using multi-LEOs data from different orbit heights, were better than the achievable results using onboard data from the same orbital height or using single LEO satellite schemes. Compared with the estimation results of single LEO solutions, the monthly stabilities and accuracies for multi-LEOs solutions from different orbit heights are improved by 25–35% approximately. Among all the tested schemes, superior stability derived from simultaneous estimation using four LEO data at different orbit heights is 0.064 ns; the optimal accuracies for DCB estimation for different GPS satellites are the scheme GRACE-A and JASON-2 (two LEOs) of 0.146 ns, approximately, compared with Center of Orbit Determination of Europe products, respectively. The stability and accuracy of LEO-based DCB estimations were approximately similar to those achieved using ground solutions.

Development of control system for quadrotor unmanned aerial vehicle using LoRa wireless and GPS tracking

In the past decades, there has been a growing interest in unmanned aerial vehicles (UAVs) for educational, research, business, and military purposes. The most critical data for a flight system is the telemetry data from the GPS and wireless transmitter and also from the gyroscope and accelerometer. The objective of this paper is to develop a control system for UAV using long-range wireless communication and GPS. First, Matlab simulation was conducted to obtain an optimum PID gains controller. Then LoRa wireless was evaluated during clear and rainy days. Static and dynamic points measurement was conducted to validate and optimize GPS accuracy. GeoMapping in Matlab and Google GPS GeoPlanner were then used to analyze the traveled UAV flight path.

Evaluating the impact of CNES real-time ionospheric products on multi-GNSS single-frequency positioning using the IGS real-time service

Multi-global navigation satellite system (GNSS) real-time (RT) single-frequency (SF) positioning with a low-cost receiver has received increasing attention in recent years due to its large amount of possible applications. One major challenge in single-frequency positioning is the effective mitigation of the ionospheric delays since it is a dominant error source. Nowadays, a high-precision RT ionospheric vertical total electron content (VTEC) product is released by the Centre National d’Etudes Spatiales (CNES) through its real-time service (RTS). The effect of this product on RT single-frequency positioning needs to be investigated. In this study, we provide an evaluation of the quality of multi-GNSS CLK93 orbit and clock products through the comparison to the final precise products, and comprehensively evaluate the impact of CNES VTEC products on multi-GNSS RT-SF-SPP (Standard Point Positioning)/PPP (Precise Point Positioning) performances. Datasets from 46 Multi-GNSS Experiment (MGEX) stations and the CLK93 corrections for 14 consecutive days in 2019 are collected to process with different scenarios. Experimental results show that the CNES VTEC products can replace the final GIM products in the single- and multi-GNSS SF-SPP with the same positioning accuracy requirements during the period of mild solar activity (Kp index is less than 3). Regarding the kinematic RT-SF-PPP, the (re-)convergence also can be improved by adopting the prior CNES-VTEC constrains. Compared with the IF RT-SF-PPP with quad-constellation, the positioning accuracy of the CNES-VTEC-constrained RT-SF-PPP can be improved by about 10.30%, in which the average RMS can achieve 17.9, 19.8 and 32.3 cm in the North, East and Up components, respectively.Compared with the final precise products of GBM, the satellite orbit accuracy of CLK93 products is 4, 5, 12 and 16 cm for GPS, Galileo, GLONASS and BDS, respectively. As for the CLK93 satellite clock, its RMS accuracy of GPS, Galileo, GLONASS and BDS is 0.3, 0.4, 2.5 and 1.8 ns, respectively.

Robust 60-GHz Beamforming for UAVs: Experimental Analysis of Hovering, Blockage, and Beam Selection

Unmanned aerial vehicle (UAV) mounted millimeter-wave (mmWave) base stations as well as aerial backhaul links will enable on-demand deployment of network resources. However, prior work has shown aerial links are prone to the frequent disruption caused by: 1) constant hovering due to GPS inaccuracies that impact narrow beamwidths; 2) blockages in the direct line of sight; and 3) suboptimal beam selection, especially if reduced angular sectors are searched in a highly dynamic environment. This article characterizes the impact of each of these phenomena for aerial mmWave links and proposes methods to distinctly identify when they occur in isolation or in combination during deployment. Furthermore, it also proposes corrective actions at the UAV, appropriate for the specific type(s) of impacting events: physical displacement from its earlier location, angular rotation around its vertical axis, or beamwidth adjustment. Our approach relies on exploiting the information contained in the angular domain of a large data set of experimentally collected beam-selection outcomes, under the above practical scenarios. We incorporate GPS accuracy models and antenna radiation patterns to create a robust model of potential outages. We then propose device-agnostic algorithms that jointly optimize UAVs' physical movement and the beamforming procedure. The experimental results obtained by mounting a pair of 60-GHz channel sounders on M600 DJI UAVs reveal loss reduction of up to 74.7%, translated into 260% physical layer bit-rate improvement compared to the classical 802.11ad standards-defined approach.