Differences
This shows you the differences between two versions of the page.
| Both sides previous revisionPrevious revisionNext revision | Previous revision | ||
| en:drones:platforms:navigation [2021/01/26 11:07] – pczekalski | en:drones:platforms:navigation [Unknown date] (current) – external edit (Unknown date) 127.0.0.1 | ||
|---|---|---|---|
| Line 1: | Line 1: | ||
| + | ===== Navigation ====== | ||
| + | |||
| + | |||
| + | ==== Global Navigation Satellite Systems GNSS ==== | ||
| + | |||
| + | |||
| + | ==== Introduction to the GNSS ==== | ||
| + | Global Navigation Satellite Systems (short GNSS) are useful to position an object (here drone) in 3D space, mostly outdoors.\\ | ||
| + | Actually, 2D, planar (longitude/ | ||
| + | |||
| + | |||
| + | <note important> | ||
| + | There is a number of factors, decreasing positioning that every UAV operator should be aware of, as they may lead to incidents and accidents: | ||
| + | * Time synchronization - it is crucial to have a common time-base for both sender and receiver. Time synchronization occurs during the so-called " | ||
| + | * Selected Availability (SA) - as introduced by the constellation owner to interfere radio signal of the satellites, thus decrease the accuracy of the controlled way. This was widely used in the case of the American GPS (Navstar) until the first war in the Persian Gulf when US Army had to switch to the commercial receivers (affected by SA) because of lack of delivery of the military products (that had SA corrected internally). Since then, GPS positioning became much more useful because of the increased accuracy of the positioning, | ||
| + | * Ionosphere delay - as solar radiation has a strong impact on the ionic sphere of the Earth, radio signal passing through it may experience deflection (thus delays). That is the second, natural phenomenon, decreasing accuracy. Solar radiation is given by the KP Index that can be read close to real-time and is related to solar activity. With KP over 3, flying UAV is not advised, or at least try to avoid flying in a tight environment when filming, i.e. northern lights as you may experience sudden shifts of your drone even some dozen of meters. You can read the current KP index and forecast, i.e. here: [[http:// | ||
| + | * Troposphere - has some minor impact (comparing to the mentioned above) yet it does exist. The troposphere is relatively thin, comparing, i.e. to the ionosphere. Advanced GPS receivers may use a built-in calendar to provide thermal compensation, | ||
| + | * Ephemeris error - sometimes, satellite orbit is altered and satellite is not where it is intended to be, so the distance between satellite and receiver is affected. GPS receiver is unaware of the position deviation; thus, it has an impact on the positioning accuracy. | ||
| + | |||
| + | Some of those phenomena can be handled in a tricky way (i.e. ionosphere deflection impacts different way signals with different frequency thus Glonass system can handle this issue almost real-time by calculating error, differential-based way) while others can be applied post-factum or live using corrections sent via other channels.\\ | ||
| + | A detailed description of the impact of the aforementioned factors for accuracy and performance is presented below in section **GNSS Performance and Accuracy**. | ||
| + | |||
| + | ==== GNSS History ==== | ||
| + | |||
| + | === US GPS NAVSTAR === | ||
| + | {{ : | ||
| + | * The United States Navy conducted satellite navigation experiments in the mid-1960s to track US submarines carrying nuclear missiles. With six satellites orbiting the poles, submarines were able to observe the satellite changes in Doppler and pinpoint the submarine' | ||
| + | * In the early 1970s, the Department of Defense (DoD) wanted to ensure a robust, stable satellite navigation system would be available. Embracing previous ideas from Navy scientists, the DoD decided to use satellites to support their proposed navigation system. DoD then followed through and launched its first Navigation System with Timing and Ranging (NAVSTAR) satellite in 1978. | ||
| + | * The 24 satellite system became fully operational in 1993. When selective availability was lifted in 2000, GPS had about a five-meter (16 ft) accuracy. | ||
| + | * The latest stage of accuracy enhancement uses the L5 band and is now fully deployed. GPS receivers released in 2018 that use the L5 band can have much higher accuracy, pinpointing to within 30 centimeters or 11.8 inches. | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === RF GLONASS === | ||
| + | {{ : | ||
| + | * The first proposal to use satellites for navigation was made by V.S.Shebashevich in 1957. This idea was born during the investigation of the possible application of radio-astronomy technologies for aeronavigation. Further investigations were conducted in a number of the Soviet institutions to increase the accuracy of navigation definitions, | ||
| + | * In 1967 the first navigation Soviet satellite " | ||
| + | * he “Cicada” system of four satellites was commissioned in 1979. The GLONASS system was formally declared operational in 1993. In 1995 it was brought to a fully operational constellation (24 GLONASS satellites of the first generation). | ||
| + | * In 2008 “Cicada” and “Cicada-M” users started to use the GLONASS system and the operation of those systems was halted. The low-orbit systems couldn' | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === EU GALILEO === | ||
| + | {{ : | ||
| + | * The first Galileo test satellite, | ||
| + | * As of July 2018, 26 of the planned 30 active satellites are in orbit. Galileo started offering Early Operational Capability (EOC) on 15 December 2016, | ||
| + | * The complete 30-satellite Galileo system (24 operational and 6 active spares) is expected by 2020. | ||
| + | * It is expected that the next generation of satellites will begin to become operational by 2025 to replace older equipment. Older systems can then be used for backup capabilities. | ||
| + | <figure label> | ||
| + | |||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === CHINA BeiDou (BDS) === | ||
| + | {{ : | ||
| + | * It consists of two separate satellite constellations. The first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites which since 2000 has offered limited coverage and navigation services, mainly for users in China and neighboring regions. Beidou-1 was decommissioned at the end of 2012. | ||
| + | * The second generation of the system, officially called the BeiDou Navigation Satellite System (BDS) and also known as COMPASS or BeiDou-2, became operational in China in December 2011 with a partial constellation of 10 satellites in orbit. | ||
| + | * Since December 2012, it has been offering services to customers in the Asia-Pacific region. | ||
| + | * On December 27, 2018, Beidou-3 officially began to provide global services. | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== GNSS SEGMENTS ==== | ||
| + | GNSS satellite systems consist of three major components or “segments”: | ||
| + | |||
| + | **Space Segment** | ||
| + | The space segment consists of GNSS satellites, orbiting about 20,000 km above the earth. Each GNSS has its own “constellation” of satellites, arranged in orbits to provide the desired coverage. Each satellite in a GNSS constellation broadcasts a signal that identifies it and provides its time, orbit, and status. | ||
| + | |||
| + | **Control Segment** | ||
| + | The control segment comprises a ground-based network of master control stations, data uploading stations, and monitor stations; in the case of GPS, two master control stations (one primary and one backup), four data uploading stations, and 16 monitor stations, located throughout the world. In each GNSS system, the master control station adjusts the satellites’ orbit parameters and onboard high-precision clocks when necessary to maintain accuracy. Monitor stations, usually installed over a broad geographic area, monitor the satellites’ signals and status and relay this information to the master control station. The master control station analyses the signals then transmits orbit and time corrections to the satellites through data uploading stations. | ||
| + | |||
| + | **User Segment** | ||
| + | The user segment consists of equipment that processes the received signals from the GNSS satellites and uses them to derive and apply location and time information. The equipment ranges from smartphones and handheld receivers to sophisticated, | ||
| + | |||
| + | **GNSS Antennas** | ||
| + | GNSS antennas receive the radio signals that are transmitted by the GNSS satellites and send these signals to the receivers. GNSS antennas are available in a range of shapes, sizes, and performances. The antenna is selected based on the application. While a large antenna may be appropriate for a base station, a lightweight, | ||
| + | |||
| + | **GNSS Receivers** | ||
| + | Receivers process the satellite signals recovered by the antenna to calculate position and time. Receivers may be designed to use signals from one GNSS constellation or more than one GNSS constellation. Receivers are available in many form factors and configurations to meet the requirements of the varied applications of GNSS. | ||
| + | |||
| + | **GNSS Augmentation** | ||
| + | Positioning based on standalone GNSS service is accurate to within a few meters. The accuracy of standalone GNSS, and the number of available satellites, may not be adequate for the needs of some users. Techniques and equipment have been developed to improve the accuracy and availability of GNSS position and time information. | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === GPS terrestrial segment === | ||
| + | {{ : | ||
| + | * 33 in-orbit spacecraft, | ||
| + | * Operator AFSPC, | ||
| + | * Type military, civilian, | ||
| + | * Orbital altitude: 20,180 km, | ||
| + | * 6 orbital planes MEO, | ||
| + | * Satellite lifetime: 10 years, | ||
| + | * Satellite mass: 1080 kg, | ||
| + | * Satellite body dimensions: 1,9 m × 1.93 m × 1.52 m, | ||
| + | * Accuracy 500-30 cm, | ||
| + | * Coverage Global, | ||
| + | |||
| + | === GLONASS terrestrial segment === | ||
| + | {{ : | ||
| + | * 26 in-orbit spacecrafts, | ||
| + | * Operator Roskosmos, | ||
| + | * Type military, civilian, | ||
| + | * Orbital altitude: 19 130 km, | ||
| + | * 3 orbital planes MEO, | ||
| + | * Satellite lifetime: 10 years | ||
| + | * Satellite mass: 1450 kg, | ||
| + | * Accuracy 2.8-7.38 m | ||
| + | * Coverage Global | ||
| + | |||
| + | === Galileo terrestrial segment === | ||
| + | {{ : | ||
| + | * 30 in-orbit spacecrafts | ||
| + | * Operator GSA, ESA | ||
| + | * Type civilian, commercial, | ||
| + | * Orbital altitude: 23,222 km, | ||
| + | * 3 orbital planes MEO, | ||
| + | * Satellite lifetime: >12 years | ||
| + | * Satellite mass: 675 kg | ||
| + | * Satellite body dimensions: 2.7 m × 1.2 m × 1.1 m | ||
| + | * Span of solar arrays: 18.7 m, | ||
| + | * Power of solar arrays: 1.5 kW, | ||
| + | * Accuracy 1 m (public), 1 cm (encrypted), | ||
| + | * Coverage Global | ||
| + | |||
| + | === BeiDou terrestrial segment === | ||
| + | {{ : | ||
| + | * 33 in-orbit spacecrafts | ||
| + | * Operator CNSA, | ||
| + | * Type military, commercial, | ||
| + | * Orbital altitude: 23,222 km, | ||
| + | * Orbital planes MEO, IGSO, GEO | ||
| + | * Satellite lifetime: >12 years | ||
| + | * Satellite mass: 675 kg, | ||
| + | * Accuracy 10 m (public) 10 cm (encrypted), | ||
| + | * Coverage Global | ||
| + | |||
| + | === GNSS systems comparison === | ||
| + | All modern and operating GNSS systems like GPS, GLONASS, Galileo, or BeiDou which were developed by different countries and organizations use terrestrial segment containing satellites orbiting over the Earth. Each satellite constellation occupies its own unique orbit segments. The entire view of the GNSS constellation is present in the picture above. Modern positioning and timing modules have evolved to take advantage of multiple GNSS constellations at once. Combining multiple satellite systems improves the availability of signals, gives operators more access, and increases accuracy. | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== GPS Signals ==== | ||
| + | The generated signals onboard the satellites are based or derived from the generation of a fundamental frequency ƒo=10.23 MHZ. The signal is controlled by an atomic clock and has stability in the range of 10−13 over one day. Two carrier signals in the L-band, denoted L1 and L2, are generated by integer multiplications of ƒo. The carriers L1 and L2 are biphase modulated by codes to provide satellite clock readings to the receiver and transmit information such as the orbital parameters. The codes consist of a sequence with the states +1 or -1, corresponding to the binary values 0 or 1. It contains information on the satellite orbits, orbit perturbations, | ||
| + | L1(t) = a1P(t)W(t)cos(2πf1t)+a1C/ | ||
| + | L2(t) = a2P(t)W(t)cos(2πf2t) | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | **GPS signals in Space** | ||
| + | The signal broadcast by the satellite is a spread spectrum signal, which makes it less prone to jamming. The basic concept of the spread spectrum technique is that the information waveform with small bandwidth is converted by modulating it with a large-bandwidth waveform. The navigation message consists of 25 frames with each frame containing 1500 bits, and each frame is subdivided into 5 sub-frames with 300 bits. The control segment periodically updates the information transmitted by the navigation message. It is well known that the presence of dual-frequency measurements (L1 and L2) has good advantages to eliminate the effect of the ionosphere and enhance the ambiguity resolution, especially for the high precision measurements. | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== Glonass signals ==== | ||
| + | Glonass transmit C/A-code on L1, P-code on L1 and L2. Glonass observables (code and phase) are similar to GPS. The main difference between GPS and GLONASS is that GLONASS uses Frequency Division Multiple Access (FDMA) technology to discriminate the signals of different satellites. Still, GPS and Galileo use (Code Division Multiple Access, CDMA) to distinguish between the satellites. All Glonass satellites transmit the same C/A- and P-codes, but each satellite has slightly different carrier frequencies. | ||
| + | 𝑓_1^𝑛 = 1602+0.5625.n MHz | ||
| + | 𝑓_2^𝑛 | ||
| + | with | ||
| + | (𝑓_1^𝑛)/ | ||
| + | where n is the frequency channel number 1 ≤ n ≤ 24 , covering a frequency range in L1 from 1602.5625MHz to 1615.5MHz. | ||
| + | * The navigation message is contained in so-called subframes, which have a duration of 2.5 minutes. | ||
| + | * Each subframe consists of five frames with a duration of 30 seconds. | ||
| + | * The navigation message contains information, | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== Galileo signals ==== | ||
| + | Galileo provides several navigation signals in right-hand circular polarization (RHCP) in the frequency ranges of 1164–1215 MHz (E5a and E5b), 1260–1300 MHz (E6) and 1559–1592 MHz (E2-L1-E1) that are part of the Radio Navigation Satellite Service (RNSS) allocation. All Galileo satellites share the same nominal frequency, making use of code division multiple access (CDMA) techniques. Galileo uses a different modulation scheme for its signals, the binary offset carrier | ||
| + | <figure label> | ||
| + | {{ en: | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | <figure label> | ||
| + | {{ en: | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== BeiDou signals ==== | ||
| + | BeiDou transmits navigation signals in three frequency bands: B1, B2, and B3, which are in the same area of L-band as other GNSS signals. To benefit from the signal interoperability of BeiDou with Galileo and GPS China announced the migration of its civil B1 signal from 1561.098 MHz to a frequency centered at 1575.42 MHz — the same as the GPS L1 and Galileo E1 civil signals — and its transformation from a quadrature phase-shift keying (QPSK) modulation to a multiplexed binary offset carrier (MBOC) modulation similar to the future GPS L1C and Galileo’s E1. | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== GNSS signal processing ==== | ||
| + | The main function of the signal processor in the receiver is the reconstruction of the carriers and extraction of codes and navigation messages. After this stage, the receiver performs the Doppler shift measurement by comparing the received signal with a reference signal generated by the receiver. Due to the motion of the satellite, the received signal is Doppler shifted. The code ranges are determined in the delay lock loop (DLL) by using code correlation. The correlation technique provides all components of bi-modulated signals. The correlation technique is performed between the generated reference signal and the received one. The signals are shifted concerning time so that they are optimally matched based on mathematical correlation. | ||
| + | The GNSS receiver could be designed to track the different GNSS signals and could be of many types: | ||
| + | * The first type could process all GNSS signals GPS L1, L2, L5, and Galileo OS, CS using L1, E5, and E6, and also Glonass L1 and L2. | ||
| + | * The second type uses free signal and codes, GPS L1 and L2C and Galileo OS, on L1 and E5. | ||
| + | * The third type uses L1 and E5. | ||
| + | * Forth type uses GPS L1 and L2 (which are already in the market). | ||
| + | * Fifth type uses GPS and Glonass signals (which already exist). | ||
| + | |||
| + | <figure GNSSBlockDiagram> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== GNSS differential position ==== | ||
| + | There is an increased interest in differential positioning due to the numerous advantages of wireless communications and networks. Most of the errors that affect GNSS are common between the receivers, which observe the same set of satellites. Thus, by making differential measurements between two or more receivers, most of these errors could be canceled. | ||
| + | The basic concept of differential position is the calculation of position correction or range correction at the reference receiver and then sending this correction to the other receiver via radio link. | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== GNSS Wide Area Augmentation System (WAAS) ==== | ||
| + | Wide Area Augmentation System (WAAS) is a new augmentation to the United States Department of Defense’s (DoD) Global Positioning System (GPS) that is designed to enhance the integrity and accuracy of the basic GPS capability. The WAAS uses geostationary satellites to receive data measured from many ground stations, and it sends information to GPS users for position correction. Since WAAS satellites are of the geostationary type, the Doppler frequency caused by their motion is very small. Thus, the signal transmitted by the WAAS can be used to calibrate the sampling frequency in a GPS receiver. The WAAS signal frequency is at 1575.42 MHz. The WAAS services are available on both L1 and L5. | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== GNSS Correction Systems ==== | ||
| + | Selection of the appropriate augmentation method or correction service depends on the performance required for vehicle or aircraft navigation software. There are essentially four levels of positioning: | ||
| + | |||
| + | Standalone uncorrected and WAAS/EGNOS type solutions provide position accuracy ranging from 1-10 meters. On the other end of the scale, RTK correction networks provide the most accurate centimeter-level solutions. While L-band solutions deliver corrections directly to the GNSS receiver via satellite, RTK solutions require a base station and a radio to get the corrections needed, limiting operator flexibility and increasing total system cost and complexity. | ||
| + | |||
| + | With subscription-based L-band correction services, users receive Precise Point Positioning (PPP) corrections to help mitigate and remove measurement errors and position jumps. PPP solutions utilize modeling and correction products including precise satellite clock and orbit data to enhance accuracy. | ||
| + | < | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== GNSS EGNOS ==== | ||
| + | The European Geostationary Navigation Overlay Service (EGNOS) is being developed by the European Space Agency (ESA), for the Safety of Air Navigation (Eurocontrol). EGNOS will complement the GNSS systems. It consists of three transponders installed in geostationary satellites and a ground network of 34 positioning stations and four control centers, all interconnected. EGNOS as WAAS broadcast the differential corrections to the GNSS users through Geostationary satellites, in the European region and beyond. | ||
| + | <figure egnosconcept1> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | <figure egnosconcept2> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | Entire EGNOS system contain **Ground Segment**, **Space Segment**, **Support segment**, **Space Segment** and **User Segment** | ||
| + | |||
| + | === Ground segment === | ||
| + | A network of 40 Ranging Integrity Monitoring Stations (RIMS), 2 Mission Control Centres (MCC), 6 Navigation Land Earth Stations (NLES), and the EGNOS Wide Area Network (EWAN), which provides the communication network for all the components of the ground segment. | ||
| + | |||
| + | * 40 RIMS: the main function of the RIMS is to collect measurements from GPS satellites and transmit these raw data each second to the Central Processing Facilities (CPF) of each MCC. The configuration used for the initial EGNOS OS includes 40 RIMS sites located over a wide geographical area. | ||
| + | * 2 MCC: receive the information from the RIMS and generate correction messages to improve satellite signal accuracy and information messages on the status of the satellites (integrity). The MCC acts as the EGNOS system’s ' | ||
| + | * 6 NLES: the NLESs (two for each GEO for redundancy purposes) transmit the EGNOS message received from the central processing facility to the GEO satellites for broadcasting to users and to ensure the synchronization with the GPS signal. | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === Support segment === | ||
| + | In addition to the stations/ | ||
| + | * PACF: provides support to EGNOS management in such areas as performance analysis, troubleshooting, | ||
| + | * ASQF: provides civil aviation and aeronautical certification authorities with the tools to qualify, validate and certify the different EGNOS applications. | ||
| + | |||
| + | === Space Segment === | ||
| + | Composed of three geostationary satellites broadcasting corrections and integrity information for GPS satellites in the L1 frequency band (1575,42 MHz). This space segment configuration provides a high level of redundancy over the whole service area in case of a geostationary satellite link failure. EGNOS operations are handled in such a way that, at any point in time, at least two of the three GEOs broadcast an operational signal. | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === User Segment === | ||
| + | The EGNOS User segment is comprised of EGNOS receivers that enable their users to compute their positions with integrity accurately. To receive EGNOS signals, the end-user must use an EGNOS-compatible receiver. Currently, EGNOS compatible receivers are available for such market segments as agriculture, | ||
| + | |||
| + | ==== GNSS RTK Network ==== | ||
| + | RTK network concept is similar to the WADGNSS, but the reference stations are generally distributed over a regional area, and the network control center is responsible for transmitting the phase measurement correction to the GNSS user (rover receiver). Mobile wireless networks are generally used in this type of application due to the need for duplex communication where the rover receiver should send the approximate position initially to the network processing center. The network processing center computes VRS observations and sends them to the user. The number of reference stations in the single RTK approach is 30 stations in 10,000 km2. | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== GNSS Performance and Accuracy ==== | ||
| + | Four parameters are used to characterize GNSS performance which is based on the RNP specification: | ||
| + | * **Accuracy**: | ||
| + | * **Availability**: | ||
| + | * | ||
| + | * **Continuity**: | ||
| + | * | ||
| + | * **Integrity**: | ||
| + | |||
| + | The basic idea of GNSS systems is establishing a satellite network in which each satellite sends a signal at a defined time to receivers. The distance from the satellite to the receiver can be calculated by measuring the time difference from the transmitter to the receiver. Using at least 4 satellites simultaneously the 3D Position of the receiver (vertical and horizontal) can be calculated if the position of each satellite is known. The accuracy of GNSS Systems is influenced by the realization of the needed infrastructure, | ||
| + | |||
| + | The positioning accuracy depends on many factors. Position and time error given by GPS receivers are influenced by: | ||
| + | * Ionospheric delay - disturbances in the speed of propagation of signals from satellites in the ionosphere (error about 7 m), | ||
| + | * Tropospheric delay - an analogous phenomenon in the troposphere caused by changes in humidity, temperature, | ||
| + | * Ephemeris error - differences between the theoretical and actual position of the satellites (± 2.5 m), | ||
| + | * satellite clock inaccuracy (± 2 m), | ||
| + | * receiving reflected signals that reach the receiver by other routes than directly from the satellite (± 1 m), | ||
| + | * Receiver errors - noise disrupting the transmission, | ||
| + | * US Department of Defense deliberate action. To reduce the accuracy of GPS receivers, disturbances known as Selective Availability (SA) were introduced into the C/A signal. GPS receivers were able to reduce SA interference. However, these disorders were turned off on May 1, 2000, and remained turned off after September 11, 2001. | ||
| + | |||
| + | The idea of Geometric DOP is to state how errors in the measurement will affect the final state estimation. This can be defined as: | ||
| + | |||
| + | GDOP = Δ(Output Location) / Δ(Measured Data) | ||
| + | |||
| + | The low DOP value represents a better positional precision due to the wider angular separation between the satellites used to calculate a unit's position. Other factors that can increase the effective DOP are obstructions, | ||
| + | |||
| + | DOP can be expressed as many separate measurements: | ||
| + | * HDOP – horizontal dilution of precision | ||
| + | * VDOP – vertical dilution of precision | ||
| + | * PDOP – position (3D) dilution of precision | ||
| + | * TDOP – time dilution of precision | ||
| + | * GDOP – geometric dilution of precision | ||
| + | |||
| + | Sample EGNOS Dilution Of Precision (HDOP) shows picture above: | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | GNSS Ionospheric signal propagation over a region shows another picture above: | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === EDCN Introduction === | ||
| + | EGNOS Data Collection Network (EDCN) was created in 2001, to acquire experience but also develop procedures on how to assess and validate the performance provided by augmentation systems like EGNOS. This data collection network is composed of multiple stations hosted often at Universities. It is complemented by the contributions from Air Navigation Service Providers interested in certifying and providing SBAS services in their national air space (among others AENA Spain, DTI/DSNA France, NATS UK, ENAV Italy, NAV Portugal, Skyguide Switzerland, | ||
| + | |||
| + | == EDCN Components == | ||
| + | * GNSS satellite constellations – GPS NAVSTAR, GLONAS, Galileo, | ||
| + | * EGNOS satellites | ||
| + | * GNSS ground-mounted receivers (NavTech, Septentrio, etc.) | ||
| + | * PC computers, LAN, WAN – Internet, | ||
| + | * Software – PEGASUS powered by EUROCONTROL | ||
| + | * Central Database, | ||
| + | |||
| + | <figure egnosmonitoringsystem1> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | <figure egnosmonitoringsystem1> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | == EGNOS availability maps == | ||
| + | * 100% >= Availability | ||
| + | * 99% > | ||
| + | * 98% > | ||
| + | * Availability | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | == EGNOS Signal Continuity == | ||
| + | Availability EGNOS SIS signal for PRN120 satellite. | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | There was no SIS broadcast during 23rd and 24th July 2011, for further details see July Performance Report available at ESSP web page | ||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== GNSS Receiver hardware chips ==== | ||
| + | Autonomous UAVs usually rely on a GPS position signal which, combined with inertial measurement unit (IMU) data, provides highly precise information that can be implemented for control purposes. To avoid accidents in an area heavily populated by other UAVs or manned vehicles, it is necessary to know exactly where the UAV is located at all times. Equipped with GPS, a UAV can not only provide location and altitude information but necessary vertical and horizontal protection levels. | ||
| + | Typical GNSS receivers which can be easily used in the UAV platforms are listed below. | ||
| + | |||
| + | === Multi-GNSS Receiver Module Model GN-87 ==== | ||
| + | GN-8720is a stand-alone, | ||
| + | * Supports GPS, GLONASS, SBAS, QZSSand Galileo, | ||
| + | * Outputs a time pulse (1PPS) synchronized to UTC time, | ||
| + | * Software upgrade capability by Flash ROM, | ||
| + | * Active Anti-jamming capability to suppress effects of CW jammers, | ||
| + | * Multipath mitigation effects, | ||
| + | * Works in both Autonomous mode and Assisted mode, | ||
| + | * GPS/GLONASS high indoor sensitivity, | ||
| + | * Fast TTFF of typically <1 second when in hot and 30seconds in warm and 33 seconds in cold start conditions, | ||
| + | * Available of an active and passive antenna, | ||
| + | * Unordered List ItemLow profile, small SMT package reducing the mounting area and mounting cost, | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === ACEINNA OpenRTK330L === | ||
| + | ACEINNA’s OpenRTK330L includes a triple-band RTK/GNSS receiver coupled with redundant inertial sensor arrays to provide cm-level accuracy, enhanced reliability, | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === BCM47755 === | ||
| + | The BCM47755 supports two frequencies (L1+L5), achieves lane-level accuracy outdoors, and much higher resistance to multipath and reflected signals in urban scenarios, as well as higher interference and jamming immunity. The BCM47755 incorporates numerous technologies that enable ultralow power consumption in both the location function and the sensor hub function. The device features a low-power RF path, a Big/Little CPU configuration composed of an ARM-based 32-bit Cortex-M4F (CM4), an ARM-based Cortex-M0 (CM0), and is built in a 28 nm process. The BCM47755 can simultaneously receive the following signals: | ||
| + | * GPS L1 C/A | ||
| + | * GLONASS L1 | ||
| + | * BeiDou (BDS) B1 | ||
| + | * QZSS L1 | ||
| + | * Galileo (GAL) E1 | ||
| + | * GPS L5 | ||
| + | * Galileo E5a | ||
| + | * QZSS L5 | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === UBLOX NEO-M9N module === | ||
| + | The NEO-M9N module is built on the robust u-Blox M9 GNSS chip, which provides exceptional sensitivity and acquisition times for all L1 GNSS systems. The u-Blox M9 standard precision GNSS platform, which delivers meter-level accuracy, succeeds the well-known u-Blox M8 product range. NEO-M9N supports the concurrent reception of four GNSS. The high number of visible satellites enables the receiver to select the best signals. This maximizes the position accuracy, in particular under challenging conditions such as in deep urban canyons. | ||
| + | NEO-M9N detects jamming and spoofing events and reports them to the host so that the system can react to such events. Advanced filtering algorithms mitigate the impact of RF interference and jamming, thus enabling the product to operate as intended. A SAW filter combined with an LNA in the RF path is integrated into the NEO-M9N module. This setup allows normal operation even under strong RF interferences, | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== UAV designed GNSS Receiver modules ==== | ||
| + | The UAV industry requires lightweight heavy-duty fully IP69K or IP67 waterproof and low-power GNSS receiver modules. | ||
| + | |||
| + | === Radiolink TS100 Mini GPS Module for Mini PIX Flight Controller === | ||
| + | The Radiolink TS100 Mini GPS Module for Mini PIX Flight Controller can measure with a 50-centimeter precision of accuracy when working with concurrent GNSS. The prc-lNA low loss circuit design has enhanced the ability to capture extremely weak signals. The TS100 can seize very weak signals and effective suppression of input interference at the same time. | ||
| + | |||
| + | **Description** | ||
| + | * Positioning 20 satellites in 6 seconds at open ground and valley station-keeping ability | ||
| + | * Reception of GPS/QZSS LI C/A, GLONASS HOf, BelDou Bl SBASll C/AWAAS, EGNOS, MSAS | ||
| + | * Radiolink TS100 Mini GPS Module for Mini PIX Flight Controller | ||
| + | * Features an M8N GPS decoder chip, with u-Blox UBX-M8030 (M8), 72-channel | ||
| + | * Max update rate: up to 10Hz | ||
| + | * Compatible with: Radiolink Mini PIX | ||
| + | |||
| + | **Specification** | ||
| + | * Positional accuracy: 50-centimeter precision GNSS | ||
| + | * Velocity precision: 0.1m/s | ||
| + | * Max height: 50000m | ||
| + | * Max speed: 515m/s | ||
| + | * Max acceleration: | ||
| + | * Max update rate: up to 10Hz | ||
| + | |||
| + | **Sensitivity** | ||
| + | * Tracking and Nav.: -167dBm, Reacquisition: | ||
| + | * Cold start: -151dBm, Hot start: -159dBm | ||
| + | * Time to first fix: Cold start: 26s, Hot start: 1s | ||
| + | |||
| + | **Connect ports** | ||
| + | * Power supply: voltage 5VDC+-5 percent, current 50-55mA | ||
| + | |||
| + | **Ports** | ||
| + | * GPS UART interface | ||
| + | * Baud rate: 1.2K/ | ||
| + | * Geomagnetic I2C interface | ||
| + | |||
| + | **configuration** | ||
| + | * Geomagnetic: | ||
| + | * Antenna: 2.5dbI high gain and selectivity ceramic antenna | ||
| + | * Double filter: SAWF(Surface acoustic wave filter) from Murata | ||
| + | |||
| + | **Dimensions** | ||
| + | * 3.20 x 3.00 x 1.20 cm / 1.26 x 1.18 x 0.47 inches | ||
| + | * Weight: 0.0200 kg | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === Here 2 GNSS module for Pixhawk 2.1 === | ||
| + | **Description** | ||
| + | * Here 2 GNSS for Pixhawk 2.1 | ||
| + | * Sensitivity: | ||
| + | * Active antenna and passive antenna | ||
| + | * 72-channel u-blox M8N engine GPS/QZSS L1C/A, GLONASSL10F BeiDou B11, etc. | ||
| + | * Navigation update rate: Max 10Hz | ||
| + | |||
| + | **Specification** | ||
| + | * Processor: STM32F302 | ||
| + | * Compass Gyro Accelerometer: | ||
| + | * Barometer: MS5611 | ||
| + | * Receive type: 72-channel u-Blox M8N engine GPS/QZSS L1C/A, GLONASSL10F BeiDou B11, Galileo E1B/C SBAS L1 C/A: WAAS, EGNOS, MSAS, GAGAN | ||
| + | * Navigation update rate: Max 10Hz | ||
| + | * Positioning Accuracy: 3D FIX | ||
| + | * Time to first fix: Cold start 26S, Aided start 2S, Reacquisition 1S | ||
| + | * Sensitivity: | ||
| + | * Assisted GNSS: Assist Now GNSS Online, AssistNow GNSS Offline (up to 35 days), AssistNow Autonomous (up to 6 days) OMA SUPL& 3GPP compliant | ||
| + | * Oscillator: TCXO(NEO-M8N/ | ||
| + | * RTC Crystal: Built-in | ||
| + | * ROM: Flash(NEO-M8N) | ||
| + | * Available Antennas: Active antenna and passive antenna | ||
| + | * Signal Integrity: Signature feature with SHA 256 | ||
| + | |||
| + | **Ports** | ||
| + | * UART/ | ||
| + | * STM32 Main programming interface: JST_SUR | ||
| + | |||
| + | **Dimensions** | ||
| + | * 76mm x 76mm x 16.6mm | ||
| + | * Weight: 49g | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === Radiolink SE100 GPS Module for PixHawk === | ||
| + | **Description** | ||
| + | * 2.5dbI high gain and selectivity ceramic antenna | ||
| + | * MMIC BGA715L7 from Infineon power amplify IC | ||
| + | * SAWF (Surface acoustic wave filter) form Murata | ||
| + | * HMC5983 from Honeywell geomagnetic | ||
| + | |||
| + | **Specification** | ||
| + | * Positional Accuracy: 1m precision when working with concurrent GNSS, 2.5m precision when working with single GNSS | ||
| + | * Velocity precision: 0.1m/s | ||
| + | * Max height: 50000m | ||
| + | * Max speed: 515m/s | ||
| + | * Max acceleration: | ||
| + | * Max update rate: up to 18Hz | ||
| + | * Sensitivity Tracking & Nav.: -167dBm; Reacquisition: | ||
| + | * Time to first fix: Cold start: 26s, Hot start: 1s | ||
| + | * Connect ports | ||
| + | * Power supply: voltage 3.3VDC+-5%, current 50~55mA | ||
| + | |||
| + | **Ports** | ||
| + | * GPS UART interface, baud rate: 1.2K/ | ||
| + | * Geomagnetic I2C interface | ||
| + | |||
| + | **Dimensions** | ||
| + | * 48.5 mm x 15.3 mm | ||
| + | * Weight: 34.2 g | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === UBLOX NEO 6M GPS Module === | ||
| + | **Description** | ||
| + | * Built-in 25*25*4 mm high gain ceramic antenna | ||
| + | * Built-in EEPROM, make sure no data loss | ||
| + | * Built-in reverse polarity protection | ||
| + | * Built-in dual-colour LED, a clear indication of GPS status | ||
| + | * | ||
| + | **Specification** | ||
| + | * SuperSense ® Indoor GPS: -162 dBm tracking sensitivity | ||
| + | * Support SBAS (WAAS, EGNOS, MSAS, GAGAN) | ||
| + | * Max speed: 500 m/s | ||
| + | * Voltage: 3.3-6 V | ||
| + | * Inner chip UBLOX NEO 6M | ||
| + | * With EEPROM memory function | ||
| + | * Baud rate 4800-115200 | ||
| + | * Refresh rate 1.5 Hz | ||
| + | * Cable length 10 cm | ||
| + | * Support rod length: 12 cm | ||
| + | |||
| + | **Dimensions** | ||
| + | * 22 mm x 30 mm x 4 mm | ||
| + | * Weight: 12 g | ||
| + | * Antenna: 25 mm x 25 mm x 7 mm | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== UAV designed GNSS Receiver external antennas ==== | ||
| + | Some GNSS modules require external satellite antennas to improve positioning and reduce the radio signal disruption in different field conditions. In general, such antennas are designed as omnidirectional, | ||
| + | |||
| + | === Spartan MA650.ST 2in1 antenna === | ||
| + | **Specification** | ||
| + | * GPS/ | ||
| + | * GPS/ | ||
| + | * Cellular 3G/2G – 850/ | ||
| + | * GSM/ | ||
| + | * Low Profile, Robust and Stylish Design | ||
| + | * Construction: | ||
| + | * No Ground Plane Required | ||
| + | * Case: IP67 and IP69K – Water Resistant | ||
| + | * Dimensions: H: 36mm, Ø: 148mm | ||
| + | * Weight: 570g | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === BN-345AJ GNSS antenna === | ||
| + | BN-345AJ is a multi-star multi-frequency satellite navigation antenna with high gain, miniaturization, | ||
| + | **Specification** | ||
| + | * Frequency Range: BDS B1/B2/B3 MHz | ||
| + | * GNSS Constellations: | ||
| + | * Gain: <5.5 dBi | ||
| + | * Antenna AR: ≤3.0 dB | ||
| + | * Phase center error: | ||
| + | * Polarization: | ||
| + | * Port Impedance: 50Ω | ||
| + | * Antenna size: 76*72*27 mm | ||
| + | * Weight: 175 g | ||
| + | * Waterproof grade: IP67 | ||
| + | |||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | === BN-244 spiral GNSS antenna === | ||
| + | The antenna has the characteristics of small volume, high positioning precision, and lightweight. The total weight of the antenna is less than 30g, which is especially suitable for equipment such as an unmanned aerial vehicle (UAV). | ||
| + | |||
| + | **Specification** | ||
| + | * Frequency Range: GPS L1/L2 MHz | ||
| + | * GNSS Constellations: | ||
| + | * Gain: 3 dBi | ||
| + | * Antenna AR: ≤3 dB | ||
| + | * VSWR: ≤1.8 | ||
| + | * Polarization: | ||
| + | * Port Impedance: 50 Ω | ||
| + | * LNA Gain: 33±2 dB | ||
| + | * Noise figure: ≤1.8 dB | ||
| + | * Operating voltage: 3.0V-18.0V | ||
| + | * Operating current: ≤42 mA | ||
| + | * Connector type: SMA-J | ||
| + | * Antenna size: Φ 27.5*58 mm | ||
| + | * Antenna weight: ≤ 30 g | ||
| + | * Waterproof grade: IP67 | ||
| + | |||
| + | <figure label> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | ==== ==== | ||
| + | <box # | ||
| + | <box # | ||
| + | ==== Indoor navigation techniques ==== | ||
| + | <box # | ||
| + | <box # | ||
| + | |||
| + | ==== Introduction to the indoor positioning ==== | ||
| + | |||
| + | In the previous chapter [[en: | ||
| + | Indoor positioning requires then different techniques, where some of them need additional infrastructure while others base on the on-board of the drone hardware and algorithms. Usually, it applies to smaller drones and requires precision positioning in 3D space, even some 1cm accuracy. There are several techniques available to solve this problem that we present below. | ||
| + | |||
| + | === Positioning methods === | ||
| + | Among the algorithms used for localization, | ||
| + | *AOA (Angle of Arrival) – this method uses the measurement of the angle of the incoming signal from the broadcasting station to approximate the location ((R. Peng and M. L. Sichitiu, "Angle of Arrival Localization for Wireless Sensor Networks," | ||
| + | *ADOA (Angle Difference of Arrival) – like the AOA method, it is based on calculating the differences of angles of the signal received from the transmitter ((B. Zhu, J. Cheng, Y. Wang, J. Yan, and J. Wang, " | ||
| + | Methods that measure the angles can be performed if the receiver is equipped with directional antennas or with a matrix of antennas. | ||
| + | *TOA (Time of Arrival) – with this method the time of arrival of the signal transmitted from the mobile client to the base stations is measured. The distance from each station is calculated by determining the time of arrival of the signal, depending on the speed of wave propagation ((M. Kanaan and K. Pahlavan Algorithm for TOA-based indoor geolocation, | ||
| + | *TDOA (Time Difference of Arrival) – It is similar to the previous method with one difference; transmitting base stations and receivers do not have to be synchronized with each other. The geometry of this technique is also used in Multirateriation ((R. Hach and A. Rommel, " | ||
| + | *TOF (Time of Flight) – it is a technique used to measure distances between several devices. A one-way TOF receiver must be precisely synchronized with the transmitter. In TW TOF (Two Way TOF, also known as RTT – Round Trip Transmission) each device has a transmitter and receiver, and the flight time measurement process includes signal exchange and measurement of results between two cooperating units ((David Bartlett Essentials of Positioning and Location Technology. Cambridge, 2013, p. 63)). One of the devices initiates the internal time measurement and sends the message to the responding unit. The answering device sends its measurements - delay from receipt to response. Using both time measurements internal and external, the initiator calculates the distance. | ||
| + | |||
| + | Among the techniques that use signal propagation, | ||
| + | *Triangulation – positioning by angle measurement ((David Bartlett Essentials of Positioning and Location Technology. Cambridge, 2013, p. 63)). Using the knowledge of geometry, we can calculate the receiver' | ||
| + | *Multilateration – also known as hyperbolic navigation, positioning by measuring the distance difference (or time difference of flight) | ||
| + | *Trilateration - positioning by measuring the distance (or time of flight) from signals coming from many transmitters ((David Bartlett Essentials of Positioning and Location Technology. Cambridge, 2013, p. 63)). Knowledge of the angle of incidence of signals is not needed here. Two intersecting circles marked with a signal from transmitters will allow us to determine the position. Due to noise in measurements, | ||
| + | |||
| + | Using the signal strength model, we can use the RSSI (received signal strength indicator) signal in the receiver, which is a measurement of the power present in a received radio signal. It is provided in Bluetooth and Wi-Fi devices. It can be used to determine the distance from the transmitter, | ||
| + | *Fingerprinting – It assumes measuring the signal strength in the tested room, at measuring points located at a fixed distance from each other (this distance determines the measurement precision), and based on this data, a map of the signal strength in the room is created. The receiving device then measures the signal strength and compares it with the map mentioned above ((Y. Wang, Q. Ye, J. Cheng, and L. Wang, " | ||
| + | |||
| + | There are some technologies based on different principles that can be used in indoor positioning systems, including radio waves, image recognition, | ||
| + | |||
| + | == Inertial and Dead reckoning == | ||
| + | These systems use inertial sensors (accelerometers, | ||
| + | |||
| + | == Ultrasound == | ||
| + | The principle of operation of systems based on ultrasonic waves comes down to measuring the difference in the time of arrival (TDOA) of information by the receiver from the transmitters, | ||
| + | |||
| + | == Magnetic field == | ||
| + | The Earth has its own natural magnetic field. The field intensity can be easily measured anywhere on its surface. Studies have shown that buildings cause changes in magnetic field values ((T. H. Riehle, S. M. Anderson, P. A. Lichter, J. P. Condon, S. I. Sheikh, and D. S. Hedin, " | ||
| + | |||
| + | == Light and vision systems == | ||
| + | Some systems utilize QR codes as markers placed on the ceiling or walls ((Suresh, Sujith & Anand, Rubesh & Lenin, D. (2015). A Novel Method for Indoor Navigation Using QR Codes. International Journal of Applied Engineering Research. 10. 451-454.)). A smartphone camera detects and decodes the markers to get the location inside a room. QR code detection and decoding are relatively simple and memory efficient. Each code contains an ID, which delivers enough information to deliver the information required to determine its reference location. | ||
| + | |||
| + | An interesting approach has been proposed by Philips ((Indoor Positioning White Paper. Philips. https:// | ||
| + | |||
| + | Both systems require that the cellular phone’s camera is pointed to the ceiling what is rather an unnatural position while using the phone. | ||
| + | |||
| + | Positioning systems can also use infrared light. There can be found systems with mobile IR transmitters (beacons) and stationary receivers ((Sakai, N.; Zempo, K.; Mizutani, K.; Wakatsuki, N. Linear Positioning System based on IR Beacon and Angular Detection Photodiode Array. In Proceedings of the International Conference on Indoor Positioning and Indoor Navigation (IPIN), Alcalá de Henares, Spain, 4–7 October 2016.)) or stationary light source and mobile IR receiver ((R. Salomon, M. Schneider, and D. Wehden, " | ||
| + | |||
| + | The image processing technology is also used to position the user. The challenge to implement such a system is the complexity and resource-intensiveness of the employed algorithms. Running these algorithms on a mobile device is usually not possible and thus has to be offloaded to a server. Another challenge is to recognize structures that are visually very similar such as plain walls which often repeat within buildings ((C. Marouane, M. Maier, S. Feld and M. Werner, " | ||
| + | |||
| + | //**Optical flow**// \\ | ||
| + | One of the oldest and most widely spread techniques for 2D flat positioning using vision systems is Optical Flow. Optical flow positioning uses a similar technique that is present in the optical computer mouse. There is a camera observing the surface under the drone, so the optical flow technique is most suitable for 2D surface positioning, | ||
| + | Sample module (same used in many computer mouse' | ||
| + | <figure OpticalFlowSensorADNS30801> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | <figure OpticalFlowSensorADNS30802> | ||
| + | {{ : | ||
| + | < | ||
| + | </ | ||
| + | |||
| + | Optical flow is easy to integrate, and many flight controllers provide almost "plug and play" support for it. Anyway, they have many serious disadvantages as well: | ||
| + | * Limited range: works best on some centimeters to a couple of meters range. One limitation is fixed optics camera unable to get the sharp image below some distance on the one hand (also drone shadow won't help when hovering close to the surface), and camera' | ||
| + | * Works best in good light conditions only: as it is a visible range camera used, it works more-less as human eyes do. It won't work correctly in darkness or low ambient light. | ||
| + | * Works only above irregular surfaces. As the camera needs to be able to identify some characteristic points, it won't work over the flat surface as, i.e. glass plane, the same way many PC mice won't work. | ||
| + | * When the surface moves, the drone will follow it! | ||
| + | <note important> | ||
| + | |||
| + | == Radio == | ||
| + | Among radio technologies used for localization, | ||
| + | *RFID - using an RFID system, tags are arranged in a fixed pattern on the floor. Absolute coordinates of the location are stored in each tag to provide the position data to the mobile receiver. An RFID reader reads the data from tags that are under the effective area of RFID antenna ((Lim, H.S., Choi, B.S. & Lee, J.M., An Efficient Localization Algorithm for Mobile Robots Based on RFID System, SICE-ICASE International Joint Conference, Busan, Korea, pp. 5945-5950, 2006.)). | ||
| + | *Bluetooth - there are some systems based on Bluetooth technology. Bluetooth Low Energy beacons are small devices that emit a signal which provides mobile applications with the context that they are running in. Using this information mobile phone can calculate the location of the user knowing where the given beacon is located. Such a system that uses information from one beacon only has rather low precision (10-50m) and can be used for applications where only information about presence in a given place is needed. The system based on this technology has been created by Apple, transmitters in this system are called IBeacon ((What is iBeacon, Apple, http:// | ||
| + | *WiFi - wireless networks can also be used to locate users ((R. Joseph and S. B. Sasi, " | ||
| + | *UWB ((Y. Cheng and T. Zhou, "UWB Indoor Positioning Algorithm Based on TDOA Technology," | ||
| + | |||
| + | |||
