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en:drones:platforms [2019/11/05 17:36]
tomykalm created
en:drones:platforms [2020/04/05 22:15] (current)
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 ====== UAV platforms ====== ====== UAV platforms ======
 +
 +===== Aerodynamics principals =====
 +
 +===== UAV building components =====
 +
 +==== Sensors (specific for UAV) ====
 +
 +==== Actuators (specific for UAV) ====
 +
 +==== Power sources ====
 +
 +==== Indoor navigation ====
 +
 +Nowadays, objects localization,​ positioning,​ and navigation is a common topic of scientific research and industrial development. The current technology allowed to create outdoor positioning systems based on satellites known as GNSS (Global Navigation Satellite Systems). Commonly known four global GNSS solutions are GPS (US), GLONASS (Russia), Galileo (EU), BeiDou (China) ((Bernhard Hofmann-Wellenhof,​ Herbert Lichtenegger,​ Elmar Wasle: “GNSS – Global Navigation Satellite Systems: GPS, GLONASS, Galileo, and more.”, Springer Science & Business Media, 2007)). Additionally,​ there are two regional systems – QZSS (Japan) and IRNSS (India). Receiver operating in these systems can calculate its current position while signals from at least three satellites are reachable. Due to the necessary visibility of satellites, GNSS systems are completely useless inside buildings.
 +=== Positioning methods ===
 +Among the algorithms used for localization,​ we can distinguish methods based on the measurement of signal propagation time or measurement of signal strength. Using the signal temporal propagation model, we can use techniques such as:
 +  *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,"​ 2006 3rd Annual IEEE Communications Society on Sensor and Ad Hoc Communications and Networks, Reston, VA, 2006, pp. 374-382.)).
 +  *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, "​Three-Dimensional VLC Positioning Based on Angle Difference of Arrival With Arbitrary Tilting Angle of Receiver,"​ in IEEE Journal on Selected Areas in Communications,​ vol. 36, no. 1, pp. 8-22, Jan. 2018.)).
 +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,​ IET Electronics letters. Volume 40, Issue 22, 28 October 2004, p. 1421 – 1422, )). The precise synchronization is required in this method.
 +  *TDOA (Time Diffrence of Arrival) – It is similar to the previous method with one difference; transmitting base stations and receiver do not have to be synchronized with each other. The geometry of this technique is also used in multirateriation ((R. Hach and A. Rommel, "​Wireless synchronization in time difference of arrival based real time locating systems,"​ 2012 9th Workshop on Positioning,​ Navigation and Communication,​ Dresden, 2012, pp. 193-195.)).
 +  *TOF (Time of Flight) – it is a technique used to measure distances between several devices. In 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,​ we find techniques that use geometric transformations. These are:
 +  *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'​s location relative to known transmitter positions. Knowing angles of incoming signals from at least three transmitters it is possible to determine the position of the receiver.
 +  *Multilateration – also known as hyperbolic navigation, positioning by measuring the distance difference (or time difference of flight) ​ between the receiver and stations placed at known positions. It is also possible to measure the difference of distance from one sending station to two receivers. As a result of measurements,​ we obtain a hyperbolic curve with a large number of possible positions. To determine the exact position, a second measurement is made, using different sending stations, in which we get another curve intersecting the first in the place that will be the designated position ((L. Asmaa, K. A. Hatim and M. Abdelaaziz, "​Localization algorithms research in wireless sensor network based on Multilateration and Trilateration techniques,"​ 2014 Third IEEE International Colloquium in Information Science and Technology (CIST), Tetouan, 2014, pp. 415-419.)).
 +  *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 at least three transmitters are used in typical applications. GPS system is a hyperbolic navigation system using TDOF technique but also determines the TOF according to the receiver'​s clock.
 +
 +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 WiFi devices. It can be used to determine the distance from the transmitter but the transmission power fluctuates due to changes in environment,​ objects movement which results in inaccurate positioning. That’s why the fingerprinting method is the preferred method for positioning.
 +  *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,  "​RSSI-Based Bluetooth Indoor Localization,"​ in 2015 11th International Conference on Mobile Ad-hoc and Sensor Networks (MSN), Shenzhen, China, 2015 pp. 165-171.)).
 +
 +There are some technologies based on different principles that can be used in indoor positioning systems including radio waves, image recognition,​ visible or infrared light, ultrasound, inertial and others. Here we shortly present some of the possible solutions.
 +=== Inertial and Dead reckoning ===
 +These systems use inertial sensors (accelerometers,​ gyroscopes) on the user to estimate relative rather than absolute location i.e. the change in position since the last update. They require little or no infrastructure to be pre-installed in buildings ((R. Harle, "A Survey of Indoor Inertial Positioning Systems for Pedestrians,"​ in IEEE Communications Surveys & Tutorials, vol. 15, no. 3, pp. 1281-1293, Third Quarter 2013.)). This method is based on a previously determined position and known or approximate speed in time. The biggest problem, in this case, is the inaccuracy of the whole process, which increases over time. To counteract this phenomenon, stationary points are used and error correction techniques are used. **Inertial Navigation System** is a system that tracks position by estimating the full 3D trajectory of the sensor at any given moment. For positioning inside buildings, the most commonly used concept is Pedestrian **Dead Reckoning** ((Lei Fang et al., "​Design of a wireless assisted pedestrian dead reckoning system - the NavMote experience,"​ in IEEE Transactions on Instrumentation and Measurement,​ vol. 54, no. 6, pp. 2342-2358, Dec. 2005.)), the accelerometer built in the smartphone ((Ms. Najme Zehra Naqvi, dr. Ashwani Kumar, Aanchal Chauhan, Kritka Sahni, Step counting using smartphone-based accelerometer,​ "​International Journal on Computer Science and Engineering",​ Vol. 4 No. 05 May 2012)) or as the separate device is attached to the body of a moving person and most often counts its steps.
 +=== 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,​ which are arranged in such a way as to cover the entire surface of the building ((S. Holm, "​Ultrasound positioning based on time-of-flight and signal strength,"​ 2012 International Conference on Indoor Positioning and Indoor Navigation (IPIN), Sydney, NSW, 2012, pp. 1-6.)). Knowing distances from transmitters receiver can calculate the current position using the trilateration algorithm. The receiver Systems based on navigation using ultrasound are strongly dependent on temperature and frequency depending on the Doppler shift.
 +=== 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, "​Indoor waypoint navigation via magnetic anomalies,"​ 2011 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Boston, MA, 2011, pp. 5315-5318.)). These changes depend on the building materials used during the construction of the building. Due to the fact that these values do not change over time, it is possible to use them to create a map of the building with a specific magnetic field strength at individual points. This allows determining the position after measuring the magnetic field. This solution does not require any additional infrastructure in the building. The magnetometer is available on virtually every smartphone. This issue was addressed by the Finnish company IndoorAtlas ((IndoorAtlas positioning overview. https://​indooratlas.freshdesk.com/​support/​solutions/​articles/​36000079590-indooratlas-positioning-overview)).
 +=== 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://​www.lighting.philips.com/​main/​systems/​themes/​led-based-indoor-positioning.#​form_white_paper)). Its indoor positioning system is based on two, well-known assumptions:​ every building has to have lights installed and every LED light flickers with some frequency. This product uses lamps as well known and calibrated reference points. Each of the lamps has a unique (across given venue) ID. This ID is encoded in the form of the frequency of the LED and is invisible to a human eye. Signals are captured by cellular phone’s camera and then the phone decodes the LED ID from its frequency and determines the lamp position on the captured frame.
 + 
 +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 transmitter (beacon) 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, "​Low-Cost Optical Indoor Localization System for Mobile Objects without Image Processing,"​ 2006 IEEE Conference on Emerging Technologies and Factory Automation, Prague, 2006, pp. 629-632.)).
 + 
 +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, "​Visual positioning systems — An extension to MoVIPS,"​ 2014 International Conference on Indoor Positioning and Indoor Navigation (IPIN), Busan, 2014, pp. 95-104.)). Although there are some examples of image processing implementations this technique seems to be too demanding to be widely used at this moment.
 + 
 +=== Radio ===
 +Among radio technologies used for localization,​ the most popular ones are RFID, Bluetooth, and WiFi. New UWB technology has built-in functionality to help to implement the positioning systems.
 +  *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 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://​www.ibeacon.com/​what-is-ibeacon-a-guide-to-beacons/​)). It is also possible to calculate position using signals from more than one beacon ((A. De Blas and D. López-de-Ipiña,​ "​Improving trilateration for indoors localization using BLE beacons,"​ 2017 2nd International Multidisciplinary Conference on Computer and Energy Science (SpliTech), Split, 2017, pp. 1-6.)). The mobile device scans for beacons around it and using trilateration determine a more accurate location based on the signal strength (RSSI) from different beacons. Such a solution works pretty well in theory, but in the real environment,​ there are many difficulties like the noise and signal variation what makes it really hard to properly calculate the position.
 +  *WiFi - wireless networks can also be used to locate users ((R. Joseph and S. B. Sasi, "​Indoor Positioning Using WiFi Fingerprint,"​ 2018 International Conference on Circuits and Systems in Digital Enterprise Technology (ICCSDET), Kottayam, India, 2018, pp. 1-3.)). Access points are usually present in buildings with a wireless network. It is possible to use them for localization purposes. Their arrangement is adjusted so that the signal reaches all places in the building where system users can be found. The user's device has the ability to measure the signal strength of all access points within its range. Each of them has its own individual MAC address. In one place, the signal strength from specific access points remains at a similar level. This allows creating a map that specifies the signal strength from specific access points in different locations (fingerprinting). In this way, it is possible to determine the position after measuring the signal strength of the network access points.
 +  *UWB ((Y. Cheng and T. Zhou, "UWB Indoor Positioning Algorithm Based on TDOA Technology,"​ 2019 10th International Conference on Information Technology in Medicine and Education (ITME), Qingdao, China, 2019, pp. 777-782.)) (Ultra Wideband) is a technology intended for wireless digital data transmission over short distances at low power density. The technology occupies a large (greater than 500MHz) bandwidth of the radio frequency spectrum. Wide bandwidth is obtained with the usage of very short radio pulses. It works with limited power not causing interferences with other radio systems like WiFi and Bluetooth. This technology can be used for high precision indoor positioning. Transmitters are equipped with hardware support to the RTT (Round Trip Transmission) time measurement. This allows measuring the TOF with good precision and using trilateration to calculate the position with centimeter accuracy. UWB seems to be the most promising technology for in-door positioning due to good accuracy, ease of implementation,​ inexpensive modules, small power consumption and no interferences with other systems. ​
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en/drones/platforms.1572968190.txt.gz · Last modified: 2019/11/05 17:36 by tomykalm
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