China
Africa
Explore chapters and articles related to this topic
Overview of GNSS
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
Radionavigation is the application of radio-frequency signals to determine one’s position on the earth. Near the middle of 20th century, scientists discovered a way to measure distances using radio signals. The concept was to measure the time it took for radio signals to travel from a transmitting station to a special device (receiver) designed to receive them. Multiplying the signal travel time by the speed of the signal gives the distance between the transmitter and the receiver. The geometrical concept of positioning was simple trilateration. If we consider three radio-signal transmitting towers located at A, B, and C (Figure 1.1c), we can determine our location by measuring the distances from these three towers (refer to Section 1.4). Hence, the transmitting towers are acting as points of reference. A person needs to use a receiver to measure the distances from these transmitters. The transmitters A, B, and C together are called a transmitter ‘chain’. A chain may have four or more transmitters in order to have better accuracy, and multiples of such chains can cover a greater area. The range of a radio transmitter was generally about 500 km (Javad and Nedda 1998). This concept was the most advanced technique used for navigation and positioning in the Radio Age. However, before achieving this advanced technique, radio navigation and positioning techniques had passed through several other phases, as outlined below.
Sensors for Autonomous Vehicles in Infrastructure Inspection Applications
Published in Diego Galar, Uday Kumar, Dammika Seneviratne, Robots, Drones, UAVs and UGVs for Operation and Maintenance, 2020
Diego Galar, Uday Kumar, Dammika Seneviratne
The five basic forms of navigation are as follows: Pilotage, which essentially relies on recognizing landmarks to know where you are.Dead reckoning, which relies on knowing where you started from, plus some form of heading information and some estimate of speed.Celestial navigation, which uses time and the angles between local vertical and known celestial objects (e.g., sun, moon, or stars).Radio navigation, which relies on radio frequency sources with known locations (including GPS satellites).Inertial navigation, which relies on knowing your initial position, velocity, and attitude and thereafter measuring your attitude rates and accelerations. It is the only form of navigation that does not rely on external references.
Propagation Effects on Satellite Navigation Systems
Published in Athanasios G. Kanatas, Athanasios D. Panagopoulos, Radio Wave Propagation and Channel Modeling for Earth–Space Systems, 2017
Navigation is related to resolving how to travel from one place to another. Throughout history, finding accurate methods of positioning and navigation has been a major challenge for scientists, astronomers, and mariners, and a mechanism of great discovery. Celestial navigation allowed latitude determination through the observation of angular measurements to the sun or known celestial bodies. The longitude determination problem was far more challenging. It was not until the eighteenth century when ships would be able to determine longitude more accurately with the use of chronometers in order to keep track of the time at departure port, which together with the actual time, would allow the estimation of the time difference into geographical separation (Sobel, 1998). The advent of radio navigation (using radio signals for determining position) during the twentieth century, proved valuable for a number of new applications including flight navigation. Several terrestrial radio navigation techniques were developed and many exist today, employing angular, range, or Doppler measurements. In the 1960s, the first satellite navigation system (Transit) was the pioneer of the current Global Navigation Satellite Systems (GNSS) (Parkinson et al., 1995).
Mitigation of DME interference in LDACS1-based future air-to-ground (A/G) communications
Published in Cogent Engineering, 2018
The DME is a radio navigation system that operates in the 960–1215 MHz frequency range and has been used in all airplanes to find the slant distance between the aircraft and DME ground beacons. The distance between aircraft and DME GS is measured based on following steps. It starts on the interrogator at aircraft transmitting a stream of Gaussian-shaped pulse pairs to the transponder at the DME GS. After a certain delay at the DME GS, the transponder sends back the received signal to the interrogator. The interrogator finds the distance between the aircraft and GS by measuring the travel time duration of the pulse pair. It consists of pair of Gaussian shaped pulses with a separation of = 12 or 36. One pulse pair in baseband is given by (Gao, 2007; Thiasiriphet et al., 2015)