Thursday, January 18, 2018

What is GPS and How Does It Help You Navigate to Work?

Everybody uses GPS yet most have no idea how the technology works. Developed for the first time by the U.S. Department of Defense in the 1973 and initially used solely for military purposes, GPS is now a common piece of technology that even any elementary school child can use it to find an imaginary Pokémon. Just like TV and Internet when they became common and affordable, the sophistication of GPS now faces the dreadful fate of underestimation by its very users. As long as people can watch Ancient Aliens, there is no need to understand how TV works; if the guy from the TV show said that extraterrestrial beings invented terrestrial TV, he lied.

Approved for civilian use in 1980s, GPS navigation system soon became a preferable feature in cars and handheld devices such as smartphones. It is also widely used in other industries such as agriculture, sports, recreation, fitness, fleet tracking, geofencing, clock synchronization, and more. There is also a good chance that some wives also use GPS to track their husbands’ whereabouts, so the technology apparently is popular among married people as well; whether it helps to improve or ruin relationships is entirely another matter.

What is GPS and How Does It Help You Navigate to Work
When you're lost, use your phone to do a Google search for "how to use a compass and read map"

Since the first time GPS began operational in the 1970s, relatively little has changed with how the basic principle works. There are 3 major elements in Global Positioning System:

  • Space Segment: the satellites that orbit the Earth. A network of 24 to 32 satellites orbits the Earth at an altitude of approximately 12,600 miles (20,200 km). Every single one of these satellites carries a super-accurate atomic clock (accurate to one-billionth of a second) that synchronizes to each other in every few nanoseconds. They constantly emit microwave signals to be received by all GPS-enabled devices on Earth, including your smartphone when you don’t use it underwater.
  • Ground Segment: also commonly referred to as Control Segment, it is composed of a Master Control Station (MSC), an Alternate Master Control Station (AMSC), 4 dedicated ground antennas, and 6 dedicated monitor stations. This segment is responsible for making sure that all satellites are orbiting in the right paths and properly updated. The U.S. Air Force monitoring stations located at Hawaii, Kwajalein Atoll, Ascension Island, Diego Garcia, Colorado Springs, Colorado and Cape Canaveral also help track the flight paths of the satellites. Control segment work collectively to monitor data transmission and perform analysis to make sure everything is accurate and efficient. 
  • User Segment: all GPS-enabled devices make up the entire user segment of the operation. In simple words, user segment includes all receivers that consists of antenna (tuned to signals and frequencies emitted by space segment), stable clock, and processors. There are millions of devices on Earth receiving signals from satellites at any given time. These devices may include vehicle navigation systems, watches, fitness trackers, outdoor-activity gears, smartphones, dog collars, wildlife trackers, and smart-home utilities.

The next day when you navigate to work using GPS, please remember that the technology can only serve you well thanks to the collaborative functions of millions of components and the hard works of thousands of operators, not witchcraft as you previously thought. They must solve ridiculously complex and difficult math equations before deciding whether you should turn left or right; people who hate math do not deserve to use GPS.

How It Works

For a GPS-enabled device – such as a fitness tracker - to work, it must be visible to at least four satellites in the space segment. Each of them sends information about where the satellite is and what time it sends the signals. As the fitness tracker receives the signals, it processes the data and calculates its distance from those four satellites. This process is known as trilateration. The basic formula is as follows:

D = vt

D: distance between receiver and satellite
v: signal speed (constant at 300,000,000 m/s)
t: time required by the signal to travel from satellite to receiver

The fitness tracker uses and solves the same equation for remaining 3 visible satellites. A receiver actually uses only distance calculations from the first 3 satellites, while the fourth one is mainly used to confirm if the calculation is accurate. Ground segment also makes sure that the flight paths of satellites allow at least 6 of them to be always in the line of sight of from almost any place on Earth.

Einstein’s theory of relativity dictates that time runs slower in a place where the gravitational force is greater and therefore the clocks in those satellites are a little bit faster than those in the receivers. Although the difference is probably a mere fraction of a second, incorrect calculation (either under or over compensation) can miss the exact location by miles away. Receivers and transmitters counteract with each other to take the difference into account. You may not think much about it when you navigate to work, but a tiny mistake in the process can guide you to a public toilet located somewhere out of town instead of your workplace. Albert Einstein, who has been dead for quite a while now, was so smart that even now he can still help you find your way home from busy cities or even wilderness. It does not mean that his ghost lingers in everybody’s car, but his discoveries and ideas are fundamental in GPS technology.

In general all GPS devices and satellites for public use are optimized so they work as effectively as possible and make most precise calculation. However, consumer-grade devices will not likely perform with pinpoint accuracy because there are restrictions of GPS on civilian use. Only the government has the most precise encrypted code GPS to determine actual ground location of receiver with nearly zero margin or miscalculation.