Geo positioning system or GPS has become more or less a norm for smart phones. Geo positioning system was first created for the navigation of defense vehicles in any part of world. But over the period of time, this system is being used in many other purposes outside defense and has proved itself to be a revolutionary technology in today’s world. Apart of the smartphone, most of the premium cars and commercial vehicle do have inbuilt GPS for fleet tracking, vehicle Telematics, and driver assistance.

Apart from such fleet navigation use cases, GPS are now being used for many applications such as locating nearby restaurants, hotels and gas stations and finds huge applications in tourism industry. Personal navigation devices also employ GPS technology.

Also most of the IoT/M2M applications use GPS modules. Some of them are as follows

  • Smart utility metering
  • Connected health and patient monitoring
  • Smart buildings
  • Security and video surveillance
  • Smart payment and PoS systems
  • Wearable devices etc

While the term GPS in general represents the technology, there are numerous systems being used to achieve this. In this blog, we will briefly describe about the various such Geo positioning systems and related concepts.

Geo Positioning System – Technology

Any geo positioning system uses about three to four satellites from more than a dozen of satellites orbiting in a group (satellite constellation) to provide autonomous geo-spatial positioning. These satellites transmit 1500 bits of data such as the satellite health, its position in space, propagation delay effects, constellation status, the time of information being sent, etc. This allows a small electronic receiver to determine its location in terms of latitude and longitude based on triangulation of the data obtained from at least three satellites. With four or more satellites, the receiver can also determine the 3D position, i.e. Latitude, longitude and altitude. In addition, a GPS receiver can provide information about the speed and direction.

Anyone with the GPS receiver can access the system. Since it is an open source and providing almost accurate 3D position, navigation and timing 24 hours a day, 7 days a week, all over the world, it is used in numerous applications even in GIS data collection, mapping and surveying.

Geo Positioning System – Types

At present there are many options available for geo positioning system each of them owned and operated by countries such as US, Russia, European Union, China, etc. They are as follows

NAVSTART GPS – GPS, Global Positioning System is a one among the various satellite navigation system designed and operated by the U.S. Department of defense. Official name of GPS is Navigational Satellite Timing and Ranging Global Positioning System (NAVSTAR GPS).

GLONASS – Global Orbiting Navigation Satellite System, GLONASS developed by Russian, is an alternative to GPS and is the second global navigational system in operation providing global coverage with comparable precision. A GLONASS satellite design has various upgraded versions and the latest is GLONASS-K2 which is expected to operate in early 2018.

Galelio – Galelio is created by European Union with the aim to provide an independent high precision positioning system for European nations.

BeiDou – BieDuo Navigation Satellite System (BDS) is a Chinese satellite navigation system consisting of two separate satellite constellations BeiDuo-1 and BeiDuo-2. BeiDuo-1 is decommissioned and BeiDuo-2 also known as COMPASS offering services to customers in the Asia-Pacific region with a partial constellation of 10 satellites in orbit.

IRNSS – Indian Regional Navigation Satellite System also known as NAVIC (Navigation with Indian Constellation) is a regional satellite navigation system covering the Indian region extending 1500Km. This constellation is already in orbit and expected to operate in early 2018.

Satellite Based Augmentation System (SBAS)

All the above systems are autonomous and governed by the respective countries. Other than autonomous systems, other regional augmented systems are available that run with the aid of other autonomous satellites. These augmentation systems will provide reference signals (Signal in Space- SIS) via satellites to the receivers including correction information with the objective of increasing the accuracy of the position. In addition to the accuracy they also help to maintain the reliability and availability of the navigation system. The whole system is known as SBAS (Satellite Based Augmentation System) and satellite providing the SIS signal are known as SBAS GEO satellites. Some of them are as follows,

GAGAN – GPS-Aided Geo Augmented Navigation – It is the implementation of SBAS by Indian government. It supports pilots to navigate in the Indian airspace by an accuracy of 3m.

QZSS Quasi Zenith Satellite System is a project governed by Japanese government and operated in order to receive the US operated GPS in the Asia-Oceania regions with Japan as a primary focus.

Other commonly available SBASs are WAAS (US), EGNOS (EU) and MSAS (Japan).

GNSS

The above mentioned satellite systems such as global, regional and augmented systems are integrated together to form Global Navigation Satellite System, GNSS. It is a standard term for satellite navigation systems providing autonomous geo spatial positioning with global coverage. It is a satellite system that is used to pinpoint the geographic location of a user’s receiver anywhere in the world. Three GNSS systems are currently in operation: the United States’ Global Positioning System (GPS), the Russian Federation’s Global Orbiting Navigation Satellite System (GLONASS) and the Europe’s Galileo.

Most degrading factor of a receiver, i.e. Line of Sight degradation can be solved with the GNSS system due to its accessibility to multiple satellites and if one satellite system fails, GNSS receivers can pick up signals from other system.

Navigation messages

Any satellite in the constellation will transmit a detailed set of information such as each satellite position, network to receiver called the navigation messages. Following are available in the navigation message, 

  1. Date and time together with the satellite status and an indication of its health 
  1. Almanac data – Contains coarse orbit and status information of all the satellites in the constellation. It allows the GPS receiver to predict which satellites are overhead, shortening acquisition time. Almanac data can be received from any of the satellites. The receiver must have a continuous fix for approximately 15 minutes to receive a complete almanac data. Once downloaded it is stored in the non volatile memory.
  1. Ephemeris data – Contains precision correction to the almanac data necessary for the receiver to calculate the position of the satellite. It is continuously updated every 2 hours and so ephemeris data of a deactivated receiver will become stale after 3 to 6 hours.

Time-To-First-Fix (TTFF)

For a receiver to get a fix, it needs a valid almanac, initial location, time and ephemeris data. When a receiver is switched ON, it requires some time delay for the first fix. This delay depends on how long since the stored data’s being used. The time delay is commonly termed as Time To Fist Fix, TTFF and it is one of the main factor for receiver selection.

About Embien

Embien Technologies is a leading provider of embedded design services for the Automotive, Semi-conductor, Industrial, Consumer and Health Care segments. Embien has successfully designed and developed many products with GPS for various domains such as Wrist wearable based tracker device for healthcare, Vehicle Telematics device for automotive, Data acquisition/logger devices for industry etc.

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