Demystifying GPS

Bosch Telematics unit

A current Yogi, philanthropist and self-proclaimed Guru, likened GPS to a Guru. He said – A GPS will guideyou whilst you are in an unknown territory, similar to professionals would! but, here’s my take on it – GPSisn’t pretty much guiding you in an unknown terrain, however can do lot greater than that! How’s that? readon….

first of all, permit’s try to answer the questionwhat is GPS?” additionally, what’s GNSS, GloNaSS? fartoo many acronyms? A GPS is worldwide positioning device, which much folks realize. however, what a lot of us don’t understand is – it’s far one of the GNSS accessible. GNSS – worldwide Navigation satellitedevice, is a group of satellites up there within the area, which helps to pinpoint your geographical vicinity.this may be achieved the use of a receiver, which receive and decipher the signal and facts despatchedby using those satellites. The receiver has to get better indicators from more than one satellites if you want to correctly compute the geographical location. greater the satellites, it’s miles more likely that theregion might be accurate. matters would be a touch clearer later. similarly to area facts, GPSadditionally gives you accurate frequency and time facts.

whilst GPS is a worldwide navigation satellite gadget managed through the individuals; Russians, euunion and chinese have their own model of GNSSs. even as Russians have GloNaSS, the Europeans the Galileo, the chinese language BeiDou; India has its own indigenous IRNSS, that is in its final stages of making. All of those are much like GPS and a number of the receivers in the marketplace have thefunctionality to receiver a couple of GNSS indicators. Receivers assisting multiple GNSS stand a higherthreat of receiving extra satellites and consequently at any point of time and at any place, they are more likely to generate accurate region data. however, let us awareness on GPS to apprehend its operation and its use.

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GPS, operational for the reason that 1978 and globally available considering 1994, is currently the mostwidely used international navigation satellite gadget. despite the fact that in the beginning intended fornavy packages – for specific transport of guns to meant targets; its utility was extended for civilian useby using diluting a number of the records so that precision is constrained to couple of meters, to preventincorrect people from misusing it for wrong cause. but, enhancing the precision is still feasible viaspecial strategies like differential GPS, and so forth. by the way, India has satellite primarily basedaugmentation machine referred to as GAGAN (GPS Aided Geo Augmented Navigation) which allows to enhance the accuracy of GNSS receiver through imparting reference alerts. GAGAN is extra meant forhelping flights and without digressing, allow us to hold to GPS.

GPS includes upto 32 satellites in medium earth orbit (~20,000 Kms) in 6 one-of-a-kind orbital planes, withprecise quantity of satellites in use at any factor of time varying as older satellites are retired and changed.by using layout, there are atleast 24 of them for correct positioning at any location on this planet. moresatellites are deployed to improve reliability and availability of the device. The orbits are organized in order that at the least six satellites are always inside line of sight from almost everywhere on the planet’s floor.these satellites ship alerts coded with information wearing time, frequency and records that could be used to decipher the location information.

The modulation method used is Direct series unfold Spectrum (DSSS) which allows more than onesatellites to percentage the equal frequency band. Code department multiple get right of entry to (CDMA)unfold-spectrum method guarantees the low-bit price message facts is encoded with a highrate pseudo-random (PRN) sequence (code) this is specific for each satellite. With the PRN codes for every of thesatellite, the receiver might be able to acquire information from each of the satellite tv for pc in view, in a sequence. CDMA spread spectrum renders the GPS signals exceedingly robust and proof againstinterferences.

GPS satellite constellation
GPS satellite tv for pc constellation
The satellite ship coded facts in reality on separate alerts – L1 (1.57542 GHz) and L2 (1.2276GHz). The L1 signal incorporates Coarse Acquisition code (C/A code) for civilian use, encrypted Precision (P(Y)) code for navy purpose and the Navigation message. The L2 signal additionally contains the encrypted precision code for navy motive. The precision code might be decoded only if the receiver has the encryption key. P(Y) code while decrypted consists of statistics required to enhance the precision – for exampledisposing of the effects of the ionosphere.

GPS alerts
GPS alerts
Any receiver supposed for civilian cause will receive each L1 and L2 alerts, however can decode and decipher simplest C/A information and therefore will not have the ability reap high stage of precision invicinity. in case you do not forget my earlier announcement that precision (in region information) is diluted for civilian use and this is how it is performed. A receiver intended for navy use can acquire L2signal and decode the precision records with the aid of having the encryption key and therefore may begreater unique. To make clear the difference between accuracy and precision – for a given set of satellitesvisible at a vicinity at a selected time and given reasonable sign strengths of their alerts, a civilian receiver may have a bigger circle on the map to pinpoint the area on a map, whilst a navy receiver can have a much smaller circle at the map to pinpoint the vicinity at the map. The receiver will be everywherewithin the circle. therefore, a military receiver would be in a function to pin factor the precise region. Theinstance below explains the difference between accuracy and precision.

Accuracy vs. precision
Accuracy vs. precision
GPS follows a method that’s a variation of Triangulation known as Trilateration, to compute the place. A GPS receiver determines its function on the surface of the earth by way of timing the signals from foursatellites. The method makes use of particular region of satellites in space, precise time information fromeach satellite and measuring distance the use of the journey time of the radio signals. [It is possible to compute location using three satellites also, but the receiver would have to use additional information from mobile network to aid the computation and/or it would have to compromise on the accuracy.]

here’s how the GPS receiver figures out its location. It makes use of distances of the receiver from multiplesatellites to compute the place on earth, supplied unique place of the satellites are acknowledged. The receiver makes use of accurate time information from the satellites to compute the time of flight of the signand from that it is able to compute its distance from the satellite tv for pc. let us anticipate that the receiver is capable of see four satellites. you can recall d1, d2, d3 and d4 as the space travelled by way ofthe signals from the satellites. if you draw 4 spheres with facilities being the vicinity in the area of thesefour satellites, with d1 to d4 as their respective radius, then those four spheres will all intersect at one factorat the floor of the earth, which is the region of the receiver.

here the velocity of the sign isn’t assumed to be identical to hurry of light! that is because the signreports slowing down when it pass thru ionosphere and troposphere. further, whilst sign enters those twolayers, it also undergoes refraction and consequently the signal sincerely travels longer distances as a result of this. The receiver elements in all of these in the course of computation. with the aid ofunderstanding the precise location of the satellites and the space to these satellites, the receivers can then compute its region.

Satellites use fairly accurate onboard atomic clocks that’s periodically synchronized to extra accurate clock in floor station, to compute the distance from satellites whose unique area in area is known. Satellites alsocontinuously send out two set of statistics – Ephemeris and Almanac. Almanac statistics is course orbital parameters for all Satellites. each satellite tv for pc announces Almanac information for ALL satellites. This Almanac records isn’t very particular and is taken into consideration legitimate for up to severalmonths. Ephemeris facts via contrast may be very unique orbital and clock correction for each satellites and is essential for particular positioning. The ephemeris information is information that allows the idealorbit of the GPS satellite to be calculated. Ephemeris also contains current time. each satellite publicizesmost effective its very own Ephemeris facts. This information is most effective considered legitimate forapproximately 30 minutes. The Ephemeris facts is broadcast by way of every satellite each 30 seconds.

There are few additional records that you ought to know about GPS. GPS receivers are about the bestRF receivers obtainable! That’s due to the fact, they receive and decode alerts which might be lotsunder the noise floor!! The noise floor on the receiver input with 2MHz bandwidth (GPS signal bandwidth) is round -111dBm (computed as kTB, where ok is Boltzmann regular, T is temperature and B is bandwidth).the typical signal tiers of the received GPS indicators are in the location of -127dBm and receivers are designed to receive alerts at degrees all the manner down to -160dBm!! this is approximately 50dB (a hundred,000 instances) lower than the noise floor!! signal stages are low due to the fact they’rejourneying over lengthy distances (~20,000Kms) and the transmit power on the satellite is confinedbecause of obstacle in available strength on the satellite. At such low sign levels, the receivers are hampered by using multipath fading (interferences due to GPS signals bouncing off reflecting surfaces likehomes, cars, etc) and obstructions like homes, tree cover, bridges, flyovers, and many others

To conserve energy and bandwidth, the sign follows low bit price and therefore takes lengthy to switch a group of facts. due to low acquire signal electricity and low bit rate, the receivers take lengthy to get the first repair. TTFF (Time To First restore) is the time taken for the receiver at some stage in turn on toobtain the satellite tv for pc indicators and compute the region. TTFF duringbloodless start” is the time taken when a receiver starts receiving sign from the satellites afresh (both there aren’t any savedstatistics or the saved data aren’t legitimate) and compute the vicinity. TTFF during cold begin can finaleverywhere from 40 seconds to numerous minutes, depending on what number of satellites are visibleand the signal energy of the obtained signals. but, receivers store the region and closing acquired facts(referring to Ephemeris and Almanac) earlier than flip off and use the identical facts for the duration oftheir next switch on. they can then reduce down the TTFF, supplied all the stored information arenevertheless legitimate (Ephemeris statistics is up to date as soon as each 2 hours and is valid for upto4 hours) and the satellites which might be visible has no longer changed plenty since the ultimatereception. In such instances, generally referred to ashot start”, the TTF may be drastically low – within the order of few seconds if the vicinity from the final stored cost has also not changed a lot.

under some other situations calledheat begin”, if part of the saved statistics (remaining place and almanac if it’s far still valid), the receiver has a trendy concept of which satellites to look for because itknows its ultimate role and the almanac statistics allows become aware of which satellites are seeninside the sky. In these instances, it takes longer than a warm start but not so long as a cold begin.

AGPS or Assisted-GPS is a method to improve TTFF, the cellular cellphone producers and cellularoperators have brought, which allows the clever phones to down load Ephemeris and Almanacinformation thru cell community and get a rough region facts thru triangulation of indicators frommobile towers. rather than receiving those records over gradual rate GPS indicators, exceptionallyhigher speed wireless information community can supply the statistics quite fast so that the receiver can compute the place quick.

Having said all of those, I must admit that there’s more to information GPS than those. these are simplythe basics protecting in advance technology of GPS alerts dealt with by Block II, IIA, IIR and IIR-Mcollection of satellites. more moderen generation satellites Block IIF have additional signal L5 at 1176MHz which make it like minded with different GNSS systems and also the indicators are transmitted at betterenergy.

this newsletter is not complete without discussing our own indigenous IRNSS from ISRO. Indian localNavigation satellite tv for pc gadget (IRNSS), an impartial navigation satellite machine inclusive of threesatellites in GEO (Geostationary) orbit and four satellites in GSO (Geosynchronous) orbit, about 36,000 km above earth floor. The country saw the last of the 7 satellites successfully released and parked on thedistinct spot late April 2016. With this, the country is self-reliant and does no longer need to depend onany one else for precision alerts and accurate area statistics. throughout the Kargil warfare, while itbecome denied the GPS records of the locality, India dedicated to expand an indigenous navigationsatellite tv for pc system and IRNSS is the final results. With this, we can be proud that India is the 5thcountry to have its personal (G)NSS after america, Russia, China and ecu Union. although IRNSS isn’tworldwide in insurance, it does nicely for the place overlaying India and its instantaneous neighboringcountries. India will no greater be arm-twisted into submission!!

Indian IRNSS and its insurance
Indian IRNSS and its coverage
Now that we understand what GPS is and the way it works, we should now take a look at diverse makes use of of GPS. maximum of us can pretty without difficulty relate to navigation, which changed into the primary software of GPS – i.e. that will help you get for your goal region. There are ratings of navigationdevicesvehicle mounted, handheld, and so onmost clever telephone provide navigation help. but, this calls for map recordsboth domestically saved information or online information. if you arerelated over 3G or 4G data plan on your mobile, you may use online Google map to navigate. within thecurrent beyond, Google has provided an option to store google map statistics of a place that is ofinterest and of affordable length, wherein case you may do without facts connectivity to the google server. There also other unfastened map statistics to be had which you could download save in yourclever smartphone, like right here Maps. Your navigation tool can also assist with “point of hobby” –guide you to the nearest point of interest – a filling station, a eating place, a clinic, an ATM, etc

Bosch vehicle navigation gadget
Bosch vehicle navigation machine
another utility of GPS is Telematics – monitoring and tracking your car (or your goods). in case you are aautomobile proprietor or a fleet proprietor, you can monitor and track the area of your car/s at any pointof time. The automobile might then have an On-board unit (OBU) with a GPS receiver and GSM/3G/4G transmitter, that allows you to constantly transmit the GPS region of the car to a predetermined server.you can then hint the course on the map the car has taken and you will recognize if it has deviated from its unique plan. With Geo-fencing, you may get an alert soon because the car breaches its meant path or geographical vicinity. E-call feature will assist crash sufferers with the aid of offering timely assistance. The OBU, on sensing a crash will ship out the closing GPS coordinates of the automobile to a server, following which both a smartphone operator can render help over a return voice call or automated dispatch of an ambulance to the area of the crash. A car mount or a deliver mount container can also be tracked with a battery powered OBU suited for the field.

Bosch Telematics unit
Bosch Telematics unit
similarly to vehicles and goods, it is viable to monitor and tune peopleantique and the weak, seniorcitizens with dementia, visually impaired, youngsters or even pets thru wearable monitoring gadgetshaving GPS receivers and wireless transmitters. wildlife officials can display and song movement of animals with radio collars having similar monitoring gadgets. In farming, harvesting machines and planting machines running on big farms / plantations, on auto-pilot mode use GPS coordinates to guide themthrough every piece of land for their operations. The plenty talked about driverless vehicles would rely upon GPS facts for their fundamental operation – getting the car to the goal location. Taxis use GPS forlocating clients and to get them to their destination.

but of path, we must not neglect their use in military, which by the way changed into the principlereason for growing the GPS– handing over the guns and warheads to the supposed objectives exactly.ultimately, GPS has been guiding aircrafts in all weather situations at some point of flight and difficultterrains (many of the mountains and on islands) throughout landing which blessings extremely fromparticular GPS location information.

similarly to vicinity, GPS can also be used for retaining unique time. Timing accuracy inside the league of nano-seconds can be carried out with ~95% opportunity using GPS alerts. verbal exchange networks use GPS time for synchronization. for instanceverbal exchange networks following TDMA (Time division a couple of access) use GPS particular timing information to synchronize nodes within the community.specific time statistics is used to synchronize and switch in electricity into electrical grids. The educateCollision Avoidance system use GPS as one of the inputs for buying accurate time, to compute velocity of the train and also region records; to hit upon if trains are in collision path and mechanically recognisebraking operation in one or each the trains to save you collisions and to keep scores of lives.

all the usages and packages that i have listed above are just a few very obvious ones. GPS receivers are used in many extra applications. but, kindly remember that, in this context, i have used GPS to consultGNSS. In reality, many GPS receivers use different already deployed GNSS alerts (GloNASS and or BeiDou)to enhance the performance. They appear to effect all parts of our lives – from improved lifestyle to emergency conditions. consequently, GPS or GNSS receivers are no more a luxurious, but an importanta part of our lives.

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