GPS. Course Program

Transkriptio

1 GPS 73 Course Program 1. Introduction to positioning 2. Applications overview 3. Basic principles and theory 4. Case studies of special positioning systems 5. GPS 6. Combinations of technologies and applications 7. Galileo and GLONASS 8. Mobile positioning and location based services 9. Short Range Wireless Networks and positioning/ Indoor Positioning and Navigation 10. Pre-studies 74 1

2 Clustering of positioning topics High end service navigation=position+speed Satellite systems Mobile Networks Aviation other technologies Positioning (location) RF methods Proximity method Fingerprint method RSS Received signal strength TOF Time of flight AOA, DOA Angle or direction of arrival 75 "Location only" Goals The students knows how Navstar GPS technically works (frequencies, coding and decoding, signalling structure, accuracy and ways to improve) Furthermore different applications how the GPS signal can be used shall students make aware of further applications (where GPS signals are used or could be used in new ways) 76 2

3 A Little Bit of the History navigation in the sea aviation positioning methods and link to the theory NDB non directional beacon AOA VOR VHF Omnidirectional Ranging AOA DME Distance Measuring Equipment TOF LORAN-C TOF (TDOA) GPS TOF (TDOA) 77 Now GPS Now we collect what we know by brainstorming 78 3

4 GPS sovellukset Reitinhaku/navigointi Koirapanta, Truckmate, ajopäiväkirja Mitä muita? Tutustu sovelluksiin U.S. Government / U.S. Coast Guard Navigation Center web-saitilla 79 GPS consists of three components Control segment User serment Space segmant 80 4

5 Control Segment The control segment is responsible for maintaining satellites and their orbits, keeping the data up to date and maintaining timing with respect to UTC(USNO) The control segment is composed of a master control station (MCS), an alternate master control station, four dedicated ground antennas and six dedicated monitor stations. The combined 12-station network will allow satellite operators to see every satellite in the 29-satellite GPS constellation continuously from at least two stations. 81 User Segment The users of the GPS service A receiver typically has channels Many GPS receivers can relay position data to a PC or other device using the NMEA 0183 protocol, or the newer and less widely used NMEA

6 83 Space Segment is composed of the orbiting GPS satellites, or Space Vehicles (SV) The GPS design is 24 SVs, six orbital planes with four satellites each. The orbital planes are centered on the Earth The six planes have approximately 55 inclination (tilt relative to Earth's equator) and are separated by 60 right ascension of the ascending node The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface. Orbiting at an altitude of approximately 20,200 kilometers, each SV makes two complete orbits each sidereal day (tähtivuorokausi), repeating the same ground track each day. As of March 2008,there are 31 actively broadcasting satellites in the GPS constellation, and two older, retired from active service satellites kept in the constellation as orbital spares. The additional satellites improve the precision of GPS receiver calculations by providing redundant measurements. With the increased number of satellites, the constellation was changed to a nonuniform arrangement. Such an arrangement was shown to improve reliability and availability of the system, relative to a uniform system, when multiple satellites fail.about eight satellites are visible from any point on the ground at any one time. Current status: see Basic Concept of GPS GPS is a time-of-flight time-of-arrival distance measuring system. It determines position and velocity in three dimensions relative to global coordinates and accurate time according to universal coordinated time (UTC). It is a unilateral system where the target receiver calculates its own position by analyzing signals from spatially distributed transmitters. The GPS receiver must measure distance to at least three transmitters in order to calculate latitude, longitude, and height. When the receiver clock is not synchronized to the transmitter clocks, as is almost always the case, a distance measurement from an additional satellite is needed to obtain a receiver clock correction value, or clock bias. It comprises three segments: space, control, and user. The full constellation began operation in An active constellation includes 24 transmitters, with additional orbiting satellites ready as spares. The nearly circular orbits are at an altitude of 20,200 km and each satellite completes its orbit in 11 hours and 58 minutes. The plane of a satellite orbit intersects the plane of the equator at an angle of 55. There are six orbital planes, spaced equally around the equator and crossing it at longitudes 60 apart. Each plane contains four operational satellites, and on the average eight satellites are in radio view at any point on the globe at any time. 84 6

7 Basic Concept of GPS cont. Frequencies of operation are MHz, referred to as L1, and MHz, referred to as L2. Modulation is binary phase shift keying, transmitted as a spread spectrum signal on two channels, with chip rates of Mbps on L1 and Mbps on L1 and L2. Navigation data that the receiver needs in order to calculate position is transmitted at a rate of 50 bps. The satellites use sets of orthogonal codes at the two chip rates for code division multiple access (CDMA) so that transmissions on the same frequency by all satellites do not interfere. The Mbps code, which has a period of 1 ms, is called the coarse acquisition code (C/A-code). It is available to all GPS users and provides a less accurate positioning and timing service than is provided by the Mbps code. The Mbpscode is called the precision code (P-code) and its period is one week. The P- code may be encrypted, in which case it is called the Y-code. Authorized users, notably U.S. and NATO military organizations, have access to the encryption keys and therefore can take advantage of the higher position resolution that the higher code rate, and thus bandwidth, can provide. 85 Basic Concept of GPS cont. The coordinate system used for the basic position calculation is Earth centered, Earth fixed (ECEF), whose origin is the mass center of the Earth. In order to measure time of flight, the clocks in the transmitters and receiver should be synchronized. The satellite clocks are highly accurate cesium and rubidium instruments but they are not physically synchronized and instead timing corrections are given in a data message that is contained in the signal of each satellite. This data is updated daily with corrections from ground monitoring and control stations. The GPS receiver clock, however, has much lower basic accuracy and its free-running time must be adjusted to give accurate distance measurements. (fourth satellite) The GPS receiver must know to a high precision and accuracy the position and time of the satellites that are in view and from which distance measurements are taken. This information is provided by each satellite in the data that it transmits. 86 7

8 Basic Concept of GPS cont. 87 GPS position calculation example (TOF) Trilateration method is used Satellite transmits: the time the message was transmitted precise orbital information (the ephemeris) Reference station (satellite) coordinates are known at the time of reference station transmission, and reference station clocks are synchronized An initial distance calculation, based on the receiver s time-of-arrival clock reading, is made (pseudorange). Deviation of the pseudorange from the actual range is the same for all satellites because the same receiver clock is used to make all time measurements The unknown parameters are the target coordinates x, y, z pseudoranges Ri, clock offset times propagation speed (Delta) four reference stations (satellites) with coordinates xi, yi, zi,i = 1 to

9 Virhetekijöitä (GPS) Ionosfääri km Dispersiivinen; signaalin vaihe- ja ryhmänopeus eivät ole sama =riippuvainen taajuudesta Vaikutus GPS signaalin näennäiseen kulkumatkaan <1m kymmeniin metriin. Vaihtelee vuorokaudenajan, vuodenajan, ja auringon aktiivisuuden mukaan (elektronitiheys) vrt, avaruussää These effects are smallest when the satellite is directly overhead and become greater for satellites nearer the horizon since the path through the atmosphere is longer Once the receiver's approximate location is known, a mathematical model can be used to estimate and compensate for these errors. SBAS eli SatelliteBased Augmentation System, GBAS eli Ground Based Augmentation System Troposfääri, ilmakehän alin kerros. Troposfäärin paksuus riippuu ilmamassasta ja vuodenajasta: napa-alueilla se on keskimäärin 6 8 km, päiväntasaajalla noin km. Ilmankosteus; more localized and changes more quickly than ionospheric effects, and is not frequency dependent Vaikutus GPS signaalin näennäiseen kulkumatkaan muutamia metrejä Monitie-eteneminen Antennit, liikkuva laite Suhteellisuusteoreettiset efektit Pieniä ja tarkasti laskettavissa Vastaanottimen virheitä Taajuusoskillaattorin virheet Laskennan epätarkkuudesta johtuvat virheet Ephemeris data (voi olla 2h vanhaa tietoa) (AGPS) Satelliitin atomikellon kohina ja drift Häiriösignaalit, jammers, Rakennelmat, katot, jne. (shadowing) 89 Käsitteitä yms. Missä ajassa signaali kulkee matkan GPS-satelliitista GPSvastaanottimeen (maanpinnalle)? Mitä aikaresoluutiota 1m vastaa? Minkälaiset speksit/ominaisuudet ovat GPS satelliitilla? Mikä in GPS:n Taajuus Kaistanleveys Lähetysteho Vastaanottoteho Mitä tarkoittaa NAVSTAR GNSS Selective availability (SA) Kuka omistaa GPS järjestelmän? Kuka operoi sitä? 90 9

10 Käsitteitä yms. Mitä tarkoittaa/sisältää Satellite health Ephemeris Almanac SPS, PPS PRN code SBAS, GBAS SiSNET NMEA Käsitteitä yms. Time to first fix (TTFF) mitä tarkoittaa? Tyypillisiä arvoja? Cold Warm Hot GDOP HDOP PDOP VDOP 92 10

11 Coordinate Systems / Koordinaattijärjestelmät Koordinaattijärjestelmä Sen avulla kyetään määräämään yksikäsitteisesti pisteen sijainti maapallolla koordinaattijärjestelmän määrittelemiseen tarvittavia suureita ovat vertausellipsoidin isoakselin puolikas (a), Maan geosentrinen vetovoimavakio (GM), dynaaminen muoto-kerroin (J2), pyörähdysliikkeen kulmanopeus (ω), koordinaatiston origon sijainti ja koordinaattiakselien suunnat. Koordinaatisto Koordinaattiakselien muodostama mitta-akselisto. Erityyppisiä koordinaatistoja ovat esimerkiksi suorakulmainen koordinaatisto, geodeettinen koordinaatisto, pallokoordinaatisto, lieriökoordinaatisto, tasokoordinaatisto ja napakoordinaatisto. Datum Vertausjärjestelmä, perustuu tiettyyn vertausellipsoidiin ja sen origon siirtoon Esim. GPS-järjestelmä käyttää maailmanlaajuista WGS84-datumia Koordinaatit ovat lukuarvoja, jotka määrittelevät pisteen sijainnin valitussa koordinaatistossa. Lukuarvoja on yhtä monta kuin koordinaatistossa on akseleita. 3D - koordinaatistoissa käytetään geodeettisia leveysja pituuskoordinaatteja ja korkeutta ellipsoidista (φ,λ,h) sekä avaruuskoordinaatteja (X,Y,Z). Karttaprojektio Todellisuutemme on kolmiulotteinen. Sitä kuvataan monesti kaksiulotteisena karttaprojektion avulla joko paperisilla kartoilla tai kuvaruuduilla. Karttaprojektioon kuuluu myös tasokoordinaatisto. Vertausellipsoidi Maan muodon yksinkertaistettu matemaattinen malli. Siinä on huomioitu vain tärkein poikkeama pallomuodosta, litistyneisyys. Pienemmät epäsäännöllisyydet huomioiva geoidi on matemaattisesti paljon monimutkaisempi malli. Geoidi maapallon muotoa kuvaava malli (keskimerenpinta) 93 Ref: wikipedia, Coordinate Systems / Koordinaattijärjestelmät Suorakulmainen tasokoordinaatisto Suomessa maastokartoilla ja yleisissä kartastotöissä käytetään lieriöprojektiota ja niiden yhteydessä muodostettuja tasokoordinaatistoja. Poikittaisasentoisessa lieriöprojektiossa tasokoordinaatisto muodostetaan seuraavasti: koordinaatiston origo eli nollapiste on päiväntasaajan ja keskimeridiaanin leikkauspisteessä origoa siirretään yleensä länteenpäin negatiivisten koordinaattiarvojen välttämiseksi, eri koordinaatistoissa käytetään erilaista siirtymää keskimeridiaani muodostaa koordinaatiston pohjoisakselin päiväntasaaja muodostaa koordinaatiston itäakselin Esim KKJ, EUREF-FIN Maantieteellinen koordinaatisto Maantieteellistä (geodeettista) koordinaatistoa käytetään yhdessä Maan muotoa kuvaavan pyörähdysellipsoidin (referenssi ellipsoidin) kanssa. Suorakulmainen avaruuskoordinaatisto akselit ovat X, Y ja Z, origo on yleisimmin Maan massakeskipiste tai pyörähdysellipsoidin keskipiste. KKJ, YKJ Suorakulmainen tasokoordinaatisto KKJ on koordinaattijärjestelmä, johon vuodesta 1970 alkaen ovat perustuneet suomalaiset maasto- ja merikartat. Järjestelmää on käytetty merikartoituksessa vuoteen 2003 asti ja maastokartoituksessa vuoteen KKJ-ja WGS84-järjestelmien koordinaatit poikkeavat toisistaan, koska WGS84 perustuu eri vertausellipsoidiin kuin KKJ. Poikkeaman suuruus vaihtelee eri osissa maata. YKJ on koko maan kattava yhtenäiskoordinaatisto ETRS-TM35FIN on suomalaisissa maastokartoissa vuodesta 2005 alkaen käytetty karttaprojektio ja projektioon liittyvä tasokoordinaatisto. Projektion yhteydessä yleensä käytetään EUREF-FIN-koordinaatistoa. Voidaan pitää Kartastokoordinaattijärjestelmän seuraajana EUREF-FIN, ETRS89 Suomen uusi koordinaattijärjestelmä. Yhteensopiva GPS:n kanssa ETRS89 määrittelee yhtenäisen Euroopan laajuisen koordinaattijärjestelmän, joka on kiinnitetty Euraasian mannerlaatan muuttumattomaan osaan. Näin ollen koordinaatit eivät muutu mannerlaatan liikkuessa. EUREF-FIN on Euraasian mannerlaattaan kiinnitetyn ETRS89-koordinaattijärjestelmän suomalainen reaalisaatio, joka poikkeaa WGS84-koordinaattijärjestelmästä alle metrin Mikään itse koordinaatissa ei kerro, onko maantieteellinen koordinaatti KKJ- vai EUREF-FIN-järjestelmän mukainen. Koordinaatit ovat kuitenkin erit, koska datumit eroavat. WGS84 94 World Geodetic System 1984 on GPS - satelliittien käyttämä koordinaattijärjestelmä. Käytetään yleisesti myös Web-karttapalveluissa Maailmanlaajuinen, geosentrinen järjestelmä, joka käyttää WGS84-referenssiellipsoidia. Ref: wikipedia, 11

12 Coordinate Systems / Koordinaattijärjestelmät Suorakulmaiset koordinaatit maantieteelliset koordinaatit Ref. ( fi/c/document_library/get_file?uuid=ce0eefee-3cc be74-160d77dbf130&groupid= ) JHS-suositus 95 Coordinate Systems / Koordinaattijärjestelmät Tutustu lisäksi esitykseen: koordinaatit.pdf Lisätietoa myös osoitteesta:

13 Koordinaatit Oulun koordinaatit WGS84 KKJ EUREF-FIN Kuinka pitkä on kaariminuutti? Kulmaminuutti eli minuutti (tunnus, yläpuolinen indeksointipilkku) on asteen kuudeskymmenesosa. Kulmaminuutti jakaantuu edelleen kuuteenkymmeneen kulmasekuntiin. Kulmaminuutin mittaista osaa ympyränkaaresta kutsutaan kaariminuutiksi. Esitystapoja 40:26:46N,79:56:55W 40:26:46.302N 79:56:55.903W 40 26'47"N 79 58'36"W 40d 26' 47" N 79d 58' 36" W N W , , GPS ja korkeus Ref: Jotkut GPS vastaanottimet antavat suoraan ortometrisen korkeuden sisäänrakennetun geoidimallin mukaan. Mikä geoidimalli on ko. GPS laitteessa? Mikä geoidi malli on käytössä Suomessa? Mitkä ilmiöt vaikuttavat? 98 13

14 Muunnos: Suorakulmaiset koordinaatit maantieteelliset koordinaatit 99 Ref: Poutanen: GPS paikanmääritys 100 Time Systems / Aika UT, UT1 TAI ( UTC DUT1=UT1-UTC Aikajärjestelmät Koska maapallo ei pyöri tasaisesti, tähtitieteellisen vuorokauden pituus ei ole välttämättä tasasekunteja. Tätä varten on kehitetty erilaisia aikajärjestelmiä, jotka käsittelevät tämän ongelman eri tavalla. UT0 Yleisaika, Universal Time. Määritellään observatorioissa tähtien näennäisen liikkeen tai galaksin ulkopuolisten radioaaltolähteiden perusteella sekä maata kiertävistä satelliiteista. Näin syntyy paikallinen virhe maapallon maantieteellisten ja todellisten napojen välisestä erosta, joten UT0-aika ei ole tarkasti ottaen universaali. UT1 UT1-aikajärjestelmässä korjataan UT0:n virhe. UT1 on sama joka puolella maapalloa. Se kertoo maapallon kiertokulman tiettyyn vakiovertauspisteeseen. Koska maan kiertoliike ei ole vakio, myös UT1- ajassa on epätarkkuutta, joka on korkeintaan ±3 millisekunnin virhe päivässä. TAI Kansainvälinen atomiaika, Temps Atomique International. Aikajärjestelmä, joka mitataan atomikelloilla. Perustana on nykyinen, cesiumatomin spektriin perustuva sekunnin määritelmä. UTC Coordinated Universal Time. Normaalisti käytettävä aika, joka seuraa kansainvälistä atomiaikaa, mutta kun ero UT1-aikaan nousee yli 0,9:ksi sekunniksi, UTC-aikaa siirretään tasan yksi sekunti eteen- tai taaksepäin karkaussekunnilla. Tämä tehdään 0 2 kertaa vuodessa, vuodenvaihteessa tai keskikesällä. GMT Greenwichin aika, Greenwich Mean Time. Aiemmin käytetty aikajärjestelmä, joka on Greenwichin observatorion kautta kulkevan pituuspiirin keskiaurinkoaika ja käytännössä sama kuin UTC. (Ref: Wikipedia) 14

15 Time Systems / Aika GPS time the atomic clocks on the satellites are set to GPS time. The difference is that GPS time is not corrected to match the rotation of the Earth, so it does not contain leap seconds or other corrections that are periodically added to UTC. GPS time was set to match Coordinated Universal Time (UTC) in 1980, but has since diverged. The lack of corrections means that GPS time remains at a constant offset with International Atomic Time (TAI) (TAI - GPS = 19 seconds). Periodic corrections are performed on the on-board clocks to correct relativistic effects and keep them synchronized with ground clocks. The GPS navigation message includes the difference between GPS time and UTC, which as of 2009 is 15 seconds due to the leap second added to UTC December 31, Receivers subtract this offset from GPS time to calculate UTC and specific timezone values. GPS week As opposed to the year, month, and day format of the Gregorian calendar, the GPS date is expressed as a week number and a seconds-into-week number. The week number is transmitted as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again every 1,024 weeks (19.6 years). GPS week zero started at 00:00:00 UTC (00:00:19TAI) on January 6, 1980, and the week number became zero again for the first time at 23:59:47 UTC on August 21, To determine the current Gregorian date, a GPS receiver must be provided with the approximate date (to within 3,584 days) to correctly translate the GPS date signal. To address this concern the modernized GPS navigation message uses a 13-bit field, which only repeats every 8,192 weeks (157 years), thus lasting until the year 2137 (157 years after GPS week zero). Epoch an epoch means an instant in time chosen as the origin of a particular era. The "epoch" then serves as a reference point from which time is measured. GPS: January 6, SV clock correction The satellite's atomic clocks experience noise and clock drift errors. The navigation message contains corrections for these errors and estimates of the accuracy of the atomic clock

16 GPS signals C/A code PRN code Mbit/s, repeats every millisecond strongly correlate highly orthogonal Each satellite transmits a unique PRN code CDMA P-code PRN; bits long, repeats once a week Mbit/s encrypted with the W-code The encrypted signal is referred to as the P(Y)-code. NAV (navigation message) GPS date and time, the satellite's status and health. orbital information (ephemeris) almanac, information and status of all the satellites (locations and PRN numbers) 103 GPS signals cont

17 Composition of Navigation message complete data signal consists of bit and at a transmission rate of 50 bit/s a total of 12.5 minutes The data signal is divided into 25 frames, each having a length of 1500 bit (meaning an interval of 30 seconds for transmission). The data frame is made up of 5 subframes, and 25 data frames make up one complete message. TLM Telemetry word contains age of the data and preamble for synchronization HOW Handover word contains number of counted z-epoches; time of transmission from the beginning of the GPS week 105 Composition of data stream Subframe 1 contains Exact time from which to measure the TOF data about status and accuracy of the transmitting satellite as well as clock correction data Subframes 2and 3 contain ephemeris parameters, properties of the elliptical orbit (Keplerian parameters) Subframe 4 contains data for the satellites number 25 32, ionospheric correction data, special information and UTC time information subframe 5 contains almanac data for the satellites 1 24 as well as time and the number of the GPS week The data in the first three subframes repeats in every frame, but the data in 4-5 subframes is entirely transmitted in 25 frames

18 Composition of data stream ephemeris parameters are 107 Satelliitin rata Ellipsirata (vrt. Keplerin lait) Geometrisia suureita Isoakselin puolikas Eksentrisyys Inklinaatio i Nousevan solmun rektaskensio Perigeumin argumentti Perigeumaika Häiriötä aiheuttavat tekijät Maan litistyminen Kuu Aurinko Kiinteän maan vuoksi Auringon säteilypaine Maan heijastuskyky Sunteellisuusteorian efektit

19 An example of a GPS receiver operation The most important GNSS receiver functions are signal acquisition and tracking i.e. finding the SV signal and maintaining a lock at least on the ranging code (i.e. C/A- or P-code) data demodulation - to decoding the necessary data elements PVT (Position-Velocity-Time) calculation - estimating the UE location. pseudorange measurement from the code phase measurements obtained from the GNSS chipset. 109 Error term are advances of the UE and SV clocks with respect to GPS time (GST=GNSS system time) I(s) and T(s) are the ionosphere and troposphere delays the last term is for measurement errors that include receiver noise, interference, multipath and receiver hardware offsets SV=space vehicle UE= user equipment Ref: An example of a GPS receiver operation cont. The SV position (xsv) is calculated from the orbit model included in the SV signal broadcast (orbit parameterization). The UE clock offset estimation, see GPS position calculation example. The SV clock offset is obtained from the SV clock model that the SVs also broadcast. In GPS the model is second-order polynomial. Tropospheric delay is in the order of few meters and can be modeled in the UE using (for example) the Saastamoinen model. The model requires information on the atmospheric conditions (pressure, temperature, partial water pressure), but the information can also be derived from the model for the standard atmosphere. In such a case only the orthometric height of the UE is needed

20 An example of a GPS receiver operation cont. Ionospheric delay s effect may be several tens of meters. The delay may be calculated based on the model or it can be estimated in the UE. GPS broadcast includes a global Klobuchar model that accounts for approximately 50% of the variation in the ionospheric delay. Finally, the UE velocity can be obtained by a direct Doppler frequency measurement made by the GNSS receiver from the SV signal. It should be noted that all the required information for positioning (especially orbit, clock and ionosphere models) are available in the GNSS broadcasts. However, the information may likewise be distributed over the telecommunication networks to the assisted GNSS UEs. 111 Time of flight measurement How is the time from satellite to receiver really measured? It is a comparison method of the PRN code received with the PRN known by shifting until the correlation is best Parhaimmillaan päästään 0.1% tarkkuuteen koodin vaiheesta How to get even better accuracy?

21 DGPS GPS coordinate accuracy can be improved significantly by getting assistance from a ground station whose location is known accurately by surveying. This is called differential GPS (DGPS). The accurately located ground station makes position measurements from the satellite network and computes the differences from the known location. Correction factors are then transmitted (directly) to GPS users in the vicinity, which can use these corrections in their own calculated data to improve their location estimation. Positioning accuracy can be improved to better than 10m, and time accuracy can similarly be augmented. DGPS is effective when the target and the DGPS assisting terminal are no more than 250 km apart 113 SBAS Satellite Based Augmentation Systems (SBAS), this name is seldomly used Its implementations arewaas (US), EGNOS (EU), MSAS (Japan), GAGAN (India) the wide area augmentation system, WAAS, makes improved accuracy available over a continental size area The area covered by WAAS, EGNOS and MSAS depends on where RIMs (Ranging and Integrity Monitor Stations) are located and if signals from geostationary satellites are being received. (note: might be low over the horizon) More info:

22 SBAS cont. 115 GBAS/GRAS ground-based augmentation system (GBAS) ground-based regional augmentation system (GRAS) describe a system that supports augmentation through the use of terrestrial radio messages. As with the satellite based augmentation systems, ground based augmentation systems are commonly composed of one or more accurately surveyed ground stations, which take measurements concerning the GNSS, and one or more radio transmitters, which transmit the information directly to the end user. Generally, GBAS networks are considered localized, supporting receivers within 20km, and transmitting in the very high frequency (VHF) or ultra high frequency (UHF) bands. GRAS is applied to systems that support a larger, regional area, and also transmit in the VHF bands

23 NPA = Non Precision Approach 117 Assisted GPS - AGPS (generally AGNSS) In compromised signal conditions the capability to decode the data payload is often limited. AGNSS addresses this problem by providing an alternative route to carry the data payload to the UE. Moreover, AGNSS assistance helps the UE also in various other ways to achieve better user experience in terms of availability, speed, accuracy and integrity. Aiding is based on relying both on the data transfer capabilities as well as on the inherent properties of the network including precise timing of radio transmissions. 118 Ref: 23

24 AGPS cont. GPS receiver needs to obtain both the navigation data and PRN code phase. PLL is needed to demodulate the navigation data from the SV broadcast (carrier phase tracking), whereas DLL is required to track the ranging signal (code phase tracking). The SV signal can attenuate approximately 15 db from its nominal level, before the error probability grows too high for the data demodulation to be possible. Such 15dB attenuation levels are found in forest canopy and suburban areas. In urban canyons and indoors the attenuation is typically greater than 15 db. However, in optimal conditions the DLL can track the ranging code even down to -160 dbm. This corresponds to approximately 30dB attenuation, which is the level of attenuation found in urban canyons and mild indoors. Therefore, in this db attenuation range AGNSS can improve the performance. 119 Ref: AGPS infrastructure The AGNSS server may obtain its data from various sources: WARN (Wide Area Reference Network) - networks of physical GNSS receivers an external service providing, for instance, orbit and clock predictions, and/or troposphere delay forecasts (right hand side in Figure 2.2) 120 Ref: 24

25 AGPS - performance improvement In the case of GPS, receiving the orbit and clock information from the SVs takes in minimum 18 seconds, because the data is distributed over three sub-frames each lasting six seconds. However, in an assisted case the information can be delivered quickly to the UE over a data link, because the amount of data is fairly small (about 500 bits/sv ). This improves the user experience due to the reduced TTFF. Moreover, the UE may retrieve the assistance data from the server, whenever the data in the UE expires. In such a case the UE always has a valid copy of the navigation data and the TTFF is further reduced. Finally, in case orbit and clock predictions are available, AGNSS-enabled UEs can be provided with navigation models extending days or even weeks ahead. In such a case the UE does not need to connect to the assistance server in the beginning of each positioning session. This improves user experience due to the time saved in not having to download the assistance. 121 TTFF=time to first fix GPS signal attenuation GPS ink budget?

26 AGPS Another approach For many applications, GPS receivers are overly complicated and expensive. Memory size and computing capability as well as product size and cost can be significantly reduced using assisted GPS (A-GPS). A very basic GPS receiver, consisting of antenna and RF downconversion facilities together with a relatively simple processor can obtain from a remote server the raw parameters needed for distance measurements, including: Precise satellite orbit and clock information; Initial position and time estimate; Satellite selection, range, and range rate. After performing essential calculations of pseudorange and timing data, the A-GPS receiver can either process the data to find its own position, or can send the information back to the server which will perform the position calculations and will distribute the results to the necessary parties. 123 Ref: Bensky: Wireless positioning Precision Point Positioning PPP can achieve decimeter-level accuracies and, therefore, the error sources and modeling needs have to be identified even further in detail (e.g. SV rotation, antenna offsets, solid-earth tides). Models Reference stations Post processing

27 Civilian L2 (L2C) GPS modernization broadcast on the L2 frequency ( MHz). It is transmitted by all block IIR-M and later design satellites. improved accuracy of navigation, providing an easy-to-track signal, and acting as a redundant signal in case of localized interference. a dual frequency receiver; Ability to remove, the ionospheric delay error for that satellite. (the largest source of error in the C/A signal). L2C contains two distinct PRN sequences: CM (for Civilian Moderate length code) is 10,230 bits in length, repeating every 20 milliseconds. CL (for Civilian Long length code) is 767,250 bits, repeating every 1500 milliseconds (i.e., every 1.5 s). Each signal is transmitted at 511,500 bits per second (bit/s), however they are multiplexed to form a 1,023,000 bit/s signal. CM is modulated with a 25 bit/s navigation message with forward error correction, whereas CL is a non-data sequence (it does not contain additional modulated data). The long, non-data CL sequence provides for approximately 24 db greater correlation protection (~250 times stronger) than L1 C/A. L2C signal characteristics provide 2.7 db greater data recovery and 0.7 db greater carrier tracking than L1 C/A The L2C signals' transmission power is 2.3 db weaker than the L1 C/A signal. In a single frequency application, L2C has 65% more ionospheric error than L1. Safety of Life (L5) Safety of Life is a civilian-use signal, broadcast on the L5 frequency ( MHz), planned to be implemented with first GPS IIF launch (2010). Improves signal structure for enhanced performance Higher transmission power than L1 or L2C signal (~3dB, or twice as powerful) Longer spreading codes (10 times longer than used on the C/A code) Wider bandwidth, yielding a 10-times processing gain Located in the Aeronautical Radionavigation Services band, a frequency band that is available world wide. WRC-2000 added space signal component to this aeronautical band so aviation community can manage interference to L5 more effectively than L2 New Civilian L1 (L1C) The L1C will be available with first Block III launch, currently scheduled for Implementation will provide C/A code to ensure backward compatibility Assured of 1.5 db increase in minimum C/A code power to mitigate any noise floor increase Non-data signal component contains a pilot carrier to improve tracking Enables greater civil interoperability with Galileo L1 Ref: ging%20technologies.pdf -New freqs -longer codes -Pilot signal -FEC for NAV 125 GPS III to launch the first GPS IIIA satellite in 2014 On May 15, 2008, the U.S. Air Force Space and Missile Systems Center, Los Angeles Air Force Base, Calif., awarded a team led by Lockheed Martin a $1.46 billion contract to build the next-generation Global Positioning System, known as GPS III. GPS III will improve position, navigation and timing services and provide advanced anti-jam capabilities yielding superior system security, accuracy and reliability. The next generation GPS IIIA satellites will deliver signals three times more accurate than current GPS spacecraft and provide three times more power for military users, while also adding a new civil signal (L1C) that is designed to be interoperable with other global navigation satellite systems. Under the Development and Production contract, the team of Lockheed Martin Space Systems Company, ITT Corporation, and General Dynamics, will produce the first two GPS IIIA satellites with options for up to 10 additional spacecraft. The contract, which features a back to basics acquisition approach to low-risk constellation sustainment and technology insertion, includes a Capability Insertion Program (CIP) designed to mature technologies and perform rigorous systems engineering for the future IIIB and IIIC increments planned for follow-on procurements. Eight GPS IIIB and 16 GPS IIIC satellites are planned for later increments, with each increment including additional capabilities based on technical maturity. When fully deployed, the GPS III constellation will feature a cross-linked command and control architecture, allowing the entire GPS constellation to be updated simultaneously from a single ground station. Additionally, a new spot beam capability for enhanced military (M-Code) coverage and increased resistance to hostile jamming will be incorporated. These enhancements will contribute to improved accuracy and assured availability for military and civilian users worldwide. Ref: The U.S. Air Force s Space and Missile Systems Center at Los Angeles Air Force Base has awarded the Next Generation GPS Control Segment (OCX) program to Raytheon (Ref: channel.jsp?channel=space&id=news/asd/2010/03/01/12.xml&headline=raytheon%20wins%20next-gen%20gps%20award)

28 For more information w/paikannus/paikannusjarjestelmat.html /6509/wirola.pdf Markku Poutanen: GPS-paikanmääritys (URSA 1999) Chipset for GPS The list of manufacturers is long A consolidation has taken place already Products (chips) are done for certain product groups (handsets, cameras, automotive) Now we look into products from Infineon Sirf STM TI U-Blox NXP (has good guidlines for HW design)

29 Latest u-blox chip announcement 129 Group work Group work based on datasheets and technical information from GPS Chip vendors Your task You analyse the information based on your theoretical knowledge Answer the questions and prepare a 5 minute presentation (give PPT to the teacher) present the results to the rest of the class with a short presentation