Analysis of the Advantage of Using the Sirfstariii Architecture for Navigational Purposes in Urban Areas

Analysis of the advantage of using the SiRFStarIII architecture for navigational purposes in urban areas Filip Biljecki* i Marko Pavasović** UDK 629.783.05:681.5:711.4(497.5) Abstract. In the last few years the market of navigational devices experienced it’s biggest boom – their everyday presense was never bigger. Meanwhile, because of a higher degree of use of navigational devices in urban ares as the engineering offensive on them some standard GPS problems are present – weak signal from satellites which leads to smaller accuracy and long Time To First Fix (TTFF). For a better situation, the company SiRF Te- chnology Holdings, Inc. made a new chipset SiRFStarIII which accent is on higher sensitivity, short TTFF and represents the newest achievement in satellite navigation. This paper shows the analysis of the advantage of using the chipset SiRFStarIII in urban areas through few practical tests on the area of The City of Zagreb, Croatia

Keywords: GNSS, GPS, navigation, microcontroler, SiRFStarIII.

1. Introduction fundamental philosophy isn’t much di- purpose is to provide the geograp- fferent from it’s beginning, the novelty hic position on a global basis. In the From the beginning of the civili- represents the huge number of users time of this paper’s writing the only sation and life in general, the task of because of a big rate of small costs for fully functional GNSS is Navigation transport represented a very important navigational systems and user-frien- Satellite Timing And Ranging Global component of every individual and dly approach which must be thanked Positioning System (NAVSTAR GPS) service. This important life segment to the market and the ability of their developed by the U.S. Department of couldn’t be imagined without the use appliance on everyday’s life and a big Defense1 which presents almost a glo- of an old skill and activity – navigati- number of activities. bal property. In the phase for the fully on which from its beginning represen- Today, the navigation of 21th cen- operation is the system Global’naya ted a brand and an activity reserved tury can’t be imagined without the Navigatsionnaya Sputnikovaya Siste- for contemporary scholastic individu- usage of the components of the set ma (GLONASS) which is currently als. Exactly the navigation on the sea called Global Navigation Satellite Sy- under the duty of the Russian Space provided the finding of America and stem (GNSS). GNSS is a term used for Forces2, and the Global navigational new routes. Today’s navigation on its satellite navigational systems which system Galileo which is under the

[*] Filip Biljecki, Undergraduate study of Geodesy and Geoinformatics, Faculty of Geodesy – University of Zagreb, Croatia, e-mail: [email protected] [**] Marko Pavasović, Graduate study of Satellite and Physical Geodesy, Faculty of Geodesy – University of Zagreb, Croatia, e-mail: [email protected] [1] United States Department of Defense; (http://www.defenselink.mil/) [2] Russian Space Force (http://www.mil.ru/eng/1862/12068/12088/12224/index.shtml) development of the European Space sitioning delivers more accurate coor- Agency3 (ESA) and the European Uni- dinates, but the process is longer than 4. Microcontroler SiRFStarIII on (EU). GNSS presents a real revolu- that of navigational purposes where and its advantages tion in all parts of navigation becau- an accurate position is not essential. se of its fast and accurate positioning With these purposes the GNSS unit The central part of every GNSS rece- service which must be thanked to the development was divided through two iver is the microcontroler. Microcon- U.S. goverment which opened its use markets: troler is, shortly, a computer-on-chip to all, not just U.S. citizens, but to • units for the purpose of positioning (microcontroller is not a microproce- the whole world, and the removal of (mostly in geomatics) and ssor which is its part). In GPS recei- the Selective Availability (SA) system • units for navigational purposes vers, microcontroler is the unit respon- which deliberately added an error on The first mentioned market is sible for the GPS signal interpretation the final result because of military in- smaller than the navigation market, and processing so a special care must terests. The revolution reflected on a but the average price of the equipment be directed into the production of the rapid development of new navigatio- is few dozen times higher than the GPS receiver’s microcontroler. Micro- nal devices for civil purposes. Thanks average price of the navigational equ- controlers are producted by just few to the above mentioned factors and ipment. Maybe proportionally to the manufacturers in the world which are increased number of manufacturers, price, the standard deviation of the selling them to the manufacturers of the number of users of navigational position derived from the positioning the navigational equipment. Accordin- systems today is bigger than ever and units is many times less than the po- gly, today two GPS receivers with the in developed countries it represents a sition derived from navigational units. same microcontroller can be found. component of everyday life. The Figu- In this paper, as the introduction and SiRFstarIII is the newest GPS micro- re 1 shows a today’s representative na- title partialy showed, the emphasis is controller which was manufactured by vigational device for civil purposes. on the navigational purposes. the very popular company SiRF Tech- The majority of users from the nology Holdings, Inc.4 from California, mentioned group is of civil character USA. This chip represents the biggest and is mostly consisted of users of achievement in this area yet. SiRF- transport vehicles, sailors, users for StarIII is special for its high sensitivity personal navigation (orientation in ci- (-159dBm), lower Time To First Fix ties, nature – trekking, etc.). when the receiver is turned on (or lost the fix) and a higher number of corre- 3. Problems in urban areas lators (200k) of its concurents. This solution was quickly adopted by the In the time of writing this article lead manufacturers in the navigational almost all users are using the ameri- equipment (e.g. Lowrance, TomTom, Figure 1. can GPS and its compactible devices. Garmin and Magellan) and started to Navigational device A very large number of navigational implement it in their products which RoadMate 2200T from the manufacturer ‘’Magellan’’; units is used in urban areas where the led to today’s situation where SiRFSta- (URL-2) device-satellite Line of Sight (LoS) as rIII is almost a standard for that very the fundamental requirement for qua- important part of a GPS receiver. lity transmission and accurate positi- 2. Navigational devices and oning is interrupted because of urban 5. Analysis of the users clasification barriers – high constructions, vegeta- microcontroler SiRFStarIII tion and a high concentration of EM The determination of position co- traffic and noise. Of course, in the case To prove these facts an analysis ordinates is one of the fundamental of transport users the vehicle barrier of the potential advantage of using the

tasks of Geodesy. There are two pur- (e.g. window with anti-UV protection) SiRFStarIII chipset has been made in F. Biljecki, M. Pavasović: Analysis of the advantage using SiRFStarIII architecture for navigational purposes in urban areas - Ekscentar 2007, No.9 poses of the position determination in must also be considered. the parts where most of the navigatio- Geodesy: the purpose of positioning With the reduced number of ava- nal equipment is used and where most and the purpose of navigation. The ilable GPS satellites and weak signal problems are present – in urban are- term navigation means to mantain a from them the final product – the geo- as. The definitive product of all GNSS constant heading over a instantaneo- graphic position of the user, with con- receivers – geographic position has usly object position determination, i.e. sidering the device capabilities, is rela- been analysed. determination of route of an object tively innacurate and the continuity of motion. Positioning is used for deter- fix isn’t long and confident. Multi-pat- 5.1 Anylised receivers mination of an object coordinates. It is hing, as a unwished efect, must also important to mention that navigation be considered, but for the goal of this The advantage of using the SiRF- is just a special case of positioning and article it will not be mentioned in the StarIII chipset was determinated from their distinction is hard to define. Po- following text. the results of the relative comparing

[3] European Space Agency (http://www.esa.int/) [4] http://www.sirf.com with an old chipset. So, it was essential to find two very similar GPS receivers so the analysis could concentrate on microcontrollers. The best choice F. Biljecki, M. Pavasović: Analysis of the advantage using SiRFStarIII architecture for navigational purposes in urban areas - Ekscentar 2007, No.9 were the Garmin devices GPSMap 60CS and GPSMap 60CSx (lend from the company Navigo Sistem d.o.o.) because 60CSx is just a continuation of the very successful receiver 60CS. The units are physically equal, but the microcontroller is different: 60CS uses the Garmin’s old generation 12-cha- nnel chipset and 60CSx the new SiR- FStarIII which makes these devices an optimal choice for this analysis.

Figure 4-1. SiRFStarIII architecture; (URL-2)

5.2 Analysis description

The analysis of above mentioned GPS receivers consists of two parts: • analysis of GPS units for navigational purposes • analysis of GPS units for positioning purposes Although the units are manufactured for the primary purpose of navigation, the positioning analysis is also Figure 5-1 i 5-1a. City walk in mentioned routes with receivers in the backpack made because of navigation’s special case of positioning. The receivers were every one second in ITRF2000 frame ITRF2000 to HDKS (Croatian State tested with disabled and then enabled on WGS84 ellipsoid and time in UTC6 Geodetic Coordinate System) 5. EGNOS5 option. system. zone Gauss-Krueger’s projection with The test was executed on March 30 the official transformation program 5.3 Analysis and interpretation in 2007, between 8:30am and 9:30am, Dat_Abmo from the Croatian State of navigational solutions with a average city walt (figure 5-1) in Geodetic Administration. mentioned streets. The GPS devices From the Figure 5-2 it is possible For the navigational test route were in the backpack, put closely to conclude that both devices had three representative parts of Zagreb, together (figure 5-1a). a stable position fix in the Klaićeva Croatia were taken into account: From the position gathered from street, what wasn’t expected because Klaićeva street, Tito’s square and the receivers, the routes were visualized of the street’s architecture and near Masarykova street. The devices were on the Zagreb digital ortophoto high buildings what implicated on a configured for the spacetime position – two paths for every receiver (with possible outage. On Tito’s square, (latitude and longitude in decimal and without enabled EGNOS) with because of a very good LoS, it was degrees, height in metres) registration past coordinate transformation from expected that both devices would not

[5] EGNOS is European Geostationary Navigation Overlay Service, DGPS system for the distribution of corrections through a geostationar satellite whose primary purpose is to enhance the final product – geographic coordinates of the device [6] Universal Time Coordinated Figure 5-2. Motion paths of the devices have any problems with the satellite fix. The tricky part was Masarykova street with its architecture (less large then Klaićeva) and with its high buildings. In this part of the test the SiRFStarIII technology showed its advantages – Garmin GPSMap 60CS recorded a position fix break soon as entered in the street. In the middle of the street the receiver obtained a short fix, but with high deviation from the real path. Instead, the Garmin GPSMap 60CSx had a constant fix and was giving a relatively accurate position. With that, the title of this paper is justified. It is important to mention that the enableation of the EGNOS differential correction of the position is affecting Figure 5-3. Point A the quality of the position, not the quality of satellite signal in urban areas.

5.4 Analysis and interpretation of position solutions F. Biljecki, M. Pavasović: Analysis of the advantage using SiRFStarIII architecture for navigational purposes in urban areas - Ekscentar 2007, No.9

After the proof of the advantage of the SiRFStarIII technology in urban areas it was interesting to explo- re this thesis in a absolute positioning case. As tests points, two points are taken: the first (point A) in the high school field with excellent LoS to satellites, stabilised with a concrete pole 20x20x50cm (figure 5-3) and a point from the GPS network of the City of Zagreb (point B) with a bad LoS to the sky. To both points the coordinates in HDKS are known. The approach was Figure 5-4. Point B F. Biljecki, M. Pavasović: Analysis of the advantage using SiRFStarIII architecture for navigational purposes in urban areas - Ekscentar 2007, No.9

Figure 5-5. Receiver screenshots on the point A without the Figure 5-6. Receiver screenshots on the point A with the EGNOS correction. 60CS is on the left, 60CSx right EGNOS correction. 60CS is on the left, 60CSx right

very similar to the navigational test the 60CSx receiver analysis which aga- (±61m, figure 10 left), this isn’t to con- where both devices where very near, in implicates the advantage of the SiR- cern, because of the lack of SiRFStarIII with the registration interval of one se- FStarIII technology, despite the very technology. cond and with EGNOS disabled and good LoS on the point A. Because of It is interesting to analyse gained then enabled. the open sky of the point A the effect statistical positioning data on the point of the EGNOS correction can be con- B. From the Table 5-3 it is visible that Point A sidered. In the case of the 60CSx devi- the values of statistical components In the time of surveying the po- ce the standard deviation of dy, dx and dy, dx, D in the case of the enabled int A, a screenshot of both devices D elements are decreasing comparing EGNOS correction for the Garmin GP- was made so the number of satellites to values when EGNOS isn’t enabled. SMap 60CS receiver (pink colour) are which are recorded by both satellites In the case of 60CS this, because of very beyond acceptable values. In fact, could be registered. This was made unknown reasons, is not the case. in this part of the analysis a complete in two cases – with disabled EGNOS disruption occured because of an in- correction and then enabled. In the Point B sufficient number of satellites (minimal first case (w/o EGNOS) the ratio of re- The point A positioning principe 3 satellites is required) so the receiver gistered satellites was 7:5 in benefit to was also applied for the point A. With wasn’t recording any current position the 60CSx receiver (figure 5-5). In the disabled EGNOS correction (figure 5- data. Statistics were made on the basis second survey (w/ EGNOS) the rece- 7) the ratio of registered satellites was of the first fix to the time of the dis- iver 60CSx had the advantage of 8:6 9:4 in the behalf of the 60CSx. With ruption. (figure 5-6). enabled EGNOS (figure 5-8) the ratio Garmin GPSMap 60CSx (Table 5- In the Tables 5-1 and 5-2 a statisti- was 7:3, also in the advantage of the 4) didn’t experience these problems cal analysis of coordinate differences 60CSx. and in both cases was fully registering and distance from the real value and As the LoS of the point B was bad, its position and prooved the advantage aquired value is given. From the stati- the fact that with the enabled EGNOS of its chipset in urban areas. Unfortu- stical analysis it is visible that the value correction the receiver 60CS showed natelly, as a result of the very bad LoS of the standard deviation is smaller in an extremely inaccurate position on the point B, the EGNOS correction

Table 5-1. Elements dy, dx i D statistics for the point A (Garmin GPSMap 60CS) in metres [m]

Table 5-2. Elements dy, dx i D statistics for the point B (Garmin GPSMap 60CSx) in metres [m] Figure 5-7. Point A screenshot of 60CS (left) and 60CSx (right) Figure 5-8. Point B screenshot of 60CS (left) and 60CSx (right) couldn’t correct the position. above mentioned results are connec- effort in a quick and constructively At the end of the analysis a hi- ted only with this research and any peer review of this paper as his use- stogram of standard deviations of further conclusion and reference from ful suggestions and support for future elements dy, dx and D of the whole this paper in the way of decision ma- work. analysis is included for an easy inter- king in the receivers buying is not ad- preation, conception, comparing and visable. References image of the results gained. Acknowledgments • Bačić, Ž.: Satelitska geodezija 2, in- 6. Conclusion terna skripta, Geodetski fakultet Sveu- Authors would like to thank the čilišta u Zagrebu, 1999. Based on this research it is possi- company Navigo Sistem d.o.o. (http:// • Bačić, Ž.: Integrirani sustavi u navi- ble to conclude that SiRFStarIII tech- www.navigosistem.hr) for the receiver gaciji, interna skripta, Geodetski fakul- nology in devices made for navigation Garmin GPSMap 60CSx, company tet Sveučilišta u Zagrebu, 1998. is a big step forward in the quality of Geofoto d.o.o. for the Zagreb digital • Geofoto d.o.o.: Cikličko aerofotogra- satellite signal reception comparing ot- orthophoto, and the Chair of state sur- metrijsko snimanje Zagreba, 2006. her devices without the mentioned ar- vey of the Faculty of Geodesy at the • Solarić, M.: Povijesni pregled smanji- chitecture. According to the meaning University of Zagreb for the GPS RTK vanja dimenzija GPS-prijamnika, Geo- of absolute positioning, i.e. it’s special receiver. Without their help this article detski list 2006, br. 3, 153-171 case – navigation, the gained accuracy couldn’t be accomplished. • URL-1: http://www.magellangps. of the position is acceptable and so- Special thanks go to our dear friend com (28.03.2007.) metimes is very “optimistic”. EGNOS and colleague Mario Kranjec, cand. • URL-2: http://gpstracklog.typepad. correction is significat only in a conve- dipl. ing. geod. for his help and sug- com (28.03.2007.) nient area of quality LoS so its inclusi- gestions through the use of GPS RTK on in urban areas isn’t essential. receiver and in writing of this paper. Picture from the article headline: Gar- Also, a big “thank you” goes to min GPSMap 60CS and 60CSx devi- Authors would like to mark that prof.dr.sc. Miljenko Solarić for his big ces at point A. F. Biljecki, M. Pavasović: Analysis of the advantage using SiRFStarIII architecture for navigational purposes in urban areas - Ekscentar 2007, No.9 Table 5-3. Elements dy, dx i D statistics for the point B (Garmin GPSMap 60CS) in metres

Table 5-4. Elements dy, dx i D statistics for the point B (Garmin GPSMap 60CSx) in metres [m] F. Biljecki, M. Pavasović: Analysis of the advantage using SiRFStarIII architecture for navigational purposes in urban areas - Ekscentar 2007, No.9

Histogram 1. Standard deviations of the elements dy, dx i D of the analysis on both points showed in metres [m]