Total Electron Content (TEC) And Estimation Of Positioning .

Proceedings of the World Congress on Engineering 2010 Vol IWCE 2010, June 30 - July 2, 2010, London, U.K.Total Electron Content (TEC) and Estimation ofPositioning Error Using Malaysia DataY. Norsuzila, M. Abdullah, M. Ismail, M. Ibrahim, Z. Zakaria Abstract— This paper studied the TEC value for Malaysiaregions, based on location of the receivers (latitude, longitude,height). The 13 location of GPS receiver stations across east andwest Malaysia were chosen and their TEC values werecompared. The determination of the TEC value in ionosphere isdone using leveling process. In the process, the error translatedfrom code-delay to the carrier-phase is assessed to reducecarrier phase ambiguities from the data. The positioning errorcan be calculated as one unit of TEC introduces a range error ofapproximately 0.16 meters at the L1 (1.6 GHz) frequency ofGPS. From the results, the calculated TEC range errors werefrom -3.1 meters to 7.2 meters at different receiver locations.Index Terms— GPS, ionosphere, leveling process, Totalelectron content (TEC), PositioningI. INTRODUCTIONGlobal Positioning System (GPS) is space-based radionavigation system operated by the US Air Force for theUnited States Government. GPS is a satellite-basednavigation system made up of a network of 24 satellites,which are distributed in six orbital planes around the globe atan altitude of about 20,162.61 km. The total signal for eachsatellite in GPS comprises of two transmission signals: the L1signal having carrier frequency of 1575.42 MHz and the L2signal of 1227.60 MHz [1]. After the turn off of the StandardPositioning Service (SPS) known as Selective Availability(SA) in May 2000, the ionosphere represents the largestsource of positioning error for GPS users [2]. In addition, theeffects of the ionosphere can cause range-rate errors for GPSsatellite users who require high accuracy measurements [3].The parameter of the ionosphere that affects the radio signalsthat propagate through this layer is known as Total ElectronContent (TEC). TEC is an integral of electron density alongthe path between the GPS satellite and the receiver.Y. Norsuzila is with the Faculty of Electrical Engineering, UniversitiTeknologi Mara, 40450 Shah Alam, Selangor, Malaysia. (correspondingauthor: 603-55436014, fax: 603-55435077, e-mail:norsuzilayaacob@yahoo.com.my).M. Abdullah, was with Universiti Kebangsaan Malaysia. She is now withthe Department of Electrical, Electronic and Systems, 43600 UKM Bangi,Selangor,Malaysia. (e-mail:mardina@eng.ukm.my).M. Ismail is with the Department of Electrical, Electronic and SystemsElectrical Engineering, Universiti Kebangsaan Malaysia, Selangor, Malaysia(e-mail:mahamod@eng.ukm.my).M. Ibrahim, was with Universiti Teknologi Mara. He is now with theDepartment of Communication Engineering, Universiti Teknologi Mara,40450 Shah Alam, Selangor, Malaysia. (e-mail::muhammad@salam.uitm.edu.my).Z. Zakaria is with the Faculty of Electrical Engineering, aysia.(e-mail:zainuddin@yahoo.com.my).ISBN: 978-988-17012-9-9ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)TEC is measured in a unit called TECU where 1 TECU 1 x1016 electrons/m2. Various methods have been developed forextracting TEC information from the amplitude and phase ofGPS signal [4]. Researches in Malaysia have also embarkedin TEC studies around the equatorial region. The studied onTEC parameters and comparing the data observed at FraserHill and compare result with the one at Parit Raja, Johor [5].The locations chosen were based on fountains effect andmagnetic equator to study the scintillation effect. Otherresearch on TEC distribution estimation using Bent, IRI andKlobucher modeling was conducted by [6] using GPS MASSstation network. Another study was done on Malaysia’s quietionosphere [7, 8].This paper describes the study of TEC over Malaysia’sionosphere base on geographical location. From thiscalculated TEC, range error can be estimated base on 1TECU approximately equivalent to 0.16m for the L1 GPSfrequency [9].II. METHODOLOGYA. Data CollectionData collection is carried out using GPS receiver networksfrom Malaysia Department of Survey and Mapping, JUPEMin a RINEX (Receiver Independent Exchange Format) dataformat. The GPS data (RTK and MASS) consists ofobservation and navigation data. A total of 13 sets of GPSdata were collected by receiver stations across east and westMalaysia on 8th of November 2005, with 24 hoursobservation in 15 seconds interval.GPS data from satellites include ephemeris data in thesignals they transmit to GPS receiver stations. Ephemerisdata is a set of parameter that can be used to accuratelycalculate the location of a GPS satellite at a particular point intime. It gives the description of the path taken by the satelliteas it orbits the Earth. Base on the location of a receiver; interms of latitude, longitude and height, the elevation anglebetween the receiver and the satellite is determined. The GPSstations are as identified by KUKP, TGPG, UTMJ, BANT,UPMS, KTPK, KUAN, IPOH, BKPL, USMP, RTPJ, GETIand ARAU. The flow chart for data processing using Matlabis as Fig. 1:WCE 2010

Proceedings of the World Congress on Engineering 2010 Vol IWCE 2010, June 30 - July 2, 2010, London, U.K.where P1 and P2 are the group path lengths, f1 and f 2are the corresponding high and low GPS frequencyrespectively. From (4), TEC can also be obtained by writingas:2 21 f1 f2 TEC P P40.3 f 2 f 2 2 1 12 (5)The TEC data derived from pseudorange measurementcontained large noise level as compare to the carrier phasemeasurement. In order to reduce the noise effect,pseudorange data is smoothed by using carrier phasemeasurement technique known as carrier phase levelingwritten as (6) [10].N12 P1i P2i L2i L1i }(6)N i 1 Fig. 1 Flow Process for TEC CalculationB. TEC calculation using levelling processEach satellite used for GPS positioning, transmits twocarrier electromagnetic waves in L-band frequencies; namelyL1 and L2. L1 frequency is 1575.42 MHz and L2 frequencyis 1227.60 MHz with a fundamental frequency (fo) of10.23MHz. (f1 154fo, f2 120fo). These carrier frequenciescontain codes modulation so that by comparing them to thereference code, we can measure the travelling time of thecodes and the carrier between the satellite and the receiver.Information from both, code and phase measurements of L1and L2, is used to study TEC with the absolute value of groupdelay as follows:I , g x80.6ds 2 N e ds2sfcomputed so as to minimize the root-sum-square differencebetween pseudorange and phase differential delay computedover the arc. The TEC observable for measurement i is thecarrier phase difference L2i L1i added to the bias B. Afteradjustment for the bias, the root-mean-square differencebetween the pseudorange and earlier phase delays isdominated by pseudorange noise [11].III. RESULTS AND DISCUSSIONTEC.Use of TEC in (1) yields two delays which can beexpressed as representation in units distance (2) orrepresentation in units of time (3)40.3TEC[ m] or2f(2)40.3TEC[ s ](3)2cfA dual-frequency GPS receiver measures the difference inionospheric delay between the L1 and L2 signal. The groupdelay for dual-frequency GPS receiver can be written as: t 11 P2 P1 40.3TEC f2 f2 21and P2i for f1 and f2 respectively, and the correspondingphase delays are L1i and L2i . The leveling bias, B is(1)where N e ds is define as the integral of electron density,I , g Let N be the number of measurements in aphase-connected arc of data for a given receiver and satellite.For each datum i, the pseudorange delay are denoted by P1i ISBN: 978-988-17012-9-9ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)The location of 13 GPS station which is used in thisresearch as illustrated in Table 1. Fig. 2 to 4 shows TECv forARAU, BANT and BKPL station. The elevation angle forreference station using PRN 1 is 38.5º and 47.5º wasdetermined at ARAU station from 1:00- 2:00 UTC, BANTstation is -3.7º and -3.6º using PRN 3 and BKPL station is-0.1º and -2.8º using PRN 1. Single Layer Model (SLM)model is used to convert slant TEC (TECs) to vertical TEC(TECv) as shown in Fig. 2 to Fig 4. The analysis at anequatorial region used SLM mapping function where thepeak altitude ranges from 350 to 500 km. The resultedvertical TEC are precise, accurate and without multipath,unless the multipath environment is really terrible, in whichcase a small, residual amount of multipath can even be seenin the differential carrier phase.(4)WCE 2010

Proceedings of the World Congress on Engineering 2010 Vol IWCE 2010, June 30 - July 2, 2010, London, U.K.for all the receiver stations can be compared. The results areplotted in Fig. 5 to 8 as below:50SLMMSLM48Plot of TEC value for station IPOH at 1 to 2 hour UT Plot of TEC value for station KTPK at 1 to 2 hour UT3448464442T E C v [T E C U ]32T E C v [T E C U ]TECv in [TECU]4630282611.11.21.31.41.51.6Time of day [hr]1.71.81.9424040384411.221.41.61.8Time of the day [hr]38211.21.41.61.8Time of the day [hr]2Plot of TEC value for station KUAN at 1 to 2 hour UT Plot of TEC value for station KUKP at 1 to 2 hour UT504Fig. 2 Vertical TEC for PRN 1 at ARAU station (1:00-2:00 UT)-3.2-3.33.5T E C v [T E C U ]T E C v [T E C U ]4846444232.5240-3.4TECv in [TECU]3811.2-3.51.41.61.8Time of the day [hr]1.5211.21.41.61.8Time of the day [hr]2-3.6Fig. 5 TEC at IPOH, KTPK, KUAN and KUKP stations at 1:00- 2:00UTC-3.7-3.811.11.21.31.41.51.6Time of day [hr]1.71.81.92Plot of TEC value for station ARAU at 1 to 2 hour UT48Fig. 3 Vertical TEC for PRN 3 at BANT (1:00-2:00 UT)46T E C v [T E C U ]-3.4443SLMMSLM-3.6422.5-3.840TECv in [TECU]23811.21.511.4 1.6 1.8Time of the day [hr]1.21.31.41.51.6Time of day [hr]1.71.81.92Vertical TEC for PRN 1 at BKPL (1:00-2:00 UT)22.5442421.54010ISBN: 978-988-17012-9-9ISSN: 2078-0958 (Print); ISSN: 2078-0966 (Online)1.41.6 1.8Time of the day [hr]Plot of TEC value for station GETI at 1 to 2 hour UT46380.5A. Calculate TEC base on stations locationThe levelling process was carried out at 13 GPS stations tostudy the effect of the location (latitude, longitude andheights) to the TEC values. The time parameter was set at1:00-2:00 UTC at all 13 stations, so that the calculated TEC1.2T E C v [T E C U ]1.11Plot of TEC value for station BKPL at 1 to 2 hour UT3T E C v [T E C U ]Fig. 41-420.50Plot of TEC value for station BANT at 1 to 2 hour UT-3.2T E C v [T E C U ]-3.911.21.4 1.6 1.8Time of the day [hr]23611.21.41.6 1.8Time of the day [hr]2Fig. 6 TEC at ARAU, BANT, BKPL and GETI stations (1:00- 2:00 UTC)WCE 2010