International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 097...
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A comparative study on spectral analysis of global navigation satellite systems

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A comparative study on spectral analysis of global navigation satellite systems

  1. 1. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME390A COMPARATIVE STUDY ON SPECTRAL ANALYSIS OF GLOBALNAVIGATION SATELLITE SYSTEMSBoney Bose Kunnel [1], Susan Abraham [2], R Kumar [3],Swarna Ravindra Babu[4][1][2][3]SRM University, Chennai, India -603203[4]Samsung, Bengaluru, IndiaABSTRACTThe introduction of new Global and regional navigation satellite systems hassimplified land, air and marine navigation. However, use of similar spectral bands wouldcause notable effects such as interference, noise and performance issues on existingnavigation satellite systems. Apart from inter system and intra system interference issuesamong these systems, researchers are more interested in making use of all these systems in asingle receiver to improve positioning accuracy. By analyzing the spectrums and modulationsof each of these Global Navigation Satellite Systems, it is possible to answer many queries oninteroperability and compatibility among them. Navigation satellite systems such as GPS,Galileo, GLONASS and Compass are considered in this paper. These systems are comparedand effect of one system on another is studied using spectral analysis.Keywords: Compass, Galileo, GLONASS, GPS, Spectral analysis.1. INTRODUCTIONMan’s desire to explore unknown places led to inventions like the magnetic compass.A Global Navigation Satellite System (GNSS) is a modern day compass, which uses artificialsatellites to find the user position anywhere on earth. Though 3D positioning can be achievedby using four satellites, greater number of satellites will drastically improve accuracy. Withavailability of multiple Global and regional navigation systems, even if one satellite system isunavailable, user can make use of another system if both navigation systems offerinteroperability. The main requirements for interoperability are common or very close centrefrequency, similar kind/family of modulations and signal characteristics, common geodeticINTERNATIONAL JOURNAL OF ELECTRONICS ANDCOMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)ISSN 0976 – 6464(Print)ISSN 0976 – 6472(Online)Volume 4, Issue 2, March – April, 2013, pp. 390-398© IAEME: www.iaeme.com/ijecet.aspJournal Impact Factor (2013): 5.8896 (Calculated by GISI)www.jifactor.comIJECET© I A E M E
  2. 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME391and time references. [1]. Thus availability of two or more satellite navigation systems furtheraids positioning accuracy.Global Positioning System (GPS), managed by the United States DOD is the mostpopular satellite navigation system. The user receiver can be fixed absolutely anywhere likevehicles, mobile phones or even in spectacles as in those developed by Google recently. GPSL1 C/A and L5 are considered in this paper. Galileo, managed by the European Union isanother active GNSS that provides highly accurate and guaranteed positioning services.Galileo E1 and E5 signals are considered here. Another global navigation satellite system isGLONASS of Russia which uses Frequency Division Multiple Access (FDMA) technique inboth L1 and L2 sub-bands [3]. Compass or Beidou Navigation Satellite system (BDS) ofChina, when fully deployed will consist of five Geostationary Earth Orbit (GEO) satellites,twenty-seven Medium Earth Orbit (MEO) satellites and three Inclined GeosynchronousSatellite Orbit (IGSO) satellites [16].The remainder of the paper is organized as follows: Section 2 describes various constellationsconsidered for spectral analysis where as section 3 explain the numerical results and figures.The paper concludes with section 4.2. GNSS CONSTELLATIONS2.1.1 GLOBAL POSITIONING SYSTEM(GPS)The United States GPS consist of 24 satellite constellation in 6 orbital planes, inclinedat 55 degrees with respect to equator. GPS signal basically consist of PRN codes and ranginginformation.2.1.2 GPS L1 C/AGPS L1 uses Coarse/Acquisition (C/A) code which is Bi-phase modulated at a chiprate of 1.023MHz. The C/A code is 1ms long and belongs to the family of Gold codes,generated using shift registers where position of feedback determine pattern of sequence. Thenavigation data rate used is 50Hz and is 20 ms long, thus requiring 20 C/A codes for eachdata bit [1,2].2.1.3 GPS L5GPS L5 uses two codes namely in phase (I5) code and quadrature phase (Q5) code at10.23Mcps. Each code is modulo-2 sum of two sub sequences XA and XB where, XA & XBare 8190 & 8191 length codes respectively that are restarted to run for 1 ms duration (lengthof 10230 chips). Data is 50 bps which is half rate convolution encoded. QPSK modulation isperformed onto an 1176.45MHz carrier [4]. The GPS L5 generation is shown in Fig 1.2.1.4 GALILEO2.1.5 Galileo E1The E1 signal is composed of three channels A, B and C. E1-A is a restricted accesssignal, E1-B is the data signal whereas E1-C is the data-free signal (pilot signal). Galileo E1uses Binary Offset Carrier modulation. A basic understanding of BOC modulation is shownin Fig 2.
  3. 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, MarchrepresenteisBOCE1 signal has a Code length of 4092 with chipping rate ofSecondary code on pilot with length 25 chips increases repetition interval to 100. Very longcode is used to reduce effects of cross correlation from other satellites [6, 8]. Galileo E1shares same frequency as GPS L1 which2.1.6 Galileo E5Galileo E5 uses an alternative of BOC modulation, Alternate Binary Offset Carrierrepresented as AltBOC(15, 10). The difference from traditional BOC is that the subfunction is a complex rectangular exponential that onlycentre frequency. Two PRN codes are modulated on orthogonal components. The two inphase components E5aI and E5bI carry the data modulation whereas the two quadraturecomponents E5aQ and E5bQ are pilot signals. The daconvolution encoding scheme. The primary codes used in the Galileo E5 signal are 10230chips long. Apart from primary codes, shorter and slower secondary codes are used to obtaintiered codes. Tiered codes have very[7].International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME392Fig 1: GPS L5 generationFig 2: BOC Modulation)ff,ffBOC(:asdrepresenteocosFrequencyReferencefRateChipfFrequencySubcarrierfocs−−−E1 signal has a Code length of 4092 with chipping rate of 1.023MHz and repeats every 4ms.Secondary code on pilot with length 25 chips increases repetition interval to 100. Very longcode is used to reduce effects of cross correlation from other satellites [6, 8]. Galileo E1shares same frequency as GPS L1 which is 1575.42MHz.Galileo E5 uses an alternative of BOC modulation, Alternate Binary Offset Carrierrepresented as AltBOC(15, 10). The difference from traditional BOC is that the subfunction is a complex rectangular exponential that only shifts the spectrum up or down of thecentre frequency. Two PRN codes are modulated on orthogonal components. The two inphase components E5aI and E5bI carry the data modulation whereas the two quadraturecomponents E5aQ and E5bQ are pilot signals. The data rate used is 250sps with a half rateconvolution encoding scheme. The primary codes used in the Galileo E5 signal are 10230chips long. Apart from primary codes, shorter and slower secondary codes are used to obtaintiered codes. Tiered codes have very good auto-correlation and cross-correlation propertiesInternational Journal of Electronics and Communication Engineering & Technology (IJECET), ISSNApril (2013), © IAEME1.023MHz and repeats every 4ms.Secondary code on pilot with length 25 chips increases repetition interval to 100. Very longcode is used to reduce effects of cross correlation from other satellites [6, 8]. Galileo E1Galileo E5 uses an alternative of BOC modulation, Alternate Binary Offset Carrierrepresented as AltBOC(15, 10). The difference from traditional BOC is that the sub-carriershifts the spectrum up or down of thecentre frequency. Two PRN codes are modulated on orthogonal components. The two inphase components E5aI and E5bI carry the data modulation whereas the two quadratureta rate used is 250sps with a half rateconvolution encoding scheme. The primary codes used in the Galileo E5 signal are 10230chips long. Apart from primary codes, shorter and slower secondary codes are used to obtaincorrelation properties
  4. 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME3932.1.7 GLONASSGLONASS uses L1 and L2 bands. L1 sub-band carrier is modulated by modulo 2operations of PRN Ranging code, Navigation message and an auxiliary meander sequencewhereas L2 sub-band carrier is modulated by modulo 2 operations of PRN Ranging code andan auxiliary meander sequence. The PRN ranging code is generated as Maximum lengthsequence of shift register and has a period of 1 ms with a bit rate of 511 kbps. The digital datain GLONASS is transmitted at a rate of 50bps [3]. The nominal frequencies used inGLONASS L1 is defined as562.5KHz∆f1602MHz,fwhere,∆fK.ff101101k1==+=K is the Frequency number (channel)2.1.8 BEIDOU B1-IThe carrier frequency of Beidou B1 signal is 1561.098 MHz. The signal consists ofcarrier frequency, ranging code and Navigation message. The final B1 signal is obtained as asum of in-phase and quadrature phase components out of which China has released only B1-Isignal details. The PRN code used in B1I has a Chip rate of 2.046Mcps and length 2046chips[16]. QPSK modulation is used to generate the Beidou B1 Signal and can be represented asfollows.)2sin().().(.)2cos().().(.)(jojQjQQjojIjIIjtftDtCAtftDtCAtSϕϕ+Π++Π=(1)Where j is the satellite number, A is signal amplitude, C is the ranging code, D representsdata modulated on ranging code., of represents carrier frequency and jφ represents the initialcarrier phase.3. SIMULATION RESULTSAll simulations were performed in MATLAB. The spectrum of GPS L1 C/A andGalileo E1 are shown in Fig 3. Both the spectrums are centred at 1575.42MHz.Fig 3: Galileo E1 and GPS L1 Spectrums-4 -2 0 2 4-200-180-160-140-120-100-80-60-40Frequency [MHz]Power[dBW/Hz]Galileo BOC(1,1)GPS C/A
  5. 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME394As observed from Fig 4, the main lobe of GPS L1 has a bandwidth of around2.046 MHz and contains maximum power. The side lobes have a little power distributedamong them. Galileo E1 using BOC (1, 1) has a spectrum that splits the main lobe into twodistinct parts each with 2 MHz bandwidth. Due to this split, the interference caused byGalileo on GPS is negligible and both can co-exist on the same carrier frequency. Thespectrums of GPS L5 and Galileo E5 are plotted in Fig 4. Both these spectrums are centred at1176.45 MHz. The main lobe occupies a bandwidth of around 20 MHz and the differentmodulations used by the signals allow for interoperability. The power spectrum ofGLONASS L1 for K=-7 channel is shown in Fig 5.Fig 4: Galileo E5 and GPS L5 SpectrumsFig 5: GLONASS L1 power spectrumAs seen from Fig 5, the main lobe of GLONASS occupies a bandwidth ofaround 1 MHz. The relatively new constellation of Beidou B1 spectrum is shown in Fig 6.The main lobe occupies a bandwidth of 4 MHz. Since the carrier frequency of Beidou is1561.098 MHz, it causes negligible interference to its neighbours GPS L1 and Galileo E1also on the 15 GHz band.-4 -3 -2 -1 0 1 2 3 4x 107-240-220-200-180-160-140-120-100-80-60-40Frequency[Hz]Power[dBW/Hz]Galileo E5 and GPS L5 Power spectrum centred at 1176.45 MHzGalileo E5GPS L5-5 -4 -3 -2 -1 0 1 2 3 4x 106-240-220-200-180-160-140-120-100-80-60-40Power Spectrum of GLONASS L1 C/A CodeFrequency (Hz)Power(dBW/Hz)
  6. 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME395Fig 6: Power Spectrum of Beidou B1Correlations of various constellations are also shown below. Fig 7 shows auto correlations ofGPS L1 C/A and Galileo E1. BPSK modulation has limited ranging capability and requireshigh performance receivers. BOC provides better performance at frequencies away fromcentre frequency thus causing negligible interference effects on each other. Autocorrelationof GLONASS L1 and Beidou B1 are shown in fig 8.Fig 7: Autocorrelation of GPS L1 and Galileo E1-6 -4 -2 0 2 4 6x 106-320-300-280-260-240-220-200-180-160-140Power Spectrum of BEIDOU B1 SignalFrequency (Hz)Power(dBW/Hz)0 0.5 1 1.5 2 2.5 3 3.5 4 4.5x 1040246x 104 GPS L1 C/A CodeAutocorreleationLag0 2 4 6 8 10 12 14 16 18x 104-50510x 104 Galileo E1 BOC(1,1)AutocorreleationLag
  7. 7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME396Fig 8: Autocorrelation of GLONASS L1 and BEIDOU B1Fig 9: Normalized autocorrelations of Galileo E5 and GPS L5Fig 9 shows the normalized correlations of GPS L5 (I code and Q code) and Galileo E5AltBOC. The E5 has a sharp correlation peak that aids in tracking.-5 -4 -3 -2 -1 0 1 2 3 4 5x 1040123x 104LagsAutocorrelationGLONASS L1-200 -150 -100 -50 0 50 100 150 200050100LagsAutocorrelationBEIDOU B1-250 -200 -150 -100 -50 0 50 100 150 200 25000.10.20.30.40.50.60.70.80.91LagsAutocorrelationCorrelation plotsGalileo E5I5 code (GPS L5)Q5 code (GPS L5)
  8. 8. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME3974. CONCLUSIONThe increasing number of Global Navigation Satellite Systems is no longer a result ofresistance against American monopoly in Satellite Navigation. Various countries with Globaland regional navigation systems are trying to support one another to provide users withaccurate positioning information. The negative effects of inter system and intra systeminterferences are negligible compared to the advantages when these constellationsinteroperate. Once inter operability is achieved, with a single user receiver, a user can receiveand acquire signals of different constellations thus improving positioning accuracy to anunimaginable level. The GPS L1 and Galileo E1 can interoperate without causing muchinterference as BOC modulation splits the main lobe of the spectrum away from L1 centrefrequency. Similarly, Galileo E5 and GPS L5 can co-exist due to AltBOC modulation inGalileo. Thus even if different GNSS use similar carrier frequency, effect of one constellationon another is very less. The future works include receiving a particular frequency spectrumand perform acquisition to obtain Doppler measurements and trying to predict anotherfrequency spectrum.REFERENCES[1] W. Liu, C.R. Zhai, X.Q. Zhan, Y.H. Zhang, “Assessment and analysis of radio frequencycompatibility among several global navigation satellite systems’’, IET Radar, Sonar andNavigation, Volume 5, Issue 2, pp 128-136, September 2011.[2]James Bao-Yen, Tsui, Fundamentals of Global Positioning System Receivers-a softwareapproach, John Wiley & sons, second edition, 2005.[3] Global Navigation Satellite System ‘Interface Control Document’, Moscow, 1998.[4] Global Positioning System Directorate Systems Engineering and Integration InterfaceSpecification IS-GPS-705B Navstar GPS Space Segment/user segment L5 Interfaces,September 2011.[5] Francosis D Cote, Ioannis N. Psaromiligkos, Warren J. Gross, “GNSS Modulation: AUnified Statistical Description," IEEE Transactions on Aerospace and Electronic Systems,Vol. 47, Issue 3, pp 1814-1836, July 2011.[6] Kai Borre, ‘The E1 Galileo signal’, Aalborg University, Denmark, May 2009.[7] Nagaraj C Shivaramaiah, Andrew G Dempster, ‘The Galileo E5 AltBOC: Understandingthe Signal Structure’, International Global Navigation Satellite Systems Society Symposium,December 2009.[8] European GNSS Galileo ‘Signal In Space Interface Control Document.’[9] Safaa Dawoud, “GNSS principles and comparison’’, Potsdam University, Potsdam,Germany[10] Sophia Y. Zheng, “Signal acquisition and tracking for a software GPS receiver’’,Virginia Polytechnic Institute and State University, Blacksburg, Virginia, February 2005.[11] M.N.Venkatesh Babu.S, K.Lakshmi Narayana, , “Implementation of the ModernizedGPS Signals L2C, L5 and their Tracking Strategies’’, International Journal of EngineeringResearch and Applications (IJERA) , Vol. 2, Issue 4 , pp.2148-2152, July-August 2012.[12] Elliott D Kaplan, Christopher J Hegarty, Understanding GPS Principles andApplications, Artech House, INC., London, second edition, 2006.[13] Roger Canalda Pedros, ‘Galileo Signal Generation’, Department of Computer andElectronic Engineering, University of Limerick, April 2009.
  9. 9. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 2, March – April (2013), © IAEME398[14] Wallner, Rodriguez, Hein, Rushanan ‘Galileo E1 OS and GPS L1C Pseudo RandomNoise Codes - Requirements, Generation, Optimization and Comparison’, 20thInternationalTechnical Meeting of the Satellite Division of Institute of Navigation, pp 1549-1563,September 2007.[15] Hein, Goddet, Issler, Martin, Erhard, Rodriguez, Pratt ‘Status of Galileo Frequency andSignal Design’, Members of the Galileo Signal Task force, European Commission ,Brussels.[16] China Satellite Navigation Office, ‘Beidou Navigation Satellite System Interface ControlDocument Test Version’, December 2011.[17] Seema vora, Prof.Mukesh Tiwari and Prof.Jaikaran Singh, “Gsm Based RemoteMonitoring of Waste Gas at Locally Monitored Gui with the Implementation of ModbusProtocol and Location Identification Through GPS”, International Journal of AdvancedResearch in Engineering & Technology (IJARET), Volume 3, Issue 2, 2012, pp. 52 - 59,ISSN Print: 0976-6480, ISSN Online: 0976-6499.[18] Cyju Varghese, John Blesswin, Navitha Varghese and Sonia Singha,, “A Novel Approachfor Satellite Imagery Storage by Classifying the Non-Duplicate Regions”, Internationaljournal of Computer Engineering & Technology (IJCET), Volume 1, Issue 2, 2010,pp. 147 - 159, ISSN Print: 0976 – 6367, ISSN Online: 0976 – 6375.[19] B.V. Santhosh Krishna, AL.Vallikannu, Punithavathy Mohan and E.S.Karthik Kumar,“Satellite Image Classification using Wavelet Transform”, International journal of Electronicsand Communication Engineering &Technology (IJECET), Volume 1, Issue 1, 2010,pp. 117 - 124, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472.

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