On Generalized Signal Waveforms for Satellite Navigation (797942), страница 12
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Zandbergen et al., 2004] and [R. Piriz et al., 2005].20Global Navigation Satellite SystemsThe European GNSS approach began with the European Geostationary Navigation OverlayService (EGNOS), which provides civil complements to GPS since mid-2005 in its initialoperation. From the very beginning, EGNOS was meant to be the bridge to Europe’s ownfull-fledged GNSS. Galileo’s first developmental satellites, GIOVE-A and GIOVE-B, werelaunched in December 2005 and April 2008 respectively. The Galileo In-Orbit Validation(IOV) phase is planned to start at the end of 2008 with four satellites and FOC should beachieved end of 2013.
Furthermore, diverse options are being considered to launch the Galileosatellites including Ariane 5, Proton, Soyuz or Zenit rockets.2.4.2Galileo Signal Plan2.4.2.1Galileo E1 BandThe E1 Open Service (OS) modulation receives the name of CBOC (Composite Binary OffsetCarrier) and is a particular implementation of MBOC (Multiplexed BOC)[J.-A.
Avila-Rodriguez et al., 2007]. This signal will be explained in detail in chapter 4.7.MBOC(6,1,1/11) is the result of multiplexing a wideband signal – BOC(6,1) – with anarrowband signal – BOC(1,1) – in such a way that 1/11 of the power is allocated, in average,to the high frequency component. This signal was the last one to be defined.The normalized (unit power) power spectral density, specified without the effect of bandlimiting filters and payload imperfections, is given byGMBOC ( 6,1,1 / 11) ( f ) =101GBOC (1,1) ( f ) + GBOC ( 6,1) ( f )1111(2.1)As shown in [Galileo SIS ICD, 2008], the generic view of the E1 Open Service signalgeneration can be depicted as follows [J.-A. Avila-Rodriguez et al., 2007]:Figure 2.9.
Modulation Scheme for the Galileo E1 OS Signals21Global Navigation Satellite SystemsThe whole transmitted Galileo E1 signal consists of the multiplexing of the three followingcomponents:•••The E1 Open Service Data channel eE1− B (t ) is generated from the I/NAV navigationdata stream DE1− B (t ) and the ranging code C E1− B (t ) , which are then modulated withthe sub-carriers scE1− BOC(1,1) (t ) and sc E1− BOC(6,1) (t ) of BOC(1,1) and BOC(6,1)respectively.The E1 Open Service Pilot channel eE1−C (t ) is generated from the ranging codeC E1−C (t ) , including its secondary code, which is then modulated with the sub-carriersscE1− BOC(1,1) (t ) and scE1− BOC(6,1) (t ) in anti-phase.The E1 PRS channel, also denoted as E1-A, which results from the modulo-twoaddition (respectively product if we consider the physical bipolar representation of thesignal) of the PRS data stream DPRS (t ) , the PRS code sequence CPRS (t ) and the subcarrier scPRS (t ) .
This sub-carrier consists of a BOC(15,2.5) in cosine phasing.For more details on the mathematical definition of the signal refer to chapter 7.7.8 where it isdescribed more in detail.Figure 2.10. Spectra of Galileo Signals in E1It is interesting to see how the spectra of the two systems described so far in E1/L1 overlap:Figure 2.11. Spectra of GPS and Galileo Signals in L122Global Navigation Satellite SystemsIt is important to note that the GPS L1C pilot and data signals are shown in quadrature in thefigure although according to [GPS ICD-800, 2006] the final phasing is still open. Furthermoreit is important to recall that for a long time the actual E1 band received the name of L1 bandin analogy with GPS and it was not until the publication of the [Galileo SIS ICD, 2008] thatL1 changed to the current E1.The E1 Open Service (OS) codes are, as well as the E6 CS codes that we will see later, alsorandom memory codes.
The plain number of choices to set the 0’s and 1’s for the whole codefamily is enormous and thus special algorithms have to be applied to generate random codesefficiently [J.-A. Avila-Rodriguez et al., 2007].Finally, the technical characteristics of all the Galileo signals in E1 can be summarized in thefollowing table:Table 2.6. Galileo E1 signal technical characteristicsGNSS SystemGalileoGalileoE1 OSService NameGalileoPRSCentre Frequency1575.42 MHzFrequency BandE1Access TechniqueCDMASpreadingmodulationCBOC(6,1,1/11)BOCcos(15,2.5)Sub-carrierfrequency1.023 MHz and 6.138(Two sub-carriers)15.345 MHzCode frequency1.023 MHz2.5575 MHzSignal ComponentDataPilotDataPrimary PRN Codelength4092N/ACode FamilyRandom CodesN/ASecondary PRN Codelength-25N/AData rate250 sps-N/AMinimum ReceivedPower [dBW]-157N/AElevation10°N/A23Global Navigation Satellite Systems2.4.2.2Galileo E6 BandAs shown in [Galileo SIS ICD, 2008], the transmitted Galileo E6 signal consists of thefollowing three components:•The E6 Commercial Service (CS) data channel: this modulating signal is the modulotwo addition of the E6 CS navigation data stream DCS (t ) with the CS data channelDcode sequence C CS(t ) .
This last one is already modulated by a BPSK(5) at 5.115 MHz.•The E6 Commercial Service (CS) pilot channel: this modulating signal is the moduloPtwo addition of the E6 CS pilot channel code C CS(t ) with a BPSK(5) at 5.115 MHz.•Finally, the E6 PRS channel is the modulo-two addition of the E6 PRS navigation datastream DPRS (t ) with the PRS channel code sequence C PRS (t ) at 5.115 MHz. Thissignal is further modulated by a sub-carrier of 10.23 MHz in cosine phasing.This is graphically shown as follows:Figure 2.12. Modulation Scheme for the Galileo E6 SignalsMoreover, the spectrum of the different E6 signals is shown to be as follows:Figure 2.13. Spectra of Galileo Signals in E624Global Navigation Satellite SystemsThe E6 Commercial Service (CS) codes are random codes [J. Winkel, 2006]. The main ideabehind is to generate a family of codes that fulfils the properties of randomness as well aspossible [J.-A.
Avila-Rodriguez et al., 2007]. The codes can be driven to fulfil specialproperties such as balance and weakened balance, where the probability of 0’s and 1’s mustnot be identical but within a well-defined range, or to realize the autocorrelation side-lobezero (ASZ) property. This latter property guarantees that the autocorrelation values of everycode correlate to zero with a delayed version of itself, shifted by one chip.Table 2.7.
Galileo E6 signal technical characteristicsGNSS SystemGalileoGalileoGalileoService NameE6 CS dataE6 CS pilotE6 PRSCentre Frequency1278.75 MHzFrequency BandE6Access TechniqueCDMASpreading modulationBPSK(5)BPSK(5)BOCcos(10,5)Sub-carrier frequency--10.23 MHz5.115 MHzCode frequencySignal ComponentDataPilotDataPrimary PRN Code length51155115N/AMemory codesN/ASecondary PRN Code length-100N/AData rate1000 sps-N/ACode FamilyMinimum Received Power [dBW]-155N/AElevation10°N/A2.4.2.3Galileo E5 BandThe different Galileo E5 signal components are generated according to the following[Galileo SIS ICD, 2008]:••••The E5a data channel: This channel is the modulo-two addition of the E5a navigationDdata stream DE 5 a (t ) with the E5a data channel PRN code sequence C E5a (t ) ofchipping rate 10.23 MHz.The E5a pilot channel: This channel is the E5a pilot channel PRN code sequenceC EP5 a (t ) of chipping rate 10.23 MHz.The E5b data channel: This channel is the modulo-two addition of the E5b navigationdata stream DE5b (t ) with the E5b data channel PRN code sequence C ED5b (t ) ofchipping rate 10.23 MHz.The E5b pilot channel: This channel is the E5b pilot channel PRN code sequenceC EP5b (t ) of chipping rate 10.23 MHz.25Global Navigation Satellite SystemsThe E5 modulation receives the name of AltBOC and is a modified version of a Binary OffsetCarrier (BOC) with code rate of 10.23 MHz and a sub-carrier frequency of 15.345 MHz.AltBOC(15,10) is a wideband signal that is transmitted at 1191.795 MHz.
More details on themathematical definition will be given in chapter 4.8.1. Next figure shows the Galileo E5signal modulation diagram:Figure 2.14. Modulation Scheme for the Galileo E5 SignalsThe power spectral density for the modified AltBOC(15,10) modulation with constantenvelope is shown to adopt the form:⎛ πf ⎞cos 2 ⎜⎜ ⎟⎟4f⎝ f c ⎠ ⎡cos 2 ⎛⎜ πf ⎞⎟ − cos⎛⎜ πf ⎞⎟ − 2 cos⎛⎜ πf ⎞⎟ cos⎛⎜ πf ⎞⎟ + 2⎤G AltBOC ( f ) = 2 c 2⎢⎜2f ⎟ ⎜4f ⎟ ⎥⎜2f ⎟⎜2f ⎟π fs ⎠s ⎠⎝ s⎠ ⎝ s⎠ ⎦⎝⎝2 ⎛ πf ⎞ ⎣⎟⎟cos ⎜⎜⎝ 2 fs ⎠(2.2)adopting the spectrum of the E5 signal modulation the following form:Figure 2.15.
Spectra of Galileo Signals in E5which was generated following the theory of chapter 4.8.1 and Appendix I. As we canrecognize from the figure above, the AltBOC(15,10) modulation is very similar to twoBPSK(10) signals shifted by 15 MHz to the left and right of the carrier frequency. Indeed,since to acquire all the main lobes of the modulation a very wide bandwidth is necessary,many receivers will operate correlating the AltBOC signal with a BPSK(10) replica.26Global Navigation Satellite SystemsTo have a better feeling about the overlapping between GPS and Galileo in E5, the next figureshows all the signals described so far for this band.Figure 2.16.
Spectra of GPS and Galileo Signals in E5The E5 primary codes can be generated with shift registers. Indeed, the outputs of two parallelregisters are modulo-two added to generate the primary codes. For more details on the startvalues of the primary codes and the corresponding secondary codes of each satellite, refer to[Galileo SIS ICD, 2008].
Finally, some details on the technical characteristics of the E5 signalare presented.Table 2.8. Galileo E5 signal technical characteristicsGNSS SystemGalileoGalileoGalileoGalileoService NameE5a dataE5a pilotE5b dataE5b pilotCentre Frequency1191.795 MHzFrequency BandE5Access TechniqueCDMASpreading modulationAltBOC(15,10)Sub-carrier frequency15.345 MHzCode frequency10.23 MHzSignal ComponentDataPilotDataPilotPrimary PRN Code length10230Code FamilyCombination and short-cycling of M-sequencesSecondary PRN Codelength201004100Data rate50 sps-250 sps-Minimum Received Power[dBW]-155 dBW-155 dBWElevation10°10°27Global Navigation Satellite Systems2.4.2.4Galileo ServicesThe Galileo signals will be assigned to provide the service categories which are summarizedin the following Table [J.-A.
Avila-Rodriguez et al., 2008].Table 2.9. Galileo Services mapped to signalsIdE5aE5bE6AE6B,CL6E1AE1B,COSSoLCSPRSSAR2.4.2.4.1 Open Service (OS)The single-frequency (SF) OS will be provided by each of the three signals: E1, E5a and E5b.The dual-frequency (DF) OS will be provided by the dual-frequency signal combinationsE1(B&C) - E5a and E1(B&C) - E5b2.4.2.4.2 Commercial Service (CS)The CS will be provided by the E6 (B&C) signal plus the OS signals – E1 (B&C), E5a andE5b.
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