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MULTIPATH OF GPS

MULTIPATH OF GPS

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Multipath of GPS refers to the phenomenon where GPS signals reflect off surfaces such as buildings or terrain before reaching the receiver, causing delays and inaccuracies in position calculations. This interference can lead to errors in determining the precise location, affecting the reliability of GPS-based navigation and positioning systems.
lightbulbAbout this topic
Multipath of GPS refers to the phenomenon where GPS signals reflect off surfaces such as buildings or terrain before reaching the receiver, causing delays and inaccuracies in position calculations. This interference can lead to errors in determining the precise location, affecting the reliability of GPS-based navigation and positioning systems.
Three and Four Carriers for Reliable Ambiguity Resolution
by Ulrich Vollath

2025, Proceedings of ENCGNSS

Trimble Terrasat as software and development engineer where he is working on high precision kinematic positioning using the future Galileo system. Dr. Ulrich Vollath received a Ph.D. in Computer Science from the Munich University of... more
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FAMCAR Approach for Efficient Multi-Carrier Ambiguity Estimation
by Knut Sauer

2024, Proceedings of ENC-GNSS

(TUM) in 1993. At Trimble Terrasat-where he is working on GPS algorithms since more than eleven years-he is responsible for the Algorithm Development team. His professional interest is focused on high-precision real-time kinematic... more
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Characterization of Compass M-1 signals
by peter teunissen

2023, GPS Solutions

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The MBOC Modulation: The Final Touch to the Galileo Frequency and Signal Plan
by Jose Angel Avila Rodriguez

2022, Navigation

After briefly recounting the evolu- tion of the Galileo Signal Plan in the past years, an overview of the techni- cal characteristics of all the baseline modulations has been provided by this article. Special attention was paid to the MBOC modulation that has recently been adopted as baseline for the Galileo El Open Service and GPS L1 Civil (L1C). Performance figures were also provided for MBOC, and we concluded the arti- [2] Avila-Rodriguez, J.-A., and G. W. Hein, S. Wallner, T. Schueler, E. Schueler, and M. Irsigler, “Revised Combined Galileo/GPS Frequency and Signal Performance Analysis,’ Proceedings of the [8] Hein, G.W., and J.-A. Avila-Rodriguez, L. Ries, L. Lestarquit, J.-L. Issler, J. Godet, and A. R. Pratt, Members of the Galileo Signal Task Force of the
TABLE 5. Galileo E1 signal technical characteristics A third important value-added safe- ty-of-life feature provided by Galileo is Safety of Life (SoL). The mono-fre- quency SoL will be provided by each of the two signals: El(B&C) and E5 dua freq -frequency SoL will be pro by the following dual-frequency signa combination: El(B&C) - E5b. It be noted that the Galileo safety- uencies are in the Aeronautica RadioNavigation Service (ARNS) allocated for GNSS, that is E5a, E5 Ha 4 El il. b. The vided has to of-life bands b, and [he integrity broadcast and the pro- tection provided in the ARNS bands are two important features of the GALILEO SoL.
It is interesting to note that the AltBOC(15,10) modulation is very simi- lar to two BPSK(10) signals shifted by 15 MHz to the left and right of the carrier frequency. Indeed, because a very wide The AltBOC multiplexing combines two signals (E5a ite constant enve [25]), which is t very wideband discussion of A G. W. Hein et a Frequency and S and E5b) in a compos- ope ((5], [16], [17] and hen injected through channel. For further tBOC in general, see lia “Status of Galileo ignal Design” and the papers by J. God et; M. Soellner and P. Erhard; and L. Ries et alia listed in addi- tional Resources. For more details on the AItBOC multiplexing refer to the paper E5 Main Signal Parameters. Table 1 summarizes the main technical charac- teristics of the Galileo E5 signals,
FIGURE 15 Average error for noncoherent early-late processing (NELP), BW=14 MHz (Ideal Brickwall filter), d=0.05 chips
The parameters P and Qare chosen such that the combined ower of the BOC(1,1) and the BOC(@,1) sub-carrier compo- TABLE 2. Galileo E6 signal technical charactertistics
A careful look at Galileo Signal Vali- dation Development reveals that all the signals, with a single exception, con- IGUAPE-NGOCE Nailsea COSINE LOAN). The square-root raised cosine (SRRC) with roll-off factor of a=0.22 was the first option for the Galileo Signal and Frequency Plan. Much time has passed since the proposal was originally made, but these first works deeply influenced the evolution of the following years. At the time when the first analyses on the future Galileo signals were made the current frequency band assignments had not taken place yet (For details, see Gali- leo Signal Validation Development by R. De Gaudenzi et alia, 2000, cited in the Additional Resources section). Thus, to limit the number of signal and frequency combinations, a set of seven candidate signal structures was identified, each of which could be independently assigned to a particular frequency.
In add possess “ tics. This MBOC wi ition, this signal should also mass market” characteris- has been fully achieved with here one can choose whether to make use of the low frequency com- ponent - BOC(1,1) - or also use the wideband BOC(6,1) part. The associ- ated code tracking noise (Figure 13), multipath envelopes (Figure 14), the running average error (which is another way of expressing the multipath enve- lopes, Figure 15), and root mean square
Some results on the performance of such solutions have been presented in the following papers: “Criteria for GNSS Multipath Performance Assessment” by M. Irsigler et alia and “Revised Com- bined Galileo/GPS Frequency and Signal ae OS ee eee eee ee ee ees J Agreement of June 2004: BOC(1,1) - BOC, (15, 2.5). After many years of fruit- ful cooperation, the member states of the European Union and the United States signed the agreement on Galileo and GPS satellite-based navigation on June 26, 2004. With it, a new world of possi- bilities in satellite navigation arose. The agreement fixed BOC(1,1) as the baseline for both Galileo and GPS future OS sig- nals, but at the same time it opened the door to future possible implementations under the following conditions: that they should have the current baseline as the
FIGURE 13 BOC(1,1), BOC(2,2), MBOC and BPSK(10) Cramer Rao Lower Bound, BW = 14 MHz
TABLE 3. E1 Safety of Life (SoL) CBOC chip- and sub-carrier rates The CBOC signal adopted for Galileo is based on the approach presented in the papers by G. W. Hein et alia, “MBOC: The New Optimized Spreading Modula- tion Recommended for GALILEO L1 OS and GPS LIC” and “A Candidate for the Galileo L1 OS Optimized Signal,” and the paper by J.-A. Avila-Rodriguez, “On Optimized signal Waveforms for GNSS.” This approach uses four-level spreading symbols formed by the weighted sum of BOC(1,1) and BOC(6,1) symbols on both data and pilot. A time domain rep- The phase points of the resulting CBOC constellation are shown in Fig- ure 10.
FIGURE 2 Galileo baseline after the Agreement of 2004 and Galileo was developing similar con- cepts with regards to signal modulation as GPS. The SRRC concept had been definitely abandoned and similar sig- nal structures as those of GPS were now under discussion for Galileo, too. Thus, the status was already in a very mature phase by 2002, and, until the final signal plan, few substantial changes would be required except in the E1/L1 band.
FIGURE 1 Spectra of GPS, Galileo, GLONASS and Compass Intended Signals in E1/L1
FIGURE 12 Spectra of Galileo Signals in E1 FIGURE 11 Normalized autocorrelation functions computed over +15 MHz bandwidth
FIGURE 14 Multipath Error Envelope for noncoherent early-late processinc (NELP), BW=14 MHz (Ideal filter), d=0.05 chips FIGURE 16 RMS bandwidth vs. two-sided receiver bandwidth (Ideal Brick- wall filter)
FIGURE 17 Reduction of the maximum C/NO Degradation due to Intersystem Interference when MBO is used instead of BOC(1,1) [19]. Minimum: 0.016 dB and maximum 0.023 dB MALS, LLL GEIS YO MEVEEOLL YO MALICE OM: DY NALS three mentioned ARNS Galileo bands, making the SoL Galileo or Galileo/GPS receivers, for instance, E5a, E5b, and El receivers. Using a probabilistic theory related to involuntary jamming of GNSS receivers (as discussed in the paper by J.-L. Issler et alia cited in Additional Resources), the probability of losing the dual frequency navigation function has been assessed and computed to be approximately 15,000 times lower in the case where a tri-frequency single : , system receiver is
nents equals 1/11 of the total power of (t) and e,, .(f), before application of eng E1-C any bandwidth limitation. This yields: resentation of a CBOC implementation is shown in Figure 7.
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Experimental Results for the Multipath Performance of Galileo Signals Transmitted by GIOVE-A Satellite
by Martin Hollreiser

2022, International Journal of Navigation and Observation

Analysis of GIOVE-A signals is an important part of the in-orbit validation phase of the Galileo program. GIOVE-A transmits the ranging signals using all the code modulations currently foreseen for the future Galileo and provides a... more
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Effects of Radio Frequency Interference on GNSS Receiver Output Masters Thesis
by Peter de Bakker

2022

Table 4-1: Comparison of INRIM results to simulator test results and theoretical predictions fo1 the LIBC-D signal
Figure F-17: OEM4 GPS L2 C/N
Figure F-13: OEM4 C/N) vs. signal power for constant J/S
Figure 4-12: Noise on the PR vs. the C/Ny on the E5a-P signal Figure 4-11: E6BC-P noise on PR 1 MHz GWN
Figure F-12: Legacy GPS L2 PR noise Figure F-11: Legacy GPS L2 C/No
Figure G-7: E5b-D C/Ny 1 MHz GWN
Figure 4-9: E6BC-P C/N) 1 MHz GWN
Figure G-1: E5a-P C/Ny 1 MHz GWN
Figure 2-2: Specified and effective antenna gain Figure 2-2 shows how the effective antenna gain can differ from the specified antenna gain as a result of one ground reflection multi-path ray (see Appendix B). The resulting antenna gain pattern varies much more with the elevation angle than the specified antenna gain. This means that the measured signal-to-noise ratio can change significantly when satellite elevation changes and this makes it more difficult to detect interference by looking at the signal-to-noise ratio.
aeerioaiar "a: ‘al When a BOC modulated signal and a BPSK modulated signal share a frequency band, the main lobes of both signals are separated by the subcarrier frequency of the BOC modulation. This can be seen in the | E6 band in Figure 2-1. An advantage of this approach is that both signals create less interference for each other. The modulation structure of the LIA and L1BC signals is quite complex because they share the frequency band with the GPS LI signals. Another advantage of a BOC modulation is the high multi-path tolerance. 2.2 Radio frequency interference
Figure 4-2: GETR C/N) vs. time Figure 4-1: PolaRx 2 C/Np vs. time
This paragraph describes the test setup that was used for the tests with the simulated GPS signals and the procedures that were used. The most important parts of this setup are the Spirent rack that produces the GPS signals and interference and the GPS receivers. The setup and procedures are described in greater detail with the help of Figure 3-1. A step by step list of actions, a link budget and the used receiver settings can be found in Appendix C. The GPS L1/L2 component of the Spirent rack as well as the interference generator is routed through the signal combiner of the Spirent rack to the calibrated RF1 out port. None of the other Spirent components generate signals during these tests. The signal power is increased by the Low Noise Amplifier with 28dB before the signal enters the four way splitter to make sure the signal power is comparable to a setup where a
Figure G-3: E5a-D C/N) 1 MHz GWN
Figure 4-15: Narrow band AM RFI on E5a