# Experimental Results for the Multipath Performance of Galileo Signals Transmitted by GIOVE-A Satellite

Authors: Andrew Simsky; David Mertens; Jean-Marie Sleewaegen; Martin Hollreiser; Massimo Crisci
Journal: International Journal of Navigation and Observation
 (2008)

---

## Abstract

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 foretaste of their performance in
real-life applications. Due to the use of advanced code
modulations, the ranging signals of Galileo
provide significant improvement of the multipath performance
as compared to current GPS. In this paper, we summarize the
results of about 1.5 years of observations using the
data from four antenna sites. The analysis of the elevation
dependence of averaged multipath errors and the multipath
time series for static data indicate significant suppression
of long-range multipath by the best Galileo codes. The E5AltBOC
signal is confirmed to be a multipath suppression champion
for all the data sets. According to the results of the observations,
the Galileo signals can be classified into 3 groups: high-performance
(E5AltBOC, L1A, E6A), medium-performance (E6BC, E5a, E5b)
and an L1BC signal, which has the lowest performance among
Galileo signals, but is still better than GPS-CA. The car
tests have demonstrated that for kinematic multipath the intersignal
differences are a lot less pronounced. The phase multipath
performance is also discussed.


---

## Body

## 1. Introduction

The first Galileo signals were transmitted on January 12, 2006, by the GIOVE-A
satellite. The first results for the tracking noise, signal power, and code
multipath performance of the live GIOVE-A signal obtained with the use of Septentrio’s GETR receiver have been
presented in October 2006 [1]. The overview of the on-going GIOVE-A signal
experimentation activity including results obtained at ESA, Septentrio NV, and
Alcatel Alenia Space can be found in [2].
Results of GIOVE-A signal testing have also been reported in [3, 4].The purpose of the current paper is to summarize the analysis of the
multipath performance of the GIOVE-A signal performed at Septentrio since the
beginning of the GIOVE-A mission up to the time of this publication that is
during the first one and half  years of
the satellite operation. Estimations of code multipath errors specific to
ranging signals are of particular interest to the user community because they
make significant contribution to the error budget of user applications. Unlike
many other error sources, multipath errors are essentially modulation-dependent,
hence there is a significant interest to improving multipath performance by
optimizing the signal definition.The ranging signals of Galileo are based on advanced code modulation
schemes, which are expected to provide significant improvement of the tracking
and multipath performance as compared to the current GPS. With the advent of GIOVE-A
these expectations have been verified. The first analysis [1]
has clearly shown the advantages of the Galileo signals in comparison to
current civilian signals of GPS (C/A and L2C). Further experience based on a
wider array of data has confirmed these results. In this paper, we summarize
the results from a number of data sets obtained at few antenna sites at
different geographic locations as well as the results of kinematic tests in
different environments.The GIOVE-A transmits ranging signals using all the currently foreseen
Galileo modulations: L1BC, L1A, E5a, E5b, E5 (or E5AltBOC), E6BC, and E6A [1, 5]. The GETR receiver has been custom-built by
Septentrio for the reception of GIOVE signals. The GETR is
capable of tracking all the transmitted modulations. The output of GETR
includes raw measurements, navigation bits and, optionally, correlation
function, and the samples of the RF signal at the intermediate frequency. The
signal acquisition in GETR is implemented with the use of a custom-tailored
fast acquisition unit [6].This paper is based on the analysis of GETR measurements (pseudoranges,
phases, Dopplers,C/N0). The emphasis is on the evaluation of the code
multipath performance, which is statistically characterized by the dependence
of the averaged multipath noise upon elevation. Our approach is to compare
empirical data for different sites and different signals and to classify the
signals in accordance with their average multipath performance.


## 2. Multipath Error Envelopes of Galileo  Code Modulations

Multipath error envelopes for GPS-CA and Galileo code modulations are
presented in Figure1. The error envelopes were computed using the standard
simulation of the tracking process of a straight code modulation superimposed
with a single reflected signal at a signal/multipath ratio of 6 dB. The
simulation of the tracking process involves the computation of the correlation
peaks of the original code and the code superimposed with multipath. The
bandwidth of RF filtering simulated by the algorithm was 40 MHz for all the
codes (55 MHz for E5AltBOC).Figure 1
Multipath error envelopes of GNSS code modulation at signal/multipath ratio of 6 dB:
GPS-C/A (magenta), Galileo L1BC (red), E6BC (green), E5a (blue), E5AltBOC (black).The results shown in Figure1 prove that the error envelopes for all the Galileo modulations
are well within the error envelope of the GPS-CA code. From the shape of the
error envelopes it is evident that the biggest advantage of Galileo modulations
is in the suppression of long-delay multipath. E5AltBOC is the only modulation,
which is expected to provide a high degree of suppression of a short-range
multipath as well. Exceptional multipath performance of E5AltBOC has been confirmed
in all the hitherto processed data.As for the other Galileo codes, their performance significantly depends
upon the typical spectra of multipath delays on a particular site. For example,
with a multipath delays of about 200 m, the L1BC multipath is expected to be
much lower than with GPS-CA, while with multipath delays of about 100 m, the
advantage of L1BC would be less pronounced. More precisely, the improvement of
Galileo BOC (1,1) with respect to BPSK(1) in the first 150 m is due to the
wider transmit bandwidth of Galileo than GPS, and not really due to the signal structure.
Indeed, if both Galileo and GPS had the same transmit BW, the multipath envelopes
would be similar for the first 150 m. The improvement due to signal
structure only comes between 150 and 300 m. All the Galileo codes
presented in the plot (except for E5AltBOC) are expected to have the same
multipath errors for delays shorter than 10 m, while for the delays between 50
and 100 m, E5a and E6BC modulations will have lower multipath errors than
L1BC.In practice, this means that relative performance of different code
modulations will be site-dependent. Of course, a modulation with a smaller
theoretical multipath error envelope is never expected to be worse (on average)
than the modulation with a bigger error envelope. However, the advantages of
more advanced code modulations will be more evident for the sites where long-delay
multipath is dominant but may disappear for the sites with significant
short-range mulitpath.All the above considerations directly apply only to static multipath. Code
multipath errors visible by the GNSS receiver in the movement, such as in car
tests, are subject to averaging at the level of tracking. Although these modulations,
which look better in Figure1 are still expected to show lower multipath errors in
the car test, it is hard to predict theoretically the measure of their
advantage. Our experimental results presented later in the paper show
relatively small differences between all the codes except for E5AltBOC which
still is a definite champion. The exceptional qualities of E5AltBOC are due to
its exceptionally high bandwidth. The tracking of E5AltBOC signal is
implemented in the GETR in accordance with the algorithm outlined in [7].


## 3. Calculation of Code Multipath Error  Based on Experimental Data

In our data analysis we computed code multipath using a well-known formula:(1)Mi=Pi−Φi+2λi2Φj−Φiλj2−λi2, where Mi is the estimate of the code multipath error on a pseudorange Pi, while Φi and Φj are the carrier phase observables (in units of length) for wavelengths λi and λj for the same satellite. j represents any band which is different than i.
With multifrequency Galileo signals, several values of j are possible, but the particular
selection of j does not significantly
affect the results. Formula (1) estimates a combination of multipath and
tracking noise, but the contribution of the tracking noise can be neglected in
most practical cases. For those signals which have pilot and data components,
we used the pilot component; the multipath is exactly the same for both
components but the tracking noise is independent. In (1), all the
effects of the movement are canceled out, hence it is applicable to both static
and kinematic data.


## 4. Static Data Collected in Leuven at  Septentrio Test Site

Most of the data presented in this paper have been collected at the
rooftop of the Septentrio office building. The wide-band GPS/Galileo antenna
provided by Space Engineering is shown in Figure2. The antenna
was mounted on the support structure and
was located higher than the other objects on the rooftop. However, the adjacent
building, which is seen at the photo, was still higher than the antenna and
acted as a source of reflected signals. Therefore, the short-range multipath at
our site is relatively low, but long-range multipath systematically affects our
data especially at low elevations when a satellite is rising or setting in the
direction opposite to the adjacent building, which was in fact quite typical
for GIOVE. The reflector building stretches in the North/South direction while
GIOVE-A would often (but not always) rise directly in the East. In fact,
day-dependent variations of multipath on our site were to a great extent due to
the variations of the direction of rising/setting of GIOVE-A with respect to
this reflecting wall.Figure 2
Space Engineering antenna mounted on the rooftop of the Septentrio office.Table1
shows the availability of the data for individual Galileo
signals in the Leuven data sets processed for this report. Although GIOVE-A is
able of transmitting all the experimental Galileo signals, it can transmit only
in two frequency bands at a time. In reality, the satellite is transmitting
either a combination of L1+E5a+E5b or a combination of L1+E6.Table 1
GIOVE-A signal components recorded during static tests in Leuven.
Data setMax elevation (deg)L1AL1BCE5AE5BE5AltBocE6AE6BC15 January 200644.8Xxxx16 January 200660.0Xxxxx08 March 200683.8Xxxx19 May 200665.3Xxxxx28 May 200684.4xxxx13 October 200675.6XxxxIn our analysis, we have joined all the processed data for averaged signal power
and code multipath errors as functions of elevation into one global array. This
data is presented in Figures3 and 4
for signal power and multipath, respectively. The
signal power matches the specifications of GSTB-V2, but it is not
representative of the final Galileo satellites, which will use different
transmitters. The drop of C/N0 at zenith for L1 signals is peculiar to the
Space Engineering antenna (see [1] for more details).Figure 3
Averaged signal power for all the tests in
Leuven.Figure 4
STD of code multipath for Galileo signals in
comparison to GPS-CA for the tests in Leuven.Figure4 contains standard deviations of code multipath for
10-degree bins of the elevation angle. Because the distance to the adjacent
building is about 100 m, typical delays of generated multipath are about 200 m
(for satellites rising or setting in the
direction opposite to the building), hence at low elevations L1BC and all the
other Galileo codes perform significantly better than GPS-C/A, where this
component of multipath is dominant. On the contrary, at high elevations where
short-range multipath is dominating, GPS-CA and 4 Galileo codes (L1-BC, E5a, E5b,
E6BC) have similar values of multipath errors.It
is also clear that at low elevations L1BC has the highest multipath compared to
other Galileo modulations. For the best modulations, such as E5AltBOC and L1A
the long-range multipath is almost completely suppressed, hence corresponding
curves in Figure4 are almost flat and show little increase at low
elevations. The Leuven site is well-suited to compare the suppression of
long-range multipath by different code modulations.Figure4 contains also the comparison of the multipath
performance of GPS-CA for 2 GPS receivers: GETR and PolaRx2. The difference
between the two (black curves) can be seen as a measure of difference between
the magnitude of multipath errors in two different receivers even if both do
not use multipath mitigation (PolaRx2 uses multipath mitigation by default but
it was turned off for this test). The difference is due to a combination of
receiver parameters such as front-end bandwidth and the type of a
discriminator.Comparison
of low-elevation and high-elevation multipaths is also presented in Table2. In this table, the Galileo modulations are grouped
into 3 groups: (i) high-performance group, which included E5AltBOC and the two
PRS modulations (L1A and E6A), (ii) medium-performance group, which includes E5a,
E5b, and E6BC, and (iii) low-performance group, which includes only L1BC and
has still better performance as compared to CPS-CA. The values of multipath
typical for the high-performance group are comparable to the values of tracking
noise for GPS-CA code and are for most of the tests nearly equal at low and
high elevations. This ranking of Galileo modulations in terms of multipath
performance is practically identical to the ranking obtained by computer
simulations in [8].Table 2
Multipath STD error (m) of Galileo signals as compared to GPS C/A code.
SignalChip rate,Jan. 15Jan. 16Mar. 08May. 19May. 28Oct. 13MHz>10°<10°>10°<10°>10°<10°>10°<10°>10°<10°>10°<10°GPS-C/A1.0230.601.19**********L1BC1.0230.360.930.400.550.390.410.380.860.380.930.340.79E5a10.23——0.550.62——0.330.510.250.51——E5b10.23——0.330.44——0.350.470.270.55——E6BC5.1150.280.28——0.270.42————0.300.67L1A2.55750.240.370.210.200.240.200.230.22——0.180.37E6A5.1150.240.22——0.230.17————0.230.58E5AltBOC10.23——0.250.23——0.200.300.140.23——Successful suppression of long-range multipath can also be directly observed in the time
series of multipath which we present here for some of the tests.In Figure5, the long-range multipath manifests itself in
high-frequency variations of multipath error near the right edge of the graph.
The same ranking of the Galileo modulations as in Table 2 can be observed; the
multipath errors of L1BC are the highest, while the multipath of E5AltBOC is
the lowest and the others fall in-between.Figure 5
Time series of code multipath for the test of May 19.The high-amplitude high-frequency variations of L1BC multipath shown in Figure5 and other similar plots correspond in fact to a
quasiperiod about 20 seconds. The zoomed plot of these variations is shown in Figure 6.
This plot clearly demonstrates how complete the
suppression of long-range multipath by the best Galileo modulations is. A
similar example, which includes E6A, is shown in Figure 7. In Figure 5
and other plots with time series, the part of the
plot with higher-amplitude and higher-frequency multipath always corresponds to
lower elevations, when the satellite is rising and setting. The variation of
multipath with elevation is illustrated by the multipath versus elevation plots
(Figure 4 and similar plots).Figure 6
Zoomed view of the high-elevation part of the previous plot.Figure 7
Similar example from another dataset which includes E6A.Although most of the Leuven data demonstrate similar behavior for all the 3 modulations
of the best group (E5, L1A, E6A), a more careful analysis gives the impression that
on average the magnitude of multipath errors increases in the sequence
E5AltBOC→L1A→E6A (which is quite in line with theoretical expectations),
and that the performance of E6A in some cases comes close to the values typical
for the “medium-performance” group. An example is presented in Figure 8. In fact, even in a summary plot (Figure 4), the E6A modulation shows visibly higher multipath
errors at low elevations than E5AltBOC+L1A. Some other tests presented later in
this paper also suggest that the best-performance group in fact includes only
E5AltBOC and L1A, while E6A gravitates to the medium-performance group. The
E5AltBOC, on the other hand, always shows an exceptionally stable performance;
its values of multipath errors are always the lowest as compared to other
modulations (see Figures 9, 10, and 11)Figure 8
An occasion of relatively high multipath errors by L1A/E6A.Figure 9
Multipath time series for May 28, 2006.Figure 10
Multipath time series for May 29, 2006.Figure 11
Multipath time series for January 16, 2006.


## 5. Antenna Site in Leuven with More Intensive  Short-Range Multipath

In order to investigate the effect of short-range multipath on Galileo signals, we
placed the Galileo antenna at another more multipath-rich position on the same
rooftop. This antenna position was located on the roof floor between the two
metal ventilation outlets (identical to these in the right bottom corner of Figure2). The antenna was located lower than many other
reflective objects on the rooftop, so it was expected to get more short-range
and middle-range multipath compared to the main site. The comparison of the two
sites is presented in Figure 12.Figure 12
Dotted line: tests of December 12 and 13 at a “multipath-rich” site. Broken line: average of tests during March–October, 2006, at the open-sky site.Figure12 shows that the multipath at the “multipath-rich”
location is indeed higher, the difference being particularly great for E5a. At
higher elevations the difference between the two sites is statistically
insignificant, which indicates that the local objects generate multipath predominantly
for low-elevation satellites. The multipath statistics for the two tests at the
“multipath-rich” site is presented in Table 3.Table 3
Multipath STD error (m) of Galileo signals for a more “multipath-rich” antenna site.
SignalChip rateDec. 12Dec. 13(MHz)>10°<10°>10°<10°L1BC1.0230.330.480.480.96E5a10.230.350.820.450.89E5b10.230.310.320.390.60L1A2.55750.230.200.280.36AltBOC10.230.160.300.210.22Table 4
Availability of GIOVE-A signals for the data sets from La Plata and Wuhan.
StationsDateMax. elevation (deg)L1AL1BCE5AE5BE5AltBoCE6AE6BCLa Plata10 & 11 Sep 200688.9xxxx5, 6 & 7 Apr 200787.7xxxxxWuhan18 & 19 Oct 200688.5xxxx20 & 21 Mar 200788.8xxxxThe time series of code multipath is presented in Figures13 and 14. It is evident that in both plots the multipath of
E5a is unusually high in comparison to all the other tests. The reason for this
strange behavior, different from all the other tests, is not clear.Figure 13
Time series for code multipath for December 12, 2006.Figure 14
Time series for code multipath for December 13, 2006.Figure 15
Multipath performance at the La Plata GESS site.Figure 16
Multipath performance at the Wuhan GESS site.


## 6. Static Data Collected at La Plata  and Wuhan GESS Sites

On top of processing the data collected by ourselves,
we also processed the GIOVE-A data collected at 2 other geographic locations
and available via GESS network: La Plata in Latin America and Wuhan in China.The analysis of multipath data from these two sites
confirms in broad terms the tendencies reported in the first section. In
particular, the superior performance of L1A and E5AltBOC has been confirmed.
However, some important differences must be mentioned. First of all, the E6BC
signal has high multipath comparable to L1BC (even higher than L1BC at low
elevations). Secondly, at the Wuhan site the elevation dependence is much less
pronounced than for the rest of the tests, probably due to the peculiarities of
local reflectors. Thirdly, the E6A signal shows worse performance than L1A and
E5AltBOC. At low elevations it still gravitates to the “high-performance
group,” while at higher elevations it shows about the same average multipath
errors than other signals.It is also quite clear that performance of GPS-CA on
both sites is about the same as the performance of L1BC. This can probably be
attributed to the prevalence of the multipath delays shorter than 150 m, in which
case both modulations are supposed to be about equivalent. The strange behavior
of GPS multipath at elevations less than 10 degrees for the La Plata site can
at least partly be explained by high masking angles from a wide range of
directions which leads to the lower than normal availability of GNSS signals
(see photo of the La Plata site, Figure25).Peculiarities of these sites can also be illustrated
by the time series of multipath errors (Figure17–20). Figure 17
illustrates relatively high multipath errors for
E6BC. Figures 19 and 20
show that the multipath for the Wuhan stations has
indeed atypical elevation dependence; at lower elevations the frequency of the
variations of multipath are increasing, while their amplitude remains the same.
The multipath results for different stations depend of course upon the
peculiarities of the multipath environment, in particular upon the presence of
reflectors oriented in a certain way relative to the GIOVE-A lines of sight at
its rising and setting.Figure 17
Time series of code multipath for La Plata, September
10, 2006.Figure 18
Time series of code multipath for La Plata, April 05, 2007.Figure 19
Time series of code multipath for Wuhan, October 18, 2006.Figure 20
Time series of code multipath for Wuhan, March 20, 2007.Figure21 demonstrates how different the multipath environments
at different stations indeed are. At La Plata station, the multipath is
generally the highest (almost a double at high elevations compared to Leuven),
while at Wuhan the multipath is not only higher in general, but also its
elevation dependence is flatter. Logically enough, the biggest differences can
be seen for L1BC, where multipath errors are the highest, while for E5AltBOC,
where multipath errors are significantly suppressed, the differences are almost
undetectable (Figure 22).Figure 21
Code multipath on L1BC at 4 locations. Here “Leuven-1” is our main open-sky antenna
site (Figure2). “Leuven-2” is more multipath-rich site located between
the ventilation outlets (see Section 5).Figure 22
Code multipath on E5AltBOC at 4 locations.
Here “Leuven-1” is our main open-sky antenna site (Figure2). “Leuven-2” is more multipath-rich site located between
the ventilation outlets (see Section 5).Investigation of the reasons for site-dependent
differences is beyond the scope of this paper. The photos of La Plata and Wuhan
antenna sites from public IGS sources show significant amount of local
reflectors. The La Plata site (Figure25) resembles a park and is surrounded with high trees
which are apparently responsible for high multipath and masking of the signal
at low elelvations. The Wuhan site (Figure 26) is on the rooftop of a two-storeyed building and is
surrounded by remote trees which are likely to serve as a source of scattered
signals. The multipath caused by scattered signals is expected to be present at
all the elevations and may be responsible for the flatter elevation dependence
of multipath at Wuhan (Figure 21). It should also be mentioned that at the La Plata
site the signal power is systematically lower than in Leuven and Wuhan (cf.
Figures 3, 23, and 24).Figure 23
Signal power at La Plata station. It is systematically lower as compared to Leuven
(Figure3) and Wuhan (Figure 24).Figure 24
Signal power at Wuhan station.Figure 25
Environment at the La Plata antenna site.Figure 26
Environment at the Wuhan antenna site.The total statistics of multipath for all the
processed data for La Plata and Wuhan is presented in Table5. The averages presented in this table illustrate the
same tendencies already visible from the plots, in particular the low elevation
dependence of multipath at the Wuhan site.Table 5
Multipath 1-sigma error (m) for the data sets of La Plata/Wuhan.
SignalChipLa PlataWuhanrateSep. 10Apr. 05Oct. 18Mar. 20(MHz)>10°<10°>10°<10°>10°<10°>10°<10°L1BC1.0230.56—0.621.060.530.660.540.66E5a10.23——0.460.94——0.420.52E5b10.23——0.460.86——0.460.48E6BC5.1150.59———0.500.49——L1A2.55750.28—0.280.470.290.16——E6A5.1150.38———0.390.28——AltBOC10.23——0.210.22——0.210.19


## 7. Kinematic Tests

The code multipath errors for kinematic tests with
GIOVE-A signals where first presented in [1]. The kinematic multipath is very different from a
static one in that its variations are dominated by fast changes of the
reflectors due to movement, and that a high degree of multipath suppression is
achieved at the tracking level due to averaging of the rapid oscillations of
in-phase/out-of-phase multipath. The time series of kinematic multipath consists
of random structure-less variations, where the differences between the
modulations are much less pronounced that in the static case.In this paper, we present the results of two car tests
performed in different environments: rural and urban. Separate statistics was
computed for the periods when the car was static and the periods when the car
was moving. As shown in Table6, the signal availability during the tests was
different; during the urban test, L1 and E6 were being transmitted, while during
the rural test L1 and E5 signals were available.Table 6
Multipath statistic for car tests (m).
Rural staticRural movementUrban staticUrban movementGPS-CA1.190.23L1BC0.270.150.400.18E6BC0.500.22E5a0.200.16E5b0.260.15E5AltBOC0.100.11Although the static portions of the car tests still
show the same tendencies as the data collected on the rooftop, the data
collected during the movement demonstrates much smaller values of multipath
errors, much smaller advantage of Galileo modulations as compared to GPS-C/A,
and much smaller differences between Galileo modulations. The differences
between static and kinematic multipath can be clearly seen in Figures27 and
28. Figure 29
illustrates that code multipath during the urban test was generally somewhat higher due to obviously
greater amount of reflectors in the urban environment.Figure 27
Code multipath during the rural car test.Figure 28
Zoom into one of the static portions of the rural test.Figure 29
Code multipath during the urban test.In particular, the results of the car tests suggest
that the replacement of L1 BOC(1,1) with MBOC will not have any significant
impact on the multipath performance in the automotive environment. Indeed, MBOC
is expected to show the performance intermediate between L1BC and E6BC, while
both modulations have about the same intensity of kinematic multipath according
to Table6.According to theory, MBOC is expected to outperform
BOC(1,1) for static scenarios, possibly bringing greater improvement relative
to BOC(1,1) than the improvement of the BOC(1,1) relative to BPSK(1). This is
to be verified after actual implementation of MBOC.


## 8. Phase Multipath

Simultaneous availability of 3 frequencies allows direct
evaluation of phase multipath from triple-frequency iono-free geometry-free
combinations of phase measurements [1, 9]:(2)MΦ123=λ32(Φ1−Φ2)+λ22(Φ3−Φ1)+λ12(Φ2−Φ3). This formula is a linear
combination of three geometry-free observables(Φi−Φj),
which all contain ionosphere delays. As it has been shown in [9], in (2) ionosphere delays cancel out. M123 contains a mix of phase multipath and tracking errors for the same satellite on
3 different frequencies and can be used as a global indicator of phase
multipath severity. It can be used in particular to study elevation dependence
and site dependence of phase multipath.In this paper, we used
one particular combination (E5a − 1.128*E5b + 0.128*L1BC) as an indicator
of phase multipath.   Figure 30 contains elevation dependence of this phase multipath
indicator for all the static sites covered in this paper. The elevation
dependence shows significant variability and does not indicate with certainty
any differences between the sites.Figure 30
Phase multipath at 4 locations. Here “Leuven-1” is our main open-sky antenna site
(Figure2). “Leuven-2” is a more multipath-rich site located between
the ventilation outlets (see Section 7).The nature of phase
multipath is in general quite different from code multipath. In particular,
phase multipath for different signals is not expected to show significant differences.
It has already been demonstrated in [1] that the phase tracking noise is identical for all
the GIOVE-A signals. Phase multipath is generally much less studied than code
multipath, so it is difficult to predict what the behavior of phase multipath
should be. The time series of our phase multipath indicator is presented in
Figure 31.Figure 31
Phase multipath indicator (triple-frequency phase combination of L1BC, E5a, and E5b) at Leuven site.The elevation dependence of phase multipath is
generally flatter and more variable that with the code multipath. There exist
significant long-term variations which have impact on the statistics in a way
of making it less stable. The pattern of phase multipath is quite different
between the sites (cf. Figures31 and 32).Figure 32
Phase multipath indicator (triple-frequency phase combination of L1BC, E5a, and E5b) at Wuhan.


## 9. Conclusions

Field experience with GIOVE-A signals has demonstrated
stable reception in a variety of external conditions and confirmed the theoretical
expectations as to superior multipath rejection of wide-band Galileo
modulations. Multipath performance results for static and kinematic tests have been reported.Comparison of the static data from different sites
shows significant variability of the multipath performance for most of the
Galileo signals. It seems that only the behavior of E5AltBOC is truly stable
and repeatable for all the tests; in all the tests, the E5AltBOC demonstrates
the highest multipath suppression as compared to other signals and very low magnitude
of average multipath errors, down to the values about 0.2 m.For all the other signals, we can talk about the
tendencies which manifest themselves on average, but with significant site-dependent
variations. The most important of these tendencies is the classification of all
the modulations in groups shown in Table2. According to this classification, E6A+L1A+E5AltBOC
form the group of high-performance signals, while the E5a, E5b, and E6BC
signals belong to the medium group, the performance of L1BC is the lowest.This classification, which agrees with theoretical
predictions and computer simulations, can be accepted as a general rule,
although in some tests E6BC and E5a,b show practically the same performance as
L1BC, and E6A in the others shows performance more typical to the medium group.The relationship between the signals for individual
sites depends upon the spectra of multipath delays. For the Leuven site where
the long-range multipath with a delay of about 200 m is clearly dominant, the
wide-band signals with essential suppression of long-range multipath component
show clearly superior performance. In other cases, when short-range multipath
is dominant, the advantage of more advanced codes will be less pronounced.The future research may take an approach of looking in
more detail into specific multipath conditions and types of reflectors at
different sites. Accumulation of much greater statistic may help to formulate
the trends in a more reliable and detailed manner and make a classification of
sites in accordance with the multipath behavior.The kinematic tests have demonstrated a lot of smaller
values of multipath errors and a much less significant dependence of multipath
upon code modulations. This means in particular that any further changes in the
signal definition of Galileo signals are not likely to bring any significant
improvement to dynamic applications, such as automotive, although modulation
changes may have impact on static applications.In this paper, the phase multipath statistics for GIOVE-A signals is
presented for the first time.



---

*Source: 416380-2008-07-13.xml*