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Discussion and technical support related to USRP, UHD, RFNoC
View all threadsRe: [USRP-users] Fwd: Angle of Arrival Measurements
I think it may have been a size of file issue. I made the image smaller. I
hope you can see it now.
On Mon, Apr 25, 2016 at 1:45 PM, Michael Duckett mathyomama@gmail.com
wrote:
I thought I attached the picture, but I may have forgotten or deleted that
draft. Let me know if you can't see the attachment on this response.
On Mon, Apr 25, 2016 at 12:22 PM, Michael Duckett mathyomama@gmail.com
wrote:
Hello Usrp Users,
Yesterday we did a couple of more tests on top of a parking garage. In an
attempt to improve our results, we extended the distance between the
antennas and tried our tests on higher ground as suggested (about 100ft
above the ground which is enough to be over the tree line in most of the
region). We had clear line of sight of two antennas, one tower and one on
top of a building. The first antenna was a translator stations and didn't
have very good strength
of signal even though we were in the presumed 60 dbm region according to
the fcc database. The second antenna was a college music station and it had
very good strength. But neither antenna seems to give the expected results.
The first antenna gave fairly erratic results. The range for each
orientation was very wide and usually never centered around the expected
result. The results for the second antenna were very tight in precision but
not in accuracy. We would hold the antenna array in the 0 degrees
orientation and get an angle of about -4 degrees and then rotate it to the
90 degree orientation and get around -8 degrees and then go back to the 0
degree orientation and get about -16 degrees.
So after seeing these results, we tried to transmit a frequency on
another B210 and find the angle based on that. The setup for this is in the
attached picture. Because our transmitted signal isn't very strong, in
order to get any decent results, we had to keep the transmitter very close
to the receiving antennas (within one wavelength of the antenna array). But
this ruins the angle of arrival approximation, so a lot of our results for
this were dubious. We did try the 0 degree orientation for which we should
still expect 0 degrees. We got mixed results which seemed to depend on the
height of the transmitter.
All in all the results were poor. We didn't get any out of range errors
(since it's built into the calculation). But the measured phase differences
for the angles didn't seem to scale with the increase in distance between
the receiving antennas. The majority of our results for the second antenna
were in the range -20 to 20 degrees no matter what the orientation was,
which means that the phase difference was also in that respective range. Is
it possible that the cables which connect the receiving antennas to the
B210 are also acting as antennas? If so, would insulating the cables with
some material help reduce that effect?
Sincerely,
Michael Duckett
On Wed, Apr 13, 2016 at 1:19 PM, Michael Duckett mathyomama@gmail.com
wrote:
Thank you everybody for the help and suggestions.
Yesterday we ran a few more tests near another radio tower. We were able
to extend the distance between the two antennas to about 90 cm using some
SMA cables that we had (we are getting more to give us the full distance we
want) and the frequency we were measuring was 104.9 MHz (wavelength is
about 285 cm). Unfortunately, we didn't have a rig set up for our B210 and
antennas, so we resorted to holding the B210 and antennas ourselves (will
this affect the signal received?). For the 0 degrees orientation, we were
getting phase offsets which were still out of range of the arcsin domain
even for the larger distance between the antennas. As we changed the
orientation, we noticed very small changes in the phase offset. The
majority of phase offsets were hanging around the pi/-pi boundary.
We then tried a few runs without the wires and instead tilted the
antennas outward so that the tips of the antennas were about 10 in. or 25.4
cm apart. This seemed to give us mixed results. My partner would hold the
device in one location at the 0 degree orientation and find phase
differences out of range of the arcsin domain and then move to another
location (about a step away) and find measurements which were at least in
the arcsin domain (the calculated angles ranged from 40 to 90 degrees, so
they were way off still). So the results for that experiment were spotty.
what antenna type are you using?
We are using an omni-directional rubber ducky antenna.
Do you do any higher order tracking before or after converting the phase
offset to an angle?
No, we are not. What do you mean by higher order tracking?
I'd really love to see multiple approaches at AoA being implemented,
that will definitely be an interesting use case for both SDR in general,
the USRP B210, and GNU Radio; I don't remember fully, but I think the
cel-kit account on github has a gr-specest repo, where you can find a few
examples of parametric spectrum estimators; amongst these MUSIC, an
algorithm actually originating in the world of direction detection, applied
to frequency estimation. It should be pretty straightforward to adapt the
algorithm to spatial problems – basically, you'd replace the estimated
signal autocovariance matrix by a antenna cross-correlation matrix.
The MUSIC algorithm seems like something we should definitely try out.
First, height is your friend. Don’t think that getting closer to the
station tower is better. The Tower probably is an array so you will not be
in the main beam anyway. Find the tallest building in the area and ask if
you can do your tests on their roof. A clear and open line of sight to the
tower is your goal here.
I think we are going to look for a tall place today or tomorrow and try
to get measurements from there.
Third, is the signal really entering the antenna? Or is it coupling to
the receiver. This can be easily tested by removing the antennas and
verifying that the signals drop by at least 10 dB. The more it drops, the
better your measurement. I would try and get at least 20 dB of isolation
for a good AoA measurement.
When we took the antennas off the SMA cables, there was a significant
drop in dB across the whole bandwidth (at least 20 dB). So it seems like
the signal was entering the antenna.
We are going to try to run more tests soon and hopefully with a
structure which will hold together our B210, cables, and antennas. Thanks
again for the support.
Sincerely,
Michael Duckett
On Tue, Apr 12, 2016 at 9:59 AM, Evan Merewether via USRP-users <
usrp-users@lists.ettus.com> wrote:
Hi Michael,
After a quick look, it seems that the methodology is sound, but you may
have problems with the way you are testing. Here are a few things you can
do to improve your measurements and test the performance.
First, height is your friend. Don’t think that getting closer to the
station tower is better. The Tower probably is an array so you will not be
in the main beam anyway. Find the tallest building in the area and ask if
you can do your tests on their roof. A clear and open line of sight to the
tower is your goal here.
Second, what else can the signal be bouncing off of? Is there a tall
water tower nearby? Could you be seeing the effects of reflected signals?
For this, again, height is your friend. By moving to a tall building, you
will minimize the number and strength of possible reflective surfaces.
Third, is the signal really entering the antenna? Or is it coupling to
the receiver. This can be easily tested by removing the antennas and
verifying that the signals drop by at least 10 dB. The more it drops, the
better your measurement. I would try and get at least 20 dB of isolation
for a good AoA measurement.
Evan
From: USRP-users [mailto:usrp-users-bounces@lists.ettus.com] *On
Behalf Of *Marcus D. Leech via USRP-users
Sent: Friday, April 08, 2016 3:17 PM
To: usrp-users@lists.ettus.com
Subject: Re: [USRP-users] Fwd: Angle of Arrival Measurements
On 04/08/2016 04:21 PM, Marcus Müller via USRP-users wrote:
Hi Michael,
So, I'm currently having a look at your flow graphs; they look sound to
me; especially the complex method (Which pretty much is equivalent to
picking one frequency bin from the FFT, if you add a sharp bandpass filter,
so that you only see one frequency) looks efficient. In fact, seeing both
approaches in one place reminded me of OFDM radar, where one actually takes
advantage of the
I use the complex-conjugate method in astronomical interferometry,
which is related to AoA, at least in an incidental sense--the emergence
of fringes is due to change in phase due to change in arrival angle
relative to the baseline between the antenna.
I also just use it for measuring and/or looking-for phase-drift between
two sources that should be phase-coherent.
time/frequency structure of the signal, and, more elementarily, the
fact that a shift in time domain is a modulation with an offset frequency
in frequency domain. Maybe [1] is a bit of a fun read to you; for the angle
of arrival problem (which for your approaches is really but a time offset
problem), things boil down to:
If [image: $x$]and [image: $y$]are the same signal, but [image:
$y(t)=x(t-\tau)$]is delayed by [image: $\tau$], then their Fourier
transforms [image: $X$]and [image: $Y$]are also the same but for the
latter [image: $Y=e^{-j2\pi\tau f} X$]being the first modulated by a
complex sinusoid. Estimating that sinusoid's frequency gives you the timing
offset; you can get the "pure" tone by just dividing [image: $\frac
YX$]. Looking at the discrete signal case, note that the frequency
resolution you can get depends on the DFT you're doing – i.e. longer
observation/larger DFT has a very positive effect on accuracy!
I'd really love to see multiple approaches at AoA being implemented,
that will definitely be an interesting use case for both SDR in general,
the USRP B210, and GNU Radio; I don't remember fully, but I think the
cel-kit account on github has a gr-specest repo, where you can find a few
examples of parametric spectrum estimators; amongst these MUSIC, an
algorithm actually originating in the world of direction detection, applied
to frequency estimation. It should be pretty straightforward to adapt the
algorithm to spatial problems – basically, you'd replace the estimated
signal autocovariance matrix by a antenna cross-correlation matrix.
Best regards,
Marcus
[1] Braun, Martin. Ofdm radar algorithms in mobile communication
networks. Diss. Karlsruhe, Karlsruher Institut für Technologie (KIT),
Diss., 2014, 2014.
http://d-nb.info/104838490X/34
On 08.04.2016 21:15, Michael Duckett via USRP-users wrote:
We are using two antennas on the same B210 and the distance between
them is 7cm (the distance between the two "TX/RX" ports). We understand
that this affects the measured phase difference and the further calculation
for the AOA. For future tests we may try to widen the distance between the
two antennas to half the wavelength (I think that would be around 1.3 to
1.7 m for FM radio station frequencies).
This distance between the two antennas brings us to the first question.
Because the distance between the antennas was small compared to half the
wavelength of the frequency, the range of valid phase differences was
shrunk, too. Most of the time when we were measuring we got phase
differences which were out of range of the valid region. In one spot close
to the tower, we positioned our antenna array at the 0 degree orientation
and phase difference values which corresponded to 60-70 degrees. In
another spot with the same orientation, we got phase difference values
which were out of range. So when we rotated the antenna array, it was
difficult to compared the AOA because most of the time that calculation
wasn't possible. But we can see noticeable changes in the phase difference
when rotating the array. But there doesn't seem to be an easily
decipherable pattern to the error.
We haven't been monitoring the time domain signal levels. We can try
that next time, as well.
On Fri, Apr 8, 2016 at 2:19 PM, Derek Kozel derek.kozel@ettus.com
wrote:
Hello Michael,
In addition to Alexander's good thoughts, are you monitoring the time
domain signal levels to ensure that the receive gain is set appropriately?
I see a QT GUI Sink (you may consider using the QT Frequency Sink), but it
would be worth while looking at a QT Time Sink as well to see if you are
clipping.
Regards,
Derek
On Fri, Apr 8, 2016 at 10:28 AM, Alexander Levedahl via USRP-users <
usrp-users@lists.ettus.com> wrote:
I do not have the ability to look at files right now so sorry if I am
asking questions that are answered in the files.
If you stand in one spot and rotate, is the error consistent? I.e., if
you are pointing the array right at it, it shows the AOA as 60-70. If you
change to pointing 30 degrees, does the AOA change to 90-100?
Are the results consistent across restarting the B210? Depending on
the answer to these questions, it may simply be a calibration problem.
I.e., when you turn it on there needs to be a calibration step.
Finally, how many antennas are you using 2 or are you using multiple
B210s? Is your antenna spaced appropriately for the operating frequency?
On Fri, Apr 8, 2016 at 12:51 PM, Michael Duckett via USRP-users <
usrp-users@lists.ettus.com> wrote:
Hello,
We are trying to measure the angle of arrival of FM using USRP B210. We
have run into some problems with the measurements and hence we are writing
this email. It would be nice if we can get some inputs from you on how to
fix this issue. We have used two methods for computing the phase
difference. We have used the first one most of the time. However, we are
posting both the methods here for you to have a look.
I have attached method 1 (phase_difference_probe.grc for probing and
phase_difference_view.grc which provides a nice GUI to look at) and method
2 (complex_method.grc). Method 1 is based on the following "paper":
We use these flow graphs and run them in another script which probes
the "top_block" to get 500 samples which are then averaged to produce one
data point.
We also attach a diagram (AoA_Figure.pdf) which shows a basic idea of
how the antennas and transmitter are setup and what the Angle of Arrival
(AoA) is, when it comes to our measurements.
We tried our code in two different situations. In our first test, our
transmitter was another B210 and we were in an open field. The frequency we
tried ranged from 200 MHz to 1.0 GHz and then 3 GHz and 4 GHz. Our Phase
difference and consequently our AoA measurement were not too far off, when
the antenna array was facing the transmitter (i.e. at an expected AoA of 0
degs). As we moved closer towards an AoA of +- 90 the accuracy of the
measurement fell off. But the consistency of the 500 samples was still
pretty good (we were getting a standard deviation under 0.10 radians).
For our second test, we tried to get the AoA from FM radio towers. We
got about 800-1000m away from a popular radio station tower and pointed the
antenna array at the tower (expecting an AoA of around 0 degs). But we got
measurements which were way off. We did this for a couple of different
spots but the measurements were all over the place (the standard deviation
for individual data points were pretty good but the measurement for the 0
deg position at one spot was different for another spot around the tower).
We did manege to get angle measurements at one point when we were about 800
meters from the tower. The expected angle was 0 but we got 60 - 70 degrees
as the measured angle. We also tried at other places, one was about 800 m
from the tower and the other about 1200m. But both these places were
problematic.
It would be nice to get your inputs on the flow graphs. What are your
thoughts about the flow graph? Do you see any glaring problems with the
flow graph or with the set up? If you have any more questions about the
setup then feel free to ask.
Most of the information about the setup that we are using are in the
attached grc files. Thanks a lot for all your time.
Sincerely,
Michael Duckett
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http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
Seeing these cars around you, multipath/fading comes to mind; how big
was the distance between RX and TX when testing with a separate B200,
and how far were the cars away? Receiving ~100MHz in the middle of big,
bent metal object is a bit like trying to find the right candle in a
maze of mirrors and lenses, I could imagine.
Best regards,
Marcus
On 04/25/2016 08:05 PM, Michael Duckett via USRP-users wrote:
I think it may have been a size of file issue. I made the image
smaller. I hope you can see it now.
On Mon, Apr 25, 2016 at 1:45 PM, Michael Duckett <mathyomama@gmail.com
mailto:mathyomama@gmail.com> wrote:
I thought I attached the picture, but I may have forgotten or
deleted that draft. Let me know if you can't see the attachment on
this response.
On Mon, Apr 25, 2016 at 12:22 PM, Michael Duckett
<mathyomama@gmail.com <mailto:mathyomama@gmail.com>> wrote:
Hello Usrp Users,
Yesterday we did a couple of more tests on top of a parking
garage. In an attempt to improve our results, we extended the
distance between the antennas and tried our tests on higher
ground as suggested (about 100ft above the ground which is
enough to be over the tree line in most of the region). We had
clear line of sight of two antennas, one tower and one on top
of a building. The first antenna was a translator stations and
didn't have very good strength
of signal even though we were in the presumed 60 dbm region
according to the fcc database. The second antenna was a
college music station and it had very good strength. But
neither antenna seems to give the expected results. The first
antenna gave fairly erratic results. The range for each
orientation was very wide and usually never centered around
the expected result. The results for the second antenna were
very tight in precision but not in accuracy. We would hold the
antenna array in the 0 degrees orientation and get an angle of
about -4 degrees and then rotate it to the 90 degree
orientation and get around -8 degrees and then go back to the
0 degree orientation and get about -16 degrees.
So after seeing these results, we tried to transmit a
frequency on another B210 and find the angle based on that.
The setup for this is in the attached picture. Because our
transmitted signal isn't very strong, in order to get any
decent results, we had to keep the transmitter very close to
the receiving antennas (within one wavelength of the antenna
array). But this ruins the angle of arrival approximation, so
a lot of our results for this were dubious. We did try the 0
degree orientation for which we should still expect 0 degrees.
We got mixed results which seemed to depend on the height of
the transmitter.
All in all the results were poor. We didn't get any out of
range errors (since it's built into the calculation). But the
measured phase differences for the angles didn't seem to scale
with the increase in distance between the receiving antennas.
The majority of our results for the second antenna were in the
range -20 to 20 degrees no matter what the orientation was,
which means that the phase difference was also in that
respective range. Is it possible that the cables which connect
the receiving antennas to the B210 are also acting as
antennas? If so, would insulating the cables with some
material help reduce that effect?
Sincerely,
Michael Duckett
On Wed, Apr 13, 2016 at 1:19 PM, Michael Duckett
<mathyomama@gmail.com <mailto:mathyomama@gmail.com>> wrote:
Thank you everybody for the help and suggestions.
Yesterday we ran a few more tests near another radio
tower. We were able to extend the distance between the two
antennas to about 90 cm using some SMA cables that we had
(we are getting more to give us the full distance we want)
and the frequency we were measuring was 104.9 MHz
(wavelength is about 285 cm). Unfortunately, we didn't
have a rig set up for our B210 and antennas, so we
resorted to holding the B210 and antennas ourselves (will
this affect the signal received?). For the 0 degrees
orientation, we were getting phase offsets which were
still out of range of the arcsin domain even for the
larger distance between the antennas. As we changed the
orientation, we noticed very small changes in the phase
offset. The majority of phase offsets were hanging around
the pi/-pi boundary.
We then tried a few runs without the wires and instead
tilted the antennas outward so that the tips of the
antennas were about 10 in. or 25.4 cm apart. This seemed
to give us mixed results. My partner would hold the device
in one location at the 0 degree orientation and find phase
differences out of range of the arcsin domain and then
move to another location (about a step away) and find
measurements which were at least in the arcsin domain (the
calculated angles ranged from 40 to 90 degrees, so they
were way off still). So the results for that experiment
were spotty.
what antenna type are you using?
We are using an omni-directional rubber ducky antenna.
Do you do any higher order tracking before or after
converting the phase offset to an angle?
No, we are not. What do you mean by higher order tracking?
I'd really love to see multiple approaches at AoA
being implemented, that will definitely be an
interesting use case for both SDR in general, the USRP
B210, and GNU Radio; I don't remember fully, but I
think the cel-kit account on github has a gr-specest
repo, where you can find a few examples of parametric
spectrum estimators; amongst these MUSIC, an algorithm
actually originating in the world of direction
detection, applied to frequency estimation. It should
be pretty straightforward to adapt the algorithm to
spatial problems – basically, you'd replace the
estimated signal autocovariance matrix by a antenna
cross-correlation matrix.
The MUSIC algorithm seems like something we should
definitely try out.
First, height is your friend. Don’t think that getting
closer to the station tower is better. The Tower
probably is an array so you will not be in the main
beam anyway. Find the tallest building in the area and
ask if you can do your tests on their roof. A clear
and open line of sight to the tower is your goal here.
I think we are going to look for a tall place today or
tomorrow and try to get measurements from there.
Third, is the signal really entering the antenna? Or
is it coupling to the receiver. This can be easily
tested by removing the antennas and verifying that the
signals drop by at least 10 dB. The more it drops,
the better your measurement. I would try and get at
least 20 dB of isolation for a good AoA measurement.
When we took the antennas off the SMA cables, there was a
significant drop in dB across the whole bandwidth (at
least 20 dB). So it seems like the signal was entering the
antenna.
We are going to try to run more tests soon and hopefully
with a structure which will hold together our B210,
cables, and antennas. Thanks again for the support.
Sincerely,
Michael Duckett
On Tue, Apr 12, 2016 at 9:59 AM, Evan Merewether via
USRP-users <usrp-users@lists.ettus.com
<mailto:usrp-users@lists.ettus.com>> wrote:
Hi Michael,
After a quick look, it seems that the methodology is
sound, but you may have problems with the way you are
testing. Here are a few things you can do to improve
your measurements and test the performance.
First, height is your friend. Don’t think that getting
closer to the station tower is better. The Tower
probably is an array so you will not be in the main
beam anyway. Find the tallest building in the area and
ask if you can do your tests on their roof. A clear
and open line of sight to the tower is your goal here.
Second, what else can the signal be bouncing off of?
Is there a tall water tower nearby? Could you be
seeing the effects of reflected signals? For this,
again, height is your friend. By moving to a tall
building, you will minimize the number and strength of
possible reflective surfaces.
Third, is the signal really entering the antenna? Or
is it coupling to the receiver. This can be easily
tested by removing the antennas and verifying that the
signals drop by at least 10 dB. The more it drops,
the better your measurement. I would try and get at
least 20 dB of isolation for a good AoA measurement.
Evan
*From:*USRP-users
[mailto:usrp-users-bounces@lists.ettus.com
<mailto:usrp-users-bounces@lists.ettus.com>] *On
Behalf Of *Marcus D. Leech via USRP-users
*Sent:* Friday, April 08, 2016 3:17 PM
*To:* usrp-users@lists.ettus.com
<mailto:usrp-users@lists.ettus.com>
*Subject:* Re: [USRP-users] Fwd: Angle of Arrival
Measurements
On 04/08/2016 04:21 PM, Marcus Müller via USRP-users
wrote:
Hi Michael,
So, I'm currently having a look at your flow
graphs; they look sound to me; especially the
complex method (Which pretty much is equivalent to
picking one frequency bin from the FFT, if you add
a sharp bandpass filter, so that you only see one
frequency) looks efficient. In fact, seeing both
approaches in one place reminded me of OFDM radar,
where one actually takes advantage of the
I use the complex-conjugate method in astronomical
interferometry, which is related to AoA, at least in
an incidental sense--the emergence
of fringes is due to change in phase due to change
in arrival angle relative to the baseline between the
antenna.
I also just use it for measuring and/or looking-for
phase-drift between two sources that should be
phase-coherent.
time/frequency structure of the signal, and, more
elementarily, the fact that a shift in time domain
is a modulation with an offset frequency in
frequency domain. Maybe [1] is a bit of a fun read
to you; for the angle of arrival problem (which
for your approaches is really but a time offset
problem), things boil down to:
If $x$and $y$are the same signal, but
$y(t)=x(t-\tau)$is delayed by $\tau$, then their
Fourier transforms $X$and $Y$are also the same but
for the latter $Y=e^{-j2\pi\tau f} X$being the
first modulated by a complex sinusoid. Estimating
that sinusoid's frequency gives you the timing
offset; you can get the "pure" tone by just
dividing $\frac YX$. Looking at the discrete
signal case, note that the frequency resolution
you can get depends on the DFT you're doing – i.e.
longer observation/larger DFT has a very positive
effect on accuracy!
I'd really love to see multiple approaches at AoA
being implemented, that will definitely be an
interesting use case for both SDR in general, the
USRP B210, and GNU Radio; I don't remember fully,
but I think the cel-kit account on github has a
gr-specest repo, where you can find a few examples
of parametric spectrum estimators; amongst these
MUSIC, an algorithm actually originating in the
world of direction detection, applied to frequency
estimation. It should be pretty straightforward to
adapt the algorithm to spatial problems –
basically, you'd replace the estimated signal
autocovariance matrix by a antenna
cross-correlation matrix.
Best regards,
Marcus
[1] Braun, Martin. /Ofdm radar algorithms in
mobile communication networks/. Diss. Karlsruhe,
Karlsruher Institut für Technologie (KIT), Diss.,
2014, 2014.
http://d-nb.info/104838490X/34
On 08.04.2016 21:15, Michael Duckett via
USRP-users wrote:
We are using two antennas on the same B210 and
the distance between them is 7cm (the distance
between the two "TX/RX" ports). We understand
that this affects the measured phase
difference and the further calculation for the
AOA. For future tests we may try to widen the
distance between the two antennas to half the
wavelength (I think that would be around 1.3
to 1.7 m for FM radio station frequencies).
This distance between the two antennas brings
us to the first question. Because the distance
between the antennas was small compared to
half the wavelength of the frequency, the
range of valid phase differences was shrunk,
too. Most of the time when we were measuring
we got phase differences which were out of
range of the valid region. In one spot close
to the tower, we positioned our antenna array
at the 0 degree orientation and phase
difference values which corresponded to 60-70
degrees. In another spot with the same
orientation, we got phase difference values
which were out of range. So when we rotated
the antenna array, it was difficult to
compared the AOA because most of the time that
calculation wasn't possible. But we can see
noticeable changes in the phase difference
when rotating the array. But there doesn't
seem to be an easily decipherable pattern to
the error.
We haven't been monitoring the time domain
signal levels. We can try that next time, as well.
On Fri, Apr 8, 2016 at 2:19 PM, Derek Kozel
<derek.kozel@ettus.com
<mailto:derek.kozel@ettus.com>> wrote:
Hello Michael,
In addition to Alexander's good thoughts,
are you monitoring the time domain signal
levels to ensure that the receive gain is
set appropriately? I see a QT GUI Sink
(you may consider using the QT Frequency
Sink), but it would be worth while looking
at a QT Time Sink as well to see if you
are clipping.
Regards,
Derek
On Fri, Apr 8, 2016 at 10:28 AM, Alexander
Levedahl via USRP-users
<usrp-users@lists.ettus.com
<mailto:usrp-users@lists.ettus.com>> wrote:
I do not have the ability to look at
files right now so sorry if I am
asking questions that are answered in
the files.
If you stand in one spot and rotate,
is the error consistent? I.e., if you
are pointing the array right at it, it
shows the AOA as 60-70. If you change
to pointing 30 degrees, does the AOA
change to 90-100?
Are the results consistent across
restarting the B210? Depending on the
answer to these questions, it may
simply be a calibration problem.
I.e., when you turn it on there needs
to be a calibration step.
Finally, how many antennas are you
using 2 or are you using multiple
B210s? Is your antenna spaced
appropriately for the operating frequency?
On Fri, Apr 8, 2016 at 12:51 PM,
Michael Duckett via USRP-users
<usrp-users@lists.ettus.com
<mailto:usrp-users@lists.ettus.com>>
wrote:
Hello,
We are trying to measure the angle
of arrival of FM using USRP B210.
We have run into some problems
with the measurements and hence we
are writing this email. It would
be nice if we can get some inputs
from you on how to fix this issue.
We have used two methods for
computing the phase difference. We
have used the first one most of
the time. However, we are posting
both the methods here for you to
have a look.
I have attached method 1
(phase_difference_probe.grc for
probing and
phase_difference_view.grc which
provides a nice GUI to look at)
and method 2 (complex_method.grc).
Method 1 is based on the following
"paper":
http://www.egr.msu.edu/classes/ece480/capstone/spring14/group02/docs/Application%20Note%20-%20Phase%20George%20Godby%20Team%202.pdf
We use these flow graphs and run
them in another script which
probes the "top_block" to get 500
samples which are then averaged to
produce one data point.
We also attach a diagram
(AoA_Figure.pdf) which shows a
basic idea of how the antennas and
transmitter are setup and what the
Angle of Arrival (AoA) is, when it
comes to our measurements.
We tried our code in two different
situations. In our first test, our
transmitter was another B210 and
we were in an open field. The
frequency we tried ranged from 200
MHz to 1.0 GHz and then 3 GHz and
4 GHz. Our Phase difference and
consequently our AoA measurement
were not too far off, when the
antenna array was facing the
transmitter (i.e. at an expected
AoA of 0 degs). As we moved closer
towards an AoA of +- 90 the
accuracy of the measurement fell
off. But the consistency of the
500 samples was still pretty good
(we were getting a standard
deviation under 0.10 radians).
For our second test, we tried to
get the AoA from FM radio towers.
We got about 800-1000m away from a
popular radio station tower and
pointed the antenna array at the
tower (expecting an AoA of around
0 degs). But we got measurements
which were way off. We did this
for a couple of different spots
but the measurements were all over
the place (the standard deviation
for individual data points were
pretty good but the measurement
for the 0 deg position at one spot
was different for another spot
around the tower). We did manege
to get angle measurements at one
point when we were about 800
meters from the tower. The
expected angle was 0 but we got 60
- 70 degrees as the measured
angle. We also tried at other
places, one was about 800 m from
the tower and the other about
1200m. But both these places were
problematic.
It would be nice to get your
inputs on the flow graphs. What
are your thoughts about the flow
graph? Do you see any glaring
problems with the flow graph or
with the set up? If you have any
more questions about the setup
then feel free to ask.
Most of the information about the
setup that we are using are in the
attached grc files. Thanks a lot
for all your time.
Sincerely,
Michael Duckett
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Perhaps as a test case, don't use over-the-air signals. Directly connect
the TX (using attenuation) to a splitter and to each RX port using equal
length cables. Measure the phase. This is the reference measurement. Then
add a cable (1 meter or less) to one of the paths and take a 2nd
measurement. Then move the cable to the other path and take a 3rd
measurement. Relative to the 1st measurement, the other two measurements
should be about 180 degrees different for a 1 meter cable (at 100 Mhz,
assuming speed of light is 3e8 * 0.67 in coax cable). One should be
positive, the other negative. If you have a shorter cable such as 1/2
meter, the phase difference should scale such that you are getting +/- 90
deg. If you are unable to get this to work correctly, then it might not
make sense trying over-the-air measurements.
Rob
On Mon, Apr 25, 2016 at 2:17 PM, Marcus Müller usrp-users@lists.ettus.com
wrote:
Seeing these cars around you, multipath/fading comes to mind; how big was
the distance between RX and TX when testing with a separate B200, and how
far were the cars away? Receiving ~100MHz in the middle of big, bent metal
object is a bit like trying to find the right candle in a maze of mirrors
and lenses, I could imagine.
Best regards,
Marcus
On 04/25/2016 08:05 PM, Michael Duckett via USRP-users wrote:
I think it may have been a size of file issue. I made the image smaller. I
hope you can see it now.
On Mon, Apr 25, 2016 at 1:45 PM, Michael Duckett mathyomama@gmail.com
wrote:
I thought I attached the picture, but I may have forgotten or deleted
that draft. Let me know if you can't see the attachment on this response.
On Mon, Apr 25, 2016 at 12:22 PM, Michael Duckett <
mathyomama@gmail.commathyomama@gmail.com> wrote:
Hello Usrp Users,
Yesterday we did a couple of more tests on top of a parking garage. In
an attempt to improve our results, we extended the distance between the
antennas and tried our tests on higher ground as suggested (about 100ft
above the ground which is enough to be over the tree line in most of the
region). We had clear line of sight of two antennas, one tower and one on
top of a building. The first antenna was a translator stations and didn't
have very good strength
of signal even though we were in the presumed 60 dbm region according
to the fcc database. The second antenna was a college music station and it
had very good strength. But neither antenna seems to give the expected
results. The first antenna gave fairly erratic results. The range for each
orientation was very wide and usually never centered around the expected
result. The results for the second antenna were very tight in precision but
not in accuracy. We would hold the antenna array in the 0 degrees
orientation and get an angle of about -4 degrees and then rotate it to the
90 degree orientation and get around -8 degrees and then go back to the 0
degree orientation and get about -16 degrees.
So after seeing these results, we tried to transmit a frequency on
another B210 and find the angle based on that. The setup for this is in the
attached picture. Because our transmitted signal isn't very strong, in
order to get any decent results, we had to keep the transmitter very close
to the receiving antennas (within one wavelength of the antenna array). But
this ruins the angle of arrival approximation, so a lot of our results for
this were dubious. We did try the 0 degree orientation for which we should
still expect 0 degrees. We got mixed results which seemed to depend on the
height of the transmitter.
All in all the results were poor. We didn't get any out of range errors
(since it's built into the calculation). But the measured phase differences
for the angles didn't seem to scale with the increase in distance between
the receiving antennas. The majority of our results for the second antenna
were in the range -20 to 20 degrees no matter what the orientation was,
which means that the phase difference was also in that respective range. Is
it possible that the cables which connect the receiving antennas to the
B210 are also acting as antennas? If so, would insulating the cables with
some material help reduce that effect?
Sincerely,
Michael Duckett
On Wed, Apr 13, 2016 at 1:19 PM, Michael Duckett mathyomama@gmail.com
wrote:
Thank you everybody for the help and suggestions.
Yesterday we ran a few more tests near another radio tower. We were
able to extend the distance between the two antennas to about 90 cm using
some SMA cables that we had (we are getting more to give us the full
distance we want) and the frequency we were measuring was 104.9 MHz
(wavelength is about 285 cm). Unfortunately, we didn't have a rig set up
for our B210 and antennas, so we resorted to holding the B210 and antennas
ourselves (will this affect the signal received?). For the 0 degrees
orientation, we were getting phase offsets which were still out of range of
the arcsin domain even for the larger distance between the antennas. As we
changed the orientation, we noticed very small changes in the phase offset.
The majority of phase offsets were hanging around the pi/-pi boundary.
We then tried a few runs without the wires and instead tilted the
antennas outward so that the tips of the antennas were about 10 in. or 25.4
cm apart. This seemed to give us mixed results. My partner would hold the
device in one location at the 0 degree orientation and find phase
differences out of range of the arcsin domain and then move to another
location (about a step away) and find measurements which were at least in
the arcsin domain (the calculated angles ranged from 40 to 90 degrees, so
they were way off still). So the results for that experiment were spotty.
what antenna type are you using?
We are using an omni-directional rubber ducky antenna.
Do you do any higher order tracking before or after converting the
phase offset to an angle?
No, we are not. What do you mean by higher order tracking?
I'd really love to see multiple approaches at AoA being implemented,
that will definitely be an interesting use case for both SDR in general,
the USRP B210, and GNU Radio; I don't remember fully, but I think the
cel-kit account on github has a gr-specest repo, where you can find a few
examples of parametric spectrum estimators; amongst these MUSIC, an
algorithm actually originating in the world of direction detection, applied
to frequency estimation. It should be pretty straightforward to adapt the
algorithm to spatial problems – basically, you'd replace the estimated
signal autocovariance matrix by a antenna cross-correlation matrix.
The MUSIC algorithm seems like something we should definitely try out.
First, height is your friend. Don’t think that getting closer to the
station tower is better. The Tower probably is an array so you will not be
in the main beam anyway. Find the tallest building in the area and ask if
you can do your tests on their roof. A clear and open line of sight to the
tower is your goal here.
I think we are going to look for a tall place today or tomorrow and try
to get measurements from there.
Third, is the signal really entering the antenna? Or is it coupling to
the receiver. This can be easily tested by removing the antennas and
verifying that the signals drop by at least 10 dB. The more it drops, the
better your measurement. I would try and get at least 20 dB of isolation
for a good AoA measurement.
When we took the antennas off the SMA cables, there was a significant
drop in dB across the whole bandwidth (at least 20 dB). So it seems like
the signal was entering the antenna.
We are going to try to run more tests soon and hopefully with a
structure which will hold together our B210, cables, and antennas. Thanks
again for the support.
Sincerely,
Michael Duckett
On Tue, Apr 12, 2016 at 9:59 AM, Evan Merewether via USRP-users <
usrp-users@lists.ettus.comusrp-users@lists.ettus.com> wrote:
Hi Michael,
After a quick look, it seems that the methodology is sound, but you
may have problems with the way you are testing. Here are a few things you
can do to improve your measurements and test the performance.
First, height is your friend. Don’t think that getting closer to the
station tower is better. The Tower probably is an array so you will not be
in the main beam anyway. Find the tallest building in the area and ask if
you can do your tests on their roof. A clear and open line of sight to the
tower is your goal here.
Second, what else can the signal be bouncing off of? Is there a tall
water tower nearby? Could you be seeing the effects of reflected signals?
For this, again, height is your friend. By moving to a tall building, you
will minimize the number and strength of possible reflective surfaces.
Third, is the signal really entering the antenna? Or is it coupling to
the receiver. This can be easily tested by removing the antennas and
verifying that the signals drop by at least 10 dB. The more it drops, the
better your measurement. I would try and get at least 20 dB of isolation
for a good AoA measurement.
Evan
From: USRP-users [mailto: usrp-users-bounces@lists.ettus.com
usrp-users-bounces@lists.ettus.com] *On Behalf Of *Marcus D. Leech
via USRP-users
Sent: Friday, April 08, 2016 3:17 PM
To: usrp-users@lists.ettus.comusrp-users@lists.ettus.com
Subject: Re: [USRP-users] Fwd: Angle of Arrival Measurements
On 04/08/2016 04:21 PM, Marcus Müller via USRP-users wrote:
Hi Michael,
So, I'm currently having a look at your flow graphs; they look sound
to me; especially the complex method (Which pretty much is equivalent to
picking one frequency bin from the FFT, if you add a sharp bandpass filter,
so that you only see one frequency) looks efficient. In fact, seeing both
approaches in one place reminded me of OFDM radar, where one actually takes
advantage of the
I use the complex-conjugate method in astronomical interferometry,
which is related to AoA, at least in an incidental sense--the emergence
of fringes is due to change in phase due to change in arrival angle
relative to the baseline between the antenna.
I also just use it for measuring and/or looking-for phase-drift
between two sources that should be phase-coherent.
time/frequency structure of the signal, and, more elementarily, the
fact that a shift in time domain is a modulation with an offset frequency
in frequency domain. Maybe [1] is a bit of a fun read to you; for the angle
of arrival problem (which for your approaches is really but a time offset
problem), things boil down to:
If [image: $x$]and [image: $y$]are the same signal, but [image:
$y(t)=x(t-\tau)$]is delayed by [image: $\tau$], then their Fourier
transforms [image: $X$]and [image: $Y$]are also the same but for the
latter [image: $Y=e^{-j2\pi\tau f} X$]being the first modulated by a
complex sinusoid. Estimating that sinusoid's frequency gives you the timing
offset; you can get the "pure" tone by just dividing [image: $\frac
YX$]. Looking at the discrete signal case, note that the frequency
resolution you can get depends on the DFT you're doing – i.e. longer
observation/larger DFT has a very positive effect on accuracy!
I'd really love to see multiple approaches at AoA being implemented,
that will definitely be an interesting use case for both SDR in general,
the USRP B210, and GNU Radio; I don't remember fully, but I think the
cel-kit account on github has a gr-specest repo, where you can find a few
examples of parametric spectrum estimators; amongst these MUSIC, an
algorithm actually originating in the world of direction detection, applied
to frequency estimation. It should be pretty straightforward to adapt the
algorithm to spatial problems – basically, you'd replace the estimated
signal autocovariance matrix by a antenna cross-correlation matrix.
Best regards,
Marcus
[1] Braun, Martin. Ofdm radar algorithms in mobile communication
networks. Diss. Karlsruhe, Karlsruher Institut für Technologie
(KIT), Diss., 2014, 2014.
http://d-nb.info/104838490X/34http://d-nb.info/104838490X/34
On 08.04.2016 21:15, Michael Duckett via USRP-users wrote:
We are using two antennas on the same B210 and the distance between
them is 7cm (the distance between the two "TX/RX" ports). We understand
that this affects the measured phase difference and the further calculation
for the AOA. For future tests we may try to widen the distance between the
two antennas to half the wavelength (I think that would be around 1.3 to
1.7 m for FM radio station frequencies).
This distance between the two antennas brings us to the first
question. Because the distance between the antennas was small compared to
half the wavelength of the frequency, the range of valid phase differences
was shrunk, too. Most of the time when we were measuring we got phase
differences which were out of range of the valid region. In one spot close
to the tower, we positioned our antenna array at the 0 degree orientation
and phase difference values which corresponded to 60-70 degrees. In
another spot with the same orientation, we got phase difference values
which were out of range. So when we rotated the antenna array, it was
difficult to compared the AOA because most of the time that calculation
wasn't possible. But we can see noticeable changes in the phase difference
when rotating the array. But there doesn't seem to be an easily
decipherable pattern to the error.
We haven't been monitoring the time domain signal levels. We can try
that next time, as well.
On Fri, Apr 8, 2016 at 2:19 PM, Derek Kozel < derek.kozel@ettus.com
derek.kozel@ettus.com> wrote:
Hello Michael,
In addition to Alexander's good thoughts, are you monitoring the time
domain signal levels to ensure that the receive gain is set appropriately?
I see a QT GUI Sink (you may consider using the QT Frequency Sink), but it
would be worth while looking at a QT Time Sink as well to see if you are
clipping.
Regards,
Derek
On Fri, Apr 8, 2016 at 10:28 AM, Alexander Levedahl via USRP-users <
usrp-users@lists.ettus.comusrp-users@lists.ettus.com> wrote:
I do not have the ability to look at files right now so sorry if I am
asking questions that are answered in the files.
If you stand in one spot and rotate, is the error consistent? I.e.,
if you are pointing the array right at it, it shows the AOA as 60-70. If
you change to pointing 30 degrees, does the AOA change to 90-100?
Are the results consistent across restarting the B210? Depending on
the answer to these questions, it may simply be a calibration problem.
I.e., when you turn it on there needs to be a calibration step.
Finally, how many antennas are you using 2 or are you using multiple
B210s? Is your antenna spaced appropriately for the operating frequency?
On Fri, Apr 8, 2016 at 12:51 PM, Michael Duckett via USRP-users <
usrp-users@lists.ettus.comusrp-users@lists.ettus.com> wrote:
Hello,
We are trying to measure the angle of arrival of FM using USRP B210.
We have run into some problems with the measurements and hence we are
writing this email. It would be nice if we can get some inputs from you on
how to fix this issue. We have used two methods for computing the phase
difference. We have used the first one most of the time. However, we are
posting both the methods here for you to have a look.
I have attached method 1 (phase_difference_probe.grc for probing and
phase_difference_view.grc which provides a nice GUI to look at) and method
2 (complex_method.grc). Method 1 is based on the following "paper":
http://www.egr.msu.edu/classes/ece480/capstone/spring14/group02/docs/Application%20Note%20-%20Phase%20George%20Godby%20Team%202.pdf
http://www.egr.msu.edu/classes/ece480/capstone/spring14/group02/docs/Application%20Note%20-%20Phase%20George%20Godby%20Team%202.pdf
We use these flow graphs and run them in another script which probes
the "top_block" to get 500 samples which are then averaged to produce one
data point.
We also attach a diagram (AoA_Figure.pdf) which shows a basic idea of
how the antennas and transmitter are setup and what the Angle of Arrival
(AoA) is, when it comes to our measurements.
We tried our code in two different situations. In our first test, our
transmitter was another B210 and we were in an open field. The frequency we
tried ranged from 200 MHz to 1.0 GHz and then 3 GHz and 4 GHz. Our Phase
difference and consequently our AoA measurement were not too far off, when
the antenna array was facing the transmitter (i.e. at an expected AoA of 0
degs). As we moved closer towards an AoA of +- 90 the accuracy of the
measurement fell off. But the consistency of the 500 samples was still
pretty good (we were getting a standard deviation under 0.10 radians).
For our second test, we tried to get the AoA from FM radio towers. We
got about 800-1000m away from a popular radio station tower and pointed the
antenna array at the tower (expecting an AoA of around 0 degs). But we got
measurements which were way off. We did this for a couple of different
spots but the measurements were all over the place (the standard deviation
for individual data points were pretty good but the measurement for the 0
deg position at one spot was different for another spot around the tower).
We did manege to get angle measurements at one point when we were about 800
meters from the tower. The expected angle was 0 but we got 60 - 70 degrees
as the measured angle. We also tried at other places, one was about 800 m
from the tower and the other about 1200m. But both these places were
problematic.
It would be nice to get your inputs on the flow graphs. What are your
thoughts about the flow graph? Do you see any glaring problems with the
flow graph or with the set up? If you have any more questions about the
setup then feel free to ask.
Most of the information about the setup that we are using are in the
attached grc files. Thanks a lot for all your time.
Sincerely,
Michael Duckett
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