I need to use a directional antenna focused on an area about 6 meters x 6
meters that can scan for Bluetooth mobile phones as they pass through the
area, and identify them very quickly. It's for a new startup business
that's focusing on a retail application running on an embedded Linux box.
The problem with the usual usb Bluetooth dongle and a normal scan is that in
a busy area with hundreds of Bluetooth phones nearby, the scan can take a
very long time, like several minutes, and will pick up lots of phones of
people all over the store. We just want to detect them when they come in
through the entrance. So, we're going to use a directional antenna that
focuses just on a 6 meter x 6 meter space in front of the entrance so it
doesn't pick up phones outside that area.
However there's still a problem that a traditional Bluetooth scan takes 15+
seconds to pickup devices, and that's too long. The shopper may pass
through the detection area in only a couple seconds. So we need to be able
to do the scans very quickly.
I don't know that much about the underlying technology, but I understand
that a typical Bluetooth scan consists of scanning across several
frequencies and hopping from frequency to frequency to find phones on each
frequency. Therefore, my question is this: instead of having 1 bluetooth
dongle that's hopping across several frequencies, can we hook up multiple
bluetooth dongles to the same antenna, and have each one locked onto just
one frequency to make the process go faster? In other words, can we balance
the 15 second scanning process across 5 Bluetooth dongles so we can do the
same scan in only 3 seconds?
If not, does anybody else have any suggestions for how to accomplish the end
goal of being able to very rapidly detect phones as they pass through an
area?
We do have a little bit of funding, so if something like the multi-dongle
approach method i mentioned works, and it requires some special coding or
mods to bluez, we could compensate a developer for helping out with this.
Thanks
Hi Marcel,
> the use of an directional antenna with a Bluetooth chip is illegal as
> far as I know. You really wanna check the regulations here.
I don't think so. What you have to observe is that the maximum isotropic
radiation does not exceed +20dBm. So if you use an directional antenna
with a gain of, lets say +16 dBm (a somehow typical value) than the
maximum transmit power that can be used is +4 dBm. And you have to
convince the regulartory body that this will not be exceeded under all
circumstances.....
Ciao,
Peter
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Hi Paul,
> I need to use a directional antenna focused on an area about 6 meters
> x 6 meters that can scan for Bluetooth mobile phones as they pass
> through the area, and identify them very quickly. It's for a new
> startup business that's focusing on a retail application running on an
> embedded Linux box.
the use of an directional antenna with a Bluetooth chip is illegal as
far as I know. You really wanna check the regulations here.
> The problem with the usual usb Bluetooth dongle and a normal scan is
> that in a busy area with hundreds of Bluetooth phones nearby, the scan
> can take a very long time, like several minutes, and will pick up lots
> of phones of people all over the store. We just want to detect them
> when they come in through the entrance. So, we're going to use a
> directional antenna that focuses just on a 6 meter x 6 meter space in
> front of the entrance so it doesn't pick up phones outside that area.
You can use the RSSI value to pick only the phones in range. This needs
some manual tuning, but works pretty well so far. And if you simply not
use the name resolving, then you will see immediately devices in range
and also devices passing by. The bluetooth-proximity example from the
bluez-gnome package does this.
> However there's still a problem that a traditional Bluetooth scan
> takes 15+ seconds to pickup devices, and that's too long. The shopper
> may pass through the detection area in only a couple seconds. So we
> need to be able to do the scans very quickly.
>
> I don't know that much about the underlying technology, but I
> understand that a typical Bluetooth scan consists of scanning across
> several frequencies and hopping from frequency to frequency to find
> phones on each frequency. Therefore, my question is this: instead of
> having 1 bluetooth dongle that's hopping across several frequencies,
> can we hook up multiple bluetooth dongles to the same antenna, and
> have each one locked onto just one frequency to make the process go
> faster? In other words, can we balance the 15 second scanning process
> across 5 Bluetooth dongles so we can do the same scan in only 3
> seconds?
If you keep calling it scanning, then you have no clue how Bluetooth
actually works. So you might wanna get one of the Bluetooth books that
describe the basics behind this technology. And your math will not work
out that easily. It is not that simple.
> We do have a little bit of funding, so if something like the
> multi-dongle approach method i mentioned works, and it requires some
> special coding or mods to bluez, we could compensate a developer for
> helping out with this.
Just a warning up-front. If you don't use the D-Bus API and wanna use
the HCI raw socket, you have to make your code public and put it under
GPL license.
Regards
Marcel
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On Tue, 30 Oct 2007, Paul Huber wrote:
> I need to use a directional antenna focused on an area about 6 meters x 6
> meters that can scan for Bluetooth mobile phones as they pass through the
> area, and identify them very quickly. It's for a new startup business
> that's focusing on a retail application running on an embedded Linux box.
Since you're using non-provincial units I assume you're in the European
Union, but in the USA there's a specific reg forbidding cellphone spam.
Pro-actively dialling the customer's phone could well give a hostile
impression. A customer-initiated interaction such as WAP is a lot more
polite, but the shopkeeper would want to make it available to everyone
including those looking through the window.
If the technical and regulatory issues can be straightened out, it would be
very valuable to both the customer and the business to provide a product
search feature, tech specs for products, etc. All the advantages of online
shopping, but you can look at the physical product and buy it on the spot.
James F. Carter Voice 310 825 2897 FAX 310 206 6673
UCLA-Mathnet; 6115 MSA; 405 Hilgard Ave.; Los Angeles, CA, USA 90095-1555
Email: [email protected] http://www.math.ucla.edu/~jimc (q.v. for PGP key)
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Brad,
I'm using the C libraries directly within my own code, so I do get the
piecemeal results, and have played with extended inquiry. But I find that
it's still not fast enough, which was why I was hoping to try simultaneous
scanning with multiple dongles, or something like that to speed it up.
Do you know if bluez has enough low-level control over the usb device to do
something like that? ie have two devices scanning different frequencies?
Or does the usb interface just have a high level 'start scanning' without
the low-level control that would be needed?
Paul
Paul
Are you using hcitool from the command line? Use the D-Bus bindings
(eg python) with a listener method for discovered devices and you'll
get piecemeal results that are likely more timely. Maybe look into
extended inquiry too.
On 10/30/07, Paul Huber <[email protected]> wrote:
> I need to use a directional antenna focused on an area about 6 meters x 6
> meters that can scan for Bluetooth mobile phones as they pass through the
> area, and identify them very quickly.
--
Brad
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