I currently have a long distance (> 1/2mi) *audio*
link between my automation system and our vehicles.
This is sufficient to interact with it and for it
to interact with us (without having to resort to
cell phone connections).
I'm looking at fattening the pipe so I can send
video and encrypted data (the audio link is licensed
for voice only -- though I can get around that
for low bandwidth data).
In the US, it seems like WiFi is limited to shorter ranges
(maybe 600 ft, with a tailwind)? Possibly longer for
PtP connections -- but that is challenging with a
moving vehicle (the house could track the vehicle's
r/theta but the vehicle would be hard pressed to
reciprocate)
Any other "unlicensed" solutions I can look at?
On Saturday, November 4, 2023 at 6:53:07 PM UTC-7, Don Y wrote:
I currently have a long distance (> 1/2mi) *audio*
link between my automation system and our vehicles.
This is sufficient to interact with it and for it
to interact with us (without having to resort to
cell phone connections).
I'm looking at fattening the pipe so I can send
video and encrypted data (the audio link is licensed
for voice only -- though I can get around that
for low bandwidth data).
In the US, it seems like WiFi is limited to shorter ranges
(maybe 600 ft, with a tailwind)? Possibly longer for
PtP connections -- but that is challenging with a
moving vehicle (the house could track the vehicle's
r/theta but the vehicle would be hard pressed to
reciprocate)
Any other "unlicensed" solutions I can look at?
Even with a spotty connection, a house station which knows
theta can communicate the best reply azimuth angle to the vehicle, eventually?
Or, at least send the info in a text to a cellphone.
The obvious other solutions are in the LoRaWAN category,
and not easily available in off-the-shelf onesies. Those too aren't
fat pipes. Even before 802.11b WiFi, there were point-to-point solutions good
for a mile, line-of-sight, with dish antennae (fixed aim); you could conceivably
make a mesh, routing narrow-focus links to omnidirectional nodes.
I currently have a long distance (> 1/2mi) *audio*
link between my automation system and our vehicles.
This is sufficient to interact with it and for it
to interact with us (without having to resort to
cell phone connections).
I'm looking at fattening the pipe so I can send
video and encrypted data (the audio link is licensed
for voice only -- though I can get around that
for low bandwidth data).
In the US, it seems like WiFi is limited to shorter ranges
(maybe 600 ft, with a tailwind)? Possibly longer for
PtP connections -- but that is challenging with a
moving vehicle (the house could track the vehicle's
r/theta but the vehicle would be hard pressed to
reciprocate)
Any other "unlicensed" solutions I can look at?
The industrial/commercial equivalents are tugs/motorized carts/
personal transports that allow a person to quickly travel
outside their normal "working range". The farther afield
an individual can "stray" before you reel him back in, the
more annoying the behavior will be seen as. ("why couldn't
you tell me BEFORE I left?")
The obvious other solutions are in the LoRaWAN category,
and not easily available in off-the-shelf onesies. Those too aren't
fat pipes. Even before 802.11b WiFi, there were point-to-point solutions good
for a mile, line-of-sight, with dish antennae (fixed aim); you could conceivably
make a mesh, routing narrow-focus links to omnidirectional nodes.
But the back channel from the omnidirectional node (vehicle) needs
to be as fat as the forward channel.
On Sat, 4 Nov 2023 18:52:38 -0700, Don Y <blockedofcourse@foo.invalid>
wrote:
I currently have a long distance (> 1/2mi) *audio*
link between my automation system and our vehicles.
This is sufficient to interact with it and for it
to interact with us (without having to resort to
cell phone connections).
I'm looking at fattening the pipe so I can send
video and encrypted data (the audio link is licensed
for voice only -- though I can get around that
for low bandwidth data).
In the US, it seems like WiFi is limited to shorter ranges
(maybe 600 ft, with a tailwind)? Possibly longer for
PtP connections -- but that is challenging with a
moving vehicle (the house could track the vehicle's
r/theta but the vehicle would be hard pressed to
reciprocate)
Any other "unlicensed" solutions I can look at?
If the vehicle has a GPS receiver, it could send the coordinates to
the house in each message and the house antenna can aim at that
direction.
With direct line-of-sight (LOS) this should work reasonably, but
requires a high tower at the house to maintain LOS. The receive signal
drops only by the square of distance. To triple the distance, 9x the
power (nearly 10 dB) stronger signal is required.
Below LOS, especially in urban areas, the signal will propagate trough multiple reflections, this the strongest signal may come from a
direction other than the geometry would suggest. Thus do not use too
narrow antenna beams.In urban areas below LOS the signal strength may
drop relative to the forth power of distance. To triple the distance
81x (19 dB) more power is required.
Low data rate systems can operate at lower RF frequencies (HF/VHF) and
do not suffer too hard from vegetation losses, when operating below
LOS. To transfer high data rates (such as video) a higher
UGF/microwave frequency must be used and it suffer more from
vegetation.
To increase the bit rate 100 times for video, 100x (20 dB) more power
is required. Also the transmission method must tolerate ,multiple
reflections (such as COFDM) especially with paths below LOS.
Thus extending the range requires a lot of power and / or higher base
station mast, which limits the licence free system range quite
severely.
On 11/5/2023 12:45 AM, upsidedown@downunder.com wrote:
On Sat, 4 Nov 2023 18:52:38 -0700, Don Y <blockedofcourse@foo.invalid>
wrote:
I currently have a long distance (> 1/2mi) *audio*
link between my automation system and our vehicles.
This is sufficient to interact with it and for it
to interact with us (without having to resort to
cell phone connections).
I'm looking at fattening the pipe so I can send
video and encrypted data (the audio link is licensed
for voice only -- though I can get around that
for low bandwidth data).
In the US, it seems like WiFi is limited to shorter ranges
(maybe 600 ft, with a tailwind)? Possibly longer for
PtP connections -- but that is challenging with a
moving vehicle (the house could track the vehicle's
r/theta but the vehicle would be hard pressed to
reciprocate)
Any other "unlicensed" solutions I can look at?
If the vehicle has a GPS receiver, it could send the coordinates to
the house in each message and the house antenna can aim at that
direction.
Yes, but that doesn't handle the return path from the vehicle.
(that is the tougher nut to crack -- without requiring
tedious modifications on that end)
With direct line-of-sight (LOS) this should work reasonably, but
requires a high tower at the house to maintain LOS. The receive signal
drops only by the square of distance. To triple the distance, 9x the
power (nearly 10 dB) stronger signal is required.
The audio link (900MHz?) works quite well without directional
antennae *or* a high-mount antenna. I.e., I can get a bit more
than 1/2mi with a desk-mounted base and handheld transceiver.
This was, initially, sufficient as speech is one of my supported
interface modalities.
But, *now* attempting to extend that to incorporate video
(e.g., for a deaf user and/or to augment the material that
can be presented over the link), a fatter pipe is required
with attendant problems...
Below LOS, especially in urban areas, the signal will propagate trough
multiple reflections, this the strongest signal may come from a
direction other than the geometry would suggest. Thus do not use too
narrow antenna beams.In urban areas below LOS the signal strength may
drop relative to the forth power of distance. To triple the distance
81x (19 dB) more power is required.
I was initially thinking of just seervoing the azimuth control
to signal strength and let the antenna "hunt" for the best
orientation -- hoping it could keep up with the movement of the
vehicle.
But, as above, the vehicle would have a similar problem
keeping its antenna oriented properly.
Eliminating that complexity seems essential for a practical solution.
Low data rate systems can operate at lower RF frequencies (HF/VHF) and
do not suffer too hard from vegetation losses, when operating below
LOS. To transfer high data rates (such as video) a higher
UGF/microwave frequency must be used and it suffer more from
vegetation.
To increase the bit rate 100 times for video, 100x (20 dB) more power
is required. Also the transmission method must tolerate ,multiple
reflections (such as COFDM) especially with paths below LOS.
Thus extending the range requires a lot of power and / or higher base
station mast, which limits the licence free system range quite
severely.
If *both* endpoints were fixed, it would be considerably easier.
But, "allowing" (!) one to move complicates things.
I can "cheat" and put some (a fair bit!) local intelligence at each end
to convert video images to low bandwidth messages which could
then be encoded into speach-ish signals for transmission. But,
that also increases the problem's complexity (as well as constraining
the material that can be presented).
[...]
In the US, it seems like WiFi is limited to shorter ranges
(maybe 600 ft, with a tailwind)? Possibly longer for
PtP connections -- but that is challenging with a
moving vehicle (the house could track the vehicle's
r/theta but the vehicle would be hard pressed to
reciprocate)
On 2023-11-05, Don Y wrote:
[...]
In the US, it seems like WiFi is limited to shorter ranges
(maybe 600 ft, with a tailwind)? Possibly longer for
PtP connections -- but that is challenging with a
moving vehicle (the house could track the vehicle's
r/theta but the vehicle would be hard pressed to
reciprocate)
It's not so much that it's "limited to X distance", but rather that 4
watts (36dBm EIRP) is only going to get you so far, especially with omnidirectional antennas. Directional antennas will help, provided you
can keep them pointed more-or-less the right way.
Then there's the rules for fixed point-to-point, which allow you to put high-gain antennas up (with a commensurate reduction in transmitted
power at the radio itself).
At least on 2.4 GHz ... 5 GHz gets fun, because you have to consider
which band, etc.
On Sun, 5 Nov 2023 04:27:56 -0700, Don Y <blockedofcourse@foo.invalid>
wrote:
The audio link (900MHz?) works quite well without directional
antennae *or* a high-mount antenna. I.e., I can get a bit more
than 1/2mi with a desk-mounted base and handheld transceiver.
You are not gain to get high speed video on quite narrow 900 MHz band
but need to use at least the 2450 MHz band with plenty of bandwidth.
However, for an omnidirectional antenna, the caption area is
proportional to the wavelength squared, thus going from 900 MHz to
2450 MHz will give about 1/10 signal thus require nearly 10x more
power. The higher bit rate may require up to 100 x (20 dB) more power.
Thus you may require up to 1000x (30 dB) more power. Alternatively use directional antenna at the house and the power requirement can be
reduced.
This was, initially, sufficient as speech is one of my supported
interface modalities.
But, *now* attempting to extend that to incorporate video
(e.g., for a deaf user and/or to augment the material that
can be presented over the link), a fatter pipe is required
with attendant problems...
Why not let the deaf person use ordinary cellular video and the rest
of the users use your own narrow band private system.
Below LOS, especially in urban areas, the signal will propagate trough
multiple reflections, this the strongest signal may come from a
direction other than the geometry would suggest. Thus do not use too
narrow antenna beams.In urban areas below LOS the signal strength may
drop relative to the forth power of distance. To triple the distance
81x (19 dB) more power is required.
I was initially thinking of just seervoing the azimuth control
to signal strength and let the antenna "hunt" for the best
orientation -- hoping it could keep up with the movement of the
vehicle.
That is one option.
How fast is the car moving ? If it is moving fast, there can be quite
bad multipath flutter, so select a proper modulation method.
[Note that I have to address different markets with likely different >operating conditions. So, I'm looking for approaches that can be
applied to all]
In a "home" environment, most residential areas have reasonably
low speed limits because it's not practical for folks to pull
out of their driveway into fast-moving traffic. 15 & 25MPH seem
to be the most common (though folks always abuse those limits
in the absence of "enforcers").
On Sun, 5 Nov 2023 11:06:23 -0700, Don Y <blockedofcourse@foo.invalid>
wrote:
[Note that I have to address different markets with likely different
operating conditions. So, I'm looking for approaches that can be
applied to all]
If you plan to sell your system to different countries, please note
that the 900 MHz band is not available on all continents.
In some countries license free NBFM phone channels may be available
just above 400 MHz.
Note also that on 2450 MHz here might be a strict +20 dBm EiRP limit.
If you use directional antennas, you must drop the transmitter power
by that gain amount to remain below the +20 dBm (100 mW) EiRP limit.
In a "home" environment, most residential areas have reasonably
low speed limits because it's not practical for folks to pull
out of their driveway into fast-moving traffic. 15 & 25MPH seem
to be the most common (though folks always abuse those limits
in the absence of "enforcers").
The NBFM mobile flutter is quite harmless on 400 MHz. I don't know
about 900 MHz but already on 1300 MHz and higher the mobile flutter
can be quite annoying. At those frequencies the multipath null is
often in places close to traffic lights, so if you stop at traffic
lights, you might fail to communicate :-) until the car is moving
again.
I currently have a long distance (> 1/2mi) *audio*
link between my automation system and our vehicles.
This is sufficient to interact with it and for it
to interact with us (without having to resort to
cell phone connections).
I'm looking at fattening the pipe so I can send
video and encrypted data (the audio link is licensed
for voice only -- though I can get around that
for low bandwidth data).
In the US, it seems like WiFi is limited to shorter ranges
(maybe 600 ft, with a tailwind)? Possibly longer for
PtP connections -- but that is challenging with a
moving vehicle (the house could track the vehicle's
r/theta but the vehicle would be hard pressed to
reciprocate)
Any other "unlicensed" solutions I can look at?
On Saturday, November 4, 2023 at 6:53:07 PM UTC-7, Don Y wrote:
I currently have a long distance (> 1/2mi) *audio* link between my
automation system and our vehicles. This is sufficient to interact with it >> and for it to interact with us (without having to resort to cell phone
connections).
I'm looking at fattening the pipe so I can send video and encrypted data
(the audio link is licensed for voice only -- though I can get around
that for low bandwidth data).
In the US, it seems like WiFi is limited to shorter ranges (maybe 600 ft,
with a tailwind)? Possibly longer for PtP connections -- but that is
challenging with a moving vehicle (the house could track the vehicle's
r/theta but the vehicle would be hard pressed to reciprocate)
Any other "unlicensed" solutions I can look at?
Sort of sounds like the standard 2-way radio problem. The mobile antenna needs to be vertical omni, but co-linear (to get some gain). That seems very possible at the usual high carrier frequencies for WiFi. But "can you buy one" is another question to be answered. The base antenna can have gain in the same way. And, if say you only drive away to the West, then it can also be directional in that way to also get additional gain.
In the US, 1 W is legal for the 2.4G band. But the cheap WiFi stuff will be at least 10 dB and possibly 20 dB lower than that. If you could figure out how to splice in a 1W amp for the TX'er on both base and mobile ends, ha ha ha, then you can increase your link budget.
If you don't have 2 diverse antennas on each end, then MIMO can't work for your WiFi. It will "downshift."
In the early days of WiFi, experimenters were shooting it across the SF bay with dishes. Not mobile tho.
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