On 11/5/2023 5:54 AM, upsidedown@downunder.com wrote:
> 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.
Yes. I use WiFi to make the connection to the car while
*proximate* to the house -- i.e., so it is treated as a "room"
WHILE there. This lets me display obstructions on one of the
in-dash displays to show the driver why he shouldn't pull in/out
of the garage (under those conditions), let him interact with the
automation system (e.g., "please lock the doors in the house",
"please prep the house for my immediate occupancy as I have
returned home", etc.).
[Some *driveways*, here, would tax that 1/2mi range and easily
exceed the range of the wifi I've deployed!]
But, if the driver is not planning on interacting with the house,
it gives the house very limited opportunities to interact with
him without inconveniencing him (i.e., "please pull over before you
drive out of range for this conversation to continue to its
intended conclusion").
The audio link provides that channel for a longer distance
without that inconvenience ("Did I shut the garage door?
If not, please shut it for me! What do you mean, you
*can't*??! Oh, OK, I will have to return home and move those
items that are in the path of the door's closing... BRB")
I would like to be able to use the video modality for
folks who can't process audio -- as well as offer more
features for those who can.
> 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.
It requires them to carry a cell phone and necessitates the
initiation of a "call" (which adds further latency). Here,
you can not "operate" a phone while you are driving a vehicle
so the driver would have to pull over for the call.
And, it makes the deaf/mute user a different type of user.
(they don't have to carry a phone around the interior of the
house so why require them to carry one in this "special
room"?)
[All users have to use a phone if they are "remote" so there
is no bias, there]
>>> 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").
In an industrial/commercial environment, 15MPH is more common
because the vehicle (a tug/PTD/motorized cart/etc) won't
be designed for "on-road" travel so its top speed will be
less - and it will likely be operated in traffic that can't
tolerate high speeds (e.g., pedestrian traffic).
By far, the worst market is dealing with elderly folks trying
to live at home without assistance. In those cases, there is
no one to interact with the user as they undertake some "bad"
behavior (e.g., "Where are you planning on going, in the car,
Sharon? No, you don't need to do that; why don't you come
back into the house?"). You want to leave these people with
as much freedom as possible (i.e., don't lock the garage door
to prevent them from driving off). Yet, still need to keep
them on a "short leash" (sad metaphor). So, you need to be
able to "talk" (interact) with them after you've discovered
they have done something "wrong" and hope they come around
to your line of thinking before they are out of range for you
to continue that interaction (because they may not be "aware"
enough to realize they should stop moving while trying to
get their wits).
[We had a neighbor that we (the remaining neighbors) were
convinced would be the subject of a "silver alert"[1], one
day, as she was in the habit of driving off for <whatever>
and we suspected her memory not sufficient to always get her
back home, intact. Her (remote) kids eventually acknowledged
the risk and hired 24/7/365 in-home caregivers essentially
to prevent her from driving off, leaving the stove on,
falling in the swimming pool, etc.]
[1] Here, we have different BROADCAST "alerts" for different
high-stakes events: <https://en.wikipedia.org/wiki/Silver_Alert>,
<https://en.wikipedia.org/wiki/Amber_Alert>