Re: ND-over-OCB hidden terminals: truck obstructing direct car-to-car and asphalt reflections

[Alexandre Petrescu <alexandre.petrescu@xxxxxxxxx>]

Le 15/04/2019 à 23:04, Brian E Carpenter a écrit :> Excuse top posting.
>
> As I've said, I am no expert, but I do know some physics, and it
> seems pretty clear to me that if there are multiple lanes of traffic,
> a large truck can easily shield signals between two cars and the
> shielding will be intermittent, regardless of how much wireless power
> is allowed, depending on traffic movement. So it's a highly dynamic
> mesh network.

Well I agree with your intuitive description of the truck-between-cars situation.  But I dont agree to call it highly dynamic mesh network, for any definition of this latter; there is very little dynamicity in it.  I dont agree to tell it has problems with ND, because I experimented it and it works[*]

Alex

---------------------------

[*] I can explain why.  This explanation comes from practice with OCB and with radars/lidars with cars on road.

The intuitive description that you make is that of a blocking of signal by a solid separator object:

                 ----------
                |          |
    -------     |  Truck   |    -------
   |  Car  |    |          |   |  Car  |
    -O---O-      -O-O-----O-    -O---O-
---------------------------------------------- asphalt

In this illustration, it may be difficult for Cars to talk to each other on OCB, because of that Truck in the middle.

But when trying it on road, we realized  the Cars do talk ok to each other on OCB, even if there are these solid objects separators.  (worse, even the radars can see each other, some times, as if the Truck was absent.  Note that the effect of radar or camera that sees below a truck is reocgnized as the main cause of a known Tesla accident, among others.)

Some expert view explained this by waves reflected by below the Truck (asphalt).  I heard it verbatim from a partner.

These two sequences of photos illustrate such behaviour with OCB on the road.  The sequences are available on the web at https://youtu.be/F-_4Wmyzh2c?t=161

This is not the first such experiment to 'see thru' vehicles.  Other organisations did it before.  The ones that I know of are Samsung and a University in Spain.

In the first sequence we see how two cars between two other cars dont obstruct the IP-over-OCB propagation of a video stream between the first and rearmost vehicles.

In the second sequence we see how a big truck between two cars doesnt obstruct the IP-over-OCB propagation of such a video stream.

1st sequence:

The photo below shows the screen in one car that contains the video streamed from the front car with IPv6 on OCB.  The two cars are immediately  following each other on highway:
https://youtu.be/F-_4Wmyzh2c?t=168

In the photo below we see the front car immediately in front of this car

https://youtu.be/F-_4Wmyzh2c?t=178

In the photo below we see an intermediary small car (white) getting in the middle.  The streaming continues, as if the intermediary car was not obstructing the OCB.

In the photo below we see a 2nd intermediary small car (still white) that gets in the middle.  The streaming continues (at least the human filmer did not see a change, because it may have happened too fast).

2nd sequence:

In the photo below we see the 1st car getting further and a truck approaching to insert between the two:

In the photo below we see the truck obstructing the view:

In the photo below we see the video displayed in this car, that is streamed on IPv6-over-OCB and that does get through: