>
>
> OFDM for the equalization and FEC for the channel errors has been a
> successful technique used in residential power-line communications.
> However, commercial buildings tend to have long and unpredictable
> power delay profiles, requiring long symbol times.  In addition, there
> are enormous sources of interference (primarily impulse noise) from
> things like elevator motors and paper shredders (!), as well as strong
> shortwave RF induced signals.  Finally, some installations use
> multiple transformers between floors, with their own very
> unpredictable channel response.
>

Hey Jonathan,

This was a super informative post, it's really interesting to hear about
experience of actually building PLC in practice.  I haven't seen very many
studies on it, but it seems like different buildings have greatly varying
profiles.  I didn't think of things like elevator motors in office
buildings, but that's got to introduce a lot of interference.

If you ever do this again, I would love to see some of the channels over
time.  I ordered some basic PLC equipment, but all I really have access to
are packets :P


>
> As an alternative, one commercial R&D contract I did a while back was
> to use DSSS/CDMA with long codes to reduce the interference by the
> coding gain, then use additional delay correlators to receive and
> combine echos (a basic RAKE receiver).  This worked extremely well for
> interference rejection, without FEC at the data level, but at the
> expense of a low bit rate and long synchronization times.  Since the
> communication requirement was a unidirectional broadcast, this worked
> out well.
>

Nice, I guess with unidirectional broadcast that does work out well for
you.  How do you actually get echoes in a PL?  I never thought about this.


>
> The initial implementation was done in GNU Radio with a chipping rate
> of 2 Mcps, then ported to the USRP2 FPGA (minus the rake) for chipping
> rates up to 25 Mcps.
>
> I think this goes to the point that GNU Radio is an excellent tool for
> experimentation, R&D, prototyping, etc., and not so much for chasing
> existing standards.
>
> > My main question regarding this topic is to figure out what would be
> > necessary to create a test bed to try it out on? Obviously, we aren't
> going
> > to stick the Rx/Tx port of the USRP into a wall socket :)
>
> That company made some generic 50-ohm to wall socket power couplers
> for the project, but I don't know if they ever made them commercially.
>  I still have a pair in my lab to play with :)
>
>
It would be really cool to be able to hook up the USRP to a PL and
understand various channels in different types of buildings.  Totally not
conducive to my dissertation, but I find it interesting.

- George
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