On Thu, Feb 16, 2012 at 10:24, Tom Rondeau <t...@trondeau.com> wrote:
> Powerline communications have been discussed for quite > a while, but they tend to be horrible channels (old copper, long distances, > bad shielding, etc.). So yes, I'd expect OFDM for the equalization and > multipath (or 'echos' in this case) issues and heavy channel coding are > required. 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. 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. 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 :) Johnathan _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
