On 11/20/2014 12:37 AM, Nowlan, Sean wrote: > It looks like there’s a dev call tomorrow. Is that 1700 or 1800 UTC?
1800 UTC. I recommend letting Google do the time zone math by joining the G+ group and adding yourself to the event there. > As for input to the digital mod and packet structure discussion, I have > a few questions, or at least food-for-thought for tomorrow: As you've seen on the agenda, this will be one of our focal points for today's call. People interested in this should definitely tune in! > - It looks like the correlate_and_sync work is promising for > allowing carrier and timing recovery loops to adjust more quickly when > dealing with bursty, packetized traffic. However, most of the GR modem > applications I’ve seen use the correlate_access_code block without the > time and phase estimates being done on the preamble. I know the paradigm > is slightly different, i.e. matched-filter preamble correlator vs. > counting access code bit errors after MF and slicing, but is the intent > to eventually merge the two approaches together? Can't state facts on this, but one thing to remember is that correlate_and_sync is way younger than the other correlators, which predate the tag system. > - What’s the best way to handle the sudden ramp in power at the > start of a burst? Use squelch to detect power above a threshold? Use > AGC? This may be a fundamental radio receiver design question but I > think it makes sense to ask it in the context of how these blocks are > implemented. In gr-air-modes it looks like the preamble detector scans > for a rapid change in sample “voltage” before initiating a preamble > search. This seems more efficient if packet traffic is expected to be > low, otherwise all you’re doing is correlating against noise > (correlate_and_sync) or junk bit decisions (correlate_access_code). If > I’ve misunderstood anything here, please advise. You're right, it's a fundamental radio rx design question :) You're right, though, and if you check out some bursty standards, you'll usually find ramp-up times at the beginning of bursts for AGC init and/or power detection. Imagine your phone would correlate for wifi headers all the time the way the ofdm_rx does, it would soon run out of juice. Cheers, M _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
