On 8/28/21 5:50 AM, jan0--- via wsjt-devel wrote: > If a channelized scheme is introduced to avoid recurrent channel collisions, > care should be taken not to reduce the network throughput. As anyone who > has visited 14.074 lately can attest, for much of the day there is more > channel demand than channel availability -- and other bands are frequently > similar. I still think channelization would help throughput, but this needs to be demonstrated by simulation and on-air testing. > > Two-pass decoding, available in many if not all FT8 software suites, enables > multiple signals to be decoded across a single transmission bandwidth.
What's the saying, "everything old is new again"? I remember this method from my early days in Qualcomm CDMA (the early 1990s). We didn't do it because it was, at that time, difficult (CDMA is 1.25 MHz wide) and it didn't provide much benefit given power control and rake reception. I'm trying to remember the assumptions on which that conclusion was based. As I recall, it involved re-encoding the decoded signal, subtracting it from the raw incoming signal, and attempting another decode. The main drawback, aside from complexity (which isn't a problem for a slow signal and our modern CPUs) is that the cancellation isn't perfect; the reconstructed signal is ideal while the signal being cancelled has fading and multipath, so there will still be a cancellation residual that interferes with the weaker signals. But in principle I don't see why it shouldn't work on both co-channel and overlapping interference, except that the interference power is less when the channels only partly overlap. You realize, of course, that this discussion can only lead to the question of whether it's time to try some real spread spectrum here. If not across the whole ham band, at least within a 3 kHz "band". But, of course, Shannon still reigns supreme... --Phil _______________________________________________ wsjt-devel mailing list wsjt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wsjt-devel
