Re: RF access point application confirmation

"Michael E Fox - N6MEF" <n6mef@...>



I think I was clear that the intended implementation is for multi-access in suburban/urban areas, not point-to-point.  The signals will not be as clean as typical point-to-point connections.


I really don’t see a need to debate the need for FEC any further.  Our measurements – including different digital radio formats -- show it will help.  And there’s a reason why it’s so commonly used in so many different digital radio formats and modulation schemes.  You may not agree.  But I’m betting that pretty much the rest of the world is not wrong.   ;-)





From: UniversalDigitalRadio@... [mailto:UniversalDigitalRadio@...]
Sent: Tuesday, February 03, 2015 6:29 PM
To: UniversalDigitalRadio@...
Subject: RE: [UniversalDigitalRadio] Re: RF access point application confirmation



The 'plan' is to release the platform into the wild and enable the community to produce the SDR components needed/wanted for higher speeds - I don't see this a long-term goal, but a very short-term one. Much of the required software already exists, I'd be surprised if it's more than a month or two before the first, practical 56 kbps transmissions start to happen. I know that I'm going to be experimenting with this as soon as the unit is available. The beauty of SDR is that if the first efforts are less than stellar it's a simple matter to push new code out to one or more nodes, if need be.

And I can say - emprically - that FEC is *not* required for 56 k to work well - the 56 k network in Vancouver had no FEC and had terrific throughput, even when one station was mobile and more than 30 miles from the repeater. Modulation technique will likely have more effect on the throughput. 9600 bps is done using FM because "it's easy" on a typical ham rig designed for voice, just as 1200 bps used AFSK into the microphone and speaker connectors because we wanted to make it accessible using just about any rig - and because some Bell 202 standard modems were available from a local bank "by the pound" @ $1.75 each in 1979. :-) Neither of these modulation techniques are particularly sturdy, and pushing the same techniques to higher speeds would certainly have performance limitations.

This radio is not limited by either of these considerations - the modulation technique can be tailored for data, not shoe-horned onto a voice radio.

FEC may help for latency-sensitive transmissions (like voice and video), but on a relatively clean channel doesn't provide that much bang for the throughput buck for other kinds of data. If you're looking at 56 k for trunking and backhaul (good first, simple uses), good antennas and locations will win out over FEC overhead. Multi-point will be a different story, but even then it will be channel control that will matter more than FEC.

BTW - the RF is being engineered by the same ham (one of the best professional RF engineers I've ever known) who did the 56 k gear implementation in Vancouver, so we're not getting typical Kenwood/ICOM/Yaesu/... warmed-over voice radio efforts.

The flip side - you don't have to order one before the release, you can wait a little while and be a high speed follower - but I expect that the order backlog will be much longer as soon as the high speed software shows up. ;-)

- Richard, VE7CVS

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