Re: PHY Layer Protocols


"Michael E Fox \(N6MEF\)" <n6mef@...>
 

True.  But the problem is, many (most?) “real world” channels in a metro area (<25 miles) are NOT “nearly loss-less”.   On many (most?) real-world channels, you will get single bit errors, causing the whole packet to be retransmitted.  Longer packets = greater probability of error.  Shorter packets = more header overhead.  End result is still lower throughput (often much lower) than with FEC.  It’s not a hard test to duplicate with 9600 baud packet.  It’s also not hard to duplicate with commercial digital radios although it does require a rather expensive analyzer to see the data.  That’s why the commercial digital radio world uses FEC.  The whole rest of the world is not wrong.

 

So, yes, it’s overhead and yes, we need it. 

 

Michael

N6MEF

 

From: UniversalDigitalRadio@... [mailto:UniversalDigitalRadio@...]
Sent: Tuesday, March 03, 2015 7:56 AM
To: UniversalDigitalRadio@...
Subject: [UniversalDigitalRadio] Re: PHY Layer Protocols

 

 

FEC is just overhead unless you really need it. On nearly loss-less channels (which is what we should expect on short haul 70 cm links), you lose more throughput than you gain with FEC.

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