Hi Take,
On 7/4/2018 9:20 AM, Tsutsumi Takehiko JA5AEA wrote:
Concerning the “second +4dB term”, I remember Bill’s suggestion included
hashing of callsign (I used the number of (28-15) x 5 = 65 bit
reduction). I also reduced five 7x7 synch to one 7x7 synch, which I am
not sure whether Bill included. I will not further describe the details
to defend my ballpark number but I can say I disagree with your 0.6dB
gain calculation, here.
Yes, if you convey less information you can achieve a lower threshold
SNR for decoding.
For this discussion I had assumed 11x28 = 308 bits for callsigns and 5x6
=30 bits for signal reports, 338 bits total. Compared with the 5x75 =
375 bits for 5xFT8, this leads to a gain of ~0.5 dB. Steve quoted 0.6
dB because he used 3-bit rather than 6-bit reports.
If we use 13-bit hashes for the callsigns being sent "RR73", the total
would be 6x28 + 5x13 + 5x6 = 263 bits. Compared to 5xFT8, this yields
10log(375/263) = 1.5 dB.
Apparently you are suggesting something like 150-bit information
content, since 10log(375/150) = 4 dB. This is not at all the same thing
as 5 FT8 messages.
As I write to Steve, I do not have any intention to sell or stick to my
+8dB number. If you feel uncomfortable, please deal it to + (1~8)dB
additional gain proposal .
No problem -- we are happy to discuss these things with you!
-- 73, Joe, K1JT
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