[Freetel-codec2] Number of carriers

[Steve]

I was experimenting with the number of carriers (8 versus 7) on the
coherent modem yesterday, and it seemed to work well.

I was wondering how the number 7 was decided on, as it seems like an odd
number.

For example, for my purposes, it will be simplified to have 32-bits every
baud. I didn't know how to change the pilots so I just added some opposite
to the end:

1.000000, -1.000000, 1.000000, -1.000000, 1.000000, -1.000000, -1.000000,
1.000000

-1.000000, 1.000000, 1.000000, -1.000000, 1.000000, 1.000000, 1.000000,
-1.000000

The 32-bits also gives you another 4-bits at the vocoder, so you can use
1-bit for text and expand something else by 3 bits, or just have 4-bits for
text. 800 bit/s versus 700.

73, Steve/k5okc

[Steve]

oops, I mean 16-bits per baud/row. 1200 bit/s

[David Rowe]

Hi Steve,

Can't recall exactly but I guess it was chosen to get the bit rate I
needed for the codec. Minimising carriers is best, to minimise
bandwidth, allowing more room for FEZC or diversity.

Sure, any choice of pilot symbol value is probably OK.

Cheers,

David

Post by Steve
I was experimenting with the number of carriers (8 versus 7) on the
coherent modem yesterday, and it seemed to work well.
I was wondering how the number 7 was decided on, as it seems like an odd
number.
For example, for my purposes, it will be simplified to have 32-bits
every baud. I didn't know how to change the pilots so I just added some
1.000000, -1.000000, 1.000000, -1.000000, 1.000000, -1.000000,
-1.000000, 1.000000
-1.000000, 1.000000, 1.000000, -1.000000, 1.000000, 1.000000, 1.000000,
-1.000000
The 32-bits also gives you another 4-bits at the vocoder, so you can use
1-bit for text and expand something else by 3 bits, or just have 4-bits
for text. 800 bit/s versus 700.
73, Steve/k5okc
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[Steve]

I did have to move the center frequency to 1200 to keep it all below 2500
Hz. With 1200 Hz center it sits between 350 Hz and 2150 Hz. @1800 Hz BW.

Nothing practical, just experimenting with the software. I measured PAPR at
7.9 dB which is odd,
but I'm also playing with Newman phases again.

73/steve