Hi.
I think the puncturing code should be part of the library (otherwise every user will have to reimplement the same thing again and again). Unfortunately I could not find any tests for the code in question so the only way to test it is by:
- add code with puncturing to the library
- replace manual puncturing with generic call
- run gprs with fixes CS* to make sure necessary code is triggered
- verify that it works as before
On 10/02/2016 09:11 AM, Vadim Yanitskiy wrote:
Hi Harald,
Why the code differs, I don't know. Maybe it was never completed in conv_gen?
It seems, I found the answer. If you look closer at gsm0503_coding.c/gsm0503_pdtch_encode(), you will see:
// Around line 1300, CS-2 encoding // ...
osmo_pbit2ubit_ext(conv, 3, l2_data, 0, 271, 1); usf = l2_data[0] & 0x7;
osmo_crc16gen_set_bits(&gsm0503_cs234_crc16, conv + 3, 271, conv + 3 + 271);
memcpy(conv, gsm0503_usf2six[usf], 6);
osmo_conv_encode(&gsm0503_cs2, conv, cB);
// for (i = 0, j = 0; i < 588; i++) if (!gsm0503_puncture_cs2[i]) cB[j++] = cB[i];
hl_hn = gsm0503_pdtch_hl_hn_ubit[1];
// ...
So, as I understand, this code applies puncture itself. But in our case, the osmo_conv_encode() applies puncture too, from the gsm0503_cs2 convolutional code definition. The same things happens in the gsm0503_pdtch_decode().
There are two possible ways to go in my mind:
- The simplest way is to merely remove puncture from both gsm0503_cs2 and gsm0503_cs3 definitions, but it may break some code, which already uses current variant.
- Change exactly the gsm0503_coding.c to use puncture from shared convolutional code definitions. For me, this way is prefered, but I don't know how to change the code yet.
Any opinions? Does any project use the convolutional code definitions from 'utils/conv_gen.py'?
With best regards, Vadim Yanitskiy.
2016-09-29 21:40 GMT+07:00 Harald Welte <laforge@gnumonks.org mailto:laforge@gnumonks.org>:
From my memory: * CS1 is rate 1/2 conv code with no puncturing. * CS2+3 apply different puncturing amounts on that conv code * CS4 has no error correction (=100% puncturing) Why the code differs, I don't know. Maybe it was never completed in conv_gen? -- Sent from a mobile device. Please excuse my brevity.