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coding: fix artificial bit errors for PDTCH CS2 and CS3 

GPRS coding schemes CS2 and CS3 (defined in 3GPP TS 45.003 sections
5.1.2 and 5.1.3, respectively) employ so-called puncturing, which
can be described as intentional removal of coded bits.  The goal
of puncturing is to reduce the number of coded bits, so that they
fit into 4 bursts.  The receiving side recovers punctured bits,
as if they were received corrupted.

The puncturing is also used for other channel types like TCH/F9.6,
TCH/F14.4, TCH/AFS and TCH/AHS, but only for CS2 and CS3 we're
doing puncturing/depuncturing *manually*.  This explains why
we're seeing artificial bit errors only for CS2 and CS3.

gsm0503_pdtch_decode() should not be reporting punctured bits as
bit errors, fix this by using osmo_conv_decode_ber_punctured().

Change-Id: I024276d167e769396187998d881f8e7626461249
Related: OS#6342, OS#6200
This commit is contained in:
Vadim Yanitskiy 2024-01-31 20:59:04 +07:00
parent 2a72d683d3
commit 6c4be02962
2 changed files with 11 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
src/coding/gsm0503_coding.c
View File

@ -1066,8 +1066,10 @@ int gsm0503_pdtch_decode(uint8_t *l2_data, const sbit_t *bursts, uint8_t *usf_p,
cB[i] = 0;
}
osmo_conv_decode_ber(&gsm0503_cs2_np, cB,
conv, n_errors, n_bits_total);
osmo_conv_decode_ber_punctured(&gsm0503_cs2_np, cB, conv,
n_errors, n_bits_total,
gsm0503_puncture_cs2);
/* 5.1.2.2 a) the three USF bits d(0),d(1),d(2) are precoded into six bits */
for (i = 0; i < 8; i++) {
@ -1102,8 +1104,9 @@ int gsm0503_pdtch_decode(uint8_t *l2_data, const sbit_t *bursts, uint8_t *usf_p,
cB[i] = 0;
}
osmo_conv_decode_ber(&gsm0503_cs3_np, cB,
conv, n_errors, n_bits_total);
osmo_conv_decode_ber_punctured(&gsm0503_cs3_np, cB, conv,
n_errors, n_bits_total,
gsm0503_puncture_cs3);
/* 5.1.3.2 a) the three USF bits d(0),d(1),d(2) are precoded into six bits */
for (i = 0; i < 8; i++) {

8
tests/coding/coding_test.ok
View File

@ -270,7 +270,7 @@ S-Bits:
7f 7f 7f 81 7f 81 81 81 81 81 81 81 81 81 7f 7f 7f 7f 7f 81 81 81 81 7f 81 81 7f 7f 7f 7f 7f 81 81 7f 7f 7f 7f 7f 7f 81 7f 7f 81 81 7f 7f 7f 81 81 7f 81 7f 7f 7f 81 81 7f 81 7f 7f 81 81 7f 81 7f 7f 81 81 7f 81 7f 7f 81 7f 7f 81 7f 81 81 7f 7f 7f 7f 7f 81 7f 81 7f 7f 7f 7f 81 81 7f 7f 81 81 7f 7f 7f 7f 81 81 7f 81 81 7f 81 81 7f 7f 81 81 7f 81 81
7f 81 81 81 81 7f 81 7f 7f 7f 81 81 7f 7f 7f 7f 81 81 81 7f 7f 7f 81 7f 81 7f 7f 7f 81 81 81 7f 81 81 81 7f 7f 7f 81 81 81 7f 81 81 7f 81 81 7f 7f 81 81 7f 81 81 81 81 81 7f 7f 7f 7f 7f 81 81 81 81 7f 7f 7f 81 81 81 7f 7f 7f 81 81 7f 81 7f 7f 7f 81 81 7f 81 81 81 7f 7f 81 7f 81 81 81 7f 81 81 81 81 81 7f 81 7f 81 81 81 81 81 7f 81 81 7f 7f 81 81
Decoded: a3 af 5f c6 36 43 44 ab d9 6d 7d 62 24 c9 d2 92 fa 27 5d 71 7a 59 a8 42 a3 af 5f c6 36 43 44 ab a3 2f
pdtch_decode: n_errors=132 n_bits_total=588 ber=0.22
pdtch_decode: n_errors=0 n_bits_total=588 ber=0.00
Encoding: a3 af 5f c6 36 43 44 ab d9 6d 7d 62 24 c9 d2 92 fa 27 5d 71 7a 59 a8 42 a3 af 5f c6 36 43 44 ab a3 af 5f c6 36 43 44 03
U-Bits:
@ -284,7 +284,7 @@ S-Bits:
81 81 7f 7f 7f 81 81 7f 7f 7f 7f 7f 7f 7f 81 7f 7f 7f 7f 81 7f 81 7f 81 7f 81 81 81 81 81 81 7f 81 7f 81 81 7f 7f 7f 81 81 81 7f 81 7f 81 81 81 81 81 7f 7f 81 81 81 81 7f 7f 7f 81 7f 7f 7f 7f 81 81 7f 81 81 7f 7f 7f 81 81 7f 7f 81 81 7f 81 81 7f 7f 81 81 7f 81 81 7f 7f 7f 7f 81 7f 81 7f 7f 7f 7f 7f 81 7f 7f 7f 7f 7f 81 7f 81 81 7f 7f 81 81 81 7f
7f 81 81 81 7f 7f 7f 7f 81 7f 81 7f 7f 7f 7f 81 7f 7f 81 7f 7f 81 7f 81 7f 7f 81 7f 7f 7f 81 7f 7f 81 81 7f 81 7f 7f 81 81 81 7f 81 7f 7f 7f 7f 81 7f 81 81 81 7f 7f 7f 7f 7f 81 81 81 81 81 7f 7f 81 81 7f 7f 7f 7f 7f 81 81 7f 7f 81 7f 7f 81 81 7f 81 81 81 7f 81 7f 7f 81 81 81 81 7f 81 7f 7f 81 7f 81 7f 7f 81 81 81 81 7f 81 7f 7f 81 81 7f 7f 81 81
Decoded: a3 af 5f c6 36 43 44 ab d9 6d 7d 62 24 c9 d2 92 fa 27 5d 71 7a 59 a8 42 a3 af 5f c6 36 43 44 ab a3 af 5f c6 36 43 44 03
pdtch_decode: n_errors=220 n_bits_total=676 ber=0.33
pdtch_decode: n_errors=0 n_bits_total=676 ber=0.00
Encoding: a3 af 5f c6 36 43 44 ab d9 6d 7d 62 24 c9 d2 92 fa 27 5d 71 7a 59 a8 42 a3 af 5f c6 36 43 44 ab a3 af 5f c6 36 43 44 ab d9 6d 7d 62 24 c9 d2 92 fa 27 5d 71 7a 28
U-Bits:
@ -326,7 +326,7 @@ S-Bits:
7f 7f 81 7f 81 81 7f 7f 7f 81 7f 7f 7f 81 81 7f 81 7f 81 7f 7f 7f 7f 7f 81 7f 81 81 81 7f 81 7f 7f 7f 81 7f 7f 81 7f 7f 81 7f 7f 7f 81 7f 81 81 81 81 7f 81 7f 81 7f 7f 81 81 7f 7f 7f 7f 81 81 7f 7f 7f 7f 7f 81 81 7f 7f 7f 81 7f 7f 7f 81 81 7f 7f 7f 81 7f 7f 81 7f 81 7f 7f 7f 81 7f 7f 7f 7f 81 7f 7f 7f 7f 7f 7f 81 7f 7f 81 7f 81 7f 7f 81 7f 81 81
81 7f 81 7f 7f 81 7f 7f 81 81 7f 7f 81 7f 81 7f 7f 81 81 81 7f 81 7f 81 81 7f 81 7f 81 7f 81 7f 81 7f 7f 7f 7f 7f 7f 81 81 7f 81 7f 7f 7f 81 7f 7f 7f 7f 7f 81 7f 81 7f 81 7f 7f 7f 81 7f 81 7f 7f 81 7f 81 81 81 7f 7f 81 7f 7f 7f 81 7f 7f 7f 7f 81 81 7f 81 81 81 7f 7f 7f 81 7f 7f 7f 7f 81 81 81 7f 7f 7f 7f 81 7f 7f 81 7f 81 7f 7f 81 81 7f 7f 81 7f
Decoded: 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 00 00 00 00 00 00 00 00 00 00 00
pdtch_decode: n_errors=132 n_bits_total=588 ber=0.22
pdtch_decode: n_errors=0 n_bits_total=588 ber=0.00
Encoding: 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
U-Bits:
@ -340,7 +340,7 @@ S-Bits:
81 7f 81 7f 81 81 7f 7f 7f 81 7f 81 7f 7f 81 7f 7f 7f 81 7f 7f 81 7f 7f 7f 7f 81 7f 7f 7f 7f 7f 81 81 7f 7f 7f 7f 7f 81 81 81 7f 7f 7f 7f 81 81 7f 81 7f 7f 7f 7f 7f 81 7f 7f 7f 7f 81 7f 81 81 7f 7f 7f 81 7f 81 81 7f 81 7f 7f 7f 81 7f 7f 7f 7f 81 7f 7f 7f 81 7f 7f 81 7f 7f 7f 7f 81 7f 81 7f 81 7f 7f 81 7f 81 7f 7f 7f 7f 7f 7f 7f 7f 81 81 81 7f 7f
7f 7f 81 7f 7f 7f 7f 81 7f 81 7f 7f 81 7f 7f 7f 7f 81 7f 81 7f 7f 7f 81 7f 7f 81 7f 7f 7f 81 81 7f 81 7f 7f 7f 81 7f 81 7f 7f 7f 7f 81 81 7f 81 7f 81 7f 7f 81 7f 81 7f 81 7f 81 7f 7f 7f 7f 7f 7f 81 7f 81 81 81 81 7f 7f 7f 7f 7f 7f 81 7f 7f 7f 81 81 7f 81 7f 81 7f 7f 7f 81 7f 7f 81 7f 81 81 7f 81 7f 81 7f 7f 7f 7f 81 7f 7f 7f 81 81 81 81 7f 7f 7f
Decoded: 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
pdtch_decode: n_errors=220 n_bits_total=676 ber=0.33
pdtch_decode: n_errors=0 n_bits_total=676 ber=0.00
Encoding: 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
U-Bits: