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coding: fix bit ordering in 11-bit RACH coding functions 

According to 3GPP TS 44.004, figure 7.4a.b, the format of 11-bit
RACH uplink / Uplink access burst block is as defined follows:

  <---------------------------------------------------

      8     7     6     5     4     3     2     1
  +--------------------------------------------------+
  |  11 bit RACH uplink / Uplink access burst block  | OCT1
  +--------------------------------------------------+
                                 |                   | OCT2
                                 +-------------------+

As was (correctly) assumed in [1], the bit ordering in 11-bit RACH
coding functions is wrong. The problem is that neither of generic
functions from bit16gen.h can be used to load / store the RA11
value (regardless of the endianness), because they assume that
the payload is 16 bit long.

With this patch applied, RA11 values from [1] look correct:

  < EGPRS Packet channel request message content > ::=
    < Signalling : 110011  < RandomBits : 00111 > > |
    < Signalling : 110011  < RandomBits : 00110 > > |
    < Signalling : 110011  < RandomBits : 01111 > > |
    < Signalling : 110011  < RandomBits : 01100 > > |
    < Signalling : 110011  < RandomBits : 00111 > > |
    < Signalling : 110011  < RandomBits : 10110 > > ;

[1] Id80e471d252b9416217b56f4c8c0a8f5f1289fee

Change-Id: I43d30611dd69f77f2b3b46f4b56056a8891d3c24
Related: OS#1548
This commit is contained in:
Vadim Yanitskiy 2020-03-31 19:40:09 +07:00
parent 41ce6753bc
commit 9e713f3828
2 changed files with 9 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
src/coding/gsm0503_coding.c
View File

@ -2879,7 +2879,7 @@ static inline int16_t rach_decode_ber(const sbit_t *burst, uint8_t bsic, bool is
osmo_ubit2pbit_ext(ra, 0, conv, 0, nbits, 1);
return is_11bit ? osmo_load16le(ra) : ra[0];
return is_11bit ? ((ra[0] << 3) | (ra[1] & 0x07)) : ra[0];
}
/*! Decode the Extended (11-bit) RACH according to 3GPP TS 45.003
@ -2974,7 +2974,8 @@ int gsm0503_rach_ext_encode(ubit_t *burst, uint16_t ra11, uint8_t bsic, bool is_
uint8_t ra[2] = { 0 }, nbits = 8;
if (is_11bit) {
osmo_store16le(ra11, ra);
ra[0] = (uint8_t) (ra11 >> 3);
ra[1] = (uint8_t) (ra11 & 0x07);
nbits = 11;
} else
ra[0] = (uint8_t)ra11;

12
tests/coding/coding_test.ok
View File

@ -40,12 +40,12 @@ S-Bits:
Decoded: 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15 16 17
xcch_decode: n_errors=60 n_bits_total=456 ber=0.13
Decoded RA11: 0x7cc
Decoded RA11: 0x6cc
Decoded RA11: 0x7cd
Decoded RA11: 0x4cd
Decoded RA11: 0x7cc
Decoded RA11: 0x6ce
Decoded RA11: 0x667
Decoded RA11: 0x666
Decoded RA11: 0x66f
Decoded RA11: 0x66c
Decoded RA11: 0x667
Decoded RA11: 0x676
Encoding: 03 03 01 00
U-Bits: 111001110011000011100111001100001101001111000000000011010000011010110111111100