Osmocom's Base Station Controller for 2G mobile networks https://osmocom.org/projects/osmobsc
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osmo-bsc/doc/gsm-hopping.txt

55 lines
1.3 KiB

according to GSM 05.02:
general parameters from CCCH:
* CA cell allocation of ARFCN's (System Information / BCCH)
* FN: TDMA frame number (t1,t2,t3') in SCH
specific parameters from channel assignment:
* MA: mobile allocation, defines set of ARFCN's, up to 64
* MAIO: index
* HSN: hopping sequence generator number (0..64)
hopping sequence generation (6.2.3):
uint8_t rntable[114] = {
48, 98, 63, 1, 36, 95, 78, 102, 94, 73,
0, 64, 25, 81, 76, 59, 124, 23, 104, 100,
101, 47, 118, 85, 18, 56, 96, 86, 54, 2,
80, 34, 127, 13, 6, 89, 57, 103, 12, 74,
55, 111, 75, 38, 109, 71, 112, 29, 11, 88,
87, 19, 3, 68, 110, 26, 33, 31, 8, 45,
82, 58, 40, 107, 32, 5, 106, 92, 62, 67,
77, 108, 122, 37, 60, 66, 121, 42, 51, 126,
117, 114, 4, 90, 43, 52, 53, 113, 120, 72,
16, 49, 7, 79, 119, 61, 22, 84, 9, 97,
125, 99, 17, 123
};
/* mai=0 represents lowest ARFCN in the MA */
uint8_t hopping_mai(uint8_t hsn, uint32_t fn, uint8_t maio,
uint8_t t1, uint8_t t2, uint8_t t3_)
{
uint8_t mai;
if (hsn == 0) /* cyclic hopping */
mai = (fn + maio) % n;
else {
uint32_t m, m_, t_, s;
m = t2 + rntable[(hsn xor (t1 % 64)) + t3];
m_ = m % (2^NBIN);
t_ = t3 % (2^NBIN);
if (m_ < n then)
s = m_;
else
s = (m_ + t_) % n;
mai = (s + maio) % n;
}
return mai;
}