Problem with softbits in osmo_ubit2pbit()

Bhaskar11 niceguy108 at gmail.com
Tue Feb 5 18:22:37 UTC 2013


While playing with ccch_scan, I came across a strange problem.

At some point the code uses:
/* Convert to softbits */
for (i=0; i<116; i++)
bursts[(116*bid)+i] = bt[i] ? - (bi->snr >> 1) : (bi->snr >> 1);


After this, "xcch_decode()" works ok and "osmo_ubit2pbit_ext()" also works
ok. But "osmo_ubit2pbit()" fails as it converts almost all softbits to 0xFF.

Is this a bug or a "feature"? Do we need to recode "osmo_ubit2pbit" so that
its bit-checking is more robust as in "osmo_ubit2pbit_ext"?

Sylvain, can you explain the idea of using softbits instead of hard binary?
Is it for GSMTAP to represent signal strength?

Thanks in advance for your help.

B
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