Illustration for SACCH/SDCCH/BCCH/PCH/AGCH [Under GSM]
Input is 184 information bits:Parity (40) and tail (4) bits (Ref 45.003:4.1.2):
Convolutional coding is applied to 228(=184+40+4) bits, 1/2 rate coding with following formulas (Ref 45.003:4.1.3):
G0 = 1 + D3 + D4
G1 = 1 + D + D3 + D4
Dy is cyclically shifted (by y bits) version of original bit sequence.
| G0 = | u(k) + | u(k - 3) + | u(k - 4) |
| G1 = | u(k) + | u(k - 1) + | u(k - 3) + | u(k - 4) |
G0 and G1 (228 bits each) are put together (G0 at even bits and G1 at odd bits) as below, totaling 456 bits.
The 456 bits are re-ordered and partitioned in 4 bursts, 114 bits in a burst (Ref 45.003:4.1.4).
Above bits are encrypted (using CK) and then actual bursts are formed. Normal burst have following format (Ref 45.002:5.2.3):
| Tail bits(3) | Info bits(57) | Steal bit | Training sequence(26) | Steal bit | Info bits(57) | Tail bits(3) |
Below are actual normal burst data (Ref 45.002:5.2.3,45.003:4.1.4/5):
References: GSM book by Mouly and Pautet.
© Copyright Samir Amberkar 2013