e odd- numbered bits of the next four bursts. The interleaving depth of the GSM interleaving for speech channels is then eight. A new data block also starts every four bursts. The interleaver for speech channels is called a block diag- onal interleaver. Interleaving For the GSM Data TCH Channels A particular interleaving scheme, with an interleaving depth equal to 22, is applied to the block of 456 bits obtained after the channel coding. The block is divided into 16 blocks of 24 bits each, 2 blocks of 18 bits each, 2 blocks of Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Radio and MS-PCUSN Interfaces Radio and MS-PCUSN Interfaces 12 bits each, and 2 blocks of 6 bits each. It is spread over 22 bursts in the fol- lowing way: 1. The first and the twenty-second bursts carry 1 block of 6 bits each. 2. The second and the twenty-first bursts carry 1 block of 12 bits each. 3. The third and the twentieth bursts carry 1 block of 18 bits each. 4. From the fourth to the nineteenth burst, 1 block of 24 bits is placed in each burst. A burst will then carry information from five or six consecutive data blocks. The data blocks are interleaved diagonally. A new data block starts every four bursts. Channel Coding in GPRS Four different coding schemes, CS-1 to CS-4, are defined for the radio blocks carrying RLC data blocks. These are summarized in Figure 6-33 with the coding scheme, the throughput in data rates, and the coding ratio. For the radio blocks carrying RLC/MAC control blocks, code CS-1, similar to SDCCH coding in GSM, is always used. Two specific coding schemes are LLC frames Figure 6-33 4 Coding Schemes: The four coding CS-1: same coding as SDCCH in GSM schemes used. CS-2 and CS-3=CS-1+ punctured bits RLC/MAC block data CS-4: no coding for error correction 1 Packet = 4 bursts RLC/MAC RLC/MAC max Coding Scheme Code Rate Block data size throughput