48, 379), channel coding has been widely used in digital communications to increase reliability in the trans- mission through a nonideal channel. Channel coding techniques make it possible to detect and correct some of the errors introduced by the channel at the expense of adding redundant information to the transmitted data. The complete channel coding scheme may be seen as a complex process in which error detection/correction techniques, rate matching, and channel interleav- ing are applied to transmitted information before being mapped onto the physical media (see Figure 3.10). The channel coding process chain in LTE (3GPP 36.212) is described in the next subsections. From Upper Layers Transport Block CRC Attachment and Segmentation Code Block(s) Channel Coding Coded Block(s) Rate Matching RM Coded Block(s) Coded Block Concatenation Codeword To Physical Channel Mapping (Modulation Mapping) Figure 3.10 Simplified channel coding scheme in LTE. C 2009 by Taylor & Francis Group, LLC Long Term Evolution: GPP LTE Radio and Cellular Technology Transport Block Transport block CRC (24 bits) Code block CRC (24 bits) Transport Block Filler bits Code block #1 Code block #2 Code block #3 Figure 3.11 Detail of the segmentation of a transport block after CRC bits are appended. 3.2.3 CRC and Segmentation A fixed 24-b CRC is calculated for each transport block coming from layer 2. The calculated CRC is appended to the transport block in order to check the data integrity at the receiver end. If the input sequence length is shorter than 40 bits, filler bits are added to the beginning of the code block. Otherwise, if the result- ing bit sequence is longer than the maximum allowed code block size (6144 bits), a segmentation process must be carried out. After the segmentation, filler bits are added to the last segment, if needed. Finally, an additional CRC sequence of 24 b is then attached to each resulting segment. Otherwise, if the input sequence length is shorter than 40 b, filler bits are added to the beginning of the code bloc