systematic and parity bits in the coded block provided as an output of the turbo encoder process. This interleaving process is aimed to mitigate the effects of error bursts likely to appear in radio mobile channels due to the time- variant fading effects. Consequently, a dual de-interleaving operation is needed at the receiver side to recover original coded blocks. The result of the interleaving process is stored into a circular buffer where a puncturing process is applied to decrease the effective coding rate according to the MCS corresponding to the considered CQI level. The complete rate matching process is depicted in Figure 3.14. This process allows different coding rates to be achieved (i.e., a higher coding rate to improve robustness against the effects of the channel at the expense of a lower spectral effi- ciency, or vice versa). Additionally, the rate matching process is used in LTE to give support to the HARQ protocol, as described in Section 3.2.5. 3.2.4.4 Coded Block Concatenation This process consists of the sequential concatenation of the rate matching outputs for the different code blocks. The result-namely, a code word-is the coded ver- sion of the original transport block to be transmitted. © 2009 by Taylor & Francis Group, LLC Radio-Interface Physical Layer From Turbo Encoder Coded Block Sub-block Sub-block Sub-block RM Interleaving interleaving interleaving interleaving Interleaving Interleaved Coded Block Circular Buffer RM Coded Block To Coded Block Concatenation Figure 3.14 Detail of interleaving process for a code word generated with turbo codes in LTE. 3.2.5 Hybrid Automatic Repeat Request (HARQ) Hybrid automatic repeat request, a combination of traditional ARQ and error cor- rection codes (such as the turbo code introduced in a previous subsection), is a common element in the physical layer of current mobile communication systems such as HSPA (high-speed packet access) or LTE. At the expense of a higher com- plexity in its implementation than required for a traditional ARQ strategy, HARQ