. The interleaver introduces randomness to decoder, which exploits this new information to update the code while leaving enough structure in it SO that its extrinsic information. The procedure repeats until the decoding is physically feasible. The size of the interleaver a posteriori LLRs converge or a maximum number of (the length of the information block) is usually very large iterations is reached. (in the order of thousands of bits) to ensure good per- Turbo coding with iterative decoding is currently one formance. If the size is large enough, any pseudo-random of the best error-correcting techniques. It significantly interleaver will perform well. However, for short outperforms convolutional codes of the same constraint interleaver sizes, the performance of the code can be length. One of the key properties of turbo codes is the significantly enhanced by a clever design of the interleaver sharp performance improvement with the increase of the input block length. Thus, to achieve near-capacity A typical turbo decoder consists of two soft-input performance, large block lengths are needed, which cause soft-output decoders (see Section 3.4.3.2), two k-bit huge latency. Therefore, applications of turbo codes are interleavers identical to the encoder interleaver, and currently limited to those that are not delay sensitive. For a deinterleaver, as shown in Figure 3.4-12. The decoding example, the new CCSDS telemetry channel coding is based on the symbol MAP rule (see Section 3.4.2.2). standard for satellite and deep-space communications The a posteriori LLRs for the information bits U1, uses turbo codes. SMART-1, launched in September CHAPTER 3.4 Channel protection fundamentals 2003 by the European Space Agency, is the first probe higher level modulation techniques achieve larger data that exploits turbo codes. Turbo codes have also been rates at the expense of a lower robustness. adopted by the leading third-generation (3G) cellular Binary phase shift keying (BPSK) allows transmission standards, such as CDMA2000 an