TABLE OF CONTENTS An information stream going through a digital radio access network such as the UTRAN must undergo several coding processes, which are depicted in Figure 6.1. The information entering this system may already be in digital format (data) or it may be analog information (voice).
The source encoding function transforms the user's traffic into a digital format. The particular source encoder depends on the type of the information in need of encoding. Speech is encoded using a speech encoder (AMR, Adaptive Multi Rate codec, in the UTRAN), video using a video encoder, etc. The source encoder tries to encode the information into the smallest possible number of bits from which the source decoder in the receiving entity can reconstruct the same original information if no errors were introduced to the data during its transmission. Various compression techniques may be used to accomplish the source coding task. But source coding removes most of the redundancy inherent in the user's information. Another from of redundancy has to be added back into the data stream so that the data can be recovered in the receiver even after suffering the trials of the radio channel.
By inserting carefully contrived redundancy back into the user's data stream, channel coding is responsible for delivering the information bits without any errors over the radio interface. The transmission channel can introduce errors to transmitted bits, which must first be detected and then corrected, if possible. These tasks...
