6.2 Wireless Communications
The subject matter of this book relates to the transmission of a digital data over a wireless channel. Several stages of processing are needed in order to do this. All these stages, along with the information-generating source and the channel itself, are seen as a wireless communications system. Often, an ease of analysis dictates that the system is considered with a simplified structure that includes only the main blocks. These blocks are in the sequential order during transmission and assuming that the source is already in a digital form,
- In the transmitter:
- Source encoder: This block is concerned with the representation of the information from the source, usually appearing as a group of samples organized in a source data block, in digital form (as a sequence of bits). The most important operation that is performed in the source encoder, in what concerns this book, is the representation of the information from the source in a compact and efficient way that usually involves compression of the source data block.
- Channel encoder: This block protects the sequence of bits from the source encoder against the errors that the wireless channel will unavoidably introduce. This is done by adding extra redundant bits and a specific structure to the sequence of bits that is presented to the input of the encoder. Because this operation adds redundant bits, the number of bits at the output of the channel encoder is never less than the number of bits at the input. ...