Digital Communication Systems

APPENDIX

F   Interleaving

Previous chapters of the book, going back to Chapter 5, have shown us how a digital wireless communication system can be separated by function into source-coding and channel-coding applications on the transmitting side and the corresponding inverse functions on the receiving side. In Chapter 6, we also learned how analog signals can be converted into a digital format. The motivation behind these techniques is to minimize the amount of information that has to be transmitted over a wireless channel. Such minimization has potential benefits in the allocation of two primary resources, namely transmit power and channel bandwidth, available to wireless communications:

1.  Reducing the amount of data that must be transmitted, which usually means that less power has to be consumed; power consumption is always a serious concern for mobile units that are typically battery operated.

2.  Reducing the spectral (or radio-frequency) resources, which are required for satisfactory performance; this reduction enables us to increase the number of users who can share the same but limited channel bandwidth.

Moreover, insofar as channel coding is concerned, forward error-correction (FEC) coding, discussed in Chapter 10, provides a powerful technique for transmitting information-bearing data reliably from a source to a sink across the wireless channel.

However, to obtain the maximum benefit from FEC coding in wireless communications, we require an additional technique known ...