TABLE OF CONTENTS The concept of flexibility in a receiver breaks down into two main areas: that of flexibility in the modulation format, coding, and framing and that of flexibility in terms of RF frequency (i.e., the ability to cover multiple bands, or provide general coverage, which is defined as covering all bands between a declared minimum and maximum frequency). This latter area, frequency flexibility, is certainly the more challenging of the two and is a concept which is the subject of much research. The former area has been much more widely addressed and most commercial communications receiver designs employ many of its basic principles, even if they do not aim to provide a wide choice of modulation formats.
Both concepts are covered in this chapter and Chapter 4, with a range of ideas being presented to enable the provision of frequency flexibility. Many of these have not yet been implemented in commercial designs and are still the subject of ongoing research; however, they are presented here as a set of basic concepts for further development.
