ABSTRACT
Traditionally, EMC has focused on the emission and immunity of commercial equipment primarily at frequencies below 1 GHz, and, at least in the EU, a lot of regulations were driven by competitive issues related to the free movement of goods. The digital revolution has had considerable impact on our electromagnetic environment but it has to be admitted that EMC still bears the imprint of its legacy in analogue radio. In recent years, the EM environment has had to accommodate a host of new wireless services, both licensed and unlicensed, that compete for the same part of the spectrum. EMC as traditionally conceived has therefore to expand to encompass broader issues related to the interoperability and coexistence of systems. The illustration in Figure 16.1 will be familiar to many readers. It shows a phone (mobile), which may encompass considerable multifunctionality both internal (e.g., camera, video, MP3 player) and external (e.g., GPS, Bluetooth). Some of the external wireless links are licensed (e.g., GSM) and others are unlicensed and nomadic (e.g., Bluetooth). The manner in which these different technologies use the frequency spectrum means that receivers and transmitters must be able to work at different frequency bands in an adaptive manner, adjust gains and power levels, and do so in as transparent and secure a manner as possible. Several ad hoc networks will be using the same part of the frequency spectrum, which are effectively heterogeneous.1,2 A multitude of functional standards have been established to cope with this situation, but new standards are needed to meet radio regulatory and EMC requirements.3,4
Rapid changes are taking place and functional standards are continuously under development to make it impossible to give an authoritative picture of the field at this stage. However, the impact of these technologies on EMC as currently understood is likely to be major and EMC engineers need to become familiar with the structure and future developments in wireless technologies. The purpose of this chapter is to sensitize EMC engineers to this challenging topic and thus facilitate interaction between professionals working in EMC and communications technologies. A more complete treatment of communications technologies is outside the scope of this book and must be sought in specialist texts.5-8
16.1 The Efficient Use of the Frequency Spectrum In the early days of radio, national governments and international bodies would allocate parts of the spectrum to different services and users. After a century of this practice and with the current explosion of wireless applications more efficient ways must be sought to utilize this asset (the frequency spectrum). Some of the ingenious ways that communications engineers have sought to get the maximum out of the available spectrum are described below.
