TABLE OF CONTENTS Radio propagation characterization is the bread and butter of communications engineers. Without knowledge of radio propagation, a wireless system could never be developed. Radio engineers have to acquire full knowledge of the channel if they want to be successful in designing a good radio communication system [1]. Therefore, knowledge of radio propagation characteristics is a prerequisite for designing radio communication systems.
A lot of measurements have been done to obtain information concerning multipath fading channels. Reference [2] has presented a good overview of this topic. Detailed discussions on characteristics of multipath fading channels can be found in [3-8]. This chapter shows the essence in the literature.
This chapter is organized as follows. Multipath fading is due to multipath reflections of a transmitted wave by local scatterers such as houses, buildings, and man-made structures, or natural objects such as forest surrounding a mobile unit. The probability density function of the received signal follows a Rayleigh or Ricean distribution. Section 2.2 presents the Rayleigh and Ricean fading channels, and multipath delay profile is discussed in Section 2.3. The wireless channel is defined as a link between a transmitter and a receiver and classified considering the coherence bandwidth and coherence time. Accordingly, a wireless channel can be frequency selective or frequency nonselective (explained in Section 2.4) and time selective or time nonselective (described in Section 2.6). Section 2.5 briefly introduces the spaced-time correlation function.
Figure 2.1 shows a typical multipath fading channel often encountered in...
