4MOBILE RADIO CHANNELS
In wireless communication, the received signal power Pr is expressed as:
where Pt is the transmit signal power, Gt the transmit antenna gain, Gr the receive antenna gain, and Lc the propagation loss in the channel. In an ideal free space, the propagation loss Lc is known as the Friis formula and is as follows:
where d is the distance between the transmit and receive points and λ is the wavelength of the radio wave. This is a simple equation. However, it is rather hard to understand in a physical sense that the wavelength λ term is included. A derivation of the formula with a concept of the antenna aperture cross section is given in Appendix 4.A.
A land mobile radio channel is characterized by out-of-sight communication to/from a moving terminal; it becomes a multipath propagation channel with fast fading. The characteristics of the mobile radio channel introduce new challenges for the designer of mobile communication systems, for example, requirements for isotropic directivity antenna, choice of appropriate carrier frequency, and techniques for stable transmission under the condition of fast fading.
Wave propagation in the multipath channel depends on the actual environment, such as antenna height, profile of buildings, roads, and terrain. Therefore, ...
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