Wireless Communications Systems Design

3Wireless Channels

Wireless communication systems are designed to recover received signals that are damaged by wireless channel impairments. In classical communication theory, wireless channels were unknown and people think unpredictable noises occur in wireless channels. However, many scientists and engineers investigated wireless channels and developed different types of wireless channel models. They can be categorized as additive white Gaussian noise, jitter, phase shift, path loss, shadowing, multipath fading, interference, and so on. They give the transmitted signals different types of damages. In addition, transmission distance, mobility, geographical feature, weather, antenna position, and signal waveform affect the parameters of wireless channel models. For example, the channel model of short range wireless communications is different from the one of cellular systems. An urban area channel model is different from that of a rural one. A mobile user has more severe frequency offset due to the Doppler effect. Therefore, it is important to understand wireless channels when designing wireless communication systems. In this chapter, we look into wireless channels and their characteristics.

3.1 Additive White Gaussian Noise

In Chapter 2, we have defined noise as Gaussian distribution due to central limit theorem. When the noise power has a flat power spectral density, we call it white noise and its single-sided power spectral density (P_wn(f) (W/Hz)) can be denoted as follows: ...