4G Wireless Video Communications

2

Wireless Communications and Networking

In the past decades, wireless communications and networking have enjoyed huge commercial success, thanks to many new wireless technologies and industrial standards. The fundamental difference between wired and wireless technologies resides in the physical channel. The unique features of wireless propagation such as reflection, refraction, and shadowing result in various channel impairments including multi-path fading, path loss, and doppler frequency, making it very challenging for high-speed information delivery over the wireless channel. Furthermore, the time-varying nature of wireless media poses new design challenges for wireless networks, since the existing Internet protocols were developed based on the assumption that all packet losses are caused by network congestions, which is no longer the case in the wireless environment. In this chapter, we will provide a brief overview of the fundamentals of wireless communications and networking, especially the technologies adopted by 4G wireless systems such as cross-layer design, adaptive modulation and coding, hybrid ARQ, MIMO and OFDM.

2.1 Characteristics and Modeling of Wireless Channels

2.1.1 Degradation in Radio Propagation

Errors which occur in data transmission through wireless channels are mainly caused by three types of degradation, i.e. interference, frequency-nonselective fading and frequency-selective fading. Note that although there are other kinds of degradation in wireless networks ...