OFDM Baseband Receiver Design for Wireless Communications

4

Signal Propagation and Channel Model

Wireless communication signals experience many adverse effects as they travel through the transmitter/receiver electronics, antennas and the radio-frequency channel. Understanding these effects and modeling them accurately will lay a solid foundation to wireless receiver design.

4.1 Introduction

Wireless communication systems offer many advantages, such as mobility, easy access and installation; however, they also suffer more limitations than wireline transmission systems, such as limited capacity, spectrum shortage and service quality uncertainties. In wireless communication systems, signals are transmitted over the air in the radio-frequency (RF) band. There are numerous non-ideal factors that affect the quality of the received signals and, thus, the reliability of wireless communication. As a result, these wireless channel effects place some fundamental limitation on the capability of wireless communication systems.

Wireless radio channels are extremely dynamic and time-varying due to channel variations and user movement. Making matters worse is the fact that wireless transmission is usually off and on owing to the inconsistent nature of the wireless channels. Hence, most analysis and estimation of the wireless channels must be re-started every so often. In addition to the effects of the wireless channels, the transmission signal also suffers distortions caused by RF front-end circuits. To construct an equivalent baseband channel model ...