ABSTRACT
In contrast to wired communications, the radio channel in wireless networks is “open” in the sense that it does not have anything to protect or guide the signal as it travels or propagates from source to destination. As a result, the wireless signal is subject to many issues that affect its propagation in the air. This chapter examines these issues and the relevant tools and solutions to combat them. Specific topics covered include the basic types of antennas used in wireless communications, signal reflections leading to multipath propagation, signal fading, delay spread, and inter-symbol interference, mathematical models to estimate pathloss, i.e., the amount of signal power lost as it propagates from the transmitter to the receiver, basics of multiple-input-multiple-output (MIMO) systems that exploit spatial diversity in signal propagation to improve coverage and throughput of wireless communications using multiple antennas, and the frequency-sensitive multiplexing techniques such as Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA). [158 words]
