Mobile Radio Transmission System -3.Fading and Diversity
Radio waves in mobile communications are subject to reflection, diffraction and scattering caused by the impact of obstacles and reflecting objects such as buildings, trees and undulations in the terrain. As a result, multiple radio waves traveling different paths can interfere with each other, causing dramatic fluctuations in the strength of the received wave. This phenomenon is known as fading.
One measure used to overcome this problem is Diversity Reception. It can realize high-quality and highly reliable connections by minimizing fading-induced fluctuations in the received wave level. This technology employs a process of synthesizing or switching among the outputs of multiple reception systems. The systems may use multiple antennas installed some distance apart, or by installing them with different focal directions or different polarization. The main methods used to synthesize the output in diversity reception systems include maximum ratio synthesizing reception, selective synthesizing reception and equal-gain synthesizing reception.
The concept of diversity receivers