TABLE OF CONTENTS To deal intelligently in wireless LANs you will need some fundamental background in transmission systems, particularly those that depend on radio. In this chapter we will focus on the factors that impact radio transmission systems, and the physical limits we face in sending digital information or bits over a radio channel. The basic relationships are spelled out in a formula called Shannon s Law, which identifies the three critical factors that will determine the maximum transmission capacity of any transmission link: bandwidth, noise, and received signal power. In particular we will look at how those elements interact, and their impact on radio networks.
We will also investigate the general difficulties involved in radio communications, including the range of impairments that will affect radio signals, especially radio systems operating in indoor environments. We will conclude by introducing the major elements in a wireless LAN including access points, antennas, and NICs, and wireless LAN Switches, which are becoming the key element in enterprise WLANs.
Capacity is the most basic factor we deal with in any transmission system. Wireless LANs are relatively low-capacity communication systems so it is particularly important that we recognize the factors that impact their capacity. Network specialists often use the term speed to identify transmission capacity, however the correct term is actually rate. The transmission rate of a digital transmission system is measured in bits per second. In determining the performance of a communications network, the speed is not nearly as important a...
