Introduction

There are a variety of unlicensed wireless networks that operate in shared frequency bands. Many of these networks are installed in portable and hand-held devices. Given that these devices are portable it is not uncommon for devices using one unlicensed network to be in close proximity to another device using another unlicensed wireless network. These unlicensed wireless networks may operate in the same frequency band and may even operate in the same channel within the band. This raises the issue of whether these two networks can coexist in the same location. This chapter describes this coexistence issue.

Section 20.2 gives an overview of the various unlicensed frequency bands in the United States. Many of these bands are also unlicensed bands in other countries. Section 20.3 is a short survey of some of the unlicensed wireless networks that share these frequency bands. Section 20.4 gives a short history of coexistence of unlicensed wireless networks. Section 20.5 illustrates how to evaluate coexistence of two unlicensed wireless networks. Section 20.6 describes several methods of improving coexistence. Sections 20.7 and 20.8 give example of evaluating coexistence of wireless networks, using two IEEE 802 standards as case studies. And finally Section 20.9 discusses the issue of dynamic spectrum access in which unlicensed wireless networks identify and use unused portions of licensed frequency bands.

Overview of Unlicensed Frequency Bands

Unlicensed wireless networks can operate in a variety of frequency bands.