Wireless Networks and Spread Spectrum Technologies
David D Coleman, David A Westcott · 2018
This chapter examines different spread spectrum transmission technologies and frequency ranges that are supported by the 802.11 standard and amendments. The chapter offers guidance on how these frequencies are divided into different channels and some of the proper and improper ways of using the channels. The chapter contains many references to FCC specifications and regulations, with the CWNA exam not testing people on any regulatory domain-specific information. Any FCC references are provided strictly to help user understand the technology better. Frequency-hopping spread spectrum (FHSS) uses Gaussian frequency-shift keying (GFSK) to encode the data. Two-level GFSK (2GFSK) uses two frequencies to represent a 0 or a 1 bit. Four-level GFSK (4GFSK) uses four frequencies, with each frequency representing 2 bits. Orthogonal frequency-division multiplexing (OFDM) is one of the most popular communications technologies, used in both wired and wireless communications. The 802.11-2016 standard specifies the use of OFDM at 5 GHz and also specifies the use of ERP-OFDM at 2.4 GHz. OFDM and ERP-OFDM are the same technology used by 802.11a and 802.11g radios, respectively.