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Networks

Introduction

Since the early 1990's there has been a tremendous growth in the wireless community. The modern idea of wireless networking was first introduced in the late 60's at the University of Hawaii with the ALOHANET. The ALOHANET was used to connect the different campus locations on the Hawaiian Islands. "The history of wireless networking stretches farther back than you might think. It was over fifty years ago, during World War II, when the United States Army first used radio signals for data transmission. They developed a radio data transmission technology, which was heavily encrypted. It was used quite extensively throughout the campaign with the US and her allies. This inspired a group of researchers in 1971 at the University of Hawaii to create the first packet based radio communications network. ALOHNET, as it was named, was essentially the very first wireless local area network (WLAN)." [2]

Figure 1 - Simple WLAN using 802.1x from Lecture13 notes.

Frequency-hopping spread spectrum

The implementation of a wireless LAN is done with the use of radio-frequency technology. The two technologies that are used in wireless LANs that include frequency-hopping and direct-sequence spread-spectrum. "Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver."[3] This technology was developed during WWII by the Army Signal Corps in a system called SIGSALY. SIGSALY was initially used for communication between Roosevelt and Churchill; this was not known for some years because the development of SIGSALY was classified top secret.[8] Under this type of communication more bandwidth is used than the usual transmission in which only a single frequency is used. This increased bandwidth is due to the signal being spread over a greater number of frequencies. FHSS is the process of hopping from one...