Wireless Computer Networking

Melanie Hanson

May 6, 2002

Outline

Types of NetworksLayers of a networkData transfer techniquesFrequency HoppingDirect Sequence Spread Spectrum InfraredOrthogonal Frequency Division

Multiplexing

Network Types

Cellular Controlled by a base

station

Ad Hoc No base station No specific structure

Network Layers

7 layers in the traditional network

Physical layer contains hardware

Applications layer is user software

Types of Data Transfer

Spread SpectrumFrequency HoppingDirect Sequence Spread Spectrum

Infrared

Orthogonal Frequency Division Multiplexing

Spread Spectrum

Allows multiple access

Little interference due to other systems

Uses ISM band Industrial 902MHz to 928MHz Scientific 2.4GHz to 2.4853Ghz Medical 5.727GHz to 5.85GHz

Frequency Hopping

Frequency is periodically changed

Generates narrow band signals

Direct Sequence Spread Spectrum

Carrier is modulated following a specific sequence of bits

For ‘0’ the chip sequence is used

For ‘1’ the inverse chip sequence is used

Infrared

Intensity Modulation with Direct Detection (IM/DD) Signal is modulated onto the instantaneous

power of the carrier signal Direct detection aspect describes the process of

a photodetector

Orthogonal Frequency Division Multiplexing

Break signal into small orthogonal parts

Transmit stepsSerial to parallel conversionModulation Inverse Fourier transformParallel to serial conversionDigital to analog conversion

Which is best?

Depends on situation and environment