Peng Li Fall2008 Ece5765 Introduction To Wireless Networks

ECE, UMD

Peng Li

Introduction to Wireless Network

www.d.umn.edu/~lixxx988

Motivation

Why we use Wireless Network

Mobility Ease of use Installation Simplicity and Flexibility Cost


Outline

The elements in Wireless Network1

Spread Spectrum2

OFDM3

Wireless Data Services4

Summary5


The elements in Wireless Network

WirelessNetwork

DataFormat

NetworkStructure

RadioSignals


The elements in Wireless Network

In terms of the OSI reference model Data format controls several of high layers.

Network Structure includes the wireless network interface adapters and base stations that send and receive the radio signals.

Radio signal operates at physical layers.


Spread Spectrum

What’s the modulation method for Radio signal in Wireless Network ?

AM ? FM ? PCM ? Something else ?

Spread Spectrum !

Spread Spectrum

What’s Spread Spectrum ? Spread spectrum is a family of

methods for transmitting a single radio signal using a relatively wide segment of the radio spectrum.



Spread Spectrum

FHSSFrequency-Hopping Spread Spectrum

DSSSDirect-Sequence Spread Spectrum

OFDMOrthogonal Frequency Division Multiplexing

OFDM

What’s OFDM ? OFDM is a combination of modulation

and multiplexing. OFDM is a special case of FDM

(Frequency Division Multiplex). The main concept in OFDM is

orthogonality of the sub-carriers.


OFDM

OFDM System Diagram


OFDM

Benefits of OFDM Very easy and efficient in dealing with

multi-path

Robust again narrow-band interference



Wireless Data Services

Wi-Fi

Cellular Mobile Wireless Services

WiMAX

Bluetooth



Wi-Fi It covers the various IEEE 802.11

technologies (including 802.11n, 802.11b, 802.11g, and 802.11a).



Wi-Fi Characteristics



Wi-Fi Type Frequency Modulation

802.11a 5 GHz OFDM

802.11b 2.4 GHz DSSS

802.11g 2.4 GHz OFDM



Cellular Mobile Wireless Services



WiMAX

Worldwide Interoperability for Microwave Access, The technology is based on the IEEE 802.16 standard (also called WirelessMAN).



Bluetooth Bluetooth is an FHSS system that splits the radio

signal into tiny pieces. It moves among 79 different frequencies 1,600 times per second in the same unlicensed 2.4 GHz range as 802.11b and 802.11g Wi-Fi services.


Summary

Connecting your computer to the Internet (or a local network) by radio offers several advantages over connecting the same computer through a wired connection.

First, wireless provides convenient access for portable computers; it’s not necessary to find a cable or network data outlet.

Second, it allows a user to make a connection from more than one location and to maintain a connection as the user moves from place to place.

ECE, UMD

Q & A

Peng Li Fall2008 Ece5765 Introduction To Wireless Networks

Technology

Transcript of Peng Li Fall2008 Ece5765 Introduction To Wireless Networks