Introduction to RF & Wireless - Part 4

Introduction to RF & Wireless

Two Day Seminar

Module 4

Course Agenda
Day One
• Morning (Module 1)
– Introduction to RF
• Afternoon (Module 2)
– RF hardware

Day Two
• Morning (Module 3)
– Older systems & mobile telephony
• Afternoon (Module 4)
– Newer systems & the future

Module 4 - Systems 2

1. Broadband Fixed Wireless

2. Wireless Networks

3. Mobile Internet

4. The Future

1. Broadband Fixed Wireless

Choices

Air Link Transmission Technologies

Local Loop
Wireless
local loop

Telephone Cable
local loop local loop

Broadband Fixed Wireless - Choices

Local Loop
Broadband Fixed Wireless
♦ Exists to compete in the local loop
♦ Used primarily for Internet access
♦ Line of sight is an issue
♦ Multipath is an issue
♦ Two configurations
♦ Four choices


Configurations
Point-To-Point


Configurations
Point-To-Multipoint


Choices
♦ MMDS
♦ LMDS
♦ Unlicensed
♦ Wireless fiber


MMDS
Multichannel Multipoint
Distribution Service
♦ Licensed
♦ 2.6 GHz
♦ 2 Mbps
♦ Point-to-multipoint
♦ 35 miles


LMDS
Local Multipoint
Distribution Service
♦ Licensed
♦ 31GHz
♦ 155 Mbps
♦ Point-to-point
♦ 3 miles


Unlicensed
Unlicensed Spread Spectrum
♦ No license required
♦ ISM frequency bands
♦ ??? Mbps
♦ Point-to-point and point-to-multipoint
♦ ??? miles


ISM Frequency Bands
Overview
♦ 900 MHz, 2.4 GHz, 5.8 GHz
♦ Industrial, scientific, medical equipment
♦ 100s of MHz of bandwidth
♦ Limited output power
♦ Must use spread spectrum
♦ Open usage


Unlicensed
Good News
♦ No license required
Bad News
♦ Interference from non-RF items
♦ Interference from RF items
♦ Interference from competitors
♦ Limited output power


Unlicensed
Typical
Deployment
t
Pt to P

H z
5 .8G

Pt to Multipoint
2.4 GHz

ISP


Unlicensed
Other Issues
♦ Inexpensive RF hardware
♦ Expensive customer premises equipment (CPE)
♦ Questionable market acceptance
• Businesses
• Single family homes
• MDUs and MTUs


Wireless Fiber
Free Space Optics
♦ Unlicensed
♦ Infrared frequency
♦ 622 Mbps
♦ Point to point
♦ Less than 1 mile


Wireless Fiber Transceiver


Wireless Fiber
Other Issues
♦ Data rates compete with fiber
♦ Adversely effected by rain and fog
♦ Well defined market
• Campuses
• Building to building
• Emergency bandwidth


Recap
MMDS LMDS Unlicensed Wireless
Fiber
Frequency 2.6 GHz 31 GHz 900 MHz 10,000 THz
2.4/5.8 GHz
Configuration PmP P2P P2P P2P
PmP
Range 35 miles 3 miles 25 miles < 1 mile
5 miles
Data Rate 2 Mbps 155 Mbps 1 Mbps 622 Mbps
100 Mbps


Challenge
♦ Some wireless services are allocated a single
lump of frequency
• Unlike cellular
♦ How to do two-way communications

Braodband Fixed Wireless - Air Link Transmissi

Two Way Communications
Simplex
♦ One frequency
♦ One party transmits at a time
• Walkie-talkies

Frequency 1

Frequency 1


Half Duplex
♦ Two frequencies
♦ One party transmits at a time
• Wireless LANs

Frequency 1

Frequency 2


Full Duplex
♦ Two frequencies
♦ Both parties can transmit at the same time
• Cellular phones

Frequency 1

Frequency 2



What
♦ To make optimum use of available bandwidth
♦ To overcome transmission problems
Choices
♦ FDD
♦ TDD
♦ OFDM


FDD
Frequency Division Duplexing
♦ Dividing the allotted frequency into sub-bands
♦ Each sub-band has a designated direction


FDD

ISM band


FDD


FDD + FDMA


TDD
Time Division Duplexing
♦ Dividing the allotted frequency into time slots
♦ Each time slot goes in one of two directions


TDD

ISM band


TDD


Multipath Is A Problem

a th
Refle cted p

Direct path


So Is Line Of Sight

a th
Refle cted p

Direct path

OFDM
Orthogonal Frequency Division Multiplexing
♦ Solves multipath
♦ Deals with Non-Line Of Sight (NLOS) situations
How
♦ By dividing up a broadband signal into multiple signals
• Which slows it down


OFDM
Visually


Recap
What Comments

FDD Divides a frequency band Good for telephony
into sub-bands for two-way
communications

TDD Divides a frequency band Optimum use of
into time slots for two-way bandwidth
communictions

OFDM Divides a broadband signal To overcome
into multiple narrowband multipath and NLOS
signals

The end

2. Wireless Networks

Local Area Networks

Personal Area Networks

Home Networks

Local Area Networks (LAN)
Parameters
♦ Limited area
• Floor or campus
♦ Some mobility
• Walking around
♦ Server centric

Wireless Networks - Local Area Networks

Basic Architecture


Basic Architecture

Basic Service Set BSS

Basic Architecture

BSS BSS

Extended Service Set

Access Point


Local Area Networks
Frequency
♦ Unlicensed bands
• ISM bands
Air Interface
♦ Mostly Spread spectrum
• Direct sequence
• Frequency hopping


FHSS
Frequency Hopping Spread Spectrum
♦ Uses a PN signal to generate a series of
random carrier frequencies
• Transmitter and receiver use the same PN signal


FHSS


FHSS
How


Comparison
FHSS vs DSSS
♦ FHSS has better noise immunity
♦ DSSS has higher instantaneous bandwidth
• 10 MHz vs 1 MHz
♦ FHSS deals better with multipath


Choices
802.11
♦ Originated in the US
♦ Based in Ethernet
♦ Shared frequency
HiperLAN
♦ Originated in Europe
♦ Based in GSM
♦ Unique frequency

Details
System Band Data Rate Technology

802.11 2.4 GHz 2 Mbps FHSS or DSSS

Wi Fi 802.11b 2.4 GHz 11 Mbps DSSS + CCK

802.11a 5.8 GHz 54 Mbps OFDM

HiperLAN 5.8 GHz 20 Mbps GMSK

HiperLAN II 5.8 GHz 50 Mbps OFDM


Personal Area Networks (PAN)
Parameters
♦ Unlimited area
• Where ever you go
♦ Some mobility
• Walking around
♦ Person centric
• You become the AP

Wireless Networks - Personal Area Networks

Requirements
♦ Interoperability
• Mobiles talking to mobiles
♦ Short range
• Low power/low interference
♦ Self discovery
• Auto initiate


Applications
♦ Impromptu
networks
Piconet


Applications
♦ Cell phone as wireless modem


PAN Standards
Bluetooth
♦ Developed by Ericsson (Sweden)
♦ Based on 802.11
♦ Voice + data
♦ Designated 802.15
♦ Internationally accepted standard &
frequency


Bluetooth
Parameter Specification

Data Rate 1 Mbps

Range 30 feet

Frequency 2.4 GHz

Technology FHSS


2.4 GHz Redux
Who Uses 2.4 GHz
♦ Microwave ovens
♦ Cordless phones
♦ Broadband fixed wireless providers
♦ Wireless networks
♦ Bluetooth networks

Home Networks
Two Systems
♦ HomeRF
• For the home
♦ IrDA
• For the home and the office

Wireless Networks - Home Networks

HomeRF
Parameters
♦ Limited area
• The home
♦ Some mobility
• Within the home
♦ Home centric
• Information appliances


HomeRF
Requirements
♦ Low cost
• Consumer market
♦ Versatile
• Data, voice, audio, video
♦ Interoperability
• 802.11 + DECT


Infrared Data Association (IrDa)
Parameters
♦ Very limited area
• A few feet
♦ Almost no mobility
• A few inches
♦ Decentralized
• Point to point


IrDa
Description
♦ An industry standard
• For data only
• Uses infrared light
• Good for about 3 feet
♦ Embedded in most gadgets


IrDA
Applications
♦ Wireless synching


IrDA
Applications
♦ Upload digital photos


Network Comparison
802.11b Bluetooth HomeRF IrDA

Frequency 2.4 GHz 2.4 GHz 2.4 GHz IR

Technology DSSS FHSS FHSS IR

Range 300 feet 30 feet 150 feet 3 feet

Data Rate 11 Mbps 1Mbps 1.6 Mbps 4 Mbps

Voice None Some Good None

No of nodes 127 8 127 2

Recap
Area Mobility Center

LAN Floor Walking Server

PAN Everywhere Walking Person

Home RF Home Walking Home

IrDA Few feet None Decentralized

Wireless Networks
The end

Mobile Internet

Wireless Internet

Mobile Internet
Defined
♦ Mobile devices
• Cell phones, PDAs, laptops
♦ Wide area
• City, state, country
♦ High mobility
• Driving around speed

Mobile Internet - Technology

Mobile Internet
Challenges
♦ Data rate
• Depends on the device
♦ Screen size
• Different content
♦ Ubiquity
• I want it everywhere


Mobile Internet Candidates

Cellular ISM LEOs


Mobile Internet Candidates

PROS CONS

Cellular Existing infrastructure Not much bandwidth
Existing customer base Need a license

ISM Lots of bandwidth Build from the ground up
No license required Limited power

LEOs Use it anywhere Very expensive buildout
Heavy frequency reuse Requires more power


Mobile Internet
Infrastructure Changes
♦ Wireless portion
♦ Internet portion


Mobile Internet
Wireless Infrastructure Changes
♦ Mobile switching center
• Gateway for separating voice from data
• Packet switching
♦ Mobile device
• Microbrowser


Mobile Internet
Packet Switching
♦ Shared access to a given channel
♦ More efficient use of spectrum
♦ Better for bursty (Internet) traffic
♦ Higher instantaneous data rates


Mobile Internet
Internet Infrastructure Changes
♦ New markup language
• C-HTML (web guys)
• WML (phone guys)
♦ Multiple servers (possibly)
• Unique content
♦ New protocols
• WAP (non-proprietary)


WAP
Wireless Access Protocol
1) Wireless Markup Language (WML)
• No tables, frames, other fancy stuff
2) Protocols
• WDP (wireless datagram protocol)
• WTP (wireless transaction protocol)
• WSP (wireless session protocol)

Mobile Internet - WAP

WAP
Infrastructure
♦ WAP gateways
• Remote access server for WAP
• wap.company.com
♦ WAP servers
• Stores WAP data
• Some translate pages on the fly


WAP
Visually

WAP WAP
Server

WAP
Works
♦ Over all technologies
• Mobile telephony
• Bluetooth
♦ Over all frequencies
• Cellular
• PCS
• ISM


M-Commerce
Mobile Commerce
♦ A trillion dollar business (some day)
♦ Take advantage of unique aspects of mobility
♦ Not meant to replace e-commerce

Mobile Internet - M-Commerce

M-Commerce
Possibilities
♦ Comparison shopping
♦ Location-specific services
♦ Advertising
♦ Financial transactions
♦ Entertainment

Mobile Internet - M-Commerce

Mobile Internet
Status
♦ Cellular
• i-Mode in Japan
♦ ISM
• Ricochet died
♦ LEOs
• Stay tuned

Mobile Internet - Status

4. The Future

New Technologies

Security Issues

Health Concerns

New Technologies
Five
1) Ultrawideband
2) MEMS
3) BLAST
4) RFID
5) Telematics

The Future - New Technolgoies

Ultrawideband
What
♦ Periodic single sine wave
• Monocycle
♦ Covers multiple licensed bands
• Must not interfere
♦ Not yet approved by the FCC


Ultrawideband
Visually

Monocycles


Ultrawideband
Problem

Same frequency


Ultrawideband
Result


Ultrawideband
What If

Time hopping spread spectrum


Ultrawideband
One More Problem
♦ A single sine wave contains no information
• Where's the modulation?


Ultrawideband
What If


MEMS
MicroElectroMechanical Systems
♦ Semiconductors that can physically move
• Superior electrical properties
• Low cost manufacturing (in volume)


Switch Comparison
PIN Electromechanical MEMS

Insertion loss 1 dB 0.1 dB 0.1 dB

Switching speed Microsec Millisec Microsec

Size Small Big Tiny

Power Moderate Substantial Tiny

Price Low High Very low

BLAST
Bell Labs LAyered Space Time
♦ Dramatically increased data rate
♦ Send multiple signals over one frequency
• Takes advantage of multipath
♦ More of a signal processing trick


BLAST


RFID
Radio Frequency IDentification
♦ Control, detect and track objects
♦ Uses unique numerical codes
♦ Not a new technology (1980s)
♦ Ubiquitous


RFID
System
♦ Interrogator
♦ Transponder ("Tag")

Interrogator Transponder

Tx Tx
Numerical
code
Rx Rx


RFID
Types Of Transponders
♦ Active
• Onboard power source (i.e., battery)
♦ Passive
• No onboard power source
• Receives power from the transponder


RFID Comparison
Active Passive

Transponder Battery Interrogator
power source

Interrogator Low High
ouptut power

Range 250 feet 1.5 feet

Frequency ISM Low frequency

Numerical code Re-programmable Factory programmed

RFID
Applications
♦ Inventory tracking
♦ Toll road readers
♦ Cashless payments
♦ Electronic article surveillance


Telematics
What
♦ Using position-locating technology for value-
added automobile services
• OnStar™

The Future - New Technologies

Wireless Security
Unique Challenges
♦ Mobile devices
♦ Limited computing power
♦ Limited bandwidth
♦ Interface weakness

The Future - Security Issues

Wireless Security
Some Solutions
♦ Point to point systems
♦ Encryption


A Better Solution
Smart Antennas


Encryption
Two Protocols
♦ Wired Equivalent Privacy (WEP)
• For use with 802.11 networks
• Weakness: Shared key
♦ Wireless Layer Transport Security (WLTS)
• For use with WAP
• Weakness: Wireless-wired interface


Encryption
How Is It Done
♦ Just like DSSS
♦ PN replaced by encryption key

Data signal

Encryption key


Health Concerns
Status
♦ Evidence inconclusive
♦ Results statistical in nature

The Future - Health Concerns

Adverse Health Effects
Two
1) Ionization
• Molecular changes
2) Thermal
• Body heating


Health Concerns
RF Factors Effecting Heating
♦ Frequency
• It depends
♦ Power density
• High is bad
♦ Time of exposure
• Long is bad


Frequency
Bad Frequencies
♦ 30 -300 MHz
• Most efficient absorption by body
♦ 2.4 GHz
• Efficient absorption by water


Power Density
In Perspective
♦ 100 mW/cm2 = microwave oven
♦ 1 mW/cm2 = measurable body heating
♦ 1 µW/cm2 = at the bottom of a cell tower


Time
Key Issue
♦ Can the body dissipate the heat
• Depends on blood flow
• Some areas more vulnerable than others


FCC
Exposure Guidelines
♦ Whole body
• Power density (mW/cm2)
• Averaged over 30 minutes
♦ Partial body
• Specific absorption rate (W/Kg)
• 1.6 W/Kg maximum


The Bottom Line

You're more likely to be
injured in a car crash
while you're talking on
your cell phone than you
are from its RF radiation


Module 4 -Systems 2
The end

Good

Introduction to RF & Wireless - Part 4

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