CSE5807 Wireless and Personal Area Networks. Peter Granville tel: 9903 2448 [email protected] Textbook: Wireless Communications and

CSE5807

Wireless

and

Personal Area Networks

Peter Granville tel: 9903 2448 [email protected]

Textbook:

Wireless Communications and Networks

Stallings, Pearson Prentice-Hall 2E also 1E is okay

Topics to be covered( May be subject to change)

Week 1 Wireless Introduction and Applications

Week 2 Radio Communications Principles

Week 3 Access Technologies

Week 4 Cellular Networks

Week 5 Cellular Networks ctd...

Week 6 IEEE802.11 Introduction

Week 7 IEEE802.11 ctd...

Week 8 Bluetooth Technology

Week 9 Network_Management_Issues

Week 10 Wireless_Security

Week 11 VPN

Week 12 Selected_Topics_in_Wireless

Week 13 Revision

Assessment:

Exam 2 hour 50%

Assignment 1 Research Essay 25%

Reports 25%

10 Reports each worth 2.5% of final result

Introduction to Wireless LANs

APPLICATION

PRESENTATION

SESSION

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

WLANs Operate at this portion of the OSI model

Infra-Red

• Infrared (IR) systems use very high frequencies, just below visible light in the electromagnetic spectrum (refer fig 4.1), to

carry data.

• Like light, IR cannot penetrate opaque objects; it is either directed (line-of-sight) or

diffuse technology.

Inexpensive directed systems provide very limited range (3 ft) and typically are used for Personal Area Networks but occasionally are used in specific WLAN applications.

High performance directed IR is impractical for mobile users and is therefore used only to

implement fixed subnetworks.

Diffuse (or reflective) IR WLAN systems do not require line-of-sight, but cells are limited to individual rooms.

Bluetooth

Bluetooth technology is a relatively new wireless personal area networking (WPAN) technology that has gained significant industry support and will coexist with most wireless LAN solutions.

The Bluetooth specification is for a 1 Mbps, small form-factor, low-cost radio solution that can provide links between mobile phones, mobile computers and other portable handheld devices and connectivity to the internet.

This technology, embedded in a wide range of devices to enable simple, spontaneous wireless connectivity is a complement to wireless LANs — which are designed to provide continuous connectivity via standard wired LAN features and functionality.

Current Radio LANs use a transmission technique called Spread Spectrum.

Instead of using the one narrow frequency range for transmitting data, in Spread Spectrum transmissions are over a range of frequencies at a time.

Radio LANs

Spread Spectrum

The basic idea is to modulate the signal so as to increase the bandwidth (spread the spectrum) of the signal to be transmitted

Advantages: Gain immunity from various kinds of noise and

multipath distortion Can be used for hiding and encrypting signals. Only a

recipient who knows the spreading code can recover the encode information

Allows several users to independently use the same bandwidth with little interference eg CDMA as used in cellular telephony

Systems use one of two techniques for communications –

Direct Sequence

Frequency Hopping

Spread Spectrum

• Refer fig 7.1, 7.6 Stallings

• Direct sequence is perhaps one of the most widely known and utilized spread spectrum systems and it is relatively simple to implement.

• A narrow band carrier is modulated by a (chip or spreading) code sequence.

• The carrier phase of the transmitted signal is abruptly changed

in accordance with this code sequence.

Direct Sequence Systems

The code sequence is generated by a pseudorandom generator that has a fixed length. After a given number of bits the code repeats itself exactly.

The speed of the code sequence is called the chipping rate, measured in chips per second (cps). For direct sequence, the amount of spreading is dependent upon the ratio of chips per bit of information.

At the receiver, the information is recovered by multiplying the signal with a locally generated replica of the code sequence.

• With frequency hopping systems, the signal is broadcast over a seemingly random series of radio frequencies, hopping from frequency to frequency at fixed intervals.

• A receiver, hopping between frequencies in synchronization with the transmitter, picks up the message.

• Would be eavesdroppers hear only unintelligible blips

• Attempts to jam the signal in one frequency succeed only at knocking out a few bits of it

Frequency Hopping Systems

Frequency Hopping Systems

Refer fig 7.2 Stallings 2E Typically, there are 2k carrier frequencies

forming 2k channels The transmitter operates on one channel at a

time for a fixed interval eg 300ms IEEE 802.11 wireless LAN

During that interval, some number of bits is transmitted using some encoding scheme

The sequence of channels used is dictated by a spreading code.

Both transmitter and receiver use the same code to tune into a sequence of channels

Components of Wireless (Radio) Lans

http://www.cisco.com

http://www.symbol.com/products/wireless/wireless_products_lit.html

Access Point (AP)Network connection point for wireless devices

Access Point (AP)Network connection point for wireless devices

Access point

Laptop computer

Hand held computer

IEEE802.11Wireless LANs operating at data rates of 1 or 2 Mbps and operating in the 2.4GHz band were defined in the original IEEE802.11 specification ratified in 1997.The specification was for a cable-free LAN at the Data link and Physical layers of the OSI model.

IEEE802.11bIn September 1999, an amendment to the original standard added 5.5 Mbps and 11 Mbps. IEEE802.11b was named Wi-Fi (TM of Wireless Ethernet Compatibility Alliance WECA).

Physical Layer Convergence Procedure PLCP

MAC

Physical Medium Dependent PMD

Reformats data into form suited to PMD sub-layer and monitors medium for traffic Controls transmission and reception of data through wireless medium

PHY

IEEE802.11b uses the Ethernet-like multiple-access with collision-avoidance (CSMA/CA) method

Ethernet proper is based on CSMA/CD, where CD stands for "collision-detection." Wireless LANs can't always detect a collision between two transmitting devices, so instead, it tries for collision-avoidance

IEEE802.11a

Released in 1999

Operates in the 5 GHz frequency range and offers the possibility of 6 to 54 Mbps

HiperLAN2 (European) has similar

capabilities.

IEEE802.11g

Operates in the 2.4 GHz frequency range and offers the possibility of up to 54 Mbps

Is interoperable with IEEE802.11b Access Points and NICs

Applications of the Technology

Examples:

Retail,Hospitality,Education and Corporate trainingManufacturing,Government,Flexible office and public space environments http://www.symbol.com/products/wireless/wireless_products_lit.html

Retail Promotional and training videos On-line music sampling Portable, graphic-rich gift registries Customer service initiatives such as self-checkout


Hospitality

Real-time connections to enable curbside or remote check-in for hotel guests avoiding lines at the front desk


High-speed Internet access for hotel guests

Convention center networking for trade shows and conferences

Support of multimedia presentations and video streaming for guest meeting and information services


Education and Corporate Training

Temporary networks for mobile training programs

Streaming multimedia to support on-line lectures

Wireless Internet and e-mail access

Security initiatives


Manufacturing

Real-time transfer of mechanical, flow and other graphic-rich files

Security initiatives

Manufacturing workstations where production line layouts are frequently changed


Government

Temporary networks for disaster area and refugee center support, including transferring photos and other vital information

Crime and accident scene support

Security initiatives via wireless monitoring systems and remotely accessed cameras


More Flexible Office and Public Space Environments

Temporary project team and ad-hoc networking

CAD/CAM file transfer for collaborative product development teams

Wireless e-mail, document and PowerPoint® transfer


Cable-less video conferencing

Flexible customer visit center configuration

Wireless local area networking where wiring isn't possible, such as landmark buildings or sites with asbestos considerations


Kiosks in malls, airports, museums and other spaces where interactive programs depend on high-speed remote data retrieval


Interference Problems

Most of the wireless LAN systems at the moment operate in the 2.4GHz band.

This is also used by Bluetooth systems. Thus interaction between radio transmissions of the various technologies may result.

Also, other radio equipment may interfere with the reception of signals.

Security/Privacy Issues

Many of the wireless LANs in use today potentially suffer from one major difference with wired LANs –the data is freely accessible due it radio transmission

Two issues arise – data privacy and authentication

WEP – Wired Equivalent Privacy deals with both issues

Data is encrypted to prevent its use following inappropriate capture

Has weaknesses, eg lack of encryption key management in the protocol

WPA – WiFi Protected AccessTemporary alternative to WEP providing better security

IEEE802.11i – new standard providing high levels of security (due soon)

Use of authentication servers (e.g. RADIUS) is promoted

VPNs – Virtual Private Networks

Assuming that wireless connections are not secure, how can you –

a) Secure your transmissions, b) Control Access

VPNs can do both at the same time.

Problem: proprietary – need client specific to VPN server.

Documents

CSE5807 Wireless and Personal Area Networks. Peter Granville tel: 9903 2448 [email protected] Textbook: Wireless Communications and