wireless lans and pans

Copyright © 2003, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved

Wireless LANs and PANs

Chapter 14


IEEE 802.11

It is the standard for wireless LANs. It specifies MAC procedures and operate in 2.4

GHz range with data rate of 1Mbps or optionally 2Mbps.

User demand for higher bit rates and international availability of 2.4 GHz band has resulted in development of a high speed standard in the same carrier frequency range.

This standard called 802.11b, specifies a PHY layer providing a basic data rate of 11 Mbps and a fall-back rate of 5.5 Mbps.


IEEE 802.11

The IEEE 802.11 and 802.11b standards can be used to provide communication between a number of PSs (Peer Stations) as an ad hoc network using peer to peer mode(Fig 14.1)

As a client server wireless configuration (Fig 14.2) Complicated distributed network (Fig 14.3)


Figure 14.1 Peer-to-peer wireless mode

Server with wireless card

Laptop with wireless card


Wireless LAN access point

Figure 14.2 Client/Server wireless configuration

Wireless card

Wired Network


Wireless Distributed Network

Station

Access point

Wired network

Access point

Distributed system

Access point

Station

StationStation


IEEE 802.11

The keys behind all the above networks are the wireless cards and wireless LAN access points.

In an ad hoc network mode, there is no central controller, the wireless access cards use CSMA/CA protocol to resolve shared access.

In client server model, many PC’s or laptops physically close to each other (20-500m) can be linked to a central hub (access point).

This access point acts as a bridge between the wireless and wired network.

A large area can be covered by installing several access points in the building.


Data rate

Power consumptionComplexity

802.15.4

802.15.IBluetooth

802.11aHiperLAN

802.11g*

802.11

WPAN

802.11b

WLAN

* Standard in progress

Scope of Various WLAN and WPAN Standards


Ricochet

A mobile data access service that is always on, provides high speed, secure mobile access to the desktop from outside the office.

It allows to link to the internet or the corporate network without needing phone lines or cable connections.

The Ricochet service is provided by Metricom.


Ricochet

The Ricochet service is a wide area wireless system using spread spectrum packet switching data.

The network operates within 902-928 MHz portion of RF spectrum.

The Ricochet wireless Micro Cellular Data Network (MCDN), consists of shoebox sized radio receivers, called Micro cell radios (Fig 14.5)

Micro cells are typically mounted to street poles. Micro cells require a small power from the street lights. Each Micro cell radio employs 162 frequency hopping

channels.


Ricochet Mobile Communication Network

Network interconnection facilityMicrocell radios onstreet lights, utility poles

Wireless access point

Name server

Router

Gateway

Gateway to Internet, Intranets, LANS, Compuserve, AOL and other on-line servicesComputer device

Modem radio


The Ricochet Wireless Modem

It weighs 13 ounces. Has the general dimensions of a small paperback

book, plugs directly into a desktop. When a Ricochet modem is configured to operate

in bridge mode, it translates signals from other Ricochet modems into signals that a wired modem can receive.


Services Provided by Ricochet

Provides immediate, dependable and secure connections without the cost and complexities of land based phone lines.

Sending E-mails, access to documents in home networks.

Many real estate agents use this to search for property listings while on road.


Key Features of Ricochet Modem

V.34, 28,800 bps access. Good Availability Unlimited access. Flexible pricing.


HomeRF

Two kind of networks: HomeRF (for home), Hiper LAN (for business workspace).

43 million US homes now contain more than one PC. A home network typically consists of one high speed

internet access port providing data to multiple networked nodes.

Home networking allows all computers in a home to simultaneously utilize the same high speed ISP (Internet Service Provider) account.

Home networking allows two options: wired solution and wireless solution.


HomeRF (cont’d)

Wired Solutions such as Ethernet, phone line offers a fast reliable secure connections, but the cost of wiring and installation is high.

Wireless networks such as PC-Centric Data offer more mobility to the users of the network.


Advantages of Wireless HomeRF

Mobility Flexibility: Simultaneous internet access while sharing

a single internet connection with other PCs. Simple: Installation time is small. Economical: Less than $100 for each networked PC. Secure Based on industry Standards: Enables interoperability

between many different manufacturers.


HomeRF Technology

In HomeRF all the devices can share the same connections for voice and data.

Provides the foundation for a broad range of interoperable consumer devices.

A specification for wireless communications in the home called Shared Wireless Access Protocol (SWAP) has been developed.


Figure 14.6 Architecture of HomeRF system


D4

U4

D4

U4

D3

U3

D2

U2

D1

U1B D3

U3

Hop

Service slot

Connection period CSMA/CA access

mechanism

D4

U4

D3

U3

D2

U2

D1

U1B D3

U3

Hop

Voice slot transmission

Forward (downlink) slots

Reverse (uplink) slots

CFP1

Control point beacon (CPB)

CFP2

Superframe 20 msRetransmission node Connection node #1

Structure of MAC Frame HomeRF


Home RF Network

A network consists of Resource providers, which are gateways to different resources like cordless phones, printers, fileservers and TV.

The goal of Home RF is to integrate all of them in to a single Network suitable for all applications and also remove all wires and utilize RF links in the network.

This will support the mobility of devices. With Home RF, cordless phone can connect to

PSTN ordinarily, but can also connect through a PC for enhanced services.


Hiper LAN

It stands for High Performance LAN. It can support Multimedia data and asynchronous data

effectively at high rates (23.5 Mbps). It is specifically designed to support as hoc computing

for multimedia systems, where there is no requirement to deploy centralized infrastructure.

It employs 5.15 GHz and 17.1 GHz frequency bands, with a coverage of 50m and mobility < 10 m/s.

It supports Packet oriented structure, which can be used for networks with or without centralized control (base station-mobile station and ad hoc).


HiperLAN contd..

It supports 25 audio connections at 32 Kbps with a max latency of 10 msec.

It supports 1 video connection of 2 Mbps with 100 msec latency and data rate of 13.4 Mbps.

HiperLAN/1 is designed to support ad hoc computing for multimedia systems.

HiperLAN/1 MAC is compatible with standard MAC service interface.


Hiper LAN goals

The goals of Hiper LAN are: QoS Strong Security Handover when moving between local area and

wide areas Increased throughput Ease of use, deployment Affordability Scalability


Features of Hiper LAN/2

High speed transmission (54 Mbps). It uses modularization method called OFDM to

transmit analog signals. The connection oriented approach makes support

for QoS easy. It supports automatic frequency allocation,

eliminating the need for manual frequency planning as in cellular networks.


Fixed Network

AP

AP AP

AP

MSMS

Figure 14.8 A simple HiperLAN system


Hiper LAN/2 The protocol architecture allows for interoperation with virtually

any type of network. A mobile terminal may at any time request the access point and

enter a low power state for a sleep period. At the end of this negotiated sleep period the mobile terminal

searches for any wake up signal. In the absence of any wake up signal it again reverts back to its

low power state for sleep period. The control is centralized to the AP (access point) which informs

the mobile terminal to transmit their data. The air interface is based on TDD (time division duplex) and

dynamic TDMA. Selective Repeat (SR) ARQ is an error control mechanism used to

increase reliability over the radio link.


Applications

Hiper LAN/2 networks can be deployed at “hot spot” areas such as airports and hotels, as an easy way of offering remote access and internet services to people.

It can also be used as an alternative access technology to 3G networks.

It can be used in home environment to create a wireless infrastructure for home devices such as PCs, cameras, printers etc.


Bluetooth It is named after the King of Denmark that unified

different factions in Christianity through the country. It is a short range RF communication. Low cost, low power, radio based wireless link eliminates

the need for short cable. Bluetooth radio technology built into both the cellular

telephone and the laptop would replace the cable used today to connect a laptop to cellular phone.

Printers, desktops can all be wireless. It also provides a universal bridge to existing data

networks (Fig 14.11).


BluetoothCellular Link

Figure 14.9 Use of Bluetooth to connect notebook

Base Station


Figure 14.10 Bluetooth connecting printers, PDA’s, desktops, fax machines, keyboards, joysticks and virtually any other digital device


Fixed Line

Figure 14.11 Bluetooth providing a universal bridge to existing data networks


Figure 14.12 Bluetooth: A mechanism to form ad hoc networks of connected devices away from fixed network infrastructures

Bluetooth

Personal Ad hoc Network


Bluetooth

The ultimate goal is to make small products (PC/Laptops) have only one wire attached to power cord.

In case of PDA, the power cord is also eliminated. A simple application of Bluetooth is updating the

phone directory of the PC from a mobile telephone.

A typical Bluetooth has a range of 10 m.


Features

Fast frequency hopping to reduce interference. Adaptive output power to minimize interference. Short data packets to maximize capacity. Fast acks allowing for low coding overhead for links. Flexible packet types that support a wide application range. CVSD (Continuous Variable Slope Delta Modulation)

voice coding that can withstand high bit error rates. Transmission/reception interface tailored to minimize

power consumption


Architecture of Bluetooth System and Scatternet

Piconet 1

Piconet 4

Piconet 3

Piconet 2

M2

M1

M3

M4

S2,1

S2,2

S2,3

S3,1 S3,2

S3,3

S2,4 /S3,4

S1,2 /S2,5

S 1,3 /S 4,4

S1,1

S1,4

S1,5

S4,1

S4,2S4,3


Bluetooth Technological Characteristics

Frequency band 2.4 GHz (unlicensed ISM band)

Technology Spread spectrum

Transmission method Hybrid direct sequence and frequency hopping

Transmission power 1 milli-watt (0 dBm)

Range 10 meters (40 feet)

Number of devices 8 per piconet, 10 piconets per coverage area

Data speed Asymmetric link: 721+57.6 kbps

Symmetric link: 432.6 kbps

Maximum voice channels 3 per piconet

Maximum data channels 7 perpiconet

Security Link layer w/s fast frequency hopping (1600 /sec)

Power consumption 30 μA sleep, 60 μA hold, 300 μA standby, 800 μA max transmit

Module size 3 square cm (0.5 square inches)

Price Expected to fall to $5 in the next few years

C/I co-channel 11 dB (0.1% BER)

C/I 1 MHz -8 dB (0.1% BER)

C/I 2 MHz -40 dB (0.1% BER)

Channel switching time 220 μs


Architecture

Bluetooth radio typically hops faster and uses shorter packets as compared to other systems operating in the same frequency band.

Use of FEC (Forward Error Correction) limits the impact of random noise.

As the interference increases, the performance decreases.


Architecture (cont’d) Bluetooth devices can interact with other Bluetooth devices. One of the devices acts as a master and others as slaves. This network is called “Piconet”. A single channel is shared among all devices in Piconet. There can be up to seven active slaves in the Piconet. Each of the active slaves has an assigned 3 bit Active Member

address. A lot of other slaves can remain synchronized to the Master

through remaining inactive slaves, referred to as parked nodes. A parked device remains synchronized to the master clock and

can become active and start communicating in the Piconet anytime.


Architecture (cont’d)

If Piconets are close to each other, they have overlapping areas.

The scenario where the nodes of two or more Piconets mingle is called Scatternet.

Before any connections in the Piconet are created all devices are in STDBY mode.

In this mode an unconnected unit periodically “listens” for message every 1.28 seconds.

Each times a device wakes up, it tunes on the set of 32 hop frequencies defined for that unit.


Upper Layer

Baseband

SDP

LMP Audio

Bluetooth Core Protocol

L2CAPE

Low Radio Layer

SDP – Service Discovery ProtocolL2CAP – Logical Link Control and Adaptation Layer Protocol

LMP – Link Manager Protocol

Bluetooth Core Protocol


Protocols

SDP: Provides a mean for applications to discover which services are provided by or available through a Bluetooth device.

L2CAP: Supports higher level protocol multiplexing, packet segmentation and reassembly and conveying of QoS information.

LMP: Used by Link managers for link set up and control.

Baseband: Enables the physical RF link between Bluetooth units forming a Piconet.


Comparison between Different Architecture (1/2)

IEEE 802.11 Ricochet HomeRF HiperLAN Bluetooth

Operational spectrum

2.400-2.4835~5.2 GHz

902-928 MHz 2.404-2.478 GHz 5.15 GHz and 17.1 GHz 2.402-2.480 GHz

Physical layer DSSS/FHSS/IR Frequency hopping 162 hops/sec

FHSS 50 hops/sec DFS (Dynamic Frequency Selection) with BPSK/ QPSK/ QAM

FHSS 1600 hops/sec

Channel access CSMA/CA TDMA Hybrid (TDMA & CSMA/CA)

TDMA/TDD Master slave, TDMA frequency hopping

Raw data rate 2 Mbps & 11 Mbps/ 6-54 Mbps

288 1and 2 Mbps 23.5 Mbps or 54 Mbps 1 Mbps

Range 150 feet 1000 feet <150 feet 150feet 10 m to 100 m with extended range

Power consumption Not specified Not specified 100 mW Not specified 1 mW, 10 mW, 100 mW

Traffic Data (DCF) Data Voice + Data Data Voice or Data

Error robustness CRC/ARQ Type 2 CRC/ARQ type 1 1/2, 9/16, 3/4 rate FEC, ARQ type 1

1/3 rate FEC, 2/3 rate FEC and ARQ Type 1

Mobility support Not specified Yes No Yes No


Comparison between Different Architecture (2/2)

IEEE 802.11 Ricochet HomeRF HiperLAN Bluetooth

Energy conservation

Directory based Yes Yes Yes

Guaranteed latency Yes (uses PCF (Point Coordination Function))

<20 msec for voice Yes (Supports DiffServ (Differentiated Services)/ ATM/ RSVP (Resource Reservation Protocol ))

No device

Speech coding Not specified Not available 32 kbps with ADPCM

OFDM 64 kbps with CSVD/ logPCM

Security 40 bit RC4 RSARC-4 Blowfish DES, 3-DES Minimal (in PHY)

Communication topology

Peer-peer, MS-BS Peer-peer Peer-peer, MS-BS Peer-peer, MS-BS Master-slave, Master-multislave

Approx. price/point $25 Variable $18 Not specified $10

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