Wireless LANs and PANs - National Taiwan University of ...

Copyright © 2002, 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 11Mbps and a fall back rate of 5.5Mbps.802.11a uses OFDM in packet based communication.


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 adhoc network using peer to peer mode(Fig 14.1)As a client server wireless configuration (Fig 14.2)Complicated distributed network (Fig 14.3)


Peer-to-Peer Wireless Mode (Fig 14.1)

Server with wireless card

Laptop with wireless card

Palm pilot

PDA


Client/Server Wireless Configuration (Fig 14.2)

Wireless LAN access pointWired network

Wireless card


Wireless Distributed Network (Fig 14.3)

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. These cards are PCMCIA cardIn 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 toeach 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.Fig 14.3 shows how LANs are interconnected using access points.


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.


The Ricochet Mobile Communication Network (Fig 14.5)

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 AvailabilityUnlimited access.Flexible pricing.


Home RF

Two kind of networks: Home RF (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 simultaneouslyutilize the same high speed ISP account.Home networking allows two options: wired solution and wireless solution.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 Home RF

MobilityFlexibility: 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.SecureBased on industry Standards: Enables interoperability between many different manufacturers.


Home RF Technology

In Home RF 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.A typical home network is shown in Fig 14.6.


Architecture of HomeRF system (Fig 14.6)

Baby Monitor

Phone - Connection

Cell Phone

Main- PC

Clock

PalmTop

Wireless Headset

Satellite Dish

Fridge Data Pad

Television HandheldCommunicator Laptop

2nd PC

CableModem


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.


HiperLAN

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 (Cont’d)

It supports 25 audio connections at 32 Kbps with a max latency of 10msec.It employs 5.15 GHz and 17.1 GHz frequency bands, has data rate of 23.5 Mbps.It supports 1 video connection of 2 Mbps with 100 mseclatency 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 HiperLAN are:QoSStrong SecurityHandover when moving between local area and wide areasIncreased throughputEase of use, deploymentAffordabilityScalability


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.


A Simple HiperLAN System (Figure 14.8)

Fixed Network

AP

AP AP

AP

MS MS


HiperLAN/2The 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.Figs 14.9 and 14.10 show general application of Bluetooth.It also provides a universal bridge to existing data networks (Fig 14.11).


Use of Bluetooth to Connect Notebook (Fig 14.9)

Bluetooth link

Cellular link

Base station


Bluetooth Connecting Some Devices (Fig 14.10)


Bluetooth Providing a Universal Bridge to Existing Data Networks (Fig 14.11)

Fixed line


Bluetooth: A Mechanism to Form Ad Hoc Networks of Connected Devices Away from Fixed Network Infrastructures (Fig 14.12)

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 (Fig 14.13)

Piconet 1Piconet 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


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.


ArchitectureBluetooth 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 upto 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

L2CAP

Low Radio Layer

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

Bluetooth Core Protocols (Fig 14.14)


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.

Wireless LANs and PANs - National Taiwan University of ...

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