Wireless Computing Technologies

Patrick J. Stockreisserp.j.stockreisser@cs.cardiff.ac.uk

Lecture Outline

In the lecture we will: Introduce wireless communication technology

Look at a brief history of wireless technology Recap on some primary applications and technologies Review the advantages and disadvantages of this

technology

Look at some core specific technologies The concept of a cell Roaming and Nomadic Access Multiplexing

Introduction Wireless telegraph inventing in 1896 by Guglielmo

Marconi (or so it is said) Alphanumeric characters encoded in an analog signal. Since then wireless technologies have led to radio,

television, mobile telephone and communication satelittes. The cellular/mobile telephone is the modern version

of Marconi’s wireless telegraph, offering 2 party, two way communication.

Moved forward from analog to digital technology More traffic, better reception, better security.

Wireless technologies are migrating to higher and higher frequencies

Move from voice to data…

Milestones in Wireless Comms

The Cellular Revolution

The wireless revolution is apparent in the mobile phone market alone. 1990 – 11 million subscribers 2005 – 2 billion subscribers

Available in the UK for over 20 years. Cumbersome, unreliable

The second generation (2G) led to increase in consumer popularity. smaller and easier to handle, longer battery, more network

coverage and more reliable.

The Global Cellular Network

There is no single cellular network Devices support 1 or 2 of a myriad of technologies

ITU (Intl. Telecommunications Union) is working towards creating a family of standards for the next generation wireless devices. Higher frequencies and less incompatibility Development of ITU-2000 to create a seamless

global network.

Analog versus Digital

Channel Capacity

Channel capacity is the maximum rate at which data can be transmitted over a given communication path

Data Rate:

This is the rate, in bits per second (bps), at which data can be communicated.

Bandwidth:This is the bandwidth of the given signal as constrained by the transmitter and the nature of the transmission medium (expressed in cycles per second or hertz.

Noise: Level of signal disruption over the communication path

Error Rate:Rate at which errors occur, reception of a 1 when a 0 was transmitted and vice versa.

Digital Transmission Issues

Digital signal can be propagated a limited distance.

A range of impairments can distort signal intended for transmission and reception. Noise is a key factor that degrades signal quality

Why Use Wireless?

Problems of creating a wired network where cabling is not possible or feasible.

Companies want their wirings to be altered frequently.

Companies want to introduce mobility in addition to the traditional wired networks in the workplace.

There are places where laying and running network cables are almost impossible.

Wireless Advantages Convenience: The wireless nature of such networks allows users

to access network resources from nearly any convenient location.

Mobility: With the emergence of public wireless networks. Productivity: Users connected to a wireless network can maintain

a nearly constant affiliation with their desired network as they move from place to place.

Deployment: Initial setup of an infrastructure based wireless network requires little more than a single access point.

Expandability: Wireless networks can serve a suddenly increased number of clients with the existing equipment. Modular and very flexible.

Cost: Wireless networking hardware is at worst a modest increase from wired counterparts.

Robustness: More robust against disasters, Easy to replace, upgrade hardware.

Wireless Disadvantages Security: Wireless packets can be intercepted by a nearby

adversaries Range: The typical range of a common 802.11g network with

standard equipment is on the order of tens of meters, further than this requires additional access points. Costs for these items can add up quickly.

Reliability: Like any radio frequency transmission, wireless networking signals are subject to a wide variety of interference, as well as complex propagation effects

Speed: Low bandwidth on most wireless networks (typically 1-54 Mbps) is far slower than even the slowest common wired networks (100Mbps up to several Gbps).

Standards: Still need for more standards, and this takes time (e.g. IEEE 802.11)

What took so long?

Slow user take up before 2000 Initially high prices for infrastructure Low data rates transmission Security drawbacks Licensing and management

Wireless Communication Technology

Network Types Standards W-LAN Topologies

LAN Extension Cross-building Interconnect Nomadic Access Ad-hoc Networking

Network Types One way to categorize the different types of computer

network designs is by their scope or scale. LAN - Local Area Network WAN - Wide Area Network MAN - Metropolitan Area Network SAN - Storage Area Network, System Area Network, Server

Area Network, or sometimes Small Area Network CAN - Campus Area Network, Controller Area Network, or

sometimes Cluster Area Network PAN - Personal Area Network DAN - Desk Area Network

LAN and WAN were the original categories of area networks, while the others have gradually emerged over many years of technology evolution.

Area Network Types

Wide Local Personal

PAN A PAN is a computer network organised around an individual

person. Personal area networks typically involve a mobile computer, a

cell phone and/or a handheld computing device such as a PDA. You can use these networks to transfer files including email and

calendar appointments, digital photos and music. Personal area networks can be constructed with cables or

wirelessly. A wired PAN often uses USB and FireWire technologies to link

together A wireless PAN typically use Bluetooth or sometimes infrared

connections. Bluetooth PANs are also called piconets. Personal area networks generally cover a range of less than 10

meters.

LAN

A networked office building, school, or home usually contains a LAN.

In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.

In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single organization.

They tend to use certain connectivity technologies, primarily Ethernet and Token Ring.

WAN The Internet is the largest WAN, spanning the Earth. A WAN is a geographically-dispersed collection of

LANs. A router connects LANs to a WAN. In IP networking,

the router maintains both a LAN address and a WAN address.

A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one

organization but rather exist under collective or distributed ownership and management.

WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.

Wireless Standards Wireless networking hardware requires the use of underlying technology

that deals with radio frequencies as well as data transmission. The most widely used standard is 802.11 produced by the Institute of Electrical and Electronic Engineers (IEEE). This is a standard defining all aspects of Radio Frequency Wireless networking.

Existing Standards: 802.11b. This is the oldest and most compatible wireless technology, and any

wireless network device can connect to an 802.11b network. 802.11b is slow, however, and you should use it only for browsing the Web, sending instant messages, and reading e-mail.

802.11g. The best choice for new wireless networks, 802.11g works with any device that supports 802.11b, while offering five times the performance. 802.11g is fast enough to stream music and some video (but not high-definition video).

802.11n. A future standard that will replace 802.11g and 802.11b networks, while still supporting existing wireless computers. 802.11n can offer better range and performance than 802.11g; however, 802.11n network equipment is more expensive, and most wireless devices do not support it.

802.11a. This is an outdated wireless technology that offers good performance but is compatible with only a few devices.

LAN Extension

Wireless LAN linked into a wired LAN on same premises Wired LAN

Backbone Support servers and stationary workstations

Wireless LAN Stations in large open areas Manufacturing plants, stock exchange trading floors,

and warehouses

Wired LAN

Wireless LAN

Wireless LANs allow workstations to communicate and to access the network using radio propagation as the transmission medium

Wireless LAN can be connected to a wired LAN: as an extension or can form the basis for a new network

The basic building block of the wireless LAN is the CELL.

The CELL The Cell – the area in which

the wireless communication take place.

Coverage area of a cell depends on: The strength of the

propagated radio signal Type and construction of

walls, partitions and other physical characteristics of an indoor environment

PC workstations, notebooks, other mobile devices can move freely in the cell.

AP – Access PointSA – Stations (workstation, laptops, other

mobile devices)

Example 1 - The Basic Wireless LAN Cell

Another example cell

Example 2 – Single Cell Wireless LAN Configuration

Cell Components - clients

1. Wireless network cards PCI (Peripheral Component Interconnect) cards

for workstations or PC cards for laptops and other mobile devices

They act: in an ad hoc mode (client-to-client) in a client-to-access point mode

Cell Components – access

1. Wireless access points (AP) It is essentially a hub that gives wireless clients

the ability to attach to the wired LAN backbone Plays the role of communication and traffic

management Stations communicate with each other via the AP Communicating stations can be hidden from one

another AP functions as a relay, extending the range of the

system.

Cell Components - bridges

1. Wireless bridge An AP can also function as a wireless bridge,

between the wireless stations and the wired LAN and the other wireless cells

The range of the system can be extended by cascading several links, one after the other

Multi Cell NetworksAP – Access Point

WB – Wireless Bridge

Example 1 – Multiple Cell Wireless LAN connectivity

Multi Cell Example

UM = User Module = Wireless Network CardCM = Control Module = Access Point Example2 – Multiple Cell Wireless LAN connectivity

Cross-Building Interconnect

Connect LANs in nearby buildings Wired or wireless LANs Point-to-point wireless link is used Devices connected are typically bridges or

routers

Nomadic Access

Wireless link between LAN hub and mobile data terminal equipped with antenna Laptop computer or notepad computer

Uses: Transfer data from portable computer to office

server Extended environment such as campus

Nomadic Access

Example 1- Infrastructure Wireless LAN

Ad Hoc Networking

Temporary peer-to-peer network set up to meet immediate need

No central server to manage the network Example:

Group of employees with laptops convene for a meeting; employees link computers in a temporary network for duration of meeting

Ad hoc LAN

Roaming

Cell coverage overlaps Each wireless station

automatically establishes the best possible connection with one of the Access Points

Overlapping coverage area import in the wireless LAN setup Enables seamless

roaming between overlapping cellsMultiple Cell Wireless

LAN connectivity

Moving Between

Mobile users move freely between overlapping cells, maintaining their network connection

Roaming is seamless Working session is

maintained while moving from one cell to another.

Roaming through overlapping cells

Load Balancing Multi-cell structure required by many

users and heavy traffic load per unit In multi-cell structure, many co-

located APs cover the same area create common coverage area increase aggregate throughput

Stations are automatically associated with the AP less loaded and provides the best signal quality

Stations equally divided between APs Helps equally share the load between

all APs Efficiency maximized

All APs work at the same law level load

The Common Coverage Area of a Multi-cell Structure

Multiplexing Capacity of the transmission medium usually

exceeds capacity required for transmission of a single signal

Multiplexing is a technique used for carrying multiple signals on a single medium

Enables more efficient use of transmission medium

Multiple Access

3 common techniques are: Time Division Multiple Access (TDMA) Frequency Division Multiple Access (FDMA) Code Division Multiple Access (CDMA)

Time Division Multiple Access

Takes advantage of the fact that the achievable bit rate of the medium exceeds the required data rate of a digital signal

Each source is given certain time intervals during which it can use all the bandwidth.

Multiple sources send at different points in time on the same frequency bandwidth.

Frequency Division Multiple Access Takes advantage of the fact that the useful bandwidth

of the medium exceeds the required bandwidth of a given signal

Each source is given its own frequency band and can use it permanently.

Multiple sources send on different frequency bands at the same time.

Code Division Multiple Access

Multiple sources send with different data encoding, at the same time, on the same bandwidth.

Each source encodes its data using a different code, from a set of orthogonal codes.

Data divided into small packets and distributed into a predetermined pattern across the frequency spectrum.

Each pattern designed by a code known as Pseudo-random Noise (PN) code.

PN corresponds to a time slot number in TDMA or a carrier frequency in FDMA.

Advantages of Multiplexing

Cost per kbps of transmission facility declines with an increase in the data rate

Cost of transmission and receiving equipment declines with increased data rate

Most individual data communicating devices require relatively modest data rate support

Lecture Summary

In the lecture we have: Introduced some key wireless communication

technology Looked at a brief history of the technology Recapped on some primary applications and technologies Reviewed the advantages and disadvantages of this technology

Looked at some core specific technologies The concept of a cell Roaming and Nomadic Access Multiplexing (CDMA, FDMA, TDMA)