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Understanding Wireless http://www.cwt.vt.edu Congressional Wireless Caucus Kickoff September 14, 2000 Rayburn Building, Washington D.C. Wireless is an old name for radio being used again to describe a wide variety of portable devices that rely on radio links for connectivity.

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understanding wireless

Understanding Wireless


Congressional Wireless Caucus Kickoff

September 14, 2000

Rayburn Building, Washington D.C.

Wireless is an old name for radio being used again to describe a wide variety of portable devices that rely on radio links for connectivity.

Wireless Devices




Direct Broadcast Satellite Receiver

Interconnections may be copper, fiber, coax, or wireless

Wireless Phone (cellular, PCS, satellite)

Cellular, PCS, Paging, Fixed Wireless

Public Switched Telephone Network

Fixed Broadband Wireless (>10 Mbps)

Wireless Local Loop

Wireless systems have a whole lot of wire!

Portable Networking

Wireless systems transmit and receive waveforms that are outside of the spectrum of visible light -- from about 800 to 30,000 MHz

Cellular, PCS, and Fixed Wireless Operate in this range

radio waves are described by a frequency or wavelength
Frequency (f) is the number of oscillations (cycles) per second. Unit is Hertz or Hz

Wavelength (l) is the distance covered by one oscillation (cycle) as the wave travels through space

Radio waves are described by a frequency or wavelength


l Wavelength



1 second, f = 5 cycles per second or 5 Hz

  • All wireless devices have at least one antenna; most use the same antenna to transmit and receive
  • The antenna must be at least one quarter wavelength in size to work well.
  • So, no matter how small you make a cellular phone, the antenna is going to have to be about this size!

Most wireless devices communicate to a central site called a “hub” or “cell” site.



Hub antennas are usually mounted on tall towers or buildings to provide clear, unobstructed “line of sight” to the users


Hub Base Station

Hub Base Station

Hub Base Station

Hubs “hand off” the user as it passes from one cell to the next. The Hub Base Stations transmit the call back to the wired public switched telephone network.

Public Switched Telephone Network

hubs can be within a hundred feet on a streetlamp or thousands of miles away on a satellite
Hubs can be within a hundred feet on a streetlamp or thousands of miles away on a satellite

Cellular and PCS phones use land-based hubs

Satellite phones use satellite hubs

mobile phones analog vs digital
Mobile Phones - Analog vs Digital
  • Analog Cellular Systems
    • Analog service, not well-suited to data applications (<14.4 kbps)
    • Most widespread service, available in many rural areas.
    • Operating frequency: 900 MHz.
  • Digital Cellular or PCS (Personal Communication System) Systems
    • Not yet pervasive, typically in metropolitan areas
    • No standard transmission method means all digital phones do not work on all digital networks
    • Digital service offers extra features like call waiting, caller ID
    • Ideal for data communications. New technologies will allow up to several Mb of bandwidth
    • Operating frequency: 900 MHz (Cellular) 1900 MHz (PCS)

Dual and Tri-mode phones allow access to both types of phone networks

mobile data
Mobile Data
  • Cellular telephone systems were designed for voice systems but have been enhanced for data. These data rates are improving but cannot compete with broadband wireless or wired connections
  • Mobile Data rates:
    • Analog cellular - up to 14.4 kbps
    • Digital PCS - 14.4 to 385 kbps where available
    • 3G PCS data - promises up to about 2 Mbps peak (although 1XTREME standard believes it will get 5 Mbps)
  • Higher Data Rates Can be Had with Fixed Wireless:
    • Unlicensed Wireless up to 155 Mbps
    • MMDS (Multichannel Multipoint Distribution Service) up to 10 Mbps
    • LMDS (Local Multipoint Distribution Service) up to 10 Gbps
multiple access systems
Multiple Access Systems
  • Mobile phone systems must fit more and more users into limited spectrum. There are three main approaches:
    • Frequency Division Multiple Access (FDMA): users transmit on different frequencies
    • Time Division Multiple Access (TDMA): users transmit at different times
    • Code Division Multiple Access(CDMA): users have different “codes”; like several conversations in same room in different languages

These three approaches are incompatible and the source of much debate

broadband wireless
Broadband Wireless
  • Broadband: a loosely-defined term that generally means high capacity, about 10Mbps or more
  • Broadband wireless technology offers a way to overcome the “last mile” bottleneck. Wireless is potentially faster than anything but dedicated fiber.
  • Especially in rural areas, broadband wireless is much cheaper and quicker to install than fiber. It provides an opportunity to bypass wired technology and quickly build telecommunications capacity.
  • Broadband wireless will give citizens and businesses access to communications-based services and job opportunities that are now available only in urban settings.
first rural deployment of lmds broadband wireless blacksburg virginia
First Rural Deployment of LMDS Broadband WirelessBlacksburg, Virginia
  • Can provide any combination of voice/data/video services.
  • Hub is tied back into wired network
  • Remote end can use LAN or wireless LAN to reach end-users
  • up to 11 Mbps to users up to 3 miles away.
  • early 2001 will boost this to 180 Mbps!

Hub antenna

Remote Antenna

why is wireless booming now

Microelectronics revolution

Convergence of computers and communications equipment


Workplace connectivity via telephone, fax, and Internet

The mobile society

Government and Economic

Competitiveness and downsizing

Economic determinism

Telecommunications deregulation

Why is Wireless Booming Now?
barriers to future growth in wireless
Barriers to Future Growth in Wireless
  • Irreducible size of antennas
  • Rising level of RF emissions - interference problems and safety concerns
  • Finite spectrum
  • Lack of standards and interoperability of hardware

These important issues are being examined and will be mitigated by university, corporate, and government laboratories.

Initiatives include:
  • LMDS Wireless Network
  • Blacksburg Electronic Village--ISP like services, Ethernet in apartments
  • Statewide ATM network (www.networkvirginia.net)
  • Cyberschool
  • Math Emporium for Online Math Education
  • Faculty Development Institute
  • Distance Learning

Campus Network Includes:

  • Telephone: 14,000 line PBX
  • LAN: 25,000 switched Ethernet over ATM backbone
  • Cable TV: 5000 ports, 55 channels
  • Satellite Teleport: C-band, Ku-band
  • Dial-up 56 Kbps modems: 1,200
  • Wireless LANs: 802.11

Erv Blythe

Vice President



Our Mission: Information Systems exists to serve the university community and the citizens of the Commonwealth by applying information resources to: enhance teaching and learning, support research, foster outreach and develop partnerships, optimize administration


CWT has a unique interdisciplinary approach to research and teaching and involves faculty, staff, and students from:

College of Arts and Sciences

Computer Science

Communications Studies



R.B. Pamplin College of Business


Management Science


College of Engineering

Electrical/Computer Engineering

Civil and Environmental Engineering

University Information Systems

Dr. Charles Bostian




CWT is the principal Virginia Tech research and teaching group in RF design, wireless networks, satellites, and the geographic and business aspects of wireless.