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Giacinto Gelli » 2.Overview of wireless


History of wireless communications
Wireless networks
Wireless applications
Wireless terminals
Spectrum and standards

Wireless communications

“Wireless” describes the way of accessing a network without a wire:

  • mainly radio transmission
  • limited free-space optical (FSO) applications using infra-red (IR) lasers or LED
Example of FSO network for last-mile connectivity

Example of FSO network for last-mile connectivity

Mobile communications

Two different kinds of mobility:

  • user mobility: the user accesses the same telecommunications service in different places
  • device portability: the communication device is moving during the service

The wireless market

Wireless communications is the fastest growing segment of the communications industry:

  • cellular systems experimented exponential growth since 1982, with over 3 billion users worldwide today
  • proliferation of laptop and palmtop computers enabled diffusion of wireless LAN based on IEEE 802.11
  • many emerging new applications (e.g., wireless sensors, automated highways, smart homes) and systems (e.g., WiMax, Zigbee, UWB)

Short history of wireless communications: the early era

Ancient “wireless” systems:

  • smoke signals, carrier pigeons, flags

First electrical communications systems are wired:

  • telegraph (Samuel Morse, 1838)
  • telephone (Antonio Meucci – Graham Bell, 1860)

Basic results on electromagnetism in 19th century:

  • Faraday (1831), Maxwell (1864), Hertz (1886)

Radio invented in 1895 by Guglielmo Marconi.

Short history of wireless communications: the technologies

First mobile telephone system in 1924.
Many sophisticated military radio systems developed during and after World War 2 (analog signals).
First digital radio (packet radio): ALOHANET (Hawaii, 1971).
Until the 80’s (start of mobile telephone systems) the use of wireless systems for personal communications was limited: CB, military systems, ship and plane communications

Wireless networks: coverage regions

WPAN (Wireless Personal Area Network):

  • room (e.g., Bluetooth, ZigBee, UWB)

WLAN (Wireless Local Area Network):

  • building, campus (e.g., IEEE 802.11/WiFi)

WMAN (Wireless Metropolitan Area Network):

  • town (e.g., IEEE 802.16/WiMax)

WWAN (Wireless Wide Area Network):

  • region, global (e.g., GSM, UMTS, satellite)

Wireless networks: basic topologies

Infrastructure-based network:

  • the wireless network has a fixed central element (base station/access point) that manages the network and through which all communications take place
  • star network

Ad hoc network:

  • the wireless network has no central element, so that the network topology can change over time without user intervention
  • peer-to-peer network
  • more flexible and robust but also more difficult to manage

Wireless network: protocol reference model

Wireless applications


  • transmission of news, road conditions, weather, music via DAB
  • personal communication using GSM
  • positioning via GPS
  • satellite anti-theft and assistance systems
  • local ad-hoc network with vehicles close-by to prevent accidents, guidance system, redundancy
  • vehicle data (e.g., from busles, high-speed trains) can be transmitted in advance for maintenance and fleet management

Example: road traffic management

Wireless applications


  • replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc …
  • crisis, war


  • early transmission of patient data to the hospital, current status, first diagnosis
  • remote patient monitoring and diagnosis

Wireless applications (cont’d)


  • Direct access to customer files stored in a central location
  • Consistent databases for all agents
  • Mobile office
  • Inventory
  • Location-aware services
  • Surveillance, security
  • M-commerce, M-banking, etc …

Wireless applications (cont’d)


  • Outdoor Internet access
  • Intelligent travel guide with up-to-date location dependent information
  • Ad-hoc networks for multi user games


  • Remote classrooms
  • M-learning

Wireless applications (cont’d)


  • Monitoring of weather and earth activities
  • Monitoring of public service networks (e.g., water)
  • Monitoring of fire hazards, toxic waste sites, stress and strain in buildings and bridges, pollution


  • Identification and tracking of enemy targets
  • Detection of chemical and biological attacks
  • Support of unmanned robotic vehicles
  • Missile guidance systems
  • Electronic warfare

Wireless terminals

Limitations of wireless terminals

Power consumption:

  • limited computing power, low quality displays, small disks due to limited battery capacity

Loss of data:

  • higher probability, has to be included in advance into the design (e.g., defects, theft)

Limited user interfaces:

  • compromise between size of fingers and portability
  • integration of character/voice recognition, abstract symbols

Limited memory:

  • limited value of mass memories with moving parts

Wireless vs. wired networks

The wireless channel is an unpredictable and difficult communications medium:

  • higher interference due to other systems
  • lower data rates
  • higher delays, higher jitter
  • lower security, simpler active attacking, encryption and security mechanisms needed

Wireless vs. wired networks (cont’d)

The radio spectrum is a scarce resource that must be allocated to many different applications and systems:

  • the spectrum is controlled by regulatory bodies and can be very expensive
  • frequencies have to be coordinated, useful frequencies are almost all occupied
  • the medium cannot be easily “replicated”

Wireless networking is a significant challenge due to mobility:

  • traffic patterns, user locations, and network conditions are constantly changing
  • the network must be able to locate a given user and route information while the user moves

Spectrum regulation

Government agencies allocate and control the use of the spectrum: FCC in USA, ETSI in Europe, ITU worldwide.
Some spectrum reserved for specific applications (commercial/military).

Spectral auctions for selling spectral blocks to the highest bidder (e.g., UMTS, WiMax):

  • Pros: most efficient way to allocate spectrum, high revenues for the governments
  • Cons: competition limited to big companies, infrastructure investments are delayed

ISM bandwidth

Some portions of spectrum not licensed (ISM, Industrial, Scientific & Medical band):

  • 900 MHz band (902-928 MHz)
  • 2.4 GHz band (2.4-2.4835 GHz)
  • 5.8 GHz band (5.725-5.850 GHz)

Everyone can use this spectrum according to a specific set of rules (modulation type, power level etc.):

  • ETSI specification EN 300 328-1 (Europe)

Spectrum of some existing systems

Wireless standards

Necessary to assure interoperability between different products/networks.
Companies want their systems adopted as standards:

  • alternatively try de-facto standards
  • usually standards do not include all the details on system design, some aspects are left unspecified to allow for innovation and competition between companies

Standards determined by several organisms in many countries:

  • TIA/CTIA and IEEE in USA, ETSI in Europe, ITU worldwide

Standardization is often a long and conflicting process:

  • successes (GSM) vs. failures (Hiperlan)

I materiali di supporto della lezione


A. Goldsmith. Wireless Communications. Cambridge University Press, 2005 (chap. 1 & app. D)

J.H. Schiller. Mobile Communications. Addison-Wesley, 2003 (chap. 1)

Supplementary material eventually available on the website

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