Pervasive Computing: WiMax and the Future

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Pervasive ComputingWiMax and the Future?
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Electromagnetic Radiation

• WiMax is accompanied by much hype
• Remember that the laws of physics prevail
• Also remember Shannons Law
• An electron is surrounded by an electric field.
• When an electron moves, a magnetic field forms
  around it.
• By increasing and decreasing the density of
  electrons in a wire (antenna), we can create a
  ripple effect in the two fields.

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Electromagnetic Radiation

• The ripples travel
• at the speed of
• lightc3108m/s.
• The frequency of an electromagnetic wave
  determines its properties. X-rays, ordinary
  light and radio waves are all electromagnetic
  waves.

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Radio Transmission
Site B
Site A
Radio Waves
Receiver
Transmitter

• Suppose we set up a transmitter that emits radio
  waves of a selected frequency.
• An aerial and receiver can be designed to
  electrically resonate with the same frequency and
  so pick up that frequency.

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Microwave Channels
Microwaves
Transmitter Dish
Receiver Dish

• Microwaves are transmitted and received using
  parabolic dishes (the special shape focuses the
  microwave beam).
• The receiver and transmitter dishes must be in
  line of sight with each other. Microwaves can
  pass through walls, trees and clouds but not
  through the ground. However, passing through
  anything subjects the signal to some kind of loss
  of energy.

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Wireless LANS

• A wireless LAN (WLAN) is a flexible data
  communication system implemented as an extension
  to, or as an alternative for, a wired LAN within
  a building or campus. Using electromagnetic
  waves, WLANs transmit and receive data over the
  air, minimizing the need for wired connections.
  Thus, WLANs combine data connectivity with user
  mobility, and, through simplified configuration,
  enable movable LANs.

• WLANs have gained strong popularity in a number
  of vertical markets, including the health-care,
  retail, manufacturing, warehousing, and academic
  arenas. These industries have profited from the
  productivity gains of using hand-held terminals
  and notebook computers to transmit real-time
  information to centralized hosts for processing.
• WLANs are becoming more widely recognized as a
  general-purpose connectivity alternative for a
  broad range of business customers.

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Types of Wireless Network

• In wireless networking, a peer-to-peer (or
  point-to-point) wireless network means that each
  computer can communicate directly with every
  other computer on the network.
• Some wireless networks are client/server. They
  have an access point, which is a wired controller
  that receives and transmits data to the wireless
  adapters installed in each computer

• There are many types of wireless networks,
  ranging from slow and inexpensive to fast and
  expensive For example-
• Bluetooth
• IrDA
• HomeRF (SWAP)
• Wi-Fi
• WiMax
• UltraWideband
• HIPERMAN

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Bluetooth

• Bluetooth technology is a wireless personal area
  networking (WPAN) technology that has gained
  significant industry support and will coexist
  with most wireless LAN solutions.

The Bluetooth specification is for a 1 Mbps,
small form-factor, low-cost radio solution that
can provide links between mobile phones, mobile
computers and other portable handheld devices and
connectivity to the internet. This technology,
embedded in a wide range of devices to enable
simple, spontaneous wireless connectivity is a
complement to wireless LANs which are designed
to provide continuous connectivity via standard
wired LAN features and functionality.
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IrDA

• IrDA (Infrared Data Association) is a standard
  for devices to communicate using infrared light
  pulses. This is how remote controls operate, and
  the fact that all remotes use this standard
  allows a remote from one manufacturer to control
  a device from another manufacturer.
• Since IrDA devices use infrared light, they
  depend on being in direct line of sight with each
  other. Although you can purchase and install an
  IrDA-based network capable of transmitting data
  at speeds up to 4 megabits per second (Mbps), the
  requirement for line of sight means that you
  would need an access point in each room, limiting
  the usefulness of an IrDA network in a typical
  home layout.

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Infrared Technology

• Infrared (IR) systems use very high frequencies,
  just below visible light in the electromagnetic
  spectrum, to carry data. Like light, IR cannot
  penetrate opaque objects
• it is either directed (line-of-sight) or diffuse
  technology. Inexpensive directed systems provide
  very limited range (3 ft) and typically are used
  for PANs but occasionally are used in specific
  WLAN applications.
• High performance directed IR is impractical for
  mobile users and is therefore used only to
  implement fixed subnetworks.
• Diffuse (or reflective) IR WLAN systems do not
  require line-of-sight, but cells are limited to
  individual rooms.

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802.11b (Wi-Fi)

• This standard is currentlythe market leader.
  802.11b operates in the 2.4GHz unlicensed
  frequency band (same as the one used by 2.4GHz
  cordless phones and microwave ovens), and uses
  DSSS (Direct Sequence Spread Spectrum) and FHSS
  modulation. It has a maximum raw data rate of
  11Mbps, with fallback rates of 5.5, 2, and 1Mbps.
  
• Widely used in businesses, 802.11b has been
  adopted for many home networks due to its
  relatively high speed, wide availability, and
  falling prices (although we've probably gotten
  pretty close to the bottom of the price curve at
  this point). It's also the standard that's used
  for wireless public access in places like
  airports, malls, etc., and for enterprising
  individuals, companies, and community groups who
  are trying to grow their own wireless broadband
  networks.
• Negatives include the fact that 2.4GHz cordless
  phones and microwave ovens operating in its
  vicinity affect throughput and range. 802.11b's
• The original WEP network security protocol was
  disastrous. However, the effect that WEP's
  weaknesses will have on the average small
  wireless network user has been much exaggerated.
  WEP has been replaced by WPA security.

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Wi-Fi

• Wi-Fi offers Ethernet speeds without the wires.
• There are Wi-Fi compatible PC cards that operate
  in peer-to-peer mode, but Wi-Fi usually requires
  access points.
• Most access points have an integrated Ethernet
  controller to connect to an existing
  wired-Ethernet network.
• They also typically have an omni-directional
  antenna to receive the data transmitted by the
  wireless transceivers.
• As an example, Apple sells an inexpensive and
  easy-to-configure access point called Airport.
  Airport has to be connected to an Apple computer
  (iMac, PowerMac, iBook), but it will accept
  signals from any 802.11b-compatible
  wireless-network card, whether it's PC or
  Mac-based.

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How WLANs Work

• Wireless LANs use electromagnetic radiation
  (radio and infrared) to communicate information
  from one point to another without relying on any
  physical connection. Radio waves are often
  referred to as radio carriers because they simply
  perform the function of delivering energy to a
  remote receiver.
• The data being transmitted is superimposed on the
  radio carrier so that it can be accurately
  extracted at the receiving end. This procedure is
  called modulation of the carrier by the
  information being transmitted. Once data is
  superimposed (modulated) onto the radio carrier,
  the radio signal occupies more than a single
  frequency, since the frequency or bit rate of the
  modulating information adds to the carrier.
• Multiple radio carriers can exist in the same
  space at the same time without interfering with
  each other if the radio waves are transmitted on
  different radio frequencies. To extract data, a
  radio receiver tunes in (or selects) one radio
  frequency while rejecting all other radio signals
  on different frequencies.

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Wireless LANS Working

• In a typical WLAN configuration, a
  transmitter/receiver (transceiver) device, called
  an access point, connects to the wired network
  from a fixed location using standard Ethernet
  cable. At a minimum, the access point receives,
  buffers, and transmits data between the WLAN and
  the wired network infrastructure.
• A single access point can support a small group
  of users and can function within a range of less
  than one hundred to several hundred feet. The
  access point (or the antenna attached to the
  access point) is usually mounted high but may be
  mounted essentially anywhere that is practical as
  long as the desired radio coverage is obtained.
• End users access the WLAN through wireless LAN
  adapters, which are implemented as PC cards in
  notebook computers, or use ISA or PCI adapters in
  desktop computers, or fully integrated devices
  within hand-held computers. WLAN adapters provide
  an interface between the client network operating
  system (NOS) and the transmission medium (via an
  antenna). The nature of the wireless connection
  is transparent to the NOS.

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Wireless LANS Configurations

• Independent WLANs
• The simplest WLAN configuration is an
  independent (or peer-to-peer) WLAN that connects
  a set of PCs with wireless adapters. Any time two
  or more wireless adapters are within range of
  each other, they can set up an independent
  network (Figure 3). These on-demand networks
  typically require no administration or
  preconfiguration.

Independent WLAN
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Wireless LAN Configurations

• Access points can extend the range of independent
  WLANs by acting as a repeater (see below)
  effectively doubling the distance between
  wireless PCs.

Extended-Range Independent WLAN Using Access
Point as Repeater
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Infrastructure WLANs

• In infrastructure WLANs, multiple access
  points link the WLAN to the wired network and
  allow users to efficiently share network
  resources. The access points not only provide
  communication with the wired network but also
  mediate wireless network traffic in the immediate
  neighborhood. Multiple access points can provide
  wireless coverage for an entire building or
  campus

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Microcells and Roaming

• Wireless communication is limited by how far
  signals carry for given power output. WLANs use
  cells, called microcells, similar to the cellular
  telephone system to extend the range of wireless
  connectivity. At any point in time, a mobile PC
  equipped with a WLAN adapter is associated with a
  single access point and its microcell, or area of
  coverage.

Individual microcells overlap to allow continuous
communication within wired network. They handle
low-power signals and hand off users as they
roam through a given geographic area.
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Range/Coverage

• The distance over which RF waves can communicate
  is a function of product design (including
  transmitted power and receiver design) and the
  propagation path, especially in indoor
  environments.
• Interactions with typical building objects,
  including walls, metal, and even people, can
  affect how energy propagates, and thus what range
  and coverage a particular system achieves.
• Most wireless LAN systems use RF because radio
  waves can penetrate many indoor walls and
  surfaces.
• The range (or radius of coverage) for typical
  WLAN systems varies from under 100 feet to more
  than 1000 feet.
• Coverage can be extended, and true freedom of
  mobility via roaming, provided through
  microcells.

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Throughput

• As with wired LAN systems, actual throughput in
  wireless LANs is dependent upon the product and
  how it is configured.
• Factors that affect throughput include
• Transmission medium congestion (number of users),
  propagation factors such as range and multipath,
• The type of WLAN system used,
• The latency and bottlenecks on the wired portions
  of the WLAN.
• Typical data rates range from 1 to 55 Mbps. For
  IEEE 802.11 Standards

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Multipath Effects

• As below shows, a radio signal can take multiple
  paths from a transmitter to a receiver, an
  attribute called multipath. Reflections of the
  signals can cause them to become stronger or
  weaker, which can affect data throughput. Affects
  of multipath depend on the number of reflective
  surfaces in the environment, the distance from
  the transmitter to the receiver, the product
  design and the radio technology.

Radio Signals Traveling over Multiple Paths
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Integrity

• Wireless data technologies have been proven
  through more than fifty years of wireless
  application in both commercial and military
  systems.
• While radio interference can cause degradation in
  throughput, such interference is rare in the
  workplace.
• Robust designs of proven WLAN technology and the
  limited distance over which signals travel result
  in connections that are far more robust than
  cellular phone connections and provide data
  integrity performance equal to or better than
  wired networking.

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Interference and Coexistence

• The unlicensed nature of radio-based wireless
  LANs means that other products that transmit
  energy in the same frequency spectrum can
  potentially provide some measure of interference
  to a WLAN system.
• Micro-wave ovens are a potential concern, but
  most WLAN manufacturers design their products to
  account for microwave interference.
• Another concern is the co-location of multiple
  WLAN systems. While co-located WLANs from
  different vendors may interfere with each other,
  others coexist without interference. This issue
  is best addressed directly with the appropriate
  vendors.

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WiMax and WiFi

• The IEEE Standard 892.11 and its derivatives,
  802.11b, 802.11a, 802.11g and 802.11e, have seen
  wide deployment in commercial governmental and
  residential LAN settings.
• There has also been some application in Public
  Service Networks primarily localised HotSpots
  where coverage is provided within a picocell.
• IEEE 802.16 has become known as WiMax and is
  supported by the Worldwide Interoperability for
  Microwave Access group

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WiMax and WiFi Standards Compared
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WiMax

• The 802.16 standard requires two separate
  physical layer standards because the propagation
  characteristics of radio waves are so different
  in the lower and upper microwave regions.
• These two categories have advantages and
  disadvantages and, as is often the case in
  data-communications, there is a trade-off in
  cost-benefit
• The two categories are compared in the following
  slides

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Lower-frequency 802.16

• Lower-frequency signals can penetrate walls and
  can travel considerable distances more than 30
  miles with highly directional (accurate) antennas
  
• Low-frequency 802.16 ranges also lend themselves
  to complex modulation techniques such as OFDM and
  Wideband Code-Division-Multiple-Access (CDMA). In
  practice these translate to high levels of
  robustness and higher spectral efficiencies i.e.
  more users per given allocation of bandwidth

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Higher-frequency 802.16

• Higher-frequency transmissions must meet strict
  line-of-sight requirements (i.e. no obstacles
  between the Tx. and Rx.), and are usually
  restricted to distances of a few kilometres.
• The singular advantage enjoyed by users of
  Higher-frequency bands is abundance of bandwidth.
  Most spectral assignments above 20GHz provide for
  several hundred megahertz minimally, and the
  57GHz to 64GHz unlicenced band available in the
  united-states, can support several gigabits per
  second at one bit-per-hertz for fiberlike speeds.

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Limitations of 802.11

• IEEE 802.11 was intended to serve the needs of
  Ethernet LAN users and is very limited in terms
  of range and the number of users that can be
  accommodated simultaneously. In practice
  transmission speed and signal integrity drop off
  precipitately at distances beyond about 500 feet
  from an access point.
• This begs the question Why has it become so
  popular?

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Limitations of IEEE 802.11

• Price.
• 802.11 gear has become a commodity. Access points
  and interface cards are very cheap. An IEE 802.11
  network can be constructed for a fraction of the
  cost of an IEEE 802.16 network.
• Some manufacturers (Tropos, Vigato and Airgo) are
  attempting to manufacture adaptive array antenna
  systems or mesh-networked base stations for
  802.11 that may emulate some of the
  characteristics of 802.16. However it seems
  likely that cost and QoS will remain major
  obstacles for this type of approach
• No one should be tempted to believe that an
  entire metropolitan area can be served with
  802.11 equipment

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Other Standards

• IEEE 802.1n
• The high-speed standard projected speeds are
  in excess of 100 MBps.
• Two variants
• IEEE 802.11e
• Endows 802.11 with Qos capabilities
• However it is Ethernet based unlike 802.16 which
  is IP based.
• IEEE 802.15 (Based on Bluetooth)
• Gigabit 802.11? Still in discussion
• 802.11s Mesh Standard? Who knows?

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Other Standards (Continued)

• High Performance radio Metropolitan Area Network
  (HIPERMAN)
• Analogous to 802.16 but generated by a different
  standards body The European Telecommunications
  Standards Institute ETSI.
• An outshoot from HIPERLAN2 (which emerged from
  HIPERLAN).
• Nobody ever used this as far as I can tell?
• However, discussions are ongoing between IEEE and
  ETSI to merge HIPERMAN2 and 802.16

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Progress

• The IEEE standards have made remarkable progress
  in a very short time
• In the next presentation we will consider some of
  the implementation issues and opportunities and
  challenges for commercial exploitation of these
  standards.

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Web Sites

• http//www.ieee.org
• http//www.wimaxforum.org/
• http//www.wimax-industry.com/