802.16 for WAN (WiMax)

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802.16 for WAN (WiMax)
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What is WiMax?

• Acronym for Worldwide Interoperability for
  Microwave Access
• Use a tall antenna to cover a relatively large
  area to provide two-directional wideband (high
  speed) connections wirelessly.
• Multiple users can be served by one base station.
• It can connect 802.11 (Wi-Fi) hotspots with each
  other and to other parts of the Internet and
  provide a wireless alternative to cable and DSL
  for the last mile (last km) broadband access.
• The new 802.16e amendment can also serve mobile
  users (see below for detail).

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Versions

• 802.16-2004 (also known as 802.16d) WiMAX. It
  uses Orthogonal Frequency Division Multiplexing
  (OFDM) and supports fixed users.
• 802.16e WiMAX. This amendment was ratified in
  December 2005 and supports both fixed and mobile
  users. It uses Scalable Orthogonal Frequency
  Division Multiple Access (SOFDMA).
• 802.16m, the newest version.

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Advantages of WiMax

• Lower cost. Equipment may be more expensive, but
  it does not require laying cables.
• Faster installation, if spectrum and base station
  locations can be obtained.
• Will be installed only for users that need the
  service. To lay cables one has to consider the
  potential users.

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Compared with other services

• One can get high speed connection using telephone
  lines (DSL), but the phone line may not be good
  enough, or may be too far from the central
  office.
• 3G is more expensive and slow for data
  transmission.
• Wi-Fi is designed for WLAN and has smaller
  coverage range.

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Basic features

• Point multiple point communications to replace
  fiber optic backbones
• Can use a large range of frequencies (2-66 GHz).
  In the US, 15 bands between 2-40 GHz can be used
  for WiMax. (It doesnt mean a service provider
  can use all those bands. One can only get a
  band, usually small, that is auctioned by FCC.)
• Range a few miles to 30 miles (see below)
• Data rate up to tens of Mbps (see below)

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Longer range

• It provides up to 50 km (31 miles) of linear
  service area range and allows connectivity
  between users without a direct line of sight (at
  lower frequency bands).
• This should not be taken to mean that users 50 km
  (31 miles) away without line of sight will always
  have connectivity. Practical limits from real
  world tests seem to be around 3 to 5 miles.
• If the density of users and thus the demand for
  resource (bandwidth) are high, the range will be
  determined by the demand for resource. (The
  bandwidth will be shared by many users, thus the
  number of users will be limited, and thus the
  range of service, too.)

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Performance

• The technology has been claimed to provide
  downlink data rates up to 70 Mbit/s (even 128
  Mbit/s with MIMO), which, according to WiMAX
  proponents, is enough bandwidth to simultaneously
  support more than 60 businesses with T1-type
  connectivity and well over a thousand homes at
  1Mbit/s DSL-level connectivity.
• Real world tests, however, show practical maximum
  data rates between 500kbit/s and 2 Mbit/s,
  depending on conditions at a given site.
• New 802.16m can reach 1 Gbit/s fixed speeds and
  100 Mbit/s for mobile users.

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802.16e

• It is designed to support mobile users.
• It uses OFDMA (Orthogonal Frequency Division
  Multiple Access), which gives 802.16e more
  flexibility when managing different user devices
  with a variety of antenna types and form factors.
  
• It brings a reduction in interference for user
  devices with omnidirectional antennas and
  improved Non-line-of-sight (NLOS) capabilities
  that are essential when supporting mobile
  subscribers.

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Subchannilization in 802.16e

• Subchannelization defines subchannels that can be
  allocated to different subscribers depending on
  the channel conditions and their data
  requirements.
• This gives the operator more flexibility in
  managing the bandwidth and transmit power, and
  leads to a more efficient use of resources.
• For instance, within the same time slot more
  transmit power can be allocated to a user with
  less favorable channel conditions, while lowering
  the power for users in better locations.
• Improved in-building coverage can be achieved by
  allocating higher power to sub-channels assigned
  to indoor user devices.

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Resource allocation

• 802.16-2004 uses OFDM. A user device transmits
  using the entire spectrum. Users are separated
  by TDMA (different users are assigned different
  time slots).
• 802.16e uses SOFDMA (Scalable Orthogonal
  Frequency Division Multiple Access). Users can
  be allocated partial spectrum as well as various
  time slots.

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Assigning sub-channels
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Handoff

• 802.16e supports different types of handoff,
  ranging from hard to soft.
• Hard handoffs use a break-before-make approach.
  The user device is connected to only one base
  station at any given time which is less complex
  than soft-handoffs but has a high latency.
• Soft handoffs allow the user device to retain the
  connection to a base station until it is
  associated with a new one (make-before-break
  approach), thus reducing latency.
• While applications like mobile Voice over
  Internet Protocol (VoIP) or gaming greatly
  benefit from low-latency soft handoffs, hard
  handoffs typically suffice for data services.

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Version Selection

• Fixed and mobile deployments have very different
  requirements and target substantially different
  market segments, with different usage patterns
  and locations, throughput needs, user device form
  factors, and SLAs.
• In a fixed deployment, 802.16-2004 and 802.126e
  offer similar performance.
• Single sector maximum throughput for both
  versions of WiMAX is about 15 Mbps for a 5 MHz
  channel, or 35 Mbps for a 10 MHz channel.
• Base station range in densely populated areas can
  go up to a few kilometers depending on the actual
  conditions.
• In networks that are capacity constrained, the
  number of base stations installed depends on
  throughput demand, rather than range.

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Advantage of 802.16-2004

• Less complex modulation. OFDM is a simpler
  modulation technique.
• Use of License-exempt bands. Fixed deployments
  have successfully used license-exempt bands in
  areas where interference levels are acceptable.
  Mobile services require licensed spectrum to
  provide coverage in wide areas.
• Higher data rates. Higher spectrum bands selected
  for the 802.16-2004 profiles result in higher
  data rates. This is a clear advantage, especially
  when targeting enterprise users requiring higher
  data rates.
• Better time to market, because 802.16-2004
  products will be available earlier.

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Advantages of 802.16e

• Support for mobility. 802.16e supports handoffs.
  Support for power-saving and sleep modes will
  extend the battery life of mobile user devices.
• Better indoor coverage achieved through
  subchannelization and channel power control or
  Adaptive Antenna System (AAS). This is
  especially important for mobile applications.
• Greater flexibility in managing spectrum
  resources. Sub-channelization allows the network
  to allocate resources to user devices as needed.
  This results in a more efficient use of spectrum,
  thus higher throughput and better indoor
  coverage.
• Wider range of form factors for user devices.
  Laptop PCMCIA cards, mini cards, indoor modems,
  PDAs, and phones will be available among 802.16e
  user devices. This variety allows operators to
  extend their services to new market segments and
  to give more freedom to their subscribers.