Wireless Data Technologies

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Wireless Data Technologies

• MM Clements

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Last Week

• w is used when we want to measure the the rate of
  change of an angle per unit time - measured in
  Hertz
• AM is produced by multiplying the input signal by
  the carrier wave.
• There are TWO distinct sidebands produced when
  using AM.
• AM is used for low quality broadcasts and is
  susceptible to induced noise.
• FM may have many sidebands and is used for high
  quality broadcasts as it does not suffer badly
  from noise

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This week.

• RAN and EDGE networks
• Base Stations
• Transmitter types
• Backhaul network
• Mobile telephony operation

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RAN and EDGE networks

• Network divided into TWO parts
• Radio Access Network (RAN) where mobile users
  interact with the network
• Edge network
• The part of the network that interconnects all
  parts of the network including RANs

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Base Stations

• Transceiver often on a mast, BST
• Controller to coordinate the action of the base
  station, BSC
• Located at the centre of an area that has mobile
  users
• Connected to rest of network by backhaul

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Sharing Facilities

• Masts or sites may be shared between mobile
  providers
• Cost-effective solution for providers
• Shared masts tend to be tall to space the
  transceivers and may require extra planning
  permission
• Visual impact of mast may be reduced with
  disguised BSTs e.g. trees, flagpoles

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Disguising Transmitters
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Available Spectra Transmitters

• Base station antennae are available for operation
  on GSM900, GSM1800, PCS1900, 3G and wireless
  broadband applications
• Busy areas may have 10 or more transceivers
  whereas a quieter area may have only one
  transceiver

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Antenna Beam Patterns

• RAN patterns are conical in nature
• Antennae angled slightly downward to extend
  coverage

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Lobes

• Near the transmitter are lobes
• They do not contribute to the required beam
  pattern
• The cones are arranged around the base station to
  provide 360 coverage
• Power drops as the distance from the mast
  increases

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Macrocells, Microcells, Picocells

• Macrocells are typically mounted on a mast, tall
  building or other high feature
• Power is 10s of watts
• Microcells may be in a High Street, often
  disguised as street furniture
• Picocells may be in an airport lounge or shopping
  mall, hung from ceiling

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Edge or Backhaul Network

• Interconnects all base stations
• Joins Internet and PSTN
• Must be reliable
• Leased lines may be used - expensive
• Often fibre and microwave rings for the backbone
  of the backhaul network
• Some base stations are daisy-chained by microwave
  links

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European Solution

• This prefers microwave to link the backhaul nodes
  together
• Sometimes fibre will be used instead of microwave
  links
• Microwave often is cheap to implement and
  maintain
• Mainly uses point-to-point links

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Microwave Data Rates

• Microwave uses data rates ranging from E1 to
  twice STM-1 at 311 Mbps.
• Frequencies in use range from 2 GHz to 38 GHz
• Microwaves travel in straight lines similar to
  lasers and their range is limited by the
  curvature of the Earth making the range typically
  maximum of 30 miles
• The capacity of the microwave link required will
  depend on the number of users' calls that are
  carried at any one time

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Backhaul Network Design

• Must be as reliable as possible for network
  availability
• Often uses SDH with each base station at an ADM
• Fibre ring backbones increase network reliability
• Connects all parts of the network to the MSC

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Hand-over

• Cell coverage overlaps with adjacent cells
• As power from the current cell drops, mobile
  monitors power from adjacent cells
• Hand-over
• As handset moves between cells, it monitors
  received power from nearby cells
• If the power from an adjacent cell rises above
  that of the current cell, the handset informs the
  network and a seamless changeover can take place.

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Frequency Hopping

• During call progress, the frequency in use
  changes constantly in a mapped manner
• This shares out bad frequencies
• Also provides a basic level of security to
  prevent casual eavesdroppers listening in to a
  data stream

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Location Updating

• Cellular system divided into areas
• Handsets broadcast their presence periodically to
  base stations
• Each user has a home agent (software) to which
  they are attached
• Each area has one or more foreign agents
• When handset arrives in foreign agents area, it
  informs the home agent of the handsets location

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Paging

• When a user is called, the call primarily goes
  to the home agent. This is able to supply the
  location of the handset being called
• The call can then be routed to the correct cell
  to allow the phone to be paged
• Otherwise all cells would need to be paged and
  this would reduce the number of users supported
  by a network

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Conclusion part 1

• Base station usually 3 or 6 sectored with conical
  beams
• Cells overlap at their edges
• This is the RAN for user access
• Backhaul network connects all base stations
• Handover takes place when power from current base
  station drops lower than adjacent base station
  power
• Frequency hopping in use - allows secrecy

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Conclusion part 2

• The mobile network keeps track of the location of
  individual handsets by location updating.
• The mobile set broadcasts its location
  periodically to allow the network, via foreign
  and home agents, to tunnel the calls through the
  backhaul network to the correct user in the
  correct cell.

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References

• http//www.antennas3.com/
• www.corrigent.com/solu_3g.php