wireless data technologies mm clements. wdt 2 last week is used when we want to measure the the...
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Wireless Data Technologies
MM Clements
WDT2
Last Week
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
WDT3
This week……….
RAN and EDGE networks Base Stations Transmitter types Backhaul network Mobile telephony operation
WDT4
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
WDT5
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
WDT6
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
WDT7
Disguising Transmitters
WDT8
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
WDT9
Antenna Beam Patterns
RAN patterns are conical in nature
Antennae angled slightly downward to extend coverage
WDT10
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
WDT11
WDT12
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
WDT13
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
WDT14
WDT15
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
WDT16
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
WDT17
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
WDT18
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.
WDT19
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
WDT20
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 agent’s area, it
informs the home agent of the handset’s location
WDT21
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
WDT22
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
WDT23
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.
WDT24
References
http://www.antennas3.com/ www.corrigent.com/solu_3g.php
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