Wireless Data Technologies MM Clements

WDT 2 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

WDT 3 This week………. RAN and EDGE networks Base Stations Transmitter types Backhaul network Mobile telephony operation

WDT 4 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

WDT 5 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

WDT 6 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

WDT 7 Disguising Transmitters

WDT 8 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

WDT 9 Antenna Beam Patterns RAN patterns are conical in nature Antennae angled slightly downward to extend coverage

WDT 10 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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WDT 12 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

WDT 13 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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WDT 15 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

WDT 16 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

WDT 17 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

WDT 18 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.

WDT 19 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

WDT 20 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

WDT 21 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

WDT 22 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

WDT 23 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.

WDT 24 References