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