wireless links

8/4/2019 Wireless Links

1/13

Summer training report on

WIRELESS SYSTEMS

Training undergone at:

Reliance communications


2/13

Structure of a typical wireless

system


3/13

Major elements of the system:

Wireless base stations

The switch

The base station controller

Home location register


4/13

Wireless base stationsProvides radio connectionbetween the mobile users and theswitch.One wireless system may have100s of base stations.

Many base stations implyunbroken coverage and sufficientcapacity to handle potentialcustomers.


5/13

The switch Each call involves joining a circuit leading to one

customer (usually on the radio side of the system)

and a circuit leading to another person (usuallyout in the Public Switched Telephone Network(PSTN).

The device that makes the actual physical

connection is called the switch. The switch is also responsible for storing billing

records, interpreting dialled numbers, routingcalls, and implementing all calling features.


6/13

The base station controller The Base Station Controller (BSC) interfaces the

Switch and the base stations

Compresses speech signals for more efficienttransmission over the scarce radio spectrum

Controls the base stations and implements thehandoff of calls from one base station to another as

users drive across the system


7/13

Home location register

The HLR (Home Location Register) is the officialdatabase of all customers on a wireless system.

It can be part of the switch, or held in a server at a

central location where multiple switches caninterrogate it.

Information held in the HLR:

current account status/validity

phones technical parameters

whether the phone is presently turned on, and if so,the identity of switch which is presently serving the

phone.


8/13

Delivering an incoming wireless call


9/13

Managing handoff

As a mobile travels through the service area, it passesfrom the coverage zone of one base station into thecoverage of another.

Signal strength measurements by the mobile or thebase station trigger the BSC and switch to hand offthe call from base station to base station, avoidingdropped calls and interference.

Each wireless technology uses its own methods toimplement the handoffs. CDMA can even simulcastto the mobile from multiple base stations to reducefading effects (this is called soft handoff).


10/13

Multiple Access Multiple Access is the simultaneous use of a

communications system by more than one user

Each users signal must be kept uniquelydistinguishable from other users signals, to allowprivate communications on demand

Users can be separated in many ways:

physically: on separate wires by arbitrarily defined channels established in

frequency, time, or any other variable imaginable


11/13

Multiple access


12/13

Wireless multiple access

methods


13/13

Thank you

wireless links

Documents