Seminar Topics & Project Ideas On Computer Science Electronics Electrical Mechanical Engineering Civil MBA Medicine Nursing Science Physics Mathematics Chemistry ppt pdf doc presentation downloads and Abstract

Handoff Strategies

[attachment=26531]


Hand off

When a mobile moves into a different cell while a conversation is in
progress, MSC transfers the call to a new channel belonging to the new
base station”

Mobile Switching Center needs to:
Identify the new base station
Allocate new Voice and Control channels associated with the new base station


Margin Δ needs to be neither too small, nor too large


Δ too small → too short time to perform handoff, The call may be dropped due to weak signal condition

Δ too large → unnecessary handoff which burden the MSC may occur.



Dropped Call Events:

Dropped call event happen when there is an excessive delay by the MSC in assigning the handoff or when threshold is too small for handoff time in the system

Excessive delays may occur during high traffic conditions due to computational load on the MSC

Or no channels available on any of the nearby stations (Forcing the MSC to wait until a channel in a nearby cell becomes free)


Guard Channel Concept

A fraction of the total available channel in a cell is reserved exclusively for handoff requests from ongoing calls which may be handed off into the cell

Disadvantage of reducing the total carried traffic, as fewer channels are allocated to originating calls

However offer efficient spectrum utilization using dynamic channel assignment strategies.

HANDOFF STRATEGIES


[attachment=28543]


WIRELESS COMMUNICATION



Wireless is a term used to describe communications in which electromagnetic waves carry the signal over part or all of the communication path.

Why Wireless communication Is Needed?

To span the communication beyond the capabilities of cable.
To overcome the obstacles such as physical structure, EMI.
To provide backup links when network fails.


THE CELLULAR CONCEPT


Segmentation of the area into cells.

Deals with replacing a single high powered transmitter with many low powered transmitters.

Channels are divided among the base stations.

Use of several carrier frequencies.

Same frequency is not used in adjoining cells.

If a mobile user changes cells the handover of the connection to the neighboring cell takes place.


THE SHAPE OF THE CELL


There are 3 criteria for selecting a cell shape:
1. The geometric shape
2. Area without overlap
3. Area of the cell

A hexagon, square, equilateral triangle can be fitted in a manner where there is no area of overlap unlike circle.

Also a hexagon has the largest area after circle.

Thus of the lot hexagon satisfies all the conditions which is why the shape of a cell is hexagonal in cellular network.


FREQUENCY REUSE


The design process of selecting and allocating channel groups for all of the cellular base stations within a system is called FREQUENCY REUSE.

The N cells which collectively use the complete set of available frequencies is called a CLUSTER.

Cells with same the same letters use the same set of frequencies.

A cell cluster is put together and replicated over the coverage area.




TYPES OF HANDOFF

HARD HANDOFF:
1. existing connection is broken before new one is established.
2.The break is short enough to remain unnoticed by the user .
3. Categorized into inter-cellular and intra-cellular hard handoffs.


SOFT HANDOFF:
1. Breaking of connection not required.
2. New connection is made before the old one is broken.

SOFTER HANDOFF:
1. New signal is added or deleted from the active set of signals.
2. Also occur when a signal is replaced by a stronger signal from a different sector under the same base station.