28-07-2012, 01:17 PM
ppt Cellular System
[attachment=29389]
What is Cellular System?
During the olden days a single, high powered transmitter with antenna was mounted on a tall tower and it used to cover a large service area (as shown in figure below)and the problem due to this method was spectral congestion.
1 The cellular concept was a major breakthrough in solving the problem of spectral congestion and user capacity.
2 It offered very high capacity in a limited spectrum.
3 In the cellular concept , single high power transmitter is replaced with many low power transmitter each providing coverage to one small portion of the service are as shown. in the figure below.
What is Frequency Reuse?
1 Each cellular base station is allotted a group of radio channels to be used within a small geographic area called cell.
2 The design process of selecting and allocating groups or all the cellular base stations within a system is called frequency reuse or frequency planning.
CHANNEL ASSIGNMENT STRATEGIES
It can be classified as
Fixed:-In fixed channel assignment strategy, each cell is assigned a fixed number of voice channels. If all the channels are in use, the call is blocked and the subscriber does not receive service.
Dynamic :-In dynamic channel assignment strategy, there is no permanent allocation of channels. When a call request is made, the base station requests a channel from MSC.
HANDOFF STRATEGIES
When mobile moves into a different cell while a conversation is in progress, the MSC automatically transfer the call to a new channel belonging to the new base station. This Process of changing frequency is done automatically by the system without any user intervention is called Hand Off.
[attachment=29389]
What is Cellular System?
During the olden days a single, high powered transmitter with antenna was mounted on a tall tower and it used to cover a large service area (as shown in figure below)and the problem due to this method was spectral congestion.
1 The cellular concept was a major breakthrough in solving the problem of spectral congestion and user capacity.
2 It offered very high capacity in a limited spectrum.
3 In the cellular concept , single high power transmitter is replaced with many low power transmitter each providing coverage to one small portion of the service are as shown. in the figure below.
What is Frequency Reuse?
1 Each cellular base station is allotted a group of radio channels to be used within a small geographic area called cell.
2 The design process of selecting and allocating groups or all the cellular base stations within a system is called frequency reuse or frequency planning.
CHANNEL ASSIGNMENT STRATEGIES
It can be classified as
Fixed:-In fixed channel assignment strategy, each cell is assigned a fixed number of voice channels. If all the channels are in use, the call is blocked and the subscriber does not receive service.
Dynamic :-In dynamic channel assignment strategy, there is no permanent allocation of channels. When a call request is made, the base station requests a channel from MSC.
HANDOFF STRATEGIES
When mobile moves into a different cell while a conversation is in progress, the MSC automatically transfer the call to a new channel belonging to the new base station. This Process of changing frequency is done automatically by the system without any user intervention is called Hand Off.