HOW TO IMPROVE CELL CAPACITY AND COVERAGE AREA

CELL:

            We all know that in wireless communication hexagonal cells are used to provide communication. But the problem is that each hexagonal cell is having specific limit on number of users it call handle.

                               Suppose consider a situation where the users are huge in small amount of area, Then the conventional cell design will not work properly there the users will face problems like call connection delay, call drop,queuing of call requests etc. So to avoid these kind of problems scientists created some cell designing techniques those are 

1)Cell splitting

2) sectoring

3) Micro cell zone concept

The cell splitting mainly focus on the capacity of the system, where as other two techniques will focus on reduction of channel interference and frequency reuse  and also on reducing number of handoff's performed.   

CELL SPLITTING:

                                As we stated earlier the main goal of cell splitting is to increase the "capacity" of the system. So in order to do that  in splitting technique one big cell is replaced by number of small cells with individual base station for each small cell.

                                                                                   Thus number of antennas will increase in the same area which will also increase number of channels allocated for communication. Imagine we have one big cell of radious R , now we have replaced that cell by 4 small cells with each antenna for all . let radious of the small cells be R/2 . If we add all the small cells radious then it will be equal to radious of bigger cell.

                                   BUT the number of users handled by smaller cells added together will be greater as compared to the users handled by single big cell due to increase in number of channels .

The below figure will illustrate the cell splitting concept.

"cell splitting "

Here the cell A is having huge traffic so it has to be splitted . so it is now split into 6 cells each having antenna at its edge. 

It is to be noted that the cells which use "same frequency " are separated by enough distance to avoid co-channel interference. If we observe G we will come to know this.

SECTORING:

                       THE one way to increase the capacity is cell splitting which uses several cells with reduced radious R. Now in second approach the radious is kept constant instead the SIR (signal to noise ratio) is increased which in turn allow reduction of "cluster size" so in the same area we will be having more number of clusters as compare to previous one cell method.

HOW IT IS DONE:

                                In normal design we will be using a single"omnidirectional" antenna , but in this method we will use several "directional" antennas to cover the area. As we know omnidirectional antenna will be radiating the signal  in all directions which will lead to channel interference.

but directional antennas will be radiating the signal only in selected or interested direction. so unwanted channel interference can be avoided, thus increasing SNR which will allow reduction in cluster size thus increasing channel capacity.

The below figure shows sectoring 

It is to be noted that the cells named 5 will be using the same channels so in order to avoid interference they will be placed apart and if it comes in direction also the strength of signal will be controlled so that it wont reach to next cell which is using same channels.

   

"sectoring  with 120 degree radiating antenna"

MICROCELL ZONE CONCEPT:

                                                      This concept is mainly used to "reduce number of handoff's" .

deff: 

        In this technique a single base station is used by number of small cells to avoid the handoffs and channel interference .

In sectoring we have used number of cells , So when a mobile user travel from one area to other area the handoff will be needed . thus there will be extra work for MSC (moblile switching center) and there are chances of call drop during the handoff due to speed of the device.

So to avoid these type of things the microcell zone concept came into picture.

HOW IT WORKS:

                              Consider there is a big cell which will be consisting of 3 microcells with each having its own antenna at its corner . All the microcells will be connected to each other either by "electric cables , optic fibers ". and all cells will be using the same base station to serve the user.

suppose a user is currently in cell A and now after some time he will move to cell B , now the channel which is used by user will not be changed instead the "zone selector " connected to the base station will just assign same channel to user as in cell A . Thus there is no need for handoff in the microcell zone concept.

The below figure illustrates the microcell zone concept .

"micro cell zone concept"

ALSO READ THE FOLLOWING TOPICS


1) TYPES OF NETWORK                             >>>>>>>>>>>>>>>>>>>       click here

2)  HAND OFF                                                >>>>>>>>>>>>>>>>>>>       click here

3)  FREQUENCY REUSE                              >>>>>>>>>>>>>>>>>>>        click here

4)  WHY HEXAGONAL CELLS ARE USED 
      IN WIRELESS COMMUNICATION       >>>>>>>>>>>>>>>>>>          click here