A cellular system is composed of both macrocells and femtocells. There are a tot

Question

A cellular system is composed of both macrocells and femtocells. There are a total of 200 voice channels available. Suppose a network engineer decided to implement frequency reuse by using a fixed partition of frequencies, some to the macrocells and the rest to femtocells. Macrocells use cluster sizes of 4 and 3 sectors per cell. Femtocells use cluster sizes of 1 and no sectoring; this assumes femtocells do not interfere with neighboring femtocells.

a. If 20 channels are assigned to each femtocell, how many channels (both macrocell and femtocell channels) are potentially available to a mobile at every location?

b. From part a, if there are 20 macrocells and 20 femtocells in the area, what is the total system capacity?

c. From part a, if the femtocells are assigned to closed subscriber groups, how many channels are available to those who are not in the closed subscriber groups?

d. Instead of the results from part a, how should the channels be distributed if at least 68 channels should be available to a mobile in a femtocell?

Explanation / Answer

Hi, I hope you have the basic understanding of cell and frequency reuse concept. But still i will give you a basic start.

Frequncy is a critical resource in network planning and if it is been used same frequency between two neighboring cell, then you will face the issue of co channel interference. So we plan the distribution of frequncy in suach a way that no two neigboring cells have same frquency.

In therotical we consider that each cell is of the shape hexagonal.

As here given the total 200 voice channels are available. And we have macro cell of cluster (Cm) 4 with 3 sectors per cell. And along with that femto cell have cluster (Cf) size of 1.

Now let's move for questions one by one.

a) If 20 channels for femto cell.
So remaining channels for macro cell = 200 - 20 = 180
As cluster sie of Macro cell = 4 So, channels in one Mac cell = 180/4 = 45.
As it have three additional sectors so channels in one cell = 45/3 = 15.
So if you are inside the edge of femto cell, then number of available channels = 20+15 = 35.
If you are not in femto cell and in only macro cell, then available channels= 15.

b) if 20 femto as well as 20 macro cells.
As Capactity is strongly related to the capacity of the cellular system.Generally, a larger C means higher capacity and higher number of calls that can take place..
Capacity = (180*20) + (20*20) = 3600+400 = 4000.

c) If femto been assigned to CSG, then only 15 macro channels would be availble.

d) If you needed atleast 68 channels to femto cell user. then femto cell have more channels reserved.
lets take it as x, so availabe for macro cell would be (200 - x).
So, x + ((200 - x)/12) >= 68
=> (12x + 200 - x)/12 >= 68
=> (11x + 200) >= (68*12)
=> 11x >= 616
=> x >= 56.
So femto cell should have atleast 56 reserved channels.

Thanks.

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