Explaining Cell Splitting with Diagrams

Question 1:
With the help of diagram/s explain the concept of cell splitting. (3 marks)
Cell splitting is a process of sub-dividing a congested cell into smaller cell. Each small or
sub-divided cell is connected with its own base station and involves corresponding reduction
in antenna size. This technique leads to increase in capacity. The process can be expressed
by the following relation.
C=MKN
And C= MS,
Where C=Capacity of cell, M= Number of cluster, K=allotted channel to cell, N= Number of
cell present in cluster, S= Capacity of cluster.
The following are the reasons of cell-splitting:
 As user increases channel capacity decreases
 Technology required to provide extra channel
 Increases channel capacity
Question2:
1. Find reuse distance if the radius of each is cell is 2km (2 marks)
Given, Radius= 2 km
D
R = √ 3 N
D=R √ 3 N
D=2× √3 ×12=2 √36= 12

Therefore , thereuse distance is 12km .
2. If each channel is multiplexed among eight (8) users how many calls can be
simultaneously processed by each cell if only 10 channels per cell are reserved
for control, assuming a total bandwidth of 30 MHz is available and each simplex
channels consist of 25 kHz. (3 marks)
One duplex channel = 2×bandwidth of one simplex channel
= 2×25 kHz = 50 kHz
Number of channel = ( 30 ×103 )
50 −10 ×12 = 600-120 = 480 channels
Number of channels per cell = 480
12 =40
Total number of calls per cell = 8 × 40 = 320
Therefore 320 numbers of calls can be simultaneously processed by each cell.
3. If each user keeps the traffic channel busy for an average of 5% time and an
average of 60 requests per hour are generated, what is the Erlang value? (3
marks)
The request tare, r = 60 / 3600 = 1/ 60 requests/sec.
Holding time = 0.05 × 3600 = 180 sec
Therefore the offered traffic load in Erlang is = request rate × holding time = (1/60)
×180 = 3 Erlangs
Question 3:
1. You are working as Network Design Engineer with local service provider and
your manager has asked you to propose the design for the below cellular
architecture shown in figure 1. In your design provide the following
information; Base station sites locations, Antenna specification, mention the area
type considering the cell size (suburban, urban, rural etc) and justify you design.
(8 marks)
This proposal is based on the micro cell concept. The zone is divided in three micro cells.
Each of these zones is connected to a single base station. Three zones can cover the entire
circle. If the base station is placed at the centre of the circle, it can cover the entire range. In
the figure we can see that the entire circle is splitted as hexagonal. As hexagonal has the
advantage of covering the maximum area. Only one base station means the number 0of
equipment required will also be less. As the same equipment can be shared for all. The zones
are connected by optical wire and coaxial cables. Multiple numbers of cells with a single base

station can make up one cell. As a mobile travels the zone can be served with strongest
signal. As in the figure we can see the population or the number of user is more at the centre,
the base station can serve the highest signal over there. The hexagonal cell spitting design
will help to reuse the same frequency over the zone without interference the cell or to avoid
the hands off.
Shadowing occurs when line of sight is blocked- Modelled by a random signal component X.
Measurement studies show that Xσ can be modeled with a lognormal distribution - normal
in dB with mean = zero and standard deviation dB
Thus at the “designed cell edge” only 50% of the locations have adequate RSS.
Since Xσ can be modelled indB as normally distributed with mean = zero and standard
deviation σ dB, σ determines the behaviour:
Pr = Pt – Lp +Xσ