1) Interference is a major limiting factor for cellular radio system capacity. It is caused by mobile stations, neighboring cells using the same or adjacent frequencies, and non-cellular signals. 2) There are two main types of interference: co-channel interference which occurs between cells using the same frequencies, and adjacent channel interference which occurs between frequencies that are adjacent. 3) Co-channel interference can be reduced by increasing the channel reuse ratio, which is the ratio between the distance of co-channel cells and the cell radius. However, this reduces system capacity. Managing interference is needed to balance capacity and quality.

1. TOPIC :- Interference and System Capacity
SUBMITED BY:-
APAR TRIVEDI :130080112057
VATSAL BODIWALA :140083112002
Under the Guidance :
Prof. D.C.Dalwadi
ET department, BVM
GUJARAT TECHNOLOGICAL UNIVERSITY
Birla Vishvakarma Mahavidhyalay
ET Department

2. Outlet: -
What Is Interferences…
Its types
1. Co-Channel Interference and System Capacity
2. Adjacent Channel Interference
3. Example

3.  It is a major limiting factor in the performance of cellular radio systems. (In
comparison with wired comm. Systems, the amount and sources of interferences in
Wireless Systems are greater.).
 Creates bottleneck in increasing capacity.
Sources of interference are :-
1. Mobile Stations
2. Neighboring Cells
3. The same frequency cells
4. Non-cellular signals in the same spectrum

4.  Interference in Voice Channels: Cross-Talk
 Interference in Control Channels: missed/blocked calls
 Urban areas usually have more interference, because of:
 a) Greater RF Noise Floor,
 b) More Number of Mobiles

5. Types
1) Co-Channel Interference (CCI)
2) Adjacent Channel Interference (ACI)
1.Co-Channel Interference and System Capacity
 The cells that use the same set of frequencies are called co-channel cells.
 The interference between signals from these cells is called Co-Channel
Interference (CCI).
 Cannot be controlled by increasing RF power. Rather, this will increase
CCI.
 Depends on minimum distance between co-channels.

6.  The yellow cells use the same set of frequency channels, and hence, interfere
with each other
 In the cellular system there are 6 first-layer co-channels
 In constant cell size and RF power, CCI is a function of Distance between the
co-channel cells(D), and the size of each cell (R).
 Increasing ratio D/R, CCI decreases.
 Define Channel Reuse Ratio = Q = D/R

7.  For hexagonal geometry, D/R can be calculated:
 Smaller Q provides larger capacity, since that would mean smaller N. (Capacity
∝ 1/N).
 Larger Q improves quality, owing to less CCI.
 For N=3, Q=3,
 N=7, Q=4.58,
 N=12, Q=6,
 N=13, Q=6.24

9.  Signal-to-interference ratio
 S is the power of the signal of interest and is the power of kth interference.
 The signal strength at distance d from a source is
 That is, received signal power is inversely related to nth power of the
distance.
 where n = path loss exponent

10.  Then we can express the SIR in terms of distance
 where the denominator represents the users in neighboring clusters using the
same channel
 Let be the distance between cell centers. Then
 Analog systems: U.S. AMPS required C/I ~= 18dB For n = 4, the reuse factor
for AMPS is N ≥ 6.49, so N = 7.
 Now, let us consider the worst case for a cluster size of N= 7. The mobile is at
the edge of the cell. Express C/I as a function of actual distances.

11. Adjacent Channel Interference
 Interference from channels that are adjacent in frequency,
 The primary reason for that is Imperfect Receive Filters which cause the
adjacent channel energy to leak into your spectrum.
 Problem is severer if the user of adjacent channel is in close proximity.
Near-Far Effect:
 The other transmitter(who may or may not be of the same type) captures the
receiver of the subscriber.
 Also, when a Mobile Station close to the Base Station transmits on a
channel close to the one being used by a weaker mobile: The BS faces
difficulty in discriminating the desired mobile user from the “bleed over” of
the adjacent channel mobile.

12. Near-Far Effect: Case 1
 The Mobile receiver is captured by the unintended, unknown
transmitter, instead of the desired base station

13. Near-Far Effect: Case 2
 The Base Station faces difficulty in recognizing the actual
mobile user, when the adjacent channel bleed over is too high.

14. Minimization of ACI
1. Careful Filtering ---- min. leakage or sharp transition
2. Better Channel Assignment Strategy
 Channels in a cell need not be adjacent: For channels within a
cell, Keep frequency separation as large as possible.
 Sequentially assigning cells the successive frequency channels.
 Also, secondary level of interference can be reduced by not
assigning adjacent channels to neighboring cells.
 For tolerable ACI, we either need to increase the frequency
separation or reduce the pass band BW.

15. Example :-

16. THANK YOU…………..