Wireless & Mobile Communications Multiple Choice Questions & Answers (MCQs) on “Interference and System Capacity”.
1. Which of the following is not a source of interference?
a) Base station in a different cluster
b) Another mobile in same cell
c) A call in progress in neighbouring cell
d) Any BS operating on same frequency
Answer: a
Clarification: Interference is a major limiting factor in the performance of cellular radio systems. Sources of interference includes another mobile in the same cell, a call in progress in neighbouring cell, other base stations operating in the same frequency band, or any non-cellular system which inadvertently leaks energy into the cellular frequency band.
2. Interference on voice channels causes _______
a) Blocked calls
b) Cross talk
c) Queuing
d) Missed calls
Answer: b
Clarification: Interference on voice channels causes crass talk. Here, the subscriber hears interference in the background due to an undesired transmission.
3. Interference in control channel leads to ________
a) Cross talk
b) Queuing
c) Blocked calls
d) Voice traffic
Answer: c
Clarification: On control channels, interference leads to missed and blocked calls. This happens due to errors in the digital signalling.
4. Interference is more severe in rural areas.
a) True
b) False
Answer: a
Clarification: Interference is more severe in rural areas. It happens due to the greater RF noise floor and the large number of base stations and mobiles.
5. What are co-channel cells?
a) Cells having different base stations
b) Cells using different frequency
c) Cells using adjacent frequency
d) Cells using same frequency
Answer: d
Clarification: Due to frequency reuse concept, there are several cells that use the same set of frequencies. These cells are called co-channel cells. And the interference between these cells is called co-channel interference.
6. Co-channel interference is a function of _________
a) Radius of cell
b) Transmitted power
c) Received power
d) Frequency of mobile user
Answer: a
Clarification: This is the case when the size of each cell is approximately the same and the base stations transmit the same power. Co-channel interference ratio is independent of the transmitted power and becomes a function of the radius of the cell ® and the distance between centers of the nearest co channel cell (D).
7. Co-channel reuse ratio is define by _________
a) Q=D*R
b) Q=D/R
c) Q=D^R
d) Q=1/R
Answer: b
Clarification: Co-channel reuse ratio is defined by Q=D/R. By increasing the ratio of D/R, the spatial separation between co-channel cells relative to the coverage distance of a cell is increased. Thus, interference I reduced from improved isolation of RF energy from the co-channel cells.
8. Co-channel ratio in terms of cluster size is defined as _________
a) (sqrt{(3N)})
b) N
c) 3N
d) √N
Answer: a
Clarification: Co-channel reuse is defined using (sqrt{(3N)}). A small value of Q provides larger capacity since the cluster size N is small. However, a large value of Q improves the transmission quality, due to smaller level of co-channel interference.
9. What is the cluster size for CDMA?
a) N=10
b) N=100
c) N=1
d) N=50
Answer: c
Clarification: CDMA systems have a cluster size of N=1.Therefore, frequency reuse is not as difficult as for TDMA or first generation cellular systems.
10. What is breathing cell effect?
a) Fixed coverage region
b) Dynamic and time varying coverage region
c) Large coverage region
d) Very small coverage region
Answer: b
Clarification: Breathing cell is a concept used by CDMA systems. They had a dynamic, time varying coverage region which varies depending on the instantaneous number of users on the CDMA radio channel.
11. Adjacent channel interference occurs due to _______
a) Power transmitted by Base station
b) MSCs
c) Same frequency of mobile users
d) Imperfect receiver filters
Answer: d
Clarification: Interference resulting from signals which are adjacent in frequency to the desired signal is called adjacent channel interference. It results from imperfect receiver filters which allow nearby frequencies to leak into the passband.
12. Which of the following problem occur due to adjacent channel interference?
a) Blocked calls
b) Cross talk
c) Near-far effect
d) Missed calls
Answer: c
Clarification: One of the main problems with adjacent channel interference is the near-far effect. It occurs when a mobile close to a base station transmits on a channel close to one being used by a weak mobile.
13. In near-far effect, a nearby transmitter captures the __________
a) Receiver of the subscriber
b) Transmitter of the subscriber
c) Nearby MSC
d) Neighbouring base station
Answer: a
Clarification: Near-far effect occurs if an adjacent channel user is transmitting in very close range to a subscriber’s receiver while the receiver attempts to receive a base station on the desired channel. In this effect, a nearby transmitter captures the receiver of the subscriber.
14. Adjacent channel interference can be minimized through _______
a) Changing frequency of base stations
b) Careful filtering and channel assignments
c) Increasing number of base stations
d) Increasing number of control channels
Answer: b
Clarification: Adjacent channel assignment can be minimized through careful filtering and channel assignments. Each cell is given only a fraction of the available channels, a cell need not be assigned channels which are all adjacent in frequency.
15. In dynamic channel assignment, any channel which is being used in one cell can be reassigned simultaneously to another cell in the system at a reasonable distance.
a) True
b) False
Answer: a
Clarification: Dynamic channel assignment (DCA) is one well known solution to the micro cellular channel assignment problem. The dynamic nature of the strategy permits adaptation to spatial and traffic variations while the distribution of control reduces the required computational load.
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