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Wireless & Mobile Communications Multiple Choice Questions on “Capacity of Cellular Systems”.
1. ____________ is the maximum number of channels that can be provided in a fixed frequency band.
a) Channel capacity
b) Radio capacity
c) Spectral capacity
d) Carrier capacity
Answer: a
Clarification: Channel capacity for a radio system can be defined as the maximum number of channels or users that can be provided in a fixed frequency band. It is useful in computer science, in electrical engineering, and in other disciplines evaluating the capacity of a channel or conduit.
2. Which of the following measures spectrum efficiency of a wireless system?
a) Channel capacity
b) Radio capacity
c) Spectral capacity
d) Carrier capacity
Answer: b
Clarification: Radio capacity is a parameter which measures spectrum efficiency of a wireless system. This parameter is determined by the required carrier to interference ratio and the channel bandwidth.
3. If D is the distance between co-channel cells and R be the cell radius, co-channel reuse ratio is given by __________
a) D*R
b) D2/R
c) D/R
d) D/R2
Answer: c
Clarification: Let, D is the distance between co-channel cells and R be the cell radius. Then the minimum ratio of D/R that is required to provide a tolerable level of co-channel interference is called the co-channel reuse ratio.
4. __________ is the interference at a base station receiver that comes from the subscriber units in the surrounding cells.
a) Forward channel interference
b) Carrier interference
c) Receiver interference
d) Reverse channel interference
Answer: d
Clarification: In a cellular system, the interference at a base station receiver will come from the subscriber units in the surrounding cells. This is called reverse channel interference.
5. In practice, TDMA systems improve capacity by ____________ compared to analog cellular systems.
a) Three to six times
b) Equal capacity
c) Two time
d) Ten to twenty times
Answer: a
Clarification: In practice, TDMA systems improve capacity by a factor of three to six times as compared to analog cellular radio systems. Powerful error control and speech coding enable better link performance in high interference environment.
6. __________ allows subscribers to monitor neighbouring base stations.
a) TDMA
b) MAHO
c) FDMA
d) ACA
Answer: b
Clarification: Mobile assisted handoff (MAHO) allows subscribers to monitor the neighbouring base stations, and the best base station choice may be made by each subscriber. MAHO allows deployment of densely packed microcells, thus giving substantial capacity gains in a system.
7. Time division multiple access introduces ACA, which stands for ________
a) Acute carrier allocation
b) Adaptive carrier allocation
c) Adaptive channel allocation
d) Acute channel allocation
Answer: c
Clarification: TDMA makes it possible to introduce adaptive channel allocation (ACA). ACA eliminates system planning since it is not required to plan frequencies for cells.
8. Which of the following standard had not adopted digital TDMA for high capacity?
a) USDC
b) GSM
c) PDC
d) IS-95
Answer: d
Clarification: Various proposed standards such as the GSM, US digital cellular (USDC), and Pacific Digital Cellular (PDC) have adopted digital TDMA for high capacity. IS-95 does not use TDMA.
9. Capacity of CDMA is bandwidth limited.
a) True
b) False
Answer: b
Clarification: The capacity of CDMA systems is interference limited. It is bandwidth limited in FDMA and TDMA. Therefore, any reduction in the interference will cause a linear increase in the capacity of CDMA.
10. In a CDMA system, link performance for each user __________ as the number of users _______
a) Increase, decrease
b) Increase, increase
c) Decrease, increase
d) Decrease, decrease
Answer: a
Clarification: In a CDMA system, the link performance for each user increases as the number of users decreases. A straightforward way to reduce interference is to use multisectorized antennas, which results in spatial isolation of users.
11. Capacity of CDMA can be increased by operating in DTX, which stands for _______
a) Discrete transmission mode
b) Discrete transmission modulation
c) Discontinuous transmission mode
d) Digital transmission mode
Answer: c
Clarification: Capacity of CDMA can be increased by operating in DTX, which stands for Discontinuous transmission mode. It takes advantage of the intermittent nature of speech. In DTX, the transmiiter is turned off during the periods of silence in speech.
12. Frequency reuse factor for CDMA system is ___________
a) One
b) Two
c) Zero
d) Ten
Answer: a
Clarification: The amount of out-of-cell interference determines the frequency reuse factor, f, of a CDMA cellular system. Ideally, each cell shares the same frequency and the maximum possible value of f (f=1) is achieved.
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