Wireless & Mobile Communications Multiple Choice Questions on “Handoff Strategies”.
1. What is the condition for handoff?
a) A mobile moves into a different cell while in conversation
b) A mobile remains in the same cell while in conversation
c) A mobile moves to different cell when idle
d) A mobile remains in the same cell and is idle
Answer: a
Clarification: Handoff occurs when a mobile moves into a different cell while a conversation is in progress. The MSC automatically transfers the call to a new channel belonging to the new base station.
2. Handoff does not require voice and control channel to be allocated to channels associated with the new base station.
a) True
b) False
Answer: b
Clarification: Handoff operation involves identifying a new base station. It also requires that the voice and control signal be allocated to channels associated with the new base station.
3. The time over which a call can be maintained within a cell without handoff is called _________
a) Run time
b) Peak time
c) Dwell time
d) Cell time
Answer: c
Clarification: The time over which a call is maintained within a cell without handoff is called as dwell time. Dwell time vary depending on speed of user and type of radio coverage.
4. Dwell time does not depend on which of the following factor?
a) Propagation
b) Interference
c) Distance between subscriber and base station
d) Mobile station
Answer: d
Clarification: Dwell time of a particular user is governed by a number of factors. They include propagation, interference, distance between the subscriber and the base station, and other time varying effects.
5. Which of the following is associated with the handoff in first generation analog cellular systems?
a) Locator receiver
b) MAHO
c) Cell dragging
d) Breathing cell
Answer: a
Clarification: Locator receiver is a spare receiver in each base station. It is used to scan and determine signal strengths of mobile users which are in neighbouring cells.
6. MAHO stands for ______
a) MSC assisted handoff
b) Mobile assisted handoff
c) Machine assisted handoff
d) Man assisted handoff
Answer: b
Clarification: MAHO stands for mobile assisted handoff. In 2G systems, handoff decisions are mobile assisted. In MAHO, every mobile station measure the received power from surrounding base station and continuously reports the results to serving base station.
7. A handoff is initiated when the power received from the base station of a neighbouring cell falls behind the power received from the current base station by certain level.
a) True
b) False
Answer: b
Clarification: MAHO measures the power received from the surrounding base station. And a handoff is initiated when the power received from the base station of a neighbouring cell begins to exceed the power received from current base station.
8. What is the condition for intersystem interference?
a) Mobile moves from one cell to another cell
b) Mobile remains in the same cell
c) Mobile moves from one cellular system to another cellular system
d) Mobile remains in the same cluster
Answer: c
Clarification: An intersystem handoff is initiated when a mobile moves from one cellular system to another during a course of a call. An MSC engages in an intersystem interference when a mobile becomes weak in a given cell and MSC cannot find another cell to which call can be transferred.
9. What is the disadvantage of guard channel?
a) Efficient utilization of spectrum
b) Cross talk
c) Near far effect
d) Reduce total carried traffic
Answer: d
Clarification: Guard channel is a concept for handling priority in handoff. Here, a fraction of the total available channels in a cell is reserved exclusively for handoff requests from ongoing calls. This method has the disadvantage of reducing the total carried traffic, as fewer channels are allocated to originating calls.
10. Which of the following priority handoff method decrease the probability of forced termination of a call due to lack of available channels?
a) Queuing
b) Guard channel
c) Cell dragging
d) Near far effect
Answer: a
Clarification: Queuing of handoff requests is a method to decrease the probability of forced termination of a call due to lack of available channels. Queuing of handoff is possible due to the fact that there is a finite time interval between the time the received signal level drops below the handoff threshold and the time the call is terminated.
11. Umbrella cell approach is possible by using _________
a) Antenna of same heights
b) Antenna of different heights
c) Different voice channels
d) Different control channels
Answer: b
Clarification: Umbrella cell approach is possible by using different antenna heights and different power levels. By using this approach, it is possible to provide large and small cells which are co-located at a single location.
12. Cell dragging is a problem occur due to __________
a) Pedestrian users
b) Stationary users
c) High speed mobile systems
d) Base stations having same frequency
Answer: a
Clarification: Cell dragging is a practical handoff problem in microcell system. It results from pedestrian users that provide a very strong signal to the base station.
13. What was the typical handoff time in first generation analog cellular systems?
a) 1 second
b) 10 seconds
c) 1 minute
d) 10 milliseconds
Answer: b
Clarification: In first generation analog cellular system, the typical time to make a handoff once the signal level is below the threshold, is about 10 seconds. This requires the value for threshold to be 6 dB to 12 dB.
14. How much time it takes for handoff in digital cellular systems like GSM?
a) 1 second
b) 10 seconds
c) 1 minute
d) 10 milliseconds
Answer: a
Clarification: In digital cellular systems, the mobile assista with the handoff procedure by determining the best candidate. Once the decision is made, it typically requires 1 to 2 seconds for handoff.
15. Soft handoff is also known as _________
a) MAHO
b) Hand over
c) Break before make
d) Make before break
Answer: d
Clarification: Soft handoff is one in which the channel in the source cell is retained and used for a while in parallel with the channel in the target cell. In this case, the connection with the receiver target is established before the connection to the source is broken, hence this handover is called make-before-break.
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