This set of Wireless & Mobile Communications Multiple Choice Questions & Answers (MCQs) focuses on “Trunking and Grade of Service”.
1. What is the concept for accommodating a large number of users in a limited radio spectrum?
a) Grade of service
Explanation: Cellular radio systems rely on trunking to accommodate a large number of users in a limited radio spectrum. The concept of trunking allows a large number of users to share the relatively small number of channels in a cell by providing access to each user, on demand.
2. On termination of call, the occupied channel is not returned to the pool of available channels in trunking. State whether True or False.
Explanation: In a trunked radio system, each user is allocated a channel on a per call basis. Upon termination of the call, the previously occupied channel is immediately returned to the pool of available channels. It is a method for a system to provide network access to many clients by sharing a set of lines or frequencies instead of providing them individually.
3. In trunking system, when the channel is already in use, the call is blocked or queued. State whether True or False.
Explanation: In a trunked mobile radio system when a particular user requests service, there is a possibility that all the channels are already in use. Then the user is blocked, or denied access to the system. Sometimes, a queue may be used to hold the requesting users until a channel becomes available.
4. Who developed the fundamental of trunking theory?
Explanation: The fundamentals of trunking theory were developed by Erlang. He was a Danish mathematician. He embarked on the study of how a large population could be accommodated by a limited number of servers in late 19th century.
5. What is the unit for the measure of traffic intensity?
Explanation: The measure of traffic intensity is given by Erlang. It is defined as the ratio of the time during which a facility is cumulatively occupied to the time this facility is available for occupancy. Telecommunication operators are vitally interested in traffic intensity as it dictates the amount of equipment they must supply.
6. One Erlang represents _________
a) One call- hour per hour
b) One call-minute per hour
c) One call- hour per minute
d) Many calls- hour per hour
Explanation: One Erlang represents the amount of traffic intensity carried by a channel that is completely occupied (i.e. one call- hour per hour or one call- minute per minute). For example, a radio channel that is occupied for 30 minutes during an hour carries 0.5 Erlangs of traffic.
7. What is the measure of the ability of user to access a trunked system during the busiest hour?
b) Grade of Service (GOS)
Explanation: The grade of service (GOS) is a measure of the ability of a user to access a trunked system during the busiest hour. The busy hour is based upon customer demand at the busiest hour during a week, month or a year.
8. GOS is typically given as a likelihood that a ________
a) Call is in progress
b) Channels are busy
c) Call is blocked
d) Channel are free
Explanation: GOS is typically given as the likelihood that a call is blocked, or the likelihood of a call experiencing a delay greater than a certain queuing time. It is the wireless designer’s job to estimate the maximum required capacity used to allocate the proper number of channels in order to meet GOS.
9. The time requires to allocate a trunked radio channel to a requesting user is called _______
a) Dwell time
b) Holding time
c) Run time
d) Set up Time
Explanation: When any user makes a call request, the time required to allocate a trunked channel to a user is known a s set up time. TETREA (Terrestrial Trunked Radio) call set up time is 0.3 seconds. GSM uses a call set up time of several seconds.
10. Average duration of a typical call is called ________
a) Holding time
b) Dwell time
c) Set up time
d) Run time
Explanation: Average time of a typical call is called holding time. It is denoted by H (in seconds). It is used to measure the traffic intensity per user. The time over which a call may be maintained within a cell, without handoff is called dwell time.
11. The average number of call requests per unit time is also known as ________
a) Request rate
c) Grade o Service
d) Traffic intensity
Explanation: Request rate is the average number of call requests per unit time. It is denoted by λ. Unit for request rate is second-1. It can also be defined as the ratio of traffic intensity of each user and the holding time.
12. Traffic intensity offered by each user is the product of __________
a) Set up time and holding time
b) Call request rate and holding time
c) Load and holding time
d) Call request rate and set up time
Explanation: The traffic intensity offered by each user is equal to the call request rate multiplied by the holding time. Each user generates a traffic intensity A=λH Erlang. Here, H is the average duration of a call and λ is the average number of call requests per unit time for each user.
13. AMPS cellular system is designed for a GOS of _____ blocking.
b) 50 %
Explanation: The AMPS (Advanced Mobile Phone System) cellular system is designed for a GOS of 2% blocking. This implies that the channel allocations for cell sites are designed so that 2 out of 100 calls will be blocked due to channel occupancy during the busiest hour.
14. Blocked calls cleared formula is also known as _______ formula.
a) Erlang C
b) Erlang A
c) Erlang D
d) Erlang B
Explanation: Erlang B formula is also known as the blocked calls cleared formula. The Erlang B formula determines the probability that a call is blocked. And, it is a measure of the GOS for a trunked system which provides no queuing for blocked calls.
15. Blocked calls delayed formula is also known as _______
a) Erlang A
b) Erlang B
c) Erlang C
d) Erlang D
Explanation: Erlang C is also known as Blocked Calls Delayed. In this trunked system, a queue is provided to hold calls which are blocked. If a channel is not available immediately, the call request may be delayed until a channel becomes available.
Sanfoundry Global Education & Learning Series – Wireless & Mobile Communications.
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