Category: Wireless & Mobile Communications Objective Questions

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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Wireless & Mobile Communications test on “Statistical Models for Multipath Fading Channels”.

1. Which of the following is not a statistical models for multipath fading channels?
a) Clarke’s model for flat fading
b) Saleh and Valenzuela indoor statistical model
c) Two ray Rayleigh fading model
d) Faraday model
Answer: d
Clarification: Several multipath models have been suggested to explain the observed statistical nature of a mobile channel. Clarke’s model for flat fading, Saleh and Valenzuela indoor statistical model, two ray Rayleigh fading model are some of the statistical model for multipath fading channels.

2. Who presented the first statistical model for multipath fading channel?
a) Ossana
b) Rayleigh
c) Newton
d) Faraday
Answer: a
Clarification: The first statistical model was presented by Ossana. It was based on interference of wave incident and reflected from the flat sides of randomly located buildings. Ossana model predicts flat fading power spectra that were in agreement with measurements in suburban areas.

3. Clarke’s model assumes a horizontal polarized antenna.
a) True
b) False
Answer: b
Clarification: Clarke developed a model where the statistical characteristics of the electromagnetic fields of the received signal at the mobile are deduced from scattering. Clarke’s model assumes a fixed transmitter with a vertically polarized antenna.

4. A wave that is incident on mobile does not undergo Doppler shift.
a) True
b) False
Answer: b
Clarification: Every wave that is incident on the mobile undergoes a Doppler shift. It is due to the motion of the receiver and it arrives at the receiver at the same time. Therefore, there is no excess delay due to multipath for any of the waves.

5. Which of the following is an important statistics of a Rayleigh fading useful for designing error control codes and diversity schemes?
a) Mobile speed
b) Doppler frequency
c) Level crossing rate (LCR)
d) Power density
Answer: c
Clarification: The level crossing rate (LCR) and average fade duration of a Rayleigh fading signal are important statistics. They are useful for designing error control codes and diversity schemes to be used in mobile communication.

6. The level crossing rate (LCR) is defined as expected rate at which _______ fading envelope crosses a specified level.
a) Rayleigh
b) Saleh
c) Vanezuela
d) Faraday
Answer: a
Clarification: The LCR is defined as the expected rate at which the Rayleigh fading envelop is normalized to the local rms signal level. And it crosses a specified level in a positive going direction.

7. Level crossing rate is a function of _______
a) Power transmitted by base station
b) Power density of receiver
c) Mobile speed
d) Bit error rate
Answer: c
Clarification: The level crossing rate is a function of mobile speed. Because, it is possible to relate the time rate of change of the received signal of the signal level and velocity of the mobile.

8. Clarke’s model considers the multipath time delay.
a) True
b) False
Answer: b
Clarification: Clarke’s model and the statistics for Rayleigh fading are for flat fading conditions. They do not consider multipath time delay.

9. Saleh and Venezuela reported the results of ______ propagation measurements.
a) Indoor
b) Outdoor
c) Air
d) High frequency
Answer: a
Clarification: Saleh and Venezuela reported the results of indoor propagation measurements. The measurements were made between two vertically polarized omnidirectional antennas located on the same floor of a medium sized office building.

10. Saleh and Venezuela show that indoor channel is _______ time varying.
a) Not
b) Very slow
c) Fast
d) Very fast
Answer: b
Clarification: The results obtained by Saleh and Venezuela shows that the indoor channel is quasi static or very slow time varying. It shows that the statistics of the channel impulse response are independent of transmitting and receiving antenna polarization.

11. What is the full form of SIRCIM?
a) Simulation of Indoor Radio Channel Impulse response Model
b) Statistical Indoor Radio Channel for Impulse Model
c) Statistical Impulse Radio Channel for Indoor Model
d) Simulation of Impulse Radio Channel for Indoor Model
Answer: a
Clarification: SIRCIM stands for Simulation of Indoor Radio Channel Impulse response Model. SIRCIM generates realistic samples of small scale indoor channel impulse response measurements.

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Wireless & Mobile Communications Multiple Choice Questions on “Rake Receiver”.

1. In CDMA spread spectrum systems, chip rate is less than the bandwidth of the channel.
a) True
b) False
Answer: b
Clarification: In CDMA spread spectrum systems, the chip rate is typically much greater than the flat fading bandwidth of the channel. Whereas conventional modulation techniques require an equalizer to undo intersymbol interference between adjacent channels.

2. A RAKE receiver collects the __________ versions of the original signal.
a) Time shifted
b) Amplitude shifted
c) Frequency shifted
d) Phase shifted
Answer: a
Clarification: RAKE receiver attempts to collect the time shifted versions of the original signal. It is due to the fact that there is useful information present in the multipath components.

3. RAKE receiver uses separate _________ to provide the time shifted version of the signal.
a) IF receiver
b) Equalizer
c) Correlation receiver
d) Channel
Answer: c
Clarification: RAKE receiver uses separate correlation receivers to provide the time shifted version of the original signal for each of the multipath signal. CDMA receivers combine these time shifted versions of the original signal to transmission in order to improve the signal to noise ratio of the receiver.

4. Each correlation receiver in RAKE receiver is adjusted in ____________
a) Frequency shift
b) Amplitude change
c) Phase shift
d) Time delay
Answer: d
Clarification: Each correlation receiver may be adjusted in time delay, so that a microprocessor controller can cause different correlation receivers to search in different time windows for significant multipath.

5. The range of time delays that a particular correlator can search is called ________
a) Search window
b) Sliding window
c) Time span
d) Dwell time
Answer: a
Clarification: The range of time delays that a particular correlator an search is called a search window. RAKE receiver attempts to collect the time shifted version of the original signal by providing a separate correlation receiver for each of the multipath signal.

6. RAKE receiver is used for _______ technique.
a) CDMA
b) TDMA
c) FDMA
d) OFDM
Answer: a
Clarification: RAKE receiver is essentially a diversity receiver which is used specifically for CDMA. It uses the fact that the multipath components are practically uncorrelated from one another when their relative propagation delays exceed a chip period.

7. A RAKE receiver uses __________ to separately detect the M strongest signals.
a) Single correlator
b) Multiple correlator
c) Single IF receiver
d) Multiple IF receivers
Answer: b
Clarification: A RAKE receiver uses multiple correlators to separately detect the M strongest multipath components. Demodulation and bit decisions are then based on the weighted ouputs of the M correlators.

8. In a RAKE receiver, if the output from one correlator is corrupted by fading, all the other correlator’s output are also corrupted.
a) True
b) False
Answer: b
Clarification: In a RAKE receiver, if the output from one correlator is corrupted by fading, the others may not be. And the corrupted signal may be discounted through weighting process.

9. A RAKE receiver uses __________
a) Equalization
b) Channel coding
c) Diversity
d) Encryption
Answer: c
Clarification: RAKE receiver is a diversity receiver. Diversity is provided by the fact that the multipath components are practically uncorrelated from one another when their relative propagation delays exceed chip period.

10. Interleaving is used to obtain ___________ diversity.
a) Time
b) Frequency
c) Polarization
d) Antenna
Answer: a
Clarification: Interleaving is used to obtain time diversity in a digital communication system without adding any overhead. It provides rapid proliferation of digital speech coders which transform analog voices into efficient digital messages.

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Wireless & Mobile Communications Questions and Answers for Entrance exams on “Development of Wireless Networks”.

1. First generation cellular and cordless telephone networks are based on _________
a) Analog technology
b) Digital technology
c) Active technology
d) Passive technology
Answer: a
Clarification: First generation cellular and cordless telephone networks are based on analog technology. All first generation cellular systems use FM modulation, and cordless telephones use a single base station to communicate with a single portable terminal.

2. Which of the following is true for first generation wireless systems?
a) Efficient
b) Digital technology
c) High data rate
d) Low rate
Answer: d
Clarification: First generation wireless systems provide analog speech and inefficient, low rate, data transmission between the base station and mobile user.

3. Which of the following network protocol is used by US cellular carriers to automatically accommodate subscribers who roam into their coverage regions?
a) IS-36
b) IS-121
c) IS-41
d) IS-14
Answer: c
Clarification: US cellular carriers implemented the network protocol standard IS-41 to allow different cellular systems to automatically accommodate subscribers who roam into their coverage region.

4. IS-41 does not rely on autonomous registration.
a) True
b) False
Answer: b
Clarification: IS-41 relies on a feature of AMPS called autonomous registration. Autonomous registration is a process by which a mobile notifies a serving MSC of its presence and location.

5. MSC distinguishes home users from roaming users based on MIN.
a) True
b) False
Answer: a
Clarification: The MSC is able to distinguish home users from roaming users based on the MIN of each active user, and maintains a real time user list in the home location register (HLR) and visitor location register (VLR).

6. The visited system creates a __________ record for each roamer and notifies home system to update __________
a) HLR, VLR
b) VLR, MIN
c) MIN, ESN
d) VLR, HLR
Answer: d
Clarification: The visited system creates a VLR record for each new roamer and notifies the home system via IS-41 so it can update its own HLR. IS-41 allows the MSCs of neighboring systems to automatically handle the registration and location validation of roamers so that users no longer need to manually register as they travel.

7. Which of the following is not an example of second generation wireless networks?
a) GSM
b) CT2
c) AMPS
d) PACS
Answer: c
Clarification: AMPS is an example of first generation wireless networks. Second generation wireless systems employ digital modulation and advanced call processing capabilities. Example includes GSM, CT2, PACS and DECT.

8. In second generation wireless networks, the handoff process is called __________
a) MAHO
b) Soft handoff
c) Hard handoff
d) Inter system handoff
Answer: a
Clarification: In second generation wireless networks, the handoff process is mobile controlled and is known as mobile assisted handoff (MAHO). The mobile units in these networks perform several other functions not performed by first generation subscriber units.

9. __________ is an example of second generation cordless telephone standard which allows each cordless phone to communicate with any number of base stations.
a) PACS
b) CT2
c) GSM
d) DECT
Answer: d
Clarification: DECT is an example of second generation cordless telephone standard which allows each cordless phone to communicate with any number of base stations. In DECT, the base stations have greater control in terms of switching, signalling, and controlling handoffs.

10. In PACS/ WACS, the BSC is called a _________
a) Radio port control unit
b) HLR
c) VLR
d) MIN
Answer: a
Clarification: In PACS/ WACS, the BSC is called a radio port control unit. This architectural change has allowed the data interface between the base station controller and the MSC to be standardized.

11. FPLMTS is recently known by the name _________
a) GSM
b) ISDN
c) IMTS-2000
d) DECT
Answer: c
Clarification: FPLMTS (Future Public Land Mobile Telecommunication Systems) is more recently been called International Mobile Telecommunication (IMT-2000). It implies emerging third generation wireless systems for hand held devices.

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Wireless & Mobile Communications Multiple Choice Questions on “Paging System”.

1. A helical antenna is used for satellite tracking because of _________
a) Circular polarization
b) Maneuverability
c) Beamwidth
d) Gain
Answer: a
Clarification: In helical antenna, the diameter and pitch of the helix are comparable to a wavelength. The antenna functions as a directional antenna radiating a beam off the ends of the helix. It radiates circularly polarized radio waves. These are used for satellite communication.

2. Repeaters inside communications satellites are known as ___________
a) Transceivers
b) Transponders
c) Transducers
d) TWT
Answer: b
Clarification: A communications satellite’s transponder is the series of interconnected units that form a communications channel between the receiving and the transmitting antennas. It is mainly used in satellite communication to transfer the received signals.

3. ___________ is the geographical representation of a satellite antenna radiation pattern.
a) Footprint
b) Spot
c) Earth
d) Region
Answer: a
Clarification: The geographical representation of a satellite’s antenna radiation pattern is called a footprint or footprint map. In essence, a footprint of a satellite is the area on Earth’s surface that the satellite can receive from or transmit to.

4. The smallest beam of a satellite antenna radiation pattern is ________
a) Zone beam
b) Hemispheric beam
c) Spot beam
d) Global beam
Answer: c
Clarification: The size of the antenna that generates these beams on earth is related directly to the peak gain at the center of the spot beams and the smallest spot beam size. The spot beams are typically defined by the contours at 3 or 4 dB down from the peak power at the center of the beam.

5. _________ detects the satellite signal relayed from the feed and converts it to an electric current, amplifies and lowers its frequency.
a) Horn antenna
b) LNA
c) Satellite receiver
d) Satellite dish
Answer: b
Clarification: LNA detects the satellite signal relayed from the feed and converts it to an electric current, amplifies and lower its frequency. The most common device used as an LNA is tunnel diode.

6. A satellite signal transmitted from a satellite transponder to earth’s station is _________
a) Uplink
b) Downlink
c) Terrestrial
d) Earthbound
Answer: b
Clarification: In satellite telecommunication, a downlink is the link from a satellite down to one or more ground stations or receivers, and an uplink is the link from a ground station up to a satellite.

7. __________ is a loss of power of a satellite downlink signal due to earth’s atmosphere.
a) Atmospheric loss
b) Path loss
c) Radiation loss
d) RFI
Answer: b
Clarification: The path loss is the loss in signal strength of a signal as it travels through free space. This value is usually calculated by discounting any obstacles or reflections that might occur in its path.

8. Which of the following is the point on the satellite orbits closest to the Earth?
a) Apogee
b) Perigee
c) Prograde
d) Zenith
Answer: b
Clarification: The point where satellite is closest to the Earth is known as the perigee. Here, the satellite moves at its fastest. The high point of the orbit, when the satellite is moving the slowest is called the apogee.

9. What kind of battery panels are used in some advanced satellites?
a) Germanium based panels
b) Silicon based panel
c) Gallium Phosphate solar panel array
d) Gallium Arsenide solar panel array
Answer: d
Clarification: Gallium Arsenide solar panel arrays are used for battery panels in some advanced satellites. These new types of cells allow smaller solar arrays to be used on future space missions.

10. A satellite battery has more power but lighter _________
a) Lithium
b) Leclanche
c) Hydrogen
d) Magnesium
Answer: a
Clarification: Lithium batteries have more power and are lighter in weight. Any mass that could be saved by the use of lighter batteries would allow a corresponding increase in the amount of useful payload equipment.

11. INTELSAT stands for ___________
a) Intel Satellite
b) International Telephone Satellite
c) International Telecommunications Satellite
d) International Satellite
Answer: c
Clarification: INTELSAT is a communications satellite services provider. INTELSAT operates a fleet of 52 communications satellites, which is one of the world’s largest fleet of commercial satellites.

12. The frequency of Ku band for satellite communications is __________
a) 6/4 GHz
b) 14/11 GHz
c) 12/14 GHz
d) 4/8 GHz
Answer: b
Clarification: The Ku band is a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 11.7 to 12.7GHz. (downlink frequencies) and 14 to 14.5GHz (uplink frequencies).

13. The most common device used as an LNA is ________
a) Zener diode
b) Tunnel diode
c) IMPATT
d) Shockley diode
Answer: b
Clarification: The LNA must provide a relatively flat response for the frequency range of interest, preferably with less than 1 dB of gain variation. The most common device used as an LNA (low noise amplifier) is tunnel diode. It is a highly sensitive, low-noise device.

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Wireless & Mobile Communications Multiple Choice Questions 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
b) Trunking
c) Multiplexing
d) Multitasking
Answer: b
Clarification: 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.
a) True
b) False
Answer: b
Clarification: 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.
a) True
b) False
Answer: a
Clarification: 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?
a) Newton
b) Ohm
c) Erlang
d) Einstein
Answer: c
Clarification: 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?
a) Meters
b) Henry
c) Ohm
d) Erlang
Answer: d
Clarification: 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
Answer: a
Clarification: 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?
a) Trunking
b) Grade of Service (GOS)
c) Multiplexing
d) Sectoring
Answer: b
Clarification: 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
Answer: c
Clarification: 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
Answer: d
Clarification: When any user makes a call request, the time required to allocate a trunked channel to a user is known as 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
Answer: a
Clarification: 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
b) Load
c) Grade o Service
d) Traffic intensity
Answer: a
Clarification: 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
Answer: b
Clarification: 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.
a) 10%
b) 50 %
c) 2%
d) 1%
Answer: c
Clarification: 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
Answer: d
Clarification: 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
Answer: c
Clarification: 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.

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