Category: Wireless & Mobile Communications Objective Questions

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.

of Wireless & Mobile Communications for Entrance exams, .

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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Wireless & Mobile Communications Assessment Questions and Answers on “Multipath Shape Factors for Small – Scale Fading”.

1. The term small scale fading describes the slow fluctuations of received power level due to changes in receiver position.
a) True
b) False
Answer: b
Clarification: The term small scale fading describes the rapid fluctuations of received power level due to changes in receiver position. This effect is due to the constructive and destructive interference of the numerous multipath waves that impinge upon a wireless receiver.

2. The rapid fluctuations due to small scale fading affect the _________ design.
a) Receiver
b) Transmitter
c) MSC
d) Base station
Answer: a
Clarification: The rapid fluctuation due to small scale fading affect every aspect of receiver design such as dynamic range, equalization, diversity, modulation scheme and channel error correction coding. These fluctuations are a function of direction of travel as related to the angle of arrival of multipath delay.

3. An approximately omnidirectional channel model accurately describes fading statistics if directional antennas are employed at the receiver.
a) True
b) False
Answer: a
Clarification: An approximately omnidirectional channel model accurately describes fading statistics if directional or smart antenna systems are employed at the receiver. Unfortunately, recent measurements and models have shown that the arriving multipath in a local area bears little resemblance to the omnidirectional propagation.

4. Which of the following is not a principle shape factor?
a) Angular spread
b) Angular constriction
c) Azimuthal direction of maximum fading
d) Angle of arrival
Answer: d
Clarification: Three principle shape factors are angular spread, angular constriction, and azimuthal direction of maximum fading. They are exactly related to the average rate at which a received signal fades.

5. Angular spread is a measure of how multipath concentrates about __________
a) Angle of arrival
b) Transmitted power
c) Single azimuthal direction of arrival
d) Received power
Answer: c
Clarification: The shape factor, angular spread is a measure of how multipath concentrates about a single azimuthal direction of arrival. It has several advantages like it is invariant under changes in transmitted power.

6. Angular constriction is a measure of how multipath concentrates about ______ azimuthal direction.
a) Single
b) Two
c) Three
d) Four
Answer: b
Clarification: The shape factor, angular constriction is a measure of how multipath concentrates about two azimuthal directions. The measure for angular constriction is invariant under changes in transmitted power.

7. Shape factor, azimuthal direction of maximum fading is a directional parameter.
a) True
b) False
Answer: a
Clarification: Azimuthal direction of maximum fading is the third shape factor which is a directional or orientation parameter. Its value corresponds to the direction in which s mobile user would move in order to experience the maximum fading rate in the local area.

8. _______ of a stationary process is actually the variance of the rate of change.
a) Mean
b) Mean square
c) Mean squared derivative
d) Mean squared integral
Answer: c
Clarification: Mean squared derivative of a stationary process is actually the variance of the rate of change. The mean derivative of the stationary process is zero; the mean squared derivative is the simplest statistics that measures the fading rate of a channel.

9. Complex received voltage is a summation of __________ that have impinged upon receiver antenna.
a) Multipath waves
b) Waves
c) Power density
d) Single path waves
Answer: a
Clarification: Complex received voltage is a baseband representation. It us a summation of numerous multipath waves that have impinged upon the receiver antenna and have excited a complex voltage component at the input of a receiver.

10. Which of the following is equal to received power?
a) Square of complex voltage
b) Complex voltage
c) Magnitude of complex voltage
d) Magnitude squared of complex voltage
Answer: d
Clarification: The received power is equal to the magnitude squared of complex voltage. The mathematical operation of taking the squared magnitude of a complex quantity is a nonlinear operation.

11. Which of the following is equal to received envelope?
a) Square of complex voltage
b) Complex voltage
c) Magnitude of complex voltage
d) Magnitude squared of complex voltage
Answer: c
Clarification: The received envelope is equal to the magnitude of the complex voltage. The channel is assumed to be Rayleigh fading in order to calculate the mean squared fading rate.

12. Which of the following describes the average fading rate within a local area?
a) Angular spread
b) Angular constriction
c) Azimuthal direction of maximum fading
d) Angle of arrival
Answer: a
Clarification: Angular spread describes the average fading rate within a local area. The average of the two fading rate variances, regardless of the orientation of the measurement, is always given by averaging the variances observed over two perpendicular directions within the local area.

13. Angular constriction affects the average fading rate within local area.
a) True
b) False
Answer: b
Clarification: Angular constriction does not affect the average fading rate within local area. It describes the variability of fading rates taken along different azimuthal directions.

of Wireless & Mobile Communications Assessment Questions, .

Wireless & Mobile Communications Multiple Choice Questions on “Block Codes and Finite Fields”.

1. In block codes, parity bits are ___________ to block of messages.
a) Added
b) Subtracted
c) Multiplied
d) Divided
Answer: a
Clarification: In block codes, parity bits are added to the block of message bits to make codewords or code blocks. They enable a limited number of errors to be detected and corrected without retransmission.

2. How many redundant bits are added in block codes for k information bits and n code bits?
a) n+k
b) n-k
c) k²
d) n²
Answer: b
Clarification: In block encoder, k information bits are encoded into n code bits. A total of n-k redundant bits are added to the k information bits for the purpose of detecting and correcting errors.

3. For (n,k) block codes, rate of the code is defined as __________
a) n²/k
b) k²/n
c) n/k
d) k/n
Answer: c
Clarification: The block code is referred to as an (n,k) code, and the rate of the code is defined as R=n/k. It is equal to the rate of information divided by the raw channel rate.

4. The ability of the block code to correct errors is a function of __________
a) Number of parity bits
b) Number of information bits
c) Number of code bits
d) Code distance
Answer: d
Clarification: The ability of a block code to correct errors is a function of the code distance. Block codes can be used to improve the performance of communication systems when other means of improvement are impractical.

5. The weight of code is given by number of _______
a) Non-zero elements in the codeword
b) Zero elements in the codeword
c) Total elements in the codeword
d) Elements in parity bits
Answer: a
Clarification: The weight of a code is given by number of non-zero elements in the codeword. For a binary code, the weight is basically the number of ones in the codeword.

6. Which of the following is not a property of block code?
a) Linearity
b) Systematic
c) Cyclic
d) Non linearity
Answer: d
Clarification: Block codes are linear, systematic and cyclic in nature. Encoding and decoding techniques make use of mathematical constructs known as finite fields.

7. In systematic codes, parity bits are appended at the __________
a) Beginning
b) End
c) End
d) Odd places
Answer: b
Clarification: A systematic code is one in which the parity bits are appended to the end of the information bits. For an (n,k) code, the first k bits are identical to the information bits, and the remaining (n-k) bits of each code word are linear combinations of k information bits.

8. Which of the following is not an example of block code?
a) Hamming code
b) Cyclic code
c) Convolution code
d) BCH codes
Answer: c
Clarification: Hamming codes, cyclic codes and BCH codes are the example of block codes. Convolution code does not come in the category of block code. Some other examples of block codes are Reed Solomon codes, Golay codes and Hadamard codes.

9. Which of the following code is a class of non-binary BCH?
a) Hamming code
b) Hadamard code
c) Golay code
d) Reed Solomon codes
Answer: d
Clarification: The most important and most common class of non binary is the family of codes known as Reed Solomon codes. BCH codes are among the most popular block codes that exist for a wide range of rates, achieve significant coding gains.

10. Which of the following linear codes achieve largest possible minimum distance?
a) Hamming code
b) Hadamard code
c) Golay code
d) Reed Solomon codes
Answer: d
Clarification: RS codes achieve the largest possible minimum distance, d_min of any linear code. They are non-binary codes which are capable of correcting errors that appears in bursts.

11. CDPD stands for ___________
a) Cellular Digital Packet Data
b) Cellular Decoded Packet Data
c) Cellular Demodulated Packet Data
d) Cellular Decoded Plane Data
Answer: a
Clarification: CDPD (Cellular Digital Packet Data) is a wide area mobile data service which uses unused bandwidth. It was mostly used in AMPS phones. Reed Solomon code in US CDPD uses m=6 bits per code symbol.

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