Category: Wireless & Mobile Communications Objective Questions

Wireless & Mobile Communications Multiple Choice Questions & Answers (MCQs) on “Reflection”.

1. Which of the following mechanism do not impact propagation in mobile communication system?
a) Reflection
b) Diffraction
c) Scattering
d) Refraction
Answer: d
Clarification: Reflection, diffraction and scattering are the three basic propagation mechanism which impact propagation in mobile communication system. Large scale propagation model and small scale fading and multipath propagation are described by the physics of reflection, diffraction and scattering.

2. What is the dimension of object as compared to wavelength of propagating wave when reflection occurs?
a) Large
b) Small
c) Same
d) Very small
Answer: a
Clarification: Reflection occurs when a propagating electromagnetic wave impinges upon an object which has very large dimensions when compared to the wavelength of the propagation wave. Reflection occurs from the surface of the Earth and from buildings and walls.

3. When does the wave propagating from one medium to another gets partially reflection and partially transmitted?
a) Both mediums have same electrical properties
b) Both mediums have different electrical properties
c) Both mediums have same magnetic properties
d) Both mediums have different magnetic properties
Answer: b
Clarification: When a radio wave propagating in one medium impinges upon another medium having different electrical properties. The wave is partially reflected and partially transmitted.

4. What is the case of reflection, in course of second medium being a perfect dielectric?
a) Loss of energy during absorption
b) Total energy reflected back to first medium
c) No loss of energy in absorption
d) Total energy transmitted into second medium
Answer: c
Clarification: If the plane wave is incident on a perfect dielectric, part of the energy is transmitted into the second medium and part of the energy is reflected back into the first medium. There is no loss of energy in absorption.

5. What is the case of reflection, in course of second medium being a perfect conductor?
a) Loss of energy during absorption
b) Total energy reflected back to first medium
c) Partly transmission and reflection
d) Total energy transmitted into second medium
Answer: b
Clarification: If the second medium is perfect conductor, then all incident energy is reflected back into the second medium. There is no loss of energy during absorption.

6. Which of the following relates the incident and reflected & transmitted wave?
a) Fresnel transmission coefficient
b) Scattering coefficient
c) Diffraction coefficients
d) Fresnel reflection coefficient
Answer: d
Clarification: The electric field intensity of the reflected and transmitted waves may be related to the incident waves in the medium of origin through the Fresnel reflection coefficient. It is equal to the ratio of the amplitude of the reflected wave to the incident wave, with each expressed as phasors.

7. Reflection coefficient is not a function of __________
a) Material property
b) Diffraction loss
c) Wave polarization
d) Angle of incidence
Answer: b
Clarification: The reflection coefficient is a function of the material properties, and generally depends upon the wave polarization, angle of incidence and frequency of propagating waves. It is a parameter that describes how much of an electromagnetic wave is reflected by an impedance discontinuity in the transmission medium.

8. Polarized wave can be mathematically represented as sum of ________
a) Four orthogonal components
b) Two spatially adjacent components
c) Two spatially orthogonal components
d) Six orthogonal components
Answer: c
Clarification: A polarized wave may be mathematically represented as sum of two spatially orthogonal components. For an arbitrary polarization, super position may be used to compute the reflected fields from a reflecting surface.

9. The plane of incidence contains only incident rays.
a) True
b) False
Answer: b
Clarification: The plane of incidence is defined as the plane containing the incident, reflected and transmitted waves. The incident light is polarized with its electric field perpendicular to the plane containing the incident, reflected, and refracted rays.

10. Permittivity and conductivity are insensitive to ______ for a good conductor.
a) Operating frequency
b) Polarization density
c) Electric field
d) Property of material
Answer: a
Clarification: The terms permittivity and conductivity are insensitive to operating frequency when the material is a good conductor. In the case of conductors, it is evident that electric field inside a conductor is zero. That is because free charges reside only on the surface of conductor and not inside.

11. Velocity of electromagnetic wave can be given by _______
a) 1/√(μ∈)
b) μ/∈
c) 1/(μ∈)
d) μ∈
Answer: a
Clarification: For a medium with permittivity, ∈ and permeability, μ the velocity of electromagnetic wave is given by 1/√(μ∈). It is also known as phase velocity. The velocity of light is given by 3*10⁸ m/s.

12. The boundary condition at the surface of incidence obeys ________
a) Kepler’s law
b) Gauss law
c) Faraday law
d) Snell’s law
Answer: d
Clarification: Snell’s law is also known as Snell–Descartes law or the law of refraction. It gives a formula to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media, such as water, glass, or air.

13. The angle at which no reflection occurs in the medium of origin is called _________
a) Azimuth angle
b) Elevation angle
c) Brewster angle
d) Inclination angle
Answer: c
Clarification: The Brewster angle is the angle at which no reflection occurs in the medium of origin. It occurs when the incident angle is such that the reflection coefficient is equal to zero. The critical Brewster’s angles for diamond, glass and water are 67.5°, 57° and 53° respectively.

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Wireless & Mobile Communications Multiple Choice Questions on “Angle modulation”.

1. FM is a part of general class of modulation known as ______
a) Angle modulation
b) Phase modulation
c) Amplitude modulation
d) Frequency modulation
Answer: a
Clarification: FM is a part of general class of modulation known as angle modulation. Angle modulation varies a sinusoidal carrier signal in such a way that the angle of the carrier is varied according to the amplitude of the modulating baseband signal.

2. FM is called constant envelope because ______ of carrier wave is kept constant.
a) Frequency
b) Amplitude
c) Phase
d) Angle
Answer: b
Clarification: FM is called the constant envelope because amplitude of the carrier wave is kept constant. It is duo to the fact that the envelope of the carrier does not change with changes in the modulating signal.

3. Which of the following are two most important classes of angle modulation?
a) Amplitude modulation, frequency modulation
b) Amplitude modulation, phase modulation
c) Frequency modulation, phase modulation
d) Single sideband amplitude modulation, phase modulation
Answer: c
Clarification: The two most important classes of angle modulation are frequency modulation and phase modulation. They provide the ways in which phase of a carrier signal may be varied in accordance with the baseband signal.

4. Frequency modulated signal is regarded as the phase modulated signal in which the modulating wave is differentiated before modulation.
a) True
b) False
Answer: b
Clarification: Frequency modulated signal is regarded as the phase modulated signal in which the modulating wave is integrated before modulation. This means that an FM signal can be generated by first integrating the message signal and then using the result as an input to a phase modulator.

5. Frequency modulation index defines the relationship between the ______ and bandwidth of transmitted signal.
a) Frequency of message signal
b) Amplitude of message signal
c) Amplitude of carrier signal
d) Frequency of carrier signal
Answer: b
Clarification: The frequency modulation index defines the relationship between the message amplitude and the bandwidth of the transmitted signal. If the modulating signal is a low pass signal, maximum bandwidth of the modulating signal is equal to the highest frequency component present in the modulating signal.

6. FM bandwidth is approximated using _______ rule.
a) Carson’s
b) Faraday’s
c) Maxwell’s
d) Armstrong’s
Answer: a
Clarification: The approximation of bandwidth is done using Carson’s rule. Carson’s bandwidth rule defines the approximate bandwidth requirements of communications system components for a carrier signal that is frequency modulated by a continuous or broad spectrum of frequencies rather than a single frequency.

7. Which of the following are two methods for generating FM signal?
a) Coherent method, noncoherent method
b) Product detector, envelope detector
c) Direct method, indirect method
d) Slope detector, Zero crossing detector
Answer: c
Clarification: Direct method and indirect method are the methods used for generating FM signals. These methods are differentiated by the variation of the carrier frequency.

8. In indirect method, the carrier frequency is directly varied in accordance with the input modulating signal.
a) True
b) False
Answer: b
Clarification: The above is the case for direct method. In the indirect method, a narrowband FM signal is generated using a balanced modulator, and frequency multiplication is used to increase both the frequency deviation and the carrier frequency to the required level.

9. Which of the following is used to vary the frequency of the carrier frequency in accordance with the baseband signal amplitude variations in direct method of FM generation?
a) Integrator
b) Envelope detector
c) Multivibrator
d) Voltage controlled oscillators
Answer: d
Clarification: In direct method, VCOs are used to vary the frequency of the carrier signal in accordance with the baseband signal amplitude variations. These oscillators use devices with reactance that can be varied by the application of a voltage.

10. Frequency demodulator is a frequency to amplitude converter circuit.
a) True
b) False
Answer: a
Clarification: Frequency demodulator produces an output voltage with instantaneous amplitude that is directly proportional to the instantaneous frequency of the input FM signal. Thus, frequency demodulator is a frequency to amplitude converter circuit.

11. Which of the following is not a technique for FM demodulation?
a) Slope detection
b) Zero crossing detection
c) Product detector
d) Phase locked discriminator
Answer: c
Clarification: Various techniques such as slope detection, zero crossing detection, phase locked discrimination and quadrature detection are used to demodulate FM. Product detector is used for demodulating AM signals.

12. Which of the following FM demodulator is sometimes known as pulse averaging discriminator?
a) Slope detection
b) Zero crossing detection
c) Quadrature detection
d) Phase locked discriminator
Answer: b
Clarification: Zero crossing detector is sometimes known as pulse averaging discriminator. The rationale behind this technique is to use the output of the zero crossing detector to generate a pulse train with an average value that is proportional to frequency of the input signal.

13. PLL in FM detection stands for ______
a) Phase locked loop
b) Programmable logic loop
c) Phase locked logic
d) Programmable locked loop
Answer: a
Clarification: PLL stands for phase locked loop. The PLL is a closed loop control system which can track the variations in the received signal phase and frequency.

14. In angle modulation, signal to noise ratio before detection is a function of ______
a) Modulation index
b) Input signal to noise ratio
c) Maximum frequency of the message
d) IF filter bandwidth
Answer: d
Clarification: In angle modulation systems, the signal to noise ratio before detection is the function of the receiver IF filter bandwidth, received carrier power, and received interference. However, signal to noise ratio after detection is a function of maximum frequency of the message, input signal to noise ratio and modulation index.

15. FM can improve the receiver performance through adjustment of transmitted power.
a) True
b) False
Answer: b
Clarification: FM can improve receiver performance through adjustment of the modulation index at the transmitter, and not the transmitted power. This is not the case in AM since linear modulation techniques do not trade bandwidth for SNR.

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Wireless & Mobile Communications Multiple Choice Questions on “Quantization Techniques”.

1. Quantization is a process of mapping a ________ range of amplitude of a signal into a finite set of __________ amplitudes.
a) Continuous, discrete
b) Discrete, continuous
c) Discrete, discrete
d) Continuous, continuous
Answer: a
Clarification: Quantization is a process of mapping a continuous range of amplitude of a signal into a finite set of discrete amplitudes. Quantizers are the devices that remove the irrelevancies in the signal.

2. For a n bit quantizer, number of levels is equal to __________
a) n
b) 2ⁿ
c) n²
d) 2n
Answer: b
Clarification: A quantizer that uses n bits can have M = 2n discrete amplitude levels. Amplitude quantization is an important step in any speech coding process, and it determines to a great extent the overall distortion as well as bit rate necessary to represent each waveform.

3. Distortion produced by quantization is directly proportion to ________ and inversely proportional to ______
a) Number of levels, step size
b) Amplitude of the signal, step size
c) Square of step size, number of levels
d) Amplitude of the signal, number of levels
Answer: c
Clarification: The distortion introduced by any quantization operation is directly proportional to the square of the step size. It is inversely proportional to the number of levels for a given amplitude range.

4. Signal to quantization noise ratio of a PCM encoder is given by _________
a) 6.02n + α
b) 3n + 6.02α
c) n + 6.02α
d) 6.02n + α
Answer: d
Clarification: Signal to quantization noise (SQNR) ratio of a PCM encoder is related to the number of bits, n used for encoding. It follows the following relation, SQNR= 6.02n + α. Here, α = 4.77 dB for peak SQNR and α = 0 dB for average SQNR.

5. Companding technique used in the US is called ____________
a) μ law
b) A law
c) Hybrid companding
d) Direct companding
Answer: a
Clarification: Companding technique known as μ law is used in US. In Europe, A law companding technique is used.

6. An adaptive quantizer varies its ___________ in accordance to input speech signal power.
a) Level
b) Step size
c) Amplitude
d) Frequency
Answer: b
Clarification: An adaptive quantizer varies its step size in accordance to the input speech signal power. Its characteristics shrink and expand in time like an accordion.

7. Shannon predicted that better performance can be achieved by coding one sample at a time.
a) True
b) False
Answer: b
Clarification: Shannon predicted that better performance can be achieved by coding many samples at a time instead of one sample at a time.

8. ________ is a delayed decision coding technique.
a) Adaptive quantization
b) Uniform quantization
c) Vector quantization
d) Non-uniform quantization
Answer: c
Clarification: Vector (VQ) quantization is a delayed decision coding technique. It maps a group of input samples called a vector to a code book index. A code book is set up consisting of a finite set of vectors covering the entire anticipated range of values.

9. The characteristics of compressor in μ-law companding are _________
a) Continuous in nature
b) Logarithmic in nature
c) Linear in nature
d) Discrete in nature
Answer: a
Clarification: In the μ law companding, the compressor characteristic is continuous. It approximates the linear dependence on x for low input signals and a logarithmic one for high input signals.

10. What is the sequence of operations in PCM?
a) Sampling, quantizing, encoding
b) Quantizing, encoding, sampling
c) Quantizing, sampling, encoding
d) None of the mentioned
Answer: a
Clarification: Sequence of operation in PCM is sampling, quantization and encoding. Sampling and quantizing operations transform an analogue signal to a digital signal. The quantizing and encoding operations are usually performed in the same circuit at the transmitter, which is called an Analogue to Digital Converter (ADC). At the receiver end the decoding operation converts the pulse back into an analogue voltage in a Digital to Analogue Converter (DAC).

11. In Adaptive Delta Modulation, the slope error reduces and ___________
a) Quantization error decreases
b) Quantization error increases
c) Quantization error remains same
d) None of the mentioned
Answer: b
Clarification: ADM reduces slope error, at the expense of increasing quantizing error. This error can be reduced by using a low-pass filter.

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Wireless & Mobile Communications Multiple Choice Questions on “Signalling System No. 7 (SS7)”.

1. Which of the following is not a service offered by SS7?
a) Touchstar
b) 800 services
c) Alternate billing services
d) 400 services
Answer: d
Clarification: There are three main types of services offered by the SS7 network. They are the Touchstar, 800 services, and alternate billing services.

2. Which of the following service is called CLASS?
a) Touchstar
b) 800 services
c) Alternate billing services
d) 400 services
Answer: a
Clarification: Touchstar is also known as CLASS. It is a group of switch controlled services that provide its users with certain call management capabilities.

3. Which of the following service of SS& provides call return, call forwarding?
a) Touchstar
b) 800 services
c) Alternate billing services
d) 400 services
Answer: a
Clarification: Touchstar is one of the three main type of services offered by SS7. It provides services such as call return, call forwarding, repeat dialling, call block, call tracing and caller ID.

4. Alternating billing service uses CCS network.
a) True
b) False
Answer: a
Clarification: Alternate billing service and line information database use the CCS network to enable the calling party to bill a call to a personal number (third party number, calling card, or collect etc.) from any number.

5. SS7 was first developed by _______
a) ITU
b) Ericsson
c) CCITT
d) Motorola
Answer: c
Clarification: SS7 is an outgrowth of the out of band signalling first developed by the CCITT under common channel signalling standard, CCS no. 6.

6. Which of the layer of OSI is associated with NSP of SS7?
a) All layers
b) Upper three
c) Lowest three
d) Middle two
Answer: c
Clarification: The lowest three layers of the OSI model are handled in SS7 by the network service part (NSP) of the protocol. NSP is made up of three message transfer parts (MTPs) and the signalling connection control part (SCCP) of the SS7 protocol.

7. The function of _______ is to transfer and deliver signalling network.
a) MTP
b) CCS
c) ARDIS
d) CDPD
Answer: a
Clarification: The function of the MTP is to ensure that signalling traffic can be transferred and delivered reliably between the end users and the network. MTP is provided at three levels.

8. Signalling data functions are provided by __________
a) MTP level 1
b) MTP level 2
c) MTP level 3
d) TCAP
Answer: a
Clarification: Signalling data link functions (MTP level 1) provide an interface to the actual physical channel over which communication takes place. Physical channels may include copper wire, twisted pair, fibre, mobile radio and are transparent to the higher layers.

9. Signalling data functions are provided by __________
a) MTP level 1
b) MTP level 2
c) MTP level 3
d) TCAP
Answer: b
Clarification: Signalling data link functions are provided by MTP level 2. They correspond to the second layer in the OSI reference model and provide a reliable link for the transfer of traffic between two directly connected signalling points.

10. _________ provide procedures that transfer messages between signalling nodes.
a) MTP level 1
b) MTP level 2
c) MTP level 3
d) TCAP
Answer: c
Clarification: Signalling network functions (MTP level 3) provide procedures that ransfer messages between signalling nodes. As in ISDN, there are two types of MTP level 3 functions: signalling message handling and signalling network management.

11. Which of the following does not include in SS7 user part?
a) MTP
b) ISUP
c) TCAP
d) OMAP
Answer: a
Clarification: The SS7 user part includes the ISDN user part (ISUP), the transaction capabilities application part (TCAP) and operations maintenance and administration part (OMAP). The telephone user part (TUP) and the data user part (DUP) are included in the ISUP.

12. The TCAP part in SS7 refers to ________ layer of OSI.
a) Physical
b) Network
c) Data Link
d) Application
Answer: d
Clarification: The transaction capabilities application part in SS7 refers to the application layer which invokes the services of the SCCP and the MTP in a hierarchical format. TCAP is concerned with remote operations.

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Wireless & Mobile Communications Multiple Choice Questions on “Long Term Evolution (LTE)”.

1. Which UE category supports 64 QAM on the uplink?
a) Only category 5
b) Only category 4
c) Only category 3
d) Category 3,4 and 5
Answer: a
Clarification: Category information is used to allow the eNB to communicate effectively with all the UEs connected to it. The UE-category defines a combined uplink and downlink capability. Only UE category 5 supports 64 QAM on the uplink.

2. What type of handovers is supported by LTE?
a) Hard handover only
b) Soft handover only
c) Hard and soft handover
d) Hard, soft and softest handover
Answer: a
Clarification: LTE supports only hard handover. It does not receive data from two frequencies at the same time because switching between different carrier frequencies is very fast so soft handover is not required.

3. What is the minimum amount of RF spectrum needed for an FDD LTE radio channel?
a) 1.4 MHz
b) 2.8 MHz
c) 5 MHz
d) 20 MHz
Answer: b
Clarification: In telecommunication, Long-Term Evolution (LTE) is a standard for high-speed wireless communication for mobile devices and data terminals, based on the GSM/EDGE and UMTS/HSPA technologies. The minimum amount of RF spectrum needed for an FDD LTE radio channel is 2.8 MHz.

4. Which organization is responsible for developing LTE standards?
a) UMTS
b) 3GPP
c) 3GPP2
d) ISO
Answer: b
Clarification: The 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications standards associations, known as the Organizational Partners. LTE (Long Term Evolution) introduced in 3GPP R8, is the access part of the Evolved Packet System (EPS).

5. Which channel indicates the number of symbols used by the PDCCH?
a) PHICH
b) PDCCH
c) PBCH
d) PCFICH
Answer: d
Clarification: PCFIH channel indicates the number of symbols used by the PDCCH. The actual number of OFDM symbols occupied in any given subframe is indicated in the PCFICH (Physical Control Format Indicator Channel), which is located in the first OFDM symbol of each subframe.

6. How often can resources be allocated to the UE?
a) Every symbol
b) Every slot
c) Every subframe
d) Every frame
Answer: c
Clarification: Resources can be located to the UE every subframe. CCE Index is the CCE number at which the control channel data (PDCCH) is allocated. Normally this index changes for each subframe, i.e. even the same PDCCH data (e.g, a PDCCH for the same UE) allocated in each subframe changes subframe by subframe.

7. What is the largest channel bandwidth a UE is required to support in LTE?
a) 10 MHz
b) 20 MHz
c) 1.4 MHz
d) 5 MHz
Answer: b
Clarification: The LTE format was first proposed by NTT DoCoMo of Japan and has been adopted as the international standard. LTE-Advanced accommodates the geographically available spectrum for channels above 20 MHz.

8. In LTE, what is the benefit of PAPR reduction in the uplink?
a) Improved uplink coverage
b) Lower UE power consumption
c) Reduced equalizer complexity
d) Improved uplink coverage, lower UE power consumption and reduced equalizer
Answer: d
Clarification: PAPR is the relation between the maximum power of a sample in a given OFDM transmit symbol divided by the average power of that OFDM symbol. PAPR reduction in the uplink leads to improved uplink coverage, lower UE power consumption and reduced equalizer complexity.

9. Which RLC mode adds the least amount of delay to user traffic?
a) Unacknowledged mode (UM)
b) Acknowledged mode (AM)
c) Low latency mode (LM)
d) Transparent mode (TM)
Answer: d
Clarification: The transparent mode entity in RLC does not add any overhead to the upper layer SDUs. The entity just transmits the SDUs coming from upper layer to MAC.

10. How much bandwidth is required to transmit the primary and secondary synchronization signals?
a) 1.08 MHz
b) 1.4 MHz
c) 930 kHz
d) 20 MHz
Answer: a
Clarification: Cell synchronization is the very first step when UE wants to camp on any cell. 1.08 MHZ is required to transmit the primary and secondary synchronization signals.

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