Category: Wireless & Mobile Communications Objective Questions

Wireless & Mobile Communications Multiple Choice Questions on “Characteristics of Speech Signals”.

1. The higher the bit rate, the more speech channels can be compressed within a given bandwidth.
a) True
b) False
Answer: b
Clarification: The lower the bit rate at which the coder can deliver toll quality speech, the more speech channels can be compressed within a given bandwidth. Thus, manufacturers are continuously in search of speech coders that provide toll quality speech at lower bit rates.

2. Which of the following are two types of speech coders?
a) Waveform coders and source coders
b) Active coders and passive coders
c) Direst coders and indirect coders
d) Time and frequency coders
Answer: a
Clarification: Speech coders can be categorised into waveform coders and source coders. Waveform coders can further be categorised into time domain and frequency domain. Source coders can be classified into linear predictive coders and vocoders.

3. Waveform coders has _______ complexity and achieves _______ economy in transmission bit rate.
a) Maximum, moderate
b) Maximum, high
c) Minimal, moderate
d) Minimal, high
Answer: c
Clarification: Waveform coders have minimal complexity. This class of coders achieves only moderate economy in transmission bit rate. They are designed to be source independent and hence code equally well a variety of signals.

4. Vocoders has _______ complexity and achieves _______ economy in transmission bit rate.
a) Maximum, moderate
b) Maximum, high
c) Minimal, moderate
d) Minimal, high
Answer: b
Clarification: Vocoders achieve very high economy in transmission bit rate. They are in general more complex. They are based on using a priori knowledge about the signal to be coded, and for this reason, they are signal specific.

5. Which of the following is not a property that is utilized in coder design?
a) Non zero autocorrelation between successive speech signals
b) Non flat nature of speech signal
c) Quasiperiodicity of voiced speech signals
d) Uniform probability distribution of speech amplitude
Answer: d
Clarification: Speech waveforms have a number of useful properties that can be exploited when designing efficient coders. They are non uniform probability distribution of speech amplitude, non-zero autocorrelation between successive speech samples, the nonflat nature of the speech spectra and quasiperiodicity of voiced speech signals.

6. Speech waveforms are _______
a) Bandlimited
b) Bandpass
c) High pass
d) Infinite bandwidth
Answer: a
Clarification: The most basic property of speech waveforms that are exploited by all speech coders is that they are bandlimited. A finite bandwidth means that it can be time-discretized at a finite rate and reconstructed complexity from its samples.

7. Which of the following is not a property of pdf of speech signals?
a) Non uniformity
b) Very high probability of non-zero amplitudes
c) Significant probability of very high amplitudes
d) Increasing function of amplitudes between these extremes
Answer: d
Clarification: There is a non-uniform probability distribution of speech amplitude. The pdf of a speech signal is in general characterized by a very high probability of non-zero amplitudes, a significant probability of very high amplitudes, and a monotonically decreasing function of amplitudes between these extremes.

8. Auto correlation function measures______ between samples of a speech signal as a function of _______
a) Similarity, frequency
b) Dissimilarity, time
c) Similarity, time
d) Dissimilarity, frequency
Answer: c
Clarification: The autocorrelation function (ACF) gives a quantitative measure of the closeness or similarity between samples of a speech signal as a function of their time separation. In every sample of speech, there is a large component that is easily predicted from the values of the previous samples.

9. Power spectral density of speech is flat.
a) True
b) False
Answer: b
Clarification: There is a nonflat characteristic in power spectral density of speech. It makes it possible to obtain significant compression by coding speech in the frequency domain.

10. Spectral flatness measure is the ratio of ______ and _____
a) Variance, Geometric mean
b) Geometric Mean, Variance
c) Arithmetic mean, geometric mean
d) Geometric mean, arithmetic mean
Answer: c
Clarification: Spectral flatness measure is defined as ratio of arithmetic to geometric mean of the samples of the PSD taken at uniform intervals in frequency. Spectral flatness measure is a qualitative measure of the theoretical maximum coding gain that can be obtained by exploiting the nonflat characteristics of speech spectra.

11. Low frequency signals contribute very little to the total speech signals.
a) True
b) False
Answer: b
Clarification: Lon term averaged PSD’s of speech show that high frequency signals contribute very little to the total speech energy. However, high frequency components are insignificant in energy, they are very important carriers of speech information.

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Wireless & Mobile Communications Multiple Choice Questions on “Integrated Services Digital Network (ISDN)”.

1. ISDN stands for ___________
a) Integrated Services Digital Network
b) Integrated Services Discrete Network
c) Integrated Services Digital Node
d) Integrated Services Discrete Node
Answer: a
Clarification: ISDN stands for integrated services digital network. It defines the dedicated signalling network that has been created to complement the PSTN for more flexible and efficient network access and signalling.

2. ISDN is based on the concept of __________
a) SS7
b) CCS
c) ARDIS
d) CDPD
Answer: b
Clarification: ISDN is a complete network framework designed around the concept of common channel signalling. While telephone users throughout the world rely on the PSTN to carry conventional voice traffic, new end-user data and signalling services can be provided with a parallel, dedicated signalling network.

3. Signalling component that supports traffic between the end-user and network is called ________
a) Network signalling
b) Digital subscriber signalling
c) Access signalling
d) Subscriber system signalling
Answer: c
Clarification: Access signalling supports traffic between the end user and the network. It defines how end users obtain access to the PSTN and the ISDN for communication or services.

4. Access signalling is governed by the SS7 suite of protocols.
a) True
b) False
Answer: b
Clarification: The second signalling component of ISDN, network signalling is governed by the SS7 suite of protocols. For wireless communication systems, the SS7 protocols within ISDN are critical to providing backbone network connectivity between MSCs throughout the world.

5. Information bearing channels in ISDN are called ______
a) D channels
b) Data channels
c) B channels
d) Voice channels
Answer: c
Clarification: The ISDN interface is divided into three different types of channels. Information bearing channels called bearer channels (B channels) are used exclusively for end user traffic (voice, data and video).

6. ISDN provides integrated end user access to only packet switched networks.
a) True
b) False
Answer: b
Clarification: ISDN provides integrated end-user access to both circuit switched and packet switched networks with digital end-to-end connectivity.

7. PRI interface in ISDN serves small capacity terminals.
a) True
b) False
Answer: b
Clarification: ISDN end users may select between two different interfaces. The BRI (basic rate interface) is intended to serve small capacity terminals while the PRI (primary rate interface) is intended for large capacity terminals.

8. Which of the following is based on ATM technology?
a) SS7
b) CCS
c) ARDIS
d) B-ISDN
Answer: d
Clarification: Emerging networking technique, broadband ISDN (B-ISDN) is based on asynchronous transfer mode (ATM) technology. It allows packet switching rates up to 2.4 Gbps and total switching capacities as high as 100 Gbps.

9. Which of the following is true for ATM?
a) Circuit switched
b) Multiple access technique
c) Multiplexing technique
d) Handle only voice users
Answer: c
Clarification: ATM is a packet switching and multiplexing technique which has been specifically designed to handle both voice users and packet data users in a single physical channel.

10. ATM supports unidirectional transfer of data.
a) True
b) False
Answer: b
Clarification: ATM supports bidirectional transfer of data packets of fixed length between two end points. It preserves the order of transmission.

11. The data unit of ATM is ___________
a) Cell
b) Atom
c) Molecule
d) Packet
Answer: a
Clarification: The data unit of ATM is cell. They are routed based on header information in each unit (called a label) that identifies the cell as belonging to a specific ATM virtual connection.

12. ATM cells have fixed length of __________
a) 48 bytes
b) 47 bytes
c) 5 bytes
d) 53 bytes
Answer: d
Clarification: ATM cells have a fixed length of 53 bytes. It consists of 48 bytes of data and 5 bytes of header information. Fixed length packets result in simple implementation of fast packet switches.

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Wireless & Mobile Communications Question Bank on “Multicast in Wireless Networks”.

1. _______ is responsible for tunneling multicast packets to the MS’s currently subscribed FA.
a) Multicast home agent
b) Mobile multicast
c) Mobile station
d) Base station
Answer: a
Clarification: Multicast home agent (MHA) is responsible for tunneling multicast packets to the MS’s currently subscribed FA. MHA serves MSs that are roaming around the foreign networks and are within its service range.

2. Every MS can have only one MHA.
a) True
b) False
Answer: a
Clarification: Every MS can have only one MHA, which dynamically changes based on the location of the MS, whereas a HA of an MS never changes. The protocol requires that each MHA must be a multicast group member.

3. _______ provides a fast and efficient handoff for MSs in foreign networks.
a) MHA
b) MMP
c) CBT
d) MS
Answer: b
Clarification: MMP provides a fast and efficient handoff for MSs in foreign networks. It also enables location-independent addressing.

4. MMP combines the concepts of _______ and ________
a) Mobile IPs, GSM
b) Core based trees, GSM
c) Mobile IPs, core based trees
d) Core based trees, LTE
Answer: c
Clarification: MMP combines the concepts of Mobile IP and core-based trees (CBT). Here the former controls communication up to the foreign network, and the latter manages movement of the MSs inside them.

5. ________ designed for an Internet work environment with small wireless cells.
a) MMP
b) RMDP
c) RM2
d) Mobicast
Answer: d
Clarification: Mobicast is designed for an Internet work environment with small wireless cells. It assumes that a set of cells are grouped together and are served by a domain foreign agent (DFA).

6. ________ serve as multicast forwarding agents and are meant to isolate the mobility of the mobile host from the main multicast delivery tree.
a) DFA
b) MHA
c) FA
d) MMP
Answer: a
Clarification: DFAs serve as multicast forwarding agents and are meant to isolate the mobility of the mobile host from the main multicast delivery tree. This hierarchical mobility management approach tries to isolate the mobility of the FAs from the main multicast delivery tree.

7. Mobicast is based on a method proposed by the IETF to support multicast over Mobile-IP.
a) True
b) False
Answer: a
Clarification: Mobicast is based on a method proposed by the IETF to support multicast over Mobile-IP. To handle the case when an MS is both the source and recipient of a multicast session, one needs to minimize the possibility of rebuilding the complete multicast tree at each foreign domain the MS visits.

8. _______ is meant to be implemented for use on the MBONE.
a) MMP
b) RMDP
c) RM2
d) Mobicast
Answer: b
Clarification: The reliable multicast data distribution protocol (RMDP) is meant to be implemented for use on the MBONE. It relies on the use of FEC and ARQ information to provide reliable multicast service.

9. __________ is a reliable multicast protocol and is used for both wired and wireless environments.
a) MMP
b) RMDP
c) RM2
d) Mobicast
Answer: c
Clarification: Reliable mobile multicast (RM2) is a reliable multicast protocol and is used for both wired and wireless environments. RM2 guarantees sequential packet delivery to all its multicast members without any packet loss.

10. ____________ relies on IGMP.
a) MMP
b) RMDP
c) RM2
d) Mobicast
Answer: c
Clarification: RM2 relies on the Internet group management protocol (IGMP) to manage multicast group membership. RM2 is a hierarchical protocol that divides a multicast tree into subtrees, whereby subcasting within these smaller regions is applied using a tree of retransmission servers.

Wireless & Mobile Communications Question Bank, .

Wireless & Mobile Communications Multiple Choice Questions on “Cordless Telephone Systems”.

1. Which of the following is a protocol used for cordless telephone system?
a) PACS
b) ERMES
c) IS-95
d) FLEX
Answer: a
Clarification: PACS (Personal Access Communication System) is a protocol used for cordless telephone system. ERMES and FLEX are used by paging system. And IS-95 is used for cellular system.

2. In which frequency range do the cordless phones mostly work?
a) 43-50 MHz
b) 88-108 MHz
c) 540-1600 KHz
d) 200-540 KHz
Answer: a
Clarification: Cordless phones mostly operate in the frequency range of 43-50 MHz. The frequency range of FM is 88-108 MHz and for AM is 540-1600 KHz.

3. Which of the following is the drawback for cordless telephones?
a) Wireless technology
b) Limited coverage area
c) Mobile
d) Security
Answer: b
Clarification: Cordless telephone systems are wireless, but they have a disadvantage of limited coverage area with cell size of approx. 300 m. Being digital, they have very less chance of eaves dropping.

4. Which of the following is a fully digital cordless system?
a) CT0
b) CT1
c) CT1+
d) DECT
Answer: d
Clarification: Digital enhanced cordless telecommunication (DECT) is a fully digital system established in 1991. CT0, Ct1, Ct1+ were analog systems established in 1980, 1984 and 1987 respectively.

5. Which of the following is an example of local wireless system?
a) GSM
b) Cordless telephone system
c) UMTS
d) EDGE
Answer: b
Clarification: GSM, UMTS and EDGE covers worldwide area whereas cordless system has vey less coverage area.

6. Which of the following is not a standard for cordless telephony?
a) CT-2
b) DECT
c) UMTS
d) PHS
Answer: c
Clarification: CT-2 is a cordless telephone standard used in Europe and Asia. DECT and PHS (Personal Handyphone System) are cordless telephone standards used in Europe and Japan respectively. UMTS is a cellular system standard.

7. What is the range of cell diameter of DECT?
a) 300 m
b) 2 km
c) 10 km
d) 70 km
Answer: a
Clarification: DECT has the cell diameter of 300 m from the base station while GSM is designed for outdoor use with a cell diameter of 70 km.

8. Which of the following standard of cordless telephone system is also approved as a 3G standard?
a) PHS
b) PACS
c) DECT
d) CT2
Answer: c
Clarification: DECT fulfills the IMT 2000 requirements and is approved as a 3G standard by ITU (International Telecommunication Union).

9. Cordless telephone system will not work under which of the following criteria?
a) Within a home
b) Within a building
c) Within campus
d) Within a city
Answer: d
Clarification: Cordless telephones are used in homes, in offices, on campus, at trade shows. But due to their limited coverage they cannot cover a whole city.

10. Which of the following is not an application of DECT?
a) Multimedia processing
b) Cordless private branch exchange
c) Wireless local loop
d) Home cordless phones
Answer: a
Clarification: Users in a neighborhood served by a telephone company wired local loop can be connected by a cordless phone that exchanges signals with a neighborhood antenna.

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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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