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Communications MCQ Set 1

1. Which of the following is a protocol used for cordless telephone system?
a) PACS
b) ERMES
c) IS-95
d) FLEX

View Answer

Answer: a [Reason:] 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

View Answer

Answer: a [Reason:] 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

View Answer

Answer: b [Reason:] 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

View Answer

Answer: d [Reason:] 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

View Answer

Answer: b [Reason:] 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

View Answer

Answer: c [Reason:] 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

View Answer

Answer: a [Reason:] 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

View Answer

Answer: c [Reason:] 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

View Answer

Answer: d [Reason:] 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

View Answer

Answer: a [Reason:] 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.

Communications MCQ Set 2

1. Diffraction occurs when radio path between Tx. And Rx. Is obstructed by ________
a) Surface having sharp irregularities.
b) Smooth irregularities
c) Rough surface
d) All types of surfaces

View Answer

Answer: a [Reason:] Diffraction occurs when radio path between transmitter and receiver is obstructed by a surface that has sharp irregularities (edges). The secondary waves resulting from the obstructing surface are present throughout the space and even behind the obstacle.

2. At high frequencies, diffraction does not depends on ______
a) Geometry of the object
b) Distance between Tx and Rx
c) Amplitude of incident wave
d) Polarization of incident wave

View Answer

Answer: b [Reason:] At high frequency, diffraction depends on the geometry of the object, as well as the amplitude, phase, and polarization of the incident wave at the point of diffraction. It gives rise to a bending of waves even when line of sight does not exist between transmitter and receiver.

3. Diffraction allows radio signals to propagate around ________
a) Continuous surface
b) Smooth surface
c) Curved surface of Earth
d) Does not allow propagation

View Answer

Answer: c [Reason:] Diffraction allows radio signals to propagate around the curved surface of the Earth. Signals can propagate beyond the horizon and to propagate behind obstruction. It is the slight bending of light as it passes around the edge of an object.

4. Which principle explains the phenomenon of diffraction?
a) Principle of Simultaneity
b) Pascal’s Principle
c) Archimedes’ Principle
d) Huygen’s principle

View Answer

Answer: d [Reason:] The phenomenon of diffraction can be explained by Huygen’s principle. It states that all points on a wavefront can be considered as point sources for the production of secondary wavelets. And these wavelets combine to produce a new wavefront in direction of propagation.

5. Diffraction is caused by propagation of secondary wavelets into _______
a) Bright region
b) Shadowed region
c) Smooth region
d) Large region

View Answer

Answer: b [Reason:] Diffraction is caused due to propagation of secondary wavelets into a shadowed region. The field strength in the shadowed region is the vector sum of the electric field components of all the secondary wavelets in the space around the obstacle.

6. Difference between the direct path and the diffracted path is called _______
a) Average length
b) Radio path length
c) Excess path length
d) Wavelength

View Answer

Answer: c [Reason:] Excess path length denoted by ∆, is the difference between the direct path and the diffracted path. It is calculated with the help of Fresnel zone geometry.

7. The phase difference between a direct line of sight path and diffracted path is function of _______
a) Height and position of obstruction
b) Only height
c) Operating frequency
d) Polarization

View Answer

Answer: a [Reason:] The phase difference between a direct line of sight path and diffracted path is a function of height and position of the diffraction. It is also a function of transmitter and receiver location.

8. Which of the following explains the concept of diffraction loss?
a) Principle of Simultaneity
b) Pascal’s Principle
c) Fresnel zone
d) Archimedes’ Principle

View Answer

Answer: c [Reason:] The concept of diffraction loss is a function of the path difference around an obstruction. It can be explained by Fresnel zones. Fresnel zones represent successive regions where secondary waves have a path length from Tx to Rx which are nλ/2 greater than total path length.

9. In mobile communication system, diffraction loss occurs due to ______
a) Dielectric medium
b) Obstruction
c) Electric field
d) Operating frequency

View Answer

Answer: b [Reason:] Diffraction loss occurs from the blockage of secondary waves such that only a portion of the energy is diffracted around an obstacle. An obstruction causes a blockage of energy from source some of the Fresnel zones, allowing only some of the transmitted energy to reach the receiver.

10. For predicting the field strength in a given service area, it is essential to estimate ______
a) Polarization
b) Magnetic field
c) Height of transmitter
d) Signal attenuation

View Answer

Answer: d [Reason:] Estimating the signal attenuation caused by diffraction of radio waves over hills and buildings is essential in predicting the field strength in a given service area. In practice, prediction is a process of theoretical approximation modified by necessary empirical corrections.

Communications MCQ Set 3

1. Cordless telephone standard, DECT stands for _______
a) Discrete European Cordless Telephone
b) Digital European Cellular Telephone
c) Discrete European Cellular Telephone
d) Digital European Cordless Telephone

View Answer

Answer: d [Reason:] The Digital European Cordless Telephone (DECT) is a universal cordless telephone standard. It was developed by the European Telecommunications Standard Institute (ETSI).

2. Which of the following is not true for DECT?
a) High traffic density
b) Long range telecommunication
c) Broad range of application
d) First pan European standard

View Answer

Answer: b [Reason:] DECT provides a cordless communication framework for high traffic density, short range telecommunications. It covers a broad range of applications and environments.

3. DECT can be used by users in an in-building PBX. State whether True or False.
a) True
b) False

View Answer

Answer: a [Reason:] The main function of DECT is to provide local mobility to portable users in an in-building Private Branch Exchange (PBX). It provides excellent quality and services for voice and data applications.

4. The DECT system is based on _______ principles.
a) TCP
b) IP
c) OSI
d) AMPS

View Answer

Answer: c [Reason:] The DECT system is based on OSI (Open System Interconnection) principles in a manner similar to ISDN. A control plane (C-plane) and a user plane (U-plane) use the services provided by the lower layers.

5. Which of the following layer consists of paging channel and control channel?
a) Physical layer
b) Network layer
c) Data link layer
d) MAC layer

View Answer

Answer: d [Reason:] The MAC (Medium Access Control) layer consists of a paging channel and a control channel for the transfer of signalling information to the C-plane. The U-plane is served with channels for the transfer of user information.

6. Which of the following layer is responsible for providing reliable data links?
a) Physical layer
b) Network layer
c) Data link control layer
d) MAC layer

View Answer

Answer: c [Reason:] The DLC (data link control) layer is responsible for providing reliable data links to the network layer. It divides up the logical and physical channels into time slots for each user.

7. _____ is the main signalling layer of DECT.
a) Physical layer
b) Network layer
c) Data link layer
d) MAC layer

View Answer

Answer: b [Reason:] The network layer is the main signalling layer of DECT. It is based on GSM and ISDN (layer 3) protocols. It provides call control and circuit switched services selected from one of the DLC services.

8. Which of the following supports the physical layer of DECT common air interface?
a) Portable Handset
b) Network specific Interface Unit
c) Radio Fixed Part
d) Cordless controller

View Answer

Answer: c [Reason:] RFP (Radio Fixed Part) supports the physical layer of the DECT common air interface. Every RFP covers one cell in the microcellular system. A full duplex operation is achieved using TDD.

9. ________ supports the call completion facility in a multihandset environment.
a) Portable Handset
b) Network specific Interface Unit
c) Radio Fixed Part
d) Cordless controller

View Answer

Answer: b [Reason:] Network specific Interface Unit supports the call completion facility in a multihandset environment. The interface recommended by the CCITT is the G.732 based on ISDN protocols.

10. ______ is a third generation Personal Communication System.
a) PACS
b) AMPS
c) IS-95
d) GSM

View Answer

Answer: a [Reason:] PACS (Personal Access Communication Systems) is a third generation Personal Communication System. It was originally developed and proposed by Bellcore in 1992.

11. _______ is also known as Japanese Digital Cellular.
a) PACS
b) AMPS
c) PDC
d) GSM

View Answer

Answer: c [Reason:] PDC (Pacific digital cellular) is also known as Japanese Digital Cellular. It was developed in 1991 to provide for needed capacity in congested cellular bands in Japan.

Communications MCQ Set 4

1. Modern mobile communication systems use analog modulation techniques. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] Modern mobile communication systems use digital modulation techniques. Advancements in VLSI and digital signal processing technology have made digital modulation more cost effective than analog transmission systems.

2. Which of the following is not an advantage of digital modulation?
a) Greater noise immunity
b) Greater security
c) Easier multiplexing
d) Less bandwidth requirement

View Answer

Answer: d [Reason:] Digital modulation offer many advantages over analog modulation. Some advantages include greater noise immunity and robustness. They provide easier multiplexing of various forms of information and greater security.

3. A desirable modulation scheme provides ____ bit error rates at _____ received signal to noise ratios.
a) Low, low
b) Low, high
c) High, high
d) High, low

View Answer

Answer: a [Reason:] A desirable modulation scheme provides low bit error rates at low received signal to noise ratios. They perform well in multipath and fading conditions, occupies a minimum bandwidth and is easy and cost effective to implement.

4. The performance of modulation scheme is not measured in terms of _____
a) Power efficiency
b) Bandwidth efficiency
c) Cost and complexity
d) Transmitted power

View Answer

Answer: d [Reason:] The performance of modulation scheme is often measured in terms of its power efficiency and bandwidth efficiency. Other factors also affect the choice of modulation scheme, such as cost and complexity of the subscriber receiver and modulation which is simple to detect.

5. In digital communication system, in order to increase noise immunity, it is necessary to increase _____.
a) Signal power
b) Signal amplitude
c) Signal frequency
d) Signal magnitude

View Answer

Answer: a [Reason:] In digital communication system, in order to increase noise immunity, it is necessary to increase signal power. However, the amount by which the signal power should be increased to obtain a certain level of fidelity depends on the particular type of modulation employed.

6. Which of the following is the ratio of signal energy per bit to noise power spectral density?
a) Bandwidth efficiency
b) Spectral density
c) Power efficiency
d) Power density

View Answer

Answer: c [Reason:] Power efficiency is often expressed as the ratio of signal energy per bit to noise power spectral density required at the receiver input for a certain probability of error. Power efficiency is a measure of how favourably the trade-off between fidelity and signal power is made.

7. Increasing the data rate implies the increase in pulse width of digital symbol. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] There is an unavoidable relationship between data rate and bandwidth occupancy. Increasing the data rate implies decreasing the pulse width of a digital symbol, which increases the bandwidth of the signal.

8. Which of the following is the ratio of the throughput data rate per Hertz?
a) Bandwidth efficiency
b) Spectral density
c) Power efficiency
d) Power density

View Answer

Answer: a [Reason:] Bandwidth efficiency reflects how efficiently the allocated bandwidth is utilized. It is defined as the ratio of throughput data rate per Hertz in a given bandwidth. It describes the ability of a modulation scheme to accommodate data within a limited bandwidth.

9. Which of the following is defined as the range of frequencies over which the signal has a non zero power spectral density?
a) Null to null bandwidth
b) Half power bandwidth
c) 3 dB bandwidth
d) Absolute bandwidth

View Answer

Answer: d [Reason:] The absolute bandwidth is defined as the range of frequencies over which the signal has a non-zero power spectral density. For symbols represented as rectangular baseband pulses, the PSD profile extends over an infinite range of frequencies, and has an absolute bandwidth of infinity.

10. _______ is equal to width of main spectral lobe.
a) Null to null bandwidth
b) Half power bandwidth
c) 3 dB bandwidth
d) Absolute bandwidth

View Answer

Answer: a [Reason:] Null to null bandwidth is a simpler and more widely accepted measure of bandwidth. It is equal to the width of main spectral lobe.

11. Half power bandwidth is also called ______
a) Absolute bandwidth
b) Null to null bandwidth
c) 3 dB bandwidth
d) Zero dB bandwidth

View Answer

Answer: c [Reason:] Half power bandwidth is also called the 3 dB bandwidth. It is defined as the interval between frequencies at which the PSD has dropped to half power, or 3 dB below the peak value.

Communications MCQ Set 5

1. Diversity requires training sequence. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] Unlike equalization, diversity requires no training overhead since a training sequence is not required by the transmitter. Diversity is a powerful communication receiver technique that provides wireless link improvement at relatively low cost.

2. Diversity decisions are made by ______
a) Receiver
b) Transmitter
c) Channel
d) Adaptive algorithms

View Answer

Answer: a [Reason:] In virtually all applications, diversity decisions are made by the receiver and are unknown to the transmitter. Diversity exploits the random nature of radio propagation by finding independent signal paths for communication.

3. Small scale fades are characterized by _____ amplitude fluctuations.
a) Large
b) Small
c) Rapid
d) Slow

View Answer

Answer: b [Reason:] Small scale fades are characterized by deep and rapid fluctuations. They occur as the mobile system moves over distances of just a few wavelengths. These fades are caused by multiple reflections from the surrounding in the vicinity of the mobile.

4. ______ is used to prevent deep fade for rapidly varying channel.
a) Modulation
b) Demodulation
c) Macroscopic diversity technique
d) Microscopic diversity technique

View Answer

Answer: d [Reason:] In order to prevent deep fades from occurring, microscopic diversity techniques can exploit the rapidly changing signal. By selecting the best signal at all times, a receiver can mitigate small scale fading effects.

5. Large scale fading can be mitigated with the help of _________
a) Modulation
b) Demodulation
c) Macroscopic diversity technique
d) Microscopic diversity technique

View Answer

Answer: c [Reason:] Large scale fading is mitigated with macroscopic diversity techniques. It is done by selecting a base station which is not shadowed when others are, the mobile can improve substantially the average signal to noise ratio.

6. Space diversity s also known as ________
a) Antenna diversity
b) Time diversity
c) Frequency diversity
d) Polarization diversity

View Answer

Answer: a [Reason:] Space diversity is also known as antenna diversity. It is one of the popular forms of diversity used in wireless communications. Signals received from spatially separated antenna on the mobile would have essentially uncorrelated envelopes for antenna separation.

7. Which of the following is not a category of space diversity technique?
a) Selection diversity
b) Time diversity
c) Feedback diversity
d) Equal gain diversity

View Answer

Answer: b [Reason:] Space diversity reception methods can be classified into four categories. They are selection diversity, feedback diversity, maximal ratio combining and equal gain diversity.

8. In selection diversity, the gain of each diversity branch provides different SNR. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] Selection diversity uses m demodulators to provide m diversity branches. Their gain is adjusted to provide the same average SNR for each branch.

9. Polarization diversity uses the ________ as the diversity element.
a) Modulation index
b) Carrier frequency
c) Reflection coefficient
d) Coherence time

View Answer

Answer: c [Reason:] Decorrelation of the signal in each polarization is caused by multiple reflections in the channel between mobile and base station antenna. Reflection coefficient for each polarization is different, which results in different amplitudes and phases for each reflection.

10. Which of the factor does not determine the correlation coefficient?
a) Polarization angle
b) Cross polarization discrimination
c) Offset angle from the main beam direction
d) Coherence time

View Answer

Answer: d [Reason:] The correlation coefficient is determined by three factors, polarization angle, offset angle from the main beam direction of the diversity antenna, and the cross polarization discrimination. The correlation coefficient generally becomes higher as offset angle becomes large.

11. Frequency diversity is implemented by transmitting information on more than one _____
a) Carrier frequency
b) Amplitude
c) Phase
d) Modulation scheme

View Answer

Answer: a [Reason:] Frequency diversity is implemented by transmitting information on more than one carrier frequency. Frequency diversity is often employed in microwave line of sight links which carry several channels in frequency division multiplex mode.

12. Frequency diversity uses ________ as a diversity element.
a) Correlation coefficient
b) Coherence time
c) Coherence bandwidth
d) SNR

View Answer

Answer: c [Reason:] The rationale behind the frequency diversity is that frequencies separated by more than the coherence bandwidth of the channel will be uncorrelated. Thus, they will not experience the same fade.

13. Frequency diversity is good for low traffic condition. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] Frequency diversity is not good for low traffic conditions. This technique has a disadvantage that it not only requires spare bandwidth but also requires that there be as many receivers as there are channels used for frequency diversity. However, for critical traffic, the expense may be justified.

14. Time diversity repeatedly transmits information at time spacings that exceed _____
a) Coherence bandwidth
b) Dwell time
c) Run time
d) Coherence time

View Answer

Answer: d [Reason:] Time diversity repeatedly transmits information at time spacings that exceed coherence time of the channel. Thus, multiple repetitions of the signal will be received with independent fading conditions, thereby providing for diversity.

15. In maximal ratio combining, the output SNR is equal to _______
a) Mean of all individual SNRs
b) Maximum of all SNRs
c) Sum of individual SNR
d) Minimum of all SNRs

View Answer

Answer: c [Reason:] Maximal ratio combining produces an output SNR equal to the sum of the individual SNRs. Thus, it has advantage of producing an output with an acceptable SNR even when none of the individual signals are themselves acceptable.