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Communications MCQ Set 1

1. Which of the following is not a characteristic of cellular telephone system?
a) Accommodate large number of users
b) Large geographic area
c) Limited frequency spectrum
d) Large frequency spectrum

View Answer

Answer: d [Reason:] Cellular systems accommodate a large number of users within a limited frequency spectrum over a large geographic area.

2. What is the responsibility of MSC in cellular telephone system?
a) Connection of mobile to base stations
b) Connection of mobile to PSTN
c) Connection of base station to PSTN
d) Connection of base station to MSC

View Answer

Answer: b [Reason:] Mobile Switching Center (MSC) is responsible for connecting all mobiles to the PSTN (Public Switched Telephone Network) in a cellular system.

3. Who has the responsibility of billing and system maintenance function in cellular system?
a) Base Station
b) PSTN
c) MSC
d) Mobile system

View Answer

Answer: c [Reason:] Mobile switching center (MSC) accommodates 100,000 subscribers and 5,000 simultaneous conversations at a time and handles all billing and system maintenance functions.

4. What is the function of FVC (Forward Voice Channel)?
a) Voice transmission from base station to mobiles
b) Voice transmission from mobile to base station
c) Initiating mobile calls
d) Broadcast all traffic request for all mobile

View Answer

Answer: a [Reason:] FVC (Forward Voice Channel) and RVC (Reverse Voice Channel) are responsible for voice transmission. FVC is used for voice transmission from base station to mobile and RVC is used for voice transmission from mobile to base station.

5. Which two channels are responsible for initiating mobile calls?
a) FVC and FCC
b) FVC and RVC
c) FCC and RCC
d) FCC and RVC

View Answer

Answer: c [Reason:] FCC (Forward Control Channel) and RCC (Reverse Control Channel) are control channels responsible for initiating mobile calls.

6. Of the total channels present in the cellular system, what is the percentage of voice and control channels?
a) 95% voice channels, 5% control channels
b) 5% voice channels, 95% control channels
c) 50% voice channels, 50% control channels
d) 25% voice channels, 75% control channels

View Answer

Answer: a [Reason:] In each cellular system, control channels are 5% of the total channels available and remaining 95% are dedicated to voice and data traffic.

7. What is MIN?
a) Subscriber’s telephone number
b) Paging message
c) Traffic request number
d) Mobile Internet

View Answer

Answer: a [Reason:] MIN (Mobile Identification Number) is a 10 digit unique number which represents the telephone number of subscriber.

8. What is transmitted along with the call initiation request during the origin of call by a mobile?
a) MIN
b) ESN
c) ESN and SCM
d) MIN, ESN and SCM

View Answer

Answer: d [Reason:] When a mobile originates the call, it sends the MIN (mobile identification number), ESN (electronic serial number) and SCM (station class mark) along with the call initiation request.

9. What does SCM indicates?
a) Maximum receiver power level for a particular user
b) Maximum transmitter power level for a particular user
c) Minimum receiver power level for a particular user
d) Minimum transmitter power level for a particular user

View Answer

Answer: b [Reason:] SCM (Station Class Mark) indicates the maximum transmitter power level for a particular user.

10. What is the shape of the cell present in the cellular system?
a) Circular
b) Square
c) Hexagonal
d) Triangular

View Answer

Answer: c [Reason:] The shape of the cell present in the cellular network is hexagonal since it can cover the entire geographical area without any gap and overlapping.

11. Why the size of the cell is kept small in cellular network?
a) Increase capacity
b) Decrease capacity
c) Increased size of base station electronics
d) Slow process of handoffs

View Answer

Answer: a [Reason:] The size of the cells in cellular network is kept small because of the need of high capacity in areas with high user density and reduced size and cost of base station electronics.

12. What is handoff?
a) Forward channel
b) Switching technique
c) Roamer
d) Guard channel

View Answer

Answer: b [Reason:] Handoff is a switching technique which refers to the process of transferring an active call or data session from one cell in a cellular network to another.

13. Which one is not an advantage of using frequency reuse?
a) Increased capacity
b) Limited spectrum is required
c) Same spectrum may be allocated to other network
d) Number of base stations is reduced

View Answer

Answer: d [Reason:] Frequency reuse is a technique of reusing frequencies and channels within a cellular system to improve capacity and spectral efficiency.

14. The process of transferring a mobile station from one base station to another is
a) MSC
b) Roamer
c) Handoff
d) Forward channel

View Answer

Answer: c [Reason:] Handoff is the process of changing the channel associated with current connection while a call is in progress.

15. The interference between the neighbouring base stations is avoided by
a) Assigning different group of channels
b) Using transmitters with different power level
c) Using different antennas
d) Using different base stations

View Answer

Answer: a [Reason:] The interference between the neighbouring base stations is avoided by assigning different group of channels and reusing the same channel after a certain amount of distance.

Communications MCQ Set 2

1. Which of the following is not an objective for channel assignment strategies?
a) Efficient utilization of spectrum
b) Increase of capacity
c) Minimize the interference
d) Maximize the interference

View Answer

Answer: d [Reason:] The objective of channel assignment strategy is to utilize the spectrum efficiently. And for efficient utilization, a frequency reuse scheme consistent with the objective of increasing capacity and minimizing interference is required.

2. The choice of channel assignment strategy does not impact the performance of the system. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] The choice of channel assignment strategy impacts the performance of the system. Particularly as to how calls are managed, when a mobile user is handed off from one cell to another.

3. In fixed channel assignment strategy, each cell is allocated a predetermined set of _______
a) Voice channels
b) Control channels
c) Frequency
d) base stations

View Answer

Answer: a [Reason:] In a foxed channel strategy, each cell is allocated a predetermined set of voice channels. Any call attempt within the cell can only be served by the unused channels in that particular cell.

4. What happen to a call in fixed channel strategy, if all the channels in a cell are occupied?
a) Queued
b) Cross talk
c) Blocked
d) Delayed

View Answer

Answer: c [Reason:] As any call attempt within a cell can be served by unused channels in fixed channel strategy. If all the channels in that cell are occupied, the call is blocked and subscriber does not receive any service.

5. What is a borrowing strategy in fixed channel assignments?
a) Borrowing channels from neighbouring cell
b) Borrowing channels from neighbouring cluster
c) Borrowing channels from same cell
d) Borrowing channels from other base station in same cell

View Answer

Answer: a [Reason:] In borrowing strategy, a cell is allowed to borrow channels from a neighbouring cell if all of its own channels are already occupied. The MSC supervises such borrowing procedure and ensures that the borrowing of channel does not interfere with any call in progress.

6. In dynamic channel assignment strategy, voice channels are allocated to different cells permanently. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] In a dynamic channel strategy, voice channels are not allocated to different cells permanently. Instead, serving base station requests a channel from MSC each time a cell request is made.

7. In dynamic channel assignment strategy, base station requests channel from ______
a) MSC
b) Neighbouring cell
c) Neighbouring cluster
d) Neighbouring base station

View Answer

Answer: a [Reason:] Each time a call request is made, the serving base station requests a channel from the MSC. The switch then allocates a channel to the requested cell following an algorithm that takes into account the likelihood of future blocking within the cell.

8. Dynamic channel assignment reduces the likelihood of blocking in comparison to fixed channel assignment. State whether True or False.
a) True
b) False

View Answer

Answer: a [Reason:] Dynamic channel assignment reduces the likelihood of blocking. Accordingly, the MSC only allocates a given frequency if that frequency is not presently in use in the cell or any other cell which falls within the minimum restricted distance of frequency reuse.

9. RSSI stands for ________
a) Radio System Signal Indicator
b) Restricted Signal Strength Indicator
c) Radio Signal Strength Indication
d) Restricted System Software Indicator

View Answer

Answer: a [Reason:] Received signal strength indicator (RSSI) is a measurement of the power present in a received radio signal. RSSI is usually invisible to a user of a receiving device.

10. What is the drawback of dynamic channel assignment?
a) Decrease channel utilization
b) Increase probability of blocked call
c) Cross talk
d) Increase storage and computational load on system

View Answer

Answer: d [Reason:] Dynamic channel assignment requires the MSC to collect real time data on channel occupancy, traffic distribution and RSSI of all channels on continuous basis. This increases the storage and computational load on the system but provides the advantage of increased channel utilization and decreased probability of blocked call.

Communications MCQ Set 3

1. The higher the bit rate, the more speech channels can be compressed within a given bandwidth.
a) True
b) False

View Answer

Answer: b [Reason:] 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

View Answer

Answer: a [Reason:] 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

View Answer

Answer: c [Reason:] 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

View Answer

Answer: b [Reason:] 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

View Answer

Answer: d [Reason:] 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

View Answer

Answer: a [Reason:] The most basic property of speech waveforms that is 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

View Answer

Answer: d [Reason:] 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

View Answer

Answer: b [Reason:] 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

View Answer

Answer: b [Reason:] 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

View Answer

Answer: c [Reason:] 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

View Answer

Answer: b [Reason:] 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.

Communications MCQ Set 4

1. In non-linear modulation, the amplitude of the carrier varies with the variation of modulating signal. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] In non-linear modulation, the amplitude of the carrier is constant regardless of the variation in the modulating signal. Many practical mobile radio communication systems use these types of nonlinear modulation methods.

2. In constant envelope family of modulation, class C amplifiers introduces degradation in spectrum occupancy. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] The constant envelope family of modulation has an advantage of satisfying various conditions. In this, power efficient Class C amplifiers can be used without introducing degradation in the spectrum occupancy of the transmitted signal.

3. Constant envelope modulation techniques occupy ______ bandwidth than linear modulation schemes.
a) Larger
b) Smaller
c) Same
d) Twice

View Answer

Answer: a [Reason:] Constant envelope modulation technique occupies a larger bandwidth than linear modulation technique. It is one of the disadvantage of constant envelope modulation. It is not well suited where bandwidth efficiency is more important than power efficiency.

4. In BFSK, _____of constant amplitude carrier signal is switched between two values.
a) Phase
b) Angle
c) Frequency
d) Amplitude

View Answer

Answer: c [Reason:] In BFSK, the frequency of a constant amplitude carrier signal is switched between two values according to the two possible message states. These states are called high and low tunes, which corresponds to binary 1 or 0.

5. MSK stands for ________
a) Maximum shift keying
b) Minimum shift keying
c) Minimum space keying
d) Maximum space keying

View Answer

Answer: b [Reason:] MSK stands for minimum shift keying. It is a special type of continuous phase shift keying. It is form of digital modulation technique that was developed in 1950s.

6. What is the modulation index of MSK?
a) 0.1
b) 1
c) 0.5
d) 0

View Answer

Answer: c [Reason:] Minimum shift keying is a special type of CPFSK. Its peak frequency deviation is equal to ¼ the bit rate. In other words, MSK is continuous phase FSK with a modulation index of 0.5.

7. The modulation index of an FSK signal is similar to modulation index of _____
a) Amplitude modulation
b) Phase modulation
c) QPSK
d) Frequency modulation

View Answer

Answer: d [Reason:] The modulation index of an FSK signal is similar to FM modulation index. It is defined by (2∆F)/Rb. Here ∆F is the peak RF frequency and Rb is the bit rate.

8. The name minimum phase shift keying implies minimum ______
a) Frequency separation
b) Amplitude separation
c) Phase change
d) Amplitude deviation

View Answer

Answer: a [Reason:] The name minimum phase shift keying implies minimum frequency separation, i.e. the bandwidth that allows orthogonal detection. A modulation index of 0.5 corresponds to the minimum frequency spacing that allows two FSK signals to be coherently orthogonal.

9. MSK is sometimes also referred as ______
a) Slow FSK
b) Fast FSK
c) Slow PSK
d) Fast PSK

View Answer

Answer: b [Reason:] Minimum shift keying is sometimes also referred as fast FSK. It is so called because frequency spacing used is only half as much as that used in conventional noncoherent frequency shift keying.

10. Which of the following is not a property of MSK?
a) Variable envelope
b) Spectral efficiency
c) Good BER performance
d) Self synchronizing capability

View Answer

Answer: a [Reason:] MSK has a constant envelope. It is a spectrally efficient scheme. It possesses properties such as constant envelope, spectral efficiency, good BER performance and self-synchronizing capability.

11. MSK is a special form of OQPSK. State whether True or False.
a) True
b) False

View Answer

Answer: a [Reason:] Yes, MSK can be thought of as a special form of offset quadrature phase shift keying. The condition is that baseband rectangular pulses are replaced with half sinusoidal pulses.

12. GMSK is a ________ of MSK.
a) Integral
b) Opposite
c) Derivative
d) Similar

View Answer

Answer: c [Reason:] Gaussian minimum phase shift keying is a simple binary modulation scheme. It is viewed as a derivative of MSK. GMSK considerably reduces the sidelobe levels in the transmitted spectrum.

13. Which of the following holds true for GMSK?
a) Minimum ISI
b) Minimum error rate
c) Good spectral efficiency
d) Variable envelope property

View Answer

Answer: c [Reason:] GMSK sacrifices the irreducible error rate caused by partial response signalling in exchange for extremely good spectral efficiency and constant envelope properties. And the premodulation Gaussian filtering introduces ISI in the transmitted signal.

14. MSK has complex demodulation and synchronization circuits. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] MSK has simple demodulation and synchronization circuits. It has various other advantages like continuous phase property makes it highly desirable for highly reactive loads. Due to these advantages, MSK is a popular modulation scheme for mobile radio communication.

Communications MCQ Set 5

1. Block codes can achieve a larger coding gain than convolution coding.
a) True
b) False

View Answer

Answer: b [Reason:] Convolution code can achieve a larger coding gain that can be achieved using a block coding with the same complexity. Their mapping is highly structured, enabling a decoding method considerably different from block codes.

2. Which of the following indicates the number of input bits that the current output is dependent upon?
a) Constraint length
b) Code length
c) Search window
d) Information rate

View Answer

Answer: a [Reason:] Constraint length determines the number of input data bits that the current output is dependent upon. The constraint length determines how powerful and complex the code is.

3. Which of the following is not a way to represent convolution code?
a) State diagram
b) Trellis diagram
c) Tree diagram
d) Linear matrix

View Answer

Answer: d [Reason:] Linear matrix is not a way to represent convolution code. Various ways of representing convolution codes are generator matrix, generator polynomial, logic tables, state diagram, tree diagram and trellis diagram.

4. Which of the following is not an algorithm for decoding convolution codes?
a) Viterbi algorithm
b) Stack algorithm
c) Fano’s sequential coding
d) Ant colony optimization

View Answer

Answer: d [Reason:] There are a number of techniques for decoding convolution codes. The most important of these methods is Viterbi algorithm. Other decoding algorithms for convolutional codes are Fano’s sequential coding, stack algorithm and feedback coding.

5. Viterbi algorithm performs ______ decoding of convolutional codes.
a) Maximum likelihood
b) Maximum a posteriori
c) Minimum square
d) Minimum mean square

View Answer

Answer: a [Reason:] Viterbi algorithm performs maximum likelihood decoding of convolutional codes. The algorithm was first developed by A.J. Viterbi. It is one of the most important algorithm used for decoding convolutional codes.

6. Fano’s algorithm searches all the paths of trellis diagram at same time to find the most probable path. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] Fano’s algorithm searches for the most probable path through the trellis diagram by examining one path at a time. The error rate performance of Fano’s algorithm is comparable to Viterbi’s algorithm.

7. Which of the following is not an advantage of Fano’s algorithm in comparison to Viterbi’s algorithm?
a) Less storage
b) Large constraint length
c) Error rate
d) Small delays

View Answer

Answer: d [Reason:] In comparison to Viterbi decoding, sequential decoding has a significantly larger delay. In advantage over Viterbi decoding is that it requires less storage, and thus codes with larger constraint lengths can be employed.

8. In comparison to stack algorithm, Fano’s algorithm is simpler.
a) True
b) False

View Answer

Answer: b [Reason:] In comparison to Fano’s algorithm, the stack algorithm is computationally simpler since there is no retracting over the same path. But stack algorithm requires more storage than Fano’s algorithm.

9. Which of the following is not an error correction and detection code?
a) Block code
b) Convolutional codes
c) Passive codes
d) Turbo codes

View Answer

Answer: c [Reason:] There are three basic types of error correction and detection codes. They are block codes, convolutional codes and turbo codes. A channel coder operates on digital message data by encoding the source information into a code sequence.

10. Which decoding method involves the evaluation by means of Fano’s algorithm?
a) Maximum Likelihood Decoding
b) Sequential Decoding
c) Maximum a priori
d) Minimum mean square

View Answer

Answer: b [Reason:] Fano’s algorithm involves the sequential decoding. It searches for the most probable path through the trellis by examining one path at a time.

11. In Viterbi’s algorithm, the selected paths are regarded as __________
a) Survivors
b) Defenders
c) Destroyers
d) Carriers

View Answer

Answer: a [Reason:] In Viterbi’s algorithm, the selected paths are regarded as survivor. The path thus defined is unique and corresponds to the decoded output.