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Communications MCQ Set 1

1. The type of traffic carried by a network is determines the routing service. State whether True or False.
a) True
b) False

View Answer

Answer: a [Reason:] The type of traffic carried by a network determines the routing services. It also determines protocols, and call handling techniques which must be employed.

2. Connection oriented services are also called __________
a) Datagram services
b) Virtual circuit routing
c) Connectionless services
d) Routing service

View Answer

Answer: b [Reason:] Connection oriented services are also called virtual circuit routing. In connection oriented routing, the communications path between the message source and destination is fixed for the entire duration of the message.

3. Connectionless services are also called __________
a) Datagram services
b) Virtual circuit routing
c) Connection oriented services
d) Routing service

View Answer

Answer: a [Reason:] Connectionless services are also called datagram services. In a connectionless service, a call set up procedure is not required at the beginning of a call, and each message burst is treated independently by the network.

4. First generation cellular systems provide connectionless services for each voice user. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] First generation cellular systems provide connection oriented services for each voice user. Voice channels are dedicated for users at the serving base station.

5. Wireless data networks are not well supported by ______
a) Datagram services
b) Circuit switching
c) Connectionless services
d) Routing service

View Answer

Answer: b [Reason:] Wireless data networks are not supported by circuit switching. It is due to their short, bursty transmissions which are often followed by periods of inactivity. Circuit switching is best suited for dedicated voice only traffic.

6. Packet switching breaks each message into smaller units. State whether True or False.
a) True
b) False

View Answer

Answer: a [Reason:] Packet switching breaks each message into smaller units for transmission and recovery. When a message is broken into packets, a certain amount of control information is added to each packet to provide source and destination identification, as well as error recovery provisions.

7. Header specifies the ______ of a new packet.
a) Ending
b) Middle part
c) Beginning
d) Data information

View Answer

Answer: c [Reason:] The header specifies the beginning of a new packet. It contains the source address, packet sequence number, and other routing and billing information.

8. The control field contains the _______
a) CRC
b) User data
c) Address
d) ARQ

View Answer

Answer: d [Reason:] The control field defines functions such as transfer of acknowledgments, automatic repeat requests (ARQs), and packet sequencing. The information field contains user data. And the final field is the frame check sequence field or the CRC (cyclic redundancy check).

9. Circuit switching provides greater efficiency in comparison to circuit switching. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] In contrast to circuit switching, packet switching provides excellent channel efficiency for bursty data transmission of short length. An advantage of packet switched data is that the channel is utilized only when sending or receiving bursts of information.

10. _____ was developed by CCITT to provide standard connectionless network access protocols for three layers of OSI model.
a) Packet switching
b) Datagram routing
c) X.25
d) CDPD

View Answer

Answer: c [Reason:] X.25 was developed by CCITT (now ITU-T) to provide standard connectionless network access (packet switching) protocols for the three layers (layer 1, 2 and 3) of the open systems interconnection (OSI) model.

11. X.25 protocols specify particular data rates. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] The X.25 protocol does not specify particular data rates or how packet switched networks are implemented. Rather, X.25 provides a series of standard functions and formats which give structure to the design of software.

Communications MCQ Set 2

1. What is the concept for accommodating a large number of users in a limited radio spectrum?
a) Grade of service
b) Trunking
c) Multiplexing
d) Multitasking

View Answer

Answer: b [Reason:] Cellular radio systems rely on trunking to accommodate a large number of users in a limited radio spectrum. The concept of trunking allows a large number of users to share the relatively small number of channels in a cell by providing access to each user, on demand.

2. On termination of call, the occupied channel is not returned to the pool of available channels in trunking. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] In a trunked radio system, each user is allocated a channel on a per call basis. Upon termination of the call, the previously occupied channel is immediately returned to the pool of available channels. It is a method for a system to provide network access to many clients by sharing a set of lines or frequencies instead of providing them individually.

3. In trunking system, when the channel is already in use, the call is blocked or queued. State whether True or False.
a) True
b) False

View Answer

Answer: a [Reason:] In a trunked mobile radio system when a particular user requests service, there is a possibility that all the channels are already in use. Then the user is blocked, or denied access to the system. Sometimes, a queue may be used to hold the requesting users until a channel becomes available.

4. Who developed the fundamental of trunking theory?
a) Newton
b) Ohm
c) Erlang
d) Einstein

View Answer

Answer: c [Reason:] The fundamentals of trunking theory were developed by Erlang. He was a Danish mathematician. He embarked on the study of how a large population could be accommodated by a limited number of servers in late 19th century.

5. What is the unit for the measure of traffic intensity?
a) Meters
b) Henry
c) Ohm
d) Erlang

View Answer

Answer: d [Reason:] The measure of traffic intensity is given by Erlang. It is defined as the ratio of the time during which a facility is cumulatively occupied to the time this facility is available for occupancy. Telecommunication operators are vitally interested in traffic intensity as it dictates the amount of equipment they must supply.

6. One Erlang represents _________
a) One call- hour per hour
b) One call-minute per hour
c) One call- hour per minute
d) Many calls- hour per hour

View Answer

Answer: a [Reason:] One Erlang represents the amount of traffic intensity carried by a channel that is completely occupied (i.e. one call- hour per hour or one call- minute per minute). For example, a radio channel that is occupied for 30 minutes during an hour carries 0.5 Erlangs of traffic.

7. What is the measure of the ability of user to access a trunked system during the busiest hour?
a) Trunking
b) Grade of Service (GOS)
c) Multiplexing
d) Sectoring

View Answer

Answer: a [Reason:] The grade of service (GOS) is a measure of the ability of a user to access a trunked system during the busiest hour. The busy hour is based upon customer demand at the busiest hour during a week, month or a year.

8. GOS is typically given as a likelihood that a ________
a) Call is in progress
b) Channels are busy
c) Call is blocked
d) Channel are free

View Answer

Answer: c [Reason:] GOS is typically given as the likelihood that a call is blocked, or the likelihood of a call experiencing a delay greater than a certain queuing time. It is the wireless designer’s job to estimate the maximum required capacity used to allocate the proper number of channels in order to meet GOS.

9. The time requires to allocate a trunked radio channel to a requesting user is called _______
a) Dwell time
b) Holding time
c) Run time
d) Set up Time

View Answer

Answer: d [Reason:] When any user makes a call request, the time required to allocate a trunked channel to a user is known a s set up time. TETREA (Terrestrial Trunked Radio) call set up time is 0.3 seconds. GSM uses a call set up time of several seconds.

10. Average duration of a typical call is called ________
a) Holding time
b) Dwell time
c) Set up time
d) Run time

View Answer

Answer: a [Reason:] Average time of a typical call is called holding time. It is denoted by H (in seconds). It is used to measure the traffic intensity per user. The time over which a call may be maintained within a cell, without handoff is called dwell time.

11. The average number of call requests per unit time is also known as ________
a) Request rate
b) Load
c) Grade o Service
d) Traffic intensity

View Answer

Answer: a [Reason:] Request rate is the average number of call requests per unit time. It is denoted by λ. Unit for request rate is second-1. It can also be defined as the ratio of traffic intensity of each user and the holding time.

12. Traffic intensity offered by each user is the product of __________
a) Set up time and holding time
b) Call request rate and holding time
c) Load and holding time
d) Call request rate and set up time

View Answer

Answer: b [Reason:] The traffic intensity offered by each user is equal to the call request rate multiplied by the holding time. Each user generates a traffic intensity A=λH Erlang. Here, H is the average duration of a call and λ is the average number of call requests per unit time for each user.

13. AMPS cellular system is designed for a GOS of _____ blocking.
a) 10%
b) 50 %
c) 2%
d) 1%

View Answer

Answer: c [Reason:] The AMPS (Advanced Mobile Phone System) cellular system is designed for a GOS of 2% blocking. This implies that the channel allocations for cell sites are designed so that 2 out of 100 calls will be blocked due to channel occupancy during the busiest hour.

14. Blocked calls cleared formula is also known as _______ formula.
a) Erlang C
b) Erlang A
c) Erlang D
d) Erlang B

View Answer

Answer: d [Reason:] Erlang B formula is also known as the blocked calls cleared formula. The Erlang B formula determines the probability that a call is blocked. And, it is a measure of the GOS for a trunked system which provides no queuing for blocked calls.

15. Blocked calls delayed formula is also known as _______
a) Erlang A
b) Erlang B
c) Erlang C
d) Erlang D

View Answer

Answer: c [Reason:] Erlang C is also known as Blocked Calls Delayed. In this trunked system, a queue is provided to hold calls which are blocked. If a channel is not available immediately, the call request may be delayed until a channel becomes available.

Communications MCQ Set 3

1. Which of the following is not a channel parameter?
a) Bandwidth
b) Coherence time
c) Rms delay spread
d) Doppler spread

View Answer

Answer: a [Reason:] Channel parameters are coherence bandwidth, rms delay spread and Doppler spread. Signal parameters are bandwidth and symbol period. Different types of fading occur depending on the relation between channel and signal parameters.

2. ______ leads to time dispersion and frequency selective fading.
a) Doppler spread
b) Multipath delay spread
c) Time dispersive parameters
d) Frequency delay spread

View Answer

Answer: b [Reason:] Multipath delay spread leads to time dispersion and frequency selective fading. Doppler spread leads to frequency dispersion and time selective fading. These two propagation mechanism are independent of each other.

3. Which of the following s not a characteristic of flat fading?
a) Mobile radio channel has constant gain
b) Linear phase response
c) Non linear phase response
d) Bandwidth is greater than the bandwidth of transmitted signal

View Answer

Answer: c [Reason:] The received signal will undergo flat fading if mobile radio channel has a constant gain and linear phase response over a bandwidth which is greater than the bandwidth of transmitted signal. It is the most common type of fading.

4. Spectral characteristics of the channel changes with time in flat fading. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] In flat fading, the multipath structure of the channel is such that spectral characteristics of the transmitted signal are preserved at the receiver. But, the strength of the received signal changes with time due to fluctuations in the gain of channel caused by multipath.

5. Flat fading channel is also known as _____
a) Amplitude varying channel
b) Wideband channel
c) Phase varying channel
d) Frequency varying channel

View Answer

Answer: a [Reason:] Flat fading channel is also known as amplitude varying channel. They are also sometimes referred to as narrowband channel. In flat fading channel, the bandwidth of the applied signal is narrow as compared to the channel flat fading bandwidth.

6. In a frequency selective fading, mobile radio channel possess a constant gain and a linear phase over bandwidth smaller than bandwidth of transmitted signal. State whether True or False.
a) True
b) False

View Answer

Answer: a [Reason:] If the channel possesses a constant gain and linear phase response over a bandwidth that is smaller than the bandwidth of transmitted signal, then the channel creates frequency selective fading on the received signal. Frequency selective fading channel are much more difficult to model than flat fading channel.

7. Frequency selective fading channels are also known as ________
a) Narrowband channel
b) Wideband channel
c) Amplitude varying channel
d) Phase varying channel

View Answer

Answer: b [Reason:] Frequency selective fading channels are also known as wideband channels. The bandwidth of the signal is wider than the bandwidth of channel impulse response.

8. Frequency selective fading does not induce intersymbol interference. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] Frequency selective fading is due to time dispersion of the transmitted symbols within the channel. Thus, the channel induces intersymbol interference (ISI). The channel have certain frequency components in the received signal spectrum that have greater gain than others.

9. For fast fading channel, the coherence time of the channel is smaller than _______ of transmitted signal.
a) Doppler spread
b) Bandwidth
c) Symbol period
d) Coherence bandwidth

View Answer

Answer: c [Reason:] In fast fading channel, the channel impulse response changes rapidly within the symbol duration. Thus, the coherence time of the channel is much smaller than the symbol period of the transmitted signal.

10. In slow fading channel, Doppler spread of the channel is much less than the ________ of baseband signal.
a) Symbol period
b) Phase
c) Coherence time
d) Bandwidth

View Answer

Answer: d [Reason:] Slow fading channel may be assumed to be static over one or several reciprocal bandwidth intervals. In the frequency domain, this implies that the Doppler spread of the channel is much less than the bandwidth of the baseband signals.

Communications MCQ Set 4

1. _________ also known as impulse or zero-carrier radio technology.
a) Ultra wideband technology
b) Femtocell technology
c) Multicasting
d) Multiplexing

View Answer

Answer: a [Reason:] Ultra-wideband (UWB) technology is also known as impulse or zero-carrier radio technology. It appears to be one of the most promising wireless radio communication technologies of recent time.

2. UWB operates across narrow bandwidth. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] Unlike conventional radio systems, which operate within a relatively narrow bandwidth, the UWB radio system operates across a wide range of the frequency spectrum by transmitting a series of extremely narrow (10–1000 per second) and low-power pulses.

3. The basic element in DSC–UWB technology is the monocycle wavelet.
a) True
b) False

View Answer

Answer: b [Reason:] The basic element in TM–UWB technology is the monocycle wavelet. Typically, wavelet pulse widths are between 0.2 and 1.5 nanoseconds, corresponding to center frequencies between 600 MHz and 5 GHz.

4. In TM–UWB, the system uses a modulation technique called _______
a) Pulse width modulation
b) Pulse code modulation
c) Pulse position modulation
d) Pulse amplitude modulation

View Answer

Answer: c [Reason:] In TM–UWB, the system uses a modulation technique called pulse position modulation. The TM–UWB transmitter emits ultra-short monocycle wavelets with tightly controlled pulse-to-pulse intervals, which are varied on a pulse-by-pulse basis in accordance with an information signal and a channel code.

5. DSC-UWB uses _________
a) Pulse width modulation
b) Pulse code modulation
c) Pulse position modulation
d) Direct sequence modulation

View Answer

Answer: d [Reason:] In DSC-UWB, the signal is spread by direct sequence modulating a wavelet pulse trains at duty cycles approaching that of a sine wave carrier. The spectrum spreading, channelization, and modulation are provided by a PN (pseudo noise) sequence, and the chipping rate is maintained as some fraction of the carrier center frequency.

6. The coherent interaction of signals in UWB arriving by many paths causes ______
a) Ricean fading
b) Nakagami fading
c) Rayleigh fading
d) Multicast fading

View Answer

Answer: c [Reason:] The coherent interaction of signals arriving by many paths causes the Rayleigh or multipath fading in RF communications. Inside buildings, when continuous sine waves are transmitted wherein the channels exhibit multipath differential delays in the nanosecond range, the multipath fading occurs naturally.

7. UWB technology supports low bit rate and low speed. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] UWB technology is appropriate for the high-performance wireless home network, which mandates support for large bit rate (50 Mbps), high-speed, affordable connectivity between devices, and simultaneous data transmission from multiple devices, and full-motion video capability.

8. Which of the following is not true for UWB?
a) Large spectrum
b) Lower price
c) Pulse data
d) Large interference

View Answer

Answer: d [Reason:] The combination of larger spectrum, lower power, and pulsed data means that UWB causes less interference than narrowband radio designs while yielding low probability of detection and excellent multipath immunity.

9. UWB systems are very complex, since they use radio frequency/intermediate frequency conversion stages. State whether True or False.
a) True
b) False

View Answer

Answer: b [Reason:] UWB systems are much less complex, since they do not use any radio frequency/intermediate frequency (RF/IF) conversion stages, local oscillators, mixers, and other expensive surface acoustic wave (SAW) filters common to traditional radio technologies.

10. Which of the following is not a drawback of UWB technology?
a) Not appropriate for WAN
b) Power limited
c) Small spectrum
d) Limited jitter requirements

View Answer

Answer: d [Reason:] UWB devices are power limited because they must coexist on a noninterfering basis with other licensed and unlicensed users across several frequency bands. For UWB systems using PPM as their modulation technique, limited jitter requirements could be an issue.

Communications MCQ Set 5

1. The dual mode USDC/AMPS system was standardized as _____
a) IS-54
b) IS-136
c) PSTN
d) GSM

View Answer

Answer: a [Reason:] The dual mode USDC/AMPS system was standardized as Interim Standard 54 (IS 54). It was standardized by Electron Industries Association and Telecommunication Industry Association (EIA/TIA) in 1990. It was later upgraded to IS-136.

2. USDC is also known as _______
a) SADC
b) NADC
c) PADC
d) N-AMPS

View Answer

Answer: b [Reason:] USDC is also known as North American Digital Cellular (NADC). It has been installed in North America in the countries like Canada and Mexico.

3. USDC was designed to share different frequencies as compared to AMPS.
a) True
b) False

View Answer

Answer: b [Reason:] The USDC system was designed to share the same frequencies, frequency reuse plan, and base stations as AMPS, so that base stations and subscriber units could be equipped with both AMPS and USDC channels within the same piece of equipment.

4. Because of the compatibility with AMPS, USDC is also known as ______
a) SADC
b) PADC
c) D-AMPS
d) K-AMPS

View Answer

Answer: c [Reason:] USDC (United States Digital Cellular System) maintains compatibility with AMPS in a number of ways. Therefore, USDC is also known as D-AMPS (digital AMPS).

5. USDC forward and reverse control channels use exactly the same signalling techniques as AMPS.
a) True
b) False

View Answer

Answer: a [Reason:] To maintain compatibility with AMPS phones, USDC forward and reverse control channels use exactly the same signalling techniques as AMPS. USDC voice channels use 4-ary π/4 DQPSK modulation with a channel rate of 48.6 kbps.

6. USDC has ____ as many control channels as AMPS.
a) Same
b) Three times
c) Twice
d) Four times

View Answer

Answer: c [Reason:] USDC has twice as many control channels as AMPS. In addition to the forty two primary AMPS control channels, USDC specifies forty two additional control channels called the secondary control channels.

7. Which of the following data channels of USDC carries the user information?
a) DTC
b) CVDCC
c) SACCH
d) FACCH

View Answer

Answer: a [Reason:] DTC (data traffic channel) is the most important data channel as far as the end user is concerned. It carries user information (i.e. speech or user data).

8. Which of the following channel is similar in functionality to the SAT used in AMPS?
a) DTC
b) CDVCC
c) SACCH
d) FACCH

View Answer

Answer: b [Reason:] CDVCC (Code Digital Verification Color Code) is a 12 bit message sent in every time slot and is similar in functionality to the SAT used in AMPS. The CDVCC is an 8 bit number ranging between 1 and 255, which is protected with four additional channel coding bits from a shortened Hamming code.

9. Which of the following channel in USDC provides a signalling channel?
a) DTC
b) CVDCC
c) SACCH
d) FACCH

View Answer

Answer: c [Reason:] The SACCH (slow associated control channel) is sent in every time slot and provides a signalling channel in parallel with the digital speech. The SACCH carries various control and supervisory messages between the subscriber unit and the base station.

10. Which of the following channel in USDC is used to send important control or specialized traffic data between the base station and mobile units?
a) DTC
b) CVDCC
c) SACCH
d) FACCH

View Answer

Answer: d [Reason:] FACCH (fast associated control channel) is a used to send important control or specialized traffic data between the base station and mobile units. The FACCH data, when transmitted, takes the place of user information data within a frame.

11. Which of the following speech coder is used in USDC?
a) Vector Sum Excited Linear Predictive coder
b) Formant Vocoder
c) Multipulse Excited Linear Predictive coder
d) Residual Excited Linear Predictive coder

View Answer

Answer: a [Reason:] The USDC speech coder is called the Vector Sum Excited Linear Predictive coder (VSELP). This belongs to the class of Code Excited Linear Predictive coders (CELP) or Stochastically Excited Linear Predictive coders.