Communications MCQ Set 1
1. What is the full form of UMTS?
a) Universal Mobile Telephone System
b) Ubiquitous Mobile Telephone System
c) Ubiquitous Mobile Telemetry System
d) Universal Machine Telemedicine System
Answer: a [Reason:] UMTS (Universal Mobile Telephone System) is a visionary air interface standard that was introduced in 1996. European carriers, manufacturers, and government regulators collectively developed the early version of UMTS as an open air interface standard for third generation wireless telecommunication.
3. UMTS uses which multiple access technique?
Answer: a [Reason:] Although UMTS is designed to operate on evolved GSM core networks, it uses code division multiple access (CDMA) for its air interface. The majority of the 3G systems in operation employ CDMA, while the rest use TDMA. CDMA allows various users to share a channel at the same time, while TDMA allows users to share the same channel by chopping it into different time slots.
3. UMTS does not has backward compatibility with ____
Answer: c [Reason:] UMTS assures backward compatibility with the second generation GSM, IS-136 and PDC TDMA technologies. It is also compatible with all 2.5G TDMA techniques like GPRS and EDGE. But it does not provide compatibility to CDMA technologies of 2G and 2.5 G. IS-95 is a CDMA standard of 2G.
4. UMTS is also known as _____
Answer: d [Reason:] UMTS uses Wideband CDMA (W-CDMA) to carry the radio transmissions. Therefore, it is also referred as W-CDMA. W-CDMA offers greater spectral efficiency and bandwidth to mobile network operators.
5. What is the chip rate of W-CDMA?
a) 1.2288 Mcps
b) 3.84 Mcps
c) 270.833 Ksps
d) 100 Mcps
Answer: b [Reason:] W-CDMA uses a chip rate of 3.84 Mcps. Chip rate is the product of symbol rate and spreading factor. If the symbol rate is 960 Kbps and spreading factor is 4 for W-CDMA, then the chip rate is 3.84 Mcps. The chip rate for Cdma2000 and GSM are 1.2288 Mcps and 27.0833 Ksps respectively.
6. W-CDMA works in FDD mode only. (True/ False)
Answer: b [Reason:] W-CDMA works in both FDD and TDD mode. W-CDMA developed for wide area cellular coverage uses FDD. And TDD is used by W-CDMA for indoor cordless type applications.
7. How much packet data rate per user is supported by W-CDMA if the user is stationary?
a) 2.048 Kbps
b) 100 Mbps
c) 2.048 Mbps
d) 1 Gbps
Answer: c [Reason:] If the user is stationary, W-CDMA supports packet data rates upto 2.048Mbps per user. Thus, it allows high quality data, multimedia, streaming audio video and broadcast type services to consumers. Future version of WCDMA will support stationary user data rates in excess of 8Mbps.
8. What is the minimum spectrum allocation required by W-CDMA?
a) 5 MHz
c) 1.25 MHz
d) 200 KHz
Answer: a [Reason:] W-CDMA/UMTS requires a minimum spectrum allocation of 5 MHz. Using this bandwidth, it has the capacity to carry over 100 simultaneous voice calls. It is able to carry data at speeds up to 2 Mbps in its original format. 20 MHz is the bandwidth defined for LTE. CdmaOne uses a bandwidth of 1.25 MHz. GSM’s bandwidth is 200 KHz.
9. W-CDMA requires a complete change of RF equipment at each base station. (True/False)
Answer: a [Reason:] W-CDMA is designed to provide backward compatibility and interoperability for all GSM, IS-136/PDC, GPRS and EDGE equipment. But due to a wider air interface bandwidth of W-CDMA, it requires a complete change of RF-equipment at each base station.
10. How much increase in spectral efficiency is provided by W-CDMA in comparison to GSM?
a) Two times
b) Three times
c) No increase
d) Six times
Answer: d [Reason:] W-CDMA can provide at least six times increase in spectral efficiency over GSM at system level. Such a wider bandwidth is chosen to higher data rates as low as 8 kbps to as high as 2 Mbps on a single 5 MHz W-CDMA radio channel.
Communications MCQ Set 2
1. Which type of cell provides the best level of service for average subscribers?
a) Acceptance cell
b) Barred cell
c) Reserved cell
d) Suitable cell
Answer: d [Reason:] A suitable cell is a cell on which the UE may camp on to obtain normal service. The UE shall have a valid USIM and such a cell shall fulfil all the following requirements. It provides the best level of service for average subscribers.
2. With the normal cyclic prefix, how many symbols are contained in 1 frame?
Answer: b [Reason:] There are two different type of Cyclic Prefix. One is normal Cyclic Prefix and the other is ‘Extended Cyclic Prefix’ which is longer than the Normal Cyclic Prefix. Normal cyclic prefix contains 140 symbols in 1 frame.
3. What is the PBCH scrambled with?
a) Current frame number
b) Physical cell ID
c) UE’s CRNTI
d) Not scrambled
Answer: b [Reason:] The PBCH is scrambled prior to modulation with a cell-specific sequence that depends on the cells’ identity. In contrast to the synchronization signals, the PBCH is transmitted on the 72 reserved subcarriers, which are QPSK-modulated.
4. What is the length of the shortest possible PDCCH in bits?
Answer: c [Reason:] PDCCH is a physical channel that carries downlink control information (DCI). Shortest possible PDCCH is 72 bits.
5. What is the average uploading speed of 4G LTE network?
a) 1-3 Gbps
b) 2-5 Gbps
c) 1-3 Mbps
d) 2-5 Mbps
Answer: d [Reason:] Verizon 4G LTE wireless broadband is 10 times faster than 3G able to handle download speeds between 5 and 12 Mbps (Megabits per second) and upload speeds between 2 and 5 Mbps.
6. Which of the following is not a part of characteristic of 4G network?
a) Multirate management
b) Fully converged services
c) Software dependency
d) Diverse user devices
Answer: a [Reason:] 4G is the fourth generation of broadband cellular network technology, succeeding 3G. Its characteristics include fully converged services, software dependency and diverse user devices.
7. What does SGSN stands for?
a) Serial Gateway Supporting Node
b) Supporting GGSN Support Node
c) Supporting GPRS Support Node
d) Supporting Gateway Support Node
Answer: c [Reason:] The Serving GPRS Support Node (SGSN) is a main component of the GPRS network, which handles all packet switched data within the network, e.g. the mobility management and authentication of the users. The SGSN performs the same functions as the MSC for voice traffic.
8. What location management feature is supported by 4G?
a) Concatenated Location Registration
b) Concurrent Location Register
c) Concatenated Management
d) Collated Location Registration
Answer: a [Reason:] 4G supports concatenated location registration. Concatenated location registration reports to the network that they are concatenated to a common object.
9. In 2007, ______ announced its plan to transmit its network to 4G standard LTE with joint efforts of Vodafone group.
a) Verizon Wireless
d) V Cast
Answer: a [Reason:] In 2007, Verizon announced plans to develop and deploy its fourth generation mobile broadband network using LTE, the technology developed within the Third Generation Partnership Project (3GPP) standards organization.
10. Hybrid ARQ is part of the ______ layer.
Answer: c [Reason:] Hybrid automatic repeat request (hybrid ARQ or HARQ) is a combination of high-rate forward error-correcting coding and ARQ error-control. It is part of MAC layer.
Communications MCQ Set 3
1. Carrier signal in modulation technique is _______ signal.
a) High frequency
b) Low frequency
c) High amplitude
d) Low amplitude
Answer: a [Reason:] Carrier signal in modulation technique is a high frequency signal. In amplitude modulation, the amplitude of a high frequency carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal.
2. Modulation index of an AM signal is ratio of _____ to the _______
a) Peak carrier amplitude, Peak message signal amplitude
b) Peak message signal amplitude, Peak carrier amplitude
c) Carrier signal frequency, Message signal frequency
d) Message signal frequency, Carrier signal frequency
Answer: b [Reason:] The modulation index k of an AM signal is defined as the ratio of the peak message signal amplitude to the peak carrier amplitude. The modulation index is often expressed as a percentage. It is also called percentage modulation.
3. If the peak message signal amplitude is half the peak amplitude of the carrier signal, the signal is _____ modulated.
Answer: c [Reason:] The modulation is also expressed in percentage. It is also called percentage modulation. The signal is said to be 50% modulated if the peak message signal amplitude is half the peak amplitude of the carrier signal.
4. A percentage of modulation greater than ____ will distort the message signal.
Answer: d [Reason:] A percentage of modulation greater than 100% will distort the message signal if detected by an envelope detector. In this case the lower excursion of the signal will drive the carrier amplitude below zero, making it negative (and hence changing its phase).
5. The RF bandwidth of AM is _____ the maximum frequency contained in the modulating message signal.
b) Two times
c) Four times
d) Ten times
Answer: b [Reason:] The RF bandwidth of an AM signal is equal to BAM=2fm. It is double the maximum frequency contained in the modulating message signal. AM spectrum consists of an impulse at the carrier frequency and two sidebands which replicate the message spectrum.
6. Single sideband AM systems occupy same bandwidth as of conventional AM systems. State whether True or False.
Answer: b [Reason:] Single sideband (SSB) AM systems transmit only one of the sidebands (either upper or lower) about the carrier. Hence, they occupy only half the bandwidth of conventional AM systems.
7. How is the performance of SSB AM systems in fading channels?
Answer: a [Reason:] SSB systems have the advantage of being very bandwidth efficient. But their performance in fading channels is very poor. For proper detection, the frequency of the oscillator at the product detector mixer in the receiver must be same as that of the incoming carrier frequency.
8. Which of the following is a disadvantage of tone-in-band SSB system?
a) High bandwidth
b) Bad adjacent channel protection
c) Effects of multipath
d) Generation and reception of signal is complicated
Answer: d [Reason:] Tone-in-band SSB systems has the advantage of maintaining the low bandwidth property of the SSB signals, while at the same time providing good adjacent channel protection. The tone in band system employs feedforward automatic gain and frequency control to mitigate the effects of multipath induced fading.
9. FFSR in AM systems stands for ________
a) Feedforward signal regeneration
b) Feedbackward signal regeneration
c) Feedbackward system restoration
d) Feedforward system restoration
Answer: a [Reason:] FFSR stands for Feedforward signal regeneration. If the pilot tone and the information bearing signal undergo correlated fading, it is possible at the receiver to counteract the effects of fading through signal processing based on tracking of pilot tone. This process is called FFSR.
10. AM demodulation technique can be divided into _____ and _____ demodulation.
a) Direct, indirect
b) Slope detector, zero crossing
c) Coherent, noncoherent
d) Quadrature detection, coherent detection
Answer: c [Reason:] AM demodulation techniques may be broadly divide into two main categories. They are called coherent and noncoherent demodulation. They are differentiated by the knowledge of transmitted carrier frequency and phase at the receiver.
11. Non coherent detection requires the knowledge of transmitted carrier frequency and phase at the receiver. State whether True or False.
Answer: b [Reason:] Non coherent detection does require the knowledge of phase information. However, coherent detection requires knowledge of the transmitted carrier frequency and phase at the receiver.
12. A product detector in AM systems is also called ______
a) Envelope detector
d) Phase detector
Answer: d [Reason:] A product detector is also called a phase detector. It forms a coherent demodulator for AM signals. It is a down converter circuit which converts the input bandpass signal to a baseband signal.
13. AM system use only product detector for demodulation. They never use envelope detectors. State whether True or False.
Answer: b [Reason:] AM systems can use either product detector or envelope detector for demodulation. As a rule, envelope detectors are useful when input signal power is at least 10dB greater than noise power, whereas product detector are able to process the AM signals with input signal to noise ratios well below 0 dB.
Communications MCQ Set 4
1. US cellular telephone system, AMPS stands for __________
a) Analog Mobile Phone System
b) Analog Modulation Packet System
c) Analog Machine Precision System
d) Analog Mobile Precision System
Answer: a [Reason:] AMPS stands for Analog Mobile Phone System. It was first deployed in late 1983 in urban and suburban areas of Chicago by Ameritech.
2. Who developed the first US cellular telephone system called AMPS?
c) AT & T Bell Laboratories
Answer: c [Reason:] In the late 1970s, AT & T Bell Laboratories developed the first US cellular telephone system called the Advanced Mobile Phone System (AMPS). In 1983, a total of 40 MHz of spectrum in the 800 MHz band was located by the Federal Communication Commission for AMPS.
3. The AMPS system uses a ____ cell reuse pattern.
Answer: d [Reason:] The AMPS system uses a seven cell reuse pattern. It also provides sectoring and cell splitting to increase capacity when needed.
4. Which of the following is virtually identical to AMPS?
Answer: a [Reason:] ETACS is virtually identical to AMPS. It was developed in middle 1980s and stands for European Total Access Communication System.
5. AMPS and ETACS use _____ and _____ for radio transmission.
a) FM, TDD
b) FM, FDD
c) AM, TDD
d) FM, FDD
Answer: b [Reason:] Like all other first generation, analog, cellular systems, AMPS and ETACS use frequency modulation (FM) and frequency division duplex (FDD) for radio transmission.
6. US AMPS system provides 42 control channel for each of the two service providers.
Answer: b [Reason:] In the US AMPS system, there are twenty one control channels for each of the two service providers in each market. However, ETACS supports forty two control channels for a single provider.
7. In each cellular market, the non wireline service provider is assigned an odd SID.
Answer: a [Reason:] In each cellular market, the non wireline service provider (the ‘A’ provider) is assigned an odd SID (system identification number). The wireline provider (the ‘B’ provider) is assigned an even SID.
8. ETACS use ____ instead of SID (system identification number).
a) Area identification number
b) Analog identification number
c) Digital identification number
d) Dual identification number
Answer: a [Reason:] For ETACS, area identification numbers (AIDs) are used instead of SIDs. ETACS subscriber units are able to access any control or voice channel in the standard.
9. _________ allows base and mobile to distinguish each other from co-channel users located in different cells.
Answer: a [Reason:] The SAT (supervisory audio tone) has one of the three different frequencies which allow the base and mobile to distinguish each other from co channel users located in different cells.
10. AMPS and ETACS use same physical channels for transmission of voice and control channels. State whether True or False.
Answer: b [Reason:] AMPS and ETACS use different physical rate channels for transmission of voice and control channels. A control channel is used by each base station in the system to simultaneously page subscriber units to alert them of incoming calls.
11. To increase capacity of AMPS, Motorola developed ______
Answer: b [Reason:] To increase capacity in large AMPS markets, Motorola developed an AMPS like system called N-AMPS (narrowband AMPS) in 1991. N-AMPS did not become widespread as 2G digital technologies displaced many of the original FM analog systems.
Communications MCQ Set 5
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 [Reason:] 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.
Answer: b [Reason:] 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 [Reason:] 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. State whether True or False.
Answer: b [Reason:] 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 [Reason:] 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
Answer: a [Reason:] 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 [Reason:] 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. State whether True or False.
Answer: b [Reason:] 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.
b) Envelope detector
d) Voltage controlled oscillators
Answer: d [Reason:] 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. State whether True or False.
Answer: a [Reason:] 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 [Reason:] 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 [Reason:] 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 [Reason:] 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 [Reason:] 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. State whether True or False.
Answer: b [Reason:] 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.