Category: Wireless & Mobile Communications Objective Questions

Wireless & Mobile Communications Multiple Choice Questions & Answers on “Frequency Domain Coding of Speech”.

1. Frequency domain coders divides the speech signal into __________
a) A set of frequency components
b) A set of different amplitudes
c) A set of time delays
d) A set of phase components
Answer: a
Clarification: In the class of frequency domain coders, the speech signal is divided into a set of frequency components. Each frequency component is quantized and encoded separately.

2. In frequency domain coding of speech, the number of bits used to encode each frequency component is constant.
a) True
b) False
Answer: b
Clarification: Frequency domain coders have an advantage that number of bits used to encode each frequency component can be dynamically varied. They can also be shared among different bands.

3. Quantization is a ________ process.
a) Linear
b) Direct
c) Non-linear
d) Indirect
Answer: c
Clarification: Quantization is a non-linear process. It produces distortion products that are typically broad in spectrum.

4. Sub band coding codes the short time transform of a windowed signal.
a) True
b) False
Answer: b
Clarification: It is function of block transform coding. However, a sub band coder divides the speech signal into many smaller sub bands and encodes each sub band separately according to some perceptual criterion.

5. Which of the following is one of the most frequently used transform in speech coding?
a) Fourier transform
b) Wavelet transform
c) Shearlet transform
d) Discrete cosine transform
Answer: d
Clarification: DCT (discrete cosine transform) is one of the most attractive and frequently used transforms for speech coding. Fast algorithms developed for computing the DCT in a computationally efficient manner are used.

6. What does ATC stands for in speech coders?
a) Automatic transform code
b) Air traffic controller
c) Active thermal convection
d) Adaptive transform coding
Answer: d
Clarification: In speech coding, ATC stands for adaptive transform coding. It is form of frequency domain coder that encodes the speech at bit rates in the range of 9.6 kbps and 20 kbps.

7. Waveform coders and Vocoders are the types of ____________
a) Speech coders
b) Modulation technique
c) Frequency translation methods
d) Channel allocation for transmission
Answer: a
Clarification: Speech coders can be classified into waveform coders and Vocoders. Waveform coders convert the analog signal into digital signal. Vocoders exploit the special properties of speech signal to reduce the bit rate.

8. The type of frequency domain coding that divides the speech signal into sub bands is _____
a) Waveform coding
b) Vocoders
c) Block transform coding
d) Sub-band coding
Answer: d
Clarification: Sub band coding (SBC) is a method where the speech signal is subdivided into several frequency bands and each band is digitally encoded separately. The audible frequency spectrum 20Hz-20 KHz is divided into frequency sub-bands using a bank of finite impulse response (FIR) filter and output of each filter is sampled and encoded.

9. Speech coders are categorized on the basis of __________
a) Signal compression techniques
b) Frequency of signal
c) Bandwidth of the signal
d) Phase of the signal
Answer: a
Clarification: Speech coders are categorised on the basis of signal compression techniques. Speech coding is an art of compressing and then encoding speech signals.

10. The speech coding technique that is dependent on the prior knowledge of the signal is __________
a) Waveform coders
b) Vocoders
c) Sub band coding
d) Block transform
Answer: b
Clarification: Vocoders are dependent on the prior knowledge of the signals. They capture the characteristic elements of audio signal and then uses this characteristic signal to affect other audio signals.

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Wireless & Mobile Communications online test on “Personal Communication Services/Networks (PCS/PCNs)”.

1. PCS/PCN provides only wired communication.
a) True
b) False
Answer: b
Clarification: The objective of personal communication systems (PCS) or personal communication networks (PCNs) is to provide ubiquitous wireless communications coverage, enabling users to access telephone network and Internet.

2. Concept of PCS/PCN is based on _________
a) Advanced intelligent network
b) Artificial intelligent network
c) CDPD
d) SS7
Answer: a
Clarification: The concept of PCS/PCN is based on an advanced intelligent network (AIN). The mobile and fixed networks will be integrated to provide universal access to the network and its databases.

3. AIN has different telephone numbers for both wireline and wireless services.
a) True
b) False
Answer: b
Clarification: AIN (advanced intelligent network) allow its users to have a single telephone number to be used for both wireless and wireline services.

4. Circuit switching has more advantage than packet switching for PCS.
a) True
b) False
Answer: b
Clarification: Packet switching technology will have more advantages for PCS/PCN than circuit switching. PCS is required to serve a wide range of services including voice, data, e-mail and digital video.

5. ______ is used for transmission of packets in the cellular switched architecture.
a) Packet switching techniques
b) Circuit switching techniques
c) Packet and circuit switched technique
d) Datagram technique
Answer: a
Clarification: Packet switching techniques are used for transmission of packets in the cellular switched architecture. Packet switching is attractive for wireless networks because the addresses and other information in packet headers make it possible for dispersed network elements to respond to a mobile user without intervention central controllers.

6. Which of the following has the function to accept information from PSTN?
a) TIU
b) WIU
c) BIU
d) CIU
Answer: a
Clarification: The function of TIU (Trunk interface unit) is to accept information from the PSTN. TIU acts as the physical layer and transforms the standard format of the PSTN into the wireless access physical layer.

7. PTI is the address of ____________
a) TIU
b) WIU
c) BIU
d) CIU
Answer: a
Clarification: PTI (Permanent terminal identifier) is the address of TIU. It is the address from where he call is originated.

8. _______ is the information contained in the packet header of TIU.
a) PTI
b) VCI
c) PRMA
d) CDPD
Answer: b
Clarification: VCI (virtual circuit identifier) is the information contained in the packet header of TIU. It is used to identify the route through which the transmission will take place.

9. Transmission protocol, PRMA stands for _________
a) Pocket reservation multiple access
b) Packet register multiple access
c) Pocket register multiple access
d) Packet reservation multiple access
Answer: d
Clarification: Transmission protocol, PRMA stands for packet reservation multiple access. PRMA is a time division multiplex (TDM) based multiple access protocol that allows a group of spatially dispersed terminals to transmit packet voice and low bit rate data over a common channel.

10. UMTS stands for ____________
a) Universal mobile telecommunication system
b) Universal mobile telephone system
c) United multiplex telecommunication system
d) Universal mobile telecommunication system
Answer: d
Clarification: UMTS stands for Universal mobile telecommunication system. It is a system that is capable of providing a variety of mobile services to a wide range of global mobile communication standards.

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Wireless & Mobile Communications Multiple Choice Questions on “4G Network Architecture”.

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
Clarification: 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?
a) 7
b) 140
c) 12
d) 40
Answer: b
Clarification: 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
Clarification: 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?
a) 144
b) 288
c) 72
d) 576
Answer: c
Clarification: 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
Clarification: 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 the characteristic of 4G network?
a) Multirate management
b) Fully converged services
c) Software dependency
d) Diverse user devices
Answer: a
Clarification: 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) Serving GPRS Support Node
b) Supporting GGSN Support Node
c) Supporting GPRS Support Node
d) Supporting Gateway Support Node
Answer: a
Clarification: 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
Clarification: 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
b) AirTouch
c) Netflix
d) V Cast
Answer: a
Clarification: 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.
a) PDCP
b) RLC
c) MAC
d) PHY
Answer: c
Clarification: 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 the MAC layer.

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Wireless & Mobile Communications Interview Questions and Answers on “Second Generation (2G) Cellular Networks”.

1. Which of the following multiple access techniques are used by second generation cellular systems?
a) FDMA/FDD and TDMA/FDD
b) TDMA/FDD and CDMA/FDD
c) FDMA/FDD and CDMA/FDD
d) FDMA/FDD only
Answer: b
Clarification: First generation cellular system used FDMA/FDD techniques. Second generation standards uses TDMA/FDD and CDMA/FDD multiple access techniques. 2G networks are digital.

2. Which one is not a TDMA standard of second generation networks?
a) GSM
b) IS-136
c) AMPS
d) PDC
Answer: c
Clarification: GSM (Global System Mobile), IS-136 (Interim Standard 136) and PDC (Pacific Digital Cellular) are the three most popular TDMA standards of second generation. AMPS is a first generation standard.

3. Which of the following is a CDMA standard of second generation network?
a) IS-95
b) IS-136
c) ETACS
d) EDGE
Answer: a
Clarification: Interim Standard 95 (IS-95) is the most popular CDMA standard of second generation networks. IS-136 is a TDMA standard of 2G. EDGE is a standard of 2.5G and ETACS is a 1G standard.

4. Popular 2G CDMA standard IS-95 is also known as ______________
a) CdmaOne
b) CdmaTwo
c) IS-136
d) IS-95B
Answer: a
Clarification: The popular 2G CDMA standard, Interim Standard (IS-95) is also known as CdmaOne. The 2.5G CDMA standard, IS-95B is called CdmaTwo. And IS-136 is a TDMA standard for 2G.

5. How many users or voice channels are supported for each 200 KHz channel in GSM?
a) Eight
b) Three
c) Sixty four
d) Twelve
Answer: a
Clarification: GSM is a circuit switched system that divides each 200 KHz channel into eight 25 KHz time slots, i.e. each radio channel is divided into eight voice channels.

6. How many voice channels are supported for each 30 KHz radio channel in IS-136?
a) Eight
b) Thirty
c) Three
d) Sixteen
Answer: c
Clarification: Interim Standard 136 (IS-136) was popularly known as North American Digital Cellular (NADC) system. It divides each 30 KHz radio channel into three time slots, each of 10 KHz.

7. How many users are supported in IS-95 for each 1.25 MHz?
a) Eight
b) Sixty four
c) Sixteen
d) Twenty five
Answer: b
Clarification: IS-95 supports upto 64 users which are orthogonally coded and simultaneously transmitted on each 1.25 MHz. The services of IS-95 standard are short messaging service, slotted paging, over-the-air activation, enhanced mobile station identities etc.

8. Which modulation technique is used by GSM?
a) GMSK
b) BPSK
c) QPSK
d) GFSK
Answer: a
Clarification: GSM uses a form of modulation known as GMSK (Gaussian Minimum Shift Keying). It is a form of modulation with no phase discontinuities and provides data transmission with efficient spectrum usage.

9. IS-95 uses which modulation technique?
a) GMSK
b) BPSK
c) QAM
d) AFSK
Answer: b
Clarification: IS- 95 uses BPSK (Binary Phase Shift Keying) with quadrature spreading. It is regarded as one of the most robust digital modulation technique and is used for long distance wireless communication.

10. IS-136 uses which modulation technique?
a) π/4 DQPSK
b) BPSK
c) GMSK
d) AFSK
Answer: a
Clarification: IS-136 uses π/4 DQPSK modulation technique. This technique allows a bit rate of 48.6 Kbit/s with 30 KHz channel spacing which gives a bandwidth efficiency of 1.62 bit/s/Hz.

11. Which is one of the disadvantages of 2G standards?
a) Short Messaging Service (SMS)
b) Digital modulation
c) Limited capacity
d) Limited Internet Browsing
Answer: d
Clarification: 2G technologies use circuit switched data modems that limits data users to a single circuit switched voice channel. The advantages of 2G network are that they are digital in nature and supports SMS service.

12. GSM (Global System for Mobile) was earlier also known as _____________
a) Group System Mobile
b) Global Special Meaning
c) Group Special Mobile
d) Global Special Mobile
Answer: c
Clarification: GSM was earlier known as Group Special Mobile. As it became more global, the meaning of acronym was changed to Global System for Mobile.

13. 2G CDMA standard, IS-95, was proposed by which company?
a) Nippon Telephone and Telegraph (NTT)
b) Qualcomm
c) Bellcore and Motorola
d) AT&T Bell Laboratories
Answer: b
Clarification: IS-95 was proposed by Qualcomm in early 1990s. Later it was adopted as a standard by Telecommunications Industry Association in TIA/EIA/IS-95 release published in 1995.

14. Which one of the following 2G standard is used in Japan?
a) IS-136
b) GSM
c) PDC
d) AMPS
Answer: c
Clarification: PDC (Personal Digital Cellular) was standardized by Japanese Ministry of Posts and Telecommunication in 1991. It is similar to IS- 136, but with 25 KHz voice channels to be compatible with the Japanese analog channels.

15. The 2G GSM technology uses a carrier separation of _____________
a) 1.25 MHz
b) 200 KHz
c) 30 KHz
d) 300 KHz
Answer: b
Clarification: The Global System for Mobile (GSM) uses a carrier separation of 200 KHz, each channel supporting upto eight users.

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Wireless & Mobile Communications Multiple Choice Questions on “Scattering”.

1. Scattering occurs when medium consists of objects with dimensions _______ compared to the wavelength.
a) Same
b) Small
c) Large
d) Very large
Answer: b
Clarification: Scattering occurs when the medium through which the wave travels consists of objects with dimensions that are small compared to the wavelength. But the number of obstacles per unit volume is large.

2. Scattered waves are produced at ________
a) Rough surface
b) Shadowed region
c) Smooth surface
d) Horizon
Answer: a
Clarification: Scattered waves are produced by rough surfaces, small objects or by other irregularities in the channel. In practice, foliage, street signs, and lamp posts induce scattering in a mobile communication system.

3. The actual received signal is ______ than what is predicted by reflection and diffraction model.
a) Weaker
b) Equal
c) Stronger
d) Very weak
Answer: c
Clarification: The actual received signal in a mobile radio environment is often stronger than what is predicted by reflection and diffraction model alone. This is because when a radio wave incidence upon the rough surface, reflected energy is spread out in all directions.

4. Scattered energy in all directions provides _________ at a receiver.
a) Channels
b) Loss of signal
c) No energy
d) Additional radio energy
Answer: d
Clarification: Objects such as lamp posts and trees tend to scatter energy in all directions. They provide additional radio energy at a receiver. Scattering may also refer to particle-particle collisions between molecules, atoms, electrons, photons and other particles.

5. Surface roughness are often tested using __________
a) Rayleigh criterion
b) Lawson criterion
c) Barkhausen stability criterion
d) Nyquist criterion
Answer: a
Clarification: Rough surface is often tested using a Rayleigh criterion. It defines the critical height of surface protuberances for a given angle of incidence. The Rayleigh criterion is the criterion for the minimum resolvable detail. The imaging process is said to be diffraction-limited when the first diffraction minimum of the image of one source point coincides with the maximum of another.

6. A surface is considered rough if protuberance is ________ than critical height.
a) Equal
b) Less
c) Greater
d) No relation
Answer: c
Clarification: A surface is considered rough if its minimum to maximum protuberance is greater than the critical height calculated using Rayleigh criterion. It is considered smooth if protuberance is less than critical height.

7. RCS of scattering object is defined as the ratio of _______
a) Power density of signal scattered to power density of radio wave incident
b) Power density of radio wave incident to power density of signal scattered
c) Power density of incident waves to power density of reflected wave
d) Power density of reflected wave to power density of incident waves
Answer: a
Clarification: The radar cross section of a scattering object is defined as the ratio of the power density of the signal scattered in the direction of the receiver to the power density of the radio wave incident upon the scattering object. It has unit of square meters.

8. Which equation is used to calculate the received power due to scattering for urban mobile radio system?
a) Laplace equation
b) Bistatic radar equation
c) Poisson’s equation
d) Maxwell equation
Answer: b
Clarification: For urban mobile radio systems, models based on bistatic radar equation is used to compute the received power due to scattering in the far field. This equation describes the propagation of wave in free space which impinges on a scattering object and then reradiated in the direction of receiver.

9. In ionosphere propagation, waves arriving at the receiving antenna using the phenomenon of _______
a) Scattering
b) Refraction
c) Diffraction
d) Radiation
Answer: a
Clarification: Scattering is a general physical process where some forms of radiation, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by one or more paths. It is due to localized non-uniformities in the medium through which they pass.

10. Power density is basically termed as ________ power per unit area.
a) Reflected
b) Refracted
c) Radiated
d) Diffracted
Answer: c
Clarification: Power density is the amount of power (time rate of energy transfer) per unit volume. It is also termed as radiated power per unit area. In energy transformers including batteries, fuel cells, motors, etc., power density refers to a volume. It is then also called volume power density.

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Wireless & Mobile Communications Multiple Choice Questions on “Pulse Shaping Techniques”.

1. Intersymbol interference (ISI) leads to ________ probability of the receiver for making an error in detecting the symbols.
a) Increased
b) Decreased
c) Zero
d) One
Answer: a
Clarification: ISI leads to increased probability of the receiver making an error in detecting a symbol. When rectangular pulses are passed through a bandlimited channel, the pulses will spread in time, and the pulse for each symbol will smear into the time intervals of succeeding symbols.

2. ISI is ________ by increasing channel bandwidth.
a) Maximized
b) Minimized
c) Zero
d) Infinite
Answer: b
Clarification: Increasing channel bandwidth is one of the method to minimize intersymbol interference. But mobile communication systems use minimal bandwidth, thus other methods to reduce ISI are desirable.

3. Why is pulse shaping technique used?
a) To increase ISI
b) To increase spectral width of modulated signal
c) To reduce ISI
d) To reduce power spectral density
Answer: c
Clarification: Pulse shaping techniques reduces the intersymbol interference. They are also used to reduce the spectral width of the modulated digital signal.

4. Who was the first to solve the problem of ISI?
a) Manchester
b) Faraday
c) Graham Bell
d) Nyquist
Answer: d
Clarification: Nyquist was the first to solve the problem of ISI. He overcome the problem of ISI while keeping the transmission bandwidth low. He observed that ISI can be completely nullified if at every instant, the response due to all symbols except the current symbol is equal to zero.

5. According to Nyquist, the impulse response of the overall communication system should have ______ decay with _______ magnitude for sample values not equal to zero.
a) Fast, small
b) Slow, small
c) Slow, large
d) Fast. Large
Answer: a
Clarification: According to Nyquist, the impulse response of the overall communication system should have fast decay with small magnitude for sample values not equal to zero. If the channel is ideal then it should be possible to realize approximate shaping filters at both transmitter and receiver.

6. Raised cosine filter does not satisfy Nyquist criteria.
a) True
b) False
Answer: b
Clarification: Raised cosine filter is the most popular pulse shaping filter used in mobile communication. It belongs to the class of filters that satisfy Nyquist criterion.

7. As the roll off factor in raised cosine rolloff filter __________ the occupied bandwidth ________
a) Increases, decreases
b) Decreases, constant
c) Increases, increases
d) Decreases, increases
Answer: c
Clarification: As the rolloff factor increases, the bandwidth of the filter also increases and the time sidelobe levels decrease in adjacent symbol slots. Thus, it implies that increasing rolloff factor decreases the sensitivity to timing jitter but increases the occupied bandwidth.

8. Gaussian pulse shaping filter follows Nyquist criterion.
a) True
b) False
Answer: b
Clarification: Gaussian pulse shaping filter uses non Nyquist technique. It is effective when used in conjunction with minimum shift keying (MSK) modulation, or other modulation which is well suited for power efficient nonlinear amplifiers.

9. Gaussian filter has zero crossings at adjacent symbol peaks.
a) True
b) False
Answer: b
Clarification: Nyquist filters have zero crossings at adjacent symbol peaks and a truncated transfer function. Gaussian filter does not follow Nyquist criterion and has a smooth transfer function with no zero crossings.

10. Which of the following is true for a Gaussian filter?
a) Large bandwidth
b) Minimum ISI
c) High overshoot
d) Sharp cut off
Answer: d
Clarification: The Gaussian filter has a narrow absolute bandwidth, and has a sharp cut off, low overshoot and pulse area preservation properties. This makes it attractive for use in mobile communication that uses nonlinear RF amplifiers.

11. Gaussian pulse shaping filter reduces the spectral occupancy and ISI.
a) True
b) False
Answer: b
Clarification: Gaussian pulse shaping does not satisfy Nyquist criterion for ISI cancellation. Thus, it reduces the spectral occupancy but there is degradation in the performance due to increased ISI.

12. Gaussian pulses are used when cost and power efficiency are major factors.
a) True
b) False
Answer: a
Clarification: Gaussian pulses are used when cost and power efficiency are major factors. But the bit error rates due to ISI are deemed to be lower than what is nominally required. Thus, there is a trade-off between desired RF bandwidth and irreducible error due to ISI.

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