Category: Wireless & Mobile Communications Objective Questions

Wireless & Mobile Communications Multiple Choice Questions on “Digital European Cordless Telephone (DECT)”.

1. Cordless telephone standard, DECT stands for ____________
a) Discrete European Cordless Telephone
b) Digital European Cellular Telephone
c) Discrete European Cellular Telephone
d) Digital European Cordless Telephone
Answer: d
Clarification: The Digital European Cordless Telephone (DECT) is a universal cordless telephone standard. It was developed by the European Telecommunications Standard Institute (ETSI).

2. Which of the following is not true for DECT?
a) High traffic density
b) Long range telecommunication
c) Broad range of application
d) First pan European standard
Answer: b
Clarification: DECT provides a cordless communication framework for high traffic density, short range telecommunications. It covers a broad range of applications and environments.

3. DECT can be used by users in an in-building PBX.
a) True
b) False
Answer: a
Clarification: The main function of DECT is to provide local mobility to portable users in an in-building Private Branch Exchange (PBX). It provides excellent quality and services for voice and data applications.

4. The DECT system is based on __________ principles.
a) TCP
b) IP
c) OSI
d) AMPS
Answer: c
Clarification: The DECT system is based on OSI (Open System Interconnection) principles in a manner similar to ISDN. A control plane (C-plane) and a user plane (U-plane) use the services provided by the lower layers.

5. Which of the following layer consists of paging channel and control channel?
a) Physical layer
b) Network layer
c) Data link layer
d) MAC layer
Answer: d
Clarification: The MAC (Medium Access Control) layer consists of a paging channel and a control channel for the transfer of signalling information to the C-plane. The U-plane is served with channels for the transfer of user information.

6. Which of the following layer is responsible for providing reliable data links?
a) Physical layer
b) Network layer
c) Data link control layer
d) MAC layer
Answer: c
Clarification: The DLC (data link control) layer is responsible for providing reliable data links to the network layer. It divides up the logical and physical channels into time slots for each user.

7. __________ is the main signalling layer of DECT.
a) Physical layer
b) Network layer
c) Data link layer
d) MAC layer
Answer: b
Clarification: The network layer is the main signalling layer of DECT. It is based on GSM and ISDN (layer 3) protocols. It provides call control and circuit switched services selected from one of the DLC services.

8. Which of the following supports the physical layer of DECT common air interface?
a) Portable Handset
b) Network specific Interface Unit
c) Radio Fixed Part
d) Cordless controller
Answer: c
Clarification: RFP (Radio Fixed Part) supports the physical layer of the DECT common air interface. Every RFP covers one cell in the microcellular system. A full duplex operation is achieved using TDD.

9. ________ supports the call completion facility in a multihandset environment.
a) Portable Handset
b) Network specific Interface Unit
c) Radio Fixed Part
d) Cordless controller
Answer: b
Clarification: Network specific Interface Unit supports the call completion facility in a multihandset environment. The interface recommended by the CCITT is the G.732 based on ISDN protocols.

10. __________ is a third generation Personal Communication System.
a) PACS
b) AMPS
c) IS-95
d) GSM
Answer: a
Clarification: PACS (Personal Access Communication Systems) is a third generation Personal Communication System. It was originally developed and proposed by Bellcore in 1992.

11. _________ is also known as Japanese Digital Cellular.
a) PACS
b) AMPS
c) PDC
d) GSM
Answer: c
Clarification: PDC (Pacific digital cellular) is also known as Japanese Digital Cellular. It was developed in 1991 to provide for needed capacity in congested cellular bands in Japan.

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Wireless & Mobile Communications Multiple Choice Questions on “Small- Scale Multipath Measurements”.

1. Which of the following is not a small scale multipath measurement technique?
a) Indirect pulse measurement
b) Direct pulse measurement
c) Spread spectrum sliding correlator measurement
d) Swept frequency measurement
Answer: a
Clarification: Because of the importance of multipath structure in determining the small scale fading effects, a number of wideband channel sounding techniques have been developed. These are direct pulse measurement, spread spectrum sliding correlator and swept frequency measurement.

2. Direct RF pulse systems are complex.
a) True
b) False
Answer: b
Clarification: Direct RF pulse systems have a very attractive system. They lack complexity because of the use of off the shelf equipment. This system can also provide a local average power delay profile.

3. What is the main disadvantage of RF pulse system?
a) Complexity
b) Not real time
c) Interference and noise
d) Simplicity
Answer: c
Clarification: The main problem with RF pulse system is that it is subject to interference and noise. This is due to wide passband filter required for multipath time resolution.

4. Why is the phase of individual multipath components are not received in RF Pulse system?
a) Due to use of duplexer
b) Due to use of ADC
c) Due to use of flip flops
d) Due to use of envelope detector
Answer: d
Clarification: Another disadvantage of RF pulse system is that phase of individual multipath components are not received due to use of an envelope detector. However, use of a coherent detector permits measurement of the multipath phase using this technique.

5. Spread spectrum sliding correlator has better ________ in comparison to RF pulse system.
a) Dynamic range
b) Frequency
c) Power density
d) Structure
Answer: a
Clarification: While the probing signal may be wideband, it is possible to detect the transmitted signal using a narrowband receiver preceded by a wideband mixer. Thus, it improves the dynamic range of the system in comparison to RF pulse system.

6. If a PN sequence has chip duration of T_c, then chip rate is given by ___________
a) T_c
b) 1/T_c
c) 2 T_c
d) T_c²
Answer: b
Clarification: In a spread spectrum channel sounder, a carrier signal is spread over a large bandwidth. It is done by mixing it with a binary pseudo number (PN) sequence having a chip duration of Tc and chip rate of 1/T^c.

7. The maximal length of PN sequence, the sequence length for n number of shift register is ______
a) 2ⁿ
b) 1/2ⁿ
c) 2ⁿ – 1
d) 2ⁿ + 1
Answer: c
Clarification: For a maximal length pseudo number (PN) sequence, the sequence length is 2ⁿ – 1. Here, n is the number of shift registers in the sequence register.

8. The ratio between transmitter chip clock rate and the difference between the transmitter chip clock and difference between transmitter and receiver chip clock rates is called ___________
a) Slide factor
b) Chip factor
c) Reuse factor
d) Shape factor
Answer: a
Clarification: The slide factor is defined as ratio between transmitter chip clock rate and the difference between the transmitter chip clock and difference between transmitter and receiver chip clock rates. It is unit less quantity.

9. Which of the following is not an advantage of spread spectrum channel sounding system?
a) Rejection of passband noise
b) Real time
c) Coverage range improvement
d) Less transmitter power required
Answer: b
Clarification: One of the main advantage of spread spectrum channel sounding system is ability to reject passsband noise. Thus, it improves the coverage range for a given transmitter power. Also, required transmitter powers can be considerably lower compared to direct pulse systems due to inherent processing gain.

10. Which of the following is a disadvantage of spread spectrum channel sounding system?
a) Passband noise
b) Less coverage area
c) Large transmitter power required
d) Not in real time
Answer: d
Clarification: A disadvantage of spread spectrum system as compared to direct RF pulse system, is that measurements are not made in real time. But they are compiled as the PN codes slide past one another.

11. There is no relationship between time domain and frequency domain techniques.
a) True
b) False
Answer: b
Clarification: There is a dual relationship between time domain and frequency domain techniques. Therefore, it is possible to measure the channel impulse response in the frequency domain. Frequency domain channel sounder is used for measuring channel impulse response.

12. Transmissivity is a _________ domain response.
a) Time
b) Frequency
c) Time-frequency
d) Spatial
Answer: b
Clarification: Transmissivity response is a frequency domain response. It is a frequency domain representation of channel impulse response. This response is then converted to the time domain using inverse discrete Fourier transform.

13. Frequency domain channel sounding technique do not require hard wired synchronization between transmitter and receiver.
a) True
b) False
Answer: b
Clarification: Frequency domain channel sounding system requires careful calibration and hardwired synchronization between transmitter and receiver. However, this technique works well and indirectly provides amplitude and phase information in the time domain.

14. Frequency domain channel sounding system is _______ in nature.
a) Real time
b) Digital
c) Non real time
d) Analog
Answer: c
Clarification: Frequency domain channel sounding system makes measurements of non real time nature. For time varying channels, the channel frequency response can change rapidly giving an erroneous impulse response measurement.

15. Faster sweep time can be accomplished by ________
a) Increasing frequency steps
b) Increasing time slots
c) Reducing time slots
d) Reducing frequency steps
Answer: d
Clarification: A faster sweep time can be accomplished by reducing the number of frequency steps. But this sacrifices the time resolution and excess delay range in the time domain.

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Wireless & Mobile Communications Multiple Choice Questions on “Fundamentals of Equalization”.

1. Which of the following is not used to improve received signal quality over small scale times and distance?
a) Modulation
b) Equalization
c) Diversity
d) Channel coding
Answer: a
Clarification: Equalization, diversity and channel coding are the three techniques which are used to improve received signal quality and link performance over small scale times and distance. But, the approach, cost, complexity and effectiveness varies in wireless communication system.

2. Equalization is used to compensate __________
a) Peak signal to noise ratio
b) Intersymbol interference
c) Channel fading
d) Noises present in the signal
Answer: b
Clarification: Equalization compensate the intersymbol interference (ISI) created by multipath within time dispersive channels. An equalizer within a receiver compensates for the average range of the expected channel amplitude and delay characteristics.

3. Training and tracking are the operating modes of _________
a) Diversity techniques
b) Channel coding techniques
c) Equalization techniques
d) Demodulation techniques
Answer: c
Clarification: General operating modes of an adaptive equalizer includes training and tracking. A known fixed length training sequence is sent by the transmitter so that the receiver’s equalizer may adapt to a proper setting for minimum bit error rate detection.

4. An equalizer is said to be converged when it is properly _______
a) Trained
b) Tracked
c) Installed
d) Used
Answer: a
Clarification: When an equalizer has been properly trained, it is said to have converged. Equalizers are commonly used in digital communication systems where user data is segmented into short time blocks or time slots.

5. Time for convergence of an equalizer is not a function of _______
a) Equalizer algorithm
b) Equalizer structure
c) Time rate of change of multipath radio channel
d) Transmitter characteristics
Answer: d
Clarification: The timespan over which an equalizer converges is a function of the equalizer algorithm, the equalizer structure and the time rate of change of the multipath radio channel. Equalizers require proper retraining in order to maintain effective ISI cancellation.

6. Equalizer is usually implemented in __________
a) Transmitter
b) Baseband or at IF in a receiver
c) Radio channel
d) Modulator stage
Answer: b
Clarification: An equalizer is implemented at baseband or at IF in a receiver. Since the baseband complex envelope expression can be used to represent bandpass waveform, the channel response, the demodulated signal and adaptive equalizer algorithm are usually simulated and implemented at baseband.

7. Equalizer is ________ of the channel.
a) Opposite
b) Same characteristics
c) Inverse filter
d) Add on
Answer: c
Clarification: An equalizer is actually an inverse filter of the channel. The goal of equalization is to satisfy that the combination of the transmitter, channel and receiver be an all pass channel.

8. ______ controls the adaptive algorithm in an equalizer.
a) Error signal
b) Transmitted signal
c) Received signal
d) Channel impulse response
Answer: a
Clarification: The adaptive algorithm is controlled by the error signal. The error signal is derived by comparing the output of the equalizer and some signal which is either an exact scaled replica of the transmitted signal or represents a property of transmitted signal.

9. The adaptive algorithms in equalizer that do not require training sequence are called ________
a) Linear adaptive algorithms
b) Blind algorithms
c) Non-linear adaptive algorithms
d) Spatially adaptive algorithms
Answer: b
Clarification: Blind algorithms exploit the characteristics of the transmitted signal and do not require training sequence. These type of algorithm are able to acquire equalization through property restoral techniques of transmitted signal.

10. Which of the following is a blind algorithm?
a) Linear adaptive algorithms
b) Constant modulus algorithm
c) Non-linear adaptive algorithms
d) Spatially adaptive algorithms
Answer: b
Clarification: Blind algorithm technique uses algorithms such as the constant modulus algorithm (CMA) and the spectral coherence restoral algorithm (SCORE). CMA is used for constant envelope modulation and forces the equalizer weights to maintain a constant envelope on the received signal.

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Wireless & Mobile Communications Multiple Choice Questions on “Spread Spectrum Multiple Access”.

1. SSMA uses signals which have a transmission bandwidth that is smaller than the minimum required RF bandwidth.
a) True
b) False
Answer: b
Clarification: Spread spectrum multiple access (SSMA) uses signals which have a transmission bandwidth that is several orders of magnitude greater than the minimum required RF bandwidth.

2. PN sequence converts _______ signal to ______ signal.
a) Narrowband, wideband
b) Wideband, narrowband
c) Unmodulated, modulated
d) Low frequency, high frequency
Answer: a
Clarification: A pseudo-noise (PN) sequence converts a narrowband signal to a wideband noise like signal before transmission. SSMA provides immunity to multipath interference and robust multiple access capability.

3. SSMA is bandwidth efficient when used with a single user.
a) True
b) False
Answer: b
Clarification: SSMA is not very bandwidth efficient when used by a single user. However, since many users can share the same spread spectrum bandwidth without interfering with one another, spread spectrum systems become bandwidth efficient in a multiple user environment.

4. ___________ is a digital multiple access system in which carrier frequencies are varied in pseudorandom order.
a) CDMA
b) FCDMA
c) FHMA
d) SDMA
Answer: c
Clarification: Frequency hopped multiple access (FHMA) is a digital multiple access system in which the carrier frequencies of the individual users are varied in a pseudorandom fashion within a wideband channel.

5. If the rate of change of the carrier frequency is greater than the symbol rate, then the system is referred as ___________
a) Fast frequency hopping system
b) Slow frequency hopping system
c) Time division frequency hopping system
d) Code division multiple access system
Answer: a
Clarification: If the rate of change of the carrier frequency is greater than the symbol rate, then the system is referred as a fast frequency hopping system. If the channel changes at a rate less than or equal to the symbol rate, it is called slow frequency hopping.

6. A frequency hopped system does not provide security.
a) True
b) False
Answer: b
Clarification: A frequency hopped system provides a level of security, especially when a large number of channels are used. Since, an unintended receiver that does not know the pseudorandom sequence of frequency slots must retune rapidly to search for the signal it wishes to intercept.

7. All users in CDMA system uses __________ carrier frequency.
a) Different
b) Two
c) Ten
d) Same
Answer: d
Clarification: All users in CDMA system use the same carrier frequency and may transmit simultaneously. Each user has its own pseudorandom codeword which is approximately orthogonal to all other codewords.

8. ___________ problem occurs when many mobile users share the same channel.
a) Near-far
b) Activation
c) Line of sight
d) Windowing
Answer: a
Clarification: The near far problem occurs when many mobile users share the same channel. In general, the strongest received mobile signal will capture the demodulator at a base station.

9. In CDMA, symbol duration is ___________ than channel delay spread.
a) Equal
b) Greater
c) Slightly greater
d) Much less
Answer: d
Clarification: In CDMA, symbol (chip) duration is very short and usually much less than the channel delay spread. Thus, channel data rates are very high in CDMA systems.

10. ____________ is used to improve reception by collecting time delayed versions of the required signal.
a) RAKE receiver
b) Equalizer
c) Frequency modulator
d) High pass filter
Answer: a
Clarification: A RAKE receiver can be used to improve reception by collecting time delayed versions of the required signals. Since PN sequences have low autocorrelation, multipath which is delayed by more than a chip appear as noise.

11. ____________ arises from the fact that the spreading sequences of different users are not orthogonal.
a) Near-far problem
b) Line of sight
c) Windowing
d) Self jamming
Answer: d
Clarification: Self jamming arises from the fact that the spreading sequences of different users are not orthogonal. Hence, in the despreading of a particular PN code, non zero contributions to the receiver decision statistic for the desired user arise from the transmissions of other users in the system.

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Wireless & Mobile Communications Multiple Choice Questions on “Network Protocols”.

1. Several protocols for upper layers in bluetooth use _________
a) UDP
b) HSP
c) ITC
d) L2CAP
Answer: d
Clarification: L2CAP is Logical Link, Control Adaptation Protocol Layer. The logical unit link control adaptation protocol is equivalent to logical link control sub layer of LAN. The ACL link uses L2CAP for data exchange. The various function of L2CAP is segmentation and reassembly, multiplexing and quality of service.

2. Protocols are set of rules to govern _________
a) Communication
b) Standard
c) Metropolitan communication
d) Bandwidth
Answer: a
Clarification: A protocol is a set of rules that governs the communications between computers on a network. These rules include guidelines that regulate the characteristics of a network including access method, allowed physical topologies, types of cabling, and speed of data transfer.

3. An internet is a __________
a) Collection of WANS
b) Network of networks
c) Collection of LANS
d) Collection of identical LANS and WANS
Answer: b
Clarification: Internet is a massive network of networks, a networking infrastructure. It connects millions of computers together globally, forming a network in which any computer can communicate with any other computer as long as they are both connected to the Internet.

4. Checksum is used in Internet by several protocols although not at the _________
a) Session layer
b) Transport layer
c) Network layer
d) Data link layer
Answer: d
Clarification: The checksum is used in the Internet by several protocols although not at the data link layer. Like linear and cyclic codes, the checksum is based on the concept of redundancy. Several protocols still use the checksum for error detection.

5. In version field of IPv4 header, when machine is using some other version of IPv4 then datagram is __________
a) Discarded
b) Accepted
c) Interpreted
d) Interpreted incorrectly
Answer: a
Clarification: A 4 bit field defines the version of IPv4 protocol. This field tells the software running in the processing machine that the datagram has the format of version 4. If the machine is using some other version of IPv4, the datagram is discarded rather than interpreted incorrectly.

6. Network layer at source is responsible for creating a packet from data coming from another ________
a) Station
b) Link
c) Node
d) Protocol
Answer: d
Clarification: ‘The network layer at the source is responsible for creating a packet from the data coming from another’ protocol (such as a transport layer protocol or a routing protocol). The network layer is responsible for checking its routing table to find the routing information.

7. Header of datagram in IPv4 has _________
a) 0 to 20 bytes
b) 20 to 40 bytes
c) 20 to 60 bytes
d) 20 to 80 bytes
Answer: c
Clarification: IP header length is a minimum of 20 bytes and a maximum of 60 bytes. The minimum value for this field is 5, which is a length of 5×32 = 160 bits = 20 bytes. Being a 4-bit value, the maximum length is 15 words (15×32 bits) or 480 bits = 60 bytes.

8. In IPv4 layer, datagram is of ________
a) Fixed length
b) Variable length
c) Global length
d) Zero length
Answer: b
Clarification: ‘IPv4 is a connectionless protocol used for packet switched networks. It operates on best effort delivery model, in which neither delivery is guaranteed, nor proper sequencing or avoidance of duplicate delivery is assured. The size of the datagram header can be of variable length from 20 bytes to 60 bytes.’

9. In IPv4, service type of service in header field, first 3 bits are called ______
a) Type of service
b) Code bits
c) Sync bits
d) Precedence bits
Answer: d
Clarification: The 8-bit ToS (type of service) in IPv4 uses 3 bits for IP Precedence, 4 bits for ToS with the last bit not being used. The 4-bit ToS field, although defined, has never been used.

10. Which is a link layer protocol?
a) ARP
b) TCP
c) UDP
d) HTTP
Answer: b
Clarification: ‘In computer networking, the link layer is the lowest layer in the Internet Protocol Suite. It is commonly known as TCP/IP, the networking architecture of the Internet. It is described in RFC 1122 and RFC 1123.’

11. Which protocol is commonly used to retrieve email from a mail server?
a) FTP
b) IMAP
c) HTML
d) TELNET
Answer: b
Clarification: ‘The Internet Message Access Protocol (IMAP) is a mail protocol used for accessing email on a remote web server from a local client. IMAP is the most commonly used Internet mail protocols for retrieving emails. It is supported by all modern email clients and web servers.’

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