Category: Wireless & Mobile Communications Objective Questions

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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Wireless & Mobile Communications Problems on “Parameters of Mobile Multipath Channels”.

1. Power delay profile is represented as plots of __________ with respect to fixed time delay reference.
a) Relative received power
b) Frequency
c) Transmitted power
d) Relative power
Answer: a
Clarification: Power delay profiles are generally represented as plots of relative received power as a function of excess delay with respect to a fixed time delay reference. They are calculated by averaging instantaneous power delay profile measurements over a local area.

2. Which of the following is not a multipath channel parameter that can be determined from power delay profile?
a) Mean excess delay
b) RMS delay spread
c) Excess delay spread
d) Doppler spread
Answer: d
Clarification: The mean excess delay, excess delay spread and rms delay spread are some multipath channel parameters. They can be determined from a power delay profile. Doppler spread is a measure of spectral broadening caused by time rate of change of mobile radio channel.

3. The time dispersive properties of wideband multipath channel are quantified by ______ and _______
a) Mean excess delay, rms delay spread
b) Doppler spread, rms delay spread
c) Doppler spread, coherence time
d) Mean excess delay, Doppler spread
Answer: a
Clarification: The time dispersive properties of wide band multipath channels are most commonly quantified by their mean excess delay and rms delay spread. Coherence time characterizes the time varying nature of frequency dispersiveness of mobile radio channel in time domain.

4. _______ is the square root of the second central moment of the power delay profile.
a) Mean excess delay
b) Rms delay spread
c) Excess delay spread
d) Coherence time
Answer: b
Clarification: The rms delay spread is the square root of the second central moment of the power delay profile. Many measurements are made at many local areas in order to determine a statistical range of multipath channel parameters for a mobile communication system over a large scale area.

5. Which of the following is the first moment of the power delay profile?
a) Rms delay spread
b) Excess delay spread
c) Mean excess delay
d) Doppler spread
Answer: c
Clarification: Mean excess delay is the first moment of the power delay profile. It is defined from a single power delay profile which is temporal or spatial average of consecutive impulse response measurements collected and averaged over a local area.

6. What is the order of typical values of rms delay spread in outdoor mobile radio channels?
a) Microseconds
b) Nanoseconds
c) Seconds
d) Minutes
Answer: a
Clarification: Typical values of rms delay spread are on the order of microseconds in outdoor mobile radio channels. For indoor mobile radio channels, they are of the order of nanoseconds.

7. Power delay profile and magnitude frequency response of a mobile radio channel are related through _______
a) Laplace Transform
b) Fourier Transform
c) S Transform
d) Wavelet Transform
Answer: b
Clarification: Power delay profile and magnitude frequency response of a mobile radio channel are related through the Fourier transform. Therefore, it is possible to obtain an equivalent description of the channel in the frequency domain using its frequency response characteristics.

8. ______ and coherence bandwidth are inversely proportional to one another.
a) Rms delay spread
b) Mean excess delay
c) Excess delay spread
d) Doppler spread
Answer: a
Clarification: The rms delay spread and coherence bandwidth are inversely proportional to one another. However, their exact relationship is a function of the exact multipath structure.

9. Coherence bandwidth is a statistical measure of range of frequencies over which channel is considered _______
a) Time dispersive
b) Frequency selective
c) Time variant
d) Flat
Answer: d
Clarification: Coherence bandwidth is a statistical measure of range of frequencies over which channel is considered flat. A flat channel is a channel which passes all spectral components with approximately equal gain and linear phase.

10. Which of the following describes time varying nature of the channel in a small scale region?
a) Delay spread and coherence time
b) Coherence bandwidth and delay spread
c) Doppler spread and coherence time
d) Delay spread and doppler spread
Answer: c
Clarification: Delay spread and coherence bandwidth describes the time dispersive nature of the channel in a local area. They do not give information about the time varying nature of the channel caused by either relative motion between the mobile and base station, or by movement of objects in the channel.

11. Doppler spread is a range of frequencies over which received Doppler spread is _______
a) Zero
b) Non zero
c) Infinite
d) One
Answer: b
Clarification: Doppler spread is a range of frequencies over which received Doppler spectrum is essentially non-zero. It is a measure of spectral broadening caused by time rate of change of mobile radio channel.

12. _______ is a statistical measure of time duration over which channel impulse response is invariant.
a) Coherence time
b) Doppler spread
c) Mean excess delay
d) Rms delay spread
Answer: a
Clarification: Coherence time is actually a statistical measure of the time duration over which the channel impulse response is essentially invariant. It quantifies the similarity of the channel response at varying times.

of Wireless & Mobile Communications Problems, .