Category: Wireless & Mobile Communications Objective Questions

Wireless & Mobile Communications Multiple Choice Questions on “Time Division Multiple Access (TDMA)”.

1. TDMA systems transmit in a continuous way.
a) True
b) False
Answer: b
Clarification: TDMA systems transmit data in a buffer and burst method. Thus, the transmission for any user is not continuous.

2. Preamble contains __________
a) Address
b) Data
c) Guard bits
d) Trail bits
Answer: a
Clarification: TDMA frame is made up of a preamble, an information message and the trail bits. In a TDMA frame, the preamble contains the address and synchronization information that both the base station and the subscribers use to identify each other.

3. __________ are utilized to allow synchronization of the receivers between different slots and frames.
a) Preamble
b) Data
c) Guard bits
d) Trail bits
Answer: c
Clarification: Guard times are utilized to allow synchronization of the receivers between different slots and frames. TDMA/FDD systems intentionally induce several time slots of delay between the forward and reverse time slots for a particular user.

4. Which of the following is not true for TDMA?
a) Single carrier frequency for single user
b) Discontinuous data transmission
c) No requirement of duplexers
d) High transmission rates
Answer: a
Clarification: TDMA share a single carrier frequency with several users, where each user makes use of non-overlapping time slots. The number of time slots per frame depends on several factors, such as modulation technique, available bandwidth etc.

5. Because of _______ transmissions in TDMA, the handoff process in __________
a) Continuous, complex
b) Continuous, simple
c) Discontinuous, complex
d) Discontinuous, simple
Answer: d
Clarification: Because of discontinuous transmissions in TDMA, the handoff process is much simpler for a subscriber unit, since it is able to listen for other base stations during idle time slots.

6. __________ synchronization overhead is required in TDMA due to _______ transmission.
a) High, burst
b) High, continuous
c) Low, burst
d) No, burst
Answer: a
Clarification: High synchronization overhead is required in TDMA systems because of burst transmissions. TDMA transmissions are slotted, and this requires the receivers to be synchronized for each data burst.

7. TDMA allocates a single time per frame to different users.
a) True
b) False
Answer: b
Clarification: TDMA has an advantage that it can allocate different numbers of time slots per frame to different users. Thus, bandwidth can be supplied on demand to different users by concatenating or reassigning time slots based on priority.

8. ___________ of TDMA system is a measure of the percentage of transmitted data that contains information as opposed to providing overhead for the access scheme.
a) Efficiency
b) Figure of merit
c) Signal to noise ratio
d) Mean
Answer: a
Clarification: Efficiency of TDMA system is a measure of the percentage of transmitted data that contains information as opposed to providing overhead for the access scheme. The frame efficiency is the percentage of bits per frame which contain transmitted data.

9. A TDMA system uses 25 MHz for the forward link, which is broken into radio channels of 200 kHz. If 8 speech channels are supported on a single radio channel, how many simultaneous users can be accommodated?
a) 25
b) 200
c) 1600
d) 1000
Answer: d
Clarification: For a TDMA system that uses 25 MHz for the forward link, which is broken into radio channels of 200 kHz. If 8 speech channels are supported on a single radio channel, 1000 simultaneous users can be accommodated as N = (25 MHz)/(200 kHz/8).

10. What is the time duration of a bit if data is transmitted at 270.833 kbps in the channel?
a) 270.833 s
b) 3 μs
c) 3.692 μs
d) 3.692 s
Answer: c
Clarification: If data is transmitted at 270.833 kbps in the channel, the time duration of a bit will be 3.692 μs, as T_b = (1/270.833 kbps) = 3.692 μs.

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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 & Answers (MCQs) on “Wireless Local Area Networks (WLANs)”.

1. What is the full form of WLAN?
a) Wide Local Area Network
b) Wireless Local Area Network
c) Wireless Land Access Network
d) Wireless Local Area Node
Answer: b
Clarification: WLAN stands for Wireless Local Area Network. Wireless networks is increasingly used as a replacement for wires within homes, buildings, and office settings through the deployment of wireless local area networks (WLANs).

2. WLANs use high power levels and generally require a license for spectrum use.
a) True
b) False
Answer: b
Clarification: WLANs use low power and generally do not require a license for spectrum. They provide ad hoc high data transmission rate connections deployed by individuals. In the late 1980s, FCC provided licence free bands for low power spread spectrum devices in ISM band, which is used by WLAN.

3. What is the name of 300 MHz of unlicensed spectrum allocated by FCC in ISM band?
a) UNII
b) Unlicensed PCS
c) Millimetre wave
d) Bluetooth
Answer: a
Clarification: FCC allocated 300 MHz of unlicensed spectrum in the ISM bands. This allocation is called the Unlicensed National Information Infrastructure (UNII) band. It was allocated for the express purpose of supporting low power license free spread spectrum data communication.

4. Which of the following specifies a set of media access control (MAC) and physical layer specifications for implementing WLANs?
a) IEEE 802.16
b) IEEE 802.3
c) IEEE 802.11
d) IEEE 802.15
Answer: c
Clarification: IEEE 802.11 is a set of media access control and physical layer specification for implementing WLAN computer communication. It was founded in 1987 to begin standardization of spread spectrum WLANs for use in the ISM bands.

5. Which of the following is not a standard of WLAN?
a) HIPER-LAN
b) HIPERLAN/2
c) IEEE 802.11b
d) AMPS
Answer: d
Clarification: AMPS is a standard of first generation network. HIPERLAN is a WLAN standard developed in Europe in mid 1990s. HIPERLAN/2 is also developed in Europe that provides upto 54 Mbps of user data.

6. Which of the following is the 802.11 High Rate Standard?
a) IEEE 802.15
b) IEEE 802.15.4
c) IEEE 802.11g
d) IEEE 802.11b
Answer: d
Clarification: IEEE 802.11b was a high rate standard approved in 1999. It provided new data rate capabilities of 11 Mbps, 5.5 Mbps in addition to the original 2 Mbps and 1 Mbps user rates of IEEE 802.11.

7. Which of the following spread spectrum techniques were used in the original IEEE 802.11 standard?
a) FHSS and DSSS
b) THSS and FHSS
c) THSS and DSSS
d) Hybrid technique
Answer: a
Clarification: Original IEEE 802.11 used both the approaches of FHSS (Frequency Hopping Spread Spectrum) and DSSS (Direct Sequence Spread Spectrum). But from late 2001s, only DSSS modems are used within IEEE 802.11.

8. Which of the following WLAN standard has been named Wi-Fi?
a) IEEE 802.6
b) IEEE 802.15.4
c) DSSS IEEE 802.11b
d) IEEE 802.11g
Answer: c
Clarification: The DSSS IEEE 802.11b standard has been named Wi-Fi by the Wireless Ethernet Compatibility Alliance. It is a group that promotes adoption of 802.11 DSSS WLAN.

9. Which of the following is developing CCK-OFDM?
a) IEEE 802.11a
b) IEEE 802.11b
c) IEEE 802.15.4
d) IEEE 802.11g
Answer: d
Clarification: IEEE 802.11g is developing CCK-OFDM (Complementary Code Keying Orthogonal Frequency Division Multiplexing) standards. It will support roaming capabilities and dual band use for public WLAN networks. It also has backward compatibility with 802.11b technologies.

10. What is the data rate of HomeRF 2.0?
a) 10 Mbps
b) 54 Mbps
c) 200 Mbps
d) 1 Mbps
Answer: a
Clarification: HomeRF 2.0 has data rate of the order of 10 Mbps. The FHSS proponents of IEEE 802.11 have formed the HomeRF standard that supports the frequency hopping equipment. In 2001, HomeRF developed a 10 Mbps FHSS standard called HomeRF 2.0.

11. HIPER-LAN stands for ____________
a) High Precision Radio Local Area Network
b) High Performance Radio Local Area Network
c) High Precision Radio Land Area Network
d) Huge Performance Radio Link Access Node
Answer: b
Clarification: HIPER-LAN stands for High Performance Radio Local Area Network. It was developed in Europe in mid 1990s. It was intended to provide individual wireless LANs for computer communication.

12. What is the range of asynchronous user data rates provided by HIPER-LAN?
a) 1-100 Mbps
b) 50-100 Mbps
c) 1-20 Mbps
d) 500 Mbps to 1 Gbps
Answer: c
Clarification: HIPER-LAN provides asynchronous user data rates of between 1 to 20 Mbps, as well as time bounded messaging of rates of 64 kbps to 2.048 Mbps. It uses 5.2 GHz and 17.1 GHz frequency bands.

13. What is the name of the European WLAN standard that provides user data rate upto 54 Mbps?
a) UNII
b) WISP
c) MMAC
d) HIPERLAN/2
Answer: d
Clarification: HIPERLAN/2 has emerged as the next generation European WLAN standard. It provides upto 54 Mbps of user data to a variety of networks. The networks includes the ATM backbone, IP based networks and the UMTS network.

14. What is WISP?
a) Wideband Internet Service Protocol
b) Wireless Internet Service Provider
c) Wireless Instantaneous Source Provider
d) Wideband Internet Source Protocol
Answer: b
Clarification: WISP is wireless Internet Service Provider used to explore public LANs (publican). It builds a nationwide infrastructure of WLAN access points in selected hotels, restaurants or airports. It then charges a monthly subscription fee to users who wish to have always on Internet access in those selected locations.

15. The price of WLAN hardware is more than 3G telephones and fixed wireless equipment.
a) True
b) False
Answer: b
Clarification: As, WLAN could be used to provide access for the last 100 meters into homes and businesses. Therefore, the price of WLAN hardware is far below 3G telephones and fixed wireless equipment.

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Wireless & Mobile Communications Interview Questions and Answers for Experienced people on “Impulse Response Model of a Multipath Channel”.

1. Small scale variations of a mobile radio signal are directly related to _______
a) Impulse response of mobile radio channel
b) Impulse response of base station
c) Frequency response of antenna
d) Frequency response of base station
Answer: a
Clarification: The small scale variations of a mobile radio signal can be directly related to the impulse response of mobile radio channel. he impulse response is a wideband channel characterization and contains all information necessary to simulate or analyze any type of radio transmission through the channel.

2. Impulse response is a narrowband characterization.
a) True
b) False
Answer: b
Clarification: Impulse response is a wideband channel characterization. It contains all information necessary to simulate or analyse any type of radio transmission through the channel.

3. Mobile radio channel can be modelled as a ______ filter.
a) Non-linear
b) Low-pass
c) Linear
d) Bandpass
Answer: c
Clarification: Mobile radio channel may be modelled as a linear filter with a time varying impulse response. The time variation is due to receiver motion in space. The filtering nature is caused by summation of amplitudes and delays of multiple arriving waves at any instant of time.

4. Impulse response does not play any role in characterization of the channel.
a) True
b) False
Answer: b
Clarification: Impulse response is a useful characterization of channel. It may be used to predict and compare the performance of different mobile communication systems and transmission bandwidth for a particular mobile channel condition.

5. Received signal can be expressed as ______ of transmitted signal with channel impulse response.
a) Addition
b) Subtraction
c) Division
d) Convolution
Answer: d
Clarification: The received signal y(t) can be expressed as a convolution of transmitted signal x(t) with impulse response of mobile radio channel. The variable t represents the time variations due to motion and the channel impulse multipath delay for fixed value of t.

6. Discretization of multipath delay axis of impulse response into equal time delay segments is called __________
a) Excess delay bins
b) Delay bins
c) Discrete bins
d) Digital bins
Answer: a
Clarification: It is useful to discretize the multipath delay axis of the impulse response into equal time delay segments called excess delay bins. The technique of quantizing the delay bins determines the time delay resolution of the channel model.

7. Small scale received power is ________ of average powers received in each multipath component.
a) Log
b) Exponential
c) Multiplication
d) Sum
Answer: d
Clarification: The average small received power is the sum of the average powers received in each multipath component. This is the case if transmitted signal is able to resolve the multipath.

8. The received power of a wideband signal fluctuates significantly when a receiver is moved about a local area.
a) True
b) False
Answer: b
Clarification: Amplitude of individual multipath components does not fluctuate widely in local area. Therefore, the received power of a wideband signal does not fluctuate significantly when a receiver is moved about a local area.

9. Average power for a CW signal is _______ to average received power for a wideband signal in small scale region.
a) Equivalent
b) Two times
c) Four times
d) Ten times
Answer: a
Clarification: Average power for a CW signal is equivalent to average received power for a wideband signal in small scale region. This can occur when either the multipath phases are identically and independently distributed or when path amplitudes are uncorrelated.

10. The received local ensemble average power of wideband and narrowband signals are ________
a) Different
b) Equivalent
c) Not dependent
d) Double
Answer: b
Clarification: The received local ensemble average power of wideband and narrowband signals is equivalent. When the transmitted signal has bandwidth greater than bandwidth of the channel, the received power varies very little. However, if transmitted signal has very narrow bandwidth, large fluctuation occurs at receiver.

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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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