## Data-Communication

 Question 1
Quadrature Amplitude Modulation means changing both:
 A Frequency and phase of the carrier. B Frequency and Amplitude of the carrier. C Amplitude and phase of the carrier. D Amplitude and Wavelength of the carrier.
Question 1 Explanation:
Quadrature Amplitude Modulation means changing both amplitude and phase of the carrier.
 Question 2
In which modulation discrete values of carrier frequencies is used to transmit binary data?
 A Phase Shift Keying B Amplitude Shift Keying C Frequency Shift Keying D Disk Shift Keying
Question 2 Explanation:
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. The technology is used for communication systems such as telemetry, weather balloon radiosondes, caller ID, garage door openers, and low frequency radio transmission in the VLF and ELF bands. The simplest FSK is binary FSK (BFSK). BFSK uses a pair of discrete frequencies to transmit binary (0s and 1s) information. With this scheme, the "1" is called the mark frequency and the "0" is called the space frequency.
 Question 3
What is the basis of KVL?
 A Conservation of charge B Conservation of energy C Conservation of power D All of the options
Question 3 Explanation:
Kirchhoff’s Voltage Law
Kirchhoff’s Voltage Law (KVL) is Kirchhoff’s second law that deals with the conservation of energy around a closed circuit path.
 Question 4
Calculate the modulation percentage if the modulating signal is 8 V and carrier is of 12 V?
 A 50 B 67 C 150 D 33
Question 4 Explanation:
Modulation index(m) = Vm/Vc
= (8/12)*100
= 66.66.
 Question 5
A special PCM system uses 32 channels of data, one whose purpose is an identification (ID) and synchronization. The sampling rate is 4 kHz. The word length is 5 bits. Find the serial data rate.
 A 1280 kHz B 160 kHz C 320 kHz D 640 kHz
 Question 6
The resistance to be connected across terminal a, b for maximum power transfer to it is:
 A 40Ω B 5Ω C 2.5Ω D 10Ω
 Question 7
The period of a signal is 100ms. then the frequency of this signal in kilohertz is ____?
 A 10 B 10-1 C 10-2 D 10-3
Question 7 Explanation:
T=100ms
= (100)10-3 sec
=10-1 sec
F=1/T
F=1/10-1 Hz
F=1/(10-1 *103) KHz
F = 10-2 KHz
 Question 8
Which of the following is/are true w.r.t. applications of mobile computing ?
(A) Travelling of salesman
(B) Location awareness services
 A (A) true; (B) false. B Both (A) and (B) are true. C Both (A) and (B) are false. D (A) false; (B) true.
Question 8 Explanation:
Mobile computing main applications:
1.Portability
2. Connectivity
3.Social Interactivity
4. Individuality
5. IMobility
Travelling of salesman applicable to mobility of application.
Location awareness services applicable to Connectivity.
 Question 9
ECL is the fastest of all logic families. High speed in ECL is possible because transistors are used in difference amplifier configuration, in which they are never driven into ____.
 A Race condition B Saturation C Delay D High impedance
Question 9 Explanation:
→ ECL is the fastest of all logic families. High speed in ECL is possible because transistors are used in difference amplifier configuration, in which they are never driven into Saturation.
→ Emitter-coupled logic (ECL) is a high-speed integrated circuit bipolar transistor logic family. ECL uses an overdriven BJT differential amplifier with single-ended input and limited emitter current to avoid the saturated (fully on) region of operation and its slow turn-off behavior.
→ As the current is steered between two legs of an emitter-coupled pair, ECL is sometimes called current-steering logic (CSL), current-mode logic (CML) or current-switch emitter-follower (CSEF) logic.[
 Question 10
The frequency band allocated for the downlink in GSM is :
 A 960 - 985 MHz B 935 - 960 MHz C 920 - 945 MHz D 930 - 955 MHz
Question 10 Explanation:
There are 2 popular GSM methods.
1. GSM-900
2. GSM-1800
GSM-900 uses 890 - 915 MHz to send information from the Mobile Station to the Base
Transceiver Station (uplink) and 935 - 960 MHz for the other direction (downlink), providing 124 RF channels (channel numbers 1 to 124) spaced at 200 kHz. Duplex spacing of 45 MHz is used.
 Question 11
Theoretically, how many 1.25 MHz Carriers are there in a CDMA cell ?
 A 18 B 22 C 9 D 64
Question 11 Explanation:
→ In CDMA, multiple users share a 1.25 MHz channel by using orthogonal spreading codes (Walsh codes)
→ IS-95a standard designed for AMPS cellular band
→ Each cellular provider is allocated 25 MHz spectrum and ten 1.25-MHz CDMA duplex channels if A AMPS Band provider, 9 if B band provider
 Question 12
The frequency reuse plan is divided into cell grouping using how many cells, where the number of cells equals N ?
 A 3 B 10 C 7 D 21
Question 12 Explanation:
The cluster size N = 7 and the frequency reuse factor is 1/7 since each cell contains one-seventh of the total number of available channels.
Total cells=7*3
=21
Frequency reuse concept, cells with the same letter use the same set of frequencies. A cell cluster is outline in blue color and replicated over the converge area.
 Question 13
Which interim standard describes inter-switching networking ?
 A IS - 54 B IS - 95 C DS - 45 D ANSI - 41
Question 13 Explanation:
→ Interim Standard 95 (IS-95) was the first ever CDMA-based digital cellular technology.
→ The IS-95 standards describe an air interface, a set of protocols used between mobile units and the network.
→ IS-95 is widely described as a three-layer stack, where L1 corresponds to the physical (PHY) layer, L2 refers to the Media Access Control (MAC) and Link-Access Control (LAC) sublayers, and L3 to the call-processing state machine.
 Question 14
The mechanism with which several uses can share a medium without interference is :
 A Frequency modulation B Amplitude modulation C Multiplexing D None of these
Question 14 Explanation:
Multiplexing is a method by which multiple analog or digital signals are combined into one signal over a shared medium. It can share a medium without interference.
 Question 15
A data cube C, has n dimensions, and each dimension has exactly p distinct values in the base cuboid. Assume that there are no concept hierarchies associated with the dimensions. What is the maximum number of cells possible in the data cube, C?
 A p​ n B p C (2​ n​ - 1)p+1 D (p + 1)​ n
Question 15 Explanation:
Option-A:​ This is the maximum number of distinct tuples that you can form with p distinct values per dimensions.
Option-B:​ You need at least p tuples to contain p distinct values per dimension. In this case no tuple shares any value on any dimension.
Option-C:​ The minimum number of cells is when each cuboid contains only p cells, except for the apex, which contains a single cell.
Option-D:​ We have p+1 because in addition to the p distinct values of each dimension we can also choose ∗.
 Question 16
Four channels are multiplexed using TDM. If each channel sends 100 bytes/second and we multiplex 1 byte per channel, then the bit rate for the link is __________.
 A 400 bps B 800 bps C 1600 bps D 3200 bps
Question 16 Explanation:
Given data,
-- 4 channels are multiplexed using TDM
-- Multiplex 1 byte per channel. So, total 4 bytes=4 channels.
-- Each channel sends 100 bytes/sec
-- Bit rate=?
Bit rate= 100 * 4 bytes(1 byte=8 bits)
= 100 * 4 *8 (we are converting into bits because we are finding bit rate)
= 3200 bps
 Question 17
In a typical mobile phone system with hexagonal cells, it is forbidden to reuse a frequency band in adjacent cells. If 840 frequencies are available, how many can be used in a given cell?
 A 280 B 110 C 140 D 120
Question 17 Explanation:
-- Mobile phone system with hexagonal( equals to 6) cells
-- 840 frequencies are available.
-- How many can be used in a cell?
In this we need maximum 3 unique cells are required.
Association
Disassociation
Error correction
Integration
Question 18 Explanation:
→ Wireless LANs are use high frequency radio waves instead of cables for connecting the devices in LAN. Users connected by WLANs can move around within the area of network coverage. Most WLANs are based upon the standard IEEE 802.11 or WiFi.
→ A wireless access point (WAP), or more generally just access point (AP), is a networking hardware device that allows other Wi-Fi devices to connect to a wired network.
→ Wireless access point in 802.11 WLAN services are association, association and Integration.
 Question 19
The _____ measures the relative strengths of two signals or a signal at two different points
 A frequency B decibel C Attenuation D throughput
Question 19 Explanation:
Decibel (dB), unit for expressing the ratio between two physical quantities, usually amounts of acoustic or electric power, or for measuring the relative loudness of sounds. One decibel (0.1 bel) equals 10 times the common logarithm of the power ratio
 Question 20
The process of converting the analog sample into discrete form is called
 A Modulation B Multiplexing C Quantization D Sampling
Question 20 Explanation:
Sampling is the process of recording an analog signal at regular discrete moments of time.
sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave (a continuous signal) to a sequence of samples (a discrete-time signal).
Quantization in digital signal processing, is the process of mapping input values from a large set (often a continuous set) to output values in a (countable) smaller set, often with a finite number of elements.
The sampling rate fs is the number of samples per second.
The time interval between samples is called the sampling interval Ts=1/fs
 Question 21
The astable multivibrator has
 A two quasi stable states B two stable states C one stable and one quasi-stable state D none of these
Question 21 Explanation:
A multivibrator is an electronic circuit used to implement a variety of simple two-state devices such as relaxation oscillators, timers and flip-flops. It consists of two amplifying devices (transistors, vacuum tubes or other devices) cross-coupled by resistors or capacitors.
 Question 22
A stable multivibrator are used as
 A comparator circuit B squaring circuit C frequency to voltage converter D voltage to frequency converter
Question 22 Explanation:
● A multivibrator is a one type of electronic circuit, that is used to implement a two state system like flip-flops, timers and oscillators.
● Multivibrators are classified into three types based on the circuit operation, namely Astable multivibrators, Bistable multivibrators and Monostable multivibrators.
● The astable multivibrator is not stable and it repeatedly switches from one state to the other. In monostable multivibrator, one state is stable and remaining state is unstable.
● When the power is turned ON consider the flip flop is cleared initially, then the o/p of the inverter will be high. The charging of the capacitor will be done using two resistors R1& R2. When the voltage of the capacitor goes above 2/3 Vcc, then the output of the higher comparator will be High, it changes the control flip flop
 Question 23
Which of the following is not a transceiver function?
 A Transmission and receipt of data B Checking of line voltages C Addition and subtraction of headers D Collision detection
Question 23 Explanation:
A transceiver is a device comprising both a transmitter and a receiver that are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter receiver.
 Question 24
Vestigial sideband most commonly used in radio transmission
 A radio transmission B telephony C television transmission D all of the above
Question 24 Explanation:
Limitation of single-sideband modulation being used for voice signals and not available for video/TV signals leads to the usage of vestigial sideband. A vestigial sideband (in radio communication) is a sideband that has been only partly cut off or suppressed. Television broadcasts (in analog video formats) use this method if the video is transmitted in AM, due to the large bandwidth used. It may also be used in digital transmission, such as the ATSC standardized 8VSB.
Vestigial sideband (VSB) is a type of amplitude modulation ( AM ) technique (sometimes called VSB-AM ) that encodes data by varying the amplitude of a single carrier frequency . Portions of one of the redundant sidebands are removed to form a vestigial sideband signal - so-called because a vestige of the sideband remains.
 Question 25
The diagram below depicts:
 A Sound in waveform B Wind frequency C Line of sight D Compressions on a map
Question 25 Explanation:
●The generic term waveform means a graphical representation of the shape and form of a signal moving in a gaseous, liquid, or solid medium.
●For sound, the term describes a depiction of the pattern of sound pressure variation (or amplitude) in the time domain
● The temporal frequencies of sound waves are generally expressed in terms of cycles (or kilocycles) per second. The simplest waveform is the sine wave, since it has only one frequency associated with it. The sound waves associated with, say, music, are constantly varying.
 Question 26
The diagram below represents
 A Resolution B Vibration C Reverberation D Frequency
Question 26 Explanation:
● Reverberation, in psychoacoustics and acoustics, is a persistence of sound after the sound is produced.
● A reverberation, or reverb, is created when a sound or signal is reflected causing a large number of reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, people, and air.
 Question 27
The process of taking a snapshot of the waveform at regular intervals and representing it as a binary number is known as
 A Sampling B Standard Assessment C Sequential Formatting D Sound Structure
Question 27 Explanation:
Digital sampling is the recording of a sound using a string of numbers to represent the sound. 1s and 0s. These numbers are called samples.
 Question 28
The percentage resolution of an eight bit D/A converter is
 A 0.39% B 0.38% C 0.50% D 0.51%
Question 28 Explanation:
→ An eight-bit D/A converter have 2​ 8​ -1 resolvable levels which is nothing but 255 levels.
→ Percentage resolution is (1/255)×100=0.39%
 Question 29
A___ multivibrator circuit is one in which both LOW and HIGH output states are stable
 A Monostable B Bistable C Multistable D Tristable
Question 29 Explanation:
● The Bistable Multivibrator is another type of two state device.
● Bistable Multivibrators have TWO stable states (hence the name: “Bi” meaning two) and maintain a given output state indefinitely unless an external trigger is applied forcing it to change state.
 Question 30
Refer to the monostable multibrator circuit in the figure below.

The trigger terminal(pin 2 of the IC) is driven by a symmetrical pulsed waveform of 10kHz. Determine the duty cycle of the output waveform.
 A 0.56 B 0.55 C 0.57 D 0.58
Question 30 Explanation:
 Question 31
The diagram below represents
 A Moore’s law B Newton raphson method C Boyle’s law D Gregor law
Question 31 Explanation:
Moore's law is the observation that the number of transistors in a dense integrated circuit doubles about every two years.
 Question 32
The closeness of the recorded version to the original sound is called
 A Fidelity B Digitization C Sampling D Nyquist Theorem
Question 32 Explanation:
→ Digitization is the process of converting information into a digital format . In this format, information is organized into discrete units of data (called bit s) that can be separately addressed (usually in multiple-bit groups called bytes).
→ sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave (a continuous signal) to a sequence of samples (a discrete-time signal).
→ "fidelity" denotes how accurately a copy reproduces its source
 Question 33
When the object making the sound is moving towards you, the frequency goes up due to he waves getting pushed more tightly together. The opposite happens when the object moves away from you and the pich goes down. This phenomenon is called
 A Band Width B Doppler effect C Sound refraction D Vibrations
Question 33 Explanation:
→ The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source.
→ The Doppler effect is observed whenever the source of waves is moving with respect to an observer.
→ The Doppler effect can be described as the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching and an apparent downward shift in frequency for observers from whom the source is receding.
 Question 34
In MOSFET fabrication, the channel length is delayed during the process of
 A Isolation oxide growth B Channel stop implantation C Poly-Silicon gate patterning D Lithography step leading to the contact pad
Question 34 Explanation:
In MOSFET fabrication channel length is defined during Poly-Silicon gate patterning process
 Question 35
A carrier A​ c​ Cos(w​ C​ )t is frequency modulated by a signal E​ m​ Cos(w​ m​ )t. The modulation index is m​ f​ . the expression for the resulting FM signal is
 A A​ c,​ Cos[w​ c​ t+ m​ f​ Sin(w​ m​ )t] B A​ c​ Cos[w​ c​ t+ m​ f​ Cos(w​ m​ )t] C A​ c​ Cos[w​ c​ t+ ​ π ​ m​ f​ Sin w​ m​ t] D A​ c​ Cos[w​ c​ t+ 2 ​ π ​ m​ f​ E​ m​ Cos(w​ m​ )t/w​ m​ ]
Question 35 Explanation:
 Question 36
​ An ideal op-amp is an ideal
 A Voltage controlled current source B voltage controlled voltage source C current controlled current source D current controlled voltage source
Question 36 Explanation:
An ideal op-amp lead us to an op-amp with input resistance is infinite, so no current flows into either input terminal (the “current rule”) and that the differential input offset voltage is zero (the “voltage rule”).
Ideal operational amplification will have
➝ High input impedance ( R in = ∞ ) and low output impedance ( R out = 0 )

➝ R in = ∞ , so zero input current
➝ Infinite voltage gain
➝ So, it is a voltage controlled voltage source device.
 Question 37
What frequency range is used for microwave communications, satellite and radar?
 A Low frequency: 30 kHz to 300 kHz B Medium frequency: 300 kHz to 3 MHz C Medium frequency: 300 kHz to 3 MHz D Extremely high frequency: 30000 kHz
Question 37 Explanation:
→ Microwave signals are often divided into three categories:
1)Ultra high frequency (UHF) (0.3-3 GHz);
2)Super high frequency (SHF) (3-30 GHz); and
3)Extremely high frequency (EHF) (30-300 GHz).
→ In addition, microwave frequency bands are designated by specific letters.
→ The term “P band” is sometimes used for ultra high frequencies below the L-band. For other definitions, see Letter Designations of Microwave Bands
→ Lower Microwave frequencies are used for longer links, and regions with higher rain fade. Conversely, Higher frequencies are used for shorter links and regions with lower rain fade.
 Question 38
ICA(in computational intelligence) stands for__
 A Intermediate Computational Algorithms B Immediate Computational and Analysis C Independent Component Analysis D Independent Computational Algorithms
Question 38 Explanation:
In signal processing, independent component analysis is a computational method for separating a multivariate signal into additive subcomponents. This is done by assuming that the subcomponents are non-Gaussian signals and that they are statistically independent from each other.
 Question 39
The sequence of operation in which PCM is done :
 A Sampling, quantizing, encoding B Quantizing, sampling, encoding C Quantizing, encoding, sampling D None of the above
Question 39 Explanation:
● Pulse code modulation (PCM) is a digital scheme for transmitting analog data. The signals in PCM are binary; that is, there are only two possible states, represented by logic 1 (high) and logic 0 (low). This is true no matter how complex the analog waveform happens to be. Using PCM, it is possible to digitize all forms of analog data, including full-motion video, voices, music, telemetry, and virtual reality (VR).
● sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave (a continuous signal) to a sequence of samples (a discrete-time signal).
● Quantization in digital signal processing, is the process of mapping input values from a large set (often a continuous set) to output values in a (countable) smaller set, often with a finite number of elements.
● The encoder encodes the quantized samples. Each quantized sample is encoded into an 8-bit code word by using A-law in the encoding process.
 Question 40
A low pass filter is:
 A Passes the frequencies lower than the specified cutoff frequency B Used to recover signal from sampled signal C Rejects higher frequencies D All of the above
Question 40 Explanation:
A low-pass filter (LPF) is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filter design.
 Question 41
T1 carrier system is used:
 A For delta modulation B Industrial moise C For frequency modulated signals D None of the above
Question 41 Explanation:
The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission. The original transmission rate (1.544 Mbps) in the T1 line is in common use today in​ Internet service provider (ISP) connections to the Internet. Another level, the T3 line, providing 44.736 Mbps, is also commonly used by Internet service providers.
The T-carrier system is entirely digital, using pulse code modulation (PCM) and time-division multiplexing (TDM). The system uses four wires and provides duplex capability (two wires for receiving and two for sending at the same time). The T1 digital stream consists of 24 64-Kbps channels that are multiplexed.
 Question 42
Which of the following steps is/are not required for analog to digital conversion?
(a)Sensing
(b)Conversion
(c)Amplification
(d)Conditioning
(e)Quantization
 A (a) and (b) B (c) and (d) C (a), (b) and (e) D None of the above
Question 42 Explanation:

 Question 43
Which of the following is not a lossy compression technique?
 A JPEG B MPEG C FFT D Arithmetic coding
Question 43 Explanation:
JPEG( Joint Photographic Experts Group) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality
MPEG (Moving Picture Experts Group): It is a method of lossy compression for coding audio-visual information (e.g., movies, video, music).
Arithmetic coding is a form of entropy encoding used in lossless data compression. Normally, a string of characters such as the words "hello there" is represented using a fixed number of bits per character, as in the ASCII code. When a string is converted to arithmetic encoding, frequently used characters will be stored with fewer bits and not-so-frequently occurring characters will be stored with more bits, resulting in fewer bits used in total.
 Question 44
Consider a discrete memoryless channel and assume that H(x) is the amount of information per symbol at the input of the channel; H(y) is the amount of information per symbol at the output of the channel; H(x|y) is the amount of uncertainty remaining on x knowing y; and I (x; y) is the information transmission. Which of the following does not define the channel capacity of a discrete memoryless channel ?
 A max I(x; y) p(x) B max [H(y) – H(y|x)] p(x) C max [H(x) – H(x|y)] p(x) D max H(x|y) p(x)
Question 44 Explanation:
Transmission rate over a noisy channel:

→ H(X) is the amount of information per symbol at the input of the channel.

→ H(Y) is the amount of information per symbol at the output of the channel.

→ H(X|Y) is the amount of uncertainty remaining on X knowing Y.

The information transmission is given by:

I(X;Y) = H(X)−H(X|Y) bits/channel use

For an ideal channel X = Y, there is no uncertainty over X when we observe Y. So all the information is transmitted for each channel use: I(X;Y) = H(X) If the channel is too noisy, X and Y are independent. So the uncertainty over X remains the same knowing or not Y, i.e. no information passes through the channel: I(X;Y) = 0.

Capacity of a noisy channel:

 Question 45
Match the following:

 A (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i) B (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i) C (a)-(i), (b)-(iii), (c)-(ii), (iv)-(iv) D (a)-(ii), (b)-(i), (c)-(iv), (d)-(iii)
Question 45 Explanation:
Line coding→ Process of converting digital data to digital signal

Block coding→ Provide redundancy to ensure synchronization and inherits error detection

Scrambling→ Provides synchronization without increasing number of bits

Pulse code modulation→ A technique to change analog signal to digital data

 Question 46
A telephone conference call is an example of which type of communications ?
 A same time / same place B same time / different place C different time / different place D different time / same place
Question 46 Explanation:
A telephone conference call is an example of same time / different place type of communications.
 Question 47
Handoff is the mechanism that
 A transfer an ongoing call from one base station to another B initiating a new call C dropping an ongoing call D none of above
Question 47 Explanation:
Handoff is the mechanism that transfer an ongoing call from one base station to another.
Hard handover (or) Hard Handoff: Early systems used hard handoff. In a hard handoff, a mobile station only communicates with one base station. When the MS moves from one cell to another, communication must first be broken with the previous base station before communication can be established with the new one.
Soft handover (or) Soft Handoff: New systems use a soft Handoff. In this case, a mobile station can communicate with base stations at the same time. This means that, during handoff, a mobile station may continue with the new base station before breaking off from the old one.
 Question 48
The cellular frequency reuse factor for the cluster size N is
 A N B N2 C 1/N D 1/N2
Question 48 Explanation:
The frequency reuse factor is related to cluster size then the frequency reuse factor=1/N
 Question 49
The amount of uncertainty in a system of symbol is called
 A Bandwidth B Entropy C Loss D Quantum
Question 49 Explanation:
→ The amount of uncertainty in a system of symbol is called entropy. → Generally we can call entropy is disorder or uncertainty.
 Question 50
______ is a satellite based tracking system that enables the determination of person’s position.
 A Bluetooth B WAP C Short Message Service D Global Positioning System
Question 50 Explanation:
Global Positioning System(GPS) is a satellite based tracking system that enables the determination of person’s position.
There are 50 questions to complete.

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