DIGITAL TELECOM BIT IV, MCA (2004 June)
I. ONE-MARK QUESTIONS:
1. One of them is the characteristic of the channel
A) Bandwidth b) frequency c) noise d) all
2. One of them is the characteristic of the channel
A) Distortion b) transmission speed c) type of coding d) all
3. The goal of a communication system is to transfer information from one place to another by using ____ energy.
A) Magnetic b) electromagnetic c) wave d) none
4. The _____ waveform that carries the information is a replica of the information signal.
A) Magnetic b) channel c) electrical d) none
5. The electrical waveform follows the variations in sound pressure impinging on the ____.
A) Microphone b) camera c) modem d) none
6. The ____ waveform is continuous in time.
A) Digital b) analog c) digitized d) anodized
7. In digital systems the electrical waveform are _____ representations of the original.
A) Duplicate b) coded c) controllable d) none
8. _____ pulses have the advantage of being more easily distinguishable in the presence of noise and interference.
A) Control b) analog c) binary d) modular
9. The process of converting the original information into a data sequence is referred to as source ___.
A) Encoding b) decoding c) copying d) controlling
10. In ____ the waveforms are analog representation of binary data
A) Demodulation b) analog c) modulation d) decoding
11. If the input is an analog waveform, then part of the job of the source encoder is to first ___ it.
A) Duplicate b) control c) digitize d) none
12. The function of channel encoding is to alter the source code words in a controlled manner in order to ________errors at the receiving end.
A) Induce b) combat noise – induced c) increase d) complex
13. For transmission, a continuous waveform is modulated by the ____.
A) Channel code words b) demodulator c) multiplexer d) none
14. The unipolar and bipolar waveforms are referred to as ___ waveform.
A) Highpass b) lowpass c) bandpass d) none
15. The waveforms whether base band or band pass are referred to an as ___ waveform.
A) Analog b) digital c) triangular d) none
16. To recover the information contained in the transmitted waveform the receiver must have ____ functions.
A) Encoding b) controlling c) decoding d) none
17. ____ System has relatively few things that can be changed, beyond adjusting the signal level, filtering, and selecting the modulation parameters.
A) Analog b) digital c) physical d) none
18. Communication system have _____ that specially define how the communication is to start, finish and recover etc.
A) Layers b) bits c) protocol d) none
19. _____ provides framing and additional information that helps the receiver determine if the message, as received contains any errors.
A) Protocol b) format c) bytes d) none
20. ___ is the span of frequencies within the spectrum occupied by a signal and used by the signal for conveying information.
A) Format b) decoding c) bandwidth d) none
21. Human Voice bandwidth is ____
A) 3 to 4 KHz b) 20 to 20kHz c) 5 MHz d) none
22. Video requires a bandwidth of ___.
A) 10 MHz b) 4MHz c) 5 MHz d) none
23. The ___ is an important parameter in communication and it depends on the type of signal or type of application.
A) Baud width b) bandwidth c) band decoding d) none
24. To convey more information in short time we need more _____.
A) Bits b) bandwidth c) baud rate d) none
25. To convey video information we require ___ band width.
A) Less b) infinite c) more d) zero
26. The ____ has been defined as the basic unit of information in digital binary system.
A) Bit b) byte c) word d) nibble
27. The speed at which information is transferred from one computer or terminal to another in a digital system is called the ____ rate.
A) Analog b) information transfer c) byte d) pixel
28. The _____ rate or signaling rate is defined as the number of symbols per second. Which specifies how fast signal states are changing in the communication channel.
A) Bit b) baud c) system d) modem
29. In a four level digital signal each digital level corresponds to ____ data group.
A) Two bit b) three bit c) four bit d) none
30. The digital communication provides ____ immunity to noise when compared with the analog communication.
A) Lesser b) greater c) fixed d) convertible
31. Digital signals are inherently compatible with computers, which have potential to be ______ for signal enhancement and improved performance.
A) Stored b) retrieved c) processed d) all
32. In ____ high degree of security of information can be maintained in the course of transmission.
A) Digital b) analog c) multiplexing d) demultiplexing
33. Using digital communication it is easy to ____ diverse source of information into a common format.
A) Integrate b) demux c) divide d) none
34. Digital communication requires higher channel ______.
A) Bandwidth b) memory c) coding d) decoding
35. The _____ of bits leads to the difference between bit rate and baud rate.
A) Multiple levels b) grouping c) multiplexing d) decoding
36. The ____ represents a group of two or more bits.
A) Symbol b) byte c) parity bit d) none
37. In a four level digital signal each digital level corresponds to ___ bit data group.
A) Three b) four c) two d) none
38. In an eight level digital signal each digital level corresponds to ___ bit data group.
A) Three b) four c) six d) eight
39. When each symbol represents two bits then the effective information rate is ____ the signaling rate or baud rate.
A) Thrice b) twice c) four times d) none
40. A 1000 baud signal using four levels ( two bit symbols) is transferring information at a rate of _______bits/ sec .
A) 2000 b) 3000 c) 4000 d) 1000
41. If a system uses eight levels ( 3 bit symbol) a 1000 baud represents an information rate of ____bits/sec.
A) 2000 b) 3000 c) 4000 d) 1000
42. If 4 level signaling format is used for data transfer with 1000 bps , it represents __bauds.
A) 500 b) 1000 c) 100 d) both a & b
43. If 4 level signaling format is used for data transfer with 5000 bps,it represents __ bauds.
A) 2500 b) 1000 c) 3000 d) 250
44. If the system uses 8 levels then a 5000 bauds represents an information rate of ____bits/sec.
A) 15000 b) 1500 c) 150 d) 10000
45. If the system uses 16 levels then a 5000 bauds represents an information rate of ___bits/sec .
A) 200 b) 2000 c) 20000 d) 10000
2 MARKS
1. The correct layering of digital communication is represented by which of the following figures.
1) protocol 2) format 3) modulation 4) coding
coding coding format modulation
format protocol protocol protocol
modulation modulation coding format
a) 4 b) 3 c) 1 d) 1 & 2
2. If 100 bits gets transferred in 10 ms the information transfer rate is ____bits/sec .
A) 100 b) 1000 c) 10000 d) 10
3. If 1000 bits gets transferred in 10 ms the information transfer rate is ___ bits/sec .
A) 100000 b) 1000 c) 100 d) 5000
4. A 1000 bauds signal using four levels transfer information at a rate of ___ bits/sec. And if the system uses 8 levels a 1000 baud represents and information rate of ___ bits/sec .
A) 2000bits/sec , 4000 bits/sec b) 2000bits/sec , 3000bits/sec
C 2000bits/sec , 2500bits/sec d) 4000bits/sec , 10000bits/sec
5. Give the correct sequence
1) source encoder , modulator , LPF, channel encoder
2) source encoder, channel encoder , modulator, LPF
3) channel encoder , modulator , LPF , source encoder
4) source encoder , LPF , channel encoder, modulator
a) 1 b) 2 c) 3 d) 4
6. Give the correct sequence
1) LPF , detector, channel decoder, source decoder, information output
2) LPF, information output, source decoder , channel decoder, detector
3) LPF , source encoder channel decoder , channel encoder , detector
4) 1 and 2
a) 3 b) 2 c) 1 d) 4
7. Give the correct sequence
1) signal source, signal converter, transmitter
2) signal source, transmitter, signal converter
3) transmitter , converter , signal source
4) converter , signal generator, signal transmitter
a) 4 b) 3 c) 1 d) 1 & 3
8. Give the correct sequence
1) receiver , signal converter, listener
2) receiver , listener , signal converter
3) listener , receiver, signal converter
4) transmitter, listener, signal source
a) 4 b) 1) c) 3) d) 2)
FOUR MARKS
1). To recover the information contained in the transmitted waveforms , the receiver must have __ functions corresponding to the ___ functions in the transmitter , and in addition self synchronising systems, the receiver requires circuitry to recover correct ___ and in case of ______ the carrier frequency.
1) encoding, decoding , baseband, bit timing
2)decoding, encoding, bit timing , base band
3)bit timing, encoding, decoding, base band
4)bit timing , decoding, base band, encoding
a)1 b) 2 c) 3 d) 4
2. Choose the correct statements
1) digital communication provides greater immunity to noise compared to analog
2) digital signals can be stored , processed , retrieved , manipulated
3) low degree of security in digital communication
4) image processing is not possible in digital but possible in analog
5) easy to integrate diverse source of information in to common format
a) 1, 5,3 b) 1,2,5 c) 5,4,3 d) 1,2,3,5
3. Choose the correct statements
1) the goal of communication system is to send information from source to destination.
2) digital communication is one where the source is in the digital form
3) the number of symbols transmitted per second is called the baud rate
4) digital require less bandwidth since it has only 1’s and 0’s .
5) baud width is the range of frequencies
a) 1,2 b) 1,2,3 c) 3,4,1,5 d) 2,3,4
4. Choose the WRONG statement
1) bit has been defined as the basic unit of information in analog communication
2) the speed of communication in analog is measured in bits/sec .
3) to convey more information in short time we need less band width
4) band width is an important parameter in communication and it depends on the type of signal or type of application
5) human voice has a band width of 3 to 50 KHz
a) 1,2,3,4 b) 1,2,3,5 c) 3,5,2, d) all
5. In a simple digital communication system, the following options show sequences of operation, choose the correct one.
1) source encoding, noise – reduction, channel encoding, modulation, channel transmission ,detection & synchronization, channel decoding and source
2) source encoding, channel encoding, modulation, noise reduction, channel transmission, detection & synchronization ,channel decoding and source decoding
3) source encoding, modulation, noise reduction ,channel encoding, channel transmission, detection & synchronization channel decoding and source decoding
4) Source encoding, modulation, channel encoding, channel transmission, detection, & synchronization, noise reduction, channel decoding and source decoding.
A) 2 b) 3 c) 4 d) 1
Unit II
ONE MARK QUESTIONS:
1. Most of the times, the signals we have to communicate will be in the ___ form.
A) digital b) multiple c) analog d) decoded
2. As a first step in digitization , the analog signal is converted to a discrete time signal
By the process of ___.
A) sampling b) multiplexing c) demultiplexing d) modulation
3. The number of samples to be taken depends on the ____ frequency.
A) minimum b) maximum c) low d) none
4. ____ provides complete information regarding the number of samples to be taken and forms the basis of digitization of analog signals.
A) analog multiplication b) sampling theorem c) digital encoding d) none
5. The sampling theorem is the fundamental principle of ____ communication.
A) analog b) digital c) complex d) physical
6. Certain baseband signal consists of all frequencies below 20 KHz . The bandwidth of the signal is ____.
A) 20 KHz b) 30 KHz c) 100 KHz d) 5KHz
7. In communication, sampling is done in principle by multiplying the given analog signal by a _____pulse train whose frequency is equal to the sampling frequency.
A) broad b) narrow c) control d) none
8. If the base band signal consists of frequency components between 5KHz and 20KHz the Nyquist rate is ____.
A) 30KHz b) 60KHz c) 40KHz d) 15KHz
9. In the case PCM a series of N-bit codes usually _______are generated, each of which represents the approximate magnitude of the signal sample at instant.
A) analog codes b) electrical codes c) binary codes d) none
10. While ______ sufficient number of samples of the signal must be taken so that the signal is completely represented in its samples.
A) encoding b) decoding c) sampling d) none
11. Any signal which is continuous in time can be completely represented by its samples and can be recovered if the sampling frequency _____.
A) fs >=3fm b) fs<=2fm c) fs/fm=0 d) fs>=2fm
12. _____ showed that an analog signal can be perfectly reconstructed from its samples without any loss of original information.
A) H. Hertz b) Eienstein c) H.Nyquist d) Simon parker
13. The rate of sampling is equal to ____ the signal bandwidth.
A) thrice b) twice c) four times d) 10 times
14. If the message signal be m(t) band limited to fm and the sampling signal S(t) be a narrow pulse train of frequency then fs= ____
A) 1/Fs b) 1/Ts c) 2/Fs d) 5Fs
15. The multiplier output in the sampling process is the signal Y(t) =
A) S(t) Y(t) b) S(t) F(t) c) S(t) m(t) d) F(t) S(t)
16. The amplitudes of the pulse trains used for sampling varies in accordance with the amplitude of the ____ signal.
A) decoding b) message c) digital d) none
17. In case of PAM signals the top of the pulse may follow the message signal in which case it is called _____.
A) natural sampling b) multiplexing c) digitization d) none
18. The sampling signal is periodic with period time _____.
A) Fs b) Ts c) 2Fs d) 2fm
19. Ts = _____.
A) 1/ 3fm b) 1/2fm c) S(t)M(t) d) none
20. S(t) m(t) = _____.
A) dt /Ts m(t) + ……………. b) dt / Fs m(t) + ………..
C) nfs d) 2fm
21. A frequency spectrum is a plot of signal amplitudes versus the frequency.
A) true b) false c) true only for digital d) false only when the signal is digital
22. When fs greater than 2fm we get _____.
A) bandwidth b) guard band c) base band d) signal band
23. When fs is smaller than 2fm we get ______.
A) control signal b) base band c) overlapping spectrum d) analog spectrum
24. An increase in sampling rate above the Nyquist increases the width of the ____ band .
A) broad b) frequency c) guard d) encoding
25. Less sampling leads to a problem of ___.
A) alignment b) aliasing c) multiplexing d) decoding
26. The sampling frequency is slightly greater than Nyquist rate thus it is usually ____%.
A) 100 b) 20 c) 50 d) 15
27. ____ is a process of rounding off the values of the flat top samples to certain predetermined levels in order to make a finite and manageable number of levels.
A) digitization b) quantisation c) qualitative analysis d) sampling
28. In quantisation process the total signal range is divided into a number of ___.
A) bits b) bytes c) words d) sub ranges
29. In quantisation the number of sub range is chosen to be an integral power of ____.
A) 4 b) 3 c) 2 d) 5
30. Each subrange in quantisation has a ___ value.
A) final b) initial c) mid d) control
31. If the sampled value lies in a sub range, then the quantized value is equal to the quantisation level corresponding to that sub range.
A) true only if 1 volt is used b) false c) true only if 5 volts is used d) true
32. An analog signal has spectral components in the range 15 KHz to 20 KHz , then what is the Nyquist rate.
A) 40KHz b) 20KHz c) 10KHz d) 30KHz
34. If S is called as step size the expression S = _______.
A) (Vh-VL)/M b) M/ Vh c) 2fm d) fm/nfs
35. In quantisation at any instant of time the m(t) has the value of the quantisation level to which ___ is closest.
A) m(q) b) m(t) c) m(s) d) m(f)
36. Quantized signal is an approximation of the ___ signal .
A) digital b) binary c) analog d) computer
37. quantisation error is given by ____.
A) m(t) –m(t) b) m() –m(t) c) m(t) –mf(s) d) none
38. Quantisation error is always less than or equal to half of the ___ .
A) digital bits b) analog wave c) analog amplitude d) step size
39. quantisation error can be reduced by ___ the step size.
A) reducing b) increasing c) manipulating d) controlling
40. quantisation error is given by e =___.
A) m(t)- mk b) m(t) –nfs c) t(f) – mk(t) d) none
41. The quantisation error is dependent on the ____.
A) signal level b) current level c) step size d) voltage size
42. Any reduction in step size also reduces the ________ capacity of the system.
A) bits b) bytes c) noise suppression d) encoding functions
43. If fs is the sampling rate and n is the number of bits used to encode the PCM then the bit rate R = ___.
A) mfs b) nfs c) Bps d) m(t)
44. For no aliasing we require ___.
A) fs>=2B b) fs <=2B c) fs>=nfs d) none
45. With unipolar NRZ wave form having big rate R we need a minimum band width of ___.
A) 1/3 R b) ½ R c) ¼R d) 3/4R
46. Band width of PCM is ___.
A) ½ mfs b) (½)nfs c) 2fm d) 2fss
47. The process of multiplexing increases the ____ requirements for the transmission.
A) signals b) voltage c) bandwidth d) frequency
49. The T1 digital system is used to convey multiple signals over telephone lines using the ___ .
A) narrow band coaxial cables b) twisted pair cables
C) fiber cables d) wide band coaxial cables
50. Vocoders are voice coders which requires very ____ bandwidth.
A) high b) less c) sensitive d) sharp
TWO MARKS
1. When ____, we get overlapping spectrum and hence no filtering is possible to recover the ______ signal.
A) fs>=2fm, base band b) fs<2fm, base band
C) fs=2fm, analog d) fm>2fs, base band
2. An increase in _____ rate above the Nyquist rate increases the width of the guard band thereby making the ____ easy.
A) sampling , width b) encoding, multiplexing
C) decoding , encoding d) sampling , filter design
3. The signal to be sampled, is firstly ______ by passing it through a filter called ____ filter.
A) band limited, LPS b) band limited, HPS
C) band limited, anti-aliasing d) sampled , HPS
4. Any information signal consists of wide range of ___ therefore it becomes ____ to decide the sampling frequency.
A) signals, easy b) frequency, difficult
C) bits, easy d) control, controllable
5. The transition in _____, from one level to another is ____ unlike the signal , which makes a smooth transition.
A) m(t) , continuous b) m(s) , abrupt c) m(t), abrupt d) m(f), simple
6. The quantized voltage is converted into a uniquely identifiable ____ representing the quantized value by the ____.
A) analog code, decoder b) binary code, encoder
c) code , digital code d) none
7. The use of a ____ quantizer is equivalent to passing the base band signal through a compressor and then applying the compressed signal to a ____ quantizer.
A) uniform, non uniform b) nonuniform , analog
C) non uniform , uniform d) direct, indirect
8. If the sampling is at the Nyquist rate of 40 samples/sec corresponding to 20 Hz bandwidth and if we use 3 bits/samples to represent each voltage sample, the bit rate is ______.
A) 1.9 Kbits/sec b) 19Kbits/sec c) 190 Kbits/sec d) 40 samples /sec
9. If the sampling is at the Nyquist rate of 40 samples /sec corresponding to 20 Hz bandwidth and if we use 4 bits/samples to represent each voltage sample, then the bit rate is ______.
A) 2560bits / sec b) 1560bits/sec c) 2500bits/sec d) 10bits/sec
10. The composite signal is given by the equation S(t) = 5 sin¬¬¬¬3000pi t + 3 cos 12000 pi t
Then the Nyquist rate is ___.
A) 10Hz b) 500 Hz c) 50 Hz d) none
FOUR MARKS
1. An audio signal consisting of a sinusoidal term v(t) 3 cos 3140 t then find the signal to quantisation noise ratio when this is uantized using 10 bit PCM .
A) 69.9dB b) 79.8dB c 39.7dB d) none
2. How may bits are required to achieve a signal to quantisation noise ratio of at least 40dB if the signal is given by v(t) = 3 cos 3140t
A) 7 bits b) 8 bits c) 10 bits d) none
3. An analog voice frequency signal, which occupies a band of frequencies from 300 Hz to 3400 is to be transmitted over a binary PCM system employing 256 levels quantization levels. Calculate the minimum sampling frequency and the bandwidth if rectangular pulse with polar NRZ wave form is used for signalling.
A) 6800Hz, 32Kbits/sec b) 7200Hz, 43Kbits / sec
C) 6800Hz, 42 Kbits/sec d) 45KHz ,34k bits/sec
4. If signal is sampled at a rate of 8000 Hz then a complete frame of 192 bits occupies a time slot of ___ and the bit rate is equal to _____.
A) 125 micro seconds , 1.544Mb/sec b) 55 micro seconds, 15 MHz
C) 45 milli seconds , 1.544 Mb/sec d) none
UNIT III
1. Modulation is the process by which some characteristics of a ____ is varied in accordance with a modulating signal.
A) carrier b) encoder c) decoder d) multiplexer
2. In a binary phase shift keying the logic 1 is represented by ___
A) 180 degrees b) no change in the phase shift c) 90 degrees d) none
3. A ______ demodulation is a process of detecting the signal by multiplying the received signal by a locally generated or recovered carrier.
A) synchronous b) asynchronous c) control d) none
4. The combination of multiplier and an integrator for a period of Tb is called ___.
A) coordinator b) co-amplifier c) correlator d) carrier frequency
5. For a polar ___ wave form of the data stream with the amplitude Vb volts the peak power is given by Vb2Tb .
A) NRZ b) RZ c) filter d) none
6. The bandwidth for BPSK signal is ___.
A) 3fb b) 4fb c) 2fb d) none
7. quadrature phase shift keying is a technique where the transmission bandwidth required is ___.
A) 2fb b) fb c) 3fb d) none
8. Noise immunity in QPSK is ___ compared to PSK.
A) less b) higher c) equal d) infinite
9. The BFSK signal consisting of two frequencies f1 and f2 is applied to two ____ connected in parallel .
A) band pass filter b) band stop filter c) high pass filter d) low pass filter
10. In ____ the positive logic the binary 1 is represented by a high level and a binary zero by a zero level.
A) control polar b) polar c) unipolar d) none
TWO MARK QUESTIONS
1. Maximum data rates of rectangular shaped pulses that can be supported with out ______ in a channel having the transfer function H(f) is given by ____.
A) ISI , 2Bmin/(1+r ) b) ISI, 2B/(1+r)
C) ISI , 2Bmax / (1+r) d) ISI, 2Bmax / m(t)
2. For the same signal to noise ratio, bipolar requires half of the average power compared to the polar format, and the band width required for RZ twice as that of NRZ signaling.
A) true , false b) false, false c) false , true d) true , True
3. A rectangular pulse train can be expressed as an _____ number of sinusoidal frequency components using _____ .
A) infinite, Fourier b) finite, Nyquist c) finite, Fourier d) none
4. In analog receivers the attempt is made to reproduce and reconstruct the wave form as closely as possible , while in digital system the main emphasize is to remove the _____ noise as much as possible without much attention to the signal ___.
A) front , strength b) background, shape c) background , current d) none
5. The operation performed by the matched filter is called ___ and the signal to noise ratio is __.
A) quantizing, 10 b) correlator, maximised
c) filtering , minimised d) none
FOUR MARKS
1. Binary ‘1’ transmit frequencies of originate modem = ____ Hz and answer modem = ____Hz.
Binary ‘1‘receive frequencies of originate modem = _____Hz and answer modem = ____.
1) 1270,2225, 2225,1070 2) 1070, 2225, 1270,2225
3) 1270, 2225,2225,1270 4) 1 & 3
a) 4 b) 2 c) 3 d) 4
2. Arrange in proper order
1) source computer , telephone channel , FSK modem , destination computer
2) source computer, FSK answer modem , destination computer, FSK originate modem.
3) Source computer, FSK originate modem , telephone channel, FSK answer modem destination computer
4) Source computer, destination computer, FSK modem , telephone channel , FSK originate modem
A) 1 b) 2 c) 3 d) 4
3. Advantages of QPSK are
1) it needs less bandwidth compared to PSK
2) noise immunity is less than PSK
3) for the same bit rate the information transmission rate is higher
4) circuit complexity is more
5) requires two phase clocked quadrature carriers
6) noise immunity can decrease with bandwidth
7) noise immunity is higher compared to PSK
a) 1,3, 7 b) 2,3,4 c) 6,7 d) 4,5,6
4. Choose the correct statement
1) matched filter is an optimum filter, which increases the probability of bit error
2) we can represent digital data in various formats such as unipolar , polar, bipolar.
3) Demodulation can be of two types i.e. coherent & non-coherent
4) Modulation can be of only of two types i.e. amplitude & frequency
5) Modulation uses low frequencies to save spectrum and to send signals to large distances
6) In Manchester signaling a binary zero is represented by a negative half bit period pulse followed by a positive half period pulse.
7) In polar signaling binary 1’s and 0’s are represented by equal positive and negative levels.
A) 2,3,47, b) 4,5,3,2 c) 2,3,6,7 d) 5,6
5. Chose the incorrect statement
1) the correlator output is applied to a decision maker
2) synchronous demodulation is used for suppressed carrier system.
3) The binary coding provide advantage overcoming the adverse effects of noise in a transmission medium and it is easy to regenerate.
4) In digital system the probability of the bit error rate is more important than the signal shape.
5) A linear system which maximizes the output signal to noise ratio and provides optimum performance is called matched filter.
6) The BPSK signal is like an AM DSB suppressed carrier signal.
A) 6,7 b) 1,4 c) 3,4 d) none
UNIT FOUR
ONE MARK QUESTIONS:
1. The lack of security is basically because of the fact that all the conventional modulations
employ ____.
A) two single carrier b) one single carrier c) digital single d) none
2. The signal power is spread over a ____ bandwidth and appears like noise so that unauthorised receivers can neither demodulate it nor jam the signal
A) small b) fixed c) large d) phase
3. The interfering signals are transparent to the spread spectrum and the spectrum is transparent to the ____ signals.
A) high pass b) low pass c) band pass d) interfering
4. Spread spectrum is a means of transmission in which the data of interest occupies a bandwidth _____ the minimum bandwidth necessary to send the data.
A) less than b) in excess of c) having zero bandwidth than d) none
5. For getting a spread spectrum an additional ____ by a high rate discrete pseudorandom code is performed.
A) demodulation b) modulation c) multiplexing d) demultiplexing
6. The pseudorandom code sequence ,say c(t) must have a rate Rc much greater than the binary message rate Rm of the ______ signal m(t).
A) base band b) bandpass c) bandstop d) none
7. The processing gain in spread spectrum is given by G =____.
A) Rc/Rm b) Rm / Rc c) output / input d) Rm/ Nfs
8. The hopping pattern is determined or controlled by a ____ code sequence, and typically there will be 10 to 100 such distinct carries.
A) slow digital b) control c) pseudorandom d) double
9. In ____ hopping , in which the symbol rate of the FSK signal is an integer multiple of the hope rate.
A) fast frequency b) slow frequency c) infinite frequency d) none
10. In ____ several symbols are transmitted on each frequency hop.
A) fast frequency hopping b) slow frequency hopping
C) infinite frequency hopping d) none
11. In ____ the hop rate is an integral multiple of the symbol rate.
A) slow frequency hopping b) fast frequency hopping
C) control hopping d) none
12. In ___ the carrier frequency will change or hop several times during the transmission of one symbol.
A) slow frequency hopping d) fast frequency hopping
C) frequency changing d) none
13. The frequency hopping is accomplished by using a mixer circuit that consists of a multiplier followed by a ______ filter
A) band stop b) band reject c) band pass d) high pass
15. An individual FH/FSK tone of shortest duration is called a ___.
A) chip b) integrated circuit c) hop rate d) none
TWO MARK QUESTIONS
1. DSSS has _______ and FHSS has _______.
A) higher data rate , lower data rate b) larger data packets, lower cost
C) both a & b d) only a
2. DSSS avoids interfering source by _____ and FHSS avoids interfering source by _____.
A) spreading energy across band , multiplying the data
B) spreading energy across band , hopping around it
C) both a & b
D) encoding , decoding
3. DSSS has ____ and FHSS has ____.
A) quicker synchronization, long synchronization
B) slow synchronization, fast synchronization
C) double security , single security
D) slower access, faster access
4. In DSSS the first stage consists of a ____ and the second stage consists of ____.
A) spread spectrum modulator, product modulator
B) product modulator , spread spectrum modulator
C) high demodulation, microprocessor
D) micro controller , micro integrated chips
5. In a slow FHSS system, the bit rate Rb of the incoming binary data , the symbol rate Rs of the FSK symbol, the chip rate Rch and the hop rate Rh ar related by Rc =Rs = ___.
Where K= _____.
A) Rb / k >= Rh , sin h/r b) Rb / m >= Rs, log h/3
C) Rb / k >= Rh, log M d) log h/2, Rb / K >=Rh
FOUR MARKS QUESTIONS
1. Chose the correct statement
1) spread spectrum is used to implement secured communication
2) simple modulation techniques are not immune to external tapping or jamming of information.
3) Spread spectrum has the ability to reject interference whether conditional or unconditional
4) Spread spectrum is a technique where by an already modulated signal is modulated second time
5) The spectrum spreading is accomplished before transmission through the use of a code that is independent of the data sequence
A) 3,4 b) 4,5 c) 1,2,4,5 d) all
2. Choose the correct statement
1) entertainment radio channel uses spread spectrum technique
2) only one time modulation is enough in spread spectrum technique
3) The concept of spread spectrum is nearly same as normal communication
4) FHSS requires guard band
5) DSSS requires efficient linear amplifier
A) 1,2 5 b) 4,5 c) 1,4,5 d) all
3. In a spread spectrum modulation condition/conditions to be satisfied for the processing gain G is / are _____.
1) pseudorandom code rate should be at least greater than 100 times that of binary message rate
2) pseudorandom code rate and binary message rate are dependent on data sequence
3) use of fiber optic cables for increasing SNR
4) use of matched filters to reduce noise
5) pseudorandom code must be statistically independent of the message signal
a) 3,4 b) 1,2 c) 2,3 d) 1 , 5
4. Find the wrong statements:
1) DSSS has lower performance, and smaller data packets
2) DSSS is simple, less efficient FSK modulation
3) FHSS requires guard band, longer sync time
4) Cannot use moiré efficient non linear amplifier
5) DSSS avoids interfering source by spreading energy across band
6) DSSS and FHSS are generally same
A) 1,2,4,6 b) 2,3,4 c) 4,5,6 d) 1,2,3,4,6
