尔雅Fundamentals of Wireless Communications课后答案(学习通2023题目答案)
91 min read尔雅Fundamentals of Wireless Communications课后答案(学习通2023题目答案)
quiz
1、尔雅Wireless communication is 课后a communication method that uses the characteristics of electromagnetic waves to propagate in space to exchange .
A、energy
B、答案information
C、学习matter
D、通题both matter and energy
2、目答Which one has the longest wavelength (i.e. the lowest frequency),尔雅 among the following electromagnetic waves?
A、Microwave
B、课后Infrared ray
C、答案Visible light
D、学习Ultrashort wave
3、通题Which description of the characteristics of millimeter wave communication is 目答incorrect?
A、It has wide available spectrum.
B、尔雅It has large transmission loss and short transmission distance.
C、课后The答案 RF devices are easy to be miniaturized.
D、The cost of RF devices is low.
4、The physicist who first confirmed that electromagnetic waves can propagate across space via experiments is
A、Michael Faraday
B、Isaac Newton
C、James Clerk Maxwell
D、Heinrich Rudolf Hertz
5、Which is NOT the wireless communications systems?
A、Satellite communication system
B、Optical fiber communication system
C、Cellular mobile communication system
D、Bluetooth communication system
6、Which is NOT the feature of the first generation cellular mobile communications (1G)?
A、Analog communications
B、Only carry voice services
C、Low cost
D、Bulky terminals
7、Which is NOT the standard of the third generation mobile communications (3G)?
A、GSM
B、WCDMA
C、TD-SCDMA
D、CDMA2000
8、Which one below does NOT belong to the millimeter wave band?
A、28 GHz
B、38 GHz
C、73 GHz
D、2.4 GHz
9、Who established information theory in 1948?
A、Martin Lawrence Cooper
B、Claude Elwood Shannon
C、Andrew J. Viterbi
D、Michael Faraday
10、Which is NOT the feature of broadcast/television communications system?
A、Unidirectional transmission
B、Wide coverage
C、Low cost
D、Able to call or be called
11、In 2019, _____ cellular mobile communications system is put into commercial use in China.
A、2G
B、3G
C、4G
D、5G
12、5G system application scenarios include .
A、enhanced mobile broadband communications (eMBB)
B、massive machine-type communications (mMTC)
C、ultra-reliable low latency communications (uRLLC)
D、Wide area coverage communications
13、In wireless communications, which characteristics of electromagnetic waves can be used to carry information.
A、Amplitude
B、Frequency
C、Polarization mode
D、Polarization mode
14、Who are the inventors of the radiotelegraph?
A、James Clerk Maxwell
B、Heinrich Rudolf Hertz
C、Alexander Stepanovich Popov
D、Guglielmo Marconi
15、Which are the features of satellite communications?
A、Wide coverage
B、The cost of building is not related to the communication distance
C、Good resistance
D、Low transmission latency
16、Which are the features of wireless local area network (WLAN)?
A、High transmission rate
B、Mainly use licensed frequency bands
C、Good compatibility
D、Miniaturization and low cost
17、Which are short-range wireless communication systems?
A、Bluetooth
B、RFID
C、UWB
D、NFC
18、Which statements about LTE are correct?
A、Including LTE FDD and TD-LTE two standards
B、High transmission rate
C、Flexible system deployment
D、Guaranteed quality of service
19、The goals of wireless communication include_____.
A、The goals of wireless communication include_____.
B、High transmission reliability
C、Low cost
D、Energy saving and environmental protection
homework
1、Please briefly describe the current challenges of wireless communications.
2、Please briefly describe the three major application scenarios of the 5th generation wireless communications (5G) and the main services?
3、Why are the frequency resources of wireless communications mostly authorized and managed by the governments, and cannot be used at will?
4、Please briefly describe the cellular mobile communication system and its feature.
homework (new)
1、Please briefly describe the current challenges of wireless communications.
2、Please briefly describe the three major application scenarios of the 5th generation wireless communications (5G) and the main services?
3、What are the reasons that the frequency resources of wireless communications mostly authorized and managed by the governments, and cannot be used at will?
4、Please briefly describe the cellular mobile communication system and its feature.
2. Radio Propagation
quiz
1、Which is used to describe the relationship between transmitted power and received power in free-space propagation?
A、Friis’ Law
B、Huygens principle
C、Snell’s Law
D、Shannon Theory
2、For direct propagation, where the transceiver is at a certain distance, the relationship between path loss and carrier frequency is_____.
A、As the frequency increases, the path loss becomes larger.
B、As the frequency increases, the path loss becomes smaller.
C、Path loss is independent of frequency.
D、As the frequency increases, the path loss changes randomly.
3、The frequency of a satellite communications system is 40 GHz, the distance from the ground receiver is 20,000 km, and the path loss is_____.
A、121.4 dB
B、210.5 dB
C、270.5 dB
D、330.5 dB
4、In general, the penetration loss of the train coach is _____ that of dense foliage.
A、equal to
B、smaller than
C、larger than
D、not able to compare with
5、The amplitude of white Gaussian noise follows_____.
A、uniform distribution
B、normal distribution
C、Gamma distribution
D、Rician distribution
6、In order to reduce the composite noise figure of the entire receiver, the receiver front end generally uses_____.
A、high gain amplifier
B、low noise amplifier (LNA)
C、mixer
D、attenuator
7、The electromagnetic waves emitted are irradiated to objects smaller than the carrier wavelength, and the phenomenon of reflecting multiple weak electromagnetic waves is called_____.
A、direct wave
B、transmission
C、diffraction
D、scattering
8、If the transmitted power is 2 Watts and the transmit antenna gain is 7 dB, the effective omnidirectional radiated power (EIRP) is ___ dBm?
A、9
B、14
C、10
D、40
9、What are the scope requirements for Friis’ law?
A、Transmission distance is much smaller than wavelength.
B、Transmission distance is much greater than wavelength.
C、Transmission distance is less than Rayleigh distance.
D、Transmission distance is greater than Rayleigh distance.
10、The mechanism of radio wave propagation includes_____.
A、direct wave
B、reflection
C、diffraction
D、scattering
11、In general, the higher the frequency, the smaller the diffraction loss.
12、Under room temperature (290K), the thermal noise spectral density is about -174dBm/Hz.
13、In free space propagation, the path loss is proportional to the square of the transmission distance and inversely proportional to the square of the wavelength.
14、Compared with the free space propagation, the path loss will be reduced when takes the ground reflected waves into consideration.
15、Antenna gain indicates the power amplification of the signal after passing through the antenna.
16、Thermal noise power will increase with increasing temperature.
17、In link budget, increasing the fading margin can reduce the outage probability of system.
18、The power spectrum of white Gaussian noise follows Gaussian distribution.
homework
1、A receiver system is composed of antenna and receiver in turn, where the receiver noise figure F=6dB, the signal bandwidth is 200KHz, if the received signal power is -102dBm. (1) What is the received signal-to-noise ratio (SNR)? (2) If you consider using a low-noise amplifier (with noise figure F=3dB and gain of 10dB) to improve the signal-to-noise ratio, where should the low-noise amplifier be added to the receiver system, and what is the composite noise figure of the receiver?
2、Please explain the meaning of additive white Gaussian noise (AWGN).
3、In the free space path loss formula (i.e. Friis’ Law), how does the path loss change with the transmission distance? What is the basic cause of the path loss?
4、Please explain the concept of fading margin, and discuss the impact of increasing fading margin on system performance?
5、Why are broadcast communications systems usually deployed in lower frequency bands?
6、A communications system works at 1800 MHz, the base station transmit power is 2 Watts, the minimum coverage level is -102dBm; using the breakpoint model, the path loss exponent n= 2.5, the breakpoint is 100m away from the base station, and the fading margin is 10dB. What is the maximum coverage radius of the base station?
3. Narrowband Channel
quiz
1、Shadow fading generally follows_____.
A、normal distribution
B、uniform distribution
C、exponential distribution
D、log-normal distribution
2、The amplitude of small-scale fading without dominant components follows_____.
A、normal distribution
B、uniform distribution
C、Rayleigh distribution
D、log-normal distribution
3、The variance of shadow fading in urban environment is generally ______ the variance of shadow fading in rural environment.
A、equal to
B、smaller than
C、greater than
D、not certain
4、The amplitude of small-scale fading with dominant components follows_____.
A、Ricean distribution
B、exponential distribution
C、Rayleigh distribution
D、log-normal distribution
5、In the Rayleigh channel, to ensure that the outage probability is 1%, the fading margin should be_____.
A、10 dB
B、20 dB
C、23 dB
D、30 dB
6、When a system works at 1900MHz and the moving speed is 40km/h, the maximum Doppler frequency shift is_____.
A、47.5Hz
B、70.4Hz
C、253.3Hz
D、76kHz
7、Which of the following statements about channel fading is correct?
A、The larger the Rician factor, the more significant the channel fading.
B、The greater the Doppler frequency shift, the slower the channel fading.
C、The more open the surrounding environment of the transmitter and receiver, the more significant the channel fading.
D、The more significant the channel fading, the greater the fading margin required.
8、Assuming that the large-scale fading follows log-normal distribution with a standard deviation of 5 dB, when the large-scale fading margin is set to 10 dB, without considering the small-scale fading, the outage probability is_____.
A、0.015
B、0.022
C、0.032
D、0.15
9、The phase of small-scale fading without dominant components follows_____.
A、Gaussian distribution
B、uniform distribution
C、Rayleigh distribution
D、log-normal distribution
10、The Doppler shift is______, when the direction of radio wave is opposite to that of the mobile station.
A、positive
B、negative
C、zero
D、uncertainty
11、Which of the following statements about the time dependence of fading is correct?
A、The level passing rate is defined the average number of times the level passes the threshold level with a positive slope during a second.
B、The average fading duration is defined as the average time that the envelope is below the threshold level.
C、The greater the Doppler frequency shift, the shorter the average fading duration.
D、The lower the threshold level, the higher the level pass rate.
12、Which of the following statements about the Rayleigh fading and Rice fading is incorrect?
A、In Ricean channel, the bigger the K, the more significantly the fading.
B、In the LOS condition, the channel is Rayleigh fading.
C、The fading margin in Rayleigh fading channel is smaller than that in Rice fading Channel with the same outage probability.
D、The Ricean factor K is defined as the ratio of scattered component energy to direct component energy.
13、Which one is the narrowband channel fading in the following?
A、Rice fading
B、Rayleigh fading
C、Nakagami fading
D、Time-varying fading
14、In general, the greater the Doppler frequency shift, the greater the average fading duration of the channel.
15、The Rayleigh channel can be regarded as a special case when the Ricean factor K tends to infinity.
16、When the receiver moves approaching the transmitter, the Doppler shift is positive.
homework
1、In Rayleigh channel, when the fading margin is 10 dB, please calculate the outage probability. If the desired outage probability is 5%, how much the fading margin is need.
2、Why the multipath propagation will result in small-scale fading?
3、Please briefly the reason of large-scale fading. How much the fading margin is need, when the standard deviation of large-scale fading is 6dB and the outage probability is 5%.
4. Broadband and Directional Channel
quiz
1、Which statement about the assumption of Wide Sense Stationary Uncorrelated Scattering (WSSUS) is incorrect?
A、Channel statistics vary with time.
B、Fading experienced by signals with different Doppler frequency shifts is uncorrelated.
C、Fading experienced by signals with different delays is uncorrelated.
D、Transfer function is stable in the frequency domain.
2、Generally, the delay spread in the urban environment is that in the suburban environment.
A、greater than
B、smaller than
C、equal to
D、not certain
3、The root mean square (RMS) delay spread is 1μs, then the coherent bandwidth is?
A、15.9 kHz
B、159 kHz
C、1 MHz
D、10 MHz
4、A system works at 1.9GHz and the mobile station moves at a speed of 100km/h. Assuming Doppler is the Classic spectrum, the channel coherence time is .
A、0.25 ms
B、1.3 ms
C、5.9 ms
D、10 ms
5、When the signal bandwidth is greater than the channel coherence bandwidth, the signal experiences .
A、flat fading
B、frequency selective fading
C、fast fading
D、slow fading
6、When the symbol duration is greater than the channel coherence time, the signal experiences .
A、flat fading
B、frequency selective fading
C、slow fading
D、fast fading
7、In a multipath environment, the delay of the first path to the receiver is 0.5 ns, the delay of the second path is 1 ns, and the delay of the last path (third path) is 2 ns. Assuming that a pulse signal with 1 ns duration is transmitted, the duration of the received pulse signal is .
A、1 ns
B、1.5 ns
C、2.5 ns
D、3 ns
8、Which one is the directional channel model?
A、Rayleigh model
B、Rice model
C、COST 207 model
D、WINNER model
9、The impacts of multipath propagation on broadband signal transmission include .
A、inter-symbol interference
B、error floor
C、frequency selective fading
D、energy attenuation
10、Techniques against multipath propagation include .
A、equalization
B、diversity
C、OFDM
D、MIMO
11、In the frequency selective fading channel, the fading of each frequency component is almost the same, the fading condition is independent of the frequency, and the received signal waveform is not distorted.
12、The channel's stationary characteristic and time-varying characteristic are the same concept.
homework
1、Please briefly describe the causes and effects of frequency selective fading.
2、Please briefly describe the relationship and difference between Doppler spread and Doppler shift?
3、Calculate the coherent bandwidth of the COST 207 RA channel, and determine whether the GSM signal (bandwidth 200kHz) and LTE signal (bandwidth 10MHz) experience flat fading or frequency selective fading respectively when transmitted on this channel.
4、How to judge whether the signal experiences fast fading or slow fading on the channel?
5. Digital Modulation and Demodulation
quiz
1、Using BPSK modulation, the raised cosine roll-off coefficient a = 0.2, then the spectrum utilization of the signal is
A、1 bit/s/Hz
B、1.67 bit/s/Hz
C、0.5 bit/s/Hz
D、0.83 bit/s/Hz
2、The maximum phase change of constellation points in the π/4-DQPSK modulation is
A、π/4
B、π/2
C、3π/4
D、π
3、One QPSK symbol carries _____ bits.
A、1
B、2
C、3
D、4
4、What is the numerical relationship between the main lobe bandwidth of the frequency band modulated by MSK and GMSK and the bit rate Rb?
A、300 bits/s
B、Rb
C、1.5 Rb
D、2 Rb
5、In AWGN channel, what is the required signal-to-noise ratio to get the bit error rate of 10^-5 in QPSK demodulation.
A、6 dB
B、6.9 dB
C、9 dB
D、9.6 dB
6、Under AWGN channel and with the same signal-to-noise ratio, the error performance of BPSK coherent demodulation is _____ the error performance of BPSK differential demodulation.
A、superior to
B、inferior to
C、the same with
D、not certain
7、In Rayleigh fading channel, the bit error rate of BPSK coherent demodulation _____ with the average signal-to-noise ratio.
A、proportionally increases
B、inversely decreases
C、exponentially decreases
D、logarithmically decreases
8、For MSK modulation, f1 = 1200Hz, f2 = 600Hz, the maximum bit rate is_____.
A、300 bits/s
B、600 bits/s
C、1200 bits/s
D、2400 bits/s
9、The guidelines to be followed when choosing a modulation scheme include .
A、high bandwidth efficiency
B、low bandwidth efficiency
C、sensitive to noise
D、not sensitive to noise
10、Under the delay and frequency dispersion channel, which parameters are related to the error floor of the bit error rate.
A、Root mean square delay spread of the channel
B、Maximum Doppler shift
C、Symbol rate
D、Average signal-to-noise ratio
homework
1、Please describe the characteristics of QPSK and 64QAM these two modulation methods and the corresponding suitable applications.
2、Explain the relationship between bit error rate and average signal-to-noise ratio in additive white Gaussian noise channel, flat slow fading channel, and delay and frequency dispersion fading channels.
3、A system uses BPSK modulation, the symbol raised cosine roll-off coefficient a = 0.2, and the bit rate is 400 kbit/s. What is the frequency band bandwidth of the signal? What is the frequency band utilization rate? If QPSK modulation is used instead, and other parameters remain unchanged, what will the signal's frequency bandwidth become? How much does the frequency band utilization rate become? Explain the bit error rate of BPSK and QPSK in the case of coherent demodulation.
4、Why do roll-ups in raised cosine rather than directly use Nyquist pulses? What is the effect of increasing the roll-off coefficient α in the raised cosine roll-off?
6. Channel Coding
quiz
1、A binary linear block code with Hamming distance 5 can correct _____ error at most.
A、6 bits
B、3 bits
C、2 bits
D、1 bit
2、Cyclic Redundancy Check (CRC) code is widely used in _____.
A、error correction
B、error correction and detection
C、error detection
D、synchronization
3、Which keyword can be used to describe the Viterbi decoding algorithm of convolutional codes?
A、Maximum likelihood decoding
B、Survival path
C、Add-compare-select
D、Cumulative distance
4、What is the role of the interleaver between the two component encoders in Turbo encoder?
A、Random coding
B、break up the error
C、Adjust the code rate
D、Get the systematic code
5、In each iteration of the Turbo decoding, _____ will be exchanged between two component decoders.
A、channel information
B、extrinsic information
C、prior Information
D、soft information
6、In fading channels, which of the following techniques can be used to discretize burst errors?
A、interleaving
B、synchronization
C、puncturing
D、duplex
7、In fading channels, concatenated convolutional codes and RS codes can be used to improve error performance. Which of the following statements are correct?
A、Convolutional code is inner code, RS code is outer code.
B、Convolutional code is outer code, RS code is inner code.
C、Convolutional codes can be soft decoded, RS codes are good at correcting burst errors.
D、Convolutional codes are good at correcting burst errors, RS codes can be soft decoded.
8、Which of the following statements about the LDPC code are correct.
A、LDPC codes are linear block codes.
B、The code rate of LDPC codes can be adjusted flexibly.
C、LDPC codes adopt iterative decoding algorithm.
D、LDPC code performance is worse than Turbo code.
9、The two component encoders in the Turbo code must use different convolutional codes.
10、The convolutional code can adjust the code rate by puncturing.
11、For Convolutional code, soft decoding has better performance than hard decoding.
12、The check matrix of LDPC codes has sparse characteristics.
13、For convolutional codes with the same code rate, the greater the constraint length is, the better the performance becomes.
homework
1、Please briefly describe the basic flow of the Viterbi algorithm.
2、In fading channels, why does channel coding need to cooperate with interleaving technology?
3、For a (7, 4) cyclic code, the generator polynomial is g(x)=x^3+x+1. If the input information sequence is 10100011 (the left bit is input to the encoder first), please give the encoder output sequence. The minimum Hamming weight of the codewords other than all zeros code in this cyclic code is 3, what is the minimum Hamming distance of the code? How many errors can be corrected?
4、The structure of the (2, 1, 3) convolutional code encoder given by the courseware, what is the impulse response? If the information sequence is U = (111), please give the encoder output sequence.
