学院_______________________ 系别____________ 班次_____________ 学号__________ 姓名________________………….……密…..……….封……..……线………..…以………..…内………....答…………...题…………..无…….….效…..………………..电子科技大学《通信原理》课程试题（B 卷）(120分钟)一 二三四五六七八九十总分评卷教师1. Blank Filling:(1) A analog waveform can be converted to digital signal (for a PCM system) by three basic operations:sampling 、 quantizing 、 coding .(2) A law and µ law companding is the two main nonuniform quantizing used in PCM system.(3) The input amplitude of a linear circuit is 5V .The output amplitude is 10V . Then the gain of the circuit is 6dB.(4) BANDPASS SAMPLING THEOREM: If a (real) bandpass waveform has a nonzero spectrum only over thefrequency interval f 1 < | f | < f 2, where the transmission bandwidth B T is taken to be the absolute bandwidth B T = f 2 – f 1, then the waveform may be reproduced from sample values if the sampling rate is fs=2B T .(5) All communications systems involve three main subsystems : transmitter 、 channel 、 receiver .2. Multiple Choice:(1) If the bandwidth of an modulation signal m(t) is f 0, the bandwidth of AM, DSB-SC and SSB signal are_____(A)________ respectively(A) 2f 0, 2f 0, f 0 (B) f 0, 2f 0, f 0 (C) 2f 0, f 0, 2f 0 (D) 2f 0, 2f 0, 2f 0(2) In the following definition, the right is __(D)______(A) A bandpass waveform has a spectral magnitude that is zero for the frequency in the vicinity of the origin andnegligible elsewhere(B) A baseband waveform has a spectral magnitude that is zero for the frequency in some band concentratedabout a frequencyc f f ±=, where 0f c >>, and negligible elsewhere(C) Modulation is the process of imparting the source information onto a bandpass signal with a carrierfrequency by introduction of amplitude or phase perturbations or both. The baseband source signal is called the modulated signal(D) Modulation is the process of imparting the source information onto a bandpass signal with a carrierfrequency by introduction of amplitude or phase perturbations or both. The baseband source signal is called the modulating signal.(3) In a communication system, the random data pattern consist of binary 1’s and 0’s, and its PSD is22sin(/2)()||4/2b b s b A T fT f fT ππ=Pwhere RT b 1= is the time needed to send 1 bit of data. The first-null bandwidth of the signal and thebandwidth efficiency are__(C)____respectly(A) R, 1 (B)4R, 0.25 (C) 2R, 0.5 (D) R, 1(4) If the PSD(Power Spectral Density) of a baseband signal s(t) is shown in the following figure, the absolutebandwidth 、3dB bandwidth and first zero-crossing bandwidth is___(D)_______ respectively.(A) f3 f2, (f1+f3)/2(B) f3, f2, (f1+f2)/2(C) f2, f3, (f1+f2)/2 (D) f3, (f1+f2)/2, f2(5)The amplitude spectra of a Raised cosine-rolloff signal is shown in the following Figure, its 6-dB bandwidth is-__(B) ____(A) (B T+f1)/4(B) (B T+f1)/2(C) (B T-f1)(D) f1(6)For distortionless transmission of bandpass signal, the channel transfer function need to satisfy__(D)______(A) The amplitude response or phase response is constant(B) The product of the amplitude response and phase response are constant(C) The amplitude response or the derivative of the phase response is constant(D)Both the amplitude response and the derivative of the phase response are constant(7)In the following description about MSK, the wrong is __(B)___(E)_____(A) MSK is a continuous FSK(B) MSK’s modulation index is minimum, and equal to 1(C) Two signals representing ‘1’ and ‘0’ are ortho gonal over the bit interval(D) MSK is identical with OQPSK when the pulse shape is sinusoidal type(E) MSK bandwidth is 3R/2 when the transmission rate of baseband signal is R(8)In the following description about QPSK, π/4 QPSK and OQPSK signal, the wrong is ___(D)______(A) They are 4-ary modulated bandpass signaling(B) For rectangular-shaped data pulses, the envelope of the QPSK signal is constant and there is no AM on thesignal(C) For nonrectangular-shaped data pulses, the phase shift and AM of QPSK are the maximum ,while the phaseshift and AM of OQPSK are the minimum(D) For rectangular-shape data pulses, the phase shift and AM of QPSK are the maximum while the phase shiftand AM of OQPSK are the minimum(9)In the following description about the matched filter, the right is ____(B)___(A) MF is a Gaussian filter(B) MF maximize the instantaneous output signal power to the average output noise power for a given inputsignal waveshape(C)For the case of white noise, the impulse response of MF is h(t)=Cs(-t) when the input signal is s(t) and C is aconstant(D)Realizing forms have the integrate-and-dump method, the correlator method and the LPF configurations(10)N onlinear amplifier output-to-input characteristic, hard (ideal) limiter characteristic and envelope detector’soutput-to-input characteristic are__(A)_____ respectivelyFig.1 Fig.2 Fig.3(A) Fig.2, Fig.3 and Fig.1 (B) Fig.1, Fig.2 and Fig.3(C) Fig.3, Fig.2 and Fig.1 (D) Fig.2, Fig.2 and Fig.13. A binary base band signal (polar NRZ) is passed through a transmitted system, the data rate is 26Mb/s, and the transponder has a bandwidth of 100MHz.(a)If the system is a base band communication system, what is the null-to-null bandwidth of transmitted signal,what is the minimum transmission bandwidth for it?(b)If the base band signal is modulated by a carrier (using BPSK, and the carrier frequency is 10GHz) and thenbe transmitted through band pass communication system, what is the null-to-null bandwidth of transmitted signal, what is the minimum transmission bandwidth for it?(c)In question b), if the base band signal is passed through a raised cosine roll off filter with a 50% roll offfactor and is then modulated onto the carrier, what is the transmission bandwidth for it?(d)If QPSK and the raised cosine roll off filter with a 50% roll off factor are used, what is the maximum data rate that the band pass system can support?Solution: (a)min26132null RB R MHz B MHz ==== (b)min2522262null RB R MHz B MHz ===⋅=(c)(1)26 1.539T B R r MHz =+=⨯=(d)max (1)(1)2200100 1.5133.3/2 1.5T RB D r r R R Mb s=+=+=⨯==4. A modulated RF waveform is given by[]t cos 50t cos 200i c ω+ω, where ,kHz 2f i = and.MHz 90f c =(a)If the phase deviation constant is 200 rad/V , find the mathematical expression for the corresponding PMvoltage m(t). What is the peak phase deviation? (b) If the frequency deviation constant is 106 rad/V-s, find the mathematical expression for the correspondingFM voltage m(t). What is the peak frequency deviation? (c) If the RF waveform appears across a 50Ω load, determine the average power and the PEP. Solution: (a)()()[]()()cos 200cos 50cos 50cos 50cos 400050200PM c c P c i P i S A t D m t t t D m t t m t tωωωωπθ=+=+∴=∴=∆=(b)()()[]()()()()65cos 200cos 50cos 50cos 50cos 4000504000sin 40000.2sin 40001011504000sin 40002210tFM c c f c i tf i d S A t D m d t t D m d t tm t t td t f t t dt F Hzωσσωωσσωπππππθππππ-∞-∞=+=+∴==∴=-⋅⋅=-⎡⎤==-⨯⨯⋅⎢⎥⎣⎦∴∆=⎰⎰5. The equivalent transfer function of a binary baseband system is as:()⎪⎩⎪⎨⎧τ≤τπ+τ=other ,021f ,f 2cos 1)f (H 000(a) Find the maxmum baud rate that is no ISI. (b) Find the spectral efficiency of this system.Solution: (a)000111(1)22(11)2D r D τττ+=→==+(b) 1/TD Bd Hz B η==6. Eleven analog signal, each with a bandwidth of 3400Hz, are sampled at an 8kHz rate and multiplexed together witha synchronization channel(8kHz) into a TDM PAM signal, Assume that the analog samples will be encoded into 4-bit PCM words. Then the TDM PCM signal is pass though a channel with an overall raised cosine-rolloff Nyquistfilter characteristic of 75.0=γ . (a) Indicating the multiplexing rate f s , and the overall bit rate of the TDM PCM signal. (b)Evaluate the absolute bandwidth required for the channel.Solution: (a) 8s f kHz =121248384/s R nf kb s ==⨯⨯=(b)()384(1) 1.75336()22T R B kHz γ=+==7. The receiver is shown in Fig 7. Assume that the Bandpass input signaling is)t (n )t f 2cos(200)t f 2cos()t 800sin(100)t (r c c +π+ππ= [V],where n(t) is white noise with a PSD of20102/N -= [W/Hz]. Find the out )N /S (Figure 7Solution:()100sin(800)cos(2)200cos(2)1200cos(2)1sin(800)2AM c c c s t t f t f t f t t πππππ=+⎡⎤=+⎢⎥⎣⎦()()()2222230111200sin(800)2281200831.252221041010lg 14.9C m c outoutA m t t A m t A m t S N NB S dBN π-====⨯⎛⎫=== ⎪⨯⨯⨯⨯⎝⎭⎛⎫= ⎪⎝⎭8.Assume that the input signal ⎩⎨⎧≤<=-otherwise ,0T t 0 ,e )t (s t is a known signal. Finda) The impulse response of the matched filter for the case of white noise.b) The maximum signal level occurs at the matched filter output.Solution:()(), 0t T ()0, otherwise T t e h t s T t --⎧<≤⎪=-=⎨⎪⎩()()2220112T TtTo s T s t dt e dt e --⎡⎤===-⎣⎦⎰⎰。
