Digital Communication

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1 Digital Communication (ECE4058) Electronics and Communication Engineering Hanyang University Haewoon Nam Lecture 1 1

2 Digital Band Pass Modulation echnique Digital and-pass modulation techniques Amplitude-shift keying Phase-shift keying Frequency-shift keying Receivers Coherent detection he receiver is synchronized to the transmitter with respect to carrier phases Noncoherent detection he practical advantage of reduced complexity ut at the cost of degraded performance

3 Digital Band Pass Modulation echnique Given a inary source he modulation process involves switching ore keying the amplitude, phase, or frequency of a sinusoidal carrier wave c( t) = A cos(π f t + φ ) c c c (7.1) All three of them are examples of a and-pass process Binary amplitude shift-keying (BASK) he carrier amplitude is keyed etween the two possile values used to represent symols 0 and 1 Binary phase-shift keying (BPSK) he carrier phase is keyed etween the two possile values used to represent symols 0 and 1. Binary frequency-shift keying (BFSK) he carrier frequency is keyed etween the two possile values used to represent symols 0 and 1. 3

4 Digital Band Pass Modulation echnique Decreasing the it duration has the effect of increasing the transmission andwidth requirement of a inary modulated wave. A = c (7.) c( t) = cos(π fct + φc ) (7.3) Differences that distinguish digital modulation from analog modulation. he transmission andwidth requirement of BFSK is greater than that of BASK for a given inary source. However, the same does not hold for BPSK. 4

5 Digital Band Pass Modulation echnique 5

6 Binary Amplitude Shift Keying he ON-OFF signaling variety ( t) = 0, E E s( t) = 0,, for inary symol1 (7.9) for inary symol 0 cos(πf t), c for symol1 for symol 0 (7.10) he average transmitted signal energy is ( the two inary symols must y equiproale) E = av E (7.11) 6

7 Binary Phase Shift Keying Binary Phase-Shift Keying (BPSK) he special case of doule-sideand suppressed-carried (DSB-SC) modulation he pair of signals used to represent symols 1 and 0, s ( t) = i E E cos(πf t), cos(πf t + π ) = An antipodal signals c c E cos(πf t), for symol1corresponding to i = 1 for symol 0 corresponding to i = A pair of sinusoidal wave, which differ only in a relative phase-shift of π radians. he transmitted energy per it, E is constant, equivalently, the average transmitted power is constant. Demodulation of BPSK cannot e performed using envelope detection, rather, we have to look to coherent detection. c (7.1) 7

8 Binary Phase Shift Keying Antipodal signal 0 1 Constellation plot Binary data stream Non-return to zero level encoder Product modulator BPSK signal si ( t) = E E cos( πf t), c cos( πf t), c cos (a) BPSK modulator BPSK signal Product modulator Low-pass filter Sample at time Decision-making device Say 1, if the threshold is exceeded Say 0, otherwise cos hreshold () Coherent detector for BPSK, for the sampler, integer 0, 1,, 8

9 Quadrature Phase Shift Keying Quadrature Phase-Shift Keying (QPSK) Efficient utilization of channel andwidth he phase of the sinusoidal carrier takes on one of the four equally spaced values, such as π/4, 3π/4, 5π/4, and 7π/4 s ( t) i = E 0, cos πf ct π + (i 1), 4 0 t elsewhere (7.13) Each one of the four equally spaced phase values corresponds to a unique pair of its called diit = (7.14) E π E π si ( t) = cos (i 1) cos(πf ct) sin (i 1) sin(πf ct) 4 4 (7.15) 9

10 Quadrature Phase Shift Keying Quadrature Phase-Shift Keying (QPSK) A QPSK signal consists of the sum of two BPSK signals he first inary sinusoidal wave with an amplitude equal to ± E/ π E / cos (i 1) cos(πf ct), 4 π E cos (i 1) 4 = E / E / (7.16) he second inary wave also has an amplitude equal to ± E/ for for i = 1, 4 i =, 3 π E / sin (i 1) sin(πf ct), 4 π E / for i = 1, E sin (i 1) = 4 E / for i = 3, 4 cosine and sine carriers are orthogonal (7.17) 10

11 Quadrature Phase Shift Keying 11

12 Quadrature Phase Shift Keying Constellation plot BPSK QPSK Bit 0 Bit

13 Quadrature Phase Shift Keying QPSK transmitter 13

14 Quadrature Phase Shift Keying QPSK receiver 14

15 M-ary Phase Shift Keying Constellation plot 8-PSK 16-PSK

16 Frequency Shift Keying Binary Frequency-Shift Keying (BFSK) Each symols are distinguished from each other y transmitting one of two sinusoidal waves that differ in frequency y a fixed amount s ( t) i = E E cos(πf t), 1 cos(πf t), for symol1corresponding to i = 1 for symol 0 corresponding to i = (7.18) Sunde s BFSK When the frequencies f1 and f are chosen in such a way that they differ from each other y an amount equal to the reciprocal of the it duration 16

17 Frequency Shift Keying 17

18 Frequency Shift Keying Continuous-phase Frequency-Shift Keying he modulated wave maintains phase continuity at all transition points, even though at those points in time the incoming inary data stream switches ack and forth Sunde s BFSK, the overall excursion δf in the transmitted frequency from symol 0 to symol 1, is equal to the it rate of the incoming data stream. MSK (Minimum Shift Keying) he special form of CPFSK Uses a different value for the frequency excursion δf, with the result that this new modulated wave offers superior spectral properties to Sunde s BFSK. 18

19 Frequency Shift Keying Noncoherent Detection of BFSK Signals he receiver consists of two paths Path 1 : uses a and-pass filter of mid-and frequency f1. produce the output v1 Path : uses a and-pass filter of mid-and frequency f. produce the output v he output of the two paths are applied to a comparator 19

20 Quadrature Amplitude Modulation M-ary Quadrature Amplitude Modulation (QAM) he mathematical description of the new modulated signal s E E 0 t) = a cos(πf t) sin(πf t), i c i c 0 ( i he level parameter for in-phase component and quadrature component are independent of each other for all I M-ary QAM is a hyrid form of M-ary modulation M-ary amplitude-shift keying (M-ary ASK) If i=0 for all i, the modulated signal si(t) of Eq. (7.40) reduces to M-ary PSK If E0=E and the constraint is satisfied i = 0,1,..., M 0 t E0 s ( t) = a cos(πf t) i = 0,1,..., M 1 i i c ( Ea i + E i ) 1/ = E, for all i 1 (7.40) 0

21 Quadrature Amplitude Modulation 1

22 Mapping of Modulated Symols Mapping of digitally modulated waveforms onto constellation of signal points for BPSK he signal-space representation of BPSK is simple, involving a single asis function φ 1( t) = cos(πf ct) (7.44)

23 Mapping of Modulated Symols Mapping of digitally modulated waveforms onto constellation of signal points for BFSK wo asis function each with different frequency φ ( t) = cos(πf 1 1 t ) (7.5) φ ( t) = cos(πf t ) (7.53) 3

ENSC327 Communication Systems 27: Digital Bandpass Modulation. (Ch. 7) Jie Liang School of Engineering Science Simon Fraser University

ENSC327 Communication Systems 27: Digital Bandpass Modulation. (Ch. 7) Jie Liang School of Engineering Science Simon Fraser University ENSC37 Communication Systems 7: Digital Bandpass Modulation (Ch. 7) Jie Liang School of Engineering Science Simon Fraser University 1 Outline 7.1 Preliminaries 7. Binary Amplitude-Shift Keying (BASK) 7.3