《电子工程师手册》学习资料（英文版）Broadcasting 69

Dorf, R C, Wan, Z, Lindsey Ill, J F, Doelitzsch, D F, Whitaker J, Roden, M.S., Salek, S, Clegg, A.H. " Broadcasting The Electrical Engineering Handbook Ed. Richard C. dorf Boca Raton CRC Press llc. 2000

Dorf, R.C., Wan, Z., Lindsey III, J.F., Doelitzsch, D.F., Whitaker J., Roden, M.S., Salek, S., Clegg, A.H. “Broadcasting” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000

69 Richard C. Dorf Broadcasting Zhen Wan University of California, davis 69.1 Modulation and Demodulation Jefferson F. Lindsey Ill Modulation· Superhet outhern Illinois University at Modulation. Frequency-Shift Keying. M-ary Phase-Shift Keying. Quadrature Amplitude Modulation Dennis e delitzsch 69.2 Rad Standard Broadcasting(Amplitude Modulation). Frequency Modulation Jerry Whitaker 69.3 Television Systen anning Lines and Fields. Interlaced Scannin Martin s. roden Fields. Synchronizing Video Signals. Television Industry Standards. Transmission Equipment. Television Reception California State University 69.4 High-Definition Television Stanley Salek Proposed Systems Hammett edison 69.5 Digital Audio Broadca The Need for dab·DA Design Almon H. Clegg Background Technical and Source Encoding. System Example: I 69.1 Modulation and demodulation Richard C. Dorf and Zhen Wan Modulation is the process of sing the source information onto a bandpass signal with a carrier frequenc fe This bandpass signal is called the modulated signal s(n), and the baseband source signal is called the nodulating signal m(t). The modulated signal could be represented by (r)=Relg(t)ejo] (69.1) s(t)=R(t)cos [o t+0(t) s(t)=x(t) cos o t-y(t)sin o t (69.3) where O.= 2Tf The complex envelope is g(t)=R(t)eje(n= x(r)+iy(r) (694) and g(t)is a function of the modulating signal m(t). That is, g(t)=gIm(t)] c 2000 by CRC Press LLC

© 2000 by CRC Press LLC 69 Broadcasting 69.1 Modulation and Demodulation Modulation • Superheterodyne Technique • Pulse-Code Modulation • Frequency-Shift Keying • M-ary Phase-Shift Keying • Quadrature Amplitude Modulation 69.2 Radio Standard Broadcasting (Amplitude Modulation) • Frequency Modulation 69.3 Television Systems Scanning Lines and Fields • Interlaced Scanning Fields • Synchronizing Video Signals • Television Industry Standards • Transmission Equipment • Television Reception 69.4 High-Definition Television Proposed Systems 69.5 Digital Audio Broadcasting The Need for DAB • DAB System Design Goals • Historical Background • Technical Overview of DAB • Audio Compression and Source Encoding • System Example:Eureka-147/DAB 69.1 Modulation and Demodulation Richard C. Dorf and Zhen Wan Modulation is the process of impressing the source information onto a bandpass signal with a carrier frequency fc. This bandpass signal is called the modulated signal s(t), and the baseband source signal is called the modulating signal m(t). The modulated signal could be represented by s(t) = Re{g(t)ejwct} (69.1) or, equivalently, s(t) = R(t) cos [wct + q(t)] (69.2) and s(t) = x(t) cos wct – y(t) sin wct (69.3) where wc = 2pfc. The complex envelope is g(t) = R(t)ejq(t) = x(t) + jy(t) (69.4) and g(t) is a function of the modulating signal m(t). That is, g(t) = g[m(t)] Richard C. Dorf University of California, Davis Zhen Wan University of California, Davis Jefferson F. Lindsey III Southern Illinois University at Carbondale Dennis F. Doelitzsch 3-D Communications Jerry Whitaker Technical Press Martin S. Roden California State University Stanley Salek Hammett & Edison Almon H. Clegg CCi

Baseband circuits RF circuits I vo= R(O cos(o t+0(o i Modulated signal out adulation Circuit may e(t) Phase modulator FIGURE 69. 1 Generalized transmitter using the AM-PM generation technique Thus gl] performs a mapping operation on m(t). The particular relationship that is chosen for g(r)in terms of m(r) defines the type of modulation used. In Table 69.1, examples of the mapping function g( m) are given for the following types of modulation AM: amplitude modulation DSB-SC: double-sideband suppressed-carrier modulation FM: frequency modulation SB-AM-SC: single-sideband AM suppressed-carrier modulation SSB-PM: single-sideband PM SSB-FM: single-sideband FM SSB-EV: single-sideband envelope-detectable modulation SSB-SQ: single-sideband square-law-detectable modulation QM: quadrature modulation Modulation In Table 69. 1, a generalized approach may be taken to obtain universal transmitter models that may be reduced to those used for a particular modulation type. We also see that there are equivalent models which correspond to different circuit configurations, yet they may be used to produce the same type of modulated signal at their outputs. It is up to communication engineers to select an implementation method that will optimize perfor mance, yet retain low cost based on the state of the art in circuit development There are two canonical forms for the generalized transmitter. Figure 69. 1 is an AM-PM type circuit as described in Eq (69.2). In this figure, the baseband signal processing circuit generates R(o) and e(r) from m(o). The R and e functions of the modulating signal m(t) as given in Table 69. 1 for the particular modulation type desired. Figure 69.2 illustrates the second canonical form for the generalized transmitter. This uses in-phase and quadrature-phase(IQ)processing. Similarly, the formulas relating x(n) and yr) are shown in Table 69.1, and the baseband signal processing may be implemented by using either analog hardware or digital hardware with software. The remainder of the canonical form utilizes radio frequency(RF)circuits as indicated Any type of signal modulation(AM, FM, SSB, QPSK, etc )may be generated by using either of these two canonical forms. Both of these forms conveniently separate baseband processing from RF processing Superheterodyne Technique Most receivers employ the superheterodyne receiving technique(see Fig 69.3). This technique consists of either down-converting or up-converting the input signal to some convenient frequency band, called the intermediate frequency(IF)band, and then extracting the information(or modulation) by using the appropriate detector. This basic receiver structure is used for the reception of all types of bandpass signals, such as television, FM, AM, satellite, and radar signals. c 2000 by CRC Press LLC

© 2000 by CRC Press LLC Thus g[·] performs a mapping operation on m(t). The particular relationship that is chosen for g(t) in terms of m(t) defines the type of modulation used. In Table 69.1, examples of the mapping function g(m) are given for the following types of modulation: • AM: amplitude modulation • DSB-SC: double-sideband suppressed-carrier modulation • PM: phase modulation • FM: frequency modulation • SSB-AM-SC: single-sideband AM suppressed-carrier modulation • SSB-PM: single-sideband PM • SSB-FM: single-sideband FM • SSB-EV: single-sideband envelope-detectable modulation • SSB-SQ: single-sideband square-law-detectable modulation • QM: quadrature modulation Modulation In Table 69.1, a generalized approach may be taken to obtain universal transmitter models that may be reduced to those used for a particular modulation type. We also see that there are equivalent models which correspond to different circuit configurations, yet they may be used to produce the same type of modulated signal at their outputs. It is up to communication engineers to select an implementation method that will optimize perfor￾mance, yet retain low cost based on the state of the art in circuit development. There are two canonical forms for the generalized transmitter. Figure 69.1 is an AM-PM type circuit as described in Eq.(69.2). In this figure, the baseband signal processing circuit generates R(t) and q(t) from m(t). The R and q are functions of the modulating signal m(t) as given in Table 69.1 for the particular modulation type desired. Figure 69.2 illustrates the second canonical form for the generalized transmitter. This uses in-phase and quadrature-phase (IQ) processing. Similarly, the formulas relating x(t) and y(t) are shown in Table 69.1, and the baseband signal processing may be implemented by using either analog hardware or digital hardware with software. The remainder of the canonical form utilizes radio frequency (RF) circuits as indicated. Any type of signal modulation (AM, FM, SSB, QPSK, etc.) may be generated by using either of these two canonical forms. Both of these forms conveniently separate baseband processing from RF processing. Superheterodyne Technique Most receivers employ the superheterodyne receiving technique (see Fig. 69.3). This technique consists of either down-converting or up-converting the input signal to some convenient frequency band, called the intermediate frequency (IF) band, and then extracting the information (or modulation) by using the appropriate detector. This basic receiver structure is used for the reception of all types of bandpass signals, such as television, FM, AM, satellite, and radar signals. FIGURE 69.1 Generalized transmitter using the AM-PM generation technique

TABLE 69.1 Complex Envelope Functions for various Types of Modulation Corresponding Quadrature Corresponding Amplitude and Mapping Functions Modulation Phase modulation Modulation x(r) e(r Remarks AM 1+m(t) 0m()> L m(r)>-l required for L Coherent detection required. u80,m()-l is required so that the In will have a real value SSB-SQca+臧∥川1+ m(t>-1 is required n1=m( ±v1+m) siny-In(l+mt ±li[+m the In will have a real value m()+m2(t) (r) tarIm (t)/m, o) L Used in NtSC color tele. L=linear, NL=nonlinear, [ is the Hilbert transform(ie, -g0 phase-shifted version)of [-]. The Hilbert transform is x(t=x(* 1_1 aUse upper signs for upper sideband signals and lower signs for lower sideband si bIn the strict sense, AM signals are not linear because the carrier term does not satisfy the linearity(superposition) condition

© 2000 by CRC Press LLC TABLE 69.1 Complex Envelope Functions for Various Types of Modulation Corresponding Quadrature Corresponding Amplitude and Type of Mapping Functions Modulation Phase Modulation Modulation g[m] x(t) y(t) R(t) q(t) Linearity Remarks AM 1 + m(t) 1 + m(t) 0 *1 + m(t)* Lb m(t) > –1 required for envelope detection. DSB-SC m(t) m(t) 0 *m(t)* L Coherent detection required. PM ejDpm(t) cos[Dpm(t)] sin[Dpm(t)] 1 Dpm(t) NL Dp is the phase deviation constant (radian/volts). FM 1 NL Df is the frequency deviation constant (radian/volt-sec). SSB-AM-SCa m(t) ± jmˆ (t) m(t) ± mˆ (t) tan–1[± mˆ (t)/m(t)] L Coherent detection required. SSB-PMa ejDp[m(t)± jmˆ (t)] e7Dpmˆ(t ) cos[Dpm(t)] e7Dpmˆ(t) sin[Dpm(t)] e7Dpmˆ (t) Dpm(t) NL SSB-FMa NL SSB-EVa e{ln[1 + m(t)]± j ln[1 + ˆ m(t )]} [1 + m(t)] cos {ln[1 + ˆ m(t)]} ±[1 + m(t)]sin{ln[1 + ˆ m(t)]} 1 + m(t) ±ln[1 + ˆ m(t)] NL m(t) > –1 is required so that the ln will have a real value. SSB-SQa e(1/2){ln[1 + m(t )]± j ln[1 + ˆ m(t )]} NL m(t) > –1 is required so that the ln will have a real value. QM m1(t) + jm2(t) m1(t) m2(t) tan–1[m2(t)/m1(t)] L Used in NTSC color tele￾vision: requires coherent detection. L = linear, NL = nonlinear, [ˆ.] is the Hilbert transform (i.e., –90° phase-shifted version) of [·]. The Hilbert transform is a Use upper signs for upper sideband signals and lower signs for lower sideband signals. bIn the strict sense, AM signals are not linear because the carrier term does not satisfy the linearity (superposition) condition. 0 1 180 1 , ( ) – , ( ) – m t m t > ° ° < Ï Ì Ó ¸ ˝ ˛ e jDf m d t (s s ) Ú-• cos ( ) – D m d f t s s Ú • È Î Í ˘ ˚ ˙ sin ( ) – D m d f t s s Ú • È Î Í ˘ ˚ ˙ D m d f t ( ) – s s Ú • [m t( ) [m t ˆ( )] 2 2 + e jDf m jm d t [ (s)± ˆ(s)] s Ú-• e D m d D m d f t f t m ˆ( ) – – cos ( ) Ú • Ú • È Î Í ˘ ˚ ˙ s s s s e D m d D m d f t f t m ˆ( ) – – sin ( ) Ú • Ú • È Î Í ˘ ˚ ˙ s s s s e D m d f t m ˆ( ) Ú–• s s D m d f t ( ) – s s Ú • 1 1 2 + = 1 Ï Ì Ó ¸ ˝ ˛ m t( ) cos l m t n[ˆ ( )] ± + + Ï Ì Ó ¸ ˝ ˛ 1 1 2 m t( ) sin l 1 m t n[ˆ ( )] 1 + m( )t ± + 1 2 ln[ˆ 1 m t( )] m t m t 1 2 2 2 ( ) + ( ) D ˆ( ) ( ) * ( ) x t x t t x t = = d -• - • Ú 1 1 p p l l l

RF circuits x(tI cos(ot) 力、x(cos(01)-y(s(0。0 y(t) Carrie s(@t) FIGURE 69.2 Generalized transmitter using the quadrature generation technique. 团等 a(intermediate Baseband Detector amplifier (to speaker CRT, etc.) FIGURE 69.3 Superheterodyne receiver. If the complex envelope g(t) is desired for generalized signal detection or for optimum reception in digital systems,the x(n) yt) quadrature components, where x(r)+ iy(t=g(t), may be obtained by using quadrature product detectors, as illustrated in Fig. 69.4. x(n) and yr) could be fed into a signal processor to extract the modulation information. Disregarding the effects of noise, the signal processor could recover m(r)from x(t) and y(t(and, consequently, demodulate the IF signal)by using the inverse of the complex envelope generation functions given in Table 69.1 PCM= pulse-code modulation DM= differential modulation DPCM=differential pulse-code modulation FSK= frequency-shift keying PSK= phase-shift keying DPSK= differential phase-shift keying MPSK= M-ary phase-shift keying QAM= quadrature amplitude modulation c 2000 by CRC Press LLC

© 2000 by CRC Press LLC If the complex envelope g(t) is desired for generalized signal detection or for optimum reception in digital systems, the x(t) and y(t) quadrature components, where x(t) + jy(t) = g(t), may be obtained by using quadrature product detectors, as illustrated in Fig. 69.4. x(t) and y(t) could be fed into a signal processor to extract the modulation information. Disregarding the effects of noise, the signal processor could recover m(t) from x(t) and y(t) (and, consequently, demodulate the IF signal) by using the inverse of the complex envelope generation functions given in Table 69.1. The generalized modulation techniques are shown in Table 69.1. In digital communication systems, discrete modulation techniques are usually used to modulate the source information signal. Discrete modulation includes: • PCM = pulse-code modulation • DM = differential modulation • DPCM = differential pulse-code modulation • FSK = frequency-shift keying • PSK = phase-shift keying • DPSK = differential phase-shift keying • MPSK = M-ary phase-shift keying • QAM = quadrature amplitude modulation FIGURE 69.2 Generalized transmitter using the quadrature generation technique. FIGURE 69.3 Superheterodyne receiver

F 2 cos(o t) LPF sin(wr) FIGURE 69.4 IQ (in-phase and quadrature-phase) detector TABLE 69.2 Performance of a PCM System with Uniform Quantizing umber of Signal power Quantizer Length of the Levels PCM Word, ower Ratios Used. M th) (S/N our (S/Nout 2B 12B 40.9 062840 10 "B is the absolute bandwidth of the input analog signal Pulse-Code modulation PCM is essentially analog-to-digital conversion of a special type, where the information contained in the instantaneous samples of an analog signal is represented by digital words in a serial bit stream. The PCM signal is generated by carrying out three basic operations: sampling, quantizing, and encoding(see Fig 69.5). The ampling operation generates a flat-top pulse amplitude modulation( PAM)signal. The quantizing converts the actual sampled value into the nearest of the M amplitude levels. The PCM signal is obtained from the quantized PAM signal by encoding each quantized sample value into a digital word Frequency-Shift Keying The FSK signal can be characterized as one of two different types. One type is called discontinuous-phase FSK since e(r)is discontinuous at the switching times. The discontinuous-phase FSK signal is represented by 4)=1+8)6 time interval when a binary o is sent (69.5) c 2000 by CRC Press LLC

© 2000 by CRC Press LLC Pulse-Code Modulation PCM is essentially analog-to-digital conversion of a special type, where the information contained in the instantaneous samples of an analog signal is represented by digital words in a serial bit stream. The PCM signal is generated by carrying out three basic operations: sampling, quantizing, and encoding (see Fig. 69.5). The sampling operation generates a flat-top pulse amplitude modulation (PAM) signal. The quantizing converts the actual sampled value into the nearest of the M amplitude levels. The PCM signal is obtained from the quantized PAM signal by encoding each quantized sample value into a digital word. Frequency-Shift Keying The FSK signal can be characterized as one of two different types. One type is called discontinuous-phase FSK since q(t) is discontinuous at the switching times. The discontinuous-phase FSK signal is represented by (69.5) FIGURE 69.4 IQ (in-phase and quadrature-phase) detector. TABLE 69.2 Performance of a PCM System with Uniform Quantizing and No Channel Noise Recovered Analog Number of Bandwidth of Signal Power-to￾Quantizer Length of the PCMSignal Quantizing Noise Levels PCM Word, (First Null Power Ratios Used, M n (bits) Bandwidth)a (S/N)pk out (S/N)out 2 1 2B 10.8 6.0 4 2 4B 16.8 12.0 8 3 6B 22.8 18.1 16 4 8B 28.9 24.1 32 5 10B 34.9 30.1 64 6 12B 40.9 36.1 128 7 14B 46.9 42.1 256 8 16B 52.9 48.2 512 9 18B 59.0 54.2 1024 10 20B 65.0 60.2 a B is the absolute bandwidth of the input analog signal. s t A t t A t t c c ( ) = ( + ) ( + ) Ï Ì Ô Ó Ô cos cos w q w q 1 1 2 2 for in time interval when a binary 1 is sent for in time interval when a binary 0 is sent

RADIO DISTANCE AND DⅠ RECTION INDICATOR Luis w alvarez Patented August 30, 1949 A excerpt from Luis Alvarez's patent application his invention relates to a communications system and d TRANSVEA more particularly to a system F/G-/7 for presenting in panoramic form the location and disposi NFRA T。A bjects as they might be seen from the air. In par ticular, the system hereinafter sin s8+hten described is a radar or radio echo detection system present- ing objects and targets princ pally on the ground lying in the 入 path of flight of an airplane ound radar systems were alternately coupled to a transmitter and receiver with the antenna swept in a radial fashion. The display con sisted of a cathode ray tube with targets represented by F/G-18 adial sweeps from the center F/G-/9 of the screen Dr alvarez took the special problem of panoramic presentation of ground targets from aircraft He solved the computation and display problems associ- ated with the hyperbolic shape of the radar beams as transmitted and received from a moving aircraft. He also described handling pitch, roll, yaw, and other disturbances.( Copyright o 1995, Dew Ray Products, Inc. Used with permission

© 2000 by CRC Press LLC RADIO DISTANCE AND DIRECTION INDICATOR Luis W. Alvarez Patented August 30, 1949 #2,480,208 n excerpt from Luis Alvarez’s patent application: This invention relates to a communications system and more particularly to a system for presenting in panoramic form the location and disposi￾tion of objects as they might be seen from the air. In par￾ticular, the system hereinafter described is a radar or radio echo detection system present￾ing objects and targets princi￾pally on the ground lying in the path of flight of an airplane. Ground radar systems were already known and used by the military. These involved a highly directional antenna alternately coupled to a transmitter and receiver with the antenna swept in a radial fashion. The display con￾sisted of a cathode ray tube with targets represented by radial sweeps from the center of the screen. Dr.Alvarez took on the special problem of panoramic presentation of ground targets from aircraft. He solved the computation and display problems associ￾ated with the hyperbolic shape of the radar beams as transmitted and received from a moving aircraft. He also described handling pitch, roll, yaw, and other disturbances. (Copyright © 1995, DewRay Products, Inc. Used with permission.) A

Bandlimited PCM transmitter (analog-to-digital conversion) PAM PCM gnal inLow-pass Instantaneous signal signal e Encoder Bandwidth B and hold PCM receiver Quantized Low-pas FIGURE 69.5 A PCM transmission system. where fi is called the mark(binary 1)frequency and f is called the space(binary 0)frequency. The other type is continuous-Phase FSK. The continuous-phase FSK signal is generated by feeding the data signal into a frequency modulator, as shown in Fig. 69.6(b). This FSK signal is represented by s(t)=A coso t +D m()dn (r)=Reg(t)eject (69.6) g(t)=Deja( (69.7) e(t)=Drm()dλ for FSK (698) Detection of FSK is illustrated in Fig. 69.7 M-ary Phase-Shift Keying If the transmitter is a PM transmitter with an M-level digital modulation signal, MPSK is generated at the transmitter output. A plot of the permitted values of the complex envelope, g(t)=A,ejb(, would contain M points, one value of g(a complex number in general) for each of the M multilevel values, corresponding to the M phases that 0 is permitted to have MPSK can also be generated using two quadrature carriers modulated by the x and y components of the complex envelope(instead of using a phase modulator) g(1)=Ae(0=x(t)+jy(t) c 2000 by CRC Press LLC

© 2000 by CRC Press LLC where f1 is called the mark (binary 1) frequency and f2 is called the space (binary 0) frequency. The other type is continuous-phase FSK. The continuous-phase FSK signal is generated by feeding the data signal into a frequency modulator, as shown in Fig. 69.6(b). This FSK signal is represented by or s(t) = Re{g(t)ej wct} (69.6) where g(t) = Acej q(t) (69.7) (69.8) Detection of FSK is illustrated in Fig. 69.7. M-ary Phase-Shift Keying If the transmitter is a PM transmitter with an M-level digital modulation signal, MPSK is generated at the transmitter output. A plot of the permitted values of the complex envelope, g(t) = Acejq(t) , would contain M points, one value of g (a complex number in general) for each of the M multilevel values, corresponding to the M phases that q is permitted to have. MPSK can also be generated using two quadrature carriers modulated by the x and y components of the complex envelope (instead of using a phase modulator) g(t) = Acejq(t) = x(t) + jy (t) (69.9) FIGURE 69.5 A PCM transmission system. s t A t D m d c c f t ( ) = + cos ( ) È Î Í ˘ ˚ ˙ Ú-• w l l q( )t D f m(l)dl t = -• Ú for FSK

ctronIc scillator Control Binary data input m(t) (a)Discontinuous-Phase FSK Binary m(t) FSK (carrier freq. =fcl FIGURE 69.6 Generation of FSK FSK in Frequency Output FSK in detecto cos(o,t) (a) Noncoherent Detection (b)Coherent(Synchronous) Detection FIGURE 69.7 Detection of FSK where the permitted values of x and y are OS yi=A sin 8. (69.11) for the permitted phase angles 0, i= 1, 2,, M, of the MPSK signal. This is illustrated by Fig 69.8, where the ignal processing circuit implements Eqs. (69.10)and(69.11) MPSK, where M=4, is called quadrature-phase-shift-keyed(QPSK) signaling Quadrature Amplitude Modulation Quadrature carrier signaling is called quadrature amplitude modulation(QAM). In general, QAM signal constellations are not restricted to having permitted signaling points only on a circle(of radius A, as was the ase for MPSK). The general QAM signal is s(t)=x(r) cos o,t-y(t) sin o t (69.12) c 2000 by CRC Press LLC

© 2000 by CRC Press LLC where the permitted values of x and y are xi = Ac cos qi (69.10) yi = Ac sin qi (69.11) for the permitted phase angles qi , i = 1, 2, ..., M, of the MPSK signal. This is illustrated by Fig. 69.8, where the signal processing circuit implements Eqs. (69.10) and (69.11). MPSK, where M = 4, is called quadrature-phase-shift-keyed (QPSK) signaling. Quadrature Amplitude Modulation Quadrature carrier signaling is called quadrature amplitude modulation (QAM). In general, QAM signal constellations are not restricted to having permitted signaling points only on a circle (of radius Ac, as was the case for MPSK). The general QAM signal is s(t) = x(t) cos wct – y(t) sin wct (69.12) FIGURE 69.6 Generation of FSK. FIGURE 69.7 Detection of FSK

Baseband processing processing ∑ s(t) M= 2 level y(t) sin(o t) Oscillator (a)Modulator for Generalized Signal Constellation g(t=x(t)+yt) Baseband processing M=2 point constellation d1( R/2 bits/sec t/2 bit serial-to-parallel R bits/sec s(o(z s0 sin(oct) (b)Modulator for Rectangular Signal Constellation FIGURE 69.8 Generation of QAM signals TABLE 69.3 Spectral Efficiency for QAM Signaling with Raised Cosine-Roll-Off Number of Size of n R evels, DAC, t M(symbols) r=0.0r=0.1 =0.25r=0.5r=0.75r=1.0 10009090.8000.6670.5710.500 4.55 r is the roll-off factor of the filter characteristic. where g(t)=x(t)+ iy(t)=R(t)eje(n) (69.13) The generation of QAM signals is shown in Fig. 69.8. The spectral efficiency for QAM signaling is shown in Table 69.3

© 2000 by CRC Press LLC where g(t) = x(t) + jy (t) = R(t)ejq(t) (69.13) The generation of QAM signals is shown in Fig. 69.8. The spectral efficiency for QAM signaling is shown in Table 69.3. FIGURE 69.8 Generation of QAM signals. TABLE 69.3 Spectral Efficiency for QAM Signaling with Raised Cosine-Roll-Off Pulse Shaping Number of Levels, Size of DAC, l M (symbols) (bits) r = 0.0 r = 0.1 r = 0.25 r = 0.5 r = 0.75 r = 1.0 2 1 1.00 0.909 0.800 0.667 0.571 0.500 4 2 2.00 1.82 1.60 1.33 1.14 1.00 8 3 3.00 2.73 2.40 2.00 1.71 1.50 16 4 4.00 3.64 3.20 2.67 2.29 2.00 32 5 5.00 4.55 4.0 3.33 2.86 2.50 DAC = digital-to-analog converter. h = R/BT = l/2 bits/s per hertz. r is the roll-off factor of the filter characteristic. h = R BT bits/s Hz