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-toQuantizer 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 disposition of objects as they might be seen from the air. In particular, the system hereinafter described is a radar or radio echo detection system presenting objects and targets principally 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 consisted 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 associated 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