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