UNIT – III I: Digital Transmission
description
Transcript of UNIT – III I: Digital Transmission
![Page 1: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/1.jpg)
UNIT – III I: Digital Transmission
![Page 2: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/2.jpg)
4-2 ANALOG-TO-DIGITAL CONVERSION
We have seen that a digital signal is superior to an analog signal. The tendency today is to change an analog signal to digital data. In this section we describe two techniques, pulse code modulation and delta modulation.
Pulse Code Modulation (PCM)Delta Modulation (DM)
Topics discussed in this section:
![Page 3: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/3.jpg)
![Page 4: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/4.jpg)
![Page 5: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/5.jpg)
![Page 6: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/6.jpg)
![Page 7: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/7.jpg)
Pulse Modulation
Analog signal
Sample pulse
Pulse width modulation
Pulse position modulation
Pulse amplitude modulation
Pulse code modulation
8 bit
ts
![Page 8: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/8.jpg)
PCM Transmission System
![Page 9: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/9.jpg)
![Page 10: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/10.jpg)
![Page 11: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/11.jpg)
PCM Sampling
![Page 12: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/12.jpg)
Figure 4.21 Components of PCM encoder
![Page 13: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/13.jpg)
Figure 4.22 Three different sampling methods for PCM
![Page 14: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/14.jpg)
According to the Nyquist theorem, the sampling rate must be
at least 2 times the highest frequency contained in the signal.
Note
![Page 15: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/15.jpg)
Figure 4.23 Nyquist sampling rate for low-pass and bandpass signals
![Page 16: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/16.jpg)
Figure 4.24 Recovery of a sampled sine wave for different sampling rates
![Page 17: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/17.jpg)
Figure 4.26 Quantization and encoding of a sampled signal
![Page 18: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/18.jpg)
Quantization
![Page 19: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/19.jpg)
Quantization• With a folded binary code, each voltage level has one code
assigned to it except zero volts, which has two codes, 100 (+0) and 000 (-0).
• The magnitude difference between adjacent steps is called the quantization interval or quantum.
• For the code shown in Table 10-2, the quantization interval is 1 V.
• If the magnitude of the sample exceeds the highest quantization interval, overload distortion (also called peak limiting) occurs.
![Page 20: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/20.jpg)
Quantization• Assigning PCM codes to absolute magnitudes is called
quantizing.
• The magnitude of a quantum is also called the resolution.
• The resolution is equal to the voltage of the minimum step size, which is equal to the voltage of the least significant bit (Vlsb) of the PCM code.
• The smaller the magnitude of a quantum, the better (smaller) the resolution and the more accurately the quantized signal will resemble the original analog sample.
![Page 21: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/21.jpg)
Input analog signal
Sampling pulse
PCM code
Quantization
PAM signal
![Page 22: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/22.jpg)
Quantization• For a sample, the voltage at t3 is approximately +2.6 V. The
folded PCM code is
sample voltage = 2.6 = 2.6 resolution 1
• There is no PCM code for +2.6; therefore, the magnitude of the sample is rounded off to the nearest valid code, which is 111, or +3 V.
• The rounding-off process results in a quantization error of 0.4 V.
![Page 23: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/23.jpg)
Quantization• The likelihood of a sample voltage being equal to one of the
eight quantization levels is remote. Therefore, as shown in the figure, each sample voltage is rounded off (quantized) to the closest available level and then converted to its corresponding PCM code.
• The rounded off error is called the called the quantization error (Qe).
• To determine the PCM code for a particular sample voltage, simply divide the voltage by the resolution, convert the quotient to an n-bit binary code, and then add the sign bit.
![Page 24: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/24.jpg)
Figure 4.27 Components of a PCM decoder
![Page 25: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/25.jpg)
![Page 26: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/26.jpg)
![Page 27: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/27.jpg)
Dynamic Range
max max
min
2 1resolution
nV VDR
V
DR = dynamic range (unitless)Vmin = the quantum valueVmax = the maximum voltage magnitude of the DACsn = number of bits in a PCM code (excl. sign bit)
2 1 2n nDR
20log 2 1ndBDR
For n > 4
20log 2 1 20 log 2 6ndBDR n n
![Page 28: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/28.jpg)
Example 2• For the PCM coding determine the quantized voltage, quantization
error (Qe) and PCM code for the analog sample voltage of + 1.07 V.
• To determine the quantized level, simply divide the sample voltage by resolution and then round the answer off to the nearest quantization level:
+1.07V = 1.07 = 1 1V
• The quantization error is the difference between the original sample voltage and the quantized level, or Qe = 1.07 -1 = 0.07
• From Table 10-2, the PCM code for + 1 is 101.
![Page 29: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/29.jpg)
![Page 30: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/30.jpg)
Signal-to-Quantization Noise Efficiency
min
minresolution 2
e e
VSQRQ Q
resolution2eQ
V
e
SQRQ
max
maxe
VSQR
Q
SQR is not constant
For input signal minimum amplitudeSQR = minimum voltage / quantization noise
For input signal maximum amplitudeSQR = maximum voltage / quantization noise
![Page 31: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/31.jpg)
![Page 32: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/32.jpg)
![Page 33: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/33.jpg)
![Page 34: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/34.jpg)
![Page 35: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/35.jpg)
![Page 36: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/36.jpg)
![Page 37: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/37.jpg)
![Page 38: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/38.jpg)
![Page 39: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/39.jpg)
Figure 4.28 The process of delta modulation
![Page 40: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/40.jpg)
DELTA MODULATION
![Page 41: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/41.jpg)
Differential DM• In a typical PCM-encoded speech waveform, there are often
successive samples taken in which there is little difference between the amplitudes of the two samples.
• This necessitates transmitting several identical PCM codes, which is redundant.
• Differential pulse code modulation (DPCM) is designed specifically to take advantage of the sample-to-sample redundancies in typical speech waveforms.
![Page 42: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/42.jpg)
Differential DM
• With DPCM, the difference in the amplitude of two successive samples is transmitted rather than the actual sample. Because the range of sample differences is typically less than the range of individual samples, fewer bits are required for DPCM than conventional PCM.
![Page 43: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/43.jpg)
Figure 4.29 Delta modulation components
![Page 44: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/44.jpg)
Figure 4.30 Delta demodulation components
![Page 45: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/45.jpg)
UNIT – III II: Multiplexing & T-Carriers
![Page 46: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/46.jpg)
6-1 MULTIPLEXING
Whenever the bandwidth of a medium linking two devices is greater than the bandwidth needs of the devices, the link can be shared. Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link. As data and telecommunications use increases, so does traffic.
Frequency-Division MultiplexingWavelength-Division MultiplexingSynchronous Time-Division MultiplexingStatistical Time-Division Multiplexing
Topics discussed in this section:
![Page 47: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/47.jpg)
Figure 6.1 Dividing a link into channels
![Page 48: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/48.jpg)
Figure 6.2 Categories of multiplexing
![Page 49: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/49.jpg)
Figure 6.3 Frequency-division multiplexing
![Page 50: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/50.jpg)
FDM is an analog multiplexing technique that combines analog signals.
Note
![Page 51: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/51.jpg)
Figure 6.4 FDM process
![Page 52: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/52.jpg)
Figure 6.5 FDM demultiplexing example
![Page 53: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/53.jpg)
Figure 6.9 Analog hierarchy
![Page 54: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/54.jpg)
Figure 6.10 Wavelength-division multiplexing
![Page 55: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/55.jpg)
WDM is an analog multiplexing technique to combine optical signals.
Note
![Page 56: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/56.jpg)
Figure 6.11 Prisms in wavelength-division multiplexing and demultiplexing
![Page 57: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/57.jpg)
Figure 6.12 TDM
![Page 58: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/58.jpg)
TDM is a digital multiplexing technique for combining several low-rate
channels into one high-rate one.
Note
![Page 59: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/59.jpg)
Figure 6.13 Synchronous time-division multiplexing
![Page 60: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/60.jpg)
In synchronous TDM, the data rate of the link is n times faster, and the unit
duration is n times shorter.
Note
![Page 61: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/61.jpg)
Figure 6.15 Interleaving
![Page 62: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/62.jpg)
Figure 6.18 Empty slots
![Page 63: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/63.jpg)
Figure 6.19 Multilevel multiplexing
![Page 64: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/64.jpg)
Figure 6.20 Multiple-slot multiplexing
![Page 65: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/65.jpg)
Figure 6.21 Pulse stuffing
![Page 66: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/66.jpg)
Figure 6.22 Framing bits
![Page 67: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/67.jpg)
Figure 6.23 Digital hierarchy
![Page 68: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/68.jpg)
Table 6.1 DS and T line rates
![Page 69: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/69.jpg)
Figure 6.24 T-1 line for multiplexing telephone lines
![Page 70: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/70.jpg)
Figure 6.25 T-1 frame structure
![Page 71: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/71.jpg)
Table 6.2 E line rates
![Page 72: UNIT – III I: Digital Transmission](https://reader035.fdocuments.in/reader035/viewer/2022062302/56816717550346895ddb892b/html5/thumbnails/72.jpg)
Figure 6.26 TDM slot comparison