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COMMUNICATION SYSTEM EEEB453 Chapter 5 (Part II) DIGITAL TRANSMISSION. Intan Shafinaz Mustafa Dept of Electrical Engineering Universiti Tenaga Nasional http://metalab.uniten.edu.my/~shafinaz. PCM Quantization.
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COMMUNICATION SYSTEM EEEB453Chapter 5 (Part II)DIGITAL TRANSMISSION
Intan Shafinaz Mustafa
Dept of Electrical Engineering
Universiti Tenaga Nasional
http://metalab.uniten.edu.my/~shafinaz
Called folded binary code – mirror image
Table1 shown a PCM code with a three-bit sign magnitude together with eight possible combinations.
(a) Analog input signal(b) sample pulse (c) PAM signal (d) PCM code
Amplitudes of the signal m(t) lie in the range (-mp.mp), which is partitioned into L intervals.
Then each magnitude, v = 2mp /L
Where L = 2n, and n = number of bits.
An example of 2-bit quantization.
An example of 3-bit quantization.
An example of 3-bit quantization with increased sample rate.
where Vmax = max voltage magnitude,
Vmin = resolution (quantum value)
DRdB = 20log
2n – 1 ≥ DR
and for a minimum number of bits
2n – 1 = DR or 2n = DR + 1
where n = number of bits in a PCM code, excluding the sign bit
DR = absolute value of dynamic range
Then DRdB = 20log (2n – 1),
and for n > 4,
DRdB ≈ 20log (2n)
≈ 6n,
Coding efficiency
From previous example,
SQRdB = 10.8 + 20 log v/q
where v = rms signal voltage
q = quantization interval
orSQRdB = 6.02n + 1.76
where n = no. of bits
(assume equal R)
SQR at lower amplitude < SQR at higher amplitude
Lower amplitude values are relatively more distorted
More of voice signal is at lower amplitude
Reduce step size at lower amplitude
More accuracy at lower amplitude
Sacrifices SQR at higher amplitude
Provides higher dynamic range