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Modulation Scheme & Bandwidth Calculation


General Formula for Bandwidth Calculation

The general formula for digital modulation bandwidth is:

BW = Bit Rate / Bits per Symbol

or equivalently:

BW = Rb / log2(M)

Where:

  • BW = Minimum Nyquist Bandwidth
  • Rb = Bit Rate (bps)
  • M = Number of signal states (modulation levels)

Baud Rate (Symbol Rate)

Rs = Rb / log2(M)

For ideal Nyquist signaling:

BWmin = Rs

Examples

1. BPSK

M = 2

log2(2) = 1

BW = Rb

2. QPSK

M = 4

log2(4) = 2

BW = Rb / 2

3. 16-QAM

M = 16

log2(16) = 4

BW = Rb / 4

Summary

Modulation Bits/Symbol Bandwidth
BPSK 1 Rb
QPSK 2 Rb / 2
8-PSK 3 Rb / 3
16-QAM 4 Rb / 4
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