Notes on Differential Pulse Code Modulation (DPCM)

Introduction to DPCM

• This session covers the importance, advantages, and disadvantages of DPCM compared to Pulse Code Modulation (PCM).

Sampling Rates

• Nyquist Rate: Sampling should occur at twice the bandwidth of the input signal.
• Increasing Sampling Rate:
  • As sampling rate increases, the number of samples becomes denser.
  • More samples lead to better correlation of the signal with the sampled output.

PCM vs. DPCM

Key Differences

• PCM: Transmits digital data of all samples.
• DPCM: Transmits differences between consecutive samples rather than all sample data.

Example of Sample Magnitudes

• PCM Example: 3.1 V, 3.5 V, 2.5 V, 2.2 V.
• DPCM Example: Differences between samples: 0.4 V, 0.1 V, 0.5 V, etc.

Advantages of DPCM

• Reduced Number of Levels:
  • Fewer amplitude levels needed in DPCM since it only sends differences.
  • Example: Instead of sending the full magnitude, we send 0.4 V, 0.1 V, etc.
• Lower Bit Rate:
  • DPCM requires less bit rate for transmission compared to PCM, leading to reduced data rates.
• Compression: DPCM provides more compression by reducing redundant information.

Characteristics of DPCM

1. Higher Sampling Rate: Increases correlation between successive samples.
2. Small Amplitude Differences: DPCM finds that the amplitude difference between successive samples is minimal.
3. Redundant Information: PCM has more redundant information due to encoding all sample levels.
4. Less Memory Requirement: DPCM requires less memory for encoding since it only encodes the differences between samples.

Mathematical Relation

• Levels Calculation: More levels in PCM lead to increased bits per second.
  • Formula: L = 2 * Xmax / delta
• DPCM Levels: Fewer levels due to transmission of differences, resulting in lower bits per second.

Conclusion

• DPCM offers significant advantages in terms of compression, reduced bit rates, and reduced memory requirements compared to PCM.
• Upcoming sessions will cover DPCM encoder and decoder to reconstruct DPCM signals.

Closing Remarks

• Stay tuned for more on the digital communication playlist.