Which modulation technique does not use past information for modulation

Pulse Code Modulation (PCM):

Binary code is varied according to the sampled value.

Block diagram of the PCM system is shown below:

It is used in Voice, Audio, and CD recording.

PCM system doesn’t use the previous samples in its processing of information.

Important Points

Delta Modulation (DM):

It is used to reduce the bandwidth or bit rate.

• It is considered as a 1 bit DPCM. So, the encoder is a 1 bit ADC
• The encoder output is either 1 or 0
• Two quantization levels are used + Δ and - Δ

The  block diagram is shown below:

DM uses past information for modulation.

Adaptive Delta Modulation (ADM):

• This Modulation is the refined form of delta modulation.
• This method was introduced to solve the granular noise and slope overload error caused during Delta modulation.
• In DM the step size is constant and depends on a maximum slope but in ADM the step size is varied according to the slope of the message signal.

The transmitter part is shown below:

ADM also uses past information for modulation.

Adaptive Differential Pulse Code Modulation: It is one of the variants of the DPCM that varies the size of the quantization step. It is used to compress the data.

The block diagram of DPCM is shown below:

DPCM also uses past information for modulation.