2019; Adaptive Delta Modulation (EE330 Digital Communication Project)

Guining Pertin
Nov 30, 2019
2 min read

Updated: Oct 7

Introduction

This work was done for EE330 course project under Dr. Ribhu, EEE Dept., IITG. Our work was greatly appreciated and earned us a +1 grade from Professor. I ended up getting an AA (A+) from the theory and with this +1 grade I ended up earning an AS grade which is obtained by very few people in the whole batch throughout BTech.

Delta Modulation(DM) is a waveform coding technique useful in reducing data rate to a larger extent in data communication. But the inherent problem encountered in delta modulation is slope overload error and granular error.

Image from https://slideplayer.com/slide/8624022/ – by Vivien Collins

Implementation

The project was on exploring and simulating different Adaptive Delta Modulation(ADM) techniques to reduce the slope overload and granular errors. The project was taken up by the following members –

Guining Pertin, ECE, IITG
Devashish Taneja, ECE, IITG
Mohnish Kumar, ECE, IITG

Delta modulation (Solving slope overload error for given data causes more granular noise)

The different ADM techniques explored have been explained below with complete simulation results –

JAYANT Algorithm:

In this method, a delta modulator which, at every sampling instant, adapts its step size Δ(for staircase approximation to the input signal) on the basis of a comparison between the two last channel symbols, Cr and Cr-1. Specifically, the ratio of the modified step size Δr to previous step size Δr-1 is either +P or –Q depending on whether Cr and Cr-1 are equal or not.

An important disadvantage of this technique is that the dynamic range of modulated signal increases.

SONG Algorithm:

Let m(t) be the input signal and be its staircase approximation. Let error, at the kth sampling instant. k = 0, 1, 2, 3 . . . e (k) can be of positive or negative value. The kth transmitted symbol is ‘1’ if e(k) > 0, otherwise it is ‘0’ if e(k) < 0.

If e(k) = 0 , either ‘1’ or ‘0’ can be transmitted.

Modified ABATE Algorithm:

This algorithm is more susceptible to slope overload than the SONG Algorithm. The specialty of this algorithm is that it adaptively follows the received signal even in a channel with high error rate.

Modified SONG Algorithm:

In this algorithm the rate of change of step-size in the slope-overload region can be So or α So or α^2 So etc., by proper choice of α>1, the rate of change of step-size can be made greater than So. It is seen that choice of gives a better performance to slope overload and the parameter β takes care of the granular noise as a result of which a better performance is obtained as compared to SONG and modified ABATE algorithms.