Report esame Techniques and systems for digital signal communications, AA 2023/2024

Transmission of a still picture (PSK, noise,

differential detection) and error rate

assessment

Matteo Dianati - 285872@studenti.unimore.it

Michele Faccone - 281657@studenti.unimore.it

Oleksandr Kyryliv - 283054@studenti.unimore.it

December 19, 2023

Abstract

Nowadays, wireless communication systems are deployed everywhere to guarantee many

different services of video/audio transmissions. In this kind of communications, the main

problem is due to the presence, in the propagation medium, of many sources of interference

that may distort the data transmitted or destroy the information in a partial or total way.

A solution to this problem may be the implementation of error-correction strategies that

can ensure the possibility to recover the original information, even if the data received

has been depleted.

1 Introduction

In this report we will discuss the simulation of a real environment in which a still picture

is transmitted in a noisy propagation medium. To simulate the total environment under

exam we used an ADALM-Pluto, a device compatible with MATLAB, used to develop

the program code for the device. The goal of the project is to generate a whole process of

picture transmission ensuring the best final result achievable, using redundancy coding,

like the Convolutional Encoding, and Viterbi Decoding.

2 Algorithms

The program developed is an updated version of a program already proposed. As shown

in Chapter 4, the earlier version of the program written cannot cope with error correction

1

even if it was used the Gray Coding which already prevents from distorting the information

by rearranging the bit order of the data; that’s why it has been decided to manipulate the

information in a different way with Convolutional Coding, developing a bigger quantity

of information to be transmitted, due to redundancy bits but more robust to disturbing

events. This type of elaboration requires a proper decoding algorithm like the Viterbi

decoding, which will be discussed in Section 2.2.

2.1 Convolutional Encoder

A convolutional encoder is a logical structure used to implement Convolutional Coding in

a transmission system. It is substantially composed by a shift register and an appropriate

set of electrical connections between the bits shifted inside the register and some adders.

This kind of data coding evaluates the coded outputs looking to the current state in input

and the past states stored in the shift register. For this reason, the redundancy code

produced can be defined as a code with memory.

Figure 1: Block scheme of the convolutional encoder

A Convolutional Encoder is defined by many elements:

1. the constraint length L, which defines the total amount of k-bits blocks considered

to produce the output;

2. the code rate R, defined as R = where k are the input bits and n is the number

k/n

of the output bits produced every iteration;

3. the generators , described as a row vector, which define the connections between

g

m

the adder and the bits inside the shift register. The connections of an adder are

usually described in octal representations.

Knowing L, k, n and the generators, w