STUDY OF MODIFIED ALGORITHMS WITH SIGNAL CONSTELLATION ROTATION IN DTMB STANDARD ON THE BASIS OF SIMULINK MODEL IN MATLAB ENVIRONMENT

Abstract

This paper discusses modified algorithms with signal constellation rotation applied in the digital
terrestrial television multimedia broadcasting standard adopted in Cuba. Compared to using
constellations without rotation, these algorithms give a significant increase in system performance under
challenging reception conditions, with industrial interference and low signal-to-noise ratio. This paper
analyzes the effect of the angle and direction of rotation of the signal constellation on the stability of the
digital terrestrial television multimedia broadcasting system. The main purpose of this paper is to analyze
the effect of the angle and direction of rotation of the signal constellation on the stability of the digital
terrestrial television multimedia broadcasting system. For the study, a proprietary architecture of digital
terrestrial television multimedia broadcasting system adopted in Cuba was developed, implemented in
Simulink in Matlab environment. This Simulink model allows analyzing the dependence of the bit error
rate on the value of white Gaussian noise for different system configurations. The model of additive white
Gaussian noise, which is mixed with the generated signal, is widely used in the research. The proposed
modifications allow the reception of digital terrestrial television multimedia broadcasting in fade-free
channels with equal values of the bit error rate for all cases analyzed. In this case, in order to obtain a
significant gain from constellation rotation, in the order of seven decibels, it is proposed to transmit the
quadrature and in-phase components on different subcarriers and at different moments of time. In the
scheme with signal constellation rotation, the quadrature component should be transmitted not on the
same subcarrier, but with a delay and on a different subcarrier. Then from one quadrature amplitude
modulation is actually two amplitude binary modulation in-phase and quadrature projection, which are
transmitted on independent subcarriers, and affected by interference differently, which provides reliable
demodulation at lower values of the signal-to-noise ratio and the impact of industrial noise. A disadvantage
of the algorithm is that it does not sufficiently counteract Gaussian noise.