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.
