Interference Between Carrying Frequencies in DRM System

Relevance. In Russia and worldwide, there is a gradual transition to digital radio broadcasting DRM. This transition offers higher quality sound reproduction, significant radio frequency resource savings, high interference resistance, substantial energy savings compared to analog broadcasting systems, and the ability to build single-frequency networks. The cliff effect inherent in DRM-systems necessitates considering the influence of the interference level between subcarriers (ICI, Intercarrier Interference) of the OFDM-signal (Orthogonal Frequency-Division Multiplexing) on the overall interference resistance of DRM-systems. This is partly due to the mismatch of generators in the transmitting and receiving paths of DRM-systems. However, the recommendations of the International Telecommunication Union (ITU-R) and available publications lack requirements for the stability of generators in the transmitting and receiving paths of digital radio broadcasting systems, which significantly affect their interference resistance. This work addresses this gap. Goal. Improve the interference resistance of the DRM-system. Methods. Based on the analysis and development of data available in publications, a method for calculating the interference level between subcarrier frequencies is proposed for situations where there is no loss of orthogonality of subcarrier frequencies during OFDM signal reception, and only white noise (AWGN - Additive White Gaussian Noise) is present in the radio channel. Results. The impact of normalized frequency shift of generators in the DRM-system's transceiver path on the degradation of the signal-to-noise ratio when modulating subcarrier frequencies with QPSK for different levels of interference resistance (PL0-PL3) has been studied and evaluated. It is shown that the interference level between subcarrier frequencies of the OFDM signal depends on reception conditions, modulation type, code rate, required minimum signal strength of the transmitter's electromagnetic field, and the required minimum signal-to-noise ratio at the reception point, receiver's own noise, and atmospheric noise level. The validity of the obtained results is confirmed by experimental data from other researchers. Novelty. The obtained results are new for the DRM-system. In mode stability under stationary reception and QAM-4 subcarrier frequency modulation, DRM-system OFDM signal reception becomes impossible when the frequency mismatch of the transceiver path generators exceeds (2.07…2.32) Hz. Practical significance. Knowledge of the ICI level of the OFDM-signal when the frequency of the generators in the transmitting and receiving clocks of DRM-systems is detuned is necessary for developing national regulatory documents that govern the operational characteristics of DRM system equipment.

DRM, digital broadcasting, DRM, interference between subcarrier frequencies of OFDM-signal