Methodology for Assessing the Noise Immunity of Digital Signal Reception in a Shortwave Communication Channel Taking into Account the Diffuseness of the Ionosphere

The paper shows the dependence of the noise immunity of signals with multiple PSK and QAM modulation of a shortwave communication channel with Rician fading on the ratio of the operating frequency to the maximum usable frequency and the degree of ionosphere diffuseness. The noise immunity was estimated based on the moment function and numerical methods. Numerical calculations of the error probability were performed using the built-in MATLAB simulation tool. The values of the permissible signal-to-noise ratio were established to ensure the required error probability for PSK signals with a modulation ratio of M = 8 and QAM signals with a modulation ratio of M = 64. The modulation ratio of the signals was selected based on the signals actually used in the shortwave communication channel established in the MIL-STD-188-110B standard. Interoperability and Performance Standards for Data Modems. To estimate the signal fading depth in the Rician channel, a known technique for estimating the dependence of the Rician parameter on the ratio of the operating frequency to the maximum usable frequency and the degree of ionosphere diffuseness was used. Also, energy losses of the permissible signal-to-noise ratio of PSK-8 and QAM-64 signals were established in comparison with signals with binary orthogonal frequency modulation BFSK depending on the ratio of the operating frequency to the maximum usable frequency and the degree of ionosphere diffuseness. For QAM-64 signals, it was found that their energy loss relative to BFSK will be about 4 dB under normal diffuseness conditions and about 2 dB under moderate diffuseness conditions. For PSK-8 signals, it was found that their energy gain relative to BFSK will be about 4 dB under normal and moderate diffuseness conditions. The developed method allows, based on the results of probing the level of ionospheric diffuseness, to select such ratios of the operating frequency to the maximum usable frequency in a single-mode short-wave communication channel that will provide an acceptable value of the probability of erroneous reception of signals with multiple phase and quadrature-amplitude modulations. It is advisable to further develop this method to evaluate the throughput of a short-wave communication channel when receiving PSK and QAM signals with Rician fading.