Wideband Frequency Hopping Spread Spectrum (FHSS) communications are widely used in both military and commercial applications. In military applications, it is very important to investigate these communications, especially when frequency hopping signals are received simultaneously by a single antenna. This paper investigates the problem of estimating interfering wideband asynchronous frequency hopping (FH) signals parameters with the same hop rate, and using narrow-band receivers. Due to minimal knowledge about the transmitted signals, the problem is analyzed in semi-blind mode. For this purpose, time-frequency (TF) processing has been applied to the modulated wideband converter (MWC) output. The proposed method consists of two stages; In the first stage, frequency-hopping signals with different amplitudes are received by a single antenna. By passing through baseband receivers, the TF distribution of the converter's output signal is obtained. In the next stage, by computing instantaneous spectral entropy (SE), and finding the local maxima in the spectrum, the hop time of each signal is obtained. We use MWC for sub-Nyquist sampling and simultaneous extraction of time and frequency information from signals while eliminating irrelevant signals. The results obtained from estimating hop time parameters demonstrate improved performance compared to other traditional source separation methods such as sparse linear regression (SLR). Based on evaluation metrics such as root mean squared error (RMSE), in lower signal-to-noise ratio (SNR) values, the amount of error has been substantially reduced. تفاصيل المقالة

Satellite communications technology developed rapidly and plays important role in communication networks. In the meantime, CNC satellite communication has received much attention due to its high spectral efficiency. However, the analysis of this type of communication signal in non-cooperative receivers is associated with many challenges due to the nature of time-frequency overlap. The proposed methods in this field have been developed assuming either symmetry or asymmetry in the amplitude of the two interfering signals. However, a reliable method to detect the amplitude symmetry in the non-cooperative receivers is missing in the literature. Thus, in this article, the symmetry or asymmetry of the amplitude of time-frequency overlapping signals of these type of communications has been analyzed using higher-order statistics. For this purpose, the mathematical relationships of higher-order statistics for the model of time-frequency interfering signals received in the non-cooperative receiver have been developed. Then, the appropriate decision function is defined based on different ratios of higher-order statistics of the received signal. This decision function is used to detect amplitude symmetry or asymmetry in time-frequency overlapping signals for CNC communication. The simulations show that the decision-making function based on the sixth and fourth ratio cumulants is a reliable metric, such that the probability of correct classification at signal-to-noise levels higher than 25dB for BPSK modulation is more than 80%, and for QPSK modulation is more than 90%. تفاصيل المقالة