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Measurement of radio signal energy parameters
The present paper discusses different techniques of measuring Carrier-to-Noise density ratio (C/N0) in navigation and information-communication systems. C/N0 means the ratio of the received signal power to the noise spectral density N0 at receiver's input (at the output of an antenna with a low-noise amplifier (LNA)). Correlation processing is performed in the receiver to obtain in-phase (I) and quadra-phase (Q) components of the input signal. Three estimation algorithms of C/N0 [Hz] have been analyzed in the paper. The first algorithm is robust: it requires minimal a priori information about signals, noise and receiver configuration. This algorithm is based on estimation in real time both expected value and the variance of in-phase component I. The second algorithm is called I-noise-immune, since it provides much more accurate estimates for C/N0, than the robust one but it needs a priori data about variance of component I. This requirement can be satisfied if value N0 is mainly determined by internal receiver noise (more precisely, - LNA noise), but not by received external interference. Both algorithms are applicable when Phase locked loop (PLL) operates quite precisely in the receiver. The third algorithm called Z-noise-immune, unlike the two first algorithms, does not need precise operation of PLL or even PLL availability in the receiver at all, but similar to the second algorithm is based on the assumption that value N0 is determined by internal noise rather than external interference. There were shown the third algorithm produces unbiased estimate of C/N0.