frequency selective fading
O.A. Nokhrin, S.V. Ivkov, V.V. Pechurin
On radio data links M-ary phase modulation is in a wide use. Receiving of such signals is performed by the coherent method based on the use of generator of local carrier, controlled by the phase locked loop (PLL). PLL systems are subjected to false lock-on, especially under fading conditions, that effects series of symbol errors. Fading conditions in the article are defined as an effect of multipath propagation: general fading, when amplitudes of rays are approximately equal and mutual delay of rays is rather shorter than pulse duration and frequency selective fading, when mutual delay of rays exceeds pulse duration. Improvement introduced into a known method of non-coherent receipt allows reject the local carrier use for signal detection. As a result, it reduces symbols errors. Besides, as it is shown by mathematical analysis, introduced improvements increase interference insusceptibility under fading. Assumption on interference insusceptibility rise of the non-coherent method demodulation, relatively coherent under fading, is confirmed by model ex-periment results.
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