ABSTRACT:
Noise in Radio Communications
Noise is a macroscopic description of quantum effects. In radio communications the most important is thermal noise. The latter is collected by an antenna from its surroundings. It is also created in passive and active components of electronic circuits. The thermal-noise intensity is described by the nose temperature and/or the noise figure. The analog signal-to-noise ratio is converted into the bit-error rate in digital communications. Thermal noise is converted in oscillators into phase noise. The latter can be observed as interference in the neighbor channel, as random rotation of the modulation constellation, as a random, residual frequency modulation and/or as clock jitter. Noise can also be used as a test signal and/or for key generation in cryptography, from short passwords up to the unbreakable one-time coding book.


POVZETEK:
Šum v radijskih komunikacijah
Šum je makroskopski opis kvantnih pojavov. V radijskih komunikacijah je najpomembnejši toplotni šum. Slednjega zbira antena iz svoje okolice. Ustvarjajo ga tudi pasivni in aktivni gradniki elektronskih vezij. Jakost toplotnega šuma opisuje šumna temperatura oziroma šumno število. Analogno razmerje signal/šum se pretvori v pogostnost napak v številski zvezi. Toplotni šum se v vsakem oscilatorju pretvarja v fazni šum. Slednjega opazimo kot motnjo v sosednjem kanalu, naključno sukanje ozvezdja modulacije, naključno frekvenčno modulacijo oziroma drhtenje takta. Šum lahko uporabimo tudi kot merilni signal oziroma za ustvarjanje ključev v kriptografiji, od kratkih gesel do nezlomljive šifrirne knjige za enkratno uporabo. Umetni nadomestek šuma so psevdonaključna zaporedja.