Accession Number : AD0837412

Title :   COMPUTER SIMULATION OF FREQUENCY-SELECTIVE FADING OF HF RADIO SIGNALS AND OF THE IMPROVEMENT AFFORDED BY MODE-AVERAGING RECEIVING TECHNIQUES.

Descriptive Note : Technical rept.,

Corporate Author : STANFORD UNIV CA STANFORD ELECTRONICS LABS

Personal Author(s) : Kawachika, N. M.

Report Date : JUN 1968

Pagination or Media Count : 70

Abstract : The amplitude of a single-frequency, ionospherically-propagated HF radio signal fluctuates, or 'fades,' with time. This fading is caused by the interference between waves traveling along different paths between transmitter and receiver and by the changing nature of the ionospheric layers. When a number of single-frequency (CW) signals within some transmission passband are transmitted, it is found that the amplitudes of the various received components are not equal. This is called frequency-selective fading. Three versions of a diversity-combining principle, called mode-averaging, were studied to determine the degree of reduction of frequency-selective fading afforded by the use of this principle. First, a computer simulation of frequency-selective fading which occurs in a single (non-diversity) receiver was devised. The actions of the three-mode-averaging schemes were then simulated and the improvement in frequency response afforded by each scheme (as compared with the single receiver) was evaluated. The influence of antenna array spacing for one of the mode-averaging schemes was also studied with the aid of a computer, and the most desirable spacing determined. (Author)

Descriptors :   *IONOSPHERIC PROPAGATION), (*DIVERSITY RECEPTION, (*RADIO SIGNALS, ATTENUATION), HIGH FREQUENCY, PERIODIC VARIATIONS, MULTIPATH TRANSMISSION, RADIOFREQUENCY INTERFERENCE, SIMULATION, DIGITAL COMPUTERS, ATTENUATION.

Subject Categories : Radio Communications

Distribution Statement : APPROVED FOR PUBLIC RELEASE