Showing papers on "Cognitive radio published in 1978"
01 Nov 1978
TL;DR: In this article, the use of spread-spectrum modulation in a common type of land-mobile radio service is studied, where the radio service contains many networks operated independently, similar to the business land mobile radio service.
Abstract: The use of spread-spectrum modulation in a common type of land-mobile radio service is studied. The radio service contains many networks operated independently, similar to the business land-mobile radio service. Network independence implies (among other things) that there is no central control of a transmitter's radiated power. A congested urban environment is assumed. If a band is allocated exclusively to spread-spectrum modulation for such a service, base stations and mobiles must operate on different channels, and all base station antennas must be located within a relatively small area. In this case, the worst interference is in the mobile-to-base channel. An explicit formulation of the "far-near" problem and a powerful computer calculation both show that in such a service spread-spectrum modulation is less spectrum efficient than conventional FM modulation. In fact, the spectrum efficiency of the spread-spectrum systems is inversely proportional to the cube root of the processing gain. However, overlaying a spreadspectrum system on conventional bands shows some promise.
6 citations
TL;DR: A method is presented for displaying the time-varying transfer characteristic of communication channels, and is illustrated by showing in detail the behavior of an HF-SSB radio channel during one minute periods, under the various fading characteristics classified by USAEL.
Abstract: A method is presented for displaying the time-varying transfer characteristic of communication channels, and is illustrated by showing in detail the behavior of an HF-SSB radio channel during one minute periods, under the various fading characteristics classified by USAEL. It is also demonstrated how this method aided study of the causes of errors in data received by digital modems.
1 citations