Data Transmission over FDM/FM Troposcatter Systems

There are more than one hundred troposcatter systems of various sizes in existence all over the world [1]. As the transmission of computer data becomes more and more common and in popular demand, such systems are certain to be involved in these services. Two methods are generally used for transmitting data over troposcatter channels: direct transmission and the frequency division multiplex/frequency modulation (FDM/FM) technique. In the latter, the individual data channels are combined into an FDM baseband to frequency or phase modulate a common radio carrierthe same technique used conventionally for the carrier transmission of multiplex telephone channels. In a study program, under a contract [2]-[4] to the U. S. Air Force Rome Air Development Center, both the direct transmission by time-division multiplex/frequency-shift keying (TDMF/SK) and the FDM/FM techniques are investigated. This paper, however, concerns the FDM/FM techniques only. It was found that both theoretically and experimentally FDM/FM troposcatter systems can support data transmission of various rates from 2.4 to 40.8 kbit/s for path lengths from 86.7 to 381.5 statute miles in smooth earth geometry with diversity reception, if proper path and equipment parameters are chosen.