A study of environmental constraints in the coastal harbor radiotelephone system |
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| Authors: | Halpern S |
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| Institution: | Bell Telephone Laboratories, Inc., Holmdel, NJ, USA; |
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| Abstract: | This paper presents a new study of the effects on communications within the coastal harbor system of such environmental factors as nonstationary signal propagation characteristics and nonstationary atmospheric noise. Propagation of signals during daylight hours is predominantly by ground-wave propagation over sea water. During the evening hours, sky-wave and ground-wave propagation takes place. The noise at receiving sites during daylight hours is predominantly set by the level of galactic or man-made noise some 40 to 45 dB above thermal. During the evening hours, the level of atmospheric noise may at times reach some 90 dB above thermal. For daylight hours, it is shown that usable quality will not be achieved for distances greater than 400 mi; while at night, usable quality will be achieved beyond 200 mi with less than 20-percent probability. The conditional distribution of intraarea signal-to-interference ratio at the receiving antenna is shown to be approximately lognormal with a standard deviation of 23 dB during the day and a standard deviation of 16 dB during the night, for an area of high atmospheric noise. It is also shown that channel frequency separations of greater than 9 kHz are necessary if the probability of detecting crosstalk is to be kept below 25 percent during interfering transmissions from the same coverage area under low noise conditions. The probability of detecting intelligible crosstalk from a eochannel interferer transmitting at night from a different coverage area located from 400 to 1200 mi away could be as high as 58 percent. |
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