Satellite data communications have been introduced in some areas to provide the means for message exchange between air traffic controller and pilot, and for aircraft surveillance in oceanic areas. Before the completion of the standards on aeronautical satellite data communications by the International Civil Aviation Organization (ICAO), we had conducted a series of flight experiments using INMARSAT satellites to validate the draft standards. In the flight experiments, we evaluated the characteristics on transmission delay for various flight environments. In the flight experiments, only one Aircraft Earth Station (AES) was used and the effect of traffic congestion on transmission delay characteristics was not evaluated.

We reorganized the experimental equipment for the flight experiment and established a satellite data link experiment system in the laboratory. The experiment system consists of four pseudo-AES, an experimental Ground Earth Station (GES), fading simulators and experimental Air Traffic Control (ATC) equipment. This system provides the environment where the transmission delay characteristics can be evaluated for multiple AES environment in a practical satellite link condition. We also developed a computer simulation software to evaluate the transmission delay characteristics for many AES environment. This report describes the transmission delay characteristics for various traffic conditions obtained from the laboratory experiments using the satellite data link experiment system and from the computer simulations.

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Nowadays every Japanese city has been tightly fabricated in the national settlement system which is affected by the recent large-scale inter-settlement migration. Pred (1973) assumed that migration between two settlements in a national settlement system was produced by diffusion of growth-inducing innovation and that the number of migrants between the settlements was proportional to the potential interaction between them. He built up an inter-settlement migration model based on this assumption.
In this paper the potential interaction between two settlements is defined as accessibility between them, and inter-settlement migration in Japan is analyzed with the help of the Pred's model. The Population Census of 1955, 1960, 1965 and 1970 are used for the analysis. Using popuation of each district and time-distance between paired districts, accessibility between them was calculated with equation (3) and numbers of inter-settlement migrants during the period of five years (from each census year to the next) were estimated with equation (2').
133 districts ayalyzed here are composed of 87 cities with more than 200, 000 inhabitants in 1975 and 46 “Prefectural districts” which include other cities, towns and villages with the population of less than 200, 000, that belong to the same prefecture.
The main results are summarized as follows:
The pattern of inter-settlement migration in Japan estimated by the Pred's model shows a close approximation to the actual one, with a few exception such as the case in the Three Large Metropolitan Areas. Estimated migrants to the Metropolitan Areas, particularly to Tokyo, increased during the period of high rate of economic growth of the nation and decreased slightly since then. It is also close to the actual change in migration in Japan.
The results indicates that the Pred's model of inter-settlement diffusion of growth-inducing innovation is a useful method to estimate the migration in the national settlement system in Japan. It illustrates that concentration of various information and administrative units is a main factor of the recent social increase in population of urban centers because those units are concentrated in highly accessible cities.
The migration to satellite cities in the Three Large Metropolitan Areas was not well estimated with accessibility, and the migration to some prefectural cities was underestimated. Therefore it is assumed that other factors rather than national accessibility such as some environmental factors might produce the migration in the Metropolitan Areas. Centrality and accessibility in a regional scale might work in certain prefectures.

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