Doppler insensitive non-terrestrial digital cellular communications network

Abstract

The Doppler insensitive non-terrestrial digital cellular communications network ensures that, independent of the aircraft direction and apparent velocity of the mobile subscriber station, at least one and very likely two cells/antennas, carry the call even though other cells/antennas in the non-terrestrial digital cellular communications network encounter an apparent velocity of the mobile subscriber station which disables system operation. Since the architecture of the non-terrestrial digital cellular communications network and the non-terrestrial communication application have a common element, namely altitude, it is also possible to minimize the Doppler/capacity problem by segmenting the non-terrestrial space into layers, or PN code words. This topology makes use of spatial diversity in the elevation plane, or “Z direction” to ensure that at least one and very likely two layers, can carry the call. Each layer in the cell is formed by an antenna beam, having different system configurations to preset the level of soft hand-off. Spatial diversity within the cell site can also be implemented in the “X & Y directions”, or azimuthally. This is accomplished by interleaving cells of different diameters or with differing azimuth sector patterns. In this manner, the periodicity of the cells is randomized, keeping calls in soft hand-off by maintaining a tangential direction of flight with respect to most cell sites, thereby minimizing the Doppler shift of the carrier frequency with respect to the serving cell site.