MIMO Applicability to UHF SATCOM

Narrowband satellite communications (SATCOM) in the ultra high frequency (UHF) band is an attractive option within the military SATCOM (MILSATCOM) community. The UHF user terminals (UTs) are typically low cost, easily deployable and have broad beamwidths so that precise pointing to the satellite is not a requirement for mobile users. At the same time, some inherent disadvantages of UHF SATCOM are limited bandwidth, the inability to apply frequency re-use in the geo-stationary arc and hence less capacity. The multiple antenna technique, popularly referred to as MIMO (multiple input multiple output) is known to increase the channel capacity using spatial multiplexing and offers the ability for frequency reuse. The intent of this paper is to analyse the applicability of MIMO to UHF SATCOM, based on some of the recent developments in MIMO SATCOM research. The SATCOM channel is principally dominated by the line of sight (LOS) path between the satellite and the ground user. To achieve spatial orthogonality in the LOS SATCOM channel, depending on the wavelength, antenna separation on the order of several kilometers is required either in space or on the ground. In this paper, we consider using multiple satellites for a large antenna separation in space to enable closer antenna separation for users on the ground. Channel modeling, capacity calculation, issues with the propagation time difference and receiver signal processing are addressed in this paper.

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