Method of estimating the link quality of a UHF SATCOM channel

While the use of geostationary satellites allows tactical radios users to achieve beyond the line-of-sight communications nearly anywhere within the footprint of a satellite system, the use of directional antennas forces the radio operator to know the precise location of the satellite that is being used. Though a pointing guide and compass can work reasonably well when positioning an antenna, the Signal to Noise Ratio (S/N) thresholds of the highest date rate modems require more precise positioning to improve the system link margin and achieve a reasonable Bit Error Rate (BER). Additionally, one of the requirements of the Integrated Waveform (DAMA UHF SATCOM), specified in MIL-STD-188-181C/182B/183B/185A, calls for the ability to measure the Carrier Power to Noise Spectral Density Ratio (C/No) of the received FOW to within a certain degree and report the measured results to the IW Channel Controller (CC). This information facilitates the allocation of TDMA time slots with the appropriate over-the-air modem to support a reasonable BER given the terminal´s channel conditions. The same techniques that can be utilized to meet the IW channel quality reporting requirements can be leveraged to create a system that assists terminal operators with antenna placement by informing them when optimal antenna placement is achieved and the appropriate over-the-air modem to utilize given the measured C/No. This paper will discuss the utilization of fast Fourier transforms (FFTs) in the determination of MILSATCOM channel quality in order to improve the ability of a system to select the optimal over-the-air modem and provide the user with the ability to manually locate geostationary satellites.