Method of Estimating Satellite Link Quality in a Time Slotted Tactical UHF SATCOM System

While the use of geosynchronous 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. Because of this, when operating in a SATCOM system it is often useful to have the capability to conduct a RSSI (received signal strength indication) check to confirm that the transceiver is configured for the correct channel and the antenna is pointed optimally. Typically, this type of measurement is done on dedicated satellite channels by transmitting a known signal on the uplink frequency and immediately turning around the transceiver and receiving the retransmitted signal on the downlink frequency. The transceiver will then analyze the received signal to determine the quality of the channel by calculating the Carrier Power to Noise Spectral Density Ratio (C/N¬0). Unfortunately, this method of satellite link quality estimation does not work on a channel that is being operated as a time slotted system, such as the Integrated Waveform specified in MIL-STD-188-181C/182B/183B/185A, as the RSSI transmission will interfere with the timeslots being utilized by other operators sharing the SATCOM channel. Furthermore, the required transmission duration to accurately calculate C/N¬0 will not be possible in a single timeslot even if the interference is avoided. This paper will discuss an alternative method to using a single contiguous transmission, comprised of a preamble and payload, through the utilization of multiple orthogonal single frequency tones that last the entire duration of the transmission. By utilizing a payload composed of a single frequency, this paper will then discuss a method for creating an RSSI check that uses an arbitrarily sized transmission to accommodate the small timeslots allocated in time slotted systems such as the Integrated Wa- eform.