Methods of Detection of Bandlimited Signals on UHF MILSATCOM Downlinks

Providing satellite terminals with an indication of whether or not traffic is present on the downlink of an ultra high frequency (UHF) military satellite communications (MILSATCOM) channel requires consideration not needed for terrestrial radio systems. The UHF satellite transponder contains a bandpass filter and a hard-limiting amplifier that results in a constant downlink power level regardless of the uplink signal level. Therefore, it's not possible to rely on a simple metric such as the receive signal strength (RSS) to tell whether or not traffic is present on the channel. Additionally, symbol rate, timing and frequency characteristic metrics may fail to detect signals of unknown modulation or bandwidth. This paper will explore three different carrier detection schemes useful for collision avoidance on a UHF MILSATCOM channel. These methods are directly applicable to a satellite communication system where transmission is uncoordinated and multiple modulation types may be present (for example, MIL-STD-188-181C single-access mode). The modulation agnostic characteristic of these methods also lends them to applications to other fields such as cognitive radio.