Partial Processing Satellite Relays for Frequency-Hop Antijam Communications

Abstract

Military satellite communications systems may be implemented with varying levels of satellite on-board processing. For frequency-hop (FH) spread-spectrum signals two options are the dehop-rehop transponder (DRT) and the symbol regenerative processor (SRP). This paper considers FH, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> -ary FSK modulation in the presence of full band and worst case partial-band noise jamming. The relationships among end-to-end signal-to-noise ratio (SNR) performance or probability of bit errors and the uplink and downlink SNR are derived. For a DRT, an additional parameter is the satellite filter bandwidth W <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> since this may differ from the despread modulation bandwidth W <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</inf> for a particular user access under TDMA variable-data-rate operation. The SNR performance in this case depends upon the ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W_{s}/W_{r}</tex> a well as the uplink and downlink SNR. The resulting penalty in the link budget of the weaker of the uplink or downlink is much less than the mismatched ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W_{s}/W_{r}</tex> and diminishes as the links become unbalanced. The SRP slightly outperforms the DRT but it is more complex and does not as easily accommodate variable data rates.