TECHNOLOGY AREA(S): Space Platforms
OBJECTIVE: Design, develop, and demonstrate an innovative and smart automated gain control (AGC) loop for anti-jamming and reducing amplitude fluctuation and associated Intermodulation (IM) products of the Spread Spectrum Frequency Hopping (SS-FH) satellite transponder output.
DESCRIPTION: Current satellite receiver systems use an AGC loop with a fixed time constant, which performs well with non-frequency hopping signals in a normal environment without jamming. The AGC loop with a fixed time constant can deal with the slow fluctuations in signal amplitudes caused by weather conditions. When a frequency hopping algorithm is applied in a satellite communication system for anti-jamming, the corresponding signal amplitude may fluctuate quickly as the signal carrier frequency hops among frequency points that are not close to one another. In addition, the current transponder’s front-end AGC only monitors the total signal power input to the channelizer. On an individual channel that may be jammed, the jamming signal (power is higher than the desired signal) will be the key driver in driving the power level of the IM products at the output of the satellite high power amplifier (HPA). A smart jammer can find a “critical” jamming power that causes the IM noise rise to an “unacceptable” level that can dominate the downlink signal.
A new and smart AGC loop is needed to track communication signals' quickly fluctuating amplitudes generated by frequency hopping spread spectrum and to monitor the corresponding input powers of the satellite transponder's digital channelizer. As expected, the combination of smart AGC and digital channelizer can track and monitor each channel independently and simultaneously in the presence of noise and jamming signals. If successful, this proposed mechanism would find a specific channel with a jamming signal and suppress it so that the IM level at the output of the HPA is at an “acceptable” level. In addition, when combined with the advanced adaptive “Linearizer” the “smart AGC” could further reduce the transmit signal's amplitude fluctuations, which in turns would enhance the link performance in the presence of smart jammers and non-linearity caused by the satellite HPA.
PHASE I: Characterize satellite communication signals’ amplitude fluctuation characteristics when a frequency hopping spread spectrum is applied. Conduct modeling fast amplitude fluctuations for the frequency hopping system considering both channel and system hardware responses. Assess jamming impacts on AGC and HPA. Predict potential AGC and HPA responses to jamming impacts. Develop a fast response smart AGC loop that when combined with a “Digital Channelizer” will provide anti-jamming to combat various Electronic Attacks (EA) from smart jammers, including but not limited to partial band EA. Evaluate the smart AGC loop using the signal amplitude fluctuations generated by the channel and system hardware associated with SS-FH SATCOM system, and verify the performance with the smart AGC model.
PHASE II: Optimize Phase I results. Fabricate, test, and evaluate the performance of a hardware prototype to demonstrate the designed AGC loop under various EA strategies employed by a smart jammer. Compare measurements of the prototype to computer simulations. Validate potential capabilities of the joint smart AGC and “Digital Channelizer” with the “Linearizer”. Assess potential impacts from practical integration considerations.
PHASE III: DUAL USE APPLICATIONS: Explore the potential to transfer the technology to military systems and civilian satellite communications applications. Work with DoD primes and industry partners for a broader set of opportunities where the proposed technology be seen as a technology discriminator
REFERENCES: 1: D. Lu, "Development And Testing Of A Space-Borne GPS Signal Strength Sensor," https://theses.lib.vt.edu/theses/available/etd-10082003-121827/unrestricted/ThesisReport.pdf2: J.H. Jang and H.J. Choi, "A fast automatic gain control scheme for 3GPP LTE TDD system," Vehicular Technology Conference, September 2010.3: "Design And Operation Of Automatic Gain Control Loops For Receivers In Modern Communications Systems," http://www.analog.com/media/en/training-seminars/tutorials/42575412022953450461111812375Design_and_Operation_of_AGC_Loops.pdfKEYWORDS: AGC, Fast Response, Frequency Hopping, Model, On Board Processing, Partial Band Jamming, Satellite Communication, Smart Jammer
CONTACT(S):
Khanh Pham
(505) 846-4823
khanh.pham.1@us.af.mil
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