Satellite TT&C Denial, Electronic Counter Measure and Mitigation

1. Satellite TT&C Denial, Electronic Counter Measure and Mitigation By Don Olsen For Presentation at Security Working Group Of CCSDS April 11-15, 2005 Athens Greece

2. Background • Satellite TT&C links are susceptible to electronic counter measures (ECM). • Spoofing • Eavesdropping • Denial/Jamming • Satellite TT&C links can be protected against ECM by • Encryption, • Authentication, and • Spread spectrum • This presentation will focus on AJ performance with spread spectrum.

3. Waveform Security and Jamming Mitigation • Some systems provide anti-jam capability through spread spectrum. • This could include frequency hopping or pseudo-noise (PN) spreading. • The measure of the improvement achieved is called processing gain. • Frequency hopping anti-jam waveforms: • Provide greater processing gain for same complexity than PN, • But has disadvantage of susceptibility to partial band and smart jamming, • Secure TRANSEC can protect against frequency agile, smart, narrow band jamming. • Presentation will restrict discussion to frequency hopping. • Power efficient modulation minimizes Eb/No in AWGN as well as jamming.

4. Waveform Security and Jamming Mitigation (Cont.) • Coding needs to maximize the required channel BER (Pcbe) so that partial band jamming is a disadvantage. • BER is inversely proportional to Eb/Nj, for partial band noise jammed (PBNJ) single diversity signals as shown next. • Nj is avg. jammer density. • Curve is tangent to the AWGN curve. (p. 11) • The slope is equal to the diversity symbol repetition combining. • Error correction coding must permit operation with the Pcbe at or above the tangent point, • For no Eb/Nj degradation from the Eb/No performance and • Forces jammer to jam entire hopping bandwidth. • Interleaving is needed to protect the decoder from burst channel errors. • The graphs in the backup charts show the Pbe with both ideal and non-ideal interleaving.

5. Scope and Limitations • Spectral allocation limits S band electronic counter counter measures (ECCM) processing gain. • X Band and Ka Band (21 GHz) would improve the processing gain over S band and are included herein as typical but not as exhaustive examples. • C and Ku are not Government bands and not included. • Since the uplink EIRP advantage is only bandwidth dependent Q band is included with its 3 dB bandwidth advantage.

6. Assumptions • Satellites are at synchronous altitude. • Secure TRANSEC will mitigate certain smart jammer attacks. • The choice of modulation, coding and interleaving will greatly influence the performance in smart partial band jamming. • Hop diversity count has a significant effect on the performance of a frequency hopped waveform in the presence of partial band jammers. • The interleaver needs to preserve a hop diversity of ~700. • To keep diversity related performance losses to 0.3 dB.

7. Link Parameters

9. Conclusions for Above Scenarios • Uplink jammer EIRP needed to degrade a 60 dBW uplink is: • 50 dBW with no frequency spreading • 96 dBW with 80 MHz frequency spreading • 130 dBW with 2 GHz frequency spreading • The Jammer EIRP needed to degrade a 30 dBW EIRP synchronous altitude satellite downlink is: • -38 dBW at S Band with no frequency spreading. • 8 dBW at S Band with 80 MHz frequency spreading. • 39 dBW at 21 GHz with 1GHz frequency spreading.

10. Backup Slides on AJ Performance with Imperfect Interleaving

12. Waveform Background • Non-ideal interleaving will allow smart jammers to degrade performance. • Slow hopping (many bits per hop) and partial band jamming creates burst errors. • Convolutional and turbo codes are very susceptible to degradation from burst errors. • Ideal interleaving will distribute bursts uniformly to mitigate the loss. • Hop diversity is the number of hops across which the code block is spread. • Or the number of hops across which the content of a convolutional code’s path memory is spread • However, the interleaver may not provide enough depth or effective use of the hopping diversity. • This limitation can degrade both processing gain and anti-jam capability. • The analysis and graphs later in this briefing show the effect of limited hop diversity.

13. Hop Diversity Analysis Approach • The analysis calculates and plots the BER curve for various Eb/Nj. • and partial band fraction for various numbers of diversity hops, Nh • with Eb/No set to 0. • The envelope of Pbe for worst case jammer fraction at each Eb/Nj was determined. • The set of envelope curves for various values of diversity were plotted. • The model sums the binomial weighted probabilities of error for each number of jammed hops out of a set of Nh hops. • This was repeated for several modulation and coding options. • The waviness of some of the lines is due to the size of the step in the partial band fraction.

14. Definitions of Parameters • The partial band Gaussian noise jammer fraction is r . • The code is either • Convolutional with rate, rc of ½ and constraint length 7 • Or convolutional turbo with rc of ½, constraint length 5 and 5120 bit block size. • The decoder transfer model was obtained • By fitting a judicious curve to the Pbe versus Pcbe relationship, • Where Pcej is the channel probability of error, • Pbe is the decoder output probability of error, • Given j of Nh diversity hops are jammed. • Code parameters definitions: • The linear scale factor for the code probability of error transfer model is a. • The exponential factor for the code probability of error transfer model is b. • It is closely related to half the minimum free distance of the code. • The curve corner fitting tightness factor for the code transfer model is n. • Pbe is the sum over j of the decoded binomialdistribution weighted Pcej.

15. Analysis for DPSK Modulation Case

16. Modulation Performance for Coherent DPSK and BPSK Cases Is Respectively

17. Where the complementary error function is given by Sklar in “Digital Communications” 2nd ed., p. 210 as:

18. Coding Parameters

23. Table of Graphs