TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.ORG Robust GPS-Based Timing for Phasor Measurement Units October 3, 2014 Grace Xingxin Gao University of Illinois at Urbana-Champaign UNIVERSITY OF ILLINOIS | DARTMOUTH COLLEGE | UC DAVIS | WASHINGTON STATE UNIVERSITY 1 FUNDING SUPPORT PROVIDED BY DOE-OE AND DHS S&T
How to Make GPS-based Timing Robust? 2 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Facts about GPS – GPS provides timing for many applications, such as PMUs – GPS civil signals are unencrypted • Only GPS military signals are encrypted • Civil users (e.g. PMUs) do not have access to the military codes – GPS civil signal structures are completely open • GPS civil signal definition is published in its Interface Control Documents (ICD) – GPS received signals are extremely weak • GPS satellites are 20,200 km (12,550 miles) away – GPS is operational • Satellites in orbits • Signals being broadcast • Billions of GPS receivers in use 3 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Outline – GPS Cooperative Authentication • Pairwise check • Decision aggregation – Position-Information-Aided Vector Tracking • Approach • Implementation • Experimental Results – Conclusions 4 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Outline – GPS Cooperative Authentication • Pairwise check • Decision aggregation – Position-Information-Aided Vector Tracking • Approach • Implementation • Experimental Results – Conclusions 5 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Cooperative Authentication: Architecture Cross-check receiver #1 Your snippet matches mine. You are not spoofed! I got my location. Can you guys check if I was spoofed? Cross-check receiver #2 A snippet of baseband GNSS signal A high correlation! You are good, bro. User receiver It doesn ’ t match mine. You might be spoofed. Cross-check receiver # N Merits: network and geographical redundancy 6 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Pair-wise Checking: Cross-correlation of P(Y) Code Lo et al. , 2009 Psiaki, Humphreys et al ., 2013 7 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Outline – GPS Cooperative Authentication • Pairwise check • Decision aggregation – Position-Information-Aided Vector Tracking • Approach • Implementation • Experimental Results – Conclusions 8 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Pairwise Check 9 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Pairwise Check – Ideal Results – Not Spoofed Spoofed 40 ms In-phase 40 Correlation peaks Baseband Correlation (C/A) Single Correlation peak No Correlation peak Quadrature- phase Spoofer cannot Baseband generate Correlation (P(Y)) 10 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Modeling Pairwise Check P(Y) codes don’t match 11 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Experiments with Different Scenarios San Francisco CA and Champaign IL, static 3000km 22km Rantoul IL, moving at ~45 mph and Champaign IL, static 12 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Experiments: San Francisco & UIUC Everitt Lab – • • • – SiGe Sampler • • 13 – TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G • • • – • •
Pairwise Results for Different Separations 3000km separation 22km separation Almost no Some Residual Residual Correlation Correlation Near ideal Correlation Could detect Could detect spoofing spoofing 14 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
SNR Affects Pair-wise Check Performance 15 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Outline – GPS Cooperative Authentication • Pairwise check • Decision aggregation – Position-Information-Aided Vector Tracking • Approach • Implementation • Experimental Results – Conclusions 16 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Modeling Unreliable Cross-Check Receivers 17 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Authentication Performance, Theoretical Results Pair-wise Pair-wise Probability of being Probability of being false missed spoofed by a spoofed by the alarm rate detection rate different spoofer same spoofer • Authentication performance improves exponentially with increasing number of cross-check receivers. • P SS causes twice as great performance deterioration as P SD does. – Choose a cross-check receiver far from the user receiver. 18 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Receiver Operating Characteristic (ROC) Curves 19 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Performance of Cooperative Authentication Assume 20% of the cross-check receivers are spoofed (an extremely challenging assumption) 0 -1 10 10 P SS = 0, P SD = 0 -2 Probability of missed detection (P MD = 1 - P D ) P SS = 0.02, P SD = 0.18 10 P MD = 0.15 P SS = 0.1, P SD = 0.1 -1 10 Probability of false alarm (P FA ) -3 P SS = 0.18, P SD = 0.02 10 P FA = 0.001 -4 10 -2 10 -5 10 -6 10 P SS = 0, P SD = 0 -3 10 P SS = 0.02, P SD = 0.18 -7 P SS = 0.1, P SD = 0.1 10 P SS = 0.18, P SD = 0.02 -4 -8 10 10 2 3 4 5 6 7 8 2 3 4 5 6 7 8 Number of cross-check receivers (N) Number of cross-check receivers (N) Probability of missed detection Probability of false alarm • Robustness grows exponentially with the number of cross-check receivers • A small number of unreliable cross-check receivers are on par with a reliable cross-check receiver. 20 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Outline – GPS Cooperative Authentication • Pairwise check • Decision aggregation – Position-Information-Aided Vector Tracking • Approach • Implementation • Experimental Results – Conclusions 21 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Approach: Position-Information-Aided (P.I.A.) Vector Tracking Approach: – Vector tracking – Reduces the search space • Aided by the true position – Kalman filtering • Recursively predict and update the errors – Narrowband loop filter 22 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Scalar Tracking Channel 1-N , 𝜚 Incoming 𝑔 𝑒 Signal NCO GPS Front-end Correlator Position and Time Code and Carrier Navigation Solutions Processing Discriminators (𝑦, 𝑧, 𝑨, 𝑢) 23 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Implementation: P.I.A. Vector Tracking Channel 1-N Navigation LOS Projection Prediction Position, Velocity, Code and Carrier Timing, Code, and Predictions Carrier Correction , 𝜚 Incoming 𝑔 Timing 𝑒 Signal Errors NCO Known True Position analysis GPS Front-end Correlator Position (𝑦, 𝑧, 𝑨) Kalman Filter: Time Code and Carrier Navigation Solution Discriminators (𝑢) Prediction 24 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
Implementation: Kalman Filter 𝜀𝑦 𝑢 0 0 0 Δ 0 0 0 0 – States: 𝜀𝑌 , 𝜀𝑊 , 𝜀𝑢 , 𝜀𝑢 𝜀𝑧 𝑢 0 0 0 0 Δ 0 0 0 – State Transition Matrix 𝜀𝑨 𝑢 0 0 0 0 0 Δ 0 0 𝜀𝑤 0 0 0 0 0 0 0 0 𝐺 = 𝑌 = 𝜀𝑤 0 0 0 0 0 0 0 0 𝜀𝑤 0 0 0 0 0 0 0 0 𝑢 𝜀𝑢 0 0 0 0 0 0 0 Δ 0 0 0 0 0 0 0 0 𝜀𝑢 – Predictions: – 𝜀𝑌 = 𝑌 − ( 𝑌 + 𝑊 Δ 𝑢 ) – 𝜀𝑊 = 𝑊 − 𝑊 – Calculation of receiver clock bias: 1 𝑢 = 𝜕 ( 𝜍 − 𝑦 − 𝑦 ) 𝜕 ∑ 1/ 𝑤𝑏𝑠 𝜗 Satellite Psuedorange Known true Position position 25 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
P.I.A. Vector Tracking Improves Accuracy – Loop filter bandwidth of 5Hz for both scalar and P.I.A tracking loops. – 9 satellites in view Maximum errors: – Traditional tracking • ~50ns – Proposed vector tracking • ~15ns No Noise Added 26 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
P.I.A. Tracking Increases Noise Tolerance – Increased noise leads to loss of lock in Noise Added # of Satellites Tracked scalar tracking. 0 dB 9 – At 4 dB of additional noise, the scalar 1 dB 8 tracking was able to produce 3 dB 5 navigation bits for 4 satellites. 4 dB 4 1 dB Noise Added 4 dB Noise Added 27 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
P.I.A. Tracking is Robust Against Jamming – Scalar tracking fails at 5 dB of added noise. – P.I.A. Vector Tracking continued to operate up until 9 dB of additional noise (5 dB more noise tolerance over scalar tracking) – Reduces a jammer’s effective radius. 5 dB Noise Added 9 dB Noise Added Scalar tracking fails Scalar tracking fails P.I.A. still tracking P.I.A. still tracking 28 TRUSTWORTHY CYBER INFRASTRUCTURE FOR THE POWER GRID | TCIPG.OR G
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