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COIN-GPS: Indoor Localization from Direct GPS Receiving

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What is GPS Global Positioning System – Developed by US DoD in the 1970s

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What is GPS Global Positioning System – 24 hours a day – global coverage – real-time – cheap – light

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How GPS works (1) Briefly speaking… – Each satellite is continuously broadcasting its timing information from its internal atomic clock

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How GPS works (2) Briefly speaking… – Each satellite is continuously broadcasting its timing information from its internal atomic clock – A GPS receiver picks up signals from different satellites, then measures the distance between satellites and itself by calculating the time it takes for each of the signals to reach the receiver – 3 satellites are needed

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How GPS works (3) Briefly speaking… – However, we use 4 satellites because of clock bias

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How GPS works (4) Briefly speaking…

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How GPS works (5) Each frame is 300 bits Transfer speed is 50 bits/sec TTFF Standalone GPS: 300 * 5 / 50 = 30+

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How GPS works (6) Each frame is 300 bits Transfer speed is 50 bits/sec TTFF A-GPS: 300 * 1/ 50 = 6+

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How GPS works (7) Each frame is 300 bits Transfer speed is 50 bits/sec TTFF Instant-GPS: 0 / 50 = 0

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How Instant-GPS works (8)

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How GPS works (9)

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Indoor Localization Indoor navigation in shopping malls Tracking friends and family member in indoor public places

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Existing Indoor Localization Methods Signature matching – Radio Frequency – Magnetic – Sound Continuously tracking – Accelerometer – Compass

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Why GPS does not work (1) GPS signals are week Multipath effects Inadequate number of satellites

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Why GPS does not work (2)

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Why GPS does not work (3) GPS signals are week Multipath effects Inadequate number of satellites

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Why GPS does not work (4)

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Why GPS does not work (5) GPS signals are week Multipath effects Inadequate number of satellites

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Solutions - Overview Directional Antenna – Provide 10 dB gain – Amplify signals from a certain direction and suppress the rest Robust Acquisition Multi-Directional Location Estimation – Does not decode info from GPS packets – Only compute sub-ms part of prop delay from GPS packets

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Solution – Directional Antenna

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Solutions - Overview Directional Antenna Robust Acquisition Multi-Directional Location Estimation

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Solutions – Robust Acquisition (1) Standard Acquisition

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Solutions – Robust Acquisition (2) Standard Acquisition PRN 5 correlated with PRN 2 PRN 5 correlated with PRN 5 shifted 350 bits

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Solutions – Robust Acquisition (3) In reality, it is not that easy because of noise PRN5 plus Noise Autocorrelation of the sum of 7 PRNs plus noise with PRN 5 shifted 350 chips

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Solutions – Robust Acquisition (4) Noise R [m] deviates from its ideal value of 1, and the peak ratio gets close to 1, which means that the highest peak becomes comparable to noise.

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Solutions – Robust Acquisition (5) How to reduce noise – Directional Antenna – Integrated correlation

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Solutions - Overview Directional Antenna Robust Acquisition Multi-Directional Location Estimation

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Solutions – Location Estimation (1) Unknowns – X, Y, Z – Common Bias Error – Coarse Time Error

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Solutions – Location Estimation (2) Unknowns Handle insufficient number of satellites

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Solutions – Location Estimation (3)

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Implementation Hardware – High-gain directional antenna – Direction controller – GPS signal logger Software – Use MS Azure Cloud as a 3 rd -party agent

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Evaluation - Setup Note actual position before experiments

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Evaluation – Time

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Evaluation – Robustness of Acquisition (1) COIN-GPS acquires 3 satellites (on average) when we integrate 50 or more correlation terms With the Garmin antenna, the average number hardly ever reaches 2, even when we integrate over 100 ms

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Evaluation – Robustness of Acquisition (2) (a) shows that as we increase the amount of signals over which we integrate the correlation, peak ratio increases (b) shows that the relative code phase error diminishes as more and more correlation terms are integrated and becomes less than 5% when 70 or more correlation terms are integrated

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Evaluation – Robustness of Acquisition (3) CO-GPS acquires 2 or more satellites with only 10% probability, and never acquires 3 or more satellites and never obtains a location ﬁx COIN-GPS acquires at least 3 satellites 60% of the time

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Evaluation – Algorithm (1) Amongst all successful ﬁxes, 63% use only one direction, 28% use 2, and 3 directions are required for the rest

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Evaluation – Algorithm (2) highly scattered off the diagonal line

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Evaluation – Algorithm (3)

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Conclusion (1) Contributions – Consider indoor movement stationary – Use longer integration Drawbacks – Does not solve multipath issue very well – The benchmarks are not so persuasive

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Conclusion (2)

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Conclusion (3)

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