1. High Sensitivity GPS Tracking Performance in Indoor Environment with Moderate Pedestrian Traffic Conditions
Nadezda Sokolova
Börje Forssell
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

2. GPS Signal Challenges Indoors (1)
Extremely weak LOS signal
Shadowing and Fading effects
Heavy attenuation
Multipath (short delay multipath)
Signal level differences
Cross-correlation problems
Interference from other RF systems
Cellular transmission
Wireless internet
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

3. GPS Signal Challenges Indoors (2)
It is important to understand the indoor propagation environment for the
development and design of future systems for positioning indoors.
Most of real life scenarios for users of handheld GPS devices include presence of other people around.
A human body can produce up to 10 dB attenuation when blocking the signal path in close proximity to the receive antenna, while a person passing by the antenna at a distance of only a few meters affects signal reception a little less (<1 dB) [1].
Effects of GPS signal obstruction by human body should also be considered.
Wave scattering by a lossy dielectric cyllinder (approximation of an upright human body).
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

4. Test Description (1) Test A Test B
Two tests were performed to investigate effects of human body interference effects on the tracking performance of a HSGPS receiver in the indoors environment.
Test A
Performed during a week day, people present in the building and along the test path.
-Same test equipment setup.
-Same satellite geometry (tests performed in 23 hours 56 minutes period).
-Same test path.
-Warm start outside the building.
Performed during a week end, no people present along the test path.
Test B
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

5. Test Description (2) Construction materials in the Electro- block.
Electro block views from the outside, passage inside the building, entrance.
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

6. Description of the Test Equipment Setup
Field test setup.
Parameter
Value
Tracking
L1, C/A code
Channels 16
Protocol
UBX binary, NMEA
Tracking Sensitivity
-158 dBm
Hot Start Sensitivity
-148 dBm
Cold Start Sensitivity
-142 dBm
Measurement path inside the Electro block, NTNU.
Main operating parameters of u-blox SuperSense HSGPS receiver.
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

7. Test results (1) Test initialisation outside
Signal strengths at the entrance varied from dBm down to -144 dBm.
C/No levels between 38 dBHz and 23 dBHz.
6 satellites acquired and tracked.
Test A - two students passed by the receive antenna in about 1.5 meter distance. Result -loss of lock and necessity to reacquire the signals.
SVs C/No levels outside, at the entrance to the Electro block, test A, people present.
SVs C/No levels outside, at the entrance to the Electro block, test B, no people present.
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

8. Test results (2) Inside the Electro block
C/No average levels measured for each particular satellite during both tests were almost the same, varying from 30.1 dBHz to 18.3 dBHz.
(giving signal levels of-156dBm to dBm).
Signal losses due to change in type of material above the test path experienced in both tests.
Test A- the receiver often loses lock on satellite signals.
Test B- the receiver was able to continue tracking for longer periods.
C/No diagrams for each SV available under the tests inside the building.
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

9. Test results (3)
Test A- navigation solutions put the receiver all the time at and around the entrance where the test was initialised.
Test B- the receiver was able to produce navigation solutions which were spread along the test path.
SuperSense LEA-4H position solutions, test B (people present).
SuperSense LEA-4H position solutions, test A (no people present).
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

10. Test results (4)
As stated by the manufacturer, the HSGPS receiver used in the tests had tracking sensitivity like -158dBm and acquisition sensitivity (hot start) like -148dBm.
GPS signal strength levels measured inside the Electro block were varying from -144,2dBm to -156dBm.
With so extremely low signal strengths, signal attenuation caused by people in the building blocking the satellite signal paths or just passing by in close distance to the antenna can result in loss of signals even if the receiver has such a good tracking sensitivity as stated.
More complex measurements and analyses should be performed to identify the exact degree of influence of this effect.
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

11. Conclusions
A person blocking the satellite signal path or just passing by in close distance to the receive antenna can cause loss of signal and degraded accuracy in indoor and other degraded signal environments.
Standing and moving people are additional and very unpredictable obstructions and sources of multipath that should be considered in combination with other effects degrading the GPS performance in pedestrian traffic environments.
A user of a handheld GPS device should be aware of such limitations in order to use his device in the best way to get satisfactory results.
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

12. References
[1] R.M.Allnutt, A.Dissanayake, K.T.Lin, C.Zaks, “Propagation considerations on L-band handheld communication service offerings via satellite”, IEEE Trans. on Antenna and Propagation, Vol.2, 1993, pp
N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

13. Integrated Low-Cost MEMS INS+HSGPS Performance for Pedestrian Navigation in a Signal Degraded Environment
Nadezda Sokolova
Börje Forssell
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

14. High- Sensitivity GPS
Signals are integrated over a longer period of time, (tens of ms
instead of just a few ms) to improve SNR.
Capable to maintain a position fix in degraded GPS signal environments, (can track down to signal levels approaching
-160dBm).
Price to pay...
Reduced positioning accuracy due to weak signals and interference.
Increased acquisition times.
Limited dynamic responsiveness.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

15. HSGPS Performance Indoors: Examples
3 tests performed in a 2-hour period.
Same test path
Different satellite constellations.
Significant variance in positioning results.
Results indicate the need of external aiding to improve the quality of the navigation solution.
HSGPS solutions indoors, Electro block, sept.07.
Satellite visibility indoors, Electro block,sept.07.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

16. Low-Cost MEMS INS+HSGPS Integration
Loosely coupled integration algorithm.
2 decentralized Kalman filters.
At least four GPS satellites recquired to provide GPS updates for INS corrections.
Loosely coupled INS/GPS integration algorithm.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

17. Description of the Field Tests
The integrated system performance was evaluated in two different test areas:
-Semi-urban area
-Indoor area
Operating scenario for all performed tests: walking mode.
Inertial sensor placement: in the users hand, kept close to the body.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

18. Equipment Setup for the Field Tests (1)
Parameter
Value
Tracking
L1, C/A code
Channels 16
Protocol
UBX binary, NMEA
Tracking Sensitivity
-158 dBm
Hot Start Sensitivity
-148 dBm
Cold Start Sensitivity
-142 dBm
Sensor
Gyro
Accelerometer
Magnetometer
Operating range
+/ deg/s
+/-17 m/s
+/-750 mGauss
Scale factor linearity
(% of operating range) -
0.05%
0.5%
Bias stability (1σ)
5 deg/s
0.02 m/s
0.5 mGauss
Noise (RMS)
0.1
0.001m/s /
Alignment error (deg.)
0.1 deg
Main operating parameters of u-blox SuperSense HSGPS receiver and Xsens Mtx IMU.
Field test setup.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

19. Equipment Setup For the Field Tests (2)
It is inefficient to use heading information derived from magnetometer measurements in indoor environments.
Magnetic field inside a building is strongly disturbed by building structure, electrical equipment, mobile phones, computers.... etc
Magnetic field measurements, outdoors, NTNU
Magnetic field measurements, indoors, Electro block, NTNU.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

20. Field Test in a Semi-Urban Area (1)
Satellite visibility, semi-urban area test.
Measurement path, semi-urban area, Trondheim.
Measurement path, semi-urban area test, Trondheim.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

21. Field Test in a Semi-Urban Area (2)
In order to investigate the performance of the integrated system during GPS outage periods, a 30-second GPS outage was introduced.
Rapid error accumulation by INS during absence of GPS navigation solutions, about 150m horisontal error.
HSGPS-only navigation solution.
Integrated HSGPS/MEMS INS navigation solution.
HSGPS navigation solution with simulated 30 seconds of GPS outage.
Integrated HSGPS/MEMS INS navigation solution
with simulated 30 seconds of GPS outage
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

22. Field Tests in an Indoor area
Construction materials of the Electro- block.
Electro block views from the outside, passage inside the building, entrance.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

23. HSGPS-only: Results
To illustrate the integrated system performance, two tests were chosen:
Test 1 – good HSGPS results, GPS available for 95 seconds out of 121.
Test 2 – poor HSGPS results, GPS available only for a few short periods, for 43 seconds out of 125 in total.
HSGPS-only results, Test 1 and Test 2.
Measurement path inside the Electro block, NTNU.
Satellite visibility inside the Electro block, Test 1 and Test 2.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

24. Integrated MEMS INS+HSGPS: Results
Integrated system accuracy is dependant on accuracy of HSGPS navigation solutions.
Integrated system rapidly accumulates errors in absence of GPS updates.
Integrated system availability is better, but errors in navigation solution are very large.
Integrated MEMS INS/HSGPS results, Test 1.
Integrated MEMS INS/HSGPS results, Test 2.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

25. Conclusions and Future Work
Use of tight HSGPS+MEMS INS coupling algorithm.
Use of other additional sensors.
Use of an additional barometric sensor to strengthen the INS vertical component.
N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance