N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

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High Sensitivity GPS Tracking Performance in Indoor Environment with Moderate Pedestrian

Traffic Conditions

Nadezda SokolovaBörje Forssell

[email protected]@iet.ntnu.no

N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

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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

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GPS Signal Challenges Indoors (2)

• 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).

It is important to understand the indoor propagation environment for the development and design of future systems for positioning indoors.

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Test Description (1)

-Same test equipment setup.

-Same satellite geometry (tests performed in 23 hours 56 minutes period).

-Same test path.-Warm start outside the

building.

Test A

Test B

Performed during a week day, people present in the building and along the test path.

Performed during a week end, no people present along the test path.

• Two tests were performed to investigate effects of human body interference effects on the tracking performance of a HSGPS receiver in the indoors environment.

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Test Description (2)

Construction materials in the Electro- block.

Electro block views from the outside, passage inside the building, entrance.

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Description of the Test Equipment 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

Field test setup.

Main operating parameters of u-blox SuperSense HSGPS receiver.

Measurement path inside the Electro block, NTNU.

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Test results (1)

• Signal strengths at the entrance varied from -136 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.

• Test initialisation outside

SVs C/No levels outside, at the entrance to the Electro block, test B, no people present.

SVs C/No levels outside, at the entrance to the Electro block, test A, people present.

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Test results (2)

• 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 -144.2dBm).

• 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.

• Inside the Electro block

C/No diagrams for each SV available under the tests inside the building.

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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 A (no people present).

SuperSense LEA-4H position solutions, test B (people present).

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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.

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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.

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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.800-803.

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Integrated Low-Cost MEMS INS+HSGPS Performance for Pedestrian Navigation in a

Signal Degraded Environment

Nadezda SokolovaBörje Forssell

[email protected]@iet.ntnu.no

N.Sokolova, B. Forssell, Integrated Low-Cost MEMS INS/HSGPS Performance

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High- Sensitivity GPS

Signals are integrated over a longer period of time, (tens of msinstead 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.


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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.

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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.

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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.


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Equipment Setup for the Field Tests (1)


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

Sensor Gyro Accelerometer Magnetometer

Operating range +/- 1200 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 / 0.5 mGauss

Alignment error (deg.) 0.1 deg 0.1 deg 0.1 deg

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Main operating parameters of u-blox SuperSense HSGPS receiver and Xsens Mtx IMU.

2

Hz2

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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.


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Field Test in a Semi-Urban Area (1)


Measurement path, semi-urban area, Trondheim.

Satellite visibility, semi-urban area test.

Measurement path, semi-urban area test, Trondheim.

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Field Test in a Semi-Urban Area (2)

HSGPS navigation solution with simulated 30 seconds of GPS outage.

• Rapid error accumulation by INS during absence of GPS navigation solutions, about 150m horisontal error.

In order to investigate the performance of the integrated system during GPS outage periods, a 30-second GPS outage was introduced.

HSGPS-only navigation solution. Integrated HSGPS/MEMS INS navigation solution.

Integrated HSGPS/MEMS INS navigation solutionwith simulated 30 seconds of GPS outage


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Field Tests in an Indoor area

Construction materials of the Electro- block.

Electro block views from the outside, passage inside the building, entrance.


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HSGPS-only: Results


Measurement path inside the Electro block, NTNU.

HSGPS-only results, Test 1 and Test 2.

Satellite visibility inside the Electro block, Test 1 and Test 2.

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.

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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.

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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.


Documents

N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments