Hsgps Hsgps Ins (1)

8/6/2019 Hsgps Hsgps Ins (1)

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High Sensitivity GPS Tracking Performance inIndoor Environment with Moderate Pedestrian

Traffic Conditions

Nadezda SokolovaBrje [email protected]

[email protected]

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 Fadingeffects

Heavy attenuationMultipath (short delay

multipath)

Signal level differencesCross-correlation problems

Interference from other RFsystems

Cellular transmissionWireless internet


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Test Description (1)

-Same test equipmentsetup.

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

-Same test path.

-Warm start outside thebuilding.

Test A

Test B

Performed during a weekday, people present in thebuilding and along thetest path.

Performed during a weekend, no people presentalong the test path.

Two tests were performed to investigate effects of humanbody interference effects on the tracking performance of aHSGPS 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 HSGPSreceiver.

Measurement path inside the Electro block, NTNU.


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Test results (1)

Signal strengths at theentrance varied from -136dBm down to -144 dBm.

C/No levels between 38

dBHz and 23 dBHz.

6 satellites acquired andtracked.

Test A - two studentspassed by the receive

antenna in about 1.5meter distance. Result -loss of lock and necessityto reacquire the signals.

Test initialisation outside

SVs C/No levels outside, at the entrance to the Electro block, test B, nopeople 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 measuredfor each particular satelliteduring both tests were almostthe same, varying from 30.1dBHz to 18.3 dBHz.(giving signal levels of-156dBmto -144.2dBm).

Signal losses due to change intype of material above the testpath experienced in both tests.

Test A- the receiver often loseslock on satellite signals.

Test B- the receiver was able tocontinue tracking for longerperiods.

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- navigationsolutions put the receiverall the time at and around

the entrance where thetest was initialised.

Test B- the receiver wasable to producenavigation solutions whichwere 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 testshad tracking sensitivity like -158dBm and acquisition sensitivity (hotstart) 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 bypeople in the building blocking the satellite signal paths or justpassing by in close distance to the antenna can result in loss ofsignals even if the receiver has such a good tracking sensitivity asstated.

More complex measurements and analyses should be performed toidentify 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 closedistance to the receive antenna can cause loss of signal and degradedaccuracy 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 incombination with other effects degrading the GPS performance inpedestrian traffic environments.

A user of a handheld GPS device should be aware of such limitationsin 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, Propagationconsiderations on L-band handheld communication service offeringsvia satellite, IEEETrans. on Antenna and Propagation, Vol.2, 1993,pp.800-803.


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

Signal Degraded Environment

Nadezda Sokolova

Brje [email protected]

[email protected]

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 ms

instead of just a few ms) to improve SNR.

Capable to maintain a position fix in degraded GPS signalenvironments, (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-hourperiod.

Same test path

Different satellite constellations.

Significant variance in positioningresults.

Results indicate the need ofexternal aiding to improve thequality 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 coupledintegration algorithm.

2 decentralized Kalmanfilters.

At least four GPSsatellites recquired toprovide 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 (1) 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

2

Main operating parameters of u-blox SuperSense HSGPSreceiver and Xsens MtxIMU.

2

Hz2


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Equipment Setup For the Field Tests (2)

It is inefficient to useheading information derivedfrom magnetometer

measurements in indoorenvironments.

Magnetic field inside abuilding is strongly disturbedby 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 30seconds of GPS outage.

Rapid error

accumulation by INSduring absence ofGPS navigationsolutions, about150m horisontalerror.

In order to investigate the performance of the integrated system duringGPS 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 systemperformance, two tests were chosen:

Test 1 good HSGPS results, GPS available for95 seconds out of 121.

Test 2 poor HSGPS results, GPS availableonly for a few short periods, for 43 seconds outof 125 in total.


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Integrated MEMS INS+HSGPS: Results

Integrated system accuracy isdependant on accuracy ofHSGPS navigation solutions.

Integrated system rapidlyaccumulates errors in absenceof GPS updates.

Integrated system availability isbetter, 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 INSvertical component.


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Hsgps Hsgps Ins (1)