LOCALIZATION WITH GPS UNAVAILABLE

ARES – SWIEE MEETING - ROME , SEPT. 26 2014

TOR VERGATA UNIVERSITY

Summary

• Introduction • Technology – State of art • Application Scenarios vs. Technology • Advanced Research in ARES

INTRODUCTION

To address issues in the field of navigation without the use of GPS, it is certainly important to have in mind a scheme through which reconstruct the various processes in a more generalized

Location and Navigation framework.

Positioning

Map

Database

Map

Matching

Route

Planning Human

Machine

Interface

Route

Guidance

Wireless

Communication

Positioning: Allows you to get

the required kinematics

information (position, velocity,

acceleration, linear and

angular) through the use of

various sensors, terrestrial or

satellite radio signals (not

necessary GNSS).

TECHNOLOGY – STATE OF ART

No-GPS Localization Techniques:

Pseudolites

Ultra Wide Band (UWB)

Simultaneous Localization and

Mapping (SLAM)

Inertial Navigation Systems (INS)

Cell ID

Timing Advance (TA)

Signal Strength (SS)

Angle Of Arrival (AOA)

Time of Arrival (TOA)

Time Difference Of Arrival (TDOA)

Enhanced Observed Time

Difference (E-OTD)

Most of the no-GPS applications involve primarily the following modules:

Positioning: sensors through which

obtain measurements on the kinematic

state of the target;

Wireless Comunication: many

technologies are based on the transfer

of information in order both to improve

the calculation of the position, and to

develop info-mobility;

Map Matching: to compare a position

obtained by the sensors with reference

maps certainly allows to improve the

accuracy.

TECHNOLOGY PSEUDOLITES

The pseudolite is based on the same principle of operation of the satellite: it is a transmitter which sends signals in a limited area, so as to be able to increase the accuracy in the determination of the position and replace the satellite navigation system when the satellite signal is not available;

With the pseudolites it can achieve very high accuracies (submetrics) if they are installed with a suitable geometry;

Currently most of the pseudolites transmit signals such as those of the GPS L1 frequency (1575.42 MHz) and possibly in L2 (1227.6 MHz). With this configuration, standard GPS receivers can be used to track the signals from the pseudolite only with a change

in firmware.

TECHNOLOGY ULTRA WIDE BAND (UWB) – (1 OF 2) If the pseudolites were to be placed in environments with a very variable geometry, the

effect of multipath can degrade the performance of accuracy;

UWB counteracts this problem by allowing its use in radar applications and especially Localization, achieving centimeter accuracies in this area;

Recently (2002) the Federal Communications Commission (FCC) decided to define a signal as Ultra Wide Band if it meets the following specifications:

%. f

)f - (f

c

LH 2010

dBfB

Thanks to the duration of signal transmission in the order of pico-nanosecond the reflected wave (No Line Of Sight) has a low probability of going to collide exactly in counter-phase with the direct wave (LOS) degrading the signal precisely.

TECHNOLOGY ULTRA WIDE BAND (UWB) – (2 OF 2)

the stThe architecture is the same as already shown for the pseudolite but now the signal has different characteristics, not being characterized by the same frequencies at which the satellite transmits. It shows how, in order to realize a service for both outdoor and indoor for operation, a receiver with a dual terminal that allows to receive the GNSS signal and UWB can work correctly.

The following table compares the standards used:

TECHNOLOGY MAP MATCHING & SIMULTANEOUS LOCALIZATION AND MAPPING (SLAM) (1 OF 2)

In the Map Matching there is a transformation of the geographical map in a topological map:

Construction of a 3D topological map (corridors, halls, stairs, ...) through sensors selected according to the application;

Sometimes, in order to have more information on the external environment, it is preferred to have a scan (2D or 3D) through optical radar, whose narrow beam ensures a good resolution;

Construction of a series of decision nodes (linked between them) through algorithms such as SLAM;

TECHNOLOGY MAP MATCHING & SIMULTANEOUS LOCALIZATION AND MAPPING (SLAM) (2 OF 2)

The SLAM algorithm aims to put a robot in a location and in an unknown environment and guide it in such an environment through the simultaneous construction of the map and the state of the cinematic robot itself;

The SLAM algorithm is based on the Extended Kalman filtering with the further foresight to include, in the state vector, also the positions of landmarks, through the knowledge of which can be uniquely reconstruct the outside environment;

TECHNOLOGY INERTIAL NAVIGATION SYSTEMS (INS)

The characteristic of an inertial system is to use a technique active autonomous, ie that does not need any tool to communicate with other structures that provide aid;

An INS can be defined as a standalone device that, starting from the knowledge of the accelerations and the angular velocities which a mobile is subject, allows to determine the trajectory followed;

Then INS module can determine position, velocity and attitude of the moving vehicle through integration processes;

dt

dt

dt

dtdtaz

dtdtay

dtdtax

z

y

x

z

y

x

)(

)(

)(

TECHNOLOGY CELL ID & TIMING ADVANCE (TA)

It is the first method adopted and requires no additional HW nor SW;

It manages to spatially locate the user (which is cooperative) within a cell site of known position;

It is evident in the figure below that the lack of accuracy obtainable - you can only understand in which cell of dimensions (variables) of the order of 500m, you will find the user - is recommended for use along with the technique of Timing Advance.

Technology Timing Advance (TA)

In this case the ranging is done through a particular call, obviously not notified to the user (which is cooperative);

The principle of operation is based on the time that the message takes to get to and from BS to MS;

To do this a small adjustment in the software BSs is required.

TECHNOLOGY SIGNAL STRENGHT (SS) & ANGLE OF ARRIVAL (AOA)

This technique exploits the principle of trilateration still, with the peculiarity of obtaining the distance measurement based on the signal power and not by time information;

In order for this method has some efficacy, it is necessary to develop a model for the distribution of the signal level as a function of the surrounding environment.

The user/target is necessary to be under transmission;

Assuming a 2D geometry, by the measure of 2 angles with respect to two base stations 1 and 2 of known position are able to reconstruct the position of the MS;

This technique requires a special arrays of antenna and receivers to determine the AOA of the signal coming from the MS.

As a hybrid technique is also used to associate with the AOA method that of TA. The advantage is that it should be theoretically a lower number of BSs.

TECHNOLOGY TIME OF ARRIVAL (TOA); TIME DIFFERENCE OF ARRIVAL (TDOA) & ENHANCED OBSERVED TIME DIFFERENCE (E-OTD)

These techniques use the principle of trilateration, achieving ranging by measuring the time (that the signal takes to cover a distance) or time differences;

the signal sent from the MS is received from at least three BSs, which measure the time independently and send the data with the information of the distance to the MS in which the calculation of the ranging is made;

In TOA a common synchronization between different BSs and the MS is a must; or use a differential technique: by assuring the only time synchronization between the BSs, the MS measures the difference of time calculated in reference to two different BSs (in TDOA);

E-OTD is based on the method of TOA but, compared with the techniques presented before, has the peculiarity in the fact that time is measured by both the MS that the LMUs (Location Measurement Units);

There are two techniques, one of conception similar to the TOA (multilateration circular), the other linked to the TDOA (multilateration hyperbolic). Both methods are based on a structure of the type shown in the figure:

BS 1 BS 3

BS 2 BS 4

MS LMU

x1, t1

x2, t2

x3, t3

x4, t4

d1, t’1

d4, t’4

d3, t’3

d2, t’2

APPLICATION SCENARIOS VS. TECHNOLOGY (1 OF 3)

Ground Scenario

Technology

Industrial areas, Multi-floor

areas, Ports, stations and

airports

Pseudolite; UWB

Personal location for the

elderly and disabled in civil

buildings

Pseudolite; UWB

Rescue operations in

difficult environments

(underground-tunnels and

subways; mines)

SLAM

Un-manned operations in

hazardous environments

(crashes, smoke, etc.)

SLAM

Notes

Accuracies to be

achieved for these

services depend on the

size of the area used by

the application and size

of the object (and / or

person) that you want to

get the tracking

APPLICATION SCENARIOS VS. TECHNOLOGY (2 OF 3)

Air Scenario Technology

Aircraft cooperative

localization and

traking

INS; TOA; TDOA;

other

Airships cooperative

flight control (&

Navigation)

INS; TOA; TDOA

UAV Flight Command

& Control

INS; TOA; TDOA;

other

Notes

Air-Ground direct link and/or

air-ground via-sat link.

APPLICATION SCENARIOS VS. TECHNOLOGY (3 OF 3)

Space Scenario Technology

Satellite positioning

and orbit

determination

INS; TDOA; other

Inter-Satellite ranging TOA; other

Notes

Ground-Space links or ISL

ADVANCED RESEARCH IN ARES (RESERVED)

Localization via Inverse Ranging

Advanced Search and Rescue

Integrated Small-Sat Formation Flying precise ranging and Wide-band ISL (W Band signal based)

NavCom system for UAV Flight Management