WP4-17

2023-03-14T12:14:46Z

Acorde: /* Validation */

==Anchor&Tag firmware of the Indoor Positioning System==
{|class="wikitable"
| ID|| WP4-17
|-
| Contributor || ACORDE
|-
| Levels || Function
|-
| Require || Indoor Positioning System anchor and tag platforms [[WP3-15_1]]
|-
| Provide || Navigation data (position)
|-
| Input || Raw sensed data from UWB transceiver. RTK enabled positioning out of the tunnel. INS data (on the tag).
|-
| Output || Position
|-
| C4D building block ||
|-
| TRL || 4
|-
| Parent Building block || [[WP3-15_1]]
|-
| Contact || fernando.herrera at acorde.com
|}

This page introduced the software developed for Indoor Positioning solution developed by ACORDE in COMP4DRONES.
It includes tag and anchor firmware (application and other underlying levels).

==Description==

The following figure shows the several software layers present on top of the HW anchor&tag devices of the ACORDE Indoor Positioning Solution (IPS) addressed.

The development of the ACORDE IPS has required actions and developments on all these layers.
Some of these layers have been tackled on other project WPs:
* BSP set up (in [[WP3)-15-1]], which includes drivers and RTOS adaptation/configuration
* Medium Access Control protocol (in [[WP5-19_ACO]]), where acorde has made specific innovation.

The higher software levels of the soltions have been addressed in the context of the WP4 of COMP4RDRONES, as described in the figure.

[[File:wp4-17_01.png|frame|center|Software Layers addressed in WP4 of C4D]]

The layers addressed are:

* '''Upper application layers''', in charge of I/O interfacing (e.g. support of Mavlink API) and configuration.
* '''geo-positioning''', which includes geo-positioning via trilateration and fusion techniques in general
* '''ranging''', in charge of computation of ranges derived from the time metrics derived from UWB message exchages

==Contributions==

The efforts invested in WP4 for the uppers layers of the ACORDE IPS solution have been fruitful in the afore introduced layers.

They can be sum up as follows:

* A first version of CCM in place
* Selection and implementation of development of a TWR ranging scheme
* Development of two versions of positioning algorithms
* Service for local and remote control, configuration and monitoring (CCM)

==Validation==
At the '''user application level''' the following figure provides an example where ACORDE validated the possibility to remotely configure, control and monitor the node.

[[File:wp4-17_02.png|frame|center|An example of remote configuration, control and monitoring (CCM) of an UWB node of the ACORDE IPS]]

In first place, a show command is issued to read the node status (monitoring). Then the position of the UWB anchor is manually configured, and then the node is reseted to ensure new configuration is applied (monitoring and control). Finally, a new show command is issued to check the effectivity of the CCM sequence.

At the "ranging layer", as mentioned, ACORDE realised the importance on not only implementing, byt selecting and appropriate Two-Way Ranging (TWR) scheme.
The following figure shows how two different TWR formulations were evaluated for four scenarios accounting tow typical error sources:

* The error frequency of both the initiator and responder clocks (Δfi, Δfr, in parts per million, PPM)
* The unbalancing on the reply times (Δt_reply).

From these two error sources, four scenarios are defined:
a) an ideal case: Δfi=0, Δfr=0, Δt_{reply}=0
b) average crystal frequency drifts crystal and minor reply time unbalance: Δfi=50PPM, Δfr=-50PPM, Δtreply=10µs
c) average crystal frequency drifts crystal and feasible unbalance: Δfi=50PPM, Δfr=-50PPM, Δtreply=100µs
d) average TCXO frequency drifts crystal and feasible unbalance: Δfi=4PPM, Δfr=-4PPM, Δtreply=100µs

<gallery widths=300px heights=200px >
File: wp4_17_rg1.png | ideal case
File: wp4_17_rg2.png | average crystal frequency drifts crystal and minor reply time unbalance
File: wp4_17_rg3.png | average crystal frequency drifts crystal and feasible unbalance
File: wp4_17_rg4.png | average TCXO frequency drifts crystal and feasible unbalance
</gallery>

The a) scenario represents an ideal case and serves to show the analytical equivalence of the considered formulations.
The b) scenario shows that for an averave drift on a platform with crystal clocks, a minor reply time unbalance, will already mean a significant range error (0.5m at 10mm distance) for 'formula2'.
The c) scenario shows that considering a further, but quite feasible unbalance (100us), the error at 100m becomes 5m, yet 0.5m for 10m for 'formula2'.
Then, d) scenario shows that even under consideration of some already provided platform inprovements (TCXO clock), the aforementioned error magnitude for 'formula2' holds, while 'formula1' remains insensitive.
Therefore, the selection of the proper formulation ('formula1') is critical for error free range estimations.

Furthermore, several indoor and outdoor physical set ups for range maximum range and accuracy estimation were set up.
Following figure shows on of the outdoor set ups. For those set ups, two different ground truth references where used, namely RTK measurements (as shown on the right part),
and also laser meters (i.e., outdoor experiments were indeed used to observed limitations of the used laser meters).

[[File:wp4_17_outdoor_meas.png|frame|center|An example of remote configuration, control and monitoring (CCM) of an UWB node of the ACORDE IPS]]

In all the experiments reported the cm-level error was confirmed, being the std error below 15cm in all experiments (including the original ones with the evaluation kit hw platform and others without final calibration). Las indoor experiment (for distances between 4m and 15m) yield maximum 1.7cm std error, and 10.1cm maximum RMSE.

With regard geo-positioning algorityms, by the formal end of the project they have been mostly tested by realying on IPS-MAF platform.
It has served to realise the high dependency with the morphology and density of the anchor deployment, and on the base range accuracy.

<gallery widths=400px heights=400px >
File: wp4_17_autopositioning_error0.png | ideal ranging conditions
File: wp4_17_autopositioning_error.png | realistic ranging errors (5cm)
</gallery>

For instance, figure above shows how the auto-positioning feature of the anchors is impacted when realistic error range errors are considered, using version 2 of anchors functionality.
In the ACORDE IPS solution, autopositioning is a feature which enables anchors inside the tunnel to compute their own position from external or already positioned anchors.
On Y axis, the positioning error is shown along time (x axis). In this figure, each coloured graph line correspondd to the error of one anchor in a deployment were the three former (foreground)
lines corresponde to external anchors (almost perfectly positioned from the beginning). What figure shows is the progressive autopositioning of anchors along time (the deeper the later).
Moreover, it also shows some growing errors with the depth in the tunnel, specially in the former times (while not all the anchors are available for autopositioning).

WP4-17

2023-03-14T12:14:10Z

Acorde: /* Validation */

==Anchor&Tag firmware of the Indoor Positioning System==
{|class="wikitable"
| ID|| WP4-17
|-
| Contributor || ACORDE
|-
| Levels || Function
|-
| Require || Indoor Positioning System anchor and tag platforms [[WP3-15_1]]
|-
| Provide || Navigation data (position)
|-
| Input || Raw sensed data from UWB transceiver. RTK enabled positioning out of the tunnel. INS data (on the tag).
|-
| Output || Position
|-
| C4D building block ||
|-
| TRL || 4
|-
| Parent Building block || [[WP3-15_1]]
|-
| Contact || fernando.herrera at acorde.com
|}

This page introduced the software developed for Indoor Positioning solution developed by ACORDE in COMP4DRONES.
It includes tag and anchor firmware (application and other underlying levels).

==Description==

The following figure shows the several software layers present on top of the HW anchor&tag devices of the ACORDE Indoor Positioning Solution (IPS) addressed.

The development of the ACORDE IPS has required actions and developments on all these layers.
Some of these layers have been tackled on other project WPs:
* BSP set up (in [[WP3)-15-1]], which includes drivers and RTOS adaptation/configuration
* Medium Access Control protocol (in [[WP5-19_ACO]]), where acorde has made specific innovation.

The higher software levels of the soltions have been addressed in the context of the WP4 of COMP4RDRONES, as described in the figure.

[[File:wp4-17_01.png|frame|center|Software Layers addressed in WP4 of C4D]]

The layers addressed are:

* '''Upper application layers''', in charge of I/O interfacing (e.g. support of Mavlink API) and configuration.
* '''geo-positioning''', which includes geo-positioning via trilateration and fusion techniques in general
* '''ranging''', in charge of computation of ranges derived from the time metrics derived from UWB message exchages

==Contributions==

The efforts invested in WP4 for the uppers layers of the ACORDE IPS solution have been fruitful in the afore introduced layers.

They can be sum up as follows:

* A first version of CCM in place
* Selection and implementation of development of a TWR ranging scheme
* Development of two versions of positioning algorithms
* Service for local and remote control, configuration and monitoring (CCM)

==Validation==
At the '''user application level''' the following figure provides an example where ACORDE validated the possibility to remotely configure, control and monitor the node.

[[File:wp4-17_02.png|frame|center|An example of remote configuration, control and monitoring (CCM) of an UWB node of the ACORDE IPS]]

In first place, a show command is issued to read the node status (monitoring). Then the position of the UWB anchor is manually configured, and then the node is reseted to ensure new configuration is applied (monitoring and control). Finally, a new show command is issued to check the effectivity of the CCM sequence.

At the "ranging layer", as mentioned, ACORDE realised the importance on not only implementing, byt selecting and appropriate Two-Way Ranging (TWR) scheme.
The following figure shows how two different TWR formulations were evaluated for four scenarios accounting tow typical error sources:

* The error frequency of both the initiator and responder clocks (Δfi, Δfr, in parts per million, PPM)
* The unbalancing on the reply times (Δt_reply).

From these two error sources, four scenarios are defined:
a) an ideal case: Δfi=0, Δfr=0, Δt_{reply}=0
b) average crystal frequency drifts crystal and minor reply time unbalance: Δfi=50PPM, Δfr=-50PPM, Δtreply=10µs
c) average crystal frequency drifts crystal and feasible unbalance: Δfi=50PPM, Δfr=-50PPM, Δtreply=100µs
d) average TCXO frequency drifts crystal and feasible unbalance: Δfi=4PPM, Δfr=-4PPM, Δtreply=100µs

<gallery widths=300px heights=200px >
File: wp4_17_rg1.png | ideal case
File: wp4_17_rg2.png | average crystal frequency drifts crystal and minor reply time unbalance
File: wp4_17_rg3.png | average crystal frequency drifts crystal and feasible unbalance
File: wp4_17_rg4.png | average TCXO frequency drifts crystal and feasible unbalance
</gallery>

The a) scenario represents an ideal case and serves to show the analytical equivalence of the considered formulations.
The b) scenario shows that for an averave drift on a platform with crystal clocks, a minor reply time unbalance, will already mean a significant range error (0.5m at 10mm distance) for 'formula2'.
The c) scenario shows that considering a further, but quite feasible unbalance (100us), the error at 100m becomes 5m, yet 0.5m for 10m for 'formula2'.
Then, d) scenario shows that even under consideration of some already provided platform inprovements (TCXO clock), the aforementioned error magnitude for 'formula2' holds, while 'formula1' remains insensitive.
Therefore, the selection of the proper formulation ('formula1') is critical for error free range estimations.

Furthermore, several indoor and outdoor physical set ups for range maximum range and accuracy estimation were set up.
Following figure shows on of the outdoor set ups. For those set ups, two different ground truth references where used, namely RTK measurements (as shown on the right part),
and also laser meters (i.e., outdoor experiments were indeed used to observed limitations of the used laser meters).

[[File:wp4_17_outdoor_meas.png|frame|center|An example of remote configuration, control and monitoring (CCM) of an UWB node of the ACORDE IPS]]

In all the experiments reported the cm-level error was confirmed, being the std error below 15cm in all experiments (including the original ones with the evaluation kit hw platform and others without final calibration). Las indoor experiment (for distances between 4m and 15m) yield maximum 1.7cm std error, and 10.1cm maximum RMSE.

With regard geo-positioning algorityms, by the formal end of the project they have been mostly tested by realying on IPS-MAF platform.
It has served to realise the high dependency with the morphology and density of the anchor deployment, and on the base range accuracy.

<gallery widths=300px heights=200px >
File: wp4_17_autopositioning_error.png | ideal ranging conditions
File: wp4_17_rg2.png | realistic ranging errors (5cm)
</gallery>

For instance, figure above shows how the auto-positioning feature of the anchors is impacted when realistic error range errors are considered, using version 2 of anchors functionality.
In the ACORDE IPS solution, autopositioning is a feature which enables anchors inside the tunnel to compute their own position from external or already positioned anchors.
On Y axis, the positioning error is shown along time (x axis). In this figure, each coloured graph line correspondd to the error of one anchor in a deployment were the three former (foreground)
lines corresponde to external anchors (almost perfectly positioned from the beginning). What figure shows is the progressive autopositioning of anchors along time (the deeper the later).
Moreover, it also shows some growing errors with the depth in the tunnel, specially in the former times (while not all the anchors are available for autopositioning).

WP4-17

2023-03-14T12:02:54Z

Acorde: /* Validation */

==Anchor&Tag firmware of the Indoor Positioning System==
{|class="wikitable"
| ID|| WP4-17
|-
| Contributor || ACORDE
|-
| Levels || Function
|-
| Require || Indoor Positioning System anchor and tag platforms [[WP3-15_1]]
|-
| Provide || Navigation data (position)
|-
| Input || Raw sensed data from UWB transceiver. RTK enabled positioning out of the tunnel. INS data (on the tag).
|-
| Output || Position
|-
| C4D building block ||
|-
| TRL || 4
|-
| Parent Building block || [[WP3-15_1]]
|-
| Contact || fernando.herrera at acorde.com
|}

This page introduced the software developed for Indoor Positioning solution developed by ACORDE in COMP4DRONES.
It includes tag and anchor firmware (application and other underlying levels).

==Description==

The following figure shows the several software layers present on top of the HW anchor&tag devices of the ACORDE Indoor Positioning Solution (IPS) addressed.

The development of the ACORDE IPS has required actions and developments on all these layers.
Some of these layers have been tackled on other project WPs:
* BSP set up (in [[WP3)-15-1]], which includes drivers and RTOS adaptation/configuration
* Medium Access Control protocol (in [[WP5-19_ACO]]), where acorde has made specific innovation.

The higher software levels of the soltions have been addressed in the context of the WP4 of COMP4RDRONES, as described in the figure.

[[File:wp4-17_01.png|frame|center|Software Layers addressed in WP4 of C4D]]

The layers addressed are:

* '''Upper application layers''', in charge of I/O interfacing (e.g. support of Mavlink API) and configuration.
* '''geo-positioning''', which includes geo-positioning via trilateration and fusion techniques in general
* '''ranging''', in charge of computation of ranges derived from the time metrics derived from UWB message exchages

==Contributions==

The efforts invested in WP4 for the uppers layers of the ACORDE IPS solution have been fruitful in the afore introduced layers.

They can be sum up as follows:

* A first version of CCM in place
* Selection and implementation of development of a TWR ranging scheme
* Development of two versions of positioning algorithms
* Service for local and remote control, configuration and monitoring (CCM)

==Validation==
At the '''user application level''' the following figure provides an example where ACORDE validated the possibility to remotely configure, control and monitor the node.

[[File:wp4-17_02.png|frame|center|An example of remote configuration, control and monitoring (CCM) of an UWB node of the ACORDE IPS]]

In first place, a show command is issued to read the node status (monitoring). Then the position of the UWB anchor is manually configured, and then the node is reseted to ensure new configuration is applied (monitoring and control). Finally, a new show command is issued to check the effectivity of the CCM sequence.

At the "ranging layer", as mentioned, ACORDE realised the importance on not only implementing, byt selecting and appropriate Two-Way Ranging (TWR) scheme.
The following figure shows how two different TWR formulations were evaluated for four scenarios accounting tow typical error sources:

* The error frequency of both the initiator and responder clocks (Δfi, Δfr, in parts per million, PPM)
* The unbalancing on the reply times (Δt_reply).

From these two error sources, four scenarios are defined:
a) an ideal case: Δfi=0, Δfr=0, Δt_{reply}=0
b) average crystal frequency drifts crystal and minor reply time unbalance: Δfi=50PPM, Δfr=-50PPM, Δtreply=10µs
c) average crystal frequency drifts crystal and feasible unbalance: Δfi=50PPM, Δfr=-50PPM, Δtreply=100µs
d) average TCXO frequency drifts crystal and feasible unbalance: Δfi=4PPM, Δfr=-4PPM, Δtreply=100µs

<gallery widths=300px heights=200px >
File: wp4_17_rg1.png | ideal case
File: wp4_17_rg2.png | average crystal frequency drifts crystal and minor reply time unbalance
File: wp4_17_rg3.png | average crystal frequency drifts crystal and feasible unbalance
File: wp4_17_rg4.png | average TCXO frequency drifts crystal and feasible unbalance
</gallery>

The a) scenario represents an ideal case and serves to show the analytical equivalence of the considered formulations.
The b) scenario shows that for an averave drift on a platform with crystal clocks, a minor reply time unbalance, will already mean a significant range error (0.5m at 10mm distance) for 'formula2'.
The c) scenario shows that considering a further, but quite feasible unbalance (100us), the error at 100m becomes 5m, yet 0.5m for 10m for 'formula2'.
Then, d) scenario shows that even under consideration of some already provided platform inprovements (TCXO clock), the aforementioned error magnitude for 'formula2' holds, while 'formula1' remains insensitive.
Therefore, the selection of the proper formulation ('formula1') is critical for error free range estimations.

Furthermore, several indoor and outdoor physical set ups for range maximum range and accuracy estimation were set up.
Following figure shows on of the outdoor set ups. For those set ups, two different ground truth references where used, namely RTK measurements (as shown on the right part),
and also laser meters (i.e., outdoor experiments were indeed used to observed limitations of the used laser meters).

[[File:wp4_17_outdoor_meas.png|frame|center|An example of remote configuration, control and monitoring (CCM) of an UWB node of the ACORDE IPS]]

In all the experiments reported the cm-level error was confirmed, being the std error below 15cm in all experiments (including the original ones with the evaluation kit hw platform and others without final calibration). Las indoor experiment (for distances between 4m and 15m) yield maximum 1.7cm std error, and 10.1cm maximum RMSE.

With regard geo-positioning algorityms, by the formal end of the project they have been mostly tested by realying on IPS-MAF platform.
It has served to realise the high dependency with the morophology and density of the anchors, and on the base range accuracy.

[[File:wp4_17_autopositioning_error.png|frame|center|Autopositioning error for v2 anchors functionality for realistic ranging errors]]

WP3-15 1

2023-03-13T16:34:24Z

Acorde: /* Anchor at Tag platforms */

=UltraWideBand (UWB) based indoor positioning=
{|class="wikitable"
| ID|| WP3-15_1
|-
| Contributor || ACORDE
|-
| Levels || Platform, Function
|-
| Require || Energy, Raw sensed data from UWB transceiver and IMU
|-
| Provide || Navigation Sensor
|-
| Input || Raw sensed data from UWB transceiver and low-cost INS
|-
| Output || Position
|-
| C4D building block || UWB-based indoor positioning system
|-
| TRL || 4
|-
| Contact || fernando.herrera at acorde.com
|}

[[File:wp3-15_1_01.png|frame|center|Building block diagram for WP3-15_1]]

==Description==

In COMP4DRONES, ACORDE has tackled the design and developmentof of an Indoor Positioning System (IPS), as a solution for the challenges posed by the construction use case, demo tunnel (UC2-demo 2). ACORDE IPS can be considered a specific instantiation of the building block of C4D architecture shown above. ACORDE IPS is specifically oriented to serve reliable and precise geo-referenced position to a drone flying on a tunnel under construction. Such a drone is in charge of the capture of raw data for tunnel digitization, to be employed for Building Information Modelling or [https://en.wikipedia.org/wiki/Building_information_modeling "BIM"]. The objective of the ACORDE IPS is two-fold, i.e., to ensure a safe navigation along a planned path, and to optimize the accuracy of the navigation data synchronized with the data sensed for digitisalization(e.g., thermography or LIDAR), which can be exploited, for instance, for a faster offline digitalization. The specific environment and the usage scenario posed by the construction stakeholder (ACCIONA) and the drone integrator&operator (FADA-CATEC in C4D), configures a set of requirements in terms of cost of the solution, power consumption, size, weight, precision, and interface capabilities, which, added to the specific geometry of the indoor infrastructure, has lead ACORDE to a novel IPS solution, outlined the following figure.

[[File:wp3-15_1_02.png|frame|center|Indoor Positioning System developed by ACORDE]]

The solution relies on a “tag node”, to be mounted on the drone, and to provide to it to the geo-reference position, based on a set of measured distances (called ranges) to a set of strategically deployed “anchor nodes”. Range estimation is based on a specific protocol of message exchanges on the Ultrawideband (UWB) spectrum. The tag integrates an INS, so that it can fuse INS information with UWB ranges, for providing a processed tag position. In addition, the tag can also provide at its output interface range data. A standard Mavlink interface supports the provision of these data to the drone navigation system.
The posed solution contributes improvements and innovations accounting the scenario and the current state of the art. ACORDE provides a vertical solution, covering the design&implementation of the solution (anchor&tags platforms and their firmware). In addition, a specific design tool, IPS Modellign and Analysis Framework ([[WP6-21|IPS-MAF]]), has been developed, which allows to perform a more holistic and efficient analysis and design of this specific type of solutions. All this activity, has been comprised by technical packages WP3-WP6 in C4D, which can be summarized as follows:

* Design and implementation of anchor and tag platforms (including the required board support package (BSP) ([[WP3-15_1]]).
* Design and implementation of anchor and tag firmware, including the configuration, positioning algorithms and interfacing ([[WP4-17]]).
* Ensuring a robust and enriched communication among anchors, and among the tag (within the drone) and the anchors, for a more robust and improved positioning ([[WP5-19_ACO]]).
* Developing an Indoor Positioning System Modelling and Analysis Framework (IPS-MAF) for indoor structures, specifically tunnels ([[WP6-21|IPS-MAF]]).
* Providing at the tag a Mavlink [29] interface to support providing both processed positioning information, and “pre-processed” information (ranges) (WP3, WP4, and WP5).

==Challenges and Contributions ==

The stakeholder (ACCIONA) described the digitization scenario at a specific time slot where the construction 7days/24hours activity stopped for 1-2hours. At that time, it is possible to set up some “mobile” anchors, together with the “fixed” anchors, and later let the drone perform a pre-programmed digitization flight, where the tunnel under-construction can present some eventual obstacles (e.g., machines, signals). The posed scenario presents '''several challenges''' in relation to other existing real-time location systems:

* The specific ''long geometry'' of the tunnel (which challenges UWB range estimation, the cost of the solution and the validity of conventional trilateration algorithms).
* Demand of features for a flexible and agile anchor deployment, which does not oblige surveyors to geo-positioning all anchors, especially mobile ones.
* Need to provide real-time, 3D geo-referenced positioning on the tag (while most solutions focus on 2D relative positioning, commonly computed on a ground platform which centralizes data from anchors).
* Cost and energy/power optimization (the latter important for fixed anchors)
* Need for system-level design tooling. The IPS is a complex system with many parameters and aspects (specific deployment, transmission powers, sensitivities, latencies of the ranging phases, algorithmic alternatives, etc) with potential significant impact on the overall performance. Means for facilitating a holistic design, accounting for those many different aspects at early design stage are required even for experienced designers in the field.

The same scenario also presented the opportunity to exploit the fact that during digitization flight only one drone, i.e., one tag, needs to be serviced. The question is how to exploit this single-tag assumption for a safer flight and better digitalization.

The ACORDE solution tackles these challenges and opportunities. So far, a number of '''contributions''' in comparison to other existing solutions are highlighted:

* Customized, cost-effective anchor and tag platforms, specifically designed to cope with the computational needs (specially for tag) and energy/power efficiency needs (specially anchors).
* Novel MAC protocol called Asynchronous Tag trigger, Slotted Anchor response with Deterministic and Random Allocation (ATSA-DRA), specifically adapted to the single-tag assumption, that ensures deterministic latency, while optimizing the number of anchors in view.
* At application level, the solution enables geo-referenced, real-time 3D positioning. Moreover, the application overcomes the challenges of the tunnel geometry. A modified trilateration algorithm has been already developed which enables positioning in regions of limited anchors visibility (coverage) and poor dilution of precision (DOP), where a conventional least-squares based approach is not working. This is specifically required for enabling anchors auto-positioning at the initial phase.
* The development of IPS-MAF, is a qualitative step on ACORDE capabilities for tackling custom design of IPS systems for long indoor infrastructures (tunnels, mines, large pipes, …). It enables a newer system-level design flow (as explained in [[WP6-21]]), capable to reveal outcomes and aspects almost imposible to notice or tackle manually.
* The support of a Mavlink interface at the tag side, to provide both completely processed (e.g., position data) and partially processed (e.g., ranges). The latter enable the ACORDE IPS to behave as a complementary positioning sub-system, whose outputs can be fused by integrators with other alternative sensor data. Moreover, ranges transfer is enabled via a “smooth” (in the form of dialect) Mavlink extension contributed by ACORDE in COMP4DRONES.

==Anchor at Tag platforms==
In C4D ACORDE has performed a customized development for the anchor and tag platforms.

On top of a base mother board design, the tag and the anchor platforms have been implemented.
Thanks to its I/O interfaces, the anchor platform supports the different types of anchor nodes defined for the solution, i.e.:
* an external ranging node
* an internal ranging node
* the Configuration, Control and Monitoring (CCM) node (this category can be applied to any of the previous

[[File:wp3-15_1_05b.png|frame|center|Indoor Positioning System developed by ACORDE]]

For the same form factor, the base platform design brings several advantages in relation to devices found in the market:
* more estable clock
* LiPO connector
* better connectivity for configuration purposes

Moreover, the tag platform adds a more powerful microcontroller, the possibility to add an INS for a powerful tag (capable to provide in real-time fused geo-location solution), and an SD card slot (e.g. to enableo local logging).

Moreover, this development has provided ACORDE a strong technological base to further develop with greater flexibility the firmare of the positioning solution ([[WP4-17]]),
where much of the added value of the solution is concentrated.

WP3-15 1

2023-03-13T16:32:39Z

Acorde: /* Anchor at Tag platforms */

=UltraWideBand (UWB) based indoor positioning=
{|class="wikitable"
| ID|| WP3-15_1
|-
| Contributor || ACORDE
|-
| Levels || Platform, Function
|-
| Require || Energy, Raw sensed data from UWB transceiver and IMU
|-
| Provide || Navigation Sensor
|-
| Input || Raw sensed data from UWB transceiver and low-cost INS
|-
| Output || Position
|-
| C4D building block || UWB-based indoor positioning system
|-
| TRL || 4
|-
| Contact || fernando.herrera at acorde.com
|}

[[File:wp3-15_1_01.png|frame|center|Building block diagram for WP3-15_1]]

==Description==

In COMP4DRONES, ACORDE has tackled the design and developmentof of an Indoor Positioning System (IPS), as a solution for the challenges posed by the construction use case, demo tunnel (UC2-demo 2). ACORDE IPS can be considered a specific instantiation of the building block of C4D architecture shown above. ACORDE IPS is specifically oriented to serve reliable and precise geo-referenced position to a drone flying on a tunnel under construction. Such a drone is in charge of the capture of raw data for tunnel digitization, to be employed for Building Information Modelling or [https://en.wikipedia.org/wiki/Building_information_modeling "BIM"]. The objective of the ACORDE IPS is two-fold, i.e., to ensure a safe navigation along a planned path, and to optimize the accuracy of the navigation data synchronized with the data sensed for digitisalization(e.g., thermography or LIDAR), which can be exploited, for instance, for a faster offline digitalization. The specific environment and the usage scenario posed by the construction stakeholder (ACCIONA) and the drone integrator&operator (FADA-CATEC in C4D), configures a set of requirements in terms of cost of the solution, power consumption, size, weight, precision, and interface capabilities, which, added to the specific geometry of the indoor infrastructure, has lead ACORDE to a novel IPS solution, outlined the following figure.

[[File:wp3-15_1_02.png|frame|center|Indoor Positioning System developed by ACORDE]]

The solution relies on a “tag node”, to be mounted on the drone, and to provide to it to the geo-reference position, based on a set of measured distances (called ranges) to a set of strategically deployed “anchor nodes”. Range estimation is based on a specific protocol of message exchanges on the Ultrawideband (UWB) spectrum. The tag integrates an INS, so that it can fuse INS information with UWB ranges, for providing a processed tag position. In addition, the tag can also provide at its output interface range data. A standard Mavlink interface supports the provision of these data to the drone navigation system.
The posed solution contributes improvements and innovations accounting the scenario and the current state of the art. ACORDE provides a vertical solution, covering the design&implementation of the solution (anchor&tags platforms and their firmware). In addition, a specific design tool, IPS Modellign and Analysis Framework ([[WP6-21|IPS-MAF]]), has been developed, which allows to perform a more holistic and efficient analysis and design of this specific type of solutions. All this activity, has been comprised by technical packages WP3-WP6 in C4D, which can be summarized as follows:

* Design and implementation of anchor and tag platforms (including the required board support package (BSP) ([[WP3-15_1]]).
* Design and implementation of anchor and tag firmware, including the configuration, positioning algorithms and interfacing ([[WP4-17]]).
* Ensuring a robust and enriched communication among anchors, and among the tag (within the drone) and the anchors, for a more robust and improved positioning ([[WP5-19_ACO]]).
* Developing an Indoor Positioning System Modelling and Analysis Framework (IPS-MAF) for indoor structures, specifically tunnels ([[WP6-21|IPS-MAF]]).
* Providing at the tag a Mavlink [29] interface to support providing both processed positioning information, and “pre-processed” information (ranges) (WP3, WP4, and WP5).

==Challenges and Contributions ==

The stakeholder (ACCIONA) described the digitization scenario at a specific time slot where the construction 7days/24hours activity stopped for 1-2hours. At that time, it is possible to set up some “mobile” anchors, together with the “fixed” anchors, and later let the drone perform a pre-programmed digitization flight, where the tunnel under-construction can present some eventual obstacles (e.g., machines, signals). The posed scenario presents '''several challenges''' in relation to other existing real-time location systems:

* The specific ''long geometry'' of the tunnel (which challenges UWB range estimation, the cost of the solution and the validity of conventional trilateration algorithms).
* Demand of features for a flexible and agile anchor deployment, which does not oblige surveyors to geo-positioning all anchors, especially mobile ones.
* Need to provide real-time, 3D geo-referenced positioning on the tag (while most solutions focus on 2D relative positioning, commonly computed on a ground platform which centralizes data from anchors).
* Cost and energy/power optimization (the latter important for fixed anchors)
* Need for system-level design tooling. The IPS is a complex system with many parameters and aspects (specific deployment, transmission powers, sensitivities, latencies of the ranging phases, algorithmic alternatives, etc) with potential significant impact on the overall performance. Means for facilitating a holistic design, accounting for those many different aspects at early design stage are required even for experienced designers in the field.

The same scenario also presented the opportunity to exploit the fact that during digitization flight only one drone, i.e., one tag, needs to be serviced. The question is how to exploit this single-tag assumption for a safer flight and better digitalization.

The ACORDE solution tackles these challenges and opportunities. So far, a number of '''contributions''' in comparison to other existing solutions are highlighted:

* Customized, cost-effective anchor and tag platforms, specifically designed to cope with the computational needs (specially for tag) and energy/power efficiency needs (specially anchors).
* Novel MAC protocol called Asynchronous Tag trigger, Slotted Anchor response with Deterministic and Random Allocation (ATSA-DRA), specifically adapted to the single-tag assumption, that ensures deterministic latency, while optimizing the number of anchors in view.
* At application level, the solution enables geo-referenced, real-time 3D positioning. Moreover, the application overcomes the challenges of the tunnel geometry. A modified trilateration algorithm has been already developed which enables positioning in regions of limited anchors visibility (coverage) and poor dilution of precision (DOP), where a conventional least-squares based approach is not working. This is specifically required for enabling anchors auto-positioning at the initial phase.
* The development of IPS-MAF, is a qualitative step on ACORDE capabilities for tackling custom design of IPS systems for long indoor infrastructures (tunnels, mines, large pipes, …). It enables a newer system-level design flow (as explained in [[WP6-21]]), capable to reveal outcomes and aspects almost imposible to notice or tackle manually.
* The support of a Mavlink interface at the tag side, to provide both completely processed (e.g., position data) and partially processed (e.g., ranges). The latter enable the ACORDE IPS to behave as a complementary positioning sub-system, whose outputs can be fused by integrators with other alternative sensor data. Moreover, ranges transfer is enabled via a “smooth” (in the form of dialect) Mavlink extension contributed by ACORDE in COMP4DRONES.

==Anchor at Tag platforms==
In C4D ACORDE has performed a customized development for the anchor and tag platforms.

On top of a base mother board design, the tag and the anchor platforms have been implemented.
Thanks to its I/O interfaces, the anchor platform supports the different types of anchor nodes defined for the solution, i.e.:
- an external ranging node
- an internal ranging node
- the Configuration, Control and Monitoring (CCM) node (this category can be applied to any of the previous

[[File:wp3-15_1_05b.png|frame|center|Indoor Positioning System developed by ACORDE]]

For the same form factor, the base platform design brings several advantages in relation to devices found in the market:
- more estable clock
- LiPO connector
- better connectivity for configuration purposes

Moreover, the tag platform adds a more powerful microcontroller, the possibility to add an INS for a powerful tag (capable to provide in real-time fused geo-location solution), and an SD card slot (e.g. to enableo local logging).

Moreover, this development has provided ACORDE a strong technological base to further develop with greater flexibility the firmare of the positioning solution ([[WP4-17]]),
where much of the added value of the solution is concentrated.

File:Wp3-15 1 05b.png

2023-03-13T16:26:09Z

Acorde:

WP3-15 1

2023-03-13T16:24:57Z

Acorde: /* Anchor at Tag platforms */

=UltraWideBand (UWB) based indoor positioning=
{|class="wikitable"
| ID|| WP3-15_1
|-
| Contributor || ACORDE
|-
| Levels || Platform, Function
|-
| Require || Energy, Raw sensed data from UWB transceiver and IMU
|-
| Provide || Navigation Sensor
|-
| Input || Raw sensed data from UWB transceiver and low-cost INS
|-
| Output || Position
|-
| C4D building block || UWB-based indoor positioning system
|-
| TRL || 4
|-
| Contact || fernando.herrera at acorde.com
|}

[[File:wp3-15_1_01.png|frame|center|Building block diagram for WP3-15_1]]

==Description==

In COMP4DRONES, ACORDE has tackled the design and developmentof of an Indoor Positioning System (IPS), as a solution for the challenges posed by the construction use case, demo tunnel (UC2-demo 2). ACORDE IPS can be considered a specific instantiation of the building block of C4D architecture shown above. ACORDE IPS is specifically oriented to serve reliable and precise geo-referenced position to a drone flying on a tunnel under construction. Such a drone is in charge of the capture of raw data for tunnel digitization, to be employed for Building Information Modelling or [https://en.wikipedia.org/wiki/Building_information_modeling "BIM"]. The objective of the ACORDE IPS is two-fold, i.e., to ensure a safe navigation along a planned path, and to optimize the accuracy of the navigation data synchronized with the data sensed for digitisalization(e.g., thermography or LIDAR), which can be exploited, for instance, for a faster offline digitalization. The specific environment and the usage scenario posed by the construction stakeholder (ACCIONA) and the drone integrator&operator (FADA-CATEC in C4D), configures a set of requirements in terms of cost of the solution, power consumption, size, weight, precision, and interface capabilities, which, added to the specific geometry of the indoor infrastructure, has lead ACORDE to a novel IPS solution, outlined the following figure.

[[File:wp3-15_1_02.png|frame|center|Indoor Positioning System developed by ACORDE]]

The solution relies on a “tag node”, to be mounted on the drone, and to provide to it to the geo-reference position, based on a set of measured distances (called ranges) to a set of strategically deployed “anchor nodes”. Range estimation is based on a specific protocol of message exchanges on the Ultrawideband (UWB) spectrum. The tag integrates an INS, so that it can fuse INS information with UWB ranges, for providing a processed tag position. In addition, the tag can also provide at its output interface range data. A standard Mavlink interface supports the provision of these data to the drone navigation system.
The posed solution contributes improvements and innovations accounting the scenario and the current state of the art. ACORDE provides a vertical solution, covering the design&implementation of the solution (anchor&tags platforms and their firmware). In addition, a specific design tool, IPS Modellign and Analysis Framework ([[WP6-21|IPS-MAF]]), has been developed, which allows to perform a more holistic and efficient analysis and design of this specific type of solutions. All this activity, has been comprised by technical packages WP3-WP6 in C4D, which can be summarized as follows:

* Design and implementation of anchor and tag platforms (including the required board support package (BSP) ([[WP3-15_1]]).
* Design and implementation of anchor and tag firmware, including the configuration, positioning algorithms and interfacing ([[WP4-17]]).
* Ensuring a robust and enriched communication among anchors, and among the tag (within the drone) and the anchors, for a more robust and improved positioning ([[WP5-19_ACO]]).
* Developing an Indoor Positioning System Modelling and Analysis Framework (IPS-MAF) for indoor structures, specifically tunnels ([[WP6-21|IPS-MAF]]).
* Providing at the tag a Mavlink [29] interface to support providing both processed positioning information, and “pre-processed” information (ranges) (WP3, WP4, and WP5).

==Challenges and Contributions ==

The stakeholder (ACCIONA) described the digitization scenario at a specific time slot where the construction 7days/24hours activity stopped for 1-2hours. At that time, it is possible to set up some “mobile” anchors, together with the “fixed” anchors, and later let the drone perform a pre-programmed digitization flight, where the tunnel under-construction can present some eventual obstacles (e.g., machines, signals). The posed scenario presents '''several challenges''' in relation to other existing real-time location systems:

* The specific ''long geometry'' of the tunnel (which challenges UWB range estimation, the cost of the solution and the validity of conventional trilateration algorithms).
* Demand of features for a flexible and agile anchor deployment, which does not oblige surveyors to geo-positioning all anchors, especially mobile ones.
* Need to provide real-time, 3D geo-referenced positioning on the tag (while most solutions focus on 2D relative positioning, commonly computed on a ground platform which centralizes data from anchors).
* Cost and energy/power optimization (the latter important for fixed anchors)
* Need for system-level design tooling. The IPS is a complex system with many parameters and aspects (specific deployment, transmission powers, sensitivities, latencies of the ranging phases, algorithmic alternatives, etc) with potential significant impact on the overall performance. Means for facilitating a holistic design, accounting for those many different aspects at early design stage are required even for experienced designers in the field.

The same scenario also presented the opportunity to exploit the fact that during digitization flight only one drone, i.e., one tag, needs to be serviced. The question is how to exploit this single-tag assumption for a safer flight and better digitalization.

The ACORDE solution tackles these challenges and opportunities. So far, a number of '''contributions''' in comparison to other existing solutions are highlighted:

* Customized, cost-effective anchor and tag platforms, specifically designed to cope with the computational needs (specially for tag) and energy/power efficiency needs (specially anchors).
* Novel MAC protocol called Asynchronous Tag trigger, Slotted Anchor response with Deterministic and Random Allocation (ATSA-DRA), specifically adapted to the single-tag assumption, that ensures deterministic latency, while optimizing the number of anchors in view.
* At application level, the solution enables geo-referenced, real-time 3D positioning. Moreover, the application overcomes the challenges of the tunnel geometry. A modified trilateration algorithm has been already developed which enables positioning in regions of limited anchors visibility (coverage) and poor dilution of precision (DOP), where a conventional least-squares based approach is not working. This is specifically required for enabling anchors auto-positioning at the initial phase.
* The development of IPS-MAF, is a qualitative step on ACORDE capabilities for tackling custom design of IPS systems for long indoor infrastructures (tunnels, mines, large pipes, …). It enables a newer system-level design flow (as explained in [[WP6-21]]), capable to reveal outcomes and aspects almost imposible to notice or tackle manually.
* The support of a Mavlink interface at the tag side, to provide both completely processed (e.g., position data) and partially processed (e.g., ranges). The latter enable the ACORDE IPS to behave as a complementary positioning sub-system, whose outputs can be fused by integrators with other alternative sensor data. Moreover, ranges transfer is enabled via a “smooth” (in the form of dialect) Mavlink extension contributed by ACORDE in COMP4DRONES.

==Anchor at Tag platforms==
In C4D ACORDE has performed a customized development for the anchor and tag platforms.

On top of a base mother board design, the tag and the anchor platforms have been implemented.
The later, in turn supports the different types of anchor nodes defined for the solution.

[[File:wp3-15_1_05b.png|frame|center|Indoor Positioning System developed by ACORDE]]

For the same form factor, these platforms have several benefits in relation to devices found in the market:
- more estable clock
- better connectivity for configuration purposes
- more powerful tag (capable to provide in real-time fused geo-location solution)

Moreover, this development has provided ACORDE a strong technological base to further develop with greater flexibility the firmare of the positioning solution ([[WP4-17]]),
where much of the added value of the solution is concentrated.

WP6-21

2023-03-13T16:22:13Z

Acorde: /* Introduction */

== Introduction ==
{|class="wikitable"
| ID|| WP6-21 (WP6-IPS-MAF)
|-
| Contributor || ACORDE
|-
| Levels || Tool
|-
| Require || Linux (or Windows+WSL), Libraries: PCL, Xerces, GeographicLib, Matplotlib
|-
| Provide || Static and Dynamic (simulation based) of holistic model of Indoor Positioning System
|-
| Input || SystemC models of tag and anchor applications, XML-based description of the anchor deployment and other crucial parameters of the solution, of the configuration of the the analysis
|-
| Output || Static analysis outputs (Visibility, DOP, range for trcv configurations) and Dynamic analysis (accuracies, timing affected behaviour)
|-
| C4D tooling || System-Level modelling and analysis
|-
| TRL || 3
|-
| Contact || fernando.herrera at acorde.com
|}

ACORDE IPS was motivated by the specific positioning needs and requirements for a drone flying on an large indoor scenario.
The need for considering different requirements, several aspects and levels of a Cyber-physical system (tunnel geometry, deployment of anchors, algorithms for 3D positioning, platform limitations, interfaces) made early evident that a more holistic, model-based design was necessary.
It motivated the development of the '''IPS Modelling and Analysis Framework (IPS-MAF)''', which, as shown in the figure below, can be used from early design stages, to build up a holistic model of the IPS system. IPS-MAF can be used to analyse and decide key aspect at different levels of the indoor positioning system (deployment of the anchors, sensitivities and transmission powers, transmission frequencies, etc) while keeping a holistic view of the system.

[[File:wp3-15_1_04.png|frame|center|IPS-MAF provides a qualitative step towards a holistic, model-based design of Indoor Positioning Solutions for long infrastructures]]

That is, IPS-MAF enables a holistic model of the IPS, while integrating some functional actual pieces of the application, so in that sense it also enables to advance some part of the application development. Therefore IPS-MAF feeds the conventional platform development and embedded application development phases, where ACORDE has already long expertise. At the same time, the measurements and characterizations that can be derived and refined from platform and application development serve to feedback and polish the holistic model. Summing up, an extended system-level design flow has been enabled, after coupling IPS-MAF to conventional ACORDE development processes for platform development (which includes PCB design, mechanical design, drivers’ development, embedded application development) and application development (where ACORDE typically develops in C or C++, relying on some cross-development environment suited to a specific microcontroller).

== IPS-MAF Architecture ==

Following figure sketches the main architecture of IPS-MAF.

[[File:ACORDE-IPS_MAF_Architecture.gif|800px]]

IPS-MAF is composed by two main tools:
* The IPS-MAF Analyzer
* The IPS-MAF Visualizer

=== IPS-MAF Analyzer ===
A main input to the IPS-MAF Analyzer is a model of the anchor and tag applications. They are developed separately from the IPS-MAF tool as SystemC models.
This is convenient, as this description is very close to a final C/C++ implementation, while relying on a SystemC API enables a target independent and standard description.
Different application models can be separately developed and compiled and (dynamically) linked to the IPS-MAF Analysis tool. Such mapping is described in XML format.

A set of XML files serves to specify such a mapping of tag and anchor applications, and other main aspects (anchors deployment, tunnel geometry, main HW parameters like UWB transceivers configuration, tag dynamics) of the IPS with large potential impact on performance.

The analyses to be performed are also described in XML format.

[[File:C4D_WP6_IPS_MAF_A_xml_deploy.png | 500px |center| Most input information is passed to IPS-MAF in XML format (anchors deployment in the image)]]

The IPS-MAF Analyzer parses all this input information and links the tag and anchor application models and performs the described analyses.
Notice that, despite the dynamic, simulatio-based analysis relies on SystemC, none of the requested analysis requires any compilation. The IPS-MAF Analyizer can be seen (as is) a command line tool that reads some inputs and produce some outputs.

Static analysis comprise visibility of the anchors and [https://en.wikipedia.org/wiki/Dilution_of_precision_(navigation) Dilution of Precision (DOP)] for any point of the infrastructure. It also comprises the analysis of the range (and in general, of the link margin) for different configuration of transmitting and receiver configurations.

Dynamic analysis refers to the possibility to perform a simulation and extract out of it different type of metrics, such as estimated positions of the tag and anchors, and errors with regard to their real position.

[[File:C4D_WP6_IPS_MAF_A_execution.png | 500px |center| Messages in console launched by IPS-MAF Analyzer]]

Analysis configuration allows to select which specific outputs will be exported, in different formats (mostly, csv and KML for dynamic analysis). Some files are exported in other convenience formats (e.g., .pcd, png). All the outputs for a configured simulation are exported to an output folder, which can be controlled from the tool configuration too.

=== IPS-MAF Visualizer ===

The IPS-MAF Visualizer is a graphical front-end that takes as input the outputs produced by the IPS-MAF analyzer and show a 3D visualization of them.
It also uses some inputs to the IPS-MAF Analyzer (bypassed to the output folder), e.g. to visualize the tunnel model, anchors deployment, obstacles, flight plan.

The IPS-MAF Visualizer supports the visualization of both, outputs of the static analyses, and of the dynamic analyses.
Following figures provide a

Below, a sample of several types of visualizations of the static analysis outputs which can be performed with the IPS-MAF Visualizer are shown.

<gallery widths=300px heights=200px >
File: WP6_21_PDOP_analysis.png | PDOP analysis
File: WP6_21_HDOP_analysis.png | HDOP analysis
File: WP6_21_IPSMAF_obstacles.png | section visualization of PDOP analysis with obstacles in the tunnel
File: WP6_21_path_analysis.png | Analysis on flight plan (histogram visualization behind)
File: C4D_WP6_IPS_MAF_A_circle_section.png | HDOP analysis on a cicle section tunnel)
File: WP6_21_IPS_MAF_obstacle_shadow.png | Shadows revealed in VDOP analysis)
</gallery>

== Status after C4D ==

IPS-MAF is related to the ACORDE IPS, and its development has been triggered and done in the frame of/thanks to COMP4DRONES.
All the aforementioned features are supported with several demonstrative examples.

It is remarkable that the outputs of the IPS-MAF simulations already served to detect issues when conventional least-squares algorithms were used, and to design and test the modified trilateration algorithm, even before the anchor or tag platforms were ready. IPS-MAF dynamic analysis revealed non-straightforward effects and outcomes as the one mentioned, difficult to advance with a manual analysis.
Similarly, for the static analysis. For instance, notice the “coverage” pattern in depending the type of DOP (PDOP vs HDOP) and the “shadow” provoked at the floor by obstacles oh the roof of the tunnel.

Some demo videos will be made available before the end of the project.

File:Wp3-15 1 05.png

2023-03-13T16:19:49Z

Acorde: Acorde reverted File:Wp3-15 1 05.png to an old version

File:Wp3-15 1 05.png

2023-03-13T16:19:09Z

Acorde: Acorde reverted File:Wp3-15 1 05.png to an old version

WP3-15 1

2023-03-13T16:15:36Z

Acorde: /* Curent Status */

=UltraWideBand (UWB) based indoor positioning=
{|class="wikitable"
| ID|| WP3-15_1
|-
| Contributor || ACORDE
|-
| Levels || Platform, Function
|-
| Require || Energy, Raw sensed data from UWB transceiver and IMU
|-
| Provide || Navigation Sensor
|-
| Input || Raw sensed data from UWB transceiver and low-cost INS
|-
| Output || Position
|-
| C4D building block || UWB-based indoor positioning system
|-
| TRL || 4
|-
| Contact || fernando.herrera at acorde.com
|}

[[File:wp3-15_1_01.png|frame|center|Building block diagram for WP3-15_1]]

==Description==

In COMP4DRONES, ACORDE has tackled the design and developmentof of an Indoor Positioning System (IPS), as a solution for the challenges posed by the construction use case, demo tunnel (UC2-demo 2). ACORDE IPS can be considered a specific instantiation of the building block of C4D architecture shown above. ACORDE IPS is specifically oriented to serve reliable and precise geo-referenced position to a drone flying on a tunnel under construction. Such a drone is in charge of the capture of raw data for tunnel digitization, to be employed for Building Information Modelling or [https://en.wikipedia.org/wiki/Building_information_modeling "BIM"]. The objective of the ACORDE IPS is two-fold, i.e., to ensure a safe navigation along a planned path, and to optimize the accuracy of the navigation data synchronized with the data sensed for digitisalization(e.g., thermography or LIDAR), which can be exploited, for instance, for a faster offline digitalization. The specific environment and the usage scenario posed by the construction stakeholder (ACCIONA) and the drone integrator&operator (FADA-CATEC in C4D), configures a set of requirements in terms of cost of the solution, power consumption, size, weight, precision, and interface capabilities, which, added to the specific geometry of the indoor infrastructure, has lead ACORDE to a novel IPS solution, outlined the following figure.

[[File:wp3-15_1_02.png|frame|center|Indoor Positioning System developed by ACORDE]]

The solution relies on a “tag node”, to be mounted on the drone, and to provide to it to the geo-reference position, based on a set of measured distances (called ranges) to a set of strategically deployed “anchor nodes”. Range estimation is based on a specific protocol of message exchanges on the Ultrawideband (UWB) spectrum. The tag integrates an INS, so that it can fuse INS information with UWB ranges, for providing a processed tag position. In addition, the tag can also provide at its output interface range data. A standard Mavlink interface supports the provision of these data to the drone navigation system.
The posed solution contributes improvements and innovations accounting the scenario and the current state of the art. ACORDE provides a vertical solution, covering the design&implementation of the solution (anchor&tags platforms and their firmware). In addition, a specific design tool, IPS Modellign and Analysis Framework ([[WP6-21|IPS-MAF]]), has been developed, which allows to perform a more holistic and efficient analysis and design of this specific type of solutions. All this activity, has been comprised by technical packages WP3-WP6 in C4D, which can be summarized as follows:

* Design and implementation of anchor and tag platforms (including the required board support package (BSP) ([[WP3-15_1]]).
* Design and implementation of anchor and tag firmware, including the configuration, positioning algorithms and interfacing ([[WP4-17]]).
* Ensuring a robust and enriched communication among anchors, and among the tag (within the drone) and the anchors, for a more robust and improved positioning ([[WP5-19_ACO]]).
* Developing an Indoor Positioning System Modelling and Analysis Framework (IPS-MAF) for indoor structures, specifically tunnels ([[WP6-21|IPS-MAF]]).
* Providing at the tag a Mavlink [29] interface to support providing both processed positioning information, and “pre-processed” information (ranges) (WP3, WP4, and WP5).

==Challenges and Contributions ==

The stakeholder (ACCIONA) described the digitization scenario at a specific time slot where the construction 7days/24hours activity stopped for 1-2hours. At that time, it is possible to set up some “mobile” anchors, together with the “fixed” anchors, and later let the drone perform a pre-programmed digitization flight, where the tunnel under-construction can present some eventual obstacles (e.g., machines, signals). The posed scenario presents '''several challenges''' in relation to other existing real-time location systems:

* The specific ''long geometry'' of the tunnel (which challenges UWB range estimation, the cost of the solution and the validity of conventional trilateration algorithms).
* Demand of features for a flexible and agile anchor deployment, which does not oblige surveyors to geo-positioning all anchors, especially mobile ones.
* Need to provide real-time, 3D geo-referenced positioning on the tag (while most solutions focus on 2D relative positioning, commonly computed on a ground platform which centralizes data from anchors).
* Cost and energy/power optimization (the latter important for fixed anchors)
* Need for system-level design tooling. The IPS is a complex system with many parameters and aspects (specific deployment, transmission powers, sensitivities, latencies of the ranging phases, algorithmic alternatives, etc) with potential significant impact on the overall performance. Means for facilitating a holistic design, accounting for those many different aspects at early design stage are required even for experienced designers in the field.

The same scenario also presented the opportunity to exploit the fact that during digitization flight only one drone, i.e., one tag, needs to be serviced. The question is how to exploit this single-tag assumption for a safer flight and better digitalization.

The ACORDE solution tackles these challenges and opportunities. So far, a number of '''contributions''' in comparison to other existing solutions are highlighted:

* Customized, cost-effective anchor and tag platforms, specifically designed to cope with the computational needs (specially for tag) and energy/power efficiency needs (specially anchors).
* Novel MAC protocol called Asynchronous Tag trigger, Slotted Anchor response with Deterministic and Random Allocation (ATSA-DRA), specifically adapted to the single-tag assumption, that ensures deterministic latency, while optimizing the number of anchors in view.
* At application level, the solution enables geo-referenced, real-time 3D positioning. Moreover, the application overcomes the challenges of the tunnel geometry. A modified trilateration algorithm has been already developed which enables positioning in regions of limited anchors visibility (coverage) and poor dilution of precision (DOP), where a conventional least-squares based approach is not working. This is specifically required for enabling anchors auto-positioning at the initial phase.
* The development of IPS-MAF, is a qualitative step on ACORDE capabilities for tackling custom design of IPS systems for long indoor infrastructures (tunnels, mines, large pipes, …). It enables a newer system-level design flow (as explained in [[WP6-21]]), capable to reveal outcomes and aspects almost imposible to notice or tackle manually.
* The support of a Mavlink interface at the tag side, to provide both completely processed (e.g., position data) and partially processed (e.g., ranges). The latter enable the ACORDE IPS to behave as a complementary positioning sub-system, whose outputs can be fused by integrators with other alternative sensor data. Moreover, ranges transfer is enabled via a “smooth” (in the form of dialect) Mavlink extension contributed by ACORDE in COMP4DRONES.

==Anchor at Tag platforms==
In C4D ACORDE has performed a customized development for the anchor and tag platforms.

On top of a base mother board design, the tag and the anchor platforms have been implemented.
The later, in turn supports the different types of anchor nodes defined for the solution.

[[File:wp3-15_1_05.png|frame|center|Indoor Positioning System developed by ACORDE]]

For the same form factor, these platforms have several benefits in relation to devices found in the market:
- more estable clock
- better connectivity for configuration purposes
- more powerful tag (capable to provide in real-time fused geo-location solution)

Moreover, this development has provided ACORDE a strong technological base to further develop with greater flexibility the firmare of the positioning solution ([[WP4-17]]),
where much of the added value of the solution is concentrated.

File:Wp3-15 1 05.png

2023-03-13T16:14:50Z

Acorde: Acorde uploaded a new version of File:Wp3-15 1 05.png