Merge pull request #60 from bitcraze/krichardsson/docs

Added TDoA3 Long Range docs

docs/building/index.md

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+---
+title: Building
+page_id: building_index
+sort_order: 1
+---
+
+This section contains instructions on how to build the firmware
+
+{% sub_page_menu %}

docs/development/index.md

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+---
+title: Development Instructions
+page_id: development_index
+sort_order: 4
+---
+
+This section contains related to development.
+
+{% sub_page_menu %}

docs/functional-areas/index.md

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+---
+title: Functional areas
+page_id: functional_areas_index
+sort_order: 3
+---
+
+This section describes the functionality of various parts of the system.
+
+{% sub_page_menu %}

docs/protocols/index.md

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+---
+title: Protocols
+page_id: protocols_index
+sort_order: 5
+---
+
+This section contains documentation of the protocols used
+
+{% sub_page_menu %}

docs/user-guides/index.md

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+---
+title: Userguides
+page_id: userguides_index
+sort_order: 2
+---
+
+In this section you will find user guides
+
+{% sub_page_menu %}

docs/user-guides/tdoa3_long_range.md

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+---
+title: TDoA 3 Long Range
+page_id: tdoa3_long_range
+---
+In the TDoA3 mode the system can be configured in Long Range mode to extend the distance that the Crazyflie can
+receive data from the anchors. We have not done any systematic measurements for the maximum distance but we believe
+it is at least around 30 - 40 meters.
+
+## How it works
+
+The bitrate of the UWB messages is reduced which increases the distance at which messages can be received. Since each
+packet takes a longer time to transmit, the packet rate is also reduced. This increases the noise in the estimated
+position a bit compared to "normal" TDoA3.
+
+## How to configure
+
+Both the anchors and the Crazyflie must be configured in the Long Range mode. You can read about [how to configure the
+Crazyflie here](https://www.bitcraze.io/documentation/repository/crazyflie-firmware/master/userguides/configuration/tdoa3-long-range-config).
+
+The anchors must be configured with the radio mode: `low bitrate, normal preamble`, [see the low level configuration section](/docs/development/anchor-low-level-config)
+
+## Limitations
+
+TDoA3 Long Range is supported from version 2022.09.
+
+Long Range only works with TDoA3
+
+If the system is very "flat", the estimate in Z will not be good, the reason is simple geometry.
+For good 3D position estimation we recommend that the ratio between the length|width in relation to the height should
+not be larger than 3. This is not an absolute requirement but we think it is a good guideline.
+When using Long Range mode this can become a problem if the size of the system is increased without moving the
+upper anchors higher. One solution is to add more anchors to the system in the ceiling and/or on the ground to create
+smaller "cells" with a good ratio between width and height.