Advice, which sensors do you recommend?

Hi!
I’m looking for sensors to be used in a outdoor position system. Can anyone please give advice/recommend sensors that can work for this application. I know that Decawave has evaluation kits, please give me more information if it can be used to test my application, or if you know other brands that can be better.

About/req.

  • One or several moving objects (tags) around ancors (with known positions).
  • The positions for each moving object (tag) must be calculated in real time IN the moving object (tag). It is enough to calculate the XY-position, the height is not required.
  • The moving object (tag) may have gyros, acc and kalman filter (if its necessary to achive good position)
  • The latency of the calculated position must be close to real time and the position accuracy<0.5 meters (the kalman filter may help here).
  • The tags can move up to 20 km/h and the area its operate in is from 100 meters to several kilometers. The system must be scaleable.
  • The tags can be on different places and also close to each other, this changes all the time.

Questions:

  • Any modules that can fulfill above? If so, please explain more, e.g. What is the limitations of nr of tags and ancors? Can it work in a area of e.g. 5000 meters (with ancors every x meters?) etc.

Best regards
Olle

Hey,
I guess the DMW1001 Module isn’t suitable for your project as it only offers operation within a range of 60m. But even the DW1000 itself only offers ranges up to 300m, so you’d need lots of modules to mount at certain locations. Also, I don’t know how well the position accuracy and precision is when the tags move so fast. Using Decawave’s PANS firmware you can get positioning rates up to 100ms. If that’s what you mean by “real-time” you should be fine with this. If not, you could try and install a custom firmware which yields results with a higher frequency.

Given the huge area you are tryig to cover, I think you’d like to stick to Time of Flight (TOF) positioning principles because in Time Difference of Arrival (TDoA) systems all anchors must be clock-synchronized with a cable which in your case might be a difficult task to do.

So after all, you should have a look what devices offer the highest range capabilities.

Regards, Max

Hi Max

Also keep in mind that in a lot of regions (most notably Europe, see EN 302 065-2), UWB radio with base stations / anchors have specific regulations when used outside. See section 4.2.7 in ARP00013 Certification guide Europe. It is my understanding these regulations are often very restrictive.

Based on your requirements, I suggest looking into a GNSS (GPS) based system, adding augmentation (e.g GBAS) if you require more accuracy. Especially since you do not seem to have stringent energy consumption requirements.

UWB radio is not very suitable for your use-case of large range and relatively low accuracy. It could however be useful to augment a GNSS solution, e.g to measure the distance between tags that are close, offering collision avoidance and rudimentary GBAS.

If you are looking for GNSS modules, u-blox has some great solutions.

Hello Maxbauer,
Just wanted a clarification. As I understood, TDoA based on TTK1000 has the anchors wireless synchronized and does not need Wired synchronization. Please correct me if I am wrong?
Regards
Sandeep Suresh.

Hi Sundeep

Yes, the TTK1000 does support wireless clock synchronization using Clock Calibration Packet (CCP) UWB Frames, but your use-case will require multiple masters, making things quite complicated.

Clock synchronization for TDoA is a difficult subject. It can be done wirelessly, but using a wired method is more reliable / easier. See APS007: Wired synchronization of anchor nodes in TDOA RTLS.

Decawave can provide more advanced methods and algorithms to synchronize the clock wirelessly, but this is sold as IP (IP1001WS). You can contact our sales department to get more information: [email protected]

Either way, to meet your scalability requirement, TWR based RTLS systems are a lot more simple and scalable for your use-case. The main reason to use TDOA is the ability to use very low power (TX only) tags.

Typical TDoA does not meet your “The positions for each moving object (tag) must be calculated in real time IN the moving object (tag)” requirement (unless reverse TDOA is used). When using TDoA, the position of tags is calculated by the Anchors, not the tags.

Hello Seppe,
Thanks for your response. In TWR, there was a limit of 128 ( if I am correct) clocks for a single Anchor master to be the “INITIATOR” and multiple Anchor slaves. What is the maximum number of Slave Anchors that can be supported by Master Anchor in TDoA Scheme? Is there more documentation on protocol in TDoA and IP1001WS?
Regards
Sandeep Suresh.

At the risk of giving an overly commercial answer, I can sell you a system to do that. :slight_smile:

You said outdoors, that makes GPS/GNSS (Global Navigation Satellite System, a catch all for systems that use a mix of GPS, Glonass, Galileo, Beidou and other regional systems) by far the simplest option if it will work in your application. Off the shelf basic GNSS will give you 10 Hz update, ~1m accuracy (but better than that short term repeatability) and is cheap. High end systems will get you down to a couple of cm error and 100 Hz update rates but cost a lot more. There are a whole range of options in between.

If you only have partial GNSS coverage (e.g. some areas the view of the sky is obscured) a combined IMU / GNSS solution would be the best option. Generally this will cost a lot more than GNSS only.

(I could supply you with any of the above as off the shelf products targeted to the automotive market. So could quite a few other companies.)

If GNSS isn’t an option then optical or UWB are alternatives. Either on their own or combined with inertial.
Depending on latency requirements and number of possible obstructions optical may not be ideal in this situation but may be possible but I have seen some fairly impressive results from combining optical and inertial sensors. This has the advantage of not requiring the infrastructure that UWB requires.

The off the shelf decawave system doesn’t do what you need but the hardware can do this with the correct firmware.

We have a combined UWB/IMU kalman filtered system which will give 5-10cm accurate positions at speeds up to 200 km/h. Data is output at the tag with a latency of ~60 ms.
The system can also transition between GNSS and UWB as needed (see the second video here for an example New product announcement - Racelogic indoor positioning for automotive testing)

In terms of UWB coverage area we need a grid of anchors at around 30 m spacing. Up to 200 anchors are supported meaning a 30m x 3 km area could be covered. If needed we could probably push this to just under 250 anchors or just over 3.5 km. The anchors only require power, no network or other cable requirements. But if you can use GNSS for some of the area then that section doesn’t need UWB coverage so 5 km may be possible depending on the site. Spacing could be increased if you could get the appropriate licenses to bump the transmit power up but how practical that is is very region and use case specific.

The downside to the system is that we don’t support many tags simultaneously, currently a max of 5 but depending on the use case there may be some games you could play to increase that. And that we’ve spent a lot of time getting this right, we’re going to charge you a lot more than an off the shelf decawave module.

The final option would be a pure inertial system. However depending on your requirements this would probably be too expensive for you, pure inertial systems without some other reference to constrain the drift either lack the accuracy you need or cost silly money

Thanks a lot for all answers! I will discuss the alternatives with my colleagues.

Again, thanks for taking time!
Best regards
Olle