Pros and Cons of WIFI Based RTLS (Part 2)
Are you interested to meet with fellow RFID developers, source out RFID Hardware folks? I recently started a RFID Spotlight Facebook Group with the aim to bring together RFID programmer and hardware providers to share resources and experience. Its just a great way to network and meet people in this field. I made it easy for you to find us, so come and join us by following the link below.
Coming back to the subject of this post. Previously I shared When do we use Real Time Location Systems (RTLS), I will continue to share on the pros and cons of using WIFI based RTLS. We had previously used both Ekahau and Placelab for projects. Although I do not rule out some situations that suggest to us RFID based RTLS system is more superior, in general there are just more tangible benefits to choose WIFI based RTLS systems.
Some benefits of using a WIFI based RTLS are:
- Depending on the requirements for location granularity, if done properly WIFI based RTLS systems like Ekahau produce high tracking accuracies. Ranging on average between 1 metre - 3 metres indoors.
- Reuse and leverage on existing WIFI infrastructure. Why spend all that money to invest in a proprietary RFID infrastructure that cannot be reused?
- Quick ROI for WIFI investments by enabling other location-based applications or wireless applications.
- With growing categories of devices built-in with WIFI, organizations can also track other assets such as PDAs, mobile phones, laptops and any other WIFI enabled devices. Ekahau client application supports a number of PDA devices.
The cons associated with WIFI based RTLS are :
- Lack of Scalability : RTLS like EPE requires pre-calibration.In the language of Placelab, it means we need to train the system to “learn” about places on the map in relation to actual real locations. It is fine if you are calibrating for a bunch of classrooms in a small area, however it becomes increasingly complex to calibrate for large spaces - *think* stadium, 30-floors building, airport. EPE has a feature to “merge” calibration data of different maps ( e.g. one map for each floor ) which allows us to distribute that load among a few good persons. However the results from the merged calibrated data often falls short of the required accuracy, in fact occasionally erratic. Packages like Placelab also do not have “merge” capabilities.
- Location Model. WIFI based RTLS builds a location model ground-up from inputs such as RSSI of any given location. RSSI as you know can be affected by structures, especially solid steel structures and even moving bodies, partitions etc. Several environment issues may potentially affect these variables - access points ( *imagine* a segment of WIFI access points crash out ), structures that block signals, new partitions etc. Particularly in a museum environment, where new exhibitions are frequently replaced every other quarter and new walls/partitions being built, the original location model may be “damaged”. In situations like this, the rule of thumb is to update the calibration model every three to four months.
- WIFI Power Intensive. This is as plain as vanilla gets. WIFI is a pure power sucker. Its pure wishful thinking that a PDA with WIFI turned on can last more than 3 hours. Bearing in mind the fact, PDA internal battery actually performs poorer over time. It means a new WIFI PDA may last 2 - 3 hour the first time it is used; after several months of continual usage, it may last no more than 1 hour with WIFI turned on.
Well I hope we provided some notes (above) to help make your final decisions on RTLS implementations. Look forward to any form of comments to add to my points…
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October 14th, 2007 at 3:11 am
David,
This is an excellent review of technologies though as Marilyn points out, you are missing a technology.
You say that RTLS requires pre-Calibration. This is true of older technology.
Tag to tag RTLS for asset tracking and locating
does not require calibration,
is highly scalable
works well in high metallic environments.
low power draw
Further it is proven to be accurate for the cost versus competitive products. See comments by Dieter Uckelman at RFID Journal Live in Orlando, May 2007
http://www.supplychainmarket.com/content/news/article.asp?docid=592ede36-2c1d-4f8f-9197-5e9ee4ff7a82&atc~c=771+s=773+r=001+l=a&VNETCOOKIE=NO
The tags are currently designed for heavy industrial, high visibility and can be buried. Ergo - yard applications, industrial and manufacturing. A good replacement for GPS
Then go to:
http://www.lbszone.com/content/view/2397/2/
A PDA can be used to run the app for tag to tag RTLS - hence the common business tool is used for mobile forms and direct inventory land ERP wireless link - beypassing battery issues.
February 5th, 2008 at 11:52 pm
David,
I like the didactic nature of your blog. Since your site is a good source of information for persons researching different RTLS offerings, especially the pros/cons of exclusive read RFID locating and wifi locating, I think it would be good to include Versus Technology, Inc. Primarily focused on improving safety, satisfaction and efficiency within the healthcare environment, the Versus system is deployed in more than 500 facilities worldwide.
Versus combines active RFID and infrared technology to provide the precise real-time location of people and assets. While wifi systems can locate (at best) to a little over 3 feet, the Versus system can locate to room-level, even bed-level (within inches, in fact). The Versus system leverages a facility’s wifi network to communicate location information, but relies on exclusive reads for more accurate information, which is necessary to automate events or for accurate billing capture. This allows hospitals to leverage existing resources and cut down on manual tasks, saving time and money.
Miranda Hahn
Communications Coordinator
Versus Technology, Inc.
www.versustech.com
February 14th, 2008 at 6:36 pm
Thanks for your input, although Versus system has some benefits I personally view active RFID to have more disadvantages than advantages. Key being the costs of implementation will likely be highly. Unlike a WIFI based RTLS system, you do not leverage a current infrastructure. Adding to that, to get inches accuracy localization, you are likely planting readers all over the place.
Secondly I see Versus system seem to slant towards the healthcare, clinic environment. Versus system is likely to work for healthcare needs but less likely applied in a more generic sense.
Acute Accuracy does not necessarily win the game here. The differentiation of localization solutions is in the accuracy - not every application requires inches based accuracy. It means, if the WIFI based solution offers an average accuracy of 3 - 5 metres, it may just be a better solution versus the hassle and cost of planting readers everywhere.