Bluetooth 5.1 layers[Edit:  I’ve been told that “cm accuracy” may mean something different to the Bluetooth standards people than it means to those of us used to hearing “meter accuracy” (meaning +/-1 meter.) It is going to get there, but I may be slightly ahead of reality in this brainstorm.]

This is a brainstorm of the use of Bluetooth 5.1 to enable cm-level location data at Archaeology sites.  I’m in touch with some gifted and informed engineers related to this, but these early thoughts  will surely need some refinement.   I have on this blog before discussed emerging technology for capturing positional data over GPS improvements in hopes it would provide professional and amateur Archaeologists faster, more efficient and accurate information in the field.

While there is promise of lower-cost cm-level GPS on the horizon, it is a far larger infrastructure shift involving satellites and the need for more processing power and subject to environmental factors such as cloud or trees.

Most people will be unfamiliar with its location finding capabilities which have been limited resolution but the application is still very popular.

“Location services is one of the fastest growing solution areas for Bluetooth technology, and is forecasted to reach over 400 million products per year by 2022. This is great traction and the Bluetooth community continues to seek ways to further grow this market with technology enhancements that better address market needs, demonstrating the community’s commitment to driving innovation and enriching the technology experience of users worldwide.”  Bluetooth SIG Executive Director Mark Powell 

Bluetooth is a protocol stack, available to any application built on the platform.   With a host layer improvement such as Bluetooth 5.1, existing location finding apps will happily use higher resolution data streams when available with no need to change the app itself.  For example, I can use my cell phone GPS for 2.5 meter accuracy, use a Qstarz GPS logger over Bluetooth for 1.5-2.0 meter accuracy or connect it to a Bad Elf Surveyor over Bluetooth and get 1 meter resolution within the same application running on my phone.  I just get better data.  If a cm-level version via Bluetooth 5.1 of that data was available, this app would likely just use it, but it is worth saying this is a big jump, and some applications might not be ready for the added decimal points of resolution, assuming they fulfill the promise!

Bluetooth’s Locating Application to Date – Low Resolution (>1 meter)

Bluetooth is a massively popular standard used for a wide variety of applications.  One of those applications is in the locating of devices, usually done with trilateration, using the known position of three reference points.  These typically use Tags or Beacons to obtain relative location of objects within the space they define.  The accuracy of these has been typically +/-1 to 5 meters, and therefore only sufficient for coarsely-defined location applications, such as key chain finders – where the last few feet of searching is supplemented by an audible signal.

Archaeological POIs with AoA and AoD Arrays and Bluetooth 5.1

Recently, however the The Bluetooth Special Interest Group (SIG) has added new direction finding features to the Bluetooth 5.1 standards that utilize the angular orientation of the Bluetooth radio signal – its Angle of Arrival (AoA) and Angle of Departure (AoD.)   This newer approach allows centimeter-level precision by combining a single array-based antenna and a Bluetooth 5.1 compatible cell phone or small Bluetooth device.  When consumers start to see the benefit of the increased accuracy, adoption could be swift, motivating app developers to invest time in updating apps to the new level of precision.

Basic Mechanism Used for AoA and AoD with Bluetooth 5.1 

The reception or transmission of signals is cycled from one end of the array to the other across multiple precisely-spaced antenna array.  Signals arrive with angular information relative to the point needing measured (see illustration, courtesy of the BSIG)  As the signal crosses the array antennae, there is a resulting phase difference due to the differences in distance from each antenna in the array to the transmitting antenna.  This mechanism has been available with WIFI antennae at lower resolution in some applications before via WIFI Access points.

Bluetooth 5.1 AoA and AoD Antennae Array

Bluetooth 5.1 Range and Power Efficiency

In addition to the precision improvements, Bluetooth 5.1’s specification describes a radius/range improvement of 4x than what we have in Bluetooth 4.2 without increasing power requirements. BTLE devices can be powered by a single battery for up to a year, and some passive devices can operate without a battery at all.  Theoretically, this allows a range of 800 feet for a single antenna, but range may be improved by incorporating Bluetooth mesh networks technology where all of the field devices “assist each other” for better data communication and accuracy.   To expand your (digital) site, you just add antennas.  Looking back at Bluetooth 4.x and before, I feel it’s likely that environmental factors such as distance and obstacles will affect the accuracy and range.  But being pessamistic for a moment, even if it’s 1/8th the predicted range, a single antenna could cover many typical Archaeology sites.

Imagined Bluetooth 5.1 Array Antennae

Imagined Bluetooth 5.1 Array Antenna positioned on an Archaeological datum

Using Bluetooth 5.1 for Fixed and Relative Reference Points and Metal Detecting Coverage Maps in Archaeology

With the array antennas positioned on known, high-precision datum (such as what might be obtained via a Total Station GPS system) software could then begin to compute relative coordinates.  For metal detecting, a passive Bluetooth tag on the detector itself could provide the basis (AoD) for generating interesting sweep coverage maps in real-time from all team members.

Imagined Bluetooth 5.1 Low Energy point gathering device

Inexpensive Hardware Tools for Archaeology Field Work

One thing that Archaeology projects don’t need is specialized, fragile, difficult-to-use, unreliable and expensive technology added to their work.

The Archaeology team could utilize small hand-held devices paired to a device via Bluetooth 5.1 such as an iPad or cell phone to interact with the application.  I envision registering the devices as Bluetooth pairings and adding them to the active devices list within an app.

In theory, this small Bluetooth 5.1 Low Energy device could be a smartwatch, cellphone or even a small specially-built tool like I’ve visualized here (orange item in the photo.) Considering the costs of others using BTLE now currently on the market, the cost could be as low as $20-30 while being weatherproof, energy efficient and durable. Every team member could have their own device, and the data points added could be attributed to the team member automatically, possibly using a blockchain.

Real-timeArchaeology GIS:  Digital and Physical Grids in Synchronization

Laying out an Archaeology Site

The physical Archaeology grid provides a more visceral means for working on a site than having to use a computer screen and I don’t see it being retired anytime soon, no matter how much our data collection tools improve.   But with the physical and digital grid in reliable, real-time synchronization, many parts of the workflow become much faster and the administrative overhead can be reduced.  Presumably, the latest data for the site would be immediately available to all team members via portable display devices (or VR headsets perhaps?   End-of-day and end-of-project type data aggregation and reporting could be done with less delay.

Combining Digital Archaeology Location Data in the Field 

With the improved setup, team members would surely find new ways of using the synchronized physical and digital space we may not have considered – possibly impacting day-to-day decisions and informing project stakeholders.   On the site, for example, the application could assist with the positioning Archaeological units or defining the edges of a site or known previous structure – all within a team planning environment.

Archaeology Site GPS Layout with Flags

Watching the Space

While this post is as much brainstorm as anything, I will be watching this standard emerge and hope to get the feedback of various engineers and developers on the feasibility of assembling a “kit” for an Archaeology site to do a proof-of-concept as new devices are released.


All Illustrations from the BTSIG 5.1 Discussion Document – All photography by the author.