UWB vs BLE: How to Choose an Indoor Positioning Method

In indoor positioning enquiries the first question is almost always the same. Does it have to be UWB, or will BLE do? Some sites name UWB from the start. Others look at UWB, then ask whether they can switch to BLE because of cost. And some start with BLE and ask, worried, whether it will actually deliver the accuracy they want.

There is no single right answer. Each method measures a different quantity, and because the quantity differs, so does the job each one is good at. It is a bit like asking whether a sedan or a truck is better. The answer only appears once you decide what you are carrying.

This article starts from what each of the three methods actually measures, then follows that difference through to accuracy, equipment count and cost. The last part covers the cases where site conditions overturn the choice.

I. The Three Methods Measure Different Things

UWB measures time

UWB derives position from differences in arrival time. When a tag emits a signal once, it reaches a nearby anchor sooner and a distant anchor later. Multiply that time difference by the speed of light and you get a difference in distance; overlay the distance differences from several anchors and a single point remains.

Light travels about 30 centimetres in one nanosecond. So if you can measure time at nanosecond resolution, you can measure position at tens of centimetres. The reason UWB is described as precise rests on that simple piece of physics. In exchange, it uses a wide bandwidth in short bursts, which costs more power and needs anchors packed more densely.

BLE measures signal strength

BLE estimates distance from how strongly the tag's signal arrives. Close means strong, far means weak.

The problem is that signal strength responds to more than distance. A person walking in front weakens it, a metal wall reflects it and makes it oddly strong, and putting the tag in a pocket changes it again. So what BLE gives you is closer to an approximate distance than a precise coordinate. In exchange it uses very little power and needs far less equipment.

BLE AoA measures angle

AoA measures the direction a signal arrives from. Several antennas are arrayed inside one anchor, and the minute differences with which the same signal reaches each antenna are used to compute a bearing.

Knowing direction lets a single anchor narrow the position down. That puts AoA in a middle band: fewer devices than UWB, more precision than plain BLE. The catch is that angle computation is sensitive to reflections, so results can wobble in spaces full of walls and structures.

II. What Actually Changes

Item	UWB	BLE	BLE AoA
What it measures	Signal time difference	Signal strength	Angle of arrival
Typical accuracy	Tens of centimetres	A few metres	Around one metre
Anchor density guide	4 per positioning zone	1 per 20m × 20m	1 per area
Tag power draw	Relatively high	Very low	Low
What it is good at	Precise position, safety interlocks	Occupancy, zone judgements	Rough position inside a zone

The row worth staring at is not accuracy but anchor density. To build one UWB positioning zone, four anchors have to surround it, and the spacing between them is recommended to stay within 20 metres. BLE needs one device for a 20 by 20 metre area. That means the number of devices required to cover the same floor area differs several times over, and that is the line item that opens up most in a quotation.

Read the accuracy figures as a reference band only. Whatever the method, the specification value is the value under good conditions, and on a real site it shifts with structures, reflections and anchor placement. Rather than trusting the number at quotation stage, it is more useful to ask what conditions produced it.

III. When Accuracy Genuinely Matters

The criterion is not "the more precise the better" but "how precise does this particular job need to be?" Laid against the purposes that come up in practice, the line falls fairly clearly.

Jobs that need centimetres. Warning of a collision between a forklift and a person, detecting approach within a radius of a hazardous zone, interlocks that stop equipment automatically, spaces where robots and people move among each other. Here an error of one metre either delays the warning or manufactures a false alarm. A human body is less than a metre across, so if the error exceeds the width of a person the judgement itself does not hold up.

Jobs where metres are enough. How many people are in a given zone, entry and exit times and dwell duration, which route someone took. For judgements at zone granularity it is enough to be sure the position is inside the zone; whether it is in the middle or near the corner does not change the result. Attendance, occupancy checks, headcount during an emergency and visitor flow analysis all sit here.

In between. Finding assets is the representative case. Locating a specific piece of equipment in a warehouse is too much for zone granularity and does not need centimetres. Here AoA becomes a candidate, or the answer is a configuration that varies the method zone by zone.

IV. When Site Conditions Overturn the Choice

Even with the method settled by purpose, site conditions sometimes reverse the decision.

Spaces full of metal. Steel walls, large columns and stacked metal stock block and reflect signals. BLE, which infers distance from signal strength, swings badly in that environment. Reflected signals arrive late, so UWB is affected too, but it retains room to compare combinations from several anchors and filter out the odd values.

Tall or multi level spaces. The fork in the road is whether you need position in the vertical direction. If you have to know which rack level or which floor, leaving anchors on a single plane will not answer it. Distinguishing height requires the anchor heights to differ as well.

Spaces where anchors cannot go where you want them. When ceilings are too high or cabling is impossible and anchor positions are constrained, the anchors end up clustered on one side. In that case accuracy drops noticeably even with the same equipment count, because what matters is not the number of anchors but the range of directions from which they see the tag. That principle is covered in detail in a separate article.

Outdoors. If the subjects are outdoor assets or vehicles, both UWB and BLE require laying new anchor infrastructure, so there are stretches where a GPS based method fits better. For subjects that move between indoors and outdoors, the design has to stitch the two methods together.

V. You Do Not Have to Pick Just One

In real deployments, mixing methods on one site is more common than using a single one.

Zones carrying accident risk, such as production lines and forklift routes, are covered densely with UWB, while zones where knowing occupancy is enough, such as offices and warehouse corridors, are covered broadly with BLE. Tags are attached differently depending on the subject, and the results are viewed on the same floor plan on the same screen.

For that configuration to work, the monitoring software has to accept and process coordinates regardless of method. ORBRO OS is built to handle positions arriving from UWB, BLE and AoA on the same floor plan, so even when the method varies by zone the screen an operator looks at stays as one. On sites with a fixed budget this turns out to be a rather practical answer, because it concentrates accuracy where it is dangerous and saves cost everywhere else.

One more note. Techniques for improving distance measurement precision are also being commercialised in the Bluetooth camp. The industry consensus, though, is closer to a separation of layers than to replacement: a layer that handles sub metre work at low cost, and a layer that needs assured precision for safety and collision avoidance, coexisting side by side. Which brings the argument back to where this article lands. What you intend to measure comes first.

Closing

UWB measures time, BLE measures signal strength, AoA measures angle. Because the measured quantity differs, so do accuracy, device count and cost. Choosing a method is therefore not a contest over which technology is superior; it is a matter of first deciding what you will do with location data on this site.

Once you have settled whether you are preventing collisions, counting people per zone, or finding assets, the method largely follows. ORBRO builds UWB, BLE and AoA equipment alike, so we have no reason to push one particular method. Tell us your site conditions and your purpose and we will look at which method suits which zone, and whether a mixed configuration works in your favour.