If you’re in the business of Wi-Fi and other wireless technology – Particularly designing and installing networks – Then you’ll likely know how common it is for architects and interior designers to go on at us about placement of wireless devices.
Sure, they realise it’s necessary to have light switches and fire alarms – But wireless access points and the like don’t get the same concessions. Here at Geekabit we firmly believe that network infrastructure is very much a necessity in any building – particularly business premises but homes too.
Bluetooth low energy beacons (or BLE beacons) broadcast to nearby portable electronic devices, enabling smartphones tablets and other similar devices to perform certain actions whilst in close proximity to the beacon.
For these to be successful, they need to be placed in certain places. And whilst we do try to keep everything looking aesthetically pleasing, we do believe that a reliable and consistent network is as important to a building as the design.
Where can BLE beacons be placed?
We’re going to look at a few different potential locations for BLE beacons and how they effect their functionality (and the design aesthetic of the premises).
Near to the Floor
In some buildings, the design means that using any kind of adhesive or screw fitting on the wall would be abhorrent! This is particularly true if the material is fabric, glass or metal. Whilst you will be mounting the BLE beacon near to the floor, you will need some kind od baseboard and will also need to take into consideration any floor cleaning processes. You don’t want the device to get damaged!
Another reason why the floor is a good option, is that it helps inhibit the BLE beacon from being seen from one floor to another. If you have floor holes, like an atrium or stairwell, the map can get easily confused. The floor then acts as a shadow for these types of areas.
Every ‘portal’ (for example, doors from stairways, lifts and lobbies) needs to have a BLE beacon. This is so the app knows to switch maps when navigating a change of floor.
On the Wall
The easiest way of placing your BLE beacon as close to your users as possible, is to place it on the wall.
Wherever a user goes in the building, they should be within 3 or 4 metres of a BLE beacon. The closer they are to the BLE beacon, the better the accuracy. The more BLE beacons you have, the the better any latency will be reduced. It is however worth noting that it takes approximately 2 to 5 seconds for the app to link to the nearest beacon due to it listening out for all the beacons in the vicinity.
On the Ceiling
It’s not ideal, but it will work if you have no other option. As we said above, your users need to be as close to the BLE beacons as possible. Thus, placing the beacon on a ceiling means that at best, the user is always about 2 metres away from it – Even when standing directly underneath it.
The Complicated Bit
That was all quite straightforward, but here’s the geeky bit to explain the why!
The wireless engineering reason behind how these placements work comes down to free space path loss.
FSPL is the ‘attenuation (the reduction of the amplitude of a signal) of radio energy between the feedpoints of two antennas, that results from the combination of the receiving antenna’s capture area plus the obstacle-free, line of sight path through free space.’
In the locations outlined above, we are making constructive use out of FSPL.
Due to the inverse square law of RF propagation, measurement of the power present in a received radio signal in the BLE beacon based on determining the exact location of a radio transmitter is optimal within about 0 to 4 metres.
The typical calibrated output of a BLE beacon is 0dBm (1mW). They operate in the 2.4GHz band on a 2MHz advertisement channel tucked between Wi-Fi channels 1 and 6, as well as one just past channel 11, and another one just below channel 1.)
There can also be some variability between receiver devices in terms of their sensitivity and even based on internal antenna configuration and how the device is held/oriented. For this reason, we assume a +/- 3dB for the purposes of this example.
Based on the Received Signal Strength Indicator (RSSI), when a receiving device sees a BLE beacon, it determines its distance from that beacon, using the beacon’s ID to correlate it with the device’s placement on the map.
When a device sees a beacon at -35dBm, it knows it’s under a metre away. If it sees it at -55dBm, that could be anywhere between 4 and 8 metres away.
The further away you get from the beacon, the wider the margin of error.
You also need to take into account any potential barriers. For example, any walls that get between can also add 3dB or more of attenuation depending on the materials used. This is just the same as when we’ve blogged about the effects of walls and similar barriers on Wi-Fi signal.
Below 1 metre, every time you halve the distance you gain 6dB – so 50cm would be -34dB, 25cm would be -28dB, 12.5cm would be -22dB, and now we’re getting really close to the beacon, and it’s already lost 99% of the transmitted power.
Remember that if you mount them on a metal surface, you gain a little bit back. If your surface is less than one wavelength (~12cm) wide, the maths behind it gets a bit tricky!
What does all this mean for BLE beacon placement?
The main takeaway from all this is that when placing BLE beacons, you should try to get them as close to the receiver as possible which is usually within 4m.
If you are mounting the BLE beacon on a wall, then you need to aim for a height of 1-2 metres maximum. You should also consider the height of traffic going past it – Like the hips, shoulders or trolleys of passing people. You don’t want to damage the beacon or rip it off! (You also don’t want to regularly injure people from bumping into it…)
We mentioned ceilings earlier. BLE beacons can be placed there, but in office buildings that generally means that the receiver is always going to be at least 2m away from it – Even if they were to stand directly underneath. Placing beacons near the floor are approximately a metre closer to the receiver device than one mounted on the ceiling.
What about aesthetic concerns?
Ahh yes. Aesthetics. If you are trying to place BLE beacons in locations where there are particular aesthetic concerns, then you could consider painting the beacons and the mounts to match the surrounding design.
If you are planning to do this, you must make sure that the paint doesn’t contain any metallic materials (lead, aluminium powder, gold leaf, iron oxide etc).
Alternatively, you could also use a vinyl skin to make the beacon more aesthetically pleasing. These can also be used on access points.
If you are planning to do either of these, always check with the vendor to make sure that painting or vinyl skins won’t void the warranty (it does in quite a few cases).
Paintable covers that can snap on to indoor AP’s are also an option which would save you having the paint the beacon directly.
Designing your beacon deployment
As with any radio frequency (RF) planning, you should try and model the BLE access points and beacons.
Make sure you set your BLE coverage requirements to the Received Signal Strength Indicator required for the maximum distance you want to be from the beacon (-52dBm).
You also need to make sure that you are always able to hear at least 3 beacons.
Hopefully this article will have helped you when it comes to the placement of BLE beacons – And how to keep those architects and interior designers off your back!
