Beacon and Wi-Fi anchors

Most things Omaya follows indoors broadcast: a tag sends a short Bluetooth signal every second or so, the gateways on the ceiling hear it, and Omaya works out the room from how loudly each gateway heard it. Some devices work the other way round. A badge such as MOKO's PS101, or a phone, listens instead: it scans for the Bluetooth beacons or Wi-Fi access points around it and reports the list of what it heard. Gateways have nothing to hear.

An anchor is what turns that list into a room: a beacon or access point that stays in one place, in a zone you know. When a scan comes in, Omaya looks up the anchors in it and places the device in the room of the ones it heard loudest.

Both end in the same place: a room on the device's trail. A tag needs gateways that can hear it; a badge that only listens needs anchors — beacons or access points whose room Omaya knows. Here the badge hears two Pantry beacons loudly and the meeting-room access point faintly through the wall, so it is placed in the Pantry.

When to use anchors

Use anchors for a device that scans rather than broadcasts:

• Cellular badges set to a Bluetooth or Wi-Fi fix, such as the MOKO PS101. Indoors, GPS has no sky to see, so a badge set to "Bluetooth, then GPS" or "Wi-Fi, then GPS" reports a scan list inside and a GPS position outside.
• Phones and other scanners whose app sends Omaya the beacons or access points it heard.

You do not need anchors for ordinary tags, cards and wristbands. They broadcast, and the gateways place them as described in Floor plans and positioning.

Anchors are kept on Space → Beacon & Wi-Fi Anchors.

What counts as an anchor

There are two kinds of anchor:

• Anchors you add. You add a beacon by its Bluetooth MAC address, or an access point by its Wi-Fi BSSID, and give it a zone. You can add them one at a time (Add anchor), paste a list (Bulk add: one line per anchor, identifier, zone, label, where the zone is its name or Floor / Zone when the name is used on more than one floor; nothing is saved unless every line reads), or pick them from the ones scanning devices have already heard (see Checking that it works).

• Registered devices. These need no typing. A gateway with a zone counts as a Bluetooth anchor, and so does a beacon, sensor or motion sensor whose zone an admin set or that is placed on the floor plan. They are listed on the From registered devices tab. A tag never counts, because it moves.

  You can switch this off under Settings. If you add an anchor with the same identifier as a registered device, the anchor you added wins.

A Bluetooth anchor only answers Bluetooth scans, and a Wi-Fi anchor only answers Wi-Fi scans.

Placing beacons

One beacon per room is the starting point. Some care in placing it decides how well it works.

• Put it in the middle of the room, high on a wall or on the ceiling, not beside a doorway or on a wall it shares with the next room. A beacon by the door is as loud in the corridor as in the room.
• Give a large or oddly shaped room two or three beacons. Omaya adds up the anchors of each room, so two beacons that agree make the choice firmer.
• Use beacons with a fixed MAC address. Many phones and some beacons change their address every few minutes for privacy. A beacon like that cannot be an anchor, because next hour it has a different identifier.
• Keep transmit power modest (0 dBm or a little below) and the advertising interval about one second. A very loud beacon is heard three rooms away and blurs the rooms together. A slow one may be missed in a short scan.
• Corridors and open-plan floors work best with a beacon every 8–10 m, each anchored to the zone it sits in.
• Mind the battery. A beacon that goes flat is a room that stops being found. The Heard recently column shows an anchor that has gone quiet.

Recording office access points

Wi-Fi anchors use access points that are already on the ceiling.

• Find the BSSIDs. The Wi-Fi controller or its management page lists each access point's BSSIDs. So does a Wi-Fi analyser app on a phone, standing under the access point.
• One access point has several BSSIDs: one per band (2.4 GHz and 5 GHz) and per network name. They usually differ only in the last part. Enter the first five parts (AA:BB:CC:DD:EE) to cover them all, or list each BSSID.
• The easiest way is often to let a badge do the survey. Walk it through the building, then open Heard, not assigned. The access points heard loudest in each room are that room's. Assign them there.
• Wi-Fi carries further than Bluetooth. An access point is often heard clearly two rooms away, so Wi-Fi places a device less sharply than beacons do. Access points in corridors are poor anchors for the rooms off them. That is why Wi-Fi has its own, stricter signal floor.

Omaya never sends scan lists to an outside location service. A scan is matched only against the anchors you recorded.

Setting up the device

The device has to report what it heard. On a MOKO PS101 you can set this from Omaya: open the badge under Device → Sensor and press Badge settings (see Badge settings and commands).

• Under Working mode & reporting, a Positioning method that includes Bluetooth or Wi-Fi for the mode the badge works in (for example Bluetooth, then GPS).
• Under How it finds its position, Bluetooth scan → Beacons to report, or Wi-Fi scan → Access points to report, of 3 or more (3 is the default), so that more than one anchor is heard;
• The badge's own Ignore weaker than thresholds (on Wi-Fi scan, and Signal threshold under Bluetooth scanning & filters) left at −127 dBm, which keeps everything, because Omaya applies its own floor.

To keep the scan list to your own beacons, open Bluetooth scanning & filters, set Which filters apply to MAC list only and enter your beacons' addresses under MAC list. Leave it on None unless other beacons nearby confuse the badge. Setting the badge up from scratch is described on MOKO PS101.

How the zone is chosen

Each scan is handled on its own, in three steps:

1. Keep what is known and loud enough. Identifiers that are not anchors are set aside and listed under Heard, not assigned. So are anchors heard more faintly than the signal floor (−90 dBm for beacons, −85 dBm for access points).

2. Score each room. Each room gets the combined signal of its anchors. Two beacons in one room count for a little more than one, and one loud beacon still beats two faint ones.

3. Ask for a clear lead. The loudest room has to lead the next one by the margin, 5 dB by default. If it does not:

   • a device already in one of the close rooms stays there (shown as "Held");
   • a device that has no room yet is not placed.

   Either way the device is known to be indoors.

The floor (−90 dBm for beacons, −85 for access points) and the margin (5 dB) are the tenant's settings, on the Settings tab of Device → Beacon & Wi-Fi Anchors. Adding up a room's anchors means two beacons in one room count for a little more than one, while one loud beacon still beats two faint ones.

Each placement also carries a confidence: the chosen room's share of all the signal heard. A badge that hears only its own room's beacons scores close to 100 %.

What a placement does

A scan places the device the same way the gateways place a tag, so everything that reads rooms reads this too:

• Trail. The device's trail, and its person's or asset's trail if it is bound to one, get a stay in the room. Sensor Trail and Why here? show it as Beacon anchor or Wi-Fi anchor, with the loudest anchor in the gateway column.
• One stay, not one row per scan. Further scans in the same room continue the stay, however far apart they are, as long as the gap is under Same room again within (30 min). After a longer gap a new stay starts.
• Live views. Entity Tracker and Roll Call see the device in the room for A placement counts as current for (10 min) after each scan. Set this longer than the time between the device's scans, or it will drop out of live views between them. Right Now and the reports count the stays on the trail.
• Indoors beats GPS. After a scan that heard an anchor, a GPS fix within the Indoor wins for window (System → Configuration → Outdoor & GPS) is kept on the map but does not move the trail, as for a tag the gateways hear. When the device goes outside and GPS takes over, the indoor stay ends at the last scan. See Indoor and outdoor.
• Store-and-forward. A badge that was out of coverage sends its stored reports later. A stored scan that is older than one already handled does not rewrite the newer position.

Settings

Space → Beacon & Wi-Fi Anchors → Settings. Each setting is per organisation. Leave a field empty to go back to the default.

Setting	Default	What it does
Ignore beacons weaker than	−90 dBm	A beacon fainter than this is too far away to say anything about the room.
Ignore access points weaker than	−85 dBm	The same for Wi-Fi. Wi-Fi carries further through walls, so its floor is stricter.
Lead needed between rooms	5 dB	How far the loudest room has to lead the next. Raise it if devices flick between two neighbouring rooms; lower it if they hold a room too long after leaving it.
A placement counts as current for	600 s	How long one scan keeps the device in its room on live views. Set it longer than the time between scans.
Same room again within	30 min	A scan in the same room within this time continues the stay on the trail.
Use registered fixed devices as anchors	On	Gateways with a zone, and beacons or sensors whose zone an admin set, count as Bluetooth anchors.

Checking that it works

1. Recent placements shows the last 50 scans that heard an anchor. For each one it shows the room, whether the room was Placed, Held or Not placed, the lead in dB and the anchors heard. Carry the badge into a room and the next scan should appear here with that room.
2. Heard recently, on the Anchors tab, shows for each anchor when a scanning device last heard it, how loudly, and which device heard it. An anchor that is never heard is in the wrong place, has a flat battery, or has the wrong identifier.
3. Heard, not assigned lists what scanning devices heard in the last two weeks that is not an anchor yet, loudest and most often heard first. Pick a zone under Assign to a zone and click Assign.
4. On the device's Sensor Trail, stays from scans show as Beacon anchor or Wi-Fi anchor.

Problems

What you see	Likely cause	What to do
Nothing under Recent placements	The device is not sending scans, or no scan contained an anchor	Check Heard, not assigned. If it is empty too, check the device's positioning strategy and that its reports reach Omaya.
Everything under Heard, nothing placed	The identifiers are not anchors	Assign them. For access points, check that the BSSID (or its first five parts) matches.
Often "Not placed"	Two rooms are heard about equally: a beacon near a shared wall or door, or two access points that cover both rooms	Move the beacon into the middle of its room, or add a second beacon to each room.
The device flicks between two neighbouring rooms	Margin too small for this building	Raise Lead needed between rooms to 8–10 dB.
The device stays in a room after leaving it	The new room's anchors are faint, or it has none	Add or move a beacon in the room it went to. Lower the margin a little if both rooms are well covered.
The device is in the room, but missing from live views between scans	Scans are further apart than the placement lasts	Raise A placement counts as current for above the device's scan interval.
A beacon heard once, then never again	Its address changes for privacy	Use a beacon with a fixed MAC, or turn its privacy mode off.
Wi-Fi places the device one room off	Access points carry through walls	Prefer beacons in rooms where it matters. Raise the Wi-Fi floor to −80 dBm. Do not anchor corridor access points to rooms.