Maximum number of AOA devices which can be tracked by an anchor

[A.P]

Hi!

I wanted to check if Nordic could give me some rough estimate of how many tags can be tracked in a 'typical' AOA system, I understand this is very likely dependent on the implementation of the application portion of the AOA system, which is not what Nordic provides, so I understand if the answer will be, at best, a bit fuzzy.

Nonetheless, I tried searching online and contacting different AOA solution suppliers but the answers vary so widely (6-500 tags is the range I got) that I'm left a bit confused. Perhaps you will be able to offer an answer

Here is our scenario:
1. Each of our locations may hold as much as several thousand tags.

2. Not all tags will advertise simultaneously. Most tags will not advertise packets with CTE, as they should only do so when they moved or periodically to ascertain their current location.

3. Tags will also advertise and be connected to periodically to gather data from different sensors they hold.

4. The anchor points which determine the location and the centrals which handle BLE connections will be separate.

I'd like to know:

1. What is the 'typical' number of simultaneously advertising (i.e moving at the same time) tags an AOA system is expected to handle?

2. What is the 'typical' number of total, not simultaneously advertising (i.e some moving, some stationary) tags an AOA system is expected to handle? is there a max limit on this number?

3. What effects do tags which advertise connectable, non CTE packets have on tags which advertise non-connectable CTE packets? in other words, how does a high noise BLE environment expected to affect location finding AOA applications?

4. Is there anything in our scenario which leads you to believe an AOA location solution is not possible in our case?

Thanks in advance!

[Elfving]

Hello Asaf,

I will have to get back to you on this.

Regards,

Elfving

[Elfving]

Hello again,

1. What is the 'typical' number of simultaneously advertising (i.e moving at the same time) tags an AOA system is expected to handle?

2. What is the 'typical' number of total, not simultaneously advertising (i.e some moving, some stationary) tags an AOA system is expected to handle? is there a max limit on this number?

I a not sure how to give an answer about what is typical, the use-cases vary a lot. But with what we provide, the amount of tags you can track might be limited by CONFIG_BT_PER_ADV_SYNC_MAX, which is at max 64. But you might find yourself limited at about 50-64 tags. 

With an AOA system (ie. multiple locators and antennas) however, you might track hundreds or thousands depending on how its implemented. You can add logic on the application layer to track more devices (dump devices out of the "track" list regularly and replace with new devices). This will allow you to track an indefinite number of devices with the cost of acquisition time. This is not part of our delivery as we do not do the algos. 

3. What effects do tags which advertise connectable, non CTE packets have on tags which advertise non-connectable CTE packets? in other words, how does a high noise BLE environment expected to affect location finding AOA applications?

As in any sort of wireless communication, creating noise --> collisions --> packet loss. A CTE is no exception, nor necessarily worse. But you will reach a saturation point where communication suddenly breaks down. Time on air is what counts, not what is in the packets. You can use excel simulation to see when this will start to be a real impact, calculate crashes of packets.
Remember that the CTE packets are all in the data channels so if the advertising is not using extended advertising then normal advertising will only impact syncing up with the periodic, if they are synced then advertising will not impact at all.

4. Is there anything in our scenario which leads you to believe an AOA location solution is not possible in our case?

No, this sounds possible, but it is no small undertaking. If you are looking for a product that provides what you just described I would recommend you to take a look at uBlox and what they provide. 

Regards