How many ble device can an android phone be found in one scan?

Question

I don't have enough devices to test and can't find this answer anywhere, how many devices can a single BLE scan be found at a time?
Say I have 20 devices in range, will the scan be able to handle the advertising packet of all of them or only seven?

Answer 1

It will handle all incoming advertisement packets while the scan is turned on. There is no limitation. Of course packets can be missed due to radio conditions.

Answer 2

One Scan is a loose terminology. Scan has a Scan Window parameter which tells the duration of the scan, ie the time the radio is in RX on a given advertisement channel. From host point of view, a scan period is a group of scan windows.

Scan waits for Advertisement Packets from Peripherals, which are retransmitted periodically, every Advertisement Interval (+ another parameter to randomize the interval a little).

Last, but not least, as there is no Carrier Sensing in BLE, Advertisement Packets from multiple peripherals may collision. They will be lost for receiver, and you'll need to wait for next packet from each of them.

So, here are some parameters needed to answer your question:

• How long does your android phone listen for during one scan ?
• How often does your peripherals send their advertisement packets ?
• Is your radio environment busy / do you consider collision as probable ?

You can have a look at Vol3, Part C, Appendix A of BLE spec to see recommended timings of scan and advertising. Most are not mandatory, though.