Maximum scan results and maximum simultaneous connections possible?

[DennisEB]

Hi Nordic DevZone User,

i want to ask if there is a limit of devices which can be found within one scan process?

And how many connections can one master have at the same time?

Background: I want to scan devices in range, but wondering if i can get all 200 devices in range (if there were 200!)

I tried to search in Bluetooth Core Specification, but did not find the answer to my question.

Thanks in advance!

[David Edwin]

I am re-phrasing the question from "How many devices can the observer see ?, to How many devices can be observer not see ?, i.e. the advertisement packet gets trashed on air.

You will need to model this a bit so the below is an approximation.

This depends on the number of transmitters(broadcaster) the receiver(observer) can see at the same time.

This will also depend on how much impact a transmitter that is further away would impact a transmitter that is closer to the receiver.

Taking a simple case of 100 transmitters that are equidistant to a receiver.

This would depend on the broadcast packet (lets assume it to be 400 bits i.e. 400uS on air)

Also depends on the advertising interval, lets assume 100ms

This would mean that the usage of the channel by 1 transmitter an an instant = .4/100 * 100%= 0.4 %

When we consider 100 transmitters this becomes 0.4% x 100 = 40%

A 40% usage is a high number and very dense, but remember this means 100 devices for the master to see that are at the same distance, so they need to be right around the phone, so if you have a 100 transmitters at different distances the co-channel interference would also need to be considered.

I.e At what distance would a transmitter further away interfere with a transmitter closer to the receiver

This means 2 devices can use the same frequency and if they are sufficiently far enough.

It appears that 100-300 devices if they are on a building or a room will be possible to use as the building/room is unlikely go have 100 transmitters equidistant from a receiver.

= How many connections can one master have at the same time? It depends on the master i.e an Andriod phone can support from 2 to 6 depending on the master, iOS can support upto 10 depending on the connection interval used. The S120 on the nRF51 can support 8 links.