We are trying to set in place a system of indoor localization based on BLE Beacons. The precize location of the client does not really matter, the valuable information is the room he is in.
The building to be equipped has large concrete walls. We thought that using one beacon per room, we could detect the closer beacon to the guest.
Are concrete wall able to stop most of the BLE signal? We tried some tests, but we are searching for serious studies.
Any wall will reduce BLE signals by some amount. A signal of -50 dBm on one side might be -60 dBm on the other side, a reduction of 10 dB. Because decibels are logarithmic, every 10 dB reduction in the signal level represents a loss of 90 percent of the power in the signal. So while it is typically true that a concrete wall will "stop most of the BLE signal", it doesn't really matter because there may still be enough signal on the other side of the wall to detect the beacon.
How much of a reduction in signal level there is depends on thickness of the wall and other materials in it (metal will increase the attenuation.) Of course, windows, doors and other breaks in walls provide other paths for the signals to travel and complicate the issue.
Since you are unlikely to create a system where signals from beacons in one room will never be detected in an adjacent room, your best bet is to use other algorithms. For example, you may detect all visible beacons in a time interval, determine which has the highest signal strength, and if above a certain threshold, use this as an indicator of which room you are in.