For a research purpose we need to see the number of devices connected to the wifi at each time step. So we are interested to know how many devices have been connected, and their usage pattern. Would you please tell me how we can access these data?
such datas are indeed stored but they are not available for the end user (and will never be). Assuming the info you can get in the webUI is not enough, I could propose the following:
setup a DHCP server on the LAN, with a very short lease time (like 1 minute)
disable the Internet-Box DHCP server, and use the newly created DHCP server
Like that, any client relying on DHCP would be forced to use this DHCP server, and you should be able to get logs from this server. The info you can get that way are the Mac address of the connected client (allowing identification of the client vendor - eg: Apple), and the duration of the connection. What will miss is the "usage pattern", but to get such info you likely need something else - maybe a firewall - but likely more complicated and expensive, designed more for SME than for residential customers.