Hi @mehditlili
EDIT: I made a mistake in my first reply. Essentially you're correct. AW7915-NP1 is 4T4R dual band, but not simultaneous dual band. The MT7915N is 2T2R DBDC. I don't have the second card. I have the AW7915-NP! and AW7615-NP1 .
I have never gotten DBDC to work right in OpenWRT. I'd still love to know if anyone else has gotten it work either.
EDIT2: I hadn't tested DBDC in a while, so I just did and it seems to work, but it's still not easy to get it running and it's seems a bit glitchy. But I also just tested it in a wi-fi repeater configuration using relayd, which itself isn't 100% solid in some cases, so that could be why. The card I am using is the AsiaRF MT7615e (my 7915 is the 4T4R one which doesn't have DBDC). I'd still advise caution if you are planning on using DBDC.