Hello, I have been using openwrt since more than a year now, with two wan connections, a very nice working config thanks to mwan3, my router its a TPLINK TL-WR940N V4 (US) with wifi N and 3x3 MIMO, capable of providing 450 Mbps of wireless speed in the stock firmware. But with the following parameters i'm just getting 150 Mbps:
Should I? I saw on openwrt documentation that hwmode 11g + adding HT40 or HT20 is the correct way to set up the WiFi N band, there’s a better and precise way to test my local speed? When I use HT20 my speed goes down to 72 Mbps
First off, realize that the link modulation speed will vary with load and other conditions, even when a couple meters away.
Second, just because the link modulation supports, say 450 Mbps, doesn't mean that you're going to get 450 Mbps of throughput in any real-world situation. There's overhead of moving "real" packets, as well as channel congestion, including that of the AP operating things such a beacons. Getting 80% of that in a real-world situation would be, in my opinion, very good.
802.11n's speed may go up to 150 megabits per second if there are not other Bluetooth, microwave or Wi-Fi emissions in the neighborhood by using two 20 MHz channels in 40 MHz mode.
Third, your router's CPU may not be able to handle 450 Mbps at all. A 750 MHz, single-core MIPS processor may not be able to do anything with the packets at that rate, even if the wireless could supply them to the CPU.
Edit: Further, your router only supports 100 Mbps Ethernet.
As Jeff said not only does router have to support MIMO but also the other device needs it, which means it must have 3 separate antennas and various other hardware and drivers etc for MIMO. It never happens in the real world except maybe between two wifi routers in a cabin in the woods.