Why is it then, that when it comes to the industry’s latest 4x4:4 APs such as the Ruckus R710, Ubiquiti’s AC HD and Meraki’s MR52, that 150Mbps x 4 = 800Mbps and not 600Mbps!?! Well these Access Points are able to advertise such data rates, due to the use of higher channel bonding and denser modulation techniques. Whilst channel bonding is ill-advised in the 2.4GHz band in a real deployment scenario, 802.11n technologies using MIMO-OFDM can make use of 40MHz wide channels, as opposed to the commonly used 20MHz wide channels. 40MHz wide channels are essentially impossible to use in practice, due to their occupation of an already narrow/saturated spectrum.
The other side to this otherwise unexplained improvement, is the use of 256QAM (Quadrature Amplitude Modulation) or TurboQAM as Broadcom call it. Typically, most clients will only support 64QAM, which provides you with the 300Mbps, 450Mbps, 600Mbps data rates for 2, 3 & 4 streams respectively. However, for those (few and far between) clients which support 40MHz wide channels, 4 spatial streams and 256QAM, the theoretical data rates improved by almost 30% to 800Mbps!