How many antennas are needed?
A Spatial Multiplexing uses multiple antenna and multiple radios (MIMO). A minimum of two antennas are needed for basic 802.11n transmitting and receiving (referred to as a 2×2 antenna system). Typical first generation 802.11n radios will have two transmit antennas and three receive antennas (2×3). Additional antenna combinations are possible (4×4) for example would be able to transmit up to four separate spatial streams in order to obtain the highest defined data rates of the 802.11n specification. Typically, at least one more receive antenna is needed than the number of transmit antenna in order to reliably receive the multiple spatial streams being sent.
