Cisco Aironet 1600 Deployment Manual page 40

802.11n Primer - Understanding Spatial Streams
Figure 50
2x3:2 means two transmitters, three receivers supporting two spatial streams.
Note
Figure 51
Unlike the AP 3500, the newer AP 3600 supports 3SS with twice as many transmitters (4 per band)
enabling faster data rates of up to 450 Mbps. Note that there is an extra radio for redundancy and
enhanced performance (upstream and downstream) and the AP 3600 can also beamform to 3SS clients
as well. The AP 2600 is similar but the extra or redundant radio is for upstream as it is a receive only
so it is unable to beamform to 3-ss clients but can beamform at the other non-3ss rates.
Using a dual-band design the AP 3600 has a total of 8 transceivers (transmitter/receivers) using only 4
antennas
Cisco Aironet Series 1600/2600/3600 Access Point Deployment Guide, Release 7.5
40
AP 3500i/e is a 2x3:2 system (supports up to 2 transmit chains)
Modulation and Coding Scheme: 2SS Bonded Channel Supports up to 300 Mbps
(Figure 52). Four radios are used in each band, 2.4 GHz and 5 GHz.