These are techniques based on number of antennas used at the transmitter and the receiver. SISO has been in use since the invention of wireless system. MIMO concept has been recently added to the wireless system. There are different MIMO algorithms which has been developed for two main reasons to increase coverage and to increase the data rates.SISO means Single Input Single Output while MIMO means Multiple Input Multiple Output.In SISO system only one antenna is used at transmitter and one antenna is used at Receiver while in MIMO case multiple antennas are used. Figure depicts 2x2 MIMO case.MIMO system achieves better Bit Error rate compare to SISO counterpart at the same SNR. This is achieved using technique called STBC (Space Time Block Coding). With STBC coverage can be enhanced.MIMO system delivers higher data rate due to transmission of multiple data symbols simultaneously using multiple antennas, this technique is called as Spatial Multiplexing (SM). With SM data rate can be enhanced.MIMO with SM and beamforming can be employed to obtain enhancement to both the coverage and data rate requirement in a wireless system.SISO is used in radio, satellite, GSM and CDMA systems while MIMO is used in next generation wireless technologies such as mobile wimax -16e, WLAN-11n.11ac,11ad, 3GPP LTE etc.   _{Your Comment}