What is 1x1 SISO?
1x1 SISO, or just SISO, represents the simplest form of radio communication. SISO devices use a single antenna to establish a single stream of data with a single antenna connected to the receiving device.
Due to the ease of constructing omnidirectional broadcast antennas and tolerance to rain SISO communication is usually vertically polarised. One notable exception is television broadcast which often favours horizontal polarised transmission. Point-to-point microwave and mmWave communication is still often SISO due to the increased challenges in manufacturing multi-polarised antennas - particularly those in the E-Band (60 to 80 GHz) and above.
SISO was popular in early radio communications such as in 2G, and 3G networks. Some SCADA and UHF packet-radio still use SISO due to the low data rate requirements. SISO is also still very popular in the manufacturing of low cost IoT frontends, such as those in NB-IoT, LoRa, and so on.