an apparatus used in a full duplex multiple - input multiple - output wireless communications system is disclosed . in an aspect , the apparatus includes a plurality of antennas , each of which is connected to a combination of at least a tx rf chain and an rx rf chain . the plurality of antennas are split into one or more transmit antennas and one or more receive antennas , and the apparatus communicates with another apparatus . other apparatuses and some methods for wireless communications also are disclosed .