Towards massive MIMO in-band full duplex radio

In-band Full Duplex (IBFD) is a promising wireless transmission technology allowing to increase data rates by up to a factor of two, via simultaneous transmission and reception, but with a potential to increase system throughput even much more in cognitive radio and random access systems thanks to simultaneous transmission and sensing. The main ingredient allowing FD is Self Interference Cancellation (SIC). To reach the required high level of SIC, normally several SIC techniques need to be combined, such as antenna isolation or circulator attenuation, analog and digital SIC. Some of these techniques, esp. analog SIC, do not scale well with the number of antennas as required for Massive MIMO. In this paper we consider two promising directions, namely Hybrid SIC (HSIC), and MIMO SI Nulling (SIN), which is based on separate transmit and receive antenna arrays. HSIC can be realized with a number of SIC branches that scale linearly with the number of antennas. On the other hand, the MIMO SI channel can be designed to be of reduced rank, leading to reduced zero-forcing requirements for MIMO SIN. Both HSIC and MIMO SIN can be combined with digital SIC which does not introduce additional hardware. In this paper we present simulation and measurement results to capture some of the characteristics of both approaches.