An in band full duplex practical implementation applying passive self-interference cancellation

Abstract

This paper presents the physical layer implementation of a wireless communications system composited of 3 nodes, one of them operates in Full Duplex (FD) mode and the others work in Half Duplex (HD) mode. The simultaneous operation of these 3 nodes is intended to simulate a hidden node structure, where one of the HD nodes is sending information to the FD node, which is expecting the signal of interest at the receiver antenna and sends a different signal thru the transmitter antenna to the other HD node, simultaneously, making use of the same frequency channel. Passive self-interference (SI) cancellation in the propagation domain is applied, performing an orthogonal alignment between the radiation fields of these antennas. By doing this, a good level of cancellation is achieved, which allows the simultaneous transmission and reception at the FD node. In order to guarantee the discrimination between the two communication links OFDM symbols with different sizes are used, both over the same bandwidth. GNU Radio Companion platform (software) and USRP boards (hardware) were used for the implementation.