Duplexer design for full-duplex based wireless communications

The full-duplex (FD) based wireless communication devices, which are capable of concurrently transmitting and receiving signals with a single frequency band, suffer from a severe self-interference (SI) due to the large power difference between the devices' own transmission and the useful signal comes from the remote transmitters. To enable the practical FD devices to be implementable, the SI power must be sufficiently suppressed to the level of background noise power, making the received signal-to-interference-plus-noise ratio (SINR) satisfy the decoding requirement. In this paper, the design and implementation of the duplexer for facilitating SI cancellation in FD based wireless communications are investigated, with a new type of duplexer (i.e. an improved directional coupler) designed for improving the spatial suppression of the SI power. Furthermore, the practical circuit boards are designed and verified for the proposed prototype, showing that the spatial suppression capability may be up to 36dB (i.e. much higher than that attainable in the commonly designed ferrite circulator) by using the proposed design.