A Power-Efficient Implementation of In-Band Full-Duplex Communication System (ReflectFX)

We propose a power-efficient implementation for ReflectFX, an in-band full-duplex wireless communication system. ReflectFX is based on backscatter modulation where the electromagnetic waves are modulated and reflected by the same antenna that receives them. With ReflectFX, the end-user receives self-interference free signals. At the end-user receiver, we use a bi-directional amplifier to amplify the reflected wave while providing sufficient power at the end-user demodulator. The bidirectional amplifier consists of two identical reflection amplifier using negative resistance and a 90 degrees, -3dB branch line coupler (BLC). A phase shifter circuit, which consists of four microstrip transmission lines, has been used to apply QPSK modulation to the reflected power. The designed ReflectFX end-user circuit, with power consumption of only 90 mu W, provides 17 dB and 16.8 dB reflection and transfer gains, respectively.