Seiran Khaledian

ReflectFX: In-Band Full-Duplex Wireless Communication by Means of Reflected Power

In this paper, we introduce a new full-duplex wireless communication system, named ReflectFX, that relies on backscatter modulation. This paper offers a new concept for two-way wireless communication: rather than avoiding self-interference as in half-duplex, or combatting self-interference as in conventional full-duplex, nodes will re-use the received interfering radio-carrier waves to transfer information. The electromagnetic waves are modulated and reflected by the same antenna that receives them. We consider two nodes, a base-station and an end-user, that wish to exchange data over a wireless Rayleigh fading channel with additive white Gaussian noise. With ReflectFX, the end-user receives a self-interference free signal. We improve the transmission range of ReflectFX by adding negative resistance to the end-user load. We derive an expression for the overall achievable throughput and ergodic capacity of ReflectFX. Simulation results show that ReflectFX outperforms both conventional full-duplex and half-duplex.

Inherent Self-Interference Cancellation for In-Band Full-Duplex Single-Antenna Systems

We propose a new analog self-interference cancellation (SIC) technique for in-band full-duplex transmission in single-antenna systems. We use an RF circulator to separate transmitted (Tx) and received (Rx) signals. Instead of estimating the SI signals and subtracting them from the Rx signals, we use the inherent secondary SI signals at the circulator, reflected by the antenna, to cancel the primary SI signals leaked from the Tx port to the Rx port. We modified the frequency response of the secondary SI signals using a reconfigurable impedance mismatched terminal (IMT) circuit, which consists of two varactor diodes at the antenna port. We can also adjust the frequency band and the bandwidth by controlling the varactor diodes bias voltages. The IMT adjustability makes it robust to antenna input impedance variations and fabrication errors. We analyze and fabricate a prototype of the proposed technique at 2.45 GHz. We achieved more than 40-dB cancellation over 65 MHz of bandwidth. Our technique is independent of the RF circulator and antenna type and it can be applied to any frequency band. It is also very relevant to small mobile devices because it provides a simple and low-power and low-cost adjustable analog SIC technique.

Reconfigurable Linear/Circular Polarization Rectangular Waveguide Filtenna

We introduce a new reconfigurable linear polarization and circular polarization (CP) antenna, based on a rectangular waveguide (RWG) and a novel reconfigurable polarizer. The polarizer consists of two orthogonal apertures. The apertures transform the linear polarization of the dominant mode of the RWG antenna to CP. Each of these apertures is loaded by a p-i-n diode to alter its electrical length. This length difference provides the phase rotation needed to obtain CP. The signal polarization of the antenna can be selected by changing the applied bias voltage of p-i-n diodes as right-handed (RH)/left-handed (LH) CP. We can also achieve linear polarization if both diodes are ON or OFF. The reconfigurable polarizer acts as a bandpass filter, since the apertures can be considered as complementary electrically small resonators. This self-filtering capability is useful for reduction out of band noise in a communication system such as satellite links. The proposed antenna is designed to operate at 2.65 GHz, but the same approach can be applied to other frequency bands. The measurement results show a very good RH/LHCP and they are in good agreement with simulations.

Ultra-low power reflection amplifier using tunnel diode for RFID applications

To increase backscatter efficiency and communication range in RFID systems, we propose an ultra-low power reflection amplifier using a tunnel diode. We measured the input impedance of a tunnel diode and used a compact matching circuit to provide the desired input impedance at 890 MHz for the RFID UHF band. The proposed circuit is designed to be free from oscillations to avoid Signal to Noise Ratio (SNR) degradation. This reflection amplifier consumes 0.2 mW DC power at bias voltage of 200 mV, making it an ideal candidate to amplify backscattered electromagnetic field in RFID transceivers. The gain of the proposed reflection amplifier is 17 dB for the incident power of −30 dBm. The fabricated circuit size is 20×25 mm² (0.06λ<inf>0</inf> × 0.075λ<inf>0</inf>) on a substrate with ε<inf>r</inf> = 3 and h = 0.762 mm. The measurement and simulation are in a good agreement.

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°, −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 90μW, provides 17 dB and 16.8 dB reflection and transfer gains, respectively.