Abstract
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.
Highlights
I N in-band full-duplex (IBFD) communication systems, nodes are able to transmit and receive simultaneously in the same frequency band
The amount of self-interference cancellation (SIC) value for an efficient IBFD system depends on the Tx signal power and the noise floor at the receiver
We presented a novel analog SI cancellation technique, named inherent SIC
Summary
I N in-band full-duplex (IBFD) communication systems, nodes are able to transmit and receive simultaneously in the same frequency band. To the best of our knowledge, the first single-antenna IBFD configuration was introduced in [7] It used two lumped-element circulators and two 3 dB quadrature hybrids to reduce SI signals. The novelty of this article is that we use the circulator inherent secondary SI signals reflected by the antenna, to cancel the primary SI signals leaked from the Tx port to the Rx port This is in contrast to the feed-forward technique which has been widely used in previous studies. Our contributions are the following: 1) We introduced a novel and efficient analog SIC technique that uses the RF circulator inherent SI signals and the RF circulator rotation property This decreases the complexity, cost and power consumption of the SIC circuit by eliminating many RF components (sampler, combiner, attenuator and phase shifter).
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