Publications

In-band full-duplex wireless communications are challenging because they require the mitigation of self-interference caused by the co-located transmitter to operate effectively. This paper presents a novel tapped delay line RF canceller architecture with multiple non-uniform pre-weighted taps to improve system isolation by cancelling both the direct antenna coupling as well as multipath effects that comprise a typical interference channel. A four-tap canceller prototype was measured over several different operating conditions, and was found to provide an average of 30 dB signal cancellation over a 30 MHz bandwidth centered at 2.45 GHz in isolated scenarios. When combined with an omni-directional high-isolation antenna, the canceller improved the overall analog isolation to 90 dB for these cases. In an indoor setting, the canceller suppressed a +30 dBm OFDM signal by 22 dB over a 20 MHz bandwidth centered at 2.45 GHz, and produced 78 dB of total analog isolation. This complete evaluation demonstrates not only the performance limitations of an optimized multitap RF canceller, but also establishes the amount of analog interference suppression that can be expected for the different environments considered.

Simultaneous transmit and receive (STAR) systems require high isolation between the transmitter and receiver to avoid self-interference. Antenna isolation degradation stems from errors in the physical construction and beamformer design, as well as reflections from scattering objects in the environment. An RF canceller subsystem can be inserted at the antenna feeds to improve the isolation in the presence of reflecting objects by 30 dB over 30 MHz centered at 2.45 GHz. This results in 90 dB of effective antenna isolation when paired with a high-isolation antenna that exhibits omni-directional radiation patterns, signifying that STAR systems can be practically deployed.

For effective operation, Simultaneous Transmit and Receive (STAR) systems require high isolation between the transmitted signals and the receiver input, the absence of which can lead to the saturation of a receiver's front end. This paper presents an adaptive RF canceller used to improve isolation. The canceller is configured as an RD tapped delay line with four taps, each with independent amplitude and phase weights that are tuned by a Dithered Linear Search algorithm. This canceller produces 30 dB of signal cancellation over a 20 MHz bandwidth centered at 2.45 GHz in an isolated environment. When combined with a high-isolation antenna, an overall STAR system isolation of 90 dB is achieved, while also maintaining omnidirectional transmit and receive antenna patterns.