Browsing by Subject "Full duplex"

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Enhanced transceiver performance through self-interference cancellation in multiple modalities
(2018-08) Nguyen, Thien-An Ngoc; Wang, Zheng, Ph. D.; Yu, Edward T; Bank, Seth; Yeh, Tim; Vishwanath, Sriram
Interference in front end transceivers directly impact system performance by saturating receiver circuitry and generating non-linearities. While proper shielding can effectively eliminate external interference, self-interference continues to limit the performance of sensing and communication systems today. Self-interference exists when the transmitted signal interferes with the received signal through parasitic signal paths and from spurious reflections. This dissertation explores the use of novel transducers, front-end designs, and active cancellers to eliminate self-interference in multiple sensing and communication modalities: acoustic, optical, and electronics. First, we demonstrate integration of electroadhesion with a piezoelectric multimaterial fiber transducer to reduce acoustic signal reflection at the interface with the target substrate. The large acoustic impedance of air introduces a 10⁵ mismatch with the acoustic transducer and the substrate. By monolithically integrating electroadhesive and acoustic functions into a single fiber device, the fiber transducer can controllably adhere to the target and subsequently eliminate the interfacial air microvoids during operation. Second, the limited directivity of optical circulators give rise to parasitic signal paths in optical Mach-Zehdner based laser Doppler vibrometers. Parasitic signal paths are signal paths in an interferometer which are unexpected and unbalanced with respect to the signal and reference arms. The path length imbalance demodulates laser phase noise as amplitude noise at the receiver which degrades sensitivity due to the decrease in signal to noise ratio. We derive an expression for this this parasitic phase induced intensity noise (P-PIIN) and develop a new interferometer design which enables mutually balanced signal, reference, and dominant parasitic paths to achieve 90 dB of signal to noise ratio and femtometer vibration sensitivity. Third, self-interference in modern electronic communication systems limit the maximum achievable throughput in a given bandwidth. Self-interference from both parasitic signal paths and spurious reflections overwhelms the significantly weaker receive signal when both are operating simultaneously. As such, communication systems such as cable only operate either in time domain duplexing (alternate between transmitting and receiving) or frequency domain duplexing (transmit and receive on different frequencies) modes. By actively eliminating self-interference, communication systems are able to send and receive information at the same time on the same frequency: full duplex operation.