This paper presents the design and implementation of the first in-band full duplex WiFi radios that can simultaneously transmit and receive on the same channel using standard WiFi 802.11ac PHYs and achieves close to the theoretical doubling of throughput in all practical deployment scenarios. Our design uses a single antenna for simultaneous TX/RX (i.e., the same resources as a standard half duplex system). We also propose novel analog and digital cancellation techniques that cancel the self interference to the receiver noise floor, and therefore ensure that there is no degradation to the received signal. We prototype our design by building our own analog circuit boards and integrating them with a fully WiFi-PHY compatible software radio implementation. We show experimentally that our design works robustly in noisy indoor environments, and provides close to the expected theoretical doubling of throughput in practice.

https://dl.acm.org/doi/pdf/10.1145/2486001.2486033

Full duplex radios

In-band full-duplex (IBFD) operation has emerged as an attractive solution for increasing the throughput of wireless communication systems and networks. With IBFD, a wireless terminal is allowed to transmit and receive simultaneously in the same frequency band. This tutorial paper reviews the main concepts of IBFD wireless. One of the biggest practical impediments to IBFD operation is the presence of self-interference, i.e., the interference that the modem's transmitter causes to its own receiver. This tutorial surveys a wide range of IBFD self-interference mitigation techniques. Also discussed are numerous other research challenges and opportunities in the design and analysis of IBFD wireless systems.

/pdf/in-band-full-duplex-wireless-challenges-and-opportunities-djlyhtrciu.pdf

In-Band Full-Duplex Wireless: Challenges and Opportunities

In-band full-duplex (IBFD) operation has emerged as an attractive solution for increasing the throughput of wireless communication systems and networks. With IBFD, a wireless terminal is allowed to transmit and receive simultaneously in the same frequency band. This tutorial paper reviews the main concepts of IBFD wireless. Because one the biggest practical impediments to IBFD operation is the presence of self-interference, i.e., the interference caused by an IBFD node's own transmissions to its desired receptions, this tutorial surveys a wide range of IBFD self-interference mitigation techniques. Also discussed are numerous other research challenges and opportunities in the design and analysis of IBFD wireless systems.

This paper presents a full duplex radio design using signal inversion and adaptive cancellation. Signal inversion uses a simple design based on a balanced/unbalanced (Balun) transformer. This new design, unlike prior work, supports wideband and high power systems. In theory, this new design has no limitation on bandwidth or power. In practice, we find that the signal inversion technique alone can cancel at least 45dB across a 40MHz bandwidth. Further, combining signal inversion cancellation with cancellation in the digital domain can reduce self-interference by up to 73dB for a 10MHz OFDM signal. This paper also presents a full duplex medium access control (MAC) design and evaluates it using a testbed of 5 prototype full duplex nodes. Full duplex reduces packet losses due to hidden terminals by up to 88%. Full duplex also mitigates unfair channel allocation in AP-based networks, increasing fairness from 0.85 to 0.98 while improving downlink throughput by 110% and uplink throughput by 15%. These experimental results show that a re- design of the wireless network stack to exploit full duplex capability can result in significant improvements in network performance.

/pdf/practical-real-time-full-duplex-wireless-48e487yqxp.pdf

Practical, real-time, full duplex wireless

We present an experiment-based characterization of passive suppression and active self-interference cancellation mechanisms in full-duplex wireless communication systems. In particular, we consider passive suppression due to antenna separation at the same node, and active cancellation in analog and/or digital domain. First, we show that the average amount of cancellation increases for active cancellation techniques as the received self-interference power increases. Our characterization of the average cancellation as a function of the self-interference power allows us to show that for a constant signal-to-interference ratio at the receiver antenna (before any active cancellation is applied), the rate of a full-duplex link increases as the self-interference power increases. Second, we show that applying digital cancellation after analog cancellation can sometimes increase the self-interference, and thus digital cancellation is more effective when applied selectively based on measured suppression values. Third, we complete our study of the impact of self-interference cancellation mechanisms by characterizing the probability distribution of the self-interference channel before and after cancellation.

/pdf/experiment-driven-characterization-of-full-duplex-wireless-3u33o8w3q1.pdf

Experiment-Driven Characterization of Full-Duplex Wireless Systems

A method for self-interference canceller tuning for a near band radio includes receiving, in a first frequency band, an RF transmit signal of the near band radio; receiving, in a second frequency band, an RF receive signal of the near band radio; generating a self-interference cancellation signal from the RF transmit signal based on a set of configuration parameters; combining the self-interference cancellation signal with the RF receive signal to create a composite receive signal; and adapting the set of configuration parameters based on the compo-site receive signal.

Systems and methods for near band interference cancellation

A method for adaptively-tuned digital self-interference cancellation includes generating a digital self-interference cancellation signal from a digital transmit signal based on a transform configuration; combining the digital self-interference cancellation signal with a receive signal to form a digital residue signal; generating a composite residue signal from the digital residue signal and the digital transmit signal; and updating the transform configuration based on the composite residue signal.

Systems and methods for adaptively-tuned digital self-interference cancellation

A method for pilot signal based self-interference cancellation tuning includes detecting a tuning trigger and in response to the tuning trigger, generating a pilot transmit signal according to the trigger data; and transmitting, at the transmitter, the pilot transmit signal; receiving, at the receiver, a pilot receive signal; cancelling, at the self-interference canceller, a portion of self-interference in the receive pilot signal, resulting in a composite pilot signal; analyzing the composite pilot signal; and tuning a configuration parameter of the self-interference canceller, based on analysis of the composite pilot signal, resulting in reduced self-interference in the composite pilot signal.

Method for pilot signal based self-inteference cancellation tuning

A system for phase shifting that produces an output signal by modifying a phase of an input signal, including a primary phase shifting stage that modifies the input signal phase in increments set by a first tuning resolution; a secondary phase shifting stage that modifies the input signal phase in increments set by a second tuning resolution; and, a tuning circuit that controls the primary phase shifting stage and the secondary phase shifting stage according to control input.

Systems for analog phase shifting

A system for multi-peak filter-based analog self-interference cancellation includes a transmit coupler that samples the analog transmit signal to create a sampled analog transmit signal; an analog self-interference canceller, using multi-peak filters, that generates an analog self-interference cancellation signal; and a receive coupler that combines the analog self-interference cancellation signal with the analog receive signal.

Jung-Il Choi

Papers

Systems and methods for near band interference cancellation

Systems and methods for adaptively-tuned digital self-interference cancellation

Method for pilot signal based self-inteference cancellation tuning

Systems for analog phase shifting

Systems for multi-peak-filter-based analog self-interference cancellation