In-band full-duplex (IBFD) technology can enable unique system capabilities and network architectures by allowing devices to transmit and receive on the same frequency at the same time. While previously considered impossible, this ability can now be used to optimize resource sharing within the crowded frequency spectrum for various communication systems, including 5G new radio. The potential of these IBFD systems can only be realized if each device incorporates a sufficient number of self-interference cancellation techniques to ensure that its receivers do not saturate. This tutorial survey offers the most comprehensive collection to date of these techniques and discusses how all of them can be implemented within the different domains of a typical transceiver. In addition, the results of a novel IBFD system study are presented for more than 50 demonstrated communication systems with more than 80 different measurement scenarios. The various system parameters are then combined into a new figure of merit, which can be used to propel future research and accelerate the inclusion of IBFD technology within an upcoming wireless standard.

In-Band Full-Duplex Technology: Techniques and Systems Survey

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.

Multitap RF Canceller for In-Band Full-Duplex Wireless Communications

Modern Antenna Design

A monostatic ultra-wideband simultaneous transmit and receive (STAR) antenna subsystem is introduced. An inherent geometrical symmetry of a four-arm spiral antenna and feeding rearrangement are exploited to achieve the simultaneous transmit (TX) and receive (RX) functionalities without any time, polarization, or frequency multiplexing. The antenna is configured such that one arm-pair is used for TX and the other for RX. Thus, even though the two antennas are spatially separated by 90°, they still share the same aperture and the system is considered monostatic. Theoretical and computational studies are conducted to demonstrate the feasibility of the proposed approach under ideal conditions as well as in the presence of feed network non-idealities. The experimental data indicate that isolation levels greater than 39.6–50 dB over multiple octaves are achievable with realistic components. To improve the TX and RX far-field patterns, the planar four-arm spiral aperture is grounded via resistor-loaded quadrifilar helix with the two-arm TX/two-arm RX feed arrangement preserved. Furthermore, to simplify the feed network and reduce the impact of hybrid imbalances, an impedance-transforming microstrip feed is integrated with each arm pair. Isolation $> {37}\;{\text {dB}}$ and similar with high-quality measured and simulated TX/RX radiation patterns are obtained over the operating bandwidth.

Wideband Monostatic Simultaneous Transmit and Receive (STAR) Antenna

Self-interference is the primary obstacle to full-duplex wireless communication on a single frequency band. This paper presents a novel convex reformulation for tuning the attenuation and phase shift parameters of a multiple-tap analog self-interference canceller. The standard optimization formulation for a multiple-tap analog canceller is non-convex, causing gradient descent algorithms to converge to local optima. By exploiting the architecture of an ideal analog canceller, an analytical solution for the global optimum is derived that minimizes mean-square error between the canceller and negative channel frequency responses. Multiple taps are necessary to emulate practical antenna coupling channels over a broad bandwidth. Simulated and measured results are presented that achieve significant wideband cancellation in multipath channel environments.

Optimal tuning of analog self-interference cancellers for full-duplex wireless communication

In order to avoid self-interference, Simultaneous Transmit And Receive (STAR) systems require low mutual coupling between their respective transmit and receive antennas. This paper discusses the development of an 8-element transmit ring array antenna on a circular ground plane with a raised receive element. When combined with a beamformer that supplies linear progressive phase shifts to the array with opposing elements phased 180-degrees apart, the receive and transmit antennas are measured to exhibit 55 dB of isolation and omni-directional patterns in the 2.4 to 2.5 GHz band.

Ring array antenna with optimized beamformer for Simultaneous Transmit And Receive

Described is a simultaneous transmit and receive antenna system having a ring array of transmit antenna elements and a receive antenna element disposed on an axis that is perpendicular to and passing through the center of the ring array. Alternatively, the ring array includes receive elements and a transmit antenna element is disposed on the axis perpendicular to the ring array. Opposite antenna elements in the ring array differ in phase by 180° so that a radiation pattern null occurs at the antenna element at the center of the ring array. Also included are at least one ground plane and an electrically-conductive cylinder disposed on the perpendicular axis inside the ring array to provide a high degree of isolation between the transmit and receive antenna elements. The system may be configured for wireless communications, for example, according to WIFI IEEE standard 802.11 or WIMAX IEEE standard 802.16.

Simultaneous transmit and receive antenna system

Practical ultrawideband phased array technology used in airborne and ground-based systems applications. Ultrawideband phased array antennas are an enabling technology for many ground-based and airborne communications and radar systems. This book surveys electromagnetic theory and phased array antenna theory and provides examples of ultrawideband phased array antenna technology. It describes some of the research on ultrawideband phased arrays undertaken by the authors and their colleagues at MIT Lincoln Laboratory over the last ten years. The book focuses on experimental prototype ultrawideband phased array technology developed at Lincoln Laboratory for applications in the VHF and UHF bands from approximately 100 MHz to 1 GHz, and addresses dipole, monopole, loop, and other antenna array elements. It offers examples of antennas for both airborne and ground vehicle applications. Most of the examples are developed in the context of rapid prototyping for quick assessment of communications and radar systems feasibility, with measurements and numerical electromagnetic simulation results provided for many prototype examples. The book is intended primarily for practicing antenna engineers, radar engineers, and communications engineers, and for graduate students and researchers in electrical engineering. Readers need no prior knowledge of ultrawideband antennas, although some background in electromagnetic theory, antennas, radar, and communications would be helpful.

Ultrawideband phased array antenna technology for sensing and communications systems

Many in-band full-duplex (IBFD) applications require omnidirectional radiation coverage in addition to multilayered self-interference cancellation (SIC). While system-level SIC approaches often require high-isolation antennas before implementing analog and/or digital methods, maintaining the desired omnidirectional transmit/receive patterns is difficult for compact designs that utilize the same polarization. This article discusses the concept development and design progression of the circular mode phasing technique applied to omnidirectional IBFD antenna arrays. The theoretical fundamentals are presented along with simulation results and then validated through the discussion of two prototype antennas, which were measured to provide up to 60 dB of isolation over 2.4–2.5 GHz, which is the highest reported for this SIC method. Additionally, the evolution of this concept for a collection of measured prototypes is summarized and characterized with a unique figure of merit, which should help advance the application of this technique within future IBFD systems.

Evolution of Circular Mode Phasing for In-Band Full-Duplex Omnidirectional Antennas

An ultrawideband (UWB) cavity-backed resistively loaded planar dipole array antenna has been developed for the 100 to 400 MHz frequency range for ground penetrating radar applications. The antenna has been designed with a 3m aperture to perform surveys of a wide swath of ground from a moving vehicle. The performance of the UWB array is quantified by moment method simulations of the electromagnetic field penetration into lossy soil. Integration of the UWB array onto a vehicle is discussed.

Peter T. Hurst

Papers

Ring array antenna with optimized beamformer for Simultaneous Transmit And Receive

Simultaneous transmit and receive antenna system

Ultrawideband phased array antenna technology for sensing and communications systems

Evolution of Circular Mode Phasing for In-Band Full-Duplex Omnidirectional Antennas

Ultrawideband cavity-backed resistively loaded planar dipole array for ground penetrating radar