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.

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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 Soli, a new, robust, high-resolution, low-power, miniature gesture sensing technology for human-computer interaction based on millimeter-wave radar. We describe a new approach to developing a radar-based sensor optimized for human-computer interaction, building the sensor architecture from the ground up with the inclusion of radar design principles, high temporal resolution gesture tracking, a hardware abstraction layer (HAL), a solid-state radar chip and system architecture, interaction models and gesture vocabularies, and gesture recognition. We demonstrate that Soli can be used for robust gesture recognition and can track gestures with sub-millimeter accuracy, running at over 10,000 frames per second on embedded hardware.

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Soli: ubiquitous gesture sensing with millimeter wave radar

This paper reviews recent advances in biomedical and healthcare applications of Doppler radar that remotely detects heartbeat and respiration of a human subject. In the last decade, new front-end architectures, baseband signal processing methods, and system-level integrations have been proposed by many researchers in this field to improve the detection accuracy and robustness. The advantages of noncontact detection have drawn interests in various applications, such as energy smart home, baby monitor, cardiopulmonary activity assessment, and tumor tracking. While many of the reported systems were bench-top prototypes for concept verification, several portable systems and integrated radar chips have been demonstrated. This paper reviews different architectures, baseband signal processing, and system implementations. Validations of this technology in a clinical environment will also be discussed.

A Review on Recent Advances in Doppler Radar Sensors for Noncontact Healthcare Monitoring

We present, to the best of our knowledge, the first demonstration of coherent solid-state light detection and ranging (LIDAR) using optical phased arrays in a silicon photonics platform. An integrated transmitting and receiving frequency-modulated continuous-wave circuit was initially developed and tested to confirm on-chip ranging. Simultaneous distance and velocity measurements were performed using triangular frequency modulation. Transmitting and receiving optical phased arrays were added to the system for on-chip beam collimation, and solid-state beam steering and ranging measurements using this system are shown. A cascaded optical phase shifter architecture with multiple groups was used to simplify system control and allow for a compact packaged device. This system was fabricated within a 300 mm wafer CMOS-compatible platform and paves the way for disruptive low-cost and compact LIDAR on-chip technology.

Coherent solid-state LIDAR with silicon photonic optical phased arrays

Frequency modulated continuous wave (FMCW) radar uses a very low probability of intercept waveform, which is also well suited to make good use of simple solid-state transmitters. FMCW is finding applications in such diverse fields as naval tactical navigation radars, smart ammunition sensors and automotive radars. The paper discusses some features of FMCW radar which are not dealt with in much detail in the generally available literature. In particular, it discusses the effects of noise reflected back from the transmitter to the receiver and the application of moving target indication to FMCW radars. Some of the strengths and weaknesses of FMCW radar are considered. The paper describes how the strengths are utilised in some systems and how the weaknesses can be mitigated. It also discusses a modern implementation of a reflected power canceller, which can be used to suppress the leakage between the transmitter and the receiver, a well known problem with continous wave radars.

Linear FMCW radar techniques

A CW radar comprises a substantially continously operable transmitter (10) and receiver (16,18,20), signal operating means (12,14) for radiating the transmitter signal and for receiving at least the return signal and a reflected power canceller (RPC) circuit (26, 28 and 30) for cancelling leakage signals in a signal path from the signal operating means to the receiver. The receiver front end comprises quadrature related mixers (18,20) which supply intermediate frequency signals (I₁ and Q₁) to a low frequency control loop (32, 34, 36) which supplies at least a pair of control signals (Ic,Qc) to a four quadrant vector modulator (28) in the RPC circuit. In order to be able to optimise the cancellation of phase as well as amplitude, the control circuit loop includes means for synthesising control vectors (I₁, -I₁, Q₁ and -Q₁) from the outputs of the quadrature related mixers (18,20). Selecting means selects a pair of quadrature related control vectors from those control vectors synthesised on the basis of minimising leakage in the outputs of the quadrature related mixers (18,20). The selected control vectors (Ic,Qc) are applied to the four quadrant vector modulator (28) which preferably comprises a pair of analogue driven biphase modulators (56,58 - Figure 4 (not shown)). In an alternative embodiment (Figure 7) the four quadrant vector modulator comprises four voltage controlled attenuators to which respective control vectors (Ic, -Ic, Qc and -Qc).

Continuously transmitting and receiving radar

To reduce probability of intercept, in most cases, the form and magnitude of the radar transmissions are designed to spread energy over as wide a range of dimensions as possible. Equally, in response to this, designs for electronic surveillance measures (ESM) systems have been postulated that increase receiver sensitivity. Their purpose is to increase detection range beyond that of the radar (or to an adequate range if they are to be forward deployed). The authors examine the evolving nature of the relationship between advanced 'low probability of intercept' (LPI) radar designs and future trends in ESM receiving capability. This relationship is far from straightforward, being both probabilistic and dependent on environmental and operational factors. Indeed this is complicated still further by the issue of affordability. The authors compute the performance of ESM and radar systems for a number of cases, including not just simple interception, but also the extraction of information from intercepted signals. In this way the key factors influencing the detectability of LPI radar systems are determined. It is demonstrated that it is never possible to be completely certain that a radar system has not been detected and that the most appropriate way to implement an LPI radar design is always closely related to the tactical environment in which the radar system will be used. Indeed this often overrides the technical aspects of system performance.

Low probability of intercept radar strategies

A projection display system comprising an array of LEDs 10 in at least first and second rows 10a,10b, the LEDs in each row being spaced from each other. The LEDs in the second row 10b are offset in a direction parallel to the length of the row relative to the LEDs in the first row 10a. A micro-electro-mechanical system (MEMs) scanning mirror 11 is mounted for movement about an axis with a movement means for moving the MEMs mirror about the axis. The array of LEDs are positioned so that light emitted therefrom is directed towards the MEMs mirror and reflected therefrom to form a display 12 comprising one or more lines, each line comprising a plurality of pixels. The movement means is arranged so that light from said first row of LEDs and light from the second row of LEDs is used to form each line of the display so the spacing between pixels along each line of the display is reduced compared to the spacing of the LEDS in the rows of the array. The display system can be used in a head up display or helmet mounted display or in a digital printing system.

Projection display system

An FMCW radar transmits a signal the frequency of which repeatedly sweeps upwards and downwards at a rate α. Any target returns are applied to a mixer (6) which is also supplied with a sample of the transmitted signal. During each sweep the mixer output signal is therefore a beat frequency signal the frequency components of which correspond to respective targets. The spectrum of the beat frequency signal is analysed by an FFT-calculating arrangement (16) and the result is applied to a data processor (18) which calculates the ranges of the targets. The constant of proportionality between beat frequency and range is inversely proportional to α, which is subject to uncertainty. In order to resolve this uncertainty, or correct α to the required value, the velocity of a given radially moving target is calculated in two different ways: from the perceived Doppler shift and from the rate of charge of the beat frequency component due to that target, only one of these being a function of α.

Andrew Gerald Stove

Papers

Linear FMCW radar techniques

Continuously transmitting and receiving radar

Low probability of intercept radar strategies

Projection display system

FMCW radar range calibration