Survey of RF Communications and Sensing Convergence Research <s> Shown in <s> A scenario involving a source, a channel, and a destination, where the destination is interested in both reliably reconstructing the message transmitted by the source and estimating with a fidelity criterion the state of the channel, is considered. The source knows the channel statistics but is oblivious to the actual channel state realization. Herein, it is established that a distortion constraint for channel state estimation can be reduced to an additional cost constraint on the source input distribution, in the limit of large coding block length. A newly defined capacity-distortion function thus characterizes the fundamental tradeoff between transmission rate and state estimation distortion. It is also shown that noncoherent communication coupled with channel state estimation conditioned on treating the decoded message as training symbols achieves the capacity-distortion function. Among the various examples considered, the capacity-distortion function for a memoryless Rayleigh fading channel is characterized to within 1.443 bits at high signal-to-noise ratio. The constrained channel coding approach is also extended to multiple access channels, leading to a coupled cost constraint on the input distributions for the transmitting sources. <s> BIB001 </s> Survey of RF Communications and Sensing Convergence Research <s> Shown in <s> We investigate cooperative radar and communications signaling. While each system typically considers the other system a source of interference, by considering the radar and communications operations to be a single joint system, the performance of both systems can, under certain conditions, be improved by the existence of the other. As an initial demonstration, we focus on the radar as relay scenario and present an approach denoted multiuser detection radar (MUDR). A novel joint estimation and information theoretic bound formulation is constructed for a receiver that observes communications and radar return in the same frequency allocation. The joint performance bound is presented in terms of the communication rate and the estimation rate of the system. <s> BIB002 </s> Survey of RF Communications and Sensing Convergence Research <s> Shown in <s> 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. <s> BIB003 </s> Survey of RF Communications and Sensing Convergence Research <s> Shown in <s> We investigate a joint radar and communications performance bound for a single pair of bistatic transmit and receive antennas that uses orthogonal frequency-division multiplexing (OFDM) transmission. The OFDM transmission signal is designed to simultaneously meet radar target detection and communications signal recovery objectives using training and information symbols on different subcarriers. Given a frequency-selective Rayleigh-distributed fading channel, equally powered and equally spaced training symbols across the occupied bandwidth minimize the mean-square error of the channel estimate, which is tied to a lower bound on ergodic channel capacity. We perform a hypothesis test on the resulting channel estimate to detect and locate targets. We examine the performance region of capacity versus probability of detection in an example scenario in which a single stationary target is present. <s> BIB004 </s> Survey of RF Communications and Sensing Convergence Research <s> Shown in <s> A new theoretical foundation for the joint design and operation (JDO) of shared spectrum access for radar and communications (SSPARC) is presented. The JDO SSPARC framework entails advanced radar-comms channel estimation, along with a real-time adaptive space-time transmit and receive optimization procedure to maximize forward channel signal-to-noise while simultaneously minimizing co-channel interference. Additionally, a new expression for radar capacity is introduced that when combined with traditional communication capacity provides a unified measure of the total capacity of the combined radar-comms network. High fidelity site-specific electromagnetic radiation propagation simulations are conducted to provide a sense of the real-world potential gains achievable with JDO SSPARC as compared with non-optimized approaches. <s> BIB005 </s> Survey of RF Communications and Sensing Convergence Research <s> Shown in <s> The constant information radar, or CIR, is a tracking radar that modulates target revisit time by maintaining a fixed mutual information measure. For highly dynamic targets that deviate significantly from the path predicted by the tracking motion model, the CIR adjusts by illuminating the target more frequently than it would for well-modeled targets. If SNR is low, the radar delays revisit to the target until the state entropy overcomes noise uncertainty. As a result, we show that the information measure is highly dependent on target entropy and target measurement covariance. A constant information measure maintains a fixed spectral efficiency to support the RF convergence of radar and communications. The result is a radar implementing a novel target scheduling algorithm based on information instead of heuristic or ad hoc methods. The CIR mathematically ensures that spectral use is justified. <s> BIB006 </s> Survey of RF Communications and Sensing Convergence Research <s> Shown in <s> This paper develops the fundamental performance bounds for a radar operating in the presence of communication interference. To do so, we recast radar as a communication problem with the radar waveform acting as a convolutional encoder, which allows for the description of the achievable information-theoretic limits of the radar problem. While information theory has been applied to communications and radar, there has been little work on applying information theory to systems that explicitly combine sensing and communications. The new viewpoint presented in this paper, which does not require new mathematics, allows one to recast the problem of a radar operating in the presence of communication interference as a Gaussian multiple access channel problem. The derived bounds describe the fundamental limits on the amount of information the radar can obtain about the scattering environment in the presence of communications interference. <s> BIB007
In this work, we discuss the general problem of spectral congestion and the future solutions to this problem. For the two-user case, RF convergence is broken down into four topologies: the joint multiple-access channel, the monostatic broadcast channel, the bi-static broadcast channel, and the IBFD channel. These topologies have been explored in recent literature by various researchers as interest in RF convergence has resurged. The joint multiple-access channel problem is addressed in BIB002 and BIB006 - BIB007 , while the bi-static broadcast channel topology is addressed in BIB001 and BIB004 . The monostatic broadcast channel is discussed in Reference BIB005 . Finally, the broad and complicated topic of IBFD is covered in detail in Reference BIB003 . While we frame the problem for applications concerning radar and communications, the discussion in this work applies to all mediums where sensing and communications are possible. The focus on RF is because the problem arises in the concern for optimizing a precious resource: RF spectrum. In approaching the problem, we first look at the various applications that can benefit from co-designing systems that require remote sensing and communications in Section II. The special case of two-user topologies for joint radarcommunications systems are developed in Section III. In Section IV, the different levels of system integration the two users can adopt are presented, ranging from mere coexistence (mitigating mutual interference) to completely co-designed systems. We present the state of the art for joint systems in Section V, and look toward bounds on future systems and solutions in Section VI. This work is meant to be a point of departure and collation of research to date for joint systems, and so we make some summarizing remarks in Section VII.