Survey of RF Communications and Sensing Convergence Research <s> K. MODERN CO-DESIGNED APPROACHES <s> The goal of the Advanced Multifunction Radio Frequency Concept (AMRFC) Program is to demonstrate the integration of many sorts of shipboard RF functions including radar, communications, and electronic warfare (EW) utilizing a common set of broad-band array antennas, signal and data processing, signal generation, and display hardware. The AMRFC Program was launched in response to the growing number of topside antennas on U.S. Navy ships, which have almost doubled from the ships launched in the 1980s to those launched in the 1990s. The AMRFC Program seeks to develop and demonstrate a wide-band generic active array antenna architecture that has the ability to transmit and receive multiple simultaneous independent beams for radar, EW, and communication functions. This paper describes a proof-of-principle test-bed that is being developed to demonstrate the AMRFC. <s> BIB001 </s> Survey of RF Communications and Sensing Convergence Research <s> K. MODERN CO-DESIGNED APPROACHES <s> The feasibility of coexistence between radar and a communication system is investigated under log-normal shadowing conditions. A key element that enables coexistence is a sensing receiver to detect the presence of a radar system and prevent transmissions when interference may occur. Initial studies where each communication terminal does its own sensing and decision-making shows that while bandsharing is possible, under stringent interference requirements, communication efficiency can be limited. Analytical and simulation results illustrate that cooperative sensing leads to an improved detection range, higher detection probability and lower complexity of sensing nodes than that of single terminal sensing. It is concluded that cooperative spectrum sensing is able to enhance detection capabilities to maximise radar spectrum-sharing usage efficiency. <s> BIB002 </s> Survey of RF Communications and Sensing Convergence Research <s> K. MODERN CO-DESIGNED APPROACHES <s> This paper presents a one-stage selective interference cancellation algorithm to demonstrate the concept of interference cancellation for the OFDM joint radar and communication (RadCom) system. Interference cancellation is needed due to the fact that the signal-to-interference ratio experienced by the radar is very low when there are multiple users, resulting in a severe degradation of the radar image and dynamic range. Since the radar signal is also a communication signal, the idea is to demodulate the received radar-communication signal and then subtract it from the received signal. The criteria in recontructing the communication signal for subtraction is much more stringent for the radar application than for conventional communication systems as will be discussed in the paper. The RadCom concept is briefly explained and the interference cancellation procedure as well as the impact on the radar's performance are described in detail in the following sections. <s> BIB003 </s> Survey of RF Communications and Sensing Convergence Research <s> K. MODERN CO-DESIGNED APPROACHES <s> In this paper, we propose a dynamic spectrum allocation approach for the coexistence of a radar system with a communications system whose operating frequency ranges overlap. We develop a combined mutual information criterion for the joint waveform and power spectrum design to optimize the performance of the radar and communications systems. The performance is evaluated in terms of the minimum separation distance between the coexisting systems under the constraint that a predefined operational SINR must be achieved for both systems. Significant performance gains close to 3.5 dB for the communication system and 1 dB for the radar system are observed in terms of the minimum separation distance compared to the scenario when the waveform with equal power allocation across the frequency bandwidth is used. <s> BIB004 </s> Survey of RF Communications and Sensing Convergence Research <s> K. MODERN CO-DESIGNED APPROACHES <s> The increasing demand for wireless ubiquitous services necessitates new spectrum allotments or a re-design of current systems to effectively manage coexistence between different types of technologies. In particular, the S-band (2-4 GHz) is in high demand for both surveillance and weather radar, communication satellites and commercial wireless networks. In the US there is strong political pressure for portions of radar spectrum to be shared with commercial wireless services. In order to effectively design coexistence strategiesit is crucial to understand how current radar and communications systems would affect each other if they were to coexist. As a starting point, this paper investigates a simple setup where one radar coexists with one communications system and considers the effect each has on the other as their relative distance is varied. Despite its simplicity, this model qualitatively validates known experimental results on the effect of communications systems on radars, and thus could be a useful tool to design coexistence schemes for future networks. <s> BIB005 </s> Survey of RF Communications and Sensing Convergence Research <s> K. MODERN CO-DESIGNED APPROACHES <s> The ever increasing demand for spectrum, due to services with data rate requirements and ongoing exponential increase in the number of wireless devices, has pushed for new methods that allow for a flexible and shared use of spectrum among different wireless and radar systems. Different systems need to sense the spectrum and adaptively design their transmitted waveforms in a manner such that they do not cause harmful interference to other systems. In this paper we consider a scenario where radar and wireless communication systems are operated jointly. The opportunistic radar constantly senses the spectrum and adapts its waveform based on the occupancy and maximum allowed power. A radar waveform is optimized for the target detection task such that it does not cause significant performance loss to the communication system. We show that the waveform optimized based on the Neyman-Pearson detector provides a very similar detection performance with the one optimized based on Mutual Information maximization. We also demonstrate that the detection performance improves if, at the radar receiver, the reflections off the target due to the communication signals are considered. <s> BIB006 </s> Survey of RF Communications and Sensing Convergence Research <s> K. MODERN CO-DESIGNED APPROACHES <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> BIB007 </s> Survey of RF Communications and Sensing Convergence Research <s> K. MODERN CO-DESIGNED APPROACHES <s> When radar and communication systems are co-located and operating simultaneously in the same frequency band, interference can be addressed by designing the systems to share resources. This paper develops a framework for cooperative operation of bistatic radar and wireless communication systems. We adopt a low-complexity linear minimum mean square error (LMMSE) optimal pilot symbol aided modulation (PSAM) scheme, and show the achievability region of the joint radar-communication system designed for simultaneous operation in a wireless channel that is both frequency and time-selective. <s> BIB008 </s> Survey of RF Communications and Sensing Convergence Research <s> K. MODERN CO-DESIGNED APPROACHES <s> A theoretical framework that embraces the competing objectives of cooperative radar-communication operations is proposed that engages the apparent trade-space in an optimal fashion. Specifically, minimization of a cooperative risk metric that extends the Neyman-Pearson criterion to include communication data rate is explored. Hence, establishing performance bounds for cooperative interaction. Ideal informed reception where simultaneous access to received data from both the radar and communication (comm.) system is shown to yield a structured covariance-based water-filling solution. Unlinked cooperation where codebooks, waveforms, and schedules are known by all, but received data is not relayed between radar and comm. conveys a complex tradespace dependent on the rate of information transmitted by the comm. system relative to the capacity of the radar-comm. data link. <s> BIB009 </s> Survey of RF Communications and Sensing Convergence Research <s> K. MODERN CO-DESIGNED APPROACHES <s> This paper describes a joint radar-communications resource management framework and modeling approach for a synergistic concept that integrates the radar and communications functionality into a single shared-spectrum system. Such systems share a single transmission — communicating with mobile radios and illuminating the target simultaneously. The results are presented as a function of system exclusivity, i.e., how performance varies as the system is tuned between communications optimized and radar optimized. A joint figure of merit is proposed and used to show how a synergistic shared-spectrum system provides more radar and communications capacity than either a stand-alone communications system or a stand-alone radar system. <s> BIB010
Modern techniques have proposed co-design and operation as a necessary construct for joint radar-communications BIB007 . Others have jointly maximized information criterion for radar and communications users to minimize mutual interference by varying radar waveform and communications OFDM parameters in response to dynamic bandwidth allocation BIB004 . In this work, the operational distance between the two users is proposed as a figure of merit. Other work has looked information exchange to reduce the minimum required standoff range between competing radar and communications users  . Similar work has looked at performance as a function of distance, and also the pitfalls of oversimplified models of interference in comparison to experimental results BIB005 . Others have investigated performance of systems in isolation compared to cooperation to demonstrate that cooperative nodes enjoy a mutual performance enhancement relative to classical isolated operation BIB002 . Others have begun to investigate joint radar communications in a similar context to full duplex communications, focusing on isolation between single hardware operation  . Some researchers are looking at highly flexible architectures to support not only radar and communications, but also electronic warfare, and are developing test beds to support future research in these areas BIB001 . Others have developed a Neyman-Pearson based cooperative metric that captures both radar detection performance and communications data rate in a joint cost metric with parameterizable weighting BIB009 . Researchers have also developed a more general framework for radar-communications joint resource management through development of joint figures of merits that encapsulate capacity, individual performance, and mutually beneficial performance BIB010 . Others have employed code division multiple access (CDMA)-like cancellation by decoding, re-encoding, and subtracting to mitigate interference for multiple, heterogeneous users BIB003 . Some researchers have looked at exploiting energy from communications users to bolster a separate radar user's probability of detection, and optimizing the radar waveform with the in-band communications system operating as the primary user BIB006 , while others have explored joint channel estimation as a means to measure communications data rate and radar probability of detection in the same band BIB008 .