Since traditional radar signals are “unintelligent,” regarding the amount of information they convey on the bandwidth they occupy, a joint radar and wireless communication system would constitute a unique platform for future intelligent transportation networks effecting the essential tasks of environmental sensing and the allocation of ad-hoc communication links, in terms of both spectrum efficiency and cost-effectiveness. In this paper, approaches to the design of intelligent waveforms, that are suitable for simultaneously performing both data transmission and radar sensing, are proposed. The approach is based on classical phase-coded waveforms utilized in wireless communications. In particular, requirements that allow for employing such signals for radar measurements with high dynamic range are investigated. Also, a variety of possible radar processing algorithms are discussed. Moreover, the applicability of multiple antenna techniques for direction-of-arrival estimation is considered. In addition to theoretical considerations, the paper presents system simulations and measurement results of complete “RadCom” systems, demonstrating the practical feasibility of integrated communications and radar applications.

Waveform Design and Signal Processing Aspects for Fusion of Wireless Communications and Radar Sensing

Sharing of the frequency bands between radar and communication systems has attracted substantial attention, as it can avoid under-utilization of otherwise permanently allocated spectral resources, thus improving efficiency. Further, there is increasing demand for radar and communication systems that share the hardware platform as well as the frequency band, as this not only decongests the spectrum, but also benefits both sensing and signaling operations via the full cooperation between both functionalities. Nevertheless, the success of spectrum and hardware sharing between radar and communication systems critically depends on high-quality joint radar and communication designs. In the first part of this paper, we overview the research progress in the areas of radar-communication coexistence and dual-functional radar-communication (DFRC) systems, with particular emphasis on application scenarios and technical approaches. In the second part, we propose a novel transceiver architecture and frame structure for a DFRC base station (BS) operating in the millimeter wave (mmWave) band, using the hybrid analog-digital (HAD) beamforming technique. We assume that the BS is serving a multi-antenna user equipment (UE) over a mmWave channel, and at the same time it actively detects targets. The targets also play the role of scatterers for the communication signal. In that framework, we propose a novel scheme for joint target search and communication channel estimation, which relies on omni-directional pilot signals generated by the HAD structure. Given a fully-digital communication precoder and a desired radar transmit beampattern, we propose to design the analog and digital precoders under non-convex constant-modulus (CM) and power constraints, such that the BS can formulate narrow beams towards all the targets, while pre-equalizing the impact of the communication channel. Furthermore, we design a HAD receiver that can simultaneously process signals from the UE and echo waves from the targets. By tracking the angular variation of the targets, we show that it is possible to recover the target echoes and mitigate the resulting interference to the UE signals, even when the radar and communication signals share the same signal-to-noise ratio (SNR). The feasibility and efficiency of the proposed approaches in realizing DFRC are verified via numerical simulations. Finally, the paper concludes with an overview of the open problems in the research field of communication and radar spectrum sharing (CRSS).

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Joint Radar and Communication Design: Applications, State-of-the-Art, and the Road Ahead

Wireless mediums, such as RF, optical, or acoustical, provide finite resources for the purposes of remote sensing (such as radar) and data communications. Often, these two functions are at odds with one another and compete for these resources. Applications for wireless technology are growing rapidly, and RF convergence is already presenting itself as a requirement for both users as consumer and military system requirements evolve. The broad solution space to this complex problem encompasses cooperation or codesigning of systems with both sensing and communications functions. By jointly considering the systems during the design phase, rather than perpetuating a notion of mutual interference, both system’s performance can be improved. We provide a point of departure for future researchers that will be required to solve this problem by presenting the applications, topologies, levels of system integration, the current state of the art, and outlines of future information-centric systems.

Survey of RF Communications and Sensing Convergence Research

We investigate methods of co-existence between radar and communications systems. Each system typically considers the other system a source of interference. Consequently, the traditional solution is to isolate the two systems spectrally or spatially. By considering a cooperative radar and communications signaling scheme, we derive achievable bounds on performance for a receiver that observes communications and radar return in the same frequency allocation. We assume the radar and communications operations to be a single joint system. Bounds on performance of the joint system are measured in terms of data information rate for communications and a novel radar estimation information rate for the radar.

Inner Bounds on Performance of Radar and Communications Co-Existence

We propose a millimeter-wave joint radar-communications (JRC) system comprising a bi-static automotive radar and vehicle-to-vehicle communications. We study the applicability of known phase-modulated-continuous-wave (PMCW) and orthogonal-frequency-division-multiple-access waveforms for bi-static-JRC. In both cases, we design multiplexing strategies to ensure the parameter identifiability, derive JRC statistical bounds and numerically demonstrate superior performance of proposed low-complexity JRC super-resolution algorithms over conventional two-dimensional fast Fourier transform/MUltiple SIgnal Classification.

A mmWave Automotive Joint Radar-Communications System

Orthogonal frequency-division multiplexing (OFDM) signal coding and system architecture were implemented to achieve radar and data communication functionalities. The resultant system is a software-defined unit, which can be used for range measurements, radar imaging, and data communications. Range reconstructions were performed for ranges up to 4 m using trihedral corner reflectors with approximately 203 m of radar cross section at the carrier frequency; range resolution of approximately 0.3 m was demonstrated. Synthetic aperture radar (SAR) image of a single corner reflector was obtained; SAR signal processing specific to OFDM signals is presented. Data communication tests were performed in radar setup, where the signal was reflected by the same target and decoded as communication data; bit error rate of was achieved at 57 Mb/s. The system shows good promise as a multifunctional software-defined sensor which can be used in radar sensor networks.

Multifunctional Software-Defined Radar Sensor and Data Communication System

This paper describes the design and architectural composition of a radar system built on OFDM platform. The radar signal is generated digitally by forming an arbitrary-length vector of OFDM sub-carrier amplitudes and translating it in analog format via 1000 Ms/s D/A conversion. The resultant baseband signal has a bandwidth of 500 MHz, and variable number and composition of sub-carriers, which may be changed on a pulse-to-pulse basis. The signal is upconverted to 7.5 GHz carrier frequency and emitted via small-form horn antenna. The receiver includes 1 Gs/s A/D converter and processing is performed in frequency domain. The system is currently configured for short-range applications (3–5 m) and can be used as radar or communication unit without any changes to hardware and with very minimal changes to software. Experimental results from high-resolution range profile imaging and broadband data communications are presented and discussed.

Wideband OFDM system for radar and communications

We present a signal processing algorithm and simulation study for aerial navigation with an ultrawideband orthogonal frequency division multiplexed (UWB-OFDM) radar in Global Positioning System (GPS)-denied environments. Stationary scatterers are detected and tracked using an M/N detector and modified global nearest neighbor (GNN) tracker. The radar measurements to the scatterers are combined with inertial navigation system (INS) measurements in an extended Kalman filter (EKF) to compute the aircraft position. The estimation error of the proposed algorithm is analyzed through computer-based simulations with/without radar measurements from the scatterers and with varying signal-to-noise ratio (SNR).

Real-Time UWB-OFDM Radar-Based Navigation in Unknown Terrain

This paper describes the architecture, testing methodology and experimental results of the software-defined ultra-wideband system built at Miami University. To achieve broadband data communication capability, spectrum-efficient OFDM method of modulation was chosen. The radar functionality using the same OFDM-coded pulses was implemented as well, and tested in short-range experiments. The system operates in X-band with a total transmit bandwidth of 1 GHz. Range resolution of 0.30 meters and data communication capability at approximately 57 Mb/s were established and the system was shown to be able to operate in either mode without any hardware adjustments. This concept may prove extremely useful in high-resolution radar sensor network scenarios.

Radar and data communication fusion with UWB-OFDM software-defined system

There is a great need to develop non-GPS based methods for position and navigation in situations where GPS is not available. This paper presents an improved feature extraction and tracking algorithm for a novel navigation sensor, an Ultra-Wideband Orthogonal Frequency Division Multiplexed radar. The radar is onboard an aerial vehicle and collects data periodically in a side-looking stripmap Synthetic Aperture Radar configuration flying over unknown terrain. An M/N detector is first used to extract range/Doppler observations from SAR features in the terrain. The observations are then associated with existing tracks using Global Nearest Neighbor. The associated measurements are then used as updates to a previously developed EKF which combines the radar observation tracks with INS measurements to compute an optimal aircraft position estimate. The filter performance is evaluated and compared with that of a previously developed threshold-based method using simulations. The algorithm performance dependence on the quality of INS measurements are also evaluated based on INS error models of commercial-grade, tactical-grade, and navigation-grade INS systems.

Kyle Kauffman

Papers

Multifunctional Software-Defined Radar Sensor and Data Communication System

Wideband OFDM system for radar and communications

Real-Time UWB-OFDM Radar-Based Navigation in Unknown Terrain

Radar and data communication fusion with UWB-OFDM software-defined system

Enhanced feature detection and tracking algorithm for UWB-OFDM SAR navigation