To get the most use out of scarce spectrum, technologies have emerged that permit single systems to accommodate both radar and communications functions. Dual-function radar communication (DFRC) systems, where the two systems use the same platform and share the same hardware and spectral resources, form a specific class of radio-frequency (RF) technology. These systems support applications where communication data, whether as target and waveform parameter information or as information independent of the radar operation, are efficiently transmitted using the same radar aperture and frequency bandwidth. This is achieved by embedding communication signals into radar pulses. In this article, we review the principles of DFRC systems and describe the progress made to date in devising different forms of signal embedding. Various approaches to DFRC system design, including downlink and uplink signaling schemes, are discussed along with their respective benefits and limitations. We present tangible applications of DFRC systems and delineate their design requirements and challenges. Future trends and open research problems are also highlighted.

Dual-Function Radar Communication Systems: A solution to the spectrum congestion problem

Frequency-hopping (FH) MIMO radar-based dual-function radar communication (FH-MIMO DFRC) enables communication symbol rate to exceed radar pulse repetition frequency, which requires accurate estimations of timing offset and channel parameters. The estimations, however, are challenging due to unknown, fast-changing hopping frequencies and the multiplicative coupling between timing offset and channel parameters. In this article, we develop accurate methods for a single-antenna communication receiver to estimate timing offset and channel for FH-MIMO DFRC. First , we design a novel FH-MIMO radar waveform, which enables a communication receiver to estimate the hopping frequency sequence (HFS) used by radar, instead of acquiring it from radar. Importantly, the novel waveform incurs no degradation to radar ranging performance. Then , via capturing distinct HFS features, we develop two estimators for timing offset and derive mean squared error lower bound of each estimator. Using the bounds, we design an HFS that renders both estimators applicable. Furthermore , we develop an accurate channel estimation method, reusing the single hop for timing offset estimation. Validated by simulations, the accurate channel estimates attained by the proposed methods enable the communication performance of DFRC to approach that achieved based on perfect timing and ideal knowledge of channel.

Waveform Design and Accurate Channel Estimation for Frequency-Hopping MIMO Radar-Based Communications

Information embedding into the emission of multiple-input multiple-output (MIMO) frequency hopping (FH) radar is analyzed. It is assumed that the radar is primary under dual function radar communication system platforms. phase shift keying (PSK) communication symbols are embedded in each hop of the FH waveforms. The impact of embedding is a significant reduction in range sidelobe levels. We examine the impact of PSK symbol embedding on the power spectral density (PSD) of the MIMO radar. It is shown that there is spectral leakage due to the disruption of the continuous phase of the FH waveforms by the PSK symbol embedding. The trade-off between low sidelobe levels and low spectral leakage is analyzed. To maintain the phase continuity between the frequency hops, modulation of FH waveforms with frequency shift keying (FSK) symbols is considered and its performance is compared with that of the FH/PSK radar communication waveforms.

Analysis of Communication Symbol Embedding in FH MIMO Radar Platforms

A view on radar and communication systems coexistence and dual functionality in the era of spectrum sensing

Breath sounds methodology

There is a presumed adverse effect on radar operation brought about from embedding communication signals in radar waveforms. Contrary to that presumption, we show in this paper that modulation of the radar pulse can indeed benefit both radar and communications in the dual system paradigm. This is shown by analyzing the impact of phase-shift keying (PSK) symbol embedding on the ambiguity function (AF) of a multiple-input multiple-output (MIMO) radar. Our analysis shows that the embedded PSK symbols yield reduction in the AF sidelobe peaks for a single pulse as well as for a series of radar pulses. To prove these results, we analyze the AF with and without the PSK symbol embedding. It is shown that the embedding of PSK symbols enable increasing the number of orthogonal transmit waveforms that can be used without increasing the sidelobe levels (SLL) of the corresponding AF.

Ambiguity Function Analysis for Dual-Function Radar Communications Using PSK Signaling

In this paper, we propose a method for information embedding into the emission of frequency hopping (FH) multiple-input multiple-output (MIMO) radar. The differential phase shift keying (DPSK) modulated communication symbols are embedded into each pulse of the FH radar waveforms. We examine the effect of DPSK symbol embedding on the radar operation by analyzing the range sidelobes performance, power spectral density (PSD) and data rate of the system. The proposed system shows significant reduction in range sidelobes, good spectral containment and achieves high communication data rates. The latter is enabled by synthesizing a large number of orthogonal waveforms.

Dual Function FH MIMO Radar System with DPSK Signal Embedding

We present a dual-function radar communication (DFRC) system applying signal embedding through a code shift keying (CSK) strategy. The information symbol is phase encoded into a sequence and then modulated by the continuous phase modulation (CPM) before embedding into frequency hopping (FH) radar sub-pulses. The CPM modulated communication symbol phase coded sequence is multiplied with the FH radar waveforms in fast-time and transmitted through multiple-input multiple-output (MIMO) radar platforms. We address the problem of range sidelobe modulation (RSM) and propose the design of the optimum CSK sequences to reduce the degree of change in the range sidelobe levels (RSLs) of the ambiguity function (AF). It is shown that the optimum CSK sequences yield significant reduction in the RSLs of the DFRC system. They also maintain the same degree of correlation between FH sub-pulses regardless of the communication symbol sequences embedded. Additionally, the proposed DFRC system with the optimized waveform design provides good spectrum containment and achieves high communication data rates.

Controlling Clutter Modulation in Frequency Hopping MIMO Dual-Function Radar Communication Systems

In this paper, we compare the performance of diﬀerent phase modulated frequency hopping (FH) multiple-input multiple-output (MIMO) radar waveforms. The communication symbols are embedded into the FH waveforms under the auspices of dual-function (DF) radar and communications system. In the proposed scheme, each embedded symbol is represented by a sequence of phases. The phase modulated sequence is embedded through multiplication with the radar hops and is transmitted through a MIMO radar platform. Using this scheme, we consider information embedding in MIMO FH radar implementing diﬀerent types of phase modulated sequence, including phase shift keying (PSK), diﬀerential phase shift keying (DPSK) and continuous phase modulation (CPM). We analyze the corresponding ambiguity functions (AFs) in terms of reducing or increasing range and Doppler sidelobes compared to the FH radar without any signal embedding. The spectral sidelobe levels and the complexity of the demodulator at the communication receiver are also examined. It is shown the proposed embedding scheme for DPSK and CPM minimizes the frequency leakage outside the radar signal bandwidth. To demonstrate the effectiveness of proposed scheme, we compare its performance with existing embedding schemes, all for FH radars. It is shown that our approach, in its significant reductions of range sidelobes, permits high data rate transmission. This is made possible because the FH radar can now afford using duplicate hopping code values without the penalty of incurring high correlations, or range sidelobe levels.

Indu Priya Eedara

Papers

Ambiguity Function Analysis for Dual-Function Radar Communications Using PSK Signaling

Analysis of Communication Symbol Embedding in FH MIMO Radar Platforms

Dual Function FH MIMO Radar System with DPSK Signal Embedding

Controlling Clutter Modulation in Frequency Hopping MIMO Dual-Function Radar Communication Systems

Performance comparison of dual-function systems embedding phase-modulated signals in FH radar