Coherent MIMO Radar Research Articles

Multi-Channel Signal Integration Approach for High-Speed Target Detection in Coherent MIMO Radar System

Multi-Channel Signal Integration Approach for High-Speed Target Detection in Coherent MIMO Radar System

Coherent MIMO radar network enabled by photonics with unprecedented resolution.

The conventional concept of radar is based on stand-alone and independent apparatuses. Superior performance is possible, exploiting distributed points of view (i.e., distributed radars) and centralized data fusion, but systems based only on radio-frequency technology are not able to guarantee the requested degree of coherence and high capacity links among radars. In the current distributed systems, radars act almost independently from each other. Thus, data fusion, which must be performed on locally pre-processed information, can only exploit partial information content, harming the imaging capability of the distributed system. Here we present, to the best of our knowledge, the first extended analysis and experiment of a distributed coherent multiple input-multiple output radar system, enabled by photonics, which maximizes the information content extracted by a centralized data fusion, providing unprecedented resolution capabilities. Stepping from previous achievements, where photonics has been demonstrated in single radars, here photonics is used also for providing coherence and high capacity links among radars. The numerical analysis also demonstrated the benefits of coherent multi-band operation for sidelobe reduction, i.e., false alarms reduction.

Capacity analysis for joint radar-communication capable coherent MIMO radars

Recently, huge attention is attracted to the concept of integrating communication and radar missions within the same platform. Joint Radar-Communications (JRC) system gives an important opportunity to reduce spectrum usage and product cost while doing concurrent operation, as target sensing via radar processing and establishing communication links. A JRC-capable coherent MIMO radar system have been proposed recently in the literature. Several methods are introduced to reach dual goal as a notable null level towards the direction of interest of the radar and MIMO radar waveform orthogonality. Due to the limitations originated form the JRC operation, communication channel may encounter unwanted amplitude variations. This unwanted modulation normally affects the communication performance by its nature, due to the fades on radiated signal amplitude towards the direction of communication. However, the effect of this unintentional modulation on communication channel is yet to be investigated. In this paper, the communication channel for JRC capable phase-coded coherent MIMO radars is analyzed and investigated under additive white Gaussian noise and Rayleigh/Rician fading conditions. Communication capacity is evaluated for each channel condition. The results reveal that, using the single-side limited null direction fixed waveform generation method displays the best capacity performance under all channel conditions.

Realizing joint radar-communications in coherent MIMO radars

The increasing interest on spectrum resources causes various efforts on developing smart and compact solutions as joint radar-communication (JRC) systems. A JRC system can offer cost-effective solution with concurrent operation, as target sensing via radar processing and establishing communication links. JRC capability has been proposed over the years for different types of MIMO radars. However, a JRC capable monostatic coherent MIMO radar system is yet to be developed. These radars offer several advantages as fully coherent signal processing and coherent transmit beamforming which provides beampatterns to minimize probability of intercept. In this paper, two new waveform generation techniques suitable for JRC operation without disturbing transmit beamforming requirements and waveform orthogonality condition in space and time domain are proposed for monostatic coherent MIMO radars. Then, new communication methods are introduced for phase coded monostatic coherent MIMO radars. First method uses chirp-wise information encoding inside the radar pulse as intra-pulse communications. Second rotates the phase of a specific waveform on radiated symbols to a specific direction and the last method applies a small amount of progressive phase shift to the radar waveforms emitted from the antennas to create relative phase modulation between selected radar waveforms. Then, the performance of the proposed communication techniques are investigated in terms of bit error rate (BER) and generated waveforms are examined according to the orthogonality and transmit beamforming requirements.

Covariance Matrix Synthesis Using Maximum Ratio Combining in Coherent MIMO Radar with Frequency Diversity

Covariance Matrix Synthesis Using Maximum Ratio Combining in Coherent MIMO Radar with Frequency Diversity

Waveform Optimization for Transmit Beamforming With MIMO Radar Antenna Arrays

For coherent MIMO radar the optimal target signal processing can be achieved for any transmitted waveforms or radiation beam pattern, making transmit beamforming through waveform design possible without degrading target detection performance. In this work, an innovative waveform optimization approach termed phase-only variable metric method (POVMM) is proposed for coherent MIMO radar waveform design to form a desired transmit beam pattern such as one with radiation nulls in certain directions. The waveform design is carried out by minimizing the radiation powers of the MIMO radar antenna in the selected directions with optimization variables constrained to the waveform phases only. The gradient function of the cost function with regard to waveform phases is analytically derived for the optimization and the POVMM is developed based on the variable metric methods with a flexible search step sizing strategy for improving optimization efficiency. The proposed approach is validated with various designs and simulations.

Antenna Placement Analysis for Coherent MIMO Radar with Phased Synchronization Errors

Phase synchronization errors are practically inevitable, so in this paper the quantitative tool to asses the effect of antenna placement for localization performance with phased synchronization errors is provided. The lower bound of mean-square error (MSE) is set by the hybrid Cramer-Rao bound (HCRB) for the joint estimation of the target location and phase synchronization errors at the receivers. It is shown that HCRB follow up to a lower limit, determined by the synchronization error variance and the number of transmit and receive sensors. For uniform antenna distributing, symmetrical placement is optimal, and all forms give exactly the same performance. The localization performance of nonuniform arrays when the antennas are spread out as much as possible is a little better than symmetrical placement at high SNR. Simulation results verify the correctness of conclusions.

Application of Frequency Diversity to Suppress Grating Lobes in Coherent MIMO Radar with Separated Subapertures

A method based on frequency diversity to suppress grating lobes in coherent MIMO radar with separated subapertures is proposed. By transmitting orthogonal waveforms from separated subapertures or subarrays, receiving beams can be formed at the receiving end with the same mainlobe direction. However, grating lobes would change to different positions if the frequencies of the radiated waveforms are incremented by a frequency offset from subarray to subarray. Coherently combining the beams can suppress or average grating lobes to a low level. We show that the resultant transmit-receive beampattern is composed of the range-dependent transmitting beam and the combined receiving beam. It is demonstrated that the range-dependent transmitting beam can also be frequency offset-dependent. Precisely directing the transmitting beam to a target with a known range and a known angle can be achieved by properly selecting a set of . The suppression effects of different schemes of selecting are evaluated and studied by simulation.