26 research outputs found
Mutual Interference Mitigation in PMCW Automotive Radar
This paper addresses the challenge of mutual interference in phase-modulated
continuous wave (PMCW) millimeter-wave (mmWave) automotive radar systems. The
increasing demand for advanced driver assistance systems (ADAS) has led to a
proliferation of vehicles equipped with mmWave radar systems that operate in
the same frequency band, resulting in mutual interference that can degrade
radar performance creating safety hazards. We consider scenarios involving two
similar PMCW radar systems and propose an effective technique for a cooperative
design of transmit waveforms such that the mutual interference between them is
minimized. The proposed approach is numerically evaluated via simulations of a
mmWave automotive radar system. The results demonstrate that the proposed
technique notably reduces mutual interference and enhances radar detection
performance while imposing very little computational cost and a negligible
impact on existing infrastructure in practical automotive radar system
Space-Time Adaptive Processing in Connected and Automated Vehicular Radar Platoons
In this study, we develop a holistic framework for space-time adaptive
processing (STAP) in connected and automated vehicle (CAV) radar systems. We
investigate a CAV system consisting of multiple vehicles that transmit
frequency-modulated continuous-waveforms (FMCW), thereby functioning as a
multistatic radar. Direct application of STAP in a network of radar systems
such as in a CAV may lead to excess interference. We exploit time division
multiplexing (TDM) to perform transmitter scheduling over FMCW pulses to
achieve high detection performance. The TDM design problem is formulated as a
quadratic assignment problem which is tackled by power method-like iterations
and applying the Hungarian algorithm for linear assignment in each iteration.
Numerical experiments confirm that the optimized TDM is successful in enhancing
the target detection performance
Joint Waveform and Passive Beamformer Design in Multi-IRS-Aided Radar
Intelligent reflecting surface (IRS) technology has recently attracted a
significant interest in non-light-of-sight radar remote sensing. Prior works
have largely focused on designing single IRS beamformers for this problem. For
the first time in the literature, this paper considers multi-IRS-aided
multiple-input multiple-output (MIMO) radar and jointly designs the transmit
unimodular waveforms and optimal IRS beamformers. To this end, we derive the
Cramer-Rao lower bound (CRLB) of target direction-of-arrival (DoA) as a
performance metric. Unimodular transmit sequences are the preferred waveforms
from a hardware perspective. We show that, through suitable transformations,
the joint design problem can be reformulated as two unimodular quadratic
programs (UQP). To deal with the NP-hard nature of both UQPs, we propose
unimodular waveform and beamforming design for multi-IRS radar (UBeR) algorithm
that takes advantage of the low-cost power method-like iterations. Numerical
experiments illustrate that the MIMO waveforms and phase shifts obtained from
our UBeR algorithm are effective in improving the CRLB of DoA estimation
Quantized Phase-Shift Design of Active IRS for Integrated Sensing and Communications
Integrated sensing and communications (ISAC) is a spectrum-sharing paradigm
that allows different users to jointly utilize and access the crowded
electromagnetic spectrum. In this context, intelligent reflecting surfaces
(IRSs) have lately emerged as an enabler for non-line-of-sight (NLoS) ISAC.
Prior IRS-aided ISAC studies assume passive surfaces and rely on the
continuous-valued phase shift model. In practice, the phase-shifts are
quantized. Moreover, recent research has shown substantial performance benefits
with active IRS. In this paper, we include these characteristics in our
IRS-aided ISAC model to maximize the receive radar and communications
signal-to-noise ratios (SNR) subjected to a unimodular IRS phase-shift vector
and power budget. The resulting optimization is a highly non-convex unimodular
quartic optimization problem. We tackle this via a bi-quadratic transformation
to split the problem into two quadratic sub-problems that are solved using the
power iteration method. The proposed approach employs the M-ary unimodular
sequence design via relaxed power method-like iteration (MaRLI) to design the
quantized phase-shifts. As expected, numerical experiments demonstrate that our
active IRS-ISAC system design with MaRLI converges to a higher value of SNR
when we increase the number of IRS quantization bits
Submodular Optimization for Placement of Intelligent Reflecting Surfaces in Sensing Systems
Intelligent reflecting surfaces (IRS) and their optimal deployment are the
new technological frontier in sensing applications. Recently, IRS have
demonstrated potential in advancing target estimation and detection. While the
optimal phase-shift of IRS for different tasks has been studied extensively in
the literature, the optimal placement of multiple IRS platforms for sensing
applications is less explored. In this paper, we design the placement of IRS
platforms for sensing by maximizing the mutual information. In particular, we
use this criterion to determine an approximately optimal placement of IRS
platforms to illuminate an area where the target has a hypothetical presence.
After demonstrating the submodularity of the mutual information criteria, we
tackle the design problem by means of a constant-factor approximation algorithm
for submodular optimization. Numerical results are presented to validate the
proposed submodular optimization framework for optimal IRS placement with worst
case performance bounded to
Moving Target Detection via Multi-IRS-Aided OFDM Radar
An intelligent reflecting surface (IRS) consists of passive reflective
elements capable of altering impinging waveforms. The IRS-aided radar systems
have recently been shown to improve detection and estimation performance by
exploiting the target information collected via non-line-of-sight paths.
However, the waveform design problem for an IRS-aided radar has remained
relatively unexplored. In this paper, we consider a multi-IRS-aided orthogonal
frequency-division multiplexing (OFDM) radar and study the theoretically
achievable accuracy of target detection. In addition, we jointly design the
OFDM signal and IRS phase-shifts to optimize the target detection performance
via an alternating optimization approach. To this end, we formulate the IRS
phase-shift design problem as a unimodular bi-quadratic program which is
tackled by a computationally cost-effective approach based on power-method-like
iterations. Numerical experiments illustrate that our proposed joint design of
IRS phase-shifts and the OFDM code improves the detection performance in
comparison with conventional OFDM radar
cis-TetraÂchloridobis(1H-imidazole-κN 3)platinum(IV)
In the title complex, cis-[PtCl4(C3H4N2)2], the PtIV ion lies on a twofold rotation axis and is coordinated in a slightly distorted octaÂhedral geometry. The dihedral angle between the imidazole rings is 69.9 (2)°. In the crystal, molÂecules are linked by N—H⋯Cl hydrogen bonds, forming a three-dimensional network
Final 3.indd
Abstract Background: The possible prognostic signi¿cance of the expression of a variety of markers has been investigated in acute lymphoblastic leukemia (ALL). Methods: In the present study we investigated the prognostic signi¿cance of CD13 and CD33 myeloid antigens (MY) aberrantly expressed on the blasts of ALL patients and Bcl-2 anti-apoptotic molecule expression in childhood ALL. Results: Aberrant expression of MY occurred in 8.8% of cases. Variant levels of Bcl-2 were expressed in patients (44.2±25.5%), with more than 20% positivity for Bcl-2 in 64.7% of patients. Bcl-2 + patients survived 959±242 days compared to 1059+230 days for Bcl-2 -patients (P=0.2). Corresponding data for complete remission duration was 682±170 and 716±173 days (P=0.3), respectively, indicating no signi¿cant association between survival and complete remission duration of patients with expression of the Bcl-2 molecule. Analysis of clinical response according to MY expression, however, showed signi¿cant association with survival and complete remission duration. MY + patients had shorter complete remission duration (383±58 days) and survival (473±68 days) than MY -patients (complete remission duration, 724±144 days; survival, 1045±186 days; P<0.001). Expression of Bcl-2 along with MY was not associated with a signi¿cant decrease in survival or complete remission duration. Conclusion: Results of this study indicated that expression of MY was a poor prognostic factor in childhood ALL. Bcl-2 expression in MY + patients could not inÀuence the response to therapy