NLOS Dies Twice: Challenges and Solutions of V2X for Cooperative Perception

Multi-agent multi-lidar sensor fusion between connected vehicles for cooperative perception has recently been recognized as the best technique for minimizing the blind zone of individual vehicular perception systems and further enhancing the overall safety of autonomous driving systems. This technique relies heavily on the reliability and availability of vehicle-to-everything (V2X) communication. In practical sensor fusion application scenarios, the non-line-of-sight (NLOS) issue causes blind zones for not only the perception system but also V2X direct communication. To counteract underlying communication issues, we introduce an abstract perception matrix matching method for quick sensor fusion matching procedures and mobility-height hybrid relay determination procedures, proactively improving the efficiency and performance of V2X communication to serve the upper layer application fusion requirements. To demonstrate the effectiveness of our solution, we design a new simulation framework to consider autonomous driving, sensor fusion and V2X communication in general, paving the way for end-to-end performance evaluation and further solution derivation.Comment: Submission to IEEE Vehicular Technology Magazin

Reduced risk of North American cold extremes due to continued Arctic sea ice loss

Copyright © 2014 American Meteorological SocietyIn early-January 2014, an Arctic air outbreak brought extreme cold and heavy snowfall to central and eastern North America, causing widespread disruption and monetary losses. The media extensively reported the cold snap, including debate on whether or not human-induced climate change was partly responsible. Related to this, one particular hypothesis garnered considerable attention: that rapid Arctic sea ice loss may be increasing the risk of cold extremes in mid-latitudes. Here we use large ensembles of model simulations to explore how the risk of North American daily cold extremes is anticipated to change in the future, in response to increases in greenhouse gases and the component of that response due solely to Arctic sea ice loss. Specifically, we examine the changing probability of daily cold extremes as (un)common as the 7 January 2014 event. Projected increases in greenhouse gases decrease the likelihood of North American cold extremes in the future. Days as cold or colder than the 7 January 2014 are still projected to occur in the mid twenty-first century (2030–49), albeit less frequently than in the late twentieth century (1980–99). However, such events will cease to occur by the late twenty-first century (2080–99), assuming greenhouse gas emissions continue unabated. Continued Arctic sea ice loss is a major driver of decreased - not increased - North America cold extremes. Projected Arctic sea ice loss alone reduces the odds of such an event by one quarter to one third by the mid twenty-first century, and to zero (or near-zero) by the late twenty-first century.National Environmental Research CouncilUS National Science Foundation Office of Polar ProgramsUS National Science Foundatio

The role of synoptic eddies in the tropospheric response to stratospheric variability

The tropospheric response to sudden stratospheric warmings (SSWs) is analyzed in an idealized model setup regarding the respective roles of planetary-scale and synoptic-scale waves. The control model run includes a full interactive wave spectrum, while a second run includes interactive planetary-scale waves but only the time-mean synoptic-scale wave forcing from the control run. In both runs, the tropospheric response is characterized by the negative phase of the respective tropospheric annular mode. But given their different latitudinal structure, the control run shows the expected response, i.e., an equatorward shift of the tropospheric jet, whereas the response in the absence of interactive synoptic eddies is characterized by a poleward jet shift. This opposite jet shift is associated with a different planetary wave variability that couples with the zonal flow between the stratosphere and the surface. These results indicate that the synoptic eddy feedback is necessary for the observed tropospheric response to SSWs

Influence of projected Arctic sea ice loss on polar stratospheric ozone and circulation in spring

The impact of projected Arctic sea ice loss on the stratosphere is investigated using the Whole Atmosphere Community Climate Model (WACCM), a state-of-the-art coupled chemistry climate model. Two 91-year simulations are conducted: one with a repeating seasonal cycle of Arctic sea ice for the late twentieth-century, taken from the fully coupled WACCM historical run; the other with Arctic sea ice for the late twenty-first century, obtained from the fully coupled WACCM RCP8.5 run. In response to Arctic sea ice loss, polar cap stratospheric ozone decreases by 13 DU (34 DU at the North Pole) in spring, confirming the results of Scinocca et al (2009 Geophys. Res. Lett. 36 L24701). The ozone loss is dynamically initiated in March by a suppression of upward-propagating planetary waves, possibly related to the destructive interference between the forced wave number 1 and its climatology. The diminished upward wave propagation, in turn, weakens the Brewer–Dobson circulation at high latitudes, strengthens the polar vortex, and cools the polar stratosphere. The ozone reduction persists until the polar vortex breaks down in late spring

Does ocean coupling matter for the northern extratropical response to projected Arctic sea ice loss?

This is the final version of the article. Available from the publisher via the DOI in this record.The question of whether ocean coupling matters for the extratropical Northern Hemisphere atmospheric response to projected late 21st century Arctic sea ice loss is addressed using a series of experiments with Community Climate System Model version 4 at 1° spatial resolution under different configurations of the ocean model component: no interactive ocean, thermodynamic slab ocean, and full-depth (dynamic plus thermodynamic) ocean. Ocean-atmosphere coupling magnifies the response to Arctic sea ice loss but does not change its overall structure; however, a slab ocean is inadequate for inferring the role of oceanic feedbacks. The westerly winds along the poleward flank of the eddy-driven jet weaken in response to Arctic sea ice loss, accompanied by a smaller-magnitude strengthening on the equatorward side, with largest amplitudes in winter. Dynamical and thermodynamic oceanic feedbacks amplify this response by approximately 50%. Air temperature, precipitation, and sea level pressure responses also show sensitivity to the degree of ocean coupling.R. Tomas and L. Sun gratefully acknowledge support from the Office of Polar Programs at the National Science Foundation. J. Screen is supported by the Natural Environment Research Council. NCAR is sponsored by NSF.We appreciate the comments from the two anonymous reviewers

C-V2X Vision in the Chinese Roadmap: Standardization, Field Tests, and Industrialization

Cellular-based V2X (C-V2X) technology promoted by Third Generation Partnership Project (3GPP) is gaining increasing attention globally, after many year-long competition with dedicated short-range communications (DSRC) supported by the Institute of Electrical and Electronics Engineers (IEEE) for vehicular to everything communication. As a rising star, China continuously and actively focuses on and contributes to the C-V2X technology development in this technology marathon. Starting from the standardization progress, a quite few Chinese-specific use cases and communication messages are defined for the complicated urban traffics. Based on these dedicatedly designed higher layer protocols, the annual field tests are progressively conducted to testify the interoperability among chipsets, modules, security certificates, and original equipment manufacturer (OEM). Putting enough efforts on industry standards and tests, China is fast commercializing the C-V2X-based road services, for example, robotaxi and robot-bus in representative cities. Thus, in this chapter, we propose to provide sufficient technology views and a summary to show such advanced Chinese C-V2X philosophy

Consistency and discrepancy in the atmospheric response to Arctic sea-ice loss across climate models

This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this recordThe decline of Arctic sea ice is an integral part of anthropogenic climate change. Sea-ice loss is already having a significant impact on Arctic communities and ecosystems. Its role as a cause of climate changes outside of the Arctic has also attracted much scientific interest. Evidence is mounting that Arctic sea-ice loss can affect weather and climate throughout the Northern Hemisphere. The remote impacts of Arctic sea-ice loss can only be properly represented using models that simulate interactions among the ocean, sea ice, land and atmosphere. A synthesis of six such experiments with different models shows consistent hemispheric-wide atmospheric warming, strongest in the mid-to-high-latitude lower troposphere; an intensification of the wintertime Aleutian Low and, in most cases, the Siberian High; a weakening of the Icelandic Low; and a reduction in strength and southward shift of the mid-latitude westerly winds in winter. The atmospheric circulation response seems to be sensitive to the magnitude and geographic pattern of sea-ice loss and, in some cases, to the background climate state. However, it is unclear whether current-generation climate models respond too weakly to sea-ice change. We advocate for coordinated experiments that use different models and observational constraints to quantify the climate response to Arctic sea-ice loss.J.A.S. and R.B. were funded by the Natural Environment Research Council (NE/P006760/1). C.D. acknowledges the National Science Foundation (NSF), which sponsors the National Center for Atmospheric Research. D.M.S. was supported by the Met Office Hadley Centre Climate Programme (GA01101) and the APPLICATE project, which is funded by the European Union’s Horizon 2020 programme. X.Z. was supported by the NSF (ARC#1023592). P.J.K. and K.E.M. were supported by the Canadian Sea Ice and Snow Evolution Network, which is funded by the Natural Science and Engineering Research Council of Canada. T.O. was funded by Environment and Climate Change Canada (GCXE17S038). L.S. was supported by the National Oceanic and Atmospheric Administration’s Climate Program Office

Downward influence of stratospheric final warming events in an idealized model

The stratospheric ???nal warming is the ???nal transition of the zonal winds from wintertime westerlies to summertime easterlies as the solar heating of the high latitude stratosphere increases in the springtime. Recent observational analyses suggested that stratospheric final warming makes a signi???cant contribution to the spring transitions in the lower troposphere, especially in the Northern Hemisphere. It is still not clear, however, whether these transitions are due to the downward in???uence from the stratosphere. We ???rst explore the hypothesis that much of the observed tropospheric signal of the ???nal warming is initiated from the stratosphere. Large ensembles of ???nal warmings are simulated in an idealized dynamical core model, by imposing a radiative equilibrium temperature transition from winter to summer only in the stratosphere. Our results suggest that a substantial fraction of the observed tropospheric changes that occur in conjunct with the ???nal warming are induced from the stratosphere. We further investigate the mechanisms of the downward in???uence of the ???nal warmings on the tropospheric circulation. Results from our zonally symmetric model suggest that stratospheric wave driving can induce a residual circulation and a???ect the tropospheric circulation. The tropospheric signals due to this mechanism are, however, very weak and are mostly con???ned to the upper troposphere. On the other hand, the stratosphere can a???ect the propagation of planetary waves from the troposphere, resulting in a burst of wave activity and the zonal wind deceleration prior to the ???nal warming in the troposphere. We also perform a series of perturbation experiments for the sudden and ???nal warmings to test the roles of the troposphere and the stratosphere in determining the predictability of stratospheric warmings. For a late ???nal warming, almost all of the predictability comes from the troposphere. For the rest of the ???nal warmings and for sudden warmings, however, the troposphere determines the predictability until very close to the time of warming onset. This ???nding, consistent with the conventional view of the warming, re???ects that center role of the troposphere in determining the stratospheric warmings. Results from a comprehensive global climate model, the Whole-Atmosphere Community Climate Model (WACCM), are used to analyze the ???nal warmings in both hemispheres. Although WACCM has zonal winds that are too strong in the spring, which causes the mean onset dates to be delayed at least one month with respect to the observations, the zonal wind evolutions resemble the observations. The similarity between the models and observations suggests that the downward in???uence of the stratospheric ???nal warming on the tropospheric circulation is real and substantial, especially in the Northern Hemisphere

Information Relaying Methods in VANET: Algorithms, Standards and Tests

This paper considers information transmission issue observed in a large scale test of cellular-based vehicular to everything (C-V2X) technology in China, which is the information blockage for the vehicle-to-vehicle (V2V) wireless communication. With such findings, we propose utilizing relaying-based information routing solutions by the support of K-means-type algorithm and an on-request relay selection method in a vehicular adhoc network (VANET). From the algorithm perspective, we refine the K-means-based VANET seeding principle with considerations on the global vehicle layout. On the other hand, base station and/or core network aided relay selection associated with vehicle maneuver is introduced for waking up relays when necessary in order to address the typical non-line-of-sight (NLOS) signal attenuation by taking the power consumption into consideration. To evaluate the system performance, we conduct Matlab and network simulator (NS)-3 simualtions to justify the algorithms, and adopt Veins-based simulations to show the data packets loss gain over non-relaying scenarios of realistic V2V scenario with NLOS signal dissemination