Wang Q.,Coordination Center |
Fan P.,Tsinghua University |
Letaief K.B.,Hong Kong University of Science and Technology
IEEE Transactions on Vehicular Technology | Year: 2012
In the paper, we investigate the information spread problem in a joint vehicle-to-infrastructure (V2I) and vehicle-to-vehicle (V2V) communication system. A scene is considered where more information centers (or base stations) are allocated along the road so that the information centers are able to broadcast timely messages to vehicles within the range of the broadcast signal of each base station, which we shall refer to as broadcast zone. The seamless information spread is used to guarantee that messages are correctly received by each vehicle, regardless of whether it pulls into broadcast zones or not. We first derive the maximum throughput of the V2I downlink system for both additive white Gaussian noise (AWGN) channels and Rayleigh fading channels with Doppler effects. A measurement-based algorithm to estimate the throughput is also proposed. We then discuss the maximum achievable amount of information that can be relayed forward along a vehicular stream. A network coding technique will then be proposed to cancel the interference caused by relay signals to vehicles that are receiving messages from the corresponding information center. These theoretical results will give more insight into the vehicular communication system design. © 2011 IEEE.
Shao J.,Zhejiang GongShang University |
Liu P.,Pennsylvania State University |
Zhou Y.,Coordination Center
Journal of Systems and Software | Year: 2012
In proxy re-encryption (PRE), a semi-trusted proxy can transform a ciphertext under the delegator's public key into another ciphertext that the delegatee can decrypt by his/her own private key. However, the proxy cannot access the plaintext. Due to its transformation property, proxy re-encryption can be used in many applications, such as encrypted email forwarding. Some of these applications require that the underlying PRE scheme is CCA-secure and key-private. However, to the best of our knowledge, none of the existing PRE schemes satisfy this security requirement in the standard model. In this paper, based on the 5-Extended Decision Bilinear Diffie-Hellman assumption and Decision Diffie-Hellman assumption, we propose the first such PRE scheme, which solves an open problem left by Ateniese et al. (2009). © 2011 Elsevier Inc. All rights reserved.
Miyachi T.,Coordination Center |
Yamada T.,Hitachi Ltd.
Proceedings of the SICE Annual Conference | Year: 2014
This paper presents a survey on cyber security issues in in current industrial automation and control systems, which also includes observations and insights collected and distilled through a series of discussion by some of major Japanese experts in this field. It also tries to provide a conceptual framework of those issues and big pictures of some ongoing projects to try to enhance it. © 2014 SICE.
Farnocchia D.,Jet Propulsion Laboratory |
Chesley S.R.,Jet Propulsion Laboratory |
Micheli M.,Coordination Center |
Micheli M.,SpaceDyS srl |
Micheli M.,National institute for astrophysics
Icarus | Year: 2015
We describe systematic ranging, an orbit determination technique suitable to assess the near-term Earth impact hazard posed by newly discovered asteroids. For these late warning cases, the time interval covered by the observations is generally short, perhaps a few hours or even less, which leads to severe degeneracies in the orbit estimation process. The systematic ranging approach gets around these degeneracies by performing a raster scan in the poorly-constrained space of topocentric range and range rate, while the plane of sky position and motion are directly tied to the recorded observations. This scan allows us to identify regions corresponding to collision solutions, as well as potential impact times and locations. From the probability distribution of the observation errors, we obtain a probability distribution in the orbital space and then estimate the probability of an Earth impact. We show how this technique is effective for a number of examples, including 2008 TC3 and 2014 AA, the only two asteroids to date discovered prior to impact. © 2015 Elsevier Inc.
The objects orbits Earth with a period of about three weeks. Because it was also observed twice in 2013 by the same survey team, astronomers have the data they need to model its orbit and trajectory, and as far anyone can tell, it's likely man-made. Solar radiation pressure, the physical "push" exerted by photons of sunlight, is proportional to a space object's area-to-mass ratio. Small, lightweight objects get pushed around more easily than heavier, denser ones. Taking that factor into account in examining WT1190F's motion over two years, the survey team has indirectly measured WT1190F's density at about 10% that of water. This is too low to be a typical asteroid made of rock, but a good fit with a hollow shell, possibly the upper stage of a rocket. It's also quite small, at most only about six feet or a couple of meters in diameter. Most or all of it is likely to burn up upon re-entry, creating a spectacular show for anyone near the scene. During the next week and a half, the European Space Agency's NEO (Near-Earth Object) Coordination Center is organizing observing campaigns to collect as much data as possible on the object, according to a posting on their website. The agency has two goals: to better understand satellite re-entries from high orbits and to use the opportunity to test our readiness for a possible future event involving a real asteroid. The latter happened once before when 2008 TC3 (a real asteroid) was spotted on October 6, 2008 and predicted to strike Earth the very next day. Incredibly, it did and peppered the Sudan with meteorites that were later recovered. Assuming WT1190F is artificial, its trans-lunar orbit (orbit that carries it beyond the Moon) hints at several possibilities. Third stages from the Saturn-V rockets that launched the Apollo missions to the Moon are still out there. It could also be a stage from one of the old Russian or more recent Chinese lunar missions. Even rockets used to give interplanetary probes a final push are game. Case in point. What was thought initially to be a new asteroid discovered by amateur astronomer Bill Yeung on September 3, 2002 proved a much better fit with an Apollo 12 S-IVB (third) stage after University of Arizona astronomers found that spectra taken of the object strongly correlated with absorption features seen in a combination of man-made materials including white paint, black paint, and aluminum, all consistent with Saturn V rockets. Apollo 13's booster was the first deliberately crashed into the Moon, where it blew out it a crisp, 98-foot-wide (30-meter) crater. Why do such a crazy thing? What better way to test the seismometers left by the Apollo 12 crew? All subsequent boosters ended their lives similarly in the name of seismography. Third stages from earlier missions—Apollos 8, 10 and 11— entered orbit around the Sun, while Apollo 12, which orbiting Earth, briefly masqueraded as asteroid J002E3. Bill Gray at Project Pluto has a page up about the November 13 impact of WT1190F with more information. Satellite and asteroid watchers are hoping to track the object before and right up until it burns up in the atmosphere. Currently, it's extremely faint and moving eastward in Orion. You can click here for an ephemeris giving its position at the JPL Horizons site. How exciting if we could see whatever's coming down before its demise on Friday the 13th! Near-Earth object J002E3 discovery images taken by Bill Yeung on September 3, 2002. The 16th magnitude object was tentatively identified as the Apollo 12 third stage rocket. Credit: Bob Denny. On April 14th 1970, the Apollo 13 Saturn IVB upper stage impacted the moon north of Mare Cognitum. The impact crater, which is roughly 30 meters in diameter, is clearly visible in this photo taken by the Lunar Reconnaissance Orbiter. Credit: NASA/Goddard/Arizona State University The nominal impact point is located about 60 miles south of the island nation Sri Lanka. Given the object’s small size and mass, it will likely be completely incinerated during re-entry. Credit: Bill Gray at Project Pluto