9,087 research outputs found
Optimizing Average-Maximum TTR Trade-off for Cognitive Radio Rendezvous
In cognitive radio (CR) networks, "TTR", a.k.a. time-to-rendezvous, is one of
the most important metrics for evaluating the performance of a channel hopping
(CH) rendezvous protocol, and it characterizes the rendezvous delay when two
CRs perform channel hopping. There exists a trade-off of optimizing the average
or maximum TTR in the CH rendezvous protocol design. On one hand, the random CH
protocol leads to the best "average" TTR without ensuring a finite "maximum"
TTR (two CRs may never rendezvous in the worst case), or a high rendezvous
diversity (multiple rendezvous channels). On the other hand, many
sequence-based CH protocols ensure a finite maximum TTR (upper bound of TTR)
and a high rendezvous diversity, while they inevitably yield a larger average
TTR. In this paper, we strike a balance in the average-maximum TTR trade-off
for CR rendezvous by leveraging the advantages of both random and
sequence-based CH protocols. Inspired by the neighbor discovery problem, we
establish a design framework of creating a wake-up schedule whereby every CR
follows the sequence-based (or random) CH protocol in the awake (or asleep)
mode. Analytical and simulation results show that the hybrid CH protocols under
this framework are able to achieve a greatly improved average TTR as well as a
low upper-bound of TTR, without sacrificing the rendezvous diversity.Comment: Accepted by IEEE International Conference on Communications (ICC
2015, http://icc2015.ieee-icc.org/
On Heterogeneous Neighbor Discovery in Wireless Sensor Networks
Neighbor discovery plays a crucial role in the formation of wireless sensor
networks and mobile networks where the power of sensors (or mobile devices) is
constrained. Due to the difficulty of clock synchronization, many asynchronous
protocols based on wake-up scheduling have been developed over the years in
order to enable timely neighbor discovery between neighboring sensors while
saving energy. However, existing protocols are not fine-grained enough to
support all heterogeneous battery duty cycles, which can lead to a more rapid
deterioration of long-term battery health for those without support. Existing
research can be broadly divided into two categories according to their
neighbor-discovery techniques---the quorum based protocols and the co-primality
based protocols.In this paper, we propose two neighbor discovery protocols,
called Hedis and Todis, that optimize the duty cycle granularity of quorum and
co-primality based protocols respectively, by enabling the finest-grained
control of heterogeneous duty cycles. We compare the two optimal protocols via
analytical and simulation results, which show that although the optimal
co-primality based protocol (Todis) is simpler in its design, the optimal
quorum based protocol (Hedis) has a better performance since it has a lower
relative error rate and smaller discovery delay, while still allowing the
sensor nodes to wake up at a more infrequent rate.Comment: Accepted by IEEE INFOCOM 201
(Methanol-κO)(methanolato-κO)oxido[N-(2-oxidobenzylidene)phenylalaninato-κ3 O,N,O′]vanadium(V)
In the title complex, [V(C16H13NO3)(CH3O)O(CH3OH)], the VV atom is six-coordinated by a tridentate ligand derived from the condensation of salicylaldehyde and l-phenylalanine, a vanadyl O atom, a methanolate O atom and a methanol O atom, forming a distorted octahedral coordination geometry. In the crystal, intermolecular O—H⋯O and C—H⋯O hydrogen bonds result in a two-dimensional structure parallel to (001)
The z < 1.2 optical luminosity function from a sample of ∼410,000 galaxies in Boötes
Using a sample of ~410,000 galaxies to a depth of IAB=24 over 8.26 deg2 in the Boötes field (~10 times larger than the z~1 luminosity function (LF) studies in the prior literature), we have accurately measured the evolving B-band LF of red galaxies at z<1.2 and blue galaxies at z<1.0 In addition to the large sample size, we utilize photometry that accounts for the varying angular sizes of galaxies, photometric redshifts verified with spectroscopy, and absolute magnitudes that should have very small random and systematic errors. Our results are consistent with the migration of galaxies from the blue cloud to the red sequence as they cease to form stars and with downsizing in which more massive and luminous blue galaxies cease star formation earlier than fainter less massive ones. Comparing the observed fading of red galaxies with that expected from passive evolution alone, we find that the stellar mass contained within the red galaxy population has increased by a factor of ~3.6 from z~1.1 to z~0.1 The bright end of the red galaxy LF fades with decreasing redshift, with the rate of fading increasing from ~0.2 mag per unit redshift at z = 1.0 to ~0.8 at z = 0.2. The overall decrease in luminosity implies that the stellar mass in individual highly luminous red galaxies increased by a factor of ~2.2 from z = 1.1 to z = 0.1
The ISM Analysis on Influence Factors of Cost Control in the Wind Power Construction Project
AbstractCost control in the wind power construction project is essential under the trend of developing wind power in China. In order to carry out cost control effectively, structural interpretation model(ISM) is used to identify and analyze the major factors that affect the implementation of cost control and the hierarchy relationships between each other. In this way, the surface causes, the middle causes and the underlying causes that affect the cost control in the wind power construction project have been found, which provides decision theory for the smooth implementation of cost control in China's current wind power construction projects
- …