15,115 research outputs found
On the Throughput-Delay Trade-off in Georouting Networks
We study the scaling properties of a georouting scheme in a wireless
multi-hop network of mobile nodes. Our aim is to increase the network
capacity quasi linearly with while keeping the average delay bounded. In
our model, mobile nodes move according to an i.i.d. random walk with velocity
and transmit packets to randomly chosen destinations. The average packet
delivery delay of our scheme is of order and it achieves the network
capacity of order . This shows a practical
throughput-delay trade-off, in particular when compared with the seminal result
of Gupta and Kumar which shows network capacity of order and
negligible delay and the groundbreaking result of Grossglausser and Tse which
achieves network capacity of order but with an average delay of order
. We confirm the generality of our analytical results using
simulations under various interference models.Comment: This work has been submitted to IEEE INFOCOM 201
Quality assessment technique for ubiquitous software and middleware
The new paradigm of computing or information systems is ubiquitous computing systems. The technology-oriented issues of ubiquitous computing systems have made researchers pay much attention to the feasibility study of the technologies rather than building quality assurance indices or guidelines. In this context, measuring quality is the key to developing high-quality ubiquitous computing products. For this reason, various quality models have been defined, adopted and enhanced over the years, for example, the need for one recognised standard quality model (ISO/IEC 9126) is the result of a consensus for a software quality model on three levels: characteristics, sub-characteristics, and metrics. However, it is very much unlikely that this scheme will be directly applicable to ubiquitous computing environments which are considerably different to conventional software, trailing a big concern which is being given to reformulate existing methods, and especially to elaborate new assessment techniques for ubiquitous computing environments. This paper selects appropriate quality characteristics for the ubiquitous computing environment, which can be used as the quality target for both ubiquitous computing product evaluation processes ad development processes. Further, each of the quality characteristics has been expanded with evaluation questions and metrics, in some cases with measures. In addition, this quality model has been applied to the industrial setting of the ubiquitous computing environment. These have revealed that while the approach was sound, there are some parts to be more developed in the future
Issues in autonomous mobile sensor networks
Autonomous mobile sensor networks consist of a number of autonomous mobile
robots equipped with various sensors and tasked with a common mission. This thesis
considers the topology control of such an ad hoc mobile sensor network. In particular,
I studied the problem of controlling the size, with respect to a distance metric, of the network
for general interactive forcing among agents. Developed is a stability result, allowing
one to design force laws to control the spread of the network. Many of the current results
assume a known and/or fixed topology of the graph representing the communication between
the nodes, i.e. the graph laplacian is assumed constant. They also assume fixed and
known force-laws. Hence, the results are limited to time-invariant dynamics. The research
considers stability analysis of sensor networks, unconstrained by specific forcing functions
or algorithms, and communication topologies. Since the graph topologies are allowed to
change as the agents move about, the system dynamics become discontinuous in nature.
Filippovâs calculus of differential equations with discontinuous right hand sides is used to
formally characterize the multi-agent system with the above attributes. Lyapunovâs Stability
Theory, applied to discontinuous systems, is then used to derive bounds on the norm of
the system states given bounds on its initial states and input.
The above derived stability results lend themselves to the derivation of methods for the
design of algorithms or force-laws for mobile sensor networks. The efficacy of the derived
results is illustrated through several examples where it is shown how they may be used for synthesizing a topology managing strategy. Examples are given of designing force-laws
that limit the network in a desired area
The true cost of unusable password policies: password use in the wild
HCI research published 10 years ago pointed out that many users cannot cope with the number and complexity of passwords, and resort to insecure workarounds as a consequence. We present a study which re-examined password policies and password practice in the workplace today. 32 staff members in two organisations kept a password diary for 1 week, which produced a sample of 196 passwords. The diary was followed by an interview which covered details of each password, in its context of use. We find that users are in general concerned to maintain security, but that existing security policies are too inflexible to match their capabilities, and the tasks and contexts in which they operate. As a result, these password policies can place demands on users which impact negatively on their productivity and, ultimately, that of the organisation. We conclude that, rather than focussing password policies on maximizing password strength and enforcing frequency alone, policies should be designed using HCI principles to help the user to set an appropriately strong password in a specific context of use
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