Swedish Institute of Computer Science Publications Database
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On the uniqueness of operation days and delivery commitment generation for train timetables
No full textIn the 2014 finalised timetable for Sweden 314 operation days had a unique set of trains i.e. a unique traffic pattern. Despite this, the finalised timetable generally provides only one conflict resolved train path for each train, and this train path is to be used for all of the
train’s operation days. Further, once the yearly timetable has been finalised train paths may not be changed, causing great inflexibility in later planning stages.
Rather than finalizing entire train paths only certain characteristics of a train path, called delivery commitments, could be finalised. This allows for more flexibility in later planning stages. Delivery commitments could e.g. be arrival and departure times at important locations or the total running time, depending on the needs of the operator. In this paper we present a method for generating delivery commitments based on analyzing a yearlong timetable, called the control timetable. The control timetable is constructed using rolling horizon planning and a MIP-model that optimises the train paths for each day individually. Further, different train path characteristics are optimized for different operators.
The proposed method was tested in a case study from Sweden. The results show that by constructing one train path for each individual day rather than one for the entire year the
resulting delivery commitments allow for a more efficient use of infrastructure. The results also show that the proposed method allows for different train path characteristics to be optimised for different operators
High Assurance Security Products on COTS Platforms
No full textWith commodity operating systems failing to establish unbreakable isolation of processes, there is a need for stronger separation mechanisms. A recently launched open source project aims at applying virtualization to achieve such isolation on the widespread embedded ARM architectures. Strong assurance is established by formal verification and common criteria certification. Coexisting guest systems are able to run unmodified on the multicore platform, in a resource and cost efficient manner. The solution is rounded anchored in a secure boot process
Using finite transducers for describing and synthesising structural time-series constraints
No full textWe describe a large family of constraints for structural time series by means of function composition. These constraints are on aggregations of features of patterns that occur in a time series, such as the number of its peaks, or the range of its steepest ascent. The patterns and features are usually linked to physical properties of the time series generator, which are important to capture in a constraint model of the system, i.e. a conjunction of constraints that produces similar time series. We formalise the patterns using finite transducers, whose output alphabet corresponds to semantic values that precisely describe the steps for identifying the occurrences of a pattern. Based on that description, we automatically synthesise automata with accumulators, as well as constraint checkers. The description scheme not only unifies the structure of the existing 30 time-series constraints in the Global Constraint Catalogue, but also leads to over 600 new constraints, with more than 100,000 lines of synthesised code
Harnessing Variability in Product-lines of Self-adaptive Software Systems
No full textThis work studies systematic reuse in the context of self-adaptive software systems. In our work, we realized that managing variability for such platforms is different compared to traditional platforms, primarily due to the run-time variability and system uncertainties. Motivated by the fact that recent trends show that self-adaptation will be used more often in future system generation and that software reuse state-of-practice or research do not provide sufficient support, we have investigated the problems and possibly resolutions in this context. We have analyzed variability for these systems, using a systematic reuse prism, and identified a research gap in variability management. The analysis divides variability handling into four activities: (1) identify variability, (2) constrain variability, (3) implement variability, and (4) manage variability. Based on the findings we envision a reuse framework for the specific domain and present an example framework that addresses some of the identified challenges. We argue that it provides basic support for engineering self-adaptive software systems with systematic reuse. We discuss some important avenues of research for achieving the vision
IEEE 802.15.4 Channel Diversity in an Outdoor Environment
No full textLow-power wireless link quality is known to be frequency-
dependent because of multipath fading and other factors.
We present a performance study of IEEE 802.15.4 radio links
that quantifies and analyzes this frequency-specific performance in a clear-field outdoor environment. Using data from 16 channels on 240 links, we show that effect from channel selection on the average link is up to 4.89 dB, comparable with the effect from 38.7 C change in temperature. These results provide a performance baseline for other environments, as the diversity can be expected to further increase in environments with more obstacles and external interference