Approximate Pure Nash Equilibria in Weighted Congestion Games

We study the existence of approximate pure Nash equilibria in weighted congestion games and develop techniques to obtain approximate potential functions that prove the existence of alpha-approximate pure Nash equilibria and the convergence of alpha-improvement steps. Specifically, we show how to obtain upper bounds for approximation factor alpha for a given class of cost functions. For example for concave cost functions the factor is at most 3/2, for quadratic cost functions it is at most 4/3, and for polynomial cost functions of maximal degree d it is at at most d + 1. For games with two players we obtain tight bounds which are as small as for example 1.054 in the case of quadratic cost functions

Power estimation of an ECDSA core applied in V2X scenarios using heterogeneous distributed simulation

Embedded systems are steadily growing in complexity and nowadays power consumption additionally plays an important role. Designing and exploring such systems embedded in its environment demand for holistic and efficient simulations. In this work we use a simulation framework based on the HLA (High-Level Architecture) and the modeling tool Ptolemy II to enable complex heterogeneous distributed simulations of embedded systems. In this context, we introduce a co-simulation based power estimation approach by integrating domain-specific simulators as well as off-the-shelf HDL simulator and synthesis tools. This enables cross-domain interaction and generation of realistic on-the-fly stimuli data for Register Transfer Level and Gate Level models as well as the gathering of power estimation data. We apply the framework to a Vehicle-2-X scenario evaluating an ECDSA signature processing core which ensures trustworthiness in vehicular wireless networks. To evaluate dynamic power reduction possibilities on application level we additionally introduce a V2X Message Evaluation technique to reduce signature verification efforts. It shows how realistic on-the-fly stimuli data obtained by the framework can improve the exploration and estimation of dynamic power consumption

Hiring Secretaries over Time: The Benefit of Concurrent Employment

We consider a stochastic online problem where n applicants arrive over time, one per time step. Upon the arrival of each applicant, their cost per time step is revealed, and we have to fix the duration of employment, starting immediately. This decision is irrevocable; that is, we can neither extend a contract nor dismiss a candidate once hired. In every time step, at least one candidate needs to be under contract, and our goal is to minimize the total hiring cost, which is the sum of the applicants’ costs multiplied with their respective employment durations. We provide a competitive online algorithm for the case that the applicants’ costs are drawn independently from a known distribution. Specifically, the algorithm achieves a competitive ratio of 2.965 for the case of uniform distributions. For this case, we give an analytical lower bound of 2 and a computational lower bound of 2.148. We then adapt our algorithm to stay competitive even in settings with one or more of the following restrictions: (i) at most two applicants can be hired concurrently; (ii) the distribution of the applicants’ costs is unknown; (iii) the total number n of time steps is unknown. On the other hand, we show that concurrent employment is a necessary feature of competitive algorithms by proving that no algorithm has a competitive ratio better than Ω(n−−√/log  n) if concurrent employment is forbidden

A V2X Message Evaluation Methodology and Cross-Domain Modelling of Safety Applications in V2X-enabled E/E-Architectures

The introduction of Vehicular Ad-Hoc Networks (VANETs) enables great potential for improving road trafic ow and especially active safety applications such as cooperative adaptive cruise control (CACC). Such applications not only rely on continuous broadcast of vehicle state information (beacons) of all vehicles, but also have strict real-time requirements. Regarding automotive E/E architectures this continuous broadcasting adds heavy internal E/E data trafic that needs to be processed in real-time by Electronic Control Units (ECUs). In this work we address this issue by proposing a novel cluster-based message evaluation methodology to significantly reduce internal E/E network trafic by discarding irrelevant messages. The approach is only depending on information received over beacons. It combines a vehicle clustering strategy as well as network and vehicle state monitoring capabilities in order to correctly evaluate messages under real-time constraints. The proposed methodology is modeled inside an abstract ECU. It is evaluated by simulating a model-based CACC application under different trafic scenarios. It is shown that a significant reduction of messages is achievable, while still guaranteeing accident-free behavior of CACC

Challenges in supporting lay carers of patients at the end of life: results from focus group discussions with primary healthcare providers

Background: Family caregivers (FCGs) of patients at the end of life (EoL) cared for at home receive support from professional and non-professional care providers. Healthcare providers in general practice play an important role as they coordinate care and establish contacts between the parties concerned. To identify potential intervention targets, this study deals with the challenges healthcare providers in general practice face in EoL care situations including patients, caregivers and networks. Methods: Focus group discussions with general practice teams in Germany were conducted to identify barriers to and enablers of an optimal support for family caregivers. Focus group discussions were analysed using content analysis. Results: Nineteen providers from 11 general practices took part in 4 focus group discussions. Participants identified challenges in communication with patients, caregivers and within the professional network. Communication with patients and caregivers focused on non-verbal messages, communicating at an appropriate time and perceiving patient and caregiver as a unit of care. Practice teams perceive themselves as an important part of the healthcare network, but also report difficulties in communication and cooperation with other healthcare providers. Conclusion: Healthcare providers in general practice identified relational challenges in daily primary palliative care with potential implications for EoL care. Communication and collaboration with patients, caregivers and among healthcare providers give opportunities for improving palliative care with a focus on the patient-caregiver dyad. It is insufficient to demand a (professional) support network; existing structures need to be recognized and included into the care

Computing pure Nash and strong equilibria in bottleneck congestion games

Bottleneck congestion games properly model the properties of many real-world network routing applications. They are known to possess strong equilibria—a strengthening of Nash equilibrium to resilience against coalitional deviations. In this paper, we study the computational complexity of pure Nash and strong equilibria in these games. We provide a generic centralized algorithm to compute strong equilibria, which has polynomial running time for many interesting classes of games such as, e.g., matroid or single-commodity bottleneck congestion games. In addition, we examine the more demanding goal to reach equilibria in polynomial time using natural improvement dynamics. Using unilateral improvement dynamics in matroid games pure Nash equilibria can be reached efficiently. In contrast, computing even a single coalitional improvement move in matroid and single-commodity games is strongly NP-hard. In addition, we establish a variety of hardness results and lower bounds regarding the duration of unilateral and coalitional improvement dynamics. They continue to hold even for convergence to approximate equilibria

A Security Scheme for Dependable Key Insertion in Mobile Embedded Devices

Public Key Cryptography enables entity authentication protocols based on a platform's knowledge of other platforms' public key. This is particularly advantageous for embedded systems, such as FPGA platforms, with limited or none read-protected memory resources. For access control systems, an access token is authenticated by the mobile system. Only the public key of authorized tokens needs to be stored inside the mobile platform. At some point during the platform's lifetime, these might need to be updated in the field due to loss or damage of tokens. This paper proposes a holistic approach for an automotive access control system based on Public Key Cryptography. Next to a FPGA-based hardware architecture, we focus on a secure scheme for key flashing of public keys to highly mobile systems. The main goal of the proposed scheme is the minimization of online dependencies to Trusted Third Parties, Certification Authorities, or the like, to enable key flashing in remote locations with only minor technical infrastructure. Introducing trusted mediator devices, new tokens can be authorized and later their public key can be flashed into a mobile system on demand