24 research outputs found
Energy-efficient and delay-aware offloading scheme using D2D-enabled mobile edge computing / Ramtin Ranji
Get PDFEnergy efficient operation of mobile/Internet of Things (IoT) devices is a major challenge due to the limited capacity of their batteries. Also, because of their limited processing power, many of them cannot perform computationally intensive applications like face recognition in a timely manner. Device to Device (D2D) communication and Mobile Edge Computing (MEC) are two technologies to mitigate these limitations by offloading the computationally intensive tasks. With D2D, mobile/IoT devices can cooperate directly without the intervention of the Base Station. MEC provides computing services at the edge of network, that is close to the user. Most of the current studies on the energy efficient offloading, put the focus either on the offloading to the edge server, or to a device in the proximity. The problem of MEC solution is scalability, because, edge servers would be overloaded in dense networks. On the other hand, to find a proper offloading destination in D2D networks, devices must consume excessive amount of energy. Recently, a few numbers of integrated schemes were proposed to mitigate those problems. However, there is lack of study to propose both MEC and D2D, as the target of offloading tasks for execution while considering the energy required for offloading and its delay. In this work, we study Energy-Efficient and Delay-aware Offloading Scheme (EEDOS). In the proposed scheme, energy constraint devices and those with low computational power, have two options to offload their work. They can either use MEC, or D2D, and the computational power of the edge server is leveraged to find a proper candidate. For EEDOS network topology, we integrate D2D communication capability in the user layer of mobile networks, so that, mobile users can communicate with MEC layer. The research problem is formulated with consideration of the required energy for task offloading and completing the task execution, under the required deadline. The EEDOS, MEC and D2D offloading schemes have been simulated to evaluate the proposed scheme and to validate the findings with the existing schemes. The numerical results showed that EEDOS was capable to save the energy of mobile devices up to 95 % in comparison to local task execution, as well as reducing the execution delay. The proposed EEDOS, outperformed the existing schemes in terms of task offloading energy consumption and execution delay. This is due to the integration of the computational capability of MEC and idle devices in the network. The resource-limited mobile devices can save more energy, because, the proposed EEDOS, used edge servers to find the proper offloading destination and took into account the high computational power of edge servers and computational resources of large number of idle devices in the network. In this scheme, the load on the edge server was decreased dramatically in comparison to current MEC offloading schemes, because of participating idle devices in the network through D2D communication
Negotiation of unlicensed spectral resources by independent wireless network operators
Get PDFThe broadcast nature of wireless communication makes it prone to signal interference, particularly in the license-exempt part of the radio spectrum. This unlicensed spectrum is free to use with only the maximum transmit power and a few other parameters being regulated. Billions of devices operate in these frequency bands worldwide today, often in close range from each other, causing performance degradation and security concerns. Particularly in urban environments, many Independent Wireless network Operators (IWOs) vie for scarce spectral resources. One set of solutions encompasses collaboration between IWOs preceded by negotiation. The primary aim of this research is to gain understanding on how IWOs can practically negotiate and share unlicensed spectral resources in an automated manner.
The first challenge in this research is to understand what exactly is the utility that operators can negotiate on. By surveying 68 researchers, we showed that throughput and Signal-to-Interference-plus-Noise Ratio (SINR) are the two most likely candidates, with a preference for throughput. We also concluded that utility is unlikely to be homogeneous among IWOs. The second challenge is therefore to understand how a system with heterogeneous utility demands can be best modelled. For this, we investigated a use case where some or all IWOs demand Physical Layer Security (PLS) in addition to SINR. We modelled this problem as a non-cooperative game with secrecy capacity as its utility function.
By numerical analysis of the model, we evidenced that varying the transmission power is the only strategy the IWOs can apply to optimise SINR under the condition of perfect secrecy. To investigate how the model could optimise secure throughput instead of SINR, we applied a discreet event simulator emulating a real-world environment. The results indicate that IWOs can indeed practically collaborate to achieve secret wireless communications and optimise throughput using today’s equipment.
By defining a multi-dimensional utility function, we then designed a Software-Defined Wireless Network for automated negotiation and collaboration, where multiple agents are tasked with the negotiation on behalf of users. By handing over the decision-making process to the IWOs, we guaranteed the agents' engagement in the process, solving the problem that collaboration cannot be forced upon actors in unlicensed spectrum. We validated our approach by measurements in a simplified implementation based on Wi-Fi
How to define utility for use in practical wireless network resource trading platforms
No full textExcessive usage of wirelessly networked equipment in densely populated areas increasingly leads to performance degradation due to interference and traffic congestion. This is particularly the case in unmanaged environments such as unlicensed frequency bands. One solution is to enable and automate constructive collaboration between the actors, leading to spectrum sharing based on trading and consensus. Various methods, including game theory, can be used to understand how actors interact and make decisions on how to obtain the highest possible utility. In this paper we address the question how to define the utility to be negotiated by these actors. A bottom-up approach of this issue is a hard, joint engineering, regulatory, social, and economic problem. Instead, we present the outcome of a survey study of 68 wireless communications and networking experts whom we asked about their opinion on the matter. The experts quite strongly agree that most interference mitigation research still needs to be focused on the 2.4 GHz unlicensed band and IEEE 802.11b/g technology. They thus acknowledge that 2.4 GHz will remain the preferred band of communication for unmanaged wireless communication, and that many more modern versions of IEEE 802.11 will fall back to b/g when the conditions for communication get tough. Throughput is the most important utility to be negotiated, recognizing that to increase the actors' satisfaction effectively, physical-layer parameters are not the only factors to be considered in the utility function.</p
A methodological study of environmental simulation in architecture and engineering. Integrating daylight and thermal performance across the urban and building scales
No full textThis study presents a methodological and conceptual framework that allows for the integration and creation of knowledge across professional borders in the field of environmental simulation. The framework has been developed on the basis of interviews with leading international practitioners, key theories of environmental performance in architecture and engineering, and a range of simulation experiments by the authors. The framework is an open structure, which can continuously be renewed and contributed to by any author. The value of the framework is demonstrated, using it to map a series of simulation studies, emphazising the multidimensionality of environmental performance optimization. Clarifying the conceptual interconnectivity between architecture and engineering, - agency and physics, - not only enhances communicative power and the dissemination of knowledge, but becomes instrumental in pointing out the need for improving metrics, software and not least the performance of the built environment itself
Supporting Exploration of Design Alternatives using Multivariate Analysis Algorithms
No full textParametric modelling allows quick generation of a large number of design alternatives. Ultimately, it can be combined with optimization algorithms for obtaining optimal performance-driven design. However, setup of design space for optimization is a very complex task requiring designer’s a priori knowledge and experience. Therefore, this paper focuses on the process that happens before the optimization. It proposes to use multivariate analysis algorithms for exploring and understanding the relations between various design parameters, after sampling the design space. Additionally, portrayal of geometry isintroduced as an extension of conventional visualization methods, which accounts for evaluation of ill-defined design criteria by using designer’s expertise. The proposed method is computationally efficient and integrated into an environment familiar to architects. It relies on multivariate analysis algorithms together with database querying capabilities and an interactive dashboard developed for geometry portrayal.Design Informatic
A Sound Working Environment: Optimizing the Acoustic Properties of Open Plan Workspaces Using Parametric Models
No full textOptimizing the acoustic environment of open plan offices is a complex task due to the large number of design parameters that must be considered. In current practice, acoustic analysis – even in a simplified form – is not naturally integrated into the design process of office spaces. Applying digital acoustic simulation in architectural design currently requires a time consuming back-and-forth transition between geometric modelling programs and specialist analysis software. In this study, an acoustic ray tracer was developed within Grasshopper and coupled to Galapagos in order to optimize the acoustics of an open office space. This tool has been tested and validated through a case study performed on an existing office space in the Netherlands. This study demonstrates the possibility to computationally optimize open plan workspaces by way of acoustic analysis performed on a parametric model. In itscurrent form the presented model is still limited in its features and calculation speed. Hence, further development of the tool is needed in order to facilitate a truly seamless iteration and hands-on evaluation of different design configurations (with respect to room acoustic performance).Design InformaticsTeachers of PracticeBuilding Physic
Application of Surrogate Models for Building Envelope Design Exploration and Optimization
No full textBuilding performance simulations are usually timeconsuming. They may account for the major portion of time spent in Computational Design Optimization (CDO), for instance, annual hourly daylight and energy simulations. In this case, the optimization may become less efficient or even infeasible within a limited time frame of real-world projects, due to the computationally expensive simulations. To handle the problem, this research aims to investigate the potentials of surrogate models (i.e. Response SurfaceMethodology - RSM) to be used in the building envelope design exploration and optimization that consider visual and energy performance. Specifically, the work investigates how, and to what extent, 1) problem scales may affect the application of RSM, and 2) different ways of using RSM may affect the quality of Pareto Front approximations. Thus, a series of multi-objective optimization tests are carried out; preliminary discussion is made based on the current results.Design Informatic
Spectral Modelling for Spatial Network Analysis
No full textSpatial Networks represent the connectivity structure between units of space as a weighted graph whose links are weighted as to the strength of connections. In case of urban spatial networks, the units of space correspond closely to streets and in architectural spatial networks the units correspond to rooms, convex spaces or star-convex spaces. Once represented as a graph, a spatial network can be analysed using graph theory and spectral graph theory. We present four steps of modelling a spectrum for an urban spatial network; present an implementation of a state-ofthe-art spectral graph-drawing algorithm and showcase a Spatial Eigenvector Centrality index, which is based on a novel definition of spatial networks based on Fuzzy Closeness indicators computed using Easiest Path distances.Design InformaticsOLD Urban Design100% Researc
Simulating natural ventilation in large sports buildings: Prediction of temperature and airflow patterns in the early design stages
No full textIn large sport’s buildings, a big part of energy can be saved by providing natural instead of mechanical ventilation. However, additional challenges arise while controlling airflow and temperatures in different zones. These measureshighly depend on the shape, construction and ventilation openings, which are mostly decided in the early design stages. Computational optimization can support these early stages of design, but needs to be performed in efficient ways. In this respect, the project proposes rapid assessment of temperature and airflow patterns using customized Grasshopper components, which would be able to evaluate a given model using CONTAM and EnergyPlus software assimulation engine. The proposed method integrates these simulations within an environment, which is familiar to architects and is largely used for parameterization of design in its early stages. A case study (Jiangmen Sports Center, Jiangmen, China) is used to test the developed process for a large indoor sports hall.Design Informatic
Optimizing wireless network throughput under the condition of Physical Layer Security using Software-Defined Networking enabled collaboration
No full textWe investigated if independent wireless operators can effectively collaborate using Software-Defined Wireless Networking (SDWN) to achieve secret wireless communications and optimize useful throughput under the condition of Physical-Layer Security enabled secrecy in heavily contended spectrum. We studied this on the level of useful throughput, in addition to Signal-to-Interference-plus-Noise Ratio. The investigation was carried out by means of a series of discrete event simulations of a realistic Wi-Fi network deployment. We found that the difference between the user throughputs of the legitimate station and the eavesdropper could be a reasonably good proxy for secrecy capacity and conclude that SDWN controllers should ideally optimize the network based on empirical feedback from the system and active learning mechanisms, rather than on hard-programmed pre-calculated network models.</p
