Аналитическая модель многошаговой передачи неординарного потока в беспроводных сетях с резервированиями канала
Для передачи по mesh-сети потоковых данных, предъявляющих высокие требования к качеству обслуживания, удобно использовать описанный в стандарте IEEE 802.11s механизм MCCA детерминированного доступа к среде. При использовании этого механизма станции резервируют для своих передач определенные периодически повторяющиеся интервалы времени, тем самым получая бесконкурентный доступ к каналу связи. Однако, чтобы обеспечить успешную доставку данных в условиях помех, необходимо устанавливать дополнительные резервирования под повторные попытки передачи. В работе построена аналитическая модель процесса передачи неординарного потока по многошаговым беспроводным сетям с помощью механизма MCCA. Модель позволяет определить наибольший период резервирований, при котором выполнены требования на время доставки и долю потерянных пакетов.
To improve the reliability of data delivery, in Wi-Fi networks stations can reserve for their transmissions periodic time intervals of the same duration in which they are allowed to transmit, while adjacent stations do not have that right. Here there arises the problem of choosing the parameters of reserved intervals that would ensure quality of service requirements for transmitted data in the smallest possible amount of reserved channel time. We consider the data transmission process in periodic intervals with the block acknowledgement policy that lets us reduce the costs by acknowledgement the set of packets with a single service message. We propose a method for mathematical modeling of such a transmission.
Ubiquitous densification of wireless networks has brought up the issue of inter- and intra-cell interference. Interference significantly degrades network throughput and leads to unfair channel resource usage, especially in Wi-Fi networks, where even a low interfering signal from a hidden station may cause collisions or block channel access as it is based on carrier sensing. In the paper, we propose a joint power control and channel time scheduling algorithm for such networks, which significantly increases overall network throughput while maintaining fairness. The algorithm is based on branch-and-bound global optimization technique and guarantees that the solution is optimal with user-defined accuracy.
Proceedings of 16th International Conference on Next Generation Wired/Wireless Advanced Networking
Proceedings of International Wireless Communications and Mobile Computing Conference (IWCMC) 2016
Proceedings of Wireless Communications and Networking Conference (WCNC) 2016
While celebrating the 21st year since the very first IEEE 802.11 “legacy” 2 Mbit/s wireless Local Area Network standard, the latest Wi-Fi newborn is today reaching the finish line, topping the remarkable speed of 10 Gbit/s. IEEE 802.11ax was launched in May 2014 with the goal of enhancing throughputper-area in high-density scenarios. The first 802.11ax draft versions, namely D1.0 and D2.0, were released at the end of 2016 and 2017. Focusing on a more mature version D3.0, in this tutorial paper, we help the reader to smoothly enter into the several major 802.11ax breakthroughs, including a brand new OFDMAbased random access approach as well as novel spatial frequency reuse techniques. In addition, this tutorial will highlight selected significant improvements (including PHY enhancements, MUMIMO extensions, power saving advances, and so on) which make this standard a very significant step forward with respect to its predecessor 802.11ac
To avoid collisions in Wi-Fi networks, access points (APs) - acting as coordinators - got the ability to use centralized contention-free channel access, e.g. HCCA, which supports parameterized QoS. However, the growth of WLANs population raises a problem of coordination between APs. As a solution to this problem, IEEE 802.11aa introduces the HCCA TXOP Negotiation mechanism, which allows APs to agree in advance on periodic time intervals used by each AP for contentionfree channel access. The paper studies the efficiency of such a mechanism, focusing on developing a model, which allows selecting appropriate reservation parameters to minimize channel resource consumption while transmitting several flows with given QoS requirements.
In Wi-Fi networks, preliminary channel reservation protects transmissions in reserved time intervals from collisions with neighboring stations. However, making changes in established reservations takes long time spent on negotiating changes with neighboring stations and dissemination of information about these changes. This complicates serving of Variable Bit Rate (VBR) flows which intensity varies with time, what leaves no choice but to reserve some additional time for handling data bursts and packet retransmissions (caused by random noise and interference from remote stations). In the paper, we consider a more flexible approach when bursts and retransmissions are handled by some random access method while a constant part of an input flow is served in preliminarily reserved intervals. We build a mathematical model of a VBR flow transmission process with this heterogeneous access method and use the model to find transmission parameters which guarantee that Quality of Service requirements of the flow are satisfied at the minimal amount of used channel time.
A model for organizing cargo transportation between two node stations connected by a railway line which contains a certain number of intermediate stations is considered. The movement of cargo is in one direction. Such a situation may occur, for example, if one of the node stations is located in a region which produce raw material for manufacturing industry located in another region, and there is another node station. The organization of freight traﬃc is performed by means of a number of technologies. These technologies determine the rules for taking on cargo at the initial node station, the rules of interaction between neighboring stations, as well as the rule of distribution of cargo to the ﬁnal node stations. The process of cargo transportation is followed by the set rule of control. For such a model, one must determine possible modes of cargo transportation and describe their properties. This model is described by a ﬁnite-dimensional system of diﬀerential equations with nonlocal linear restrictions. The class of the solution satisfying nonlocal linear restrictions is extremely narrow. It results in the need for the “correct” extension of solutions of a system of diﬀerential equations to a class of quasi-solutions having the distinctive feature of gaps in a countable number of points. It was possible numerically using the Runge–Kutta method of the fourth order to build these quasi-solutions and determine their rate of growth. Let us note that in the technical plan the main complexity consisted in obtaining quasi-solutions satisfying the nonlocal linear restrictions. Furthermore, we investigated the dependence of quasi-solutions and, in particular, sizes of gaps (jumps) of solutions on a number of parameters of the model characterizing a rule of control, technologies for transportation of cargo and intensity of giving of cargo on a node station.
Event logs collected by modern information and technical systems usually contain enough data for automated process models discovery. A variety of algorithms was developed for process models discovery, conformance checking, log to model alignment, comparison of process models, etc., nevertheless a quick analysis of ad-hoc selected parts of a journal still have not get a full-fledged implementation. This paper describes an ROLAP-based method of multidimensional event logs storage for process mining. The result of the analysis of the journal is visualized as directed graph representing the union of all possible event sequences, ranked by their occurrence probability. Our implementation allows the analyst to discover process models for sublogs defined by ad-hoc selection of criteria and value of occurrence probability
The geographic information system (GIS) is based on the first and only Russian Imperial Census of 1897 and the First All-Union Census of the Soviet Union of 1926. The GIS features vector data (shapefiles) of allprovinces of the two states. For the 1897 census, there is information about linguistic, religious, and social estate groups. The part based on the 1926 census features nationality. Both shapefiles include information on gender, rural and urban population. The GIS allows for producing any necessary maps for individual studies of the period which require the administrative boundaries and demographic information.
Existing approaches suggest that IT strategy should be a reflection of business strategy. However, actually organisations do not often follow business strategy even if it is formally declared. In these conditions, IT strategy can be viewed not as a plan, but as an organisational shared view on the role of information systems. This approach generally reflects only a top-down perspective of IT strategy. So, it can be supplemented by a strategic behaviour pattern (i.e., more or less standard response to a changes that is formed as result of previous experience) to implement bottom-up approach. Two components that can help to establish effective reaction regarding new initiatives in IT are proposed here: model of IT-related decision making, and efficiency measurement metric to estimate maturity of business processes and appropriate IT. Usage of proposed tools is demonstrated in practical cases.
This proceedings publication is a compilation of selected contributions from the “Third International Conference on the Dynamics of Information Systems” which took place at the University of Florida, Gainesville, February 16–18, 2011. The purpose of this conference was to bring together scientists and engineers from industry, government, and academia in order to exchange new discoveries and results in a broad range of topics relevant to the theory and practice of dynamics of information systems. Dynamics of Information Systems: Mathematical Foundation presents state-of-the art research and is intended for graduate students and researchers interested in some of the most recent discoveries in information theory and dynamical systems. Scientists in other disciplines may also benefit from the applications of new developments to their own area of study.
A form for an unbiased estimate of the coefficient of determination of a linear regression model is obtained. It is calculated by using a sample from a multivariate normal distribution. This estimate is proposed as an alternative criterion for a choice of regression factors.