Abstract-The Point Coordination Function (PCF) of the IEEE 802.11 standard represents a well-known Medium Access Control (MAC) protocol providing Quality-of Service guarantees in Wireless Local Area Networks (WLANs). However, with the currently employed polling mechanism WLANs consume a significant amount of the energy resources from batterypowered user devices. To provide energy saving, an improved MAC protocol is presented in this paper, where bidirectional transmissions of fixed duration are incorporated into PCF in order to enable dynamic scheduling of real-time traffic. Based on this new strategy, wireless access points (APs) can estimate the proper duration of the Contention Free Period (CFP), in order to allow mobile stations to acknowledge any received data packet with a data packet equal to the received packet in size. Having this information, a mobile station, following the data exchange with the AP, can determine its wake-up timer and activate the sleep mode for the rest of the CFP interval. Comprehensive computerbased simulations demonstrate the feasibility of the proposed MAC improvements to achieve energy efficiency with negligible impact on packet delivery delay.
The aim of the research is to identify and quantify the direct economic effects resulting from the improved seaport nautical access and capacity expansion. This case study considers a regional port located in the Baltic sea and relates to port users, i.e., shipping operators and shippers. The effects were identified for maritime transport by comparing transport performance in two scenarios: with-the-investment and without-the-investment. Incremental calculus addresses freights (containers, dry bulk, and cereals) traded to and from the given port, changes in size of vessels, and the shipping route alternatives vis-a-vis adjacent ports in the range. Sustainable impact concerns generalized maritime transport cost, i.e., shipping operating costs and port-to-port transit time, as well as energy consumption and external costs of maritime shipping. To capture effects, daily and unit dry bulk, as well as container shipping cost, values of time, and marginal external costs were revealed in freight sea transport. As investigated, shipping operators and shippers will benefit from the reduction in ships’ operating (including ships’ fuel cost savings) and time cost, while the community will enjoy the reduction in externalities. However, the main economic effect is the reduction in shipping operating cost resulting from the increased vessel size (economies of scale).
Deepening the fairway Świnoujście-Szczecin to a depth of 12.5 m will improve access to the port of Szczecin from the sea. Larger vessels will be able to call at the port of Szczecin and thus the current trends in cargo turnover will probably change. To make it possible, it is also necessary to invest in improving port access from the mainland. In the article the authors present estimates and forecasts of the annual average daily traffic of vehicles (AADT) on national road no. 10 (DK 10) and access roads to the port of Szczecin (so called the "last mile" sections). Estimation was based on the author's own traffic research carried out in September-October 2016 as part of Feasibility Study for the project Modernization of the access roads to the port of Szczecin: reconstruction of the transport system in the area of Międzyodrze implemented by the city of Szczecin.
Abstract:The aim of the paper is to present the socio-economic effects which will appear in relation with the realization of the large-scale investments consisting in (1) the deepening of the fairway Świnoujście-Szczecin down to 12.5 m and (2) the adjustment of the infrastructure in the port of Szczecin (deepening of the port water area and modernization and deepening of the selected berths) to handle larger seagoing vessels. Those are complementary projects and their combined realization will allow the handling of fully laden vessels with deadweight of 40 thou. tonnes (at present that is 15 thou. tonnes). The realization of the investment projects will contribute to the creation of the socio-economic benefits which will arise in: -the land section of the transportation chain running through the port of Szczecin; within the hinterland transport there will arise savings in the land transportation costs and in the external costs resulting from the shortening of transportation distance and changes in the sectoral structure of transports (modal shift); -the sea section of the transportation chain running through the port of Szczecin; within the sea transport there will arise savings in the sea transportation costs and in the external costs resulting from the shortening of transportation distance, and in the costs of exploitation of vessels resulting from the increase of their size (economies of seagoing vessel's size); -the port of Szczecin in the form of the increased gross value added (GVA) in the port activity, additionally created value of port services. The socio-economic analysis covered all planned complementary investments. The socio-economic effects have been identified with the use of the cost benefit analysis (CBA). 56Dariusz Bernacki, Christian Lis
The objective of this paper is to investigate the future evolution of port systems considering the development of major and minor ports, inter-port competition, and feasible cargo shifts resulting from improved capacity or congestion faced by ports. The literature review on port system dynamics indicates that the relationships that emerge between major and minor ports located in the range stem from competition and cooperation. However, we argue that there are essential ports that play a predominant role in shaping these relationships, while inter-port relations in the system are based on competition. With the use of transshipment forecasts, existing and emerging interdependencies among major and minor ports in the system, and capacity development and/or changes in the level of capacity utilisation, the ex-ante dynamics of the port system are evaluated. The subject of research is two port systems, namely, the Polish port system and the Rhine–Scheldt Delta port system. We investigate the future dynamics in each port system and find that the evolution pattern has different features if the minor ports improve capacity or challenge the major ports by offering free capacity. This paper contributes to research on the evolution of multi-port formations and provides new insights to the peripheral port challenge phenomenon.
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