Performance model for two-tier mobile wireless networks with macrocells and small cells

[EN] A new analytical model is proposed to evaluate the performance of two-tier cellular networks composed of macrocells (MCs) and small cells (SCs), where terminals roam across the service area. Calls being serviced by MCs may retain their channel when entering a SC service area, if no free SC channels are available. Also, newly offered SC calls can overflow to the MC. However, in both situations channels may be repacked to vacate MC channels. The cardinality of the state space of the continuous-time Markov chain (CTMC) that models the system dynamics makes the exact system analysis unfeasible. We propose an approximation based on constructing an equivalent CTMC for which a product-form solution exist that can be obtained with very low computational complexity. We determine performance parameters such as the call blocking probabilities for the MC and SCs, the probability of forced termination, and the carried traffic. We validate the analytical model by simulation. Numerical results show that the proposed analytical model achieves very good precision in scenarios with diverse mobility rates and MCs and SCs loads, as well as when MCs overlay a large number of SCs.Authors would like to thank you the anonymous reviewers for the review comments provided to our work that have decisively contributed to improve the paper. Most of the contribution of V. Casares-Giner was done while visiting the Huazhong University of Science and Technolgy (HUST), Whuhan, China. This visit was supported by the European Commission, 7FP, S2EuNet project. The authors from the Universitat Politecnica de Valencia are partially supported by the Ministry of Economy and Competitiveness of Spain under grant TIN2013-47272-C2-1-R and TEC2015-71932-REDT. The research of Xiaohu Ge was supported by the National Natural Science Foundation of China (NSFC) grant 61210002, the Fundamental Research Funds for the Central Universities grant 2015XJGH011, and China International Joint Research Center of Green Communications and Networking grant 2015B01008.Casares-Giner, V.; Martínez Bauset, J.; Ge, X. (2018). Performance model for two-tier mobile wireless networks with macrocells and small cells. Wireless Networks. 24(4):1327-1342. https://doi.org/10.1007/s11276-016-1407-8S13271342244ABIresearch. (2016). In-building mobile data traffic forecast. ABIreseach, Technical Report.NGMN Alliance. (2015). Recommendations for small cell development and deployment. NGMN Alliance, Technical Report.Chandrasekhar, V., Andrews, J., & Gatherer, A. (2008). Femtocell networks: A survey. IEEE Communications Magazine, 46(9), 59–67.Yamamoto, T., & Konishi, S. (2013). Impact of small cell deployments on mobility performance in LTE-Advanced systems. 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Efficient admission control schemes in cellular IP networks

The rapid growth of real-time multimedia applications over IP (Internet Protocol) networks has made the Quality of Service (QoS) a critical issue. One important factor affecting the QoS in the overall IP networks is the admission control in the fast expanding wireless IP networks. Due to the limitations of wireless bandwidth, wireless IP networks (cellular IP networks in particular) are generally considered to be the bottlenecks of the global IP networks. Admission control is to maintain the QoS level for the services admitted. It determines whether to admit or reject a new call request in the mobile cell based on the availability of the bandwidth. In this thesis, the term “call” is for general IP services including voice calls (VoIP) and the term “wireless IP” is used interchangeably with “cellular IP”, which means “cellular or mobile networks supporting IP applications”. In the wireless IP networks, apart from new calls, there are handoff (handover) calls which are calls moving from one cell to another. The general admission control includes the new call admission control and handoff call admission control. The desired admission control schemes should have the QoS maintained in specified levels and network resources (i.e. bandwidth in this case) are utilised efficiently. The study conducted in this thesis is on reviewing current admission control schemes and developing new schemes. Threshold Access Sharing (TAS) scheme is one of the existing schemes with good performance on general call admission. Our work started with enhancing TAS. We have proposed an improved Threshold Access Sharing (iTAS) scheme with the simplified ratebased borrowing which is an adaptive mechanism. The iTAS aims to lower handoff call dropping probability and to maximise the resource utilisation. The scheme works at the cell level (i.e. it is applied at the base station), on the basis of reserving a fixed amount of bandwidth for handoff calls. Prioritised calls can be admitted by “borrowing” bandwidth from other ongoing calls. Our simulation has shown that the new scheme has outperformed the original TAS in terms of handoff prioritisation and handling, especially for bandwidth adaptive calls. However, in iTAS, the admission decision is made solely based on bandwidth related criteria. All calls of same class are assumed having similar behaviour. In the real situation, many factors can be referred in decision making of the admission control, especially the handoff call handling. We have proposed a novice scheme, which considered multiple criteria with different weights. The total weights are used to make a decision for a handoff. These criteria are hard to be modelled in the traditional admission models. Our simulated result has demonstrated that this scheme yields better performance in terms of handoff call xiv dropping compared with iTAS. We further expand the coverage of the admission control from a cell level to a system level in the hierarchical networks. A new admission control model was built, aiming to optimise bandwidth utilisation by separating the signalling channels and traffic channels in different tiers. In the new model, handoff calls are also prioritised using call classification and admission levels. Calls belonging to a certain class follow a pre-defined admission rule. The admission levels can be adjusted to suit the traffic situation in the system. Our simulated results show that this model works better than the normal 2-tier hierarchical networks in terms of handoff calls. The model settings are adjustable to reflect real situation. Finally we conclude our research and suggest some possible future work

Flows and fates of nickel-cadmium batteries in the City of Cape Town

Includes bibliographical references .Current patterns of economic activity entail high rates of material extraction from the natural environment and the generation of large amounts of waste. Alternative strategies must be found if we are to avoid the exhaustion of resources and the environment's capacity to safely absorb our wastes. Examining current resource use is an important step towards achieving a more sustainable society, and the toxic substances widely applied in our technologies form a crucial part of this examination. The heavy metal cadmium is one such substance. The use and disposal of nickel-cadmium secondary cells (the basic components of NiCd batteries) in Cape Town, South Africa, has been investigated with the objective of quantifying the associated flows of cadmium. This was achieved by applying substance flow analysis methodology to the year 2005 with a steady-state approach to quantify the disposal commitment arising from inflows in that year. Uncertainty in the calculated results was quantified by means of Monte Carlo simulation. Small sealed cells were found to make the dominant contribution to overall cadmium flows, with cordless power tools and separately imported cells accounting for most of these. Essentially all of these cells either have or will enter the municipal solid waste streams of the city. Large industrial cells made a smaller but significant contribution to overall inflows (3.4-14%), but none were known to have entered municipal waste. These went primarily to hazardous waste disposal outside the city or recycling abroad, with some going into storage. In order to assess the environmental significance of the cadmium sent to landfill, hypothetical "best worst-case" scenarios were developed which involved the worst case of total cadmium release from landfill, and best-case calculations of the potential contamination of agricultural land that could result from such release. A total release to agriculture was found to contaminate the city's croplands in under twenty years. Although these scenarios considered contamination potential but not the likelihood of contamination, and hence were not predictive, it could nevertheless be concluded that the amounts of cadmium destined for landfill disposal justified concern and caution. The disposal of environmentally significant amounts of cadmium in Cape Town and the very limited understanding of landfill behaviour necessitate the elimination ofNiCd batteries from municipal solid waste streams. Some approaches are briefly discussed by which this might be achieved, with regard to both environmental protection and resource conservation in general and the changing landscape of waste management in South Africa. Significant challenges were encountered from limited data availability during the application of substance flow analysis within a developing-world urban setting. This necessitated primary data collection and adaptation of data from other geographical and temporal scales. Adjusting national data to the city scale required the development of scaling factors which were more plausible than the use of population share or regional GDP Some similarities were noted between the cadmium metabolism of Cape Town and that of previously studied regions in the developed world. This supported the suggestion that some insights from substance flow analysis studies can be transferred to other regions when resources are not available for thorough local study. Important differences were also present, however, and further research is required to develop this possibility

Supply Chain Optimization for Sourced Production

Abstract. Title: Supply Chain Optimization – for Sourced Production. Authors: Patricia Möller and Andreas Paulsson. Tutors: Jan Eskil Hollen – Business Developer, Lilleborg as, Orkla, Everth Larsson – Department of Industrial Management and Logistics, Division of Engineering Logistics, Lund University, Carl-Henric Nilsson – Department of Economics and Business Administration, School of economics and management, Lund University. Problem: To source components from China is less expensive than setting up and running an own plant in any western country, but sourcing from low cost countries is related to challenges regarding business culture, logistics, quality and supply chain management. Cultural differences can make operations run less smoothly and the number of warehouses and transports need to be investigated. Communication processes must be reengineered and established, quality controls become a factor of outmost significance and the management of the entire supply chain needs to be intensified. Purpose: The purpose of this thesis is to investigate and propose how supply chain optimization for sourced production should be addressed. To achieve practical relevance a case study is performed of Lilleborg and their sourcing of components from China. Method: An inductive approach has been applied when conducting the study. The work process has been iterative and empirical qualitative data has been gathered through semi-structured interviews and literature studies. Conclusions: By applying a framework that consists of empirics and several relevant theories that form a cohesive and coherent tower towards set of objectives is the optimal strategic behavior for optimizing a supply chain according to this study

Analysis of adaptive algorithms for an integrated communication network

Techniques were examined that trade communication bandwidth for decreased transmission delays. When the network is lightly used, these schemes attempt to use additional network resources to decrease communication delays. As the network utilization rises, the schemes degrade gracefully, still providing service but with minimal use of the network. Because the schemes use a combination of circuit and packet switching, they should respond to variations in the types and amounts of network traffic. Also, a combination of circuit and packet switching to support the widely varying traffic demands imposed on an integrated network was investigated. The packet switched component is best suited to bursty traffic where some delays in delivery are acceptable. The circuit switched component is reserved for traffic that must meet real time constraints. Selected packet routing algorithms that might be used in an integrated network were simulated. An integrated traffic places widely varying workload demands on a network. Adaptive algorithms were identified, ones that respond to both the transient and evolutionary changes that arise in integrated networks. A new algorithm was developed, hybrid weighted routing, that adapts to workload changes