Queueing Networks for Vertical Handover

PhDIt is widely expected that next-generation wireless communication systems will be heterogeneous, integrating a wide variety of wireless access networks. Of particular interest recently is a mix of cellular networks (GSM/GPRS and WCDMA) and wireless local area networks (WLANs) to provide complementary features in terms of coverage, capacity and mobility support. If cellular/ WLAN interworking is to be the basis for a heterogeneous network then the analysis of complex handover traffic rates in the system (especially vertical handover) is one of the most essential issues to be considered. This thesis describes the application of queueing-network theory to the modelling of this heterogeneous wireless overlay system. A network of queues (or queueing network) is a powerful mathematical tool in the performance evaluation of many large-scale engineering systems. It has been used in the modelling of hierarchically structured cellular wireless networks with much success, including queueing network modelling in the study of cellular/ WLAN interworking systems. In the process of queueing network modelling, obtaining the network topology of a system is usually the first step in the construction of a good model, but this topology analysis has never before been used in the handover traffic study in heterogeneous overlay wireless networks. In this thesis, a new topology scheme to facilitate the analysis of handover traffic is proposed. The structural similarity between hierarchical cellular structure and heterogeneous wireless overlay networks is also compared. By replacing the microcells with WLANs in a hierarchical structure, the interworking system is modelled as an open network of Erlang loss systems and with the new topology, the performance measures of blocking probabilities and dropping probabilities can be determined. Both homogeneous and non-homogeneous traffic have been considered, circuit switched and packet-switched. Example scenarios have been used to validate the models, the numerical results showing clear agreement with the known validation scenarios

Performance evaluation of an enhanced distributed channel access protocol under heterogeneous traffic

Recently there have been considerable interests focusing on the performance evaluation of IEEE 802.11e Medium Access Control (MAC) protocols, which were proposed for supporting Quality of Services (QoS) in Wireless Local Area Networks (WLANs). Different from most existing work, this study has conducted comprehensive performance evaluation and analysis of the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) protocol in the presence of heterogeneous network traffic including non-bursty Poisson, bursty ON/OFF, and self-similar traffic generated by wireless multimedia applications. The performance results on throughput, access delay and medium utilization have demonstrated that the protocol is able to achieve satisfying QoS differentiation for heterogeneous multimedia traffic. On the other hand the results have showed that IEEE 802.11e EDCA suffering from the low medium utilization due to the overhead generated by transmission collisions and back-off processes. 1

Applications of Soft Computing in Mobile and Wireless Communications

Soft computing is a synergistic combination of artificial intelligence methodologies to model and solve real world problems that are either impossible or too difficult to model mathematically. Furthermore, the use of conventional modeling techniques demands rigor, precision and certainty, which carry computational cost. On the other hand, soft computing utilizes computation, reasoning and inference to reduce computational cost by exploiting tolerance for imprecision, uncertainty, partial truth and approximation. In addition to computational cost savings, soft computing is an excellent platform for autonomic computing, owing to its roots in artificial intelligence. Wireless communication networks are associated with much uncertainty and imprecision due to a number of stochastic processes such as escalating number of access points, constantly changing propagation channels, sudden variations in network load and random mobility of users. This reality has fuelled numerous applications of soft computing techniques in mobile and wireless communications. This paper reviews various applications of the core soft computing methodologies in mobile and wireless communications

Analysis of interworking functions in heterogeneous networks

Future cellular radio networks will enable mobile terminals to communicate in environments populated by a multitude of devices, technologies and business actors using several radio interfaces. In this environment, one important task is to develop common control functions for elements in such networks. One of today's challenges is to provide service continuity in those highly heterogeneous networks. The service continuity can be measured in terms of a satisfied user criteria, which consists e.g. of the perceived end to end data packet delay, i.e. transport layer packet delay. The IEEE 802.21 standard focuses on the support of media independent handover for a broad range of technologies, but with strong emphasis on 802 technologies. The Framework Programme (FP)7 European Project OMEGA investigates the performance of home networks, which consist of technologies like Wireless Local Area Networks (WLAN), Hybrid Wireless Optics (HWO) or Power Line Communications (PLC). The aim of this work is to investigate in the context of the OMEGA project, which functions of the IEEE 802.21 standard are needed in order to co-operate in heterogeneous home networks. Subsequently, their performance in terms of QoS evaluation are developed. One of the most important functions is the path selection since it establishes the flow between source and destination and simultaneously, deals with the reservation of resources. In this work an approach for the identification and selection of possible paths using signal flow graphs analytically has been evaluated. The scheme is based on ad hoc networks and the proposed algorithm is Bandwidth Guaranteed Source Routing (BGSR). The analysis provides information about the required delay in the selection and helps to evaluate the influence of the route selection in the uninterrupted provision of service. Another concept to be considered is the path re-selection mechanism. A comparative analysis of centralized and decentralized solutions is developed using SFGs as well and basing the evaluation on the latency of both mechanisms

Adaptive stochastic radio access selection scheme for cellular-WLAN heterogeneous communication systems

This study proposes a novel adaptive stochastic radio access selection scheme for mobile users in heterogeneous cellular-wireless local area network (WLAN) systems. In this scheme, a mobile user located in dual coverage area randomly selects WLAN with probability of ω when there is a need for downloading a chunk of data. The value of ω is optimised according to the status of both networks in terms of network load and signal quality of both cellular and WLAN networks. An analytical model based on continuous time Markov chain is proposed to optimise the value of ω and compute the performance of proposed scheme in terms of energy efficiency, throughput, and call blocking probability. Both analytical and simulation results demonstrate the superiority of the proposed scheme compared with the mainstream network selection schemes: namely, WLAN-first and load balancing

Collaborative signal and information processing for target detection with heterogeneous sensor networks

In this paper, an approach for target detection and acquisition with heterogeneous sensor networks through strategic resource allocation and coordination is presented. Based on sensor management and collaborative signal and information processing, low-capacity low-cost sensors are strategically deployed to guide and cue scarce high performance sensors in the network to improve the data quality, with which the mission is eventually completed more efficiently with lower cost. We focus on the problem of designing such a network system in which issues of resource selection and allocation, system behaviour and capacity, target behaviour and patterns, the environment, and multiple constraints such as the cost must be addressed simultaneously. Simulation results offer significant insight into sensor selection and network operation, and demonstrate the great benefits introduced by guided search in an application of hunting down and capturing hostile vehicles on the battlefield

Motorized cart

Motorized cart is known as an effective tool and timeless that help people carry heavy loads. For farmers, it has an especially vital tool for moving goods. Oil palm farmers typically uses the wheelbarrow to move the oil palm fruit (Figure 10.1). However, there is a lack of equipment that should be further enhanced in capabilities. Motorized carts that seek to add automation to wheelbarrow as it is to help people save manpower while using it. At present, oil palm plantation industry is among the largest in Malaysia. However, in an effort to increase the prestige of the industry to a higher level there are challenges to be faced. Shortage of workers willing to work the farm for harvesting oil palm has given pain to manage oil palm plantations. Many have complained about the difficulty of hiring foreign workers and a high cost. Although there are tools that can be used to collect or transfer the proceeds of oil palm fruits such as carts available. However, these tools still have the disadvantage that requires high manpower to operate. Moreover, it is not suitable for all land surfaces and limited cargo space. Workload and manpower dependence has an impact on farmers' income