1,971 research outputs found
On the Minimization of Handover Decision Instability in Wireless Local Area Networks
This paper addresses handover decision instability which impacts negatively
on both user perception and network performances. To this aim, a new technique
called The HandOver Decision STAbility Technique (HODSTAT) is proposed for
horizontal handover in Wireless Local Area Networks (WLAN) based on IEEE
802.11standard. HODSTAT is based on a hysteresis margin analysis that, combined
with a utilitybased function, evaluates the need for the handover and
determines if the handover is needed or avoided. Indeed, if a Mobile Terminal
(MT) only transiently hands over to a better network, the gain from using this
new network may be diminished by the handover overhead and short usage
duration. The approach that we adopt throughout this article aims at reducing
the minimum handover occurrence that leads to the interruption of network
connectivity (this is due to the nature of handover in WLAN which is a break
before make which causes additional delay and packet loss). To this end, MT
rather performs a handover only if the connectivity of the current network is
threatened or if the performance of a neighboring network is really better
comparing the current one with a hysteresis margin. This hysteresis should make
a tradeoff between handover occurrence and the necessity to change the current
network of attachment. Our extensive simulation results show that our proposed
algorithm outperforms other decision stability approaches for handover decision
algorithm.Comment: 13 Pages, IJWM
Spectrum Utilization and Congestion of IEEE 802.11 Networks in the 2.4 GHz ISM Band
Wi-Fi technology, plays a major role in society thanks to its widespread availability, ease of use and low cost. To assure its long term viability in terms of capacity and ability to share the spectrum efïŹciently, it is of paramount to study the spectrum utilization and congestion mechanisms in live environments. In this paper the service level in the 2.4 GHz ISM band is investigated with focus on todays IEEE 802.11 WLAN systems with support for the 802.11e extension. Here service level means the overall Quality of Service (QoS), i.e. can all devices fulïŹll their communication needs? A crosslayer approach is used, since the service level can be measured at several levels of the protocol stack. The focus is on monitoring at both the Physical (PHY) and the Medium Access Control (MAC) link layer simultaneously by performing respectively power measurements with a spectrum analyzer to assess spectrum utilization and packet snifïŹng to measure the congestion. Compared to traditional QoS analysis in 802.11 networks, packet snifïŹng allows to study the occurring congestion mechanisms more thoroughly. The monitoring is applied for the following two cases. First the inïŹuence of interference between WLAN networks sharing the same radio channel is investigated in a controlled environment. It turns out that retry rate, Clear-ToSend (CTS), Request-To-Send (RTS) and (Block) Acknowledgment (ACK) frames can be used to identify congestion, whereas the spectrum analyzer is employed to identify the source of interference. Secondly, live measurements are performed at three locations to identify this type of interference in real-live situations. Results show inefïŹcient use of the wireless medium in certain scenarios, due to a large portion of management and control frames compared to data content frames (i.e. only 21% of the frames is identiïŹed as data frames)
An Overview of Vertical Handoff Decision Algorithms in NGWNs and a new Scheme for Providing Optimized Performance in Heterogeneous Wireless Networks
Because the increasingly development and use of wireless networks and mobile technologies, was implemented the idea that users of mobile terminals must have access in different wireless networks simultaneously. Therefore one of the main interest points of Next Generation Wireless Networks (NGWNs), refers to the ability to support wireless network access equipment to ensure a high rate of services between different wireless networks. To solve these problems it was necessary to have decision algorithms to decide for each user of mobile terminal, which is the best network at some point, for a service or a specific application that the user needs. Therefore to make these things, different algorithms use the vertical handoff technique. Below are presented a series of algorithms based on vertical handoff technique with a classification of the different existing vertical handoff decision strategies, which tries to solve these issues of wireless network selection at a given time for a specific application of an user. Based on our synthesis on vertical handoff decision strategies given below, we build our strategy based on solutions presented below, taking the most interesting aspect of each one.Vertical Handoff, Genetic Algorithms, Fuzzy Logic, Neural Networks, AHP
Access Network Selection in Heterogeneous Networks
The future Heterogeneous Wireless Network (HWN) is composed of multiple Radio Access
Technologies (RATs), therefore new Radio Resource Management (RRM) schemes
and mechanisms are necessary to benefit from the individual characteristics of each RAT
and to exploit the gain resulting from jointly considering the whole set of the available
radio resources in each RAT. These new RRM schemes have to support mobile users
who can access more than one RAT alternatively or simultaneously using a multi-mode
terminal. An important RRM consideration for overall HWN stability, resource utilization,
user satisfaction, and Quality of Service (QoS) provisioning is the selection of the
most optimal and promising Access Network (AN) for a new service request. The RRM
mechanism that is responsible for selecting the most optimal and promising AN for a
new service request in the HWN is called the initial Access Network Selection (ANS).
This thesis explores the issue of ANS in the HWN. Several ANS solutions that attempt
to increase the user satisfaction, the operator benefits, and the QoS are designed, implemented,
and evaluated.
The thesis first presents a comprehensive foundation for the initial ANS in the H\VN.
Then, the thesis analyses and develops a generic framework for solving the ANS problem
and any other similar optimized selection problem. The advantages and strengths of the
developed framework are discussed. Combined Fuzzy Logic (FL), Multiple Criteria
Decision Making (MCDM) and Genetic Algorithms (GA) are used to give the developed
framework the required scalability, flexibility, and simplicity.
The developed framework is used to present and design several novel ANS algorithms
that consider the user, the operator, and the QoS view points. Different numbers of
RATs, MCDM tools, and FL inference system types are used in each algorithm. A
suitable simulation models over the HWN with a new set of performance evolution
metrics for the ANS solution are designed and implemented. The simulation results show
that the new algorithms have better and more robust performance over the random, the service type, and the terminal speed based selection algorithms that are used as reference
algorithms. Our novel algorithms outperform the reference algorithms in- terms of the
percentage of the satisfied users who are assigned to the network of their preferences and
the percentage of the users who are assigned to networks with stronger signal strength.
The new algorithms maximize the operator benefits by saving the high cost network
resources and utilizing the usage of the low cost network resources. Usually better
results are achieved by assigning the weights using the GA optional component in the
implemented algorithms
An intelligent path management in heterogeneous vehicular networks
Achieving reliable connectivity in heterogeneous vehicular networks is a challenging task, owing to rapid topological changes and unpredictable vehicle speeds. As vehicular communication demands continue to evolve, multipath connectivity is emerging as an important tool, which promises to enhance network interoperability and reliability. Given the limited coverage area of serving access technologies, frequent disconnections are to be expected as the vehicle moves. To ensure seamless communication in dynamic vehicular environments, an intelligent path management algorithm for Multipath TCP (MPTCP) has been proposed. The algorithm utilizes a network selection mechanism based on Fuzzy Analytic Hierarchy Process (FAHP), which dynamically assigns the most appropriate underlying network for each running application. The selection process takes into account multiple factors, such as path quality, vehicle mobility, and service characteristics. In contrast to existing solutions, our proposed method offers a dynamic and comprehensive approach to network selection that is tailored to the specific needs of each service to ensure that it is always paired with the optimal access technology. The results of the evaluation demonstrate that the proposed method is highly effective in maintaining service continuity during vertical handover. By tailoring the network selection to the specific needs of each application, our path manager is able to ensure optimal connectivity and performance, even in challenging vehicular environments, delivering a better user experience, with more reliable connections, and smoother data transfers.FCT - Fundação para a CiĂȘncia e a Tecnologia(PD/BDE/150506/2019
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