ABSTRACT The Long-Term Evolution (LTE) standard is a promising solution to mobile connectivity. I... more ABSTRACT The Long-Term Evolution (LTE) standard is a promising solution to mobile connectivity. It provides high data rates at a relatively low cost. At the same time, video traffic has so far outpaced other traffic types in growth, making it the dominant traffic type in current wireless networks. In this paper we study the concept of Quality of Experience (QoE) for video traffic in LTE systems. Since video users are more annoyed by unpredictable disruptions than overall reduced video fidelity, we developed an adaptive video coding scheme that aims to improve QoE in LTE networks. In the proposed model users of the same quality class are classified into a number of service levels providing different QoE satisfaction thresholds to their members. The QoE driven adaptation scheme adapts the rate of the transmitted video, so that the QoE experienced by the users remains in satisfactory levels. Two different policies for transmission rate adaptation are studied, namely the adaptive and the coordinated approach. The level of the transmission rate for both policies is regulated by the linear slow start and/or the exponential increase. Simulation results showed that the proposed algorithm for the both transmission rate adaptation policies succeeds in minimizing packet loss and delay in the video transmission, by adjusting the video resolution.
One of the major problems in wireless multihop networks is the scheduling of
transmissions in a ... more One of the major problems in wireless multihop networks is the scheduling of transmissions in a fair and efficient manner. Time Division Multiple Access (TDMA) seems to be one of the dominant solutions to achieve this goal since it is a simple scheme and can prolong the devices' lifetime by allowing them to transmit only a portion of the time during conversation. For that reason, several TDMA scheduling algorithms may be found in the literature. The scope of this article is to classify the existing TDMA scheduling algorithms ...
IEEE 802.11s Wireless Mesh Networks (WMNs) constitute a cost-effective solution for broadband ubi... more IEEE 802.11s Wireless Mesh Networks (WMNs) constitute a cost-effective solution for broadband ubiquitous Internet access. The IEEE 802.11s standard employs the Enhanced Distributed Channel Access (EDCA) as the Medium Access Control (MAC) mechanism in order to provide differentiated channel access and Quality of Service (QoS) guarantees for multimedia flows. Under EDCA, traffic is distinguished into four Access Categories (ACs) that have different priority levels, corresponding to Voice, Video, Best Effort and Background, respectively. In this paper, we evaluate the performance of the EDCA in IEEE 802.11s WMNs by simulating pedestrian users moving at low speed for a variety of demanding multimedia applications, such as Real-Time Gaming, video, Voice over IP (VoIP), as well as, web browsing. It should be noted that we have applied IEEE 802.11n as the underlying PHY Layer of the considered IEEE 802.11s network. Our results show that the ACs defined in EDCA do not perform satisfactory resulting in the inappropriateness of the EDCA mechanism for multimedia applications support in WMNs. Furthermore, an additional shortcoming of the IEEE 802.11s amendment that emerged through our simulation results is its inefficiency to support mobility since the velocity of the users significantly impacts the provided QoS.
The MPEG-Dynamic Adaptation Streaming over HTTP (MPEG-DASH) tries to improve the quality perceive... more The MPEG-Dynamic Adaptation Streaming over HTTP (MPEG-DASH) tries to improve the quality perceived by the user by allowing the user's centric access to different resolutions of the video content via the Hypertext Transfer Protocol (HTTP). However, although it eliminates data packet loss, depending on the rate adaptation strategy adopted by the user, as well as, the network conditions, there may be playback interruptions. In this paper a novel MPEG-DASH adaptation scheme, the FDASH, is proposed, which, by employing fuzzy logic to control the buffering time and the resolution achieves the following: a) distributes the best possible resolution of video segments, b) delivers undisrupted video playback as a result of buffer underflows at the client, c) avoids unnecessary changes of video resolution owing to frequent fluctuations of the available connection throughput. Simulation results showed that the FDASH in comparison with other schemes succeeds in various network scenarios in providing the client with the best possible video rates avoiding buffer underflows and frequent changes of video resolution.
Next generation wireless networks consist of many heterogeneous access technologies that should s... more Next generation wireless networks consist of many heterogeneous access technologies that should support various service types with different quality of service (QoS) constraints, as well as user, requirements and provider policies. Therefore, the need for network selection mechanisms that consider multiple factors must be addressed. In this paper, a network selection method is proposed by applying the analytic network process to estimate the weights of the selection criteria, as well as a fuzzy version of technique for order preference by similarity to ideal solution to perform the ranking of network alternatives. The method is applied to a heterogeneous network environment providing different QoS classes and policy characteristics. Each user applies the method to select the most appropriate network, which satisfies his or her requirements in respect of his or her service-level agreement (SLA). Performance evaluation shows that when the user requests only one service, the proposed method performs better compared to the original technique for order preference by similarity to ideal solution, as well as the Fuzzy AHP-ELECTRE method. Moreover, the proposed method can be applied in cases where a user requires multiple services simultaneously on a device. The sensitivity analysis of the proposed method shows that it can be properly adjusted to conform to network environment changes.
In modern wireless networking technologies, the need to support the nodes mobility is growing rap... more In modern wireless networking technologies, the need to support the nodes mobility is growing rapidly. This need is even greater in vehicular environments, in which the nodes are characterized by high mobility. In this paper, we study the basic protocols for mobility support in vehicular environments, such as Fast Handovers for Proxy Mobile IPv6 (PMIPv6) and Transient
Although MPEG-Dynamic Adaptation Streaming over HTTP (MPEG-DASH) eliminates data packet loss, bas... more Although MPEG-Dynamic Adaptation Streaming over HTTP (MPEG-DASH) eliminates data packet loss, based on the rate adaptation strategy adopted by the user and the network conditions, still playback interruptions may not be avoided. In this paper an algorithm for rate adaption in MPEG-DASH is proposed that employs fuzzy logic to estimate the resolution of the next video segment that each client should obtain from the server. In this way, the buffering time at each client is kept above a target buffering time and thus buffer overflows and unnecessary bit rate fluctuations are avoided. Simulation results showed that the proposed rate adaptation strategy has a beneficial effect on the quality each user perceives.
With the availability of cloud computing infrastructures, migrating business-critical functionali... more With the availability of cloud computing infrastructures, migrating business-critical functionality to public clouds is becoming commonplace. Cloud providers typically offer a variety of computing capabilities and pricing options. Therefore, the problem of selecting the ones that suit enterprise needs becomes critical. Our major focus is on the migration of enterprise communication services, such as IP-telephony, to the cloud. We design a tool to assist in optimally deciding among the set of available hosting and network connectivity Service-Level Agreements (SLAs) under Quality-of-Experience (QoE) and budget constraints. In particular, we propose a multi-objective optimization framework making use of application-specific QoE estimation tools to tackle with the conflicting objectives of price and quality and demonstrate its application to a cloud-based teleconferencing service as a case study.
Wireless Mesh Networks are considered as a promising solution for offering low-cost access to bro... more Wireless Mesh Networks are considered as a promising solution for offering low-cost access to broadband services. However, one of the main challenges in the design of these networks is their vulnerability to security attacks. In this paper, we analyze the fundamental security challenges and constraints of these networks, classify several possible attacks, and survey several intrusion prevention, detection, and response mechanisms found in the literature.
The LTE standard is a promising solution to wireless connectivity. It promises high data rates at... more The LTE standard is a promising solution to wireless connectivity. It promises high data rates at a low cost. At the same time, video traffic has so far outpaced other traffic types in growth, making it now the dominant traffic type in wireless networks. In this paper we study the concept of Quality of Experience for video traffic in LTE systems, Since video users are more annoyed by unpredictable packet loss, rather than reduced video fidelity, we developed an adaptive video coding scheme that aims to improve QoE in LTE networks, by continuously adapting the video fidelity, in order to keep the packet loss at acceptable levels.
Recently, network researchers have taken a great interest in quality of experience (QoE) and in t... more Recently, network researchers have taken a great interest in quality of experience (QoE) and in the new aspects it brings in the study of the link between network conditions and user satisfaction. Also, the realization that the information of users' satisfaction can be directly applied in the network management in a real-time manner has resulted in a fair amount of publications. Although the systems and frameworks presented in these publications tackle the subject of QoE-driven management quite successfully, they often concentrate on certain applications or technologies. We present a generic QoE management framework, which is applicable to a broad range of systems. We also demonstrate an instantiation of this framework as a network access point management system for RTP-based video. This system is not only able to positively affect the perceived quality of the multimedia application considered, but also to reduce over-prioritization and optimize resource usage. (J. Seppänen), [email protected] (M. Varela), [email protected] (A. Sgora).
Wireless Mesh Networking is a continuous growing technology that can be used used for several app... more Wireless Mesh Networking is a continuous growing technology that can be used used for several application scenarios, such as military tactical operations, etc. in next generation wireless networks. The IEEE 802.11s Standard defines the procedures that wireless nodes follow in order to interconnect and create a Wireless Local Area Network (WLAN) mesh network. It, also, defines the routing protocol and the metric that are used by a IEEE 802.11s mesh network to route data. However, although the energy consumption of mesh nodes is a crucial parameter for the network's lifetime in specific purpose operations (e.g. military and health) the default metric proposed by the standard doesn 't take into account the energy of the nodes. In this paper, a new energy -aware routing metric for the IEEE 802.11s mesh networks has been implemented. Simulation results showed that the proposed metric prolongs the lifetime of a WMN in comparison with the the default metric used by IEEE 802.11s Standard while causing a little higher total delay in the network.
Quality of service in WLANs has been a major concern of both academia and industry for many years... more Quality of service in WLANs has been a major concern of both academia and industry for many years. A number of methods have been published regarding delay analysis of 802.11 networks, but little research has been carried out for the jitter analysis, even though jitter can be more important than delay for real time applications, like voice over IP, multimedia streaming, etc. In this paper we introduce a new analytical method for estimating the jitter caused by the distributed coordination function of the 802.11 MAC protocol. This model is also evaluated by a series of simulations.
The Long-Term Evolution (LTE) standard is a promising solution to mobile connectivity. It provide... more The Long-Term Evolution (LTE) standard is a promising solution to mobile connectivity. It provides high data rates at a relatively low cost. At the same time, video traffic has so far outpaced other traffic types in growth, making it the dominant traffic type in current wireless networks. In this paper we study the concept of Quality of Experience (QoE) for video traffic in LTE systems. Since video users are more annoyed by unpredictable disruptions than overall reduced video fidelity, we developed an adaptive video coding scheme that aims to improve QoE in LTE networks. In the proposed model users of the same quality class are classified into a number of service levels providing different QoE satisfaction thresholds to their members. The QoE driven adaptation scheme adapts the rate of the transmitted video, so that the QoE experienced by the users remains in satisfactory levels. Two different policies for transmission rate adaptation are studied, namely the adaptive and the coordinated approach. The level of the transmission rate for both policies is regulated by the linear slow start and/or the exponential increase. Simulation results showed that the proposed algorithm for the both transmission rate adaptation policies succeeds in minimizing packet loss and delay in the video transmission, by adjusting the video resolution.
The IP Multimedia System (IMS) is a promising solution for converging new technologies with exist... more The IP Multimedia System (IMS) is a promising solution for converging new technologies with existing networks. The interworking environment and service flexibility that IMS offers to the currently deployed wireless broadband technologies, makes it appealing to users, service developers and network operators. In our previous work a heterogeneous network model based on IMS that integrates the Worldwide Interoperability for Microwave Access (WiMAX), Universal Mobile Telecommunications System (UMTS) and Wireless Local Area Network (WLAN) technologies and provides guaranteed QoS was proposed. In this paper an analytical model is derived in order to evaluate the signalling cost of mobility management during a vertical handoff.
Wireless Mesh Networks (WMNs) consist of mesh routers and mesh clients. Mesh routers have minimal... more Wireless Mesh Networks (WMNs) consist of mesh routers and mesh clients. Mesh routers have minimal mobility and form the backbone of WMNs, while mesh clients can be either stationary or mobile, and can form a client mesh network among themselves and with mesh routers. WMNs are characterized by dynamic self-organization, self-configuration and selfhealing to enable flexible integration, quick deployment, easy maintenance, low cost, high scalability and reliable services. WMNs may be also used to improve the performance of multi-hop ad-hoc networks, Wireless local area networks (WLANs) and Wireless Metropolitan Area Networks (WMANs). One of the factors that influence the performance of WMNs is the routing protocol that is used. Many routing protocols for WMNs can be found in the literature. However, not all these protocols are suitable for health communication systems. In this paper, based on the operational requirements of the health applications, we classify several routing protocols for wireless mesh networks and highlight their advantages and performance issues when they are used in healthcare.
The problem of network selection across heterogeneous wireless networks has recently received muc... more The problem of network selection across heterogeneous wireless networks has recently received much attention because of a drive for converged communication systems. However, since the selection of an access network depends on several parameters with different relative importance, such as the network and the application characteristics, the user preferences, the service cost, etc, it is a difficult task to be achieved. In this paper an effective access network selection algorithm for heterogeneous wireless networks is proposed that combines two Multi Attribute Decision Making (MADM) methods, the Analytic Hierarchy Process (AHP) method and the fuzzy Total Order Preference by Similarity to the Ideal Solution (TOPSIS) method. More specifically, the AHP method is used to determine weights of the criteria, and the fuzzy TOPSIS method is used to obtain the final access network ranking.
Wireless multi-hop networks have recently been conceived as a networking paradigm. However, their... more Wireless multi-hop networks have recently been conceived as a networking paradigm. However, their deployment has been limited, mainly due to the fact that they lack fairness. In this research effort, we briefly review the state of art in fairness mechanisms in multi-hop networks and we propose an algorithm that tries to differentiate the traffic among the connections in a wireless multi-hop ad-hoc sensor network, so that the fairness is enhanced. This is achieved by an adaptive scheme, which tries to assign a higher priority to the traffic connections that experience delay greatly larger than the average, so that their delay is reduced, and the fairness of the system is improved.
A promising solution for wireless environments is the wireless mesh technology that envisages sup... more A promising solution for wireless environments is the wireless mesh technology that envisages supplementing wired infrastructure with a wireless backbone for providing Internet connectivity to mobile nodes (MNs) or users in residential areas and offices. The IEEE 802.11 TGs has started to work in developing a mesh standard for local area wireless networks. Although a lot of progress has been made and a few new drafts have been released recently, there exist many issues that demand enhanced or even new solutions to 802.11s mesh networking. This paper aims to overview the latest version of the IEEE 802.11s protocol (Draft 2.02), especially the MAC and routing layers, and to point out the challenges that these networks have to overcome in these layers.
Ubiquitous service delivery requires the selection of the optimal access network in a heterogeneo... more Ubiquitous service delivery requires the selection of the optimal access network in a heterogeneous wireless environment. However, since the selection of an access network in such an environment depends on several parameters with different relative importance (such as the network and the application characteristics, the user preferences, the service cost), it is a difficult task to be achieved. In this paper, an effective access network selection algorithm for heterogeneous wireless networks is proposed that combines two Multi Attribute Decision Making (MADM) methods, the Analytic Hierarchy Process (AHP) method and the Total Order Preference by Similarity to the Ideal Solution (TOPSIS)
ABSTRACT The Long-Term Evolution (LTE) standard is a promising solution to mobile connectivity. I... more ABSTRACT The Long-Term Evolution (LTE) standard is a promising solution to mobile connectivity. It provides high data rates at a relatively low cost. At the same time, video traffic has so far outpaced other traffic types in growth, making it the dominant traffic type in current wireless networks. In this paper we study the concept of Quality of Experience (QoE) for video traffic in LTE systems. Since video users are more annoyed by unpredictable disruptions than overall reduced video fidelity, we developed an adaptive video coding scheme that aims to improve QoE in LTE networks. In the proposed model users of the same quality class are classified into a number of service levels providing different QoE satisfaction thresholds to their members. The QoE driven adaptation scheme adapts the rate of the transmitted video, so that the QoE experienced by the users remains in satisfactory levels. Two different policies for transmission rate adaptation are studied, namely the adaptive and the coordinated approach. The level of the transmission rate for both policies is regulated by the linear slow start and/or the exponential increase. Simulation results showed that the proposed algorithm for the both transmission rate adaptation policies succeeds in minimizing packet loss and delay in the video transmission, by adjusting the video resolution.
One of the major problems in wireless multihop networks is the scheduling of
transmissions in a ... more One of the major problems in wireless multihop networks is the scheduling of transmissions in a fair and efficient manner. Time Division Multiple Access (TDMA) seems to be one of the dominant solutions to achieve this goal since it is a simple scheme and can prolong the devices' lifetime by allowing them to transmit only a portion of the time during conversation. For that reason, several TDMA scheduling algorithms may be found in the literature. The scope of this article is to classify the existing TDMA scheduling algorithms ...
IEEE 802.11s Wireless Mesh Networks (WMNs) constitute a cost-effective solution for broadband ubi... more IEEE 802.11s Wireless Mesh Networks (WMNs) constitute a cost-effective solution for broadband ubiquitous Internet access. The IEEE 802.11s standard employs the Enhanced Distributed Channel Access (EDCA) as the Medium Access Control (MAC) mechanism in order to provide differentiated channel access and Quality of Service (QoS) guarantees for multimedia flows. Under EDCA, traffic is distinguished into four Access Categories (ACs) that have different priority levels, corresponding to Voice, Video, Best Effort and Background, respectively. In this paper, we evaluate the performance of the EDCA in IEEE 802.11s WMNs by simulating pedestrian users moving at low speed for a variety of demanding multimedia applications, such as Real-Time Gaming, video, Voice over IP (VoIP), as well as, web browsing. It should be noted that we have applied IEEE 802.11n as the underlying PHY Layer of the considered IEEE 802.11s network. Our results show that the ACs defined in EDCA do not perform satisfactory resulting in the inappropriateness of the EDCA mechanism for multimedia applications support in WMNs. Furthermore, an additional shortcoming of the IEEE 802.11s amendment that emerged through our simulation results is its inefficiency to support mobility since the velocity of the users significantly impacts the provided QoS.
The MPEG-Dynamic Adaptation Streaming over HTTP (MPEG-DASH) tries to improve the quality perceive... more The MPEG-Dynamic Adaptation Streaming over HTTP (MPEG-DASH) tries to improve the quality perceived by the user by allowing the user's centric access to different resolutions of the video content via the Hypertext Transfer Protocol (HTTP). However, although it eliminates data packet loss, depending on the rate adaptation strategy adopted by the user, as well as, the network conditions, there may be playback interruptions. In this paper a novel MPEG-DASH adaptation scheme, the FDASH, is proposed, which, by employing fuzzy logic to control the buffering time and the resolution achieves the following: a) distributes the best possible resolution of video segments, b) delivers undisrupted video playback as a result of buffer underflows at the client, c) avoids unnecessary changes of video resolution owing to frequent fluctuations of the available connection throughput. Simulation results showed that the FDASH in comparison with other schemes succeeds in various network scenarios in providing the client with the best possible video rates avoiding buffer underflows and frequent changes of video resolution.
Next generation wireless networks consist of many heterogeneous access technologies that should s... more Next generation wireless networks consist of many heterogeneous access technologies that should support various service types with different quality of service (QoS) constraints, as well as user, requirements and provider policies. Therefore, the need for network selection mechanisms that consider multiple factors must be addressed. In this paper, a network selection method is proposed by applying the analytic network process to estimate the weights of the selection criteria, as well as a fuzzy version of technique for order preference by similarity to ideal solution to perform the ranking of network alternatives. The method is applied to a heterogeneous network environment providing different QoS classes and policy characteristics. Each user applies the method to select the most appropriate network, which satisfies his or her requirements in respect of his or her service-level agreement (SLA). Performance evaluation shows that when the user requests only one service, the proposed method performs better compared to the original technique for order preference by similarity to ideal solution, as well as the Fuzzy AHP-ELECTRE method. Moreover, the proposed method can be applied in cases where a user requires multiple services simultaneously on a device. The sensitivity analysis of the proposed method shows that it can be properly adjusted to conform to network environment changes.
In modern wireless networking technologies, the need to support the nodes mobility is growing rap... more In modern wireless networking technologies, the need to support the nodes mobility is growing rapidly. This need is even greater in vehicular environments, in which the nodes are characterized by high mobility. In this paper, we study the basic protocols for mobility support in vehicular environments, such as Fast Handovers for Proxy Mobile IPv6 (PMIPv6) and Transient
Although MPEG-Dynamic Adaptation Streaming over HTTP (MPEG-DASH) eliminates data packet loss, bas... more Although MPEG-Dynamic Adaptation Streaming over HTTP (MPEG-DASH) eliminates data packet loss, based on the rate adaptation strategy adopted by the user and the network conditions, still playback interruptions may not be avoided. In this paper an algorithm for rate adaption in MPEG-DASH is proposed that employs fuzzy logic to estimate the resolution of the next video segment that each client should obtain from the server. In this way, the buffering time at each client is kept above a target buffering time and thus buffer overflows and unnecessary bit rate fluctuations are avoided. Simulation results showed that the proposed rate adaptation strategy has a beneficial effect on the quality each user perceives.
With the availability of cloud computing infrastructures, migrating business-critical functionali... more With the availability of cloud computing infrastructures, migrating business-critical functionality to public clouds is becoming commonplace. Cloud providers typically offer a variety of computing capabilities and pricing options. Therefore, the problem of selecting the ones that suit enterprise needs becomes critical. Our major focus is on the migration of enterprise communication services, such as IP-telephony, to the cloud. We design a tool to assist in optimally deciding among the set of available hosting and network connectivity Service-Level Agreements (SLAs) under Quality-of-Experience (QoE) and budget constraints. In particular, we propose a multi-objective optimization framework making use of application-specific QoE estimation tools to tackle with the conflicting objectives of price and quality and demonstrate its application to a cloud-based teleconferencing service as a case study.
Wireless Mesh Networks are considered as a promising solution for offering low-cost access to bro... more Wireless Mesh Networks are considered as a promising solution for offering low-cost access to broadband services. However, one of the main challenges in the design of these networks is their vulnerability to security attacks. In this paper, we analyze the fundamental security challenges and constraints of these networks, classify several possible attacks, and survey several intrusion prevention, detection, and response mechanisms found in the literature.
The LTE standard is a promising solution to wireless connectivity. It promises high data rates at... more The LTE standard is a promising solution to wireless connectivity. It promises high data rates at a low cost. At the same time, video traffic has so far outpaced other traffic types in growth, making it now the dominant traffic type in wireless networks. In this paper we study the concept of Quality of Experience for video traffic in LTE systems, Since video users are more annoyed by unpredictable packet loss, rather than reduced video fidelity, we developed an adaptive video coding scheme that aims to improve QoE in LTE networks, by continuously adapting the video fidelity, in order to keep the packet loss at acceptable levels.
Recently, network researchers have taken a great interest in quality of experience (QoE) and in t... more Recently, network researchers have taken a great interest in quality of experience (QoE) and in the new aspects it brings in the study of the link between network conditions and user satisfaction. Also, the realization that the information of users' satisfaction can be directly applied in the network management in a real-time manner has resulted in a fair amount of publications. Although the systems and frameworks presented in these publications tackle the subject of QoE-driven management quite successfully, they often concentrate on certain applications or technologies. We present a generic QoE management framework, which is applicable to a broad range of systems. We also demonstrate an instantiation of this framework as a network access point management system for RTP-based video. This system is not only able to positively affect the perceived quality of the multimedia application considered, but also to reduce over-prioritization and optimize resource usage. (J. Seppänen), [email protected] (M. Varela), [email protected] (A. Sgora).
Wireless Mesh Networking is a continuous growing technology that can be used used for several app... more Wireless Mesh Networking is a continuous growing technology that can be used used for several application scenarios, such as military tactical operations, etc. in next generation wireless networks. The IEEE 802.11s Standard defines the procedures that wireless nodes follow in order to interconnect and create a Wireless Local Area Network (WLAN) mesh network. It, also, defines the routing protocol and the metric that are used by a IEEE 802.11s mesh network to route data. However, although the energy consumption of mesh nodes is a crucial parameter for the network's lifetime in specific purpose operations (e.g. military and health) the default metric proposed by the standard doesn 't take into account the energy of the nodes. In this paper, a new energy -aware routing metric for the IEEE 802.11s mesh networks has been implemented. Simulation results showed that the proposed metric prolongs the lifetime of a WMN in comparison with the the default metric used by IEEE 802.11s Standard while causing a little higher total delay in the network.
Quality of service in WLANs has been a major concern of both academia and industry for many years... more Quality of service in WLANs has been a major concern of both academia and industry for many years. A number of methods have been published regarding delay analysis of 802.11 networks, but little research has been carried out for the jitter analysis, even though jitter can be more important than delay for real time applications, like voice over IP, multimedia streaming, etc. In this paper we introduce a new analytical method for estimating the jitter caused by the distributed coordination function of the 802.11 MAC protocol. This model is also evaluated by a series of simulations.
The Long-Term Evolution (LTE) standard is a promising solution to mobile connectivity. It provide... more The Long-Term Evolution (LTE) standard is a promising solution to mobile connectivity. It provides high data rates at a relatively low cost. At the same time, video traffic has so far outpaced other traffic types in growth, making it the dominant traffic type in current wireless networks. In this paper we study the concept of Quality of Experience (QoE) for video traffic in LTE systems. Since video users are more annoyed by unpredictable disruptions than overall reduced video fidelity, we developed an adaptive video coding scheme that aims to improve QoE in LTE networks. In the proposed model users of the same quality class are classified into a number of service levels providing different QoE satisfaction thresholds to their members. The QoE driven adaptation scheme adapts the rate of the transmitted video, so that the QoE experienced by the users remains in satisfactory levels. Two different policies for transmission rate adaptation are studied, namely the adaptive and the coordinated approach. The level of the transmission rate for both policies is regulated by the linear slow start and/or the exponential increase. Simulation results showed that the proposed algorithm for the both transmission rate adaptation policies succeeds in minimizing packet loss and delay in the video transmission, by adjusting the video resolution.
The IP Multimedia System (IMS) is a promising solution for converging new technologies with exist... more The IP Multimedia System (IMS) is a promising solution for converging new technologies with existing networks. The interworking environment and service flexibility that IMS offers to the currently deployed wireless broadband technologies, makes it appealing to users, service developers and network operators. In our previous work a heterogeneous network model based on IMS that integrates the Worldwide Interoperability for Microwave Access (WiMAX), Universal Mobile Telecommunications System (UMTS) and Wireless Local Area Network (WLAN) technologies and provides guaranteed QoS was proposed. In this paper an analytical model is derived in order to evaluate the signalling cost of mobility management during a vertical handoff.
Wireless Mesh Networks (WMNs) consist of mesh routers and mesh clients. Mesh routers have minimal... more Wireless Mesh Networks (WMNs) consist of mesh routers and mesh clients. Mesh routers have minimal mobility and form the backbone of WMNs, while mesh clients can be either stationary or mobile, and can form a client mesh network among themselves and with mesh routers. WMNs are characterized by dynamic self-organization, self-configuration and selfhealing to enable flexible integration, quick deployment, easy maintenance, low cost, high scalability and reliable services. WMNs may be also used to improve the performance of multi-hop ad-hoc networks, Wireless local area networks (WLANs) and Wireless Metropolitan Area Networks (WMANs). One of the factors that influence the performance of WMNs is the routing protocol that is used. Many routing protocols for WMNs can be found in the literature. However, not all these protocols are suitable for health communication systems. In this paper, based on the operational requirements of the health applications, we classify several routing protocols for wireless mesh networks and highlight their advantages and performance issues when they are used in healthcare.
The problem of network selection across heterogeneous wireless networks has recently received muc... more The problem of network selection across heterogeneous wireless networks has recently received much attention because of a drive for converged communication systems. However, since the selection of an access network depends on several parameters with different relative importance, such as the network and the application characteristics, the user preferences, the service cost, etc, it is a difficult task to be achieved. In this paper an effective access network selection algorithm for heterogeneous wireless networks is proposed that combines two Multi Attribute Decision Making (MADM) methods, the Analytic Hierarchy Process (AHP) method and the fuzzy Total Order Preference by Similarity to the Ideal Solution (TOPSIS) method. More specifically, the AHP method is used to determine weights of the criteria, and the fuzzy TOPSIS method is used to obtain the final access network ranking.
Wireless multi-hop networks have recently been conceived as a networking paradigm. However, their... more Wireless multi-hop networks have recently been conceived as a networking paradigm. However, their deployment has been limited, mainly due to the fact that they lack fairness. In this research effort, we briefly review the state of art in fairness mechanisms in multi-hop networks and we propose an algorithm that tries to differentiate the traffic among the connections in a wireless multi-hop ad-hoc sensor network, so that the fairness is enhanced. This is achieved by an adaptive scheme, which tries to assign a higher priority to the traffic connections that experience delay greatly larger than the average, so that their delay is reduced, and the fairness of the system is improved.
A promising solution for wireless environments is the wireless mesh technology that envisages sup... more A promising solution for wireless environments is the wireless mesh technology that envisages supplementing wired infrastructure with a wireless backbone for providing Internet connectivity to mobile nodes (MNs) or users in residential areas and offices. The IEEE 802.11 TGs has started to work in developing a mesh standard for local area wireless networks. Although a lot of progress has been made and a few new drafts have been released recently, there exist many issues that demand enhanced or even new solutions to 802.11s mesh networking. This paper aims to overview the latest version of the IEEE 802.11s protocol (Draft 2.02), especially the MAC and routing layers, and to point out the challenges that these networks have to overcome in these layers.
Ubiquitous service delivery requires the selection of the optimal access network in a heterogeneo... more Ubiquitous service delivery requires the selection of the optimal access network in a heterogeneous wireless environment. However, since the selection of an access network in such an environment depends on several parameters with different relative importance (such as the network and the application characteristics, the user preferences, the service cost), it is a difficult task to be achieved. In this paper, an effective access network selection algorithm for heterogeneous wireless networks is proposed that combines two Multi Attribute Decision Making (MADM) methods, the Analytic Hierarchy Process (AHP) method and the Total Order Preference by Similarity to the Ideal Solution (TOPSIS)
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Papers by Aggeliki Sgora
transmissions in a fair and efficient manner. Time Division Multiple Access (TDMA) seems to
be one of the dominant solutions to achieve this goal since it is a simple scheme and can
prolong the devices' lifetime by allowing them to transmit only a portion of the time during
conversation. For that reason, several TDMA scheduling algorithms may be found in the
literature. The scope of this article is to classify the existing TDMA scheduling algorithms ...
be addressed. In this paper, a network selection method is proposed by applying the analytic network process to estimate the weights of the selection criteria, as well as a fuzzy version of technique for order preference by similarity to ideal solution to perform the ranking of network alternatives. The method is applied to a heterogeneous network environment providing different QoS classes and policy characteristics. Each user applies the method to select the most appropriate network, which satisfies his or her requirements in respect
of his or her service-level agreement (SLA). Performance evaluation shows that when the user requests only one service, the proposed method performs better compared to the original technique for order preference by similarity to ideal solution, as well as the Fuzzy AHP-ELECTRE method. Moreover, the proposed method can be applied in cases where a user requires multiple services simultaneously on a device. The sensitivity analysis of the proposed method shows that it can be properly adjusted to conform to network environment changes.
transmissions in a fair and efficient manner. Time Division Multiple Access (TDMA) seems to
be one of the dominant solutions to achieve this goal since it is a simple scheme and can
prolong the devices' lifetime by allowing them to transmit only a portion of the time during
conversation. For that reason, several TDMA scheduling algorithms may be found in the
literature. The scope of this article is to classify the existing TDMA scheduling algorithms ...
be addressed. In this paper, a network selection method is proposed by applying the analytic network process to estimate the weights of the selection criteria, as well as a fuzzy version of technique for order preference by similarity to ideal solution to perform the ranking of network alternatives. The method is applied to a heterogeneous network environment providing different QoS classes and policy characteristics. Each user applies the method to select the most appropriate network, which satisfies his or her requirements in respect
of his or her service-level agreement (SLA). Performance evaluation shows that when the user requests only one service, the proposed method performs better compared to the original technique for order preference by similarity to ideal solution, as well as the Fuzzy AHP-ELECTRE method. Moreover, the proposed method can be applied in cases where a user requires multiple services simultaneously on a device. The sensitivity analysis of the proposed method shows that it can be properly adjusted to conform to network environment changes.