This paper proposes the application of Reverse Direction (RD) protocol to enhance performance in ... more This paper proposes the application of Reverse Direction (RD) protocol to enhance performance in future Full Duplex (FD) Wireless Local Area Networks (WLANs). Full duplex communications in WLANs will be possible when a receiving node has frames ready for the transmitting node. This requires the receiver to decode the frame header for each and every frame in the Transmission Opportunity (TXOP) of the transmitter, in order to obtain the source and destination addresses. It is shown that, in FD-capable WLANs, this procedure may lead to suboptimal performance, reducing the benefits of FD communications. A simple and effective method, based on the usage of RD protocol, is proposed in order to enhance efficiency in future FD WLANs. The performance of the proposed solution is evaluated and compared to the standard method in terms of maximum achievable throughput.
Radar absorbing materials (RAM) design for a desired frequency and angle range is presented. We e... more Radar absorbing materials (RAM) design for a desired frequency and angle range is presented. We evaluate the performance of particle swarm optimization (PSO) and differential evolution (DE) regarding their applicability to absorber design. The results show that the DE algorithm outer performs PSO variants.
A dynamic fuzzy neural system is proposed, for time series anomaly detection. The model is entitl... more A dynamic fuzzy neural system is proposed, for time series anomaly detection. The model is entitled BFuzzTiD (Block-diagonal Fuzzy Time-series Detector) and consists of fuzzy rules whose consequent parts are three-layer small recurrent neural networks. The hidden layer of each network has blocks of neurons that feed back to each other. BFuzzTid is trained by the Dynamic Resilient Propagation algorithm. The model learns the dynamics of the time series such that it can classify them by detecting the anomaly points. A comparative analysis is conducted with a series of time series anomaly detection models, in order to investigate the capabilities of the proposed detector.
A block-diagonal fuzzy neural network for short-term load forecasting is proposed. DBD-FELF consi... more A block-diagonal fuzzy neural network for short-term load forecasting is proposed. DBD-FELF consists of fuzzy rules with consequent parts that are neural networks with internal recurrence. These networks have a hidden layer which consists of pairs of neurons with feedback connections between them. The overall fuzzy model partitions the input space in partially overlapping fuzzy regions, where the recurrent neural networks of the respective rules operate. The partition of the input space and determination of the fuzzy rule base is performed by use of Fuzzy C-Means clustering algorithm and the RENNCOM constrained optimization method is applied for consequent parameter tuning. The electric load time-series of the Greek power system is examined, and hourly-based forecasting for the whole year is performed. The performance of DBD-FELF is tested via extensive experimental analysis and the results are promising, since an average percentage error of 1.18% is attained, along with an average ...
The main task of the dissertation is the modeling of user behavior in a telecommunications networ... more The main task of the dissertation is the modeling of user behavior in a telecommunications network in order to detect fraudulent activities. User behavior characterization is achieved by means of appropriate user profiles. These can be either one- or multi-dimensional structures. One-dimensional user activity representations are actually time-series of a network usage measure, e.g. calls per day or bulk of downloaded data. Multi-dimensional profiles may use more usage characteristics such as calls per day, corresponding duration, cost, hour-of-day, etc. User profiles are analyzed through artificial intelligence, statistical and data mining methods. The dissertation uses both a dofferential and an absolute approach to the problem. Problem heuristics as well as all experimentation and conclusions are based on real worldΗ παρούσα διατριβή ασχολείται με το πρόβλημα της μοντελοποίησης της συμπεριφοράς χρηστών σε τηλεπικοινωνιακά δίκτυα με στόχο τον εντοπισμό περιπτώσεων τηλεπικοινωνιακής...
2018 7th International Conference on Modern Circuits and Systems Technologies (MOCAST)
Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enabl... more Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enables modern Wireless Local Area Networks (WLANs) to efficiently exploit network resources. It is essentially a resource allocation technique that enables a contention winning station with multiple backlogged frames belonging to a specific traffic class to transmit a burst of packets for a pre-defined time interval without having to re-content for medium access. However, while multimedia traffic flows are allowed to benefit from TXOP, best effort applications are precluded from utilizing it. In the recent IEEE 802.11ac amendment an enhanced TXOP version allows multiple applications belonging to different traffic classes (including best effort and background traffic) to share the contention-free period and transmit simultaneously. That feature is available only when the Down-Link Multi-User Multiple-Input Multiple-Output (DL-MU-MIMO) is enabled in a Quality of Service (QoS) Access Point (QAP) of a WLAN that operates in infrastructure mode. In this paper, an alternative mechanism is presented that allows the sharing of the TXOP in a sequential manner and can be applied to stations in ad-hoc WLANs with co-existing Voice over IP (VoIP) and non-multimedia flows. The proposed mechanism is analyzed and the results obtained are encouraging.
2018 7th International Conference on Modern Circuits and Systems Technologies (MOCAST)
Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enabl... more Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enables modern Wireless Local Area Networks (WLANs) to efficiently exploit network resources. It is essentially a resource allocation technique that enables a contention winning station with multiple backlogged frames belonging to a specific traffic class to transmit a burst of packets for a pre-defined time interval without having to re-content for medium access. However, while multimedia traffic flows are allowed to benefit from TXOP, best effort applications are precluded from utilizing it. In the recent IEEE 802.11ac amendment an enhanced TXOP version allows multiple applications belonging to different traffic classes (including best effort and background traffic) to share the contention-free period and transmit simultaneously. That feature is available only when the Down-Link Multi-User Multiple-Input Multiple-Output (DL-MU-MIMO) is enabled in a Quality of Service (QoS) Access Point (QAP) of a WLAN that operates in infrastructure mode. In this paper, an alternative mechanism is presented that allows the sharing of the TXOP in a sequential manner and can be applied to stations in ad-hoc WLANs with co-existing Voice over IP (VoIP) and non-multimedia flows. The proposed mechanism is analyzed and the results obtained are encouraging.
2018 7th International Conference on Modern Circuits and Systems Technologies (MOCAST)
Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enabl... more Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enables modern Wireless Local Area Networks (WLANs) to efficiently exploit network resources. It is essentially a resource allocation technique that enables a contention winning station with multiple backlogged frames belonging to a specific traffic class to transmit a burst of packets for a pre-defined time interval without having to re-content for medium access. However, while multimedia traffic flows are allowed to benefit from TXOP, best effort applications are precluded from utilizing it. In the recent IEEE 802.11ac amendment an enhanced TXOP version allows multiple applications belonging to different traffic classes (including best effort and background traffic) to share the contention-free period and transmit simultaneously. That feature is available only when the Down-Link Multi-User Multiple-Input Multiple-Output (DL-MU-MIMO) is enabled in a Quality of Service (QoS) Access Point (QAP) of a WLAN that operates in infrastructure mode. In this paper, an alternative mechanism is presented that allows the sharing of the TXOP in a sequential manner and can be applied to stations in ad-hoc WLANs with co-existing Voice over IP (VoIP) and non-multimedia flows. The proposed mechanism is analyzed and the results obtained are encouraging.
2018 41st International Conference on Telecommunications and Signal Processing (TSP), 2018
Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contributio... more Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contribution of the IEEE 802.11ac amendment. It is essentially an enhanced version of the standard TXOP mechanism initially introduced by the IEEE 802.11e amendment, specifically engineered to improve performance of the Downlink Multi-User Multiple-Input-Multiple-Output (DL MU-MIMO) technology. DL MU-MIMO transmissions with TXOP sharing are performed only by the Access Point (AP) allowing multiple frames from multiple traffic classes to be transmitted simultaneously towards multiple users in the downlink. However, in the reverse path, acknowledgments must be transmitted sequentially. The default acknowledgment scheme selected by the IEEE 802.11ac is the Block Acknowledgments (BlockACK) which is a poll-based approach. In this paper, we investigate the application of an acknowledgment-free scheme, known as No Acknowledgment (NoACK), during DL MU-MIMO transmissions in IEEE 802.11ac Wireless Local Area Networks (WLANs). Its impact on the overall achieved throughput is evaluated through an analytical study.
2018 41st International Conference on Telecommunications and Signal Processing (TSP), 2018
Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contributio... more Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contribution of the IEEE 802.11ac amendment. It is essentially an enhanced version of the standard TXOP mechanism initially introduced by the IEEE 802.11e amendment, specifically engineered to improve performance of the Downlink Multi-User Multiple-Input-Multiple-Output (DL MU-MIMO) technology. DL MU-MIMO transmissions with TXOP sharing are performed only by the Access Point (AP) allowing multiple frames from multiple traffic classes to be transmitted simultaneously towards multiple users in the downlink. However, in the reverse path, acknowledgments must be transmitted sequentially. The default acknowledgment scheme selected by the IEEE 802.11ac is the Block Acknowledgments (BlockACK) which is a poll-based approach. In this paper, we investigate the application of an acknowledgment-free scheme, known as No Acknowledgment (NoACK), during DL MU-MIMO transmissions in IEEE 802.11ac Wireless Local Area Networks (WLANs). Its impact on the overall achieved throughput is evaluated through an analytical study.
2018 41st International Conference on Telecommunications and Signal Processing (TSP), 2018
Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contributio... more Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contribution of the IEEE 802.11ac amendment. It is essentially an enhanced version of the standard TXOP mechanism initially introduced by the IEEE 802.11e amendment, specifically engineered to improve performance of the Downlink Multi-User Multiple-Input-Multiple-Output (DL MU-MIMO) technology. DL MU-MIMO transmissions with TXOP sharing are performed only by the Access Point (AP) allowing multiple frames from multiple traffic classes to be transmitted simultaneously towards multiple users in the downlink. However, in the reverse path, acknowledgments must be transmitted sequentially. The default acknowledgment scheme selected by the IEEE 802.11ac is the Block Acknowledgments (BlockACK) which is a poll-based approach. In this paper, we investigate the application of an acknowledgment-free scheme, known as No Acknowledgment (NoACK), during DL MU-MIMO transmissions in IEEE 802.11ac Wireless Local Area Networks (WLANs). Its impact on the overall achieved throughput is evaluated through an analytical study.
This paper proposes the application of Reverse Direction (RD) protocol to enhance performance in ... more This paper proposes the application of Reverse Direction (RD) protocol to enhance performance in future Full Duplex (FD) Wireless Local Area Networks (WLANs). Full duplex communications in WLANs will be possible when a receiving node has frames ready for the transmitting node. This requires the receiver to decode the frame header for each and every frame in the Transmission Opportunity (TXOP) of the transmitter, in order to obtain the source and destination addresses. It is shown that, in FD-capable WLANs, this procedure may lead to suboptimal performance, reducing the benefits of FD communications. A simple and effective method, based on the usage of RD protocol, is proposed in order to enhance efficiency in future FD WLANs. The performance of the proposed solution is evaluated and compared to the standard method in terms of maximum achievable throughput.
Radar absorbing materials (RAM) design for a desired frequency and angle range is presented. We e... more Radar absorbing materials (RAM) design for a desired frequency and angle range is presented. We evaluate the performance of particle swarm optimization (PSO) and differential evolution (DE) regarding their applicability to absorber design. The results show that the DE algorithm outer performs PSO variants.
A dynamic fuzzy neural system is proposed, for time series anomaly detection. The model is entitl... more A dynamic fuzzy neural system is proposed, for time series anomaly detection. The model is entitled BFuzzTiD (Block-diagonal Fuzzy Time-series Detector) and consists of fuzzy rules whose consequent parts are three-layer small recurrent neural networks. The hidden layer of each network has blocks of neurons that feed back to each other. BFuzzTid is trained by the Dynamic Resilient Propagation algorithm. The model learns the dynamics of the time series such that it can classify them by detecting the anomaly points. A comparative analysis is conducted with a series of time series anomaly detection models, in order to investigate the capabilities of the proposed detector.
A block-diagonal fuzzy neural network for short-term load forecasting is proposed. DBD-FELF consi... more A block-diagonal fuzzy neural network for short-term load forecasting is proposed. DBD-FELF consists of fuzzy rules with consequent parts that are neural networks with internal recurrence. These networks have a hidden layer which consists of pairs of neurons with feedback connections between them. The overall fuzzy model partitions the input space in partially overlapping fuzzy regions, where the recurrent neural networks of the respective rules operate. The partition of the input space and determination of the fuzzy rule base is performed by use of Fuzzy C-Means clustering algorithm and the RENNCOM constrained optimization method is applied for consequent parameter tuning. The electric load time-series of the Greek power system is examined, and hourly-based forecasting for the whole year is performed. The performance of DBD-FELF is tested via extensive experimental analysis and the results are promising, since an average percentage error of 1.18% is attained, along with an average ...
The main task of the dissertation is the modeling of user behavior in a telecommunications networ... more The main task of the dissertation is the modeling of user behavior in a telecommunications network in order to detect fraudulent activities. User behavior characterization is achieved by means of appropriate user profiles. These can be either one- or multi-dimensional structures. One-dimensional user activity representations are actually time-series of a network usage measure, e.g. calls per day or bulk of downloaded data. Multi-dimensional profiles may use more usage characteristics such as calls per day, corresponding duration, cost, hour-of-day, etc. User profiles are analyzed through artificial intelligence, statistical and data mining methods. The dissertation uses both a dofferential and an absolute approach to the problem. Problem heuristics as well as all experimentation and conclusions are based on real worldΗ παρούσα διατριβή ασχολείται με το πρόβλημα της μοντελοποίησης της συμπεριφοράς χρηστών σε τηλεπικοινωνιακά δίκτυα με στόχο τον εντοπισμό περιπτώσεων τηλεπικοινωνιακής...
2018 7th International Conference on Modern Circuits and Systems Technologies (MOCAST)
Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enabl... more Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enables modern Wireless Local Area Networks (WLANs) to efficiently exploit network resources. It is essentially a resource allocation technique that enables a contention winning station with multiple backlogged frames belonging to a specific traffic class to transmit a burst of packets for a pre-defined time interval without having to re-content for medium access. However, while multimedia traffic flows are allowed to benefit from TXOP, best effort applications are precluded from utilizing it. In the recent IEEE 802.11ac amendment an enhanced TXOP version allows multiple applications belonging to different traffic classes (including best effort and background traffic) to share the contention-free period and transmit simultaneously. That feature is available only when the Down-Link Multi-User Multiple-Input Multiple-Output (DL-MU-MIMO) is enabled in a Quality of Service (QoS) Access Point (QAP) of a WLAN that operates in infrastructure mode. In this paper, an alternative mechanism is presented that allows the sharing of the TXOP in a sequential manner and can be applied to stations in ad-hoc WLANs with co-existing Voice over IP (VoIP) and non-multimedia flows. The proposed mechanism is analyzed and the results obtained are encouraging.
2018 7th International Conference on Modern Circuits and Systems Technologies (MOCAST)
Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enabl... more Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enables modern Wireless Local Area Networks (WLANs) to efficiently exploit network resources. It is essentially a resource allocation technique that enables a contention winning station with multiple backlogged frames belonging to a specific traffic class to transmit a burst of packets for a pre-defined time interval without having to re-content for medium access. However, while multimedia traffic flows are allowed to benefit from TXOP, best effort applications are precluded from utilizing it. In the recent IEEE 802.11ac amendment an enhanced TXOP version allows multiple applications belonging to different traffic classes (including best effort and background traffic) to share the contention-free period and transmit simultaneously. That feature is available only when the Down-Link Multi-User Multiple-Input Multiple-Output (DL-MU-MIMO) is enabled in a Quality of Service (QoS) Access Point (QAP) of a WLAN that operates in infrastructure mode. In this paper, an alternative mechanism is presented that allows the sharing of the TXOP in a sequential manner and can be applied to stations in ad-hoc WLANs with co-existing Voice over IP (VoIP) and non-multimedia flows. The proposed mechanism is analyzed and the results obtained are encouraging.
2018 7th International Conference on Modern Circuits and Systems Technologies (MOCAST)
Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enabl... more Transmission Opportunity (TXOP) is the key Medium Access Control (MAC) layer mechanism that enables modern Wireless Local Area Networks (WLANs) to efficiently exploit network resources. It is essentially a resource allocation technique that enables a contention winning station with multiple backlogged frames belonging to a specific traffic class to transmit a burst of packets for a pre-defined time interval without having to re-content for medium access. However, while multimedia traffic flows are allowed to benefit from TXOP, best effort applications are precluded from utilizing it. In the recent IEEE 802.11ac amendment an enhanced TXOP version allows multiple applications belonging to different traffic classes (including best effort and background traffic) to share the contention-free period and transmit simultaneously. That feature is available only when the Down-Link Multi-User Multiple-Input Multiple-Output (DL-MU-MIMO) is enabled in a Quality of Service (QoS) Access Point (QAP) of a WLAN that operates in infrastructure mode. In this paper, an alternative mechanism is presented that allows the sharing of the TXOP in a sequential manner and can be applied to stations in ad-hoc WLANs with co-existing Voice over IP (VoIP) and non-multimedia flows. The proposed mechanism is analyzed and the results obtained are encouraging.
2018 41st International Conference on Telecommunications and Signal Processing (TSP), 2018
Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contributio... more Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contribution of the IEEE 802.11ac amendment. It is essentially an enhanced version of the standard TXOP mechanism initially introduced by the IEEE 802.11e amendment, specifically engineered to improve performance of the Downlink Multi-User Multiple-Input-Multiple-Output (DL MU-MIMO) technology. DL MU-MIMO transmissions with TXOP sharing are performed only by the Access Point (AP) allowing multiple frames from multiple traffic classes to be transmitted simultaneously towards multiple users in the downlink. However, in the reverse path, acknowledgments must be transmitted sequentially. The default acknowledgment scheme selected by the IEEE 802.11ac is the Block Acknowledgments (BlockACK) which is a poll-based approach. In this paper, we investigate the application of an acknowledgment-free scheme, known as No Acknowledgment (NoACK), during DL MU-MIMO transmissions in IEEE 802.11ac Wireless Local Area Networks (WLANs). Its impact on the overall achieved throughput is evaluated through an analytical study.
2018 41st International Conference on Telecommunications and Signal Processing (TSP), 2018
Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contributio... more Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contribution of the IEEE 802.11ac amendment. It is essentially an enhanced version of the standard TXOP mechanism initially introduced by the IEEE 802.11e amendment, specifically engineered to improve performance of the Downlink Multi-User Multiple-Input-Multiple-Output (DL MU-MIMO) technology. DL MU-MIMO transmissions with TXOP sharing are performed only by the Access Point (AP) allowing multiple frames from multiple traffic classes to be transmitted simultaneously towards multiple users in the downlink. However, in the reverse path, acknowledgments must be transmitted sequentially. The default acknowledgment scheme selected by the IEEE 802.11ac is the Block Acknowledgments (BlockACK) which is a poll-based approach. In this paper, we investigate the application of an acknowledgment-free scheme, known as No Acknowledgment (NoACK), during DL MU-MIMO transmissions in IEEE 802.11ac Wireless Local Area Networks (WLANs). Its impact on the overall achieved throughput is evaluated through an analytical study.
2018 41st International Conference on Telecommunications and Signal Processing (TSP), 2018
Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contributio... more Transmission Opportunity (TXOP) sharing is the main Medium Access Control (MAC) layer contribution of the IEEE 802.11ac amendment. It is essentially an enhanced version of the standard TXOP mechanism initially introduced by the IEEE 802.11e amendment, specifically engineered to improve performance of the Downlink Multi-User Multiple-Input-Multiple-Output (DL MU-MIMO) technology. DL MU-MIMO transmissions with TXOP sharing are performed only by the Access Point (AP) allowing multiple frames from multiple traffic classes to be transmitted simultaneously towards multiple users in the downlink. However, in the reverse path, acknowledgments must be transmitted sequentially. The default acknowledgment scheme selected by the IEEE 802.11ac is the Block Acknowledgments (BlockACK) which is a poll-based approach. In this paper, we investigate the application of an acknowledgment-free scheme, known as No Acknowledgment (NoACK), during DL MU-MIMO transmissions in IEEE 802.11ac Wireless Local Area Networks (WLANs). Its impact on the overall achieved throughput is evaluated through an analytical study.
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