L. Loyola - Profile on Academia.edu (original) (raw)
Papers by L. Loyola
EDCA-HCCA Combination Scheme for Gateway APs in IEEE 802.11-compliant Mesh WLANs
Analysis of methods for controlling QOS agreements among IP mobile networks
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 2007
... MOBILE NETWORKS Eleni Kamateri and Lefteris Mamatas Demokritos University of Thrace Vas. ... ... more ... MOBILE NETWORKS Eleni Kamateri and Lefteris Mamatas Demokritos University of Thrace Vas. ... [4] J. Manner, G. Karagiannis, and A. McDonald. 'NSLP for Quality-of-Service signalling.' Internet Draft - Work in progress, Internet Engineering Task Force, January 2006. ...
An explicit-deadline prioritization scheduling for bandwidth allocation in fixed-length packet wireless networks
The proposed medium access protocol deals especially with the timely-transmission of real-time pa... more The proposed medium access protocol deals especially with the timely-transmission of real-time packets in wireless multimedia networks where users of various types of traffic are present. It works based on the time division multiple access (TDMA) with time division duplex (TDD) technique as well as fixed-length packet switching incorporating two policies, which work differently during non-congestion and congestion states. The simulation results show good performance of the proposed method, even under high-load conditions, and a good trade-off characteristic between real-time access delay and non-real time buffer occupancy, during periods of congestion
A Multi-channel infrastructure based on DCF access mechanism for Wireless LAN Mesh Networks compliant with IEEE 802.11
2005 Asia-Pacific Conference on Communications
The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promis... more The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promising architecture for achieving a ubiquitous wireless Internet access in the future. However, the current IEEE 802.11 protocol is aimed at single access point (AP) environments and many problems related to the wireless meshed interconnection of APs and mobile terminals (MTs) remain to
Speed-aware resource allocation and transmission scheme for the uplink channel of highly mobile MC-CDMA systems
APCC/MDMC '04. The 2004 Joint Conference of the 10th Asia-Pacific Conference on Communications and the 5th International Symposium on Multi-Dimensional Mobile Communications Proceeding
We propose a new transmission and resource allocation technique based on multicarrier direct-sequ... more We propose a new transmission and resource allocation technique based on multicarrier direct-sequence CDMA (MC-DS-CDMA). The proposed system allocates subcarriers and spreading codes to users by considering their current bandwidth requirements and frequency shifts caused by their movement. Through the use of low-correlation spreading codes in close subcarriers the scheme reduces the inter-carrier interference generated by high-speed users while keeping
Speed-aware multicarrier transmission and resource allocation scheme for the uplink channel of highly mobile networks
We propose a new transmission and resource allocation technique based on multicarrier direct-sequ... more We propose a new transmission and resource allocation technique based on multicarrier direct-sequence CDMA (MC-DS-CDMA). The proposed system allocates subcarriers and spreading codes to users by considering their current bandwidth requirements and frequency shifts caused by their movement. Through the use of low-correlation spreading codes in close subcarriers, the scheme reduces the intercarrier interference generated by high-speed users while keeping the intersymbol interference at a low level due to multicarrier transmission. The analysis and results show that a substantial mitigation of both the intercarrier interference and bit error rate, without reducing the system bandwidth efficiency, can be achieved.
An OFDMA/CDMA-based bandwidth resource allocation scheme for future broadband mobile networks
Vehicular Technology Conference, 1988, IEEE 38th
We propose a new transmission and multiple access method for future broadband wireless networks. ... more We propose a new transmission and multiple access method for future broadband wireless networks. The scheme combines the advantages of orthogonal frequency division multiple access (OFDMA) and code division multiple access (CDMA) to cope simultaneously with both frequency spread produced by the Doppler effect, and time spread caused by the multipath channel. Through the code orthogonalization of neighboring (close) OFDM subcarriers, the method mitigates the intercarrier interference generated by high speed users while keeping the advantages offered by OFDMA to diminish the intersymbol interference produced by multipaths. In this way, the method optimizes the reliability of the communication channel provided to every user according to its speed, position and channel characteristics. The allocation of subcarriers and orthogonal codes to users is carried out dynamically with time by considering parameters such as required bitrate, speed, level of interference, multipath effects and phy...
Opportunistic relaying vs. selective cooperation
Proceedings of the 11th international symposium on Modeling, analysis and simulation of wireless and mobile systems - MSWiM '08, 2008
Design and Evaluation of a Routing-Informed Cooperative MAC Protocol for Ad Hoc Networks
IEEE INFOCOM 2008 - The 27th Conference on Computer Communications, 2008
Abstract—Cooperative relaying has been shown to provide diversity gains which can significantly i... more Abstract—Cooperative relaying has been shown to provide diversity gains which can significantly improve the Packet Error Rate (PER) in wireless transmissions. In ad hoc wireless rout- ing where packets may travel over a number of hops before reaching the destination, hop-wise cooperative relaying may severely reduce network capacity. This approach was mainly addressed in literature so far. In this paper,
Multi-channel wireless LAN mesh architecture with DCF-based inter-AP communication and idle channel search packet forwarding
GLOBECOM '05. IEEE Global Telecommunications Conference, 2005., 2005
The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promis... more The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promising architecture for achieving a ubiquitous wireless Internet access in the future. However, the current IEEE 802.11 protocol is aimed at single-AP (access point) environments and many problems related to the wireless meshed interconnection of APs and mobile terminals (MTs) remain to be solved. Some proposed solutions to build such mesh architectures are based on single-channel ad-hoc oriented schemes in which IEEE 802.11 protocol has been modified. The main problem with this type of schemes, however, lies in the very low performance of the single-channel architecture itself. The task group S of IEEE 802.11 is currently working out standards for IEEE 802.11-compliant mesh architectures in a number of usage scenarios including residential, office and campus/community/public access network but a lot of work remains to be done since the group was established just on last year. In this paper we propose a new multi-radio multi-channel mesh architecture for hot zones which works using a distributed coordination function (DCF)-based technique for interconnecting APs and a simple but effective radio routing mechanism. A major advantage of our proposed scheme is that, putting routing issues aside, it introduces no change into the MAC protocol of IEEE 802.11. Our simulations results obtained in OPNET show the great effectiveness of radio routing for balancing the traffic load within the network as well as interesting results related with the size of packets and the mesh architecture itself that could lead to further research in the future. Moreover, the results show the proposed architecture yields a very good performance in terms of total throughput and transmission delay
A new transmission and multiple access scheme based on multicarrier cdma for future highly mobile networks
14th IEEE Proceedings on Personal, Indoor and Mobile Radio Communications, 2003. PIMRC 2003., 2003
In this paper, we propose a new transmission and resource allocation technique on multicarrier di... more In this paper, we propose a new transmission and resource allocation technique on multicarrier direct-sequence CDMA (MC-DS-CDMA). The proposed system allocates subcarriers and spreading codes to users by considering their current bandwidth requirements and frequency shifts caused by their movement. Through the use of low-correlation spreading codes in close subcarriers the scheme reduces the inter-carrier interference generated by high-speed users
[Registration of an anomalous pathway potential in a patient with ventricular pre-excitation. A case report]
Arquivos brasileiros de cardiologia, 1984
Real-time services over best-effort networks, such as teleconferencing over unspecified , bit rat... more Real-time services over best-effort networks, such as teleconferencing over unspecified , bit rate (UBR) class asynchronous transfer mode (ATM) networks or the Internet, are expected to be in high demand in the near future as such services become more cost effective. However, cell loss caused by buffer overflow at switches is a serious problem in this service class, and is responsible for degradation of the Quality of Service (QoS). A promising technology for improving the QoS of best-effort networks is the recovery of lost cells by forward error correction (FEC). Conventional FEC methods utilize a FEC matrix with fixed dimensions and which is usually designed to cope with the worst case of cell loss. In this paper, a new method that provides dynamic recovery capacity to deal with the current cell loss ratio through the use of a variable-dimension FEC matrix is proposed. The scheme also takes into account the coding method of the matrix to provide data prioritization. Numerical results show that the cell loss ratio and transmission efficiency of the proposed method are superior to those of conventional methods.
Empirical efficiency gains of high-speed UDP-based protocols in realistic settings
Different cloud and data/video delivery applications require the use of high-speed links to fulfi... more Different cloud and data/video delivery applications require the use of high-speed links to fulfill a reasonable qu ality of experience. However, Internet connections in developing c ountries like Chile are -in many casesfar from being suitable for transferring large data files in a fast and efficient manner toend (non-business) users. These are usually non-dedicated lin ks, with no more than 10-20 Mbps at the user’s end, showing patterns of congestion (and high latency) when connecting to distant servers. In this context, it has been shown in controlled/l ab situationsthat certain UDP based protocols outperform TCP. In this work, we aim to empirically evaluate upper bounds of performance for a set of UDP-based protocols, comparing their efficiency with respect to TCP, in realistic settings. We performed a long-term measurement campaign, transmitting1 GB files from Santiago, Chile to Atlanta, US, allowing us to compute eventual efficiency gains of UDP, Tsunami and UDT over TCP. Our results show that UDT and UDP perform better than TCP and Tsunami when comparing their achievable rates, stability and completion time to download large files. In terms of their attainable throughput, UDP and UDT duplicate TCP (on average), where UDT has the added benefit of acknowledging receptions of data blocks, being then suitable for reliablehighspeed transmissions. Therefore, typical home-users with l imited download bandwidth would significantly improve their quali ty of experience if UDT is employed as an application-layer proto col for reliable transmissions, being not only transparent to them but also highly efficient.
Radio terminal, radio communication system and radio communication method
Recommender system for contextual advertising in IPTV scenarios
The 2010 14th International Conference on Computer Supported Cooperative Work in Design, 2010
Inter-Network Routing in Ambient Networks
2007 16th IST Mobile and Wireless Communications Summit, 2007
The ambient networks project is developing advanced networking capabilities, such as dynamic mult... more The ambient networks project is developing advanced networking capabilities, such as dynamic multi-access, network mobility, together with availability of ensured service or network context. The Ambient framework offers a "plug-and-play" flexibility to accommodate different routing schemes for alternative scenarios, ranging from completely flat topologies hanging off a common core network to deeply nested topologies attached to a core. This paper
Increasing the Capacity of IEEE 802.11 Wireless LAN through Cooperative Coded Retransmissions
VTC Spring 2008 - IEEE Vehicular Technology Conference, 2008
2008 Fourth Workshop on Network Coding, Theory and Applications, 2008
We consider the problem of finding the minimum number of transmissions in an ad-hoc network for a... more We consider the problem of finding the minimum number of transmissions in an ad-hoc network for all-to-all broadcasting using network coding. This work generalizes previous results for canonical topologies such as the circle and the wraparound grid to the finite-sized line, and non-wrap-around grid. The latter topologies better reflect network coding in random topologies, since the dissemination of information is "directional", in a sense that information usually arrives via the neighbors on the path to its originator instead of from all possible directions. We find that while the line topology requires a higher number of transmissions compared to the circle, this is interestingly not the case for the grid. We further present simulation results on a heuristic that estimates the required minimum number of transmissions in random wireless topologies and compare it to the optimum solution, as well as previously proposed heuristics.
Evaluation of a practical video fingerprinting system
2010 10th International Symposium on Communications and Information Technologies, 2010
Video fingerprinting is one of the most promising technologies to uniquely identify video content... more Video fingerprinting is one of the most promising technologies to uniquely identify video content in the Internet in a totally format-independent way. The logic behind the creation of the video fingerprints or perceptual hashes is a key factor for the performance of the system, especially in terms of storage and search efficiency. Although several video fingerprinting methods have been proposed,
EDCA-HCCA Combination Scheme for Gateway APs in IEEE 802.11-compliant Mesh WLANs
Analysis of methods for controlling QOS agreements among IP mobile networks
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 2007
... MOBILE NETWORKS Eleni Kamateri and Lefteris Mamatas Demokritos University of Thrace Vas. ... ... more ... MOBILE NETWORKS Eleni Kamateri and Lefteris Mamatas Demokritos University of Thrace Vas. ... [4] J. Manner, G. Karagiannis, and A. McDonald. 'NSLP for Quality-of-Service signalling.' Internet Draft - Work in progress, Internet Engineering Task Force, January 2006. ...
An explicit-deadline prioritization scheduling for bandwidth allocation in fixed-length packet wireless networks
The proposed medium access protocol deals especially with the timely-transmission of real-time pa... more The proposed medium access protocol deals especially with the timely-transmission of real-time packets in wireless multimedia networks where users of various types of traffic are present. It works based on the time division multiple access (TDMA) with time division duplex (TDD) technique as well as fixed-length packet switching incorporating two policies, which work differently during non-congestion and congestion states. The simulation results show good performance of the proposed method, even under high-load conditions, and a good trade-off characteristic between real-time access delay and non-real time buffer occupancy, during periods of congestion
A Multi-channel infrastructure based on DCF access mechanism for Wireless LAN Mesh Networks compliant with IEEE 802.11
2005 Asia-Pacific Conference on Communications
The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promis... more The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promising architecture for achieving a ubiquitous wireless Internet access in the future. However, the current IEEE 802.11 protocol is aimed at single access point (AP) environments and many problems related to the wireless meshed interconnection of APs and mobile terminals (MTs) remain to
Speed-aware resource allocation and transmission scheme for the uplink channel of highly mobile MC-CDMA systems
APCC/MDMC '04. The 2004 Joint Conference of the 10th Asia-Pacific Conference on Communications and the 5th International Symposium on Multi-Dimensional Mobile Communications Proceeding
We propose a new transmission and resource allocation technique based on multicarrier direct-sequ... more We propose a new transmission and resource allocation technique based on multicarrier direct-sequence CDMA (MC-DS-CDMA). The proposed system allocates subcarriers and spreading codes to users by considering their current bandwidth requirements and frequency shifts caused by their movement. Through the use of low-correlation spreading codes in close subcarriers the scheme reduces the inter-carrier interference generated by high-speed users while keeping
Speed-aware multicarrier transmission and resource allocation scheme for the uplink channel of highly mobile networks
We propose a new transmission and resource allocation technique based on multicarrier direct-sequ... more We propose a new transmission and resource allocation technique based on multicarrier direct-sequence CDMA (MC-DS-CDMA). The proposed system allocates subcarriers and spreading codes to users by considering their current bandwidth requirements and frequency shifts caused by their movement. Through the use of low-correlation spreading codes in close subcarriers, the scheme reduces the intercarrier interference generated by high-speed users while keeping the intersymbol interference at a low level due to multicarrier transmission. The analysis and results show that a substantial mitigation of both the intercarrier interference and bit error rate, without reducing the system bandwidth efficiency, can be achieved.
An OFDMA/CDMA-based bandwidth resource allocation scheme for future broadband mobile networks
Vehicular Technology Conference, 1988, IEEE 38th
We propose a new transmission and multiple access method for future broadband wireless networks. ... more We propose a new transmission and multiple access method for future broadband wireless networks. The scheme combines the advantages of orthogonal frequency division multiple access (OFDMA) and code division multiple access (CDMA) to cope simultaneously with both frequency spread produced by the Doppler effect, and time spread caused by the multipath channel. Through the code orthogonalization of neighboring (close) OFDM subcarriers, the method mitigates the intercarrier interference generated by high speed users while keeping the advantages offered by OFDMA to diminish the intersymbol interference produced by multipaths. In this way, the method optimizes the reliability of the communication channel provided to every user according to its speed, position and channel characteristics. The allocation of subcarriers and orthogonal codes to users is carried out dynamically with time by considering parameters such as required bitrate, speed, level of interference, multipath effects and phy...
Opportunistic relaying vs. selective cooperation
Proceedings of the 11th international symposium on Modeling, analysis and simulation of wireless and mobile systems - MSWiM '08, 2008
Design and Evaluation of a Routing-Informed Cooperative MAC Protocol for Ad Hoc Networks
IEEE INFOCOM 2008 - The 27th Conference on Computer Communications, 2008
Abstract—Cooperative relaying has been shown to provide diversity gains which can significantly i... more Abstract—Cooperative relaying has been shown to provide diversity gains which can significantly improve the Packet Error Rate (PER) in wireless transmissions. In ad hoc wireless rout- ing where packets may travel over a number of hops before reaching the destination, hop-wise cooperative relaying may severely reduce network capacity. This approach was mainly addressed in literature so far. In this paper,
Multi-channel wireless LAN mesh architecture with DCF-based inter-AP communication and idle channel search packet forwarding
GLOBECOM '05. IEEE Global Telecommunications Conference, 2005., 2005
The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promis... more The mesh topology based on the standard IEEE 802.11 for wireless LANs appears to be a very promising architecture for achieving a ubiquitous wireless Internet access in the future. However, the current IEEE 802.11 protocol is aimed at single-AP (access point) environments and many problems related to the wireless meshed interconnection of APs and mobile terminals (MTs) remain to be solved. Some proposed solutions to build such mesh architectures are based on single-channel ad-hoc oriented schemes in which IEEE 802.11 protocol has been modified. The main problem with this type of schemes, however, lies in the very low performance of the single-channel architecture itself. The task group S of IEEE 802.11 is currently working out standards for IEEE 802.11-compliant mesh architectures in a number of usage scenarios including residential, office and campus/community/public access network but a lot of work remains to be done since the group was established just on last year. In this paper we propose a new multi-radio multi-channel mesh architecture for hot zones which works using a distributed coordination function (DCF)-based technique for interconnecting APs and a simple but effective radio routing mechanism. A major advantage of our proposed scheme is that, putting routing issues aside, it introduces no change into the MAC protocol of IEEE 802.11. Our simulations results obtained in OPNET show the great effectiveness of radio routing for balancing the traffic load within the network as well as interesting results related with the size of packets and the mesh architecture itself that could lead to further research in the future. Moreover, the results show the proposed architecture yields a very good performance in terms of total throughput and transmission delay
A new transmission and multiple access scheme based on multicarrier cdma for future highly mobile networks
14th IEEE Proceedings on Personal, Indoor and Mobile Radio Communications, 2003. PIMRC 2003., 2003
In this paper, we propose a new transmission and resource allocation technique on multicarrier di... more In this paper, we propose a new transmission and resource allocation technique on multicarrier direct-sequence CDMA (MC-DS-CDMA). The proposed system allocates subcarriers and spreading codes to users by considering their current bandwidth requirements and frequency shifts caused by their movement. Through the use of low-correlation spreading codes in close subcarriers the scheme reduces the inter-carrier interference generated by high-speed users
[Registration of an anomalous pathway potential in a patient with ventricular pre-excitation. A case report]
Arquivos brasileiros de cardiologia, 1984
Real-time services over best-effort networks, such as teleconferencing over unspecified , bit rat... more Real-time services over best-effort networks, such as teleconferencing over unspecified , bit rate (UBR) class asynchronous transfer mode (ATM) networks or the Internet, are expected to be in high demand in the near future as such services become more cost effective. However, cell loss caused by buffer overflow at switches is a serious problem in this service class, and is responsible for degradation of the Quality of Service (QoS). A promising technology for improving the QoS of best-effort networks is the recovery of lost cells by forward error correction (FEC). Conventional FEC methods utilize a FEC matrix with fixed dimensions and which is usually designed to cope with the worst case of cell loss. In this paper, a new method that provides dynamic recovery capacity to deal with the current cell loss ratio through the use of a variable-dimension FEC matrix is proposed. The scheme also takes into account the coding method of the matrix to provide data prioritization. Numerical results show that the cell loss ratio and transmission efficiency of the proposed method are superior to those of conventional methods.
Empirical efficiency gains of high-speed UDP-based protocols in realistic settings
Different cloud and data/video delivery applications require the use of high-speed links to fulfi... more Different cloud and data/video delivery applications require the use of high-speed links to fulfill a reasonable qu ality of experience. However, Internet connections in developing c ountries like Chile are -in many casesfar from being suitable for transferring large data files in a fast and efficient manner toend (non-business) users. These are usually non-dedicated lin ks, with no more than 10-20 Mbps at the user’s end, showing patterns of congestion (and high latency) when connecting to distant servers. In this context, it has been shown in controlled/l ab situationsthat certain UDP based protocols outperform TCP. In this work, we aim to empirically evaluate upper bounds of performance for a set of UDP-based protocols, comparing their efficiency with respect to TCP, in realistic settings. We performed a long-term measurement campaign, transmitting1 GB files from Santiago, Chile to Atlanta, US, allowing us to compute eventual efficiency gains of UDP, Tsunami and UDT over TCP. Our results show that UDT and UDP perform better than TCP and Tsunami when comparing their achievable rates, stability and completion time to download large files. In terms of their attainable throughput, UDP and UDT duplicate TCP (on average), where UDT has the added benefit of acknowledging receptions of data blocks, being then suitable for reliablehighspeed transmissions. Therefore, typical home-users with l imited download bandwidth would significantly improve their quali ty of experience if UDT is employed as an application-layer proto col for reliable transmissions, being not only transparent to them but also highly efficient.
Radio terminal, radio communication system and radio communication method
Recommender system for contextual advertising in IPTV scenarios
The 2010 14th International Conference on Computer Supported Cooperative Work in Design, 2010
Inter-Network Routing in Ambient Networks
2007 16th IST Mobile and Wireless Communications Summit, 2007
The ambient networks project is developing advanced networking capabilities, such as dynamic mult... more The ambient networks project is developing advanced networking capabilities, such as dynamic multi-access, network mobility, together with availability of ensured service or network context. The Ambient framework offers a "plug-and-play" flexibility to accommodate different routing schemes for alternative scenarios, ranging from completely flat topologies hanging off a common core network to deeply nested topologies attached to a core. This paper
Increasing the Capacity of IEEE 802.11 Wireless LAN through Cooperative Coded Retransmissions
VTC Spring 2008 - IEEE Vehicular Technology Conference, 2008
2008 Fourth Workshop on Network Coding, Theory and Applications, 2008
We consider the problem of finding the minimum number of transmissions in an ad-hoc network for a... more We consider the problem of finding the minimum number of transmissions in an ad-hoc network for all-to-all broadcasting using network coding. This work generalizes previous results for canonical topologies such as the circle and the wraparound grid to the finite-sized line, and non-wrap-around grid. The latter topologies better reflect network coding in random topologies, since the dissemination of information is "directional", in a sense that information usually arrives via the neighbors on the path to its originator instead of from all possible directions. We find that while the line topology requires a higher number of transmissions compared to the circle, this is interestingly not the case for the grid. We further present simulation results on a heuristic that estimates the required minimum number of transmissions in random wireless topologies and compare it to the optimum solution, as well as previously proposed heuristics.
Evaluation of a practical video fingerprinting system
2010 10th International Symposium on Communications and Information Technologies, 2010
Video fingerprinting is one of the most promising technologies to uniquely identify video content... more Video fingerprinting is one of the most promising technologies to uniquely identify video content in the Internet in a totally format-independent way. The logic behind the creation of the video fingerprints or perceptual hashes is a key factor for the performance of the system, especially in terms of storage and search efficiency. Although several video fingerprinting methods have been proposed,