Luis Bernardo | Universidade Nova de Lisboa (original) (raw)

Papers by Luis Bernardo

2018 IEEE 17th International Symposium on Network Computing and Applications (NCA), 2018

This paper studies what mechanisms a network must have to offer a very low-latency service to app... more This paper studies what mechanisms a network must have to offer a very low-latency service to applications (featuring a maximum end-to-end packet delay). We assume very concrete requirements, not seen in the literature, that raise the challenge level: i) applications might be unresponsive to traffic warnings from the network; and ii) applications do not inform or require any network resources, exactly as the Internet works today (i.e., there is no admission control procedures). We present an architecture/algorithm with a minimum of state information and good scalability properties. Obviously, it is not applicable to the wide Internet. Even more, the architecture is not TCP-friendly (because control loops must be shorter than the Round Trip Time (RTT) magnitudes and oscillations, and packet losses are higher). Instead, it is appropriate to an end-to-end slice network based on a virtualization of the physical network with independent queues and line bandwidths. It is designed for inte...

IEEE Transactions on Network Science and Engineering, 2019

Algebra has made the tasks of modelling routing algorithms and proving their correct operation ve... more Algebra has made the tasks of modelling routing algorithms and proving their correct operation very clear. However, traditional models are only concerned with the convergence to a stable routing solution not covering distributed hop-by-hop forwarding on multiple paths (within a flow or separately per flow). This paper addresses this challenge. Currently, loop-free distributed multipath forwarding is only proven if a strict decrease in the preference of a path occurs with every added link. This is very rigid for multipath routing, limiting the amount of equal preferred paths. In this work we prove that correct distributed forwarding behaviour is possible, without the strict decrease in preference, if the possible pairs of policy values applied to the directed edges connecting two nodes obey to a particular condition. If this is not true, correct behaviour is still possible if the policies applied to links forming circuits in the network graph are constrained according to two other conditions. Modern technologies are bringing the possibility to build new routing protocols using network programmability while distributed operation is still needed in many scenarios due to scaling issues. We show how our results can be relevant in this setting and serve as a tool in the design process and/or for formal protocol verification. Organic semiconductors Reconfigurable logic Cloud gaming Floppy disks Synchrocyclotrons Ultra-dense networks. Kirk field collapse effect Oral communication Chemical oxygen iodine lasers Technology forecasting Automobile manufacture Data warehouses Electromagnetic reflection Universal motors Web and internet services Obesity. Cataracts Lithium-sulfur batteries Nanogenerators Bioceramics Resource description framework Internal combustion engines Whales. PSNR Sea surface roughness Semiconductor device modeling Thermooptic effects Neuromorphic engineering Phishing Land mobile radio Domain Name System Nanoporous materials Semantic Web Optical switches Network function virtualization.

IEEE Transactions on Cognitive Communications and Networking, 2016

2016 IEEE 24th International Conference on Network Protocols (ICNP), 2016

Software Defined Networks (SDNs) provides a separation between the control plane and the forwardi... more Software Defined Networks (SDNs) provides a separation between the control plane and the forwarding plane of networks. The software implementation of the control plane and the built in data collection mechanisms of the OpenFlow protocol promise to be excellent tools to implement Machine Learning (ML) network control applications. A first step in that direction is to understand the type of data that can be collected in SDNs and how information can be learned from that data. In this work we describe a simple architecture deployed in an enterprise network that gathers traffic data using the OpenFlow protocol. We present the data-sets that can be obtained and show how several ML techniques can be applied to it for traffic classification. The results indicate that high accuracy classification can be obtained with the data-sets using supervised learning.

2016 IEEE International Conference on Communications (ICC), 2016

This paper presents a scalable solution for guaranteeing bandwidth to interactions/communications... more This paper presents a scalable solution for guaranteeing bandwidth to interactions/communications assuming no information is provided by the applications. The objective is to define and assess what the network can do with so little information both in terms of guaranteeing quality and preventing being throttled by overloads. The suggestion of having applications indicating their needs did not materialize in the past and it is not credible to happen in the future. Applications tend to adapt to the conditions of the network (instead of requiring resources), and can drive the network to a halt. With no explicit information, the network must firstly protect itself from being driven into an uncontrolled saturation situation with unacceptable delays, and secondly devise what kind of guarantees can still be provided to applications. In this paper, if interactions live enough time, they become flows without any disruption in traffic or initial delays for flow establishment. Traffic is aggregated in the core and all flows access the network up to a maximum rate that is calculated when they begin. When the network becomes loaded, traffic that was granted guarantees is protected. New traffic is never blocked from accessing the network and may even get guarantees.

IEEE Vehicular Technology Conference, 2011

ABSTRACT Packet Combining (PC) and Multipacket Reception (MPR) techniques have great potential to... more ABSTRACT Packet Combining (PC) and Multipacket Reception (MPR) techniques have great potential to deal with lost packets since both take full advantage of the signals associated to all failed transmission attempts. However, their performance evaluation in practical systems is difficult because lengthy simulations are needed to obtain the packet error rates for specific channel conditions. The paper presents an analytical tool to obtain the Bit Error Rate (BER) and Packet Error Rate (PER) performances for Packet Combining (PC), Multipacket Reception (MPR) and the hybrid of both schemes, based on Iterative Block Decision Feedback Equalization (IB-DFE) receivers for Single-Carrier with Frequency-Domain Equalization (SC-FDE). A set of simulation results show that the proposed analytical approach has accurate Bit Error Rate (BER) and Packet Error Rate (PER) results with a simple and relatively fast method.

Lecture Notes in Computer Science, 2013

Future wireless systems will need to cope with highly dispersive channels in order to support hig... more Future wireless systems will need to cope with highly dispersive channels in order to support high data rates. A slotted Prefix-assisted DS-CDMA allows the multiplexing of various Mobile Terminals (MTs) at the uplink with appropriate Frequency Domain Equalization (FDE) to support the dispersive channels. However data packets can be received with errors due to channel interference or from a deep fade that persists for several slots; to cope with those errors a type II Hybrid Automatic Repeat reQuest (H-ARQ) protocol could be employed to re-use the signals from past packet copies to diminish errors. Most wireless CDMA models that employ H-ARQ assume a simplified characterization of the wireless channel, based on an average Signal to Interference-Noise Ratio (SINR), with simultaneous data transmissions from the MTs to a Base Station (BS). This paper proposes a DS-CDMA model that accounts the MTs’ channel interference and channel noise simultaneously; packet reception is possible with the aid of a linear equalization method previously published by the authors. The wireless MAC model is characterized with Discrete-Time Markov Chain (DTMC), where the delay and throughput are obtained for a Poisson packet generator. The performance of the wireless model shows accurate results against the simulation values.

2014 IEEE International Conference on Communications (ICC), 2014

ABSTRACT Ethernet is the Layer 2 infrastructure of choice for modern data center networks and ser... more ABSTRACT Ethernet is the Layer 2 infrastructure of choice for modern data center networks and service provider metro networks. These networks need to scale to a high number of end hosts and bridges, provide isolation between tenants and support host mobility with an efficient bandwidth use and reduced operating costs. Ethernet uses controlled flooding of frames and the spanning tree protocol, falling short on demands like scalability and full usage of the topology. Solutions at Layer 3 solve some of the problems but they are harder to configure, more expensive and pose difficulties to host mobility. Recent efforts try to bring some of the advantages of L3 to L2 by using equal cost multipath (ECMP) control planes to populate the bridges forwarding tables. In this paper we go beyond and propose a non-ECMP solution where the paths are selected by policy. This means that very different paths (in terms of the physical topology) can be considered equal. It provides an extra layer of flexibility in traffic distribution with a high utilization of the network in a single L2 Ethernet domain. Our design is based on routing algebra theory and its correct behaviour can be proved for both centralized and distributed implementations.

ABSTRACT Traditionally, Low Earth Orbit (LEO) satellite networks use hard handovers when a Mobile... more ABSTRACT Traditionally, Low Earth Orbit (LEO) satellite networks use hard handovers when a Mobile Terminal (MT) moves between the footprints of two satellites. Such approach introduces a transitory disconnection interval, which may limit the capacity to provide demanding real-time requirements. A soft- handover approach that applies distributed packet combining on a satellite diversity scenario is proposed in this paper. Considering inexpensive MT hardware and low transmission powers, the paper analyses the performance gains and the difficulties that are associated to different Doppler and time-of-arrival shifts when the MT signal is broadcast to two satellites during the short handover period where both satellite's footprint overlap. A Single-Carrier with Frequency Domain Equalization (SC-FDE) transmission technique is considered in this paper. It is shown that it is possible to have an inter-satellite handover almost without quality of service (QoS) degradation for a Satellite Network Diversity Multiple Access (S-NDMA) scheme.

ICT 2014 International Conference on Telecommunications, 2014

ABSTRACT Femtocells were proposed as a solution to improve the performance in dense networks. The... more ABSTRACT Femtocells were proposed as a solution to improve the performance in dense networks. They complement the macro base stations (eNB) with a dense set of low power micro base stations (HeNB). However, they also bring increased interference problems and consequently more collisions and lost packets. This paper considers the use of femtocells running the Single Carrier with Frequency Domain Equalization (SC-FDE) transmission technique. It evaluates the performance of an Iterative Block Decision-Feedback Equalizer (IB-DFE) receiver employing Interference Cancellation (IC) techniques in the downlink channel. Using the interference cancellation capability, it is possible to dynamically adjust the network deployment and reduce the network total energy consumption. This paper also proposes a HeNB control algorithm and evaluates the energy saving capabilities of the reception technique for different load levels. Results show that it is possible to turn off femtocells and still satisfy the user's requirements, with significant energy saving.

ABSTRACT Random access approaches in Low Earth Orbit (LEO) satellite networks are usually incompa... more ABSTRACT Random access approaches in Low Earth Orbit (LEO) satellite networks are usually incompatible with the Quality of Service (QoS) requirements for multimedia traffic, especially when hand-held terminals must operate with a very low signal-to-noise ratio. This paper proposes the Satellite Random Network Diversity Multiple Access (SR-NDMA) protocol that handles multimedia traffic under this context through the combination of a random and scheduled access scheme. The protocol uses a multi-packet receiver, for Single Carrier with Frequency Domain Equalization (SC-FDE) in the uplink, that gradually reduces the packet error rate with additional transmissions. The paper proposes analytical performance models for the throughput, delay and energy efficiency - as long as terminals have finite queues. System parameters are defined to enhance the energy efficiency while satisfying the QoS requirements for limited queue and bit-rate constraints. Results show that the proposed system is energy efficient and provides enough QoS to support multimedia services such as video telephony.

IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 2007

The strong research on the performance of the IEEE 802.11 standard seen lately contributes to a b... more The strong research on the performance of the IEEE 802.11 standard seen lately contributes to a better understanding of the network and as a starting point for the design of future networks (specially in the ad-hoc area). In a recent work[6] we proposed a model to study the IEEE ...

IEEE Wireless Communications and Networking Conference, WCNC, 2010

This paper considers the use of SC modulations (Single-Carrier) with FDE (Frequency-Domain Equali... more This paper considers the use of SC modulations (Single-Carrier) with FDE (Frequency-Domain Equalization) with low-complexity soft combining ARQ schemes (Automatic Repeat reQuest). With our technique, packets associated to different transmission attempts are combined in a soft way, allowing improved performances. Its low complexity makes it particularly interesting for the uplink of wireless systems. This paper proposes an accurate analytical model

IEEE Vehicular Technology Conference, 2010

Abstract - This paper considers the use of low-complexity diversity combining hybrid ARQ schemes ... more Abstract - This paper considers the use of low-complexity diversity combining hybrid ARQ schemes (Au-tomatic Repeat reQuest) on a TDMA (Time Division Multiple Access) system. Its low complexity makes it particularly interesting for battery-powered nodes of a wireless sensor network ( ...

IEEE Wireless Communications and Networking Conference, WCNC, 2010

This paper deals with multi-packet detection for SC modulations (Single-Carrier) with FDE (Freque... more This paper deals with multi-packet detection for SC modulations (Single-Carrier) with FDE (Frequency- Domain Equalization). We consider iterative frequency-domain receivers that jointly perform equalization, multi-packet separation and channel decoding operations, for up to Qmax mobile terminals transmitting in one slot. In this paper we propose an accurate analytical model for a p-persistent random access MAC protocol, designed to handle a

IEEE Wireless Communications and Networking Conference, WCNC, 2010

This paper proposes the Mobile MH-MAC (Multimode Hybrid-Medium Access Control) protocol, an exten... more This paper proposes the Mobile MH-MAC (Multimode Hybrid-Medium Access Control) protocol, an extension of MH-MAC with enhanced support for mobility on wireless sensor networks. It provides an asynchronous mode for energy efficiency during idle (unconnected) periods, and a synchronous mode for high throughput periods. Mode change is controlled by the application in a cross-layer approach. MMH-MAC was specially designed to tolerate asynchronous mobile nodes in the neighborhood of synchronous nodes, providing fast transition and interference mitigation mechanisms. Current MAC protocols rely on a passive method to associate a mobile node to a static cluster, triggered by the reception of a beacon. We propose an active approach that allows a mobile node to start sending data packets shortly after entering into data range of a static node, with negligible data loss in existing synchronous data connections. MMH-MAC was implemented in TinyOS and tested on TelosB motes and TOSSIM simulator.

IEEE Vehicular Technology Conference, 2011

... in Vehicular ad hoc Networks R. Oliveira † , A. Garrido † , R. Pasquini ‡ , M. Luıs †§ , L. B... more ... in Vehicular ad hoc Networks R. Oliveira † , A. Garrido † , R. Pasquini ‡ , M. Luıs †§ , L. Bernardo † , R. Dinis †§ , P. Pinto † ... In unicast position-based routing protocols [2], the nodes do not need to store any route or routing table to the destination. ...

Proceedings - International Conference on Computer Communications and Networks, ICCCN, 2011

ABSTRACT Traditionally, a packet with errors, either due to channel noise or collisions, is disca... more ABSTRACT Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retrans- mitted, leading to performance losses. Network Diversity Multiple Access (NDMA) handles collisions by combining a multipacket detection scheme with time diversity. In NDMA, the Base Station (BS) forces Mobile Terminals (MTs) to transmit J copies of each packet when J MTs collide. Diversity combining is limited to J copies of the packets, not allowing it to adapt to severe errors due to channel noise. This paper considers a multipacket detection scheme recently proposed, which reduces the packet error rate (PER) when more than J copies of the packets are available. In this paper, an Hybrid-ARQ NDMA access mechanism is proposed. The access mechanism forces contending MTs during a collision resolution epoch to transmit more than J times when errors are detected. Analytical models are proposed for the goodput and delay, considering Poisson traffic. The proposed system performance is evaluated for a Single-Carrier with Frequency Domain Equalization (SC-FDE) scheme, and compared to classical NDMA. 1

2018 IEEE 17th International Symposium on Network Computing and Applications (NCA), 2018

This paper studies what mechanisms a network must have to offer a very low-latency service to app... more This paper studies what mechanisms a network must have to offer a very low-latency service to applications (featuring a maximum end-to-end packet delay). We assume very concrete requirements, not seen in the literature, that raise the challenge level: i) applications might be unresponsive to traffic warnings from the network; and ii) applications do not inform or require any network resources, exactly as the Internet works today (i.e., there is no admission control procedures). We present an architecture/algorithm with a minimum of state information and good scalability properties. Obviously, it is not applicable to the wide Internet. Even more, the architecture is not TCP-friendly (because control loops must be shorter than the Round Trip Time (RTT) magnitudes and oscillations, and packet losses are higher). Instead, it is appropriate to an end-to-end slice network based on a virtualization of the physical network with independent queues and line bandwidths. It is designed for inte...

IEEE Transactions on Network Science and Engineering, 2019

Algebra has made the tasks of modelling routing algorithms and proving their correct operation ve... more Algebra has made the tasks of modelling routing algorithms and proving their correct operation very clear. However, traditional models are only concerned with the convergence to a stable routing solution not covering distributed hop-by-hop forwarding on multiple paths (within a flow or separately per flow). This paper addresses this challenge. Currently, loop-free distributed multipath forwarding is only proven if a strict decrease in the preference of a path occurs with every added link. This is very rigid for multipath routing, limiting the amount of equal preferred paths. In this work we prove that correct distributed forwarding behaviour is possible, without the strict decrease in preference, if the possible pairs of policy values applied to the directed edges connecting two nodes obey to a particular condition. If this is not true, correct behaviour is still possible if the policies applied to links forming circuits in the network graph are constrained according to two other conditions. Modern technologies are bringing the possibility to build new routing protocols using network programmability while distributed operation is still needed in many scenarios due to scaling issues. We show how our results can be relevant in this setting and serve as a tool in the design process and/or for formal protocol verification. Organic semiconductors Reconfigurable logic Cloud gaming Floppy disks Synchrocyclotrons Ultra-dense networks. Kirk field collapse effect Oral communication Chemical oxygen iodine lasers Technology forecasting Automobile manufacture Data warehouses Electromagnetic reflection Universal motors Web and internet services Obesity. Cataracts Lithium-sulfur batteries Nanogenerators Bioceramics Resource description framework Internal combustion engines Whales. PSNR Sea surface roughness Semiconductor device modeling Thermooptic effects Neuromorphic engineering Phishing Land mobile radio Domain Name System Nanoporous materials Semantic Web Optical switches Network function virtualization.

IEEE Transactions on Cognitive Communications and Networking, 2016

2016 IEEE 24th International Conference on Network Protocols (ICNP), 2016

Software Defined Networks (SDNs) provides a separation between the control plane and the forwardi... more Software Defined Networks (SDNs) provides a separation between the control plane and the forwarding plane of networks. The software implementation of the control plane and the built in data collection mechanisms of the OpenFlow protocol promise to be excellent tools to implement Machine Learning (ML) network control applications. A first step in that direction is to understand the type of data that can be collected in SDNs and how information can be learned from that data. In this work we describe a simple architecture deployed in an enterprise network that gathers traffic data using the OpenFlow protocol. We present the data-sets that can be obtained and show how several ML techniques can be applied to it for traffic classification. The results indicate that high accuracy classification can be obtained with the data-sets using supervised learning.

2016 IEEE International Conference on Communications (ICC), 2016

This paper presents a scalable solution for guaranteeing bandwidth to interactions/communications... more This paper presents a scalable solution for guaranteeing bandwidth to interactions/communications assuming no information is provided by the applications. The objective is to define and assess what the network can do with so little information both in terms of guaranteeing quality and preventing being throttled by overloads. The suggestion of having applications indicating their needs did not materialize in the past and it is not credible to happen in the future. Applications tend to adapt to the conditions of the network (instead of requiring resources), and can drive the network to a halt. With no explicit information, the network must firstly protect itself from being driven into an uncontrolled saturation situation with unacceptable delays, and secondly devise what kind of guarantees can still be provided to applications. In this paper, if interactions live enough time, they become flows without any disruption in traffic or initial delays for flow establishment. Traffic is aggregated in the core and all flows access the network up to a maximum rate that is calculated when they begin. When the network becomes loaded, traffic that was granted guarantees is protected. New traffic is never blocked from accessing the network and may even get guarantees.

IEEE Vehicular Technology Conference, 2011

ABSTRACT Packet Combining (PC) and Multipacket Reception (MPR) techniques have great potential to... more ABSTRACT Packet Combining (PC) and Multipacket Reception (MPR) techniques have great potential to deal with lost packets since both take full advantage of the signals associated to all failed transmission attempts. However, their performance evaluation in practical systems is difficult because lengthy simulations are needed to obtain the packet error rates for specific channel conditions. The paper presents an analytical tool to obtain the Bit Error Rate (BER) and Packet Error Rate (PER) performances for Packet Combining (PC), Multipacket Reception (MPR) and the hybrid of both schemes, based on Iterative Block Decision Feedback Equalization (IB-DFE) receivers for Single-Carrier with Frequency-Domain Equalization (SC-FDE). A set of simulation results show that the proposed analytical approach has accurate Bit Error Rate (BER) and Packet Error Rate (PER) results with a simple and relatively fast method.

Lecture Notes in Computer Science, 2013

Future wireless systems will need to cope with highly dispersive channels in order to support hig... more Future wireless systems will need to cope with highly dispersive channels in order to support high data rates. A slotted Prefix-assisted DS-CDMA allows the multiplexing of various Mobile Terminals (MTs) at the uplink with appropriate Frequency Domain Equalization (FDE) to support the dispersive channels. However data packets can be received with errors due to channel interference or from a deep fade that persists for several slots; to cope with those errors a type II Hybrid Automatic Repeat reQuest (H-ARQ) protocol could be employed to re-use the signals from past packet copies to diminish errors. Most wireless CDMA models that employ H-ARQ assume a simplified characterization of the wireless channel, based on an average Signal to Interference-Noise Ratio (SINR), with simultaneous data transmissions from the MTs to a Base Station (BS). This paper proposes a DS-CDMA model that accounts the MTs’ channel interference and channel noise simultaneously; packet reception is possible with the aid of a linear equalization method previously published by the authors. The wireless MAC model is characterized with Discrete-Time Markov Chain (DTMC), where the delay and throughput are obtained for a Poisson packet generator. The performance of the wireless model shows accurate results against the simulation values.

2014 IEEE International Conference on Communications (ICC), 2014

ABSTRACT Ethernet is the Layer 2 infrastructure of choice for modern data center networks and ser... more ABSTRACT Ethernet is the Layer 2 infrastructure of choice for modern data center networks and service provider metro networks. These networks need to scale to a high number of end hosts and bridges, provide isolation between tenants and support host mobility with an efficient bandwidth use and reduced operating costs. Ethernet uses controlled flooding of frames and the spanning tree protocol, falling short on demands like scalability and full usage of the topology. Solutions at Layer 3 solve some of the problems but they are harder to configure, more expensive and pose difficulties to host mobility. Recent efforts try to bring some of the advantages of L3 to L2 by using equal cost multipath (ECMP) control planes to populate the bridges forwarding tables. In this paper we go beyond and propose a non-ECMP solution where the paths are selected by policy. This means that very different paths (in terms of the physical topology) can be considered equal. It provides an extra layer of flexibility in traffic distribution with a high utilization of the network in a single L2 Ethernet domain. Our design is based on routing algebra theory and its correct behaviour can be proved for both centralized and distributed implementations.

ABSTRACT Traditionally, Low Earth Orbit (LEO) satellite networks use hard handovers when a Mobile... more ABSTRACT Traditionally, Low Earth Orbit (LEO) satellite networks use hard handovers when a Mobile Terminal (MT) moves between the footprints of two satellites. Such approach introduces a transitory disconnection interval, which may limit the capacity to provide demanding real-time requirements. A soft- handover approach that applies distributed packet combining on a satellite diversity scenario is proposed in this paper. Considering inexpensive MT hardware and low transmission powers, the paper analyses the performance gains and the difficulties that are associated to different Doppler and time-of-arrival shifts when the MT signal is broadcast to two satellites during the short handover period where both satellite's footprint overlap. A Single-Carrier with Frequency Domain Equalization (SC-FDE) transmission technique is considered in this paper. It is shown that it is possible to have an inter-satellite handover almost without quality of service (QoS) degradation for a Satellite Network Diversity Multiple Access (S-NDMA) scheme.

ICT 2014 International Conference on Telecommunications, 2014

ABSTRACT Femtocells were proposed as a solution to improve the performance in dense networks. The... more ABSTRACT Femtocells were proposed as a solution to improve the performance in dense networks. They complement the macro base stations (eNB) with a dense set of low power micro base stations (HeNB). However, they also bring increased interference problems and consequently more collisions and lost packets. This paper considers the use of femtocells running the Single Carrier with Frequency Domain Equalization (SC-FDE) transmission technique. It evaluates the performance of an Iterative Block Decision-Feedback Equalizer (IB-DFE) receiver employing Interference Cancellation (IC) techniques in the downlink channel. Using the interference cancellation capability, it is possible to dynamically adjust the network deployment and reduce the network total energy consumption. This paper also proposes a HeNB control algorithm and evaluates the energy saving capabilities of the reception technique for different load levels. Results show that it is possible to turn off femtocells and still satisfy the user's requirements, with significant energy saving.

ABSTRACT Random access approaches in Low Earth Orbit (LEO) satellite networks are usually incompa... more ABSTRACT Random access approaches in Low Earth Orbit (LEO) satellite networks are usually incompatible with the Quality of Service (QoS) requirements for multimedia traffic, especially when hand-held terminals must operate with a very low signal-to-noise ratio. This paper proposes the Satellite Random Network Diversity Multiple Access (SR-NDMA) protocol that handles multimedia traffic under this context through the combination of a random and scheduled access scheme. The protocol uses a multi-packet receiver, for Single Carrier with Frequency Domain Equalization (SC-FDE) in the uplink, that gradually reduces the packet error rate with additional transmissions. The paper proposes analytical performance models for the throughput, delay and energy efficiency - as long as terminals have finite queues. System parameters are defined to enhance the energy efficiency while satisfying the QoS requirements for limited queue and bit-rate constraints. Results show that the proposed system is energy efficient and provides enough QoS to support multimedia services such as video telephony.

IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 2007

The strong research on the performance of the IEEE 802.11 standard seen lately contributes to a b... more The strong research on the performance of the IEEE 802.11 standard seen lately contributes to a better understanding of the network and as a starting point for the design of future networks (specially in the ad-hoc area). In a recent work[6] we proposed a model to study the IEEE ...

IEEE Wireless Communications and Networking Conference, WCNC, 2010

This paper considers the use of SC modulations (Single-Carrier) with FDE (Frequency-Domain Equali... more This paper considers the use of SC modulations (Single-Carrier) with FDE (Frequency-Domain Equalization) with low-complexity soft combining ARQ schemes (Automatic Repeat reQuest). With our technique, packets associated to different transmission attempts are combined in a soft way, allowing improved performances. Its low complexity makes it particularly interesting for the uplink of wireless systems. This paper proposes an accurate analytical model

IEEE Vehicular Technology Conference, 2010

Abstract - This paper considers the use of low-complexity diversity combining hybrid ARQ schemes ... more Abstract - This paper considers the use of low-complexity diversity combining hybrid ARQ schemes (Au-tomatic Repeat reQuest) on a TDMA (Time Division Multiple Access) system. Its low complexity makes it particularly interesting for battery-powered nodes of a wireless sensor network ( ...

IEEE Wireless Communications and Networking Conference, WCNC, 2010

This paper deals with multi-packet detection for SC modulations (Single-Carrier) with FDE (Freque... more This paper deals with multi-packet detection for SC modulations (Single-Carrier) with FDE (Frequency- Domain Equalization). We consider iterative frequency-domain receivers that jointly perform equalization, multi-packet separation and channel decoding operations, for up to Qmax mobile terminals transmitting in one slot. In this paper we propose an accurate analytical model for a p-persistent random access MAC protocol, designed to handle a

IEEE Wireless Communications and Networking Conference, WCNC, 2010

This paper proposes the Mobile MH-MAC (Multimode Hybrid-Medium Access Control) protocol, an exten... more This paper proposes the Mobile MH-MAC (Multimode Hybrid-Medium Access Control) protocol, an extension of MH-MAC with enhanced support for mobility on wireless sensor networks. It provides an asynchronous mode for energy efficiency during idle (unconnected) periods, and a synchronous mode for high throughput periods. Mode change is controlled by the application in a cross-layer approach. MMH-MAC was specially designed to tolerate asynchronous mobile nodes in the neighborhood of synchronous nodes, providing fast transition and interference mitigation mechanisms. Current MAC protocols rely on a passive method to associate a mobile node to a static cluster, triggered by the reception of a beacon. We propose an active approach that allows a mobile node to start sending data packets shortly after entering into data range of a static node, with negligible data loss in existing synchronous data connections. MMH-MAC was implemented in TinyOS and tested on TelosB motes and TOSSIM simulator.

IEEE Vehicular Technology Conference, 2011

... in Vehicular ad hoc Networks R. Oliveira † , A. Garrido † , R. Pasquini ‡ , M. Luıs †§ , L. B... more ... in Vehicular ad hoc Networks R. Oliveira † , A. Garrido † , R. Pasquini ‡ , M. Luıs †§ , L. Bernardo † , R. Dinis †§ , P. Pinto † ... In unicast position-based routing protocols [2], the nodes do not need to store any route or routing table to the destination. ...

Proceedings - International Conference on Computer Communications and Networks, ICCCN, 2011

ABSTRACT Traditionally, a packet with errors, either due to channel noise or collisions, is disca... more ABSTRACT Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retrans- mitted, leading to performance losses. Network Diversity Multiple Access (NDMA) handles collisions by combining a multipacket detection scheme with time diversity. In NDMA, the Base Station (BS) forces Mobile Terminals (MTs) to transmit J copies of each packet when J MTs collide. Diversity combining is limited to J copies of the packets, not allowing it to adapt to severe errors due to channel noise. This paper considers a multipacket detection scheme recently proposed, which reduces the packet error rate (PER) when more than J copies of the packets are available. In this paper, an Hybrid-ARQ NDMA access mechanism is proposed. The access mechanism forces contending MTs during a collision resolution epoch to transmit more than J times when errors are detected. Analytical models are proposed for the goodput and delay, considering Poisson traffic. The proposed system performance is evaluated for a Single-Carrier with Frequency Domain Equalization (SC-FDE) scheme, and compared to classical NDMA. 1