Communications in Computer and Information Science
This paper presents MANET-VoVON, a new Internet application for mobile ad-hoc networks (MANETs) p... more This paper presents MANET-VoVON, a new Internet application for mobile ad-hoc networks (MANETs) providing voice over virtual overlay networks. A MANET-enabled version of JXTA peer-to-peer modular open platform (MANET-JXTA) is used to support user location and optionally, audio streaming over the JXTA virtual overlay network. Using MANET-JXTA, a client can search asynchronously for a user, and delay the call setup until a path is available to reach the user. The application uses a private signalling protocol based on the exchange of XML messages over MANET-JXTA communication channels. Nevertheless, it is fully interoperable with normal SIP clients through an embedded gateway function. This paper describes a prototype implementation of the proposed application and of the MANET-JXTA, and presents some performance measurements.
To understand the symbolic elements and the hierarchical system of representations of elderly peo... more To understand the symbolic elements and the hierarchical system of representations of elderly people on falls, according to Abric's structural analysis and Neuman's theory. Abric structural approach developed at the home of primary care users in a city of Minas Gerais. A free evocation technique of images triggered by images was performed in 2016 with elderly individuals (≥65 years old). Data treated by dictionary of equivalent terms; processed in Evoc 2000 software converging, analytically, according to Neuman. Ethical/legal criteria were met. 195 people participated, 78.5% were women, and 45.1% were aged ≥75 years. Summarized 897 words; 155 different ones. Central nucleus containing cognates: dizziness-vertigo-labyrinthitis and slipper-shoes (behavioral and objective dimension). The word disease integrated the area of contrast. Environmental and personal stressors were identified according to Neuman. Final considerations: Objects and risk behaviors for falls integrated the...
Prefix-assisted direct-sequence code-division multiple access (DS-CDMA) is a viable transmission ... more Prefix-assisted direct-sequence code-division multiple access (DS-CDMA) is a viable transmission technique for high-data-rate wireless broadband systems, capable of coping with highly dispersive channels at the uplink. Packet combining (PC) ARQ with an iterative block decision feedback equalization (IB-DFE) technique can be used to cope with errors. However, extracting the IB-DFE's packet error rate (PER) for MAC-layer simulations can be time consuming. Most works that model the DS-CDMA behavior with PC ARQ use simplified asymptotic PER models in the study of the system performance, which are not precise for low signal-to-noise ratios and for a low number of mobile terminals (MTs). In this paper, the MAC performance is modeled using a discrete-time Markov chain that relies on a PER model. As an example, this paper describes a PER analytical model for an uncoded prefix-assisted DS-CDMA system with PC ARQ that considers the following inputs: the number of MTs accessing the channel, the MTs' number of transmissions, and the channel realizations for a given bit energy over noise ratio. The results show that the model portrays with better accuracy the simulations' results, compared with an alternative asymptotic model.
Even codes are prefix-free codes where every encoding contains an even number of 1's, thus having... more Even codes are prefix-free codes where every encoding contains an even number of 1's, thus having ability of detecting the occurrence of an odd number of 1-bit errors in a message. The motivation for defining such codes comes from a problem posed by Hamming in 1980. Even codes have been studied for the case in which symbols have uniform probabilities. In this work, we consider the general case of arbitrary probabilities. An exact algorithm for constructing an optimal even code is described with complexity O(n 3), where n is the number of symbols. Further, two approximation algorithms for constructing nearly optimal even codes are presented, both requiring O(n log n) time; in addition, the running time is O(n) if the symbols are given ordered by their probabilities. The cost of the even code constructed by the second approximation algorithm is at most 16.7% higher than the cost of a Huffman code, for the same probabilities. However, computational experiments suggest that, in practice, this difference is about 5%, for n large enough.
1998 1st IEEE International Conference on ATM. ICATM'98
Network technology is becoming simpler in order to support the widest possible range of user appl... more Network technology is becoming simpler in order to support the widest possible range of user applications. Therefore, the specific requirements of each application must be performed outside of the network and the adaptation mechanisms should be done by the applications. For the case of multimedia applications the programming task can even be more simplified if several "low-level" aspects can be made transparent by the use of a suitable framework. This paper presents such a framework with some algorithms to control some of the previous aspects, namely data handling and dynamic QoS control. It provides the application with a mechanism to constantly adapt the quality of the continuous media being transmitted. The algorithm takes into account not only the network conditions but the end host conditions as well. Some experiments are presented.
Communications in Computer and Information Science, 2007
Mobile ad hoc network (MANET) is an infrastructure less network, in where all mobile nodes are fr... more Mobile ad hoc network (MANET) is an infrastructure less network, in where all mobile nodes are free for any movement to any side. Thus the network is going toward zero configurations that would create some problems. Ad hoc network is faced with various limitations that need to be considered among design and implementation of any protocol for it. Service Advertisement (SA) is one of the important services that are offered in each network. To have a fast service discovery in a network with minimum energy consumption, distributing of services' information and their management play important roles. In this paper for avoiding packet flooding in the MANET we used Cluster Based Routing Protocol (CBRP). For reducing amount of communication messages we moved service advertisement from application layer to routing layer. Thus we distribute the active services in the network among clustered nodes. However, the results of our experiment show that our method does not add any extra overhead to the network.
Proceedings - Advanced Industrial Conference on Telecommunications/Service Assurance with Partial and Intermittent Resources Conference/E-Learning on Telecommunications Workshop AICT/SAPIR/ELETE 2005, 2005
Integration of different radio access networks will become a reality in a near future. Our interw... more Integration of different radio access networks will become a reality in a near future. Our interworking architecture assumes a ubiquitous primary network (the cellular one) and secondary networks used on an availability basis. Secondary networks form islands of coverage providing partial and intermittent resources with greater Quality of Service as the user moves along. This paper describes an application architecture that manages these resources in an opportunistic way. It makes use of the Open Service Access (OSA) to control the core network and the OSA application servers to host the new applications that can take advantage of the pi-resources. These applications create a context for secondary networks and the context can survive losses of coverage.
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 2006
Most studies on performance of IEEE 802.11 DCF networks do not contemplate the existence of broad... more Most studies on performance of IEEE 802.11 DCF networks do not contemplate the existence of broadcast traffic. They model network behaviour in presence of unicast traffic alone. In a real scenario, broadcast frames exist, and they will influence the overall network behaviour. This work presents a new traffic generalized model for CSMA/CA saturated single-hop networks able to describe the network behaviour in presence of both unicast and broadcast frames. Interesting statistics like station transmission probability, average time needed to complete a frame transmission, and network aggregate throughput are deduced from the model. The paper compares the performance of our model with other models proposed only for unicast traffic. Our model is validated for broadcast and unicast traffic through simulations, using an IEEE 802.11 DCF network scenario. Results are presented and analysed for different scenarios of broadcast/unicast network loads, different number of nodes and different frame data lengths.
IFIP Advances in Information and Communication Technology, 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 for a TDMA (Time Division Multiple Access) scheme where packet combining ARQ is applied. It evaluates the uplink non-saturated packet delay for a generic message arrival process. Our analytical results are validated using physical and MAC layer simulations.
This paper presents an algorithm to control QoS for distributed multimedia applications. The algo... more This paper presents an algorithm to control QoS for distributed multimedia applications. The algorithm approaches the problem in an integrated way solving both the problems of the network bandwidth and the load at the workstations. It interacts with the applications by an abstract sequence to describe values for QoS that are more meaningful to application programmers than the low-level entities such as cell loss rate, throughput, etc. Some experimental results of the algorithm are presented.
Proceedings of the third ACM international conference on Multimedia - MULTIMEDIA '95, 1995
This paper addresses algorithms to meet the QoS parameters related with the synchronization of is... more This paper addresses algorithms to meet the QoS parameters related with the synchronization of isochronous (or continuous) media. It is broadly accepted to divide the synchronization problem into high level (extrinsic) synchronization; and low level (intrinsic) synchronization. The first refers to the media presentation control problem and is related to the object model and the composition concepts of the basic parts of the objects (when they begin, end, etc.). There are already some standards (HyTime[12], MHEG[7]) and also other academic contributions ([19],[10] and [14]).
Scalable Internet services are based on sets of peer application servers. A decentralized locatio... more Scalable Internet services are based on sets of peer application servers. A decentralized location service is used to resolve human readable application identifiers and return the nearest application server reference. This paper evaluates several services and algorithms from the Internet, grid and peer-to-peer community services. It identifies two potential problems and proposes a new approach for handling them. Existing techniques structure the overlay networks using tree structures. The proposed service enhances the structure with meshed structures at each level, creating dynamically multiple paths to enhance scalability. We present a study and simulation results on one aspect of scalability-sudden load of requests from users. Our service adapts to the load reaching a stable stage and performing resolution requests before a certain time limit.
MILCOM 2007 - IEEE Military Communications Conference, 2007
This paper presents a study on a scalable inter-domain signaling protocol to provide quality of s... more This paper presents a study on a scalable inter-domain signaling protocol to provide quality of service to the Internet. The protocol uses a hard-state approach and separates data forwarding procedures, control procedures, and resource allocation procedures. Current solutions adopt a soft-state label switching approach where border routers are responsible for maintaining resource accounting and the path's next-hop information for every aggregated flow. Due to the Internet's almost hierarchical structure, the routers at the core can become a bottleneck to the system's overall scalability. Our protocol, SIDSP, reduces the core routers complexity by transferring most of the state data to the peripheral routers. This is accomplished by the usage of source routing for the flows. As a hard-state approach, it does not require periodical refreshing messages. However it puts more pressure on state coherence and state stabilization algorithms. SIDSP's performance was tested using ns-2 simulations, and was compared to BGRP's performance.
Background Mycoplasma hyopneumoniae is a highly infectious swine pathogen and is the causative ag... more Background Mycoplasma hyopneumoniae is a highly infectious swine pathogen and is the causative agent of enzootic pneumonia (EP). Following the previous report of a proteomic survey of the pathogenic 7448 strain of swine pathogen, Mycoplasma hyopneumoniae, we performed comparative protein profiling of three M. hyopneumoniae strains, namely the non-pathogenic J strain and the two pathogenic strains 7448 and 7422. Results In 2DE comparisons, we were able to identify differences in expression levels for 67 proteins, including the overexpression of some cytoadherence-related proteins only in the pathogenic strains. 2DE immunoblot analyses allowed the identification of differential proteolytic cleavage patterns of the P97 adhesin in the three strains. For more comprehensive protein profiling, an LC-MS/MS strategy was used. Overall, 35% of the M. hyopneumoniae genome coding capacity was covered. Partially overlapping profiles of identified proteins were observed in the strains with 81 prot...
The Quality of Service (QoS) requirements for modern broadband wireless systems can be very high,... more The Quality of Service (QoS) requirements for modern broadband wireless systems can be very high, with small error rates and delays. To preclude significant degradation on the spectral efficiency, these systems also require high throughputs. Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance degradation. An efficient alternative to simple retransmissions is to combine the signals associated to different transmission attempts. This paper analyses two time diversity approaches to cope with lost packets that are relatively similar at physical layer but treat different packet loss causes: a low-complexity diversity combining ARQ scheme (Automatic Repeat reQuest) employed in a TDMA (Time Division Multiple Access) architecture; and a Network Diversity Multiple Access (NDMA), which is a multi-packet reception approach able to separate multiple mobile terminals transmitting simultaneously in one slot using temporal diversity. This paper combines the use of these techniques in Single Carrier Frequency Domain Equalization (SC-FDE) systems, which are widely recognized as the best candidates for the uplink of future broadband wireless systems. It aims to present a comparison among the approaches focusing on error rate, throughput and delay performances, not discarding the implementation complexity issues.
Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and ... more Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retransmitted, 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 P copies of each packet when P MTs collide. Diversity combining is limited to P 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 P packet copies are available. In this paper, a Hybrid-ARQ NDMA (H-NDMA) access mechanism is proposed. The access mechanism forces MTs with reception errors during a collision resolution epoch to transmit more than P times. Analytical models for Poisson traffic are proposed for the throughput and delay. The proposed system's performance is evaluated for a Single-Carrier with Frequency Domain Equalization (SC-FDE) scheme, and compared to classical NDMA. H-NDMA parameter configuration is defined in terms of Quality of Service (QoS) requirements. 1 2
The ATLAS combined test beam in the second half of 2004 saw the first deployment of the ATLAS Hig... more The ATLAS combined test beam in the second half of 2004 saw the first deployment of the ATLAS High-Level Trigger (HLT). The next steps are deployment on the pre-series farms in the experimental area during 2005, commissioning and cosmics tests with the full detector in 2006 and collisions in 2007. This paper reviews the experience gained in the test beam, describes the current status and discusses the further enhancements to be made. We address issues related to the dataflow, integration of selection algorithms, testing, software distribution, installation and improvements.
Communications in Computer and Information Science
This paper presents MANET-VoVON, a new Internet application for mobile ad-hoc networks (MANETs) p... more This paper presents MANET-VoVON, a new Internet application for mobile ad-hoc networks (MANETs) providing voice over virtual overlay networks. A MANET-enabled version of JXTA peer-to-peer modular open platform (MANET-JXTA) is used to support user location and optionally, audio streaming over the JXTA virtual overlay network. Using MANET-JXTA, a client can search asynchronously for a user, and delay the call setup until a path is available to reach the user. The application uses a private signalling protocol based on the exchange of XML messages over MANET-JXTA communication channels. Nevertheless, it is fully interoperable with normal SIP clients through an embedded gateway function. This paper describes a prototype implementation of the proposed application and of the MANET-JXTA, and presents some performance measurements.
To understand the symbolic elements and the hierarchical system of representations of elderly peo... more To understand the symbolic elements and the hierarchical system of representations of elderly people on falls, according to Abric's structural analysis and Neuman's theory. Abric structural approach developed at the home of primary care users in a city of Minas Gerais. A free evocation technique of images triggered by images was performed in 2016 with elderly individuals (≥65 years old). Data treated by dictionary of equivalent terms; processed in Evoc 2000 software converging, analytically, according to Neuman. Ethical/legal criteria were met. 195 people participated, 78.5% were women, and 45.1% were aged ≥75 years. Summarized 897 words; 155 different ones. Central nucleus containing cognates: dizziness-vertigo-labyrinthitis and slipper-shoes (behavioral and objective dimension). The word disease integrated the area of contrast. Environmental and personal stressors were identified according to Neuman. Final considerations: Objects and risk behaviors for falls integrated the...
Prefix-assisted direct-sequence code-division multiple access (DS-CDMA) is a viable transmission ... more Prefix-assisted direct-sequence code-division multiple access (DS-CDMA) is a viable transmission technique for high-data-rate wireless broadband systems, capable of coping with highly dispersive channels at the uplink. Packet combining (PC) ARQ with an iterative block decision feedback equalization (IB-DFE) technique can be used to cope with errors. However, extracting the IB-DFE's packet error rate (PER) for MAC-layer simulations can be time consuming. Most works that model the DS-CDMA behavior with PC ARQ use simplified asymptotic PER models in the study of the system performance, which are not precise for low signal-to-noise ratios and for a low number of mobile terminals (MTs). In this paper, the MAC performance is modeled using a discrete-time Markov chain that relies on a PER model. As an example, this paper describes a PER analytical model for an uncoded prefix-assisted DS-CDMA system with PC ARQ that considers the following inputs: the number of MTs accessing the channel, the MTs' number of transmissions, and the channel realizations for a given bit energy over noise ratio. The results show that the model portrays with better accuracy the simulations' results, compared with an alternative asymptotic model.
Even codes are prefix-free codes where every encoding contains an even number of 1's, thus having... more Even codes are prefix-free codes where every encoding contains an even number of 1's, thus having ability of detecting the occurrence of an odd number of 1-bit errors in a message. The motivation for defining such codes comes from a problem posed by Hamming in 1980. Even codes have been studied for the case in which symbols have uniform probabilities. In this work, we consider the general case of arbitrary probabilities. An exact algorithm for constructing an optimal even code is described with complexity O(n 3), where n is the number of symbols. Further, two approximation algorithms for constructing nearly optimal even codes are presented, both requiring O(n log n) time; in addition, the running time is O(n) if the symbols are given ordered by their probabilities. The cost of the even code constructed by the second approximation algorithm is at most 16.7% higher than the cost of a Huffman code, for the same probabilities. However, computational experiments suggest that, in practice, this difference is about 5%, for n large enough.
1998 1st IEEE International Conference on ATM. ICATM'98
Network technology is becoming simpler in order to support the widest possible range of user appl... more Network technology is becoming simpler in order to support the widest possible range of user applications. Therefore, the specific requirements of each application must be performed outside of the network and the adaptation mechanisms should be done by the applications. For the case of multimedia applications the programming task can even be more simplified if several "low-level" aspects can be made transparent by the use of a suitable framework. This paper presents such a framework with some algorithms to control some of the previous aspects, namely data handling and dynamic QoS control. It provides the application with a mechanism to constantly adapt the quality of the continuous media being transmitted. The algorithm takes into account not only the network conditions but the end host conditions as well. Some experiments are presented.
Communications in Computer and Information Science, 2007
Mobile ad hoc network (MANET) is an infrastructure less network, in where all mobile nodes are fr... more Mobile ad hoc network (MANET) is an infrastructure less network, in where all mobile nodes are free for any movement to any side. Thus the network is going toward zero configurations that would create some problems. Ad hoc network is faced with various limitations that need to be considered among design and implementation of any protocol for it. Service Advertisement (SA) is one of the important services that are offered in each network. To have a fast service discovery in a network with minimum energy consumption, distributing of services' information and their management play important roles. In this paper for avoiding packet flooding in the MANET we used Cluster Based Routing Protocol (CBRP). For reducing amount of communication messages we moved service advertisement from application layer to routing layer. Thus we distribute the active services in the network among clustered nodes. However, the results of our experiment show that our method does not add any extra overhead to the network.
Proceedings - Advanced Industrial Conference on Telecommunications/Service Assurance with Partial and Intermittent Resources Conference/E-Learning on Telecommunications Workshop AICT/SAPIR/ELETE 2005, 2005
Integration of different radio access networks will become a reality in a near future. Our interw... more Integration of different radio access networks will become a reality in a near future. Our interworking architecture assumes a ubiquitous primary network (the cellular one) and secondary networks used on an availability basis. Secondary networks form islands of coverage providing partial and intermittent resources with greater Quality of Service as the user moves along. This paper describes an application architecture that manages these resources in an opportunistic way. It makes use of the Open Service Access (OSA) to control the core network and the OSA application servers to host the new applications that can take advantage of the pi-resources. These applications create a context for secondary networks and the context can survive losses of coverage.
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC, 2006
Most studies on performance of IEEE 802.11 DCF networks do not contemplate the existence of broad... more Most studies on performance of IEEE 802.11 DCF networks do not contemplate the existence of broadcast traffic. They model network behaviour in presence of unicast traffic alone. In a real scenario, broadcast frames exist, and they will influence the overall network behaviour. This work presents a new traffic generalized model for CSMA/CA saturated single-hop networks able to describe the network behaviour in presence of both unicast and broadcast frames. Interesting statistics like station transmission probability, average time needed to complete a frame transmission, and network aggregate throughput are deduced from the model. The paper compares the performance of our model with other models proposed only for unicast traffic. Our model is validated for broadcast and unicast traffic through simulations, using an IEEE 802.11 DCF network scenario. Results are presented and analysed for different scenarios of broadcast/unicast network loads, different number of nodes and different frame data lengths.
IFIP Advances in Information and Communication Technology, 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 for a TDMA (Time Division Multiple Access) scheme where packet combining ARQ is applied. It evaluates the uplink non-saturated packet delay for a generic message arrival process. Our analytical results are validated using physical and MAC layer simulations.
This paper presents an algorithm to control QoS for distributed multimedia applications. The algo... more This paper presents an algorithm to control QoS for distributed multimedia applications. The algorithm approaches the problem in an integrated way solving both the problems of the network bandwidth and the load at the workstations. It interacts with the applications by an abstract sequence to describe values for QoS that are more meaningful to application programmers than the low-level entities such as cell loss rate, throughput, etc. Some experimental results of the algorithm are presented.
Proceedings of the third ACM international conference on Multimedia - MULTIMEDIA '95, 1995
This paper addresses algorithms to meet the QoS parameters related with the synchronization of is... more This paper addresses algorithms to meet the QoS parameters related with the synchronization of isochronous (or continuous) media. It is broadly accepted to divide the synchronization problem into high level (extrinsic) synchronization; and low level (intrinsic) synchronization. The first refers to the media presentation control problem and is related to the object model and the composition concepts of the basic parts of the objects (when they begin, end, etc.). There are already some standards (HyTime[12], MHEG[7]) and also other academic contributions ([19],[10] and [14]).
Scalable Internet services are based on sets of peer application servers. A decentralized locatio... more Scalable Internet services are based on sets of peer application servers. A decentralized location service is used to resolve human readable application identifiers and return the nearest application server reference. This paper evaluates several services and algorithms from the Internet, grid and peer-to-peer community services. It identifies two potential problems and proposes a new approach for handling them. Existing techniques structure the overlay networks using tree structures. The proposed service enhances the structure with meshed structures at each level, creating dynamically multiple paths to enhance scalability. We present a study and simulation results on one aspect of scalability-sudden load of requests from users. Our service adapts to the load reaching a stable stage and performing resolution requests before a certain time limit.
MILCOM 2007 - IEEE Military Communications Conference, 2007
This paper presents a study on a scalable inter-domain signaling protocol to provide quality of s... more This paper presents a study on a scalable inter-domain signaling protocol to provide quality of service to the Internet. The protocol uses a hard-state approach and separates data forwarding procedures, control procedures, and resource allocation procedures. Current solutions adopt a soft-state label switching approach where border routers are responsible for maintaining resource accounting and the path's next-hop information for every aggregated flow. Due to the Internet's almost hierarchical structure, the routers at the core can become a bottleneck to the system's overall scalability. Our protocol, SIDSP, reduces the core routers complexity by transferring most of the state data to the peripheral routers. This is accomplished by the usage of source routing for the flows. As a hard-state approach, it does not require periodical refreshing messages. However it puts more pressure on state coherence and state stabilization algorithms. SIDSP's performance was tested using ns-2 simulations, and was compared to BGRP's performance.
Background Mycoplasma hyopneumoniae is a highly infectious swine pathogen and is the causative ag... more Background Mycoplasma hyopneumoniae is a highly infectious swine pathogen and is the causative agent of enzootic pneumonia (EP). Following the previous report of a proteomic survey of the pathogenic 7448 strain of swine pathogen, Mycoplasma hyopneumoniae, we performed comparative protein profiling of three M. hyopneumoniae strains, namely the non-pathogenic J strain and the two pathogenic strains 7448 and 7422. Results In 2DE comparisons, we were able to identify differences in expression levels for 67 proteins, including the overexpression of some cytoadherence-related proteins only in the pathogenic strains. 2DE immunoblot analyses allowed the identification of differential proteolytic cleavage patterns of the P97 adhesin in the three strains. For more comprehensive protein profiling, an LC-MS/MS strategy was used. Overall, 35% of the M. hyopneumoniae genome coding capacity was covered. Partially overlapping profiles of identified proteins were observed in the strains with 81 prot...
The Quality of Service (QoS) requirements for modern broadband wireless systems can be very high,... more The Quality of Service (QoS) requirements for modern broadband wireless systems can be very high, with small error rates and delays. To preclude significant degradation on the spectral efficiency, these systems also require high throughputs. Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance degradation. An efficient alternative to simple retransmissions is to combine the signals associated to different transmission attempts. This paper analyses two time diversity approaches to cope with lost packets that are relatively similar at physical layer but treat different packet loss causes: a low-complexity diversity combining ARQ scheme (Automatic Repeat reQuest) employed in a TDMA (Time Division Multiple Access) architecture; and a Network Diversity Multiple Access (NDMA), which is a multi-packet reception approach able to separate multiple mobile terminals transmitting simultaneously in one slot using temporal diversity. This paper combines the use of these techniques in Single Carrier Frequency Domain Equalization (SC-FDE) systems, which are widely recognized as the best candidates for the uplink of future broadband wireless systems. It aims to present a comparison among the approaches focusing on error rate, throughput and delay performances, not discarding the implementation complexity issues.
Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and ... more Traditionally, a packet with errors, either due to channel noise or collisions, is discarded and needs to be retransmitted, 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 P copies of each packet when P MTs collide. Diversity combining is limited to P 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 P packet copies are available. In this paper, a Hybrid-ARQ NDMA (H-NDMA) access mechanism is proposed. The access mechanism forces MTs with reception errors during a collision resolution epoch to transmit more than P times. Analytical models for Poisson traffic are proposed for the throughput and delay. The proposed system's performance is evaluated for a Single-Carrier with Frequency Domain Equalization (SC-FDE) scheme, and compared to classical NDMA. H-NDMA parameter configuration is defined in terms of Quality of Service (QoS) requirements. 1 2
The ATLAS combined test beam in the second half of 2004 saw the first deployment of the ATLAS Hig... more The ATLAS combined test beam in the second half of 2004 saw the first deployment of the ATLAS High-Level Trigger (HLT). The next steps are deployment on the pre-series farms in the experimental area during 2005, commissioning and cosmics tests with the full detector in 2006 and collisions in 2007. This paper reviews the experience gained in the test beam, describes the current status and discusses the further enhancements to be made. We address issues related to the dataflow, integration of selection algorithms, testing, software distribution, installation and improvements.
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