Proceedings of ICUPC 97 - 6th International Conference on Universal Personal Communications
The effects of interference threshold and SNR acceptance threshold on channel capacity have been ... more The effects of interference threshold and SNR acceptance threshold on channel capacity have been determined for several distributed channel assignment algorithms using unsupervised FDMA (UFDMA), a multiple access scheme for the terrestrial radio environment. It is found that the effect of tightening the interference threshold reduces the call dropping probability at the expense of increasing the blocking probability for a
EURASIP Journal on Wireless Communications and Networking, 2008
We investigate the performance and coexistence techniques for worldwide interoperability for micr... more We investigate the performance and coexistence techniques for worldwide interoperability for microwave access (WiMAX) delivered from high altitude platforms (HAPs) and terrestrial systems in shared 3.5 GHz frequency bands. The paper shows that it is possible to provide WiMAX services from individual HAP systems. The coexistence performance is evaluated by appropriate choice of parameters, which include the HAP deployment spacing radius, directive antenna beamwidths based on adopted antenna models for HAPs and receivers. Illustrations and comparisons of coexistence techniques, for example, varying the antenna pointing offset, transmitting and receiving antenna beamwidth, demonstrate efficient ways to enhance the HAP system performance while effectively coexisting with terrestrial WiMAX systems.
The purpose of this paper is to represent an adaptive neighbour detection scheme for rapid sensor... more The purpose of this paper is to represent an adaptive neighbour detection scheme for rapid sensor network configuration, especially in wireless sensor network (WSN) systems. In typical WSNs, the sensor nodes have no knowledge about the locations of other nodes and the connections between them after deployment. For the purpose of network configuration and future data transmission schedule assignments, neighbour detection process should be carried out, but this work are usually ignored in most communication protocol designs. In our real network establishment, it is proved that neighbour detection is critically important at the beginning configuration state of the entire network and when the topology is changed. Therefore, an adaptive neighbour detection scheme is introduced, which uses signalling packet broadcasting and the corresponding adaptive back-off mechanism to guarantee a high connectivity detection probability. The work is verified by simulation and testbed experiments, and has been used in practical large scale sensor networks.
2013 Saudi International Electronics, Communications and Photonics Conference, 2013
ABSTRACT This paper proposes a novel Carrier Sensing Multiple Access with Collision Avoidance (CS... more ABSTRACT This paper proposes a novel Carrier Sensing Multiple Access with Collision Avoidance (CSMA-CA) scheme for multi-hop wireless networks. The proposed protocol provides up to a six-fold delay reduction, up to 20% energy consumption saving and doubles throughput compared with other CSMA-CA protocols, notably those employed in the IEEE 802.11 and IEEE 802.15.4 standards. These bountiful benefits are engendered by employing an intelligent back-off algorithm which reflects the dynamic characteristics of multi-hop networks. The fundamental principle is to exploit the flexible statistical properties of the Gamma distribution which allow each node to autonomously adjust its back-off and sensing strategy. Collisions are alleviated by introducing an innovate collision resolution algorithm. In terms of practicality, the protocol is lightweight and can be applied to any wireless device as it does not require modification of the physical layer standards.
2010 7th International Symposium on Wireless Communication Systems, 2010
Abstract Ultra Wide Band (UWB) and Cognitive Radio (CR) offer radically different approaches to e... more Abstract Ultra Wide Band (UWB) and Cognitive Radio (CR) offer radically different approaches to efficiently use the seemingly scarce spectrum in wireless communications. In this paper, we study the combined cognitive multiuser spectrum sharing and power ...
2011 11th International Symposium on Communications & Information Technologies (ISCIT), 2011
In this paper we study a cognitive power allocation scheme for a fully distributed Ultra Wide Ban... more In this paper we study a cognitive power allocation scheme for a fully distributed Ultra Wide Band (UWB) system. We show that the highly restricted spectrum power density and multiuser interference can be mitigated by means of a game based solution. The impact of UWB frequency selective fading on our cognitive power allocation scheme is examined and we compare our scheme with the existing iterative water filling technique. The results show that our proposed power allocation scheme is equal to or more power efficient than the iterative water filling technique in a UWB fading channel, while also converging significantly faster.
Abstract Ethynyltriisopropoxytitanium has been generated in situ from ethynyllithium and chlorotr... more Abstract Ethynyltriisopropoxytitanium has been generated in situ from ethynyllithium and chlorotriisopropoxytitanium at− 80 C. It forms 1/1 adducts with pyrimidin-2 (1H)-ones with exclusive carbon-carbon bond formation at C (6). The products after quenching ...
The labeling of biomolecules for positron emission tomography (PET) with no-carrier-added fluorin... more The labeling of biomolecules for positron emission tomography (PET) with no-carrier-added fluorine-18 is almost exclusively accomplished using prosthetic groups in a two step procedure. The inherent complexity of the process renders full automation a challenge and leads to protracted synthesis times. Here we describe a new (18)F-labeled prosthetic group based on nicotinic acid tetrafluorophenyl ester. Reaction of [(18)F]fluoride at 40 degrees C with the trimethylammonium precursor afforded 6-[(18)F]fluoronicotinic acid tetrafluorophenyl ester ([(18)F]F-Py-TFP) directly in 60-70% yield. [(18)F]F-Py-TFP was conveniently purified by Sep-Pak cartridge prior to incubation with a peptide containing the RGD sequence. The desired conjugate was formed rapidly and in good yields. An in vitro receptor-binding assay for the integrin alpha(v)beta(3) was established to explore competition with peptide and peptidomimetic prepared from F-Py-TFP with (125)I-echistatin. The nonradioactive conjugates were found to possess high binding affinities with calculated K(i) values in the low nanomolar range.
International Journal of Wireless Information Networks, 2006
The interest of the scientific and industrial communities on the application of high altitude str... more The interest of the scientific and industrial communities on the application of high altitude stratospheric platforms to communications is increasingly growing. Several research projects and field trials are being carried out by international consortia and specific portions of the electromagnetic spectrum have been allocated by the International Telecommunications Union (ITU) for communications applications. The channel experienced by such systems plays a key role for the provision of reliable communications services but, unfortunately, its inherent characteristics are substantially different from those of other channel typologies. Therefore, in order to design and simulate effective propagation impairment mitigation techniques such as adaptive modulation and coding or adaptive beamforming and equalization algorithms, an ad hoc channel model and simulator is definitively required. In this paper a novel channel model and a related channel simulator especially tailored for HAP-based communication systems are presented. The model is conceived for link-level simulations of point-to-point communication links, wherein both the transmitter and the receiver may be equipped with an array of antennas. Peculiar physical effects of the stratospheric channel are taken into account as well as impairments due to the possible presence of scatterers and relative movement of both transmitting and receiving stations. The structure of the channel simulator has been conceived to maintain the computational burden at required by the channel simulator is kept low by an efficient tapped delay line implementation. w This work is supported by the CAPANINA project (FP6 IST-2003-506745): Communications from aerial platform networks delivering broadband communications for all, http://www.capanina.org.
ABSTRACT This study introduces two novel approaches, pre-partitioning and weight-driven explorati... more ABSTRACT This study introduces two novel approaches, pre-partitioning and weight-driven exploration, to enable an efficient learning process in the context of cognitive radio. Learning efficiency is crucial when applying reinforcement learning to cognitive radio since cognitive radio users will cause a higher level of disturbance in the exploration phase. Careful control of the tradeoff between exploration and exploitation for a learning-enabled cognitive radio in order to efficiently learn from the interactions with a dynamic radio environment is investigated. In the pre-partitioning scheme, the potential action space of cognitive radios is reduced by initially randomly partitioning the spectrum in each cognitive radio. Cognitive radios are therefore able to finish their exploration stage faster than more basic reinforcement learning-based schemes. In the weight-driven exploration scheme, exploitation is merged into exploration by taking into account the knowledge gained in exploration to influence action selection, thereby achieving a more efficient exploration phase. The learning efficiency in a cognitive radio scenario is defined and the learning efficiency of the proposed schemes is investigated. The simulation results show that the exploration of cognitive radio is more efficient by using pre-partitioning and weight-driven exploration and the system performance is improved accordingly.
IEEE Transactions on Wireless Communications, 2003
In a wireless communications network served by a high altitude platform (HAP) the cochannel inter... more In a wireless communications network served by a high altitude platform (HAP) the cochannel interference is a function of the antenna beamwidth, angular separation and sidelobe level. At the millimeter wave frequencies proposed for HAPs, an array of aperture type antennas on the platform is a practicable solution for serving the cells. We present a method for predicting cochannel interference based on curve-fit approximations for radiation patterns of elliptic beams which illuminate cell edges with optimum power, and a means of estimating optimum beamwidths for each cell of a regular hexagonal layout. The method is then applied to a 121 cell architecture. Where sidelobes are modeled as a flat floor at 40-dB below peak directivity, a cell cluster size of four yields carrier-to-interference ratios (CIRs), which vary from 15 dB at cell edges to 27 dB at cell centers. On adopting a cluster size of seven, these figures increase, respectively, to 19 and 30 dB. On reducing the sidelobe level, the improvement in CIR can be quantified. The method also readily allows for regions of overlapping channel coverage to be shown.
IEEE Journal on Selected Areas in Communications, 2004
... FOR BROADBAND INTERNET SERVICE DELIVERY OVER GEOSTATIONARY SATELLITE 547 Fig. 1. Star-based s... more ... FOR BROADBAND INTERNET SERVICE DELIVERY OVER GEOSTATIONARY SATELLITE 547 Fig. 1. Star-based satellite scenario. Fig. 2. An ON/OFF packet generation process. access to the terrestrial Internet through a gateway terminal and via a geostationary satellite with ...
EURASIP Journal on Advances in Signal Processing, 2009
Recommended by K. Subbalakshmi Cognitive wireless mesh networks have great flexibility to improve... more Recommended by K. Subbalakshmi Cognitive wireless mesh networks have great flexibility to improve spectrum resource utilization, within which secondary users (SUs) can opportunistically access the authorized frequency bands while being complying with the interference constraint as well as the QoS (Quality-of-Service) requirement of primary users (PUs). In this paper, we consider intercluster connection between the neighboring clusters under the framework of cognitive wireless mesh networks. Corresponding to the collocated clusters, data flow which includes the exchanging of control channel messages usually needs four time slots in traditional relaying schemes since all involved nodes operate in half-duplex mode, resulting in significant bandwidth efficiency loss. The situation is even worse at the gateway node connecting the two colocated clusters. A novel scheme based on network coding is proposed in this paper, which needs only two time slots to exchange the same amount of information mentioned above. Our simulation shows that the network coding-based intercluster connection has the advantage of higher bandwidth efficiency compared with the traditional strategy. Furthermore, how to choose an optimal relaying transmission power level at the gateway node in an environment of coexisting primary and secondary users is discussed. We present intelligent approaches based on reinforcement learning to solve the problem. Theoretical analysis and simulation results both show that the intelligent approaches can achieve optimal throughput for the intercluster relaying in the long run.
ABSTRACT High-altitude platforms (HAPs) provide a possible solution to the `last-mile' pr... more ABSTRACT High-altitude platforms (HAPs) provide a possible solution to the `last-mile' problem in broadband telecommunications. The frequencies assigned for HAPs (28 and 48 GHz) are subject to attenuation and scatter by rain. These effects are explored in relation to ground station (GS) antenna beamwidth and sidelobe levels
Thirty-four painful deformed rheumatoid feet treated by excision of all five metatarsal heads wer... more Thirty-four painful deformed rheumatoid feet treated by excision of all five metatarsal heads were compared with 34 similar feet in which the lesser metatarsal heads were excised and the first metatarsophalangeal joint was arthrodesed. In the latter group, one third had failure of fusion of the hallux, and this produced the worst results. Metatarsalgia and plantar callosities were more common after excision arthroplasty, but shoe fitting and correction of deformity were better in this group. However, the results were more variable in the fusion group, and the complication and reoperation rates were higher. For this reason, excision arthroplasty, rather than fusion of the hallux, is recommended when the lesser metatarsal heads are removed.
Proceedings of ICUPC 97 - 6th International Conference on Universal Personal Communications
The effects of interference threshold and SNR acceptance threshold on channel capacity have been ... more The effects of interference threshold and SNR acceptance threshold on channel capacity have been determined for several distributed channel assignment algorithms using unsupervised FDMA (UFDMA), a multiple access scheme for the terrestrial radio environment. It is found that the effect of tightening the interference threshold reduces the call dropping probability at the expense of increasing the blocking probability for a
EURASIP Journal on Wireless Communications and Networking, 2008
We investigate the performance and coexistence techniques for worldwide interoperability for micr... more We investigate the performance and coexistence techniques for worldwide interoperability for microwave access (WiMAX) delivered from high altitude platforms (HAPs) and terrestrial systems in shared 3.5 GHz frequency bands. The paper shows that it is possible to provide WiMAX services from individual HAP systems. The coexistence performance is evaluated by appropriate choice of parameters, which include the HAP deployment spacing radius, directive antenna beamwidths based on adopted antenna models for HAPs and receivers. Illustrations and comparisons of coexistence techniques, for example, varying the antenna pointing offset, transmitting and receiving antenna beamwidth, demonstrate efficient ways to enhance the HAP system performance while effectively coexisting with terrestrial WiMAX systems.
The purpose of this paper is to represent an adaptive neighbour detection scheme for rapid sensor... more The purpose of this paper is to represent an adaptive neighbour detection scheme for rapid sensor network configuration, especially in wireless sensor network (WSN) systems. In typical WSNs, the sensor nodes have no knowledge about the locations of other nodes and the connections between them after deployment. For the purpose of network configuration and future data transmission schedule assignments, neighbour detection process should be carried out, but this work are usually ignored in most communication protocol designs. In our real network establishment, it is proved that neighbour detection is critically important at the beginning configuration state of the entire network and when the topology is changed. Therefore, an adaptive neighbour detection scheme is introduced, which uses signalling packet broadcasting and the corresponding adaptive back-off mechanism to guarantee a high connectivity detection probability. The work is verified by simulation and testbed experiments, and has been used in practical large scale sensor networks.
2013 Saudi International Electronics, Communications and Photonics Conference, 2013
ABSTRACT This paper proposes a novel Carrier Sensing Multiple Access with Collision Avoidance (CS... more ABSTRACT This paper proposes a novel Carrier Sensing Multiple Access with Collision Avoidance (CSMA-CA) scheme for multi-hop wireless networks. The proposed protocol provides up to a six-fold delay reduction, up to 20% energy consumption saving and doubles throughput compared with other CSMA-CA protocols, notably those employed in the IEEE 802.11 and IEEE 802.15.4 standards. These bountiful benefits are engendered by employing an intelligent back-off algorithm which reflects the dynamic characteristics of multi-hop networks. The fundamental principle is to exploit the flexible statistical properties of the Gamma distribution which allow each node to autonomously adjust its back-off and sensing strategy. Collisions are alleviated by introducing an innovate collision resolution algorithm. In terms of practicality, the protocol is lightweight and can be applied to any wireless device as it does not require modification of the physical layer standards.
2010 7th International Symposium on Wireless Communication Systems, 2010
Abstract Ultra Wide Band (UWB) and Cognitive Radio (CR) offer radically different approaches to e... more Abstract Ultra Wide Band (UWB) and Cognitive Radio (CR) offer radically different approaches to efficiently use the seemingly scarce spectrum in wireless communications. In this paper, we study the combined cognitive multiuser spectrum sharing and power ...
2011 11th International Symposium on Communications & Information Technologies (ISCIT), 2011
In this paper we study a cognitive power allocation scheme for a fully distributed Ultra Wide Ban... more In this paper we study a cognitive power allocation scheme for a fully distributed Ultra Wide Band (UWB) system. We show that the highly restricted spectrum power density and multiuser interference can be mitigated by means of a game based solution. The impact of UWB frequency selective fading on our cognitive power allocation scheme is examined and we compare our scheme with the existing iterative water filling technique. The results show that our proposed power allocation scheme is equal to or more power efficient than the iterative water filling technique in a UWB fading channel, while also converging significantly faster.
Abstract Ethynyltriisopropoxytitanium has been generated in situ from ethynyllithium and chlorotr... more Abstract Ethynyltriisopropoxytitanium has been generated in situ from ethynyllithium and chlorotriisopropoxytitanium at− 80 C. It forms 1/1 adducts with pyrimidin-2 (1H)-ones with exclusive carbon-carbon bond formation at C (6). The products after quenching ...
The labeling of biomolecules for positron emission tomography (PET) with no-carrier-added fluorin... more The labeling of biomolecules for positron emission tomography (PET) with no-carrier-added fluorine-18 is almost exclusively accomplished using prosthetic groups in a two step procedure. The inherent complexity of the process renders full automation a challenge and leads to protracted synthesis times. Here we describe a new (18)F-labeled prosthetic group based on nicotinic acid tetrafluorophenyl ester. Reaction of [(18)F]fluoride at 40 degrees C with the trimethylammonium precursor afforded 6-[(18)F]fluoronicotinic acid tetrafluorophenyl ester ([(18)F]F-Py-TFP) directly in 60-70% yield. [(18)F]F-Py-TFP was conveniently purified by Sep-Pak cartridge prior to incubation with a peptide containing the RGD sequence. The desired conjugate was formed rapidly and in good yields. An in vitro receptor-binding assay for the integrin alpha(v)beta(3) was established to explore competition with peptide and peptidomimetic prepared from F-Py-TFP with (125)I-echistatin. The nonradioactive conjugates were found to possess high binding affinities with calculated K(i) values in the low nanomolar range.
International Journal of Wireless Information Networks, 2006
The interest of the scientific and industrial communities on the application of high altitude str... more The interest of the scientific and industrial communities on the application of high altitude stratospheric platforms to communications is increasingly growing. Several research projects and field trials are being carried out by international consortia and specific portions of the electromagnetic spectrum have been allocated by the International Telecommunications Union (ITU) for communications applications. The channel experienced by such systems plays a key role for the provision of reliable communications services but, unfortunately, its inherent characteristics are substantially different from those of other channel typologies. Therefore, in order to design and simulate effective propagation impairment mitigation techniques such as adaptive modulation and coding or adaptive beamforming and equalization algorithms, an ad hoc channel model and simulator is definitively required. In this paper a novel channel model and a related channel simulator especially tailored for HAP-based communication systems are presented. The model is conceived for link-level simulations of point-to-point communication links, wherein both the transmitter and the receiver may be equipped with an array of antennas. Peculiar physical effects of the stratospheric channel are taken into account as well as impairments due to the possible presence of scatterers and relative movement of both transmitting and receiving stations. The structure of the channel simulator has been conceived to maintain the computational burden at required by the channel simulator is kept low by an efficient tapped delay line implementation. w This work is supported by the CAPANINA project (FP6 IST-2003-506745): Communications from aerial platform networks delivering broadband communications for all, http://www.capanina.org.
ABSTRACT This study introduces two novel approaches, pre-partitioning and weight-driven explorati... more ABSTRACT This study introduces two novel approaches, pre-partitioning and weight-driven exploration, to enable an efficient learning process in the context of cognitive radio. Learning efficiency is crucial when applying reinforcement learning to cognitive radio since cognitive radio users will cause a higher level of disturbance in the exploration phase. Careful control of the tradeoff between exploration and exploitation for a learning-enabled cognitive radio in order to efficiently learn from the interactions with a dynamic radio environment is investigated. In the pre-partitioning scheme, the potential action space of cognitive radios is reduced by initially randomly partitioning the spectrum in each cognitive radio. Cognitive radios are therefore able to finish their exploration stage faster than more basic reinforcement learning-based schemes. In the weight-driven exploration scheme, exploitation is merged into exploration by taking into account the knowledge gained in exploration to influence action selection, thereby achieving a more efficient exploration phase. The learning efficiency in a cognitive radio scenario is defined and the learning efficiency of the proposed schemes is investigated. The simulation results show that the exploration of cognitive radio is more efficient by using pre-partitioning and weight-driven exploration and the system performance is improved accordingly.
IEEE Transactions on Wireless Communications, 2003
In a wireless communications network served by a high altitude platform (HAP) the cochannel inter... more In a wireless communications network served by a high altitude platform (HAP) the cochannel interference is a function of the antenna beamwidth, angular separation and sidelobe level. At the millimeter wave frequencies proposed for HAPs, an array of aperture type antennas on the platform is a practicable solution for serving the cells. We present a method for predicting cochannel interference based on curve-fit approximations for radiation patterns of elliptic beams which illuminate cell edges with optimum power, and a means of estimating optimum beamwidths for each cell of a regular hexagonal layout. The method is then applied to a 121 cell architecture. Where sidelobes are modeled as a flat floor at 40-dB below peak directivity, a cell cluster size of four yields carrier-to-interference ratios (CIRs), which vary from 15 dB at cell edges to 27 dB at cell centers. On adopting a cluster size of seven, these figures increase, respectively, to 19 and 30 dB. On reducing the sidelobe level, the improvement in CIR can be quantified. The method also readily allows for regions of overlapping channel coverage to be shown.
IEEE Journal on Selected Areas in Communications, 2004
... FOR BROADBAND INTERNET SERVICE DELIVERY OVER GEOSTATIONARY SATELLITE 547 Fig. 1. Star-based s... more ... FOR BROADBAND INTERNET SERVICE DELIVERY OVER GEOSTATIONARY SATELLITE 547 Fig. 1. Star-based satellite scenario. Fig. 2. An ON/OFF packet generation process. access to the terrestrial Internet through a gateway terminal and via a geostationary satellite with ...
EURASIP Journal on Advances in Signal Processing, 2009
Recommended by K. Subbalakshmi Cognitive wireless mesh networks have great flexibility to improve... more Recommended by K. Subbalakshmi Cognitive wireless mesh networks have great flexibility to improve spectrum resource utilization, within which secondary users (SUs) can opportunistically access the authorized frequency bands while being complying with the interference constraint as well as the QoS (Quality-of-Service) requirement of primary users (PUs). In this paper, we consider intercluster connection between the neighboring clusters under the framework of cognitive wireless mesh networks. Corresponding to the collocated clusters, data flow which includes the exchanging of control channel messages usually needs four time slots in traditional relaying schemes since all involved nodes operate in half-duplex mode, resulting in significant bandwidth efficiency loss. The situation is even worse at the gateway node connecting the two colocated clusters. A novel scheme based on network coding is proposed in this paper, which needs only two time slots to exchange the same amount of information mentioned above. Our simulation shows that the network coding-based intercluster connection has the advantage of higher bandwidth efficiency compared with the traditional strategy. Furthermore, how to choose an optimal relaying transmission power level at the gateway node in an environment of coexisting primary and secondary users is discussed. We present intelligent approaches based on reinforcement learning to solve the problem. Theoretical analysis and simulation results both show that the intelligent approaches can achieve optimal throughput for the intercluster relaying in the long run.
ABSTRACT High-altitude platforms (HAPs) provide a possible solution to the `last-mile' pr... more ABSTRACT High-altitude platforms (HAPs) provide a possible solution to the `last-mile' problem in broadband telecommunications. The frequencies assigned for HAPs (28 and 48 GHz) are subject to attenuation and scatter by rain. These effects are explored in relation to ground station (GS) antenna beamwidth and sidelobe levels
Thirty-four painful deformed rheumatoid feet treated by excision of all five metatarsal heads wer... more Thirty-four painful deformed rheumatoid feet treated by excision of all five metatarsal heads were compared with 34 similar feet in which the lesser metatarsal heads were excised and the first metatarsophalangeal joint was arthrodesed. In the latter group, one third had failure of fusion of the hallux, and this produced the worst results. Metatarsalgia and plantar callosities were more common after excision arthroplasty, but shoe fitting and correction of deformity were better in this group. However, the results were more variable in the fusion group, and the complication and reoperation rates were higher. For this reason, excision arthroplasty, rather than fusion of the hallux, is recommended when the lesser metatarsal heads are removed.
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Papers by David Grace