2014 Ieee 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks, Dec 1, 2014
ABSTRACT We present and analyze an Electric Vehicle (EV) charging management model for a fast cha... more ABSTRACT We present and analyze an Electric Vehicle (EV) charging management model for a fast charging station network in a smart grid environment. The proposed model considers a charging station network that provides service to multiple EV charging-classes. The basic feature of the proposed model is when EVs are blocked by their preferred station due to the unavailability of charging outlets, they are prompted via a communication system to select their next station, which either provides fixed or elastic charging services.We derive an analytical framework for the determination of the arrival procedure to the additional stations, which is then used for the derivation of the distribution of occupied charging outlets in both stations. Simulation results verify the high accuracy of the proposed analysis. The proposed analysis can be used for the determination of the number of stations that should be installed in a specific geographical area, so that EVs do not suffer charging delays.
In this PhD dissertation multi-rate models are examined for the performance analysis of telecommu... more In this PhD dissertation multi-rate models are examined for the performance analysis of telecommunication networks through mathematical analysis and simulation. Particular emphasis is given to optical networks. The main goal is the development of analytical models for the calculation of network performance metrics, such as blocking probabilities, transmission delay and utilization of the common channel. The proposed analytical models are distinguished according to the network technologies. Three different technologies are considered: A) Wavelength routed optical networks. B) Optical access networks. C) Wireless Internet access networks. Multi-rate loss models are proposed for the performance evaluation of wavelength routed optical networks. Firstly, the case of a single link is considered and then a mesh all-optical network is examined. In addition, analytical models are proposed for Optical Packet Switching (OPS) networks, for the case of an all-optical OPS switch and of an OPS mes...
2014 IEEE 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), 2014
ABSTRACT We present and analyze an Electric Vehicle (EV) charging management model for a fast cha... more ABSTRACT We present and analyze an Electric Vehicle (EV) charging management model for a fast charging station network in a smart grid environment. The proposed model considers a charging station network that provides service to multiple EV charging-classes. The basic feature of the proposed model is when EVs are blocked by their preferred station due to the unavailability of charging outlets, they are prompted via a communication system to select their next station, which either provides fixed or elastic charging services.We derive an analytical framework for the determination of the arrival procedure to the additional stations, which is then used for the derivation of the distribution of occupied charging outlets in both stations. Simulation results verify the high accuracy of the proposed analysis. The proposed analysis can be used for the determination of the number of stations that should be installed in a specific geographical area, so that EVs do not suffer charging delays.
A theoretical model is developed and exploited for characterizing the behavior of an all-optical ... more A theoretical model is developed and exploited for characterizing the behavior of an all-optical circuit that deploys a Fabry-PÊrot filter (FPF) and a semiconductor optical amplifier (SOA)-assisted Sagnac switch driven by an intense continuous wave (cw) holding beam to extract the clock signal from a received ultra-fast data stream. The role of each unit is thoroughly studied, and its understanding allows us to identify the critical operational parameters, which include the cw power, the energy of the data pulses, the SOA small ...
Abstract. The operation of a semiconductor-optical-amplifier-assisted Sagnac recirculating shift ... more Abstract. The operation of a semiconductor-optical-amplifier-assisted Sagnac recirculating shift register with an inverter is studied theoretically and analyzed using a numerical model developed for this purpose. The impact of critical operational parameters, such as the SOA small-signal gain and carrier lifetime, the controlling pulses' energy and width, and the Sagnac loop asymmetry, on the switching energy and contrast ratio metrics is thoroughly investigated. The performance of the shift register is first evaluated at 10 GHz by ...
The instantaneous frequency deviation of the pulses switched from a semiconductor optical amplifi... more The instantaneous frequency deviation of the pulses switched from a semiconductor optical amplifier (SOA)–assisted Sagnac interferometer is theoretically studied and analyzed. By using explicit expressions for the phase response and its temporal derivative and applying a numerical model, a set of curves is obtained that allows us to investigate and assess the dependence of the function of interest on the critical operational parameters. From their interpretation, the basic design rules that must govern them in order for its profile to ...
proposed in IEEE 802.11 standard for wireless local area networks, is the Distributed Coordinatio... more proposed in IEEE 802.11 standard for wireless local area networks, is the Distributed Coordination Function (DCF). DCF uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) to resolve contention between wireless stations and to verify successful transmissions. In this work we present an analytical model of the IEEE 802.11 MAC protocol validated by simulation results for the DCF throughput, for both packet transmission schemes employed by DCF, the basic access and the RTS/CTS access mechanism. Moreover, we depict the saturation throughput and the average packet delay for 1, 5.5 and 11 Mbps in order to highlight the effect of the bit rate on network performance for both mechanisms.
2014 16th International Conference on Transparent Optical Networks (ICTON), 2014
ABSTRACT Hybrid Wavelength-Time Division Multiplexing (WDM-TDM) Passive Optical Networks (PONs) b... more ABSTRACT Hybrid Wavelength-Time Division Multiplexing (WDM-TDM) Passive Optical Networks (PONs) become strong candidates for Next Generation PONs and, therefore, merit deep performance evaluation. In this paper, we concentrate on the performance of a Dynamic Wavelength Allocation (DWA) protocol, under multi-dimensional traffic which is modeled by a Pareto ON-OFF model; it resembles the bursty nature of traffic by considering ON and OFF transmission periods, whose duration is Pareto distributed. The investigated protocol may cause service delay to existing connections, if they will be found in state OFF, while no connection is found in state ON at the same time. In this case, the occupied wavelength is released, and a new wavelength (however, not always available, hence the delay) will be allocated to OFF connections, upon request from a connection to return to state ON. The delay caused by the so-called Delay Wavelength Release (D-WR) protocol, as well as other performance measures, are evaluated via simulation, and compared with the delay and corresponding measures of the same protocol, when the ON-OFF traffic under service has exponentially distributed ON and OFF periods.
Proceedings of the 2013 18th European Conference on Network and Optical Communications & 2013 8th Conference on Optical Cabling and Infrastructure (NOC-OC&I), 2013
ABSTRACT Passive Optical Networks (PONs) are attractive fiber-based access systems providing broa... more ABSTRACT Passive Optical Networks (PONs) are attractive fiber-based access systems providing broadband access solutions at a low cost. A hybrid Wavelength Division Multiplexing (WDM) - Time Division Multiple Access (TDMA) PON is a favorite PON configuration, in which the researchers have drawn much attention. We have analysed and proposed several protocols for dynamic wavelength allocation in a WDM-TDMA PON, by separately considering random or quasi-random input-traffic. By modelling the bursty in-service traffic as an ON-OFF model, we have proposed three protocols for random call arrivals. The same protocols have also been proposed for quasi-random call arrivals, resulting however in different evaluation conclusions (than in the case of random arriving calls). This fact gave rise to a fourth protocol, the Priority Wavelength Release (Pr-WR) Protocol, suitable for quasi-random input-traffic. According to this protocol, the service-classes accommodated in the PON are distinguished in two groups: the high and low priority groups. A connection between an Optical Node Unit (ONU) and the Optical Line Terminal (OLT) (the common link of the PON) can be terminated and the occupied wavelength is released, only when the common link is empty or holds low priority calls in state OFF. In this paper, we examine the Pr-WR protocol in the WDM-TDMA PON under a mixture of quasi-random and random arriving calls. The ON-OFF teletraffic model for the mixture of random and quasi-random arrivals is presented. We evaluate the behaviour of this protocol in comparison with the other three protocols in respect of: a) the Connection Failure Probability (due to the unavailability of a wavelength), and b) the Delay (low priority calls may delay in state OFF, until a new wavelength becomes available upon a new call arrival). For the Pr-WR Protocol, we also calculate the Call Blocking Probability (due to the restricted bandwidth of the wavelength) and the Burst Blocking Probability (burst of calls delays - n state OFF, due to temporal unavailability of wavelength bandwidth). We come to safe conclusion which is favourite for the Pr-Wr protocol.
Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 2015
ABSTRACT In this paper we present a survey of recent trends on short-term electricity-price predi... more ABSTRACT In this paper we present a survey of recent trends on short-term electricity-price prediction models. We classify the proposed price prediction methods based on the forecasting horizon into short- medium- and long-term approaches. We provide the key features of the medium- and long- solutions, while we emphasize on short-term prediction models, by providing their classification into statistical, computational intelligent and hybrid methods. We also highlight the key characteristics of the available prediction methods, while the strengths and weaknesses of these solutions are also discussed and analyzed. These important aspects should be considered by researchers that target on the derivation of more efficient and accurate electricity-price prediction models, especially for smart grid applications.
2014 16th International Conference on Transparent Optical Networks (ICTON), 2014
ABSTRACT Passive Optical Networks (PONs) constitute a predominant point-to-multipoint architectur... more ABSTRACT Passive Optical Networks (PONs) constitute a predominant point-to-multipoint architectures for an efficient and cost-effective fiber-based broadband access. We have analyzed several PON configurations, which either have been already standardized, like Wavelength Division Multiplexing - Time Division Multiplexing (WDM-TDM) PONs, or are highly promising PON technologies, like Optical Code Division Multiple Access (OCDMA) PONs. Based on Markov chains, we have developed teletraffic loss models for the call-level performance evaluation in the upstream PON direction. The PONs accommodate multiple service-classes of bursty traffic; to reflect the bursty nature of traffic and to simplify the analysis, we resort to ON-OFF traffic modeling. Call-connection requests are considered random (infinite population of traffic sources) or quasi-random (finite population of traffic sources). The main call-level performance index is the Call Blocking Probability (CBP). For the efficient CBP calculation, we result in approximate recursive formulas, whose the accuracy is completely satisfactory, as it has been verified through simulation.
ABSTRACT In this paper, we consider a single-link multirate loss system, which accommodates diffe... more ABSTRACT In this paper, we consider a single-link multirate loss system, which accommodates different service-classes with different traffic and peak-bandwidth requirements. Calls of each service-class arrive in the system according to a random (Poisson) or a quasi-random process, and have an exponentially distributed service time. Poisson or quasi-random arriving calls belong to service-classes of infinite or finite number of traffic sources, respectively. The service-classes are also distinguished, according to the behaviour of calls under service, in elastic and adaptive service-classes. Elastic calls can compress their bandwidth by simultaneously increasing their service time, while, adaptive calls do not affect their service time. A new call (either elastic or adaptive) is accepted in the system with its peak-bandwidth requirement, if there is available link bandwidth. If not, the call retries one or more times (single and multi-retry loss model, respectively) with a reduced bandwidth. If the available link bandwidth is lower than the call’s last bandwidth requirement, the call can still compress its last bandwidth requirement (down to a certain bandwidth), together with the bandwidth of all inservice calls. Call blocking occurs, if, after compression, the call’s bandwidth still exceeds the available link bandwidth. The system incorporates the Bandwidth Reservation (BR) policy, whereby we can achieve certain Quality of Service (QoS) for each service class, through a proper bandwidth allocation defined by the BR parameters. To calculate in an approximate but efficient way, time and call congestion probabilities, as well as link utilization, we propose recurrent formulas for the determination of the link occupancy distribution. The accuracy of the proposed formulas is verified by simulation, and is found to be very satisfactory. We show the consistency and the necessity of the proposed models.
ABSTRACT This work presents the design and implementation of a stand-alone linear power amplifier... more ABSTRACT This work presents the design and implementation of a stand-alone linear power amplifier at 2.4 GHz with high output power. A GaN HEMT transistor is selected for the design and implementation of the power amplifier. The device exhibits a gain of 11.7 dB and a drain efficiency of 39 % for an output power of 36.7 dBm at 2.4 GHz for an input power of 25 dBm. The carrier to intermodulation ratio is better than 25 dB for a two tone input signal of 25 dBm of total power and a spacing of 5 MHz. The fabricated device is also tested with LTE input signals of different bandwidths (5 MHz to 20 MHz).
2014 Ieee 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks, Dec 1, 2014
ABSTRACT We present and analyze an Electric Vehicle (EV) charging management model for a fast cha... more ABSTRACT We present and analyze an Electric Vehicle (EV) charging management model for a fast charging station network in a smart grid environment. The proposed model considers a charging station network that provides service to multiple EV charging-classes. The basic feature of the proposed model is when EVs are blocked by their preferred station due to the unavailability of charging outlets, they are prompted via a communication system to select their next station, which either provides fixed or elastic charging services.We derive an analytical framework for the determination of the arrival procedure to the additional stations, which is then used for the derivation of the distribution of occupied charging outlets in both stations. Simulation results verify the high accuracy of the proposed analysis. The proposed analysis can be used for the determination of the number of stations that should be installed in a specific geographical area, so that EVs do not suffer charging delays.
In this PhD dissertation multi-rate models are examined for the performance analysis of telecommu... more In this PhD dissertation multi-rate models are examined for the performance analysis of telecommunication networks through mathematical analysis and simulation. Particular emphasis is given to optical networks. The main goal is the development of analytical models for the calculation of network performance metrics, such as blocking probabilities, transmission delay and utilization of the common channel. The proposed analytical models are distinguished according to the network technologies. Three different technologies are considered: A) Wavelength routed optical networks. B) Optical access networks. C) Wireless Internet access networks. Multi-rate loss models are proposed for the performance evaluation of wavelength routed optical networks. Firstly, the case of a single link is considered and then a mesh all-optical network is examined. In addition, analytical models are proposed for Optical Packet Switching (OPS) networks, for the case of an all-optical OPS switch and of an OPS mes...
2014 IEEE 19th International Workshop on Computer Aided Modeling and Design of Communication Links and Networks (CAMAD), 2014
ABSTRACT We present and analyze an Electric Vehicle (EV) charging management model for a fast cha... more ABSTRACT We present and analyze an Electric Vehicle (EV) charging management model for a fast charging station network in a smart grid environment. The proposed model considers a charging station network that provides service to multiple EV charging-classes. The basic feature of the proposed model is when EVs are blocked by their preferred station due to the unavailability of charging outlets, they are prompted via a communication system to select their next station, which either provides fixed or elastic charging services.We derive an analytical framework for the determination of the arrival procedure to the additional stations, which is then used for the derivation of the distribution of occupied charging outlets in both stations. Simulation results verify the high accuracy of the proposed analysis. The proposed analysis can be used for the determination of the number of stations that should be installed in a specific geographical area, so that EVs do not suffer charging delays.
A theoretical model is developed and exploited for characterizing the behavior of an all-optical ... more A theoretical model is developed and exploited for characterizing the behavior of an all-optical circuit that deploys a Fabry-PÊrot filter (FPF) and a semiconductor optical amplifier (SOA)-assisted Sagnac switch driven by an intense continuous wave (cw) holding beam to extract the clock signal from a received ultra-fast data stream. The role of each unit is thoroughly studied, and its understanding allows us to identify the critical operational parameters, which include the cw power, the energy of the data pulses, the SOA small ...
Abstract. The operation of a semiconductor-optical-amplifier-assisted Sagnac recirculating shift ... more Abstract. The operation of a semiconductor-optical-amplifier-assisted Sagnac recirculating shift register with an inverter is studied theoretically and analyzed using a numerical model developed for this purpose. The impact of critical operational parameters, such as the SOA small-signal gain and carrier lifetime, the controlling pulses' energy and width, and the Sagnac loop asymmetry, on the switching energy and contrast ratio metrics is thoroughly investigated. The performance of the shift register is first evaluated at 10 GHz by ...
The instantaneous frequency deviation of the pulses switched from a semiconductor optical amplifi... more The instantaneous frequency deviation of the pulses switched from a semiconductor optical amplifier (SOA)–assisted Sagnac interferometer is theoretically studied and analyzed. By using explicit expressions for the phase response and its temporal derivative and applying a numerical model, a set of curves is obtained that allows us to investigate and assess the dependence of the function of interest on the critical operational parameters. From their interpretation, the basic design rules that must govern them in order for its profile to ...
proposed in IEEE 802.11 standard for wireless local area networks, is the Distributed Coordinatio... more proposed in IEEE 802.11 standard for wireless local area networks, is the Distributed Coordination Function (DCF). DCF uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) to resolve contention between wireless stations and to verify successful transmissions. In this work we present an analytical model of the IEEE 802.11 MAC protocol validated by simulation results for the DCF throughput, for both packet transmission schemes employed by DCF, the basic access and the RTS/CTS access mechanism. Moreover, we depict the saturation throughput and the average packet delay for 1, 5.5 and 11 Mbps in order to highlight the effect of the bit rate on network performance for both mechanisms.
2014 16th International Conference on Transparent Optical Networks (ICTON), 2014
ABSTRACT Hybrid Wavelength-Time Division Multiplexing (WDM-TDM) Passive Optical Networks (PONs) b... more ABSTRACT Hybrid Wavelength-Time Division Multiplexing (WDM-TDM) Passive Optical Networks (PONs) become strong candidates for Next Generation PONs and, therefore, merit deep performance evaluation. In this paper, we concentrate on the performance of a Dynamic Wavelength Allocation (DWA) protocol, under multi-dimensional traffic which is modeled by a Pareto ON-OFF model; it resembles the bursty nature of traffic by considering ON and OFF transmission periods, whose duration is Pareto distributed. The investigated protocol may cause service delay to existing connections, if they will be found in state OFF, while no connection is found in state ON at the same time. In this case, the occupied wavelength is released, and a new wavelength (however, not always available, hence the delay) will be allocated to OFF connections, upon request from a connection to return to state ON. The delay caused by the so-called Delay Wavelength Release (D-WR) protocol, as well as other performance measures, are evaluated via simulation, and compared with the delay and corresponding measures of the same protocol, when the ON-OFF traffic under service has exponentially distributed ON and OFF periods.
Proceedings of the 2013 18th European Conference on Network and Optical Communications & 2013 8th Conference on Optical Cabling and Infrastructure (NOC-OC&I), 2013
ABSTRACT Passive Optical Networks (PONs) are attractive fiber-based access systems providing broa... more ABSTRACT Passive Optical Networks (PONs) are attractive fiber-based access systems providing broadband access solutions at a low cost. A hybrid Wavelength Division Multiplexing (WDM) - Time Division Multiple Access (TDMA) PON is a favorite PON configuration, in which the researchers have drawn much attention. We have analysed and proposed several protocols for dynamic wavelength allocation in a WDM-TDMA PON, by separately considering random or quasi-random input-traffic. By modelling the bursty in-service traffic as an ON-OFF model, we have proposed three protocols for random call arrivals. The same protocols have also been proposed for quasi-random call arrivals, resulting however in different evaluation conclusions (than in the case of random arriving calls). This fact gave rise to a fourth protocol, the Priority Wavelength Release (Pr-WR) Protocol, suitable for quasi-random input-traffic. According to this protocol, the service-classes accommodated in the PON are distinguished in two groups: the high and low priority groups. A connection between an Optical Node Unit (ONU) and the Optical Line Terminal (OLT) (the common link of the PON) can be terminated and the occupied wavelength is released, only when the common link is empty or holds low priority calls in state OFF. In this paper, we examine the Pr-WR protocol in the WDM-TDMA PON under a mixture of quasi-random and random arriving calls. The ON-OFF teletraffic model for the mixture of random and quasi-random arrivals is presented. We evaluate the behaviour of this protocol in comparison with the other three protocols in respect of: a) the Connection Failure Probability (due to the unavailability of a wavelength), and b) the Delay (low priority calls may delay in state OFF, until a new wavelength becomes available upon a new call arrival). For the Pr-WR Protocol, we also calculate the Call Blocking Probability (due to the restricted bandwidth of the wavelength) and the Burst Blocking Probability (burst of calls delays - n state OFF, due to temporal unavailability of wavelength bandwidth). We come to safe conclusion which is favourite for the Pr-Wr protocol.
Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 2015
ABSTRACT In this paper we present a survey of recent trends on short-term electricity-price predi... more ABSTRACT In this paper we present a survey of recent trends on short-term electricity-price prediction models. We classify the proposed price prediction methods based on the forecasting horizon into short- medium- and long-term approaches. We provide the key features of the medium- and long- solutions, while we emphasize on short-term prediction models, by providing their classification into statistical, computational intelligent and hybrid methods. We also highlight the key characteristics of the available prediction methods, while the strengths and weaknesses of these solutions are also discussed and analyzed. These important aspects should be considered by researchers that target on the derivation of more efficient and accurate electricity-price prediction models, especially for smart grid applications.
2014 16th International Conference on Transparent Optical Networks (ICTON), 2014
ABSTRACT Passive Optical Networks (PONs) constitute a predominant point-to-multipoint architectur... more ABSTRACT Passive Optical Networks (PONs) constitute a predominant point-to-multipoint architectures for an efficient and cost-effective fiber-based broadband access. We have analyzed several PON configurations, which either have been already standardized, like Wavelength Division Multiplexing - Time Division Multiplexing (WDM-TDM) PONs, or are highly promising PON technologies, like Optical Code Division Multiple Access (OCDMA) PONs. Based on Markov chains, we have developed teletraffic loss models for the call-level performance evaluation in the upstream PON direction. The PONs accommodate multiple service-classes of bursty traffic; to reflect the bursty nature of traffic and to simplify the analysis, we resort to ON-OFF traffic modeling. Call-connection requests are considered random (infinite population of traffic sources) or quasi-random (finite population of traffic sources). The main call-level performance index is the Call Blocking Probability (CBP). For the efficient CBP calculation, we result in approximate recursive formulas, whose the accuracy is completely satisfactory, as it has been verified through simulation.
ABSTRACT In this paper, we consider a single-link multirate loss system, which accommodates diffe... more ABSTRACT In this paper, we consider a single-link multirate loss system, which accommodates different service-classes with different traffic and peak-bandwidth requirements. Calls of each service-class arrive in the system according to a random (Poisson) or a quasi-random process, and have an exponentially distributed service time. Poisson or quasi-random arriving calls belong to service-classes of infinite or finite number of traffic sources, respectively. The service-classes are also distinguished, according to the behaviour of calls under service, in elastic and adaptive service-classes. Elastic calls can compress their bandwidth by simultaneously increasing their service time, while, adaptive calls do not affect their service time. A new call (either elastic or adaptive) is accepted in the system with its peak-bandwidth requirement, if there is available link bandwidth. If not, the call retries one or more times (single and multi-retry loss model, respectively) with a reduced bandwidth. If the available link bandwidth is lower than the call’s last bandwidth requirement, the call can still compress its last bandwidth requirement (down to a certain bandwidth), together with the bandwidth of all inservice calls. Call blocking occurs, if, after compression, the call’s bandwidth still exceeds the available link bandwidth. The system incorporates the Bandwidth Reservation (BR) policy, whereby we can achieve certain Quality of Service (QoS) for each service class, through a proper bandwidth allocation defined by the BR parameters. To calculate in an approximate but efficient way, time and call congestion probabilities, as well as link utilization, we propose recurrent formulas for the determination of the link occupancy distribution. The accuracy of the proposed formulas is verified by simulation, and is found to be very satisfactory. We show the consistency and the necessity of the proposed models.
ABSTRACT This work presents the design and implementation of a stand-alone linear power amplifier... more ABSTRACT This work presents the design and implementation of a stand-alone linear power amplifier at 2.4 GHz with high output power. A GaN HEMT transistor is selected for the design and implementation of the power amplifier. The device exhibits a gain of 11.7 dB and a drain efficiency of 39 % for an output power of 36.7 dBm at 2.4 GHz for an input power of 25 dBm. The carrier to intermodulation ratio is better than 25 dB for a two tone input signal of 25 dBm of total power and a spacing of 5 MHz. The fabricated device is also tested with LTE input signals of different bandwidths (5 MHz to 20 MHz).
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Papers by John Vardakas