F.-N. Pavlidou - Academia.edu (original) (raw)

Papers by F.-N. Pavlidou

2007 IEEE International Symposium on Power Line Communications and Its Applications, 2007

In this paper we study how power line communications are affected by different coding techniques.... more In this paper we study how power line communications are affected by different coding techniques. We investigate the case of LDPC coding scheme and its application to the PLC channel. The modulation method applied is BPSK while the transmission technique used is OFDM. We study regular LDPC codes, which is the worst case scenario concerning the performance of LDPC codes. The OFDM symbol size is initially defined at 4096 carriers, since certain characteristics of LDPC codes, like their sparse parity check matrix, imply that a larger block size improves their performance. In this paper, the coding and decoding technique have firstly been applied to a realistic power line channel. The attenuation caused by the PLC channel is derived from actual measurements. We test the performance of LDPC codes of ½ code rate, by means of BER, compared to Reed-Solomon codes of similar code rate and convolutional codes, when they are all applied to the PLC channel and under the same conditions. Additionally, impulsive noise is generated and the system's performance is tested under the coding schemes mentioned above. Afterwards, we examine how different code rates affect the BER. All the above results are obtained via computer simulations.

2007 IFIP International Conference on Wireless and Optical Communications Networks, 2007

Mobile Ad hoc Networks (MANETs) are networks with dynamic topology and limited resources, where r... more Mobile Ad hoc Networks (MANETs) are networks with dynamic topology and limited resources, where routing is highly correlated to their performance. Most routing algorithms focus on the establishment of a single path between the source and the destination. However, multiple routes have been proven beneficial, when used either for load balancing or as backup routing paths. In this paper we

2008 IEEE International Symposium on Power Line Communications and Its Applications, 2008

... With the aim of checking how the model's parameters affect the system's performance... more ... With the aim of checking how the model's parameters affect the system's performance, we use a range of values for two basic parameters and we ... A. Channel model For the system's realization, we utilize a channel model for the PLC channel. ... factor weighting i p i i k e e g fH

Proceedings EUROCON, 2001

... [2] I.Ali et al, “Doppler Characterization for LEO Satellites”, Proc. IEEE Trans. on Commun. ... more ... [2] I.Ali et al, “Doppler Characterization for LEO Satellites”, Proc. IEEE Trans. on Commun. vol.46, no.3, pp.309-313, March 1998. [3] I. Ali et al, “ Doppler Based Multiple Access (DBMA): A novell flow control mechanism for LEO Satellite Systems”, Proc. Milicom 1997. ...

This paper deals with the performance evaluation of various path selection strategies that are su... more This paper deals with the performance evaluation of various path selection strategies that are suitable for nonGEO satellite systems. The Modified Dijkstra algorithm is used for different link cost functions. These various cost functions result to different performance in terms of system utilization, rerouting failure probability and delay parameters. In particular four metrics have been examined for the establishment of paths. The first two are based on the propagation delay and the traffic at the network, whereas the other two are based on new, special factors that characterize the operation of ISLs. The scenarios are tested through extended real-time simulations and fruitful conclusions are derived at the end of the study.

IEEE Transactions on Aerospace and Electronic Systems, 2005

The problem of dynamic handover management in Low Earth Orbit (LEO) satellite systems is addresse... more The problem of dynamic handover management in Low Earth Orbit (LEO) satellite systems is addressed in this paper. Particularly, an analytical study of a newly proposed method for handover management, called Dynamic Doppler-based Handover Prioritization scheme (DDBHP), will be presented. DDBHP utilizes Doppler shift monitoring of each communicating user terminal onboard the satellite and geometric characteristics to accurately predict the handover load. As a result, handover requests are more effectively managed, resulting to an improved performance in terms of blocking and forced termination probabilities. Moreover, by supporting guaranteed handovers, DDBHP can be used to provide QoS to users of future broadband satellite networks. An extensive mathematical model that justifies Doppler shift monitoring will be presented along with a detailed queueing model used not only to evaluate DDBHP performance but also to provide a methodology for associating DDBHP operational parameters with desired performance. Comparison of analytical and simulation results validate the proposed model.

IEEE Transactions on Aerospace and Electronic Systems, 2009

An integrated high altitude platform (HAP)-satellite communication system appears to be very suit... more An integrated high altitude platform (HAP)-satellite communication system appears to be very suitable for a large set of scenarios including emergency situations, exceptional events, etc. In fact, the satellite capability to provide a broadband and ubiquitous access can be enhanced by the deployment of HAP that allows the use of low-power consuming, cost-efficient, and portable terminals. To obtain an optimum utilization of radio resource, without renouncing to QoS satisfaction, a suitable call admission control scheme must be implemented. Nevertheless, transmission control protocol (TCP) behavior, mainly affected by the high latency and shadowing events, can impact call admission control (CAC) performance. Therefore, it would be desirable that the CAC scheme takes into account also the TCP congestion window real evolution. We present an innovative CAC scheme that uses TCP statistics as one of its inputs and is able to manage different classes of users. Results show that CAC performance is significantly improved by introducing TCP statistics about network congestion as an input parameter.

Electronics Letters, 2004

The error performance of collaborative dual-hop wireless transmissions with maximal-ratio combini... more The error performance of collaborative dual-hop wireless transmissions with maximal-ratio combining diversity is presented. Specifically, using the well-known inequality between geometric and harmonic mean of positive random variables, an upper bound for the end-to-end signal-to-noise-ratio is derived, and it is used to efficiently evaluate the average error probability.

Two different routing algorithm categories are studied in this paper for a typical LEO satellite ... more Two different routing algorithm categories are studied in this paper for a typical LEO satellite constellation. Shortest path algorithms and optimal routing. Their performance is investigated through extended real time simulations. In the context of satellite constellations the basic parameters for a typical network such as delay, throughput, link utilization must be supplemented by new factors imposed by the nature of satellite operation, like the handover procedures, the non-uniformity of load distribution in the space segment and the continuous topology variation. The pros and cons of the techniques are illustrated and helpful conclusions for the network design are provided. I.

Journal of Communication and Information Systems

In this paper Space-Time Block Coding (STBC) is examined in powerline and satellite communication... more In this paper Space-Time Block Coding (STBC) is examined in powerline and satellite communications, comparing the gains that this coding-modulation technique provides to these communications systems. The powerline environment is assumed to be a frequency-selective, multipath fading environment with Additive White Class A Noise (AWCN), which is used to model the actual powerline noise characteristics. The satellite channel for urban area, modeled as a combination of Rayleigh and lognormal processes with the presence of Additive White Gaussian Noise (AWGN) is also studied. System efficiency is enhanced by the application of Orthogonal Frequency Division Multiplexing (OFDM), convolutional coding and block interleaving and the performance of different Phase Shift Keying (PSK) modulation schemes under the imposed channel conditions is investigated. The performance of the system is assessed by the commonly used Bit Error Rate (BER) vs. Signal to Noise Ratio (SNR) diagrams and there is also a comparison regarding the throughput efficiency among the examined systems. As stated in the results section, STBC can be used in powerline and satellite communications providing remarkable results, comparable to those in terrestrial wireless communications where STBC is nowadays a rather mature technique.

5th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Wireless Networks - Catching the Mobile Future., 2000

In this paper a direct sequence spread-spectrum multiple access communication system is studied f... more In this paper a direct sequence spread-spectrum multiple access communication system is studied for a frequency selective mobile radio channel. The reverse link (mobile to base station) is analysed, assuming Rayleigh fading channel and K asynchronous users, with M orthogonal sequences per user. The analysis is based on the consideration of the quadrature components of the signal and noise. The

Low Earth Orbit (LEO) satellite networks are characterized by topology variations. Although space... more Low Earth Orbit (LEO) satellite networks are characterized by topology variations. Although space segment topology varies periodically, connections of mobile stations (MS's) to the satellite network alter stochastically. As a result the quality of service delivered to users may degrade. Different procedures have been proposed either as part of a resource allocation mechanism or as part of an end-to-end routing protocol to manage transitions of MS's from one satellite to another (handover). All of these procedures are based on predictions of the requested handovers to facilitate network operation and therefore enhance quality of service. This paper proposes a new handover procedure that exploits all geometric characteristics of a satelliteto-MS connection to provide an equable handover.

IP Networking over Next-Generation Satellite Systems, 2008

... A first observation reveals that CRTP is more prone to packet loss compared to ECRTP. Under f... more ... A first observation reveals that CRTP is more prone to packet loss compared to ECRTP. Under further scrutiny, we observe that for low error intensities ECRTP does not suffer from packet loss due to desync. ... 325 Fig. 21.3 Percentage of packets lost due to desync Fig. ...

IEEE Seventh International Symposium on Spread Spectrum Techniques and Applications,, 2002

... Tlir inlother code rate that was used in this work was 113 and the constraint length ai'... more ... Tlir inlother code rate that was used in this work was 113 and the constraint length ai' the coiivolutional encoder was 3. The puncturing period P was chosen to be P=8. Sa the availnhle code raies \vert 8!9,..,1/3 according to the formula: ... [I I J K. Muhnniniod and Khaled Ben Letaief ...

2007 IEEE International Symposium on Power Line Communications and Its Applications, 2007

We study the performance of Non-Collision Packet Reservation Multiple Access (NC-PRMA) scheme as ... more We study the performance of Non-Collision Packet Reservation Multiple Access (NC-PRMA) scheme as a MAC protocol for powerline communication networks. A PHY-MAC cross layer design is considered in order to provide Quality of Service (QoS) guarantees for integrated voice, data and video services. System performance is evaluated via simulations in terms of packet dropping probability and mean access delay.

6th International Conference on Telecommunications in Modern Satellite, Cable and Broadcasting Service, 2003. TELSIKS 2003., 2003

ABSTRACT In this paper we use a channel model based on measurements from Costas Assimakopulos, et... more ABSTRACT In this paper we use a channel model based on measurements from Costas Assimakopulos, et al. (2003) to test the performance of a coded multicarrier CDMA system over the powerline channel from the secondary transformer coil to the subscriber. We focus on the different coding techniques which show that coding can make the difference under such a hostile medium. The comparison of coding, modulation types and the presence/absence of interleaving is depicted by BER vs. SNR diagrams and complexity tables.

2000 IEEE Sixth International Symposium on Spread Spectrum Techniques and Applications. ISSTA 2000. Proceedings (Cat. No.00TH8536), 2000

The selection of an appropriate multiple access (MA) technique is a fundamental issue in any wire... more The selection of an appropriate multiple access (MA) technique is a fundamental issue in any wired or wireless communications system. Over the past thirty years thousands of papers have been written on multiple access protocols. In this tutorial a review of Techniques is tried due to their increasing importance in recent years. Some topics open for further research are also indicated.

2007 IEEE International Symposium on Power Line Communications and Its Applications, 2007

In this paper we study how power line communications are affected by different coding techniques.... more In this paper we study how power line communications are affected by different coding techniques. We investigate the case of LDPC coding scheme and its application to the PLC channel. The modulation method applied is BPSK while the transmission technique used is OFDM. We study regular LDPC codes, which is the worst case scenario concerning the performance of LDPC codes. The OFDM symbol size is initially defined at 4096 carriers, since certain characteristics of LDPC codes, like their sparse parity check matrix, imply that a larger block size improves their performance. In this paper, the coding and decoding technique have firstly been applied to a realistic power line channel. The attenuation caused by the PLC channel is derived from actual measurements. We test the performance of LDPC codes of ½ code rate, by means of BER, compared to Reed-Solomon codes of similar code rate and convolutional codes, when they are all applied to the PLC channel and under the same conditions. Additionally, impulsive noise is generated and the system's performance is tested under the coding schemes mentioned above. Afterwards, we examine how different code rates affect the BER. All the above results are obtained via computer simulations.

2007 IFIP International Conference on Wireless and Optical Communications Networks, 2007

Mobile Ad hoc Networks (MANETs) are networks with dynamic topology and limited resources, where r... more Mobile Ad hoc Networks (MANETs) are networks with dynamic topology and limited resources, where routing is highly correlated to their performance. Most routing algorithms focus on the establishment of a single path between the source and the destination. However, multiple routes have been proven beneficial, when used either for load balancing or as backup routing paths. In this paper we

2008 IEEE International Symposium on Power Line Communications and Its Applications, 2008

... With the aim of checking how the model's parameters affect the system's performance... more ... With the aim of checking how the model's parameters affect the system's performance, we use a range of values for two basic parameters and we ... A. Channel model For the system's realization, we utilize a channel model for the PLC channel. ... factor weighting i p i i k e e g fH

Proceedings EUROCON, 2001

... [2] I.Ali et al, “Doppler Characterization for LEO Satellites”, Proc. IEEE Trans. on Commun. ... more ... [2] I.Ali et al, “Doppler Characterization for LEO Satellites”, Proc. IEEE Trans. on Commun. vol.46, no.3, pp.309-313, March 1998. [3] I. Ali et al, “ Doppler Based Multiple Access (DBMA): A novell flow control mechanism for LEO Satellite Systems”, Proc. Milicom 1997. ...

This paper deals with the performance evaluation of various path selection strategies that are su... more This paper deals with the performance evaluation of various path selection strategies that are suitable for nonGEO satellite systems. The Modified Dijkstra algorithm is used for different link cost functions. These various cost functions result to different performance in terms of system utilization, rerouting failure probability and delay parameters. In particular four metrics have been examined for the establishment of paths. The first two are based on the propagation delay and the traffic at the network, whereas the other two are based on new, special factors that characterize the operation of ISLs. The scenarios are tested through extended real-time simulations and fruitful conclusions are derived at the end of the study.

IEEE Transactions on Aerospace and Electronic Systems, 2005

The problem of dynamic handover management in Low Earth Orbit (LEO) satellite systems is addresse... more The problem of dynamic handover management in Low Earth Orbit (LEO) satellite systems is addressed in this paper. Particularly, an analytical study of a newly proposed method for handover management, called Dynamic Doppler-based Handover Prioritization scheme (DDBHP), will be presented. DDBHP utilizes Doppler shift monitoring of each communicating user terminal onboard the satellite and geometric characteristics to accurately predict the handover load. As a result, handover requests are more effectively managed, resulting to an improved performance in terms of blocking and forced termination probabilities. Moreover, by supporting guaranteed handovers, DDBHP can be used to provide QoS to users of future broadband satellite networks. An extensive mathematical model that justifies Doppler shift monitoring will be presented along with a detailed queueing model used not only to evaluate DDBHP performance but also to provide a methodology for associating DDBHP operational parameters with desired performance. Comparison of analytical and simulation results validate the proposed model.

IEEE Transactions on Aerospace and Electronic Systems, 2009

An integrated high altitude platform (HAP)-satellite communication system appears to be very suit... more An integrated high altitude platform (HAP)-satellite communication system appears to be very suitable for a large set of scenarios including emergency situations, exceptional events, etc. In fact, the satellite capability to provide a broadband and ubiquitous access can be enhanced by the deployment of HAP that allows the use of low-power consuming, cost-efficient, and portable terminals. To obtain an optimum utilization of radio resource, without renouncing to QoS satisfaction, a suitable call admission control scheme must be implemented. Nevertheless, transmission control protocol (TCP) behavior, mainly affected by the high latency and shadowing events, can impact call admission control (CAC) performance. Therefore, it would be desirable that the CAC scheme takes into account also the TCP congestion window real evolution. We present an innovative CAC scheme that uses TCP statistics as one of its inputs and is able to manage different classes of users. Results show that CAC performance is significantly improved by introducing TCP statistics about network congestion as an input parameter.

Electronics Letters, 2004

The error performance of collaborative dual-hop wireless transmissions with maximal-ratio combini... more The error performance of collaborative dual-hop wireless transmissions with maximal-ratio combining diversity is presented. Specifically, using the well-known inequality between geometric and harmonic mean of positive random variables, an upper bound for the end-to-end signal-to-noise-ratio is derived, and it is used to efficiently evaluate the average error probability.

Two different routing algorithm categories are studied in this paper for a typical LEO satellite ... more Two different routing algorithm categories are studied in this paper for a typical LEO satellite constellation. Shortest path algorithms and optimal routing. Their performance is investigated through extended real time simulations. In the context of satellite constellations the basic parameters for a typical network such as delay, throughput, link utilization must be supplemented by new factors imposed by the nature of satellite operation, like the handover procedures, the non-uniformity of load distribution in the space segment and the continuous topology variation. The pros and cons of the techniques are illustrated and helpful conclusions for the network design are provided. I.

Journal of Communication and Information Systems

In this paper Space-Time Block Coding (STBC) is examined in powerline and satellite communication... more In this paper Space-Time Block Coding (STBC) is examined in powerline and satellite communications, comparing the gains that this coding-modulation technique provides to these communications systems. The powerline environment is assumed to be a frequency-selective, multipath fading environment with Additive White Class A Noise (AWCN), which is used to model the actual powerline noise characteristics. The satellite channel for urban area, modeled as a combination of Rayleigh and lognormal processes with the presence of Additive White Gaussian Noise (AWGN) is also studied. System efficiency is enhanced by the application of Orthogonal Frequency Division Multiplexing (OFDM), convolutional coding and block interleaving and the performance of different Phase Shift Keying (PSK) modulation schemes under the imposed channel conditions is investigated. The performance of the system is assessed by the commonly used Bit Error Rate (BER) vs. Signal to Noise Ratio (SNR) diagrams and there is also a comparison regarding the throughput efficiency among the examined systems. As stated in the results section, STBC can be used in powerline and satellite communications providing remarkable results, comparable to those in terrestrial wireless communications where STBC is nowadays a rather mature technique.

5th IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, Wireless Networks - Catching the Mobile Future., 2000

In this paper a direct sequence spread-spectrum multiple access communication system is studied f... more In this paper a direct sequence spread-spectrum multiple access communication system is studied for a frequency selective mobile radio channel. The reverse link (mobile to base station) is analysed, assuming Rayleigh fading channel and K asynchronous users, with M orthogonal sequences per user. The analysis is based on the consideration of the quadrature components of the signal and noise. The

Low Earth Orbit (LEO) satellite networks are characterized by topology variations. Although space... more Low Earth Orbit (LEO) satellite networks are characterized by topology variations. Although space segment topology varies periodically, connections of mobile stations (MS's) to the satellite network alter stochastically. As a result the quality of service delivered to users may degrade. Different procedures have been proposed either as part of a resource allocation mechanism or as part of an end-to-end routing protocol to manage transitions of MS's from one satellite to another (handover). All of these procedures are based on predictions of the requested handovers to facilitate network operation and therefore enhance quality of service. This paper proposes a new handover procedure that exploits all geometric characteristics of a satelliteto-MS connection to provide an equable handover.

IP Networking over Next-Generation Satellite Systems, 2008

... A first observation reveals that CRTP is more prone to packet loss compared to ECRTP. Under f... more ... A first observation reveals that CRTP is more prone to packet loss compared to ECRTP. Under further scrutiny, we observe that for low error intensities ECRTP does not suffer from packet loss due to desync. ... 325 Fig. 21.3 Percentage of packets lost due to desync Fig. ...

IEEE Seventh International Symposium on Spread Spectrum Techniques and Applications,, 2002

... Tlir inlother code rate that was used in this work was 113 and the constraint length ai'... more ... Tlir inlother code rate that was used in this work was 113 and the constraint length ai' the coiivolutional encoder was 3. The puncturing period P was chosen to be P=8. Sa the availnhle code raies \vert 8!9,..,1/3 according to the formula: ... [I I J K. Muhnniniod and Khaled Ben Letaief ...

2007 IEEE International Symposium on Power Line Communications and Its Applications, 2007

We study the performance of Non-Collision Packet Reservation Multiple Access (NC-PRMA) scheme as ... more We study the performance of Non-Collision Packet Reservation Multiple Access (NC-PRMA) scheme as a MAC protocol for powerline communication networks. A PHY-MAC cross layer design is considered in order to provide Quality of Service (QoS) guarantees for integrated voice, data and video services. System performance is evaluated via simulations in terms of packet dropping probability and mean access delay.

6th International Conference on Telecommunications in Modern Satellite, Cable and Broadcasting Service, 2003. TELSIKS 2003., 2003

ABSTRACT In this paper we use a channel model based on measurements from Costas Assimakopulos, et... more ABSTRACT In this paper we use a channel model based on measurements from Costas Assimakopulos, et al. (2003) to test the performance of a coded multicarrier CDMA system over the powerline channel from the secondary transformer coil to the subscriber. We focus on the different coding techniques which show that coding can make the difference under such a hostile medium. The comparison of coding, modulation types and the presence/absence of interleaving is depicted by BER vs. SNR diagrams and complexity tables.

2000 IEEE Sixth International Symposium on Spread Spectrum Techniques and Applications. ISSTA 2000. Proceedings (Cat. No.00TH8536), 2000

The selection of an appropriate multiple access (MA) technique is a fundamental issue in any wire... more The selection of an appropriate multiple access (MA) technique is a fundamental issue in any wired or wireless communications system. Over the past thirty years thousands of papers have been written on multiple access protocols. In this tutorial a review of Techniques is tried due to their increasing importance in recent years. Some topics open for further research are also indicated.