Dobri Dobrev - Academia.edu (original) (raw)

Papers by Dobri Dobrev

Journal of Optical Communications, 2009

The paper deals with some investigations aimed at applying compensation techniques to reduce nonl... more The paper deals with some investigations aimed at applying compensation techniques to reduce nonlinear signal distortion in the Mach-Zehnder modulator of HFC CATV systems. The frequency distribution of second-and third-order intermodulation products of N-channel transmission systems is shown. Models of dual-parallel and dual-cascade Mach-Zehnder modulators are suggested based on both the mathematical model of a conventional Mach-Zehnder modulator and the features of the CATV system itself, thus making it possible for the modulator parameters to be determined in a way to ensure CSO products cancellation and CTB products minimization. The dependence of the C/CTB parameter on the modulation index is studied for N-channel HFC CATV systems applying a dual-parallel or dual-cascade Mach-Zehnder modulator. Optical channels implementing dual-parallel or dual-cascade Mach-Zehnder modulator instead of a conventional one are compared and the possibilities to improve the RF signals' dynamic range are analyzed. Relations to determine the increase of the optical loss introduced by dual Mach-Zehnder modulators are suggested that help compare it with that caused by a conventional Mach-Zehnder modulator.

The paper deals with the results of EDFA simulation that has been carried out to study the modes ... more The paper deals with the results of EDFA simulation that has been carried out to study the modes of operation and to determine the amplifier parameters' values at which maximum flatness of the gain spectrum curve is obtained. The mathematical model applied is based on the propagation equations and known parameters of the erbium-doped fiber. Dependencies to determine the wavelength operation range, the fractional upper-state population and the length of the erbiumdoped fiber are given. A formula to be used in engineering practice is proposed for the determination of the pump-power optimum value of EDFA with constant gain, the power level of the input multi-wavelength signal being taken into consideration. In order to estimate the accuracy of the EDFA simulation model its gain and noise spectrum characteristics have been compared to those of a real amplifier.

EUROCON 2005 - The International Conference on "Computer as a Tool", 2005

In this paper we investigate the influence of the delay line accuracy on the spectrum of impulse ... more In this paper we investigate the influence of the delay line accuracy on the spectrum of impulse radio that utilizes transmitted-reference quaternary phase modulation. The acceptable accuracy of delay lines is determined. The power spectral density derived by Welch periodogram method verifies the theoretical results

EUROCON 2005 - The International Conference on "Computer as a Tool", 2005

In this paper we propose a new modulation scheme for impulse radio. This modulation shapes the si... more In this paper we propose a new modulation scheme for impulse radio. This modulation shapes the signal spectrum in such a way that coexistence of ultra wide-band (UWB) and IEEE 802.11a devices is possible. Power spectral density of the UWB signal obtained by Welch periodogram method verifies analytical predictions

The paper deals with what causes the signal parameters in the reverse path channel of hybrid fibe... more The paper deals with what causes the signal parameters in the reverse path channel of hybrid fiber-coaxial CATV system to worsen. Besides the analysis, a mathematical model of the channel is also suggested with the funnel effect being taken into consideration. If the carrier-to-noise ratio at the receiver input of the headend is known then the model makes it possible to optimize the topology of the coaxial distribution network and the number of optical nodes whose signals are summarized in the receiver. Experimental and analytical results are shown that enable the engineer to determine the RF signal dynamic range at the modulation input of the reverse path lasers if both the bit error ratio at the receiver output and the acceptable laser clipping are given.

This article represents the results of a simulation study of the characteristics of a satellite t... more This article represents the results of a simulation study of the characteristics of a satellite television channel shaped under the DVB-S2 standard. The formulas for determining BER of a radio channel when using QPSK, 8QPSK and 16APSK modulation are produced. The algorithms determining the probability of error after LDPC and BCH decoders are represented. Based on the analysis of the characteristics of the DVB-S2 channel, its noise immunity is evaluated, as well as the permissible transmission rate of video information and the power efficiency of the system.

This article represents the results of a simulation study of the characteristics of a satellite t... more This article represents the results of a simulation study of the characteristics of a satellite television channel shaped under the DVB-S2 standard. The formulas for determining BER of a radio channel when using QPSK, 8QPSK and 16APSK modulation are produced. The algorithms determining the probability of error after LDPC and BCH decoders are represented. Based on the analysis of the characteristics of the DVB-S2 channel, its noise immunity is evaluated, as well as the permissible transmission rate of video information and the power efficiency of the system.

Engineering, Technology & Applied Science Research, 2014

This article represents the algorithms of APSK constellation and mapping optimization. The depend... more This article represents the algorithms of APSK constellation and mapping optimization. The dependencies of the symbol error probability Ps on the parameters of the 16APSK and 32APSK constellations are examined and several options that satisfy the requirements to the minimum value of Ps are selected. Mapping optimization is carried out for the selected APSK constellations. BER characteristics of the satellite DVB-S2 channels are represented when using optimized and standard 16APSK and 32APSK constellations and a comparative analysis of the results achieved is made.

Microelectronics Journal, 2006

ABSTRACT

Engineering, Technology & Applied Science Research, 2014

This article represents the algorithms of APSK constellation and mapping optimization. The depend... more This article represents the algorithms of APSK constellation and mapping optimization. The dependencies of the symbol error probability Ps on the parameters of the 16APSK and 32APSK constellations are examined and several options that satisfy the requirements to the minimum value of Ps are selected. Mapping optimization is carried out for the selected APSK constellations. BER characteristics of the satellite DVB-S2 channels are represented when using optimized and standard 16APSK and 32APSK constellations and a comparative analysis of the results achieved is made.

Engineering, Technology & Applied Science Research, 2014

This article presents the results of a study on the noise immunity of DVB channels when higher-or... more This article presents the results of a study on the noise immunity of DVB channels when higher-order M-ary APSK modulation schemes and concatenated BCH-LDPC codes are used. Dependencies to determine the probability at the decoder output are given taking into consideration the BCH and LDPC code parameters and the error probability in the communication channel. The influence of the BCH packets length, the BCH code rate, the number of maximum iteration and the parameters of LDPC parity-check matrix on the code efficiency is analyzed. Research of the influence of the concatenated LDPC-BCH code parameters on the radio channel noise immunity is conducted and dependencies to determine the required CNR at the input of the satellite receiver are given.

International Journal of Reasoning-based Intelligent Systems, 2015

This article presents the results of a study on the noise immunity of satellite DVB channels. Dep... more This article presents the results of a study on the noise immunity of satellite DVB channels. Dependencies which determine the error probability at the decoder output are presented taking into consideration the parameters of the used RS, convolutional, BCH and LDPC codes and the error probability at the decoder input. Research of the influence of the packet length, constraint length and code rate on the BER characteristics of Reed-Solomon and convolutional decoder is conducted. The values of the parameters under research, at which the highest code effectiveness is achieved, are determined following an analysis of the results. Investigations have been carried out to determine the influence of the BCH packets length, the BCH code rate, the parameters of LDPC parity-check matrix and the number of iteration in the LDPC decoder on the radio channel noise immunity. BER characteristics of satellite DVB channels are presented upon using concatenated RS-convolutional and BCH-LDPC codes with optimised parameters and are compared to the standard ones for such systems.

Optical Fiber Technology, 2006

The paper deals with HFC CATV systems. System parameters determinative in obtaining the desired c... more The paper deals with HFC CATV systems. System parameters determinative in obtaining the desired carrier-to-noise ratio (CNR) and acceptable nonlinear distortions are considered. Formulae for the gain and the maximum number of RF amplifiers in the longest coaxial trunk line are developed. A mathematical model of the optical channel is suggested that makes it possible for the signal minimum level at the optical receiver input to be calculated if the value of CNR and the number of TV channels transmitted are known. Analytical expressions to determine the RF signal voltage in the input and output of the optical line are given that take into consideration the nonlinear distortions in the laser transmitter, the number of TV channels and the losses within the optical fiber and passive elements. Experimental results are given to illustrate the application of the formulae in the design of a HFS system section.

Summary The paper deals with coaxial part of HFC CATV system. System parameters determinative in ... more Summary The paper deals with coaxial part of HFC CATV system. System parameters determinative in obtaining the desired signal level, carrier-to-noise ratio and acceptable nonlinear distortions are considered. Formulae for the gain and the maximum number of RF amplifiers in the longest coaxial link are developed. A mathematical model of the return path channel is suggested with the noise-funneling effect being taken into consideration. Experimental and analytical results are shown that enable the engineer to determine the optimum operating level for a return path laser. A special attention is drawn to the design of the subscribers’ distribution network and to the equalization of the downstream and upstream signal levels in particular. Two methods to set and maintain the balance of the return path are described that make it possible for some of the signal characteristics to be monitored.

Journal of Optical Communications, 2009

The paper deals with some investigations aimed at applying compensation techniques to reduce nonl... more The paper deals with some investigations aimed at applying compensation techniques to reduce nonlinear signal distortion in the Mach-Zehnder modulator of HFC CATV systems. The frequency distribution of second-and third-order intermodulation products of N-channel transmission systems is shown. Models of dual-parallel and dual-cascade Mach-Zehnder modulators are suggested based on both the mathematical model of a conventional Mach-Zehnder modulator and the features of the CATV system itself, thus making it possible for the modulator parameters to be determined in a way to ensure CSO products cancellation and CTB products minimization. The dependence of the C/CTB parameter on the modulation index is studied for N-channel HFC CATV systems applying a dual-parallel or dual-cascade Mach-Zehnder modulator. Optical channels implementing dual-parallel or dual-cascade Mach-Zehnder modulator instead of a conventional one are compared and the possibilities to improve the RF signals' dynamic range are analyzed. Relations to determine the increase of the optical loss introduced by dual Mach-Zehnder modulators are suggested that help compare it with that caused by a conventional Mach-Zehnder modulator.

The paper deals with the results of EDFA simulation that has been carried out to study the modes ... more The paper deals with the results of EDFA simulation that has been carried out to study the modes of operation and to determine the amplifier parameters' values at which maximum flatness of the gain spectrum curve is obtained. The mathematical model applied is based on the propagation equations and known parameters of the erbium-doped fiber. Dependencies to determine the wavelength operation range, the fractional upper-state population and the length of the erbiumdoped fiber are given. A formula to be used in engineering practice is proposed for the determination of the pump-power optimum value of EDFA with constant gain, the power level of the input multi-wavelength signal being taken into consideration. In order to estimate the accuracy of the EDFA simulation model its gain and noise spectrum characteristics have been compared to those of a real amplifier.

EUROCON 2005 - The International Conference on "Computer as a Tool", 2005

In this paper we investigate the influence of the delay line accuracy on the spectrum of impulse ... more In this paper we investigate the influence of the delay line accuracy on the spectrum of impulse radio that utilizes transmitted-reference quaternary phase modulation. The acceptable accuracy of delay lines is determined. The power spectral density derived by Welch periodogram method verifies the theoretical results

EUROCON 2005 - The International Conference on "Computer as a Tool", 2005

In this paper we propose a new modulation scheme for impulse radio. This modulation shapes the si... more In this paper we propose a new modulation scheme for impulse radio. This modulation shapes the signal spectrum in such a way that coexistence of ultra wide-band (UWB) and IEEE 802.11a devices is possible. Power spectral density of the UWB signal obtained by Welch periodogram method verifies analytical predictions

The paper deals with what causes the signal parameters in the reverse path channel of hybrid fibe... more The paper deals with what causes the signal parameters in the reverse path channel of hybrid fiber-coaxial CATV system to worsen. Besides the analysis, a mathematical model of the channel is also suggested with the funnel effect being taken into consideration. If the carrier-to-noise ratio at the receiver input of the headend is known then the model makes it possible to optimize the topology of the coaxial distribution network and the number of optical nodes whose signals are summarized in the receiver. Experimental and analytical results are shown that enable the engineer to determine the RF signal dynamic range at the modulation input of the reverse path lasers if both the bit error ratio at the receiver output and the acceptable laser clipping are given.

This article represents the results of a simulation study of the characteristics of a satellite t... more This article represents the results of a simulation study of the characteristics of a satellite television channel shaped under the DVB-S2 standard. The formulas for determining BER of a radio channel when using QPSK, 8QPSK and 16APSK modulation are produced. The algorithms determining the probability of error after LDPC and BCH decoders are represented. Based on the analysis of the characteristics of the DVB-S2 channel, its noise immunity is evaluated, as well as the permissible transmission rate of video information and the power efficiency of the system.

This article represents the results of a simulation study of the characteristics of a satellite t... more This article represents the results of a simulation study of the characteristics of a satellite television channel shaped under the DVB-S2 standard. The formulas for determining BER of a radio channel when using QPSK, 8QPSK and 16APSK modulation are produced. The algorithms determining the probability of error after LDPC and BCH decoders are represented. Based on the analysis of the characteristics of the DVB-S2 channel, its noise immunity is evaluated, as well as the permissible transmission rate of video information and the power efficiency of the system.

Engineering, Technology & Applied Science Research, 2014

This article represents the algorithms of APSK constellation and mapping optimization. The depend... more This article represents the algorithms of APSK constellation and mapping optimization. The dependencies of the symbol error probability Ps on the parameters of the 16APSK and 32APSK constellations are examined and several options that satisfy the requirements to the minimum value of Ps are selected. Mapping optimization is carried out for the selected APSK constellations. BER characteristics of the satellite DVB-S2 channels are represented when using optimized and standard 16APSK and 32APSK constellations and a comparative analysis of the results achieved is made.

Microelectronics Journal, 2006

ABSTRACT

Engineering, Technology & Applied Science Research, 2014

This article represents the algorithms of APSK constellation and mapping optimization. The depend... more This article represents the algorithms of APSK constellation and mapping optimization. The dependencies of the symbol error probability Ps on the parameters of the 16APSK and 32APSK constellations are examined and several options that satisfy the requirements to the minimum value of Ps are selected. Mapping optimization is carried out for the selected APSK constellations. BER characteristics of the satellite DVB-S2 channels are represented when using optimized and standard 16APSK and 32APSK constellations and a comparative analysis of the results achieved is made.

Engineering, Technology & Applied Science Research, 2014

This article presents the results of a study on the noise immunity of DVB channels when higher-or... more This article presents the results of a study on the noise immunity of DVB channels when higher-order M-ary APSK modulation schemes and concatenated BCH-LDPC codes are used. Dependencies to determine the probability at the decoder output are given taking into consideration the BCH and LDPC code parameters and the error probability in the communication channel. The influence of the BCH packets length, the BCH code rate, the number of maximum iteration and the parameters of LDPC parity-check matrix on the code efficiency is analyzed. Research of the influence of the concatenated LDPC-BCH code parameters on the radio channel noise immunity is conducted and dependencies to determine the required CNR at the input of the satellite receiver are given.

International Journal of Reasoning-based Intelligent Systems, 2015

This article presents the results of a study on the noise immunity of satellite DVB channels. Dep... more This article presents the results of a study on the noise immunity of satellite DVB channels. Dependencies which determine the error probability at the decoder output are presented taking into consideration the parameters of the used RS, convolutional, BCH and LDPC codes and the error probability at the decoder input. Research of the influence of the packet length, constraint length and code rate on the BER characteristics of Reed-Solomon and convolutional decoder is conducted. The values of the parameters under research, at which the highest code effectiveness is achieved, are determined following an analysis of the results. Investigations have been carried out to determine the influence of the BCH packets length, the BCH code rate, the parameters of LDPC parity-check matrix and the number of iteration in the LDPC decoder on the radio channel noise immunity. BER characteristics of satellite DVB channels are presented upon using concatenated RS-convolutional and BCH-LDPC codes with optimised parameters and are compared to the standard ones for such systems.

Optical Fiber Technology, 2006

The paper deals with HFC CATV systems. System parameters determinative in obtaining the desired c... more The paper deals with HFC CATV systems. System parameters determinative in obtaining the desired carrier-to-noise ratio (CNR) and acceptable nonlinear distortions are considered. Formulae for the gain and the maximum number of RF amplifiers in the longest coaxial trunk line are developed. A mathematical model of the optical channel is suggested that makes it possible for the signal minimum level at the optical receiver input to be calculated if the value of CNR and the number of TV channels transmitted are known. Analytical expressions to determine the RF signal voltage in the input and output of the optical line are given that take into consideration the nonlinear distortions in the laser transmitter, the number of TV channels and the losses within the optical fiber and passive elements. Experimental results are given to illustrate the application of the formulae in the design of a HFS system section.

Summary The paper deals with coaxial part of HFC CATV system. System parameters determinative in ... more Summary The paper deals with coaxial part of HFC CATV system. System parameters determinative in obtaining the desired signal level, carrier-to-noise ratio and acceptable nonlinear distortions are considered. Formulae for the gain and the maximum number of RF amplifiers in the longest coaxial link are developed. A mathematical model of the return path channel is suggested with the noise-funneling effect being taken into consideration. Experimental and analytical results are shown that enable the engineer to determine the optimum operating level for a return path laser. A special attention is drawn to the design of the subscribers’ distribution network and to the equalization of the downstream and upstream signal levels in particular. Two methods to set and maintain the balance of the return path are described that make it possible for some of the signal characteristics to be monitored.