P. Lazaridis | University of Huddersfield (original) (raw)

Papers by P. Lazaridis

2015 1st URSI Atlantic Radio Science Conference (URSI AT-RASC), 2015

WSEAS Transactions on Information Sciences and Application

2013 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB), 2013

In DVB-T2 broadcasting applications, errors occur due to channel imperfections, reducing the syst... more In DVB-T2 broadcasting applications, errors occur due to channel imperfections, reducing the system's throughput. The use of a channel estimator and equalizer counteracts the channel induced distortions and thus improves the system's Bit Error Rate (BER). In our study, a simple-to-implement channel estimator is proposed. It is based on averaging the sub-channel frequency responses of successive OFDM symbols in time, considering a very slow time-varying channel. In the frequency domain, spline interpolation is applied. The proposed estimator can be used in practical receivers with limited computation power and low memory capacity.

IEEE Transactions on Broadcasting, 2000

In this paper the precise foreground mask is obtained in a complex environment by applying simple... more In this paper the precise foreground mask is obtained in a complex environment by applying simple and effective methods on a video sequence consisting of multi-colour and multiple foreground object environment. To detect moving objects we use a simple algorithm based on block-based motion estimation, which requires less computational time. To obtain a full and improved mask of the moving object, we use an openingand-closing-by-reconstruction mechanism to identify the minima and maxima inside the foreground object by applying a set of morphological operations. This further enhances the outlines of foreground objects at various stages of image processing. Therefore, the algorithm does not require the knowledge of the background image. That is why it can be used in real world video sequences to detect the foreground in cases where we do not have a background model in advance. The comparative performance results demonstrate the effectiveness of the proposed algorithm.

Accurate geographical coverage predictions maps for FM and TV are needed for channel and frequenc... more Accurate geographical coverage predictions maps for FM and TV are needed for channel and frequency allocations and in order to avoid unwanted interferences. The Longley-Rice model has been used for this purpose over the last four decades and still being used almost exclusively by the FCC in the United States. In this work a comparison is presented between the relative accuracy of this model in the VHF-FM and UHF-TV frequency bands. Simulations were made with accurate and up to date input data (antenna height, location, gain, transmit power, etc.) for the FM-TV stations provided by the ERT S.A. public broadcaster in the region of Thessaloniki – Greece. Finally, the calculated – simulated results were confronted to field measurements using a Rohde & Schwarz FSH3 portable spectrum analyzer and high precision calibrated biconical and log-periodic antennas, and the errors between predictions and measurements were statistically analyzed in the two frequency bands. It has been found in thi...

With the rapid deployment of digital TV, there is an increasing need for accurate point-to-area p... more With the rapid deployment of digital TV, there is an increasing need for accurate point-to-area prediction tools. There is a great deal of propagation models for coverage prediction of DTV. Some of them are pure empirical models, and others are mixed, empirical-analytical models, based on measurement campaigns and electromagnetic theory. The aim of this paper is to compare accurate measurements taken by a Rohde & Schwarz FSH-3 portable spectrum analyzer and precision antennas (biconical and log-periodic), with simulation results derived from coverage prediction models, like the NTIA-ITS Longley-Rice model, the ITM (Irregular Terrain Model) using the 3-arc-second SRTM (Satellite Radar Topography Mission) data that is available freely, and the newer ITWOM (Irregular Terrain with Obstructions Model) model which combines equations from ITU-R P.1546 model with Beer's law and Snell's law. Furthermore, measurements for analog FM broadcasting are compared to predictions from the abo...

2014 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting, 2014

The problem of channel estimation for Orthogonal Frequency Division Multiplexing (OFDM) systems i... more The problem of channel estimation for Orthogonal Frequency Division Multiplexing (OFDM) systems in fast timevarying and frequency selective radio channels has attracted the attention of scientists and receiver manufacturers. The wireless communication suffers from Additive White Gaussian Noise (AWGN), fading due to the multipath nature of the channel and spectral dispersion caused by the relative movement of the receiver with respect to the transmitter. In this paper a novel channel estimator for the Next Generation Terrestrial Digital Video Broadcasting (DVB-T2) is proposed. It is based on the estimation of the Doppler Shift (DS) from the variations of the envelope of the edge pilots (EP), in order to estimate the time interval where the channel could be considered as flat and then adaptively adjusting a buffer where the scattered pilots (ScP) carried within the received OFDM symbols during this time interval, are stored and averaged. Because the noise is considered AWGN with zero mean, the averaging process discards the noise and by interpolating the pilots an estimation of the channel is obtained.

2014 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting, 2014

This paper compares precision field-strength measurements taken by a Rohde & Schwarz FSH-3 portab... more This paper compares precision field-strength measurements taken by a Rohde & Schwarz FSH-3 portable spectrum analyzer with simulation results derived from the ITM coverage prediction model (Irregular Terrain Model), also known as NTIA-ITS Longley-Rice model, in conjunction with the 3-arc-second SRTM (Satellite Radar Topography Mission) geographical data, the propagation predictions of ITU-R Recommendation P.1546 and those of the empirical Hata-Davidson model using HAAT.

Measurements of UHF-TV band spectra and field-strength levels in the pre-and post-analogue switch... more Measurements of UHF-TV band spectra and field-strength levels in the pre-and post-analogue switch-off periods in the cities of Thessaloniki and Skopje clearly demonstrate the much reduced spectrum occupancy, the lower signal levels, and the feasibility of digital dividend allocations to cellular operators in the 800 MHz band, as well as the feasibility of opportunistic secondary spectrum utilization in extensive parts of the spectrum. The risk of LTE-4G interference to TV services and vice-versa is also pointed out and clearly observed from spectrum measurements near a cellular base station.

IEEE Transactions on Broadcasting, 2000

A near-optimal base-station antenna array synthesis suitable for broadcasting applications is pre... more A near-optimal base-station antenna array synthesis suitable for broadcasting applications is presented. The array is required to provide a high-gain radiation pattern with a main lobe slightly tilted from the horizontal plane and null filling inside an angular sector under the main lobe. To satisfy the above requirements, a novel invasive weed optimization (IWO) variant called Taguchi initialized IWO (TI-IWO) is proposed in this paper. In TI-IWO, the Taguchi's optimization method is employed to initialize effectively the positions of the weeds used by the IWO method. In this way, the fitness function starts from lower values and, thus, the TI-IWO method finds better near-optimal solutions than the conventional IWO method. The proposed method has been applied to linear arrays. Due to its easy implementation in practice, a uniform-amplitude excitation distribution is considered to be applied on the array elements. Two cases of isotropic source arrays are studied under specific requirements for maximum possible gain, main lobe tilting, and null filling. Also, the TI-IWO method is applied to optimize realistic cases of collinear wire dipole arrays in front of a mast under the same requirements and an additional one concerning the impedance matching of all the dipoles.

2014 4th International Conference on Wireless Communications, Vehicular Technology, Information Theory and Aerospace & Electronic Systems (VITAE), 2014

A powerful evolutionary method called Invasive Weed Optimization (IWO) is applied to achieve opti... more A powerful evolutionary method called Invasive Weed Optimization (IWO) is applied to achieve optimal designs of log-periodic antennas. The antennas are designed for operation in the UHF-TV band, i.e. 470-860 MHz, and are optimized with respect to the standing wave ratio (SWR), the front-to-rear (F/R) ratio, and the forward gain. The parameters under optimization are the dipole lengths, the dipole diameters, the distances between adjacent dipoles and the characteristic impedance of the transmission line that feeds the dipoles. The optimized antenna geometries that resulted from the above method seem to be significantly better than the respective ones derived from the classical design method.

2014 International Conference on Telecommunications and Multimedia (TEMU), 2014

The Invasive Weed Optimization (IWO) is an effective evolutionary and recently developed method. ... more The Invasive Weed Optimization (IWO) is an effective evolutionary and recently developed method. Due to its better performance in comparison to other well-known optimization methods, IWO has been chosen to solve many complex non-linear problems in telecommunications and electromagnetics. In the present study, the IWO is applied to optimize the geometry of a realistic log-periodic dipole array (LPDA) that operates in the frequency range 800-3300 MHz and therefore is suitable for signal reception from several RF services. The optimization is applied under specific requirements, concerning the standing wave ratio, the forward gain, the gain flatness and the side lobe level, over a wide frequency range. The optimization variables are the lengths and the radii of the dipoles, the distances between them, and the characteristic impedance of the transmission line that connects the dipoles. The optimized LPDA seems to be superior compared to the antenna derived from the practical design procedure.

IEEE Transactions on Broadcasting, 2000

A new antenna array beamformer based on neural networks (NNs) is presented. The NN training is pe... more A new antenna array beamformer based on neural networks (NNs) is presented. The NN training is performed by using optimized data sets extracted by a novel invasive weed optimization (IWO) variant called modified adaptive dispersion IWO (MADIWO). The trained NN is utilized as an adaptive beamformer that makes a uniform linear antenna array steer the main lobe toward a desired signal, place respective nulls toward several interference signals, and suppress the side lobe level (SLL). Initially, the NN structure is selected by training several NNs of various structures using MADIWO-based data and by making a comparison among the NNs in terms of training performance. The selected NN structure is then used to construct an adaptive beamformer, which is compared to MADIWO-based and ADIWO-based beamformers, regarding the SLL and the ability to properly steer the main lobe and the nulls. The comparison is made, considering several sets of random cases with different numbers of interference signals and different power levels of additive zero-mean Gaussian noise. The comparative results exhibit the advantages of the proposed beamformer.

2013 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB), 2013

Digital broadcasting services require higher prediction accuracy than traditional analogue networ... more Digital broadcasting services require higher prediction accuracy than traditional analogue networks because digital services are planned with tighter margins on the received signal strength and interference. With the rapid deployment of digital TV, there is an increasing need for accurate point-to-area prediction tools. There are several propagation models for coverage prediction of DVB-T. Some of them are purely empirical models, and others are mixed, empirical-analytical models, based on measurements campaigns and electromagnetic theory. The aim of this paper is to compare precision fieldstrength measurements taken by a Rohde & Schwarz FSH-3 portable spectrum analyzer with simulation results derived from coverage prediction models, like the NTIA-ITS Longley-Rice model, the ITM (Irregular Terrain Model) using the 3-arc-second SRTM (Satellite Radar Topography Mission) data that is available freely, and the newly developed ITWOM (Irregular Terrain with Obstructions Model).

Microwave and Optical Technology Letters, 2007

Optics Letters, 1997

A generalized solution of the linear propagation equation is proposed in terms of chirped Gauss -... more A generalized solution of the linear propagation equation is proposed in terms of chirped Gauss -Hermite orthogonal functions. Some well-known special cases are pointed out, and the usefulness of this approach in analyzing arbitrarily shaped chirped pulses in rapidly converging series is discussed.

Microwave and …, Jan 1, 2007

2015 1st URSI Atlantic Radio Science Conference (URSI AT-RASC), 2015

WSEAS Transactions on Information Sciences and Application

2013 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB), 2013

In DVB-T2 broadcasting applications, errors occur due to channel imperfections, reducing the syst... more In DVB-T2 broadcasting applications, errors occur due to channel imperfections, reducing the system's throughput. The use of a channel estimator and equalizer counteracts the channel induced distortions and thus improves the system's Bit Error Rate (BER). In our study, a simple-to-implement channel estimator is proposed. It is based on averaging the sub-channel frequency responses of successive OFDM symbols in time, considering a very slow time-varying channel. In the frequency domain, spline interpolation is applied. The proposed estimator can be used in practical receivers with limited computation power and low memory capacity.

IEEE Transactions on Broadcasting, 2000

In this paper the precise foreground mask is obtained in a complex environment by applying simple... more In this paper the precise foreground mask is obtained in a complex environment by applying simple and effective methods on a video sequence consisting of multi-colour and multiple foreground object environment. To detect moving objects we use a simple algorithm based on block-based motion estimation, which requires less computational time. To obtain a full and improved mask of the moving object, we use an openingand-closing-by-reconstruction mechanism to identify the minima and maxima inside the foreground object by applying a set of morphological operations. This further enhances the outlines of foreground objects at various stages of image processing. Therefore, the algorithm does not require the knowledge of the background image. That is why it can be used in real world video sequences to detect the foreground in cases where we do not have a background model in advance. The comparative performance results demonstrate the effectiveness of the proposed algorithm.

Accurate geographical coverage predictions maps for FM and TV are needed for channel and frequenc... more Accurate geographical coverage predictions maps for FM and TV are needed for channel and frequency allocations and in order to avoid unwanted interferences. The Longley-Rice model has been used for this purpose over the last four decades and still being used almost exclusively by the FCC in the United States. In this work a comparison is presented between the relative accuracy of this model in the VHF-FM and UHF-TV frequency bands. Simulations were made with accurate and up to date input data (antenna height, location, gain, transmit power, etc.) for the FM-TV stations provided by the ERT S.A. public broadcaster in the region of Thessaloniki – Greece. Finally, the calculated – simulated results were confronted to field measurements using a Rohde & Schwarz FSH3 portable spectrum analyzer and high precision calibrated biconical and log-periodic antennas, and the errors between predictions and measurements were statistically analyzed in the two frequency bands. It has been found in thi...

With the rapid deployment of digital TV, there is an increasing need for accurate point-to-area p... more With the rapid deployment of digital TV, there is an increasing need for accurate point-to-area prediction tools. There is a great deal of propagation models for coverage prediction of DTV. Some of them are pure empirical models, and others are mixed, empirical-analytical models, based on measurement campaigns and electromagnetic theory. The aim of this paper is to compare accurate measurements taken by a Rohde & Schwarz FSH-3 portable spectrum analyzer and precision antennas (biconical and log-periodic), with simulation results derived from coverage prediction models, like the NTIA-ITS Longley-Rice model, the ITM (Irregular Terrain Model) using the 3-arc-second SRTM (Satellite Radar Topography Mission) data that is available freely, and the newer ITWOM (Irregular Terrain with Obstructions Model) model which combines equations from ITU-R P.1546 model with Beer's law and Snell's law. Furthermore, measurements for analog FM broadcasting are compared to predictions from the abo...

2014 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting, 2014

The problem of channel estimation for Orthogonal Frequency Division Multiplexing (OFDM) systems i... more The problem of channel estimation for Orthogonal Frequency Division Multiplexing (OFDM) systems in fast timevarying and frequency selective radio channels has attracted the attention of scientists and receiver manufacturers. The wireless communication suffers from Additive White Gaussian Noise (AWGN), fading due to the multipath nature of the channel and spectral dispersion caused by the relative movement of the receiver with respect to the transmitter. In this paper a novel channel estimator for the Next Generation Terrestrial Digital Video Broadcasting (DVB-T2) is proposed. It is based on the estimation of the Doppler Shift (DS) from the variations of the envelope of the edge pilots (EP), in order to estimate the time interval where the channel could be considered as flat and then adaptively adjusting a buffer where the scattered pilots (ScP) carried within the received OFDM symbols during this time interval, are stored and averaged. Because the noise is considered AWGN with zero mean, the averaging process discards the noise and by interpolating the pilots an estimation of the channel is obtained.

2014 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting, 2014

This paper compares precision field-strength measurements taken by a Rohde & Schwarz FSH-3 portab... more This paper compares precision field-strength measurements taken by a Rohde & Schwarz FSH-3 portable spectrum analyzer with simulation results derived from the ITM coverage prediction model (Irregular Terrain Model), also known as NTIA-ITS Longley-Rice model, in conjunction with the 3-arc-second SRTM (Satellite Radar Topography Mission) geographical data, the propagation predictions of ITU-R Recommendation P.1546 and those of the empirical Hata-Davidson model using HAAT.

Measurements of UHF-TV band spectra and field-strength levels in the pre-and post-analogue switch... more Measurements of UHF-TV band spectra and field-strength levels in the pre-and post-analogue switch-off periods in the cities of Thessaloniki and Skopje clearly demonstrate the much reduced spectrum occupancy, the lower signal levels, and the feasibility of digital dividend allocations to cellular operators in the 800 MHz band, as well as the feasibility of opportunistic secondary spectrum utilization in extensive parts of the spectrum. The risk of LTE-4G interference to TV services and vice-versa is also pointed out and clearly observed from spectrum measurements near a cellular base station.

IEEE Transactions on Broadcasting, 2000

A near-optimal base-station antenna array synthesis suitable for broadcasting applications is pre... more A near-optimal base-station antenna array synthesis suitable for broadcasting applications is presented. The array is required to provide a high-gain radiation pattern with a main lobe slightly tilted from the horizontal plane and null filling inside an angular sector under the main lobe. To satisfy the above requirements, a novel invasive weed optimization (IWO) variant called Taguchi initialized IWO (TI-IWO) is proposed in this paper. In TI-IWO, the Taguchi's optimization method is employed to initialize effectively the positions of the weeds used by the IWO method. In this way, the fitness function starts from lower values and, thus, the TI-IWO method finds better near-optimal solutions than the conventional IWO method. The proposed method has been applied to linear arrays. Due to its easy implementation in practice, a uniform-amplitude excitation distribution is considered to be applied on the array elements. Two cases of isotropic source arrays are studied under specific requirements for maximum possible gain, main lobe tilting, and null filling. Also, the TI-IWO method is applied to optimize realistic cases of collinear wire dipole arrays in front of a mast under the same requirements and an additional one concerning the impedance matching of all the dipoles.

2014 4th International Conference on Wireless Communications, Vehicular Technology, Information Theory and Aerospace & Electronic Systems (VITAE), 2014

A powerful evolutionary method called Invasive Weed Optimization (IWO) is applied to achieve opti... more A powerful evolutionary method called Invasive Weed Optimization (IWO) is applied to achieve optimal designs of log-periodic antennas. The antennas are designed for operation in the UHF-TV band, i.e. 470-860 MHz, and are optimized with respect to the standing wave ratio (SWR), the front-to-rear (F/R) ratio, and the forward gain. The parameters under optimization are the dipole lengths, the dipole diameters, the distances between adjacent dipoles and the characteristic impedance of the transmission line that feeds the dipoles. The optimized antenna geometries that resulted from the above method seem to be significantly better than the respective ones derived from the classical design method.

2014 International Conference on Telecommunications and Multimedia (TEMU), 2014

The Invasive Weed Optimization (IWO) is an effective evolutionary and recently developed method. ... more The Invasive Weed Optimization (IWO) is an effective evolutionary and recently developed method. Due to its better performance in comparison to other well-known optimization methods, IWO has been chosen to solve many complex non-linear problems in telecommunications and electromagnetics. In the present study, the IWO is applied to optimize the geometry of a realistic log-periodic dipole array (LPDA) that operates in the frequency range 800-3300 MHz and therefore is suitable for signal reception from several RF services. The optimization is applied under specific requirements, concerning the standing wave ratio, the forward gain, the gain flatness and the side lobe level, over a wide frequency range. The optimization variables are the lengths and the radii of the dipoles, the distances between them, and the characteristic impedance of the transmission line that connects the dipoles. The optimized LPDA seems to be superior compared to the antenna derived from the practical design procedure.

IEEE Transactions on Broadcasting, 2000

A new antenna array beamformer based on neural networks (NNs) is presented. The NN training is pe... more A new antenna array beamformer based on neural networks (NNs) is presented. The NN training is performed by using optimized data sets extracted by a novel invasive weed optimization (IWO) variant called modified adaptive dispersion IWO (MADIWO). The trained NN is utilized as an adaptive beamformer that makes a uniform linear antenna array steer the main lobe toward a desired signal, place respective nulls toward several interference signals, and suppress the side lobe level (SLL). Initially, the NN structure is selected by training several NNs of various structures using MADIWO-based data and by making a comparison among the NNs in terms of training performance. The selected NN structure is then used to construct an adaptive beamformer, which is compared to MADIWO-based and ADIWO-based beamformers, regarding the SLL and the ability to properly steer the main lobe and the nulls. The comparison is made, considering several sets of random cases with different numbers of interference signals and different power levels of additive zero-mean Gaussian noise. The comparative results exhibit the advantages of the proposed beamformer.

2013 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB), 2013

Digital broadcasting services require higher prediction accuracy than traditional analogue networ... more Digital broadcasting services require higher prediction accuracy than traditional analogue networks because digital services are planned with tighter margins on the received signal strength and interference. With the rapid deployment of digital TV, there is an increasing need for accurate point-to-area prediction tools. There are several propagation models for coverage prediction of DVB-T. Some of them are purely empirical models, and others are mixed, empirical-analytical models, based on measurements campaigns and electromagnetic theory. The aim of this paper is to compare precision fieldstrength measurements taken by a Rohde & Schwarz FSH-3 portable spectrum analyzer with simulation results derived from coverage prediction models, like the NTIA-ITS Longley-Rice model, the ITM (Irregular Terrain Model) using the 3-arc-second SRTM (Satellite Radar Topography Mission) data that is available freely, and the newly developed ITWOM (Irregular Terrain with Obstructions Model).

Microwave and Optical Technology Letters, 2007

Optics Letters, 1997

A generalized solution of the linear propagation equation is proposed in terms of chirped Gauss -... more A generalized solution of the linear propagation equation is proposed in terms of chirped Gauss -Hermite orthogonal functions. Some well-known special cases are pointed out, and the usefulness of this approach in analyzing arbitrarily shaped chirped pulses in rapidly converging series is discussed.

Microwave and …, Jan 1, 2007