U fokusu istraživanja je vršna performansa prijenosa OFDM signala višestaznim kanalom, odnosno in... more U fokusu istraživanja je vršna performansa prijenosa OFDM signala višestaznim kanalom, odnosno intenzitet neuklonjivih pogrešaka bita - rezidualni BER, u uvjetima visokog odnosa snaga signala i šuma i manje vremenske disperzije (npr. u zatvorenom prostoru). Na temelju postavljenoga analitičkog modela mehanizma generiranja pogrešaka - inherentne slabosti OFDM s aspekta zadržavanja ortogonalnosti u uvjetima višestazne propagacije, izvedena je originalna formula za procjenu rezidualnog BER-a. Dobiveni izraz uključuje kako odgovarajuće modificirani standardni parametar vremenske disperzije kanala – srednje kvadratno raspršenje kašnjenja profila, tako i parametre OFDM signala. Valjanost modela najprije je verificirana rezultatima problemski specifičnih Monte Carlo simulacija, a zatim odgovarajućim ispitivanjem za LTE silaznu vezu, provedenom na industrijski standardnom LTE programskom simulatoru. Analitički i programskim simulacijama, pokazana je zavisnost performanse ne samo od vrijedno...
Deep regression models are widely employed to solve computer vision tasks, such as human age or p... more Deep regression models are widely employed to solve computer vision tasks, such as human age or pose estimation, crowd counting, object detection, etc. Another possible area of application, which to our knowledge has not been systematically explored so far, is proportion judgment. As a prerequisite for successful decision making, individuals often have to use proportion judgment strategies, with which they estimate the magnitude of one stimulus relative to another (larger) stimulus. This makes this estimation problem interesting for the application of machine learning techniques. In regard to this, we proposed various deep regression architectures, which we tested on three original datasets of very different origin and composition. This is a novel approach, as the assumption is that the model can learn the concept of proportion without explicitly counting individual objects. With comprehensive experiments, we have demonstrated the effectiveness of the proposed models which can predi...
This paper provides a simple estimation of the Long Term Evolution (LTE) physical and Medium Acce... more This paper provides a simple estimation of the Long Term Evolution (LTE) physical and Medium Access Control (MAC) layer peak transmission performance-the irreducible Block-Error-Rate (BLER) that determines the Hybrid Automatic Repeat Request (HARQ) residual channel available to higher-layer protocols. With this regard, the general pre-HARQ BLER prediction is developed for the redundancy version 0 (RV0) codeword transmission, expressed by the Bit-Error-Rate (BER)), considering the cyclic prefix protection against inter-symbol interference sufficient to prevent long error bursts. This implies only sporadic bit error occurrences, exhibiting moderate mutual interdependence that we modelled considering errored bits of each block of data as a sample without replacement and consequently describing it with the hypergeometric distribution instead of the mostly used binomial one. The HARQ BLER estimation model is verified by both problem-dedicated Monte-Carlo simulations and industry-standard...
2017 25th International Conference on Software, Telecommunications and Computer Networks (SoftCOM)
Residual BER — error floor is the ultimate metrics for the end-to-end transmission performance, b... more Residual BER — error floor is the ultimate metrics for the end-to-end transmission performance, but in practice can be assessed only by out-of-service tests, which network operators in particular try to avoid best they can, preferring in-service practical test methods. In this regard, constellation analysis is an excellent tool to not only identify and visualize various error generating analog impairments such as power amplifier compression, carrier lock angle and quadrature errors, but also enable in-service estimation of BER with OFDM transmission over multipath channel. In this paper, after reviewing concepts of constellation analysis, we relate the crucial constellation analysis parameter — closure to the delay dispersion standard describing parameter — mean delay spread, so modeling the multipath delay dispersion with the equivalent additive white Gaussian noise source that would produce the same degradation of the accordingly modified residual BER expression. For the exemplar test situation in the LTE downlink environment, very good matching was found between the in-service constellation — based and the predicted error floor values.
In this paper, we address practical wander measurements, which are usually regarded as less impor... more In this paper, we address practical wander measurements, which are usually regarded as less important than the jitter ones, though sometimes unjustifiably, as wander, if accumulated steadily, can seriously harm the bit-error-rate performance. With this respect, we firstly present the mechanisms of jitter and wander generation in digital transmission systems, and then provide an overview of standard functions that quantify these impairments according to relevant ITU-T recommendations, primarily focusing wander, which is usually regarded as less important than jitter and so sometimes neglected though its excessive values, too, can harm the transmission performance. Measurements were accomplished on live 155 Mbit/s SDH microwave radio-relay transmission system, encompassing 4 hops. The analysis of the obtained wander test results well reflects the health of the synchronization system.
The main OFDM drawbacks are Carrier Frequency Offset (CFO) and large Peak-to-Average Power Ratio ... more The main OFDM drawbacks are Carrier Frequency Offset (CFO) and large Peak-to-Average Power Ratio (PAPR), which both degrade the Bit Error Rate (BER). Specifically, we consider here clipping or any other PAPR reduction method sufficient to prevent the nonlinear high-power amplifier from generating errors. Moreover, in small cells, the signal-to-noise ratio is large, while the small time dispersion allows the OFDM symbol cyclic prefix to prevent intersymbol interference. This retains the CFO to solely determine the BER and vice versa, enabling indirect estimation of CFO-induced phase distortion by simple BER testing. However, a particular problem is measuring very low BER values (generated by alike residual CFO), which could last a long time in order to acquire statistically enough errors. The test time can be drastically reduced if the noise margin is reduced in a controllable way, by adding the interfering signal to each subcarrier at the receiver. This approach is shown to enable e...
For quite a while, it has been evident that homogeneous network architectures, based on cells wit... more For quite a while, it has been evident that homogeneous network architectures, based on cells with a uniform radiation pattern, cannot fulfill the ever increasing demand of mobile users for capacity and service quality while still preserving spectrum and energy. However, only with the introduction of the Fourth Generation mobile communication networks to deal with the surging data traffic of multimedia applications, have smaller cells been widely used to break down service zone areas of macro base stations into multiple tiers, thus improving network performance, reducing traffic congestion, and enabling better management of spectrum and energy consumption in a macro network. In this paper, we present an analytical model for assessing the efficiency of bandwidth and energy usage, as well as of network deployment, taking into account overall network investment and maintenance costs. This paves the way to the improved planning of network coverage, and its capacity and reliability, thus...
EURASIP Journal on Wireless Communications and Networking, 2021
As the PHY/MAC-layer IR-HARQ and RLC-layer ARQ error recovery procedures, adopted in LTE, may imp... more As the PHY/MAC-layer IR-HARQ and RLC-layer ARQ error recovery procedures, adopted in LTE, may impose additional delay when their code-block retransmissions occur, the arising question is whether these significantly contribute to IP and consequently RTP packet delays, and finally degrade the overall application-layer end-to-end QoE, especially when voice is transmitted over LTE? With this regard, we propose and demonstrate a VoLTE QoS and QoE test procedure based on PHY/MAC/RLC/IP/TCP-UDP/RTP cross-layer protocol analysis and perceptual speech quality QoE measurements. We identified monotonic relationship between the paired observations: QoE and HARQ RTT, i.e. between the PESQ voice quality rating and the IP/RTP packet latency, for given BLER of the received MAC/RLC code-blocks. Specifically, we found out that, for the HARQ RTT value of about 8 ms, only up to 2 HARQ retransmissions (and consequently no RLC-ARQ one) is appropriate during any voice packet, otherwise delay accumulation ...
2018 Advances in Wireless and Optical Communications (RTUWO), 2018
Carrier Frequency Offset (CFO) and (high) Peak-to-Average Power Ratio (PAPR) are well-known major... more Carrier Frequency Offset (CFO) and (high) Peak-to-Average Power Ratio (PAPR) are well-known major drawbacks of the Orthogonal Frequency-Division Multiplexing (OFDM) signal. So, in many practical situations, specifically with LTE-Advanced downlink introducing carrier aggregation, estimation of PAPR and CFO-induced OFDM symbol phase deviation is of interest. However, this demands complex test equipment, such as e.g. Vector Signal Analyzer (VSA), which might not be always and everywhere available. Therefore, we applied the link abstraction principle on the residual BER that is considered to be determined just by the CFO-caused phase deviation, i.e. as if the channel is noiseless and time-dispersion-free (so that evident errors occur just due to actual CFO). Moreover, as recently it has been shown that the phase deviation is linear with the instantaneous (per-OFDM-symbol) PAPR, we develop a simple model for analytical estimating of BER-based CFO, considering the easy-to-measure BER degr...
2017 25th International Conference on Software, Telecommunications and Computer Networks (SoftCOM), 2017
Residual BER — error floor is the ultimate metrics for the end-to-end transmission performance, b... more Residual BER — error floor is the ultimate metrics for the end-to-end transmission performance, but in practice can be assessed only by out-of-service tests, which network operators in particular try to avoid best they can, preferring in-service practical test methods. In this regard, constellation analysis is an excellent tool to not only identify and visualize various error generating analog impairments such as power amplifier compression, carrier lock angle and quadrature errors, but also enable in-service estimation of BER with OFDM transmission over multipath channel. In this paper, after reviewing concepts of constellation analysis, we relate the crucial constellation analysis parameter — closure to the delay dispersion standard describing parameter — mean delay spread, so modeling the multipath delay dispersion with the equivalent additive white Gaussian noise source that would produce the same degradation of the accordingly modified residual BER expression. For the exemplar ...
Long lasting Ethernet standards have grown beyond traditional LAN networks through MAN to WAN env... more Long lasting Ethernet standards have grown beyond traditional LAN networks through MAN to WAN environment, where it has become the technology which many providers use for developing convergent networks that transport new generation services, such as triple-play widely deployed everywhere – from airports and hotels to large cruise ships. The question of network suitability for providing various communication services has to be considered in practice, especially in case of large ships, as the content of traffic is very diverse with exceptionally variable intensity. Under such specific circumstances for ships theoretical models cannot be directly applied. Rather, network design and implementation depend on practical preliminary test results and analysis. To this end, the out-of-service simulation of either network or user equipment was done according to the RFC 2544 recommendation by means of a smart test device that generates the appropriate test traffic over the Ethernet link from a ...
U fokusu istraživanja je vrsna performansa prijenosa OFDM signala visestaznim kanalom, odnosno in... more U fokusu istraživanja je vrsna performansa prijenosa OFDM signala visestaznim kanalom, odnosno intenzitet neuklonjivih pogresaka bita - rezidualni
In this paper we present an analytical model for planning and using network resources to improve ... more In this paper we present an analytical model for planning and using network resources to improve network coverage, capacity and reliability, reduce network investment and maintenance costs, as well as reduce the electrical power consumption. The analysis considers the downlink of an arbitrary heterogeneous cellular network by using tools of stochastic geometry that adopts the distribution of base stations in the form of Poisson Point Process (PPP). To prove the analytical model, simulation based on ns-3 network simulator has been conducted, with accurately matching the theoretical values and boundaries.
In this paper, a novel error floor prediction model is proposed for estimating the peak performan... more In this paper, a novel error floor prediction model is proposed for estimating the peak performance of the OFDM transmission in a small- time-dispersion environment – typically indoor. The obtained analytical formula involves both the accordingly modified common channel time- dispersion parameters such as the rms delay spread, but distinct for the advanced multipath echoes and the delayed ones (with respect to the chosen sampling instant), as well as the OFDM signal-specific parameters. The validity of the model was confirmed by the results of the corresponding Monte-Carlo simulations.
U fokusu istraživanja je vršna performansa prijenosa OFDM signala višestaznim kanalom, odnosno in... more U fokusu istraživanja je vršna performansa prijenosa OFDM signala višestaznim kanalom, odnosno intenzitet neuklonjivih pogrešaka bita - rezidualni BER, u uvjetima visokog odnosa snaga signala i šuma i manje vremenske disperzije (npr. u zatvorenom prostoru). Na temelju postavljenoga analitičkog modela mehanizma generiranja pogrešaka - inherentne slabosti OFDM s aspekta zadržavanja ortogonalnosti u uvjetima višestazne propagacije, izvedena je originalna formula za procjenu rezidualnog BER-a. Dobiveni izraz uključuje kako odgovarajuće modificirani standardni parametar vremenske disperzije kanala – srednje kvadratno raspršenje kašnjenja profila, tako i parametre OFDM signala. Valjanost modela najprije je verificirana rezultatima problemski specifičnih Monte Carlo simulacija, a zatim odgovarajućim ispitivanjem za LTE silaznu vezu, provedenom na industrijski standardnom LTE programskom simulatoru. Analitički i programskim simulacijama, pokazana je zavisnost performanse ne samo od vrijedno...
Deep regression models are widely employed to solve computer vision tasks, such as human age or p... more Deep regression models are widely employed to solve computer vision tasks, such as human age or pose estimation, crowd counting, object detection, etc. Another possible area of application, which to our knowledge has not been systematically explored so far, is proportion judgment. As a prerequisite for successful decision making, individuals often have to use proportion judgment strategies, with which they estimate the magnitude of one stimulus relative to another (larger) stimulus. This makes this estimation problem interesting for the application of machine learning techniques. In regard to this, we proposed various deep regression architectures, which we tested on three original datasets of very different origin and composition. This is a novel approach, as the assumption is that the model can learn the concept of proportion without explicitly counting individual objects. With comprehensive experiments, we have demonstrated the effectiveness of the proposed models which can predi...
This paper provides a simple estimation of the Long Term Evolution (LTE) physical and Medium Acce... more This paper provides a simple estimation of the Long Term Evolution (LTE) physical and Medium Access Control (MAC) layer peak transmission performance-the irreducible Block-Error-Rate (BLER) that determines the Hybrid Automatic Repeat Request (HARQ) residual channel available to higher-layer protocols. With this regard, the general pre-HARQ BLER prediction is developed for the redundancy version 0 (RV0) codeword transmission, expressed by the Bit-Error-Rate (BER)), considering the cyclic prefix protection against inter-symbol interference sufficient to prevent long error bursts. This implies only sporadic bit error occurrences, exhibiting moderate mutual interdependence that we modelled considering errored bits of each block of data as a sample without replacement and consequently describing it with the hypergeometric distribution instead of the mostly used binomial one. The HARQ BLER estimation model is verified by both problem-dedicated Monte-Carlo simulations and industry-standard...
2017 25th International Conference on Software, Telecommunications and Computer Networks (SoftCOM)
Residual BER — error floor is the ultimate metrics for the end-to-end transmission performance, b... more Residual BER — error floor is the ultimate metrics for the end-to-end transmission performance, but in practice can be assessed only by out-of-service tests, which network operators in particular try to avoid best they can, preferring in-service practical test methods. In this regard, constellation analysis is an excellent tool to not only identify and visualize various error generating analog impairments such as power amplifier compression, carrier lock angle and quadrature errors, but also enable in-service estimation of BER with OFDM transmission over multipath channel. In this paper, after reviewing concepts of constellation analysis, we relate the crucial constellation analysis parameter — closure to the delay dispersion standard describing parameter — mean delay spread, so modeling the multipath delay dispersion with the equivalent additive white Gaussian noise source that would produce the same degradation of the accordingly modified residual BER expression. For the exemplar test situation in the LTE downlink environment, very good matching was found between the in-service constellation — based and the predicted error floor values.
In this paper, we address practical wander measurements, which are usually regarded as less impor... more In this paper, we address practical wander measurements, which are usually regarded as less important than the jitter ones, though sometimes unjustifiably, as wander, if accumulated steadily, can seriously harm the bit-error-rate performance. With this respect, we firstly present the mechanisms of jitter and wander generation in digital transmission systems, and then provide an overview of standard functions that quantify these impairments according to relevant ITU-T recommendations, primarily focusing wander, which is usually regarded as less important than jitter and so sometimes neglected though its excessive values, too, can harm the transmission performance. Measurements were accomplished on live 155 Mbit/s SDH microwave radio-relay transmission system, encompassing 4 hops. The analysis of the obtained wander test results well reflects the health of the synchronization system.
The main OFDM drawbacks are Carrier Frequency Offset (CFO) and large Peak-to-Average Power Ratio ... more The main OFDM drawbacks are Carrier Frequency Offset (CFO) and large Peak-to-Average Power Ratio (PAPR), which both degrade the Bit Error Rate (BER). Specifically, we consider here clipping or any other PAPR reduction method sufficient to prevent the nonlinear high-power amplifier from generating errors. Moreover, in small cells, the signal-to-noise ratio is large, while the small time dispersion allows the OFDM symbol cyclic prefix to prevent intersymbol interference. This retains the CFO to solely determine the BER and vice versa, enabling indirect estimation of CFO-induced phase distortion by simple BER testing. However, a particular problem is measuring very low BER values (generated by alike residual CFO), which could last a long time in order to acquire statistically enough errors. The test time can be drastically reduced if the noise margin is reduced in a controllable way, by adding the interfering signal to each subcarrier at the receiver. This approach is shown to enable e...
For quite a while, it has been evident that homogeneous network architectures, based on cells wit... more For quite a while, it has been evident that homogeneous network architectures, based on cells with a uniform radiation pattern, cannot fulfill the ever increasing demand of mobile users for capacity and service quality while still preserving spectrum and energy. However, only with the introduction of the Fourth Generation mobile communication networks to deal with the surging data traffic of multimedia applications, have smaller cells been widely used to break down service zone areas of macro base stations into multiple tiers, thus improving network performance, reducing traffic congestion, and enabling better management of spectrum and energy consumption in a macro network. In this paper, we present an analytical model for assessing the efficiency of bandwidth and energy usage, as well as of network deployment, taking into account overall network investment and maintenance costs. This paves the way to the improved planning of network coverage, and its capacity and reliability, thus...
EURASIP Journal on Wireless Communications and Networking, 2021
As the PHY/MAC-layer IR-HARQ and RLC-layer ARQ error recovery procedures, adopted in LTE, may imp... more As the PHY/MAC-layer IR-HARQ and RLC-layer ARQ error recovery procedures, adopted in LTE, may impose additional delay when their code-block retransmissions occur, the arising question is whether these significantly contribute to IP and consequently RTP packet delays, and finally degrade the overall application-layer end-to-end QoE, especially when voice is transmitted over LTE? With this regard, we propose and demonstrate a VoLTE QoS and QoE test procedure based on PHY/MAC/RLC/IP/TCP-UDP/RTP cross-layer protocol analysis and perceptual speech quality QoE measurements. We identified monotonic relationship between the paired observations: QoE and HARQ RTT, i.e. between the PESQ voice quality rating and the IP/RTP packet latency, for given BLER of the received MAC/RLC code-blocks. Specifically, we found out that, for the HARQ RTT value of about 8 ms, only up to 2 HARQ retransmissions (and consequently no RLC-ARQ one) is appropriate during any voice packet, otherwise delay accumulation ...
2018 Advances in Wireless and Optical Communications (RTUWO), 2018
Carrier Frequency Offset (CFO) and (high) Peak-to-Average Power Ratio (PAPR) are well-known major... more Carrier Frequency Offset (CFO) and (high) Peak-to-Average Power Ratio (PAPR) are well-known major drawbacks of the Orthogonal Frequency-Division Multiplexing (OFDM) signal. So, in many practical situations, specifically with LTE-Advanced downlink introducing carrier aggregation, estimation of PAPR and CFO-induced OFDM symbol phase deviation is of interest. However, this demands complex test equipment, such as e.g. Vector Signal Analyzer (VSA), which might not be always and everywhere available. Therefore, we applied the link abstraction principle on the residual BER that is considered to be determined just by the CFO-caused phase deviation, i.e. as if the channel is noiseless and time-dispersion-free (so that evident errors occur just due to actual CFO). Moreover, as recently it has been shown that the phase deviation is linear with the instantaneous (per-OFDM-symbol) PAPR, we develop a simple model for analytical estimating of BER-based CFO, considering the easy-to-measure BER degr...
2017 25th International Conference on Software, Telecommunications and Computer Networks (SoftCOM), 2017
Residual BER — error floor is the ultimate metrics for the end-to-end transmission performance, b... more Residual BER — error floor is the ultimate metrics for the end-to-end transmission performance, but in practice can be assessed only by out-of-service tests, which network operators in particular try to avoid best they can, preferring in-service practical test methods. In this regard, constellation analysis is an excellent tool to not only identify and visualize various error generating analog impairments such as power amplifier compression, carrier lock angle and quadrature errors, but also enable in-service estimation of BER with OFDM transmission over multipath channel. In this paper, after reviewing concepts of constellation analysis, we relate the crucial constellation analysis parameter — closure to the delay dispersion standard describing parameter — mean delay spread, so modeling the multipath delay dispersion with the equivalent additive white Gaussian noise source that would produce the same degradation of the accordingly modified residual BER expression. For the exemplar ...
Long lasting Ethernet standards have grown beyond traditional LAN networks through MAN to WAN env... more Long lasting Ethernet standards have grown beyond traditional LAN networks through MAN to WAN environment, where it has become the technology which many providers use for developing convergent networks that transport new generation services, such as triple-play widely deployed everywhere – from airports and hotels to large cruise ships. The question of network suitability for providing various communication services has to be considered in practice, especially in case of large ships, as the content of traffic is very diverse with exceptionally variable intensity. Under such specific circumstances for ships theoretical models cannot be directly applied. Rather, network design and implementation depend on practical preliminary test results and analysis. To this end, the out-of-service simulation of either network or user equipment was done according to the RFC 2544 recommendation by means of a smart test device that generates the appropriate test traffic over the Ethernet link from a ...
U fokusu istraživanja je vrsna performansa prijenosa OFDM signala visestaznim kanalom, odnosno in... more U fokusu istraživanja je vrsna performansa prijenosa OFDM signala visestaznim kanalom, odnosno intenzitet neuklonjivih pogresaka bita - rezidualni
In this paper we present an analytical model for planning and using network resources to improve ... more In this paper we present an analytical model for planning and using network resources to improve network coverage, capacity and reliability, reduce network investment and maintenance costs, as well as reduce the electrical power consumption. The analysis considers the downlink of an arbitrary heterogeneous cellular network by using tools of stochastic geometry that adopts the distribution of base stations in the form of Poisson Point Process (PPP). To prove the analytical model, simulation based on ns-3 network simulator has been conducted, with accurately matching the theoretical values and boundaries.
In this paper, a novel error floor prediction model is proposed for estimating the peak performan... more In this paper, a novel error floor prediction model is proposed for estimating the peak performance of the OFDM transmission in a small- time-dispersion environment – typically indoor. The obtained analytical formula involves both the accordingly modified common channel time- dispersion parameters such as the rms delay spread, but distinct for the advanced multipath echoes and the delayed ones (with respect to the chosen sampling instant), as well as the OFDM signal-specific parameters. The validity of the model was confirmed by the results of the corresponding Monte-Carlo simulations.
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Papers by Adriana Lipovac