Reconfigurable intelligent surface (RIS) is a promising technology to avoid signal blockage by cr... more Reconfigurable intelligent surface (RIS) is a promising technology to avoid signal blockage by creating line-ofsight (LOS) connectivity for free-space optical (FSO) and radio frequency (RF) wireless systems. There is limited research on the use of multiple RIS between a source and destination for wireless communications. This paper analyzes the performance of a RISassisted multi-hop transmission for vehicular communications by employing multiple RIS to enable LOS communication and reliable connectivity for a hybrid FSO and RF system. We develop an analytical framework to derive statistical results of the signalto-noise ratio (SNR) of a multi-RIS communication system over general fading models. We use decode-and-forward (DF) and fixed-gain (FG) relaying protocols to mix multi-RIS transmissions over RF and FSO technologies, and derive probability density and distribution functions for both the relaying schemes by considering independent and non-identical double generalized gamma (dGG)...
We present asymptotic expressions for user throughput in a multi-user wireline system with a line... more We present asymptotic expressions for user throughput in a multi-user wireline system with a linear decoder, in increasingly large system sizes. This analysis can be seen as a generalization of results obtained for wireless communication. The features of the diagonal elements of the wireline channel matrices make wireless asymptotic analyses inapplicable for wireline systems. Further, direct application of results from random matrix theory (RMT) yields a trivial lower bound. This paper presents a novel approach to asymptotic analysis, where an alternative sequence of systems is constructed that includes the system of interest in order to approximate the spectral efficiency of the linear zero-forcing (ZF) and minimum mean squared error (MMSE) crosstalk cancelers. Using works in the field of large dimensional random matrices, we show that the user rate in this sequence converges to a non-zero rate. The approximation of the user rate for both the ZF and MMSE cancelers are very simple t...
Reconfigurable intelligent surface (RIS) is an excellent use case for line-of-sight (LOS) based t... more Reconfigurable intelligent surface (RIS) is an excellent use case for line-of-sight (LOS) based technologies such as free-space optical (FSO) communications. In this paper, we analyze the performance of RIS-empowered FSO (RISE-FSO) systems by unifying Fisher–Snedecor (F), Gamma-Gamma (GG), and Malága (M) distributions for atmospheric turbulence with zero-boresight pointing errors over deterministic as well as random path-loss in foggy conditions with heterodyne detection (HD) and intensity modulation/direct detection (IM/DD) methods. By deriving the probability density function (PDF) and cumulative distribution function (CDF) of the direct-link (DL) with the statistical effect of atmospheric turbulence, pointing errors and random fog, we develop exact expressions of PDF and CDF of the resultant channel for the RISE-FSO system. Using the derived statistical results, we present exact expressions of outage probability, average bit-error-rate (BER), ergodic capacity, and moments of sign...
We propose an iterative crosstalk cancellation scheme based on the generalized minimal residual (... more We propose an iterative crosstalk cancellation scheme based on the generalized minimal residual (GMRES) algorithm for large-scale digital subscriber line (DSL) systems. The proposed scheme does not require channel inversion and stores fewer vectors for crosstalk cancellation. We analyze the convergence of the GMRES algorithm and derive computable bounds on the residual error and signal-to-noise ratio in terms of system parameters at each iteration for upstream DSL systems. We show that the GMRES algorithm typically requires a single iteration for very large vectored systems to achieve crosstalk-free performance for the very high-speed DSL (VDSL) frequencies and only a few more in the highest frequency bands of the G.fast spectrum. This yields significant complexity savings and reduction in memory storage, compared to the zero forcing scheme under certain conditions.
Signal fading due to atmospheric channel impairments and pointing error is a major bottleneck for... more Signal fading due to atmospheric channel impairments and pointing error is a major bottleneck for the performance of optical wireless communication (OWC). In this paper, we consider an amplify-and-forward (AF) optical relaying to enhance the performance of the OWC system with a negligible line-of-sight (LOS) link under the combined effect of fog and pointing error. We analyze the end-to-end performance of the relay-assisted system, which consists of complicated probability distribution functions. We derive analytical expressions of the outage probability, average signal-to-noise ratio (SNR), and ergodic rate in terms of OWC system parameters. We also develop an exact integral-form expression of these performance metrics using the half-harmonic mean of individual SNRs to validate the tightness of the derived analytical expressions. The numerical and simulation analysis shows that the proposed dual-hop relaying has significant performance improvement when comparing to the direct trans...
Optical wireless communication (OWC) over atmospheric turbulence and pointing errors is a well-st... more Optical wireless communication (OWC) over atmospheric turbulence and pointing errors is a well-studied topic. Still, there is limited research on signal fading due to random fog and pointing errors in outdoor environments. In this paper, we analyze the performance of a decode-and-forward (DF) relaying under the combined effect of random fog, pointing errors, and atmospheric turbulence with a negligible line-of-sight (LOS) direct link. We consider a generalized model for the end-toend channel with independent and not identically distributed (i.ni.d.) pointing errors, random fog with Gamma distributed attenuation coefficient, asymptotic exponentiated Weibull turbulence, and asymmetrical distance between the source and destination. We derive distribution functions of the signal-to-noise ratio (SNR), and then we develop analytical expressions of the outage probability, average SNR, ergodic rate, and average bit error rate (BER) in terms of OWC system parameters. We also develop simplifi...
2016 IEEE International Conference on the Science of Electrical Engineering (ICSEE), 2016
In this paper, we present a novel approximation to the spectral efficiency at the output of a zer... more In this paper, we present a novel approximation to the spectral efficiency at the output of a zero-forcing (ZF) receiver in a DSL upstream system. This approximation is extracted by a new asymptotic analysis, where we construct an alternative sequence of systems that includes the system of interest. Drawing on works in the field of large dimensional random matrices, we show that the user rate in this sequence converges to a non-zero rate. We also provide numerical simulations which show that this approximation is accurate even for relatively low dimensional systems.
Interference cancellation is the main driving technology in enhancing the transmission rates over... more Interference cancellation is the main driving technology in enhancing the transmission rates over telephone lines above 100 Mbps. Still, crosstalk interference in multi-pair digital subscriber line (DSL) systems at higher frequencies has not been dealt with sufficiently. The upcoming G.(mg) fast DSL system envisions the use of extremely high bandwidth and full-duplex transmissions generating significantly higher crosstalk and self-interference signals. More powerful interference cancellation techniques are required to enable multi-gigabit per second data rate transmission over copper lines. In this article, we analyze the performance of interference cancellation techniques, with a focus on novel research approaches and design considerations for efficient interference mitigation for multi-gigabit transmission over standard copper lines. We also detail novel approaches for interference cancellation in the upcoming technologies.
Mitigating channel fading and transceiver impairments are desirable for high-speed terahertz (THz... more Mitigating channel fading and transceiver impairments are desirable for high-speed terahertz (THz) wireless links. This paper analyzes the performance of a multi-antenna THz wireless system by considering the combined effect of pointing errors and fluctuating two-ray (FTR) fading model. We provide a statistical characterization of the maximal ratio combining (MRC) receiver over independent and nonidentical (i.ni.d.) channel conditions in terms of multi-variate Fox’s H by deriving density and distribution functions of the signal-tonoise ratio (SNR) of a single-link THz link using incomplete Gamma function. We develop exact analytical expressions of outage probability, average bit-error-rate (BER), and ergodic capacity for both single-antenna and MRC receivers. We also present the diversity order of the system by deriving asymptotic expressions for outage probability and average BER at high SNR to obtain insights into the system performance. We validate our derived analytical expressi...
Reconfigurable intelligent surface (RIS) is a promising technology to avoid signal blockage by cr... more Reconfigurable intelligent surface (RIS) is a promising technology to avoid signal blockage by creating virtual lineof-sight (LOS) connectivity for free-space optical (FSO) and radio frequency (RF) wireless systems. This paper considers a mixed FSO-RF system by employing multiple RISs in both the links for multihop transmissions to extend the communication range. We develop probability density function (PDF) and cumulative density function (CDF) of the signal-to-noise ratio (SNR) for the cascaded channels by considering double generalized gamma (dGG) turbulence with pointing errors for the FSO link and the dGG distribution to model the signal fading for the RF. We derive exact closed-form expressions of the outage probability, average bit-error-rate (BER), and ergodic capacity using the decode-andforward (DF) relaying for the mixed system. We also present asymptotic analysis on the performance in the high SNR regime depicting the impact of channel parameters on the diversity order o...
Impulse noise presents a severe performance bottleneck in multicarrier systems. For digital subsc... more Impulse noise presents a severe performance bottleneck in multicarrier systems. For digital subscriber lines (DSL), the use of a common-mode (CM) sensor is a viable technique to mitigate the impulse noise that couples into the useful differential-mode (DM) signal. In this paper, we use time and frequency domain approaches to develop algorithms using the joint processing of CM and DM signals and analyze the performance of dual-sensor based interference cancellation schemes for downstream DSL systems. First, we consider the frequency domain approach and analyze the performance of a per-tone impulse noise canceler without requiring an impulse detector. We derive closed-form expressions on the performance of canceler in various interference scenarios in terms of system parameters. Next, we develop a novel per-symbol time-domain impulse noise canceler by simultaneous estimation of the CM2DM transfer function and the CM impulse noise using a limited number of null carriers. The proposed algorithm eliminates the issues of convergence of the per-tone canceler and stationarity of the impulse noise over multiple symbols. Using derived analytical expressions, we show that the proposed canceler effectively mitigates the impulse noise on a per-symbol basis. We also demonstrate the performance of the considered canceler schemes using measurement and simulation results.
Reconfigurable intelligent surfaces (RIS) can have an excellent use case for terahertz (THz) wire... more Reconfigurable intelligent surfaces (RIS) can have an excellent use case for terahertz (THz) wireless transmissions. In this letter, we analyze the performance of a RIS-empowered THz system over the combined effect of α-μ fading and pointing errors. We derive exact closed-form expressions of density and distribution functions of the resultant signal-to-noise ratio (SNR) considering an independent and not identically distributed (i.ni.d.) channel model. Using the derived statistical results, we present an exact analysis on outage probability, ergodic capacity, and average bit-error-rate (BER) of the considered system. We also develop asymptotic analysis on the outage probability and average BER to derive diversity order in terms of system parameters. The proposed analysis provides insights to mitigate the effect of pointing errors and shows that the RIS can significantly improve the performance of THz communications. We validate the analytical results using numerical and Monte Carlo simulations and demonstrate the scaling of system performance with an increase in the number of RIS elements.
Reconfigurable intelligent surface (RIS) is a promising technology to avoid signal blockage by cr... more Reconfigurable intelligent surface (RIS) is a promising technology to avoid signal blockage by creating line-ofsight (LOS) connectivity for free-space optical (FSO) and radio frequency (RF) wireless systems. There is limited research on the use of multiple RIS between a source and destination for wireless communications. This paper analyzes the performance of a RISassisted multi-hop transmission for vehicular communications by employing multiple RIS to enable LOS communication and reliable connectivity for a hybrid FSO and RF system. We develop an analytical framework to derive statistical results of the signalto-noise ratio (SNR) of a multi-RIS communication system over general fading models. We use decode-and-forward (DF) and fixed-gain (FG) relaying protocols to mix multi-RIS transmissions over RF and FSO technologies, and derive probability density and distribution functions for both the relaying schemes by considering independent and non-identical double generalized gamma (dGG)...
We present asymptotic expressions for user throughput in a multi-user wireline system with a line... more We present asymptotic expressions for user throughput in a multi-user wireline system with a linear decoder, in increasingly large system sizes. This analysis can be seen as a generalization of results obtained for wireless communication. The features of the diagonal elements of the wireline channel matrices make wireless asymptotic analyses inapplicable for wireline systems. Further, direct application of results from random matrix theory (RMT) yields a trivial lower bound. This paper presents a novel approach to asymptotic analysis, where an alternative sequence of systems is constructed that includes the system of interest in order to approximate the spectral efficiency of the linear zero-forcing (ZF) and minimum mean squared error (MMSE) crosstalk cancelers. Using works in the field of large dimensional random matrices, we show that the user rate in this sequence converges to a non-zero rate. The approximation of the user rate for both the ZF and MMSE cancelers are very simple t...
Reconfigurable intelligent surface (RIS) is an excellent use case for line-of-sight (LOS) based t... more Reconfigurable intelligent surface (RIS) is an excellent use case for line-of-sight (LOS) based technologies such as free-space optical (FSO) communications. In this paper, we analyze the performance of RIS-empowered FSO (RISE-FSO) systems by unifying Fisher–Snedecor (F), Gamma-Gamma (GG), and Malága (M) distributions for atmospheric turbulence with zero-boresight pointing errors over deterministic as well as random path-loss in foggy conditions with heterodyne detection (HD) and intensity modulation/direct detection (IM/DD) methods. By deriving the probability density function (PDF) and cumulative distribution function (CDF) of the direct-link (DL) with the statistical effect of atmospheric turbulence, pointing errors and random fog, we develop exact expressions of PDF and CDF of the resultant channel for the RISE-FSO system. Using the derived statistical results, we present exact expressions of outage probability, average bit-error-rate (BER), ergodic capacity, and moments of sign...
We propose an iterative crosstalk cancellation scheme based on the generalized minimal residual (... more We propose an iterative crosstalk cancellation scheme based on the generalized minimal residual (GMRES) algorithm for large-scale digital subscriber line (DSL) systems. The proposed scheme does not require channel inversion and stores fewer vectors for crosstalk cancellation. We analyze the convergence of the GMRES algorithm and derive computable bounds on the residual error and signal-to-noise ratio in terms of system parameters at each iteration for upstream DSL systems. We show that the GMRES algorithm typically requires a single iteration for very large vectored systems to achieve crosstalk-free performance for the very high-speed DSL (VDSL) frequencies and only a few more in the highest frequency bands of the G.fast spectrum. This yields significant complexity savings and reduction in memory storage, compared to the zero forcing scheme under certain conditions.
Signal fading due to atmospheric channel impairments and pointing error is a major bottleneck for... more Signal fading due to atmospheric channel impairments and pointing error is a major bottleneck for the performance of optical wireless communication (OWC). In this paper, we consider an amplify-and-forward (AF) optical relaying to enhance the performance of the OWC system with a negligible line-of-sight (LOS) link under the combined effect of fog and pointing error. We analyze the end-to-end performance of the relay-assisted system, which consists of complicated probability distribution functions. We derive analytical expressions of the outage probability, average signal-to-noise ratio (SNR), and ergodic rate in terms of OWC system parameters. We also develop an exact integral-form expression of these performance metrics using the half-harmonic mean of individual SNRs to validate the tightness of the derived analytical expressions. The numerical and simulation analysis shows that the proposed dual-hop relaying has significant performance improvement when comparing to the direct trans...
Optical wireless communication (OWC) over atmospheric turbulence and pointing errors is a well-st... more Optical wireless communication (OWC) over atmospheric turbulence and pointing errors is a well-studied topic. Still, there is limited research on signal fading due to random fog and pointing errors in outdoor environments. In this paper, we analyze the performance of a decode-and-forward (DF) relaying under the combined effect of random fog, pointing errors, and atmospheric turbulence with a negligible line-of-sight (LOS) direct link. We consider a generalized model for the end-toend channel with independent and not identically distributed (i.ni.d.) pointing errors, random fog with Gamma distributed attenuation coefficient, asymptotic exponentiated Weibull turbulence, and asymmetrical distance between the source and destination. We derive distribution functions of the signal-to-noise ratio (SNR), and then we develop analytical expressions of the outage probability, average SNR, ergodic rate, and average bit error rate (BER) in terms of OWC system parameters. We also develop simplifi...
2016 IEEE International Conference on the Science of Electrical Engineering (ICSEE), 2016
In this paper, we present a novel approximation to the spectral efficiency at the output of a zer... more In this paper, we present a novel approximation to the spectral efficiency at the output of a zero-forcing (ZF) receiver in a DSL upstream system. This approximation is extracted by a new asymptotic analysis, where we construct an alternative sequence of systems that includes the system of interest. Drawing on works in the field of large dimensional random matrices, we show that the user rate in this sequence converges to a non-zero rate. We also provide numerical simulations which show that this approximation is accurate even for relatively low dimensional systems.
Interference cancellation is the main driving technology in enhancing the transmission rates over... more Interference cancellation is the main driving technology in enhancing the transmission rates over telephone lines above 100 Mbps. Still, crosstalk interference in multi-pair digital subscriber line (DSL) systems at higher frequencies has not been dealt with sufficiently. The upcoming G.(mg) fast DSL system envisions the use of extremely high bandwidth and full-duplex transmissions generating significantly higher crosstalk and self-interference signals. More powerful interference cancellation techniques are required to enable multi-gigabit per second data rate transmission over copper lines. In this article, we analyze the performance of interference cancellation techniques, with a focus on novel research approaches and design considerations for efficient interference mitigation for multi-gigabit transmission over standard copper lines. We also detail novel approaches for interference cancellation in the upcoming technologies.
Mitigating channel fading and transceiver impairments are desirable for high-speed terahertz (THz... more Mitigating channel fading and transceiver impairments are desirable for high-speed terahertz (THz) wireless links. This paper analyzes the performance of a multi-antenna THz wireless system by considering the combined effect of pointing errors and fluctuating two-ray (FTR) fading model. We provide a statistical characterization of the maximal ratio combining (MRC) receiver over independent and nonidentical (i.ni.d.) channel conditions in terms of multi-variate Fox’s H by deriving density and distribution functions of the signal-tonoise ratio (SNR) of a single-link THz link using incomplete Gamma function. We develop exact analytical expressions of outage probability, average bit-error-rate (BER), and ergodic capacity for both single-antenna and MRC receivers. We also present the diversity order of the system by deriving asymptotic expressions for outage probability and average BER at high SNR to obtain insights into the system performance. We validate our derived analytical expressi...
Reconfigurable intelligent surface (RIS) is a promising technology to avoid signal blockage by cr... more Reconfigurable intelligent surface (RIS) is a promising technology to avoid signal blockage by creating virtual lineof-sight (LOS) connectivity for free-space optical (FSO) and radio frequency (RF) wireless systems. This paper considers a mixed FSO-RF system by employing multiple RISs in both the links for multihop transmissions to extend the communication range. We develop probability density function (PDF) and cumulative density function (CDF) of the signal-to-noise ratio (SNR) for the cascaded channels by considering double generalized gamma (dGG) turbulence with pointing errors for the FSO link and the dGG distribution to model the signal fading for the RF. We derive exact closed-form expressions of the outage probability, average bit-error-rate (BER), and ergodic capacity using the decode-andforward (DF) relaying for the mixed system. We also present asymptotic analysis on the performance in the high SNR regime depicting the impact of channel parameters on the diversity order o...
Impulse noise presents a severe performance bottleneck in multicarrier systems. For digital subsc... more Impulse noise presents a severe performance bottleneck in multicarrier systems. For digital subscriber lines (DSL), the use of a common-mode (CM) sensor is a viable technique to mitigate the impulse noise that couples into the useful differential-mode (DM) signal. In this paper, we use time and frequency domain approaches to develop algorithms using the joint processing of CM and DM signals and analyze the performance of dual-sensor based interference cancellation schemes for downstream DSL systems. First, we consider the frequency domain approach and analyze the performance of a per-tone impulse noise canceler without requiring an impulse detector. We derive closed-form expressions on the performance of canceler in various interference scenarios in terms of system parameters. Next, we develop a novel per-symbol time-domain impulse noise canceler by simultaneous estimation of the CM2DM transfer function and the CM impulse noise using a limited number of null carriers. The proposed algorithm eliminates the issues of convergence of the per-tone canceler and stationarity of the impulse noise over multiple symbols. Using derived analytical expressions, we show that the proposed canceler effectively mitigates the impulse noise on a per-symbol basis. We also demonstrate the performance of the considered canceler schemes using measurement and simulation results.
Reconfigurable intelligent surfaces (RIS) can have an excellent use case for terahertz (THz) wire... more Reconfigurable intelligent surfaces (RIS) can have an excellent use case for terahertz (THz) wireless transmissions. In this letter, we analyze the performance of a RIS-empowered THz system over the combined effect of α-μ fading and pointing errors. We derive exact closed-form expressions of density and distribution functions of the resultant signal-to-noise ratio (SNR) considering an independent and not identically distributed (i.ni.d.) channel model. Using the derived statistical results, we present an exact analysis on outage probability, ergodic capacity, and average bit-error-rate (BER) of the considered system. We also develop asymptotic analysis on the outage probability and average BER to derive diversity order in terms of system parameters. The proposed analysis provides insights to mitigate the effect of pointing errors and shows that the RIS can significantly improve the performance of THz communications. We validate the analytical results using numerical and Monte Carlo simulations and demonstrate the scaling of system performance with an increase in the number of RIS elements.
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Papers by SM Zafaruddin