Kostas Peppas

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Papers by Kostas Peppas

Dual-hop transmissions with fixed-gain relays over Generalized-Gamma fading channels

Computing Research Repository, 2010

In this paper, a study on the end-to-end performance of dual-hop wireless communication systems e... more In this paper, a study on the end-to-end performance of dual-hop wireless communication systems equipped with fixed-gain relays and operating over Generalized-Gamma (GG) fading channels is presented. A novel closed form expression for the moments of the end-to-end signal-to-noise ratio (SNR) is derived. The average bit error probability for coherent and non-coherent modulation schemes as well as the end-to-end outage probability of the considered system are also studied. Extensive numerically evaluated and computer simulations results are presented that verify the accuracy of the proposed mathematical analysis.

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Moments generating function of the harmonic mean of two non-identical gamma random variables and its applications in wireless communications

In this paper, a closed-form expression for the moments generating function of the half-harmonic ... more In this paper, a closed-form expression for the moments generating function of the half-harmonic mean of two independent, not necessarily identically distributed gamma random variables with arbitrary parameters is presented. This statistical result is useful to the performance analysis of dualhop wireless communication systems with amplify-and-forward relays in a Nakagami-m fading environment. The proposed mathematical analysis is substantiated by various numerically evaluated and computer simulation results. communication systems. More specifically, in Simon and Alouini it is shown that the so-called MGF-based approach significantly simplifies the mathematical analysis required for the evaluation of important performance metrics, such as the average bit error probability (ABEP) and allows unification under a common framework in a large variety of digital communications systems, covering all known modulation techniques and fading models.

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Evaluation of Interoperability Criteria and Mechanisms for Seamless Inter-Working Between UMTS-HSDPA and WLAN Networks Enhanced with MIMO Techniques

This article proposes criteria and mechanisms that achieve seamless inter-working between the mul... more This article proposes criteria and mechanisms that achieve seamless inter-working between the multiradio access technologies that will compose the fourth-generation (4G) wireless mobile environment. We address the problem of incorporating system interoperability in order to provide the user with seamless mobility across different radio access technologies; namely we focus on inter-working UMTS-High Speed Downlink Packet Access (HSDPA) and WLAN networks, as these two networks are believed to be major components of the 4G wireless network. Interoperability results in providing the user with a rich range of services across a wide range of propagation environment and mobility conditions, using a single terminal. Specifically, the article aims at defining the criteria and mechanisms for interoperability between the two networks. Our approach considers the use of Cost functions to monitor the essential parameters at the system level in order to trigger an interoperability procedure. Initial user assignment and inter-system handover are considered the incidents that initiate the interoperability algorithm execution. The overall objective of this work is to assess the performance of our developed interoperability platform and to optimize system performance by guarantying a minimum QoS requirement and maximizing network capacity.

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Erratum to: Performance Evaluation of Space–Time Block Codes Over Keyhole Weibull Fading Channels

Wireless Personal Communications, 2010

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Performance Evaluation of Space–Time Block Codes Over Keyhole Weibull Fading Channels

Wireless Personal Communications, 2008

It is well known that degenerate channel phenomena known as keyholes may significantly reduce the... more It is well known that degenerate channel phenomena known as keyholes may significantly reduce the capacity of multiple-input and multiple-output (mimo) channels. Keyhole mimo channels were predicted theoretically and also observed experimentally. In this paper, a novel method of analyzing the performance of keyhole mimo channels is proposed. The proposed method is based on the assumption that the received signal at the keyhole encompasses an arbitrary number of multipath components and the propagation environment is such that the resulting signal is observed as a non-linear function of the modulus of the sum of these components. Based on this assumption, we initially introduce the double Weibull fading model, constructed by the product of two independent Weibull distributed fading envelopes. Closed-form expressions for its moments-generating function, probability density function, cumulative distribution function, and moments are also derived. Based on these formulas, we analytically evaluate the performance of a 2 × 2 mimo space–time block-coding (stbc) system, where performance metrics such as the average symbol error probability for several modulation schemes, outage probability, amount of fading and ergodic capacity are given in closed form. Various performance evaluation results are presented in order to verify the proposed analysis.

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System level performance comparison of MIMO and SISO Hiperlan/2 networks

In this paper the system level performance of a Hiperlan/2 network enhanced through MIMO techniqu... more In this paper the system level performance of a Hiperlan/2 network enhanced through MIMO techniques is investigated and compared to the performance of the conventional Single-Input-Single-Output (SISO) network. The MIMO scheme applied is closed loop power allocation based on Singular Value Decomposition (SVD). The work has been partly performed within the frame of IST-FITNESS project [1]. The above investigations are carried out by means of a software based simulation platform and for a number of test cases taking into account specific spacetime algorithms, antenna configurations, propagation environment, traffic load, mobility and user requirements. The performance evaluation is achieved by monitoring the system throughput and the percentage of satisfied users. Extensive simulations have been carried out that prove the superiority of MIMO techniques especially for heavy traffic load conditions.

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Probability Distribution of Aggregate Impulsive Interference in Wireless Networks

Asymptotic Error Performance Analysis of Spatial Modulation under Generalized Fading

This letter presents a comprehensive framework analyzing the asymptotic error performance of a mu... more This letter presents a comprehensive framework analyzing the asymptotic error performance of a multipleinput-multiple-output (MIMO) wireless system employing spatial modulation (SM) with maximum likelihood detection and perfect channel state information. Generic analytical expressions for the diversity and coding gains are deduced that reveal fundamental properties of MIMO SM systems. The presented analysis can be used to obtain closed-form upper bounds for the average bit error probability (ABEP) of MIMO SM systems under generalized fading which become asymptotically tight in the high signal-tonoise ratio (SNR) region.

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Probability of fade estimation for FSO links with time dispersion and turbulence modeled with the gamma–gamma or the IK distribution

In this work, we study the influence of the time dispersion and atmospheric turbulence effects on... more In this work, we study the influence of the time dispersion and atmospheric turbulence effects on the performance of a free space optical communication system, which is using longitudinal Gaussian pulses as information bit carriers. The scintillation effect, is modeled with the gamma-gamma or the I-K distribution, which, both, are suitable to emulate irradiance fluctuations due to weak to strong atmospheric turbulence conditions. Additionally, we estimate the influence of the time dispersion effect on chirped pulse's propagation. Taking into account these effects, closed form mathematical expressions for the evaluation of fade's probability of the wireless optical link, are derived. Additionally, the possibility of improving the availability results by choosing the appropriate link and pulse's parameter values is further investigated. Finally the numerical results from the derived mathematical expressions are presented.

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The influence of the wearable antenna type on the on-body channel modeling at 2.45 GHz

ABSTRACT This paper discusses the impact of the antenna type on the on-body channel modeling, bas... more ABSTRACT This paper discusses the impact of the antenna type on the on-body channel modeling, based on a systematic measurement campaign at 2.45 GHz. Two different microstrip antennas were used for the measurements, a coaxial fed rectangular patch antenna, that shields the human body from back radiation and a coplanar patch antenna, which radiates towards the human body. An extensive statistical analysis was performed and the empirical CDFs were compared to eight well-known fading distributions. Among the distributions tested only lognormal, gamma and α-μ models provided best fit to the data. It was observed that the channel modeling depends on the antenna type used. Moreover, deviations of up to 3.5 dB were reported between the envelope CDFs of the two antennas.

Performance Analysis of Multi-Hop AF Relaying Systems with a Poisson Field of Interferers in Nakagami-m Fading Channels

ABSTRACT In this paper, we investigate the performance of a wireless transmission system that emp... more ABSTRACT In this paper, we investigate the performance of a wireless transmission system that employs amplify-and-forward (AF) relays and operates in an interference-limited environment. We consider a multi-hop network in which the co-channel interferers are scattered according to a spatial Poisson process and the desired and interfering signals at each relay and the destination experience Nakagami-m fading. Exact expressions for the average bit error probability and the average channel capacity of the considered system are obtained as single integrals that can be reliably evaluated numerically. In addition, the diversity and coding gains per hop are obtained. The novel expressions can be used to show the impact of system and interference model parameters such as the number of hops and the transmit power, path loss exponent, and spatial density of interferers, respectively, on the performance of multi-hop systems. Simulation results are further provided to demonstrate the accuracy of the analytical expressions.

Hierarchical Multilevel Space-Shift Keying for Unequal Error Protection under Rician Fading

ABSTRACT Hierarchical Multilevel Space-Shift Keying Modulation is proposed for Unequal Error Prot... more ABSTRACT Hierarchical Multilevel Space-Shift Keying Modulation is proposed for Unequal Error Protection under Line-Of Sight conditions in Rician fading channels. The High Priority (HP) information is conveyed via the number of active antennas employed to transmit a codeword. The Low Priority (LP) information is transmitted employing Generalized Space Shift Keying (GSSK) in the codeword subsets corresponding to the transmission of the HP symbols. Hierarchical modulation is accomplished by associating phase shifts with every transmit antenna and adjusting these phase shifts to achieve different levels of Unequal Error Protection. The simulations demonstrate the performance and design options offered by the proposed scheme.

Evaluation of average bit error rate for wireless networks with alpha-stable interference

ABSTRACT The performance of a digital wireless network that operates in a Rayleigh fading environ... more ABSTRACT The performance of a digital wireless network that operates in a Rayleigh fading environment in the presence of Gaussian noise and heavy-tailed impulsive interference that can be modelled by an α-stable process is investigated. Such wireless networks include ad hoc or cognitive radio networks that operate in an unbounded fading/shadowing environment with a Poisson interference field. For the system under consideration, a novel closed-form expression for the average bit error probability of digital modulation schemes, valid for any arbitrary real values of the characteristic exponent, α, is derived. The validity of the proposed formulation is attested through Monte Carlo simulation results.

Dual-Hop Relaying Communications with Cochannel Interference Over-/spl mu/Fading Channels

Layered Offset Hierarchical QAM Modulation for Intersymbol Interference Reduction

Layered offset hierarchical QAM modulation scheme is proposed to enhance the high priority stream... more Layered offset hierarchical QAM modulation scheme is proposed to enhance the high priority stream error performance by reducing the intersymbol interference from the superimposed symbols of the low priority stream. The proposed scheme shifts the symbols of the two priority layers by half the symbol duration, whereas the detector performs multistage maximum-likelihood detection with interference cancellation. The simulations demonstrate the performance and design options offered by the proposed scheme compared to conventional hierarchical schemes where no time offset exists between the superimposed symbols

Capacity analysis of dual amplify-and-forward relayed free-space optical communication systems over turbulence channels with pointing errors

ABSTRACT This paper elaborates on the end-to-end capacity of dual-hop free-space optical (FSO) co... more ABSTRACT This paper elaborates on the end-to-end capacity of dual-hop free-space optical (FSO) communication systems employing amplify-and-forward (AF) relaying, assuming channel state information is only known at the receiving terminals. The relay is assumed to either possess perfect channel state information or have a fixed gain. The performance of the considered system is affected by the combined effects of atmospheric turbulence-induced fading, pointing errors (i.e., misalignment fading), and path loss. Atmospheric turbulence conditions are modeled using the gamma-gamma distribution. For the system under consideration, accurate analytical approximations as well as upper bounds to the ergodic capacity are derived. In addition, bound approximations in the high signal-to-noise ratio regime are deduced that provide valuable insights into the impact of model parameters on the capacity of AF FSO dual-hop relaying systems. Numerically evaluated and computer simulation results are further provided to demonstrate the validity of the proposed mathematical analysis.

Performance Analysis of Dual-Hop AF Relaying Systems over Mixed and Fading Channels

ABSTRACT This paper investigates the end-to-end performance of a dual-hop amplify-and-forward (AF... more ABSTRACT This paper investigates the end-to-end performance of a dual-hop amplify-and-forward (AF) relaying communication system where the source-to-relay and the relay-to-destination channels are subject to different fading conditions. The relay is assumed to either possess perfect channel state information (CSI) or have a fixed gain. We consider the case where the one hop&#39;s channel is subject to eta-mu fading while the other one is subject to kappa-mu fading. This mixed fading propagation channel is capable of accurately modeling various practical dual-hop transmissions. Examples of such environments are encountered in micro/macro cellular systems and/or hybrid satellite/terrestrial wireless communication systems, where typically only the one hop&#39;s channel has a line-of-sight component. For both CSI-assisted and fixed-gain relaying and for integer-valued fading parameters, exact analytical expressions in the form of rapidly convergent infinite series for the outage probability (OP) and average bit error probability (ABEP) of several modulation schemes are derived. Moreover, for CSI-assisted relaying and arbitrary-valued fading parameters, closed-form lower bounds (tight for high values of the signal-to-noise (SNR)) for the OP and ABEP performance are obtained. The analysis is also substantiated by obtaining previously published equivalent performance expressions as special cases of our generic fading models, namely those available for Nakagami-m and Rice fading channels. In addition, the derived analytical expressions have been numerically evaluated and the performance evaluation results have been further validated by comparing them with equivalent results which have been obtained by means of Monte Carlo computer simulations.

An Interoperability Mechanism for Seamless Interworking between WLAN and UMTS-HSDPA Networks

Global Telecommunications Conference, . GLOBECOM . IEEE, 2006

Future wireless communication systems are expected to provide seamless inter-working between exis... more Future wireless communication systems are expected to provide seamless inter-working between existing and 3G radio networks providing the user with a wide variety of services, while maintaining a large area of coverage and minimum user QoS requirements. In this paper, a new mechanism that implements interoperability between HSDPA and WLAN systems is proposed. The proposed interoperability mechanism is activated via the optimization of a suitably defined cost function, which takes into account all the appropriate system level parameters that trigger the interoperability process. The performance evaluation of the proposed scheme is assessed by means of a software - based simulation platform. A number of simulations have been carried out in order to demonstrate the performance enhancements achieved by the proposed mechanism in terms of user throughput, handovers statistics, and system throughput.

Multilevel Spatial Hierarchical Modulation: An Efficient Scheme for Unequal Error Protection under Rician Fading

by Martin Zamkotsian and Kostas Peppas

IEEE Transactions on Vehicular Technology, 2014

Under strong line-of-sight (LOS) conditions, in a con- ventional spatial modulation scheme, the s... more Under strong line-of-sight (LOS) conditions, in a con- ventional spatial modulation scheme, the signal domain exhibits better error performance than the spatial domain, thus rendering the accomplishment of unequal error protection (UEP) a diffi- cult task. To this end, multilevel spatial hierarchical modulation (MSHM) is proposed to provide UEP in Rician fading channels when both the high priority (HP) and the low-priority information streams are jointly encoded in the spatial and signal domains. A phase-aided multilevel space-shift keying scheme is employed in the spatial domain to enhance HP performance, whereas in the signal domain, hierarchical modulation is employed. The joint space-signal constellation related to the LOS component of the re- ceived signal is appropriately formed to provide higher protection to the HP stream while, at the same time, being capable of pro- viding different levels of protection by adjusting the transmission parameters of the spatial and signal schemes when they are jointly employed. By incorporating the Rician factor to the parameters of the proposed MSHM scheme, the latter is made adaptive to the fading conditions. Simulations have been performed to assess the performance and demonstrate the design options offered by the proposed MSHM scheme.

Improving spectral efficiency in broadcasting employing hierarchical QAM

by Martin Zamkotsian and Kostas Peppas

2014 IEEE Wireless Communications and Networking Conference (WCNC), 2014

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