Petros Karadimas

Human Body Shadowing Characterization for 60-GHz Indoor Short-Range Wireless Links

We statistically characterize received signal power variations in the time domain caused by human activity affecting 60-GHz indoor short-range wireless links. Our approach is based on propagation measurements in indoor environments considering human activity intercepting the line-of-sight (LOS) path. It has been previously shown that the ensemble of received power levels in decibel (dB) scale cannot be modeled by a Gaussian distribution, as is the case for spatial shadowing variations. In this letter, we present a theoretical stochastic approach showing that received power variations can follow a Gaussian statistical model when considered within the time intervals of similar shadowing processes. Our model is shown to have good comparison to experimental data.

The Weibull–Lognormal Fading Channel: Analysis, Simulation, and Validation

In frequency-nonselective fading channels, the partial waves arriving at the mobile receiver cannot explicitly be of homogeneous nature due to nonuniform scattering caused by objects of specific reflective nature. Moreover, shadowing influences the received signal level by causing slow variations to its local mean. In this paper, we investigate a mixture stochastic process accounting for both inhomogeneous scattering and shadow fading by multiplying a Weibull process with a lognormal process. The first process models the possible scattering nonuniformities of the channel, whereas the second process accounts for the slow-term variations of the local mean due to shadowing. An exact solution for the composite probability density function (pdf) will be given, together with approximate solutions for the second-order statistics, i.e., the level crossing rate (LCR) and the average duration of fades (ADF). The approximate solutions come from the assumption of a slowly time-varying lognormal process compared with the Weibull process, the validity of which will be tested via an efficient deterministic simulation scheme that implements the analytical model on a digital computer. Finally, a curve fitting of the LCR to real-world data drawn from channel measurements will demonstrate the flexibility and usefulness of the proposed model.

Ergodic capacity for the SIMO Nakagami-m channel

This paper presents closed-form expressions for the ergodic channel capacity of SIMO (single-input and multiple output) wireless systems operating in a Nakagami- fading channel. As the performance of SIMO channel is closely related to the diversity combining techniques, we present closed-form expressions for the capacity of maximal ratio combining (MRC), equal gain combining (EGC), selection combining (SC), and switch and stay (SSC) diversity systems operating in Nakagami- fading channels. Also, the ergodic capacity of a SIMO system in a Nakagami- fading channel without any diversity technique is derived. The latter scenario is further investigated for a large amount of receive antennas. Finally, numerical results are presented for illustration.

A Modified Loo Model with Partially Blocked and Three Dimensional Multipath Scattering: Analysis, Simulation and Validation

This paper presents a novel mobile fading channel model, belonging to the class of Loo models, in which the multipath power arrives both in three dimensions (3-D) and in two angular sectors at the azimuth receiver’s plane. Moreover shadowing affects the amplitude of the line of sight (LOS) component, making it time varying and following a lognormal distribution, as required for a Loo model. The Doppler power spectral density (PSD) is analytically calculated, after Fourier transforming the closed form autocorrelation function. Afterwards exact solutions for the probability density function (PDF) of the envelope and phase are presented. What follows are approximate solutions for the second order statistics, i.e. the level crossing rate (LCR) and the average duration of fades (ADF’s). A new, appropriate for 3-D scattering cases, deterministic simulation scheme is developed, which implements the analytical model on a digital computer and is used to test the validity of the approximate solutions. Moreover the deterministic model is thoroughly investigated for all the possible cases, in terms of its convergence to the analytical one. Finally a curve fitting of the LCR to real world data, drawn from channel measurements, will demonstrate the flexibility and usefulness of the modified Loo model.

A Generalized Modified Suzuki Model with Sectored and Inhomogeneous Diffuse Scattering Component

This paper presents a mixture stochastic process by multiplying a Weibull process with a lognormal one. The first one models the possible scattering non-uniformities of the channel, whereas the second accounts for the slow term variations of the local mean due to shadowing. Moreover we incorporate sectored arrival of multipath power (anisotropic scattering) via a correlation scheme between the zero mean Gaussian processes, generating the Rayleigh part of the Weibull process. An exact solution for the mixture probability density function (PDF) will be given, together with approximate solutions for the second order statistics, level crossing rate (LCR) and average duration of fades (ADF’s). The validity of the approximate solutions will be tested via an efficient simulation scheme, which implements the analytical model on a digital computer. Finally a curve fitting of the LCR to real world data, drawn from channel measurements, will demonstrate the flexibility and usefulness of the proposed model.

Energy Detection Based Spectrum Sensing Over Two-Wave With Diffuse Power Fading Channels

One of the most important factors that affects the performance of energy detection (ED) is the fading channel between the wireless nodes. This paper investigates the performance of ED-based spectrum sensing, for cognitive radio (CR), over two-wave with diffuse power (TWDP) fading channels. The TWDP fading model characterizes a variety of fading channels, including well-known canonical fading distributions, such as Rayleigh and Rician, as well as worse-than-Rayleigh fading conditions modeled by the two-ray fading model. Novel analytic expressions for the average probability of detection over TWDP fading that account for single-user and cooperative spectrum sensing and square law selection diversity reception are derived. These expressions are used to analyze the behavior of ED-based spectrum sensing over moderate, severe, and extreme fading conditions and to investigate the use of cooperation and diversity as a means of mitigating the fading effects. The obtained results indicate that TWDP fading conditions can significantly degrade sensing performance; however, it is shown that detection performance can be improved when cooperation and diversity are employed. The presented outcomes enable identifying the limits of ED-based spectrum sensing and quantifying the tradeoffs between detection performance and energy efficiency for CR systems deployed within confined environments, such as in-vehicular wireless networks.

Indoor-indoor and indoor-outdoor propagation trial results at 2.6 GHz

This paper presents delay spread, coherence bandwidth, and angle-of-arrival statistics derived from an extensive MIMO channel measurement campaign carried out at a central frequency of 2.6GHz. The measurement scenarios include indoor-indoor, indoor-outdoor and indoor-outdoor-indoor. The results are useful for analytical and performance studies of post-3G wireless communication systems such as femtocell design and deployment.

A Generalized Analysis of Three-Dimensional Anisotropic Scattering in Mobile Wireless Channels-Part I: Theory

In this paper, we present a generalized theoretical analysis for multipath scattering in mobile wireless channels where scattered power arrives into three dimensions (3-D). Moreover, multipath power can arrive into any arbitrary number of discrete angular sectors under an anisotropic propagation regime. A new expression for the azimuth and elevation angle of arrival (AOA) joint distribution of the arriving multipath power is presented. In the general case of multi-modal arrival, we show that the azimuth and elevation AOA are statistically dependent. The latter issue is further investigated by providing certain conditions for statistically independent azimuth and elevation AOA. Due to space limitations, in a follow up paper, a parameterized case study will be analyzed with multi-modal arrival into four angular sectors.

Simple Closed-Form Channel Capacity Formulas for the SIMO Nakagami Channel

This paper presents simple closed-form expressions for the ergodic channel capacity of SIMO (single-input and multiple output) wireless systems operating in a Nakagami fading channel. As the performance of SIMO channel is closely related to the diversity combining techniques, we present close form expressions for the capacity of maximal ratio combining (MRC), equal gain combining (EGC) and selection combining (SC) diversity systems for Nakagami fading channels. Also for the first time in international literature, the ergodic capacity of a SIMO system in a Nakagami fading channel with none diversity combining technique applied, is derived. Finally numerical results are presented for illustration.

A Generalized Analysis of Three-Dimensional Anisotropic Scattering in Mobile Wireless Channels-Part II: Second-Order Statistical Characterization

In a recent paper [1], we presented a generalized theoretical analysis for the diffuse multipath power in mobile wireless channels accounting for three-dimensional (3-D) multi-modal (i.e., clustered) scattering. In this paper, a parameterized case-study stemming from [1] is analyzed with multi-modal arrival of diffuse multipath power within four angular sectors. Those sectors are parametrically defined with respect to the mobile receivers direction of motion. One sector per each quadrant is considered and the parametric probability density function (PDF) of the angle of arrival (AOA) is derived. From this PDF, the second order statistics of mobile channels with multi-modal scattering are derived, namely, the temporal autocorrelation function (ACF), the power spectral density (PSD), or Doppler spectrum, the level crossing rate (LCR) and average fade duration (AFD). Extension to generalized multi-modal arrival within any arbitrary number of angular sectors can be treated similarly.