A. Michalopoulou

Statistical Analysis for On-Body Spatial Diversity Communications at 2.45 GHz

An investigation of the fading experienced by on-body diversity channels at 2.45 GHz is presented by focusing on the effects of the receive antennas position and the human body movement. This investigation is based on the conduction and analysis of signal measurements in an indoor office environment using bodyworn antennas. Three principal combining techniques, namely selection combining (SC), equal gain combining (EGC) and maximal ratio combining (MRC) are considered. A statistical characterization of the fading experienced by dual diversity on-body channels is performed in terms of first and second order statistics. Our investigations have shown that among several distributions tested, the α - μ distribution provides sufficient fit to measured combined signal envelopes and also offers a good approximation to second order statistics for the majority of test cases.

On the Oscillations Appearing in Numerical Solutions of Solvable and Nonsolvable Integral Equations for Thin-Wire Antennas

Differences between certain solvable and nonsolvable ill-posed integral equations, with the same nonsingular kernel, are discussed. The main results come from constructing a solvable equation in the context of straight thin-wire antennas. The kernel of this equation is the usual approximate (also called reduced) kernel, while its exact solution is the familiar sinusoidal current. Numerical solutions to this solvable equation are compared to corresponding numerical solutions of the usual-Halle¿n and Pocklington-equations with the approximate kernel; it is known from previous publications that these last two equations are nonsolvable and that their numerical solutions present severe oscillations when the number of basis functions is sufficiently large. It is found that the difficulties encountered in the former (solvable) equation are much less important compared to those of the nonsolvable ones. The same conclusion is brought out from other integral equations, arising in different contexts (thin-wire circular-loop antenna, Method of Auxiliary Sources, and straight wire antenna of infinite length). We discuss the consistency of our results with Picards theorem. The results in this paper supplement previous publications regarding the difficulties of numerically solving thin-wire integral equations with the approximate kernel.

On-body channel modelling: Measurements and statistical analysis

This paper investigates the propagation phenomena and the fading experienced by on-body channels at 2.45 GHz, focusing on the effect of the human body. This investigation is based on signal measurements conducted for both stationary and mobile user cases using bodyworn antennas placed in various positions on the human body. The effect of the antenna location and the human body movement on the fading characteristics of the on-body channels is extensively studied through statistical analysis of the measurement data.

On the Use of Entire-Domain Basis Functions in Galerkin Methods Applied to Certain Integral Equations for Wire Antennas With the Approximate Kernel

When the approximate kernel is used, Hallens integral equation for the current distribution on a center-driven, straight-wire antenna does not have a solution. This is true for at least two types of feed: the delta-function generator and the frill generator. For the case of subsectional basis functions in Galerkins method, recent papers have shown that the main associated difficulty is the unavoidable appearance of oscillations near the center and/or the ends of the antenna. In this paper, we investigate the nature of the difficulties for the case of entire-domain, cosine basis functions. We find that the difficulties are similar to those of the subsectional case, something that we had not expected beforehand. In particular, undesirable oscillations appear when the number of basis functions is greater than a number dependent on the length-to-radius ratio, giving one a simple rule for choosing the number of basis functions so as to yield smooth solutions. We also compare results to ldquotruerdquo solutions, study the separate but important effects of roundoff, and give extensions to equations of the Pocklington type.

The Impact of the Position of MIMO Terminal User's Hand on Channel Capacity

In this paper the impact of the position of users hand holding a multiple-input-multiple-output (MIMO) terminal on system performance and more specifically on channel capacity is investigated. We consider a 4times4 MIMO system with a personal digital assistant (PDA) equipped with a compact array of 4 patch elements. Radiation field patterns of the antenna elements in the presence of the other elements as well as in the presence of a users hand are simulated. Different positions of the users hand are taken into account. The covariance matrix of the receiving antennas is evaluated by means of the obtained patterns. A correlation-based channel model is considered, where the antenna patterns are incorporated. Extensive simulations showed that the performance of the MIMO systems varies significantly with the position of the users hand.

Investigation of wearable antennas performance in static LOS and NLOS on-body channels

In this paper modelling of specific on-body channels is conducted by using three different antenna types. Our goal is to investigate antennas performance in different on-body contexts and examine antennas propagation mechanisms. For this purpose, a measurement campaign is performed. Results will be provided in terms of channel gain, slow and fast fading modelling by performing statistical analysis of received signal envelope.

Handheld terminal vs. bodyworn antenna systems: A comparative study of MIMO systems performance

In this paper a comparative study of MIMO systems performance is presented by investigating a bodyworn antenna system and a handheld terminal system, taking into account the presence of the users body. The effects of the correlation coefficient, the radiation efficiency and the number of receiving antennas on MIMO channel capacity are addressed. Extensive study is carried out to examine how these three parameters influence the performance of the two MIMO systems under study, in order to be able to select between a handheld multiple antennas terminal and a bodyworn multiple antennas system for a MIMO system implementation.

Comparative study of cooperative transmission techniques in multipath rician fading environments

Several cooperative transmission techniques have been studied in previous research works but very few of them have considered the trade-off between diversity gain and energy efficiency, which is important in cases, such as wireless sensor networks. Two cooperative transmission techniques are examined, namely decode-and-forward (DF) and network coding (NC), both with selection combining (SC) at the receiver, in order to evaluate the performance of the aforementioned techniques with respect to the variation of the k-factor in Rician fading channels. Computer-based simulations show that, in most of the considered scenarios, NC scheme can result in smaller diversity gain compared to DF scheme, however it achieves significantly lower energy consumption at the relay node.