Angelos A. Goulianos

UWB Path Arrival Times in Body Area Networks

A first-order, nonhomogeneous Markov model for predicting the path arrival times in ultrawideband (UWB)-body area network (BAN) scenarios is presented. New parameters of this model, that describe this specific propagation environment and the human body effects, have been extracted. The path arrival probabilities suggest a very close fitting to the experimental data. The cumulative path density functions are modeled according to the Delta-K model with enhancement over the pure Poisson model. The presented methodology can be used for UWB-BAN channel simulations and for evaluating multipath-combining receiver structures

Wideband Power Modeling and Time Dispersion Analysis for UWB Indoor Off-Body Communications

A statistical model for ultrawideband (UWB) off-body communication channels is proposed. The presented results are the outcome of extensive real-body measurements carried out in the frequency range between 3.5 and 6.5 GHz in typical indoor environments. The signal power gain is modeled by a log-linear dual-breakpoint model, the parameters of which depend on both the body orientation as well as the distance between the transmitter and the on-body sensor. The general trend implies that in large distances, the received signal strength is less sensitive to changes in the body orientation angle, especially if propagation occurs in dense multipath environments. Furthermore, the small-scale channel variations of the total received signal strength are found to follow a normal distribution. This fact was verified by means of the central limit theorem (CLT), since correlation between multipath components is found to be negligible. Moreover, time dispersion analysis is provided by means of RMS delay spread. Finally, based on the newly estimated parameters, a model implementation for wideband power is proposed and several comparisons between the empirical data and the simulation results are presented.

Ultra-wideband measurements and results for sparse off-body communication channels

This paper presents a measurement-based statistical channel model for describing UWB off-body propagation and is valid for the frequency range from 3.5 to 6.5 GHz. This model is expressed with respect to both radial and azimuth coordinates, and is physically motivated by creeping wave propagation around smooth convex surfaces, such as the human body. Consequently, it maintains the exponential decay path loss trend with respect to the body orientation angle. Furthermore, it is shown that the same model can be used for RMS delay spread prediction, by simply applying the appropriate parameters resulting from time dispersion analysis. Therefore, delay spread results are presented for threshold values of 10 and 20 dB within the peak of each power delay profile. Following the presented modeling method model parameters can be used as criterion for characterization of respective dense multipath channels.

Path-Loss and Throughput Prediction of IEEE 802.11ad Systems

This paper presents a path-loss prediction analysis and a performance evaluation of the 60GHz IEEE 802.11ad standard. Received signal strength measurements were performed in indoor locations and the decay coefficients were estimated over a number of measured routes. Furthermore, real world maps were incorporated into a 3-D mm wave ray- tracing tool for the purpose of employing realistic channel matrices into an 802.11ad bit level simulator. Finally, performance metrics for various MCS modes are presented and analyzed for both Orthogonal Frequency Division Multiplexing (OFDM) and Single Carrier (SC) transmissions.

Evaluation of 802.11 and LTE for Automotive Applications

This paper evaluates coverage prediction and radio performance for automotive infotainment applications. The work compares IEEE 802.11af operating in the TV White Space (TVWS) bands with LTE operating at 800MHz and 2.6GHz. Real world rural and urban databases are incorporated into a 3D ray tracing tool for the purposes of exploring signal coverage and data rates along with virtual drive tests. Results are presented as a function of radio standard, operating band, vehicle speed, user location and packet size. LTE is shown to outperform 802.11af since it is less affected by the multipath channel and the significant levels of Doppler Spread experienced by vehicular users. Results also indicate that 802.11af systems provide superior coverage, especially in rural environments.

Time-domain sounder validation and reflectivity measurements for mm-Wave applications

This paper presents a wideband channel sounder for mmWave radiowave propagation measurements. Three test environments are described and a number of channel sounding validation techniques are proposed. The temporal performance of the sounder is assessed through real-time wideband measurements using two metallic reflectors placed within an anechoic chamber. Furthermore, high directional antennas are employed for the purpose of power validation, as well as for measuring the received signal strength reflected by various building materials. Finally, the depolarization of the building materials is assessed by means of measuring and characterizing the received cross-polar components.

Design and Verification of a Virtual Drive Test Methodology for Vehicular LTE-A Applications

In this paper, a virtual drive test (VDT) emulation methodology for vehicle-to-infrastructure long-term evolution-advanced (LTE-A) communications is proposed, evaluated, and compared against a traditional drive test approach. A generic antenna and radio test process is developed based on 3-D ray-traced channel models, theoretic and measured antenna patterns, radio frequency (RF) channel emulation, and hardware-in-the-loop (HIL) radio measurements. The spatial and temporal multipath components of the radio propagation channel between the multiple-input and multiple-output (MIMO)-enabled LTE-A base stations (BS) and the vehicle under test are accurately modeled for a site-specific virtual environment. Measured BS and LTE-A vehicular antenna patterns are incorporated into the system via spatial and polarimetric convolution with the synthetic ray data. The resulting channels are streamed into a wideband channel emulator that connects a multichannel LTE-A BS emulator to a smartphone representing the vehicular on-board-unit (OBU). The laboratory-based LTE-A HIL system is used to study the handover process between two serving LTE-A BSs according to the received RF powers at the vehicular OBU. Emulated RF powers and data throughputs are compared with data from a traditional drive test to verify the legitimacy of the proposed methodology. Our VDT results in terms of reference signal received power and physical downlink shared channel throughput match well the real-world LTE-A measurements for single-input and single-output and MIMO operation. This new process benefits from being repeatable and via the use of ray-tracing scales to support a wide range of urban and rural operating environments.

LTE-A Virtual Drive Testing for Vehicular Environments

In this paper, a Virtual Drive Testing (VDT) methodology for a MIMO LTE Vehicle to Infrastructure (V2I) urban scenario is proposed and compared with actual road drive tests. We have developed a unique and generic radio performance analysis process based on 3D ray traced channel models, theoretic or measured antenna patterns, RF channel emulation and hardware-in-the-loop radio measurements. A 3D ray-tracing channel model is used to predict the spatial and temporal multipath ray components of the radio propagation channel between an LTE BS and the vehicle. Measured LTE vehicular antenna patterns were then applied using a spatial and polarimetric convolution process. The resulting channels were streamed into a Keysight PropSim F8 channel emulator, which was programmed to communicate with the multi-channel LTE BSs emulator and a Samsung S5 mobile client performing a handover procedure. The VDT emulation method proposed in this paper is shown to be reliable and repeatable and the accuracy of the emulated throughput agreed well with real measurements for MIMO operation.

Link quality and path based clustering in IEEE 802.15.4-2015 TSCH networks

Advance clustering techniques have been widely used in Wireless Sensor Networks (WSNs) since they can potentially reduce latency, improve scheduling, decrease end-to-end delay and optimise energy consumption within a dense network topology. In this paper, we present a novel clustering algorithm for high density IEEE 802.15.4-2015 Time-Slotted Channel Hopping (TSCH). In particular, the proposed methodology merges a variety of solutions into an integrated clustering design. Assuming an homogeneous network distribution, the proposed configuration deploys a hierarchical down-top approach of equally numbered sub-groups, in which the formation of the separate sub-groups is adapted to the network density and the node selection metric is based on the link quality indicator. The presented algorithm is implemented in Contiki Operating System (OS) and several test vectors have been designed in order to evaluate the performance of the proposed algorithm in a COOJA simulation environment. Performance results demonstrate the capability of the clustering structure since compared to the default scheme it significantly improves the energy efficiency up to 35%, packet drops more than 40% as well the packet retransmission rate. Last but not least, the outcome of this study indicates a major increase in the network lifetime, i.e., up to 50%.

Large-Scale Modeling and Cell-Edge Coverage for Future HetNet Deployments

This paper evaluates the large-scale channel parameters and the cell-edge coverage for various LTE-WiFi based, heterogeneous networks. Real world urban databases are incorporated into two separate 3D ray tracing software tools, specifically designed for the characterization of both microwave and millimeter (mm)-wave radio links. The study is performed for both LTE-800MHz and LTE-2.6GHz macro-cell configurations whereas it demonstrates the coverage enhancement attained by deploying 802.11n/ac/ad micro-cell structures. The significance of this study lies on the radio planning aspects of future heterogeneous networks.