Panagiotis I. Dallas

Measurements and Wideband Channel Characterization for Over-the-sea Propagation

This study focuses on sea propagation environments and presents results on the characterization of the over-the-sea wideband mobile radio channel. Conducted measurements led to the development of path loss, log-distance models. The behavior of the power delay profile is also investigated in detail. In general, the mean excess delay and delay spread values were estimated below 0.5 musec for line-of-sight propagation. However, loss of line-of-sight can cause rapid worsening of the propagation parameters

MIMO Channel Characterization for Short Range Fixed Wireless Propagation Environments

This paper reports results from wideband MIMO measurements performed in short range fixed wireless environments at 5.2 GHz. The objective is to provide MIMO channel characterization results for the measured environments and contribute to the limited available similar studies. Two kinds of propagation scenarios are investigated, rooftop to rooftop and street to rooftop, at three different sites always under LOS propagation conditions. The analysis of measurement data is performed in the context of non physical modeling, providing insight into the statistics of the measured channels. In particular, the slow time varying nature of the channel is studied and the narrow Doppler spectrum shape is approximated. Furthermore, frequency correlation results are obtained and the typical delay dispersion measures are extracted. Then, the antenna correlation is studied and the error of the Kronecker product approximation is evaluated. Finally, capacity results are provided and the channel measurements are characterized in terms of spatial multiplexing quality and multipath richness through condition number analysis.

Novel Channel and Polarization Assignment Schemes for 2---11 GHz Fixed---Broadband Wireless Access Networks

The scarcity of available spectrum in the 2–11 GHz frequency range and the continuously increasing number of users that require broadband communication services suggest that emerging fixed-broadband wireless access (F-BWA) networks will be deployed with aggressive frequency re-use to cope with capacity demands. In this context, co-channel interference may arise in high levels compromising the systems capacity and robust operation. Interference is further increased when limited directionality terminal antennas are employed to support non line-of-sight operation and in the case where an adaptive-time division duplex is selected for efficient radio resource management in asymmetric and time-varying traffic conditions. In this paper frequency channel assignment (CA) and antenna polarization assignment (PA) are considered as a means of mitigating interference. Two novel CA schemes that consider the distinct characteristics of F-BWA are proposed; the rotated-interleaved channel assignment and the non-uniform channel assignment. According to statistical interference simulation analysis the proposed schemes are more efficient in suppressing interference, achieving higher capacity compared to existing schemes while incurring no further complexity. In addition, instead of exploiting the performance of CA and PA schemes independently a framework for a joint CA-PA consideration is presented, where for a particular CA scheme an optimized PA pattern is developed. Results show that this approach improves the CA-PA interoperability increasing the overall performance. The efficiency of the proposed schemes is investigated for both FDD and adaptive-TDD schemes and is verified for various sectorization, frequency re-use and terminal antenna directivity configurations to ensure compatibility with different deployment scenarios.

Measuring and modeling the wideband mobile channel for above the sea propagation paths

This paper presents the results on mobile channel characterization for the above the sea propagation paths at 1.9 GHz. The study is based on measurement campaigns conducted in various locations, carefully selected in order to cover all kind of environments that can be met in the Aegean Sea. The purpose was to model the over-the-sea channel. This study presents conclusions and results on large scale as well as on small scale characterization (time dispersive and time variant nature of the channel). Large scale modeling was accomplished with the use of the log-distance model. As far as the time dispersive nature of the channel is concerned, the study focuses on the Power Delay Profile (PDP). A simple methodology for predicting the delays of possible incoming signal echoes is also included. Moreover, mean excess delay and rms delay spread were calculated and empirical cumulative density functions of these quantities for each group were estimated. Finally the envelope distribution for each identified path (direct or not) was estimated. Results on the average estimated K-factor for various types of environment are also presented.

Short-term wind speed forecasting model based on ANN with statistical feature parameters

The intermittent and unstable nature of wind raises significant challenges for the operation of wind power systems, either residential installations or utility-scale implementations, necessitating the development of reliable and accurate wind power forecasting techniques. Given that wind speed forecasting is typically considered the intermediate step for wind power forecasting, the present work proposes a novel short-term wind speed forecasting model based on an artificial neural network (ANN), with the key characteristic that statistical feature parameters of wind speed, wind direction and ambient temperature are employed in order to reduce the input vector and thus the complexity of the model. The results obtained indicate that the proposed model strikes a reasonable balance between accuracy and computational requirements for a forecasting time horizon of 24 hours, providing a light-weight solution that can be integrated as part of energy management systems for small scale applications.

Cost-Efficient WIMAX Network Deployment: The Hybrid Outdoor / Indoor Dual-Layer Coverage Approach

The process of WIMAX radio network design and deployment is greatly affected by the nature of the customer premises equipment and the intended access service, which may be fixed, nomadic or indoor. This paper advances network design methodologies, traditionally used for fixed access, in the scope of hybrid fixed outdoor / indoor-nomadic networks. With the main objective being performance, time-to-market and cost optimisation, a dual layer outdoor / indoor coverage deployment is proposed which allows for co-existence and performance balancing of different customer profiles. By comparing to purely outdoor or indoor deployments, this approach provides benefits, both in terms of equipment reduction and spectrum usage and optimises the deployment costs, especially in the initial phases of the network. This approach is applicable both for OFDM and future OFDMA systems.

A Survey of IoT Key Enabling and Future Technologies: 5G, Mobile IoT, Sematic Web and Applications

The Internet of Things (IoT) is the communications paradigm that can provide the potential of ultimate communication. The IoT paradigm describes communication not only human to human (H2H) but also machine to machine (M2M) without the need of human interference. In this paper, we examine, review and present the current IoT technologies starting from the physical layer to the application and data layer. Additionally, we focus on future IoT key enabling technologies like the new fifth generation (5G) networks and Semantic Web. Finally, we present main IoT application domains like smart cities, transportation, logistics, and healthcare.

Adaptive TDD Synchronisation for WIMAX Access Networks

In adaptive time division duplex (ATDD) wireless systems, severe co-channel interference conditions can occur if the movable downlink/uplink (UL) TDD boundary is not synchronised among all frames in base stations. To reduce interference outage and to improve a systems spectral efficiency, a new single frequency cell (SFC) network architecture is proposed, which allows for distributed boundary synchronisation (DBS) via inter-sector signalling. SFC-DBS dynamically synchronises TDD boundaries among neighbouring sectors for each frame, thus avoiding sector-to-sector interference, while preserving the ATDD radio resource assignment efficiency. Analysis shows that SFC-DBS achieves an additional 6–11 dB in the average UL signal-to-interference ratio, compared with existing channel assignment schemes, which corresponds to 25–50 % capacity gain subject to traffic asymmetry in different sectors. More importantly, the proposed SFC scheme does not incur any further cost in the frequency planning, whereas the DBS scheme requires only minor system modifications. Compared with interference cancellation via antenna arrays and beamforming, SFC-DBS achieves similar performance, albeit without the cost for complex radio transceivers and multiple antenna elements.

Development and On-Field Testing of Low-Cost Portable System for Monitoring PM2.5 Concentrations

Recent developments in the field of low-cost sensors enable the design and implementation of compact, inexpensive and portable sensing units for air pollution monitoring with fine-detailed spatial and temporal resolution, in order to support applications of wider interest in the area of intelligent transportation systems (ITS). In this context, the present work advances the concept of developing a low-cost portable air pollution monitoring system (APMS) for measuring the concentrations of particulate matter (PM), in particular fine particles with a diameter of 2.5 μm or less (PM2.5). Specifically, this paper presents the on-field testing of the proposed low-cost APMS implementation using roadside measurements from a mobile laboratory equipped with a calibrated instrument as the basis of comparison and showcases its accuracy on characterizing the PM2.5 concentrations on 1 min resolution in an on-road trial. Moreover, it demonstrates the intended application of collecting fine-grained spatio-temporal PM2.5 profiles by mounting the developed APMS on an electric bike as a case study in the city of Mons, Belgium.

Cognitive Radio Engine Design for IoT Using Real-Coded Biogeography-Based Optimization and Fuzzy Decision Making

The Internet of Things (IoT) paradigm expands the current Internet and enables communication through machine to machine, while posing new challenges. Cognitive radio (CR) Systems have received much attention over the last decade, because of their ability to flexibly adapt their transmission parameters to their changing environment. Current technology trends are shifting to the adaptability of cognitive radio networks into IoT. The determination of the appropriate transmission parameters for a given wireless channel environment is the main feature of a cognitive radio engine. For wireless multicarrier transceivers, the problem becomes high dimensional due to the large number of decision variables required. Evolutionary algorithms are suitable techniques to solve the above-mentioned problem. In this paper, we design a CR engine for wireless multicarrier transceivers using real-coded biogeography-based optimization (RCBBO). The CR engine also uses a fuzzy decision maker for obtaining the best compromised solution. RCBBO uses a mutation operator in order to improve the diversity of the population and enhance the exploration ability of the original BBO algorithm. The simulation results show that the RCBBO driven CR engine can obtain better results than the original BBO and outperform results from the literature. Moreover, RCBBO is more efficient when applied to high-dimensional problems in cases of multicarrier system.