Dimitra Zarbouti

Subcarrier allocation algorithms for multicellular OFDMA networks without Channel State Information

Scope of this paper is to analyse four subcarrier allocation algorithms for multicellular OFDMA networks, namely coordinated, sequential, random and an innovative technique of cell splitting, that uses both random and coordinated subcarrier allocation. Common characteristic of these subcarrier allocation algorithms is that they do not require knowledge of channel state information (CSI) at the transmitter, a fact that leads to more efficient use of available bandwidth, lower algorithmic complexity and faster decision making. The algorithms are studied for an OFDMA multicellular network. Simulation results show that a multicellular OFDMA network is able to provide real broadband wireless access, with offered bit rate to reach 20 Mbps per cell, even without CSI knowledge.

OFDMA techniques in multicellular networks with total frequency reuse

Orthogonal frequency division multiple access (OFDMA) techniques are investigated in this paper. Five subchannel allocation algorithms are analysed and their performance in a multicellular environment is evaluated with simulations. Four schemes of lower complexity, suitable for the early deployment of wireless systems, are compared with a more computationally demanding scheme with respect to their blocking probability, loading factor and offered bit rate. The channel condition of each carrier is calculated and its knowledge is used for power controlled adaptive modulation, as an essential feature of the OFDMA technique. The general radio resource management process is divided into two steps: in the first step a base station allocates carriers to users while in the second step the modulation and power levels for each allocated carrier are defined. The simulation results demonstrate that a wireless system in its early deployment phase (up to 15-30% blocking probability) can employ simple OFDMA techniques capable of achieving high throughput. Furthermore, it is demonstrated that two of the proposed lower complexity schemes, (those based on cell coordination), offer good performance gain for higher data rate services. Nevertheless, these schemes achieve relatively lower gains with adaptive modulation, when compared with the techniques which exploit interference averaging or adaptive interference mitigation.

The Effective Radiation Pattern Concept for Realistic Performance Estimation of LTE Wireless Systems

Radio channels induce distortions to the radiation pattern of beamforming systems such as beam broadening as well as sidelobe level and null rising. If these effects are ignored, the system performance is overestimated. This paper proposes the simple concept of an effective radiation pattern (ERP) calculated by optimally fitting the “real-world” radiation pattern to the ERP. The proposed ERP method is incorporated into a multicell bad urban 4G LTE operational scenario which employs beamforming for both the BSs and the RNs. The performed simulations provide evidence that the ideal instead of the real radiation pattern overestimates the SIR and capacity by almost 3 dB and 13 Mbps, respectively, for the reference scenario without RNs. It also proves that the ERP method produces almost identical performance results with the real radiation pattern, and hence it is a simple and viable option for realistic performance analysis. Finally, the network performance is studied as a function of the number of RNs with the help of the ERP method. Results show that a beamforming LTE network with RNs that also employ beamforming provides 3 dB SIR gain with the addition of 1 RN per cell and 15 dB gain with 4 RNs per cell.

DVB-T Network Planning: A Case Study for Greece

Terrestrial digital video broadcasting (DVB-T) network planning is the main interest of this article, along with a case study for Greece. The basic principles and the guidelines of the DVB-T planning process are presented, in conjunction with their application to the establishment of the Greek DVB-T allotment plan. The procedures described in this article were followed by the authors during the International Telecommunication Union (ITU) DVB-T planning project that concluded with the ITUs Regional Radiocommunication Conference 2006 (RRC-06), and the Geneva (GE-06) frequency plan for terrestrial digital radio broadcasting.

Fairness and Throughput Trade-Off Analysis for UMTS WCDMA Network Planning

The issue of fairness and throughput trade-off in universal mobile telecommunications system network planning based on wideband code division multiple access is discussed in this paper. The employed radio resource management (RRM) fully supports rate adaptation and hence, new potentials arise in terms of system throughput and fairness. The authors study four low complexity RRM algorithms that perform efficient rate adaptation in order to resolve typical operational bottlenecks that occur in a network environment (overloading, connection failure, etc.). Furthermore, a new hybrid approach that builds upon the aforementioned strategies is introduced. The results presented in the paper show that this technique enables the control of network performance towards throughput and fairness, according to the operational requirements in cellular and/or network level. Finally, random beamforming options are explored in the same context, and the respective results show that this technique penalizes users with good channel quality, thus providing higher system fairness.

Performance Evaluation of OFDMA RRM Algorithms with Spectrum Reuse 1

The scope of this paper is the presentation of simulation results concerning the performance of an OFDMA cellular system. Three different RRM (radio resource management) algorithms are applied on an OFDMA system with omni-directional antennas. The magnitude of comparison was achievable total data rate in downlink. Since users are considered to request various bit rates (BR), their spatial distribution according to the requested BR is also investigated. Finally, an insight on how these algorithms handle users of different requested rates is presented.

Basestation antenna pattern reconfiguration for minimum transmit power network planning

Optimization of basestation antenna patterns and transmitted powers in heterogeneous 4g networks with geographically inhomogeneous throughput requirements is not an easy problem to tackle, and hence, frequently omitted. Moreover, the initial phase of network dimensioning and planning often fails to meet growing throughput demands, and hence, network operation becomes problematic, especially around hotspots. This paper formulates the coverage and capacity optimization problem in the context of 4g systems and uses a multi-objective genetic algorithm in order to optimize the basestation antenna patterns with respect to their pointing direction, 3dB beamwidth and transmitted power. The proposed optimization algorithm is then applied to provide the most energy efficient network setup in a test scenario with varying area capacity requirements. It is shown that the reconfigured network setups featured neatly adjusted radiation patterns, increase capacity capabilities while reducing network cost and energy consumption and, most importantly, improve safety with regards to reduced power emissions.

Performance of Vehicular Nomadic Node Operation in Realistic Multicellular Wireless Networks

The need for 5G to adapt the radio access network to the spatial and temporal traffic variations makes the paradigm of moving networks essential. Dynamic network topology and moving cells through vehicular nomadic nodes (NN) will provide coverage extension and capacity improvement on demand as well as achieve reduced capital and operational expenditure when compared to fixed node deployment, such as microcells. Thus, it is of great importance to validate the envisioned performance of this paradigm change in a realistic scenario. To this end, this paper investigates the performance of NN operation in the context of a realistic multicellular wireless network, with the help of site-specific propagation modelling and real geographical databases. The results show that the NN operation can provide clear improvements relative to macrocell-only deployment and also propose the best values for the key systemic parameters that offer the optimum trade-off between throughput and complexity.

Wireless channel capacity estimation in the THz band

Carrier frequencies beyond 300 GHz have recently received attention primarily due to the potential for impressive capacity for future multi-gigabit wireless communication systems. In this context, this paper considers the different attenuation factors at the THz band and estimates the available bandwidth and the corresponding maximum data rate in the THz band. Results show that capacity values beyond 1Tbps can be achieved under certain conditions for the transmitted power, antenna gains and weather conditions.

An Arduino-based subsystem for controlling UAVs through GSM

Long distance and beyond sight of view communication between a ground control station and an Unmanned Aerial Vehicle (UAV) is mainly achieved using high-gain antennas, antenna trackers or satellites. These implementations demand expensive, heavy and not easily deployed equipment, while in many cases cannot provide a sufficient communication range. The current work proposes and demonstrates a lightweight and low-cost Arduino-based telecommunication subsystem that is capable of sending control commands to the UAV based on GSM or GPRS the most widely deployed cellular networks standard. During field trials control commands successfully transferred from a mobile phone as well as a laptop to the UAV autopilot, with an average time of 2.6 sec and 0.5 sec respectively. The proposed subsystem can be embedded independently or coexist with other control systems, contributing to a ubiquitous UAVs management system.