Markus Putzke

Performance evaluation of time-critical communication networks for Smart Grids based on IEC 61850

Driven by the increasing application of Smart Grid technologies in todays power systems, communication networks are becoming more and more important for exchanging monitoring, control and protection information on local and wide area level. For communication the IEC 61850 standard is a candidate for the Smart Grid and has been introduced for Substation Automation Systems (SAS) some years ago. IEC 61850 provides interoperability among various manufactures and enables systemwide communication between intelligent components of future power systems. However, as IEC 61850 addresses Ethernet (ISO/IEC 8802-3 family) as network technology, especially high performance aspects of Ethernet have become increasingly important for time-critical communication within substation automation systems. In this paper we introduce the generic architecture of IEC 61850 and present our modelling approach for evaluating high performance and real-time capability of communication technologies for future smart grid application. First, we give a short overview of the IEC 61850 protocol and present communication flows in substation automation systems according to the standard. Here we focus on substation automation at bay level, located inside an exemplary substation node taken from the IEEE 39-bus power system network. Afterwards we demonstrate our modeling approach for communication networks based on IEC 61850. For performance evaluation we developed a simulation model along with an analytical approach on basis of Network Calculus, enabling to identify worst case boundaries for intra-substation communication. Finally results for simulative and analytical modelling are provided and cross validated for two bay level scenarios, showing the applicability of Network Calculus for real-time constrained smart grid communication.

Influence of M2M communication on the physical resource utilization of LTE

The number of Machine-to-Machine (M2M) applications is rapidly increasing in cellular communication systems. In order to ensure a maximum system capacity, the impact of this special kind of traffic on common Human-to-Human (H2H) communication needs to be analyzed. In this paper, a system model for performance evaluation of cellular networks like Long Term Evolution (LTE) in the presence of M2M communication and under different Quality of Service (QoS) constraints is presented. By means of a Markovian model, which is parameterized by laboratory measurements and ray tracing simulations, an estimation of the behavior of LTE for different traffic characteristics is shown. We present blocking probabilities for an LTE network with heterogeneous M2M and H2H traffic and compare different transmission strategies for M2M communication to minimize the impact on human users. The results show that particularly a large number of devices with a low data rate influences the utilization of an LTE cell very negatively.

Channel sensitive transmission scheme for V2I-based Floating Car Data collection via LTE

In this paper, we present a channel sensitive transmission scheme which reduces the negative impact of Vehicle-to-Infrastructure (V2I) traffic on the Quality of Services (QoS) of Human to Human (H2H) communication in cellular networks. The performance evaluation of Long Term Evolution (LTE) for different traffic characteristics is based on an introduced Markovian model. This describes the utilization of the shared LTE Resource Blocks (RBs). The model is parameterized by laboratory measurements and ray tracing simulations. We present blocking probabilities for an LTE network with heterogeneous V2I and H2H traffic and propose different transmission strategies for V2I data with the goal to minimize the impact on human users. The results show that the number of V2I devices can be doubled by using channel sensitive transmission schemes ensuring equal QoS for H2H communication compared to periodically data transmission.

Performance analysis of radio propagation models for Smart Grid applications

Realizing future Smart Grid applications highly depend on the communication technologies being used. For this purpose, an ubiquitous communication infrastructure is essential, providing real time communication and reliable connectivity to Smart Grid components. Especially nowadays wireless radio networks offer a cost-efficient, reliable and well-engineered solution. In this paper we present a performance analysis based on a comparison of analytic channel models and Ray Tracing simulations for wireless digital cellular networks with respect to actual Smart Grid deployment scenarios. Both methods are applied especially under consideration of a typical outdoor-to-indoor transition models. Based upon these results a coverage analysis for wireless digital cellular networks (e.g. GSM or UMTS) is shown considering different Smart Metering and energy management application scenarios including position-based radio characteristics, like basement, indoor and outdoor installations. The network topology is described using a simulation environment including various analytic models in order to analyze the capacity of the transmission technology in real-world scenarios. Our analysis shows the impact on the path loss, caused by frequencies, geographical position and indoor deployment, which leads to an additional deviation up to 25 dB.

Three dimensional channel characterization for low altitude aerial vehicles

Based on the recent developments in the area of lithium polymer batteries and carbon fiber-reinforced plastic materials Micro Unmanned Aerial Vehicles (MUAV) have significantly gained in importance. Therefore, the use of MUAV based swarms is a feasible approach for remote sensing, surveillance and in particular for emergency and rescue missions [1][2]. Developing MUAVs which operate at low altitudes opens a new and challenging use case for both aerial mesh networks and existing cellular networks. The channel characteristics are crucial for the design of the required communication system. Since channel models for cellular networks typically assume that the users are at ground level, the use of these models for aerial deployment is a questionable attempt. For this reason, we are focusing in this paper on the channel characterization and analysis of an aerial mesh network based on a MUAV swarms. A choice of well known analytical and empirical channel models are adapted to the boundary conditions of low altitude platforms and subsequently validated by raytracing measurements in order to state their applicability.

Self-organizing OFDMA systems by random frequency hopping

This paper analyzes the use of Random Frequency Hopping to enable self-organizing Orthogonal Frequency Division Multiple Access systems (RFH-OFDMA). While LTE (Long Term Evolution) macrocell resource planning is typically based on centralized planning of orthogonal deterministic frequency hopping patterns, the integration of femtocells located within macrocells introduces either complex planning efforts or uncontrolled interference issues. The results presented in this paper show that random frequency hopping is a new effective way to reduce interference for the integration of femtocells without resource planning into macrocells. An analytical model for the SINR (Signal-to-Interference-and-Noise Ratio) and a simulation model for the BER (Bit Error Rate) are presented for interfering RFH-OFDMA systems. All OFDMA parameters can be freely selected in time and frequency in the model, enabling to dimension systems with minimal interference. Based on the analytical model, a performance evaluation is presented, which uses typical LTE parameters. Compared to the performance of systems without resource planning and random frequency hopping, a significant gain is achieved for self-organizing RFH-OFDMA systems with respect to the SINR and BER.

Self-organizing fractional frequency reuse for femtocells using adaptive frequency hopping

In this paper, an adaptive and self-organizing spectrum allocation policy for ad hoc femtocells in two-tier networks based on usage of random frequency hopping is presented. As femto- and macrocells normally share the same frequency resources, the proposed approach is able to minimize InterCell Interference (ICI) in an adaptive manner. Each femto- and macrocell user chooses random carrier frequencies for transmission corresponding to a given probability density function (pdf). If the level of interference reaches a certain limit, which is typically the case for femtocell edge users, the probability density function of the carrier frequencies is changed in a way that it is quasi-orthogonal to the one of the macrocell users nearby. The changeover point between different probability density functions is realized in a self-organizing manner regarding the detected level of interference. Hence, the approach is able to adjust the trade-off between spectral efficiency and introduced interference during operation. We present analytical models for the Signal-to-Interference-and-Noise-Ratio (SINR), the Bit Error Ratio (BER) and the required transmission power of Orthogonal Frequency Division Multiple Access (OFDMA) femtocells applying adaptive random frequency hopping. The mobile radio channel is characterized by non-frequency selective Rayleigh fading and all results are verified by simulations implemented in MATLAB. In order to evaluate the improvements, the results are compared to systems using centralized orthogonal planning, systems using neither centralized nor distributed planning, and systems using static random frequency hopping. The comparison shows that adaptive random frequency hopping is capable of reducing the BER by a factor of 15 and the transmission power of femtocells by 17 dBm compared to systems where the macrocell user transmits in the same subbands as the femtocell user.

Traffic engineering analysis of Smart Grid services in cellular networks

This paper presents analytical and simulative traffic engineering models for Smart Grid communication processes in cellular networks. In order to dimension ICT networks for a decentralized and automated Smart Grid infrastructure, a detailed analysis of the expected data volume and required data rate for Smart Metering Services, Demand and Supply Side Management as well as Monitoring Services is needed. Based upon different wireless infrastructure scenarios applying different technology approaches, a comparison between traffic models using stochastic and deterministic inter-arrival times is presented. In order to validate the usability and capability of the proposed stochastic and deterministic models, analytical and simulative methods are compared. The stochastic method is based on a multidimensional Markovian model, whereas the deterministic system is described by a novel analytical approach based on the Network Calculus. The results show different key performance indicators of wireless technology approaches using GPRS, UMTS and LTE within different traffic scenarios and reflect the expected Smart Grid traffic volume, which needs to be taken into account for future network deployments. The performed analysis determines the impact of the Smart Grid services on common speech and data traffic in cellular networks as well as the expected influence of additional network load caused by Smart Grid applications.

Coexistence of 802.11b and 802.15.4a-CSS: Measurements, Analytical Model and Simulation

IEEE 802.15.4a Wireless Sensor Networks (WSN) and IEEE 802.11b Wi-Fi networks are operating in the 2.4GHz band. In order to examine co-channel interference scenarios and the impact on key performance indicators, this paper combines an analytical model, measurements and simulations. It is a pilot study which reflects the interference caused by the new IEEE 802.15.4a-CSS (Chirp Spread Spectrum). An analytical model for adaptive bitrate adjustment and throughput optimization reflects the performance impact and the system behaviour of IEEE 802.11b. Measurements are used for model validation before simulation results show the system behaviour for changing node constellations, radio conditions and system setups. The validated simulation model is then applied to a use case scenario for indoor localization, which shows the impact on the performance of a realistic co-existence scenario.

Self-organizing ad hoc femtocells for cell outage compensation using random frequency hopping

This paper analyzes self-organization of ad hoc femtocells within a macrocell infrastructure by using random frequency hopping. Femtocell users select their frequency subbands randomly, so that corresponding femtocells are capable of integrating themselves into macrocells without any exchange of information. No sensing equipment is required in femtocell devices and no time is consumed for self-organization. This makes random frequency hopping highly attractive as a self-organization policy in outage situations, i.e. where macrocell base stations fail and immediate coverage has to be provided by femtocells. We present an exact analytical model for the Bit Error Rate (BER) of femtocell users and access points using random frequency hopping, based on Signal to Interference and Noise Ratio (SINR) and Laplace transform techniques. Moreover, for performance evaluation, the model is applied to frequency-nonselective and frequency-selective channels and is verified by simulations implemented in MATLAB. The results of random frequency hopping are compared to classical resource planning with orthogonal patterns and to systems without resource planning. It is shown that random frequency hopping introduces a reduction of the BER up to a factor of 7 compared to systems where the interferer is transmitting in the same subband as the femtocell user.