Driven by the increasing application of Smart Grid technologies in today's 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.

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.

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.

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.

IEEE 802.15.4a Wireless Sensor Networks (WSN) and IEEE 802.11b Wi-Fi networks are operating in the 2.4 GHz 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.