Helmut Kellermann

Angle-Dependent Path Loss Measurements Impacted by Car Body Attenuation in 2.45 Ghz ISM Band

In the past few years more and more wireless applications (e.g. WLAN and Bluetooth) have migrated into the automotive domain. With the increasing number of devices, coexistence investigations in the 2.45 GHz ISM band are gaining importance to enable reliable communications with real time requirements like voice transmission and streaming applications. This paper presents initial results on angle dependent path loss measurements impacted by the influence of a car body on electro-magnetic wave propagation. To this effect, a measurement methodology was developed to gather the attenuation effects of the car according to different antenna positions and measurement angles. Various kinds of attenuation measurements were performed. Vehicle shell attenuation measurements were transformed into angular-dependent path loss metrics and related to vehicle-specific attenuation properties like window inserts, roof columns, trunk or engine hood. Focus of attention was drawn to free space attenuation and intra-vehicle attenuation measurements.

Analysis of Medium Access Protocols for Power Line Communication Realizing In-Car Networks

The number of electronic control units in todays vehicles is permanently increasing. The complexity of the in-car communication also increases because of the growing demand for information exchange. In the past decades rising demands have been countered with adding bus-segments. In order to reduce the complexity and the costs for the future in-car communication infrastructure, power line communication (PLC) provides an alternative. In this paper, we focus on PLC which can reduce the cabling to a minimum. After summarizing the requirements for future in-car systems, the HomePlug Green PHY standard, originally designed for Smart Grid applications, is analyzed according to its applicability to the in-car communication. Due to the availability of standard components, also cost reasons motivate the use of the HomePlug Green PHY standard. To cope with the small message size of in-car communication, we propose a concept for data transfer inside the Frame Control to reduce protocol overhead. In addition to CSMA/CA based medium access, we evaluate and compare two further collision-free variants requiring only slight protocol modifications. As one evaluation result, a priority-based access scheme shows the most promising results.

Priority-based energy-efficient MAC protocols for the in-car power line communication

An increasing number of electronic control units in todays vehicles leads to rising communication demands. So far, growing demands were countered with adding additional communication buses at the cost of vastly increasing complexity. One possibility to reduce complexity and costs for the future in-car communication infrastructure is the usage of Power Line Communication (PLC). PLC reduces the cabling to the minimum - the power lines. In this paper, after summarizing main requirements for future in-car communication systems, a recently proposed medium access protocol based on the HomePlug and IEEE 1901 standard is discussed. The protocol is based on unique message priorities and shows good performance regarding throughput and flexibility. In order to decrease the energy consumption, in this paper further new protocol variants are evaluated and compared with the pure priority-based medium access protocol. For the comparison, effects on throughput, delay and loss in flexibility are taken into account. As a result, a combination of rotating prefix and additional pending frame indication slot is found most promising.