Johannes Hund

Overview of MAC layer enhancements for IEEE 802.15.4a

Ultra wideband impulse radio (IR-UWB) based on the IEEE 802.15.4a PHY standard offers unique features which are exploitable in MAC designs for wireless personal area networks (WPANs) and wireless sensor networks (WSNs) to improve performance and robustness. To achieve this, different strategies of cross-layer optimizations to the IEEE 802.15.4 MAC using features of UWB have been proposed. This paper compares current approaches and exposes individual advantages and disadvantages regarding energy efficiency and positioning.

Toward the Web of Things: Applying Web Technologies to the Physical World

Just as Internet connectivity has enabled intuitive information sharing and interaction through the Web, so the Internet of Things might be the basis for the Web of Things, enabling equally simple interaction among devices, systems, users, and applications.

Evaluation and optimization of robustness in the IEEE 802.15.4a standard

In this paper, we introduce ways to improve the robustness by lowering the packet loss rates of transmissions using ultra-wideband impulse radio (UWB-IR). It has been shown that the packet loss rate caused by erroneous synchronization can be tremendously decreased compared to the preamble specified in the standard IEEE 802.15.4a by our approach. These improvements are particularly intended for low-power, low-complexity transceivers operating in environments with harsh multi path propagation and high noise levels, such as industrial control. These improvements include novel ways for receiver implementation to reduce detection errors for low-power energy detection receivers with slow sampling rates. We also introduce a modified preamble that significantly reduces packet loss caused by failed preamble synchronizations We evaluate our improvements by simulation. Our approach to receiver implementation enables receiver to achieve the same packet loss rate at a signal-to-noise ratio (SNR) 10 dB lower than traditional receiver designs.

Extension of IEEE 802.15.4a to improve resilience for wireless automation using soft-bit combination

Ultra-Wideband Impulse Radio is a promising technology for industrial automation applications because of its inherent multipath robustness and coexistence features. In our efforts to deploy UWB-IR for industrial automation, we use an adapted version of the IEEE 802.15.4a PHY. In this paper, we present a way to improve robustness for low-latency sensor-actor networks with short cyclic packets of process data, as found in industrial control applications. Due to the low cycle times of the wireless network, which can be shorter than the application cycle, soft-bit combinations across multiple repetitions of a packet can be used to collect enough information to recover packets that would not be decodable by a single transmission. To determine if a packet is a repetition or contains different data than the last transmission, a change indicator is inserted into the packet by the sender. The findings are proven by simulation against IEEE industrial channel models and show a significant improvement.

A packet-level adaptive forward error correction scheme for wireless networks

Especially for synchronization-critical wireless networks like ultrawideband impulse radio (UWB-IR), data packets are lost not only due to single bit errors in the payload but also to a large degree because of synchronization errors or preamble failures. Current FEC codes only address bit errors inside a packet. Packets that are lost because of errors in preambles or headers can only be recovered on packet level. In this Paper we propose a low-complexity adaptive packet-level FEC and prove by simulation that it can reduce packet loss with very small overhead.

Exploiting Short MAC Superframe Cycles for Fast Bit Synchronization in IEEE 802.15.4 UWB-IR

Ultra-Wideband Impulse Radio is a promising technology for industrial automation applications due to its inherent multipath robustness and coexistence features. The ultra-wideband impulse radio PHY standardized in IEEE 802.15.4, however, is optimized for low duty cycles and not optimized for real-time communication. Especially the long preambles that are needed for synchronization cause a large overhead that might not be necessary in systems with a high duty cycle. We propose an efficient synchronization scheme, which is a cross-layer improvement and which combines this PHY layer with a MAC layer for wireless real-time communication in low latency deterministic networks based on draft IEEE 802.15.4e. This scheme splits synchronization into a network-wide frame synchronization via a broadcast beacon with a standard preamble and bit-level synchronization using just very short preambles per data frame. To achieve this, we exploit the short communication cycles and the centralized communication flow common in factory automation networks. We present and discuss simulation results of our proposed scheme that verify its higher efficiency.