Christian Schwingenschlögl

Performance Analysis of the Real-time Capabilities of Coordinated Centralized Scheduling in 802.16 Mesh Mode

The IEEE 802.16-2004 standard specifies wireless broadband networks with optional support for multi-hop mesh operation (mesh mode). The provision and support of high-quality real-time services such as voice over IP is crucial, if wireless networks based on the IEEE 802.16-2004 standard are to challenge wired network services. In this paper we investigate and identify critical factors in enabling real-time services in 802.16 based networks operating in the mesh mode. We present an analytical performance analysis and a simulation study investigating the coordinated centralized scheduling mechanism as specified in the 802.16-2004 standard. Our results show that the scalability and efficiency of such mesh networks with respect to real-time services are at stake. Our results, moreover, aid in the adjustment of critical system parameters allowing for optimized network performance

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.

Reliable Broadcast Mechanism for the IEEE 802.16 Mesh Extension

The simultaneous transmission of data messages to a group of neighbors forms the basis for many essential services in wireless ad hoc and mesh networks, for example to communicate link status information or to assist route discovery. Despite the fact that communication on a wireless medium is inherently of broadcast nature, there exist situations, where data broadcasting is non-trivial. In particular, reservation-based medium access control (MAC) schemes such as employed in the optional mesh mode of the IEEE 802.16 standard are optimized with respect to maximizing the number of concurrent unicast transmissions. While broadcast control messages are supported in the standard, no mechanisms are specified to efficiently and reliably schedule broadcast data messages. We present an extension to the IEEE 802.16 standard, which enables a reliable, reservation-based broadcast method for usage within the mesh mode. We thoroughly analyze the performance of our mechanism vs. broadcast as unicast - currently the only feasible method to deliver broadcast data according to the standard. Our results indicate the superior performance of our scheme, i.e. a significant gain in broadcast efficiency as well as in broadcast reliability.

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.