Michael Bahr

Update on the Hybrid Wireless Mesh Protocol of IEEE 802.11s

HWMP, the default routing protocol of IEEE 802.11s has been revised during the comment resolution of the first letter ballot. The paper gives an update on three areas where major changes have been introduced to HWMP: support for interworking with other networks; revised concept for proactive routing trees to root MPs; and a better aligned extensible path selection framework.

An Inter-MAC architecture for heterogeneous gigabit home networks

The home network of the near future will be a heterogeneous broadband network supporting the use of wired as well as wireless transmission technologies. The variety of services will range from HDTV via gaming to emergency services in the telemedicine area. In this paper, we introduce a technology-independent protocol layer called Inter-MAC which provides a common infrastructure to all home networking devices. The Inter-MAC can establish a connection via different transmission technologies while ensuring appropriate QoS. Key to this is the capability to correctly interpret technology-dependent PHY and MAC parameters for determining QoS when selecting initial and alternative paths, as well as the feature of admission control. Our simulations indicate clearly that the Inter-MAC approach can cope with varying loads, for instance, the time the jitter needed to stabilize was as short as 4 s. The reduced QoS was not noticeable by the user since the jitter introduced by handling additional HDTV flows was less than 0.2 ms for the existing and less than 0.7 ms for the new flow.

Simulative analysis of the Hybrid Wireless Mesh Protocol (HWMP)

Within the last few years, prevalence and importance of wireless networks increased significantly. Especially, wireless mesh networks received a lot of attention in both academic research and commercial deployments. Wireless mesh networks are characterized by wireless multi-hop connectivity and facilitate a simple and cost-effective establishment of wireless networks while providing large coverage areas. The ongoing standardization of IEEE 802.11s WLAN Mesh Networking defines the Hybrid Wireless Mesh Protocol (HWMP) for link layer path selection. This protocol offers various modes of operation that are suitable for different environments. In this paper, a detailed simulative evaluation of these modes allows for conclusions about their performance and suitability for specific environments.

Intra-Mesh Congestion Control for IEEE 802.11s Wireless Mesh Networks

Wireless mesh networks (WMNs) are a convenient type of Internet access networks, because they are self-configuring and self-healing wireless multi-hop networks. This is in particular true for IEEE 802.11 based WMNs as they cover large areas, are easy and cheap to setup, and provide sufficient capacity. Despite these advantages, WMNs have not yet entered the mass market. One of the reasons for this is, that many existing WLAN mesh networks use their own specific combination of higher layer protocols and IEEE 802.11 MAC extensions what makes it hard to characterize their performance and to provide interoperability. The recently published IEEE 802.11s-2011 standard addresses this issue by introducing standardized MAC layer mechanisms for WLAN mesh networking. One of these mechanisms is the IEEE 802.11s intra-mesh congestion control (IMCC) framework which addresses one of the key challenges in contention-based WMNs, namely congestion on the wireless medium. In this paper we quantify the benefits of this framework by introducing and evaluating three IEEE 802.11s-compliant IMCC algorithms. An extensive simulation study reveals that in dependence on the different levels of complexity of the algorithms-node-specific (TCC), link-specific (LSCC), or path-specific (PSCC)-the network performance in terms of throughput and fairness can be significantly improved.

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.