WLAN mesh networks are one of the key technologies for upcoming smart city applications and are characterized by a flexible and low-cost deployment. The standard amendment IEEE 802.11s introduces ...low-level mesh interoperability at the WLAN MAC layer. However, scalability limitations imposed by management traffic overhead, routing delays, medium contention, and interference are common issues in wireless mesh networks and also apply to IEEE 802.11s networks. Possible solutions proposed in the literature recommend a divide-and-conquer scheme that partitions the network into clusters and forms smaller collision and broadcast domains by assigning orthogonal channels. We present CHaChA (Clustering Heuristic and Channel Assignment), a distributed cross-layer approach for cluster formation and channel assignment that directly integrates the default IEEE 802.11s mesh protocol information and operating modes, retaining unrestricted compliance to the WLAN standard. Our concept proposes further mechanisms for dynamic cluster adaptation, including subsequent cluster joining, isolation and fault detection, and node roaming for cluster balancing. The practical performance of CHaChA is demonstrated in a real-world 802.11s testbed. We first investigate clustering reproducibility, duration, and communication overhead in static network scenarios of different sizes. We then validate our concepts for dynamic cluster adaptation, considering topology changes that are likely to occur during long-term network operation and maintenance.
The aim of design space exploration (DSE) is to identify implementations with optimal quality characteristics which simultaneously satisfy all imposed design constraints. Hence, besides searching for ...new solutions, a quality evaluation has to be performed for each design point. This process is typically very expensive and takes a majority of the exploration time. As nearly all the explored design points are sub-optimal, most of them get discarded after evaluation. However, evaluating a solution takes virtually the same amount of time for both good and bad ones. That way, a huge amount of computing power is literally wasted. In this paper, we propose a solution to the aforementioned problem by integrating efficient approximations in the background of a DSE engine in order to allow an initial evaluation of each solution. Only if the approximated quality indicates a promising candidate, the time-consuming exact evaluation is executed. The novelty of our approach is that (1) although the evaluation process is accelerated by using approximations, we do not forfeit the quality of the acquired solutions and (2) the integration in a background theory allows sophisticated reasoning techniques to prune the search space with the help of the approximation results. We have conducted an experimental evaluation of our approach by investigating the dependency of the accuracy of used approximations on the performance gain. Based on 120 electronic system level problem instances, we show that our approach is able to increase the overall exploration coverage by up to six times compared to a conservative DSE whenever accurate approximation functions are available.
Piecewise linear approximation of sensor signals is a well-known technique in the fields of Data Mining and Activity Recognition. In this context, several algorithms have been developed, some of them ...with the purpose to be performed on resource constrained microcontroller architectures of wireless sensor nodes. While microcontrollers are usually constrained in computational power and memory resources, all state-of-the-art piecewise linear approximation techniques either need to buffer sensor data or have an execution time depending on the segment's length. In the paper at hand, we propose a novel piecewise linear approximation algorithm, with a constant computational complexity as well as a constant memory complexity. Our proposed algorithm's worst-case execution time is one to three orders of magnitude smaller and its average execution time is three to seventy times smaller compared to the state-of-the-art Piecewise Linear Approximation (PLA) algorithms in our experiments. In our evaluations, we show that our algorithm is time and memory efficient without sacrificing the approximation quality compared to other state-of-the-art piecewise linear approximation techniques, while providing a maximum error guarantee per segment, a small parameter space of only one parameter, and a maximum latency of one sample period plus its worst-case execution time.
IEEE 802.11s introduces MAC-layer extensions to enable vendor-independent and inter-operable WLAN mesh networks. Featuring automatic device interconnection and routing, 802.11s networks provide a ...higher scalability, flexibility, and robustness compared to common centralized WLAN infrastructures. As logical Peer-to-Peer (P2P) networks exhibit many of the characteristics of physical WLAN mesh networks on the application layer, it is obvious to consider solutions where both technologies interact to leverage robust distributed wireless applications, such as collaborative data distribution and synchronization in future smart cities. Envisioned scenarios include the administration and update deployment to specific device groups or the distributed caching and delivery of on-demand multi-media content to selected end points within a city-area wireless mesh network. Nevertheless, common P2P protocols, such as BitTorrent (BT), do not consider the structure of the physical underlay as they were primarily designed to be used over wired communication networks, such as large parts of the Internet. Hence, the default BT peer selection mechanism does not adapt to the network topology and varying medium utilization in wireless multi-hop networks. We present MeNTor, a set of optimizations to enable underlay-aware BT peer selection in WLAN mesh networks. It relies on cross-layer integration of default 802.11s information, only requiring minor extension of the BT application layer without introducing any MAC-layer modifications or traffic overhead. Our solution was evaluated in a 25-node real-world mesh test bed, using 10 different seed/leecher placements and comparing 18 parameter combination variants of MeNTor. Results show that average download times can be reduced by 30–40%, depending on the seed/leecher placement and parameter combination variant. Finally, we recommend the variant that performed best across all scenarios as prospective default configuration.
WLAN mesh networks are one of the key technologies for upcoming smart city applications and characterized by a flexible and low-cost deployment. The amendment IEEE 802.11s introduces low-level mesh ...interoperability at the WLAN MAC layer. On the physical layer, IEEE 802.11n introduced major improvements such as HT data rates, MIMO techniques, and frame aggregation. However, building large-scale 802.11n/s testbeds and reproducible setups is challenging and costly. On the other hand, existing attempts for down-scaling real-world setups are limited to works without support for 802.11n and 802.11s. We therefore present Mini-Mesh, a miniaturized indoor 802.11n/s testbed. Following a transmission range scaling approach, we deploy a 6×6-node mesh grid on an area of only 1 m 2 . We validate the applicability of our method via comparative measurements, exhibiting a deviation of less than 6 % between a scaled indoor and unscaled outdoor setup. Based on these results, we parameterize a path loss model helping us to estimate outdoor dimensions for arbitrary indoor mesh topologies.
The new standard IEEE 802.11s enables vendor-independent wireless mesh networks based on the 802.11 WLAN technology. Transmission Control Protocol (TCP) is the most widespread transport protocol for ...reliable data delivery and still the basis for many network applications. TCP supports different mechanisms for flow and congestion control. However, designed for wired networks, it does not consider the dynamics of wireless networks and especially multi-hop wireless mesh networks. In addition, 802.11s provides own mechanisms such as Automatic Repeat Request (ARQ) for frame retransmissions to hide wireless loss from the upper layers. Being transparent to each other, retransmission schemes on both layers may interfere and operate redundantly, if not properly adjusted. We study the effects of ARQ retry limit variation on TCP throughput in a real-world multi-hop 802.11s test bed. As a result, we suggest ARQ adaptation based on the 802.11s standard's Airtime Link Metric (ALM) for path selection, serving as indicator for overall frame travel time. Our proposed approach solely relies on standard features and imposes no modifications to 802.11s or TCP.
The growing capabilities of wireless communication technologies such as WLAN-based systems enable their successful adoption in an ever-increasing range of applications. Particularly in the domain of ...the internet of things, the trend towards wireless interconnection is driven by its improved scalability and flexible, low-cost deployment compared to wired systems such as Ethernet. To handle the growing complexity of their design, developers need a process for early performance evaluation of these communication-intensive networked embedded systems. For this, established network simulation frameworks like ns-3 and {OMNeT}++ are often utilized. These frameworks require developers to model every part of their system, including the protocol stack and the target application they are developing. From the developers' perspective, a workflow that would enable them to use real target software as much as possible is desirable. The available solutions to couple real target software with a network simulation, however, often exhibit several limitations. These range from a lacking detail level of the channel simulation to the requirement of access to the source code of every part of the system under design, and often prevent adoption of these coupling solutions. In this paper, we propose a data interface for the established simulator ns-3 that allows coupling to the Linux kernel at a very low level of the protocol stack, namely the lower WLAN MAC layer. This interface allows the performance evaluation of WLAN-based systems, in which real target code of almost the entire software stack can be used. With such an interface, developers can write real target software and test it under different wireless network scenarios and channel conditions, powered by a simulation using ns-3. We show the practicality of our interface by comparing it to a simulation solely performed in ns-3, as well as to another framework for coupling real target software to a channel simulation.
Mesh networks based on the wireless local area network (WLAN) technology, as specified by the standards amendment IEEE 802.11s, provide for a flexible and low-cost interconnection of devices and ...embedded systems for various use cases. To assess the real-world performance of WLAN mesh networks and potential optimization strategies, suitable testbeds and measurement tools are required. Designed for highly automated transport-layer throughput and latency measurements, the software FLExible Network Tester (Flent) is a promising candidate. However, so far Flent does not integrate information specific to IEEE 802.11s networks, such as peer link status data or mesh routing metrics. Consequently, we propose Flent extensions that allow to additionally capture IEEE 802.11s information as part of the automated performance tests. For the functional validation of our extensions, we conduct Flent measurements in a mesh mobility scenario using the network emulation framework Mininet-WiFi.
Due to the increasing complexity of distributed embedded systems, the development process demands early substantiation of design decisions for the targeted system. Virtual prototypes enable an early ...validation of hardware/software systems and they have proven to be very beneficial for target software development. However, these prototypes often do not include models for inter-device communication aspects of distributed systems. Especially the use of wireless communication has a significant impact on the overall system behavior and performance. This paper introduces a SystemC model of an essential part of IEEE 802.11 Wireless LAN communication, the Enhanced Distributed Channel Access (EDCA) protocol. In comparison to widely used network simulations, the modeling with SystemC promises an easier integration into existing virtual prototypes. EDCA is the main part of the lower medium access layer (MAC) of IEEE 802.11 and interfaces to the physical-layer communication as well as to non-time-critical higher MAC-layer functions. We conducted experiments with an additional simple physical communication channel model to compare our solution in terms of precision and performance to the well-established network simulator ns-3. We show that our model differs by \approx 0.3 \% of retransmitted frames and an accompanied difference of the overall simulated transmission time of \approx 0.45 \%. It meets the overall expectations for the stochastic EDCA protocol. Moreover, the presented model has a significantly better simulation performance with 3 \cdot 10^{-5} s wall-clock time per frame, which is at least two orders of magnitude better than with the compared ns-3 simulation.
WLAN mesh networks are one of the key technologies for upcoming smart city applications and characterized by a flexible and low-cost deployment. The amendment IEEE 802.11s (.11s) introduces low-level ...mesh interoperability at the WLAN MAC layer. However, scalability limitations imposed by management traffic overhead, routing delays, medium contention, and interference are common issues in wireless mesh networks and also apply to. 11s networks. Possible solutions proposed in research recommend a divide-and-conquer scheme that partitions the network into clusters and forms smaller broadcast and collision domains by assigning different channels. We present CHaChA, a distributed cross-layer approach for clustering and channel assignment that directly integrates the default. 11s mesh protocol information and operation modes, retaining unrestricted compliance to the standard. The practical performance and implied benefits of CHaChA are demonstrated in a real-world testbed.
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