Martin Serror

Channel Coding versus Cooperative ARQ: Reducing Outage Probability in Ultra-Low Latency Wireless Communications

Nowadays wireless communications still lack the ability to provide high reliability and low latency, although mission-critical applications, such as found in industrial automation, rely on both requirements. The main challenge is that an improved reliability often comes at the price of an increased latency. It has been shown that cooperative schemes can effectively increase the reliability by leveraging spatial diversity. However, an important question remains how to integrate cooperative schemes when dealing with very short latency bounds and especially how much time should be reserved for potential retransmissions. In this work, we propose and evaluate a centralized communication system that uses cooperative ARQ to achieve high reliability under the constraint of a strict latency bound of 1 ms. We evaluate this system analytically, using an outage-capacity model with average channel state information, by varying the reserved time for retransmissions, where a shorter time for retransmissions allows to apply stronger channel codes in the original transmission. As a baseline, we use a system without cooperation mechanism, thus applying the given time for stronger channel codes in the direct transmission of a message. In case of cooperation, a third station may act as a relay if the original transmission failed. Our results reveal that an optimal size of the reserved retransmission time exists around 15% to 30% of the total frame time, increasing the reliability by several orders of magnitude, even for a large number of transmissions within a communication cycle.

Enabling ubiquitous interaction with smart things

Within the Internet of Things (IoT), Smart Things (STs) promise to permeate all contexts of daily life, offering digital access to their physical functionality. Mobile users then would be able to ubiquitously and spontaneously interact with things they encounter, enabling a wealth of diverse usage scenarios and applications. Currently, however, ST interaction requires a pre-controlled Internet or network connection as well as the prior installation of the ST-specific interaction interface, i.e., smartphone app. Users can thus only interact with known things, in contrast to the vision of spontaneous, ubiquitous discovery and interaction. We thus propose STIF (Smart Things Interaction Framework), enabling local wireless discovery of STs spontaneously via Wi-Fi, Bluetooth Low Energy, Visible Light Communication, or Acoustic Communication. STIF allows STs to transmit their interaction interface directly to users and supports interaction based on user input via touch and AR GUIs as well as motion and speech recognition. We implement STIF for Android phones as well as Arduino and Raspberry Pi things and demonstrate the real-life applicability of the supported communication and interaction techniques.

DHT-based localized service discovery in wireless mesh networks

Wireless mesh networks (WMNs) provide high-bandwidth wireless network access to mobile clients in extensible, robust multi-hop networks. WMNs support distributed service provision and data storage, catering to the advanced capabilities of current mobile devices. Services and data discovery using undirected broadcast or multicast messages, as in traditional discovery protocols, significantly harms network performance due to interference and collisions. In contrast, distributed hash tables (DHTs) offer consistent mapping of service and data identifiers to the providing devices and therefore allow a directed unicast discovery and access. However, traditional DHTs place identifiers at arbitrary distant devices in the network, resulting in frequent use of long multi-hop routing paths. Such multi-hop transmissions suffer from performance loss at each hop and also degrade the overall network performance. We propose DLSD, a DHT-based localized index structure that establishes a hierarchy of locally bounded address spaces ranging from a few nearby devices to the whole network. Iterating through this hierarchy bottom-up allows devices to find the most local provider of the requested item, thereby minimizing multi-hop transmissions while ensuring global reachability. Through this reduction of routing hops, we maintain high transmission performance and minimize interference in the network. We evaluate the feasibility of our approach and show that it significantly reduces routing overhead and outperforms traditional service discovery and DHT approaches.

Performance analysis of cooperative ARQ systems for wireless industrial networks

The proliferation of wireless communications has lead to a high interest to establish this technology in industrial settings. The main arguments in favor of wireless are reduced costs in deployment and maintenance, as well as increased flexibility. In contrast to home and office environments, industrial settings include mission-critical machine-to-machine applications, demanding stringent requirements for reliability and latency in the area of 1-10-9 PDR and 1ms, respectively. One way to achieve both is cooperative Automatic Repeat reQuest (ARQ), which leverages spatial diversity. This paper presents a wireless multi-user Time Division Multiple Access system with cooperative ARQ for mission-critical communication. We evaluate two design options analytically, using an outage-capacity model, to investigate whether the relaying of messages should be performed centrally at a multi-antenna AP with perfect Channel State Information (CSI) or decentrally at simultaneously transmitting stations with average CSI. Results indicate that both options are able to achieve the targeted communication guarantees when a certain degree of diversity is implemented, showing a stable system performance even with an increasing number of stations.

WARPsim: A code-transparent network simulator for WARP devices

Analyzing a communication protocol by means of simulation and real-world experimentation requires careful protocol implementation in both domains. Differences in the implementation may lead to significantly diverging performance results, which may affect the protocol design process adversely. A code-transparent simulation and experimentation framework for Wireless Access Research Platform (WARP) devices is proposed, which is called WARPsim. By extending the simulation engine appropriately, the same application code that runs on WARP devices can be used for simulation. This work studies the implications of this approach using the example of implementing time-critical Medium Access Control Layer (MAC) protocols on WARP devices. In the demonstration, various MAC protocols will be simulated using WARPsim, while changing protocol parameters, but also crucial aspects of the emulated hardware. A graphical representation integrated into the framework allows for an intuitive examination of the protocol behavior.

Towards In-Network Security for Smart Homes

The proliferation of the Internet of Things (IoT) in the context of smart homes entails new security risks threatening the privacy and safety of end users. In this paper, we explore the design space of in-network security for smart home networks, which automatically complements existing security mechanisms with a rule-based approach, i. e., every IoT device provides a specification of the required communication to fulfill the desired services. In our approach, the home router as the central network component then enforces these communication rules with traffic filtering and anomaly detection to dynamically react to threats. We show that in-network security can be easily integrated into smart home networks based on existing approaches and thus provides additional protection for heterogeneous IoT devices and protocols. Furthermore, in-network security relieves users of difficult home network configurations, since it automatically adapts to the connected devices and services.

Code-transparent Discrete Event Simulation for Time-accurate Wireless Prototyping

Exhaustive testing of wireless communication protocols on prototypical hardware is costly and time-consuming. An alternative approach is network simulation, which, however, often strongly abstracts from the actual hardware. Especially in the wireless domain, such abstractions often lead to inaccurate simulation results. Therefore, we propose a code-transparent discrete event simulator that enables a direct simulation of existing code for wireless prototypes. With a focus on lower layers of the communication stack, we enable a parametrization of the simulation timings based on real-world measurements to increase the simulation accuracy. Our evaluation shows that we achieve close results for throughput (deviation below 3% for UDP and latency (corrected deviation about 13% compared to real-world setups, while providing the benefits of code-transparent simulation, i.e., to flexibly simulate large topologies with existing prototype code. Moreover, we demonstrate that our approach finds implementation defects in existing hardware prototype software, which are otherwise difficult to track down in real deployments.

Communication and Networking for the Industrial Internet of Things

In the past, communication in industrial monitoring, automation, and control was mostly realized locally, often relying on wired solutions, restricting communication and control to single factory environments. To overcome this limitation, the Industrial Internet of Things (IIoT) envisions the integration of these local communication structures into larger systems, such as the interconnection between factories and suppliers, or even the Internet. Moreover, to achieve flexibility with regard to automation processes and to save costs in deployment and maintenance, wireless solutions more and more find their way into factories. In this chapter, we present recent efforts and standardized solutions to realize wireless communication for local industrial automation and ultimately identify the requirements and mechanisms for connecting these setups to globally accessible communication infrastructures. To this end, we focus on special requirements unique to the IIoT, e.g., the use of highly constraint devices and the resulting effects on the use of standardized protocols.

Demo: a realistic use-case for wireless industrial automation and control

This demo showcases a typical industrial automation scenario of a robot picking and placing work pieces from a moving conveyor belt. It involves sensory data inputs to a Programmable Logic Controller (PLC), and instructions from the PLC to a robot for the pick and place operation. The scenario requires communication from sensors to the PLC and from the PLC to a robot with ultra-low latency and extremely high reliability. While none of today’s wireless standards is capable of satisfying these stringent communication demands, our early prototype implementation of some of the design features of the future 5G standard enables industrial control using wireless communication. Our demo will show the live performance characteristics of the 5G design features for low latency and high reliability.

Collaborative On-demand Wi-Fi sharing

While users can ubiquitously access the Internet via their Wi-Fi network or their mobile carrier network, access to foreign private Wi-Fi networks is mostly prohibited. This is because private APs have no means of authenticating foreign mobile users prior to granting access to their network, entailing severe security and liability risks. However, such Wi-Fi roaming would make the vast network resources of private users available on a collaborative basis. We propose Collaborative On-demand Wi-Fi Sharing (COWS), offering 802.1×-equivalent authentication of foreign users at private APs without the need for elaborate, hierarchical authentication infrastructures. COWS embeds authentication credentials into 802.11 association requests, enabling APs to establish 802.11 AP networks exclusively on-demand and after an authentication of the mobile user at her home network provider. Our evaluation using Android smartphones and various authentication provider instances shows the real-life applicability of COWS, enabling lightweight, collaborative Wi-Fi roaming at the APs of private users.