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Recent challenges and novel approaches of wireless communication networks are characterized by high performance requirements on the radio channel and by concepts of self-organization, in-network processing, or resource optimization which ultimately lead to distributed network applications, communication architectures, and radio transceivers.
Associated evaluation is driven by a multitude of ever-increasing requirements that call for multidisciplinary expertise. Depending on the discipline, simulation is one of the most widely used technologies, whereby often abstract assumptions and models do not allow for sufficiently accurate, comparable results.
In contrast, real-world measurements and field-tests can only be performed on actual systems, commonly under non-reproducible conditions.
This thesis establishes with the Split-Protocol-Stack a new type of evaluation method that intends to help closing the gap between purely simulative analyzes and real-world tests.
With the inclusion of real radio hardware and radio channels in the event-based simulation, this central hybrid approach in connection with the Radio-in-the-Loop methodology creates synergies in interdisciplinary fields.
The approach contains analytical discussions, methodological strategies, and practical contributions that are summarized as key elements in the subsequent central considerations and challenges.
With Real-Time-Shift, a pseudo-real-time synchronization approach for parallel simulation and radio channel emulation of communication flows is introduced.
Based on the underlying time compensation scheme, the discrete event simulation is decoupled from real-time constraints when exchanging event messages with real-world wireless hardware.
A physical layer emulation methodology and radio channel interface concept, called Radio-in-the-Loop, is introduced along with two practical realization approaches.
Furthermore, strategic details on radio network planning with an approach to automatic hardware resource allocation are presented for radio channel emulation-capable network testbeds.
The contributions of this work are evaluated using real-world reference measurements, practical application scenarios, and experiments that provide proof of concepts.
By means of an exemplary selected cross-layer optimization scenario, the benefits are practically demonstrated and discussed.
Finally, based on IEEE 802.15.4 as the reference protocol standard for low-power wireless networks, this thesis provides feasibility studies and analysis results using the representative prototype SEmulate for the Split-Protocol-Stack approach.
With the integration of smart objects into the Internet users should gain new possibilities to directly interact with their physical environment. This vision is called Internet of Things (IoT) and is enabled by the development of micro Internet Protocol (IP) stacks that allow one to directly connect smart objects to the Internet. IP alone cannot ensure a seamless integration because advanced services (e.g., service discovery, identity management) can only be provided at the application layer. The current development of application protocols for the IoT focuses on the Machine-to-Machine (M2M) communication and introduces specialized protocol gateways, smart object-specific code or data representations that hinder a seamless integration. This thesis deals with the seamless integration, discovery, and employment of smart objects into the current Internet infrastructure under Human-to-Machine (H2M) communication aspects by using and adapting already established protocols that have been standardized by the Internet Engineering Task Force (IETF), such as the Extensible Messaging and Presence Protocol (XMPP), Multicast DNS (mDNS), and DNS Service Discovery (DNS-SD). The proposed approach is called Chatty Things. So smart objects may become a natural part of the network making the IoT readily usable for (non-technical) users and network administrators providing them with the same level of usability that is predominant in the current Internet infrastructure.
The applicability of XMPP and mDNS/DNS-SD for smart objects has been evaluated with implementations of minimized, modular, and extensible software stacks for the IoT operating system Contiki. This includes a readily usable Application Programming Interface (API), an essential set of XMPP extension protocols, a proposal for lightweight and user-friendly event notification, a standardized bootstrapping, and a seamless fallback mechanism for ad hoc use cases when infrastructure services are failing for XMPP-driven smart objects. Furthermore, this thesis presents optimizations for the used protocols to reduce the network traffic in low data rate smart object networks (e.g., sensor-specific groups, enhanced message compression mechanisms). To sum up, this thesis shows how XMPP and mDNS/DNS-SD can be used economically on smart objects for the seamless integration with low effort into the current Internet infrastructure to enable a transparent (H2M) interaction and service discovery for the IoT.