Scalable Mobile Ad-Hoc Networks
Nowadays, the uninterrupted availability of communication networks is self-evident for the vast majority of people. However, natural disasters like the flood in Germany in July 2021 show that the existence of a reliable communication infrastructure can not always be presumed. Mobile Ad-Hoc Networks, in the remaining referred to as MANETs, do not require any fixed infrastructure, wherefore they are considered to be highly flexible and disaster-resistant. They can be particularly employed to establish mission-critical communication systems in case the conventional infrastructure-based networks collapse which makes MANETs highly attractive for public authorities’ security and safety institutions. However, currently one major bottleneck is their scalability due to the large overhead that is required to distribute routing messages which limits the applicability in scenarios where a large number of nodes is necessary. Cooperative broadcasting on the physical layer is one promising approach to overcome this issue.The main aims of the planned research work can be basically sub-divided into two groups: the theoretical scalability and the practical applicability. On the one hand, it is important to investigate which transmit coding scheme is best suited to enable an efficient up-scaling and how it has to be adapted for the desired application. On the other hand, the designed coding approach will be investigated from a practical point of view. For that an SDR-based demonstration system will be developed and successively expanded in parallel to the theoretical studies which will enable measurements utilizing real hardware. Lastly, an efficient physical layer cooperative broadcasting protocol will be proposed. To summarize, following research questions arise:
- Which transmit diversity scheme is best suited to improve the scalability of MANETs and how can it be applied for randomly distributed nodes?
- To what extent is it possible to improve the efficiency in the scaling process of this coding scheme and which modifications are required therefore?
- What is the impact of hardware and system imperfections and to what extent is it possible to combat them by an appropriate coding scheme?
- What are suited synchronization and parameter estimation methods for distributed MANETs?
- How can these be scaled in an efficient manner?
- Which aspects should be covered by an efficient physical layer cooperative broadcasting protocol and how can such a protocol be designed?
- How can the MAC-layer support cooperative broadcasting of routing information?
- How does such a network perform in a real environment?
For our MANET research activities we have implemented an SDR-based Demonstration-System (Demo-System) which we will gradually expand in alignment to our theoretical studies. Basically, the Demo-System is aimed to reflect a MANET, whereforeit consists of nodes which can be assigned to act as a transmitter (TX) or receiver (RX). Generally, it enables
- to verify the theoretical findings,
- to identify problems and weaknesses of the codes for practical systems,
- to test the proposed synchronization and parameter estimation techniques and lastly
- to study the impacts of imperfections that are introduced by non-ideal hardware component
To build the Demo-System only a few components are necessary, namely Software-Defined Radios (SDRs), a reference clock and controlling PCs with their peripherals.Software-Defined Radios (SDRs) are highly flexible devices which allow to replace typical hardware components like modulators, mixers, etc. with digital signal processing algorithms. Thus, SDRs can be changed in their configuration and behaviour by an appropriate software. For the Demo-System the Ettus Research USRP B210 model is being used which is shown below. The Ettus Research CDA-2990 Octoclock is used for time and frequency synchronization. To control the SDRs and operate the Demo-System,PCs are necessary which have MATLAB, Simulink as well as C/C++ Compiler installed.
Graphical User Interface
The SDRs are controlled with MATLAB, whereas C/C++ is used to access all functions of the provided API, since the MATLAB API is limited in its functionalities.Thus, a conversion using mexfiles is necessary. In addition, Simulink is used to implement a Graphical User Interfaces (GUIs). The figure shows the GUI for a TX-node and an RX-node.