Current research topic: Adaptive QoS in wireless sensor networks

The main objective of our currently ongoing project is to specify, develop and evaluate algorithms and mechanisms for providing the adaptive QoS (Quality of Service) in WSN (Wireless Sensors Network) that support real-time applications and therefore to demonstrate the effective use of the WSN technology for building CPS (Cyber-Physical Systems) and the Internet of Things. If the monitoring of the physical world benefited from promising results obtained within the last ten years on WSN, these WSN have to be enriched by adding actuators, forming thus a WSAN (Wireless Sensor and Actuator Network), as soon as we consider applications that require not only monitoring but also reacting on the physical world with high precision, support of long unattended operations, promptness of reaction. Moreover and most importantly, the QoS of the existing WSN must be enhanced since monitoring and acting form together a closed loop within which the control decision should be made in real-time.

Although WSN technology is economically a very interesting solution for building CPS, unfortunately its current QoS is not sufficient for supporting such applications. In this project, we defend the idea that currently existing WSN can be enhanced to provide desired QoS. This could be achieved in two coordinated directions: one is to develop the on-line adaptive QoS management in network to cope with the time varying performance requirement of an application; another is to enable applications to adapt to the network working condition changes if they go beyond the network QoS control range.

In this project, we follow a pragmatic approach by assuming the use of the COTS components (e.g. IEEE802.15.4) at the lower levels. The adaptive QoS are mainly studied at the routing level with MAC-Routing cross-layer optimization and by defining and developing a QoS middleware allowing the necessary on-line interaction between the network and the application.

Different recent PhD work that I supervised (or still supervise) contributes to this objective:

- A network-MAC cross-layer framework for packet scheduling, congestion control and energy consumption minimization has been developed as part of the PhD work of B. Nefzi. The work is based on a very simple idea of “collecting-and-burst transmitting” scheme. The underlying MAC protocol is the widely adopted and product-supported CSMA/CA of IEEE802.15.4. An algorithm is designed making the network self-adapts to the dynamic traffic changes and provides improved performance. This is typically a robust solution without or with minimized configuration requirement. An ideal solution for large-scale soft real-time applications.

- Completely at opposite to the above-mentioned approach, we also have explored, similar to the industrial wireless network initiatives (e.g. WirelessHART, ISA SP100, IEEE802.15.4e), the optimal configuration schemes based on TDMA. The aim is to find dynamic TDMA cycle configuration, optimizing both time-slot and frequency channel assignment of networks using UWB (IEEE802.15.4a). Typical application could be large-scale hospital networks. This work is part of J. Ben Slimane’s PhD thesis.

- The PhD work of N. Boughanmi aimed at developing wireless networked control systems by an application-network co-design approach. CSMA/CA MAC protocol is reinforced using blackburst scheme to introduce priorities. According to the observed quality of control (e.g. tracking error), the priorities are online reassigned, guaranteeing thus the required quality of control.

- In addition to the industrial communication domain, another interesting application domain is the use of WSN for providing an ambient assisted living environment to elderly people at home (PhD work of S. Nourizadeh under LORIA-MEDETIC contract). We also addressed the problem of the integration of WSN into the existing home automation networks. A first demonstration platform has been settled down at LORIA. To solve the interoperability problem, a gateway called MPIGate has been developed. The aim is also to develop a middleware between applications and the networks for dynamic QoS negotiation and management.

- The PhD work of Y. Li provides a large spectrum of solutions for providing QoS in WSN including asymmetric link channel modeling of WSN, node deployment strategies (sensing coverage heuristic solutions with probabilistic connectivity), multi-hop based geographic routing, and data fusion.

To experiment and further validate the above solutions, several WSN platforms are also established composed of nodes under either TinyOS or Contiki, or with industrial owner systems (e.g., Jennic, Libelium).