Xavier Araújo

Context

Future Cities is a project that is currently being implemented in the city of Porto, in Portugal. The main idea of this project is to transform the city of Porto in an urban-scale living lab, where new technologies, services and products, can be developed, tested and evaluated. These technologies, services and products can explore several subjects like sustainable mobility, urban-scale sensing or even the quality of life of the citizens.
One of the challenges still unsolved is the creation of low-cost solar powered video-surveillance systems based in Wi-Fi, to cover large unconnected areas such as parks or beaches. These systems fit in the definition of Wireless Multimedia Sensor Network (WMSN). WMSNs are networks of interconnected wireless devices, that allow retrieving multimedia content, like video streams, audio streams or static images. WMSNs are a recent technology that emerged from Wireless Sensor Networks (WSN), which in its turn emerged from Wireless Mesh Networks (WMN). These networks can be useful in numerous applications such as person locator systems, traffic avoidance systems, control systems, environmental monitoring systems and multimedia surveillance systems.

Problem Characterization

This thesis, focuses on the design of a networking solution to improve the performance of a Carrier Sense Multiple Access (CDMA) based WMSN, regarding two major factors: the network capacity and the network lifetime. The network capacity is a major limitation because the WMSN has to be capable of transmitting large amounts of data, extracted from the video-surveillance system, to the appropriate destination, within a minimum pre-defined delay time. Capacity can clearly limit the network performance, if not taken into account. The network lifetime is also a major limitation, since it is expected to deploy a WMSN powered by solar energy, and due to this fact the network lifetime may be greatly reduced, restraining the network operation.
It is essential to come up with solutions to overcome these limitations, in order to deploy a functional, reliable and effective WMSN. This is really important since this emerging type of network can bring great advantages. This work focuses on trying to design a single solution that, at the same time, increases the network capacity and extends the network lifetime. By doing this, it is possible to improve the performance of WMSNs, allowing them to transmit a higher amount of multimedia data, within a minimum pre-defined delay time, and increasing the period in which they can collect information. This allows the deployment of WMSNs with better characteristics in terms of performance and reliability.
There are several strategies to increase the capacity of the network and to extend its lifetime. This thesis will adopt a multi-channel approach. With this approach it will be possible to increase the network capacity and, with a proper dynamic channel assignment procedure, it will also be possible to extend the network lifetime. Thus this thesis attempts to specify an energy-aware channel assignment algorithm which takes into account the battery level of the WMSNs nodes, and the solar energy availability. The idea is to develop a centralized channel assignment algorithm capable of adapting to changes in the energy parameters of the network. The reason behind the centralized approach has to do with the low processing and memory resources, owned by the WMSN nodes.
The energy-aware channel assignment algorithm that it is expected to be developed is an improvement of the channel assignment algorithm named TILIA. The idea is to add an energy factor to this channel assignment algorithm, in order to adapt TILIA to situations where the energy availability is a strong limitation.

Contributions

The main expected contribution of this thesis will be a centralized energy-aware channel assignment algorithm for WMSNs capable of extend the lifetime of the network. This algorithm will take as input the network graph, with all the gateways and all the connections between the network nodes, and will output the channel assigned to each node.

Methodology

To achieve the proposed goals this thesis will mainly use the simulation tool NS-3. With NS-3 it will be possible to evaluate the algorithm developed and test its behaviour. If the algorithm pass this validation phase it will then be evaluated in real conditions, using a Raspberry Pi testbed. This way it will possible to understand if the algorithm developed achieves the proposed goals.