Constraining the network topology in IEEE 802.15.4

The IEEE 802.15.4 standard defines a MAC association procedure that allows devices of a Wireless Personal Area Network (WPAN) to associate one each other in accordance to parent-child relationships. This standard can be adopted in Wireless Sensor Networks (WSNs) used to monitor environmental phenomena and to collect data in specific nodes named sinks. The ZigBee Alliance, with the Zig-Bee Specification, defines upper layers of a WSN architecture based on the IEEE 802.15.4. Tree shaped multi-sink networks can be formed by adopting in conjunction these two standards. A key aspect to be evaluated for these kind of networks is how their performance are affected by constraining some topological characteristics. In this paper, in accordance to the ZigBee Specification, we constraint the tree depth of a WSN and evaluate some performance metrics that have a remarkable relevance for WSNs. Moreover, we propose a new strategy to join an existing WPAN that allows a node to select a suitable coordinator to connect with. Performance results show the trade-off in the selection of the maximum tree depth. While benefits of having reduced tree depths can be measured during traffic delivery, due to a reduction of the energy consumption, a counter-party is the energy spent in the network formation that deeply depends on this topological parameter. Moreover, the maximum tree depth has also a great impact on the percentage of nodes that are able to join a network.