Connectivity Problems in Wireless Sensor Networks with Directional Antennas

With the capabilities to monitor their surrounding environment and deliver data using radio signals, Wireless Sensor Networks (WSNs) have found applications in various areas including health (to monitor disabled patients), home, industry (machine monitoring) and military (for control, communication and target detection) monitoring. As these sensor devices transmit signals wirelessly, they may cause interference. Moreover, having a bounded energy resource, the transmission distance and lifetime of sensor devices are restricted. These constraints yield several optimization problems in WSNs that have attracted attention from many researchers. In the first part of this dissertation, we investigate the optimization problem to minimize the number of timeslots in which data can be aggregated to a sink node which is known as the Minimum Latency Aggregation problem in WSNs.

In contrast to low-gain omni-directional antenna, high-gain directional antenna can focus its power in a certain direction. The use of directional antennas enables energy conservation and interference reduction, which prolong the lifetime and increases the efficiency of networks. However, maintaining connectivity for directional antennas WSNs (DWSNs) is much more complex. In the remaining chapters of this dissertation, we focus on solving the topology control problem for DWSNs to establish symmetric connectivity where each sensor node is equipped with 1 ≤ k ≤ 5 directional antennas having beam-width θ ∈ [0; 2 π]. The objective of the Directional Antenna Orientation (AO) problem is to determine an orientation of the antennas with a minimum uniform transmission power range r such that the induced symmetric communication graph is connected. Another related problem is Antenna Orientation and Power Assignment (AOPA) where we try to obtain symmetric connectivity in DWSNs while minimizing the total power assigned to the sensors.