Cooperative protocols for WSNs

Cooperative Strategies for Low-Energy Wireless Networks

One promising approach to increase the capacity of wireless systems or decrease the energy consumption consists in allowing relay nodes to cooperate. In wireless distributed networks where multiple antennas can not be installed in one wireless node, cooperative relay and cooperative MIMO techniques can indeed be used to exploit spatial and temporal diversity gains. Since the wireless nodes are physically separated in cooperative MIMO systems, the imperfect time synchronization between cooperative nodes leads to an unsynchronized MIMO transmission. The performance degradation of this cooperative transmission synchronization error was evaluated by simulations and a robust cooperative scheme has been proposed. New cooperative MIMO relay models have been proposed and their analytical performance and energy efficiency have been investigated by using a realistic power consumption model. The comparison between these cooperative techniques helps us to choose the optimal cooperative strategy in terms of energy consumption for different application scenarios such as road infrastructure networks in ITS applications. However, the aforementioned approaches introduce an overhead in terms of information exchange, increasing the complexity of the receivers. A simpler way of exploiting spatial diversity is referred to as opportunistic routing, where a cluster of nodes still serves as relay candidates but only a single node in the cluster forwards the packet. A thorough analysis of opportunistic routing efficiency under different realistic radio channel conditions has been proposed to find the best trade-off between two objectives: energy and latency minimizations, under a hard reliability constraint.