Energy-efficient communication is an important issue in wireless sensornetworks (WSNs) consisting of large number of energy-constrained sensor nodes.Indeed, sensor nodes have different energy budgets assigned to datatransmission at individual nodes. Therefore, without energy-aware transmissionschemes, energy can deplete from sensor nodes with smaller energy budget fasterthan from the rest of the sensor nodes in WSNs. This reduces the coverage areaas well as the lifetime of WSNs. Collaborative beamforming (CB) has beenproposed originally to achieve directional gain, however, it also inherentlydistributes the corresponding energy consumption over the collaborative sensornodes. In fact, CB can be seen as a physical layer solution (versus the mediaaccess control/network layer solution) to balance the lifetimes of individualsensor nodes and extend the lifetime of the whole WSN. However, theintroduction of energy-aware CB schemes is critical for extending the WSNslifetime. In this paper, CB with power allocation (CB-PA) is developed to extend thelifetime of a cluster of collaborative sensor nodes by balancing the individualsensor node lifetimes. A novel strategy is proposed to utilize the residualenergy information available at each sensor node. It adjusts the energyconsumption rate at each sensor node while achieving the required averagesignal-to-noise ratio (SNR) at the destination. It is a semi-distributedstrategy and it maintains average SNR. Different factors affecting the energyconsumption are studied as well. Simulation results show that CB-PA outperformsCB with Equal Power Allocation (CB-EPA) in terms of extending the lifetime of acluster of collaborative nodes.
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