Cooperative Broadcast for Maximum Network Lifetime

We consider cooperative data broadcast in a wireless network with the objective to maximize the network lifetime. To increase the energy-efficiency, we allow the nodes that are out of the transmission range of a transmitter to collect the energy of unreliably received overheard signals. As a message is forwarded through the network, nodes will have multiple opportunities to reliably receive the message by collecting energy during each retransmission. We refer to this strategy as cooperative (accumulative) broadcast. We present the Maximum Lifetime Accumulative Broadcast (MLAB) algorithm that specifies the nodes’ order of transmission and transmit power levels. We prove that the solution found by MLAB algorithm is optimal but not necessarily unique. The power levels found by the algorithm ensure that the lifetimes of the relays are the same, causing them to fail simultaneously. Therefore, the algorithm performs optimum load balancing. For the same battery levels at all the nodes, the optimum transmit powers become the same. Cooperative broadcast not only increases the energy-efficiency during the broadcast by allowing for more energy radiated in the network to be collected, but also makes optimum load balancing possible, by relaxing the constraint imposed by the conventional broadcast, that a relay has to transmit with power sufficient to reach its most disadvantaged child. Simulation results demonstrate that cooperative broadcast significantly increased network lifetime compared to conventional broadcast.