Node Activation to maximize expected progress in wireless networks with energy constraints

In wireless networks, the conventional routing approach is to pre-select the next-hop receiver for a packet based on knowledge of the network topology. However, when the nodes experience fading that changes on the order of the packet duration, a conventional routing approach will often offer poor performance because the pre-selected receiver may not be able to recover the packet because of fading. An alternative approach is to use geographic transmission, in which the packet is transmitted in the direction of the destination but the next-hop receiver is not pre-selected. In this approach, multiple receivers in the direction of the destination attempt to receive the packet, and one of the receivers that is able to recover the packet will be selected as the next-hop relay. Multiuser diversity can be achieved because the different receivers in the direction of the destination are likely to experience independent fading. In order to conserve energy, it may be desirable to turn on only a subset of the nodes surrounding the transmitter. Thus, we consider the problem of designing a node-activation function that allows a node to determine whether it should turn on to receive a message in order to maximize the expected progress towards the destination under a constraint on the expected number of nodes that turn on. The optimal node-activation function is difficult to find analytically, so we develop a suboptimal solution and show that it offers good performance.