Opportunistic Large Arrays

In this paper, we introduce a new scheme that allows transmission from a set of asynchronous transmitters to a remote destination which, otherwise, would not be capable to forward the data individually. In our scheme the small devices form an Opportunistic Large Array (OLA) by reacting to the signal sent by a special node in the network, called the leader. The problem solution provides as a byproduct a communication technique for the network itself, based on a unique physical layer design where the signals are broadcasted to the other nodes without contending for the channel. I. How it works? The main goal of many applications of wireless ad hoc networks is not only the mutual communication among the nodes themselves but also to enable the transmission of locally generated data to a distant receiver which has extremely low SNR with respect to each individual node. In this paper, a set of ad hoc wireless nodes are used to form an Opportunistic Large Array (OLA) by responding to the signal of the transmission leaders. In this way, the nodes in the network create an avalanche of signals similar to the ola performed by the spectators in a stadium. The OLA structure provides fast reliable transmission and diversity with very simple node cooperation. The multi-node diversity provided is in both spatial and temporal. A. The transmitter alphabet Let the leader transmit an M-ary pulse pm(t), the complex envelope of the resulting signal at the receiver is