Opportunistic ALOHA and cross layer design for sensor networks

We propose a novel distributed medium access control scheme called opportunistic ALOHA for reachback in sensor networks with mobile agents. Each sensor transmits its information with a probability that is a function of its channel state (propagation channel gain). This function called transmission control is then designed under the assumption that orthogonal CDMA is employed to transmit information. The gains achieved in the throughput by use of transmission control are analyzed and evaluated numerically. The variation of the average number of transmitting users with distance from the collecting agent is analyzed. The proposed reachback protocol can be used in a variety of sensor network applications. We end by giving two examples of how the reachback protocol can be used by the sensor network to transmit information reliably to the collecting agent. The maximum rate at which the information can be reliably transmitted with the proposed schemes is evaluated as a function of the performance parameters of the reachback protocol.