Online Algorithm For Energy Efficient Broadcast In Satellite Networks With Multiple Power Levels

In recent years,satellite launching number has gradually increased with the increasing application demand and rapid development of satellite communication technology.When the number of satellites is small,the satellite can communicate with the ground only when it is running over the ground station.With the increase of the number of satellites,the satellite can use the inter-satellite links for information forwarding.Broadcast is a fundamental operation in satellite networks,which is required for satellites self-organization,routing discovery,coordination and collaborations.Energy is always a scarce resource of a satellite.They cannot generate energy when satellites are passing through a shadow region behind the earth as to the sun.Adjustable signal transmitting power at the satellite node means that the satellite can use multiple discrete power levels for data transmission.So the energy conservation is an important issue about satellite network quality.Satellite network is different from the traditional wireless network.It is difficult to design routing algorithm because of the high-speed movements of satellites over time and predictable feature.The following work is done in terms of reliable and unreliable inter satellite links(ISL).Under the condition that ISL are reliable,the broadcast operation in satellite networks will be completed according to a pre-calculated broadcast tree.The selection of multiple power levels in a satellite has an impact on the network topology,so a spacetime graph with multiple power levels is proposed on the basis of space-time graph.We propose the TPA algorithm and BO algorithm which are based on a space-time graph with multiple power levels.The TPA algorithm repeatedly finds the most energy efficient with highest power level and optimizes one-hop transmission with high power level to multi-hop transmissions with low power level in the future.The BO algorithm replaces the edges in the original broadcast tree with more energy efficient ones to optimize the broadcast tree.The flooding algorithm,SPT algorithm,EWMA algorithm and Greedy Path algorithm are compared with our algorithms under different satellite constellation systems.It is verified that the TPA algorithm and BO algorithm are better than other algorithms in different network structures and BO algorithm has the best performance.Under the condition that ISL are unreliable,the broadcast option in satellite network will not be completed in accordance with the pre-calculated broadcast tree.Introducing the ISL error rate into the space-time graph with multiple power levels,the opportunistic broadcast with multiple power levels(MPOB)algorithm is proposed.MPOB algorithm uses the idea of opportunistic routing to dynamically complete the broadcast option in satellite network based on an original broadcast tree.It will reduce the number of data retransmission and select a reasonable time for data retransmission based on the regularity of the operation of the satellite network.Compared with the situation of direct retransmission and Ex OR algorithm under different satellite constellation systems,it is verified that MPOB algorithm performs better than other algorithms under different network structures.