Impact of outdated channel state information on energy efficiency of co-operative hybrid automatic repeat reQuest in wireless sensor networks

Co-operative communication has been shown to significantly improve energy efficiency in wireless sensor networks. The outdated channel state information (CSI) problem will result in severe performance degradation of co-operative communication systems including energy efficiency. In this study, the authors analyse the impact of outdated CSI on energy efficiency of amplify-and-forward co-operative hybrid automatic repeat reQuest system. The authors derive the expression of the average energy consumption per bit of data transmission under outdated CSI. Numerical results show the deteriorating effects of outdated CSI on the performance of energy efficiency and transmission reliability in co-operative communication system. It is also shown that energy efficiency can be improved by error correcting codes mechanism when end-to-end signal-to-noise ratio at the destination node is within a certain range.