A multi-channel cooperative MIMO MAC protocol for clustered wireless sensor networks

Recently, several multi-channel MAC protocols have been proposed for wireless sensor networks (WSNs) to improve network capacity and boost energy efficiency. In addition, cooperative multiple-input multiple-output (MIMO) technique has been shown to be able to significantly enhance the energy efficiency of WSNs if properly configured. However, these two promising techniques have not been jointly considered in clustered WSNs. In this paper, we explore such a joint design by proposing a novel MAC protocol for clustered WSNs that takes advantage of both multiple channels and cooperative MIMO to further boost network performance. Specifically, sensor nodes in a WSN are organized into clusters and each cluster head selects some cooperative nodes to help forward traffic to or receive from other clusters by utilizing a cooperative MIMO technique. For intra-cluster communications, different channels are assigned to adjacent clusters to reduce collisions, while for inter-cluster communications, cooperative MIMO links are scheduled to improve energy efficiency and concurrent transmissions are enabled by assigning different channels to them. We also provide a network-wide time synchronization approach to facilitating the functionality of this protocol. We carry out extensive simulations and the results demonstrate that the proposed protocol can significantly increase throughput and improve energy efficiency compared to other schemes. For example, for a WSN with 150 sensors in a 250×250m2field, with five available channels, the protocol can achieve three times saturated throughput while saving 14% energy per bit for inter-cluster communications.