Cooperative MIMO transmissions using threshold based MAC protocol in wireless sensor network

Sensor network requires robust and efficient communication protocols to maximise the network lifetime. Radio irregularity, channel fading and interference results in larger energy consumption and latency for packet transmission over wireless channel. Cooperative multi-input multi-output (MIMO) scheme can significantly improve the communication performance when incorporated in wireless sensor network (WSN). The medium access control (MAC) protocol designed for the network must be stable and should improve the performance gains of MIMO. Hence, this paper proposes a distributed threshold based MAC protocol for cooperative MIMO transmissions using space time block code (STBC). The protocol uses thresholding scheme that is updated dynamically based on queue length at the sending node to achieve lesser energy consumption and minimise latency ensuring stability of transmission queues at the nodes. STBC and code combining techniques are applied to utilise inherent spatial diversity in wireless cooperative MIMO systems. The performance of the proposed protocol is evaluated and compared with fixed group size cooperative MIMO MAC protocol with and without STBC coding. Results show that the proposed protocol outperforms point to point communication and MIMO MAC protocol that use fixed cooperative group size. For the proposed MAC protocol, STBC technique provides significant energy savings and minimises the packet delay by leveraging MIMO diversity gains.