Cross-layer energy optimization in cooperative MISO wireless sensor networks

Cooperative multi-input single-output (CMISO) is proved to be higher energy saving in long distance communication than single-input single-output (SISO) based on the physical layer energy consumption model, thus this technique applied in wireless sensor networks for reducing energy consumption has become a hot issue. However, CMISO needs depend on MAC layer protocol to control signals synchronization among all cooperative nodes and pilot symbols transmission for channel gain estimation at receiver, both of which increase additional energy overhead. Meanwhile, all the cooperative nodes which listen to the contention-based channel in the backoff time at the MAC layer also consume a lot of energy. Therefore, the conclusions derived only from the physical layer energy consumption model may be impractical without considering the neighboring nodes’ interference and additional MAC layer overhead. It is unknown whether CMISO is higher energy efficiency than SISO at the MAC layer. In our paper, a MAC protocol for CMISO is designed, and based on this protocol a cross-layer energy consumption model is proposed. This cross-layer model considers not only transmitting power and circuit power, but also additional energy overhead in listening to the channel, transmitting pilot symbols, control frames, etc. With the model, minimum energy consumption is derived at the different parameters such as contention window, number of cooperative nodes, radius of a cluster and constellation size. At the same time, our numerical results prove that CMISO saves about 27% energy consumption compared with SISO at the MAC layer. Since our results run under the heavy traffic environment with the highest transmission collision probability, we reasonably believe that CMISO communication will achieve better energy efficiency than SISO in ordinary traffic scenarios.