The main resource constraint in the wireless body area network is the energy. The energy consumption can be reduced by maintaining the state of a sensor. The senor node consumes less energy in the sleep state as compare to the active state. This paper develops a dynamic model that decides the state of the sensor node by using the mutual information within the nodes. The model proposes uses a short preamble to change the state of the sensor node. The model can use different routing mechanisms so the paper, firstly compares various routing technique over IEEE 802.15.4 standard which is standard for LRWPAN. The best technique among them is used for proposed model evaluation. The simulation results show the better performance of the proposed as compare to existing MAC.