The Study On The Energy Efficiency In Low-Rate WPANs

WPAN is a wireless communication network, the same as WWAN, WMAN and WLAN but it covers shorter range. LR-WPAN, defined by TG4 of IEEE 802.15, is similar to WSNs. So it is studied by many institutions as the communication specification of WSNs. As sensors are energy limited, how to save energy is the most important thing in LR-WPAN. So our work focused on the energy efficiency in LR-WPAN.Transmission and collision processes consume large part of energy in communication which occupies large amount of energy in LR-WPAN. So decreasing the energy consumption in these two processes can efficiently resolve the energy-limited problem in LR-WPAN.In this paper, we firstly studied CSMA-CA scheme in slotted beacon-enabled star network for IEEE 802.15.4. We put forward an enhance back-off scheme, in which the initial back-off window could be dynamically changed as the past transmission conditions. The proposed scheme can decrease the collision ratio and the retransmission ratio, resulting in significantly power saving and throughput improvement when the traffic load is high or the packet size is small, which are verified through extensive simulations. But the result also indicates the fairness problem resulted from the enhanced scheme, which makes us take the balance between them.Another contribution of this paper is the power control scheme in IEEE 802.15.4 to lower the transmission power. We can get the minimum transmission power according to the transmission power from the sender last time, the receive power and the threshold for the correct detection and decoding. We modified the MAC frame structure to keep the power level of transmit power, then the MAC sublayer can inform the PHY layer to transmit the frame in the relevant transmit power. The simulation result also showed the power decrement in the network.So we can get to the conclusion that the enhanced back-off scheme and the power control scheme can both efficiently lower the energy consumption of LR-WPAN to resolve the energy-limited problem of WSN.