Enhancement of the IEEE 802.11 Power Saving Mode by Prioritized Reservations

Abstract

The increasing demand for real-time applications in WSN has raised the requirement of protocols considering both energy efficiency and end-to-end delay. A PSM is proposed in the IEEE 802.11 protocol to reduce the power consumptions of wireless nodes. Wireless nodes can stay in doze mode and periodically wake up to retrieve the frames buffered in the APs. However, the 802.11 PSM is not such energy efficiency for WSN. First, in the process of the node's transmitting polling frames to AP, channel contentions may cause sensor nodes to deplete power quickly. Second, the mechanism of retrieving buffered frames can be inefficient since a polling frame is able to pick up only one data frame. Third, a prioritized service for urgent needs is not supported. In this paper, we propose a prioritized reservation scheme to enhance the IEEE 802.11 PSM. The concept of PSCW is suggested, during which PSM sensor nodes can retrieve the buffered frames using the reserved SPs, where the priorities of the PSM nodes are considered in scheduling the SPs. Through analytic models and discrete simulations, we show that our proposed mechanism outperforms the existing PSM schemes in terms of energy efficiency and prioritized services.

Improving Energy Efficiency in Idle Listening of IEEE 802.11 WLANs

“…Moreover, many mechanisms have been proposed to reduce the energy dissipation in the ILT. Considering that the energy is the product of power and time, they can be classified into two categories: (i) decreasing power in the ILT [4,[15][16][17] and (ii) decreasing the ILT [18][19][20][21][22]. The first approach makes STAs switch to a low-power state (e.g., semisleep) in the ILT, without attempting to decrease the ILT, whereas the second approach aims to minimize ILT resulting from channel access, collision, or reception of nonintended frames.…”

“…The micropower management mechanism proposed in [18] lets STAs sleep for a very short idle time (in the order of microseconds) by leveraging a prediction mechanism of frame arrival, so that the short ILT is transformed to sleep time. Similar to PSMP, the studies in [19][20][21][22] propose a scheduling-based or reservation-based approach to avoid unnecessary ILT. The mechanism in [19] proposes dividing the frame into a control subframe for channel contention and data subframe for data transmission, so that it can be free from unnecessary energy dissipation for accessing the channel and for receiving nonintended or collided frames.…”

“…In this way, only STAs involved in communication wake up during the designated time, and other STAs can go to sleep. The mechanism in [22] proposes a prioritized reservation scheme, with which the contention among PS-Poll messages can be avoided and STAs are allowed to retrieve data frames at the reserved time.…”

“…We validate the weakness of this approach via analysis and simulation and propose an effective and simple solution to magnify the benefit of this approach. (ii) The approach based on scheduling or reservation [19][20][21][22] requires significant modifications of the channel access mechanism in the current IEEE 802.11 WLANs, such that it cannot maintain a backward compatibility. Our mechanism can be practically implemented without violating the compliance with the IEEE 802.11 standard.…”

“…Our mechanism can be practically implemented without violating the compliance with the IEEE 802.11 standard. (iii) None of the previously discussed approaches [4,10,12,[15][16][17][18][19][20][21][22] deal with collision and retransmission, which is another primary source of energy dissipation and performance degradation. Our mechanism incorporates an effective solution to collision for energy efficiency and performance enhancement.…”