Subject: Mobile Communication and Computing

Topic: Wireless Local Area Networks

Difficulty: High

Power Management

1. Power management is the feature that turns off the power or switches the system to a low power state when inactive.

2. The basic idea to save power in WLAN is to switch off the transceiver whenever it is not needed.

Power management in infrastructure based network

1. In infrastructure based network, an access point is responsible for the power management.
2. Access point buffers data packet for all sleeping station.
3. Access point transmits a Traffic Indication Map (TIM) with a beacon frame.
4. TIM consists of a list of destination of buffered data.
5. Additionally, the access point also maintains a Delivery Traffic Indication Map(DTIM) interval.
6. DTIM is used for sending broadcast/multicast frames.
7. The DTIM interval is always a multiple of TIM interval.
8. All station wakes up prior to an expected TIM and DTIM.
9. Figure shows Power management in IEEE 802.11 infrastructure based network.

Power management in Ad-hoc network

1. In ad-hoc network, each station buffers data packet that it wants to send to power saving station.
2. There is no access point.
3. In Ad-hoc network, all station announces a list of buffered frame during a period when they are all awake.
4. All station announce destination for which packets are buffered using Ad-hoc Traffic Indication Map (ATIM) during the ATM interval.
5. Figure shows Power Management in IEEE 802.11 Ad-hoc Network.