Wireless Networking: Power Management Techniques

2011-05-31

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The extensive use of a Graphic User Interface (GUI), clubbed with an increased demand for remaining connected while being mobile, translates into a heavy burden on the power resources of a wireless network. The wireless networks have restricted power resources and these must be efficiently used in order to increase the battery lifetime of the system. There are several techniques that can be used to conserve energy in WLANs, WPANs and WSNs. Let’s take a look at your options to conserve power in different types of wireless networks, in order to avail the best usage time from the battery.

WLAN: Turn Off the Radio

Maximum power of the system is used during transmission or uploading and reception or downloading of data. To reduce power consumption, the radio of the system should be turned off, which is one major source of power usage. With the radio switched off, the system swaps between the active mode and the power save mode – it uses power while the client works and sleeps off during

the intermittent phases, thus reducing power consumption. This uses the Traffic Indication Maps (TIMs) to buffer the data during the power save mode, and this data is sent to the power save clients at fixed time intervals, as and when they change into active mode.

The client informs the access point that its power save mode is active and the access point keeps a note of the modes of all the clients attached to it. Before transmitting the data, the access point sends a message to the client about the buffered data. The client in turn sends a request to the access point for the data which is then transferred to the client. After the process client again goes into power save mode and the process continues. This process helps in conserving energy on a very large scale, but at the same time it hampers the performance.

WPAN: Shift to Sniff, Hold and Park

WPANs, or Bluetooth networks as they are commonly known, has all the clients arranged in groups which are referred to as piconets. In this network, one is the master node and the rest are the clients or slaves. A single piconet can have seven live nodes at a time, whereas 256 nodes can exist in total. These also follow the similar sleep pattern as mentioned above, but different communication threads exist between master to slave and slave to slave.

These networks have eight working stages, out of which three stages called Sniff, Hold and Park relate to the low power usage. In the Sniff stage, all the communication takes place at a reduced power consumption rate. The communication shuts down in the Hold mode, but the two devices remain connected. In the Park state, the communication shuts down and turns off between the two nodes.

Lower Power Consumption with WSN

Wireless Sensor Network’s 802.15.4 standard, offers less consumption of power along with a reduced data rate. This standard is also based on the synchronous sleeping pattern, where the nodes become active and go off to sleep alternatively. The only difference between the other standards and this one, is the frequency of the activation of nodes and data transmission, which results in an overall dip in the power consumption.

In addition to the above there are numerous protocols, as well as standards, which can be used for wireless networking power management. Apart from these, different techniques are used to lower the rate of power consumption at different layers of networking. But, the above discussed are a few most commonly used techniques to conserve power in wireless networks and provide high usage capabilities.

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