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Although many power-reduction methods have been standardized for WLANs and Bluetooth, the way a wireless chip implements these techniques has a profound effect on power consumption in real-world applications.
For example, shortening the time needed to go into standby mode achieves better results than reducing the amount of power consumed in standby mode. Increasing data rates can also achieve significant power reductions.
Power relationships such as these are explored in this article—the second in a two-part series on power-reduction methods for wireless devices. The first article in the series provided an overview of device operating modes and the power-saving protocols available in today’s wireless standards.
To read Part 1:
System behavior and host interaction
Beyond protocol-based power savings, several additional methods can save power equally well for Bluetooth or WLAN systems:
Quick wakeup and return to sleep
System and host interaction
These methods look at the entire host system and involve interactions between a wireless chip and its host.
As Table 1 shows, high data rates can save power. This idea is somewhat counterintuitive because higher data rates usually increase a device’s instantaneous power consumption while actively transmitting and receiving.
Table 1: Effect of Data Rate on Power Consumption.
The truth is that radios have a large amount of power-consumption overhead that is independent of the data rate. The synthesizer, low-noise amplifier (LNA), mixers, filters, and other components have to be on for transmitting and receiving independent of the data rate. That power consumption is a fixed overhead.
The increase in the power of the ADC and digital processing to support higher data rates is actually fairly modest. For most wireless systems, scaling the data rate up and down does not significantly change the average power consumption while in active transmit-and-receive mode.
However, the protocols allow the radio to enter an order-of-magnitude, lower-power sleep mode as soon as data has been transferred. So when moving a file or sending data for VoIP or video, the system can spend more of its time in sleep if the data rate is high.

embedded.com