I‘ve promised to come back to this topic in my comments to earlier blog postings and now it’s time to do it. Let me start by telling the very recent conversation between my team member and one of the APAC area cellular network operator. It went like this:
Nokia: Are you planning to deploy this feature X in you cellular network?
Operator: Why don’t you rather tell me about your display power optimizations? Isn’t it so that displays are consuming most of the power in the smartphones?
This dialog highlighted the need of telling people that how power consumption breaks down in the device between different use cases. Display is one of the biggest battery drainers but cellular radio also belongs to that same category and therefore shouldn’t be ignored. By reading further this post you’ll notice that display backlights is turned off during phone call and this means 0 mW power consumption for display in that particular use case. That said, no help of display optimisation if you just want to talk longer.
Power consumption breakdown (mW) examples
Above we have four different use cases and their power consumption breakdown. Those pie charts are based on real figures from one of the Nokia Symbian device platforms. Some variation occurs between our HW platforms and especially display share can be much bigger or smaller depending on display technology (LCD, OLED), physical size (larger consume more) and brightness settings (backlight dominate display sub system power consumption). By looking the pies, following can concluded:
- Typically three most power hungry units are processor, display and cellular radio. Breakdown is always use case specific and shares differ a lot.
- During voice call cellular modem is consuming vast majority of the power and other HW parts are most of the time in sleep mode
- Video call over 3G network and Browsing are good examples of the use cases which load the system heavily and basically all three major units are utilized.
- 3D gaming loads GPU and CPU and display and typically modem is turned off (when not playing online game)
But remember, that in order to understand the full picture, we need to know total power consumption of the use case and also how often it is used. Your application can consume 1W power if it is never used but if it is popular and gets used a lot, then even figure that sounds small starts to make sense to optimise.
In Symbian you get total power consumption of the device by running Nokia Energy Profiler (NEP). Good starting point to get ballpark of application level power consumption is to calculate delta when application is running vs. when it is not installed. Nokia Battery Monitor is another way of getting valuable information of how much your application is contributing to total power consumption. Version 2.0 will be soon available and it provides application level energy monitoring.
How much is daily usage then? People spend lot’s of time with popular applications and those will become major shareholder of the device daily energy consumption. At this point energy efficiency starts to show up.