- Image by The Udall Legacy Bus Tour: Views from the Road via Flickr
Green IT was all the rage at last year’s Interop show, with lots of companies looking for ways to help reduce both a datacenter’s power bill and its impact on the planet. But from a business perspective, the biggest reason for energy efficiency isn’t either of those. It’s simple survival: The less power your systems use, the longer they’ll be able to keep running from a UPS in the event of an outage.
Mobile users know this only too well. Most of the same technologies used for making data centers more efficient also apply to laptops or phones, and many of them (from sold-state storage to the latest CPUs) even started out there. The intent is the same: to increase performance per watt. And the end goal is even more clear: to extend battery life.
But with most mobile devices connected wirelessly, it isn’t just the design of the device itself that impacts battery life and energy efficiency. Technology within the wireless network can also have a big effect by reducing both the amount of power that a mobile device needs to pump out of its radio transmitter and the time it has to spend switched on. As laptops, phones and other mobile gadgets get smaller, this effect gets more significant.
The main factors affecting how much power a radio needs to transmit are the distance the signal has to travel and the gain of the antenna. The former makes it particularly important for Wi-Fi devices to connect to the nearest AP, something that doesn’t happen automatically in most 802.11 networks. They leave it up to the client to determine which AP is closest, a process that itself uses up energy and can result in “sticky clients”: devices that remain connected to an AP even as they move into closer range of another.
Meru’s Virtual Cell architecture is an exception, leaving management decisions to the network. Client links are automatically load balanced by Meru’s Air Traffic Control technology, routed through the most appropriate AP. This was designed mainly to simply network management, maximize bandwidth and reduce handoff time (as far as the client is concerned, handoff of invisible) but one nice side effect is that it reduces power consumption and extends battery life.
With Wi-Fi, a better radio link can save power in another way: by reducing the amount of time that a radio needs to spend transmitting. All 802.11 standards automatically drop down to lower data rates in the presence of interference, and this effect grows more important with the move to 802.11 as its data rates have such a wide range wide range – from 300 Mbps to down to 6 Mbps. Battery life (and overall network performance) is optimized by ensuring that clients spend as much time as possible at the full 300 Mbps.
The same principle – that efficiency leads to greater uptime – can apply in other areas. For example, the radio spectrum itself available to Wi-Fi networks is limited, especially at 2.4 GHz. The Virtual Cell architecture allows a complete wireless network to be built using just one physical radio channel, whereas others need at least three to mitigate co-channel interference. That leaves the remaining channels free to be used for other purposes. Some can be used for extra capacity, but the most critical use may be redundancy: A spare radio channel kept on hot standby in case of interference, making Wi-Fi as reliable as Ethernet.
