Green Wireless Access

By some estimates, cellular networks consume 0.5 % of world-wide energy consumption, with 1 % consumed by the user handsets and 99 % consumed by the network [18]. Meanwhile, multiple-interface phones (Cellular with WiFI, Bluetooth, ANT+, etc.) have been observed to deplete their batteries much faster when all the radios are active all the time. Not surprisingly, then, that several initiatives and research projects have focused on reducing the energy requirements of wireless and mobile networks over the past few years. The projects, in general, vary in their approaches and their objectives. Some, for example, have focused on energy reduction through interference management – reducing the energy requirements of mobile handsets to reliably transmit its data. Network design plays an important role, whereby the location of the fixed base stations and the trajectory of the mobile stations are decided in a manner that also reduces handset energy expenditure. Meanwhile, energy can definitely be added to the considerations of network selection. Advances in dynamic spectrum allocation will also play a major role.

These enhancements, however, focus on handset energy expenditure. To alleviate some of the network expenditure, it is possible (to) utilize renewable energy sources such as solar and wind turbines. More advanced mechanisms, however, can also be employed. For example, it is possible to deploy high density access configurations whereby the all base stations would be turned in instances of high demand, and only a portion of the base stations would operate when the demand decreases. Naturally, a small coverage would be used when all base stations are turned on, and a wider coverage when only a portion is operating.

As in the case with the design of RRM frameworks, there are certain tradeoffs bound to how “green” the operation of a wireless network can be [19]. These include the tradeoff between deployment efficiency and energy efficiency, where deployment efficiency refers to the network throughput per cost performance vs. the network's energy consumption. There is also the tradeoff between spectrum efficiency and energy efficiency – directly relevant to the optimization-overhead tradeoff discussed above. Spectrum efficiency, particularly, is an energy-exhaustive process, as it requires sensing in several spectrum bands, possibly simultaneously. Such sensing also needs to be made during secondary user transmission, as secondary users are required to vacate the primary user's spectrum once the latter begins communicating. The remaining tradeoffs include the bandwidth vs. power and delay vs. power tradeoffs. These tradeoffs, while open for optimizations, should be minded in the design of green networks.