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C. Optimizing Power Consumption of the Remaining Components
When the networks are optimized and the load is minimized, the power consumption of the elements should be reduced.
In next generation PONs (NG-PON), OLTs will be designed for higher bit rates (up to 10 Gbps per port) and higher split ratios (up to 1:128 or even 1:256). Additionally, the range of the signal will be increased, supporting up to 60 to 100 km. In itself, a higher range will lead to a higher power consumption per OLT and can require active remote nodes which add additional power demands. However, in large operator networks there is an ongoing trend of node consolidation reducing the number of central offices and leading to long-reach access areas. This network consolidation can enable important power consumption reductions.
The energy efficiency of wireless access networks can be improved by increasing the ranges of the base stations. Thus, larger areas can be covered by a single base station and less base stations are necessary. This can be done by the use of multiple transmitting and receiving antennas. This technique is known as MIMO (Multiple Input Multiple Output). When using for example 2 transmitting and receiving antennas, i.e. 2x2 MIMO, the range increases with 66%, while the power consumption increases only with 2 to 4% resulting in a higher energy efficiency. In the next generation technologies, LTE-Advanced and WiMAX 802.16m, up to 8 transmitting and 8 receiving antennas can be used.
The technique of optical bypass illustrated an evolution from point-to-point WDM networks to more optical circuit-switched networks. Optical burst switching and optical packet switching take this technique further and are supposed to provide an even finer switching granularity. In optical packet switching, individual packets are switched optically on the correct out-going fibre. Since optical buffers with an appropriate size are currently infeasible, optical burst switching is proposed as an intermediate technology. A control signal is sent in advance of the packets, allowing the burst-switched router to set up a light path for the data, thus eliminating the need for buffering.
While optical packet switching can lead to low power consuming solutions since it eliminates power-hungry optical-electrical-optical conversions, it is not yet technically feasible [9]. On the other hand, it is argued that with the line card buffers and switch fabric, the two main candidates for optical implementation, consuming only about 15% of the total power consumption of an electronic router, potential energy savings are not as high as commonly expected [10]. A hybrid approach in which optical switches still use electronic buffering seems a more feasible low-power approach for the next decade.
It is not yet clear if the technique of optical burst switching is a viable alternative, the main issue being the relatively low throughput requiring an overbuild.
For continent-sized core networks, increasing the maximum optical path length (i.e., not requiring regeneration of the optical signal) can reduce power consumption. For a pan-European network, savings can be up to 10%.
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