Energy consumption of telecommunication access networks

PoP size Number of PoPs Number of subscribers 1,000 21 20,856 750 2 1,438 500 3 1,207 250 7 1,556 100 3 254 50 0 0 Total 36 25,311 Figure 24: Number of PoPs in the model region, calculation based on their spatial location. The different PoP sizes are therefore important, since the energy efficiency increases with the subscriber density per PoP. In other words, the power consumption per subscriber decreases with increasing subscribers per PoP. As the table in Figure 25 shows, the power consumption per subscriber with 10 watts is more than four times higher in a small 50 subscriber PoP than with 2.3 watts in a 1,000 subscriber PoP. This is especially a result of secondary systems like the air conditioning or the power supply. These systems operate much more efficiently at higher subscriber densities. The power consumption for the optical transmission in all PoP sizes is around 1.5 watt. The data on the power consumption for the different PoP sizes are measured consumption figures of operating FTTH networks from different network operators. In total, the power consumption for the 36 PoPs in the model region is about 64.4 kW. This corresponds to CO 2 emissions of approximately 301 tonnes. Power consumption access network PoP size Power consumption (incl. air conditioning) per subscriber [W] Number of PoPs Number of subscribers Total power consumption P [W] 1,000 2.30 21 20,856 47,969 750 2.60 2 1,438 3,739 500 3.20 3 1,207 3,862 250 4.50 7 1,556 7,002 100 7.20 3 254 1,829 50 10.00 0 0 0 Total 36 25,311 64,401 Figure 25: Power consumption of the FTTH – Point-to-Point access network. 6.4.2 GPON access network GPON has a different network structure than Point-to- Point networks. It is based on a passive distribution network with optical splitters. The downstream signal from the PoP is passively separated into several subscriber signals by the splitter. The upstream signal is generated by merging the individual subscriber upstream signals. The location of the splitters can be very different. For example, they can be located somewhere in the field close to the subscriber, like the street cabinets in the copper twisted pair network or they can be located directly at the PoP – a so-called GPON over Point-to- Point structure. In this study, the GPON over Point-to- Point is considered. This allows the same network structure to be assumed as in the previous chapter. The use of splitters allows a very high density of subscribers in a PoP. Today splitting factors of 1:128 are possible. This means that 128 subscribers can be connected to a single GPON-port. However, with GPON the subscribers at a single splitter have to share the maximum transmission capacity of the GPON-port – today approximately 2.5 GBit/s downstream and 1.25 GBit/s upstream. To realise the minimum data rate of 50 Mbit/s per subscriber a splitting factor of 1:32 or less is needed. Typically, the PoPs (OLT) are modular today and have GPONmodules with approximately 16 GPON ports per module. It follows that the 36 PoPs determined (see Point-to-Point) can be mapped into two PoP size classes (512 subscribers and 1,024 subscribers), see Figure 26. In that configuration the power consumption for the access network is approximately 18.6 kW, according to information of equipment manufacturers. This corresponds to annual CO 2 emissions of 87 tonnes. It has to be considered that the minimum data rate per subscriber in this configuration is approximately 78 Mbit/s downlink and 39 Mbit/s uplink. 25