23 July 2009

Artificial noise saves energy

There is now a plan under development that will allow xDSL systems to function more energy-efficiently and cost-effectively.

Ecological and economic factors are prompting telecommunications companies to deploy energy-saving systems. The broadband DSL access network consumes about 20 billion kilowatt-hours of energy per year worldwide—equivalent to 4% of Germany’s annual energy consumption. The use of a low-power mode (L2 mode) in standard ADSL2/ADSL2+ systems could significantly reduce the amount of electricity consumed by the DSL network. At present, broadband access always runs on full power, but the L2 mode could reduce the transmission output of the system and therefore its power usage during quiescent communication. Although the mode is already a standard and is present in quite a few devices on the customer and network side, it is not seeing any use. The problem is L2 mode causes considerable interference to neighboring DSL systems.

When a modem connects to the Internet while neighboring modems are still in L2 mode, only a small degree of interference occurs, and the data transmission rate is high. If, however, systems in neighboring houses or apartments become active, the interference to the first system is so great the connection can crash and the modem can only go online again after a prolonged restart phase. Furthermore, the data speed is significantly lower. For this reason, the operators of broadband networks deactivated the low-power mode and did not include it in the standardization for future broadband connections with faster data transmission rates.

By using artificial or virtual noise, scientists at the Fraunhofer Institute for Communication Systems ESK were able to stabilize DSL connections so they can deploy L2 mode. The artificial noise simulates typical cable bundle interference to the broadband receivers. When a modem tries to connect to the Internet, the system registers normal interference even if the device next door is in low-power mode. Although the connection does not take place at the highest-possible transmission rate, it remains stable when a neighbor goes online. The L2 mode and artificial noise can now come into play.

Network operators could reduce their electricity consumption by several million kilowatt-hours per year, which in Germany alone would mean an annual saving of $21.3 million (€15 million) on operating costs.

For related information, go to www.isa.org/manufacturing_automation.