How to build energy-efficient transmissions?

14/4/2023

The development of transmission is not only an increase in the amount of data. Both the transmission speed and the cost of maintaining it matter. Rapid inflation, dwindling raw material resources and the climate crisis are forcing the telecom industry to conserve energy. What until recently was mainly image activities, today has become a necessity.

It is estimated that telecoms companies already consume almost 3 percent of the world's energy, largely due to the rapid increase in traffic that accompanies the growing 5G services. Constantly expanding networks and data centers create huge energy demands. And a greater burden on the natural environment.

In 2021, according to research firm GSMA Intelligence, energy consumption accounted for 15 to 40 percent of operators' operating expenses (opex). Their analysis also shows that nearly half of operators expect energy efficiency technologies to bring operational cost savings.

Ways to reduce electricity consumption

The increase in the demand for bitrate results in the need to expand the infrastructure, the use of more bands for mobile services and the use of more complex antenna systems. Mobile system operators are forced to manage bandwidth sparingly, for example by periodically turning off frequencies that are not needed. These are organizational changes, similar to those we implement in homes by turning off unnecessary light or pulling chargers out of sockets. But how, from the technological side, to reduce energy consumption in the network? There are several ways to do this:

transmission without amplifiers
miniaturization of the technology in the chips used
less energy intensive integrated signal amplifiers
more sensitive receiving systems allowing consequently to work with lower transmission power
use of other, less energy-intensive CDR (Clock Data Recovery) chips

We will discuss in practice the application of several ways to build an energy-efficient network.

DWDM or IPO-DWDM?

For edge transmissions over a distance of 25-30km, Internet providers are constantly increasing the bitrate. When there is a need to transmit 800Gbit/s using one pair of optical fibers, it can be realized in Wave Multiplication Technology (DWDM). However, DWDM requires the use of amplifiers, which generates the need to consume more energy resources and, of course, additional space in the rack cabinets.

Solutions are gaining popularity IP-over-DWDM type. The concept assumes that optical transport modules are mounted directly in IP devices. The omission in the structure of muxponders, transponders and gray optics allows significant energy savings. Depending on the area of the network, it can reach levels ranging from 70% at the edge of the network to 90% in its backbone.

O-Band — transmission without amplifiers

In search of energy-saving solutions for transmissions up to 25 km, it is worth turning to O-Band technology. This solution allows you to save almost 900kWh per year for one 8x100GBit link. What is the advantage O-Band?

O-Band technology consists of passive multiplexers and optical modules in the form of an interface QSFP28 GBC fotonika. The great advantage of O-Band technology is the fact that it does not require the use of optical amplifiers, since transmission over distances of up to 25km is carried out thanks to the power budget coming from the transceiver itself. In addition, chromatic dispersion correctors are not used, since the “O” band is not sensitive to chromatic dispersion, which means that the signal is not subject to distortion.

In addition, by using patented nCP4™ processor technology on the PH18 Silicon Photonics Tower Semiconductor platform, the power consumption required for demanding PAM4 modulation has been reduced.

100G Coherent Modulation

The 100G transmission, until recently present mainly in the core of the infrastructure, is transferred to the edges of the network. This, of course, is associated with an increase in the demand for traffic. So far, coherent modulation has been implemented by DSP processors requiring high power consumption (about 16W for one module) and has been used for 400G bit rates.

The progressive miniaturization of the technology allowed to produce a DSP processor with a consumption of 2W. By mounting it in the interface QSFP28 100G GBC fotonika we obtained a coherent module with a consumption of 5W. Thanks to this type of change, one of the operators achieved a reduction in energy consumption by 65 percent!

Big changes start with small savings. The third generation QSFP28 ZR4 100Gbit/s modules feature a new internal SOA amplifier that reduces power consumption by 1W. Modules of this type are used in gray technology in transmission over 80km. The operator needs a huge number of them, so saving 1W on each module is important (it gives a saving of ~18kWh per year on just one point-to-point connection).

EML laser: further and cheaper

Work on energy savings can also be seen in applications based on different types of lasers: EML and DML. So far, solutions based on EML lasers have been more energy-intensive, but allow transmission over longer distances (over 10 km) and at higher data rates compared to DML solutions.

EML lasers are characterized by:

a much higher extinction coefficient, i.e. attenuation of the light beam (typically for EML > 8, DML > 3.5).
greater by 10-15% optical eye pattern margin.
less jitter (an indicator of interference).
lower chromatic dispersion

The latest EML laser solutions are used in modules with 100G speed per 10km and have only 3.5W power consumption (QSFP28 100G LR4 10km modules). In this case, the energy saving is due to the use of a less energy-intensive CDR system. In terms of energy consumption, this equates the solution to a module based on a DML laser.

The highest transmission shelf

For the latest 400G modules, the possibilities of reducing energy consumption are considerable. This is due to a rather prosaic issue: the first constructions are usually not optimized for energy, so the starting base is quite high.

In the latest developments, DSP processors of direct laser control are used. In this case, a reduction in power consumption of more than 3W is possible.

The changes described above give savings in power consumption from half to a dozen Watts per link. After summing up the power consumption of all devices, it turns out that considerable OPEX savings can be achieved for the entire telecom company. Savings arise here both on the energy consumption side (power x time) and the possibility of reducing the contractual capacity declared and paid by the company.

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