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Digital power management enables lower power consumption

Posted: 06 Aug 2007 ?? ?Print Version ?Bookmark and Share

Keywords:global communications? information and communications technology? digital power management?

By Patrick Le F┬vre
Ericsson Power Modules AB

Certainly, ICT contributes to making our lives better and more efficient. However, the development of global communications and new technologies do!to an extent!contribute to global warming.

During the Gartner Symposium "ITxpo 2007 Emerging Trends," analysts said that the global ICT industry accounts for approximately 2 percent of global carbon dioxide emissions!a figure that is equivalent to aviation, according to a recent conclusion by Gartner.

This number is an estimation and ICT spans a huge array of applications that includes from power hungry data centers to Wi-Fi hotspots and they all performing differently when it comes to energy efficiency and levels of energy savings reached throughout the years.

Among the applications included under the banner of ICT, there is one that merits consideration as example and case study for the next step of implementing digital power management vs. existing analog, mobile radio and radio base station applications.

Mobile communication unfolds
It was only 51 years ago!in April 25, 1956!that the world's first fully automatic system for mobile telephony was launched in Stockholm.

What was called at the time Mobile Telephone System A (MTA) shown in Figure 1 began with eight subscribers, and by expending the service to Goteborg, ended the year with 26 subscribers!

In 50 years, the mobile phone industry has grown extremely rapidly. According to the global trade association GSM Association (GSMA), the number of global subscribers will increase by 40 million per month during 2007.

In early May, Ericsson announced that the one millionth radio base station was shipped to a customer and Powerwave announced that they have deployed over 1.3 million tower mounted amplifiers for hundreds of cellular, PCS, GSM and 3G networks around the globe.

Figure 1: The world's first fully automatic system for mobile telephony was launched 51 years ago.

Both announcements reflect the volume of equipment enabling mobile communication. and with the growing demand for long and mid-range mobile communication systems including GSM, 3G and femtocells, it is easy to see that the amount of energy consumed by the aggregated number of equipment deployed worldwide will continue to grow, requiring a number of measures to limit their environmental impacts.

Radio base station is good but
Compared to other industries, the pure telecom industry has relatively low CO2 emissions. Ericsson estimates that the industry is responsible for 0.4 percent of global primary energy consumption and 0.3 percent of CO2 equivalent emissions. Out of about 2.6 billion subscribers, it is estimated that the mobile telecom's CO2 equivalent represents just 0.09 percent.

Looking over the evolution of energy consumed by mobile radio and CO2 emissions (Figure 2), it shows that since the introduction of the first-generation mobile systems that energy efficiency has improved, while performances and capacity have continuously increased. Environmental impact though, has to be further decreased.

Figure 2: It is estimated that the mobile telecom's CO2 equivalent represents just 0.09 percent.

Ericsson's life-cycle-assessment estimates that 52 percent for GSM and 54 percent for WCDMA splits with CO2 emission occur when the networks are in operation. These are the parts where digital power and digital power management could contribute to further reduce CO2 emissions while improving systems' efficiency.

Power efficiency in mobile radio
The result of many different measures and technical innovations, as shown in Figure 1, the level of CO2 emission reduced throughout the years follows a general improvement in the efficiency of DC/DC converters (Figure 3).

Driven by new components and innovative topologies, the power industry has managed over two decades to drastically improve the power efficiency of DC/DC converters and DC/DC regulators, reaching an upper limit that becomes more and more challenging to surpass.

Components and technologies will continue to improve. Meanwhile, recent examples from by the microprocessor industry have proven that energy and data management can be much better optimized to increase performance while reducing energy consumption. A good example is using multicore processors instead of single core, PMOS technology and sleep transistors.

Figure 3: The level of CO2 emission reduced throughout the years follows a general improvement in the efficiency of DC/DC converters.

At APEC 2006, Pierre Gilbert presented that different parts of a radio system can be greatly improved in terms of energy management. And without disclosing advanced research on the radio transmission part, it is evident that performance improvements will not only depend on natural components' evolution but more on a combination of different technologies such as digital power management associated to new components such as Silicon Carbide.

Telecoms systems are very dependent on traffic and inter-operation between the different cells (Figure 4). Besides software managing the split between cells and allocation, the technology will be tasked to manage at signal processor level, the energy consumption in real time and to predict in advance what the energy system might require before requested by traffic, that is using pro-active energy management.

As it is for portable and nomadic equipment, reaching the most optimum energy-efficiency-management will require managing energy by function at the board level. Such based on today's analog solution is very complex, requiring multiple interfaces making things difficult to work together and to communicate with the rest of the system.

Before considering the implementation of a kind of intelligence in power conversion and power management at system level, it is important to set a common instruction and language, freely available, that everyone understood.

That was the first task undertaken by the electronics industry, which has been successfully conducted under the PMBus initiative, from which results a standardized protocol adopted by most of the industry leaders like Intel and Dell.

In parallel comes the products dimension and how to convert analog DC/DC converters and DC/DC regulators into units that work with or respond to a digital signal without adding extra interfaces and cost.

This step is now partly completed and different papers presented by Ericsson at DPF, APEC and PCIM demonstrated that the migration from analog to digital power management was technically possible and the implementation of the standardized communication PMBus is a reality.

Figure 4: Telecoms systems are very dependent on traffic and inter-operation between the different cells.

From that point, how will such technology help telecoms manufacturers and operators to operate their systems in a more efficient way, resulting in less power consumption and lower CO2 emission?

When digital power becomes a reality
Often, one only considers the core processor as being "the component" requiring tight control. But if that is a very important part of the system, such components are relatively easy to control because they are already digital.

For some time, the voltage regulator module and the voltage regulator down have been able to communicate with the processor, so digital control is virtually there. And by adopting PMBus, Intel has given a clear signal that future products can easily communicate with their neighbouhood.

As mentioned, power consumption in mobile radio applications is very much driven by traffic. And by combining traffic management and intelligent power management, it will be possible to only power the required part of the system needed at that time and to standby the rest of the time if not required. Otherwise, when traffic increases, the traffic management controller will enable additional functionalities.

For example, traffic management can control the number of power amplifiers in operation and decide to power on or off some of them, when traffic increases or decreases or to adjust the polarization voltage to the most efficient profile at time.

At cabinet level, certain boards that include mixed functionalities, which are only required at a certain times during the operation, can be powered on/off or adjusted to suit vital parameters. Moreover, it can be precisely monitored to enable the traffic management controller to report in real-time to the site manager on different parameters.

Driving power management down to the vital few is also very important to reduce the fixed operational power and especially the power consumed by air-conditioning and ventilation. On average, 30 percent of the power consumed in a radio base station is for cooling.

By adding digital control to individual boards and PMBus, it becomes simpler to control cooling and ventilation, optimizing operational conditions to suit specific traffic conditions and statistically profile the power demand for the requirements of the next flow of traffic.

If considered at start of the project, the same topology can easily be deployed to fix access and other ICT applications such as data centers, reducing power consumption and CO2 emission.

It is always difficult to precisely predict tangible numbers on a new technology and how far such technology will drive the reduction of power consumed by a system though, as reported by Ericsson, among several activities to reduce CO2 emission, the implementation of a standby capability during low load and implementation toward the parking of base stations deployed since 1995 will save between 10 and 20 percent of energy, resulting in a saving of 1 million tons or more of CO2 per year.

Indeed, the implementation of digital power management will strongly contribute to further reduce energy consumption. What we are seeing today as result of energy management is only the early beginnings of digital power benefits at systems level.

About the author
Patrick Le F┬vre
is a marketing director at Ericsson Power Modules AB.

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