Energy is becoming a very scarce resource. Hence, a shift towards a Green paradigm is increasingly dominating all kinds of industries nowadays. Energy saving is not the only goal of the green paradigm. Reducing pollution and waste emissions, especially CO2, is among the foreseen targets. A high percentage of research efforts, in all areas of industries, is devoted to reducing the CO2 footprint. Although ICT contributes to the CO2 emission only with a low percentage, ICT is not much different. Many research efforts have been devoted to decrease the CO2 footprint of ICT. C2POWER, an EU funded project which aims at decreasing power consumption within mobile terminals in a multi-standard wireless environment, is one of those research efforts.
C2POWER adopts an innovative approach in this field. Within the scope of the project, cognitive radios and cooperation among mobile terminals are utilized for saving battery power of mobile terminals. Cognition and cooperation have already been addressed in the wireless mobile world. Cognitive radios are usually used for better spectrum utilization, while cooperation is usually targeted to enhance the channel radio quality. C2POWER plans to go beyond the state-of-the-art and becomes one of the pioneers in using cognition and cooperation jointly for power saving purposes.
As its main outcome, C2POWER is expected to achieve a high reduction in energy consumption of mobile terminals, that is foreseen to reach 50% energy saving. These savings will affect not only the mobile terminal usage but also the overall well being of society.
On the operational side, less energy consumption, especially in the transmission side, can result in a higher capacity of the networks due to less interference, as well as in longer battery lifetime of mobile terminals. Hence, users can experience the real mobile experience, which means roaming freely and not being bound to any single location, without worrying about what type of RAT the mobile terminal is accessing or running out of battery.
For the well being of the society, C2POWER will decrease the average required transmission power of mobile terminals, leading to a decrease in both pollution/emissions and harmful radiations for the human being.
Despite the fact that C2POWER main concern is reducing energy consumption on the mobile terminal side, the outcome of C2POWER is expected to reduce the total energy consumption in the whole mobile network, as well as to provide visions for reducing energy consumption on the network side alone. Reducing the total energy of the mobile network decreases the undesirable CO2 emissions of these networks, thus making them more environmentally friendly.
In this article, we are going to introduce the C2POWER project. The main ideas and innovations of C2POWER will be presented. Current results are shown with some insights about expected future ones. C2POWER contributions toward green communications and reducing wasteful emissions will be highlighted as well.
4G systems are expected to provide a true mobile experience to mobile users, with higher data rates and better QoS (Quality of Service). True mobile experience means the freedom to roam freely, while always being connected to some type of network. In fulfilling these goals, 4G systems consist of overlapping heterogeneous networks, requiring multi-standard wireless mobile devices. Multi-standard mobile devices have higher ability to stay connected, but also higher power requirements.
With the increase in data rates and the multi-standard interfaces, the power requirements of mobile devices are increasing. Additionally, other advanced capabilities (for example GPS and advanced imaging features like camera, high-definition displays, etc…) are deployed on mobile devices. These advanced features increase the power requirements of mobile devices even more.
Mobile devices depend on rechargeable batteries for their power supply. Battery capacity is finite and the progress in battery technology is slow. Battery capacity has increased by only 80% within the last decade , compared to processing performance, which doubles every 18 months following Moore’s law. No breakthrough is foreseen in the battery industry in the near future unless completely new technologies are invented.
It is clear that there is a growing gap between energy requirements of emerging wireless MTs and what can be achieved by the progress in battery technology, circuit design, and thermal and cooling techniques. Hence, one of the biggest impediments of future wireless communications systems is the need to limit the energy consumption of the battery-driven devices so as to prolong the operational times and to avoid active cooling. There is a definite necessity for new approaches for power saving in wireless mobile systems, in order to allow mobile devices to utilize the advanced applications offered in present and future networks. In fact, without new approaches for energy saving, there is a significant threat that the 4G mobile users will be searching for power outlets rather than network access, and becoming once again bound to a single location, a phenomena which is sometimes referred to as “energy trap” of 4G system .
Even if new technologies could achieve the energy and thermal requirements of future mobile devices, environmental and human exposure to radiation issues will continue to exist.According to the International Telecommunication Union (ITU), (Information and Communication Technologies) ICT was estimated to contribute around 2-2.5 per cent of global greenhouse gas (GHG) emissions in 2007, and a typical communications company spends nearly 1% of its revenues on energy, which for a large operator can amount to hundreds of millions of dollars . In particular, a study reports that currently 13.7 billion kWh of electricity would, among the other effects, means the emission of 1.07 million metric tons of carbon equivalent greenhouse gas . These values can be used to consider the effect of energy saving on the environment. Compared to other sectors, the ICT industry is responsible for a relatively small portion of global greenhouse gas emissions, but ICT usage is expected to grow rapidly over the coming decade, especially in developing countries. The ICT contribution to global greenhouse gas emissions will at least double over the next decade as more people seek to connect with each other and with more content in new, richer ways.
Based on the above discussion, there is a definite need for new disruptive strategies to address all aspects of power efficiency from the user devices through to the core infrastructure of the network and how these devices and equipment interact with each other in an energy-efficient manner. ICT-C2POWER (Cognitive radio and Cooperative strategies for POWER saving in multi-standard wireless devices) project is the vehicle to address these issues through cognition and cooperation.
Cognitive radio and cooperative networks are becoming key disruptive technologies in the field of wireless communications. Cognitive radios have always been used to improve spectrum efficiency and cooperative strategies are mainly developed for enhancing wireless link capacity. C2POWER project will go beyond the state-of-the-art by investigating how cognitive radios and cooperation can be jointly utilized for reducing power consumption of MTs.
Although C2POWER main concern is power efficiency on the mobile terminal side, the anticipated results are expected to decrease the total energy consumption of all entities of the network or at least give indicative directions for solutions to reduce power consumption on the network side as well.
The article is organized as follows. Section 2 introduces the motivations behind C2POWER. The considered scenarios are explained in Section 3. Section 4 presents C2POWER methodology, highlighting the main innovations of the project. Section 5 lists the impacts and Section 6 concludes.
The promise of a truly mobile experience is to have the freedom to roam around anywhere and not be bound to a single location, however, the energy required to keep mobile devices connected to the network over extended periods of time quickly dissipates. In fact, energy is a critical resource in the design of wireless networks since wireless devices are usually powered by batteries. Battery life time has been identified by TNS report as the number one criteria of the majority of the consumers purchasing a mobile device . Reaffirming this, concern with using up battery is one of the top reasons why consumers do not use advanced multimedia applications on their mobile more frequently.
Current 4G vision envisages higher data rates and multi standard radio interfaces (UMTS, LTE, Wi-Fi, DVB-H, Bluetooth, etc) to provide users with a continuous connection. However, stateof the art multi standard devices have high power requirements for maintaining two or more radio interfaces, in addition, advanced imaging features (camera, high-definition display, etc.) and GPS/Galileo receivers will increase considerably the power demand of 4G handsets. This rise of power consumption combined with the wished reduction in size of handset devices causes temperatures to increase because the transfer of heat is proportional to the surface area. Increased temperatures have two effects. The first is that the temperature of the casing of the device can go up such that it becomes too hot to handle for the user. The second effect is that higher temperatures make the electronic components unreliable and more likely to fail. It is envisaged that a dramatic increase in energy consumption of 4G mobile device will make active cooling a necessity. Even though active cooling is not an attractive solution for users and manufactures, recent works have recently started studying the performance of fans within mobile phone architectures . From the mobile manufacturer’s perspective the energy consumption problem is critical, not only technically but also taking into account the market expectations from a newly introduced technology. This is in fact becoming a key concern: there exists a continuously growing gap between the energy consumption of emerging radio systems and what can be achieved by:
· Battery technology evolution.
· Scaling and circuit design progress.
· System level architecture progress.
· Thermal and cooling techniques.
Therefore, one of the biggest impediments of future wireless communications systems is the need to limit the energy consumption of the battery-driven devices so as to prolong the operational times and to avoid active cooling. In fact, without new approaches for energy saving, there is a significant threat that the 4G mobile users will be searching for power outlets rather than network access, and becoming once again bound to a single location. Some authors describe this effect as the “energy trap” of 4G system .
Another challenge of future wireless radio systems is to globally reduce the electromagnetic radiation levels to have a better coexistence of wireless system (less interference) as well as a reduced human exposure to radiation leading to the so called Green Wireless technologies . In this context, in September 2008 the European Parliament adopted a resolution on the mid-term review of the European Environment and Health Action Plan, which highlights the health risks posed by emissions from MTs . It notes, in this respect, that the limits on exposure to electromagnetic fields are obsolete and should be amended, because they do not take into account recent developments in new wireless technologies, like multi-standard devices. Low-power communication can potentially contribute to ameliorate public concerns about health issues related to mobile communication.
There is a need to reduce the harmful gas emissions of different types of industries, including ICT. According to ITU, ICT was estimated to contribute around 2-2.5% of global greenhouse gas emission in 2007. Mobile communication technologies contribute to 9% of this ICT emissions. Although the ICT and the mobile industry are responsible for a relatively small portion of GHG emissions compared to other sectors, ICT impact (including mobile communication) is predicted to rapidly rise. The Global e-Sustainability Initiative (GeSI) research estimated an increase of 72% in direct ICT energy usage from 0.83 GtCO2e (Giga tons of Carbon dioxide equivalent) in 2007 to 1.43 GtCO2e in 2020, if the industry remains on the current trajectory . There is a need to cut down on CO2 emissions in mobile communication industries.
Another motivation for research on energy saving in ICT industries is the study done by Bell Labs, which estimates that today’s ICT networks have the potential to be 10,000 times more efficient than they currently are, according to the physical limits imposed for example by Shannon’s law .
Based on this discussion, there is a clear need for new disruptive innovations to address power efficiency in multi-standard MTs, if mobile networks are to provide the real mobile experience with a lower harmful emissions that affect the well being of our environment.
3. Proposed Scenarios
In our work, we consider cognitive radios and cooperation among MTs for the main goal of reducing energy consumption on the MT side. To use as guidelines, we define three reference scenarios, which help in identifying the technical challenges of our approach. The three scenarios are:
The first two scenarios exploit the two main approaches explored in our work, namely cooperation among MTs and smart green handovers. The third scenario is the combination of the two other scenarios. In brief, we describe the three scenarios.
Short range cooperation in homogeneous networks
In this scenario one infrastructure-based RAT, which can be UMTS, LTE, WiFi or WiMAX, is available. MTs are equipped with a short-range cooperative air interface, which is based on low power technology, like UWB, Bluetooth, etc. MTs located in the vicinity of each other form a cooperative cluster, which is mainly motivated by power saving. Some MTs may need some incentives to join the cluster. These incentives create new opportunities for business models for network operators, where MTs can use auctions to sell their resources (i.e. battery energy, bandwidth, etc.). MTs with good channel conditions can relay data from other MTs with worse channel conditions. This scenario takes advantage of the spatial proximity and diversity within a group of cooperative MTs. The scenario is illustrated in Figure 1, where node A is connected to the RAT but is running low on battery. Based on context information, node A becomes aware of the presence of a short-range cluster in its vicinity and decides to use short-range communication to connect to the RAT. Node A uses cooperative short-range communication with node B and/or node C to reach the same centralized RAT.
Figure 1. Short-range cooperation in a homogeneous network
Energy efficient handover exploiting heterogeneous networks
This scenario is based on the fact that multiple RATs coexist in the same location. Multi-standard MTs have the ability to connect to different types of RATs. In this scenario, the MT always tries to use the most energy efficient RAT, based on current conditions (e.g. location of MT, channel conditions, RATs loads, etc.). MTs explore their chances to connect to different RATs, evaluate the performance of each available RAT connection, and then determines which RAT is the most suitable to connect to. The MT can take into consideration different factors beside energy efficiency. For instance, one MT can be more concerned with the price to be paid for certain RAT connection, while other MT can care more about the QoS. Figure 2 presents the scenario of energy efficient handover between heterogeneous RATs. In the figure, the channel conditions between the MT and RAT2 are better than the channel conditions toward RAT1. The MT knows about RAT2 using cognitive radios and context information. Hence, the MT decides to perform vertical handover from RAT1 to RAT2 for the sake of saving its battery power.
Figure 2. Energy efficient handover exploiting heterogeneous RATs
Short range cooperation among heterogeneous RATs
This scenario is the combination of the previous two scenarios. In this scenario, the presence of multiple RATs is assumed. In addition, MTs are equipped with a short-range cooperative air interface. MTs located in the vicinity of each other form a cooperative cluster, which is mainly motivated by power saving. Within the cooperative cluster, different MTs posses different RAT interfaces, allowing them to connect to different RATs. Hence, MTs exploit all energy saving possibilities, including short-range cooperation and energy efficient vertical handover between different RATs. Figure 3 describes this scenario, where Node B is initially connected to RAT 2. Using context-awareness capabilities, Node B detects the presence of a node in its vicinity, which is ready to cooperate using short range communication (e.g. UWB). After the negotiation between both nodes, it is determined that Node A can provide the QoS required by Node B, through relaying to RAT1. In addition, this short-range cooperation has lower power requirements, resulting in increasing the battery life time of Node B.
Figure 3. Short range cooperation among MTs using heterogeneous RATs
4. C2POWER Methodology
The objectives within C2POWER will be implemented according to the scenarios defined and the end goal will be to design, develop and evaluate the algorithms that will be the enablers for energy efficient based on short-range cooperation and cognitive protocols/algorithms.
The key concept of C2POWER relies on the ability of the mobile devices to use multi-standard air interfaces, which enable mobile devices to use intelligent handovers between heterogeneous RATs, as well as to establish cooperation with nearby devices using low-power short-range communication, to achieve the least energy consumption. C2POWER main scheme resides in the intersection of cooperation, heterogeneous networks, and advanced short-range communications, while exploiting context aware information about the surrounding environment using cognitive radios.
The architecture and algorithm design will progress along four collaborative tracks, with milestones that include the implementation of the key hardware module/components that will be integrated in the proof-of-concept phase to demonstrate two major technology showcases on cooperative short range for power saving, and energy-efficient cognitive handover procedures. The methodology includes:
· Context awareness and signalling for power saving strategies:
Using cognitive radios, context aware information is extracted. Information about available RATs and nodes in the vicinity of mobile nodes is extracted using cognition and cooperative sensing and is used by mobile devices in the process of network/node discovery. Additionally, C2POWER concept will make use of available information in entities like ANDSF in 3GPP  and MIIS in IEEE 802.21 . Useful parameters like frequency bands used by available networks and short range collaborative clusters are also extracted to save energy needed for scanning different frequency bands. Context aware information, like battery level and speed of nodes and capabilities of RATs, will be used to determine the most energy efficient connection option. Under this umbrella, node and network discovery mechanism will be studied and tested to determine the most energy efficient mechanism to use.
C2POWER will also predict, based on history of context parameters, the user (MT) future behaviour, which can help in saving energy in various ways. Based on these context information, C2POWER mechanism can instruct the mobile device to switch ON/OFF certain radio interfaces to save energy, in addition to which frequency bands to scan instead of scanning a wide range of frequencies.
· Cooperative short range communications for power saving:
Cooperative short-range communication procedures for power saving will be defined. Utility functions will be used to determine the best nodes to cooperate with. In addition, energy efficient routing and cooperative relaying will be studied to achieve the most energy efficient communication, using context aware information such as battery levels and mobility profiles of nodes.
· Energy-efficient cognitive handover:
C2POWER investigates energy-efficient cognitive handover algorithms (scenario 2), then implements and validates a context-aware architecture for testing energy-efficient handovers in a heterogeneous networking environment for proof-of-concept. Handover procedures make use of available context aware information to save energy by always switching to most energy efficient RAT available in the vicinity.
· Energy-efficient reconfigurable radio transceivers:
All previous techniques will be designed on top of energy efficient multi-standard transceivers, which will be designed within the scope of C2POWER. Design of multi-standard transceivers and the hardware design must be ruled by energy savings, but with inherent flexibility. C2POWER MTs will have multiple radio interfaces, which use innovative techniques for efficiently switching between different technologies including short range communications.
5. C2POWER Impact
C2POWER main objective is to contribute to decrease the envisaged rise of power demand in 4G handsets as shown in Figure 4.
Figure 4. C2POWER impact on power consumption in MTs
The result of the energy saving techniques will be a larger number of hours of uptime for MTs, related to a smaller number of joules consumed by the mobile terminal. A possible metric for measuring the energy saved is:
Energy Saving Gain=1- (Energy with technique / Energy without technique) %
The improvement that is targeted by C2POWER is 50% of the current used energy for cooperation, 15-20% for vertical handovers.
Although C2POWER main concern is the energy consumption of MTs, the outcomes of C2POWER are expected to reduce the total energy consumption of the whole mobile network in general, as well as to provide visions for reducing energy consumption on the network side. Reducing the total energy of the mobile network reduces the undesirable CO2 emissions of these networks, which is a common goal for the well being of our environment.
With the advanced service offered by 4G and future networks, increased energy requirements are expected. Mobile devices depend on batteries for their power supply. Battery capacity is finite and a breakthrough in the battery industry is not expected in the near future. Without any new disruptive approaches for energy saving, 4G mobile users will relentlessly be searching for power outlets rather than network access, and becoming once again bound to a single location. On the other hand, although ICT (including mobile communication industry) contributions to the CO2 emission is low compared to other sectors, it is expected for this percentage to rapidly increase due to the advances in the ICT industry and the increase in usage. To avoid the 4G “Energy Trap” and help decrease wireless mobile devices contribution to CO2 emissions, there is a definite need for new approaches to address ways of power saving for communications from mobile devices to the core infrastructure of networks. In this context, the ICT-C2POWER project is presented. C2POWER exploits new approaches, by jointly targeting cognitive radios and cooperation strategies, to devise energy-efficient mechanisms for wireless communications of mobile devices. C2POWER is expected to reduce the energy consumption of MTs.
ACKNOWLEDGMENT: The research leading to these results has received funding from the European Community’s Seventh Framework [FP7/2007-2013] under grant agreement number 248577 [C2POWER].
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