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Wireless mode of communication have had an explosive growth in the recent years.Within the last decade wireless networks have significantly impacted the world communication system. It can also be safely said that like internet wireless systems have a long forseeable future.Today more than four billion people have access to the mobile phones.Wireless internet commection are growing at a supersonic rate.Such popularity of wireless networks demand high efficiency be brought into developing these system and a major part of this depends on the energy efficency.
The cellular wireless system is currently transitioning to LTE ,due to the tremendous upswing of mobile Internet access demand. This next-generation mobile infrastructure provides broadband access and enables new classes of applications for mobile users.
With the emerging traffic demand, mobile operators are under pressure to enhance their infrastructure in a competitive time frame. However, the investment to enhance the infrastructure does not always pay off because the average revenue per connection continues to decrease.Consumers today not only expect high performance but also high efficiency.Wirless manufactures and service providers have come to aknowledge the fact that reduction in energy consumption have become vital. The facts say that 3% of the total energy consumed by the world comes from information and communication technology. Most of these energy comsumption comes from non reneuable sources and thus effectively causes 2% of the total carbondioxide emmison to the atmosphere.
To overcome such a price-pressure trend, energy saving is one of the key subjects for mobile operators' total cost of ownership reduction. Because the base station accounts for most of the energy consumption by mobile operators, improving the energy efficiency of base station key components, such as power amplifiers and air conditioners, is of great importance.
Social responsibility is yet another driver for an energy-efficient mobile infrastructure. By deploying energy-efficient base stations, operators can reduce the CO2 emission from their network. Vendors can contribute to the efforts against climate change by providing technologies that lower network equipment's power consumption.
Achieving the highest possible energy efficiency is very important, independent of the actual energy source that is used for powering the access network.
Effective energy management is a key to address these requirements, and therefore the Green Radio solution was introduced for Long Term Evolution, highlighting some NEC developments in this area, as well as standardization aspects in terms of future green technologies.
The specific objective of the Green Radio programme is to investigate and create innovative methods for the reduction of the total power needed to operate a radio access network and to identify appropriate radio architectures which enable such a power reduction.
The typical power consumption of different elements of a current wireless network are
This result clearly show that reducing the power consumption of base station or access point (BS/AP)is an important element .More than 50% of the total energy consumed is by the base station equipments. Base station is the center which is responsible for controlling the trafic between mobile phones and other wireless networks and equipments.As more and more volume of transmitted data contiouus to increase there is a need for more base station or atleast base station which can handle high volume of traffic.
In the lifecycle of a base station, power consumption is more dominant in the deployment and operational phase than in the production phase. Therfore reducing the power consumption of these base station and ease of deployment are critical for an energy-efficient mobile infrastructure.
The objective of green radio can be achieved by using the combination of the renuuable source of energy and simultaneously finding ways to reduce the power consumption by improving the technology and quality of the systems.
The Green Radio programme sets the ambitious goal of achieving a 100-fold reduction in power consumption over current designs for wireless communication networks. This challenge is rendered non-trivial by the requirement to achieve this reduction without compromising the Quality of Service of the user or the deployment and operational cost of equipment manufacturers, network operators, content providers, etc.. For example, a reduction in radiated power is not of benefit if it is achieved at the expense of a greater increase in power consumed in signal processing or vice versa
Technical Scope Of The Challenges:
The overarching green radio goal of achieving the above 100-fold power reduction will be addressed by pursuing reduction in the two complementary domains
Architectural Aspects for Green Radio :
To examine alternatives to the existing network structures of cellular and Wireless LAN to offer the potential to reduce energy and power consumption. Moving the access network closer to the user enables a reduction in the transmit power required. This is achieved at the expense of more BS/AP's with consequent increased complexity in the backhaul requirements. An increased density of Base Station will also require effective utilisation of spectrum in order to ensure that the overall interference situation is not altered in a detrimental fashion. Incorporation of relaying into the network architecture has the potential to extend the reach for a BS/AP to a mobile terminal to achieve energy savings.
Some of the more important architectural components and behaviours that could characterise a future wide area coverage cellular network includes
- delaying conventional cellular transmissions until the mobile terminal comes into range
- in-building femto-cell relaying
- multi-hop relaying
- relaying with a different signal transmission standard
Multi-hop routing as used in relaying, mesh and ad-hoc networking is an important factor in saving energy as shorter transmission paths from the BS/AP to mobile user give considerable savings in the required overall transmitted power. Thus multi-hop routing might be exploited to achieve the power reduction target in Green Radio. From a backhaul perspective mesh networking is important for providing multiple routes to an end destination. Options for mesh networking include leased lines, cable/fibre, radio-over-fibre, or wireless links. Relaying can be used to improve base station coverage and throughput through fixed, mobile or indoor relays.Also,energy efficiency could be traded for increased packet delay, where transmissions are delayed until the mobile is within range of the BS/AP.
Using of Small Cellsand wireless LAN hop-shots:
The use of small cells, such as wireless hotspots and indoor femto-cells which operate with low transmission power over short ranges could reduce the power consumption significantly. Wireless LAN hop-spots also have low transmission power levels when compared to a cellular base-station. In addition, simple cooperative techniques to optimize network performance and minimize interference should also be studied to further enhance energy efficiency.
Techniques across the Protocol Stack for Power Reduction :
These may be employed either to reduce the required radiated power to achieve the required QoS or to achieve the required radiated power using less overall power. Effective Radio Resource Management and Signal Processing may bbe used effectively to reduce the radiated power requirement and thereby acquire the required Quality of Service. Power and energy efficient hardware implementation of necessary functionality will facilitate a reduction in total energy consumed relative to the radiated power.
Energy saving for the mobile communication infrastructure requires a comprehensive approach. It incorporates both energy-efficient components and adaptable system platforms for base stations and its network elements, as well as a network-level architecture that supports coordination and full operator control.
Optimising the Architecture:
Energy saving can be viewed as an optimization function that reduces power consumption by adapting the provided network capacity to the actual demand at a given time.
Minimizing energy consumption can benefit from a wide range of architectural approaches, which have recently come to the forefront in communications. There is enormous potential to reduce the energy consumption of wireless networks through an appropriate choice of radio access architecture and associated backhaul. Equally, there is a huge challenge in respect of identifying new design approaches that will provide the best trade-off between energy efficiency versus QoS.
The concept of energy efficient architectures contains two related notions.
- Firstly, it is important to be able to measure the energy efficiency of a wireless network. Any metric that is developed in the project should be able to quantify the total energy efficiency of a given deployed wireless topology. In relation to the protocol stacks used in wireless applications, it is important to accurately quantify energy parameters that drive protocols and algorithms.
- Secondly, the energy efficiency measures should be applied to different architecture configurations to understand and optimize their energy consumption behaviour.
Energy saving approach is thus based on corresponding coordination and management features, supporting different architecture alternatives.
Distributed architecture, where base stations initiate the energy saving functions based on local knowledge and inter-coordination.
Centralized architecture, where base stations propagate energy-saving-related information towards OAM, which initiates energy saving functions and executes the related algorithms for re-configuring base stations accordingly.
Hybrid architecture, where the OAM can assist distributed energy saving by providing policies and enhanced information for local energy saving decisions
The most suitable approach chosen depends on the specific deployment and operator strategies. The distributed and hybrid approach can enable optimized, self-organized energy saving, which will be beneficial in large-scale deployments. In a hybrid architecture, base stations would provide distributed energy saving functions, e.g., by exchanging load information for determining redundant cells that can be switched off.
Architecture Issues and its solutions:
In this research programme, four main technical approaches considered are
- Energy Metrics
- Energy Efficient Architectures
- Multi-hop Routing
- Frequency Management.
key questions for a the green radio programme includes
- Which metrics should be used to determine an appropriate radio access network architecture?
- What is the appropriate radio access network architecture for wide area coverage scenarios?
- What is the appropriate backhaul architecture?
This fundamental task aims to develop metrics to assess the energy efficiency of current and future wireless networks. One major issue to be resolved is how to trade off the number of base stations, number of relays, cell sizes and the backhaul locations and bandwidth in order to maximize network overall energy efficiency. Network data throughput,is taken into account for coverage and the resulting quality of service (QoS) needs to be identified. In addition, the energy consumption of mobile terminals and customer access points/femto-cells should be accounted for in order to avoid simply pushing the burden onto consumers. In order to highlight the metrics that are being developed, results will be obtained for some example scenarios to highlight the trade-offs between using small and large cells for existing network designs.
Energy Efficient Architectures: This task focuses more on studying architectural issues for efficient wireless networks. Research will consider the trade-offs between large and small cells, as well as enabling technologies, such as relaying, network coding, cooperative networking and free space optical (FSO) links for improving performance and enabling efficient backhaul. Three major scenarios studied in this task, are wide area cellular systems, enterprise networks and small-scale home networks. Using the metrics developed, the most energy efficient network layouts for these three scenarios will be identified.
This task focuses on architectural issues relating to multihop routing, exploring in depth the relationship between trying to achieve energy efficiency in a wireless network and the resulting QoS that is possible.
The first approach to this problem is to understand how energy consumption in a wireless network is affected by strict end-to-end QoS requirements, which could conceivably require increases rather than decreases in energy consumption.
The second approach considers the converse situation where permitting extremely loose end-to-end delay requirements could allow data packets to be sent at convenient times to permit further reduction in energy consumption.
The results of the work should quantify the relationship between energy consumption and QoS requirements over a wide range of potential service types.
This task focuses on the architectural impact of the increased availability of frequency bands in future networks. Release of radio spectrum worldwide opened up many new licensed bands between 300 MHz and 10 GHz. Frequency management considers how dynamic spectrum access (DSA) in multiband future networks could be used to save energy and how differences in path-loss and available bandwidths in different bands could be used to equalize traffic load, tackle interference and minimize energy consumption.
DSA can also be used by relays in multihop links to select time and frequency slots for relaying in-cell and backhaul transmissions, in order to maximize spectrum usage and minimize interference to other terminals in the network. The results of this work provides an indication of how licensed bands could be managed to provide power reductions.
Green Radio Hardware Technologies
Energy-efficient hardware is essential for reducing the power consumption of base stations. To reduce RF signal attenuation inside base stations, the Remote Radio Head (RRH) architecture is increasingly adopted in modern base stations. However, it is often hard to deploy RRHs near the base station antenna due to the dimension requirements.Therefore an all-in-one compact LTE base station was developed, including RF, baseband, and a transmission unit, that which could be mounted anywhere on a antenna masts or a building walls.This enables the base stations to extend its broadband coverage when compared to existing equipment architecture .
The key components that affect base station power consumptions are a transmitter power amplifier and a cooling fan for air conditioning traffic load conditions, the efficiency of the transmitter power amplifier is critical. In low traffic conditions, the power consumption of devices in standby mode and of cooling fans becomes dominant. Besides using state-of-the-art key devices, greeen radio employs fanless architecture to reduce power consumption .
Transmitter Power Amplifier :
Transmitter power amplifiers are devices that increase the strength of RF signals transmitted from base stations to terminals. Generally, they consume considerable energy in mobile base stations .Greenradio programme provides one of the world's most efficient transmitter amplifiers for base stations: a 2.1-GHz model that produces 45 W of output power per 100 W of power consumption,thereby produced these latest amplifiers by adopting high-performance and highly reliable RF transistor technologies, in addition to independently optimizing Doherty RF circuitry. Fanless Base Station :
In a conventional base station, a cooling fan consumes 10-20% of the overall energy . Using efficient heat transfer packaging allowed greenradio to move to fanless operation.
Self-organizing Green Radio Technologies :
Base station resources are commonly provisioned so that they can accommodate the traffic demand at peak times. Therefore it is must that a researching mechanisms for actively exploiting the tradeoff between the capacity and the energy consumption for both intra- and inter-base station adaptations to capacity demand, which can lead to significant power saving
Intra-Base Station Energy Saving
Conventional base stations are designed with a focus on spectrum efficiency rather than on energy conservation. Hence, base stations try to allocate radio resources while there is data to send, irrespective of the channel condition. To reduce the power consumption in low-traffic periods, the scheduler in a base station may queue the data in the packet buffer until the varying channel gain becomes good .. Thus, the required amount of energy to send the same packet decreases as the channel gain increases. The scheduler also selects the appropriate modulation and coding schemes, and controls the power amplifier to switch off when there is no data to send to reduce energy without causing congestion Moreover, parts of the base station components can be turned off according to hourly traffic conditions. During off-peak hours, less processing capability is needed, and therefore parts of the unit can be transferred to sleep mode. Such fractional operation of base stations will further decrease power consumption .
Inter-Base Station Energy Saving
While energy saving on the base station level is important to enable a base station to utilize its physical resources in the most efficient way, it has to be noted that much higher energy savings can be achieved when relations between multiple base stations are considered appropriately. Such inter-base station energy saving could, allow coordination of base stations to optimize energy saving decisions by leveraging actual knowledge of capacity and coverage demand. Such coordination involves the exchange of certain information among base stations, including load, coverage, and interference, and a collective decision for the energy saving state of particular network elements.
Green Radio Scenarios:
Two Market Profiles:
- Developed Infrastructure
- Saturated Markets
- Quality of Service Key Issue
- Drive is to Reduce Cost
- Less Established Infrastructure
- Rapidly Expanding Markets
- Large Geographical Areas
- Often no mains power supply
Considering what the architecture of a future Green Radio system would look like,is also important to address radio based techniques that can be used to improve the efficiency of future wireless networks.
Novel Radio Techniques:
These techniques will span all of the protocol layers from modifications of the physical layer and radio frequency circuitry to techniques applied by the services that run over future networks. Recent wireless standards, such as 3GPP Long Term Evolution (LTE) and IEEE 802.16 (WiMAX) can achieve high data efficiencies on point-to-point links when compared to the Shannon limit. Thus, no major advances are anticipated in future cellular standards at least to modulation and coding formats.
However, there are other areas where significant improvements can be made, particularly from the viewpoint of energy and power efficiency. The techniques should ensure efficient use and control of RF power are be studied carefully. The duplexer/combining loss is now considered high as it relates to the RF combining of narrowband PAs. In 3G LTE systems, we have issues relating to the higher PAPR of the waveform, making the PA efficiency harder to achieve, but the combining loss is avoided.
In this research programme, there are four main clusters of techniques that will be considered, relating to:
- Power efficient hardware.
- Power efficient digital signal processing (DSP) techniques.
- Efficient resource allocation algorithms.
- Other approaches including those derived from sensor networks.
These technique clusters will be studied in order to understand individually the potential power gain that can be obtained, as well the collective benefits of combining the most promising approaches in future radio systems.
Despite the enormous advances made in radio technology in the last two decades, there is still room for further improvement in antennas and radio frequency components to meet the challenges of low power radio systems. The recent appearance of multiple antenna technology in emerging wireless standards such as IEEE 802.11n Wi-Fi, IEEE 802.16 WiMAX and 3GPP LTE means that enabling beamforming and multiple input multiple output technologies (MIMO) illustrate their importance of deploying multiple antennas in future wireless networks. However, the move toward low impact base stations and continuing requirement for small form factor mobile terminals means that antenna arrays must be designed to operate efficiently, taking into account small antenna sizes, close antenna spacings and potential increased mutual coupling effects. Another important concept is the deployment of orthogonal frequency division multiplex (OFDM) techniques to combat multi-path fading and the use of this for subscriber access i.e. OFDMA. Radio frequency amplifiers and components are still power inefficient and the move towards high peak-to-average power waveforms, such as orthogonal frequency division multiplexing (OFDM) signals, makes the task of achieving very high power efficiencies even more challenging.
An important factor in energy efficiency is interference. Given a specified radio access technology, a requirement for performance in terms of, e.g., throughput, implies a required ratio of received signal level to received interference level at a receiver. Hence if interference is increased by a given factor, the transmitted power level must be increased by that same factor in order to maintain the required performance, which has the effect of reducing energy efficiency for the system. Interference must therefore be carefully addressed in order to improve energy efficiency.This is particularly important when considering the potential addition of further transmitters to support relaying, given that such transmitters may be disassociated somewhat from the radio management mechanisms of the systems they are serving.
Digital Signal Processing:
DSP techniques for radio systems have been extensively studied in the last 10-15 years to improve signal transmission and detection, mitigate interference and increase spectral efficiency. However, when maximising power efficiency in wireless networks, there are major challenges in designing DSP techniques that will effectively tackle interference in order to improve the efficiency of wireless transmission, without introducing sophisticated power hungry algorithms. Techniques that can operate efficiently in the heterogeneous network architectures described in the Architecture section above need to be studied. There are also emerging techniques for designing waveforms that specifically avoid interference and the benefits of such approaches need to be quantified. In addition to studying techniques that work on the physical layer signals directly, it is also important to investigate coding approaches that operate closer to the service level. Novel relaying protocols and network coding techniques are two promising new approaches that can provide performance enhancement across a distributed network of base stations and relay nodes.
Resource Allocation and Management:
This is an increasingly important topic for future distributed wireless network architectures. If the full power efficiency of the network is to be obtained, it is important that efficient resource allocation techniques are used to exploit varying channel conditions and minimize interference. Several different approaches will be taken in this project to understand how resource management should be employed in wireless networks. From the theoretical side, recent results on the energy efficiency of wireless networks and on the Shannon capacity of multiple co-channel links may provide useful tools to develop more practical resource allocation approaches. Novel radio resource management and scheduling techniques that optimize energy efficiency in multihop networks with QoS constraints will also be studied as well as techniques that mitigate intra- and inter-cell interference.
These topics have been identified as the most important research areas of focus in the programme. However, it is also important that the research programme is open to alternative techniques like low power sensor networks have been researched intensively in recent years and the research results from this area should be studied to look for additional power reduction approaches. In addition, novel power reduction techniques which exploit specific features of recent and emerging standards, such as IEEE 802.11n Wi-Fi or 3GPP LTE, may exist. Therefore greenradio programme devotes time to consider both of these possibilities.
Novel Radio Solutions
The clusters of techniques is addressed through four corresponding research tasks.
Power Efficient Hardware:
The first task will focus on improved hardware and hardware-related designs to minimize power consumption in base stations/access points. The work considers highly efficient power amplifier designs, particularly targeted towards simultaneous support of multiple wireless standards. Efficient antenna solutions to support beamforming, interference cancellation and MIMO operation across multiple frequency bands will also be investigated. This task will quantify the hardware power savings that can be achieved through novel design techniques.
Power Efficient Digital Signal Processing:
The second task will focus on signal processing algorithms to minimize radio frequency transmissions and co-channel interference. Several complementary techniques will be considered including a number of distributed techniques that can operate across several terminals and/or access points. These include distributed power control algorithms, distributed co-channel interference cancellation algorithms and multiple transmitter antenna techniques to avoid interference where possible. Methods for measuring signal quality and interference for use in multiuser diversity scheduling techniques will also be investigated. The results of this work will specify how the distributed techniques can be applied and define the expected overall power gains that can be expected from their use.
The third task will focus in depth on how resource allocation techniques can be used to deliver significant power reduction. Four distinctive approaches will explored to address this problem. The first approach comes from the viewpoint of the multiuser diversity gain achievable in fast schedulers, seeking to minimize power consumption and ensure that QoS guarantees are met. The second approach comes from the viewpoint of Shannon capacity analysis of multiuser scenarios with interference. This work will explore the tradeoffs between allocating channel resources and power control to optimize performance. The third approach will study improvements to medium access control protocols in wireless local area networks to minimize power consumption. The final approach to resource allocation will study how connectivity between base stations in a cellular network can be used to shape interference and minimize power consumption while maximizing throughput. The relative contribution to power reduction and the interaction between these resource allocation approaches will also be considered as part of the research task.
The final research task will identify and evaluate power reduction techniques not covered by the other tasks. One approach that can be taken arises from applying the extensive literature on enabling and optimizing low power sensor networks via approaches such as sleep modes, power efficient scheduling and energy efficient routing in multihop networks. Other approaches to improving power efficiency are expected to be identified as the program progresses and will be addressed in due course by this task.
Energy-efficient operation of next-generation mobile communication technologies is a key success factor for OPERATIONAL POWER reduction and satisfying corporate social responsibility.this could be accomplished by applying the Green Radio approach to all aspects of overall system development.A comprehensive approach,Green Radio includes efficient hardware and software platforms and careful integration into SON functions to ensure maximum energy efficiency in different deployment scenarios.