Energy saving for LTE networks using Smart Antennas

In a recent study from ITU, ICT is responsible for 2.5% of the Global Greenhouse Gas emissions, and about 10% of these emissions come from mobile telecoms. In the past the wireless network operator configure their network with optimum power and seldom consider saving power, however this will change in the future. In this research, we are trying to reduce un-necessary power consuming as well as offering the same quality of services. LTE is the next generation mobile communication standard, The downlink for LTE and LTE-Advanced uses OFDMA technology to maximise spectrum efficiency as well as providing flexible resource allocation. The system performance in terms of throughput is limited by many factors including power level at base stations and interference from neighbouring cells. In this study, we proposed an adaptive antenna system for LTE that can be combined with cooperative interference management. The base station can dynamically change coverage pattern according to traffics. The results are improved throughput performance and energy efficiency.

 

Mobile networks create a carbon footprint equivalent to ~3 million 3-bedroom family homes[1], or the whole of the global aviation industry[2]: 61 billion kWH. With current projections, this consumption will double by 2011. Consequently, with pressure to reduce carbon emission, “efficient networks” are a priority for network operators. Vodafone pin-point the extent of the problem, stating “…our network accounts for around 80% of carbon dioxide emissions from our total energy use, and is therefore our main focus for reducing emissions”[3].

Current approaches do not reduce the energy used in radio transmission, which is fundamentally the source of energy efficiency in the network.

The aim of this research is to produce a demonstrator software tool that will allow network operators to plan, and then build, networks that significantly reduce carbon emissions.

This tool is based on a combination of patented co-operative smart antenna technology developed at Queen Mary University of London (QMUL) and methods on interference management in a distributed multi-antenna system developed at Beijing University of Post and Telecommunications (BUPT). The latter of these techniques uses a unique proprietary approach to turn destructive interference into constructive interference.

This project builds on an established collaboration, bringing together complementary skills to achieve the commercial end-goal of a software tool that can be directly show-cased to mobile network operators. The target for the tool is LTE, the next generation of mobile network. Standards for LTE have recently been completed, the first networks being expected to start operation in 2011.

The co-operative semi-smart antennas[4] technology developed at QMUL uses array antennas (typically 4 element – as shown in Figure 1a) and algorithms to control dynamically the beam patterns over a wide area in real time to cover the change of traffic load and hence increase network capacity – see the diagram in Figure 1b. The same approach, can be used to reduce the power of the network while keeping the capacity the same. For example in hotspots it has been demonstrated that semi-smart antennas can reduce power consumption by around 30%.

This research combines the semi-smart antenna technology with BUPT’s multi-cell interference management technology, using artificial intelligent algorithms, to optimise LTE system’s throughput and power efficiency performance. Initial research has showed that using this approach, LTE system with semi-smart antenna system could use much less RF power (over 50%) to achieve slightly higher system performance (3%) in certain scenarios.


Figure 2: Simulation snapshot for 7 LTE cells with semi-smart antenna’s coverage pattern

Further research is carried on to make this approach more mature, including speeding up the AI algorithm (currently using Genetic Algorithm) and verify over different user scenarios.

[1] http://www.cellular-news.com/story/25028.php
[2] http://knowledge.allianz.com/en/globalissues/climate_change/climate_solutions/green_it_energy_efficiency.html
[3] http://www.vodafone.com/start/responsibility/environment/energy/reducing_energy_use.html
[4] Fully-adaptive smart antennas use digital signal processing unit to generate spot beams.

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