Gilbert Micallef

Cell size breathing and possibilities to introduce cell sleep mode

Global warming has put the energy consumption of all industries into focus. In 2005 mobile communications contributed to about 0.2% of global CO2 emissions. Mobile operators have been reporting annual increases from 300% to 700% in 3G data traffic volumes. Such a steady growth in traffic requires regular upgrades in the infrastructure. While network equipment is in itself becoming more efficient, these upgrades still increase the overall energy consumption of the networks. This paper investigates the energy saving potential of exploiting cell size breathing by putting low loaded cells into sleep mode. The energy consumption and network performance of the resulting network are used to quantify the potential of this feature. The investigation is carried out on a tilt optimized network. Since putting cells into sleep mode results in a non- optimum antenna tilt configuration, this paper also investigates the possible gains of re-optimizing antenna tilting. The results show that by allowing sleep mode, over a restricted period of 12 hours, an energy saving of 33% is possible. While this energy saving comes at no expense of the overall network performance, the gain in average user data rate is noted to decrease by 21%.

Dual-Cell HSDPA for Network Energy Saving

The increasing demand for mobile broadband is pushing existing 3G networks closer to their capacity limit. Additional carriers together with new HSPA features (HSPA+) are expected to provide the next necessary boost in network capacity. One specific feature in HSPA+ is referred to as Dual-Cell HSDPA (or Dual-Carrier HSDPA). This feature allows for a single user to be simultaneously scheduled over two carriers, effectively doubling its achievable data rate. The addition of a secondary carrier will require additional radio equipment at the base station site, increasing the overall energy consumption. This paper proposes an energy saving feature that exploits variations in network traffic. Based on the individual load of each sector, the feature determines if the secondary carrier is detrimental for reaching some pre-set minimum requirements. Each sector is allowed to switch off one of its two carriers, during periods of low network traffic. It is concluded that an energy saving ranging between 14% and 36% is possible. This saving comes without degradation of network performance.

Energy Efficient Evolution of Mobile Networks: Macro-Only Upgrades vs. a Joint-Pico Deployment Strategy

With the increasing popularity of mobile broadband, mobile network operators (MNOs) are experiencing a continuous boost in network traffic. Some MNOs have stopped offering unlimited data plans, replacing them with a variety of data bundles. At the same time operators are looking at the different options for how to evolve their networks, allowing them to carry the expected increase in traffic. The best solution is generally selected based on two main criteria, performance and cost. However, pushed by a variety of environmental and energy challenges, MNOs are now also showing interest in understanding the impact that different options can have on the energy consumption of their networks. This paper investigates the possible energy gains of evolving a mobile network through a joint pico deployment and macro upgrade solution over a period of 8 years. Besides the network energy consumption, energy efficiency in Mbps/kW is also analyzed. Furthermore, a cost analysis is carried out, to give a more complete picture of the different options being considered. Focusing on the last year of the evolution analysis, results show that deploying more pico sites reduces the energy consumption of the network, by a maximum of 30%. With regards to the energy efficiency, high deployment of pico sites allowed the network to carry 16% more traffic for the same amount of energy. This, however, results in an increase in cost, specifically operational costs.

Energy Savings in Mobile Broadband Network Based on Load Predictions: Opportunities and Potentials

The deployment of new network equipment is resulting in increasing energy consumption in mobile broadband networks (MBNs). This contributes to higher CO2 emissions. Over the last 10 years MBNs have grown considerably, and are still growing to meet the evolution in traffic volume carried in wireless networks. To save energy in MBNs, one of the options is to turn off parts of the network equipment in areas where traffic falls below a specific predefined threshold. This paper looks at a methodology for identifying periods of the day when cells or sites carrying low traffic are candidates for being totally or partly switched off, given that the decrease in service quality can be controlled gracefully when the sites are switched off. Based on traffic data from an operational network, potential average energy savings of approximately 30% with some few low traffic cells/sites reaching up to 99% energy savings can be identified.

Realistic Energy Saving Potential of Sleep Mode for Existing and Future Mobile Networks

This paper presents an extensive overview on an energy saving feature referred to as ‘site sleep mode’, designed for existing and future mobile broadband networks. In addition to providing a detailed understanding of the main concept, the paper also provides various studies and results to highlight potential savings, and emphasize some of the expected limitations. Since site measurements show that the energy consumption of base station sites is largely load-independent, this makes such a feature highly effective for reducing the energy consumption of mobile networks during hours of low traffic. After going through a number of different alternatives of the feature, this is applied to different network topologies, macro-only based networks, and a set of heterogeneous networks that employ the use of small cells in traffic hotspots. Results obtained through detailed case studies show that sleep mode can reduce the average daily energy consumption of a network by around 30%. This can be achieved while maintaining a predefined level of performance, used as a measure of comparing different scenarios.

Mobile operators have set ambitious targets--is it possible to boost network capacity while reducing its energy consumption?

While operators have to upgrade the capacity of their networks, they have committed themselves to reduce their CO2 emissions, partly by reducing their energy consumption. This article investigates the challenges faced by operators and quantifies, through a number of case studies, the impact of specific solutions and how the energy consumption trend can be expected to develop over the next decade. With different options for upgrading capacity, studies show that a hybrid macro-pico upgrade is more energy-efficient than a macro or pico only solution. The study is extended further by quantifying the possible savings by adopting an energy-efficient capacity evolution together with an equipment replacement and site upgrade strategy. Results show that network operators can get relatively close to their targets, with energy reductions of up to 40% noted. While this can be improved further through software-based energy saving features, further CO2 emissions can be offset through the use of carbon-neutral energy sources.

Impact of picocells on the capacity and energy efficiency of mobile networks

The deployment of small cells in mobile networks has aroused a large interest in the last few years. This paper investigates the impact of picocell deployment on the performance and power consumption of mobile networks. Since different network upgrades introduce different performance gains, comparing different configurations exclusively on their overall power consumption can be rather biased. For this reason, a new key performance indicator, termed “energy efficiency”, is introduced and used throughout this study, bringing together network performance and its overall power consumption. In the first section of the study, a theoretical analysis for the Erlang-like capacity of a network, considering a uniform topology and traffic, is performed, using queuing theory analysis, namely processor-sharing queues. Results show that in all cases the deployment of picocells improve the performance of the network, however the energy efficiency is noted to be dependent on the deployment scenario considered. In the second part of the study, a more realistic scenario with non-uniform topology and traffic is considered, which is carried out through a large-scale system level simulator. Results show that by deploying picocells in areas experiencing high levels of traffic, the energy efficiency of the network can be considerably improved.

Nation-Wide Mobile Network Energy Evolution Analysis

Mobile network operators are facing a challenging dilemma. While on the one hand they are committed to reducing their carbon emissions, and energy consumption, they are also required to continuously upgrade existing networks, ensuring that the relentless growth in data traffic can still be supported. In most cases, these upgrades increase the energy consumption of the network even further. This paper presents a nation-wide case study, based on a commercial network of a leading European operator, intended to provide a clear understanding of how the energy consumption of mobile networks is expected to evolve from 2012 until 2020. The study also considers an efficient network capacity evolution path, including base station equipment improvement forecasts.

Spectrum Reorganization and Bundling for Power Efficient Mobile Networks

Technological improvements and evolving user requirements have led to operators running and supporting three distinct wireless access technologies, GSM, UMTS, and LTE. While the most recent layer (LTE) introduces improvements in spectral efficiency and peak data rates, the remaining layers are still required for supporting legacy devices and providing wider network coverage. In order to facilitate and reduce the cost of rolling out a new network, mobile operators often reuse existing sites. Radio frequency modules in base station sites house power amplifiers, which are designed to operate within a specific frequency band. Since some access technologies have spectrum split onto multiple bands, this results in operators installing multiple modules for each access technology. This paper quantifies the power savings that can be achieved by assuming that the available spectrum for an operator can be reorganized within a single band, and have multiple carriers bundled together to fully exploit the capabilities of modern equipment. These modifications are applied on all network layers, maintaining the same number of carriers and baseband capacity. For the presented case, this results in the elimination of at least four separate modules in each site, reducing the power consumption of by 31%. Indirectly, this also translates into a reduced site space of 40%. These savings are crucial for mobile network operators to reach the energy and carbon emission targets they have committed for.

Reversing the Energy Trend in Mobile Networks: Equipment Replacement for Increased Capacity at a Fraction of the Energy

In order to meet the expected boost in mobile data traffic, mobile network operators are planning and upgrading the capacity of their networks. Through a previous study it has been shown that over a period of eight years, different network upgrade strategies have a different impact on the energy consumption and cost of the network. However, irrespective of the upgrade strategy, all lead to an overall increase in the energy consumption of the network. This is based on the assumption that all sites are equipped with the same version of the equipment. In reality, it is likely to find a variety of equipment generations at different base station sites. This paper extends the previous study by considering a realistic equipment replacement strategy. In addition to considering three equipment generations, a number of sites are also upgraded to remote radio head, which reduces the energy consumption even further. Results show, that over the evolution period, it is in fact possible to boost capacity while maintaining or even reducing the energy consumption of the network. For the macro-only upgrade case, a reduction of 9% is experienced between the first and the last year. For the joint macro-pico case, a reduction in energy consumption of 41% is noted. Such reductions are well in line with what mobile network operators are aiming at achieving over the next years.