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Top1. Introduction
Energy consumption and carbon dioxide (CO2) emissions has recently become the subject of special interest to the mobile telecommunications industry. In Murthy (2012), it is emphasized that base stations (BSs) are the most energy intensive consumers in the cellular networks of mobile operators. Hence, during last year’s, significant attention was given by equipment manufacturers, mobile operators and researchers from academia to the solutions dedicated to improving energy efficiency of BSs in cellular networks. For achieving this, some of the recognized techniques are: energy-efficient hardware or BS site design, dynamic management of network resources through sleep modes and cell zooming, a self-organizing network (SON) concept or using renewable energy sources to power BS sites.
As an example of the use of energy efficient hardware design, the Nokia Siemens Networks Flexi base transceiver station (BTS) has been introduced to the market (NSN, 2009). This type of BTS is energy-efficient and features multi-radio technologies inside one hardware unit. The advantages of these BSs are: reduced installation time and material costs, reduced size and weight (for 20%), reduced energy consumption (70%) due to usage of remote radio heads and power amplifiers with improved efficiency, readiness for using renewable energy sources and flexible location: either indoor or outdoor without the need for air conditioning and.
As an example of energy saving through innovative BS site design, company Ericsson introduced the Ericsson Tower Tube (Ericsson, 2011). It is an ergonomically designed concrete tower having lower environmental impact than traditional steel and consuming up to 40 percent less power from a life cycle perspective. This is due to the fact that such a concept is based on wind powering the BS that is positioned at the height of the tower tube, which helps to reduce feeder loss and eliminate the need for active cooling. The solution supports different antennas and radio equipment, multi-operator site sharing, and enables a reduction of the space leased by telecom operators.
However, to achieve significant energy savings, an approach based on the dynamic management of wireless network resources seems to be the most promising. Such expectations have led to previous studies on energy efficiency improvements at the level of complete Wireless Local Area Networks (WLANs) (Lorincz and7 Bogarelli, 2010; Lorincz, 2011, p. 540; Lorincz, 2011, p. 648; Lorincz, 2010, p. 195). By means of integer linear programming and heuristic algorithms, we propose different optimization models based on the dynamic management of network resources. When dynamic management of the access point’s activity is implemented, the obtained results show that significant energy savings can be accomplished for the cease of large-scale WLANs. These optimization models have been extended for wide area cellular access networks. In Lorincz (2012, p. 24), analysis of possible energy savings is studied for cases when dynamic management of macro BSs activity and corresponding transmit powers will be implemented. This analysis also shows enormous energy saving potential if dynamic on/off powering of BSs and transmit (Tx) power adjustment takes place in accordance with space and time variations of traffic patterns. Influence of adjusting BS Tx power (known as cell zooming) and daily variations of traffic pattern on instantaneous BS power consumption were investigated in Lorincz (2012, p. 4310) and Lorincz and Dimitrov (2012), respectively. Furthermore, the analysis of the influence of introducing BSs of newer technologies (e.g. Long Term Evolution – LTE) on network energy metrics is performed in Lorincz (2012, p. 161).