# Energy Efficiency Perspectives of PMR Networks +
## 1 Introduction  
Professional Mobile Radio (PMR) systems represent a subset of mobile communications networks which are designed for mission critical communications. Since they provide a mobile wireless service to their users, as in the public radio network case, such systems are mainly addressed to public safety and security organisations to guarantee fail-safe and secure voice and data communications. On the other hand, the target requirements of the provided service are quite different than the public case, particularly in terms of system availability, security, resilience and reliability that are typical of mission critical communications [1]. Recently, PMR and public radio systems share common needs and interests. As a matter of fact, the possibility of providing broadband services is taken into account also by the PMR operators and manufacturers who are currently working on extending their systems capabilities. In order to increase the throughput and be able to support broadband services like video communications, Long Term Evolution (LTE) is now under investigation as the platform for future PMR systems [2]. Moreover, a greater sensibility toward environmental and energetic issues has been raised in research and the industrial world, and a lot of inherent international research activities have been funded [3; 4; 5; 6]. The energetic costs are one of the major drivers of operational expenditures (OPEX) [7]. At the same time, controlling the cost of energetic waste allows for cutting greenhouse gas emissions, thus reducing air pollution with positive consequences on environment. An energy efficient cellular network can be achieved in multiple ways. First of all, an opportune deployment, taking into account the optimal site location, is needed to minimize the transmission power budget and the number of needed base stations. Moreover, considering that new technologies will be progressively introduced in an already deployed network, the hardware optimization is expected to significantly reduce the current energy waste, especially due to power amplifiers, the most power-consuming devices in a base station's equipment [8]. In this regard, replacing the old network devices with new and less power consuming ones will introduce a substantial energy efficiency gain. However, such energy gain should be further improved through radio resource management solutions aiming at optimizing the network usage with respect to the actual needs. As a matter of fact, the daily power consumption of a base station has a rather constant profile over time with respect to the transmitted traffic, as depicted in Figure 1. This behavior justifies the goal of using energy efficiency strategies to shape the power consumption to the actual energy demand. To this aim, many promising radio resource management strategies, mainly focused on power control and power amplifiers' sleep mode, have been proposed [9; 10; 11; 12]. This paper discusses the feasibility of energy efficient solutions for current and future PMR networks. First of all, a review of the state-of-the-art of such systems is provided, mainly referring to the most popular system in Europe, which is Terrestrial Trunked Radio (TETRA). The main TETRA features are described highlighting the evolution to a broadband system through TETRA Enhanced Data Service (TEDS). Moreover, since the availability of IP broadband services will be a PMR target requirement, the feasibility of the transition to a TETRA over LTE system is discussed. In order to evaluate the energy impact of such a system, a TETRA/TEDS power consumption model is introduced, as well as some energy saving radio resource management techniques developed for commercial wireless systems. Then, an evaluation of the energy performance of an optimized TETRA/TEDS system has been done, also taking into account the potential energy efficiency gain, due to hardware improvements and radio resource management flexibility that will be allowed by the transition to an LTE infrastructure.