# Energy Efficiency Perspectives of PMR Networks +
## 2 Present and Future PMR Systems
### The PMR Evolution through the LTE System  
Currently, most TETRA manufacturers are looking to the future by implementing a TETRA over LTE system [18; 19] in order to provide higher data rate and lower latency services. LTE is the state-of-the-art standard for commercial mobile communications, providing an all-IP connectivity through an infrastructure designed for very high speed services. Even if LTE has been developed for commercial use, some work groups in 3 GPP have been working on the adaptation of the standard to mission critical communications [20]. In particular, the following items are currently under investigation:  
* Group communication and push-to-talk (PTT),
* Proximity based services,
* Network resilience,
* High power user equipments,
* Enhanced Radio Access Network (RAN) sharing,
* Priority and Quality of Service (QoS) control. More specifically, group communications, PTT and proximity based services, that enable device-to-device (D2D) communications, are the key requirements for public safety mission critical voice services. The work on such subjects has been carrying on within the LTE Release 12 and LTE Release 13 groups [21; 22; 23]. In the framework of these releases, some issues about resilience and RAN sharing are also being discussed. For example, in order to face a disaster causing the failure of some devices, any base station should be able to act alone in connecting the served users with the rest of the network [24]. Moreover, an enhanced flexibility in sharing network resources could allow the adoption of smart radio resource management strategies between critical and non-critical users [25]. As for high power user equipment and priority and QoS control, such features are already provided by the LTE technology and the work that is being carried on is related to future enhancements [26; 27]. Whilst these outcomes will clearly directly affect infrastructure vendors, the market for user equipment, applications and other end-user equipment, and services can be expected to be less impacted. In other words, whether or not the bearer network is owned and operated by the user organization, or services are provided by mobile network operators, users will still require terminal devices and applications. In a standardized market, competition and innovation, as well as economies of scale resulting from the wider global LTE user equipment ecosystem, can be expected to influence prices. A strong standards-based approach will ensure interoperability between different vendors leading to a competitive equipment market. Besides the opportunities offered by exploiting the LTE technology for PMR services, the main issue resides in the way such services should be provided. Since there is no commercial interest to develop and integrate all the PMR functionalities over the LTE infrastructure, especially the ones related to security end encryption operations, only private networks should be preferred. Private networks could be self-deployed by the interested organizations for its own activities or \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **25 kHz** & **50 kHz** & **100 kHz** & **150 kHz** \\ \hline
**8/4-DQPSK, r = 2/3** & 15.6 kbps & & & \\
**8/8-DSPSK, r = 2/3** & 24.3 kbps & & & \\
**4-QAM, r = 1/2** & 11 kbps & 27 kbps & 58 kbps & 90 kbps \\
**16-QAM, r = 1/2** & 22 kbps & 54 kbps & 116 kbps & 179 kbps \\
**64-QAM, r = 1/2** & 33 kbps & 80 kbps & 175 kbps & 269 kbps \\
**64-QAM, r = 2/3** & 44 kbps & 107 kbps & 233 kbps & 359 kbps \\
**64-QAM, r = 1** & 66 kbps & 160 kbps & 349 kbps & 538 kbps \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Channel coding and TETRA Enhanced Data Service (TEDS) throughput. provided by a third-party. In both cases, once the LTE system will be compliant with mission critical communications requirements, the main open issue will be the actual channelization, since LTE is designed to operate with bandwidths starting from 1.4 MHz.