# Towards the Internet of Smart Trains:
## 4 Long Term Evolution (LTE): One Step Ahead of Broadband Communication Systems
### Current Status of Standardization
The concept of CR has been highlighted as an attractive solution to the problem of the congestion of the radio spectrum occupied by licensed users. Furthermore, it is able to integrate all the heterogeneous wireless networks deployed. Besides, LTE will be the baseline technology for the next generation of broadband public safety networks. National Public Safety Telecommunications Council (NPSTC), TETRA + Critical Communications Association (TCCA), and Critical Communication Broadband Group (CCBG) are contributing to the standardization processes [57]. This functionality will become available in products from 2017 onwards in LTE Release 13 (functional freeze date 2016). Release 13, in addition to enhancements to existing services and features, includes the completion of the first set of specifications covering mission-critical services, in particular Mission Critical Push To Talk over LTE (MCPTT). 3 GPP continued to work on the characterization of carrier aggregation across additional band combinations to provide increased bandwidth within the limited frequency allocations to individual operators. Radio propagation was further improved with studies on MIMO antennas and sophisticated beamforming techniques. Other major advances achieved included enhancements to machine-type communications, public safety features, small cell dual-connectivity and architecture, indoor positioning, single cell point-to-multipoint and work on latency reduction. In 2015, 3 GPP began to work on the next generation cellular technology or 5G, with the aim of submitting a candidate technology to the IMT-2020 process. Meanwhile, work started on Release 14 and numerous features and studies had been defined including Multimedia Broadcast Supplement for Public Warning Systems, mission-critical video and data services, LTE support for Vehicle-to-Anything (V2X), latency reduction, high power LTE for certain bands, channel model above 6 GHz and robust call set-up for Voice over LTE (VoLTE). By the second half of 2017, the focus of 3 GPP work will shift to Release 15 in order to deliver the first set of 5G standards. For instance, the importance of forward compatibility in both radio and protocol design was stressed. Its functional freeze date including stable protocols would be on September 2018, thus the timeframe for a commercial deployment will be at the end of the decade. \begin{table}
\begin{tabular}{p{34.1 pt} p{34.1 pt}} \hline \hline
**Railway** & **Implementation** \\ \hline \multirow{7}{*}{General spec.} & \multirow{7}{*}{*} & \multirow{7}{*}{*} \\  & & \\  & & \\  & & \\  & & \\  & & \\  & & \\ \end{tabular}
\end{table} 
Table 8: Main specifications to address railway requirements. One of the most remarkable proposals for the definition of 5G is the utilization of Filter Bank Multicarrier (FBMC) modulations instead of the well-known Orthogonal Frequency-Division Multiplexing (OFDM). The next are the most important advantages offered by FBMC with respect to OFDM for the railway environment:  
* FBMC offers higher bandwidth efficiency, which is very beneficial since the simultaneous communications between different trains can be more efficiently allocated into the scarce spectrum available in railway environments. * Coexistence between the current GSM-R and the new broadband systems is a major concern in the railway industry. OFDM-based systems usually exhibit a high co-channel interference, leading to a potential performance impact on current GSM-R systems. FBMC-based systems are much more efficient, thus allowing for better coexistence with current systems. * Improved multiple-access facilities in the UL: due to the use of close-to-perfect subcarrier filters that ensure frequency localized subcarriers, FBMC does not require sophisticated synchronization methods for avoiding multiple-access interference.