## 5 Conclusions  
In this research work, different research questions have been answered using simulation and experimental approaches to increase the efficiency of future IoT technologies. This includes methods to improve coverage and reduce the probability of communications outage, increasing battery lifetime using compression techniques, and reducing latency. We proposed small cell deployment and D2D communications to improve coverage for UEs experiencing outage conditions and compression algorithms to improve communications efficiency. Thus, we could conclude the paper in two parts; simulation and empirical parts.  
In the simulation section, we have studied coverage using different path-loss models, and realistic shadow-fading maps to evaluate cellular coverage for NB-IoT data services, a significant reduction in the proportion of outage users by deploying pico-cells--from 30% for no small cells to around 5-7% for 200 pico-cells--has been shown as one of the main results of this paper. Furthermore, we used a realistic power consumption model to study how energy consumption can be reduced by compressing data packets or reducing the reporting interval when using NB-IoT. Additionally, we proposed the Huffman compression technique to reduce the data volume and increase the battery lifetime of IoT devices. Moreover, we have analyzed the performance of NB-IoT for different smart grid applications as an LPWAN communication technology in terms of coverage area, data packets and the active number of smart meters in a Macro-cell.  
Finally, in the experimental section, we have explored the characteristics of Huffman and LZW compression algorithms on 3G and 4G cellular communication technologies, and the impact of these compression algorithms on latency has been evaluated. It was found that Huffman coding generally performed better than LZW and could offer a modest reduction in communications latency of up to 10-20%. But for data packets close to the maximum transmit unit (MTU) in TCP, the Huffman performance will increase 30-40%. This better performance is because communicating one MTU in TCP protocol can be transmitted in a single network-layer transaction.  
In future research, alternative compression methods need to be investigated, considering the impact of packet loss and errors on communication systems. Additionally, the realistic energy consumption of devices using LPWAN technologies (especially NB-IoT) need to  
\begin{table}
\begin{tabular}{l l l l} \hline \hline  & **NB-IoT** & **4G** & **3G** \\ \hline Typical Latency & 300 ms [27; 29]-few seconds [27; 30] & 50 ms & 100 ms \\ \hline Data Rate (bps) & \(<\)150 K & 15–50 M & 1.5–8 M \\ \hline \hline \end{tabular}
\end{table}
Table 7: Characteristics of 3 GPP standardized wireless technologies used in the testbed.  
be investigated considering joint compression and retransmission mechanisms to provide a high probability of successful transmission in the proposed communication architecture.  
Conceptualization, M.Z. and J.S.T.; methodology, M.Z. and J.S.T.; software, M.Z.; validation, M.Z. and J.S.T.; formal analysis, M.Z.; investigation, M.Z.; resources, J.S.T.; data curation, M.Z.; writing--original draft preparation, M.Z.; writing--review and editing, J.S.T.; visualization, M.Z.; supervision, J.S.T.; project administration, J.S.T.; funding acquisition, J.S.T. All authors have read and agreed to the published version of the manuscript.  
The authors gratefully acknowledge funding from the UK Government Department for Business, Energy and Industrial Strategy (BEIS) Project Quickturn 1273/01/2017-ND114 for this work.  
Not Applicable.  
The software used for the experiments reported in this paper is available on request from the authors via email.  
The authors gratefully acknowledge [PERSON] and [PERSON] from Flexitricity for helpful discussions concerning this work.  
The authors declare no conflict of interest.