## 6 Conclusions and Future Research  
Performance-enhancing mechanisms were examined with respect to their impact on successful detection of the two NB-IoT uplink channels, the NPUSCH and the NPRACH. The number of repetitions, N\({}_{\mathrm{rep}}\), and the modulation-coding scheme, MCS, were considered for NPUSCH configuration. Additionally, the impact of NPRACH repetitions was examined. The purpose behind the investigations presented in this paper was to emulate a real-life propagation environment with extremely high \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**IoT System** & **IoT Family** & **EIRP [dBm]** & **BW [kHz]** & **CNIR\({}_{\mathrm{min}}\) [dB]** & **MCL [dB]** \\ \hline LoRa & & & 125 & \(-\)5 & 142 \\  & & & 500 & \(-\)19 & 150 \\ \hline \multirow{2}{*}{Weightless} & \multirow{2}{*}{LPWAN} & \multirow{2}{*}{14} & 12.5 & \(+\)10 & 137 \\  & & & 100 & \(-\)11 & 149 \\ \hline SigFox & UNB & & 0.1 & \(+\)11 & 157 \\ \hline NB-IoT & CIoT & 23 (in uplink) & 180 & \(+\)10.4 & 164 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Performance comparison between NB-IoT and low-power wide-area network (LPWAN) and ultra-narrowband (UNB) systems. Figure 5: The narrowband physical random access channel (NPRACH) detection success ratio profiles for two different chipset vendors. pathloss in order to force the NB-IoT radio modules to operate at their performance boundaries, which is to say near the MCL = 164 dB point, at which the system is still required to operate. The experiment was thus intended to provide measurement-based verification to theoretical speculations found throughout the available literature or derived from simplified measurements, in which NB-IoT operation was investigated at operational regions far from the extreme MCL edge. As could be expected, measurements performed with the use of the carefully assembled measurement setup in a specialized EMC laboratory provided figures that confirmed the anticipated effect of repetition mechanisms on performance in the qualitative sense (in the sense of the positive effect of an increasing number of repetitions on the performance), albeit not in the quantitative sense (by falling short of the expected absolute improvement in decibels). In particular, the following findings have been attained and confronted with figures predicted in the available literature (if available). These conclusions can be treated as practical recommendations regarding the handling of basic channel settings in order to plan and optimize NB-IoT operation:  
* As shown in Section 5.1, the measured impact of Nrep on both NPUSCH and NPRACH performance appears to equal roughly 3 dB per every two-fold increase in repetitions. Thus, it is two times less significant than the claimed average 3 dB improvement per every doubling of Nrep, as predicted in [13] or measured with a simplified set-up in [14];
* As was also demonstrated in Section 5.1, transiting MCS between its extreme settings (i.e., from MCS0 to MCS5 and then from MCS5 to MCS10) caused NPUSCH performance to degrade by about 3 dB per each transition. The entire attainable scope of change in performance thus equaled 6 dB, which was equivalent to the effect obtained when switching Nrep between 1 and 64, as stems from the finding in the previous point;
* The outcomes presented in Section 5.2 reveal that differences between vendors providing the radio module chipsets are rather insignificant (i.e., falling below 1 dB) for the NPRACH channel when no repetitions are used (N1), but grow up to above 2 dB at N128. Future investigations of NB-IoT performance are intended to cover the following aspects:
* Investigate the channel performance of NB-IoT inband and guardband deployments;
* A (EPA) and extended typical urban (ETU), defined originally for LTE [32], assuming a 1 Hz Doppler shift in both (after [12]);
* Investigate the impact of inter-cell interferences, including the coexistence of NB-IoT and LTE systems;
* Investigate NB-IoT performance at different bands. **Author Contributions:** Conceptualization, K.S. and B.C.