# Time Domain Analysis of NB-IoT Signals
## 5 Results  
### Time Domain Analysis of NB-IoT Subcarriers  
Figure 6 shows an acquisition in frequency domain of the LTE800 band of one of the network operators. It shows the presence of the NB-IoT signal in guard-band mode in the lower part of the spectrum. The same figure shows the detail that allows the identification of the sub-carriers on which the NRS is transmitted. The NB-IoT signal is transmitted in the 801. 3125: \(\div\) 801. 4925 MHz band with a central frequency equal to 801. 4025 MHz with an offset of 4.5975 MHz with respect to the LTE carrier (see Table 2). The sub-carriers' frequencies and the position of the NRS are shown in Figure 7. As mentioned, the position depends on the Cell_ID of the LTE cell and more specifically on the combination of the Cell_ID Group (values 0 \(\div\) 167) and the Cell_ID Sector (values 0 \(\div\) 2).  
Figure 6: LTE800 signal with guard-band NB\(-\)IoT and detail of subcarriers transmitting the NRS.  
Figure 8 shows a acquisition in time domain (20 ms) of one of the sub-carriers (801.440 MHz) transmitting the NRS. It is possible to distinguish the NPBCH control channel and the expected signals (NRS, NPSS, NSSS). In the even frame, subframe # 4 is occupied by the transmission of an NPDSCH channel, probably containing the Narrowband System Information Block type1 (SIB-NB 1) [13].  
Figure 9 shows an acquisition of the last subcarrier (801.485 MHz) which also transmits the NRS. The trend is similar to that of Figure 8. Again, control channels and signals are easily identifiable and the power amplitude received during NRS transmission is about the same as that at 801.440 MHz. As previously mentioned, the NPSS signals are not provided in the last subcarrier. The signals detected in the subframes reserved for NPSS transmission are about 15 dB lower than those of the NRS in Figure 8 and are due to the near subcarrier. Here also, in the even frame, subframe # 4 is occupied by the transmission of an NPDSCH channel.  
Finally, Figure 10 shows a time acquisition of a subcarrier (801.425 MHz) that does not transmit the NRS. In this case, the detected NRS is that relating to one of the near cells. The ratio between the power detected for the NRS on this subcarrier and that of the previous figures represents the ratio between the signal received due to the two cells at the measurement point.  
Figure 8: Example of time acquisition of a subcarrier transmitting the NRS (801.440 MHz).  
Figure 7: Subcarriers and NRS position.  
The acquisitions shown here demonstrate that the time domain analysis allows us to identify the channels and signals transmitted in the NB-IoT frame and, particularly, to measure the power received during the transmission of the NRS.  
Similar trends to those shown in previous figures were found in the acquisition of the NB-IoT signal in the LTE800 band of other network operators. In this case, however, the NB-IoT  
Figure 10: Example of acquisition of a subcarrier not transmitting NRS (801.425 MHz).  
Figure 9: Example of time acquisition of last subcarrier (801.485 MHz).  
signals were transmitted in the 791.1025 \(\div\) 791.\(\div\) 2825 MHz and 811.2075 \(\div\) 811.3875 MHz bands (Figure 11), with central frequencies equal to 791.1925 MHz and 811.2975 MHz, respectively. Frequency offsets related to the LTE carrier are 4.8075 MHz for the first and 4.7025 MHz for the second case (see Table 2).