## 5 Results and Analysis
### Interference Measurement Results and Analysis  
This section presents the measurement results, observations, and analysis of data from five different Glasgow CBD locations. The observation is based on the view of signal activity in the occupied sub-bands. The analysis of the data is performed to determine the  
Figure 8: RSSI (**A**) and SNR (**B**) for \(868.1\) MHz SF12 transmissions across a business district over a seven day period. Hour 12 indicates midday and hour 24 indicates midnight. probability of having signal interference that affect LoRa transmission in LoRa mandatory uplink and downlink channels. In presenting the measurement results, the spectrogram is more preferred than the power spectral density due to a display that provides a valuable insight into signal activity and power levels of transient RF signals. In this study, the spectrogram will be used instead of the histogram. The International Telecommunication Radio (ITU-R) in [47] indicates that presenting spectrum occupancy measurement results with a spectrogram provides quality visual representation of signal activity and power levels. This tool is employed to help visually represent the activity of signal power levels in the sub-bands between 863-870 MHz ISM band in CBD. The 868 MHz sub-bands, 863-865 MHz, 865-868 MHz, and 868-870 MHz for audio, alarms, and LPWAN technologies, respectively, are individually examined to gain more intuition into the signal activity. Next, calculating the probability of signal interference in each location for LoRa mandatory uplink, and downlink channels, 868.1, 868.3, and 868.5 MHz in Europe follows. Usually, LoRa must comply with 25 mW transmit power limits, and the 1% DC follows. The sub-bands, 868.0-868.6 MHz and 869.4-869.65 MHz for LoRa uplink and downlink, respectively, are considered as occupied with signals if the power levels are 10 dB [35; 47] above sensitivity of the spectrum analyser. The possibility that signals in these sub-bands experience interference either from LoRa installations, other ISM band technologies, or other sources is determined based on the accumulation of signals in the collected samples being above or below the threshold of \(-97\) dBm, that is 10 dB above sensitivity of RSA306B measurement up. The probability, \(p\) of signal interference in these sub-bands is determined by the sum of signal power levels above the threshold, -97 dBm to the total measurement samples and is calculated as follows:  
\[p=\frac{\sum_{i=1}^{N}S(R_{i})}{N} \tag{1}\]  
where  
\[S(R_{i})= \begin{cases}1&\text{If }\mathbf{R}_{i}>-97\\ 0&\text{If }\mathbf{R}_{i}\leq-97\end{cases}  \tag{2}\]  
and \(R_{i}\) is the received signal power levels in the 10 kHz \(\times\) 100 \(\upmu\)s measurement samples \(S\), and \(N\) is the total number of measurements per location. The measurement results in Figure 9 were recorded from Glasgow Caledonian University (GCU), and sub-bands with significant signal activity in 868 MHz ISM band are investigated separately. The sub-band, 865.0-868.0 MHz standardised for radio frequency identification (RFID) [48], displayed high signal activity. The measurement results show four frequent discontinuous transmissions centred at 865.6 MHz, 866.2 MHz, 866.9 MHz, and 867.4 MHz with power levels at around \(-63.75\) dBm, \(-67.49\) dBm, \(-69.95\) dBm, and \(-67.42\) dBm, respectively. These transmissions appeared at the rate of 1 s and were either access control systems at GCU or the tracking systems at a nearby traffic police station. The 868.0-868.6 MHz sub-band for mandatory LoRa uplink channels measurement results showed sporadic transmissions centred at 868.0 MHz, 868.1 MHz, 868.3 MHz at an interval of 4.03 min and power levels at \(-85.44\) dBm, \(-85.25\) dBm, and \(-83.36\) dBm, respectively. The change in power levels over the monitoring duration was not significant. There were strong emissions in some channels, for instance, 868.1 MHz, which appeared to spread into the adjacent channels. The rate of signal activity level in this sub-band was high and seemed to violate the DC.