# Positioning-Based Uplink Synchronization Method for NB-IoT in LEO Satellite Networks
## 3 Position-Aided Uplink Synchronization Method
### Energy Consumption and Algorithm Complexity Analysis  
For NB-IoT terminals, power consumption is a critical metric in evaluating performance. The uplink synchronization algorithm based on position assistance proposed in this paper can serve as an alternative to GNSS. To validate its superiority in terms of power consumption, this section compares the power consumption generated by this uplink synchronization scheme without external system assistance to that of GNSS-assisted uplink synchronization. According to the power consumption study in [14], the power consumption caused by computations during the uplink synchronization process has negligible impact on the battery life, with the primary determinant of power consumption being the duration of the NB terminal's states. For simplicity, this paper classifies the NB terminal's states into reception, transmission, light sleep, and PSM. As pointed out in the 3 GPP report, the workflow for a terminal using a GNSS-based solution is as follows:  
In Figure 12, before transmitting uplink data, the terminal needs to perform GNSS positioning, and during the GNSS positioning process, the Radio Resource Control (RRC) connection must be disconnected. According to data from the 3 GPP standard, this portion of the power consumption accounts for 30-50% of the UE's total power consumption. By utilizing its own signals for positioning calculations, the terminal can save a significant amount of power during this process. Although the positioning accuracy of GNSS is higher than that of the BOS method, NB terminals do not require such high positioning accuracy to successfully complete uplink synchronization. For IoT terminals of this type, the solution presented in this paper is more valuable. The following section provides a detailed analysis of the states and duration of the NB terminal during the uplink synchronization process in both solutions, followed by a power consumption comparison analysis. Power Consumption Analysis of the BOS Method: Assuming that an IoT terminal reports data at a 2-h reporting interval, this section analyzes the terminal's state transitions and computes the corresponding power consumption according to the NB-IoT protocol. Finally, the results are compared with those of the GNSS-based method. Figure 11: Receiver architecture diagram. Figure 12: GNSS system flowchart. The total power consumption of the BOS-based scheme can be expressed as:  
\[E_{BOS}=E_{sync}+E_{RA}+E_{UL}+E_{DRX}+E_{PSM}+E_{extra} \tag{38}\]  
\[E_{RA}=P_{TX}(T_{msg1}+T_{msg3})+P_{RX}(T_{msg2}+T_{msg4})+2P_{DRX}T_{RTT}\]  
denotes the energy consumed during the random access;\(E_{UL}=P_{TX}T_{date}+P_{DRX}T_{RTT}\) refers to the energy consumed during uplink data transmission; \(E_{DRX}=P_{DRX}(T_{DRX}-T_{PO})+P_{RX}T_{PO}\) denotes the energy consumed in DRX; \(E_{PSM}=P_{PSM}(T_{PSM}-T_{DRX})\) denotes the energy consumed in PSM; \(E_{extra}\) indicates the power consumption of the barometric altitude sensor; and \(E_{sync}=P_{RX}T_{sync}\) represents the energy consumed by the NB-IoT terminal during downlink synchronization and terminal positioning using the proposed method. The definitions and values of the remaining parameters are provided in Table 1.  
Power Consumption Analysis of the GNSS-based Method:  
\[ \begin{array}{ll}E_{GNSS}=&P_{RX}(T_{GNSS-acq}+N_{GNSS}T_{GNSS-track})\\ &+N_{GNSS}(E_{sync}+E_{RA})+E_{UL}\\ &+E_{DRX}+E_{PSM}\end{array}  \tag{39}\]  
The definitions and values of all parameters involved are listed in Table 1. A detailed comparative simulation analysis of the power consumption for both schemes is presented in the next section. We analyze the algorithm complexity in Table 2. In the MSA, the main computational burden comes from complex multiplications during correlation operations as well as a large number of complex multiplications involved in the FFT process. In contrast, the maximum likelihood algorithm only involves complex multiplications during correlation.