# Interspectral Error Tracking and Compensation of DSDT in Satellite Internet of Things
## 4 Synchronization in Multiple RF Channels  
To experimentally validate the proposed schemes, a wireless transceiver platform was built based on NI-USRP, and two independent RF channels of USRP X310 were used to simulate two satellite transponders. The system environment is shown in Figure 5. NI USRP from National Instruments in Texas, USA. The NI-USRP consists of a host and wireless signal transceiver hardware. The host side programming was performed using LabVIEW, and the RIO (Reconfigurable I/O) side was processed using the Field Programmable Gate Array (FPGA) provided by LabVIEW for streaming processing. To ensure accurate synchronization of the received signal, conventional communication systems often use the method of inserting pilots. However, for DSDT systems, the original signal recovered by aggregating multiple sub-spectra will accumulate synchronization errors from each sub-spectrum. Even if the sub-spectra are synchronized using pilots, the reconstructed signal will still have significant distortion that is difficult to eliminate further using pilots. Therefore, in the implementation of the DSDT system, the algorithm proposed in this paper is used to track and compensate for the amplitude-frequency-phase errors of the synchronized sub-spectra, thus further reducing the bit error rate. The signal frame structure, as shown in Figure 6, includes multiple sub-spectra. In the DSDT system, independent multiple RF channels are used for transmission. Each sub-spectrum is allocated to a different RF channel. For example, sub-spectra 1 and 3 are assigned to RF channel 1, while sub-spectra 2 and 4 are assigned to RF channel 2. Apart from the high requirements for synchronization accuracy, the hardware implementation of the DSDT system faces the following challenges:  
Figure 5: NI-USRP wireless transceiver platform. Figure 6: Multi-subspectrum data frame structure. One of the major challenges is the limitation of FPGA logic resources in the hardware devices. Due to the requirement for multi-subband filtering with arbitrary bandwidths and multi-frequency point synchronization of the sub-bands, the logic resource consumption on the RIO of the USRP is excessively high. Additionally, the processing speed of the host's host side is slow, thus resulting in poor real-time performance. Another challenge is how to reduce the data link load. High-speed sampling of the signal can impose a heavy load on the data transmission link, thus leading to potential data congestion and loss. To address this issue and allocate resources effectively, the system's receiver-end structure framework is illustrated in Figure 7. The Labview implementation of the error synchronization tracking and adaptive compensation can be seen in Figure 8.  
After synchronization of the signal on the RIO side, frame synchronization is achieved by utilizing the auto-correlation characteristics of Barker codes in the main sub-spectrum. Since the optimal sampling point for the main sub-spectrum is the same as that for the other sub-spectra, symbol rate sampling can be performed on all sub-spectra, thus reducing the consumption of logic resources and lowering the data link overload. Through this system architecture design, the performance degradation caused by resource limitations is to some extent avoided while ensuring the real-time performance of the system. To assess hardware limitations and resource usage, the scheme is estimated according to the resource consumption shown in the comprehensive report generated by FPGA processing and combined with the amount of FPGA resources available in the USRP-X310 RIO.Reference is provided below in Table 1. \begin{table}
\begin{tabular}{c c c} \hline \hline
**FPGA Resource Type** & **Resource Consumption** & **Available Resource** \\ \hline Slice LUTs & 17,000–19,000 & 254,200 \\ Slice registers & 32,000–34,000 & 508,400 \\ DSPs & 900–1000 & 1540 \\ Block RAMs & 20–25 & 795 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of resource consumption with available resources on the X310 RIO.