# A Fast Acquisition Algorithm for Hybrid Signals of 5G and BeiDou B1
## 2 Proposed Method
### Compatibility Analysis of 5G and BeiDou B1 Signal
#### 2.1.2 5G Signal System  
According to the latest version of 3 GPP R16 38.104 in March 2020, the operating band of 5G is divided into two parts, FR1 (450 MHz-6.0 GHz) and FR2 (24.25 GHz-52.6 GHz), where the FR1 part is roughly the same as the previous 4G band, and the new FR2 band is the millimeter-wave band. The scope of this study is in the FR1 band, and its specific band number division is shown in Table 4.  
The frequency resources of 5G systems are dynamically allocated. The signal bandwidth, subcarrier space (SCS), and number of resource blocks (NRB) can be configured according to the scheme shown in Table 5. The actual signal frequency location used by 5G devices during communication is a factor in studying the compatibility of BeiDou and 5G signals. A 5G system is designed to calculate the number of resource blocks in the bandwidth according to the scheme of 12 subcarriers as one resource block. Table 5 shows that the signal's bandwidth in one communication can only occupy part of the operating band if it meets the basic requirements. According to Figure 2 and Table 4, we can sort the 5G signal bands near the BeiDou L-band as shown in Table 6. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**NR Frequency Band** & **Uplink Frequency Band** & **Downlink Frequency Band** & **Duplex Mode** \\ \hline n1 & 1920–1980 & 2110–2170 & FDD \\ n2 & 1850–1910 & 1930–1990 & FDD \\..... &..... &..... &..... \\ n50 & 1432–1517 & 1432–1517 & TDD \\ n51 & 1427–1432 & 1427–1432 & TDD \\..... &..... &..... &..... \\ n74 & 1427–1470 & 1475–1518 & FDD \\ n75 & N/A & 1432–1517 & SDL \\ n76 & N/A & 1427–1432 & SDL \\..... &..... &..... &..... \\ n95 & 2010–2025 & N/A & SUL \\ \hline \hline \end{tabular}
\end{table} 
Table 4: 5G FR1 frequency band details. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**SCS** & **5 MHz** & **10 MHz** & **15 MHz** & **20 MHz** & **...** & **70 MHz** & **80 MHz** & **90 MHz** & **100 MHz** \\ \hline
**(KHz)** & **NRB** & **NRB** & **NRB** & **NRB** & **NRB** & **NRB** & **NRB** & **NRB** \\ \hline
15 & 25 & 52 & 79 & 106 &... & N/A & N/A & N/A & N/A \\
30 & 11 & 24 & 38 & 51 &... & 189 & 217 & 245 & 273 \\
60 & N/A & 11 & 18 & 24 &... & 93 & 107 & 121 & 135 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: 5G band transmission bandwidth configuration. Research on BeiDou and 5G compatibility must consider how to apply BeiDou in scenarios where BeiDou and 5G coexist during actual engineering applications. The 5G FR1 bands near BeiDou, shown in Table 6, are assigned to eMBB and IoT scenarios. In addition to considering the specific application scenarios of 5G signals, it is also necessary to consider the basic parameters of 5G signals in these bands, whose related parameters and technologies are shown in Table 7.  
According to Table 7, the 5G band adjacent to BeiDou mainly uses QPSK and QAM modulation, and the multi-carrier mode is OFDM. The 5G system downlink physical channels include the physical broadcast channel (PBCH), the physical downlink shared channel (PDSCH), and the physical downlink control channel (PDCCH). Since the downlink has a higher transmit power, it must be considered seriously in the compatibility study. The 5G NG is allocated various transmission channels within the limited time-frequency resources, and the time-frequency resources of these transmission channels are allocated to different users at different times. We deduce the radiation of 5G falling into the range of the BeiDou signal band based on the spectrum. Although the resource mapping will be different in different scenarios, for different devices, and at different times, the spectrum of the final generated signal will be similar because the multi-carrier approach is the same. Therefore, we only need to generate a 3 GPP-compliant 5G signal when studying the compatibility between BeiDou and 5G and use this 5G signal as a representative to study its impact on BeiDou. The multi-carrier approach for 5G signals is OFDM, which can be regarded as a particular filter bank multi-carrier (FBMC).