# A Fast Acquisition Algorithm for Hybrid Signals of 5G and BeiDou B1
## 2 Proposed Method
### Compatibility Analysis of 5G and BeiDou B1 Signal
#### 2.1.3 5G and BeiDou B1 Band Compatibility Analysis
The 5G bands adjacent to BeiDou L-bands B1, B2, and B3 are n50, n51, n74, n75, and n76, with the same NR parameters, and the frequency range of n50 covers the other four bands. The n50 upper boundary is only 45 MHz away from the BeiDou B1 signal, so it can be initially speculated that the 5G signal is located in the upper boundary of n50 when it causes the most significant impact on the BeiDou system. The impact on the BeiDou system is the greatest. When the BeiDou navigation signal is received and processed, the acquisition peak, carrier phase tracking error, and code phase tracking error can be used as important parameters to evaluate the performance of the navigation signal. The total carrier phase tracking error of BeiDou signals under the combined effect of white noise and interference is \(\sigma_{PLL}=\sqrt{\sigma_{nPLL}^{2}+\sigma_{IPLL}^{2}}\). The code tracking error is \(\sigma_{DLL}=\sqrt{\sigma_{nDLL}^{2}+\sigma_{IDLL}^{2}}\). The 5G band is deployed at 2.6 GHz, far from the three frequency points of the BeiDou system. This 2.6 GHz will not affect BeiDou navigation signals. In addition, the B2 and B3 bands are also far away from the frequency interval of each band of the 5G system, so it can be presumed that there will be no compatibility problem between 5G and B2 and B3. Because the landing power of BeiDou signals is meager and has been submerged below the noise, the BeiDou system will not affect the 5G system. In summary, the study of BeiDou's compatibility with 5G can be translated into a study of how compatible the 5G signals near the BeiDou L-band are. Among the FR1 bands, n50 has the broadest range of 5G signals near the BeiDou L-band and covers other frequency bands so that n50 can be the leading research object, and its findings can be extended to other 5G bands. As shown in Figure 5, the n50 band is closest to the BeiDou B1 signal. Because the transmitting power of 5G base stations is generally around \(-10\) dBw, this makes the 5G signal power on the ground much stronger than the landing power of BeiDou (\(-133\) dBm), and even the 5G out-of-band spurious radiation at the same frequency point may be stronger than the BeiDou signal. The multi-carrier form of the 5G signal is OFDM, and its out-of-band radiation or spurious part will fall into the BeiDou B1 signal. Since QPSK and QAM modulate 5G signals, it is necessary to simulate the modulation of 5G signals by traversal. Therefore, in order to study the compatibility between BeiDou and 5G, we need to perform a traversal simulation in three dimensions:  
1. The type of 5G signal. 2. The power of the 5G signal arriving at the BeiDou receiver. 3. The frequency interval between the BeiDou signal and the 5G signal. Since performing direct acquisition of the original signal at RF frequencies is not practical, the simulation and actual acquisition should be performed at IF frequencies. The 5G system frequency points change while the nominal frequency of BeiDou is fixed. When the OB bandwidth of the n50 band is 5 MHz, and the center frequency point is located anywhere from the lower to the upper boundary of the operating band, the center frequency point of BeiDou B1I is about 47 MHz-131 MHz from the center frequency point of the 5G signal. The center frequency point of B1C is 60 MHz-145 MHz from the center frequency point of the 5G signal. In order to simulate the change in frequency interval between the BeiDou signal and the n50 signal, the 5G IF is set to 10 MHz, while the BeiDou B1I signal IF is set to 60 MHz-110 MHz, and the BeiDou B1C signal IF is set to 70 MHz-100 MHz, as shown in Figure 5.