# A Fast Acquisition Algorithm for Hybrid Signals of 5G and BeiDou B1
## 2 Proposed Method
### Receiver Acquisition Algorithm Design  
#### 2.2.1 Receiver Hardware Architecture Design  
At the signal level, Dou adopts the direct sequence spread-spectrum (DSSS) modulation scheme, while 5G employs orthogonal frequency division multiplexing (OFDM). Both schemes are based on code division multiple access (CDMA), but 5G utilizes orthogonal subcarriers for spectrum allocation and data transmission, resulting in efficient spectrum utilization and resistance to multipath fading, making it suitable for high-speed mobile and wideband communication. The BeiDou radio navigation satellite system (RNSS) signals do not require bidirectional communication, and a single-carrier approach is sufficient to meet the system design requirements. From the analysis of the signal schemes mentioned above, it can be observed that due to the resemblance between the two signal schemes, a single receiving method theoretically can be used for the reception of mixed signals from both types. This receiving method exhibits high similarity in the RF circuitry, baseband signal preprocessing, acquisition and tracking, and despreading stages. The main difference lies in the multi-carrier nature of 5G signals, which requires local generation of multiple carriers for carrier separation of the received signal. Additionally, the generation method for local pseudocodes also differs. The hardware architecture of the mixed-signal receiver of BeiDou and 5G signals is shown in Figure 6, which is divided into RF front-end, baseband processing, and information processing. The BeiDou signal and 5G signal are received by the antenna and sent to the RF front-end processing circuit. The RF front-end circuit first amplifies the mixed signal through a low-noise amplifier (LNA), where the LNA is placed in the front position to reduce the receiver's overall noise figure (NF). The amplified signal must also go through anti-image filtering, a power divider, a mixer, and anti-alias filtering before being captured by the ADC. After the above processing, the digital IF signal is obtained. The high-speed digital IF signal is first digitally downconverted to obtain the digital baseband signal. The digital baseband signal is then passed through the signal acquisition algorithm, which mainly processes the carrier Doppler frequency and pseudocode phase of the BeiDou B1 and 5G signals in the signal to obtain coarse raw observation information, which is also the focus of this study. We propose a fast acquisition algorithm for the hybrid BeiDou B1 and 5G signals. This raw observation information is later sent to the baseband  
Figure 5: (**a**) Diagram of the corresponding BeiDou B1I signal and n50 radio frequency during simulation. (**b**) Diagram of the corresponding BeiDou B1C signal and n50 radio frequency during simulation. Figure 6: Receiver hardware architecture. tracking algorithm. Based on the coarse Doppler frequency and pseudocode phase, it accurately tracks the carrier and pseudocode phases through the carrier and pseudocode loops. Finally, it restores the original carrier and pseudocode envelope. The signal processed by the tracking algorithm is the envelope of the spread-spectrum code signal. The envelope signal can extract accurate message information only after bit-synchronous and frame-synchronous processing. In the information processing part, BeiDou signals must complete the equation solving of position, velocity, and clock difference. They can be considered accurate and trustworthy after being processed by the receiver autonomous integrity monitoring (RAIM) algorithm to be output. Furthermore, 5G signals also enter into higher-level processing after extracting frame information. The antenna receives the hybrid signal, and the RF front-end is divided into two branches of B1 and 5G signals. The B1 signal is downconverted by RF and sampled by ADC to obtain a 20 MHz digital IF signal, and the 5G n50 signal is downconverted by RF and sampled by ADC to obtain a 120 MHz digital IF signal.