## 3 System Model
### Model of Multi-Beam Satellite Communication System  
We focus on the satellite communication system of B5G and 6G. The technology can advance on the basis of the system model of OneWeb. As a result, we have fully considered the new technology of 5G which can support the multi-beam satellite communication system. The system model of the multi-beam satellite communication system is composed of the OneWeb system model, 5G NR new technology, and the satellite channel model. As shown in Figure 1, the model of multi-beam satellite communication systems is introduced. The LEO constellation is built which is composed of 720 satellites on the basis of OneWeb. The satellites uniformly distribute in 18 polar orbits at a distance of 1200 km. The number of the satellite is 40 in one polar orbit. The inclination angle of each orbital surface is 87\({}^{\circ}\). Each satellite revolves around the earth. There are most three satellites that can cover the same service area. With the development of spaceborne phased array antenna, multi-port amplifier, renewable technology, and software radio technology, the beams can be flexibly adjusted and the radio resources can be allocated efficiently in the multi-beam satellite communication system. 1. **Spaceborne phased array antenna:** The phased array antenna controls the feed phase and realizes the beam sweep. By controlling the feed phase of the radiating element in the array antenna, the shape of the pattern can be changed. At present, the bandwidth of the phased array antenna is 4 GHz. The antenna volume is less than 1 dm\({}^{3}\), and the scanning Angle is greater than \(\pm 60^{\circ}\), which can effectively improve the system throughput. 2. **Multi-port amplifier:** Multi-port amplifier is mainly composed of the input matrix, output matrix, and high power amplifier. Input signals are distributed to all input matrices. After being distributed through the high-power amplifier, they are recombined in the output matrix. At present, multi-port amplifiers can be suitable for frequency bands such as S/L/Ka/Ku. 3. **Renewable technology:** Renewable technology is to receive satellite multi-source payload data and perform information fusion processing on it. With the development of OFDM, multiple access, and power control, the data processing capability of satellites has been effectively improved. 4. **Software radio technology:** Software radio refers to the realization of various radio communication functions (such as working frequency band, modem type, data format, encryption mode, and communication) through software loading on an open, standardized, and modular general hardware platform. By reloading part of the software in orbit, satellites can support the latest waveform and protocol standards to update the corresponding technology. At present, software radio can support 256 Mbit, repetitive programming on-orbit, and 100 Mbit/s. According to the options in the 3 GPP, a four-color multiplexing scheme is used between beams. Spectrum is shared between satellites. The protocol between satellites and users includes control plane protocol and user plane protocol, which processes the data packets with different delays, different QoS requirements, and different sizes generated by users. Physical signals between satellites and users are processed by Low Density Parity Check Code (LDPC) and Quadrature Phase Shift Keying (QPSK). Channel multiplexing is realized by OFDM. There are several satellites and users in the multi-beam satellite communication system. Multi-beam satellites are denoted as \(S=\{s_{1},s_{2},\ldots,s_{P}\}\), \(P\) is the number of multi-beam  
Figure 1: Model of multi-beam satellite communication system. satellites. Users are denoted as \(U=\left\{u_{1},u_{2},\ldots,u_{Q}\right\}\), \(Q\) is the number of users. The user \(u_{q}\) connected to the satellite \(s_{p}\) is denoted as \(u_{qp}=1\).