# A B5G Non-Terrestrial-Network (NTN) and Hybrid Constellation Based Data Collection System (DCS)
## 7 Simulations and Experiments
### Satellites Constellation Simulations  
As described in Section 3, a hybrid constellation containing Walker and Polar is designed. There are 42 CubeSats between 500 km altitude and 550 km altitude. Those CubeSats can scan the world periodically. As described in Section 5, the traffic density is related to latitude. Some key parameters with different latitudes are simulated in this chapter.  
To verify the orbit design, several key performances are simulated. Such as connection opportunity, connection duration, total duration, and duty cycle. The connection opportunity indicates the maximum number of connections at different latitudes during the simulation period. Connection duration indicates the longest and shortest time of each connection during the simulation period. The total duration indicates the total connection time in the simulation period at different latitudes. The duty cycle is an optimization parameter, indicating the access capability of the constellation.  
Several simulations are performed by the commercial software STK and Matlab. To be more representative, these simulations are performed by a unified model and interface. The basic simulation parameters are described as follows:  
* Simulation period 24 h;
* BW: 1 Mbps for each satellite;
* Node number: 36 nodes for walker constellation and 6 nodes for polar constellations;
* Latitude range: \(-90^{\circ}\)\(-\)\(+90^{\circ}\);  
As shown in Figure 13a, different connection opportunities are obtained at different latitudes. The maximum connection opportunity appears in middle latitude, and the  
Figure 12: Ground gateway design: (**a**) flow design; (**b**) equipment design.  
minimum connection opportunity is more than 16. The connection durations are described in Figure 13b. It also follows the population distribution. However, in polar regions, the connection duration is long because of the orbit cross.  
The total duration in 24 h at different latitudes is shown in Figure 14a. This parameter can comprehensively represent the access capability of the orbit. The throughput between a specific CubeSat and regions can be exported from Equations (1) and (2) in Section 5.  
To optimize the efficiency of DCS, a duty cycle (DC) parameter can be used to control the operation state of CubeSats. DC is related to time and latitude. It can be deduced from the total duration and Equation (3). The results calculated by Matlab are shown in Figure 14b. Under the same throughput requirement, the DC parameter represents the working saturation of CubeSats at different latitudes. This working saturation contains output power, data rate, and storage ratio.  
This parameter can also be used to control the onboard operation. An optimized control plan for CubeSat can accomplish energy balance and communication guarantee. However, the BW and connection will dynamically change in the actual operation. An adaptive control strategy is necessary in the B5G control plane.  
Figure 14: Satellite-to-ground duration analysis: (**a**) The total durations for different latitudes; (**b**) The duty cycle for different latitudes.  
Figure 13: Satellite-to-ground connections: (**a**) The connect opportunities for different latitudes; (**b**) The max and min connect durations for different latitudes.