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摘要:
随着业务需求的全球性增长，传统低频波段有限的频谱资源已不能满足低轨（LEO）卫星的业务承载要求，采用Ka频段的LEO星座系统设计成为了主流。然而，采用Ka频段的LEO星座系统不可避免地会对同频段已经存在的静止轨道（GEO）卫星系统产生干扰。首先，通过基于空间隔离的干扰规避方法，采用对LEO与GEO的频谱共用系统设置隔离角来进行上下行场景的干扰消除，使该LEO系统能满足国际电信联盟（ITU）对同频段内通信干扰的约束条件；然后，通过引入GEO带的概念，分析并研究了干扰规避区域的确定方法和其对LEO星座密度的影响。最后，通过仿真得出了干扰隔离角、GEO带与LEO星座密度的关系，得到了在采用隔离角的方式进行干扰避让时满足LEO星座系统业务不中断所需要的最小卫星数量，对LEO星座设计具有一定的指导意义。
Abstract:The increase demand for global services in recent years has led to the deficiency of resources in traditional low frequency band in low earth orbit (LEO) satellite communication. Thus designs of LEO satellite constellation in Ka band have drawn a lot of interests. However, utilization of Ka band in LEO design inevitably causes interference to the existing geostationary (GEO) satellite system in the same band. A method of the discrimination angle based on spatial isolation in LEO-GEO coexistence systems is adopted to mitigate the interference both in uplink and downlink scenarios and to guarantee that the interference level from LEO system can meet the constraint requirements of communication interference in the same frequency band which are stipulated by International Telecommunication Union (ITU). Furthermore, a concept of GEO band is developed to determine the interference exclusion zone and to research the impact on the LEO satellite constellation density. Finally, simulations of the relationship among the discrimination angle, the GEO band and the LEO constellation density are given and the minimum satellite amount in this method without interrupting satellite services is found, which is significant in LEO satellite constellation design.
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图 5 下行场景α与θ和地面站天线仰角关系示意图
Figure 5. Schematic of relationship among α, θ and elevation angle of ES antenna in downlink scenario
图 6 上行场景α与θ和地面站天线仰角关系示意图
Figure 6. Schematic of relationship among α, θand elevation angle of ES antenna in uplink scenario
图 14 不同θ值时星座密度参数仿真结果
Figure 14. Simulation result of constellation density parameter at different θ
表 1 仿真参数
Table 1. Simulation parameters
参数 数值 LEO轨道高度/km 850 GEO轨道高度/km 35 786 地球半径/km 6 371 地面站最小仰角/(°) 10 轨道倾角/(°) 87 发射功率/dBw 0 载波带宽/MHz 54 上行频率/GHz 28 下行频率/GHz 18.2 LEO地面站天线口径/m 1.2 GEO地面站天线口径/m 1 LEO卫星天线口径/m 0.4 GEO卫星天线口径/m 3a 地面站天线增益 见文献[17] LEO卫星天线增益 见文献[18] GEO卫星天线增益 见文献[16] 地面站密度/(°) 1b 注：a.上行EPFD值对2~4区间的变化不敏感; b.设沿纬度线均匀分布，在赤道线上地面站间隔经度值为1°。 
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