Low Earth orbit (LEO) satellite systems enable close to global coverage and are therefore expected to become important pillars of future communication standards. However, a particular challenge faced by LEO satellites is the high orbital velocities due to which a precise channel estimation is difficult. We model this influence as an erroneous angle of departure (AoD), which corresponds to imperfect channel state information (CSI) at the transmitter (CSIT). Poor CSIT and non-orthogonal user channels degrade the performance of space-division multiple access (SDMA) precoding by increasing inter-user interference (IUI). In contrast to SDMA, there is no IUI in orthogonal multiple access (OMA), but it requires orthogonal time or frequency resources for each user. Rate-splitting multiple access (RSMA), unifying SDMA, OMA, and non-orthogonal multiple access (NOMA), has recently been proven to be a flexible approach for robust interference management considering imperfect CSIT. In this paper, we investigate RSMA as a promising strategy to manage IUI in LEO satellite downlink systems caused by non-orthogonal user channels as well as imperfect CSIT. We evaluate the optimal configuration of RSMA depending on the geometrical constellation between the satellite and users.
翻译:低地球轨道(LEO)卫星系统能够接近全球覆盖范围,因此预计将成为未来通信标准的重要支柱。然而,低地轨道卫星面临的一个特殊挑战是轨道速度高,因此很难准确估计频道。我们将这种影响作为错误的起飞角度(AoD)来模拟,这与发射机(CSIT)的不完善的频道状态信息(CSI)相对应;差的CSIT和非横向用户渠道通过增加用户之间的干扰,降低空间分层多存取(SDMA)前的功能。与SDMA相比,低地轨道多存取(OMA)没有IU,但每个用户都需要有或有时间或频率的资源。率分裂的多重存取(RSMA),统一SDMA、OMA和非孔径多访问(NOMA),最近被证明是一种灵活的方法,考虑到不完善的CSIT,我们发现RSMA是管理低地轨道下链接系统(INUI)系统的一个大有希望的战略,由非轨道用户在Weconomal RSIMA上对最佳的系统进行不完善的评估。