In helicopter satellite communication systems, the received signal is blocked by the helicopter rotor blades during propagation, incurring the unstableness of traditional methods of channel estimation due to unknown channel state. To this end, a joint occlusion detection and phase estimation algorithm is proposed by factor graph in this paper. For occlusion detection to acquire channel state, the occlusion channel model is established relying on a Markov chain with a priori blocking ratio, in which the probability distribution of the channel state is calculated by the proposed message-passing algorithm. To obtain the occlusion position and update the blocking ratio, a cross-correlation method is designed. Furthermore, a joint block detection and phase estimation algorithm is developed based on the proposed occlusion detection algorithm to realize phase estimation by iterative receiver, where occlusion detection, phase estimation, and decoding are performed in turn for one turbo iteration and the result of decoding is then sent back to the occlusion detection step for the next iteration. Simulation results show that the proposed algorithm is adaptive to the dynamical change in the blocking ratio and can achieve bit error rate performance that is close to the performance bounds based on perfect channel state.

中文翻译：

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直升机卫星通信联合遮挡检测与相位估计算法

在直升机卫星通信系统中，接收信号在传播过程中被直升机旋翼叶片阻挡，由于信道状态未知，导致传统信道估计方法不稳定。为此，本文提出了一种基于因子图的联合遮挡检测和相位估计算法。对于阻塞检测获取信道状态，依赖于具有先验阻塞率的马尔可夫链建立阻塞信道模型，其中信道状态的概率分布由所提出的消息传递算法计算。为了获得遮挡位置并更新阻塞率，设计了互相关方法。此外，在提出的遮挡检测算法的基础上，开发了一种联合块检测和相位估计算法，实现迭代接收器的相位估计，其中遮挡检测、相位估计和解码依次进行一次turbo迭代，然后发送解码结果返回到下一次迭代的遮挡检测步骤。仿真结果表明，该算法能够适应阻塞率的动态变化，能够实现接近基于完美信道状态的性能界限的误码率性能。