We consider a two-ray ground reflection scenario with unknown distance between transmitter and receiver. By utilizing two frequencies in parallel, we can mitigate possible destructive interference and ensure ultra-reliability with only very limited knowledge at the transmitter. In order to achieve this ultra-reliability, we optimize the frequency spacing such that the worst-case receive power is maximized. Additionally, we provide an algorithm to calculate the optimal frequency spacing. Besides the receive power, we also analyze the achievable rate and outage probability. It is shown that the frequency diversity scheme achieves a significant improvement in terms of reliability over using a single frequency. In particular, we demonstrate the effectiveness of the proposed approach by a numerical simulation of a unmanned aerial vehicle (UAV) flying above flat terrain.

翻译：我们考虑的是发射机和接收机之间距离不明的两射地面反射情景。通过同时使用两个频率,我们可以减少可能的破坏性干扰,确保极可靠的发射机只有非常有限的知识。为了实现这一极端可靠性,我们优化了频率间隔,使最坏情况获得的能量最大化。此外,我们提供了计算最佳频率间隔的算法。除了接收力外,我们还分析了可实现的频率和超速概率。我们发现,频率多样性计划比使用单一频率的可靠性大有改进。特别是,我们通过对飞越平坦地形的无人驾驶飞行器进行数字模拟,展示了拟议方法的有效性。