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Outage analysis of the hybrid free-space optical and radio-frequency channel

机译:自由空间光和射频混合信道的中断分析

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We study the hybrid free-space optical (FSO) and radio-frequency (RF) channel from an information theoretic perspective. Since both links operate at vastly different carrier frequencies, we model the hybrid channel as a pair of parallel channels. Moreover, since the FSO channel signals at a higher rate than the RF channel, we incorporate this key feature in the parallel channel model. Both channels experience fading due to scintillation, which is slow compared to typical signalling rates. Under this framework, we study the fundamental limits of the hybrid channel. In particular, we analyse the outage probability in the large signal-to-noise ratio (SNR) regime, and obtain the outage diversity or SNR exponent of the hybrid system. First we consider the case when only the receiver has perfect channel state information (CSIR case), and obtain the exponents for general scintillation distributions. These exponents relate key system design parameters to the asymptotic outage performance and illustrate the benefits of using hybrid systems with respect to independent FSO or RF links. We next consider the case when perfect CSI is known at both the receiver and transmitter, and derive the optimal power allocation strategy that minimises the outage probability subject to peak and average power constraints. The optimal solution involves non-convex optimisation, which is intractable in practical systems. We therefore propose a suboptimal algorithm that achieves significant power savings (on the order of tens of dBs) over uniform power allocation. We show that the suboptimal algorithm has the same diversity as the optimal power allocation strategy.
机译:我们从信息理论的角度研究混合自由空间光(FSO)和射频(RF)通道。由于两条链路的工作频率相差很大,因此我们将混合信道建模为一对并行信道。此外,由于FSO通道的信号传输速率高于RF通道,因此我们将此关键功能纳入并行通道模型中。由于闪烁,两个信道都经历了衰落,与典型的信令速率相比,这是缓慢的。在此框架下,我们研究了混合渠道的基本限制。特别是,我们分析了大信噪比(SNR)情况下的中断概率,并获得了混合系统的中断分集或SNR指数。首先,我们考虑只有接收者具有完善的信道状态信息的情况(CSIR情况),并获得一般闪烁分布的指数。这些指数将关键系统设计参数与渐进式中断性能相关联,并说明了相对于独立FSO或RF链路使用混合系统的好处。接下来,我们考虑在接收器和发射器都知道完美CSI的情况下,并推导最佳功率分配策略,该策略将在出现峰值和平均功率约束的情况下将中断概率降到最低。最佳解决方案涉及非凸优化,这在实际系统中是很难解决的。因此,我们提出了一种次优算法,该算法在均匀功率分配上实现了显着的功率节省(数十dB量级)。我们表明,次优算法与最优功率分配策略具有相同的多样性。

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