Abstract
This study develops an optimal performance monitoring metric for a hybrid free space optical and radio wireless network, the Outage Capacity Objective Function. The objective function—the dependence of hybrid channel outage capacity upon the error rate, jointly quantifies the effects of atmospheric optical impairments on the performance of the free space optical segment as well as the effect of RF channel impairments on the radio frequency segment. The objective function is developed from the basic information-theoretic capacity of the optical and radio channels using the gamma-gamma model for optical fading and Ricean statistics for the radio channel fading. A simulation is performed by using the hybrid network. The objective function is shown to provide significantly improved sensitivity to degrading performance trends and supports of proactive link failure prediction and mitigation when compared to current thresholding techniques for signal quality metrics.
Highlights
Current techniques of free-space optical (FSO) and radio frequency (RF) link performance measuring and monitoring are traditionally applied at the physical and lower link layer, at the RF and FSO signal in space (SiS) and at the bit/packet levels
The derivative of the bit error rate (BER) vs optical signal-to-noise ratio (OSNR) measurement in the high BER regime shows no change between 0.2 and 0.29 BER, and for much of the high BER regime starting with an optical MIMO system of 10 transmitters
The control system that is adjusting the offered load based on a BER measurement can effect very little correction in this case, due to low or zero gain, in this regime for large MIMO arrays
Summary
Current techniques of free-space optical (FSO) and radio frequency (RF) link performance measuring and monitoring are traditionally applied at the physical and lower link layer, at the RF and FSO signal in space (SiS) and at the bit/packet levels. Performance metrics commonly used include received signal level, optical signal-to-noise ratio (OSNR) for the optical links, quality (Q) factor, eye diagram, signal-to-noise ratio (SNR) or signal-to-interference ratio (SIR) for the RF links, and bit error rate (BER). In good atmospheric conditions the received optical signal level and OSNR will be high and will fluctuate within some previously-defined normal range as determined by the optical channel fading characteristics. In good RF propagation conditions, the received signal level will be correspondingly high as the SNR/SIR, and in turn it will fluctuate within a bounded acceptable range. By the time the performance monitor (PM) component of the network management system (NMS) has determined that the SNR and other performance metrics have crossed the acceptable threshold, user data are lost. It is demonstrated that the objective function provides an extremely sensitive measure of the network performance, identifying impending failure well in advance of signal quality thresholding alone
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