EMPIRICAL STUDY OF RAIN FADE SLOPE CONDITIONAL STATISTICS ON SATELLITE LINKS

摘要

The temporal dynamic aspects of propagation effects are essential information for the design of adaptive Fade Countermeasure Intelligent Systems (FCMIS) The required tracking speed of such systems can be estimated using jnformation on fade slope, while the frequency and the duration of their functioning can be assessed using information on fade duration and number of fades per year [1]. Knowledge of the fade slope enables a better short-term prediction of the slow-varying components of the signal dominated by rain attenuation, The fast fluctuations of the signal due to scintillations are however difficult to predict on a time scale of several seconds [2]. Hence an accurate extraction of rain attenuation from amplitude scintillations is also required for efficient real-time applications. A statistical fade slope model can be applied to the accurate short-term prediction of rain fades used to optimise the performance of a FCMIS through a predictive control technique (PCT). The schematic of the FCMIS can be seen on Figure 1. The principle introduced by Chung [5] is particularly applicable to cases, where a fade may increase rapidly, so that the link may reach an outage before the actual FCM is effectively brought in. Luglio in [6] mentions that it is necessary to implement an algorithm to provide a realtime prediction of the rain attenuation by correlating the initial parameters linked to the rain fading itself with the actual dynamic characteristics of the phenomenon. The FCMIS system in Figure 1 utilises such an approach by being able to predict the relevant propagation parameters from pre-processed real time observation. To be any good, FCMIS must be statistical and it should also consider the characteristics of the previous events.