## 1 Introduction  
When a natural disaster occurs, relief work is severely hampered by telecommunication infrastructure damage. This is best illustrated with the landfall of Hurricane Katrina and the subsequent flooding of New Orleans in 2005 [1]. Most of the telecommunication infrastructure was destroyed by the storm [2]. Given that the electricity distribution was also disrupted, the few remaining cell towers operated on backup batteries for another 4 h, after which they ceased to work as well [3]. The roads into the disaster were flooded, which left the entire disaster zone, an area of 200 km \(\times\) 200 km, without access and telecommunications. In such circumstances, as an alternative,ionospheric radiocommunication systems could be used to provide instantaneous access to the entire area. The ionosphere is a natural plasma between 60 and 1000 km height, sustained by solar radiation [4][PERSON] Several regions can be distinguished [4], as shown in Figure 1. The peak electron density occurs between 150 and 250 km height in the F-region. Ionospheric radio systems may send radio waves nearly vertically upwards, to be refracted in the ionosphere and returned to earth, as depicted in Figure 2a. This [PERSON] is called 'Near Vertical Incidence Skywave' (NVIS) propagation [5]. The refraction in the ionosphere depends on the electron density in the ionosphere [6]. Driven by the radiation of the sun, the electron density follows a diurnal cycle, the seasons and the 11-year solar cycle [7]. For NVIS propagation, the frequency of the radio waves must be smaller than the maximum plasma frequency of the ionosphere, for mid-latitudes typically between 3 and 10 MHz[PERSON]  
The ionosphere is bi-refractive. [PERSON] and [PERSON] showed that radio waves entering the ionosphere, under the influence of the Earth's magnetic field, are split in two circularly polarized characteristic waves in opposite rotational directions, the ordinary and the extraordinary wave [8]. [PERSON] and his contemporaries [9; 10] were able to develop this'magneto-ionic theory' based on work of [PERSON] and [PERSON] [11], that explained the polarization rotation discovered by [PERSON] in 1845 [12]. The polarization of the characteristic waves depends on the angle between their direction of propagation and the magnetic field vector. In the northern hemisphere, the polarization of the ordinary wave is right-hand circular (RHCP) upwards and left-hand circular (LHCP) downwards, as shown in  
Figure 1: The ionosphere is a natural plasma, sustained by solar radiation [4].  
Figure 2: (a) Near Vertical Incidence Skywave (NVIS) propagation; (b) Magneto-ionic propagation: ordinary (red) and extraordinary wave (green). Polarization is shown for the northern hemisphere.  
Figure 2b. In the Southern hemisphere, the sense of rotation is reversed. For NVIS propagation at mid-latitudes and at frequencies above 5 MHz, the polarization of the characteristic waves is almost circular [6]. Both characteristic waves follow a different path through the ionosphere, which can be shown using ray-tracing techniques [13; 14]. And as the ionosphere is not homogeneous, they suffer different attenuation, time delay and delay spread, Doppler shift and Doppler spread and fading.