Propagation effects on spread-spectrum mobile satellite systems

In contrast to the situation at L-band, wide bandwidths of 500 MHz or more have been allocated for mobile satellite service at frequencies between 20 and 50 GHz. These broad bandwidths are well suited for the use of spread-spectrum. Certain system considerations about the use of such high frequencies for mobile satellite service are mentioned first, and attention is then given to propagation effects on high-frequency broad-band systems. Attenuation due to rain is a constant at 20 to 50 MHz, but would not be a serious problem if outages occurring for one to three percent of the time, depending on location, are considered to be acceptable. Clear air absorption becomes a significant factor above 40 GHz, but should not exceed 2 dB at a 10 degree elevation angle and frequencies below 40 GHz. Spread-spectrum provides a form of frequency diversity that helps to minimize the effects of multipath.