Transmission Schemes.

In the future, radio communication systems will offer different services through single user equipment; furthermore, it is expected that different radio communication systems will merge into one universal communication system. Today, there are two known concepts for providing wireless communication services: terrestrially based communication systems and satellite communication systems. Each concept has its specific characteristics, and consequently, advantages and disadvantages. The main disadvantages of terrestrially based systems are: poor radio channel quality, Rayleigh fading limits the cell radius and transmitted data rate and; and Terrain shadowing causes gaps in radio coverage.