6 Technical bases of performance and availability objectives for digital fixed wireless systems employing multi-state modulation
In order to efficiently utilize the limited resource of radio-frequency spectrum, multi-state modulation schemes may be employed for high capacity digital fixed wireless systems. As the number of modulation states increases, the performance of the modem and the radio system is impaired by several factors. These are:
– the stability of carrier and clock synchronization circuits,
– amplitude distortion due to the transmission path,
– distortion caused by saturation of the high power amplifier,
– interference from other systems (adjacent channels, satellite, adjacent route, etc.),
– multipath fading.
It is therefore necessary to consider the mechanisms causing the impairments and devise the appropriate countermeasures. The following topics should be studied. Fuller details may be found in Recommendation ITU‑R F.1093.
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