Radio spectrum utilization efficiency is an important factor to be considered in the design of digital fixed wireless systems and it is determined by the “information transferred over a distance” in relation to the frequency bandwidth utilization, the geometric (geographic) spatial utilization and the time denied to other potential users. The measure of utilization (U) is given by the product:
where:
BRF : radio-frequency bandwidth occupied
S : geometric space occupied (usually area for fixed wireless systems)
T : time.
The utilization efficiency, E, for a system operating continuously in time is expressed by:
where:
N : total number of “go” and “return” channels in the radio band BRF
B : channel gross bit rate.
In the case of single high or medium capacity multi-channel long-haul routes, in which spurious emissions are adequately controlled and the dimensions of space and time can be ignored, the radio-frequency spectrum utilization efficiency reduces to a bandwidth utilization efficiency EB, given by:
where N includes both polarizations on the route.
It can be seen that the use of multi-state modulation methods increases the bandwidth utilization efficiency in this case by an increase of B.
Detailed information on this subject is given in Recommendation ITU-R SM.1046.
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