3. Improved performance of short loops
The goal of this mode is to maximize the performance of short loops keeping performance degradation of the Long loops limited.
NEG: Can be implemented for only one short loop. With more than one short loop performance degradation of long loops can’t be limited.
4. Spectral mask compatibility with other services
A specific PSD mask is specified for each loop length with no reference on the performance degradation in the particular loop. The initial definition of PSD mask could be based on any of the modes
POZ: Predicts all spectral compatibility problems with existing and future services. Selected as the UPBO mode in ITU.
NOTE: The exact implementation technique for this method is under discussion.
Methods of UPBO
Method of UPBO specifies how to reach the goal defined by the mode. Sometimes the same goal could be reached by different methods. Compatibility of different methods should be taken in account. The following PBO methods are widely discussed:
•Reference PSD
•Reference Length
•Multiple Reference Length
•Equalized FEXT
•Reference Frequency
•Reference Noise
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