This parameter is used to restrict the percentage of TSs that can be used as PDCHs (both static and dynamic).
Consider a typical 4TRX cell with 1BCCH and 2 SDCCHs. Then:
Total number of TSs that can be used for traffic(voice or data)=4*8 – 3 = 29.
Now, if ur ‘maximum ratio threshold of PDCHs in cell’ is 30 for this cell, then:
Maximum no. of PDCHs = 0.3*29 = 8.7. This means that a maximum of 9 TSs in this cell can be used as PDCHs.
This also means that if you have eg 2 static PDCHs, then you can have a maximum of 7 dynamic PDCHs.