Add TODO.

applications/lofar2/model/rtdsp/multirate.py

@@ -876,6 +876,13 @@ def non_maximal_upsample_bpf(xBase, Nup, k, Ndft, coefs, verbosity=1):
     for the whole input xBase. Instead it needs to be FIR filtered per block of
     Nup output samples, using pfs.polyDelays in pfs.filter_up().
 
+    TODO
+    . This code only runs ok for Ros = 1, 2 when Ndft = 16, but not for
+      Ros = 4, so need to fix that. According to [CROCHIERE 7.2.7] the
+      polyphase structure is only suitable for Ros is integer >= 1. For other
+      Ros > 1 the weighted overlap-add (WOLA) structure is  suitable, so
+      need to add WOLA.
+
     Input:
     . xBase: Input equivalent baseband signal xBase[m]
     . Nup: upsample factor