In FIG. 7, the Fri (i=1, 2, 3 . . . ) represents frames, it is n times of the usual TDM period of a frame, wherein frequency of the frame can be 8 k i.e. 8 k frame, n is a integer greater than zero; for example, the period of 8 k frame is 125 ??s, the period of Fri can be 125 ??s, 250 ??s or 375 ??s etc. depending on the system design.