The cell capacity of a CDMA system is mainly determined by the sum of interferences generated by call connections. Focusing on downlink interferences in a WCDMA system, we address a threshold-type call control scheme. Finding the characteristic pattern of an expected cell-throughput, we formulate a mathematical program maximizing the system throughput. The solution shows the optimal interference threshold value for each cell, which also demonstrates the effects of allowing differences in thresholds among cells (C) 2003 Elsevier Science B.V. All rights reserved.