The time slot assignment problem (TSAP) or Satellite Communications scheduling problem (SCSP) for a satellite performs n×n ground station data traffic switching has been known NP-hard problem. This paper suggests O(n²) time complexity algorithm for TSAP of a satellite that performs n²×n² ground station data traffic switching. This problem is more difficult than n×n TSAP as NP-hard problem. Firstly, we compute the average traffic for n -transponder’s basic coverage zone and applies ground station exchange method that swap the ground stations until all of the transponders have a average value as possible. Nextly, we transform the D matrix to DLB traffic matrix that sum of rows and columns all of transponders have LB. Finally, we select the maximum traffic of row and column in DLB, then decide the duration of κth switch mode to minimum traffic from selected values. The proposed algorithm can be get the optimal solution for experimental data.