Fig. 6

a Minimum residual energy of NOMA under different amounts of IoTDs K. b Minimum residual energy of NOMA under the different amounts of IoTDs in each group D. Blue bar in a K = 6—the NOMA scheduling under K = 6; orange bar in a—K = 12—the NOMA scheduling under K = 12; blue bar in b—D = 3—the NOMA scheduling under D = 3; orange bar in b—D = 4—the NOMA scheduling under D = 4 and yellow bar in b—D = 6—the NOMA scheduling under D = 6