A computer-executed method is provided for IEEE 802.15.4 devices based on an active carrier sense based carrier-sense multiple access with collision avoidance (ACS-CSMA/CA) control program and standard CSMA/CA control program for coexistence of an IEEE 802.15.4 network composing of IEEE 802.15.4 devices and IEEE 802.11 network composing of IEEE 802.11 devices sharing frequency spectra between the networks. The computer-executed method is provided on an IEEE 802.15.4 device, and causes a processor of the IEEE 802.15.4 device to perform steps that include estimating a severity of IEEE 802.11 interference based on a severity estimation metric, selecting the ACS-CSMA/CA control program based on the estimated severity. The ACS-CSMA/CA control program is configured to perform dynamically updating a maximum number of backoffs (macMaxCSMABackoffs) based on the estimated severity,cdetermining if a number of backoffs (NB) exceeds the updated macMaxCSMABackoffs, performing consecutive CCA operation to continuously detect channel status, and transmitting frames when the detected channel status is an idle state or incrementing number of retransmissions (NR) when the detected channel status is a busy state.