The IEEE 802.15.4 has been studied for its possible use to support networked control systems. A careful management of the network resources allows the enhancement of the quality of control (QoC) of the controlled system. This can be achieved by a co-design approach to manage the interaction between the WNCS and the wireless network in order to online adapt the QoC. This approach allows control loops to have access to the communication medium according to the state of the controlled system meanwhile attempting to optimize the overall control performance. When the QoC of the controlled system is not sufficient, the quality of service of the network is adapted online. This adaptation is realized by modifying the macMinBE parameter of the MAC protocol of the IEEE 802.15.4. Moreover, an implementation way of this scheme using the IEEE 802.15.4 protocol is presented. Simulation results show that this approach improves the control performance.