IEEE 802.11 Wireless LANs (WLANs) are highly sensitive to Denial of Service (DoS) attacks carried out with jamming devices. In this paper we focus on 2.4GHz wideband constant jammers. The interest in the wideband jammer lies in the fact that it beats all possible channels at the same time, leaving no possible escape following traditional channel-switching defenses. After studying and developing an effective detection mechanism, we propose the implementation of a load balancing technique based on cell breathing for mitigating the harmful effects of the jammer over an IEEE 802.11 WLAN. Cell breathing is achieved by dynamically tuning the transmission power to adjust the size of a WLAN cell.