CAM-MAC proposed recently is a well designed wireless multichannel MAC protocol. By cooperating with neighbor nodes and using relative time instead of absolute time, CAM-MAC performs better than most of other multichannel MACs and do not need global synchronization. The deficiency of CAM-MAC is that it has not broadcast mechanism and thus, fails to exploit the broadcast nature of wireless medium and experience performance degradation in broadcast scenarios. In this paper, a broadcast enhanced MAC protocol called BMAC is proposed. The proposed protocol provides both unicast and broadcast service and do not need global synchronous clock either. A transmitter-based reservation scheme of channel selection is introduced in to support broadcast traffic. Simulation results show that the aggregate throughput of this broadcast MAC is significantly higher than its original non-enhanced MAC protocol when there's broadcast traffic in the network, and, this performance gap becomes larger as the proportion of broadcast traffic increases.