IEEE 802.15 working group established a new study group, body area network (SG-BAN), to develop short range wireless communication technology in and around human body recently. Wearable healthcare is an important category of potential applications of BAN. This paper introduces the IEEE SG-BAN and investigates the performance of 802.15.4b and 802.15.4a for wearable healthcare applications in the heterogeneous networks environment. The object is better understanding of healthcare requirement of BAN and how and where BAN works to be started. In addition to the scalability issue, we found asymmetric clear channel assessment (CCA) abilities among different types of wireless technology. The asymmetric CCA has significant impact on system performance.