Reliable is a common requirement for Wireless Body Area Networks (WBANs). In a WBAN, the connection between a sensor node and the data collector may become unstable due to interference from other sensor nodes, causing excessive delays and poor packet arrival rate. IEEE 802.15.4 and 802.15.6 are two standards that can be used for WBANs. However, these two standards consider neither the channel quality nor the connection reliability and thus the transmission performance can be improved. In this paper, considering the environment where the channel quality may be poor, we propose the Channel-quality Awareness Scheduling (CAS) protocol. Built on top of IEEE 802.15.6, the CAS protocol is capable of dynamically adjusting the length of a superframe to increase packet arrival rate. Simulation results verify that the CAS protocol can increase the successful packet reception percentage around 20 %.