Sleep-mode power-saving mechanisms introduced by IEEE 802.16e/m aim to save power. Existing studies on the sleep-mode performance only assume the intra-Base Station (BS) movement for a mobile station. How the sleep-mode operation affects the handover and, sequentially, the power-saving efficiency when the inter-BS movement is frequent has not been carefully investigated. In this paper, we develop an analytical model describing the operation of various versions of IEEE 802.16e/m sleep-mode power-saving mechanisms and study their connection dropping probabilities and energy saving efficiencies. We show that existing sleep-mode mechanisms do not work well and often lead to frequent connection drops and low power-saving efficiency when mobility is high. Based on insights provided by the analytical model, we propose to use the dynamic BS cluster scheme to improve the performance of the existing sleep-mode schemes. The simulation results show that the proposed scheme can effectively solve the connection dropping problem and, sequentially, significantly improve the power-saving efficiency even when the inter-BS crossing is frequent. © 2007-2012 IEEE.