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The power saving class of type II (PSC II), one of the sleep mode operations in the IEEE 802.16e standard, is designed to reduce power consumption for unsolicited grant service (UGS) and real-time variable-rate (RT-VR) connections. However, the configuration of fixed-length listening windows in the PSC II incurs unnecessary energy consumption or packet loss for these types of connections. In order to enhance the performance of sleep mode operations, an approach with adaptive listening window (ALW) is proposed. The ALW scheme dynamically adjusts the length of each listening window based on the number of both arrival and retransmission packets as well as the delay constraint. Numerical analysis and simulation results show that the proposed ALW approach can effectively reduce the packet loss rate for UGS connections, whereas better energy conservation with reduced packet loss rate is achieved for RT-VR connections.