To support mobility, wireless mobile devices are powered by batteries; however, a battery can only store a limited amount of energy. According to the experiment, for a 3G handheld device, the wireless interface consumes the largest proportion of the total power (up to 40%). In particular, the 4G wireless communications will adopt OFDMA as the wireless access technology. In this case, the wireless interface in a mobile device will consume more power. IEEE 802.16 is one of the promising technologies for future wireless communications. To save power, some studies focus on how to schedule the sleep of mobile stations (MSs) to minimize the total active time; others try to reduce the transmission power of MSs with satisfying MSs' demands as the constraint. However, none of them considers both sleep scheduling and power control at the same time in IEEE 802.16 networks. To conserve energy, a thorough study of both MAC and physical layers is required. In this paper, we propose a cross-layer design to jointly schedule the sleep and control the transmission power of MSs in the uplink direction of IEEE 802.16 networks. Extensive simulation results verify that the proposed scheme significantly decreases the total power consumption of the MSs while guarantee their QoS requirements.