With the design of data communications in mind, 3GPP LTE-Advanced is probably the most promising technology for next generation mobile communications. For mobile applications, continuous communications at the user equipments (UEs) over a long period of time, imposing stringent requirements on power saving. To manage power consumption, 3GPP LTE-Advanced has defined the Discontinuous Reception (DRX) mechanism to allow UEs to turn off their radio interfaces and go to sleep in various patterns. Existing literature has paid much attention to evaluate the performance of DRX; however, how to tune DRX parameters to optimize energy cost is still left open. This paper addresses the optimization problem of the DRX mechanism, by asking how to minimize the wake-up periods of the UEs while guarantee their QoS, especially on the aspects of traffic bit-rate, packet delay, and packet loss rate in mobile applications. Efficient schemes to optimize DRX parameters and schedule UEs' packets at the evolved Node B (eNB) are proposed. The key idea of these schemes is to analyze and balance the impacts between QoS parameters and DRX configurations. Simulation results show that our scheme can fully satisfy QoS requirements of the UEs while save considerable energy, compared to the existing schemes.