We first investigate the enhanced BE-SM (binary exponential sleep mode) operations to approach the upper bound of energy efficiency while satisfying quality-of-service (QoS) requirements. To achieve the energy efficiency close to that of the conventional threshold scheme while satisfying QoS requirements, we propose both a relaxed QoS (RQ) scheme with relaxed QoS requirements and a stringent QoS (SQ) scheme with relaxed QoS requirements. Next, we consider quality-of-experience (QoE) to measure human's subjective quality as a requirement of UE as well as QoS requirements, and propose a remaining energy-aware QoE model according to LoRE and QoS factors. In addition, we propose a sleep cycle allocation algorithm to reflect energy-aware QoE based BE-SM operation while minimizing the energy consumption of the UE. Furthermore, we investigate a batch packet server instead of a single packet server in order to reflect the variable size of resource and analyze the exact DRX mechanism. The batch packet server shows high performance for energy saving under high arrival rates. As a further study, we consider the machine-to-machine (M2M) group communication in the LTE/LTE-A network, and analyze an M2M group communication scenario in terms of the consumed energy and resource utilization according to the group size and the length of uplink data. However, the adjustment of system parameters is not effective from the viewpoint of energy saving, compared with the gain achieved by the management of resource utilization. In order to reduce the delay and energy consumption of machine nodes, we propose a virtually connected state to provide low latency services and also propose an energy-efficient state transition model.