## 4 Energy Conserving Solutions in Wireless Networking-Based IoT
### Energy Conserving Solutions for WWAN-Based IoT
#### 4.1.2 Solutions for Paging Cycle Optimization  
For efficient power saving in 3 GPP networks, some works have looked into LTE paging cycle mechanisms (also known as DRX cycles). [PERSON] _et al._[41] proposed the concept of self-adaptive DRX, which is based on the adaptive selection of normal and extended DRX cycles. Using a self-adaptive DRX technique, an IoT device has to wake up twice to listen to a paging message. The length of these two mixed normal and extended DRX cycles is fixed, but it can be adjusted later according to the last values. [PERSON] _et al._[42] provided a solution that exploits the nature of infrequent IoT data transmission, possibly using the extended DRX cycles, which can result in increased power saving. Power saving can also be improved by decreasing the Radio Resource Control (RRC) inactivity timer for any paging cycle. A DRX optimization solution with QoS consideration is proposed in [43], in which firstly the values of short DRX, long DRX, the DRX inactivity timer, and the DRX start offset are calculated by an eNB and assigned to each User Equipment (UE). All UE wakeup periods are an integer multiple of others. Next, the DRX inactivity timer is optimized by reducing the timer value. As a third step, devices should go to a deep sleep state, when there is no data transmission or reception. By using the proposed solution, significant energy saving can be achieved while guaranteeing QoS. To improve the paging mechanism, [PERSON] _et al._[44] provided a solution to allocate larger DRX cycles for UE High Power Saving Reception Mode (HPSRM) as compared to UEs in normal modes. [PERSON] _et al._[45] proposed so-called a stateful paging guard device that is used to determine the state of terminal devices, either reduced energy consumption states or active states. To improve device standby time, [PERSON] _et al._[46] proposed including information such as session interval and a device's connection state indicators in signaling messages from the network. Based on the information contained in the signaling messages, a device will remain in an idle state, connected state, or low power state for a particular amount of time instructed by the network. [PERSON] _et al._[57] proposed turning the LTE radio processor off, instead of going to an idle state. This can result in significant power saving when there is no data transmission. A framework for application-assisted power saving is proposed in [58]. For instance, if a user application wants to access any network, it first checks the radio state of that device. If the device is in a sleep mode, then it buffers request messages (in a delay tolerant way) and will transmit messages on device's next wakeup. 3 GPP introduced the concept of low cost MTC (LC-MTC) terminals to reduce power consumption in LTE networks. In [47], different methods have been discussed for UE power consumption optimization, including extending DRX in an idle mode, extending DRX using UE assistance information, and power saving states for devices. The standard document [52] provides information about the factors which can affect power consumption of IoT devices, for example, the reduction of maximum bandwidth, a single receive RF chain, the reduction of transmitting power, half duplex operation, the reduction of the peak rate, and the reduction of supported downlink transmission modes. [PERSON] _et al._[48] presented a method to reduce the energy consumption of M2M devices in an LTE network. They considered the DRX mechanism for reducing the energy consumption of devices during active and non-active periods. By modeling different parameter settings for M2M devices, an energy consumption analysis is performed. The results of this analysis indicate that making the current DRX cycle period longer will reduce energy consumption in M2M devices. Paging messages sent from eNBs to UEs can also be a cause for energy consumption in H2H or M2M devices. To handle the amount ofthese IoT/M2M paging messages, [PERSON] _et al._[93] proposed a three layered IoT/M2M paging mechanism.