# Power Consumption Modeling of Discontinuous Reception for Cellular Machine Type Communications
## 3 Literature Review  
In the literature, several efforts were made to study the DRX mechanism in an LTE-A network. Moreover, these efforts were made in order to study the DRX mechanism for both MTC and HTC traffic by taking into account various parameters of DRX. For instance, the authors of [12] studied power consumption for active and background traffic, thus proposing two semi-Markov models. Furthermore, in the case of active traffic, each session consists of multiple packet calls, whereas each session in the case of background traffic mainly consists of one or two short packets. However, the proposed \begin{table}
\begin{tabular}{l l} \hline \hline
**DRX Parameters** & \multicolumn{1}{c}{**Definitions**} \\ \hline Inactivity Timer \(T_{I}\) & No. of consecutive transmission time intervals (TTIs) for which a device \\  & decodes a PDCCH \\ On Duration Timer \(T_{ON}\) & No. of consecutive TTIs for which a device monitors PDCCH for radio \\  & resource allocation \\ Short Cycle Timer \(T_{SC}\) & No. of consecutive TTIs a device shall enter the short DRX cycle after \(T_{I}\) \\  & expires \\ Short Cycle Number \(N_{SC}\) & No. of utilized Short DRX Cycle (optional) \\ Long Cycle Timer \(T_{LC}\) & No. of consecutive TTIs a device shall enter the long DRX cycle after short \\  & DRX cycle \\ RRC Connection Timer \(T_{RC}\) & No. of consecutive TTIs a device needs to reconnect to eNB after releasing from the network \\ Tail Time \(T_{tail}\) & The time a device spends for transition from \(RRC\_Connected\) to \(RRC\_Idle\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: List of various DRX parameters with definitions [9; 13]. Figure 1: An overview of the discontinuous reception (DRX) mechanism in LTE-A. semi-Markov models are designed for modern mobile Internet data. In addition, the authors of [14] proposed an analytical model for studying power consumption in the case of MTC in an LTE-A network. Several parameters were taken into account, such as the DRX inactivity timer, short DRX cycle, long DRX cycle, etc. However, the RRC connection time and the RRC release time (also called tail time) were neglected in Reference [14]. In addition, the authors of [15] proposed an alternative DRX model for estimating power consumption in cellular MTC. Moreover, the authors introduced RRC active mode, RRC connection, and the release timer in their proposed model for analyzing the DRX mechanism. However, the expected arrivals during the RRC release period and possible power consumption variations during the active state were not taken into account. Further, in References [16; 17; 18], various DRX models were proposed for conventional HTC traffic, thus not directly applicable to MTC traffic. In addition, the authors of [19] considered multiple received packets within a short or a long sleep state, and thus estimated the average delay and power consumption for Poisson-based MTC traffic. Unlike in Reference [19], the multimedia traffic which is modeled as a heavy-tailed type I Pareto distribution was considered for modeling a DRX mechanism in Reference [20]. Moreover, the authors of [21] proposed a partially observable Markov decision process (POMDP) framework to configure the relationship between short and long cycles to maximize the energy-saving efficiency under the certain constraint of delay. Nevertheless, the RRC connection, tail time as well as the power consumption variations within the active mode were neglected in References [19; 20; 21]. In addition to the existing models given in Table 2 for analyzing a DRX mechanism, the authors of [22; 23] proposed power consumption models for the universal mobile telecommunication systems (UMTS) user equipment (UE) with constant power consumption values, such as idle state (1W) and active connections (3W). In addition, the authors of [24] proposed a more differentiated model consisting of five states, namely standby (weak signal), standby (strong signal), ringing, talking, and attempting call, which were investigated in terms of minimum, maximum, and average power consumption.