# Energy Efficiency and Coverage Trade-Off in 5G for Eco-Friendly and Sustainable Cellular Networks
## 3 System Model and Problem Formulation
### System Model and Proposed BSs Switching On/Off Mechanism
#### 3.1.2 Low Traffic Load (0 < \(\lambda\)\(\leq\) 0.4)  
The goal is to strike an equilibrium among network performance and EE. In this scenario, the 5G BSs will be switched off, with the assurance that the service and coverage for users will be protected by the LTE BSs, which can meet the demand of data speed rates of subscribers with 100 Megabits per second (Mbps) and can increase up to 1 Gigabit per second (Gbps) via carrier aggregation and bandwidth extensions of up to 100 MHz. The 5G BSs switch-off strategies entails three steps: (i) pre-processing status; (ii) decision status; and (iii) post-processing status. Figure 5 summarizes these steps. In addition, the details of the 5G BSs switch-off procedures are provided in the following points. Figure 4: Daily traffic load pattern of a BS. 1. _Pre-processing Status_: The 5G BS is assigned with the task of monitoring the generated traffic load often (e.g., every few minutes) and decides if it would be best, performance-wise, to turn off 5G BSs, depending on the given traffic load. In situations where the traffic load decreases below a given benchmark (\(\lambda\leq 0.4\)) and remains below it for a specific duration, then the 5G BSs switch-off decision algorithm can be executed. The 5G BSs are the sole determinant of this information. 2. _Decision Status_: At the onset, a unicast control signal is sent from the 5G BSs to the switching off/on module located in the central office requesting that they be switched off. On the receipt of a go-ahead response signal from the module, the 5G BSs initiate a gradual decrease in their transmission power mechanism that will ultimately result in a switch-off. Meanwhile, UEs that are in control of the switched-off 5G BSs are reassigned to active LTE BSs within the neighborhood. Of course, this will be determined by the signal strength. This procedure is akin to the current handover scheme, the only difference being that this involves handing over group of UEs other than a single UE. Considerable research has been performed on group handovers. Most of the relevant studies targeted the support of commuters on mass transit systems like buses and trains. There might be a need for a strategy to predict the group handover a priori. In this case, one of the current group handover techniques [34], in conjunction with our proposed switching-off algorithm, may be adopted for the implementation of our group handover policy. Figure 5: The decision-making algorithm proposed for the BS switching-off/on process. 3. _Post-processing Status_:The 5G BSs that are switched off listen for the wake-up control signal from the switching off/on server.. Meanwhile, the active LTE BSs are in full functionality and are capable of supplying subscribers' QoS requirements. In addition, LTE BSs are mandated to monitor traffic across the network based on LTE BSs' information, which is based on the decision to keep the 5G BSs off or start switching them on if the traffic increases to more than 0.4. The primary objective of CNOs is solving coverage issues as well as guaranteeing wireless service coverage for cell membership areas in switched-off mode. The mathematical details and the associated conceptual work meant to tackle the cell coverage optimization problems will be discussed in Section 3.2. II. 5G BSs Switching-On Procedures  
Reverse switching-off algorithm is one of the techniques to execute the 5G BSs' switching-on algorithm. The philosophy behind the switching-on algorithm is that each of the 5G BSs should be switched on if the system traffic load reaches the original value before they were switched off. Incapacitated by the lack of global system information, the switched-off 5G BSs are not able to undertake a switch-on decision. As a result, an alternate route is to rely on LTE BSs measurements with reference to the instantaneous traffic load as well as the switching-off/on module control signal. Just like the switching-off algorithm already discussed, the switching-on algorithm is tripartite, as discussed and shown below in Figure 5.  
1.