# Joint Balanced Routing and Energy Harvesting Strategy for Maximizing Network Lifetime in WSNs
## 4 The Proposed Strategy
### The Proposed SPT-EBR Strategy
#### 4.2.2 The Energy Harvesting Scheme  
Wireless renewable sensor network is another major research issue in this paper. Assuming that the nodes have energy capture capabilities, the sensing nodes can replenish energy from the energy radiated by the solar or RF base stations. Here, an integration of power charging rate and data forwarding rate is proposed as shown in Figure 5. The operation calculation cycle is scheduled from \(t(0)\), \(t(1)\), \(t(2)\) to \(t(n)\) time slots. At each operation cycle, each node has the opportunity to capture random ambient energy \(a(i)\), which represents the power capture rate of the \(i\)  
Figure 4: The illustrated flowchart of packet forwarding rate scheme.  
From Equation (3), the charge rate of the battery capacity unit \(\Delta b\) can be obtained. The \(\Delta b\) represents the deviation of the current battery capacity with the battery capacity in the previous cycle \(b(i-1)\). It is also the result of the rate of harvested energy minus the rate of consumed power in each node.  
To achieve the immortal WSNs, an additional parameter called battery charging rate \(\Delta b\) is introduced to be the forward awareness factor. If the parameter \(\Delta b\) is greater than 0, it means that the battery of the sensing node is always in the positive charging state and will not be affected by the power consumption of packet transmission. The battery charging rate is the main considering parameter to update the path cost of each node. If the parameter is less than or equal to 0, it means that the power consumption rate of the node is faster than the power charging rate, and the power consumption rate is regarded as the main consideration factor. Therefore, the path cost design of the energy harvesting scheme can be considered together with both the packet forwarding rate and energy harvest rate.  
The operation of the forward awareness factor as the path cost of power harvesting scheme can be described as follows. In each time slot, it is required to consider whether the \(\Delta b\) parameter is a positive value. If \(\Delta b\) is greater than 0, the path cost still keeps the same. In contrast, if the charging rate is less than or equal to 0, it is considered to follow the design principle of the first power consumption scheme. When the power consumption rate \(p(i)\) in each node is greater than the average power consumption threshold value \(p_{avg}\) (\(i\)), the path cost is increased by 2. If the \(p(i)\) is less than or equal to the \(p_{avg}(i)\), the path cost is incremented by 1. The detail design flowchart of the energy harvesting scheme are shown in Figure 6.  
In real operation, the extra cost is generated to deploy the energy harvesting device and it will increase some subordinate costs. However, it can effectively extend the lifecycle of the sensing network and eliminate the requirement to replace the battery. To joint consider the energy balanced routing and energy harvesting benefits, the design aim of the immortal WSNs can be achieved when the energy harvesting rate in the hotspots is greater than energy consumption rate for packet transmission.  
Figure 5: The illustration of the battery charging rate of the energy harvesting scheme.