# Efficient Cluster Tree Topology Operation and Routing for IEEE 802.15.4-Based Smart Grid Networks
## 4 Proposed Scheme
### Proposed Network Operation Process  
Figure 13 shows an example of the multi-channel operation of the proposed scheme.  
As shown in Figure 13, the gateway repeatedly broadcasts a beacon frame for each channel. In this case, each channel comprises a different PAN. Subsequently, the gateway receives the superframe during the activation period through the main channel CH1. If an emergency data transmission occurs in the deactivation section of the main channel, the emergency data can be received using the superframe of the auxiliary channel through auxiliary channel CH2.  
As shown in Figure 3, three cluster trees are constructed around the gateway using different channels. The superframe schedule information for each cluster tree is different. Each tree is adjacent to the other trees. If a CH21 coordinator using CH2 needs to transmit emergency data in the current inactive section after transmitting data in the superframe section, it does not wait until the next superframe section and rather transmits the emergency data in accordance with the activation section. Thus, the data can be transmitted rapidly and efficiently without waiting for the next activation period.  
Figure 14 shows an example of the proposed multichannel operation method.  
As shown in Figure 14, each cluster transmits data using the CSMA/CA mechanism in its SD section. However, if data have not been transmitted during the SD period or if they need to be transmitted urgently, this wakes up the activation interval of another auxiliary channel and transmits data. This reduces the latency and prevents data loss.  
First, considering the multi-hop transmission delay time during a normal delivery, CM221 (the third-level node of the CH2 channel) transmits data to CH22 (the cluster head) in its activation section. Thereafter, CH22 (a cluster member at the second level of the CH2 channel) transmits data to CH21 (the cluster head) during its activation period.  
Figure 12: Sixth example of the proposed SD allocation algorithm.  
Figure 13: Example of proposed multi-channel operation method using a superframe.  
Next, considering the multi-hop transmission delay during data congestion, CM231 (a third-level cluster member of the CH2 channel) transmits data to CH22 (a cluster head) in its activation section. Then, if CH22 (as a cluster member of the second level of the CH2 channel) fails to transmit data to its initial activation section, these are transmitted to its cluster head CH21. Subsequently, CH21 (as a cluster member of the first level of the CH2 channel) transmits data to the gateway during its activation period.  
Next, considering the multi-hop transmission delay time when using the auxiliary channel in the proposed technique, CM231 (a third-level cluster member of the CH2 channel) transmits data to its cluster head CH22 in the activation section. If CH22 (a cluster member of the second level of the CH2 channel) fails to transmit data to its initial activation section, the CH3 channel is used as an auxiliary channel to transmit data to CH31 (the first node of the CH3 channel). Thereafter, the first node of the CH3 channel (CH31) transmits data to the gateway during the activation period. Accordingly, the transmission delay time is shorter when an auxiliary channel is used in the multi-channel method during data congestion.