## 4 Local Transmission Control: Redundancy-Based Transmission
### Local Route Establishment
#### 4.1.2 Local Route Reply
* CLUS denotes a cluster-based transmission control, and it chooses cluster heads by considering the number of neighbor nodes and remaining battery lifetime; however, the probability of being selected as a cluster head decreases with each succeeding selection [18]. These schemes were evaluated in the same environment to ensure a fair comparison. In fact, the methods in [17,18] are well-known controls, and we implemented important functions: route request and establishment, route failure management, cluster-header selection, and cluster-header switching. Figure 6 shows the performance when the network size was 1 km \(\times\) 1 km. Figure 6 compares the throughput, showing how many data packets could be sent successfully from the source to the destination. The proposed control exploits redundant paths as backup links or relayed cooperative links. Backup links increase the throughput by reducing the time for link recovery, and relayed cooperative links can increase throughput by sending the same information at the same time to enhance the signal-to-noise ratio. In contrast, in SOUR and CLUS, information is sent along a single path based on a noncooperative mode. Comparing SOUR and CLUS, the proposed control provided 26% and 12% enhanced throughput. Figure 6 also compares the control packet overhead to successfully deliver data traffic from the source to the destination. Control packet overhead is strongly related to transmission-path management tasks such as finding new routes and recovering from link failures. The proposed approach reduced the control packets using predetermined stable hub paths and redundant local paths, minimizing frequent route discovery processes. It also used simpler maintenance messages--i.e., HelloHub and ByeHub messages. In contrast, in SOUR, the intermediate node started the source routing whenever there was a link failure. Frequent route-retrieval processes that rely on network-wide flooding mechanisms increase control overhead. The CLUS had higher overhead because of its complex cluster and gateway selection mechanism and various cluster head and gateway messages. Comparing SOUR and CLUS, the proposed control gave 19% and 9% lower overhead. On the other hand, in a low mobility environment, the proposed (\(\pi\)) gave a higher performance than the proposed (\(\pi\)/2). However, as the movement speed increased, the proposed (\(\pi\)/2) gave a better performance than the proposed (\(\pi\)), because the number of synchronized nodes is more important than the synchronization strength in the slow movement, and the synchronization strength is more important than the number of synchronized nodes in the fast movement. The larger is \(\theta\), the greater is the number of synchronized nodes, but the weaker is the synchronization. Figure 7 shows the performance when the network size was 2 km \(\times\) 2 km. Comparing SOUR and CLUS, the proposed control gave 32% and 15% enhanced throughput, and 34% and 13% reduced overhead. From these simulations, we can see that the performance gain increased as the network size grew larger. ## 6 Conclusions

In this paper, we propose a distributed and localized hub based on a hierarchical transmission-control scheme for large-scale wireless networks. The proposed control consists of macroscopic and local transmission controls. For the macroscopic control, we exploit stable nodes with low mobility to construct a virtual hub infrastructure that can stochastically support stochastic end-to-end delay constraints. We also suggest a stochastic integer programming model and virtual flooding-based heuristic search algorithm capable of providing high-performing hub transmission paths. For the

Figure 6: Networks size: 1 km \(\times\) 1 km. Figure 7: Networks size: 2 km \(\times\) 2 km. local control, we suggest a way to establish redundant local transmission paths between hubs and a way to use the redundant links as backup links, relays, or cooperative links.