**6. Conclusions**

348 Energy Efficiency – The Innovative Ways for Smart Energy, the Future Towards Modern Utilities

**Figure 6.** Operation of the routing protocol for divergent traffic

number of hops over nodes in relation to the sink node.

The main idea of the routing algorithm based on gradient is to forward the package towards the sink node choosing the neighbors with the lowest height, where height represents the

In order to enable the routing process, the sink node broadcasts a message with its height equals to zero (H=0) in the initialization phase. The nodes that receive the "gradient initialization" package assign the incremented value to their height variable and, later on, broadcast the message to other nodes on the network, in order to assign heights to all

The logic of the protocol consists of transmitting a package to only one neighbor, according to the lowest height. The proposed protocol differs from the previous works because it considers other aspects to forward the package in case the neighbors have identical heights. In addition, in case acknowledgment messages identify a failure in transmission, the package is retransmitted to other neighbors, and the retransmissions are limited to only one

The protocol is based on choosing the neighbors for retransmitting the message according to the number of attempts made. The next hop is selected based on a list that is sorted in descending order by the longest distance and populated with all neighbors, except the neighbor from the last hop. On the first transmission, among the neighbors with the lowest heights, the most distant node from the current node will be chosen; in other words, the first element from the list. If it is the first retransmission, the second most distant element will be chosen, and so on. If no nodes with the same lowest height are chosen, the next group to be

network nodes, creating height levels (H) on the network, as indicated in Figure 7.

**5.2. Convergent traffic** 

transmitter node per data flow.

The public lighting system provides automation for control process, diagnostics and alarms from possible failures in the structure. Therefore, an improvement in public lighting service is expected, plus a rationalization of energy consumption.

The two task forces related to the IEEE 802.15.4 standard (IEEE 802.15 WPAN TASK GROUP 4G, 2011; IEEE 802.15 WPAN TASK GROUP 4E, 2011) assure a protocol extension to the lower layers in order to increasingly meet urban networks requirements, as well as smart grid applications.

Although this work comprises a specific application for public lighting, it can also be applied to other applications, such as monitoring energy and water consumption meters, measurement of climatic factors in order to implement weather forecast systems, with humidity sensors, temperature sensors, etc.
