# Enhanced Beacons Dynamic Transmission over TSCH
## 2 Time Slotted Channel Hopping Background and Related Work
### Related Work  
Several researchers have focused their attention on improving network formation time, also taking into account its contribution to counteract the energy restrictions of the nodes. The network completes its formation when all the devices are associated and establish effective communication. A shorter duration of the network formation process is guaranteed by reducing the association time of the nodes, contributing to extending their useful life and immediate information transmission. In [13; 14], the authors proposed mechanisms to decrease the network's formation time by properly manipulating the scheduling for beacon transmissions. Specifically, in [14] it is assumed that the network coordinator has no energy constraints and can reserve more slots for beacon transmissions. [PERSON] et al. manipulate the scheduling and divide the slotframe into the advertisement and communication planes in [15; 16]. All beacons are transmitted in the advertisement plane while the communication plane is used for data transmissions. In [17], the authors also consider the estimated link quality before transmitting the beacons.  
The authors of [18; 19] proposed that once a node receives a beacon it immediately retransmits the beacon, increasing the number of beacon transmissions in the network, decreasing the association time. The increase in the number of beacons in the network to maximize the association opportunities was also explored by other authors. In [20], an increase in shared slots is proposed. Meanwhile, in [21; 22], the slots for beacon transmissions are divided into multiple sub-slots. In each sub-slot, a beacon is transmitted using a different channel; this strategy increases the number of beacons in the network, decreasing the association time.  
In [23], the idea of sending beacons more frequently is explored. In this work, the time between beacons is modified, according to the estimated channel occupation rate. The occupation rate is computed as a function of the occupied and empty slots. In this proposal, the association time decreases at the expense of complexity. In [24], the authors propose that nodes that try to associate execute an active channel scan by transmitting beacon request packets. The active scan increases the probability that the node already associated with the network detects new nodes, resulting in a shorter association time but increasing the node energy consumption.  
The research mentioned above mostly involves reducing node association time by increasing the beacon transmission rate. However, permanently increasing this rate increases energy consumption and traffic, which could limit both slot availability in the schedule and the communication between other network devices in networks with high node density. In our work, a dynamic beacon scheduling algorithm is proposed. In the intensive phase, the beacon transmission rate is high to accelerate the network formation. In the predeter  
Figure 2: TSCH linear network association process.  
mined phase, this rate is decreased to avoid unnecessary traffic and corresponding energy consumption. The main contributions of our work are the following:  
* The proposed mechanism achieves a shorter network formation time than the default association mechanism (i.e., default minimal 6 TiSCH configuration) without a relevant increase in implementation complexity.
* The proposal is accompanied by a mathematical model validated through simulation, showing a good correspondence between theoretical and simulation results.
* Simulation results demonstrated that the proposed mechanism not only reduces the network formation time, resulting in data packets beginning to be transmitted earlier, but also reduces the energy consumption during the network formation process.