# Management of Distributed Renewable Energy Resources with the Help of a Wireless Sensor Network
## 3 System Description
### Link Scheduling
In Figure 3b, the slot frame configuration considering channel offsets and timeslot offsets is presented for link transmission scheduling in the 6 TiSCH network. The channel state information of the link at time slot \(t\) for link scheduling is expressed along the channel offsets axis. \(T_{IPN}\), \(T_{M}\), \(T_{O}\), \(T_{S}\), and \(T_{B}\) are included in the cell configuration. Timeslots from \(t_{1}\) to \(t_{6}\) represent \(T_{IPN}\), \(T_{M}\), \(T_{O}\), and \(T_{S}\), and timeslots from \(t_{7}\) to \(t_{12}\) represent \(T_{B}\). At each member node, the first time slot is used to measure IPN. Each member node with an omni-directional antenna sends out a dummy signal with the same transmission power as that of packet transmission. Member nodes situated in the vicinity of the 6 TiSCH network are likely to have higher IPN levels than those on the edge and are subject to higher IPN unless proper link transmission priorities are provided to the member nodes. The IPN on the first channel offset over the first time slot is measured by each member node in the 6 TiSCH network. During time slots, each member node uses a different cell to broadcast to the sink node within a slot frame. The time slot \(T_{O}\) is used to determine the best priority for member nodes that are only active during the slotted frame in question. The sink node transmits over the time slot \(T_{S}\) after the evaluation of member node priorities. Sensor nodes for data transmission can only be accessed by one link out of a set of links. After the  
Figure 2: Tree topology for 6 TiSCH networks with 40 sensor nodes. completion of set-up timeslots from \(t_{1}\) to \(t_{6}\), data transmission is performed at the time slot \(t_{7}\). On the first channel offset, node 2, with higher priority, except for the sink node, begins transmission to the sink node. Node 2 transmits to node 1 (sink), while node 3 cannot transmit to the sink node that has to receive a packet from node 2. Node 6 recognizes that it is farther than 40 m from node 2 and transmits data to node 3. The same process is continued in the proceeding time slots. Figure 4 depicts the time slot compliant with the 6 TiSCH network standard. The upper time slot is for the Tx (transmitter) and the lower time slot is for the Rx (receiver). After the time interval of TsTxOffset, the data packet is transferred by the transmitting sensor node. The receiving sensor node accepts the incoming data packets before the time period of TsTxOffset. When the data packet is properly received, Rx sends an acknowledge (ACK)  
Figure 3: Cell usage of the 6 TiSCH wireless network: (**a**) tree topology in 6 TiSCH network; (**b**) channel offsets for link scheduling in the 6 TiSCH network. signal to Tx after the delay time interval. As a result, a single time slot is used to carry out data packet transmission between a child node and a parent node. Node parameters such as rank, IPN, and the number of packets to transmit are taken into account when determining node priority. The rank characteristic is significant because the high-rank nodes near the sink node, e.g., the rank 0 node, are often the source of data that incurs traffic bottlenecks. The number of data packets transmitted is considered for the assessment of hub node parameters. Data packets are created and used for transmission between the parent node and each child node. As a result, high-rank nodes communicate in each slot frame and are prioritized more than low-rank nodes. IPN factor is also considered during the link scheduling. When a node has a high IPN, it is more likely to be an interfering node reducing the total throughput of the 6 TiSCH network. Higher priorities are provided to nodes with high IPN values, allowing their data packets to be broadcasted in early time allotments [61]. The main three attributes for the link scheduling optimization are rank, IPN, and the number of packets to transmit.