# A TDMA-Based Access Protocol for Dense Networks with Moving Nodes for IoT Applications
## 3 Algorithm Description
### Operation of the Proposed Algorithm
As analyzed below, the amended versions of [6] have different operational characteristics in order to provide a wider enveloping for the performance comparisons with MOTILO. There are two significant observations from the above algorithm. Firstly, due to the relation between speed of motion, the transmission range and the number of nodes for each system, we do not consider the cases that a node will move so fast to cover more than the range of a single SF zone between phase one and phase two of the proposed algorithm. The second observation is related to a possible \"dead slot\" situation (lines 26-27): as every node waits for its turn based on its ID, whenever the time of the first assigned slot (the one to the lower SF) has already elapsed due to the priority of the previous nodes and the node has migrated to the higher SF zone, the node will not be able to transmit without collision. For that reason, in case of a dead slot, every node amends on the fly its schedule and transfers its time slot to the end of the schedule for its higher SF option (variable _newslot_ in line 27). Therefore, whenever a node faces a dead slot situation, postpones its transmission until all the other nodes, which are scheduled to transit to the higher SF, end their second phase. Afterwards, the node starts its transmission at the first available time slot and the same applies also for all other nodes that have faced a dead slot case (Figure 3). Due to the fact that all the nodes are aware of the program and the possible  
Figure 2: Sequence diagram of the proposed MOTILO approach. collisions of each node, they are able to calculate all the dead slots and react accordingly. This is performed via a single preamble overhear. As the possible dead slot distribution is known beforehand, every node overhears the preamble of the previous node id that faces a possible dead slot. The interested node opens its circuitry at the scheduled slot for the previous node id that will face a possible dead slot. Whenever the previous node transmits a message, the next node will be aware of this information from the preamble. If the latter node does not receive the appropriate preamble, it will automatically schedule its lost transmission knowing that the previous node will utilize a slot at the end of the higher SF. This process has to be carried out for all the interested nodes and the higher the ID of the node, the higher the number that may open their circuitry as they have to be aware of all the previous used/unused slots.While the probability of a dead slot situation is increased for higher ED IDs, the operation of the MOTILO ensures that all the nodes will transmit their data without any lost transmission. As mentioned above, when utilizing the preamble overhearing mechanism, all the involved nodes schedule their transmission. As a consequence, some nodes may face increased latency as they will have to postpone their transmission for the free slots at the end of the MOTILO scheduling. For these nodes, there is no metric about their increased latency but the same applies for all the nodes that have a high ID, as most of the algorithms base their node prioritization on their node ID. In other words, nodes with higher IDs will be ranked at the end of any list that has to sort them without any other characteristic. With the same rationale, some nodes will face increased latency based on the dead slot situation of the MOTILO, but this is similar to having an initially increased ID.