# Implementation of a Topology Independent MAC (TiMAC) Policy on a Low-Cost IoT System
## 1 Introduction
However, there are network scenarios where the synchronization problem is not present (e.g., the use of the already present GPS receivers in Vehicular Networks) and new ways may be discovered as technology advances. In addition to the synchronization problem, _time-slots_ assignment to the network nodes within a TDMA _frame_ is also a prerequisite for a TDMA policy to work properly. In this paper, the idea known from the literature TDMA-based policy is revisited. Then, this policy's theoretical expectations are evaluated for their effectiveness on a system consisting of low-cost devices while a decentralized approach is followed regarding synchronization. More specifically, the proposed by [PERSON] and [PERSON] in [17] TDMA-based topology independent medium access control (to be referred to as TiMAC in the sequel) policy is adopted. TiMAC policy's primary goal is to allow for at least one successful transmission per node per frame, independently of the underlying topology. In order to achieve this goal, TiMAC's time-slot assignment method is based on the properties of Galois polynomials, also presented in [17]--thus allowing for its implementation on applications of tight delay constraints. The system considered here for implementing TiMAC on consists of devices of low-cost boards (i.e., Arduino [18]) carrying simple RF modules at 433 MHz [19; 20]. Note that, in their initial condition, devices are free of any software or coding installed on them (e.g., MAC). The challenge met in this paper using the previously mentioned low-cost devices is twofold: (i) to implement TiMAC following the rules and properties of Galois polynomials as described in [17]; and (ii) to synchronize the devices (also referred as nodes in the sequel) in a multi-hop decentralized manner. As it is shown, TiMAC is successfully implemented (i.e., one successful transmission per frame is shown that is guaranteed) on the low-cost system and the decentralized synchronization approach manages to successfully synchronize the nodes in a multi-hop manner. The above contributions rely on experiments conducted and presented in Section 5. Note that the experiments mentioned above are limited to only five nodes in a full graph topology configuration, thus allowing for getting a detailed insight of the particulars of the implementation (e.g., the Galois polynomials assigned to nodes). As for the synchronization part of the experiments, it is implemented in a multi-hop manner despite the single-hop topology and time periods dedicated to synchronization are employed between time frames. As it is demonstrated, the nodes are successfully synchronized, showing that this method can be easily implemented in a more realistic and multi-hop topology. The rest of this paper is organized by including past related work in Section 2 and a brief description of TiMAC in Section 3. Details about the low-cost device, the 433 MHz RF modules and the TDMA synchronization approach are given in the system's description Section 4. The experimental setup (i.e., the topology and various parameters) along with the experimental results are presented in Section 5 and the conclusions are drawn in Section 6.