# Implementation of a Topology Independent MAC (TiMAC) Policy on a Low-Cost IoT System
## 2 Past Related Work  
MAC policies for IoT have been the case in many works over the past few years. [PERSON] et al., in their 2019 work [PERSON] et al. (2019), survey MAC policies used in IoT, providing a detailed description of each one. More specifically, they categorize the reviewed policies in short and long-distance coverage. Under the latter categorization, they survey most of the known policies used by, e.g., Radio Frequency Identification (RFID), Bluetooth Low Energy (BLE), Wireless Highway Addressable Remote Transducer Protocol (Wireless-HART), Long Range Protocol (LoRa), and many more. Like [PERSON] et al., [PERSON] et al., in their work in [PERSON] et al. (2019), survey MAC policies in IoT. The authors there categorize the considered MAC policies according to the channel access method each one uses. In addition, they give the essential properties of MAC policies for IoT and the common causes of energy consumption. Finally, they address some pros and cons for each surveyed policy. Other surveys, more dedicated to the applications each IoT system is designed for, can be found in the literature. For example, [PERSON] et al., in [PERSON] et al. (2019), provide a detailed analysis of MAC policies exclusively for energy harvesting IoT systems. In contrast, a review and evaluation of MAC policies for satellite IoT systems using nano-satellites are given in [PERSON] et al. (2019) by [PERSON] et al. TDMA policies for IoT, hybrid policies that consider the cooperation of TDMA with other channel access methods, and improvements for TDMA policies have been the case in several works in the literature over the past five years. A distributed and adaptive hybrid medium access control (DAH-MAC) is proposed in [PERSON] and [PERSON] (2018) by [PERSON] and [PERSON]. In the policy considered there, a distributed TDMA approach is employed for voice packet transmissions to guarantee a voice packet loss rate bound, while truncated CSMA/CA (TCSMA/CA) is used for data nodes to access the channel. The same authors in [PERSON] et al. (2019) propose a token-based adaptive medium access control (TA-MAC) scheme for a two-hop Internet of Things (IoT)-enabled mobile ad hoc network. TA-MAC bases its operation on super-frames created by the devices and these super-frames' duration, along with the number of token rotation cycles, are optimized and adapted to the network's traffic load, so as to achieve a consistently minimal average end-to-end packet delay. Another hybrid approach is given in [PERSON] et al. (2019) by [PERSON] et al. There, a hybrid slotted-CSMA/CA-TDMA (HSCT) policy is proposed, where a contention-based slotted-CSMA/CA period (SCP) divided into multiple CSMA/CA access windows is assumed, along with a contention-free slotted-TDMA period divided into multiple slots. Both CSMA/CA and slotted-TDMA are cooperating in order to achieve the registration of machine-to-machine (M2M) communications in large scale environments where many devices try to access a single and centralized access point. An algorithm for fair resource allocation in TDMA-based distributed sensor networks for IoT is proposed in [PERSON] et al. (2019) by [PERSON] et al. The authors of the latter paper implement a multi-hop desynchronization (DESYNC) algorithm for tackling the hidden-node problem in multi-hop TDMA-based networks, by proposing a new frame structure and a procedure dedicated to approaching the problem. Scheduling in TDMA-based IoT systems is studied in [28] by [PERSON] et al. The authors in this paper propose a distributed TDMA slot scheduling algorithm that takes into account nodes' energy and the network's topology. In this approach, the residual energy of nodes and the topology knowledge about the number of nodes' neighbors play a significant role in the time slot allocation, in providing higher priority in nodes of lower residual energy and more neighbors than the other nodes.