# LTM-LoRaWAN: A Multi-Hop Communication System for LoRaWAN
## 1 Introduction
However, class C-enabled devices consume more power compared to classes A and B.  
LoRaWAN employs an Adaptive Data Rate (ADR) mechanism as a method to adjust and control some of the network configuration parameters to reach an optimal operation [6]. ADR's main motivation is to efficiently set the data rate, which consequently affects network capacity and power consumption [7]. It operates on two sides: the network server and the end devices. The one at the end device side is designed to entitle an end device to increase its transmission range via increasing transmission power and spreading factor. The end device maintains a counter to figure out whether it has received any ADR command or downlink messages from the server. If the counter reaches a threshold, the transmission power and spreading factor are accordingly increased. On the other hand, the network server ADR works on demand as requested by an end device. The network server measures the link budget between itself and an end device based on the last 20 packets exchanged. The collected information is used by the network server to first decrease the spreading  
Figure 1: Standard LoRaWAN Network. factor and then adjust the transmission power. The recommendation is finally sent to the end device. Several works have been proposed in the literature to handle the deployment of multi-hop LoRaWAN. Most of the proposed works are dependent on some assumptions which make their solutions appropriate for special cases. An example of that is the assumption of the use of synchronization where end devices and gateway are synchronized. Such synchronization would enable communicating devices to control activity time. This, however, contradicts the typical MAC approach used by LoRaWAN, ALOHA protocol. Other solutions assume the prior knowledge of the network topology to allow the use of some specific network construction technique, such as building a tree topology. This paper proposes Listen-To-Talk-based Multi-hop LoRaWAN (LTM-LoRaWAN) to support multi-hop communication in LoRaWAN. The proposed system first entitles an end device to determine whether or not the device is in the range of a gateway by optimizing the existing ADR mechanism. The proposed system then provides a lightweight procedure for transmitting and forwarding out-of-range device traffic to a gateway. This requires the proposed system to employ a different mechanism for medium access similar to Listen-before-Talk. The contribution of this paper is the detailed design of LTM-LoRaWAN and a comprehensive simulative evaluation of the proposed system. Moreover, the paper provides a comparative assessment of the proposed multi-hop system compared to one-hop LoRaWAN using several performance metrics. The remainder of this paper has been organized as follows. Section 2 introduces the existing related work in the literature. The proposed system is then presented in Section 3. The evaluation of the proposed system is addressed in Section 4. The section begins by introducing the network model and the configuration parameters. It then defines the evaluation metric and introduces and discusses the result of the evaluation. The conclusion is finally drawn in Section 5.