### Proposed Contribution and Related Works  
In the context of Wireless Sensor Networks (WSNs) and monitoring infrastructures for underground environments, most of the existing works have focused on mine [3] and pipeline [4; 5] scenarios. All the systems proposed in these papers focus on the realization of reliable wireless data transmission infrastructures in the presence of severe wireless propagation conditions that ask for the implementation of multi-hop linear networks. The concept of LSN has then emerged [6; 7]. In this scenarios, the sensing devices are arranged according to linear or semi-linear layout where each node is part of a communication chain that requires each node to transmit its own data and/or forward the packets transmitted by the adjacent nodes. According to [6], LSNs can be classified following either a Topological or a Hierarchical point of view. From the Topological point of view, they can be classified according to three typologies: _thin, thick_ or _very-thick. Thin_ LSNs are composed by a single chain arranged in one-dimensional fashion. _Thick_ networks envisage the presence of a linear backbone that is able to collect data from Basic Sensor Nodes (BSN) randomly placed in the surroundings of the so-called Data Relay (DRN) and Data Dissemination (DDN) Nodes. Finally, in _Very Thick_ Networks several parallel linear paths exist. In this case, every node can transmit in all directions to the surrounding nodes while the information flows linearly. The Hierarchical classification foresees the division of LSN in three categories: _One-Level_, _Two-Level_ and _Three-Level_. in _One-Level_ networks only BSNs are present. _Two-Level_ networks allow the presence of both BNSs and DDNs while DRNs are present only in _Three-Level_ networks. Due to their importance for different application scenarios, wireless sensor networks based on LSNs have been considered in several studies. As an example, [PERSON] and [PERSON] [8] proposed a complete architecture for Chain-Type WSNs based on a hierarchical structure, discussing possible protocols both at a PHY and MAC level. An improvement of this architecture embedding the concept of Clustering is discussed in [9]. Other studies focus on single technical aspects of LSN. [PERSON] and [PERSON] [10] propose an analytical method to evaluate the maximum throughput in general-purpose chain-type wireless networks, while a methodology to calculate the connectivity probability in thin one-dimensional LSNs is provided in [11]. The case of ZigBee-based LSN implementation is discussed in [PERSON] et al. [12], where a methodology for nodes' auto-discovery and a strategy for ad-hoc hierarchical addressing is proposed. Furthermore, [13] focuses on the problem of scheduling while [14] proposes a routing algorithm customized to this scenario. While all the previous papers present interesting solutions to optimize parameters regarding data transmission in LSNs (throughput, scheduling, routing, etc....), none of them deals with the problem of energy efficiency and then with the adoption of duty-cycling policies like the ones described in this paper. Nevertheless, power consumption is an important line of research that has been discussed in several papers [15; 16; 17; 18; 19; 20; 21]. In particular, a MAC-level protocol customized to the LSN scenario is proposed in [15], while a TDMA-based scheduling algorithm for LSNs is discussed in [16]. Similarly, [PERSON] et al. [17] propose a HDLC protocol for LSNs based on a TDMA MAC scheme, relying on the IEEE 802.15.4 PHY layer, and compare its performances with the ones of similar, widely adopted protocols. [PERSON] et al. [18; 19] propose an energy efficient routing protocol for LSN. More specifically, a Minimum Energy Relay Routing (MERR) and an alternative adaptive version of the same protocol (AMERR) are proposed, respectively. Finally, some other papers focus on identifying the ideal topology and placement scheme for sensor nodes to maximize energy efficiency [20], also adopting transmission range adjustment policies [21].