## 1 Introduction  
Wireless Sensor Networks (WSNs) are one of the most promising technologies in decades. WSNs are frequently utilized in applications such as medical, autonomous vehicles, networking, smart homes, environmental areas and other emergency applications [1; 2; 3; 4; 5; 6; 7; 8]. They are composed of huge quantities of sensor nodes capable of sensing, communication, processing, and storage [9; 10]. Transferring sensing data between these nodes faces several challenges due to the node's constraints, e.g., energy limitation [11], low computational capability, and low memory. Without the proper solution to these challenges, the current situation of WSNs cannot meet the requirements of Internet of Things (IoT) [12]. Since these nodes operate with little battery power, an important focus in research is making the sensor nodes live as long as possible. The majority of works, however, assume the link connecting two nodes to be fully symmetric. Asymmetric links, however, create possibilities where the same data is resent, wasting valuable energy. Link asymmetry is considered to be one of the most important characteristics of radio links, which can significantly affect the medium access layer's performance. In low power WSNs, many of the wireless links are asymmetric [13]. Figure 1 gives scenarios where the links can be asymmetric. Figure 1a shows the scenario in which the sender is able to send data but the receiver cannot. In Figure 1b, the receiver is able to send the beacon and the sender cannot. Finally, in Figure 1c, neither side is able to send data and control information. In this research work, we consider a mixture of above three types whenever any link asymmetry occurs. Several research works describe physical, logical, operational and legal reasons for link asymmetry [14; 15]. Firstly, transmission range is the primary reasons for link asymmetry. [PERSON] et al. found that the percentage of asymmetric links is negligible at short distances and increases significantly with higher distances [16]. Maximum transmission range of a sensor node is determined by the hardware properties such as the antenna and RF circuits. In these cases, transmission range problem cannot be solved without changing the nodes' hardware such as the antenna or RF circuit. Secondly, link asymmetry may arise due to power limitation, which is a major challenge for WSN. It is highly likely that different nodes in WSN have different level of residual energy. For instance, Node \(A\) has enough energy to transmit data to Node \(B\); however, Node \(B\) does not have enough energy to reach \(A\) or may choose not to reach Node \(A\) to save energy. Thus, non-uniform residual energy of sensor nodes is another major cause of link asymmetry. Thirdly, interference is another significant factor that causes asymmetric link. Suppose that Nodes \(A\) and \(B\) can reach each other, however, if Node \(B\) transmits at a power level that suffices to reach Node \(A\), it may cause interfere with a Node \(C\) that is a valid user of the same frequency spectrum. This unintended situation occurs due to the co-existence of of different wireless technologies using a same frequency band. Thus, Node \(B\) is not allowed to transmit at a power level above a given threshold, which causes the link asymmetry. Finally, some environmental factors, obstacles, and even weather conditions may cause the link asymmetry [17]. In this paper, we only consider the varying transmission range of the sensor nodes as the cause of link asymmetry. The link quality of wireless nodes can be measured by Link Quality Estimator (LQE). Two types of LQE are described in [18; 19]: hardware-based and software-based. Received Signal Strength Indicator (RSSI) and Link Quality Indicator (LQI) are two types of hardware-based approaches. Sensor nodes provide a RSSI register that estimates the signal strength of the received packet. A LQI is another hardware-based vendor specific indicator where the first eight symbols are considered for scoring from 50 to 110.