## 2 Related Work
### Localization-Aware Routing Protocols  
[PERSON] et al. in [23] avoided unnecessary data transmissions in the network by proposing focused beam routing (FBR) algorithm. The FBR uses R/CTS (ready/clear to send) based mechanism with adaptive power transmission level. When the network gets sparse, every source node makes several attempts to select forwarder node by broadcasting RTC packet. This mechanism dissipates surplus energy along with higher delay. Fuzzy logic is used to calculate the desirableness factor to forward the data packets in acoustic networks [24]. The information of energy and position is utilized to compute the effectiveness of next hop node in fuzzy based forwarding protocol. The fuzzy logic system takes as input, the node battery level, trajectory and distance of the node from the sink node. The consideration of multiple parameters helped in achieving higher network lifetime and lower end-to-end delay. To control the flooding of information, directional flooding-based routing (DFR) scheme is proposed in [25]. The earlier said scheme restricts the participation of forwarders between source to destination. The communication area of flooding is defined based on acquired link quality and angle between the transmitter and receiver nodes. The DFR saves significant amount of energy by using directional flooding. Further, the effective neighbor is difficult to elect as the sparsity of the network increases. In addition, it adjusts from the defined static power levels, which consume more battery, especially when the distance is high. A localization algorithm is proposed in [26] to handle the uncertainty of the anchor nodes. The use of pressure sensors allowed the authors to find only two-dimensional coordinates. The work computed the uncertainty of the targeted node along with the issues of bending ray. The performance is measured via simulating against schemes with known anchor nodes location and locations calculated through straight line mechanism between two nodes. The errors of straight line is mapped via measuring time of flight and range errors are catered through multivariate gaussian distribution. The trajectory is calculated through gaussian beam tracing method. This scheme gained localization accuracy up to 49.4% against the traditional schemes. In [27], a vector-based forwarding (VBF) scheme saves energy using pipeline mechanism. This restricts the node involvement; however, rigid forwarding range degrades the network lifetime. [PERSON] et al. extended VBF to HH-VBF (hop-by-hop VBF) [28] protocol. This algorithm makes forwarding range decision at each hop based on the neighbor information, which makes it suitable for sparse networks. However, due to constant network radius in HH-VBF, the load is distributed unevenly among the entire networks nodes. In [29], an adaptive hop-by-hop VBF (AHH-VBF) routing protocol is presented. In AHH-VBF, during packet transmission, the radius of pipeline is adaptively adjusted at each hop to reduce energy expenditure. Furthermore, the holding time of the packet is computed according to the distance between forwarder node and destination to reduce end-to-end delay. In AHH-VBF, increasing the radius of pipeline does not resolve the void hole problem. The existing schemes: WDFAD-DBR [14], Hydrocast [15] and H2-DAB [16] avoid void hole problem using different approaches. The WDFAD-DBR uses neighbor information up to two hops to overcome void issue. The Hydrocast traverses backwards until it finds a suitable forwarder which can deliver the data packet. H2-DAB involves unique id mechanism to deliver the data to the sink node. These schemes take precautionary measures when void node occurs. However, our proposed work is different in terms of data forwarding mechanism. The complete route is discovered before delivering the data to neighbor node because information up to two hops never eliminates the void hole problem. If void problem occurs, we only move one hop in the backward direction to resume the greedy forwarding process.