# Two Hop Adaptive Vector Based Quality Forwarding for Void Hole Avoidance in Underwater WSNs
## 2 Related Works
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Techniques** & **Features** & **Parameters** & **Limitations** \\ \hline Proactive routing protocols (OLSR, DSDV, etc.) [5; 6] & Routing tables are updated regularly to maintain routing information & Routes are always available & Large signaling overhead for establishing routing tables \\ \hline Reactive routing protocols (AODV, DSR, etc.) [7; 8] & Route discovery, Route maintenance & Bandwidth efficient, on demand approach & Higher latency, energy consumption \\ \hline Beacon-based routing protocols such as H2-DAB [9] & Without location information, unique ID assignment to every node based on hop counts from sink & Improved reliability & Infeasible for low node mobility speed, high network overhead \\ \hline Clustering routing [10; 11] in UWSNs & Cluster head selection based on residual energy or location, nodes report data to cluster heads & Communication overhead minimization, efficient network management & Longer end-to-end delay, poor performance in time critical applications \\ \hline DBR [12], depth-based routing protocol for UWSNs & Greedy forwarder selection, constant forwarding region all of the time & Energy conservation, network lifetime maximization & Inappropriate void hole avoidance mechanism, inefficient forwarder selection \\ \hline EE-DBR [13], depth-based routing protocol for UWSNs & Energy conservation based routing protocol, depth-based routing protocol for UWSNs & Low end-to-end delay, energy tax & Inefficient void hole mechanism, large network overhead \\ \hline WDFAD-DBR [14], depth-based routing protocol for UWSNs & Forwarder selection on the basis of two hop depth information, adaptive changes the forwarding area & Void hole avoidance, suppression of duplicate packets in local area network & Unnecessary energy consumption due to packet drop \\ \hline Inter and Re-Intarrouting protocol [15], for UWSNs & One hop back transmission to avoid void hole, forwarder selection based on cost function & Void hole avoidance, high throughput & High accumulated propagation distance \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summarized related works. H2-DAB, hop by hop dynamic addressing-based; EE, energy-efficient; WDFAD, weighting depth and forwarding area division; Re-Intar, reliable and interference-aware routing; VBF, vector-based forwarding; HH, hop by hop; AHH, adaptive hop by hop. Geographical routing techniques have the ability to minimize the end-to-end latency and overhead, where information is not flooded between the source and destination. However, information regarding the location of the neighbor and destination is utilized for transmission. The limitation for the adaptation of this routing mechanism is that the global positioning system (GPS) does not work well due to high absorption and quick attenuation of the signal in the acoustic medium. While keeping in mind the aforementioned constraints, the research community has been devoted to bringing continuous improvement of underwater protocols. Keeping different considerations into account, routing protocols for UWSNs are classified into beacon-based routing, clustering routing, depth-based routing and location-based routing protocols. The hop by hop dynamic addressing-based (H2-DAB) protocol does not keep location information of the nodes. Unique ID assignment to every node is performed based on hop counts from the sink. Reliable data delivery is achieved, compromising the network overhead [9]. In cluster-based routing [10; 11], cluster heads are selected based on residual energy or location. Features like efficient network management and communication overhead minimization are achieved. Due to longer end-to-end delays, it gives poor performance in time-critical applications. In the depth-based routing (DBR) scheme, nodes greedily forward data packets to the upper nodes. If it does not find the next hop forwarder node due to a coverage hole or energy hole, packet drop occurs, which affects packet delivery in DBR [12].