# Virtual Grid-Based Routing for Query-Driven Wireless Sensor Networks
## 2 Related Work  
In this section, we discuss existing mobile sink-based routing protocols developed for WSNs. Hexagonal cell-based Data Dissemination (HexDD) [18] partitions the network into six sectors using three principal lines: horizontal lines, vertical lines, and diagonal lines. Consequently, a hexagonal-shaped virtual infrastructure is created. These lines serve as designated areas for querying and data forwarding, functioning as rendezvous points. The sink initiates its query towards the central cell, which acts as the intersection point for the three primary lines. Now, the query is flooded within the lines until it encounters the requested data. Like queries, data also traverse towards the center cell and then are transmitted to the mobile sink. Rendezvous-based Data Dissemination (RDDM) protocol [19] is a cluster-based mechanism. It first divides the sensor networks into multiple clusters and then constructs a rendezvous-based data dissemination tree by connecting all the cluster heads. The cluster head is a node that is elected from each cluster and forwards queries and data packets. One randomly moving mobile sink stays in a cluster, which is known as a rendezvous cluster head. Apart from this, all the cluster heads and sink send their query and data to the rendezvous cluster head. The selection of rendezvous cluster head is carried out according to the energy. The Query-Driven Virtual Grid-Based Data Dissemination (QDVGDD) protocol [20] functions by partitioning the sensor field into numerous virtual grid cells. Within each cell, a specific node is designated as the Cell Header (CH). To facilitate efficient data dissemination, a mobile sink traverses along the boundary of the sensor network and transmits its query to the CH located at the boundary. Subsequently, this boundary CH forwards the query to the CH(s) within the sink's AoI. Upon receiving the query, the sensor nodes within the network sense their environment and relay the collected data to the respective CH. These CHs then take charge of sending the accumulated data to the mobile sink. Energy and Delay-Efficient Data Acquisition (EDEDA) [21] is also a grid-based routing protocol. It considers both base station and mobile sink. Rather than moving randomly or following a specified path, a few of the grid cells are identified, where the mobile sink sojourns for collecting the data. From each sojourning location, the mobile sink directly collects the data from nine grid cell heads. The trajectory of the mobile sink is designed in such a way that its data collection journey begins and ends at the base station, following the Hamiltonian cycle. After collecting the data, the mobile sink hands over the data to the base station in each round. The Trajectory Planning and Route Adjustment (TARA) technique [22] adopts a grid-based approach by constructing square-shaped grid cells within the sensor network. These grid cells are evenly numbered and serve as the fundamental units of organization. A cell head is elected for each grid cell through a process that takes into account its distance from the cell's midpoint and its remaining energy level. These cell heads are responsible for transmitting the accumulated data to the sink. To ensure effective data collection, the mobile sink follows a trajectory that traces the perimeter of the sensor field while also passing through its center. This trajectory is carefully designed to distribute the data load evenly across the network. Whenever the mobile sink pauses at a specific grid cell during its journey, all the corresponding cell heads adjust their routes towards the sink. This adjustment process adheres to a predefined set of rules, facilitating efficient data transmission and coordination. Query-driven Ring Routing Protocol (QRRP) [23] constructs multiple, equidistant, concentric rings in the network according to the length of the network and communication range of the sensor node. When a sink stays at a particular location, it informs ring nodes. Ring nodes save this information for transmitting the data.