## 2 Related Work  
The subject of SLP protection in WSNs has received widespread attention in the literature since it was first introduced in 2004 [2; 11; 21]. There exist many routing protocols for SLP protection [2; 3; 11]. In Reference [2], the SLP protection techniques were classified into the following categories, (1) phantom routing protocols, (2) fake packet injection protocols, (3) the multiple routing path protocols, (4) random walk routing, (5) hiding protocols, (6) ring routing protocols, (7) protocols based on the ring routing and the fake packet injection, (8) protocols based on the phantom routing and the fake packet injection, (9) data mule protocols, (10) cryptography and authentication protocols, (11) network encoding protocols, (12) directional communication protocols, and (13) the isolation protocols. In Reference [11], the routing protocols were classified into the following categories, (1) phantom node routing, (2) fake source routing, (3), intermediate node routing, (4) tree-based routing, and (5) the angle-based routing protocols. In Reference [21], the solutions for SLP protections were categorized into several strategies including (1) random walk routing, (2) fake source packet routing, (3) cyclic entrapment, and (4) geographic routing. In Reference [10], the solutions for providing the SLP protection were classified into eleven categories including (1) fake source packet routing, (2) random walk routing, (3) geographic routing, (4) cyclic entrapment, (5) separate path routing, (6) location anonymization, (7) cross-layer routing, (8) network coding, (9) delay, and (10) limiting the node detectability. In this study, we focus on phantom routing, fake source packet routing, and the protocols which adopt both phantom routing and fake source packet routing. The phantom routing technique involves two main phases during the packet routing. In the first phase, packets are routed from the source node to a location where a phantom source is located through a random walk. At the phantom source, the packets are then forwarded to the sink node through flooding, single-path routing, or other strategies. The phantom routing strategy has been widely explored in the literature, and it has been adopted in many existing protocols. Examples of routing protocols which adopt phantom routing include the trace cost based source location privacy protection scheme [9], phantom walkabouts routing protocol [13], the phantom routing with locational angle [22], and the energy efficient privacy preserved routing algorithm [23]. Similarly, the phantom routing strategy is adopted in the multiple-phantom nodes routing scheme [24], the grid-based single phantom node and grid-based dual phantom node source location privacy protection schemes [25], the self-adjusting directed random walk approach [26], and the pseudo normal distribution-based phantom routing protocol [27]. The baseline phantom routing protocol offers low levels of SLP protection because it employs short and predictable routing paths. Adversaries can successfully perform back tracing attack on the short routing paths within a short time period. Furthermore, the phantom routing offers reduced levels of SLP protection when multiple source nodes exist in the network [28]. The fake source packet routing protocols involve the process of selecting a set of nodes in the WSN to act as fake sources and mimic the real sources. The fake sources and real sources send packets simultaneously to confuse the adversary. The fake source packet routing strategy has been adopted in many existing protocols including the dummy packet injection scheme [12], the dynamic fake sources-based algorithm [16], and the hybrid online dynamic single path routing algorithm [18].