## 1 Introduction  
Wireless sensor networks (WSNs) are resource-constrained with limited processing power, memory, battery, and bandwidth. In monitoring applications, the WSNs are often deployed in open and inaccessible locations that are difficult to control, manage or safeguard from unauthorized physical access [1; 2]. Consequently, packet transmission in WSNs is susceptible to eavesdropping adversaries. Furthermore, the transmissions may result in lost or corrupted packets due to routing failures or collisions. Subsequently, the design of security protocols for WSNs must take into consideration the performance features of the WSNs. The networks may be faced with many types of attacks including privacy attacks where an adversary focuses on monitoring and analyzing the network traffic to obtain critical information such as the location information of important nodes [1]. To address the issue of privacy attacks in WSNs, numerous source location privacy (SLP) protocols have been proposed in the literature. SLP protection is denoted as the process of minimizing the traceability and observability of a source node by an adversary in WSNs [3]. It can also be indicated as the process of keeping the location information of a source node hidden from an eavesdropping adversary in WSNs [4; 5]. SLP protection is important in monitoring WSNs because it warranties the security of the source nodes by ensuring the information which is gathered by the source nodes is only observed or deciphered by the authorized parties [6; 7; 8; 9; 10; 11]. There exist many types of SLP routing protocols [2; 10; 11]. In this study, we focus on routing protocols which are based on phantom routing and fake packet routing strategies. In the phantom routing strategy, phantom nodes are selected and packets from the source nodes are first sent to the phantom nodes through random routing paths. Then, the packets are transmitted from the phantom node to the destination sink node through flooding, single-path routing, or some alternative strategies [2; 12]. The phantom routing strategy is simple and offers low SLP protection when used in its simple form [13]. In the fake packet routing strategy, fake sources are designed to mimic the functions of the real source nodes. The fake sources transmit fake packets simultaneously with the transmission of real packets from the real source nodes [1; 11; 14; 15; 16]. Often, the fake packets are of the same size as the real packets and they are transmitted at the same transmission interval and transmission rate as the real packets. Fake packet routing protocols are effective at preserving the SLP because it is difficult for adversaries to differentiate the real packets from the fake packets. However, to effectively obfuscate an adversary, the protocols often distribute a large amount of fake packet traffic in the network. Consequently, the protocols incur exhaustive energy consumption, routing congestion problems, packet collisions, and packet loss events [2; 13; 17; 18; 19]. As a result, the packet delivery ratio (PDR) and end-to-end delay (EED) performance of the protocols are affected [11]. The protocols may not be suitable for real-time applications which have strict requirements on EED. There exist several SLP routing protocols which integrate the phantom routing and fake packet routing strategies. Examples of the protocols include the tree-based diversionary routing (TreeR) [4] and the probabilistic source location privacy protection protocol (ProbR) [20]. The TreeR protocol achieves strong SLP protection by integrating many routing strategies. It employs phantom nodes which are located far away from the source node. It creates backbone routes which are directed to the network border with many diversionary routes. At the end of each diversionary route, fake packets are emitted periodically to obfuscate the adversary.