# Redundancy Mitigation Mechanism for Collective Perception in Connected and Autonomous Vehicles
## 2 State of Art about Collective Perception for Connected and Autonomous Vehicle
### Communication Aspect  
Concerning the creation of CPM, the frequency of CPM generation is crucial since vehicles would overload the communications channel by creating/sending many CPMs. Therefore, ETSI has suggested the first set of guidelines for CPM creation for CP applications [32]. These rules dictate when and what collective perception messages CAVs must transmit. In this sense, frequent transmission of CPMs might enhance the knowledge about the CAVs surroundings. However, the transmission rate for CPM should be between 5 Hz and 10 Hz without coordination, which lead to multiple observations of the same object will frequently be broadcast through the network. The increased network demand might result in transmission delays, reducing the usefulness of CP applications. As a result, it is important to consider advanced techniques for dynamically controlling CPM redundancy transmitted over wireless channel, while maintaining greater awareness of the driving environment. [PERSON] et al. [22] investigated the data redundancy issue in highway scenarios and demonstrated that repeated transmissions might lead to significant network loads, specially in dense traffic circumstances. The authors also discussed transmission redundancy effects and proposed a probabilistic data selection scheme to suppress redundant transmissions. The scheme enables CAVs to adapt the transmission of each tracked object based on position, carrying density, and road geometry. The results demonstrated that the suggested technique may minimize the communication cost for both V2V and V2I-based CP while retaining the appropriate perception sharing ratio. [PERSON] et al. [31] created an algorithm that modified the ETSI generation rules to rearrange the transmission of CPM data, which leads CAVs to broadcast fewer CPMs than the ETSI standard. In this sense, each CPM contains information about a higher number of identified objects. As a result, the suggested method decreased channel load, enhanced the reliability of V2X communications, and improved CAV sensing capabilities. [PERSON] et al. [30] introduced an overview about congestion control for collective awareness and CP applications and suggested the relative position-based priority method to control congestion. This work regulates the frequency of beacon messages transmission based on their relative positions among neighboring vehicles. In this sense, CAVs decide how often beacon messages with information about detected objects are sent out based on how close they are to other vehicles. The method can be used with other strategies, such as the current ETSI generation rule and its variations. The proposed method cuts down on CPM traffic by using a simple rule based on where a CAV is about the other vehicles around it. Figure 1: ETSI collective perception message (CPM) general structure [32]. [PERSON] et al. [27] examined the performance of the CPs service in IEEE 802.11p networks in regards to its impact on traffic participants' acquired environmental perception and drew the conclusion that the service should be developed further. The primary objective is to help the ongoing ETSI standardization work in this domain. In addition, the authors modify the analytical model used to evaluate the performance of the C-V2 Xs CPs service. [PERSON] et al. [29] proposed a set of generation rules for the CPs Service that provides a trade-off between two factors. The proposed rules have the potential to significantly impact the delivered service quality for receiving intelligent transport system stations, as well as the generated network load on the used radio channel. As a result, the proposed generation rules include a message segmentation mechanism that enables the generation of sequential independent CPMss. In this approach, the proposed generation rules are subjected to a thorough simulation study to assess their behavior in various traffic scenarios and radio configurations.