## 3 Cooperative Perception Information-Sharing
### Cooperative Perception Information-Sharing Strategy  
The cooperative perception information-sharing strategy plays a key role in alleviating network load and enhancing the cooperative perception effect. If the cooperative sensing information is shared too frequently, the wireless channel will be overburdened, resulting in channel congestion. It will lead to the perception information age being too old, reducing the accuracy of perception. Similarly, sharing all sensory data will result in information redundancy, leading to wasted computing and communication resources. If part of the perception information is shared, the perception will be incomplete, and the accuracy and integrity of the perception will be reduced. Therefore, a reasonable sharing strategy is particularly important for autonomous driving cooperative perception, including how often vehicles share perception data, which perception data to share, and the format of the shared data. For research on perception information-sharing strategy, the ETSI recently approved a technical report, which is the first proposal to standardize the CPM and the CPM generation rules [82]. The CPM generation rules define the frequency of vehicle generation and the transmission of CPM as well as the content of CPM, including onboard sensors (detection range, field of view, etc.) and detection targets (position, speed, size, etc.) [83]. The current ETSI CPM generation rules establish that a vehicle has to check every T_GenCpm if a new CPM should be generated and transmitted, with 0.1 s \(\leq\) T_GenCpm \(\leq\) 1 s (100 ms by default). However, these generation rules are preliminary and only a first proposal (hence subject to possible changes). A vehicle should generate a new CPM if it has detected a new object or if any of the following conditions are satisfied for any of the previously detected objects:  
1. Its absolute position has changed by more than 4 m since the last time its information was included in a CPM. 2. Its absolute speed has changed by more than 0.5 m/s since the last time its information was included in a CPM. 3. The last time the detected object was included in a CPM was one or more seconds ago. [PERSON] et al. [84; 85] compared the dynamic CPM generation strategy formulated by ETSI with the periodic generation strategy (the periodic generation strategy is that the vehicle periodically broadcasts the information from all detected objects). The results show that the dynamic CPM generation strategy is more flexible than the systematic generation strategy, which effectively reduces the transmission of low-value data. Furthermore, on this basis, the dynamic generation CPM strategy is optimized. In the proposed optimization strategy, when CAV receives updated information about an object from other vehicles, the vehicle does not repeat the broadcast of the object's information, further reducing information redundancy and decreasing communication overhead. To undertake cooperative perception comparisons and investigate the relationship between communication bandwidth and the amount of transmitted data, [PERSON] et al. [26] used raw sensor data, processed sensory data, and compressed data. The results reveal that as the amount of data communicated increases, so does the communication latency. Instead of exchanging raw sensor data, [PERSON] et al. [86] analyzed the influence of communication delay and transmission range on cooperative perception and proposed that the shared detected object data strategy is more time-effective. The majority of data transmission methods are now provided to the target vehicle via broadcasts. If an appropriate coordination mechanism is not in place throughout the transmission process, it will cause data transmission confusion, raise the likelihood of data retransmission, diminish transmission efficiency, and increase the likelihood of packet loss, all while raising network channel load. [PERSON] et al. [87] addressed the problem of [86] by using a context-based message acknowledgment method.