# Two-Level Sharing and Extraction of Sensing Information with Hybrid V2X Communications
## 2 Related Work  
Collective perception in V2X increases the awareness of other vehicles and obstacles by allowing vehicles to share the sensing information with other vehicles [3]. Cooperative awareness is enabled by dissemination of the vehicle state, such as the current position and speed. The typical messages in collective perception involves the a cooperative awareness message (CAM) or a basic safety message (BSM). The transmission frequency of these messages affects the traffic load generated in the collective perception. In [5], the authors examined the congestion control in collective perception. In [14], the authors examined the efficiency of CAM and BSM dissemination among vehicles based on different mechanisms of collective perception. Redundancy migration in collective perception was investigated in [6]. In [3], the authors examined the performance of collective perception with different metrics, including environmental perception, the effect on communication channels, and safety metrics. To asses the impact on the safety improvement by utilizing collective perception, new metrics were introduced to measure the environmental risk awareness of the traffic participants. Cooperative driving with free space awareness was examined in [15] using interdisciplinary approaches. Platooning or cooperative automated driving is an intelligent transport system that forms groups of vehicles together on roads. Vehicles in a group follow each other at a close distance in an autonomous manner and with a common shared leader. Extending the sensing accuracy and capacity by the collection of sensing results from different users in wireless networks has been discussed. With an aim to improve sensing reliability and accuracy in a cognitive ratio, clustering sensing entities has been studied for the reliable collection of sensing results at different positions, so as to correctly detect the primary users [7; 8]. In [9], the authors proposed a cooperative sensing method for a multi-band wireless LAN (WLAN). To overcome the constraint of channel sensing at the AP of a WLAN, a number of STAs were utilized to perform channel sensing, leading to an increase in spatial coverage and spectrum coverage in channel sensing. A broadcast is an important communication method in message dissemination in vehicle networks. Four types of broadcast are categorized in [16] in terms of reliability, priority, and the scope of broadcast. In [17], the authors introduced a framework of safety message dissemination in V2X communications. V2I and V2V resource allocation methods for safety messages were proposed. The objective was to reduce the delay and increase the reliability of safety message dissemination. A priority difference was assigned to various applications, and a high priority was assigned to safety message dissemination and a low priority was assigned to applications such as video downloads. In [18], the authors provided a review of emergency message dissemination in vehicle networks and introduced the studies that have aimed to reduce communication delay and improve the packet delivery ratio. In [19], the authors studied the reliable and efficient dissemination of traffic events among vehicles. The proposed method involved relay control, duplicate dissemination control, and vehicle clustering control to increase the event dissemination rate and reduce the event duplication rate. Conventional studies have shown that the utilization of multiple communication interfaces is one approach to reducing the consumption of wireless resources and increasing communication reliability. In [10], the authors proposed a method of sharing map information among robots that have a low speed of movement. A large communication range was utilized for communications to the map server, while short-range communication was utilized for the sharing of map information in a robot cluster. The cluster leader downloaded the map information, which was disseminated to other robots in its cluster to reduce wireless resource consumption.