# An Effective Wide-Bandwidth Channel Access in Next-Generation WLAN-Based V2X Communications
## 1 Introduction  
Intelligent Transport Systems (ITSs) have been developed and widely deployed with Vehicle-to-Everything (V2X) communication. Vehicles equipped with various sensors (e.g., radar, Lidar, and cameras) combined with Vehicle-to-Vehicle (V2V) communication to exchange sensed data enable automatic driving and platooning. Vehicle-to-Pedestrian (V2P) communication prevents traffic accidents by providing warning signals. In addition, various V2X applications enable driving convenience, road safety, traffic efficiency, road management, and infotainment. As various applications using V2X communication are developed, the required throughput and reliability are diversified. Moreover, as more onboard sensors are equipped in each vehicle, the communication requirements of throughput and reliability have increased. At the time of this writing, the most widely deployed V2X communication system is Dedicated Short Range Communication (DSRC) using a set of Wireless Access in Vehicular Environments (WAVE) standards (Institute of Electrical and Electronics Engineers (IEEE) 1609 [1; 2; 3] and IEEE 802.11p [4]). Worldwide research projects and tests have proven that DSRC is a stable and efficient V2X communication system. Whereas DSRC is sufficient to provide basic and some advanced ITS services, more advanced future ITS services such as automated driving require more enhanced wirelesscommunication performance. Two important requirements in next-generation V2X communication systems are throughput and delay reduction. In order to meet the requirements of next-generation V2X communication systems, the IEEE 802.11 bd Task Group (TG) commenced V2X communication standardization in January 2019. IEEE 802.11 bd's objective is to improve the throughput, transmission range, and positioning performance, preserving backward compatibility and fairness with conventional Outside Context of a Basic Service Set (OCB) devices [5; 6; 7]. One of the proposed features to improve throughput is wideband transmission using a 20-MHz channel for large data transmission. A 20-MHz channel can double the throughput performance compared to legacy DSRC systems using 10-MHz channels. When the channel extension approach of IEEE 802.11n/ac is applied to 20-MHz transmission in V2X communication, the adjacent channel interference problem should be carefully considered. However, even though the channel access procedure is able to avoid adjacent channel interference problem in 20-MHz transmission, the channel extension approach of IEEE 802.11n/ac still cannot be applied in the V2X OCB environment owing to fairness concerns with conventional OCB devices and 10-MHz transmissions conducted by IEEE 802.11 bd devices. When the channel load levels of two 10-MHz channels are not equal, the conventional channel extension scheme has higher channel access priority in the extended channel than the conventional OCB devices' 10 MHz channel access because the conventional channel extension scheme has no back-off procedure on the extended channel. One of the most important requirements that IEEE 802.11 bd must meet is fairness with legacy devices deployed with IEEE 802.11p devices. Since the IEEE 802.11p OCB configuration does not require association with Access Points (APs), there are no primary or secondary channels as in the Basic Service Set (BSS) of other IEEE 802.11 networks such as IEEE 802.11n/ac. In addition, each channel is used independently for its own purpose with equal importance. Therefore, the fairness issue in V2X environments is more severe than in other IEEE 802.11 networks. There are prior researches to provide enhanced channel access mechanisms considering throughput and fairness under various IEEE 802.11 environments. Authors in reference [8] addresses unfairness caused by the wide-bandwidth transmission of IEEE 802.11 ac in case of overlapping channels between neighboring APs. It provides channel allocation and scheduling methods to minimize the interference and enhance the fairness and network throughput considering different channel bonding levels.