# Enhancing Route Guidance with Integrated V2X Communication and Transportation Systems: A Review
## 4 V2X Communication Architecture
### V2X Communications Protocols  
#### 4.1.1 IEEE 802.11p--DSRC  
Dedicated Short-Range Communication (DSRC) technologies are introduced for short-range wireless radio-equipped automobiles, and they can be used to communicate data between vehicles and roadside infrastructures. IEEE 802.11p DSRC can be used in RGSs to provide real-time information to drivers about traffic conditions, road hazards, and suggested alternative routes. By exchanging information between vehicles and infrastructure units, such as traffic lights and road signs, DSRC can help drivers navigate more efficiently and avoid traffic congestion. In a typical route guidance system, a vehicle equipped with a DSRC communication module can send and receive messages to and from nearby infrastructure units [90]. For example, vehicles may receive real-time information about traffic congestion and road closures from traffic cameras and other infrastructure sensors. The vehicles' drivers can then use this information to suggest alternative routes that avoid congestion and provide faster travel times. DSRC can also provide real-time information to drivers about road hazards, such as construction zones, accidents, and weather-related risks. By receiving this information in real time, drivers can adjust their driving behavior and avoid accidents. In addition, DSRC can be used to support cooperative driving scenarios, such as platooning, where a group of vehicles travels close to each other to reduce fuel consumption and improve traffic flow. Vehicles can maintain a safe and efficient traffic flow by exchanging information about speed, direction, and acceleration. The Federal Communications Commission (FCC) of the United States launched an endeavor in 1998 to complete a regulation for the allocation of the 5.850-5.925 GHz band [81]. DSRC as a technology has now become more and more common due to the rapid develop ment of ITS. The International Telecommunication Union (ITU) has established a number of system requirements and operational features for millimeter wave (mmWave) radio communication systems. The mmWave radio communication recommendation covers vehicular collision avoidance radars operating in the 76-77 GHz and 77-81 GHz bands and for ITS at the 57-66 GHz range for V2V and V2I. Both active (transceiver) and backscatter (transponder) DSRC systems are described for the 5.725-5.875 GHz range. In October 1999, the US Federal Communications Commission launched the 75 MHz spectrum (FCC). This frequency band was reserved for various DSRC communication ITS applications, including traffic light control, traffic monitoring, passenger alerts, automatic toll collecting, and other areas. Then, IEEE upgraded the edition of the IEEE 802.11 protocol to IEEE 802.11p in 2010 [91]. This standard's primary goal was to outline the physical (PHY) and medium access control (MAC) layers for exchanging wireless broadcast messages in a vehicular environment. The 5.770-5.850 GHz spectrum is divided into 14 channels. Each is 5 MHz, seven of which are downlinks, and the remaining seven are uplinks. These standards define the radio communication interface for electronic tolling, passenger information gathering, event and disaster information collection, and various entertainment events. The 700 MHz radio frequency range offers a link between roadside-to-vehicle communications and inter-roadside communications. DSRC standards aim at optimizing the resource transfer uplink, which demands a high data rate (10 Mbps). Under diverse situations, the measured vehicle-to-infrastructure latency averages 4.3 ms [88]. One potential alternative is to utilize an extended-range DSRC. Nevertheless, transmission delay would increase as the number of intermediary nodes increases, limiting the use of safety messages [92]. Another disadvantage of DSRC is the low distribution of data packets during peak intervals [81]. In addition, the device authentication process could be incorrectly handled through heavily congested traffic networks.