# Review of V2X-IoT Standards and Frameworks for ITS Applications
## 2 Core ITS Standards
### Standards for Dedicated Short-Range Communications (DSRC) Technology
These frequency bands are further subdivided into sub-categories/classes: the (5.470-5.725) GHz band is classified as ITS-G5C and is intended for the radio local area networks (RLAN, BRAN, WLAN); the (5.855-5.875) GHz band belongs to ITS-G5B and dedicated to ITS non-safety applications; the (5.875-5.905) GHz band is ITS-G5A and dedicated to ITS for safety-related applications; the (5.905-5.925) GHz band is classified as ITS-G5D and reserved for future ITS standard expansion. Similar to the IEEE 802.11p standard, the (5.855-5.925) GHz band is divided into 7 fixed 10 MHz channels, with one dedicated for the control channel and the other six reserved for service channels [31]. Meanwhile, the entire 255 MHz band of the sub-category ITS-G5C is shared with the radio local area network (RLAN) band, used by Wi-Fi devices, and can have 10 MHz or 20 MHz channel spacing. The physical layer of the (5.795-5.815) GHz band is described by the European Committee for Standardization (CEN) standard CEN EN12253 [32]. This standard specifies the physical parameters for both OBU and RSU, and distinguishes two types of communications: downlink (from RSU to OBU) and uplink (from OBU to RSU). According to this standard, this frequency band is divided into four channels, each having a width of 5 MHz, where the downlink carrier is allocated: 5.7975 GHz, 5.8025 GHz, 5.8075 GHz and 5.8125 GHz. Meanwhile, two possible sub-carrier frequencies can be used in the uplink: an offset of either 1.5 MHz or 2 MHz from the carrier frequency. According to the standard specifications, this frequency band is intended for road transport and traffic telematics systems. Two frequency bands are distinguished for ITS in Japan: (5.770-5.850) GHz and (755.5-764.5) MHz regulated by the standards of the Association of Radio Industries and Businesses (ARIB). The physical, data and application layers of the first frequency band are described by ARIB STD-T55 [33] and ARIB STD-T75 [34]. This (5.770-5.850) GHz band is divided into 14 channels of 5 MHz, 7 of which are downlink and the remaining 7 are uplink. These standards specify the radio communication interface for the electronic toll collection, passenger information collection, event and disaster information, and various entertainment events. Meanwhile, the use of the 700 MHz radio frequency band is regulated by the ARIB STD-T109 [35] standard and is intended to provide a link between the roadside-to-vehicle communications and the inter-roadside communications. The main purpose of the systems described in this standard is to:  
* Reduce the number of accidents on the road;
* Regulate the flow of vehicles;
* Ensure the transmission of information for safe driving and to provide a variety of services. The ARIB STDT109 standard specifies the (755.5-764.5) MHz band with a center frequency of 760 MHz and a channel width of up to 9 MHz. DSRC standards shall optimize the resource use of the control plane and/or user plane for transfer of continuous uplink data that requires both a high data rate (e.g., 10 Mbps) and a very low end-to-end latency in the range of 1-10 ms. An earlier paper reports practical latency research results obtained during a moving field test, taking into account the vehicle speed and packet loss percentage [36]. The measured vehicle-to-roadside latency under various conditions averages to 4.3 ms with a maximum value of around 5 ms, which is within the officially approved DSRC standard specifications. DSRC is a wireless communication method with a limited range in order of tens of meters. In order to establish an active sideling to any roadside device, the speed of the automobile has to be relatively low, so as to allow enough time for switching. One of the proposed solutions is to use extended range DSRC repeater, but this poses another problem [37]. With an increased number of intermediary nodes, transmission delay times are also increased, which limits the use of safety messages. Other downside of DSRC is the distribution of data packets during intensive traffic [37; 38].