# Review of V2X-IoT Standards and Frameworks for ITS Applications
## 2 Core ITS Standards
### Standards for 4G- and 5G-Based Cellular (C-V2X) Technology  
C-V2X stands for cellular communication for data transmission between vehicles and its environment (V2X). C-V2X technology is regulated by the 3 GPP (3 rd Generation Partnership Project) international organization, taking into account the growing needs of the automotive industry and the development of the V2X services. Furthermore, automotive, telecommunication, other mobility and transport technology industry-leading companies have created the 5G Automotive Association (5 GAA) with the goal to expedite the development and real-world implementation of the C-V2X. The LTE Advanced Pro V2X services, architectures, radio access network regulations and four use case scenarios (V2V, V2I, V2N, V2P) have been defined in detail in the 3 GPP (3 rd Generation Partnership Project) Service aspects (\"stage 1\") and LTE (Evolved UTRA), LTE-Advanced, LTE-Advanced Pro radio technology series technical specifications and technical reports starting with Release 14. C-V2X communication is based either on a single band using PC5 or inter-band concurrent communication using both PC5 and Uu interfaces. The LTE Uu interface is used for connection to the cellular station, while PC5 interface is used for direct communication between V2X nodes. [38; 39]. The initial C-V2X release only supported half duplex PC5 interface on band 47, which coincides with the North America DSRC (5.850-5.925) GHz frequency range, but later specification extensions added support for the Uu interface. For 3 GPP Release 15, TS 36.101 specification distinguishes 10 frequency bands for Uu interface while keeping a single PC5 interface on band 47 [40]. While Uu communication does not support carrier aggregation and is limited to a bandwidth of 20 MHz (10 MHz being used in most cases), PC5 interface can use up to three intra-band carriers with bandwidth options of 10 and 20 MHz, with total bandwidth not exceeding 30 MHz. Frequency bands for the LTE-based C-V2X communication are provided in Table 1.  
3 GPP Release 15, TS 36.101 specification chapter 14 describes the main user equipment (UE) parameters; it does not include latency parameters [40]. LTE-based C-V2X service latency requirements are defined by the TS 22.185 specification [41], while insight into specific use cases is provided in TR 22.885 [42]. Crash avoidance-oriented V2V services have the most strict latency requirement--no more than 20 ms. For non-critical V2V services, also for V2P, V2I uses case scenarios where the latency cannot exceed 100 ms and for V2N--no more than 1000 ms. The 3 GPP International Release 16 Specification Set expanded on the C-V2X operating scenarios for the 5G new radio (NR), which include standalone (SA) and non-standalone (NSA) deployments. TS 38.101.1 defines two frequency ranges, FR1 and FR2, where 5G NR-based radio communication could be established [43]. The corresponding frequency ranges are 410 MHz-7125 MHz and 24.25 GHz-52.6 GHz for FR1 and FR2, respectively. Radio coverage for the Uu sidelink during the initial rollouts of the 5G NR networks will be not as extensive as LTE, hence, C-V2X control should be handled by both with seamless handovers. The PC5 interface is based on both 5G NR and LTE. TR 38.885 provides insight on different operating scenarios, where sidelink communication can be done in both FR1 and FR2 if a common design framework is used [44]. According to TR 38.886, the 5G NR C-V2X operating band n47 should use up to 40 MHz channel bandwidth--a two-fold increase from LTE-based C-V2X [45]. Uu sidelinks remain in the same licensed bands. 5G NR-based C-V2X service latency requirements are in TR 22.886 [46]. The most strict latency requirement is for fully automated driving--no more than 3 ms, with data rates peaking at 1000 Mbps, although most of the communication scenarios maximum end-to-end latencies are given around 20 ms--100 ms (can be as high as 500 ms for non-critical services) and data rates not exceeding 100 Mbps.