2.1. Important KPIs of Positioning for C-V2X

With the evolution of V2X services from assisted driving to autonomous driving, the use case requirements are also changing the availability of network coverage, level of uncertainty, availability of features for simultaneous localization and mapping (SLAM)-based positioning techniques, reliability, latency, speed, data rate, communication range, as well as positioning accuracy, which varies from meter level to sub-meter level. Some important KPIs are described as follows [13]:

Position Accuracy: describes the closeness of the measured position of the UE to its true position value. The accuracy can describe the accuracy either of an absolute position or a relative position. It can be further derived into a horizontal position accuracy—referring to the position error in a 2D reference or horizontal plane, and into a vertical position accuracy—referring to the position error on the vertical axis or altitude.

Availability: percentage of time when a positioning system can provide the required position-related data within the performance targets or requirements.

Update rate: the rate at which the position-related data is generated by the positioning system. It is the inverse of the time elapsed between two successive position-related data.

Reliability: the measure of the ability of a positioning system to provide the position-related data under stated conditions for a specified period.

Latency: time elapsed between the event that triggers the determination of the position-related data and the availability of the position-related data at the positioning system interface. At the initialization of the positioning system, the latency is also defined as the Time to First Fix. Though it is capable of achieving centimeter-level accuracy and is widely used for mapping, its application to real-time positioning is problematic due to the scanning and processing latency.

Power consumption: electrical power (usually in milliwatt) used by the positioning system to produce the position-related data.

The accuracy requirements are different according to different business scenarios. Table 1 shows some positioning accuracy requirements in different use cases for business scenarios involving information service, vehicle safety, and traffic efficiency [14].

Positioning accuracy requirements in different use cases.