 of DMRS is increased to track fast changes in the radio channel. PRACH design includes considerations for high-speed mobility. For short sequences, large subcarrier spacings (15 and 30 kHz) provide in-built protection against the 10 5G Performance Doppler shift. For long sequences and low subcarrier spacings (1.25 and 5 kHz), restricted sets can be used. These are based on specific cyclic shifts that can be used for the Zadoff Chu sequence with high Doppler. Layer 3 (RRC based) mobility framework with flexible filtering and reporting capa- bility. Beam management framework with configurable Channel State Information Refer- ence Signal (CSI-RS) transmission and reporting. When the UE is moving, it will experience a Doppler shift that changes the carrier frequency of the base station radio transmission. The amount of Doppler shift depends on the angle a between the direction of motion of the UE and the propagation vector of the radio wave. The Doppler shift is calculated as follows: Dopper shift= where V is the UE speed in meters per second, C is the speed of light in meters per second, fc is the carrier frequency in Hz, and a is the angle between the velocity vector and LOS with the receiver. The Doppler shift is maximum if the UE moves along the radio propa- gation line, while it is zero if the UE moves perpendicularly against the radio propagation vector. The Doppler shift and the change of shift are illustrated in Figure 10.71 for the case where the UE passes the base station and the Doppler shift changes rapidly from positive to negative values. The practical Doppler shift experienced by the UE can be smaller since the UE synchronizes to the downlink signal. On other hand, the Doppler shift in the uplink can be correspondingly higher. OFDM-based systems rely on the orthogonal spacing between the subcarriers, and receiver performance depends on their good localization in the frequency domain. Oth- erwise, OFDM receivers suffer from inter-carrier and inter-symbol interferences. Fre- quency error may also be cau