ed around an SS block or not. This is related to the fact that the gNB may choose not to transmit some SS blocks, as we mentioned in previous chapters. PDSCH DMRS One difference between LTE and PDSCH mapping is the position of the Demodulation Reference Signal (DMRS). In NR, the PDSCH DMRS is front-loaded. This means that DMRS is located very early in the slot. Thus, a device can make a channel quality estimation sooner and start decoding very early in the slot transmission, which results in reduced latency. There are two mapping types for the modulation reference signals, namely, DMRS mapping Type A and DMRS mapping Type B. Type A uses slot-based scheduling. In Type A, the DMRS OFDM symbol is fixed regardless of the PDSCH assignment, and it is configurable between OFDM symbols 2 and 3. In Type B, the first OFDM symbol is assigned to the PDSCH: 5G Air Interface and Physical Layer Procedures - Part 3 1 or 2 front-loaded symbols 1 or 2 front-loaded - plus late DMRS symbols 2 or 3 additional DM RS for high Doppler symbols symbols Figure 6.2 - PDSCH mapping Type A Type B employs non-slot-based scheduling in which assignments are not referred to the slot boundaries. This makes it impossible to use a fixed location for the DMRS in the slot due to the mini slots, which can be assigned anywhere in the slot. 2 symbol PxSCH symbols 4 symbol PxSCH symbols 1 additional DMRS can be configured for 7 symbol PxSCH symbols 1st/2nd and 5th/6th symbols Figure 6.3 PDSCH mapping Type B If a single channel estimation at the beginning of a slot is not enough for example, in high-speed mobility scenarios- additional DMRS symbols can be configured. This is the case, for instance, for a PDSCH that carries broadcast information, Remaining Minimum System Information (RMSI), or multicast information. The gNB will have to transmit this information to many devices and it will not know which devices are in high-speed or not, SO it will use these extra DMRS symbols as a precaution. Now, we will cover other PDSCH-related aspects. The PDSCH proces