where the first DM-RS is located in the second and the third symbol of the slot and the DM-RS is mapped relative to the start of the slot boundary, regardless of where in the slot the actual data transmission occurs. This mapping type is primarily intended for the case where the data occupy (most of) a slot. The reason for the use of the second or the third symbol in the downlink slot is to locate the first DM-RS occasion after a CORESET that is positioned at the beginning of a slot (see Fig. 4.2). Mapping Type B, where the first DM-RS is positioned in the first symbol of the data allocation, that is, the DM-RS location is not given relative to the slot boundary, rather relative to where the data are located. This mapping is intended for transmissions over a small fraction of the slot to support very low latency and other transmissions that cannot wait until a slot boundary starts regardless of the transmission duration. The mapping type for PDSCH transmission can be dynamically signaled as part of the downlink control information (DCI), while for the physical uplink shared channel (PUSCH) the mapping type is semi-statically configured (see Fig. 4.2). The different time-domain locations for (PDSCH) DM-RS mapping types are illustrated in Figs. 4.2 and 4.3, including both single-symbol and double-symbol DM-RS patterns. The purpose of the double-symbol DM-RS is primarily to provide a larger number of antenna ports than what is possible with a single-symbol structure as discussed later. Note that the time-domain location of the DM-RS depends on the scheduled data duration. Multiple orthogonal reference signals can be generated in each DM-RS occasion. Different DM-RS patterns can be configured which are separated in time, frequency, and code domains. The DM-RS has two types: that is, Types 1 and 2, which are distinguished in frequency-domain mapping and the maximum number of orthogonal reference signals. Type 1 can provide up to four orthogonal signals using a single-symbol DM-RS and up to eight orthogonal reference s