Extract the technique feature of the following claim and make a list with index:1. A method for transmitting demodulation reference signals (DMRSs) for data in a wireless communication system, the method comprising:  transmitting a basic DMRS on a first OFDM symbol within a time domain unit; and  transmitting one or more additional DMRSs on one or more second OFDM symbols located after the first OFDM symbol within the time domain unit;  wherein a position of the first OFDM symbol is variable based on mapping type of a data region related with a location of starting OFDM symbol and a length of the data region,  wherein the position of the first OFDM symbol, used for a first mapping type, is determined as a first position or a second position within the time domain unit,  wherein positions of the second OFDM symbols are determined based on a presence of the first OFDM symbol, a number of the second OFDM symbols and a number of OFDM symbols within the data region, and  wherein the positions of the second OFDM symbols, used for the first mapping type, are determined regardless of determined position of the first OFDM symbol as the first position or the second position. Write exactly 5 paragraphs each separated with two new lines answering this question. The first paragraph must start with "freeze".
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