A data communication apparatus , for transmitting one or more blocks of data within a frame comprising a two-dimensional grid of transmission symbol positions , wherein the data communication apparatus is configured to select a group of transmission symbol positions, which is a subset of the two-dimensional grid of transmission symbol positions, for a transmission of a data portion, wherein a length of a selected group of transmission symbol positions is a short transmission time interval; wherein one or more reference symbol positions (DMRS; 1840a,1841a,1842a,1843a,1844a,1845a,1846a) are associated to the selected group of transmission symbol positions; wherein the data communication apparatus is configured to determine which one or more symbol positions are used as one or more reference symbol positions based on the selection of the group of transmission symbol positions or together with the selection of the group of transmission symbol positions; and wherein the reference symbol positions are variable with respect to one or more borders of time slots of the frame or with respect to one or more borders of sub-frames of the frame, and/or wherein the one or more reference symbol positions (DMRS; 1840a, 1841a, 1842a, 1843a, 1844a, 1845a, 1846a) are variable with respect to the selected group of transmission symbol positions; wherein the data communication apparatus is configured to receive a signaling which overall resource allocation scheme out of a plurality of possible overall resource allocation schemes should be used, wherein the overall resource allocation scheme indicates reference symbol positions for a plurality of groups of transmission symbol positions which are short transmission time intervals; and wherein the data communication apparatus is configured to obtain an information about the one or more reference symbol positions for the selected group of transmission symbol positions from the overall resource allocation scheme. wherein the data communication apparatus is configured to select a group of transmission symbol positions, which is a subset of the two-dimensional grid of transmission symbol positions, for a transmission of a data portion, wherein a length of a selected group of transmission symbol positions is a short transmission time interval; wherein one or more reference symbol positions (DMRS; 1840a,1841a,1842a,1843a,1844a,1845a,1846a) are associated to the selected group of transmission symbol positions; wherein the data communication apparatus is configured to determine which one or more symbol positions are used as one or more reference symbol positions based on the selection of the group of transmission symbol positions or together with the selection of the group of transmission symbol positions; and wherein the reference symbol positions are variable with respect to one or more borders of time slots of the frame or with respect to one or more borders of sub-frames of the frame, and/or wherein the one or more reference symbol positions (DMRS; 1840a, 1841a, 1842a, 1843a, 1844a, 1845a, 1846a) are variable with respect to the selected group of transmission symbol positions; wherein the data communication apparatus is configured to receive a signaling which overall resource allocation scheme out of a plurality of possible overall resource allocation schemes should be used, wherein the overall resource allocation scheme indicates reference symbol positions for a plurality of groups of transmission symbol positions which are short transmission time intervals; and wherein the data communication apparatus is configured to obtain an information about the one or more reference symbol positions for the selected group of transmission symbol positions from the overall resource allocation scheme. <EOS>