NR (new radio) demodulation reference signal (DMRS) ports mapping and related signaling

A user equipment comprising:

• a receiver, which, in operation,
• receives a parameter defining a configuration for assigning to ports respective resources for carrying reference signals, and
• receives, from a base station, control information indicating one of a set of layer-to-port mapping combinations which is to be applied for data transmission and/or reception;
• and
• circuitry, which, in operation, performs the data transmission and/or reception based on the indicated layer-to-port mapping combination;
• wherein the resources carrying the reference signals are located on one or more symbols in a time domain, wherein the set of layer-to-port mapping combinations are continuously indexed including one-symbol layer-to-port mapping combinations for the reference signals located on one symbol and two-symbol layer-to-port mapping combinations for the reference signals located on two symbols,
• wherein first indices of the continuous indices indicate the one-symbol layer-to-port mapping combinations followed by second indices for the two-symbol layer-to-port mapping combinations, and
• wherein, of the set of layer-to-port mapping combinations, the two-symbol layer-to-port mapping combinations for n layers (where n is 2 or more) include first mapping combinations and a second mapping combination which is continuously indexed next to the first mapping combinations, the first mapping combinations having consecutive port numbers of which at least one port number is duplicated in the second mapping combination.