| CPC H04B 7/0626 (2013.01) [H04L 25/0224 (2013.01); H04B 17/309 (2015.01); H04L 25/0202 (2013.01)] | 20 Claims |

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1. An operating method of a user equipment (UE), the operating method comprising:
receiving channel state information-reference signal (CSI-RS) configuration information from a base station, the CSI-RS configuration information including time and frequency location information of a first CSI-RS, and the first CSI-RS corresponding to a first density value of 0.5, 1 or 3;
determining whether to request a second CSI-RS having a second density value based on a comparison between a first delay spread and a reference value, the second density value being different from the first density value, the first delay spread corresponding to a channel between the UE and the base station, and the first delay spread being determined from the first CSI-RS;
transmitting a CSI-RS density change request message to the base station in response to determining to request the second CSI-RS;
receiving the second CSI-RS from the base station based on the CSI-RS configuration information, the second CSI-RS being based on the CSI-RS density change request message;
estimating the channel based on the second CSI-RS to obtain a channel estimate; and
transmitting a CSI-RS report to the base station, the CSI-RS report being based on the channel estimate.
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