TECHNICAL FIELD

The present disclosure relates to a user terminal and a radio communication method of a next-generation mobile communication system.

BACKGROUND ART

In Universal Mobile Telecommunications System (UMTS) networks, for the purpose of higher data rates and lower latency, Long Term Evolution (LTE) has been specified (Non-Patent Literature 1). Furthermore, for a larger volume and higher sophistication of LTE (LTE Rel. 8 and 9), LTE-Advanced (LTE-A or LTE Rel. 10, 11, 12 and 13) has been specified.

LTE successor systems (also referred to as, for example, Future Radio Access (FRA), the 5th generation mobile communication system (5G), 5G+(plus), New Radio (NR), New radio access (NX), Future generation radio access (FX) or LTE Rel. 14, 15 or subsequent releases) have been also studied.

According to legacy LTE (e.g., LTE Rel. 13), a user terminal (UE: User Equipment) transmits a Sounding Reference Signal (SRS) to measure a channel on uplink.

Furthermore, a base station (e.g., eNodeB (eNB)) transmits a downlink control channel (UL grant) for instructing scheduling of UL data (uplink shared channel (PUSCH: Physical Uplink Shared Channel)), and the UE transmits the UL data according to the UL grant.

CITATION LIST

Non-Patent Literature

Non-Patent Literature 1: 3GPP TS 36.300 V8.12.0 “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 8)”, April 2010

SUMMARY OF INVENTION

Technical Problem

It has been studied that, in a future radio communication system (e.g., NR), a UE decides a precoder for PUSCH transmission based on at least an SRS Resource Index (SRI). The precoder based on the SRI may be referred to as an SRS precoder.

It has been studied that the UE determines the SRS precoder based on a CSI-RS. However, study regarding specifically which CSI-RS is used to determine the SRS precoder, i.e., a UE operation related to the CSI-RS for determining the SRS precoder has not developed yet. There is a risk that, if the operation is not appropriately determined, a system throughput lowers.

It is therefore one of objects of the present disclosure to provide a user terminal and a radio communication method that can appropriately determine an SRS precoder.

Solution to Problem

A user terminal according to one aspect of the present disclosure includes: a control section that identifies a resource for a Channel State Information-Reference Signal (CSI-RS); and a transmitting section that transmits a Sounding Reference Signal (SRS) by using a precoder based on the latest transmitted resource.

Advantageous Effects of Invention

According to the present disclosure, it is possible to appropriately determine an SRS precoder.

