In the UMTS (Universal Mobile Telecommunications System) network, the specifications of long term evolution (LTE) have been drafted for the purpose of further increasing high speed data rates, providing lower delay and so on (see non-patent literature 1). In LTE, as multiple access schemes, a scheme that is based on OFDMA (Orthogonal Frequency Division Multiple Access) is used in downlink channels (downlink), and a scheme that is based on SC-FDMA (Single Carrier Frequency Division Multiple Access) is used in uplink channels (uplink). Also, successor systems of LTE (referred to as, for example, “LTE-advanced” or “LTE enhancement” (hereinafter referred to as “LTE-A”)) are under study for the purpose of achieving further broadbandization and increased speed beyond LTE, and the specifications thereof have been drafted as Rel. 10/11.
Also, the system band of the LTE-A system (Rel. 10/11) includes at least one component carrier (CC), where the system band of the LTE system constitutes one unit. Gathering a plurality of CCs to achieve a wide band in this way is referred to as “carrier aggregation” (CA). Note that CCs will be hereinafter simply referred to as “cells.”
Also, in LTE Rel. 10/11, cross-carrier scheduling (CCS) is introduced in order to realize stable transmission/reception of control signals. CCS makes it possible to report downlink control information (DCI) pertaining to a cell that transmits/receives signals using a shared data channel (PDSCH (Physical Downlink Shared Channel)/PUSCH (Physical Uplink Shared Channel)), via a control channel (PDCCH: Physical Downlink Control Channel) that is allocated to another cell.
In another successor system of LTE (LTE Rel. 12), various scenarios, in which a plurality of cells use frequency bands (carriers), are under study. When the radio base stations to form a plurality of cells are substantially the same, above-described CA (also referred to as “intra-eNB CA”) can be applied. On the other hand, when the radio base stations to form a plurality of cells are completely different, dual connectivity (DC) (also referred to as “inter-eNB CA”) may be applied. When DC is used, a user terminal needs to be structured to be able to allocate uplink control information (UCI) to an uplink control channel (PUCCH: Physical Uplink Control Channel) and send feedback to the radio base stations, not only in the primary cell (PCell), but also in at least one secondary cell (SCell). Hereinafter, the sending of UCI feedback via the PUCCH in at least one SCell will be also referred to as “PUCCH on SCell.”