Abstract: The present invention is designed to reduce interference between cells even when a plurality of cells are placed at a high density. In a radio base station, a receiving section that receives an uplink signal transmitted from a user terminal, and an interference estimation section that estimates the level of interference received from an other cell based on an uplink signal transmitted from a user terminal of the other cell, are provided, and the interference estimation section estimates the level of interference of each cell based on the uplink signal, and a blank state is assumed in the uplink signal at a resource position that varies on a per cell basis. Furthermore, a control section that controls a predetermined resource position in an uplink signal transmitted from a serving user terminal to assume the blank state, is provided.

Abstract: In order to achieve enough randomization of uplink control signals between a plurality of small cells located in a macro cell and to simplify cell planning of the small cells, the present invention provides a user terminal that is capable of communicating with a macro base station covering a macro cell and a small base station covering a small cell located within the macro cell. The user terminal generates uplink signals using uplink signal sequences of zero autocorrelation except at a synchronization point, and allocates the uplink signals to subframes by using a hopping pattern where a sequence number of an uplink signal sequence is switched per subframe in a predetermined cycle. A hopping cycle of the uplink signal sequences in a hopping pattern for the small base station is longer than a hopping cycle of the uplink signal sequences in a hopping pattern for the macro base station.

Abstract: In order to compensate for frequency errors even when introducing a new carrier, the present invention provides a radio base station having a configuring section that configures a first carrier type subframe in which cell-specific reference signals are mapped at a predetermined density, and a second carrier type subframe in which cell-specific reference signals are mapped at a density that is lower than the density of the first carrier type subframe; a generating section that, when configuring the second carrier type subframe, generates at least a synchronization signal to use for frequency synchronization; and a transmitting section that transmits association information for associating the synchronization signal with an other downlink signal that is transmitted in the second carrier type subframe.

Abstract: The present invention is designed to establish synchronization between transmission points when downlink signals are transmitted from a plurality of transmission points to a user terminal. A radio communication system has a first radio base station that forms a first cell, a second radio base station that forms a second cell, which is placed on the area of the first cell in an overlapping manner, and a user terminal that is capable of carrying out radio communication with the first radio base station and the second radio base station, and the second radio base station has a receiving section that receives synchronization correction information, which is for establishing synchronization with a synchronization target, from the user terminal, and a synchronization correction section that corrects synchronization based on the synchronization correction information.

Abstract: The present invention aims to realize an uplink assignment information structure that is optimal for signaling of uplink assignment information when a plurality of frequency bands are assigned to an uplink data channel. In a radio communication system where a plurality of frequency bands are assigned to one user on the uplink, uplink assignment information including uplink resource allocation information in which resources are allocated in a bitmap format is defined, this uplink assignment information is formed in the same bit size as downlink assignment information (for example, DCI format 1), in which downlink resource allocation information in which resources are allocated on a bitmap basis is included, and the interpretation of part of the bits of the downlink assignment information (DCI format 1) is changed, so that it is possible to identify the uplink assignment information of the same bit size.