TECHNICAL FIELD

The present invention relates to a communication control method, a radio communication system, a radio base station and a user terminal that are applicable to cellular systems and so on.

BACKGROUND

In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rates. With this UMTS network, long-term evolution (LTE) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1).

In a third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in an LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band, which ranges from 1.4 MHz to 20 MHz. Also, in the UMTS network, successor systems of the LTE system (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.

In radio communication, as uplink (UL) and downlink (DL) duplexing methods, there are frequency division duplexing (FDD), which divides between the uplink and the downlink based on frequency, and time division duplexing (TDD), which divides between the uplink and the downlink based on time. In the event of TDD, the same frequency is applied to uplink and downlink transmission, so that the uplink and the downlink are divided based on time and transmitted from one transmitting point. Since the same frequency is used between the uplink and the downlink, a transmitting point (radio base station) and a user terminal both have to switch between transmission and reception alternately.

Also, in TDD in the LTE system, frame configurations (transmission ratios between uplink subframes and downlink subframes (DL/UL configurations)) to support a plurality of different types of asymmetrical uplink/downlink resource allocation are defined (seeFIG. 1). In the LTE system, as shown inFIG. 1, seven frame configurations, namely DL/UL configurations0to6, are defined, where subframes #0and #5are allocated to the downlink and subframe #2is allocated to the uplink. Also, to prevent interference between transmitting points (or between cells), the same DL/UL configuration is applied between neighboring transmitting points.

CITATION LIST

Non-Patent Literature

Non-Patent Literature 1: 3GPP, TR25.912 (V7.1.0), “Feasibility Study for Evolved UTRA and UTRAN,” September 2006

SUMMARY OF INVENTION

However, in TDD in the LTE-A system, in order to allow efficient use of radio resources, a study is in progress to change the transmission ratio of DL and UL dynamically or semi-statically in the time domain, per transmitting/receiving point—that is, change the DL/UL configuration to apply on a per transmitting/receiving point basis. When different DL/UL configurations are applied between neighboring transmitting/receiving points, cases might occur where, in the same time region/frequency region, a DL subframe and a UL subframe are transmitted at the same time between neighboring transmitting/receiving points (cases where an uplink signal and a downlink signal are transmitted at the same time).

In this case, depending on the location and transmission power of each transmitting/receiving point (or user terminal) and so on, there is a threat that interference is produced between transmitting/receiving points and between user terminals, and the performance of communication quality deteriorates.

The present invention has been made in view of the above, and it is therefore an object of the present invention to provide communication control method, a radio communication system, a radio base station and a user terminal that can reduce the deterioration of communication quality even when different DL/UL configurations are applied between neighboring transmitting/receiving points (radio base stations).

The communication control method of the present invention is a communication control method in a radio communication system in which a plurality of radio base stations that communicate with a user terminal by means of time division duplexing each change a DL/UL configuration independently, and this communication control method includes the steps in which each radio base station generates a control signal that designates the number and positions of subframes to be allocated for DL and/or UL transmission among subframes constituting a radio frame, and transmits the control signal to the user terminal on a downlink control channel of a specific subframe constituting the radio frame.

According to the present invention, it is possible to reduce the impact of interference even when different DL/UL configurations are applied between neighboring transmitting/receiving points (radio base stations).

