TECHNICAL FIELD

The present invention relates to a user terminal, a radio base station and a radio communication method in a next-generation mobile communication system.

BACKGROUND ART

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 latency and so on (see non-patent literature 1). Also, the specifications of LTE-A (also referred to as “LTE-advanced,” “LTE Rel. 10,” “LTE Rel. 11,” or “LTE Rel. 12”) have been drafted for further broadbandization and increased speed beyond LTE (also referred to as “LTE Rel. 8” or “LTE Rel. 9”), and successor systems of LTE (also referred to as, for example, “FRA (Future Radio Access),” “5G (5th generation mobile communication system),” “NR (New Radio),” “NX (New radio access),” “New RAT (Radio Access Technology),” “FX (Future generation radio access),” “LTE Rel. 13,” “LTE Rel. 14,” “LTE Rel. 15” or later versions) are under study.

In LTE Rel. 10/11, carrier aggregation (CA) to integrate multiple component carriers (CC) is introduced in order to achieve broadbandization. Each CC is configured with the system bandwidth of LTE Rel. 8 as one unit. In addition, in CA, multiple CCs under the same radio base station (eNB (eNodeB)) are configured in a user terminal (UE (User Equipment)).

Meanwhile, in LTE Rel. 12, dual connectivity (DC), by which multiple cell groups (CGs) are formed by different radio base stations and configured in UE, is also introduced. Each cell group is comprised of at least one cell (CC). Since multiple CCs of different radio base stations are aggregated in DC, DC is also referred to as “inter-base station CA (inter-eNB CA).”

Also, in existing LTE systems (for example, LTE Rel. 8 to 13), in order to reduce the power consumption of user terminals, the operation of discontinuous reception (DRX) in idle mode is supported. Also, user terminals in idle mode control measurements of RSRP/RSRQ for cell reselection, monitoring/reception of the paging channel (PCH), and so on, based on the DRX cycle. Incoming calls, changes of broadcast information (system information), ETWS, and so on are reported to user terminal via the paging channel.

CITATION LIST

Non-Patent Literature

Non-Patent Literature 1: 3GPP TS 36.300 “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2”

SUMMARY OF INVENTION

Technical Problem

Future radio communication systems (for example, 5G, NR, etc.) are anticipated to implement various radio communication services by fulfilling various requirements (for example, ultra-high speed, large capacity, ultra-low latency, and so on).

For example, in 5G, research has been conducted to provide radio communication services, referred to as “eMBB (enhanced Mobile Broad Band),” “IoT (Internet of Things),” “MTC (Machine Type Communication),” “M2M (Machine To Machine),” “URLLC (Ultra Reliable and Low Latency Communications)” and so on. Note that M2M may be referred to as “D2D (Device To Device),” “V2V (Vehicle To Vehicle)” and so on, depending on what communication device is used. To fulfill the requirements for various types of communication such as listed above, studies are in progress to design new communication access schemes (new RAT (Radio Access Technology)).

For 5G, studies are underway to provide services using a very high carrier frequency of 100 GHz, for example. Generally speaking, it is more difficult to secure coverage when the carrier frequency increases. Reasons for this include that the distance-induced attenuation becomes more severe and the rectilinearity of radio waves becomes stronger, the transmission power density decreases because ultra-wideband transmission is performed, and so on.

Therefore, in order to fulfill the requirements for various types of communication such as those mentioned above even in high frequency bands, there are on-going studies to examine the use of massive MIMO (Multiple Input Multiple Output), which uses a very large number of antenna elements. When a very large number of antenna elements are used, beams (antenna directivities) can be formed by controlling the amplitude and/or the phase of signals transmitted/received in each element. This process is also referred to as “beamforming (BF),” and makes it possible to reduce the propagation loss of radio waves.

A radio base station that uses beamforming can communicate properly by applying appropriate transmitting beams (beam patterns) to each user terminal and transmitting and/or receiving signals accordingly. Meanwhile, the radio base station cannot determine which beam pattern is appropriate for user terminals that are in idle mode. Therefore, a method for transmitting and/or receiving signals that are suitable for user terminals in idle mode and so on, by using beamforming, is in demand.

The present invention has been made in view of the above, and it is therefore an object of the present invention to provide a user terminal, a radio base station and a radio communication method that allow beamforming to be executed properly even when user terminals are in idle mode.

Solution to Problem

A user terminal according to one aspect of the present invention communicates with a radio base station that uses a plurality of beam patterns, and has a receiving section that performs a receiving process for paging information which is transmitted in varying beam patterns, in a paging time period comprised of a plurality of unit periods, and a transmission section that transmits an uplink signal.

Advantageous Effects of Invention

According to the present invention, it is possible to execute beamforming properly even when user terminals are in idle mode.

