Radio base station, user terminal and radio communication method

Patent metadata

Field	Value
Publication number	US-2016197709-A1
Application number	US-201414916586-A
Country	US
Kind code	A1
Filing date	Sep 2, 2014
Priority date	Sep 6, 2013
Publication date	Jul 7, 2016
Grant date	—

Abstract

The present invention is designed so that, in a communication system to employ massive MIMO, data signals to which beamforming is applied can be transmitted adequately. A radio base station transmits a data signal to a user terminal by applying beamforming using a plurality of antenna elements, and has a determining section that determines the type of a weight to apply to the data signal for beamforming, a generating section that generates a reference signal which the user terminal uses in channel estimation, a weight control section that controls weights to apply to transmitting signals, and a transmitting section that transmits the data signal and the reference signal, and the weight control section determines whether or not to apply a weight to the reference signal based on the type of the weight.

First claim

1 . A radio base station that transmits a data signal to a user terminal by applying beamforming using a plurality of antenna elements,
the radio base station comprising: a determining section that determines a type of a weight to apply to the data signal for beamforming; a generating section that generates a reference signal which the user terminal uses in channel estimation; a weight control section that controls weights to apply to transmitting signals; and a transmitting section that transmits the data signal and the reference signal, wherein the weight control section determines whether or not to apply a weight to the reference signal based on the type of the weight.

2 . The radio base station according to claim 1 , wherein:
the determining section determines the number of streams to apply to the transmission of the data signal, in addition to the type of the weight; and the generating section generates reference signals to match the number of streams.

3 . The radio base station according to claim 1 , wherein, when the determining section selects a fixed weight as the type of the weight, the weight control section applies predetermined fixed weights to the reference signal and the data signal, and the transmitting section transmits the reference signal and the data signal to which the predetermined fixed weights are applied.

4 . The radio base station according to claim 3 , wherein the predetermined fixed weights are fixed weights applied to synchronization signals which the user terminal detects upon cell search.

5 . The radio base station according to claim 1 , wherein, when the determining section selects an adaptive weight as the type of the weight, the transmitting section transmits the reference signal without applying beamforming, and the weight control section generates weights based on channel state information that is fed back from the user terminal in response to a reference signal to which beamforming is not applied, and applies the generated weight to the data signal.

6 . The radio base station according to claim 2 , wherein, when the determining section selects a plurality of streams, the transmitting section orthogonalizes and transmits reference signals corresponding to each stream.

7 . The radio base station according to claim 6 , wherein, when the determining section selects a fixed weight as the type of the weight and also selects the plurality of streams, the weight control section applies varying weights to reference signals and data signals corresponding to each stream.

8 . The radio base station according to claim 2 , wherein the transmitting section reports information about the type of the weight and/or the number of streams to the user terminal.

9 . A user terminal that receives a data signal to which beamforming is applied and which is transmitted from a radio base station comprising a plurality of antenna elements, the user terminal comprising:
an acquiring section that acquires channel state information base on a reference signal transmitted from the radio base station; a weight generating section that generates a receiving weight based on the channel state information; and a feedback control section that controls feedback of the channel state information based on a type of the reference signal transmitted from the radio base station.

10 . A radio communication method for a radio base station that comprises a plurality of antenna elements and a user terminal that receives a data signal to which beamforming is applied and which is transmitted from the radio base station, the radio communication method comprising, in the radio base station, the steps of:
determining a type of a weight to apply to the data signal for beamforming; generating a reference signal which the user terminal uses in channel estimation; determining whether or not to apply a weight to the reference signal based on the type of the weight; and transmitting the data signal and the reference signal, wherein, when the type of the weight is a fixed weight, the reference signal and the data signal are applied predetermined weights and transmitted, and, when the type of the weight is an adaptive weight, the reference signal is transmitted without being applied beamforming.

11 . The radio base station according to claim 2 , wherein, when the determining section selects a fixed weight as the type of the weight, the weight control section applies predetermined fixed weights to the reference signal and the data signal, and the transmitting section transmits the reference signal and the data signal to which the predetermined fixed weights are applied.

12 . The radio base station according to claim 2 , wherein, when the determining section selects an adaptive weight as the type of the weight, the transmitting section transmits the reference signal without applying beamforming, and the weight control section generates weights based on channel state information that is fed back from the user terminal in response to a reference signal to which beamforming is not applied, and applies the generated weight to the data signal.

Assignees

• Ntt Docomo Inc

Inventors

• Shen Jiyun
• Suyama Satoshi
• Okumura Yukihiko

Classifications

• H04B7/0417

  Feedback systems · CPC title

• H04W16/28

  using beam steering · CPC title

• H04L5/0048 Primary

  Allocation of pilot signals, i.e. of signals known to the receiver (allocation of control signalling H04L5/0053; use of control signalling H04L5/0091) · CPC title

• H04W88/08

  Access point devices · CPC title

• H04B7/0617

  for beam forming · CPC title