US-12621026-B2 - Radio communication apparatus, method for radio communication apparatus, and non-transitory computer readable medium

US12621026B2US 12621026 B2US12621026 B2US 12621026B2US-12621026-B2

Abstract

An object of the present disclosure is to provide a radio communication device, a method for a radio communication device, and a program with which it is possible to perform calibration of an antenna easily. A radio communication device according to the present disclosure comprises: a calibration control unit that performs DL control to transmit a calibration downlink (DL) signal from an antenna other than one of a plurality of antennas DA and to receive a calibration DL signal by the one antenna, and UL control to transmit a calibration uplink (UL) signal from the one antenna and to receive a calibration UL signal by the antenna other than the one antenna; and a calibration coefficient calculating unit that calculates a calibration coefficient on the basis of a DL channel coefficient of a transmitter and a UL channel coefficient of a receiver.

Inventors

Noriaki TAWA
Toshihide Kuwabara

Assignees

NEC CORPORATION

Dates

Publication Date: 20260505
Application Date: 20211105
Priority Date: 20201217

Claims (8)

1 . A radio communication apparatus comprising: at least one memory storing instructions, and at least one processor configured to execute the instructions to: perform, for each of a plurality of antennas, down link (DL) control for transmitting a calibration DL signal from an antenna other than one antenna among a plurality of the antennas and receiving the calibration DL signal by the one antenna, and up link (UL) control for transmitting a calibration UL signal from the one antenna and receiving the calibration UL signal by the antenna other than the one antenna; calculate a DL channel coefficient of a transmitter and a UL channel coefficient of a receiver that are connected to the antenna for each of a plurality of the antennas, based on the calibration DL signal being transmitted from a plurality of the antennas and the calibration DL signal being received by a plurality of the antennas in the DL control, and the calibration UL signal being transmitted from a plurality of the antennas and the calibration UL signal being received by a plurality of the antennas in the UL control; calculate a calibration coefficient for calibrating a radio DL signal, based on the DL channel coefficient and the UL channel coefficient; adjust a phase and an amplitude of the radio DL signal being transmitted from each of a plurality of the antennas, based on the calibration coefficient; calculate, for each of a plurality of the antennas, a plurality of the DL channel coefficients being associated with the antenna other than the one antenna, based on the calibration DL signal during transmission being transmitted from the antenna other than the one antenna and the calibration DL signal during reception being received by the one antenna; calculate, for each of a plurality of the antennas, a plurality of the UL channel coefficients being associated with the antenna other than the one antenna, based on the calibration UL signal during transmission being transmitted from the one antenna and the calibration UL signal during reception being received by the antenna other than the one antenna; calculate the calibration coefficient for calibrating the radio DL signal, based on the DL channel coefficient and the UL channel coefficient that are calculated from a plurality of calibration measurements acquired by the DL control and the UL control; calculate, as a channel coefficient ratio, a proportion of the DL channel coefficient to the UL channel coefficient being calculated from a plurality of the calibration measurements; select, as a reference channel coefficient ratio, one of the channel coefficient ratios of a plurality of the calibration measurements; calculate, as a correction coefficient between a plurality of calibration measurements, a proportion of the reference channel coefficient ratio to the channel coefficient ratio of a plurality of the calibration measurements; and correct a proportion of the DL channel coefficient to the UL channel coefficient with respect to a plurality of the calibration measurements by using the correction coefficient between a plurality of the calibration measurements.
2 . The radio communication apparatus according to claim 1 , wherein the at least one processor is further configured to: calculate an average correction coefficient by taking an average of the correction coefficient between a plurality of the calibration measurements being calculated in a plurality of the calibration measurements; and newly set the average correction coefficient as the correction coefficient.
3 . The radio communication apparatus according to claim 1 , wherein the at least one processor is further configured to: perform the calibration measurement for a plurality of times, and acquire a weighted coefficient, based on received power of the calibration DL signal or the calibration UL signal, when a plurality of the DL channel coefficients and the UL channel coefficients are acquired for the one antenna; calculate, as a UL/DL channel coefficient ratio, a ratio of the DL channel coefficient to the UL channel coefficient for each of the calibration measurements from the DL channel coefficient and the UL channel coefficient; perform, by using the correction coefficient, correction between the calibration measurements on the UL/DL channel coefficient ratio for each of the calibration measurements; calculate, for each of a plurality of the antennas, a weighted average UL/DL channel coefficient ratio acquired by performing weighted averaging between a plurality of the calibration measurements, based on the weighted coefficient, on the UL/DL channel coefficient ratio for each of the corrected calibration measurements; and newly set the weighted average UL/DL channel coefficient ratio as the calibration coefficient.
4 . The radio communication apparatus according to claim 1 , wherein the at least one processor is configured to perform control in such a way that the calibration DL signal having a different frequency is transmitted from each of a plurality of the antennas.
5 . The radio communication apparatus according to claim 1 , wherein, when a difference between a temperature of any of a plurality of the antennas and a temperature during previous calibration is equal to or more than a predetermined temperature, or when a difference between an average temperature of all of the antennas and a temperature during previous calibration is equal to or more than the predetermined temperature, the at least one processor is configured to adjust a phase and an amplitude of the radio DL signal again.
6 . The radio communication apparatus according to claim 1 , wherein: the antenna other than the one antenna is an antenna constituting a multiple input multiple output (MIMO), and the one antenna is an external antenna that is not an antenna constituting the MIMO.
7 . A method for a radio communication apparatus, comprising: performing, for each of a plurality of antennas, down link (DL) control for transmitting a calibration DL signal from an antenna other than one antenna among a plurality of the antennas and receiving the calibration DL signal by the one antenna, and up link (UL) control for transmitting a calibration UL signal from the one antenna and receiving the calibration UL signal by the antenna other than the one antenna; calculating a DL channel coefficient of a transmitter and a UL channel coefficient of a receiver that are connected to the antenna for each of a plurality of the antennas, based on the calibration DL signal being transmitted from a plurality of the antennas and the calibration DL signal being received by a plurality of the antennas in the DL control, and the calibration UL signal being transmitted from a plurality of the antennas and the calibration UL signal being received by a plurality of the antennas in the UL control; calculating a calibration coefficient for calibrating a radio DL signal, based on the DL channel coefficient and the UL channel coefficient; adjusting a phase and an amplitude of the radio DL signal being transmitted from each of a plurality of the antennas, based on the calibration coefficient; calculating, for each of a plurality of the antennas, a plurality of the DL channel coefficients being associated with the antenna other than the one antenna, based on the calibration DL signal during transmission being transmitted from the antenna other than the one antenna and the calibration DL signal during reception being received by the one antenna; calculating, for each of a plurality of the antennas, a plurality of the UL channel coefficients being associated with the antenna other than the one antenna, based on the calibration UL signal during transmission being transmitted from the one antenna and the calibration UL signal during reception being received by the antenna other than the one antenna; calculating the calibration coefficient for calibrating the radio DL signal, based on the DL channel coefficient and the UL channel coefficient that are calculated from a plurality of calibration measurements acquired by the DL control and the UL control; calculating, as a channel coefficient ratio, a proportion of the DL channel coefficient to the UL channel coefficient being calculated from a plurality of the calibration measurements; selecting, as a reference channel coefficient ratio, one of the channel coefficient ratios of a plurality of the calibration measurements; calculating, as a correction coefficient between a plurality of calibration measurements, a proportion of the reference channel coefficient ratio to the channel coefficient ratio of a plurality of the calibration measurements; and correcting a proportion of the DL channel coefficient to the UL channel coefficient with respect to a plurality of the calibration measurements by using the correction coefficient between a plurality of the calibration measurements.
8 . A non-transitory computer readable medium storing a program configured to cause a computer to execute: performing, for each of a plurality of antennas, down link (DL) control for transmitting a calibration DL signal from an antenna other than one antenna among a plurality of the antennas and receiving the calibration DL signal by the one antenna, and up link (UL) control for transmitting a calibration UL signal from the one antenna and receiving the calibration UL signal by the antenna other than the one antenna; calculating a DL channel coefficient of a transmitter and a UL channel coefficient of a receiver that are connected to the antenna for each of a plurality of the antennas, based on the calibration DL signal being transmitted from a plurality of the antennas and the calibration DL signal being received by a plurality of the antennas in the DL control, and the calibration UL signal being transmitted from a plurality of the antennas and the calibration UL signal being received by a plurality of the antennas in the UL control; calculating a calibration coefficient for calibrating a radio DL signal, based on the DL channel coefficient and the UL channel coefficient; adjusting a phase and an amplitude of the radio DL signal being transmitted from each of a plurality of the antennas, based on the calibration coefficient; calculating, for each of a plurality of the antennas, a plurality of the DL channel coefficients being associated with the antenna other than the one antenna, based on the calibration DL signal during transmission being transmitted from the antenna other than the one antenna and the calibration DL signal during reception being received by the one antenna; calculating, for each of a plurality of the antennas, a plurality of the UL channel coefficients being associated with the antenna other than the one antenna, based on the calibration UL signal during transmission being transmitted from the one antenna and the calibration UL signal during reception being received by the antenna other than the one antenna; calculating the calibration coefficient for calibrating the radio DL signal, based on the DL channel coefficient and the UL channel coefficient that are calculated from a plurality of calibration measurements acquired by the DL control and the UL control; calculating, as a channel coefficient ratio, a proportion of the DL channel coefficient to the UL channel coefficient being calculated from a plurality of the calibration measurements; selecting, as a reference channel coefficient ratio, one of the channel coefficient ratios of a plurality of the calibration measurements; calculating, as a correction coefficient between a plurality of calibration measurements, a proportion of the reference channel coefficient ratio to the channel coefficient ratio of a plurality of the calibration measurements; and correcting a proportion of the DL channel coefficient to the UL channel coefficient with respect to a plurality of the calibration measurements by using the correction coefficient between a plurality of the calibration measurements.

Description

This application is a National Stage Entry of PCT/JP2021/040738 filed on Nov. 5, 2021, which claims priority from Japanese Patent Application 2020-209739 filed on Dec. 17, 2020, the contents of all of which are incorporated herein by reference, in their entirety. TECHNICAL FIELD The present disclosure relates to a radio communication apparatus, a method for the radio communication apparatus, and a program, and particularly relates to a radio communication apparatus, a method for the radio communication apparatus, and a program that can easily perform calibration of a distributed antenna. BACKGROUND ART In a recent base station, an improvement in communication capacity is achieved by using a multiple input multiple output (MIMO) transmission method. A base station associated with the MIMO transmission method includes a plurality of antennas and a modulator-demodulator, and transmits and receives a different radio signal from each of the plurality of antennas and the modulator-demodulator. Frequency use efficiency is increased by spatially multiplexing a radio signal (user signal) by using the plurality of radio signals (transmission/reception signals). The base station associated with the MIMO transmission method can increase an antenna gain in a specific direction by using the plurality of antennas, suppress interference due to null formation, and the like. The technique is referred to as beam forming, and mainly includes two kinds. One is analog beam forming, and the other is digital beam forming. The analog beam forming is a technique for increasing an antenna gain in a specific direction by distributing (dispersing) one or more radio signals to a plurality of antennas and providing a different phase to each radio signal by a phase shifter and the like. Meanwhile, the digital beam forming is a technique for adjusting a phase and an amplitude of a transmission/reception signal of each antenna. A base station associated with the digital beam forming includes a transceiver in the same number as an antenna number, and digitally controls a transmission/reception signal from each antenna. In this way, a spatial multiplexing technique such as zero forcing (ZF) and minimum mean square error (MMSE) can be used. In the ZF and MMSE, control in a null direction of an antenna gain is also performed, and thus interference of a plurality of transmission/reception signals can be suppressed, and a signal can be more efficiently multiplexed. In order to use the spatial multiplexing technique, a channel coefficient indicating a propagation environment of a radio wave needs to be obtained. By using, for example, a reception signal (uplink (UL) signal) of the base station, the base station estimates a channel coefficient from a reference signal included in the reception signal. Processing of estimating a channel coefficient is referred to as channel estimation. When the base station receives a UL signal from a plurality of user terminals (UE: user equipment), the UL signals interfere with each other. Thus, the base station can perform UL communication with each of the UEs by separating a multiplexed UL signal by using a channel coefficient being obtained from the channel estimation and the spatial multiplexing technique. Meanwhile, in down link (DL) communication from the base station to the UE, multiplexed DL communication is performed by transmitting a DL signal to which the spatial multiplexing technique is adapted in advance by using the channel coefficient estimated from the UL signal. Processing of generating a DL signal to which the spatial multiplexing technique is adapted in advance by using a channel coefficient is referred to as precoding. The base station can suppress interference between UEs in the DL communication by performing the precoding, and can communicate with the plurality of UEs. In this way, the base station can communicate with a plurality of users in the same frequency band and in the same time period, and can improve frequency use efficiency. In the DL communication, a DL signal to which the spatial multiplexing technique is adapted in advance is transmitted by using a channel coefficient estimated from a UL signal. This uses reciprocity of a propagation channel in the UL communication and the DL communication, and is used in communication of a time division duplex (TDD) method. In order to use reciprocity of a channel in the MIMO transmission method, a transmission/reception signal being transmitted and received from each antenna needs to be calibrated. When the calibration is incomplete, an error due to a receiver is included in a channel coefficient acquired by channel estimation, and a radio signal cannot be accurately spatially multiplexed. Further, an error of a transmitter also affects spatial multiplexing and deteriorates a communication characteristic. Thus, a base station may include a calibration transmission/reception circuit in addition to a transmission/reception circuit used in commun