JP7144808B2 - Wireless communication device and wireless communication method - Google Patents

Description

The present invention relates to a wireless communication device and wireless communication method.

Wireless LANs based on the IEEE802.11a standard, 11n standard, and 11ac standard are known as high-speed wireless access systems using radio waves in the 5 GHz band. The 11a standard is based on an orthogonal frequency division multiplexing (OFDM) modulation system, and stabilizes characteristics in a multipath fading environment to achieve a maximum transmission rate of 54 Mbit/s. Furthermore, in the 11n standard, multiple input multiple output (MIMO), which performs space division multiplexing on the same radio channel using multiple antennas, and channel bonding, which uses two 20 MHz frequency channels at the same time and uses a 40 MHz frequency channel. technology, it has achieved transmission speeds of up to 600 Mbit/s. In addition, the 11ac standard includes a channel bonding technology that simultaneously uses up to eight 20 MHz frequency channels as a maximum frequency channel of 160 MHz, and a downlink that simultaneously transmits different signals to multiple destinations on the same radio channel. Using multi-user MIMO technology, etc., we have realized wireless communication that is faster and more efficient than the 11n standard.

At present, the IEEE 802.11ax standard is being developed with a focus on improving transmission efficiency in addition to improving transmission speed. 11ax plans to promote spatial frequency reuse through simultaneous transmission, improve the efficiency of OFDM modulation schemes, and add uplink OFDMA transmission and uplink multiuser MIMO transmission as multiuser transmission.

Also, in order to perform high-speed transmission, a technique of suppressing interference waves using a CMA (Constant Modulus Algorithm) adaptive array is known (see, for example, Non-Patent Document 1).

Kentaro Nishimori, 2 others, "Operational Analysis of CMA Adaptive Array for QAM Signal", The Institute of Electronics, Information and Communication Engineers Transactions B-II, December 1996, Vol. J79-B-II No. 12, p. 984-993

FIG. 10 shows an example of the configuration of a conventional radio base station. The radio base station 4 has a plurality of antennas 40 , the same number of RF units 41 as the antennas 40 , and the same number of A/D conversion units 42 and demodulation units 43 as the antennas 40 . Note that FIG. 10 shows only the main functional blocks required for the radio base station 4 to perform reception, and does not show other functional blocks generally installed in the radio base station. .

Antenna 40 receives, for example, a MIMO-OFDM signal. The antennas 40 are each connected to the RF section 41 and output the received MIMO-OFDM signal to the RF section 41 .

The RF unit 41 applies analog processing such as amplification, frequency change, filtering, etc. to the MIMO-OFDM signal input from the antenna 40 , and outputs the processed signal to the A/D conversion unit 42 . That is, the RF unit 41 is equipped with the RF front-end function of a general wireless device.

The A/D conversion section 42 converts the analog signal input from the RF section 41 into a digital signal and outputs the digital signal to the demodulation section 43 .

The demodulation unit 43 performs MIMO-OFDM demodulation processing defined by wireless LAN systems and the like on a plurality of digital signals input from each of the A/D conversion units 42 .

Thus, in the conventional radio base station 4, in order to perform MIMO-OFDM demodulation on the received signal, it is necessary to provide RF units 41 and A/D conversion units 42 corresponding to the number of antennas 40. rice field. Furthermore, in recent wireless communication systems such as 5G, the number of antennas has increased dramatically like massive MIMO transmission. It is required to solve the problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a radio communication apparatus and radio communication method capable of receiving a plurality of signals by reducing at least one of the number of antennas and/or the number of circuits used for reception.

A radio communication apparatus according to an aspect of the present invention includes an antenna device that receives a transmission signal while changing directivity a plurality of times within one symbol of a modulated transmission signal, and a reception signal received by the antenna device . a signal dividing unit that divides into a plurality of signals for each directivity; a selection unit that selects based on a threshold; and a demodulation unit that MIMO-OFDM-demodulates a combination of signals selected by the selection unit, wherein the antenna device includes a plurality of antennas and signals received by the plurality of antennas and a plurality of amplitude-phase variable units that change the amplitude and phase of the input signals and output them , and a plurality of signals output by the plurality of amplitude-phase variable units that are combined and output as the received signals. and a plurality of amplitude-phase varying units, while minimizing the distortion component of the envelope of the received signal, the amplitude and phase of the input signal are adjusted within one symbol of the received signal. and a control unit for controlling the directivity to be changed a plurality of times within one symbol of the received signal by changing the directivity a plurality of times.

A wireless communication method according to an aspect of the present invention includes a receiving step of acquiring a received signal obtained by receiving the transmitted signal while changing directivity a plurality of times within one symbol of a modulated transmitted signal ; a signal dividing step of dividing into a plurality of signals for each directivity; A selection step of selecting based on a threshold; A step of changing the amplitude and phase to be changed, and a step of combining a plurality of signals whose amplitudes and phases are changed in the step of changing the amplitude and phase to obtain the received signal, and a step of changing the amplitude and phase, in which the signals are received by a plurality of the antennas. by changing the amplitude and phase of each of the received signals a plurality of times within one symbol of the received signal while minimizing the distortion component of the envelope of the received signal, thereby changing the directivity to the received signal and a control step of controlling to change a plurality of times within one symbol of .

According to the present invention, it is possible to receive a plurality of signals by reducing at least one of the number of antennas and the number of circuits used for reception.

1 is a diagram illustrating a configuration example of a wireless communication system according to an embodiment; FIG. FIG. 3 is a diagram showing a configuration example of a wireless terminal station; 1 is a diagram illustrating a configuration example of a radio base station according to an embodiment; FIG. FIG. 4 is a diagram showing an example of a received signal pattern synthesized by a synthesizing unit; 1 is a diagram showing an overview of the operating principle of CMA; FIG. FIG. 2 is a diagram showing an example of an uplink communication sequence of a radio communication system; FIG. 7(a) shows the reception result of the comparative example. FIG. 7(b) shows the reception result of a conventional radio base station. FIG. 7(c) shows the reception result of the radio base station according to the embodiment. FIG. 8A is a diagram showing a first modification of the plurality of antennas 11. FIG. FIG. 8B is a diagram showing a second modification of the plurality of antennas 11. As shown in FIG. FIG. 8(c) is a diagram showing a third modification of the plurality of antennas 11. As shown in FIG. FIG. 4 is a diagram showing a configuration example of a modification of the radio base station according to one embodiment; 1 is a diagram showing an example of the configuration of a conventional radio base station; FIG.

An embodiment of a wireless communication system will be described below with reference to the drawings.

FIG. 1 shows a configuration example of a wireless communication system according to one embodiment. As shown in FIG. 1, a radio communication system includes, for example, a radio base station 1 as a radio communication device and n radio terminals existing within a service area within which radio communication is possible with the radio base station 1. It is composed of stations 2-1 to 2-n. The wireless terminal stations 2-1 to 2-n asynchronously transmit upstream signals to the wireless base station 1. FIG. Hereinafter, when any one of the wireless terminal stations 2-1 to 2-n is not specified, it is simply referred to as the wireless terminal station 2.

FIG. 2 shows a configuration example of the wireless terminal station 2. As shown in FIG. As shown in FIG. 2, the wireless terminal station 2 has, for example, a modulation section 21, a D/A conversion section 22, an RF section 23 and an antenna 24. FIG. In addition, in FIG. 2, only the main functional blocks required for the wireless terminal station 2 to perform transmission are described, and other functional blocks generally installed in the wireless terminal station are not described. .

The modulation unit 21 performs modulation processing of MIMO-OFDM defined in, for example, a wireless LAN system or the like, and outputs the modulated signal to the D/A conversion unit 22 .

The D/A conversion section 22 converts the digital signal input from the modulation section 21 into an analog signal and outputs the analog signal to the RF section 23 .

The RF unit 23 performs processing such as amplification, frequency change, and filtering on the signal input from the D/A conversion unit 22 and outputs the processed transmission signal to the antenna 24 . That is, the RF unit 23 has the function of an RF front end of a general wireless communication device.

The antenna 24 radiates the transmission signal input from the RF section 23 into the air.

FIG. 3 shows a configuration example of the radio base station 1 according to one embodiment. As shown in FIG. 3, the radio base station 1 includes, for example, a plurality of antennas 11, a plurality of amplitude phase varying units 12, a combining unit 13, an RF unit 14, an A/D conversion unit 15, a signal division unit 16, a demodulation unit 17 and a control unit 18 . In addition, in FIG. 3, only the main functional blocks required for the radio base station 1 to perform reception are described, and other functional blocks generally installed in the radio base station are not described. .

A plurality of antennas 11 form an array antenna and receive modulated transmission signals such as MIMO-OFDM signals transmitted by the wireless terminal stations 2-1 to 2-n. Here, the antenna 11 receives the MIMO-OFDM signal while changing the directivity a plurality of times (for example, P times) within one symbol of the modulated transmission signal, and outputs the signal to the amplitude/phase varying section 12 .

The amplitude/phase varying section 12 changes the amplitude and phase of the received signal received by the antenna 11 according to the control signal input from the control section 18, and outputs the adjusted signal (received signal pattern) to the combining section 13. Output for For example, the amplitude/phase varying section 12 outputs a plurality of (for example, P) received signal patterns within one symbol of the received signal under the control of the control section 18 .

The synthesizing unit 13 synthesizes a plurality of (for example, P) received signal patterns output within one symbol of the received signal by the amplitude/phase varying unit 12 and outputs the result to the RF unit 14 .

FIG. 4 shows an example of received signal patterns (antenna characteristics) synthesized by the synthesizing unit 13 . For example, the synthesizing unit 13 performs synthesizing so that a main lobe, side lobes, and back lobes are generated in four directions shifted by 90° as shown in FIG.

RF unit 14 ( FIG. 3 ) performs processing such as amplification, frequency change, and filtering on the signal input from synthesis unit 13 and outputs the processed signal to A/D conversion unit 15 . That is, the RF unit 14 has the function of an RF front end of a general wireless communication device.

The A/D converter 15 converts the analog signal input from the RF unit 14 into a digital signal and outputs the digital signal to the signal divider 16 . Also, the A/D conversion unit 15 notifies the control unit 18 of the sampling period. Here, the A/D converter 15 performs sampling at a rate P times the symbol rate of the received signal.

The signal division unit 16 divides the signal input from the A/D conversion unit 15 for each antenna characteristic controlled by the control unit 18 and outputs the divided signal to the demodulation unit 17 .

The demodulator 17 demodulates the signal divided by the signal divider 16 according to MIMO-OFDM defined by wireless LAN systems and the like.

The control unit 18 controls each unit that configures the radio base station 1 . For example, the control unit 18 controls the amplitude/phase changing unit 12 to change the amplitude and phase of the received signal a plurality of times (for example, P times) while the antenna 11 receives the signal of one OFDM symbol, The amplitude/phase varying unit 12 is caused to generate a plurality of (for example, P) received signal patterns.

Then, when the radio base station 1 changes the antenna characteristics P times within one symbol of the received signal, and the A/D converter 15 performs A/D conversion at P times the symbol rate of the received signal, We will have P virtual branches with different propagation characteristics.

Conventionally, in order to perform MIMO-OFDM demodulation processing using P different received signals acquired within one OFDM symbol as array data, it was necessary to acquire propagation channels at different times.

Therefore, the radio base station 1 uses a Constant Modulus Algorithm (CMA) for weight control of the array antenna. In CMA, weights are controlled so as to minimize the distortion component of the envelope of the array output using the property that the transmitted signal has a constant envelope.

FIG. 5 outlines the operating principle of the CMA. A feature of CMA is that the weights are controlled so as to keep the envelope of the output signal of the array antenna constant. For example, in CMA, a first arriving wave, which is a desired wave, and a second arriving wave are combined to generate a combined wave y (output voltage of an array antenna), and a combined wave y and a desired envelope value σ are combined as follows: is used, evaluation is performed by the CMA evaluation function represented by the following equation (1). Note that E[•] in the formula (1) represents an operation for obtaining an expected value.

Then, in CMA, the second arriving wave is extracted from the composite wave y to extract the first arriving wave. X shown in the above equation (1) is the received signal vector of the array antenna. However, in the radio base station 1, there is only one system of signals output from the array antenna. Therefore, the radio base station 1 uses a vector consisting of P received signals with different antenna characteristics instead of X obtained with different antennas of the array antenna. CMA does not require timing synchronization or propagation channel estimation because it is an algorithm that does not require timing synchronization. The basic characteristics of CMA are also described in Non-Patent Document 1.

In other words, the control unit 18 controls to minimize the distortion component of the envelope of the received signal, and the amplitude/phase varying unit 12 changes the amplitude and phase of the received signal multiple times within one symbol of the received signal. is controlled to output a plurality of received signal patterns.

FIG. 6 shows an example of an uplink communication sequence in a wireless communication system according to an embodiment. As shown in FIG. 6, in the wireless communication system according to one embodiment, for example, it is assumed that wireless terminal stations 2-1 and 2-2 asynchronously transmit signals. At this time, if the signal transmitted by the wireless terminal station 2-1 is an uplink MIMO-OFDM signal, which is the desired wave, the signal transmitted by the wireless terminal station 2-2 is an interference signal.

The radio base station 1 can obtain a plurality of branches with different antenna characteristics by performing conversion by oversampling in one symbol by the A/D conversion unit 15 even if the reception port is one element. By applying CMA, which achieves interference cancellation only by itself, to different branches of multiple patterns, timing synchronization and channel estimation are not required.

FIG. 7 shows comparison between a plurality of signals received and demodulated by the radio base station 1 and a comparative example. FIG. 7A shows reception results when a plurality of signals are received by the comparative example. FIG. 7(b) shows reception results when a plurality of signals are received by the conventional radio base station shown in FIG. FIG. 7(c) shows reception results when a plurality of signals are received by the radio base station 1 according to one embodiment. Here, it is assumed that the radio base station is in an environment where one desired signal wave from a radio terminal station and one interference signal wave arriving from another radio station with an arrival angle difference of 5 degrees are simultaneously received. It is also assumed that the modulation method is QPSK (Quadrature Phase Shift Keying).

The comparative example shown in FIG. 7(a) shows the results when a plurality of signals are received with the number of reception ports set to 1. It is not possible to demodulate those signals with the number of ports.

In the reception result of the conventional radio base station shown in FIG. 7(b), demodulation is performed with, for example, four reception ports. .9 dB).

In the reception result of the radio base station 1 shown in FIG. 7(c), it can be seen that a plurality of signals can be demodulated (SINR=15.8 dB) even though the number of reception ports is one.

Note that the radio base station 1 shown in FIG. 3 forms an array antenna with a plurality of antennas 11, and while changing the directivity a plurality of times (for example, P times) within one symbol of the transmitted signal, Although the MIMO-OFDM signal is received, the signal may be received by generating a plurality of antenna characteristics using antennas with other configurations below.

FIG. 8 shows a modification of the multiple antennas 11 that the radio base station 1 has. FIG. 8(a) shows a first modification of the plurality of antennas 11. FIG. FIG. 8(b) shows a second modification of the plurality of antennas 11. As shown in FIG. FIG. 8(c) shows a third modification of the plurality of antennas 11. As shown in FIG.

A first modification of the plurality of antennas 11 shows a configuration in which the plurality of antennas 30 are switched at high speed by a changeover switch 31 . A second modification of the plurality of antennas 11 shows a configuration in which the directional antennas 32 are rotated by a rotating mechanism 33. FIG. A third modification of the plurality of antennas 11 shows a configuration in which the parasitic element 35 rotates around the antenna 34 . Each of the first to third modifications of the plurality of antennas 11 has a single receiving port or a configuration in which the received signal is output from a port number smaller than the number of communication paths (the number of received signals). ing.

Next, a modified example of the radio base station 1 will be described.

FIG. 9 shows a configuration example of a modification (radio base station 1a) of the radio base station 1 according to one embodiment. As shown in FIG. 9, the radio base station 1a includes, for example, a plurality of antennas 11, a plurality of amplitude phase varying units 12, a combining unit 13, an RF unit 14, an A/D conversion unit 15, a signal division unit 16, a demodulation unit 17 , a selector 19 and a controller 18 . In addition, in the radio base station 1a shown in FIG. 9, the same reference numerals are assigned to substantially the same configuration as the radio base station 1 shown in FIG.

That is, the radio base station 1a has a configuration in which a selector 19 is added to the radio base station 1 described above. Here, the selection unit 19 selects a part of the plurality of signals divided by the signal division unit 16 based on the respective values of the plurality of signals divided by the signal division unit 16 . For example, the selection unit 19 selects Q combinations of branches with high received power and branches with low correlation from the above-described P signals, with a predetermined threshold provided. Let Q be a value equal to or less than P.

Then, the demodulator 17 MIMO-OFDM-demodulates part of the plurality of signals selected by the selector 19 . In this manner, the radio base station 1a reduces the number of signals to be demodulated by the selection unit 19, so that speeding up of weight control convergence in CMA can be realized.

Thus, the radio base station 1 and the radio base station 1a can receive a plurality of signals by reducing at least one of the number of antennas and the number of circuits used for reception.

1, 1a... radio base station, 2-1 to 2-n... radio terminal station, 11, 30, 34... antenna, 12... amplitude phase variable section, 13... synthesizing section, 14... RF unit, 15... A/D conversion unit, 16... signal division unit, 17... demodulation unit, 18... control unit, 19... selection unit, 31... Changeover switch 32... Directional antenna 33... Rotation mechanism 35... Parasitic element

Claims (2)

an antenna device that receives the transmission signal while changing the directivity a plurality of times within one symbol of the modulated transmission signal;
a signal dividing unit that divides a received signal received by the antenna device into a plurality of signals according to the directivity;
a selection unit that selects, based on a predetermined threshold value, a combination of signals with high received power or a combination of signals with low correlation from among the plurality of signals divided by the signal division unit;
a demodulation unit that MIMO-OFDM-demodulates the combination of signals selected by the selection unit;
has
The antenna device is
a plurality of antennas;
a plurality of amplitude and phase varying units that respectively receive signals received by the plurality of antennas, change the amplitude and phase of the input signals, and output the signals ;
a synthesizing unit for synthesizing a plurality of signals output from the plurality of amplitude and phase varying units and outputting the received signal as the received signal;
The amplitude and phase of the input signal are changed a plurality of times within one symbol of the received signal, while minimizing the distortion component of the envelope of the received signal. and a control unit that controls to change the directivity a plurality of times within one symbol of the received signal by
A wireless communication device comprising: a receiving step of acquiring a received signal received from the transmitted signal while changing the directivity a plurality of times within one symbol of the modulated transmitted signal;
a signal division step of dividing the received signal into a plurality of signals for each directivity;
A selection step of selecting, based on a predetermined threshold value, a combination of signals with high received power or a combination of signals with low correlation from among the plurality of signals divided in the signal division step;
a demodulation step of MIMO-OFDM demodulating the combination of signals selected in the selection step;
including
The receiving step includes
an amplitude phase changing step of changing the amplitude and phase of each signal received by a plurality of antennas;
A step of synthesizing a plurality of signals whose amplitudes and phases have been changed in the step of changing the amplitude and phase to obtain the received signal;
In the amplitude phase changing step, the amplitude and phase of each signal received by the plurality of antennas are changed to a plurality within one symbol of the received signal while minimizing the distortion component of the envelope curve of the received signal. a control step of controlling the directivity to change a plurality of times within one symbol of the received signal by changing the directivity a plurality of times;
A wireless communication method comprising:

Images