JP7647993B2 - Transmitting device and transmitting method - Google Patents

Description

The present invention relates to technology for spatially multiplexing transmission of radio signals.

In wireless communication transmitters, it is common to set a backoff that takes into account the PAPR (Peak To Average Ratio) of the transmitted signal and amplify it in the linear characteristic range of the power amplifier to transmit a signal with little distortion. However, this constraint can cause problems such as insufficient power to be secured during long-distance transmission. This is particularly a significant problem in uplink transmissions from terminals with low transmission power in wireless communication such as cellular communication.

In response to this, for example, non-patent document 1 discloses a wideband Doherty amplifier that covers multiple bands for the purpose of amplifying signals with a large PAPR (Peak To Average Ratio) with high efficiency.

Yuji Komatsuzaki et al., "Ultra-wideband GaN Doherty amplifier for next-generation mobile communication base stations," Mitsubishi Electric Technical Review, Vol. 93, No. 3, pp. 27-31, 2019

However, the conventional wireless transmission technology described above requires multiple amplifiers for one transmission signal, which poses problems in terms of miniaturization and cost, and is a major obstacle when performing MIMO transmission with a large number of spatial layers. There is also the problem that the PAPR of the transmission signal itself cannot be reduced.

The disclosed technology aims to reduce the PAPR of a transmitted signal while suppressing an increase in the number of amplifiers in wireless communication.

The disclosed technology is a transmitting device comprising: a signal processing unit that processes a baseband signal to use MIMO multiplexing transmission; and a transmitting unit that decomposes the baseband signal corresponding to one MIMO layer into a plurality of signals and assigns one RF chain to each of the plurality of decomposed signals for transmission; and a transmitting unit that vector decomposes the baseband signal corresponding to one MIMO layer into a plurality of modulated signal vectors and assigns one RF chain to each of the plurality of modulated signal vectors for transmission , wherein the transmitting unit performs vector decomposition so as to align the phases of the plurality of modulated signal vectors .

In wireless communication, it is possible to reduce the PAPR of the transmitted signal while suppressing an increase in the number of amplifiers.

1 is a configuration diagram of a communication system according to an embodiment of the present invention. FIG. 1 is a diagram illustrating an example of a general MIMO configuration. FIG. 1 is a diagram for explaining a method of long-distance transmission using a general MIMO configuration. FIG. 2 is a diagram illustrating an example of a configuration of a transmission unit according to the first embodiment of the present invention. FIG. 2 is a signal constellation diagram showing an example of modulated signal vector decomposition according to the first embodiment of the present invention; FIG. 11 is a diagram illustrating an example of a configuration of a transmitting unit according to a second embodiment of the present invention. FIG. 11 is a signal constellation diagram showing an example of modulated signal vector decomposition according to Example 2 of the embodiment of the present invention.

Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. The embodiment described below is merely an example, and the embodiment to which the present invention is applicable is not limited to the following embodiment.

(Configuration of communication system)
1 is a block diagram of a communication system according to an embodiment of the present invention. The communication system includes a transmitting device 100 and a receiving device 200.

The transmitting device 100 transmits a MIMO-multiplexed signal to the receiving device 200. The transmitting device 100 includes an antenna 110, a transmitting unit 120, and a signal processing unit 130. The antenna 110 is composed of antennas whose number corresponds to the maximum number of MIMO layers. The transmitting unit 120 transmits the MIMO-multiplexed signal via the antenna 110.

The signal processing unit 130 generates a baseband signal and transmits it to the transmitting unit 120. The signal processing unit 130 also determines whether to transmit with the maximum number of MIMO layers depending on the channel state, etc.

When the signal processing unit 130 determines not to transmit with the maximum number of MIMO layers, the transmitting unit 120 decomposes the baseband signal corresponding to one MIMO layer into multiple signals, assigns one RF chain to each of the multiple decomposed signals, and transmits them.

Furthermore, when the signal processing unit 130 determines to transmit with the maximum number of MIMO layers, the transmitting unit 120 may transmit using one RF chain for one MIMO layer.

The receiving device 200 receives the MIMO multiplexed signal.

The receiving device 200 includes an antenna 210, a receiving unit 220, and a signal processing unit 230. The antenna 210 is composed of antennas whose number corresponds to the maximum number of MIMO layers. The receiving unit 220 receives the MIMO multiplexed signal via the antenna 210. The signal processing unit 230 separates the received MIMO multiplexed signal by MIMO equalization processing.

(General MIMO configuration)
FIG. 2 is a diagram showing an example of a general MIMO configuration. In a general MIMO configuration, one baseband signal corresponds to one RF chain. An RF chain is a power amplifier or an associated analog circuit corresponding to one antenna or one antenna group including a subarray structure. For example, in the case of 4×4 MIMO, the simplest example is to associate one RF chain with each of four baseband modulated signals generated by a QAM (Quadrature Amplitude Modulation) modulation circuit or the like.

Figure 3 is a diagram for explaining a method of long-distance transmission using a general MIMO configuration. Conventionally, in the case of long-distance transmission, the number of layers of MIMO is reduced because the power required for long-distance transmission cannot be secured with one RF chain due to the constraints of the total transmission power, or because orthogonality cannot be secured from the viewpoint of spatial correlation of MIMO.

For example, in the case of 4x4 MIMO, within the constraints of the total transmission power, the transmitting device uses only two RF chains corresponding to two layers (layer #0 and layer #1) with an increased amplification factor compared to when all four spatial layers are used, and does not use the remaining two layers (layer #2 and layer #3). In this case, if the amplification in the nonlinear region occurs due to the increased amplification factor, distortion occurs in the transmitted signal. On the other hand, if it is subject to the constraints of the back-off setting that avoids amplification in the nonlinear region, the amplification factor required for long-distance transmission cannot be obtained.

(Outline of the present embodiment)
The transmitting device of this embodiment is based on a configuration that can have a greater number of RF chains than the number of spatial multiplexing layers, such as a Massive-MIMO configuration, and in a long-distance transmission area where high output is required, assigns a plurality of RF chains to one baseband signal, i.e., a MIMO layer, and further performs a decomposition process that decomposes the baseband signal into a plurality of low-PAPR signals, which are amplified individually and spatially combined.

Below, examples 1 to 3 of this embodiment are described.

Example 1
In this embodiment, an example will be described in which a transmitter performs decomposition processing into a high-power modulated signal vector whose power is set to a constant value by a limiter, and other low-power modulated signal vectors.

Figure 4 is a diagram showing an example of the configuration of a transmission unit according to a first embodiment of the present invention. The transmission unit 120 includes a QAM modulation circuit 121, a vector decomposition circuit 122, and an RF chain 123.

While the radio is capable of 4x4 MIMO transmission, this embodiment assumes long-distance transmission and performs two-layer spatial multiplexing.

The QAM modulation circuit 121 QAM modulates the baseband signal.

The vector decomposition circuit 122 decomposes the QAM-modulated digital baseband signal into multiple (e.g., two) modulated signal vectors using a vector decomposition function D. The signals corresponding to the decomposed modulated signal vectors are converted to analog signals by D/A conversion and input to the RF chain 123.

The RF chains 123 transmit signals corresponding to the decomposed modulated signal vectors to the receiving device 200 via the antennas 110 corresponding to each RF chain.

5 is a signal point constellation diagram showing an example of modulated signal vector decomposition according to the first embodiment of the present invention. The vector decomposition circuit 122 decomposes the modulated signal vector corresponding to the signal point to be transmitted into a first modulated signal vector 901 and a second modulated signal vector 902.

The first modulated signal vector 901 is a high-power modulated signal vector that has a specified threshold power and corresponds to a signal having a large amplitude that is constant or close to a constant value.

The second modulation signal vector 902 is a low-power modulation signal vector that complements the high-power modulation signal vector and the signal point to be transmitted.

The transmitter 120 may decompose the first modulated signal vector 901 and the second modulated signal vector 902 so that they are aligned (in phase) toward the signal point to be transmitted in a signal point constellation diagram, for example. In this way, the processing is simple and the total transmission power of the decomposed signals can be minimized, thereby improving power efficiency.

According to this embodiment, the vector decomposition circuit 122 performs vector decomposition into a high-power modulated signal vector (first modulated signal vector 901) and a low-power modulated signal vector (second modulated signal vector 902) of a specified power. The transmission signal corresponding to the high-power modulated signal vector (first modulated signal vector 901) has a small PAPR because it is controlled by the limiter to approach a constant value, and as a result, the back-off can be kept small. In addition, the low-power modulated signal vector (second modulated signal vector 902) has a large amplitude swing but low power, so the back-off can be made large.

In other words, in this embodiment, by utilizing an RF chain that was not previously utilized when transmitting at a spatial multiplexing number lower than the spatial multiplexing capability of the radio equipment, it is possible to further improve amplification efficiency while suppressing an increase in the number of amplifiers that must be provided to improve amplification efficiency, and by reducing the PAPR itself of the transmission signal input to the RF chain where back-off is an issue.

Although an example in which there is one high-power modulation signal vector (first modulation signal vector 901) has been shown, there may be multiple high-power modulation signal vectors. Similarly, although an example in which there is one low-power modulation signal vector (second modulation signal vector 902) has been shown, there may be multiple low-power modulation signal vectors.

Example 2
In this embodiment, an example is described in which a transmitting device performs a decomposition process to vector-decompose multiple modulated signals with low PAPR, and assigns an RF chain to each modulated signal at a power ratio such that the signal to be transmitted is obtained by superimposing each of the decomposed modulated signals on a hierarchy.

6 is a diagram showing an example of the configuration of a transmission unit according to a second embodiment of the present invention. The transmission unit 120 includes a Demux (Demultiplexer) circuit 124, a PSK (Phase Shift Keying) modulation circuit 125, an amplitude adjustment weighting circuit 126, and an RF chain 123.

The Demux circuit 124 decomposes the serial bit stream into multiple parallel bit streams.

The PSK modulation circuit 125 performs phase shift keying on the decomposed bit stream. The transmission power of each modulated signal is set to a power ratio such that the signal to be transmitted is obtained by superimposing them on the hierarchy. The signal corresponding to the decomposed modulated signal vector is converted to an analog signal by D/A conversion, and the coefficient ratio (power ratio) is adjusted by the amplitude adjustment weight circuit 126 before being input to the RF chain 123.

The RF chains 123 transmit signals corresponding to the decomposed modulated signal vectors to the receiving device 200 via the antennas 110 corresponding to each RF chain.

7 is a signal point constellation diagram showing an example of modulated signal vector decomposition according to Example 2 of an embodiment of the present invention. The PSK modulation circuit 125 performs phase shift keying on the modulated signal vector decomposed by the Demux circuit 124, and the transmitter 120 decomposes the modulated signal vector corresponding to the signal point to be transmitted into a first modulated signal vector 903 and a second modulated signal vector 904.

The first modulated signal vector 903 is a high-power modulated signal vector corresponding to the first modulated signal decomposed by the Demux circuit 124, and corresponds to a signal having a small amplitude that is close to constant.

The second modulated signal vector 904 is a low-power modulated signal vector corresponding to the second modulated signal decomposed by the Demux circuit 124.

The coefficient ratio (power ratio) of the amplitude adjustment weighting circuit 126 is adjusted so that the first modulation signal vector 903 and the second modulation signal vector 904 are added together to obtain the signal to be transmitted.

Note that Figure 7 shows an example in which the distances between signal points are not the same, but depending on the distribution of power ratios, the distances between signal points may be the same.

According to this embodiment, the Demux circuit 124 decomposes the bit stream into multiple parallel bit streams. For example, when 4-bit/symbol transmission is required, 16QAM is conventionally used, whereas in this embodiment, the signal point arrangement of the transmission signal corresponding to the high-power modulation signal vector (first modulation signal vector 903) is limited to the QPSK modulation method, and the amplitude modulation element is eliminated (constant amplitude modulation). This reduces the PAPR and keeps the backoff small. Similarly, the signal points of the low-power modulation signal vector (second modulation signal vector 904) are also limited to the QPSK modulation method, and the amplitude modulation element is eliminated (constant amplitude modulation).

In other words, in this embodiment, by utilizing an RF chain that was not previously utilized when transmitting at a spatial multiplexing number lower than the spatial multiplexing capability of the radio equipment, it is possible to further improve amplification efficiency while suppressing an increase in the number of amplifiers that must be provided to improve amplification efficiency, and by reducing the PAPR itself of the transmission signal input to the RF chain where back-off is an issue.

Although an example in which there is one high-power modulation signal vector (first modulation signal vector 903) has been shown, there may be multiple high-power modulation signal vectors. Similarly, although an example in which there is one low-power modulation signal vector (second modulation signal vector 904) has been shown, there may be multiple low-power modulation signal vectors.

Example 3
In this embodiment, an example will be described in which a transmitting device corrects, by feedback, a phase difference between vector decomposition signals that occurs at a receiving point due to an antenna position difference (path length difference).

The receiving device 200 determines one of the vector-decomposed signals as a reference signal, detects the path length difference occurring between the transmitting device 100 and the receiving device 200 based on the difference in the arrangement positions between the RF chains as a phase difference at the reception point, and transmits feedback information indicating the detected phase difference to the transmitting device 100. The feedback information indicating the detected phase difference may be, for example, information indicating a transmission path estimation value using an orthogonal pilot.

The transmitting device 100 receives feedback information. Then, the signal processing unit 130 corrects the phase difference of the signals other than the vector-decomposed reference signal based on the received feedback information. Then, the signal processing unit 130 inputs the corrected vector-decomposed signal to each RF chain.

According to this embodiment, even if a phase difference occurs in the multiple decomposed signals due to the arrangement of the antennas 110 of multiple RF chains, the phase difference can be corrected by obtaining feedback information from the receiving device 200.

In addition, according to each of the above-mentioned embodiments, the transmitted signals are assigned to multiple RF chains, which has the effect of making eavesdropping more difficult.

(Summary of the embodiment)
This specification describes at least the transmission apparatus and transmission method described in the following items.
(Section 1)
A signal processing unit that processes a baseband signal so as to use MIMO multiplexing transmission;
A transmitter that decomposes the baseband signal corresponding to one MIMO layer into a plurality of signals, assigns one RF chain to each of the plurality of decomposed signals, and transmits the signals.
Transmitting device.
(Section 2)
The signal processing unit determines whether to perform transmission with a maximum number of MIMO layers;
When transmission is not performed with the maximum number of MIMO layers, the transmission unit decomposes the baseband signal corresponding to one MIMO layer into a plurality of signals, assigns one RF chain to each of the decomposed signals, and transmits the signals.
2. A transmitting device as described in claim 1.
(Section 3)
The transmitter performs vector decomposition of the baseband signal into one or more constant value high-power modulated signal vectors and other low-power modulated signal vectors.
3. The transmitting device according to claim 1 or 2.
(Section 4)
the transmitting unit performs vector decomposition so as to align the phases of the high-power modulated signal vector and the low-power modulated signal vector.
A transmitting device as described in claim 3.
(Section 5)
the transmitting unit vector-decomposes the baseband signal into a plurality of modulated signals, and assigns one RF chain to each modulated signal at a power ratio such that a signal to be transmitted is obtained by superimposing each of the decomposed modulated signals on a hierarchy, and transmits the modulated signals.
A transmitting device according to any one of claims 1 to 4.
(Section 6)
The transmitter corrects phase differences of the plurality of transmission signals based on feedback information indicating phase differences at reception points of the vector-decomposed plurality of signals.
A transmitting device according to any one of claims 1 to 5.
(Section 7)
processing a baseband signal to use MIMO multiplexing transmission;
Decomposing the baseband signal corresponding to one MIMO layer into a plurality of signals, and assigning one RF chain to each of the plurality of decomposed signals for transmission.
A transmission method executed by a transmitting device.

Any of the above configurations provides a technology that enables the PAPR of a transmission signal to be reduced while suppressing an increase in the number of amplifiers in wireless communication. According to the second term, when transmission is not performed with the maximum number of MIMO layers, the PAPR of the transmission signal can be reduced by utilizing surplus RF chains. According to the third term, back-off can be reduced by decomposing a high-power modulated signal vector and a low-power modulated signal vector with low PAPR. According to the fourth term, processing is simple and power efficiency can be increased. According to the fifth term, PAPR can be reduced and back-off can be reduced by decomposing into multiple modulated signals. According to the sixth term, the phase difference between the multiple decomposed signals can be corrected.

Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

100 Transmitter 110 Antenna 120 Transmitter 121 QAM Modulator 122 Vector Decomposition Circuit 123 RF Chain 124 Demux Circuit 125 PSK Modulator 126 Amplitude Adjustment Weighting Circuit 130 Signal Processing Unit 200 Receiving Device 210 Antenna 220 Receiving Unit 230 Signal Processing Unit

Claims (7)

A signal processing unit that processes a baseband signal so as to use MIMO multiplexing transmission;
a transmitting unit that performs vector decomposition of the baseband signal corresponding to one MIMO layer into a plurality of modulated signal vectors , assigns one RF chain to each of the plurality of modulated signal vectors , and transmits the modulated signal vectors ;
The transmitter performs vector decomposition so as to align the phases of the multiple modulation signal vectors.
Transmitting device. The signal processing unit determines whether to perform transmission with a maximum number of MIMO layers;
When transmission is not performed with the maximum number of MIMO layers, the transmission unit decomposes the baseband signal corresponding to one MIMO layer into the plurality of modulated signal vectors , assigns one RF chain to each of the plurality of modulated signal vectors , and transmits the vectors.
The transmitting device according to claim 1 . The transmitter performs vector decomposition of the baseband signal into one or more constant-value high-power modulated signal vectors and one or more low-power modulated signal vectors.
3. A transmitting device according to claim 1 or 2. the transmitting unit performs vector decomposition so as to align the phases of the high-power modulated signal vector and the low-power modulated signal vector.
The transmitting device according to claim 3. the transmitting unit vector-decomposes the baseband signal into a plurality of modulated signal vectors , and assigns one RF chain to each modulated signal at a power ratio such that a signal to be transmitted is obtained by superimposing each of the vector -decomposed modulated signal vectors on a hierarchy, and transmits the modulated signal.
A transmitting device according to any one of claims 1 to 4. The transmitter corrects phase differences of the plurality of modulated signal vectors based on feedback information indicating phase differences at a reception point of the vector-decomposed plurality of modulated signal vectors .
A transmitting device according to any one of claims 1 to 5. The transmitting device,
processing a baseband signal to use MIMO multiplexing transmission;
a transmitting step of vector -decomposing the baseband signal corresponding to one MIMO layer into a plurality of modulated signal vectors , and assigning one RF chain to each of the plurality of modulated signal vectors to transmit the vectors ;
The transmitting step includes vector decomposing the plurality of modulated signal vectors so as to align the phases of the plurality of modulated signal vectors.
Transmission method.

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