Wireless communication method, wireless communication system, and transmitting device

Abstract

This wireless communication method according to one embodiment includes: a pre-coding step for using a FIR filter to pre-code a transmission signal stream in a time region; a transmission power control step for controlling the transmission power of the pre-coded stream; and an amplification step for amplifying the pre-coded stream to be at the controlled transmission power. Also included is a tap length control step for controlling a change of the tap length in the pre-coding step such that, for a threshold value calculated on the basis of reception signal quality information fed back from a reception device that received the amplified stream or reception signal quality information calculated using at least a characteristic of the amplification unit, the tap length is decreased if the size of the last tap coefficient in the pre-coding step is smaller than the threshold value, and the tap length is increased if the size is greater than the threshold value.

Description

[Technical field]

[0001] The present invention relates to a wireless communication method, a wireless communication system, and a transmitting device. [Background technology]

[0002] For example, in a wireless communication system using a single-carrier multi-level modulation scheme, if excessive transmission power is input to the amplifier of the transmitting device, distortion will occur in the signal, so communication is generally carried out with transmission power amplified within a linear region where no distortion occurs.

[0003] On the other hand, when a large peak power occurs, the peak power may be amplified within the nonlinear region of the amplifier, which may cause degradation of communication quality due to nonlinear distortion (see, for example, Non-Patent Document 1).

[0004] Furthermore, in a single carrier system that performs precoding in the time domain using an FIR filter (see, for example, Non-Patent Document 2), the tap length of precoding is a fixed value. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] MOHAMED IBNKAHLA, et al., "High-Speed ​​Satellite Mobile Communications: Technologies and Challenges", PROCEEDINGS OF THE IEEE, VOL. 92, NO. 2, FEBRUARY 2004, p.312-339 [Non-Patent Document 2] Keita Kuriyama, Hayato Fukuzono, Masafumi Yoshioka, Tsutomu Tatsuta, "FIR-type transmit beamforming for wideband single-carrier MIMO transmission", IEICE Technical Report, Jan. 2019, pp. 31-36 Summary of the Invention [Problem to be solved by the invention]

[0006] For example, in a single-carrier system that performs precoding in the time domain using an FIR filter, when the precoding tap length is fixed to M, the m-th tap coefficient varies in magnitude depending on the channel state.

[0007] When the m-th tap coefficient is very small, the precoding tap length may be excessive compared to the tap length required to obtain the desired BER (bit error rate) characteristics. In this case, excessive weight multiplication may cause the PAPR (Peak to Average Power Ratio) to increase more than necessary, which may result in nonlinear distortion.

[0008] On the other hand, if the m-th tap coefficient is very large, the tap length may be insufficient, which may increase inter-stream interference and inter-symbol interference.

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a wireless communication method, a wireless communication system, and a transmitting device that can improve the quality of wireless communication even if the channel conditions vary. [Means for solving the problem]

[0010] According to one aspect of the present invention, a wireless communication method for transmitting a signal from a transmitting device to a receiving device includes a precoding step of precoding a stream of a transmission signal in a time domain using an FIR filter, a transmission power control step of controlling the transmission power of the precoded stream, and an amplification step of amplifying the precoded stream so as to achieve the controlled transmission power, and the step of amplifying the precoded stream in the precoding step is performed with respect to a threshold value calculated based on quality information of a received signal fed back from the receiving device that has received the amplified stream, or quality information of a received signal calculated using at least a characteristic of an amplifier unit of the transmitting device.FIR Filter If the magnitude of the last tap coefficient is small, FIR Filter Reduce the tap length, if it is large FIR Filter In the precoding step, the tap length is increased. FIR Filter The method further includes a tap length control step for controlling a change in the tap length.

[0011] Moreover, a wireless communication system according to one aspect of the present invention is a wireless communication system for transmitting a signal from a transmitting device to a receiving device, the system comprising: a precoding unit that precodes a stream of a transmission signal in a time domain using an FIR filter; a transmission power control unit that controls the transmission power of the stream precoded by the precoding unit; an amplifier that amplifies the stream precoded by the precoding unit according to the control of the transmission power control unit; and a control unit that amplifies the stream precoded by the precoding unit according to the control of the transmission power control unit. FIR Filter If the magnitude of the last tap coefficient is small, FIR Filter Reduce the tap length, if it is large FIR Filter The precoding unit is configured to increase the tap length. FIR Filter and a tap length control unit for controlling the change of the tap length.

[0012] A transmission device according to one aspect of the present invention includes a precoding unit that precodes a stream of a transmission signal in the time domain using an FIR filter, a transmission power control unit that controls the transmission power of the stream precoded by the precoding unit, an amplifier that amplifies the stream precoded by the precoding unit in accordance with the control of the transmission power control unit, and a control unit that amplifies the stream precoded by the precoding unit based on quality information of a received signal fed back from a receiving device that receives the stream amplified by the amplifier unit, or based on quality information of the received signal calculated using at least a characteristic of the amplifier unit. FIR FilterIf the magnitude of the last tap coefficient is small, FIR Filter Reduce the tap length, if it is large FIR Filter The precoding unit is configured to increase the tap length. FIR Filter and a tap length control unit for controlling the change of the tap length. Effect of the Invention

[0013] According to the present invention, it is possible to improve the quality of wireless communication even when the channel condition varies. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a wireless communication system according to an embodiment. [Diagram 2] FIG. 11 is a functional block diagram illustrating functions of a transmitting device of a comparative example. [Diagram 3] 1A is a graph illustrating an example of the amplification characteristic of the amplifier, and FIG. 1B is a diagram illustrating an example of a constellation of a transmission signal amplified by the amplifier. [Figure 4] 1 is a graph illustrating the relationship between the amplification characteristic of an amplifier and the magnitude of PAPR. [Diagram 5] 1 is a graph showing communication quality versus the magnitude of tap coefficients in precoding. [Figure 6] 1 is a diagram illustrating a relationship between a threshold value α used by a transmitting device according to an embodiment and a tap length M used for precoding. [Figure 7] FIG. 2 is a functional block diagram illustrating functions of a transmitting device according to an embodiment. [Figure 8] 10 is a flowchart illustrating an example of an operation of a transmitting device according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] An embodiment of a wireless communication system will be described below with reference to the drawings. Fig. 1 is a diagram showing a configuration example of a wireless communication system 1 according to an embodiment. As shown in Fig. 1, the wireless communication system 1 is, for example, a MIMO system in which a transmitting device 2 performs MIMO (Multiple Input Multiple Output) transmission to a receiving device 4.

[0016] Note that, although a MIMO system will be described as an example here, the wireless communication system according to one embodiment is not limited to a MIMO system, and may be a SISO (Single Input Single Output) system or the like as long as it performs precoding using a FIR (Finite Impulse Response) filter.

[0017] The transmitting device 2 includes multiple antennas, precodes multiple streams of a transmission signal in the time domain, and performs MIMO transmission to the receiving device 4. The transmitting device 2 also transmits to the receiving device 4 a training signal for calculating communication path information (e.g., CSI: Channel State Information).

[0018] The receiving device 4 receives the multi-stream transmitted by the transmitting device 2, and feeds back quality information of the received signal to the transmitting device 2. The quality information of the received signal that the receiving device 4 feeds back to the transmitting device 2 includes, for example, a CQI (Channel Quality Indicator) and a PMI (Precoding Matrix Indicator). In addition, the receiving device 4 calculates communication channel information using the received training signal, and transmits the calculated communication channel information to the transmitting device 2.

[0019] The communication path information may or may not be known to the transmitting device 2. The transmitting device 2 and the receiving device 4 may each have the same functions to transmit and receive data.

[0020] Here, to help understand the configuration of the transmission device according to an embodiment, a configuration example of a transmission device 2a of a comparative example will be described. Fig. 2 is a functional block diagram illustrating functions of the transmission device 2a of the comparative example.

[0021] 2, the transmitting device 2a of the comparative example includes a plurality of information bit generating units 20, a plurality of modulating units 21, a precoding unit 22, a plurality of D / A converting units 23, a plurality of transmission power control units 24, a plurality of amplifying units 25, and a plurality of antennas 26. The transmitting device 2a can be used to configure the wireless communication system 1 in place of the transmitting device 2 shown in FIG.

[0022] Each information bit generator 20 generates information bits (data signals) that become a transmission signal, and outputs the information bits to a modulator 21. The data signals generated by the information bit generators 20 each become a stream.

[0023] Each of the modulation units 21 modulates the data signal input from the information bit generation unit 20 using a predetermined modulation method, and outputs the modulated signal to the precoding unit 22. The modulation method includes, for example, Quadrature Phase Shift Keying (QPSK) where one symbol has four values, Quadrature Amplitude Modulation (16QAM) where one symbol has 16 values, and 64QAM where one symbol has 64 values.

[0024] The precoding unit 22 precodes multiple streams of data signals (transmission signals) in the time domain using an FIR filter, and outputs each stream to a plurality of D / A conversion units 23. When the precoding unit 22 performs precoding, the PAPR increases.

[0025] Each D / A converter 23 performs D / A conversion on the stream input from the precoding unit 22 and outputs the converted stream to a transmission power control unit 24 .

[0026] Each of the transmission power control units 24 controls the transmission power of the stream input from the D / A conversion unit 23 and outputs the stream to the amplification unit 25. That is, the multiple transmission power control units 24 each control the transmission power of the multi-stream precoded by the precoding unit 22.

[0027] The multiple amplifiers 25 amplify the multi-streams precoded by the precoding unit 22 in accordance with the control of the respective transmission power control units 24, and radiate the amplified multi-streams via the antennas .

[0028] Fig. 3 is a diagram illustrating an example of the amplification characteristic of the amplifier 25. Fig. 3(a) is a graph illustrating an example of the amplification characteristic of the amplifier 25. Fig. 3(b) is a diagram illustrating an example of the constellation of the transmission signal amplified by the amplifier 25.

[0029] As shown in FIG. 3(a), the amplifier 25 has a linear region where the amplifier amplifies and outputs the input in proportion to the input, and a nonlinear region where the amplifier nonlinearly amplifies an excessively large input.

[0030] 3(b), no distortion occurs in the transmission constellation when the amplifier 25 amplifies the data signal in the linear region, but distortion occurs in the transmission constellation when the amplifier 25 amplifies the data signal in the nonlinear region. When distortion occurs in the transmission constellation, the streams are no longer orthogonal, and inter-stream interference occurs.

[0031] 4 is a graph illustrating the relationship between the amplification characteristic and the magnitude of the PAPR of the amplifier 25. Even if the average transmission power input to the amplifier 25 is the same, when the PAPR is large, a large peak power is generated compared to when the PAPR is small.

[0032] When transmission signals with the same average transmission power are input to the amplifier unit 25, even if the transmission signals are always amplified within the linear region when the PAPR is small, when the PAPR is large, the transmission signals may be amplified in the non-linear region, resulting in non-linear distortion in the transmission constellation.

[0033] Therefore, the transmission device of the wireless communication system according to an embodiment described later is configured to be able to control the tap length of pre-coding so as to improve the quality of wireless communication even when the channel state fluctuates.

[0034] When the channel state changes, the tap coefficients change. For example, when the CIR length is L, the transfer function between the n-th t transmission antenna and the n-th r reception antenna is shown by the following formula (1).

[0035]

Equation

[0036] Also, the transfer function of the FIR filter between the s-th t transmission stream and the n-th t transmission antenna is shown by the following formula (2).

[0037]

Equation

[0038] Here, when L < M and the following formula (3) holds, the magnitude of the tap coefficients shown in the following formula (4) is small, and the tap length may be excessive.

[0039]

Equation

Equation

[0040] Furthermore, when L>M and the following equation (5) holds, the tap coefficients shown in the above equation (4) may be large and the tap length may be insufficient.

[0041]

number

[0042] Fig. 5 is a graph showing communication quality versus the magnitude of tap coefficients in precoding. Here, area A shown in Fig. 5 is an area where quality degradation due to nonlinear distortion caused by a small tap coefficient and a large PAPR is dominant. Area B is an area where quality degradation due to inter-stream interference and inter-symbol interference caused by a large tap coefficient and an insufficient tap length is dominant.

[0043] In other words, if the tap coefficient is too small or too large, the communication quality will be degraded. Therefore, the transmitting device of the wireless communication system according to one embodiment is configured to set a threshold value α for the magnitude of the tap coefficient and to control the tap length of the precoding using the threshold value α.

[0044] 6 is a diagram showing a relationship between a threshold value α used by a transmitting device according to an embodiment and a tap length M used for precoding. In the wireless communication system 1, the threshold value α may be determined while measuring reception quality before communication, or may be updated during communication. In addition, the wireless communication system 1 may determine the threshold value α in advance based on system design values ​​(such as characteristics of the amplifier 25 used by the transmitting device 2 and desired BER characteristics).

[0045] For example, a transmitting device according to one embodiment sets a threshold value α for the magnitude of the tap coefficient shown in the following equation (6), calculates the maximum m for which the following equation (7) holds, and uses m+1 as the tap length M.

[0046]

number

number

[0047] Furthermore, the transmission device according to one embodiment may determine the tap length M by calculating the minimum m for which the following formula (8) holds.

[0048]

number

[0049] Furthermore, the transmitting device in one embodiment may determine the tap length using the value shown in the following equation (9) or the magnitude of the tap coefficient converted into another easy-to-handle form, rather than using the magnitude of the tap coefficient shown in the above equation (4).

[0050]

number

[0051] For example, a transmitting device according to an embodiment may not use the magnitude of the tap coefficient as it is, but may perform normalization with, for example, the maximum tap coefficient, as shown in the following equation (10), and determine a threshold value for a relative value, etc.

[0052]

number

[0053] Next, a specific configuration example of the transmission device 2b according to an embodiment will be described below. Fig. 7 is a functional block diagram illustrating the functions of the transmission device 2b according to an embodiment.

[0054] As shown in FIG. 7, the transmitting device 2b in one embodiment includes a plurality of information bit generating units 20, a plurality of modulating units 21, a precoding unit 22, a plurality of D / A converting units 23, a plurality of transmission power control units 24, a plurality of amplifying units 25, a plurality of antennas 26, a switching unit 27, a receiving unit 28, a communication path information acquiring unit 29, a weight calculating unit 30, a quality information acquiring unit 31, a threshold calculating unit 32, a tap length controlling unit 33, and a threshold storing unit 34.

[0055] In the transmitting device 2b shown in Fig. 7, the same reference numerals are used for the configurations that are substantially the same as those of the transmitting device 2a shown in Fig. 2. Also, the transmitting device 2b can be used to configure the wireless communication system 1 in place of the transmitting device 2 shown in Fig. 1.

[0056] The switching unit 27 has a function of switching between transmission and reception via the antenna 26, causing the output signal of the amplifier 25 to be transmitted from the antenna 26, and outputting the signal received by the antenna 26 to the receiving unit .

[0057] The receiving unit 28 processes the signal received via the antenna 26 and outputs the signal to the communication path information acquiring unit 29 or the quality information acquiring unit 31 .

[0058] The communication channel information acquisition unit 29 acquires communication channel information based on the training signal for the communication channel between the transmitting device 2 and the receiving device 4 from the signal processed by the receiving unit 28, and outputs it to the weight calculation unit 30 and the threshold calculation unit 32.

[0059] The weight calculation unit 30 uses the communication channel information acquired by the communication channel information acquisition unit 29 to calculate precoding weights for the precoding unit 22 for each communication channel, and outputs the communication channel information and the weights to the tap length control unit 33.

[0060] The quality information acquisition unit 31 acquires quality information from the signal processed by the receiving unit 28, and outputs the quality information to the threshold calculation unit 32. The quality information includes the SNR and BER acquired by the receiving device 4 using the training signal (known signal) transmitted by the transmitting device 2, and also includes the influence of nonlinear distortion caused by the amplifying unit 25 of the transmitting device 2 and inter-stream interference caused by insufficient precoding.

[0061] The threshold calculation unit 32 calculates the above-mentioned threshold α based on the quality information acquired by the quality information acquisition unit 31 , and outputs the threshold α to the tap length control unit 33 .

[0062] The tap length control unit 33 controls changing the tap length of the precoding unit 22 so that, when the magnitude of the last tap coefficient of the precoding unit 22 is small, the tap length is decreased, and when the magnitude is large, the tap length is increased, relative to a threshold α calculated based on quality information of the received signal fed back from the receiving device 4 that received the stream amplified by the amplifier 25, or based on quality information of the received signal calculated using at least the characteristics of the amplifier 25.

[0063] The tap length control unit 33 may also control changing the tap length of the precoding unit 22 using a threshold value α stored in a threshold value storage unit 34 described later. The tap length control unit 33 also controls changing the tap length of the precoding unit 22 every time the weight calculation unit 30 calculates a precoding weight using communication channel information.

[0064] The threshold storage unit 34 stores a threshold value α calculated in advance in accordance with the characteristics of the amplifier unit 25 and outputs the threshold value to the tap length control unit 33 in response to an access from the tap length control unit 33 .

[0065] Next, an operation example of the transmission device 2b according to an embodiment will be described with reference to a flowchart of FIG 8.

[0066] As shown in FIG. 8, in step 100 (S100), the transmitting device 2b transmits a training signal to the receiving device 4, and the communication path information acquiring unit 29 acquires communication path information from the receiving device 4.

[0067] In step 102 (S102), the weight calculation unit 30 of the transmitting device 2b calculates the precoding weight.

[0068] In step 104 (S104), the tap length control unit 33 of the transmitting device 2b sets the tap length of the precoding unit 22 based on the threshold value α.

[0069] In step 106 (S106), the transmitting device 2b performs precoding with the tap length set by the precoding unit 22, and the process returns to S100.

[0070] In this way, the transmitting device 2b according to one embodiment controls the tap length based on the threshold value, and therefore, even if the channel state varies, the quality of wireless communication can be improved.

[0071] Moreover, the receiving device 4 shown in FIG. 1 may also calculate a threshold value by performing processing similar to that of the transmitting device 2, depending on the amplification characteristics of the receiving device 4 and the like.

[0072] Note that each unit constituting the transmission device 2b in the above-described embodiment may be partially or entirely configured by hardware, or may be configured by causing a processor to execute a program.

[0073] Furthermore, when each part constituting the transmitting device 2b is constituted in part or in whole by having a processor execute a program, the program may be recorded on a recording medium and supplied, or may be supplied via a network. [Explanation of symbols]

[0074] 1 wireless communication system, 2, 2a, 2b transmitting device, 4 receiving device, 20 information bit generating unit, 21 modulation unit, 22 precoding unit, 23 D / A conversion unit, 24 transmission power control unit, 25 amplifier unit, 26 antenna, 27 switching unit, 28 receiving unit, 29 communication path information acquiring unit, 30 weight calculation unit, 31 quality information acquiring unit, 32 threshold calculation unit, 33 tap length control unit, 34 threshold storage unit

Claims

1. A wireless communication method for transmitting a signal from a transmitting device to a receiving device, a precoding step of precoding the stream of transmitted signals in the time domain using an FIR filter; a transmission power control step of controlling a transmission power of the precoded stream; amplifying the precoded stream to a controlled transmission power; Including, A tap length control step of controlling the tap length of the FIR filter in the precoding step to be changed so that the tap length of the FIR filter is decreased when the magnitude of the last tap coefficient of the FIR filter in the precoding step is small, and the tap length of the FIR filter is increased when the magnitude of the last tap coefficient of the FIR filter is large, relative to a threshold value calculated based on quality information of the received signal fed back from the receiving device that has received the amplified stream, or quality information of the received signal calculated using at least the characteristics of the amplifier unit of the transmitting device. The wireless communication method further comprising:

2. a communication path information acquisition step of acquiring communication path information based on a training signal for a communication path between the transmitting device and the receiving device; a weight calculation step of calculating a precoding weight in the precoding step by using the communication channel information; Further comprising: In the tap length control step, Controlling to change a tap length of an FIR filter in the precoding process every time a precoding weight is calculated using the communication channel information.

2. The wireless communication method according to claim 1,

3. In a wireless communication system for transmitting a signal from a transmitting device to a receiving device, a precoding unit for precoding a stream of transmission signals in the time domain using an FIR filter; a transmission power control unit that controls a transmission power of the stream precoded by the precoding unit; an amplifier that amplifies the stream precoded by the precoding unit in accordance with control of the transmission power control unit; a tap length control unit that performs control to change the tap length of the FIR filter of the precoding unit so as to decrease the tap length of the FIR filter when the magnitude of the last tap coefficient of the FIR filter of the precoding unit is small relative to a threshold value calculated based on quality information of a received signal fed back from the receiving device that has received the stream amplified by the amplifier unit, or quality information of the received signal calculated using at least a characteristic of the amplifier unit, and to increase the tap length of the FIR filter when the magnitude of the last tap coefficient of the FIR filter of the precoding unit is large; A wireless communication system comprising:

4. a communication path information acquisition unit that acquires communication path information based on a training signal for a communication path between the transmitting device and the receiving device; a weight calculation unit that calculates a precoding weight for the precoding unit using the communication channel information; and The tap length control unit Controlling to change a tap length of an FIR filter of the precoding unit every time the weight calculation unit calculates a precoding weight using the communication channel information.

4. The wireless communication system according to claim 3,

5. a precoding unit for precoding a stream of transmission signals in the time domain using an FIR filter; a transmission power control unit that controls a transmission power of the stream precoded by the precoding unit; an amplifier that amplifies the stream precoded by the precoding unit in accordance with control of the transmission power control unit; a tap length control unit that performs control to change the tap length of the FIR filter of the precoding unit so that the tap length of the FIR filter is decreased when the magnitude of the last tap coefficient of the FIR filter of the precoding unit is small and the tap length of the FIR filter is increased when the magnitude of the last tap coefficient of the FIR filter of the precoding unit is large, relative to a threshold value calculated based on quality information of a received signal fed back from a receiving device that receives the stream amplified by the amplifier unit or quality information of a received signal calculated using at least a characteristic of the amplifier unit; A transmitting device comprising:

6. a communication path information acquisition unit that acquires communication path information based on a training signal for a communication path between the receiving device and the communication path information acquisition unit; a weight calculation unit that calculates a precoding weight for the precoding unit using the communication channel information; and The tap length control unit Controlling to change a tap length of an FIR filter of the precoding unit every time the weight calculation unit calculates a precoding weight using the communication channel information.

6. The transmitting device according to claim 5,

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