Wireless communication device, system, and method

Abstract

The purpose of the present invention is to provide a wireless communication device, system, method, and program capable of demodulating an orthogonal time frequency space (OTFS) signal with high precision and using a small amount of calculation while maintaining a high data rate OTFS signal. The wireless communication device (11) according to the present disclosure comprises a reception unit (111) that performs channel estimation by using a first reference signal, performs phase correction by using a second reference signal, and uses the results of the channel estimation and the phase correction to demodulate the received OTFS signal.

Description

[Technical field]

[0001] The present disclosure relates to a wireless communication device, a system, a method, and a program, and in particular to a wireless communication device, a system, a method, and a program capable of demodulating an Orthogonal Time Frequency Space (OTFS) signal with high accuracy and with a small amount of calculation while maintaining an OTFS signal with a high data rate. [Background technology]

[0002] In recent years, large-capacity communications between a base station (BS) and user equipment (UE) moving at high speed have been considered. However, the Orthogonal Frequency Division Multiplexing (OFDM) modulation method used in the 4th generation (4G) and 5th generation (5G) has a problem of low resistance to frequency errors caused by the Doppler effect. In recent years, the use of high-frequency band frequencies such as millimeter waves, which are greatly affected by the Doppler effect, has been considered, and increasing resistance to the Doppler effect has been an issue.

[0003] In order to correct the Doppler effect in OFDM, it is necessary to increase the number of reference signals and frequently update and correct the results of propagation channel estimation (channel estimation). However, increasing the number of reference signals reduces the number of elements that can be used for data, resulting in a drop in the data rate. In addition, frequent updates of channel estimation increase the amount of calculation required to process data, which is an issue.

[0004] Therefore, an Orthogonal Time Frequency Space (OTFS) modulation method has been proposed in Non-Patent Document 1. OTFS modulation arranges data in a Delay Doppler (DD) space, instead of arranging data in a Frequency Time (FT) space as in OFDM modulation.

[0005] OTFS modulation places data in DD space and modulates it, so it has high resistance to frequency errors caused by the Doppler effect, etc. Therefore, it is expected to enable high-speed communication (high data rate) for fast-moving UE.

[0006] In OTFS modulation, the influence of the propagation channel between the UE and the base station is corrected by calculating the channel impulse response (CIR) using a reference signal (RS). In order to calculate the CIR, a wide DD space is generally required. Therefore, if RS is placed frequently, the data rate will decrease.

[0007] Therefore, for example, instead of arranging RS in all subframes, it is possible to arrange RS intermittently. However, the accuracy of the CIR calculated in different subframes is degraded due to frequency errors caused by the Doppler effect, etc. The deterioration of the accuracy of the CIR leads to a decrease in demodulation accuracy, which results in a decrease in the data rate (throughput).

[0008] In addition, in an OTFS modulated signal, data is placed in the DD space. In order to correct the influence of the data propagation channel in the DD space, it is necessary to perform a convolution operation between the correction coefficient calculated from the CIR and the received data. However, the convolution operation requires a large amount of calculation, and a large amount of calculation is also required to calculate the correction coefficient (see Non-Patent Document 2).

[0009] Therefore, a method was needed to demodulate the OTFS signal with high accuracy and with a small amount of calculation while maintaining the high data rate of the OTFS signal.

[0010] Paragraph 0237 of Patent Document 1 states, "For example, when a target antenna port is a specific NZP CSI-RS, the NZP CSI-RS antenna ports can be instructed / configured to be QCLed with a specific TRS from the perspective of QCL-Type A and with a specific SSB from the perspective of QCL-Type D. A terminal that receives such instruction / configuration can receive the NZP CSI-RS using the Doppler and delay values ​​measured in the QCL-TypeA TRS, and can apply the reception beam used for QCL-TypeD SSB reception to the NZP CSI-RS reception." Patent Document 1 does not describe demodulating an OTFS signal with high accuracy and with a small amount of calculation while maintaining an OTFS signal with a high data rate.

[0011] Paragraph 0076 of Patent Document 2 states that "The receiver receives a combination of direct and replicated OTFS pilot bursts as a channel-convolved OTFS pilot burst. The order of arrival of the OTFS pilot bursts at the receiver is 1) direct OTFS pilot burst, followed by frequency-shifted replicated OTFS pilot burst." Also, paragraph 0199 of Patent Document 2 states that "Each data symbol is distributed in a lossless and reversible manner across a plurality of distinguishable (e.g., typically mutually orthogonal) waveforms over a plurality of different times and different frequencies selected according to the time delay and Doppler shift channel response parameters of the wireless multidimensional data channel." Patent Document 2 does not describe demodulating an OTFS signal with high accuracy and with a small amount of calculation while maintaining the OTFS signal at a high data rate. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Special Publication No. 2021-502783 [Patent Document 2] JP 2020-205641 A [Non-patent literature]

[0013] [Non-Patent Document 1] R. Hadani et al., "Orthogonal Time Frequency Space Modulation," 2017 IEEE Wireless Communications and Networking Conference (WCNC), 2017, pp. 1-6. [Non-Patent Document 2] GD Surabhi and A. Chockalingam, "Low-Complexity Linear Equalization for OTFS Modulation," in IEEE Communications Letters, vol. 24, no. 2, pp. 330-334, Feb. 2020. Summary of the Invention [Problem to be solved by the invention]

[0014] As described above, there was a need for a method for demodulating an OTFS signal with high accuracy and with a small amount of calculation while maintaining the high data rate of the OTFS signal.

[0015] An object of the present disclosure is to provide a wireless communication device, system, method, and program that solves the above-mentioned problems. [Means for solving the problem]

[0016] A wireless communication device according to the present disclosure includes: The receiver performs channel estimation using a first reference signal, mainly performs phase correction using a second reference signal, and demodulates a received Orthogonal Time Frequency Space (OTFS) signal using the results of the channel estimation and the phase correction.

[0017] The system according to the present disclosure comprises: The present invention relates to a user equipment and a base station. The user device comprises: A transmitter that transmits a first reference signal, an orthogonal time frequency space (OTFS) signal, and a second reference signal, The base station, The receiver includes a receiver that performs channel estimation using the first reference signal, performs phase correction using the second reference signal, and demodulates the received OTFS signal using results of the channel estimation and the phase correction.

[0018] The method according to the present disclosure comprises: performing channel estimation using a first reference signal, performing phase correction using a second reference signal, and demodulating a received Orthogonal Time Frequency Space (OTFS) signal using results of the channel estimation and the phase correction; Equipped with.

[0019] The program according to the present disclosure is performing channel estimation using a first reference signal, performing phase correction using a second reference signal, and demodulating a received Orthogonal Time Frequency Space (OTFS) signal using results of the channel estimation and the phase correction; to be executed by the computer. Effect of the Invention

[0020] According to the present disclosure, it is possible to provide a wireless communication device, system, method, and program capable of demodulating an Orthogonal Time Frequency Space (OTFS) signal with high accuracy and with a small amount of calculation while maintaining an OTFS signal with a high data rate. [Brief description of the drawings]

[0021] [Figure 1] 1 is a block diagram illustrating a wireless communication device according to a first embodiment. [Diagram 2] 1 is a block diagram illustrating a system according to a first embodiment. [Diagram 3] FIG. 2 is a block diagram illustrating the configuration of a UE and a base station according to the first embodiment. [Figure 4] 2 is a block diagram illustrating a channel estimation unit according to the first embodiment. FIG. [Diagram 5] FIG. 2 is a schematic diagram illustrating an example of an arrangement of CIR-RS, PCRS, and data according to the first embodiment. [Figure 6A] FIG. 4 is a constellation diagram illustrating the effect of correction by the base station according to the first embodiment. [Figure 6B] FIG. 4 is a constellation diagram illustrating the effect of correction by the base station according to the first embodiment. [Figure 7A] FIG. 11 is a constellation diagram illustrating the effect of correction in the delay direction by the base station according to the first embodiment. [Figure 7B] FIG. 11 is a constellation diagram illustrating the effect of correction in the delay direction by the base station according to the first embodiment. [Figure 8] FIG. 11 is a block diagram illustrating an OTFS post-processing unit according to the second embodiment. [Figure 9A] FIG. 1 is a schematic diagram illustrating signal mapping when two users have multiple connections. [Figure 9B] FIG. 1 is a schematic diagram illustrating signal mapping when two users have multiple connections. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding elements are given the same reference numerals, and for clarity of explanation, duplicate explanations will be omitted as necessary.

[0023] [Embodiment 1] <Summary> FIG. 1 is a block diagram illustrating a wireless communication device according to the first embodiment. FIG. 1 shows a minimum configuration of a wireless communication device according to the first embodiment. FIG. 2 is a block diagram illustrating a system according to the first embodiment.

[0024] As shown in Fig. 1, the wireless communication device 11 according to the first embodiment includes a receiver 111. The receiver 111 performs channel estimation using a first reference signal, performs phase correction using a second reference signal, and demodulates a received Orthogonal Time Frequency Space (OTFS) signal using the results of the channel estimation and phase correction. Note that the wireless communication device may also be referred to as a wireless base station or a base station.

[0025] The receiving unit 111 receives and demodulates an OTFS signal including, for example, a subframe in which a first reference signal is allocated and a subframe in which a second reference signal is allocated.

[0026] As shown in Fig. 2, a system 10 according to the first embodiment includes a base station (BS) 11 and a user equipment (UE) 12. The UE 12 has a transmitting unit (not shown) that transmits a first reference signal, an OTFS signal, and a second reference signal. The base station 11 has a receiving unit (not shown) that receives the first reference signal, data, and the second reference signal.

[0027] The UE 12 is mounted on, for example, a vehicle and moves at high speed. In the first embodiment, an uplink transmitted from the UE 12 to the base station 11 will be described, but the present invention is not limited to this. The first embodiment can also be applied to a downlink transmitted from the base station 11 to the UE 12 in the same manner as the uplink.

[0028] An OTFS modulated high frequency signal is transmitted from the transmitting unit of UE 12 to the receiving unit of base station 11. The high frequency signal reaches base station 11 after being attenuated during propagation and being reflected, diffracted, and transmitted by obstacles such as buildings. The effects of attenuation and reflection are collectively referred to as a propagation channel. Furthermore, when UE 12 moves at high speed, the frequency of the high frequency signal transmitted from UE 12 is received by base station 11 with a slight shift due to the Doppler effect.

[0029] The receiving unit of the base station 11 receives the OTFS modulated high frequency signal, performs channel estimation of the propagation channel using the first reference signal of the down-converted OTFS signal, performs phase correction using the second reference signal, and demodulates the received OTFS signal using the results of the channel estimation and phase correction. The receiving unit of the base station 11 corrects and demodulates the OTFS signal (high frequency signal) affected by the propagation channel and Doppler effect using a technique described later.

[0030] The first reference signal is a Channel Impulse Response Reference Signal (CIR-RS) for calculating a Channel Impulse Response (CIR), and the second reference signal is a Phase Compensation Reference Signal (PCRS) for mainly performing phase compensation.

[0031] <Configuration> FIG. 3 is a block diagram illustrating the configuration of a UE and a base station according to the first embodiment. FIG. 3 shows a transmitter 122 of the UE 12 and a receiver 111 of the base station 11 . In this example, the uplink from UE 12 to base station 11 is described.

[0032] 3, the transmission unit 122 of the UE 12 includes an OTFS pre-processing unit 1221 that performs OTFS pre-processing, an OFDM modulation unit 1222 that performs Orthogonal Frequency Division Multiplexing (OFDM) modulation, a D to R unit that converts a digital signal into an RF (Radio Frequency) signal, and an antenna (ANT). Note that the signal may also be referred to as data.

[0033] The OTFS preprocessing unit 1221 includes a mapping unit that arranges a reference signal (RS), data, and the like in each element, and an ISFFT0 unit that performs an inverse SFFT (Symplectic Finite Fourier Transform).

[0034] The OFDM modulation unit 1222 performs the same process as normal OFDM modulation. The OFDM modulation unit 1222 includes an Add Zero unit that adds zero data outside the band of data, an IFFT unit that performs an inverse Fourier transform, an Add CP unit that adds a CP (Cyclic prefix), and a P to S unit that converts data from parallel to serial.

[0035] The receiving unit 111 of the base station 11 includes an antenna (ANT), an R to D unit that converts a received RF signal into a digital signal, an OFDM demodulation unit 1112, and an OTFS post-processing unit 1111.

[0036] The OFDM demodulation unit 1112 performs the same process as normal OFDM demodulation. The OFDM demodulation unit 1112 includes an S to P unit that converts digital data from serial to parallel, an Rm CP unit that removes CP, an FFT unit that performs a fast Fourier transform (FFT), and an Rm Zero unit that removes out-of-band components.

[0037] The OTFS post-processing unit 1111 includes a channel estimating unit that estimates a propagation channel, a first equalizer EQ1, an SFFT0 unit that performs SFFT, and a second equalizer EQ2.

[0038] The first equalizer EQ1 performs channel correction based on a first reference signal in the FT space, while the second equalizer EQ2 performs phase correction based on a second reference signal in the DD space.

[0039] After the first equalizer EQ1 performs channel correction, the second equalizer EQ2 performs phase correction.

[0040] The channel estimator performs channel estimation using the first reference signal to obtain a channel impulse response (CIR). The first equalizer EQ1 performs channel correction on the OTFS signal based on the obtained CIR.

[0041] FIG. 4 is a block diagram illustrating a channel estimation unit according to the first embodiment. FIG. 4 shows the channel estimation unit in detail.

[0042] As shown in FIG. 4, the channel estimation unit includes an SFFT1 unit that performs SFFT, a CIR-RS extraction unit that extracts an element region around a channel impulse response-reference signal (CIR-RS), an ISFFT1 unit that performs ISFFT, and an ISFFT2 unit that performs ISFFT on the reference signal (RS).

[0043] <Operation> <UE Operation> The transmission unit 122 of UE 12 arranges RS and data in the DD space by the mapping unit. FIG. 5 is a schematic diagram illustrating the arrangement of CIR-RS, PCRS, and data according to Embodiment 1. The horizontal axis of FIG. 5 indicates the Doppler Index, and the vertical axis indicates the Delay Index.

[0044] In this example, the total number of indexes M in the Delay direction in one subframe is M = 1200, the total number of indexes N in the Doppler direction is N = 14, and 10 subframes are defined as one frame.

[0045] The number of subframes in which only CIR-RS (the first reference signal) is arranged may be one per frame, and the number of subframes in which data and PCRS (the second reference signal) are arranged may be two or more.

[0046] Specifically, in the 0th subframe, only CIR-RS is arranged, and all elements where CIR-RS is not arranged are set to zero (blank). CIR-RS is arranged at the element position with the delay index l0 = 150 and the Doppler index k0 = 1. In this example, CIR-RS is arranged at only one element, but it is not limited to this. CIR-RS may be arranged within a certain element range. Also, data may be arranged within a range that does not affect the CIR-RS analysis range described later.

[0047] In the 1st subframe to the 9th subframe, data and a phase compensation reference signal (PCRS) are arranged. In this example, PCRS has the delay index l p = 0, 48, 95,..., 1152, and the Doppler index k p= 0 element position. The PCRS is a known QPSK signal distributed in a random manner. However, the element positions and data of the PCRS are not limited to this.

[0048] As shown above, the i-th subframe signal arranged in the DD space is expressed as x i(l,k) DD Here, l=0,1,...,M-1, k=0,1,...,N-1, i=0,1,...,9. In particular, the signal x 0(l,k) DD is expressed as equation (1). TIFF0007647906000001.tif1158(1)

[0049] signal x i(l,k) DD is OTFS modulated for each subframe. The modulation method is the same as the method shown in Non-Patent Document 1 and Non-Patent Document 2.

[0050] First, the signal x i(l,k) DD The ISFFT converts the signal x from the DD space to the FT space. i(m,n) FT , (m=0,1,…,M-1, n=0,1,…,N-1). Signal x i(m,n) FT As shown in equation (2), is calculated by performing Fourier transform and inverse Fourier transform in the delay direction and Doppler direction, respectively, using ISFFT. TIFF0007647906000002.tif1586(2)

[0051] signal x i(m,n) FT is OFDM modulated in the usual manner by the OFDM modulation unit 1222. i(p,q) , (where p = 0, 1, ..., M-1 and q = 0, 1, ..., N-1) are expressed as in equations (3) and (4). TIFF0007647906000003.tif1759(3) TIFF0007647906000004.tif1645(4)

[0052] For simplicity, the addition of out-of-band zero data in the Add Zero section and the addition of CP in the Add CP section are ignored (omitted). 0(p,q) From equations (1) and (4), we obtain equation (5). TIFF0007647906000005.tif1761(5)

[0053] The P to S section of the transmitter 122 of the UE 12 transmits the signal s i(p,q) The D to R section converts the digital baseband signal into an analog baseband signal, and then converts the analog baseband signal into an RF signal in the carrier band. The RF signal is emitted into the air from the ANT.

[0054] <Base station operation> The receiver 111 of the base station 11 receives an RF signal from the UE 12 via ANT, and converts the RF signal into a digital baseband signal in the R to D section. The S to P section serial-to-parallel converts the digital baseband signal into a received signal r i(p,q) to.

[0055] The OFDM demodulation unit 1112 demodulates the received signal r i(p,q) Here, it is assumed that the UE 12 and the base station 11 are synchronized with each other in timing in a normal manner. The Rm CP part of the OFDM demodulation part 1112 demodulates the received signal r i(p,q) Then, the FFT unit performs a Fourier transform, and the Rm Zero unit removes the out-of-band zero components. The OFDM demodulation unit 1112 demodulates the signal y i(m,n) FT can be expressed as equations (6) and (7). TIFF0007647906000006.tif1766(6) TIFF0007647906000007.tif1791(7)

[0056] For simplicity, the CP removal, the out-of-band zero data removal, and the noise components are ignored (omitted). (m,n) is the propagation channel, ω0 is the angular frequency corresponding to the frequency offset due to the Doppler effect, t s is the sampling interval (the inverse of the sampling rate). Therefore, e in equation (7) (jω0ts(MNi+Mn+p)) indicates the phase change due to the Doppler effect.

[0057] Signal y i(m,n) FT In this example, channel estimation is performed using the 0th subframe in which the CIR-RS is placed, and the CIR is calculated. The channel estimation is performed in the order shown in FIG. 4. First, the SFFT1 unit calculates the signal y 0(m,n) FT Then, SFFT is performed on the signal y 0(l,k) DD Convert the signal y 0(l,k) DD is shown in equation (8). TIFF0007647906000008.tif1694(8)

[0058] The CIR-RS extractor extracts the signal y 0(l,k) DD Only the surrounding elements where CIR-RS is placed are extracted from. This extracted range is called the CIR-RS extraction range. In this example, as shown by the dotted line in Figure 5, a range of + / -150 indexes in the delay direction and + / -3 indexes in the Doppler direction is extracted from the element where CIR-RS is placed. If the CIR-RS extraction range exceeds the end of the subframe, the range is set by wrapping around within the subframe as shown by the dotted line in Figure 5. In this case, the values ​​of elements outside the CIR-RS extraction range are set to zero. The signal after CIR-RS extraction is represented as y r(l,k) DD Let us assume that.

[0059] The reason why the CIR-RS extraction range is made larger than the range in which the CIR-RS is placed is to extract the CIR-RS that has been affected by radio wave propagation. That is, the CIR-RS is received at a position different from the original element position or distributed to multiple element positions due to delay, Doppler effect, etc. Then, the CIR is estimated based on such changes in the CIR-RS.

[0060] Also, by extracting the periphery of the CIR-RS, the influence of thermal noise and the like can be suppressed, and the accuracy of channel estimation can be improved. In this example, only the CIR-RS is placed in the 0th subframe, but this is not limited to this. Data or CIR-RS for other UEs may be placed in an element area that does not affect the CIR-RS extraction range.

[0061] The signal y after CIR-RS is extracted r(l,k) DD is transformed in the ISFFT1 section, i.e., in the same manner as the processing (transformation) shown in equation (2), and the signal y r(m,n) FT The signal y is converted to r(m,n) FT Since is considered to be the received signal when only CIR-RS is transmitted, it is expressed as equation (9) based on equations (7) and (5). TIFF0007647906000009.tif11101(9)

[0062] Since the CIR-RS is a known signal, the base station 11 also uses the 0th subframe signal x r(l,k) DD In this example, we create a signal x r(l,k) DD is the signal x shown in equation (1). 0(l,k) DD In UE 12, only CIR-RS is arranged in the 0th subframe, but even if data or the like is arranged in the 0th subframe in UE 12, only CIR-RS is arranged in the 0th subframe generated by base station 11.

[0063] Signal x in DD space r(l,k) DD is transformed by ISFFT2 in the same way as equation (2), and the signal x r(m,n) FT The signal x is converted to r(m,n) FT is shown in Equation (10) and Equation (11).

[0064] TIFF0007647906000010.tif1692(10) TIFF0007647906000011.tif1139(11)

[0065] If the same signal is used as the CIR-RS in each frame, then the signal x r(m,n) FT It is not necessary to calculate x , but it may be calculated once at the beginning and then used repeatedly. Also, in this example, the signal x r(l,k) DD From signal x r(m,n) FT However, the present invention is not limited to this. r(m,n) FT may be stored in a memory in the base station 11 and used.

[0066] CIR coefficient h calculated by the channel estimation section e(m,n) is the CIR-RS FT space signal y r(m,n) FT and the signal x in the FT space of CIR-RS that is not affected by the propagation channel. r(m,n) FT That is, the channel estimation unit calculates the quotient of CIR-RS (first reference signal) calculated from the received OTFS signal in the FT space by CIR-RS (first reference signal) that is not affected by the propagation channel, as the CIR coefficient h e(m,n) The CIR coefficient h e(m,n) is shown in Equation (12) and Equation (13). TIFF0007647906000012.tif749(12) TIFF0007647906000013.tif745(13)

[0067] This allows the channel coefficients to be calculated, including the effect of frequency error due to the Doppler effect. The CIR coefficient h e(m,n) is repeatedly used until a subframe in which CIR-RS is assigned is received again.

[0068] The first equalizer EQ1 uses the CIR coefficient h e(m,n) The channel correction is performed in the FT space using the corrected signal z i(m,n) EQ1 is shown in Equation (14) and Equation (15). TIFF0007647906000014.tif952(14) TIFF0007647906000015.tif1877(15)

[0069] signal z i(m,n) EQ1 is transformed by SFFT0, and the signal z i(l,k) DD is converted to z i(l,k) DD is shown in Equation (16) and Equation (17). TIFF0007647906000016.tif1895(16) TIFF0007647906000017.tif855(17)

[0070] As shown in equations (16) and (17), the signal z i(l,k) DD In this case, the phase shift due to the Doppler effect remains and cannot be completely corrected.

[0071] The phase shift due to the Doppler effect has two components. The first component is e (jω0tsMNi) is a phase shift for each subframe, which occurs because the CIR calculated in the 0th subframe is used in the subsequent subframes. The second component is e (jω0ts(l-l0))and this phase shift depends on the difference in the delay direction from the position where the CIR-RS is placed.

[0072] This phase shift is corrected by the second equalizer EQ2 using PCRS. i(l,k) is obtained by calculating the quotient of the original PCRS signal (a known signal previously agreed upon between the transmitting side and the receiving side) and the received signal, as shown in equations (18) and (19). TIFF0007647906000018.tif877(18) TIFF0007647906000019.tif438(19)

[0073] Here, the subframe number i is an integer between 1 and 9. Correction coefficient for delay indexes that do not exist in PCRS TIFF0007647906000020.tif673 is calculated by interpolation and extrapolation from nearby correction coefficients. Also, the correction coefficient for Doppler indexes that do not have PCRS is TIFF0007647906000021.tif657 is the correction factor w for the Doppler index where PCRS exists. i(l,k∈kp) Use a value equal to TIFF0007647906000022.tif10126.

[0074] When placing data in the 0th subframe, add PCRS to a position that does not affect the extraction range of CIR-RS, and perform correction in the same manner as above. Or, use the correction coefficient w i(l,k) It may be obtained by extrapolation using the correction coefficients of the same Delay index (i=1, 2, ..., 9).

[0075] The second equalizer EQ2 uses a correction coefficient w i(l,k) The received signal z i(l,k) DD The signal z after correction by the second equalizer EQ2 is i(l,k) EQ2 is shown in Equation (20) and Equation (21). TIFF0007647906000023.tif848(20) TIFF0007647906000024.tif819(21)

[0076] By using the second equalizer EQ2, the phase shift caused by the Doppler effect is corrected, and the transmitted signal is received correctly. In this example, the amplitude change is ignored for simplicity, but the amplitude change for each subframe can also be corrected by using the second equalizer EQ2.

[0077] <Effects> The base station 11 according to the first embodiment performs channel correction in the FT space. This makes it possible to reduce the amount of calculations. For example, consider a case where one UE 12 and the base station 11 are communicating with each other. In this case, when performing channel correction in the DD space, it is necessary to calculate the inverse of a (MNxMN)-dimensional matrix and perform a convolution operation with the received signal (see Non-Patent Document 2). On the other hand, in the first embodiment, it is only necessary to calculate the inverse of each element of the MxN-dimensional matrix and multiply it by each element of the received signal, so that it is possible to reduce the amount of calculations.

[0078] In addition, since the base station 11 according to the first embodiment performs channel correction in the FT space, even when an OTFS signal is used, the spatial multiplexing technique can be used in a normal manner. This allows multiple UEs 12 to connect simultaneously to the same frequency, thereby increasing the communication capacity of the base station 11.

[0079] As a result, it is possible to provide a wireless communication device, system, method, and program capable of demodulating an Orthogonal Time Frequency Space (OTFS) signal with high accuracy and with a small amount of calculation while maintaining an OTFS signal with a high data rate.

[0080] Furthermore, base station 11 according to the first embodiment uses two types of RS, CIR-RS and PCRS, which makes it possible to correct both the influence of the propagation channel and the influence of the Doppler effect.

[0081] Specifically, by using the second equalizer EQ2 using PCRS, it is possible to use the CIR calculated in a subframe different from the data to be corrected. Since channel estimation using CIR-RS in every subframe leads to a decrease in data rate, a high data rate can be maintained by using subframes where channel estimation is not performed.

[0082] 6A and 6B are constellation diagrams illustrating the effect of correction by the base station according to the first embodiment. 6A and 6B, the horizontal axis indicates the I channel, and the vertical axis indicates the Q channel.

[0083] 6A and 6B show the results when the UE moves toward the base station at a walking speed (about 4 km / s). The carrier frequency is 28 GHz (gigahertz). FIG. 6A is a constellation diagram when the second equalizer EQ2 does not perform correction for each subframe. FIG. 6B is a constellation diagram when the second equalizer EQ2 performs correction for each subframe.

[0084] As shown in Fig. 6A, if the second equalizer EQ2 does not perform correction, the phase rotates for each subframe after the first subframe. On the other hand, as shown in Fig. 6B, if the second equalizer EQ2 performs correction, the phase rotation is corrected.

[0085] Furthermore, since the influence of the Doppler effect, which depends on the Delay index, cannot be estimated by using only the CIR, this influence remains with only the first equalizer EQ1 (see Equation 17). The base station 11 according to the first embodiment can correct this influence by using the second equalizer EQ2 using the PCRS, thereby improving the demodulation accuracy.

[0086] 7A and 7B are constellation diagrams illustrating the effect of correction in the delay direction by the base station according to the first embodiment. 7A and 7B, the horizontal axis indicates the I channel, and the vertical axis indicates the Q channel. Figures 7A and 7B show the measurement results when the UE is assumed to be moving at high speed and a frequency error of 4 kHz (kilohertz) is applied to the UE transmitter and the base station receiver. A frequency error of 4 kHz is equivalent to a situation in which the UE is moving toward the base station at approximately 150 km / h. The carrier frequency is 28 GHz (gigahertz).

[0087] FIG. 7A is a constellation diagram when the second equalizer EQ2 does not perform correction in the delay direction. FIG. 7B is a constellation diagram when the second equalizer EQ2 performs correction in the delay direction. 7A and 7B show constellations for one subframe.

[0088] As shown in Fig. 7A, when the second equalizer EQ2 does not perform correction in the delay direction, dispersion occurs in the circumferential direction. On the other hand, as shown in Fig. 7B, when the second equalizer EQ2 performs correction in the delay direction, dispersion in the circumferential direction is corrected.

[0089] In addition, base station 11 according to embodiment 1 converts the signal of the 0th subframe into DD space using the SFFT1 unit, and extracts the surroundings of the CIR-RS using the CIR-RS extraction unit, thereby making it possible to extract only the CIR-RS that is affected by the propagation channel while suppressing noise.

[0090] Here, the features of the base station according to the first embodiment will be described below. By using two types of reference signals (CIR-RS and PCRS) and using different equalizers for each, the OTFS signal can be demodulated accurately with a small amount of calculation while maintaining a high data rate.

[0091] [Embodiment 2] FIG. 8 is a block diagram illustrating an OTFS post-processing unit according to the second embodiment.

[0092] 8, the base station 21 according to the second embodiment differs from the base station 11 according to the first embodiment in that a first selector SE1 and a second selector SE2 are added. The base station 21 also differs from the base station 11 in that the SFFT0 unit and the SFFT1 unit are common. The other elements (functional units) of the base station 21 are similar to those of the base station 11.

[0093] The first selector SE1 and the second selector SE2 are used to bypass the first equalizer EQ1 when estimating the CIR. For example, as in the first embodiment, when using a signal in which CIR-RS is assigned to the 0th subframe, the first selector SE1 and the second selector SE2 are switched so as to bypass the first equalizer EQ1 in the 0th subframe. On the other hand, in the 1st to 9th subframes, the first selector SE1 and the second selector SE2 are switched so as to use the first equalizer EQ1.

[0094] That is, the first selector SE1 and the second selector SE2 are set so that the subframe in which only the CIR-RS is arranged bypasses the first equalizer EQ1. Also, the first selector SE1 and the second selector SE2 input the signal obtained by OFDM demodulation to the first equalizer EQ1 in the subframe in which the CIR-RS is not arranged.

[0095] In addition, when the first selector SE1 and the second selector SE2 are not used, the CIR coefficient h e(m,n) may be changed to 1 so that correction is not performed in the first equalizer EQ1.

[0096] Furthermore, the SFFT0 unit and the SFFT1 unit according to the first embodiment may be a common unit. To achieve this, as shown in FIG. 8, the channel estimation unit may include a CIR-RS (first reference signal) extraction unit and an inverse SFFT transformation unit (ISFFT1 unit). The SFFT0 unit (SFFT transformation unit) performs SFFT transformation on the signal on which the first equalizer EQ1 has performed channel correction. The CIR-RS extraction unit extracts the CIR-RS from the signal converted by the SFFT transformation unit. The ISFFT1 unit performs inverse SFFT transformation on the signal extracted by the CIR-RS extraction unit.

[0097] This makes it possible to omit the calculation of the SFFT (reduce the number of SFFTs by one) (see FIGS. 4 and 8), thereby reducing the amount of calculation in the receiving section compared to the first embodiment.

[0098] [Embodiment 3] 9A and 9B are schematic diagrams illustrating signal mapping when two users have multiple connections. FIG. 9A shows the signal mapping for a first UE (UE 32a). FIG. 9B shows the signal mapping for a second UE, UE 32b.

[0099] The third embodiment can also be used in a multi-user environment in which a plurality of UEs 32 communicate simultaneously with the base station 31. In the third embodiment, the CIR-RS and PCRS are arranged for each UE 32 by changing the element positions.

[0100] As shown in Figures 9A and 9B, the CIR-RS undergoes changes such as changes in element position on mapping and diffusion (dispersion) to multiple elements due to delays caused by radio wave propagation and the Doppler effect. As a result, if the CIR-RS affects the CIR-RS extraction range of another UE, the CIR estimation accuracy decreases and the demodulation accuracy decreases. Therefore, in the third embodiment, the CIR-RS is placed in a position sufficiently separated from each other so that multiple CIR-RS extraction ranges do not affect each other, as shown in Figures 9A and 9B.

[0101] Specifically, the CIR-RS (first reference signal) for the first UE is arranged within a predetermined first element range for the first UE. The CIR-RS (first reference signal) for the second UE is arranged within a predetermined second element range for the second UE. The first element range and the second element range are arranged at positions separated by a predetermined distance or more. The CIR-RS extraction range may also be referred to as an element range.

[0102] In the third embodiment, the CIR-RS for UE 32a and the CIR-RS for UE 32b are placed at separate locations, so that the CIR-RS extraction unit can extract only the CIR-RS for each UE, and the CIR for each UE can be reliably determined.

[0103] Also, PCRS may be arranged for each UE so that the element positions do not overlap.

[0104] In addition, in the first to third embodiments, since the channel correction using the CIR is performed in the FT space, spatial multiplexing techniques such as the zero-forcing method and the minimum mean square error method can be used. This makes it possible to multiplex multiple signals simultaneously in the same frequency band, thereby increasing the communication traffic.

[0105] The increase in communication traffic due to spatial multiplexing technology can be applied not only to upstream signals, but also to downstream signals by utilizing the reciprocity of the propagation channel, which makes it possible to increase communication traffic in the downstream as well.

[0106] In the above embodiment, the present invention has been described as being configured as hardware, but the present invention is not limited to this. The present invention can also be realized by having a CPU (Central Processing Unit) execute a computer program to process each component.

[0107] In the above embodiment, the program can be stored and supplied to the computer using various types of non-transitory computer readable media. The non-transitory computer readable media includes various types of tangible storage media. Examples of the non-transitory computer readable media include magnetic recording media (specifically, flexible disks, magnetic tapes, and hard disk drives), magneto-optical recording media (specifically, magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, semiconductor memories (specifically, mask ROMs, PROMs (Programmable ROMs), and EPROMs (Erasable PROMs)), flash ROMs, and RAMs (Random Access Memory). The program may also be supplied to the computer by various types of transitory computer readable media. Examples of the transitory computer readable media include electrical signals, optical signals, and electromagnetic waves. The transitory computer readable media can supply the program to the computer via wired communication paths such as electric wires and optical fibers, or wireless communication paths.

[0108] Additionally, although operations are depicted in a particular order, this should not be understood as requiring such operations to be performed in the particular order or sequential order depicted, or that all of the depicted operations be performed, to achieve desirable results. In certain situations, multitasking and parallel processing may be advantageous. Similarly, although details of several specific embodiments are included in the above discussion, these should not be construed as limitations on the scope of the disclosure, but rather as descriptions of features specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable combination.

[0109] Although the present invention has been described above with reference to the embodiment, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

[0110] The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit and scope of the present invention.

[0111] A part or all of the above-described embodiments can be described as, but is not limited to, the following supplementary notes. (Appendix 1) A wireless communication device comprising a receiver that performs channel estimation using a first reference signal, performs phase correction using a second reference signal, and demodulates a received Orthogonal Time Frequency Space (OTFS) signal using results of the channel estimation and the phase correction. (Appendix 2) The receiving unit receives and demodulates the OTFS signal including a subframe in which the first reference signal is arranged and a subframe in which the second reference signal is arranged. 2. The wireless communication device of claim 1. (Appendix 3) The first reference signal is a channel impulse response reference signal (CIR-RS: Channel Impulse Response-Reference Signal) for obtaining a channel impulse response (CIR), The second reference signal is a phase compensation reference signal (PCRS: Phase Compensation Reference Signal) for performing the phase compensation. 3. The wireless communication device of claim 1 or 2. (Appendix 4) The receiving unit is A first equalizer that performs channel correction based on the first reference signal in a frequency-time (FT) space; A second equalizer that performs the phase correction process based on the second reference signal in a delay Doppler (DD) space. 4. The wireless communication device of claim 3. (Appendix 5) After the first equalizer performs the channel correction, the second equalizer performs the phase correction. 5. The wireless communication device of claim 4. (Appendix 6) the receiving unit further includes a channel estimator that performs the channel estimation using the first reference signal to obtain the CIR; The first equalizer performs the channel correction on the received data based on the CIR. 6. The wireless communication device of claim 4 or 5. (Appendix 7) The channel estimation unit calculates, in the FT space, a quotient obtained by dividing the first reference signal obtained from the received OTFS signal by the first reference signal that is not affected by a propagation channel, as the CIR. 7. The wireless communication device of claim 6. (Appendix 8) The number of subframes in which only the first reference signal is arranged is one per frame; The number of subframes in which the data and the second reference signal are arranged is two or more. 7. The wireless communication device of claim 6. (Appendix 9) A selector that sets a subframe in which only the first reference signal is arranged to bypass the first equalizer, In a subframe in which the first reference signal is not allocated, a signal obtained by Orthogonal Frequency Division Multiplexing (OFDM) demodulation is input to the first equalizer. 8. A wireless communication device according to any one of claims 4 to 7. (Appendix 10) an SFFT transform unit that performs an SFFT transform on the signal that has been subjected to the channel compensation by the first equalizer; a first reference signal extraction unit that extracts the first reference signal from the signal converted by the SFFT conversion unit; an inverse SFFT transform unit that performs an inverse SFFT transform on the signal extracted by the first reference signal extraction unit; Further comprising: 5. The wireless communication device of claim 4. (Appendix 11) The first reference signal for a first UE (User Equipment) is arranged within a predetermined first element range for the first UE; the first reference signal for a second UE is located within a predetermined second element range for the second UE; The first element range and the second element range are disposed at positions spaced apart by a predetermined distance or more. 11. A wireless communication device according to any one of claims 1 to 10. (Appendix 12) The present invention relates to a user equipment and a base station. The user device comprises: A transmitter that transmits a first reference signal, an orthogonal time frequency space (OTFS) signal, and a second reference signal, The base station, A receiver that performs channel estimation using the first reference signal, performs phase correction using the second reference signal, and demodulates the received OTFS signal using results of the channel estimation and the phase correction. system. (Appendix 13) performing channel estimation using a first reference signal, performing phase correction using a second reference signal, and demodulating a received Orthogonal Time Frequency Space (OTFS) signal using results of the channel estimation and the phase correction; A method for providing the above. (Appendix 14) performing channel estimation using a first reference signal, performing phase correction using a second reference signal, and demodulating a received Orthogonal Time Frequency Space (OTFS) signal using results of the channel estimation and the phase correction; A program that causes a computer to execute the following.

[0112] Although the present invention has been described above with reference to the embodiment, the present invention is not limited to the above. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the invention.

[0113] This application claims priority based on Japanese Patent Application No. 2021-160872, filed on September 30, 2021, the disclosure of which is incorporated herein in its entirety. [Explanation of symbols]

[0114] 10. System 11, 21, 31...Wireless communication equipment, base station 111…Receiver 1111…OTFS post-processing section 1112...OFDM demodulation section 12, 32…UE 32a…First UE 32b…Second UE 122...Transmitter 1221…OTFS preprocessing section 1222...OFDM modulation section M, N: total number of indexes EQ1…1st equalizer EQ2…Second equalizer SE1…First selector SE2: Second selector UE: Terminal

Claims

1. A receiving means for performing channel estimation using a first reference signal, performing phase correction using a second reference signal, and demodulating a received Orthogonal Time Frequency Space (OTFS) signal using results of the channel estimation and the phase correction, The first reference signal for a first User Equipment (UE) is arranged within a predetermined first element range for the first UE; the first reference signal for a second UE is located within a predetermined second element range for the second UE; The first element range and the second element range are disposed at positions spaced apart by a predetermined distance or more. Wireless communication device.

2. the receiving means receives and demodulates the OTFS signal including a subframe in which the first reference signal is placed and a subframe in which the second reference signal is placed; The wireless communication device of claim 1 .

3. The first reference signal is a channel impulse response reference signal (CIR-RS: Channel Impulse Response-Reference Signal) for obtaining a channel impulse response (CIR), The second reference signal is a phase compensation reference signal (PCRS: Phase Compensation Reference Signal) for performing the phase compensation.

3. A wireless communication device according to claim 1 or 2.

4. The receiving means includes: a first equalizer that performs channel correction based on the first reference signal in a frequency-time (FT) space; a second equalizer that performs the phase correction process based on the second reference signal in a delay Doppler (DD) space. The wireless communication device according to claim 3 .

5. After the first equalizer performs the channel correction, the second equalizer performs the phase correction.

5. The wireless communication device according to claim 4.

6. The receiving means further includes a channel estimating means for performing the channel estimation using the first reference signal to obtain the CIR; The first equalizer performs the channel correction on the received data based on the CIR.

6. A wireless communication device according to claim 4 or 5.

7. the channel estimation means calculates, in the FT space, a quotient obtained by dividing the first reference signal obtained from the received OTFS signal by the first reference signal not affected by a propagation channel, as the CIR; 7. The wireless communication device according to claim 6.

8. The present invention relates to a user equipment and a base station. The user device comprises: A transmitting means for transmitting a first reference signal, an orthogonal time frequency space (OTFS) signal, and a second reference signal, The base station, a receiving means for performing channel estimation using the first reference signal, performing phase correction using the second reference signal, and demodulating the received OTFS signal using results of the channel estimation and the phase correction; The first reference signal for a first User Equipment (UE) is arranged within a predetermined first element range for the first UE; the first reference signal for a second UE is located within a predetermined second element range for the second UE; The first element range and the second element range are disposed at positions spaced apart by a predetermined distance or more. system.

9. performing channel estimation using a first reference signal, performing phase correction using a second reference signal, and demodulating a received Orthogonal Time Frequency Space (OTFS) signal using results of the channel estimation and the phase correction; Equipped with The first reference signal for a first User Equipment (UE) is arranged within a predetermined first element range for the first UE; the first reference signal for a second UE is located within a predetermined second element range for the second UE; The first element range and the second element range are disposed at positions spaced apart by a predetermined distance or more. method.

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