Receiving device, receiving method, and receiving program

Abstract

To efficiently perform active user detection processing, communication channel estimation processing, and carrier frequency offset estimation processing in a GF-NOMA system using OFDM.SOLUTION: A communication unit (321) receives a plurality of reception signals from a plurality of transmission devices (21) using a plurality of antennas (341). A detection unit (322) detects active users (22) of the plurality of transmission devices, the active users having transmitted pilot signals included in the plurality of reception signals during a predetermined period. An estimation unit (323) estimates, on the basis of the active users, a carrier frequency offset representing a deviation of a carrier frequency of a transmission signal from a reference frequency of each of the active users. An update unit (324) updates a pilot matrix that represents impact of the carrier frequency offset on the pilot signals. A detection unit re-detects active users on the basis of the updated pilot matrix.SELECTED DRAWING: Figure 5A

Description

[Technical Field]

[0001] The present invention relates to a receiving device, a receiving method, and a receiving program, which can be suitably used in, for example, a grant-free communication system. [Background technology]

[0002] In recent years, the fifth-generation mobile communication system (5G), its advanced version (5G+), and sixth-generation mobile communication system (6G) have required technologies that can simultaneously connect to a large number of terminals and provide low latency.Grant-free non-orthogonal multiple access (GF-NOMA) technology has attracted attention as a technology that can achieve both high-speed simultaneous connections and low latency.Furthermore, to address the frequency selectivity of communication channels, GF-NOMA systems using orthogonal frequency-division multiplexing (OFDM) are being considered.

[0003] In GF-NOMA technology, multiple terminals communicate without obtaining a communication grant from the base station. Therefore, the base station needs to detect the active users (active terminals) that actually transmitted data and estimate the communication paths corresponding to the active users.

[0004] To realize the GF-NOMA technology, it is necessary to perform a process of detecting active users who have communicated, a process of estimating the communication paths corresponding to the detected active users, and a multi-user detection process of demodulating the transmission data sent by each active user.

[0005] In relation to the above, Non-Patent Document 1 (L. Liu and W. Yu, "Massive connectivity with massive MIMO - Part I: Device activity detection and channel estimation," IEEE Trans. Signal Process., vol. 66, no. 11, pp. 2933-2946, June 2018) proposes a method of simultaneously performing active user detection processing and communication channel estimation processing using MMV-AMP (Multiple Measurement Vector Approximate Message Passing) technology.

[0006] The technique of Non-Patent Document 1 assumes an ideal state in which the carrier frequencies are synchronized between all terminals and the base station. However, in a communication system that uses a large number of IoT (Internet of Things) terminals, a relatively inexpensive crystal oscillator is used in each terminal, which causes an offset (deviation) in the carrier frequency between each terminal and the base station, and this CFO (Carrier Frequency Offset) causes a problem of degradation in communication quality.

[0007] In relation to the above, non-patent document 2 (G. Sun et al., "Massive grant-free OFDMA with timing and frequency offsets", IEEE Trans. Wireless Commun., pp. 1-16, 2021) proposes a method for simultaneously performing active user detection, communication channel estimation, and carrier frequency offset estimation in a GF-NOMA system using OFDM.

[0008] However, in the method of Non-Patent Document 2, the pilot sequence of each terminal is extended, which causes a problem that the estimation dimension increases linearly with the carrier frequency offset. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] L. Liu and W. Yu, "Massive connectivity with massive MIMO-Part I: Device activity detection and channel estimation," IEEE Trans.Signal Process., vol.66, no.11, pp.2933-2946, June 2018. [Non-patent document 2] G. Sun et al., "Massive grant-free OFDMA with timing and frequency offsets," IEEE Trans.Wireless Commun., pp.1-16, 2021. Summary of the Invention [Problem to be solved by the invention]

[0010] In view of the above circumstances, an object of the present disclosure is to provide a receiving device, a receiving method, and a receiving program for efficiently performing active user detection processing, communication channel estimation processing, and carrier frequency offset estimation processing in a GF-NOMA system using OFDM. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0011] The following describes the means for solving the problems using the numbers used in the (Mode for Carrying Out the Invention). These numbers are added to clarify the correspondence between the statements in the (Claims) and the (Mode for Carrying Out the Invention). However, these numbers should not be used to interpret the technical scope of the invention described in the (Claims).

[0012] According to one embodiment, the receiving device (3) includes a communication unit (321), a detection unit (322), an estimation unit (323), an update unit (324), and an output unit (325). The communication unit (321) receives a plurality of received signals from a plurality of transmitting devices (21) that transmit transmission signals using grant-free communication that omits authentication, via a plurality of antennas (341). The detection unit (322) detects active users (22) that transmitted pilot signals included in the plurality of received signals during a predetermined period from the plurality of transmitting devices (21). The estimation unit (323) estimates a carrier frequency offset representing a deviation of the carrier frequency of the transmission signal of each of the active users (22) from a reference frequency, based on the active users (22). The update unit (324) updates a pilot matrix representing the effect of the carrier frequency offset on the pilot signal. The output unit (325) outputs information representing a set of active users and the carrier frequency offset to the outside. The detection unit (322) detects the active users (22) again based on the updated pilot matrix. The communication unit (321) decodes the data signals included in the plurality of received signals based on the estimated value of the carrier frequency offset.

[0013] According to one embodiment, the receiving method includes receiving (S01) multiple received signals from multiple transmitting devices (21) that transmit transmission signals using grant-free communication without authentication, detecting active users (22) from the multiple transmitting devices (21) that transmitted pilot signals included in the multiple received signals during a predetermined period (S03, S06), estimating a carrier frequency offset representing a deviation of the carrier frequency of the transmission signal of each of the active users (22) from a reference frequency based on the active users (22) (S04), updating a pilot matrix representing the effect of the carrier frequency offset on the pilot signals (S05), and outputting information representing a set of active users (22) and the carrier frequency offset to the outside (S09). The detecting (S03, S06) includes re-detecting the active users (22) based on the updated pilot matrix (S06). The receiving method further includes decoding data signals included in the multiple received signals based on the estimated carrier frequency offset.

[0014] According to one embodiment, the receiving program is executed by a computing device to realize a predetermined process. The process includes receiving (S01) a plurality of received signals from a plurality of transmitting devices (21) that transmit transmission signals using grant-free communication without authentication, detecting (S03, S06) active users (22) that transmitted pilot signals included in the plurality of received signals during a predetermined period from the plurality of transmitting devices (21), estimating (S04) a carrier frequency offset representing a deviation of the carrier frequency of the transmission signal from a reference frequency for each of the active users (22) based on the active users (22), updating (S05) a pilot matrix representing the effect of the carrier frequency offset on the pilot signal, and outputting (S09) information representing a set of active users (22) and the carrier frequency offset to the outside. The detecting (S03, S06) includes re-detecting (S06) the active users (22) based on the updated pilot matrix. The processing further includes decoding data signals included in the plurality of received signals based on the estimate of the carrier frequency offset. [Effects of the Invention]

[0015] According to one embodiment, it is possible to efficiently perform the process of detecting active users, the process of estimating a communication path, and the process of estimating a carrier frequency offset. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a communication system according to an embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of a configuration of a base station according to an embodiment. [Figure 3] FIG. 3 is a diagram illustrating an example of a configuration of a transmission signal according to an embodiment. [Figure 4] FIG. 4 is a diagram showing an example of the configuration of a received signal modeled in one embodiment. [Figure 5A]FIG. 5A is a flowchart illustrating an example of a process of a communication method according to one embodiment. [Figure 5B] FIG. 5B is a flowchart illustrating an example of a process of a communication method according to one embodiment. [Figure 5C] FIG. 5C is a flowchart illustrating an example of a process of a communication method according to one embodiment. [Figure 6] FIG. 6 is a diagram schematically illustrating an equation for expressing a received signal using an extended pilot matrix and an estimated value of an extended channel matrix in one embodiment. [Figure 7] FIG. 7 is a diagram illustrating the bisection method used to update the candidate range of the CFO in one embodiment. [Figure 8] FIG. 8 is a graph showing the results of a computer simulation of the performance of a receiving method according to one embodiment. [Figure 9] FIG. 9 is a graph showing the results of a computer simulation of the performance of a receiving method according to one embodiment. [Figure 10] FIG. 10 is a graph showing the results of a computer simulation of the performance of a receiving method according to one embodiment. [Figure 11] FIG. 11 is a graph showing the results of a computer simulation of the performance of a receiving method according to one embodiment. [Figure 12] FIG. 12 is a graph showing the results of a computer simulation of the performance of a receiving method according to one embodiment. [Figure 13] FIG. 13 is a graph showing the results of a computer simulation of the performance of a receiving method according to one embodiment. [Figure 14] FIG. 14 is a graph showing the results of a computer simulation of the performance of a receiving method according to one embodiment. [Figure 15] FIG. 15 is a graph showing the results of a computer simulation of the performance of a receiving method according to one embodiment. [Figure 16]FIG. 16 is a graph showing the results of a computer simulation of the performance of a receiving method according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a receiving device, a receiving method, and a receiving program according to the present disclosure will be described below with reference to the accompanying drawings.

[0018] (Embodiment) 1, a communication system 1 according to one embodiment includes users 21 as transmitting terminals and a base station 3 as a receiving device. Each user 21 transmits a transmission signal to the base station 3 without obtaining a communication permission (grant) from the base station 3 by a Grant Free Non-Orthogonal Multiple Access (GF-NOMA) system that uses Orthogonal Frequency-Division Multiplexing (OFDM).

[0019] As an example, let the total number of users 21 be N. Of the N users 21, the users 21 that have transmitted transmission signals to the base station 3 during a certain period of time are called active users 22. As an example, let the total number of active users 22 be K. The base station 3 is equipped with multiple antennas 341. As an example, let the total number of antennas 341 be M. The base station 3 receives, as received signals, transmission signals transmitted from the K active users 22 via each of the M antennas 341.

[0020] As shown in Fig. 2, the base station 3 according to one embodiment may be configured as, for example, a computer. In the example of Fig. 2, the base station 3 includes a bus 31, a computing device 32, a storage device 33, a communication device 34, and an input / output device 35. The bus 31 may be configured to connect the computing device 32, the storage device 33, the communication device 34, and the input / output device 35 so that they can communicate with each other.

[0021] The arithmetic device 32 includes a communication unit 321, a detection unit 322, an estimation unit 323, an update unit 324, and an output unit 325. The storage device 33 includes a reception program storage unit 331 that stores a reception program. The arithmetic device 32 executes the reception program to realize the processes of the communication unit 321, the detection unit 322, the estimation unit 323, the update unit 324, and the output unit 325. The communication unit 321, the detection unit 322, the estimation unit 323, the update unit 324, and the output unit 325 are virtual functional blocks that realize processes through cooperation between the arithmetic device 32 and the storage device 33. Details of the processes realized by the communication unit 321, the detection unit 322, the estimation unit 323, the update unit 324, and the output unit 325 will be described later.

[0022] The reception program may be read from the recording medium 330 and stored in the reception program storage unit 331. The recording medium 330 may be a non-transitory and tangible medium.

[0023] The communication device 34 includes a plurality of antennas 341. Each of the plurality of antennas 341 receives, as a received signal, a transmission signal transmitted from a plurality of active users 22. The communication device 34 processes the plurality of received signals received by the plurality of antennas 341, respectively.

[0024] The communication device 34 may further perform wireless and / or wired communication with another communication device (not shown). The reception program may be received from the outside via the communication device 34 and stored in the reception program storage unit 331.

[0025] The input / output device 35 outputs information to the user and accepts operations input by the user. As an example, the input / output device 35 includes a display device that outputs images, a speaker that outputs audio, a microphone that accepts audio input, buttons that accept press operations, a keyboard that accepts key input operations, a touch panel that accepts touch operations and outputs images, etc.

[0026] An example of the configuration of a transmission signal according to an embodiment will be described with reference to Fig. 3. In Fig. 3, the horizontal axis represents time, and the vertical axis represents frequency. Time is divided into predetermined periods, and frequency is divided into predetermined frequency bands. For convenience, a combination of one period and one frequency band is referred to as one communication resource 41.

[0027] Each active user 22 transmits a transmission signal including one OFDM symbol using one communication resource 41. In the GF-NOMA communication system 1 according to one embodiment, Nc subcarriers included in a predetermined range are available for use in the OFDM symbol of the transmission signal.

[0028] The transmission signals transmitted by the active users 22 may be data signals for transmitting desired data, or may be pilot signals for transmitting information required by the base station 3. The allocation of the data signal resources 42 and the pilot signal resources 43 among the communication resources 41 is determined in advance.

[0029] In one embodiment, the effect of CFO (Carrier Frequency Offset) is modeled as follows. First, it is assumed that the CFO of each user 21 falls within the range that satisfies the 3GPP (Third Generation Partnership Project) standard. The 3GPP standard requires that the CFO of each user be kept within ±0.1 ppm. Next, the CFO value of each user 21 is modeled as a random variable that follows a uniform distribution.

[0030] More specifically, the CFO of each user 21 is modeled as satisfying the following "Equation 1".

[0031]

number

[0032] In one embodiment, the phase shift matrix due to the CFO is modeled as shown in the following equation (2).

[0033]

number

[0034] In the above formula (2), the cumulative phase shift φ t is expressed as the following "Equation 3".

[0035]

number

[0036] Of the above equations (2) and (3), the angular frequency ω is expressed as in the following equation (4).

[0037]

number

[0038] In one embodiment, the received signal in the frequency domain is expressed as in the following equation (5).

[0039]

number

[0040] When the total number of OFDM symbols is G, the received signal over all of these OFDM symbols is expressed as in the following "Numerical Expression 6" and "Numerical Expression 7".

[0041]

number

[0042]

number

[0043] In the above "Numerical Formula 7", the equivalent pilot matrix X is expressed as in the following "Numerical Formula 8".

[0044]

number

[0045] In the above "Number 8", the influence of CFO P(ε n ) is expressed as in the following equation (9).

[0046]

number

[0047] With reference to FIG. 4, an example of the configuration of a received signal modeled in one embodiment will be described. In FIG. 4, matrix Y is a complex matrix with L rows and M columns representing the received signal. L is the total number of pilot signals included in the received signal, and M is the total number of antennas 341 provided in the communication device 34. Matrix X is a pilot matrix including the influence of CFO and is a complex matrix with L rows and N columns. N is the total number of users 21 included in the communication system 1. Matrix H is a channel matrix and is a complex matrix with N rows and M columns. The N row vectors in the channel matrix H correspond to the N users 21, respectively. Of the N row vectors included in matrix H, K row vectors corresponding to K active users 22, respectively, have non-zero elements because the corresponding active users 22 transmit transmission signals. Conversely, of the N row vectors included in the channel matrix H, N K row vectors corresponding to N K inactive users 21 other than the K active users 22 have zero elements because the corresponding users 21 do not transmit transmission signals. The matrix Z is a complex matrix with L rows and M columns that represents noise.

[0048] An example of the processing of a receiving method according to one embodiment will be described with reference to the flowcharts of Figures 5A, 5B, and 5C. Figure 5B is a flowchart for explaining in detail the processing of steps S03 and S06, which will be described later, of the flowchart of Figure 5A. Figure 5C is a flowchart for explaining in detail the processing of step S04, which will be described later, of the flowchart of Figure 5A. Note that the receiving program according to one embodiment may be configured to realize the processing of the flowcharts of Figures 5A, 5B, and 5C by being executed by the arithmetic device 32.

[0049] The processes of Figures 5A, 5B and 5C may start when the base station 3 starts up. When the processes of Figures 5A, 5B and 5C start, step S01 of Figure 5A is executed.

[0050] 5A, the communication unit 321 of the base station 3 receives a received signal. More specifically, the communication unit 321 controls the communication device 34 of the base station 3 to receive, as received signals, transmission signals transmitted by K active users 22 of the N users 21, via M antennas 341. The received signals may be stored in the storage device 33.

[0051] After step S01, step S02 in Fig. 5A is executed. In step S02, the estimation unit 323 of the base station 3 initializes a first counter variable. The first counter variable is a variable for managing repeated processing of steps S03, S04, S05, S06, and S07, which will be described later. The initialized first counter variable is, for example, 1.

[0052] After step S02, step S03 in Fig. 5A is executed. In step S03, the detection unit 322 of the base station 3 detects active users 22. In one embodiment, the active users 22 are detected using the Multiple Measurement Vector Approximate Message Passing (MMV-AMP) technique.

[0053] The specific processing of step S03 in Fig. 5A will be described with reference to the flowchart in Fig. 5B. When step S03 in Fig. 5A starts, step S11 in Fig. 5B is executed.

[0054] In step S11, the detection unit 322 of the base station 3 initializes a second counter variable. The second counter variable is a variable for managing the number of times steps S12, S13, and S14, which will be described later, are repeated. The initial value of the second counter variable is, for example, 0.

[0055] After step S11, step S12 in Fig. 5B is executed. In step S12, the detection unit 322 of the base station 3 updates the channel matrix H. Each element of the channel matrix H is calculated as shown in the following "Formula 10".

[0056]

number

[0057] However, while step S03 in Fig. 5A is executed once, step S12 in Fig. 5B is executed for the first time, and in a state where the second counter variable m is equal to its initial value, the initial value of each value is used instead of each value of the "previous" value in the above "Equation 10." The initial value of each value is a value obtained when ignoring the influence of CFO (Carrier Frequency Offset) estimated in step S04 in Fig. 5A, which will be described later. CFO is the offset (deviation) of the carrier frequency that occurs between each user 21 and the base station 3.

[0058] After step S12, step S13 in Fig. 5B is executed. In step S13, the detection unit 322 of the base station 3 updates the residual matrix R. The residual matrix R is calculated as shown in the following "Formula 11".

[0059]

number

[0060] After step S13, step S14 in Fig. 5B is executed. In step S14, the detection unit 322 of the base station 3 increments the second counter variable.

[0061] After step S14, step S15 in Fig. 5B is executed. In step S15, the detection unit 322 of the base station 3 determines whether the second counter variable has reached the threshold value. If the second counter variable has not reached the threshold value (No), the process returns to step S12 in Fig. 5B. Conversely, if the second counter variable has reached the threshold value (Yes), the process proceeds to step S16 in Fig. 5B.

[0062] In step S16, the detection unit 322 of the base station 3 detects active users 22. More specifically, based on the estimated value of the channel matrix H updated in step S12 and the estimated value of the residual matrix R updated in step S13, a set of users 21 that satisfies the condition of the following "Equation 12" is detected as a set of active users 22.

[0063]

number

[0064] When step S16 is completed, the process of FIG. 5B is completed, step S03 of FIG. 5A is completed, and the process proceeds to step S04 of FIG. 5A.

[0065] 5A, the estimation unit 323 of the base station 3 estimates the CFO based on the active users 22 detected in step S03. Note that in one embodiment, the detection of active users 22 in step S03 and the estimation of CFO in step S04 are performed separately. However, step S03, which is executed in the initial stage when an estimated CFO value has not yet been obtained, is a process of roughly narrowing down the active users 22.

[0066] The specific processing of step S04 in Fig. 5A will be described with reference to the flowchart in Fig. 5C. When step S04 in Fig. 5A starts, step S21 in Fig. 5C is executed.

[0067] In step S21, the estimation unit 323 of the base station 3 initializes a third counter variable. The third counter variable is a variable for managing the number of times steps S22, S23, S24, S25, and S26, which will be described later, are repeated. The initial value of the third counter variable is, for example, 1.

[0068] In step S21, the estimation unit 323 of the base station 3 further initializes a first candidate value and a second candidate value of CFO, which will be described later. As an example, the initial value of the first candidate value of CFO is set to the minimum value "-ε" in the range that satisfies the 3GPP standard, as shown in the above "Equation 1." max Similarly, the initial value of the second candidate value of CFO is the maximum value "ε max "

[0069] After step S21, step S22 in FIG. 5C is executed. In step S22, the estimation unit 323 of the base station 3 updates the extended pilot matrix for the active users 22. The extended pilot matrix is ​​obtained by extracting column vectors corresponding to the active users 22 from the pilot matrix X corresponding to all users 21, and then replacing each of the extracted column vectors with two column vectors. One of the two replaced column vectors corresponds to a first CFO candidate value, and the other corresponds to a second CFO candidate value. The first CFO candidate value and the second CFO candidate value are the minimum and maximum values ​​of the CFO candidate range at that time, respectively. The initial value of the extended channel matrix is ​​calculated based on the initial values ​​of the first CFO candidate value and the second CFO candidate value. The subsequent process of updating the first CFO candidate value and the second CFO candidate value will be described later. The extended pilot matrix is ​​expressed as in the following "Equation 13."

[0070]

number

[0071] The received signal matrix Y is the augmented pilot matrix X b Using the above, it is expressed as the following "Equation 14".

[0072]

number

[0073] After step S22, step S23 in Fig. 5C is executed. In step S23, the estimation unit 323 of the base station 3 updates the extended channel matrix for the active users 22. As with the extended pilot matrix Xb calculated in step S22, the extended channel matrix is ​​obtained by extracting row vectors corresponding to the active users 22 from the channel matrix H, and then replacing each of the extracted row vectors with two row vectors corresponding to the first and second CFO candidate values, respectively. The extended channel matrix is ​​estimated using MMSE (Minimum Mean Square Error) estimation, as shown in the following equation (15).

[0074]

number

[0075] The received signal matrix Y is converted into the extended pilot matrix X b and the estimated value H^ of the extended channel matrix b (To be precise, the hat symbol "^" is above the "H") is shown in Figure 6. In the example of Figure 6, the estimated value H^ of the extended channel matrix b (To be precise, the hat symbol "^" is above the "H") indicates the minimum value of the CFO candidate range (ε n1,1 (i) ) and maximum and minimum values ​​(ε n1,2 (i) and so on).

[0076] After step S23, step S24 in FIG. 5C is executed. In step S24, the estimation unit 323 of the base station 3 selects an estimate of the CFO. More specifically, first, the estimation unit 323 calculates the norms of two elements of the extended channel matrix corresponding to each active user 22. Next, the estimation unit 323 selects the larger norm of the two calculated norms for each active user 22. Furthermore, the estimation unit 323 selects, for each active user 22, the minimum or maximum value of the candidate range of the CFO that corresponds to the selected norm as the estimate of the CFO.

[0077] After step S24, step S25 in FIG. 5C is executed. In step S25, the estimation unit 323 of the base station 3 updates the CFO candidate range. More specifically, the estimation unit 323 narrows the candidate range including the estimated CFO value using a bisection method. The estimation unit 323 first calculates the median value between the minimum and maximum values ​​of the current CFO candidate range. The estimation unit 323 then sets the range between the calculated median value and the CFO candidate value selected in step S24 as the new CFO candidate range. At this time, if the median value is smaller than the CFO candidate value selected in step S24, the selected candidate value and median value are set as the minimum and maximum values ​​of the new CFO candidate range, respectively. Otherwise, the selected candidate value and median value are set as the maximum and minimum values ​​of the new CFO candidate range, respectively.

[0078] The bisection method used to update the candidate range of CFO will be described with reference to Fig. 7. As shown in the example of Fig. 7, if the minimum and maximum values ​​of the candidate range of CFO at a certain point in time are ε̂ n,1 (1) and ε^ n,2 (1) In step S24, the maximum value ε^ n,2 (1) If the first one is selected, the minimum value of the new candidate range for CFO is ε^ n,1 (2) is ε^ n,1 (1) and ε^ n,2(1) The intermediate value of ε^ n,3 (1) and the maximum value of the new candidate range of CFO, ε^, is set to n,2 (2) is ε^ n,2 (1) where, to be precise, the circumflex "^" is above the "ε".

[0079] After step S25, step S26 in Fig. 5C is executed. In step S26, the estimation unit 323 of the base station 3 increments the third counter variable.

[0080] After step S26, step S27 in Fig. 5C is executed. In step S27, the estimation unit 323 of the base station 3 determines whether the third counter variable has reached the threshold value. If the third counter variable has not reached the threshold value (No), the process returns to step S22 in Fig. 5C. Conversely, if the third counter variable has reached the threshold value (Yes), the process in Fig. 5C ends, step S04 in Fig. 5A also ends, and the process proceeds to step S05 in Fig. 5A.

[0081] 5A, the update unit 324 of the base station 3 updates the pilot sequence based on the estimated CFO. The pilot matrix X^ (to be precise, the hat symbol "^" is above "X") representing the updated pilot sequence is expressed as shown in the following "Equation 16".

[0082]

number

[0083] After step S05, step S06 in Fig. 5A is executed. In step S06, the detection unit 322 of the base station 3 detects active users 22 based on the updated pilot sequence. The process of step S06 is similar to the process of step S03 in Fig. 5A, except that the pilot sequence updated in step S05 in Fig. 5A is used.

[0084] After step S06, step S07 in Fig. 5A is executed. In step S07, the estimation unit 323 of the base station 3 increments the first counter variable.

[0085] After step S07, step S08 in FIG. 5A is executed. In step S08, the estimation unit 323 of the base station 3 determines whether the first counter variable has reached the threshold value. If the first counter variable has not reached the threshold value (No), the process returns to step S04 in FIG. 5A. Conversely, if the first counter variable has reached the threshold value (Yes), the process proceeds to step S09 in FIG. 5A. Note that the estimation of CFO in step S04 and the detection of active users 22 in step S06 are repeated individually and alternately until the first counter variable reaches the threshold value.

[0086] 5A, the output unit 325 of the base station 3 outputs information indicating the set of last detected active users 22 and the last estimated CFO to the outside. More specifically, the output unit 325 may control the input / output device 35 to output this information to the outside. Alternatively, the output unit 325 may control the communication device 34 to transmit this information to the outside.

[0087] 5A ends when step S09 ends. The communication unit 321 of the base station 3 may decode the data signals included in the multiple received signals based on the estimated value of the carrier frequency offset and the result of the communication channel estimation.

[0088] As described above, according to one embodiment, the process of detecting active users 22 and estimating the communication path, and the process of estimating the carrier frequency offset can be performed efficiently by performing them separately and alternately.

[0089] (Variation) In the configuration according to the above embodiment, in step S03 of FIG. 5A and each step of FIG. 5B, the MMV-AMP technique is used to detect active users 22. This is merely an example, and the present disclosure is not limited to this example. As a modification of this configuration, instead of the MMV-AMP technique, the active users 22 may be detected using a CD (Coordinate Descent) method or a GMMV-AMP (Generalized Multiple Measurement Vector Approximate Message Passing) technique.

[0090] The inventors have confirmed through computer simulation that the performance of the base station 3 as a receiving device, receiving method, and receiving program according to one embodiment is superior to that of the MMV-AMP technique when CFO is ignored. The results of this computer simulation will be described with reference to Figures 8, 9, 10, 11, 12, 13, 14, 15, and 16.

[0091] The parameters used in this computer simulation are as follows: The total number N of users 21 is 200. The total number K of active users 22 is 8. The total number L of pilot signals is 72. The total number M of antennas 341 of the base station 3 is 4. The total number N of OFDM subcarriers cis 2048. The total number of pilot subcarriers S is 36. The total number of pilot OFDM symbols G is 2. The maximum value of CFO ε max is 0.0133. The length of the CP, N CP is 144. The number of times to repeat the process of FIG. 5A, i.e., the threshold of the first counter variable, is 3. The number of times to repeat the process of FIG. 5B, i.e., the threshold of the second counter variable, is 60. The number of times to repeat the process of FIG. 5C, i.e., the threshold of the third counter variable, is 7.

[0092] The horizontal axis of FIG. 8 represents SNR (Signal to Noise Ratio) in dB (decibels), and the vertical axis represents the missed miss probability. The missed miss probability represents the probability of misjudging an active user 22. FIG. 8 includes a total of three graphs G11, G12, and G13. Graph G11 corresponds to MMV-AMP when CFO is ignored. Graph G12 corresponds to one embodiment. Graph G13 corresponds to ideal MMV-AMP when CFO is known. It can be seen from FIG. 8 that one embodiment is superior to MMV-AMP when CFO is ignored.

[0093] The horizontal axis of FIG. 9 represents SNR in dB, and the vertical axis represents false alarm probability. The false alarm probability represents the probability of misjudging an inactive user. FIG. 9 includes a total of three graphs G21, G22, and G23. Graph G21 corresponds to MMV-AMP when CFO is ignored. Graph G22 corresponds to an embodiment. Graph G23 corresponds to ideal MMV-AMP when CFO is known. From FIG. 9, it can be seen that an embodiment is superior to MMV-AMP when CFO is ignored.

[0094] The horizontal axis of Fig. 10 represents SNR in dB, and the vertical axis represents NMSE (Normalized Mean Squared Error), which evaluates the performance of channel estimation. Fig. 10 includes a total of three graphs G31, G32, and G33. Graph G31 corresponds to MMV-AMP when CFO is ignored. Graph G32 corresponds to one embodiment. Graph G33 corresponds to ideal MMV-AMP when CFO is known. From Fig. 10, it can be seen that one embodiment is superior to MMV-AMP when CFO is ignored.

[0095] The horizontal axis of FIG. 11 represents the active rate, and the vertical axis represents the missed-event probability. The active rate represents the proportion of active users 22 among users 21. FIG. 11 includes a total of three graphs G41, G42, and G43. Graph G41 corresponds to MMV-AMP when CFO is ignored. Graph G42 corresponds to one embodiment. Graph G43 corresponds to ideal MMV-AMP when CFO is known. From FIG. 11, it can be seen that one embodiment is superior to MMV-AMP when CFO is ignored.

[0096] The horizontal axis of FIG. 12 represents the active rate, and the vertical axis represents the false alarm probability. FIG. 12 includes a total of three graphs G51, G52, and G53. Graph G51 corresponds to MMV-AMP when CFO is ignored. Graph G52 corresponds to one embodiment. Graph G53 corresponds to ideal MMV-AMP when CFO is known. From FIG. 12, it can be seen that one embodiment is superior to MMV-AMP when CFO is ignored.

[0097] The horizontal axis of FIG. 13 represents the active rate, and the vertical axis represents the NMSE, which evaluates the performance of the channel estimation. FIG. 13 includes a total of three graphs G61, G62, and G63. Graph G61 corresponds to MMV-AMP when CFO is ignored. Graph G62 corresponds to one embodiment. Graph G63 corresponds to ideal MMV-AMP when CFO is known. From FIG. 13, it can be seen that one embodiment is superior to MMV-AMP when CFO is ignored.

[0098] The horizontal axis of FIG. 14 represents the maximum value of CFO, and the vertical axis represents the probability of missing an error. Here, the SNR is 6 dB. FIG. 14 includes a total of three graphs G71, G72, and G73. Graph G71 corresponds to MMV-AMP when CFO is ignored. Graph G72 corresponds to one embodiment. Graph G73 corresponds to an ideal MMV-AMP when CFO is known. From FIG. 14, it can be seen that one embodiment is superior to MMV-AMP when CFO is ignored.

[0099] The horizontal axis of FIG. 15 represents the maximum value of CFO, and the vertical axis represents the false alarm probability. Here, SNR is 6 dB. FIG. 15 includes a total of three graphs G81, G82, and G83. Graph G81 corresponds to MMV-AMP when CFO is ignored. Graph G82 corresponds to one embodiment. Graph G83 corresponds to an ideal MMV-AMP when CFO is known. From FIG. 15, it can be seen that one embodiment is superior to MMV-AMP when CFO is ignored.

[0100] The horizontal axis of FIG. 16 represents the maximum value of CFO, and the vertical axis represents NMSE, which evaluates the performance of channel estimation. FIG. 16 includes a total of three graphs G91, G92, and G93. Graph G91 corresponds to MMV-AMP when CFO is ignored. Graph G92 corresponds to one embodiment. Graph G93 corresponds to ideal MMV-AMP when CFO is known. From FIG. 16, it can be seen that one embodiment is superior to MMV-AMP when CFO is ignored.

[0101] As described above, in all of the cases shown in FIGS. 8 to 16, it can be confirmed that the embodiment is superior to the MMV-AMP when CFO is ignored.

[0102] The invention made by the inventor has been specifically described above based on the embodiments, but it goes without saying that the present invention is not limited to the embodiments and can be modified in various ways without departing from the spirit of the invention. Furthermore, the features described in the embodiments can be freely combined within the scope of technical compatibility. [Explanation of symbols]

[0103] 1. Communication Systems 21 User (transmitting device) 22 active users 3 Base station (receiving device) 31 Bus 32 Arithmetic unit 321 Communications Department 322 Detection unit 323 Estimation Department 324 Update Department 325 Output Section 33 Storage device 330 Recording Media 331 Reception program storage unit 34 Communication equipment 341 Antenna 35 Input / Output Devices 41 Communication Resources 42 Data signal resources 43 Pilot Signal Resources G11, G12, G13 graphs G21, G22, G23 graphs G31, G32, G33 graphs G41, G42, G43 graphs G51, G52, G53 graphs G61, G62, G63 graphs G71, G72, G73 graphs G81, G82, G83 graphs G91, G92, G93 graphs H equivalent channel matrix H^ b (To be precise, the circumflex "^" is above the "H") L number of lines M number of columns N number of rows and columns N C Number of subcarriers X equivalent pilot matrix Y Received signal matrix Z noise ε^ (1) n,1 , ε^ (2) n,1 , ε^ (1) n1,1 The minimum value (more precisely, the circumflex "^" above the "ε") ε^ (1) n,2 , ε^ (2) n,2 , ε^ (1) n1,2 Maximum value (specifically, the circumflex "^" above the "ε") ε^ (1) n,3 , ε^ (2) n,3 The middle value (more precisely, the circumflex "^" above the "ε")

Claims

1. a communication unit that receives a plurality of reception signals by a plurality of antennas from a plurality of transmission devices that transmit transmission signals by grant-free communication in which authentication is omitted; a detection unit that detects an active user among the plurality of transmitting devices that has transmitted a pilot signal included in the plurality of received signals during a predetermined period; an estimation unit that estimates a carrier frequency offset representing a deviation of a carrier frequency of the transmission signal from a reference frequency for each of the active users based on the active users; an update unit for updating a pilot matrix representing the effect of the carrier frequency offset on the pilot signals; an output unit that outputs information representing the set of active users and the carrier frequency offset to the outside; Equipped with the detection unit re-detects the active users based on the updated pilot matrix; The communication unit decodes data signals included in the plurality of received signals based on the estimated value of the carrier frequency offset. Receiving device.

2. 2. The receiving device according to claim 1, the estimation unit re-estimates the carrier frequency offset based on the newly detected active users; the updating unit re-updates the pilot matrix based on the re-estimated carrier frequency offset; The estimation unit, the update unit, and the detection unit each repeat the estimation, the update, and the detection a first number of times. Receiving device.

3. 3. The receiving device according to claim 1, The estimation unit, for each of the active users, setting a minimum value and a maximum value of a candidate range including the candidate value of the carrier frequency offset as a first candidate value and a second candidate value; calculating a norm of the communication channel estimate when the carrier frequency offset is the first candidate value as a first candidate norm; calculating a norm of the communication channel estimate when the carrier frequency offset is the second candidate value as a second candidate norm; The candidate value corresponding to the larger of the first candidate norm and the second candidate norm is set as the estimated value of the carrier frequency offset. Receiving device.

4. 4. The receiving device according to claim 3, The estimation unit resetting the candidate range so that the estimated value of the carrier frequency offset and an intermediate value between the first candidate value and the second candidate value are set as the minimum and maximum values ​​of the candidate range; recalculating the first candidate norm based on the newly set minimum value; recalculating the second candidate norm based on the newly set maximum value; re-establishing the estimated value of the carrier frequency offset based on the newly calculated first candidate norm and the newly calculated second candidate norm; The estimation unit repeats the setting of the candidate range, the calculation of the first candidate norm, the calculation of the second candidate norm, and the setting of the estimated value of the carrier frequency offset a second number of times, respectively. Receiving device.

5. 5. The receiving device according to claim 4, The estimation unit sets the initial values ​​of the minimum value and the maximum value so as to satisfy the standards of 3GPP (Third Generation Partnership Project, registered trademark). Receiving device.

6. The receiving device according to any one of claims 1 to 5, The detection unit calculating a channel matrix representing a communication channel from the plurality of transmitting devices to the receiving device based on a residual matrix; calculating the residual matrix based on the channel matrix; Estimating the set of active users based on the channel matrix and the residual matrix. Receiving device.

7. 7. The receiving device according to claim 6, The detection unit repeating the calculation of the channel matrix and the calculation of the residual matrix a third number of times; The set of active users is estimated based on the channel matrix and the residual matrix calculated repeatedly the third number of times. Receiving device.

8. A base station receives a plurality of received signals from a plurality of transmitting devices that transmit transmission signals using grant-free communication that omits authentication, using a plurality of antennas; the base station detects, from among the plurality of transmitting devices, an active user that transmitted a pilot signal included in the plurality of received signals during a predetermined period; the base station estimating a carrier frequency offset representing a deviation of a carrier frequency of the transmission signal of each of the active users from a reference frequency based on the active users; the base station updating a pilot matrix that represents the effect of the carrier frequency offset on the pilot signals; the base station externally outputs information representing the set of active users and the carrier frequency offset; Including, The detecting step includes: The base station re-detects the active users based on the updated pilot matrix. Including, the base station decoding data signals included in the plurality of received signals based on the estimated carrier frequency offset. Also includes Receiving method.

9. A receiving program for causing a computing device to execute a predetermined process, The process comprises: receiving a plurality of reception signals from a plurality of transmission devices that transmit transmission signals by grant-free communication in which authentication is omitted, using a plurality of antennas; Detecting an active user from among the plurality of transmitting devices that has transmitted a pilot signal included in the plurality of received signals during a predetermined period; estimating a carrier frequency offset representing a deviation of a carrier frequency of the transmitted signal from a reference frequency for each of the active users based on the active users; updating a pilot matrix that represents the effect of the carrier frequency offset on the pilot signals; outputting information representing the set of active users and the carrier frequency offset to an external device; Including, The detecting step includes: detecting the active users again based on the updated pilot matrix; The process comprises: decoding data signals included in the plurality of received signals based on the estimated carrier frequency offset; Also includes Receiving program.

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