Communication device, control method, and program

Abstract

To provide a communication device and the like capable of inexpensively and accurately estimating DL / UL switching timing in a TDD method even when inter-carrier interference caused by carrier frequency errors exists.SOLUTION: In a communication device of an embodiment, a signal receiving unit converts an OFDM signal into a baseband OFDM signal. A time waveform calculation unit extracts a portion of a time axis waveform signal and calculates a degree of similarity with a known signal. A carrier frequency correction unit corrects a carrier frequency of the time axis waveform signal on the basis of the degree of similarity. A FFT unit performs Fourier transform on the time axis waveform signal. A frequency waveform calculation unit extracts a portion of a frequency axis waveform signal and calculates a degree of similarity between the extracted signal and a known signal. A switching timing estimation unit estimates the switching timing between uplink communication and downlink communication in its own device on the basis of a result of the frequency waveform calculation unit.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] An embodiment of the present invention relates to a communication device, a control method, and a program. [Background technology]

[0002] Distributed Antenna Systems (DAS) are known as one type of wireless communication system. In a distributed antenna system, communication is performed by a time division duplex (TDD) method that switches between downlink (DL) transmission from a base station to a terminal and uplink (UL) transmission from a terminal to a base station at a predetermined period. Such a distributed antenna system needs to detect the DL period and UL period of a wireless signal and switch appropriately.

[0003] Conventionally, communication devices perform AD conversion at the beginning of a series of processes to convert radio signals from analog to digital. AD conversion often employs oversampling, which samples at a rate higher than the data rate of the input signal, in order to increase the S / N ratio and resolution as well as to relax the requirements for anti-aliasing filters. Next, carrier frequency conversion is performed to down-convert the AD-converted signal to a baseband signal. Then, sampling rate conversion is performed to down-convert the sampling rate of the baseband signal from the clock frequency used during AD conversion to the system clock frequency. TDD synchronization with the base station is achieved by analyzing the synchronization signal contained in the signal obtained after sampling rate conversion.

[0004] In digital transmission such as OFDM (Orthogonal Frequency Division Multiplexing), the carrier frequency generated by the carrier frequency converter on the receiving side does not completely match the carrier frequency on the transmitting side due to differences in accuracy, individual differences, and the degree of deterioration over time of the local oscillators on the transmitting and receiving sides. In the case of OFDM, this carrier frequency error appears as degradation and phase rotation for each sample in the constellation after the received time-axis waveform signal is demodulated by FFT (Fast Fourier Transform) processing. As described above, when phase-shift keyed (PSK) data is judged in the presence of inter-carrier interference caused by carrier frequency error, the reception characteristics are significantly deteriorated. Therefore, data judgment is generally performed after correcting inter-carrier interference. In order to correct inter-carrier interference, a mechanism for controlling the frequency and phase of the clock for the local oscillator and the baseband system clock, and waveform equalization processing for correcting the waveform after FFT processing are required. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-053769 A [Patent Document 2] JP 2020-504568 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional inter-carrier interference compensation techniques are costly to implement.

[0007] Therefore, the present invention has been made in consideration of the above circumstances, and aims to provide a communication device, a control method, and a program that can inexpensively and accurately estimate DL / UL switching timing in a TDD system in which DL communication and UL communication are switched at predetermined intervals, even when inter-carrier interference caused by carrier frequency error is present. [Means for solving the problem]

[0008] A communication device according to an embodiment is a communication device that functions as the master station device or the slave station device in a distributed antenna system including a master station device connected to a base station and one or more slave station devices that relay signals between a terminal device that communicates with the base station and the master station device, and receives an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method, and includes a signal receiving unit, a time waveform calculation unit, a carrier frequency correction unit, an FFT unit, a frequency waveform calculation unit, and a switching timing estimation unit. The signal receiving unit receives the OFDM signal and converts it into a baseband OFDM signal. The time waveform calculation unit extracts a part of a time axis waveform signal that is an output of the signal receiving unit, and calculates a similarity between the extracted signal and a known signal. The carrier frequency correction unit corrects a carrier frequency of the time axis waveform signal that is an output of the signal receiving unit based on the similarity between the extracted signal and a known signal calculated by the time waveform calculation unit. The FFT unit performs a Fast Fourier Transform (FFT) on the time axis waveform signal output from the carrier frequency correction unit. The frequency waveform calculation unit extracts a part of the frequency axis waveform signal output from the FFT unit and calculates the degree of similarity between the extracted signal and a known signal. The switching timing estimation unit estimates the switching timing between uplink communication and downlink communication in the own device based on the result of the frequency waveform calculation unit. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 is a diagram illustrating an example of a schematic configuration of a distributed antenna system according to the first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of a data structure of a radio frame. [Diagram 3] FIG. 3 is a diagram showing an example of an arrangement pattern of SSBs in a radio frame. [Figure 4] FIG. 4 is a diagram showing an example of a DL / UL configuration and an SSB arrangement in the TDD system. [Diagram 5] FIG. 5 is a diagram illustrating an example of a functional configuration of the master station device in the first embodiment. [Figure 6] FIG. 6 is a diagram illustrating an example of a functional configuration of a control unit in the first embodiment. [Figure 7] FIG. 7 is a diagram illustrating an example of a functional configuration of the switching timing generation unit according to the first embodiment. [Figure 8] FIG. 8 is a diagram illustrating an example of a functional configuration of a PSS detection unit according to the first embodiment. [Figure 9] FIG. 9 is a diagram illustrating an example of a functional configuration of a frequency error detection unit according to the first embodiment. [Figure 10] FIG. 10 is a diagram showing an example in which the argument angles of the correlation values ​​calculated by the correlation calculation unit of the frequency error detection unit are arranged in data order. [Figure 11] FIG. 11 is a diagram illustrating an example of a functional configuration of the frequency error correction unit according to the first embodiment. [Figure 12] FIG. 12 is a diagram illustrating an example of a functional configuration of the SSS detection unit according to the first embodiment. [Figure 13] FIG. 13 is a diagram illustrating an example of a functional configuration of a DMRS detector according to the first embodiment. [Figure 14] FIG. 14 is a flowchart illustrating an example of the TDD detection process in the first embodiment. [Figure 15] FIG. 15 is a flowchart showing an example of the time waveform processing according to the first embodiment. [Figure 16] FIG. 16 is a flowchart showing an example of the sampling phase conversion process according to the first embodiment. [Figure 17] FIG. 17 is a flowchart showing an example of the frequency error detection process according to the first embodiment. [Figure 18] FIG. 18 is a flowchart showing an example of the frequency error conversion process according to the first embodiment. [Figure 19] FIG. 19 is a flowchart showing an example of the FFT process according to the first embodiment. [Figure 20] FIG. 20 is a flowchart showing an example of frequency waveform processing according to the first embodiment. [Figure 21] FIG. 21 is a flowchart showing an example of the SSS detection process according to the first embodiment. [Figure 22] FIG. 22 is a flowchart illustrating an example of the DMRS detection process according to the first embodiment. [Diagram 23] FIG. 23 is a flowchart showing an example of the switching timing estimation process according to the first embodiment. [Figure 24] FIG. 24 is a diagram showing an example of a functional configuration of a frequency error detector 21b included in the switching timing generator according to the first modification. [Diagram 25] FIG. 25 is a diagram showing an example in which the deviation angles of the autocorrelation values ​​calculated by the autocorrelation calculation unit in FIG. 24 are arranged in the order of data. [Figure 26] FIG. 26 is a flowchart illustrating an example of a frequency error detection process according to the first modification. [Figure 27] FIG. 27 is a diagram illustrating an example of a functional configuration of a switch timing generation unit according to Comparative Example 1. As illustrated in FIG. [Figure 28] FIG. 28 is a diagram for explaining a constellation when there is a difference in carrier frequency error, taking quadrature phase shift keying-modulated data as an example, when the switching timing generation unit according to Comparative Example 1 is used. [Figure 29A] FIG. 29A is a diagram illustrating an example of a functional configuration of a switching timing generation unit according to the second embodiment. [Figure 29B] FIG. 29B is a diagram illustrating an example of a functional configuration of the phase detection unit 31 in the second embodiment. [Figure 29C]FIG. 29C is a diagram illustrating an example of a functional configuration of the phase conversion section 32 in the second embodiment. [Diagram 30] FIG. 30 is a flowchart illustrating an example of a TDD detection process in the second embodiment. [Diagram 31] FIG. 31 is a flowchart showing an example of a sampling phase conversion process according to the second embodiment. [Diagram 32] FIG. 32 is a diagram illustrating an example of a functional configuration of a switch timing generation unit according to Comparative Example 2. As illustrated in FIG. [Diagram 33] FIG. 33 is a diagram for explaining a constellation when a switching timing generation unit according to Comparative Example 2 is used, taking quadrature phase-shift keying modulated data as an example, there is a difference in carrier frequency error, and the sampling phase of the baseband time axis waveform signal deviates from the sampling phase at the time of transmission. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The communication device, the control method, and the program will be described in detail below with reference to the accompanying drawings. In the following description of each embodiment and modification, parts with the same reference numerals have substantially the same functions, and descriptions of overlapping parts will be omitted as appropriate.

[0011] (First embodiment) 1 is a diagram showing an example of a schematic of a distributed antenna system 1 according to the first embodiment. The distributed antenna system 1 includes a master station device 10 (MU), a relay device 45 (HU), a slave station device 47 (RU), and a transmission path 40 connecting them. More specifically, the distributed antenna system 1 includes the master station device 10 connected to a base station 50, and one or more slave station devices 47 that relay signals between the master station device 10 and a terminal device 60 that communicates with the base station 50.

[0012] The master station device 10 is connected to a plurality of slave station devices 47 inside the distributed antenna system 1. As shown in Fig. 1, the master station device 10 may be connected to the plurality of slave station devices 47 via relay devices 45, or may be connected directly to the plurality of slave station devices 47. Also, as shown in Fig. 1, the master station device 10 may be connected to the relay devices 45 in cascade.

[0013] The master station device 10 is connected to the base station 50 via a coaxial cable, and transmits and receives wireless signals to and from the base station 50. Here, the wireless signals are signals in a wireless communication band that are transmitted to the terminal devices 60. The master station device 10 relays wireless signals received from the base station 50 to the relay device 45 or the slave station device 47. The master station device 10 also relays wireless signals received from the relay device 45 or the slave station device 47 to the base station 50.

[0014] The slave station device 47 is connected by a wired cable to an antenna 70 for wireless communication with the terminal device 60, and transmits and receives wireless signals to and from the terminal device 60 via this antenna 70. The slave station device 47 relays wireless signals received from the terminal device 60 to the master station device 10 or the relay device 45. The slave station device 47 also relays wireless signals received from the master station device 10 or the relay device 45 to the terminal device 60.

[0015] The distributed antenna system 1 having such a configuration makes it possible to connect wireless terminals that cannot be directly reached by radio waves to the base station 50, thereby expanding the communication range of the mobile communication network covered by the base station 50. For example, the distributed antenna system 1 is applicable to mobile communication networks such as 5G.

[0016] On the other hand, conventional mobile communications use a TDD (Time Division Duplex) method in which upstream and downstream communications are switched at predetermined intervals. Therefore, when the distributed antenna system 1 is applied to a mobile communications network, the distributed antenna system 1 needs to detect this switching and appropriately switch between DL processing and UL processing. Therefore, in order to expand the communication range of the mobile communications network without degrading the communication quality, it is necessary to accurately detect the switching between upstream and downstream communications.

[0017] In conventional wireless signals such as 4G, the presence or absence of a DL signal from a base station 50 is determined by power detection, and DL / UL switching is performed according to the result of the determination. In addition, in a communication device that shares one DAS with multiple mobile operators, if the timing of DL / UL switching of the multiple operators differs, interference occurs between them, so the first symbol of the DL wireless frame is detected to detect the difference in the timing of DL / UL switching between operators.

[0018] However, in a wireless signal such as 5G, there are cases where power (signal) does not exist in the first symbol of a wireless frame. Therefore, it is difficult for the master station device 10 to accurately detect the DL / UL switching timing using a conventional power detection method or a method for detecting the first symbol.

[0019] In the distributed antenna system 1 including a master station device 10 connected to a base station 50 and one or more slave station devices 47 that relay signals between the master station device 10 and a terminal device 60 that communicates with the base station 50, the master station device 10 is a communication device that functions as the master station device 10 or the slave station device 47 and receives an orthogonal frequency division multiplexing (OFDM) signal transmitted by a time division multiplexing method. In the distributed antenna system 1 using a TDD method in which DL communication and UL communication are switched every predetermined period, the master station device 10 receives a radio frame including a synchronization signal block (SSB: SS / PBCH Block). The SSB includes a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a physical broadcast channel (PBCH). The master station device 10 detects and decodes the SSB from the received radio frame to ascertain where the received SSB was located in the radio frame.

[0020] Then, the master station device 10 estimates the DL / UL switching timing based on the position of the SSB in the wireless frame and the DL / UL pattern of the TDD system. This allows the master station device 10 to estimate the DL / UL switching timing even when there is no power (signal) in the first symbol of the wireless frame of the 5G wireless signal or the like.

[0021] FIG. 2 is a diagram showing an example of the data structure of a radio frame. FIG. 2 shows an example of a 5G radio frame. One frame is transmitted in 10 ms. One frame is composed of 10 subframes transmitted in 1 ms. Here, 5G supports multiple subcarrier frequency intervals, and the length of one symbol varies depending on the difference. For this reason, the concept of slots is introduced into the radio frame, the number of symbols per subframe is divided into multiple slots, and the difference in one symbol length due to the difference in the subcarrier frequency interval is absorbed by the number of slots per subframe. One slot has 14 symbols regardless of the subcarrier frequency interval. FIG. 2 shows the case where the subcarrier frequency interval is 30 kHz, and one subframe has two slots and is composed of 28 symbols. As shown in FIG. 2, the SSB is placed at a specific position in the radio frame.

[0022] FIG. 3 is a diagram showing an example of an arrangement pattern of SSBs in a radio frame. An SSB is composed of four symbols. An SSB has two synchronization signals, PSS and SSS, and a PBCH signal. The PBCH signal has a DMRS (DeModulation of Reference Signal) for PBCH signal, which is a reference signal for decoding the PBCH signal. An SSB index number is assigned to each SSB position in the radio frame. For example, in Japan, values ​​from 0 to 7 are assigned as shown in FIG. 3. Since the location where an SSB is arranged is up to the operator, after detecting an SSB, it is necessary to identify where it is arranged.

[0023] FIG. 4 is a diagram showing an example of DL / UL configuration and SSB arrangement of the TDD method. The SSB shown in FIG. 4 shows a case where the subcarrier frequency interval is 30 kHz, the SSB period is 20 ms, and the transmission period is 5 ms. The transmission period includes 10 slots, the first 6 slots are assigned to DL, the last 3 slots are assigned to UL, and a buffer slot is assigned between the DL slot and the UL slot. In this way, the number of consecutive DL slots and the number of consecutive UL slots in the transmission period are set in advance. In addition, the buffer slot is also assigned consecutive DL symbols, consecutive UL symbols, and blank symbols that function as a guard between them. The SSB shown in FIG. 4 shows a configuration in which 3 symbols are assigned to DL symbols and 3 symbols are assigned to UP symbols, and 8 symbols are assigned as a guard.

[0024] From the above, if the master station device 10 can detect the index number of an SSB placed at a specific position in a radio frame, it can estimate the position in the transmission cycle where the SSB is placed. Furthermore, if the master station device 10 knows the DL / UL configuration information of the TDD system, it can estimate the DL / UL switching timing within the transmission cycle in relation to the position of the SSB.

[0025] In the following, the communication direction from the base station 50 to the terminal device 60 is referred to as the downstream direction (downlink), and the opposite direction is referred to as the upstream direction (uplink). Correspondingly, a signal transmitted in the downstream direction is referred to as a "DL signal" and a signal transmitted in the upstream direction is referred to as a "UL signal."

[0026] Furthermore, a downstream signal transmitted in the form of a frame is called a "downstream frame," and an upstream signal transmitted in the form of a frame is called an "upstream frame." Also, the upstream side of a certain device may be called the "upstream" side, and the downstream side may be called the "downstream." Correspondingly, a device connected to the upstream side of a certain device may be called the "upstream device," and a device connected to the downstream side may be called the "downstream device."

[0027] For example, the master station device 10 is a higher-level device than the relay device 45 and the slave station device 47, and the relay device 45 is a higher-level device than the slave station device 47. On the other hand, conversely, the relay device 45 and the slave station device 47 are lower-level devices than the master station device 10, and the slave station device 47 is a lower-level device than the master station device 10 and the relay device 45.

[0028] FIG. 5 is a diagram showing an example of a functional configuration of the master station device 10 in the first embodiment. The master station device 10 includes a CPU (Central Processing Unit), a memory, an auxiliary storage device, and the like, which are connected by a bus, and executes a program. The master station device 10 includes an upper side input / output unit 11, a lower side input / output unit 12, a downlink processing unit 13, an uplink processing unit 14, and a control unit 15 by executing the program. All or part of the functions of the master station device 10 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The program may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, or a CD-ROM, or a storage device such as a hard disk built into a computer system. The program may be transmitted via an electric communication line.

[0029] The upper input / output unit 11 is a communication interface for inputting and outputting radio signals between the upper device of the parent station device 10 and the base station 50 via a coaxial cable. The upper input / output unit 11 outputs a DL signal received from the base station 50 to the downlink processing unit 13, and outputs a UL signal input from the uplink processing unit 14 to the base station 50.

[0030] The lower-side I / O unit 12 is a communication interface that inputs and outputs radio signals to and from lower-level devices of the parent station device 10. Specifically, the lower-side I / O unit 12 is a communication interface that inputs and outputs radio signals to and from the child station device 47. The lower-side I / O unit 12 outputs a UL signal received from the child station device 47 to the uplink processing unit 14, and outputs a DL signal input from the downlink processing unit 13 to the child station device 47.

[0031] The downlink processing unit 13 executes a process (hereinafter referred to as "DL processing") in which the parent station device 10 outputs a DL signal received from a higher-level device to a lower-level device. Specifically, the DL processing of the parent station device 10 includes an AD (Analog to Digital) conversion process for the DL signal received from the base station 50, a mapping process for associating a digital signal with a frame, and the like. The downlink processing unit 13 outputs a downstream frame associated with the DL signal in the DL processing to the lower-side input / output unit 12.

[0032] The uplink processing unit 14 executes a process (hereinafter referred to as "UL processing") in which the master station device 10 outputs a UL signal received from a lower device to a higher-level device. Specifically, the UL processing of the master station device 10 includes a demapping process for acquiring a UL signal from an upstream frame received from the relay device 45 or the slave station device 47, and a DA (Digital to Analog) conversion process for the UL signal acquired by the demapping process. The uplink processing unit 14 outputs the UL signal converted to an analog signal in the UL processing to the upper-level input / output unit 11.

[0033] The control unit 15 has a function of switching between upstream communication and downstream communication in the master station device 10. Specifically, the control unit 15 has a function of detecting a switch between upstream communication and downstream communication, and switches between DL processing and UL processing (transmission operation) at the timing when the control unit 15 detects a switch between upstream communication and downstream communication.

[0034] 6 is a diagram showing an example of a functional configuration of the control unit 15 in the first embodiment. The control unit 15 includes a switching timing generation unit 153 and a switching unit 154.

[0035] The switching timing generation unit 153 estimates a UL period or a DL period, and notifies the timing of switching between UL processing and DL processing. Specifically, the switching timing generation unit 153 notifies the start timing of the estimated UL period or DL ​​period. The start timing may be notified as the start time of the UL period or DL ​​period, or may be notified as the elapsed time from the current time. Furthermore, the notification of the start timing may be a notification of the arrival of the start timing.

[0036] The switching unit 154 switches between the UL process and the DL process at the switching timing notified by the switching timing generation unit 153.

[0037] 7 is a diagram showing an example of the functional configuration of the switching timing generation unit 153 according to the first embodiment. The switching timing generation unit 153 includes a signal receiving unit 1001, a time waveform calculation unit 1002, a carrier frequency correction unit 20, an FFT (Fast Fourier Transform) unit 1004, a frequency waveform calculation unit 1005, and a switching timing estimation unit 1006.

[0038] The signal receiving unit 1001 includes an ADC unit 1010, a carrier frequency conversion unit 1011, and a sampling rate conversion unit 1012. The signal receiving unit 1001 receives an OFDM signal and converts it into a baseband time domain waveform signal. More specifically, the signal receiving unit 1001 receives a radio frame including an SSB. That is, the signal receiving unit 1001 receives an SSB having a PSS, an SSS, and a PBCH including a DMRS.

[0039] The ADC unit 1010 converts the input analog signal into a digital signal and outputs it to the carrier frequency conversion unit 1011. The carrier frequency conversion unit 1011 down-converts the frequency of the input digital signal into a baseband signal and outputs it to the sampling rate conversion unit 1012. The sampling rate conversion unit 1012 converts the sampling rate of the input baseband signal to generate a baseband time-domain waveform signal that is a baseband time-domain waveform signal. The sampling rate conversion unit 1012 then outputs the baseband time-domain waveform signal to the PSS detection unit 1013 and the carrier frequency correction unit 20.

[0040] The time waveform calculation unit 1002 includes a PSS detection unit 1013. The time waveform calculation unit 1002 extracts a portion of the baseband time domain waveform signal that is the output of the signal receiving unit 1001, and calculates the degree of similarity (for example, a correlation value) between the extracted signal and a known signal.

[0041] The PSS detector 1013 detects a PSS signal included in the time domain waveform signal. More specifically, the PSS detector 1013 detects a PSS signal arranged at the beginning of an SSB from the baseband signal after sampling rate conversion, and outputs the detected timing as SSB timing to the carrier frequency correction unit 20 and the FFT unit 1004. The PSS detector 1013 also determines which of a plurality of PSS code sequences the detected PSS signal corresponds to, and outputs it to the carrier frequency correction unit 20 and the SSS detector 1016 of the frequency waveform calculator 1005 as NID2, which is a cell identifier of the physical layer. The configuration of the PSS detector 1013 will be described in detail later.

[0042] The carrier frequency correction unit 20 receives a baseband time domain signal from the sampling rate conversion unit 1012 of the signal receiving unit 1001 and an SSB timing from the PSS detection unit 1013, and executes carrier frequency correction processing.

[0043] The frequency error detection unit 21 extracts a signal from the input sampling rate converted baseband signal based on the input SSB timing, detects a carrier frequency error using a PSS code sequence based on the input physical layer cell identifier NID2, and outputs the carrier frequency error to the frequency error correction unit 22. The configuration of the frequency error detection unit 21 will be described in detail later.

[0044] The frequency error correction unit 22 generates a complex sine wave of a specified frequency based on the input carrier frequency error, corrects the carrier frequency by complex multiplying it by the input sampling rate converted baseband signal, and outputs the result to the FFT unit 1004. The configuration of the frequency error correction unit 22 will be described in detail later.

[0045] The FFT unit 1004 performs FFT on the frequency-converted (corrected) baseband time-domain signal that is the output of the frequency error correction unit 22. More specifically, the FFT unit 1004 extracts the SSB from the baseband time-domain waveform signal after sampling phase conversion based on the input SSB timing, and performs a Fourier transform. Then, the FFT unit 1004 outputs the frequency-domain waveform signal of the SSB acquired by the Fourier transform to the frequency waveform calculation unit 1005.

[0046] The frequency waveform calculation unit 1005 includes an SSS detection unit 1016 and a DMRS detection unit 1017. The frequency waveform calculation unit 1005 extracts a portion of the frequency axis waveform signal that is the output of the FFT unit 1004, and calculates the degree of similarity between the extracted signal and a known signal.

[0047] The SSS detector 1016 detects an SSS signal included in the frequency domain waveform signal. More specifically, the SSS detector 1016 detects an SSS signal from the SSB frequency domain waveform signal. The SSS detector 1016 also determines which of a plurality of SSS sequences the detected SSS signal corresponds to. The SSS detector 1016 then outputs the determined SSS signal to the DMRS detector 1017 as NID1 indicating a group of cell identifiers of the physical layer. The configuration of the SSS detector 1016 will be described in detail later.

[0048] DMRS detection section 1017 detects a DMRS signal included in the frequency domain waveform signal. More specifically, DMRS detection section 1017 detects a DMRS signal from the frequency domain waveform signal of SSB. DMRS detection section 1017 determines which of a plurality of DMRS sequences the detected DMRS signal corresponds to. Then, DMRS detection section 1017 outputs ibar_SSB corresponding to the DMRS sequence to switching timing estimation section 1006. The configuration of DMRS detection section 1017 will be described in detail later.

[0049] The switching timing estimation unit 1006 estimates the switching timing between uplink and downlink communication in the own device based on the calculation result of the frequency waveform calculation unit 1005. More specifically, the switching timing estimation unit 1006 estimates the position in the transmission cycle in which the SSB is placed from the input ibar_SSB. The switching timing estimation unit 1006 estimates the DL / UL switching timing in the transmission cycle from the placement position of the SSB to be estimated and DL / UL configuration information in a known TDD system.

[0050] 8 is a diagram illustrating an example of a functional configuration of the PSS detection unit 1013 according to the first embodiment. The PSS detection unit 1013 includes a time signal extraction unit 1131, a PSS generation unit 1132, a first correlation calculation unit 1133, and an NID2 detection unit 1134.

[0051] The time signal extraction unit 1131 extracts a part of the time domain waveform signal. More specifically, the time signal extraction unit 1131 extracts data having a length of an OFDM symbol period from the input baseband time domain waveform signal, and outputs the data to the first correlation calculation unit 1133. That is, the time signal extraction unit 1131 outputs a part of the baseband time domain waveform signal to the first correlation calculation unit 1133.

[0052] The PSS generation unit 1132 outputs a plurality of PSS code sequences of the PSS signal and a code sequence number for identifying the PSS code sequences. More specifically, the PSS generation unit 1132 outputs the plurality of PSS code sequences as a PSS sequence to the first correlation calculation unit 1133. In addition, the PSS generation unit 1132 outputs a PSS index, which is a code sequence number for identifying the PSS code sequence, to the NID2 detection unit 1134.

[0053] The first correlation calculation unit 1133 performs correlation calculation between the time axis waveform signal output from the time signal extraction unit 1131 and the PSS sequence, which is the PSS code sequence from the PSS generation unit 1132, and outputs a correlation value. The first correlation calculation unit 1133 is an example of a first correlation calculation unit. That is, the first correlation calculation unit 1133 performs correlation calculation between the baseband time axis waveform signal input from the time signal extraction unit 1131 and the PSS sequence, and outputs the correlation value, which is the calculation result, to the NID2 detection unit 1134.

[0054] The NID2 detection unit 1134 outputs the timing at which the correlation value calculated by the first correlation calculation unit 1133 is highest within a predetermined time range as the SSB timing, and outputs the PSS sequence, which is the PSS code sequence number corresponding to the PSS code sequence with the highest correlation value, as the physical layer cell identifier NID2. More specifically, the NID2 detection unit 1134 outputs the timing at which the input correlation value is highest within a predetermined time range as the SSB timing. Also, the NID2 detection unit 1134 outputs the PSS index corresponding to the PSS sequence with the highest correlation value as the physical layer cell identifier NID2.

[0055] 9 is a diagram showing an example of a functional configuration of the frequency error detection unit 21 according to the first embodiment. The frequency error detection unit 21 includes a PSS code sequence selection unit 210a, a data holding unit 214a, a second correlation calculation unit 216a, and an error detection unit 218a.

[0056] The PSS code sequence selection unit 210a selects one of a plurality of PSS code sequences based on the input physical layer cell identifier NID2, and outputs it to the second correlation calculation unit 216a.

[0057] The data holding section 214a extracts and holds a signal from the input baseband time domain signal based on the input SSB timing, and outputs the signal to the second correlation calculation section 216a.

[0058] The second correlation calculation unit 216a calculates a correlation value between the input baseband time domain signal and the input PSS code sequence, and outputs the result to the error detection unit 218a.

[0059] The error detection unit 218a calculates the amount of phase rotation of the baseband time domain signal from the input correlation value, and outputs it as a carrier frequency error of the baseband time domain signal.

[0060] 10 is a diagram showing an example of the argument of the correlation value calculated by the second correlation calculation unit 216a of the frequency error detection unit 21 arranged in data order. When there is no frequency error, the phase difference between the corresponding data between the PSS code sequence and the baseband time domain signal is fixed, so the argument of the complex data of the correlation value also has a fixed value. On the other hand, when there is a frequency error, the baseband time domain signal rotates in phase with respect to the PSS code sequence by the amount of the frequency error, so that the argument of the complex data of the correlation value shows a monotonically increasing straight line, and the slope of the straight line has a value according to the magnitude of the frequency error. The error detection unit 218a of the frequency error detection unit 21 calculates the frequency error of the baseband time domain signal from the slope of this straight line.

[0061] 11 is a diagram showing an example of a functional configuration of the frequency error correcting unit 22 according to the first embodiment. The frequency error correcting unit 22 includes a sine wave generating unit 220 and a frequency converting unit 222.

[0062] The sine wave generating section 220 generates a complex sine wave of a specified frequency based on the input frequency error, and outputs it to the frequency converting section 222 .

[0063] The frequency conversion unit 222 complex-multiplies the input complex sine wave by the baseband time domain signal to convert the carrier frequency of the baseband time domain signal, and outputs the converted signal to the FFT unit 1004 .

[0064] 12 is a diagram showing an example of the functional configuration of the SSS detection unit 1016 according to the first embodiment. The SSS detection unit 1016 includes an SSS extraction unit 1161, an SSS generation unit 1162, a data determination unit 1163, a comparison operation unit 1164, and an NID1 detection unit 1165.

[0065] The SSS extraction unit 1161 extracts the frequency components in which the SSS signal is allocated from the frequency axis waveform signal. More specifically, the SSS extraction unit 1161 extracts the frequency components in which the SSS signal is allocated from the SSB symbol, which is the input frequency axis waveform signal, and outputs the extracted frequency components to the data determination unit 1163. That is, the SSS extraction unit 1161 outputs the frequency components of the SSS signal.

[0066] The SSS generation unit 1162 outputs a plurality of SSS sequences corresponding to NID2, which is a cell identifier of the physical layer that is the output of the PSS detection unit 1013, and an SSS index that identifies the SSS sequence. More specifically, the SSS generation unit 1162 generates a plurality of SSS code series based on the input NID2, and outputs them as SSS sequences to the comparison calculation unit 1164. The SSS generation unit 1162 also outputs an SSS index that identifies the SSS sequence to the NID1 detection unit 1165.

[0067] The data determination unit 1163 determines demodulated data corresponding to the IQ complex coordinate position of the SSS signal that is the output of the SSS extraction unit 1161, and outputs a series of data determined for the entire SSS signal to the comparison calculation unit 1164 as an SSS sequence.

[0068] The comparison operation unit 1164 compares the SSS sequence from the data determination unit 1163 with the SSS sequence from the SSS generation unit 1162, and outputs the number of matching values ​​as a comparison result to the NID1 detection unit 1165. Note that the comparison operation unit 1164 may output to the NID1 detection unit 1165 a similarity degree indicating the degree of similarity between the SSS sequence from the data determination unit 1163 and the SSS sequence from the SSS generation unit 1162.

[0069] The NID1 detection unit 1165 determines the one with the highest number of matches from the comparison results that are outputs from the comparison operation unit 1164. Then, the NID1 detection unit 1165 outputs the SSS index corresponding to the SSS sequence with the highest number of matches as the NID1 indicating a group of cell identifiers in the physical layer.

[0070] 13 is a diagram showing an example of the functional configuration of the DMRS detector 1017 according to the first embodiment. The DMRS detector 1017 includes a DMRS extractor 1171, a DMRS generator 1172, a data determiner 1173, a comparison calculator 1174, and an ibar_SSB detector 1175.

[0071] DMRS extraction section 1171 extracts the frequency components in which the DMRS signal is assigned from the frequency axis waveform signal. More specifically, DMRS extraction section 1171 extracts the frequency components in which the DMRS signal is assigned from the SSB symbol that is the input frequency axis waveform signal, and outputs the extracted frequency components to data determination section 1173. That is, DMRS extraction section 1171 outputs the frequency components of the DMRS signal.

[0072] The DMRS generation unit 1172 outputs a plurality of DMRS sequences corresponding to NID1 indicating a group of cell identifiers in the physical layer, which is the output of the SSS detection unit 1016, and an ibar_SSB index that identifies the DMRS sequences. More specifically, the DMRS generation unit 1172 generates a plurality of code sequences based on the input NID1, and outputs them as DMRS sequences to the comparison calculation unit 1174. The DMRS generation unit 1172 also outputs the DMRS index that identifies the DMRS sequence to the ibar_SSB detection unit 1175.

[0073] The data decision section 1173 decides the demodulated data corresponding to the IQ complex coordinate position of the DMRS signal that is the output of the DMRS extraction section 1171, and outputs a series of decided data for the entire DMRS signal to a comparison calculation section 1174 as a DMRS sequence.

[0074] Comparison calculation section 1174 compares the DMRS sequence from data determination section 1173 with the DMRS sequence from DMRS generation section 1172 and outputs the number of matches as the comparison result to ibar_SSB detection section 1175.

[0075] The ibar_SSB detection section 1175 determines the one with the highest number of matches from the comparison results that are outputs from the comparison calculation section 1174. Then, the ibar_SSB detection section 1175 outputs the ibar_SSB index corresponding to the DMRS sequence with the highest number of matches as the ibar_SSB.

[0076] Next, the TDD detection process executed by the master station device 10 according to the first embodiment and various processes executed in the TDD detection process, such as sampling phase conversion process, will be described.

[0077] FIG. 14 is a flowchart illustrating an example of the TDD detection process in the first embodiment.

[0078] Here, it is assumed that the distributed antenna system 1 is receiving either an analog wireless signal, a DL signal or a UL signal, and that the distributed antenna system 1 is capable of referring to identification information indicating whether the TDD detection processing period is enabled or disabled, and DL / UL configuration information of the TDD.

[0079] The signal receiving unit 1001 performs AD conversion, frequency down-conversion, and sampling rate conversion on the input analog signal, and obtains a baseband time-domain waveform signal as a received signal (step S1).

[0080] Next, the time waveform calculation unit 1002 executes time waveform processing (step S2). That is, the time waveform calculation unit 1002 detects a PSS signal placed at the beginning of an SSB from the baseband signal, and notifies the frequency error detection unit 21 and the FFT unit 1004 of the detected timing as SSB timing. The time waveform calculation unit 1002 also determines which of a plurality of PSS code sequences the detected PSS signal corresponds to, and outputs it to the FFT unit 1004 and the SSS detection unit 1016 of the frequency waveform calculation unit 1005 as NID2, which is a cell identifier of the physical layer.

[0081] Next, the carrier frequency correction unit 20 receives the baseband time domain signal from the sampling rate conversion unit 1012 of the signal receiving unit 1001 and the SSB timing from the PSS detection unit 1013, and executes carrier frequency correction processing (step S3). Specifically, in the carrier frequency correction unit 20, the frequency error detection unit 21 extracts a signal from the baseband signal based on the SSB timing notified by the PSS detection unit 1013, and detects a carrier frequency error. The frequency error correction unit 22 corrects the carrier frequency error based on the frequency error detected by the frequency error detection unit 21, and notifies the FFT unit 1004 of the SSB timing.

[0082] Next, the FFT unit 1004 extracts the SSB from the baseband signal after carrier frequency error correction based on the notified SSB timing, performs a Fourier transform on it, and notifies the frequency waveform calculation unit 1005 of the completion of the FFT process (step S4).

[0083] Next, the frequency waveform calculation unit 1005 detects the index number of the SSB, which indicates where in the transmission period the SSB is placed (step S5).

[0084] If the TDD detection process is within a valid period (step S6; Yes), the signal receiving unit 1001, the time waveform calculation unit 1002, the FFT unit 1004, and the frequency waveform calculation unit 1005 repeatedly execute the above steps S1 to S4.

[0085] When the TDD detection processing period ends (step S6; No), the switching timing estimation unit 1006 estimates where the SSB is placed within the transmission period, and estimates the DL / UL switching timing within the transmission period from this SSB placement position and the known TDD DL / UL configuration information (step S7).

[0086] Fig. 15 is a flowchart showing an example of the time waveform processing according to the first embodiment. That is, the flowchart shown in Fig. 15 is the time waveform processing of step S2 shown in Fig. 14.

[0087] The time signal extraction unit 1131 determines whether the TDD detection processing period is valid (step S20). If the TDD detection processing period is invalid (step S21; No), the time signal extraction unit 1131 ends the time waveform processing. On the other hand, if the TDD detection processing period is valid (step S21; Yes), the time waveform calculation unit 1002 executes the subsequent processing.

[0088] Next, the first correlation calculation unit 1133 calculates a correlation value by executing a correlation calculation between the baseband time domain waveform signal and a plurality of PSS code sequences (step S22).

[0089] Next, the NID2 detection unit 1134 determines whether a significant correlation value exists among the multiple correlation calculations (step S23). A significant correlation value here may be one that exceeds a predetermined threshold value, or one that is the maximum from the start of time waveform processing to the present. If a significant correlation value does not exist (step S23; No), the NID2 detection unit 1134 returns to step S11. On the other hand, if a significant correlation value exists (step S23; Yes), the NID2 detection unit 1134 executes the subsequent process.

[0090] The NID2 detection unit 1134 stores the PSS sequence, which is the PSS code sequence number corresponding to the significant correlation value, as NID2 (step S24).

[0091] The NID2 detection unit 1134 stores the system time at which the significant correlation value was calculated as a PSS correlation detection time (step S25).

[0092] The NID2 detection unit 1134 notifies the carrier frequency correction process (step S3) of the system time at which the significant correlation value was calculated as the SSB timing in step S3 (step S26).

[0093] 16 is a flowchart showing an example of the carrier frequency correction process according to the first embodiment. That is, the flowchart shown in FIG. 16 is the carrier frequency correction process of step S3 shown in FIG.

[0094] The frequency error detection unit 21 of the carrier frequency correction unit 20 determines whether the SB timing has been notified from the time waveform calculation unit 1002 (step S31). If there has been no notification, the carrier frequency correction unit 20 exits from the carrier frequency correction process (No in step S31), and if there has been a notification, the carrier frequency correction unit 20 executes the process of the subsequent step S32 (Yes in step S31).

[0095] Next, the frequency error detection unit 21 reads out the NID2 stored in step S24 (step S32).

[0096] Next, the frequency error detection unit 21 executes a frequency error detection process (step S33).

[0097] Next, the frequency error correction unit 22 executes a frequency error correction process (step S34).

[0098] Next, the frequency error correction unit 22 notifies the FFT processing of the SSB timing (step S35).

[0099] 17 is a flowchart showing an example of the frequency error detection process according to the first embodiment. That is, the flowchart shown in FIG. 17 shows the frequency error detection process in step S33 shown in FIG.

[0100] The data holding unit 214a of the frequency error detection unit 21 holds the baseband time domain signal based on the notified SSB timing (step S330).

[0101] Next, the PSS code sequence selection unit 210a of the frequency error detection unit 21 reads out the NID2 stored in step S24 (step S331).

[0102] Next, the PSS code sequence selection unit 210a of the frequency error detection unit 21 selects a PSS code sequence from among a plurality of PSS code sequences (from PSS code sequence 0, PSS code sequence 1, and PSS code sequence 2 in the example of FIG. 9) based on NID2 (step S332). The PSS code sequence selection unit 210a outputs the selected PSS code sequence to the second correlation calculation unit 216a.

[0103] Next, the second correlation calculation unit 216a of the frequency error detection unit 21 calculates a correlation value between the time axis signal held by the data holding unit 214a and the PSS code sequence selected by the PSS code sequence selection unit 210a (step S333). The second correlation calculation unit 216a outputs the calculated correlation value to the error detection unit 218a.

[0104] Next, the error detector 218a of the frequency error detector 21 calculates the amount of phase rotation of the time domain signal from the correlation value calculated by the second correlation calculator 216a, and adopts the calculated amount of phase rotation as the carrier frequency error of the time domain signal (step S334). The error detector 218a outputs the adopted carrier frequency error to the frequency error corrector 22.

[0105] 18 is a flowchart showing an example of the frequency error correction process according to the first embodiment. That is, the flowchart shown in FIG 18 is the frequency error correction process in step S34 shown in FIG 16.

[0106] The sine wave generating unit 220 of the frequency error correcting unit 22 generates a complex sine wave of a specified frequency based on the frequency error detected by the error detecting unit 218a of the frequency error detecting unit 21 (step S340). The sine wave generating unit 220 outputs the generated complex sine wave to the frequency converting unit 222.

[0107] Next, the frequency conversion unit 222 of the frequency error correction unit 22 converts the carrier frequency of the time domain signal by complex multiplying the time domain signal received from the sampling rate conversion unit 1012 by the complex sine wave received from the sine wave generation unit 220 (step S341).

[0108] Fig. 19 is a flowchart showing an example of the FFT process according to the first embodiment. That is, the flowchart shown in Fig. 14 shows the FFT process of step S4.

[0109] The FFT unit 1004 determines whether or not the SSB timing has been notified (step S40). If there has been no notification (step S40; No), the FFT unit 1004 ends the FFT process. On the other hand, if there has been a notification (step S40; Yes), the FFT unit 1004 executes the subsequent process.

[0110] Based on the notified SSB timing, the FFT unit 1004 extracts the SSB from the frequency-converted (corrected) baseband signal received from the frequency error correction unit 22 (step S41).

[0111] The FFT unit 1004 performs a Fourier transform on the extracted SSB time domain waveform signal to a frequency domain waveform signal (step S42).

[0112] The FFT unit 1004 notifies the frequency waveform processing shown in step S4 of the completion of the FFT processing (step S43).

[0113] Fig. 20 is a flowchart showing an example of frequency waveform processing according to the first embodiment. That is, the flowchart shown in Fig. 20 is the frequency waveform processing of step S5 shown in Fig. 14.

[0114] The frequency waveform calculation unit 1005 judges whether or not the completion of FFT processing has been notified (step S50). If there is no notification (step S50; No), the frequency waveform calculation unit 1005 ends the frequency waveform processing. On the other hand, if there is a notification (step S50; Yes), the frequency waveform calculation unit 1005 executes the subsequent processing.

[0115] Next, the SSS detection unit 1016 executes an SSS detection process (step S51).

[0116] Next, the frequency waveform calculation unit 1005 judges whether or not a significant SSS has been detected (step S52). A significant SSS is judged to be a sequence whose similarity to the SSS sequence calculated in the SSS detection process exceeds a predetermined threshold and is maximum, for example. If no significant SSS exists (step S52; No), the frequency waveform calculation unit 1005 ends the frequency waveform process. On the other hand, if a significant SSS exists (step S52; Yes), the frequency waveform calculation unit 1005 executes the subsequent process.

[0117] Next, the DMRS detector 1017 executes a DMRS detection process (step S53).

[0118] Next, the frequency waveform calculation unit 1005 judges whether or not a significant DMRS has been detected (step S54). A significant DMRS is judged to be a DMRS whose similarity to the DMRS sequence calculated in the DMRS detection process exceeds a predetermined threshold and is maximum, for example. If no significant DMRS exists (step S54; No), the frequency waveform calculation unit 1005 ends the frequency waveform processing. On the other hand, if a significant DMRS exists (step S54; Yes), the frequency waveform calculation unit 1005 executes the subsequent processing.

[0119] Next, the frequency waveform calculation unit 1005 notifies the switching timing estimation process shown in step S6 of the completion of the frequency waveform processing (step S55).

[0120] 21 is a flowchart showing an example of the SSS detection process according to the first embodiment. That is, the flowchart shown in FIG 21 is the SSS detection process in step S51 shown in FIG 20.

[0121] The SSS extraction unit 1161 extracts the frequency components in which the SSS signal is assigned from the frequency axis waveform signal (step S510).

[0122] Next, the SSS generating unit 1162 reads out the NID2 stored in step S14 (step S511).

[0123] Next, the SSS generation unit 1162 generates a plurality of SSS sequences and an SSS index for identifying the SSS sequences based on NID2 (step S512).

[0124] Next, the comparison operation unit 1164 detects the SSS sequence that is most similar to the extracted SSS signal (step S513).

[0125] Next, the NID1 detection unit 1165 stores the SSS index corresponding to the most similar SSS sequence as NID1 (step S514).

[0126] 22 is a flowchart showing an example of the DMRS detection process according to the first embodiment. That is, the flowchart shown in FIG. 22 is the DMRS detection process of step S53 shown in FIG.

[0127] The DMRS extraction unit 1171 extracts the frequency components to which the DMRS signal is assigned from the frequency axis waveform signal (step S530).

[0128] Next, the DMRS generation unit 1172 reads out NID1 stored in step S514 (step S531).

[0129] Next, DMRS generation section 1172 generates a plurality of DMRS sequences based on NID1 and an ibar_SSB index that identifies the DMRS sequence (step S532).

[0130] Next, comparison operation section 1174 detects the DMRS sequence that is most similar to the extracted DMRS signal (step S533).

[0131] Next, ibar_SSB detection section 1175 stores the ibar_SSB index corresponding to the DMRS sequence with the highest similarity as ibar_SSB (step S534).

[0132] 23 is a flowchart showing an example of the switching timing estimation process according to the first embodiment. That is, the flowchart shown in FIG. 23 is the switching timing estimation process of step S7 shown in FIG.

[0133] The switching timing estimation unit 1006 judges whether or not the completion of the frequency waveform processing has been notified (step S70). If there has been no notification (step S70; No), the switching timing estimation unit 1006 ends the switching timing estimation process. On the other hand, if there has been a notification (step S70; Yes), the switching timing estimation unit 1006 executes the subsequent process.

[0134] Next, the switching timing estimation unit 1006 reads out the PSS correlation detection time stored in step S24 (step S71).

[0135] Next, the switching timing estimation unit 1006 reads out ibar_SSB stored in step S534 (step S72).

[0136] Next, the switching timing estimation unit 1006 estimates the position of the frame in which the currently detected SSB was placed, based on the known SSB placement pattern and the ibar_SSB read in step S72 (step S73).

[0137] Next, the switching timing estimation unit 1006 estimates the timing when the next TDD switching will occur based on the known TDD DL / UL configuration information, the PSS correlation detection time read in step S71, and the SSB frame position estimated in step S73 (step S74).

[0138] (Variation 1) Next, the switching timing generation unit 153 according to the first modification will be described.

[0139] In OFDM transmission, in order to strengthen the resistance to multipath interference and inter-symbol interference, a copy of the tail of an OFDM symbol is added to the head of the OFDM symbol to provide a guard section called a cyclic prefix (CP). In the case of such a signal format, the carrier frequency error can be detected by performing an autocorrelation calculation of the baseband time domain signal. The switching timing generation unit 153 according to the first modification detects the carrier frequency error by using the autocorrelation calculation of the baseband time domain signal.

[0140] Fig. 24 is a diagram showing an example of a functional configuration of a frequency error detection unit 21b included in the switching timing generation unit 153 according to Modification 1. As shown in Fig. 24, the frequency error detection unit 21b includes a data holding unit 210b, an autocorrelation calculation unit 211b, and an error detection unit 212b.

[0141] The data holding unit 210b extracts and holds a signal from the baseband time domain signal received from the sampling rate conversion unit 1012 based on the SSB timing received from the PSS detection unit 1013, and outputs the signal to the autocorrelation calculation unit 211b.

[0142] The autocorrelation calculation unit 211b calculates the autocorrelation value between the leading and trailing parts of the baseband time domain signal received from the data holding unit 210b, and outputs the calculated value to the error detection unit 212b.

[0143] The error detection unit 212b calculates the amount of phase rotation of the baseband time domain signal from the correlation value received from the autocorrelation calculation unit 211b, and outputs it to the frequency error correction unit 22 as the carrier frequency error of the baseband time domain signal.

[0144] Fig. 25 is a diagram showing an example in which the argument of the autocorrelation value calculated by the autocorrelation calculation unit 211b in Fig. 24 is arranged in data order. As shown in Fig. 25, when there is no frequency error, there is no phase difference between the head part of the signal and the tail part, which is the copy source, and the argument of the complex data of the correlation value is 0. On the other hand, when there is a frequency error, a phase rotation according to the frequency error occurs between the head part and the tail part, which is separated by the effective symbol period, so that the argument of the complex data of the autocorrelation value takes a fixed value according to the magnitude of the frequency error. The error detection unit 212b calculates the frequency error of the baseband time axis signal from this fixed value of the argument.

[0145] Fig. 26 is a flowchart showing an example of a frequency error detection process according to Modification 1. That is, the flowchart shown in Fig. 26 is obtained by applying the frequency error detection process of Modification 1 to step S33 shown in Fig. 16. Note that, when the carrier frequency correction process according to Modification 1 is compared with the carrier frequency correction process according to the first embodiment, only the frequency error detection process in step S33 in Fig. 16 is different.

[0146] The data holding unit 210b of the frequency error detection unit 21b holds the baseband time domain signal based on the notified SSB timing (step S330a).

[0147] Next, the autocorrelation calculation unit 211b of the frequency error detection unit 21b calculates an autocorrelation value between the leading portion and the trailing portion of the time axis signal stored in the data storage unit 210b (step S331a). The autocorrelation calculation unit 211b outputs the calculated autocorrelation value to the error detection unit 212b.

[0148] Next, the error detector 212b of the frequency error detector 21b calculates the amount of phase rotation of the time domain signal from the autocorrelation value received from the autocorrelation calculator 211b, and adopts it as the carrier frequency error of the time domain signal (step S332a). The error detector 212b outputs the adopted frequency error to the frequency error corrector 22.

[0149] As described above, the switching timing generating unit 153 according to the first embodiment includes a signal receiving unit 1001, a time waveform calculating unit 1002, a carrier frequency correction unit 20, an FFT unit 1004, a frequency waveform calculating unit 1005, and a switching timing estimating unit 1006. The signal receiving unit 1001 receives an OFDM signal and converts it into a baseband OFDM signal. The time waveform calculating unit 1002 extracts a part of the time axis waveform signal that is the output of the signal receiving unit, and calculates the similarity between the extracted signal and a known signal. The carrier frequency correcting unit 20 corrects the carrier frequency of the time axis waveform signal that is the output of the signal receiving unit 1001, based on the similarity between the known signal calculated by the time waveform calculating unit 1002. The FFT unit 1004 performs a Fourier transform on the time axis waveform signal that is the output of the carrier frequency correcting unit 20. The frequency waveform calculation unit 1005 extracts a part of the frequency axis waveform signal that is the output of the FFT unit 1004, and calculates the degree of similarity between the extracted signal and a known signal. The switching timing estimation unit 1006 estimates the switching timing between uplink communication and downlink communication in the own device based on the result of the frequency waveform calculation unit 1005.

[0150] According to the switching timing generating unit 153 of the first embodiment, the carrier frequency of the time domain waveform signal is corrected based on the degree of similarity between a part of the signal extracted from the time domain waveform signal and a known signal, and an error occurring in the carrier frequency can be reduced. Therefore, it is possible to realize the reduction of the inter-carrier interference caused by the carrier frequency error by a simple method that does not require the frequency control of the local oscillator clock. As a result, even if there is the inter-carrier interference caused by the carrier frequency error in the TDD system, it is possible to estimate the DL / UL switching timing inexpensively and accurately.

[0151] The effect of the switching timing generation section 153 according to the first embodiment will be described in more detail with reference to a switching timing generation section 153a according to a first comparative example.

[0152] Fig. 27 is a diagram showing an example of a functional configuration of a switching timing generation unit 153a according to comparative example 1. When Fig. 27 is compared with Fig. 7, the switching timing generation unit 153a according to comparative example 1 shown in Fig. 27 does not include the carrier frequency correction unit 20 shown in Fig. 7.

[0153] FIG. 28 is a diagram for explaining a constellation when there is a difference in carrier frequency error, taking as an example data that has been quadrature phase shift keyed (QPSK) when the switching timing generating unit 153a according to the first comparative example is used.

[0154] Figure 28(a) shows an example of a constellation when there is no carrier frequency error. As shown in Figure 28(a), when there is no carrier frequency error, the data of the constellation converges to one point for each of the four quadrants.

[0155] Figure 28(b) shows an example of a constellation when the carrier frequency error is 10% of the subcarrier spacing. As shown in Figure 28(b), when the carrier frequency error is 10% of the subcarrier spacing, phase rotation occurs in the constellation and data that converged to a single point in each quadrant spreads. This data spread is caused by demodulation with the OFDM center frequency shifted by the carrier frequency error. When demodulation is performed with the center frequency shifted, the orthogonality between OFDM subcarriers is lost, inter-carrier interference occurs, and as a result, data spreads.

[0156] Fig. 28(c) shows an example of a constellation when the carrier frequency error is 20% of the subcarrier spacing. As shown in Fig. 28(c), when the carrier frequency error is 20% of the subcarrier spacing, the data spread becomes even larger, and when the data moves beyond 1 / 2 the Euclidean distance between adjacent signal points, it is determined as an erroneous value by the frequency waveform calculation unit located after the FFT unit 1004.

[0157] As described above, when phase shift keyed (PSK) data is judged in the presence of inter-carrier interference caused by carrier frequency error, the reception characteristics are significantly degraded. Therefore, data judgment is generally performed after correcting the inter-carrier interference.

[0158] Here, in order to correct inter-carrier interference, it is possible to use a mechanism for controlling the frequency and phase of the clock for the local oscillator or the baseband system clock, or to perform waveform equalization processing to correct the waveform after FFT processing. However, these processes are complex and costly to realize. In particular, in order to control the frequency and phase of the clock, it is necessary to collect error information from many functional blocks arranged after the A / D conversion and to carefully change the clock, and it is costly to realize the mechanism. Furthermore, due to the time regulation for switching between transmission and reception by the time division multiplexing method, there is a restriction on the time from when the signal is received to when the demodulation processing of the synchronization signal block is completed. The control of the frequency and phase of the clock and the waveform equalization processing are also subject to this time restriction.

[0159] As a result, in order to correct inter-carrier interference, the processing circuits for demodulation, clock control, and waveform equalization must operate at high speed, which increases the cost of implementing the device.

[0160] In contrast, the switching timing generation unit 153 according to this embodiment can estimate the DL / UL switching timing inexpensively and accurately, without requiring the above-mentioned costs, even when there is inter-carrier interference caused by carrier frequency error.

[0161] Second Embodiment Next, a description will be given of a switching timing generating unit 153 according to the second embodiment. The switching timing generating unit 153 according to the second embodiment performs a carrier frequency correction process when performing a sampling phase conversion process for correcting a sampling phase deviated from an original phase.

[0162] Fig. 29A is a diagram showing an example of a functional configuration of the switching timing generation unit 153 of the second embodiment. When Fig. 29A is compared with Fig. 7, it is different in that the switching timing generation unit 153 of the second embodiment shown in Fig. 29A further includes a sampling phase conversion unit 30.

[0163] The sampling rate conversion unit 1012 in the signal receiving unit 1001 outputs a baseband time axis waveform signal to the PSS detection unit 1013 and the sampling phase conversion unit 30 .

[0164] The sampling phase converter 30 executes a sampling phase conversion process for converting the sampling phase of the time domain waveform signal that is the output of the signal receiver 1001. Specifically, the sampling phase converter 30 includes a phase detector 31 and a phase converter 32.

[0165] The phase detection unit 31 detects the optimum phase at which the sampling phase of the time domain waveform signal is the best, based on the SSB timing and the physical layer cell identifier NID2 that are the outputs of the PSS detection unit 1013. That is, the phase detection unit 31 extracts a signal from the inputted sampling rate converted baseband signal based on the inputted SSB timing, detects the optimum phase from among a plurality of predetermined sampling phases based on the inputted physical layer cell identifier NID2, and outputs the optimum phase to the phase conversion unit 32.

[0166] 29B is a diagram illustrating an example of a functional configuration of the phase detection unit 31 in the second embodiment. Specifically, the phase detection unit 31 includes a data holding unit 310, a phase conversion unit 311, a PSS code sequence selection unit 312, a third correlation calculation unit 313, and a phase determination unit 314.

[0167] The data holding unit 310 extracts and holds a signal from the input baseband time domain signal based on the input SSB timing, and outputs the signal to the phase conversion unit 311 .

[0168] The phase converter 311 converts the input baseband time domain signal into a plurality of predetermined sampling phases and outputs the signal to the third correlation calculator 313 .

[0169] The PSS code sequence selection unit 312 selects one from among a plurality of PSS code sequences based on the input physical layer cell identifier NID 2 , and outputs it to the third correlation calculation unit 313 .

[0170] The third correlation calculation unit 313 calculates a correlation value between the input PSS code sequence and each of the input phase-converted baseband time domain signals, and outputs the calculated correlation value to the phase determination unit 314 .

[0171] The phase determination unit 314 determines the time axis signal that is most similar to the PSS code sequence from the input correlation value, and outputs the sampling phase corresponding to that signal as the optimal phase.

[0172] The phase conversion unit 32 converts the sampling phase of the baseband time domain waveform signal received from the sampling rate conversion unit 1012, based on the optimal phase that is the output of the phase detection unit 31. That is, the phase conversion unit 32 converts the sampling phase of the input baseband signal after sampling rate conversion to an optimal phase, based on the input optimal phase, and outputs the converted phase to the carrier frequency correction unit 20 (i.e., the frequency error detection unit 21 and the frequency error correction unit 22).

[0173] 29C is a diagram showing an example of the functional configuration of the phase conversion section 32 in the second embodiment. The phase conversion section 32 includes a filter coefficient selection section 320 and a filter calculation section 321.

[0174] The filter coefficient selection unit 320 selects one of a plurality of filter coefficients based on the input optimum phase, and outputs the selected filter coefficient to the filter calculation unit 321. For example, the filter coefficient selection unit 320 selects a filter coefficient for making the sampling phase coincident with or approach the optimum phase from among filter coefficient 0, filter coefficient 1, filter coefficient 2, and filter coefficient 3. Note that the four filter coefficients 0, 1, 2, and 3 shown in Fig. 29C are merely examples, and the number of filter coefficients as selection candidates can be set arbitrarily.

[0175] The filter calculation unit 321 converts the input baseband time domain signal into a predetermined sampling phase based on the input filter coefficient, and outputs the converted signal.

[0176] Returning to FIG. 29A, the frequency error detection unit 21 extracts a signal from the baseband signal after sampling phase conversion received from the phase conversion unit 32 based on the input SSB timing, detects a carrier frequency error using a PSS code sequence based on the input physical layer cell identifier NID2, and outputs the carrier frequency error to the frequency error correction unit 22.

[0177] The frequency error correction unit 22 generates a complex sine wave of a specified frequency based on the input carrier frequency error, corrects the carrier frequency by complex multiplying it by the baseband signal after sampling phase conversion received from the phase conversion unit 32, and outputs the result to the FFT unit 1004.

[0178] Fig. 30 is a flowchart showing an example of the TDD detection process in the second embodiment. Comparing Fig. 30 with Fig. 14, it is different in that a sampling phase conversion process (step S3a) is inserted before the carrier frequency correction process in step S3b (corresponding to the carrier frequency correction process in step S3 shown in Fig. 14).

[0179] Fig. 31 is a flowchart showing an example of the sampling phase conversion process according to the second embodiment. That is, the flowchart shown in Fig. 31 is the sampling phase conversion process of step S3a shown in Fig. 30.

[0180] The phase detection unit 31 of the sampling phase conversion unit 30 determines whether or not the SB timing has been notified from the time waveform calculation unit 1002 (step S31a). If there has been no notification, the phase detection unit 31 exits from the sampling phase conversion process (No in step S31a), and if there has been a notification, executes the process of the subsequent step S32a (Yes in step S31a).

[0181] Next, the phase detection unit 31 reads out the NID2 stored in step S24 (step S32a).

[0182] Next, the phase detection unit 31 executes a phase detection process (step S33a).

[0183] Next, the phase detection unit 31 executes a phase detection process (step S33a).

[0184] Next, the phase conversion unit 32 executes a phase conversion process (step S34a).

[0185] Next, the phase conversion unit 32 notifies the carrier frequency correction unit 20 of the SSB timing (step S34a).

[0186] Next, the effect of the switching timing generation section 153 according to the second embodiment will be described in more detail with reference to a switching timing generation section 153b according to a second comparative example.

[0187] Fig. 32 is a diagram showing an example of a functional configuration of a switching timing generation unit 153b according to comparative example 2. When Fig. 32 is compared with Fig. 29A, the switching timing generation unit 153b according to comparative example 2 shown in Fig. 32 does not include the carrier frequency correction unit 20 shown in Fig. 29A.

[0188] FIG. 33 is a diagram for explaining a constellation when using the switching timing generation unit 153b according to the second comparative example, taking as an example data that has been quadrature phase-shift keying as an example, there is a difference in carrier frequency error, and the sampling phase of the baseband time axis waveform signal deviates from the sampling phase at the time of transmission.

[0189] The top part of Figure 33 shows an example of a constellation when there is only a carrier frequency error and no deviation from the sampling phase (corresponding to Figure 28). As shown in the top part of Figure 33, data diffusion due to the carrier frequency error can be seen, but there is no effect related to the deviation from the sampling phase.

[0190] The middle part of FIG. 33 shows an example of a constellation when the sampling phase deviates by 25% from the upper part.

[0191] The lower part of FIG. 33 shows an example of a constellation when the sampling phase deviates by 50% from that of the upper part.

[0192] As can be seen by comparing (a), (d), and (g) in the left column of Figure 33, when the sampling phase deviates, the constellation rotates in the phase direction, and the amount of phase rotation increases as the degree of deviation increases. When focusing on the rotation in the phase direction in the center and right columns, they show the same tendency as the left column.

[0193] When the signals in the middle and lower parts of Fig. 33 are provided to the switching timing generating unit 153b according to the second comparative example, the sampling phase conversion unit 30 suppresses phase rotation due to deviation of the sampling phase, and (d) and (g) in Fig. 33 are corrected to a state close to (a), (e) and (h) to (b), and (f) and (i) to (c). However, the switching timing generating unit 153b according to the second comparative example does not have a carrier frequency correction unit 20. Therefore, the inter-carrier interference caused by the carrier frequency error cannot be suppressed, and the data spread remains as it is as shown in (b) and (c).

[0194] In contrast, the switching timing generating unit 153 according to the second embodiment can correct the carrier frequency of the time domain waveform signal based on the degree of similarity between a part of the signal extracted from the time domain waveform signal and a known signal when performing a sampling phase conversion process to correct a sampling phase deviated from the original phase, thereby reducing errors occurring in the carrier frequency. Therefore, it is possible to realize reduction of inter-carrier interference caused by carrier frequency errors with a simple method that does not require frequency control of the local oscillator clock. As a result, in the TDD system, even if inter-carrier interference caused by carrier frequency errors exists, it is possible to estimate the DL / UL switching timing inexpensively and accurately.

[0195] In addition, the program executed by the parent station device 10 of this embodiment is provided as a file in an installable or executable format, recorded on a computer-readable recording medium such as a semiconductor storage device such as a DVD (Digital Versatile Disk), a USB (Universal Serial Bus) memory, or an SSD (Solid State Drive).

[0196] The program may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network.The program may be provided or distributed via a network such as the Internet.The program may be provided by being pre-installed in a ROM or the like. [Explanation of symbols]

[0197] 1... distributed antenna system, 10... master station equipment (MU), 11... upper side input / output section, 12... lower side input / output section, 13... downlink processing section, 14... uplink processing section, 15... control section, 20... carrier frequency correction section, 21... frequency error detection section, 22... frequency error correction section, 30... sampling phase conversion section, 31... phase detection section, 32... phase conversion section, 45... repeater equipment (HU), 47... slave station equipment (RU), 40... transmission path, 50... base station, 60... terminal equipment, 70... antenna, 153... switching timing generation section, 154... switching section , 210a...PSS code sequence selection unit, 210b, 214a...data holding unit, 211b...autocorrelation calculation unit, 216a...second correlation calculation unit, 212b, 218a...error detection unit, 220...sine wave generation unit, 222...frequency conversion unit, 310...data holding unit, 311...phase conversion unit, 312...PSS code sequence selection unit, 313...third correlation calculation unit, 314...phase determination unit, 320...filter coefficient selection unit, 321...filter calculation unit, 1001...signal receiving unit, 1002...time waveform calculation unit, 1004...FFT (Fourier transform: Fast Fourier Transform (FFT) unit, 1005... frequency waveform calculation unit, 1006... switching timing estimation unit, 1010... ADC unit, 1011... carrier frequency conversion unit, 1012... sampling rate conversion unit, 1013... PSS detection unit, 1016... SSS detection unit, 1131... time signal extraction unit, 1132... PSS generation unit, 1133... first correlation calculation unit, 1134... NID2 detection unit, 1161... SSS extraction unit, 1162... SSS generation unit, 1163, 1173... data determination unit, 1164, 1174... comparison calculation unit, 1165... NID1 detection unit, 1171... DMRS extraction unit, 1172... DMRS generation unit, 1175... ibar_SSB detection unit

Claims

1. A distributed antenna system including a master station device connected to a base station, and one or more slave station devices that relay signals between a terminal device that communicates with the base station and the master station device, Functioning as the master station device or the slave station device, A communication device for receiving an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method, a signal receiving unit that receives the OFDM signal and converts it into a baseband time domain waveform signal; a time waveform calculation unit that extracts a portion of the time-axis waveform signal that is an output of the signal receiving unit and calculates a degree of similarity between the extracted signal and a known signal; a carrier frequency correction unit that corrects a carrier frequency of a time-domain waveform signal that is an output of the signal receiving unit, based on the degree of similarity to a known signal calculated by the time waveform calculation unit; an FFT unit that performs a Fast Fourier Transform (FFT) on a time-axis waveform signal that is an output of the carrier frequency correction unit; a frequency waveform calculation unit that extracts a portion of a frequency axis waveform signal that is an output of the FFT unit and calculates a degree of similarity between the extracted signal and a known signal; a switching timing estimation unit that estimates a switching timing between upstream communication and downstream communication in the own device based on a result of the frequency waveform calculation unit; A communication device comprising:

2. The signal receiving unit receives a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a synchronization signal block (SSB: SS / PBCH Block) having a physical broadcast channel (PBCH: Physical Broadcast Channel) including a demodulation reference signal (DMRS: DeModulation of Reference Signal); The communication device according to claim 1 .

3. The time waveform calculation unit includes a PSS detection unit that detects a PSS signal included in the time axis waveform signal. The communication device according to claim 2 .

4. The PSS detection unit is a time signal extraction unit that extracts a portion of the time axis waveform signal; a PSS generator that outputs a plurality of PSS code sequences of the PSS signal and code sequence numbers that identify the PSS code sequences; a first correlation calculation unit that performs correlation calculation between a time-axis waveform signal that is an output of the time signal extraction unit and a PSS code sequence from the PSS generation unit, and outputs a correlation value; an NID2 detection unit that outputs, within a predetermined time range, a timing at which the correlation value is highest as an SSB timing, and outputs, as a physical layer cell identifier NID2, a PSS code sequence number corresponding to the PSS code sequence at which the correlation value is highest; The communication device according to claim 3 .

5. The carrier frequency correction unit is a frequency error detection unit that detects a carrier frequency error of the time domain waveform signal based on the SSB timing and a physical layer cell identifier NID2 output from the PSS detection unit; a frequency error correction unit that corrects a carrier frequency of the time domain waveform signal based on a frequency error that is an output of the frequency error detection unit; The communication device according to claim 4 .

6. The frequency error detection unit a data storage unit that stores a portion of the time domain waveform signal based on an SSB timing that is an output of the PSS detection unit; a PSS code sequence selection unit that selects one of a plurality of PSS code sequences based on a physical layer cell identifier NID2 that is an output of the PSS detection unit; a second correlation calculation unit that calculates a correlation value between the time-axis waveform signal stored in the data storage unit and the PSS code sequence selected by the PSS code sequence selection unit; an error detection unit that calculates a phase rotation amount of a time axis from the correlation value calculated by the second correlation calculation unit and detects a carrier frequency error of the time axis waveform signal; The communication device according to claim 5 .

7. The frequency error correction unit a sine wave generating unit that generates a complex sine wave of an arbitrary frequency based on a frequency error that is an output of the frequency error detecting unit; a frequency conversion unit that converts a carrier frequency of the time-domain waveform signal by complex-multiplying a complex sine wave output from the sine wave generation unit by the time-domain waveform signal; The communication device according to claim 6 , comprising:

8. The OFDM signal has a guard period called a cyclic prefix (CP), which is a copy of the end of an OFDM symbol added to the beginning of the symbol, The frequency error detection unit a data storage unit that stores a portion of the time domain waveform signal based on an SSB timing that is an output of the PSS detection unit; an autocorrelation calculation unit that calculates an autocorrelation value between a leading portion and a trailing portion of the time-axis waveform signal stored in the data storage unit; an error detection unit that calculates a phase rotation amount of the time domain waveform signal from the autocorrelation value calculated by the autocorrelation calculation unit and detects a carrier frequency error of the time domain waveform signal; The communication device according to claim 5 .

9. The frequency error correction unit a sine wave generating unit that generates a complex sine wave of a specified frequency based on the frequency error that is an output of the frequency error detecting unit; a frequency conversion unit that converts a carrier frequency of the time-domain waveform signal by complex-multiplying a complex sine wave output from the sine wave generation unit by the time-domain waveform signal; The communication device of claim 8 .

10. A master station connected to the base station; one or more slave station devices that relay signals between terminal devices that communicate with the base station and the master station device; A distributed antenna system comprising: Functioning as the master station device or the slave station device, A communication device for receiving an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method, a signal receiving unit that receives the OFDM signal and converts it into a baseband time domain waveform signal; a time waveform calculation unit that extracts a portion of the time-axis waveform signal that is an output of the signal receiving unit and calculates a degree of similarity between the extracted signal and a known signal; a sampling phase conversion unit that converts a sampling phase of a time-domain waveform signal that is an output of the signal receiving unit, based on the degree of similarity to a known signal calculated by the time waveform calculation unit; a carrier frequency correction unit that corrects a carrier frequency of a time-domain waveform signal that is an output of the sampling phase conversion unit, based on the degree of similarity to a known signal calculated by the time waveform calculation unit; an FFT unit that performs a Fast Fourier Transform (FFT) on a time-axis waveform signal that is an output of the carrier frequency correction unit; a frequency waveform calculation unit that extracts a portion of a frequency axis waveform signal that is an output of the FFT unit and calculates a degree of similarity between the extracted signal and a known signal; a switching timing estimation unit that estimates a switching timing between upstream communication and downstream communication in the own device based on a result of the frequency waveform calculation unit; A communication device comprising:

11. The signal receiving unit receives a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a synchronization signal block (SSB: SS / PBCH Block) having a physical broadcast channel (PBCH: Physical Broadcast Channel) including a demodulation reference signal (DMRS: DeModulation of Reference Signal); The communication device according to claim 10.

12. The communication device according to claim 11 , wherein the time waveform calculation section includes a PSS detection section that detects a PSS signal included in the time domain waveform signal.

13. The PSS detection unit is a time signal extraction unit that extracts a portion of the time axis waveform signal; a PSS generator that outputs a plurality of PSS code sequences of the PSS signal and code sequence numbers that identify the PSS code sequences; a first correlation calculation unit that performs correlation calculation between a time-axis waveform signal that is an output of the time signal extraction unit and a PSS code sequence from the PSS generation unit, and outputs a correlation value; an NID2 detection unit that outputs, within a predetermined time range, a timing at which the correlation value is highest as an SSB timing, and outputs, as a physical layer cell identifier NID2, a PSS code sequence number corresponding to the PSS code sequence at which the correlation value is highest; The communication device of claim 12 .

14. The sampling phase conversion unit includes: a phase detection unit that detects an optimal phase in which the sampling phase of the time domain waveform signal is the best based on the SSB timing and a physical layer cell identifier NID2 that are outputs of the PSS detection unit; a phase conversion unit that converts a sampling phase of the time domain waveform signal based on an optimal phase that is an output of the phase detection unit; The communication device of claim 13 .

15. The carrier frequency correction unit is a frequency error detection unit that detects a carrier frequency error of a time domain waveform signal output from the sampling phase conversion unit based on an SSB timing output from the PSS detection unit and a physical layer cell identifier NID2; a frequency error correction unit that corrects a carrier frequency of a time domain waveform signal that is an output of the sampling phase conversion unit, based on a frequency error that is an output of the frequency error detection unit; The communication device of claim 14 .

16. The frequency error detection unit Based on the SSB timing, which is the output of the PSS detector a data storage unit that stores a portion of a time-domain waveform signal that is an output of the sampling phase conversion unit; a PSS code sequence selection unit that selects one of a plurality of PSS code sequences based on a physical layer cell identifier NID2 that is an output of the PSS detection unit; a third correlation calculation unit that calculates a correlation value between the time axis waveform signal stored in the data storage unit and the PSS code sequence selected by the PSS code sequence selection unit; an error detection unit that calculates a phase rotation amount of the time domain waveform signal that is an output of the sampling phase conversion unit from the correlation value calculated by the third correlation calculation unit, and detects a carrier frequency error of the time domain waveform signal that is an output of the sampling phase conversion unit; The communication device of claim 15 .

17. The frequency error correction unit a sine wave generating unit that generates a complex sine wave of a specified frequency based on the frequency error that is an output of the frequency error detecting unit; a frequency conversion unit that converts a carrier frequency of the time-domain waveform signal by complex-multiplying a complex sine wave output from the sine wave generation unit by the time-domain waveform signal; 20. The communication device of claim 16, comprising:

18. The OFDM signal has a guard period called a cyclic prefix (CP), which is a copy of the end of an OFDM symbol added to the beginning of the symbol. the frequency error detection unit includes a data holding unit that holds a part of a time domain waveform signal that is an output of the sampling phase conversion unit based on an SSB timing that is an output of the PSS detection unit; an autocorrelation calculation unit that calculates an autocorrelation value between a leading portion and a trailing portion of the time-axis waveform signal stored in the data storage unit; an error detection unit that calculates a phase rotation amount of a time domain waveform signal that is an output of the sampling phase conversion unit from the autocorrelation value calculated by the autocorrelation calculation unit, and detects a carrier frequency error of the time domain waveform signal that is an output of the sampling phase conversion unit; The communication device of claim 15 .

19. The frequency error correction unit a sine wave generating unit that generates a complex sine wave of a specified frequency based on the frequency error that is an output of the frequency error detecting unit; a frequency conversion unit that converts a carrier frequency of the time-domain waveform signal by complex-multiplying a complex sine wave output from the sine wave generation unit by the time-domain waveform signal; 20. The communication device of claim 18, comprising:

20. A distributed antenna system including a master station device connected to a base station, and one or more slave station devices that relay signals between a terminal device that communicates with the base station and the master station device, A control method for a communication device that functions as the master station device or the slave station device and receives an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method, comprising: Receive the OFDM signal and convert it into a baseband time domain waveform signal; extracting a portion of the time domain waveform signal, and calculating a first degree of similarity between the extracted signal and a known signal; correcting a carrier frequency of the time domain waveform signal based on the first degree of similarity; performing a Fast Fourier Transform (FFT) on the time-domain waveform signal whose carrier frequency has been corrected; A portion of the frequency axis waveform signal obtained by the Fourier transform is extracted, and a second similarity degree between the extracted signal and a known signal is calculated; estimating a switching timing between upstream communication and downstream communication in the own device based on the second similarity degree; A control method for a communication device comprising:

21. A distributed antenna system including a master station device connected to a base station, and one or more slave station devices that relay signals between a terminal device that communicates with the base station and the master station device, A computer included in a communication device that functions as the master station device or the slave station device and receives an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method, a signal receiving unit that receives the OFDM signal and converts it into a baseband time domain waveform signal; a time waveform calculation unit that extracts a part of a time-axis waveform signal that is an output of the signal receiving unit and calculates a degree of similarity between the extracted signal and a known signal; a carrier frequency correction unit that corrects a carrier frequency of a time-domain waveform signal that is an output of the signal receiving unit, based on the degree of similarity to a known signal calculated by the time waveform calculation unit; an FFT unit that performs a Fast Fourier Transform (FFT) on a time-axis waveform signal that is an output of the carrier frequency correction unit; a frequency waveform calculation unit that extracts a portion of a frequency axis waveform signal that is an output of the FFT unit and calculates a degree of similarity between the extracted signal and a known signal; a switching timing estimation unit that estimates a switching timing between upstream communication and downstream communication in the own device based on a result of the frequency waveform calculation unit; A program to make it function as such.

22. A master station connected to the base station; one or more slave station devices that relay signals between terminal devices that communicate with the base station and the master station device; A distributed antenna system comprising: Functioning as the master station device or the slave station device, A method for controlling a communication device that receives an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method, comprising the steps of: Receive the OFDM signal and convert it into a baseband time domain waveform signal; extracting a portion of the time domain waveform signal, and calculating a first degree of similarity between the extracted signal and a known signal; converting a sampling phase of the time domain waveform signal based on the first degree of similarity; correcting a carrier frequency of the time domain waveform signal whose sampling phase has been converted based on the first degree of similarity; performing a Fast Fourier Transform (FFT) on the time-domain waveform signal whose carrier frequency has been corrected; A portion of the frequency axis waveform signal obtained by the Fourier transform is extracted, and a second similarity between the extracted signal and a known signal is calculated; estimating a switching timing between upstream communication and downstream communication in the own device based on the second similarity degree; A control method for a communication device comprising:

23. A master station connected to the base station; one or more slave station devices that relay signals between terminal devices that communicate with the base station and the master station device; A distributed antenna system comprising: Functioning as the master station device or the slave station device, A computer is provided in a communication device that receives an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method, a signal receiving unit that receives the OFDM signal and converts it into a baseband time domain waveform signal; a time waveform calculation unit that extracts a part of a time-axis waveform signal that is an output of the signal receiving unit and calculates a degree of similarity between the extracted signal and a known signal; a sampling phase conversion unit that converts a sampling phase of a time-domain waveform signal that is an output of the signal receiving unit, based on the degree of similarity to a known signal calculated by the time waveform calculation unit; a carrier frequency correction unit that corrects a carrier frequency of a time-domain waveform signal that is an output of the sampling phase conversion unit, based on the degree of similarity to a known signal calculated by the time waveform calculation unit; an FFT unit that performs a Fast Fourier Transform (FFT) on a time-axis waveform signal that is an output of the carrier frequency correction unit; a frequency waveform calculation unit that extracts a portion of a frequency axis waveform signal that is an output of the FFT unit and calculates a degree of similarity between the extracted signal and a known signal; a switching timing estimation unit that estimates a switching timing between upstream communication and downstream communication in the own device based on a result of the frequency waveform calculation unit; A program to make it function as such.

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