Communication device, control method, and program

Abstract

In a communication device according to an embodiment, a signal reception unit receives an OFDM signal and converts said signal into a baseband OFDM signal. A temporal waveform calculation unit extracts a portion of a time-axis waveform signal and calculates the degree of similarity to a known signal. An FFT unit carries out a Fourier transform on the temporal waveform signal that is the output of the temporal waveform calculation unit. A frequency waveform phase correction unit corrects, on the basis of the degree of similarity to a known signal, the phase of the frequency-axis waveform signal that is the output of the FFT unit. A frequency waveform calculation unit extracts a portion of the frequency-axis waveform signal that is the output of the frequency waveform phase correction unit and calculates the degree of similarity between the extracted signal and a known signal. A switching timing estimation unit estimates, on the basis of the results from the frequency waveform calculation unit, the timing for switching between uplink communication and downlink communication in a host device.

Description

Communication device, control method, and program

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

[0002] Distributed Antenna Systems (DAS) are known as one type of wireless communication system. In a distributed antenna system, communication is performed using a time division duplex (TDD) method, in which downlink (DL) communication from a base station to a terminal and uplink (UL) communication from the terminal to the base station are switched at predetermined intervals. 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 first perform AD conversion, which converts radio signals from analog to digital signals, at the beginning of a series of processes. AD conversion often employs oversampling, which involves sampling at a rate higher than the data rate of the input signal, in order to increase the S / N ratio and resolution and to alleviate the requirements of anti-aliasing filters. Next, carrier frequency conversion is performed, which down-converts the AD-converted signal to a baseband signal. Sampling rate conversion is then performed, which down-converts the sampling rate of the baseband signal from the clock frequency used during AD conversion to the system clock frequency. TDD synchronization with a base station is achieved by analyzing the synchronization signal contained in the resulting sampling-rate-converted signal.

[0004] Generally, Orthogonal Frequency Division Multiplexing (OFDM) signals are susceptible to phase noise because they frequency-multiplex a large number of subcarriers. Phase noise has two effects on OFDM signals. One is subcarrier phase fluctuations caused by the low-frequency components of the phase noise. This is called common phase error because all subcarriers fluctuate at the same angle. The other is inter-carrier interference, in which the signal-to-noise ratio of a carrier deteriorates due to interference from the phase noise of other subcarriers. In particular, in the case of OFDM, common phase error appears as a phase rotation in the constellation after the received time-domain waveform signal is demodulated by the FFT unit.

[0005] JP 2020-053769 A JP 2020-504568 A

[0006] When data modulated by phase shift keying (PSK) or quadrature amplitude modulation (QAM) is judged in the presence of phase rotation due to a common phase error, reception characteristics are significantly degraded. Therefore, data judgment is generally performed after correcting the common phase error. Correcting the common phase error requires a mechanism for controlling the frequency and phase of the local oscillator clock and the baseband system clock, as well as waveform equalization processing that estimates transmission path characteristics and corrects the waveform after FFT.

[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 the DL / UL switching timing in a TDD system in which DL communication and UL communication are switched at predetermined intervals, even when a common phase error due to phase noise exists.

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

[0009] 1 is a diagram showing an example of an outline of a distributed antenna system according to a first embodiment. FIG. 1 is a diagram showing an example of a data configuration of a radio frame. FIG. 2 is a diagram showing an example of an SSB allocation pattern in a radio frame. FIG. 3 is a diagram showing an example of a DL / UL configuration and SSB allocation of a TDD system. FIG. 4 is a diagram showing an example of a functional configuration of a master station device according to the first embodiment. FIG. 5 is a diagram showing an example of a functional configuration of a control unit according to the first embodiment. FIG. 6 is a diagram showing an example of a functional configuration of a switching timing generation unit according to the first embodiment. FIG. 7 is a diagram showing an example of a functional configuration of a PSS detection unit according to the first embodiment. FIG. 8 is a diagram showing an example of a functional configuration of a phase error detection unit according to the first embodiment. FIG. 9 is a diagram showing an example of complex data of correlation values ​​calculated by a correlation calculation unit of the phase error detection unit, expressed on a complex plane. FIG. 10 is a diagram showing an example of the functional configuration of a phase correction unit according to the first embodiment. FIG. 11 is a diagram showing an example of the functional configuration of an SSS detection unit according to the first embodiment. FIG. 12 is a diagram showing an example of the functional configuration of a DMRS detection unit according to the first embodiment. A flowchart showing an example of TDD detection processing according to the first embodiment. A flowchart showing an example of time waveform processing according to the first embodiment. A flowchart showing an example of FFT processing according to the first embodiment. A flowchart showing an example of frequency waveform phase correction processing according to the first embodiment. 1 is a flowchart showing an example of a phase error detection process according to the first embodiment. 2 is a flowchart showing an example of a phase correction process according to the first embodiment. 3 is a flowchart showing an example of a frequency waveform processing according to the first embodiment. 4 is a flowchart showing an example of an SSS detection process according to the first embodiment. 5 is a flowchart showing an example of a DMRS detection process according to the first embodiment. 6 is a flowchart showing an example of a switching timing estimation process according to the first embodiment. 7 is a diagram showing an example of the functional configuration of a switching timing generation unit according to Comparative Example 1. 8 is a diagram for explaining a constellation when there is a difference in common phase error, taking quadrature phase shift keyed data as an example, when using the switching timing generation unit according to Comparative Example 1. 9 is a diagram showing an example of the functional configuration of a switching timing generation unit according to a second embodiment. 10 is a diagram showing an example of the functional configuration of a phase detection unit according to the second embodiment. 11 is a diagram showing an example of the functional configuration of a phase conversion unit according to the second embodiment. 12 is a flowchart showing an example of a TDD detection process according to the second embodiment. 13 is a flowchart showing an example of a sampling phase conversion process according to the second embodiment. 14 is a diagram showing an example of the functional configuration of a switching timing generation unit according to Comparative Example 2.10 is a diagram for explaining a constellation when there is a difference in common phase error and the sampling phase of the baseband time domain waveform signal deviates from the sampling phase at the time of transmission, using quadrature phase shift keying keyed data as an example, when a switching timing generation unit according to Comparative Example 2 is used. FIG. 11 is a diagram for explaining a constellation when there is a difference in common phase error and the sampling phase of the baseband time domain waveform signal deviates from the sampling phase at the time of transmission, using quadrature phase shift keyed keyed data as an example, when a switching timing generation unit according to Comparative Example 2 is used. FIG. 12 is a diagram for explaining a constellation when there is a difference in common phase error and the sampling phase of the baseband time domain waveform signal deviates from the sampling phase at the time of transmission, using quadrature phase shift keyed keyed data as an example, when a switching timing generation unit according to Comparative Example 2 is used. FIG. 13 is a diagram for explaining a constellation when there is a difference in common phase error and the sampling phase of the baseband time domain waveform signal deviates from the sampling phase at the time of transmission, using quadrature phase shift keyed keyed data as an example, when a switching timing generation unit according to Comparative Example 2 is used. FIG. 14 is a diagram for explaining a constellation when there is a difference in common phase error and the sampling phase of the baseband time domain waveform signal deviates from the sampling phase at the time of transmission, using quadrature phase shift keyed keyed data as an example, when a switching timing generation unit according to Comparative Example 2 is used. FIG. 15 is a diagram for explaining a constellation when there is a difference in common phase error and the sampling phase of the baseband time domain waveform signal deviates from the sampling phase at the time of transmission, using quadrature phase shift keyed keyed data as an example, when a switching timing generation unit according to Comparative Example 2 is used. FIG. 16 is a diagram for explaining a constellation when there is a difference in common phase error and the sampling phase of the baseband time domain waveform signal deviates FIG. 10 is a diagram for explaining a constellation when a switching timing generation unit according to Comparative Example 4 is used, using quadrature phase-shift keyed data as an example, there is a difference in the common phase error, the sampling phase of the baseband time domain waveform signal deviates from the sampling phase at the time of transmission, and there is a difference in the carrier frequency error.

[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 the description of overlapping parts will be omitted as appropriate.

[0011] 1 is a diagram illustrating an example of a schematic configuration of a distributed antenna system 1 according to a 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 80 connecting these devices. 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 within the distributed antenna system 1. As shown in Fig. 1 , the master station device 10 may be connected to a plurality of slave station devices 47 via relay devices 45, or may be connected to a plurality of slave station devices 47 directly. Furthermore, as shown in Fig. 1 , the master station device 10 may be connected to a plurality of 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 radio signals to and from the base station 50. Here, the radio signals are signals in the radio communication band that are transmitted to the terminal devices 60. The master station device 10 relays radio 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 radio 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 employ a TDD (time division multiplexing) method in which uplink communication and downlink communication are switched at predetermined intervals. Therefore, when the distributed antenna system 1 is applied to a mobile communications network, the distributed antenna system 1 must 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 communication quality, it is necessary to accurately detect the switching between uplink communication and downlink communication.

[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 determination result. Furthermore, in a communication device that shares one DAS with multiple mobile operators, if the DL / UL switching timing of the multiple operators differs, interference occurs, so the first symbol of the DL wireless frame is detected to detect the difference in the DL / UL switching timing between operators.

[0018] However, in wireless signals such as 5G, there are cases where there is no power (signal) in the first symbol of a wireless frame, making it difficult for the master station device 10 to accurately detect the DL / UL switching timing using conventional power detection methods or methods that detect the first symbol.

[0019] In a 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 terminal devices 60 that communicate with the base station 50, the master station device 10 functions as either the master station device 10 or the slave station device 47 and is a communication device that receives an orthogonal frequency division multiplexing (OFDM) signal transmitted using a time division multiplexing method. The master station device 10 receives a radio frame including a synchronization signal block (SS / PBCH block) in the distributed antenna system 1 that uses a TDD method in which DL communication and UL communication are switched at predetermined intervals. 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 determine the position of the received SSB within the radio frame.

[0020] 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 a 5G wireless signal or the like.

[0021] FIG. 2 is a diagram illustrating an example of the data structure of a radio frame. FIG. 2 shows an example of a 5G radio frame. One frame is transmitted every 10 ms. Each frame consists of 10 subframes, each transmitted every 1 ms. 5G supports multiple subcarrier frequency intervals, which result in different symbol lengths. For this reason, the concept of slots is incorporated into the radio frame, where the number of symbols per subframe is divided into multiple slots. The difference in symbol length due to the difference in subcarrier frequency intervals is absorbed by the number of slots per subframe. One slot has 14 symbols, regardless of the subcarrier frequency interval. FIG. 2 shows a case where the subcarrier frequency interval is 30 kHz, with one subframe consisting of two slots and 28 symbols. As shown in FIG. 2, SSBs are placed at specific positions in the radio frame.

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

[0023] Figure 4 shows an example of a DL / UL configuration and SSB allocation in a TDD system. The SSB shown in Figure 4 shows a case where the subcarrier frequency spacing is 30 kHz, the SSB period is 20 ms, and the transmission period is 5 ms. The transmission period includes 10 slots, with the first 6 slots assigned to DL and the last 3 slots assigned to UL, and a buffer slot assigned between the DL and UL slots. In this way, the number of consecutive DL slots and the number of consecutive UL slots within the transmission period are set in advance. The buffer slot is also assigned consecutive DL symbols, consecutive UL symbols, and blank symbols that function as guards between them. Note that the SSB shown in Figure 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 guards.

[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 within the transmission period of that SSB. 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 period relative to the placement position of the SSB.

[0025] In the following description, the direction of communication 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." Furthermore, the upstream side of a device may be referred to as the "upstream" side, and the downstream side as the "downstream." Correspondingly, a device connected to the upstream side of a device may be referred to as the "upstream device," and a device connected to the downstream side may be referred to as the "downstream device."

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

[0028] FIG. 5 is a diagram illustrating an example of the functional configuration of the master station device 10 according to the first embodiment. The master station device 10 includes a central processing unit (CPU), memory, auxiliary storage device, and other components connected via a bus, and executes a program. The master station device 10 includes a high-level input / output unit 11, a low-level input / output unit 12, a downlink processing unit 13, an uplink processing unit 14, and a control unit 15 through the execution of the program. Note that all or part of the functions of the master station device 10 may be implemented using hardware such as an application-specific integrated circuit (ASIC), a programmable logic device (PLD), or a field-programmable gate array (FPGA). The program may be recorded on a computer-readable recording medium. Examples of the computer-readable recording medium include portable media such as a flexible disk, a magneto-optical disk, a ROM, and a CD-ROM, and storage devices such as a hard disk built into a computer system. The program may be transmitted via a telecommunications line.

[0029] The upper input / output unit 11 is a communication interface that inputs and outputs radio signals to and from a higher-level device of the parent station device 10. Specifically, the upper input / output unit 11 is a communication interface that inputs and outputs radio signals to and from the base station 50 via a coaxial cable. The upper input / output unit 11 outputs DL signals received from the base station 50 to the downlink processing unit 13, and outputs UL signals input from the uplink processing unit 14 to the base station 50.

[0030] The lower-level input / output unit 12 is a communication interface for inputting and outputting radio signals to and from lower-level devices of the master station device 10. Specifically, the lower-level input / output unit 12 is a communication interface for inputting and outputting radio signals to and from the slave station device 47. The lower-level input / output unit 12 outputs a UL signal received from the slave station device 47 to the uplink processing unit 14, and outputs a DL signal input from the downlink processing unit 13 to the slave station device 47.

[0031] The downlink processing unit 13 executes a process (hereinafter referred to as "DL processing") in which the master station device 10 outputs a DL signal received from a higher-level device to a lower-level device. Specifically, the DL processing of the master 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 the 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-level 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 an UL signal received from a lower-level device to a higher-level device. Specifically, the UL processing of the master station device 10 includes a demapping process for acquiring an 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 into 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 the 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 the UL period or the DL period and notifies the timing of switching between the UL processing and the DL processing. Specifically, the switching timing generation unit 153 notifies the start timing of the estimated UL period or the DL period. The start timing may be notified as the start time of the UL period or the DL period, or may be notified as the elapsed time from the current time. Furthermore, the notification of the start timing may notify 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, an FFT (Fast Fourier Transform) unit 1004, a frequency waveform phase correction unit 40, 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 PBCH including a PSS, an SSS, and 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, which 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 FFT unit 1004.

[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 (e.g., correlation value) between the extracted signal and a known signal.

[0041] The PSS detector 1013 detects the PSS signal included in the time domain waveform signal. More specifically, the PSS detector 1013 detects the PSS signal placed at the beginning of the SSB from the baseband signal after sampling rate conversion, and outputs the detected timing as SSB timing to the FFT unit 1004 and the phase error detector 41 of the frequency waveform phase corrector 40. The PSS detector 1013 also determines which of multiple PSS code sequences the detected PSS signal corresponds to, and outputs this as NID2, a physical layer cell identifier, to the phase error detector 41 of the frequency waveform phase corrector 40 and the SSS detector 1016 of the frequency waveform calculator 1005. The configuration of the PSS detector 1013 will be described in detail later.

[0042] The FFT unit 1004 performs an FFT on the baseband time-domain waveform signal that is the output of the sampling rate conversion unit 1012 of the signal receiving unit 1001. More specifically, the FFT unit 1004 extracts the SSB from the baseband time-domain waveform signal after sampling rate conversion based on the input SSB timing and performs a Fourier transform on it. The FFT unit 1004 then outputs the SSB frequency-domain waveform signal obtained by the Fourier transform to the phase correction unit 42 of the frequency waveform phase correction unit 40.

[0043] Frequency waveform phase correction unit 40 receives a baseband time axis waveform signal from sampling rate conversion unit 1012 in signal receiving unit 1001, a frequency axis waveform signal from FFT unit 1004, and SSB timing and physical layer cell identifier NID2 from PSS detection unit 1013 in time waveform calculation unit 1002, and performs phase correction processing on the frequency axis waveform signal. Specifically, frequency waveform phase correction unit 40 includes a phase error detection unit 41 and a phase correction unit 42.

[0044] The phase error detector 41 extracts a signal from the input baseband time domain waveform signal based on the input SSB timing, detects a phase error using a PSS code sequence based on the input physical layer cell identifier NID2, and outputs the phase error to the phase corrector 42. The configuration of the phase error detector 41 will be described in detail later.

[0045] The phase correction unit 42 generates a complex signal having a specified argument and absolute value based on the input phase error, converts the phase by complex multiplying it by the input frequency axis waveform signal, and outputs the result to the frequency waveform calculation unit 1005. The configuration of the phase correction unit 42 will be described in detail later.

[0046] The SSS detection unit 1016 detects an SSS signal included in the frequency domain waveform signal. More specifically, the SSS detection unit 1016 detects an SSS signal from the SSB frequency domain waveform signal. The SSS detection unit 1016 also determines which of a plurality of SSS sequences the detected SSS signal corresponds to. The SSS detection unit 1016 then outputs the determined SSS signal to the DMRS detection unit 1017 as NID1 indicating the group of physical layer cell identifiers. The configuration of the SSS detection unit 1016 will be described in detail later.

[0047] The DMRS detector 1017 detects a DMRS signal included in the frequency domain waveform signal. More specifically, the DMRS detector 1017 detects a DMRS signal from the SSB frequency domain waveform signal. The DMRS detector 1017 determines which of multiple DMRS sequences the detected DMRS signal corresponds to. The DMRS detector 1017 then outputs ibar_SSB corresponding to the DMRS sequence to the switching timing estimation unit 1006. The configuration of the DMRS detector 1017 will be described in detail later.

[0048] The switching timing estimation unit 1006 estimates the timing of switching between uplink and downlink communications 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 within the transmission cycle at which the SSB is arranged from the input ibar_SSB. The switching timing estimation unit 1006 estimates the DL / UL switching timing within the transmission cycle from the arrangement position of the SSB to be estimated and known DL / UL configuration information in the TDD system.

[0049] 8 is a diagram illustrating an example of the 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.

[0050] The time signal extraction unit 1131 extracts a portion of the time domain waveform signal. More specifically, the time signal extraction unit 1131 extracts data having a length of the 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 portion of the baseband time domain waveform signal to the first correlation calculation unit 1133.

[0051] The PSS generation unit 1132 outputs a plurality of PSS code sequences of the PSS signal and code sequence numbers that identify the PSS code sequences. More specifically, the PSS generation unit 1132 outputs the plurality of PSS code sequences as PSS sequences to the first correlation calculation unit 1133. The PSS generation unit 1132 also outputs a PSS index, which is a code sequence number that identifies the PSS code sequence, to the NID2 detection unit 1134.

[0052] The first correlation calculation unit 1133 performs a correlation calculation between the time domain 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 a correlation calculation between the baseband time domain 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.

[0053] The NID2 detection unit 1134 outputs the timing within a predetermined time range at which the correlation value calculated by the first correlation calculation unit 1133 is highest 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 NID2, which is the cell identifier of the physical layer. More specifically, the NID2 detection unit 1134 outputs the timing within a predetermined time range at which the input correlation value is highest as the SSB timing. Furthermore, the NID2 detection unit 1134 outputs the PSS index corresponding to the PSS sequence with the highest correlation value as NID2, which is the cell identifier of the physical layer.

[0054] 9 is a diagram showing an example of the functional configuration of the phase error detection unit 41 according to the first embodiment. The phase error detection unit 41 includes a PSS code sequence selection unit 410, a data holding unit 411, a second correlation calculation unit 412, and a phase error detection unit 413.

[0055] The PSS code sequence selection section 410 selects one of a plurality of PSS code sequences based on the input physical layer cell identifier NID 2 and outputs it to the second correlation calculation section 412 .

[0056] The data holding section 411 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 412 .

[0057] The second correlation calculation unit 412 calculates a correlation value between the input baseband time domain signal and the input PSS code sequence, and outputs the result to the phase error detection unit 413 .

[0058] The phase error detector 413 calculates a common phase error of the baseband time domain signal from the input correlation value, and outputs it as the phase error of the baseband time domain signal.

[0059] 10 is a diagram showing an example of complex data of the correlation value calculated by the second correlation calculation unit 412 of the phase error detection unit 41, expressed on a complex plane. When there is no common phase error, there is no phase difference between the corresponding data between the PSS code sequence and the baseband time domain signal, so the complex data of the correlation value is placed on a line with a deflection angle of 0 degrees, i.e., on the I axis. On the other hand, when there is a common phase error, the baseband time domain signal is phase-rotated by the amount of the common phase error relative to the PSS code sequence, so the complex data of the correlation value is placed on a line indicating a deflection angle corresponding to the magnitude of the common phase error. The phase error detection unit 413 of the phase error detection unit 41 calculates the common phase error of the baseband time domain signal from the slope of this line.

[0060] 11 is a diagram showing an example of the functional configuration of the phase correction unit 42 according to the first embodiment. The phase correction unit 42 includes a complex signal generation unit 420 and a phase conversion unit 421.

[0061] The complex signal generator 420 generates a complex signal having a specified argument and absolute value based on the input phase error, and outputs it to the phase converter 421 .

[0062] The phase converter 421 performs complex multiplication of the input complex signal and the baseband frequency axis signal to convert the phase of the baseband frequency axis signal, and outputs the converted signal to the frequency waveform calculator 1005 .

[0063] 12 is a diagram illustrating 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.

[0064] SSS extraction unit 1161 extracts frequency components in which the SSS signal is allocated from the frequency axis waveform signal. More specifically, SSS extraction unit 1161 extracts frequency components in which the SSS signal is allocated from the SSB symbol that is the input frequency axis waveform signal, and outputs the extracted frequency components to data determination unit 1163. That is, SSS extraction unit 1161 outputs the frequency components of the SSS signal.

[0065] The SSS generation unit 1162 outputs a plurality of SSS sequences corresponding to NID2, which is a physical layer cell identifier output from the PSS detection unit 1013, and an SSS index that identifies the SSS sequences. More specifically, the SSS generation unit 1162 generates a plurality of SSS code series based on the input NID2, and outputs these as SSS sequences to the comparison operation unit 1164. The SSS generation unit 1162 also outputs the SSS index that identifies the SSS sequence to the NID1 detection unit 1165.

[0066] The data determination unit 1163 determines the demodulated data corresponding to the IQ complex coordinate position of the SSS signal output from the SSS extraction unit 1161, and outputs a series of data determined for the entire SSS signal to the comparison operation unit 1164 as an SSS sequence.

[0067] 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 the comparison result to the NID1 detection unit 1165. Note that the comparison operation unit 1164 may also output a degree of similarity 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 to the NID1 detection unit 1165.

[0068] The NID1 detection unit 1165 determines the SSS sequence 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 NID1 indicating a group of cell identifiers in the physical layer.

[0069] 13 is a diagram illustrating 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.

[0070] The DMRS extraction unit 1171 extracts frequency components in which the DMRS signal is allocated from the frequency axis waveform signal. More specifically, the DMRS extraction unit 1171 extracts frequency components in which the DMRS signal is allocated from the SSB symbol that is the input frequency axis waveform signal, and outputs the extracted frequency components to the data determination unit 1173. That is, the DMRS extraction unit 1171 outputs the frequency components of the DMRS signal.

[0071] The DMRS generation unit 1172 outputs a plurality of DMRS sequences corresponding to NID1 indicating a group of physical layer cell identifiers, 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 operation unit 1174. The DMRS generation unit 1172 also outputs a DMRS index that identifies the DMRS sequence to the ibar_SSB detection unit 1175.

[0072] The data determination unit 1173 determines the demodulated data corresponding to the IQ complex coordinate position of the DMRS signal output from the DMRS extraction unit 1171, and outputs a series of data determined for the entire DMRS signal to the comparison operation unit 1174 as a DMRS sequence.

[0073] The comparison operation unit 1174 compares the DMRS sequence from the data determination unit 1173 with the DMRS sequence from the DMRS generation unit 1172, and outputs the number of matches as the comparison result to the ibar_SSB detection unit 1175.

[0074] The ibar_SSB detection unit 1175 determines the DMRS sequence with the highest number of matches from the comparison results output by the comparison operation unit 1174. Then, the ibar_SSB detection unit 1175 outputs the ibar_SSB index corresponding to the DMRS sequence with the highest number of matches as ibar_SSB.

[0075] 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 frequency waveform phase correction process, will be described.

[0076] FIG. 14 is a flowchart illustrating an example of the TDD detection process according to the first embodiment.

[0077] Here, it is assumed that the distributed antenna system 1 is receiving either a DL signal or an UL analog radio signal, and that the distributed antenna system 1 is capable of referencing identification information indicating whether the TDD detection processing period is enabled or disabled and TDD DL / UL configuration information.

[0078] 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 the received signal (step S1).

[0079] Next, the time waveform calculation unit 1002 executes time waveform processing (step S2). That is, the time waveform calculation unit 1002 detects the PSS signal placed at the beginning of the SSB from the baseband signal, and outputs the detected timing as SSB timing to the FFT unit 1004 and the phase error detection unit 41 of the frequency waveform phase correction unit 40. The time waveform calculation unit 1002 also determines which of multiple PSS code sequences the detected PSS signal corresponds to, and notifies the phase error detection unit 41 of the frequency waveform phase correction unit 40, the FFT unit 1004, and the SSS detection unit 1016 of the frequency waveform calculation unit 1005 of this as NID2, which is a cell identifier of the physical layer.

[0080] Next, the FFT unit 1004 extracts the SSB from the baseband signal based on the notified SSB timing, performs a Fourier transform on it, and notifies the frequency waveform phase correction unit 40 of the completion of the FFT process (step S3).

[0081] Next, the frequency waveform phase correction unit 40 receives the baseband time axis waveform signal from the sampling rate conversion unit 1012 of the signal receiving unit 1001, the frequency axis waveform signal from the FFT unit 1004, and the SSB timing and physical layer cell identifier NID2 from the PSS detection unit 1013 of the time waveform calculation unit 1002, and performs phase correction processing on the frequency axis waveform signal (step S4).

[0082] Specifically, in frequency waveform phase correction unit 40, phase error detection unit 41 extracts a signal from the baseband time domain waveform signal input from sampling rate conversion unit 1012 based on the SSB timing notified by PSS detection unit 1013, and detects a phase error using a PSS code sequence based on the physical layer cell identifier NID2 input from PSS detection unit 1013. Phase correction unit 42 converts the phase based on the phase error detected by phase error detection unit 41, and notifies frequency waveform calculation unit 1005 of the completion of frequency waveform phase correction.

[0083] Next, the frequency waveform calculation unit 1005 detects the index number of the SSB, which indicates where the SSB is located within the transmission period (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, the frequency waveform phase correction unit 40, and the frequency waveform calculation unit 1005 repeatedly execute steps S1 to S5.

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

[0086] 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.

[0087] The time signal extraction unit 1131 determines whether the TDD detection processing period is valid (step S21). 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 correlation values ​​by performing correlation calculations 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 largest since the start of time waveform processing. If a significant correlation value does not exist (step S23; No), the NID2 detection unit 1134 returns to step S21. On the other hand, if a significant correlation value exists (step S23; Yes), the NID2 detection unit 1134 performs the subsequent processing.

[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 the PSS correlation detection time (step S25).

[0092] The NID2 detection unit 1134 notifies the FFT processing (step S3) shown in step S3 of the system time at which a significant correlation value was calculated as the SSB timing (step S26).

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

[0094] The FFT unit 1004 determines whether or not the SSB timing has been notified (step S31). If the SSB timing has not been notified (step S31; No), the FFT unit 1004 ends the FFT process. On the other hand, if the SSB timing has been notified (step S31; Yes), the FFT unit 1004 performs the subsequent process.

[0095] Based on the notified SSB timing, the FFT unit 1004 extracts the SSB from the frequency-converted (corrected) baseband signal received from the sampling rate conversion unit 1012 of the signal receiving unit 1001 (step S32).

[0096] The FFT unit 1004 performs a Fourier transform on the extracted SSB time-axis waveform signal to convert it into a frequency-axis waveform signal (step S33).

[0097] The FFT unit 1004 notifies the frequency waveform phase correction process shown in step S4 of the completion of the FFT process (step S34).

[0098] Fig. 17 is a flowchart showing an example of the frequency waveform phase correction process according to the first embodiment. That is, the flowchart shown in Fig. 17 is the frequency waveform phase correction process of step S4 shown in Fig. 14.

[0099] The frequency waveform phase correction unit 40 determines whether or not the SSB timing has been notified (step S40). If there has been no notification (step S41; No), the phase error detection unit 41 ends the frequency waveform phase correction. On the other hand, if there has been notification (step S41; Yes), the frequency waveform phase correction unit 40 executes the subsequent processing.

[0100] The frequency waveform phase correction unit 40 reads out the NID2 stored in step S24 (step S42).

[0101] Next, the frequency waveform phase correction unit 40 executes a phase error detection process (step S43).

[0102] Next, the frequency waveform phase correction unit 40 executes a phase correction process (step S44).

[0103] Next, the frequency waveform phase correction unit 40 notifies the frequency waveform processing unit of the end of the frequency waveform phase correction processing (step S45).

[0104] 18 is a flowchart showing an example of the phase error detection process according to the first embodiment. That is, the flowchart shown in Fig. 18 is the phase error detection process of step S43 shown in Fig. 17.

[0105] The data holding unit 411 of the phase error detection unit 41 holds the baseband time domain signal based on the notified SSB timing (step S431).

[0106] Subsequently, the PSS code sequence selection unit 410 of the phase error detection unit 41 reads out the NID2 stored in step S24 (step S432).

[0107] Next, the PSS code sequence selection unit 410 of the phase error detection unit 41 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 S433). The PSS code sequence selection unit 410 outputs the selected PSS code sequence to the second correlation calculation unit 412.

[0108] Next, the second correlation calculation unit 412 of the phase error detection unit 41 calculates a correlation value between the time axis signal held by the data holding unit 411 and the PSS code sequence selected by the PSS code sequence selection unit 410 (step S434). The second correlation calculation unit 412 outputs the calculated correlation value to the phase error detection unit 413.

[0109] Next, the phase error detector 413 of the phase error detector 41 calculates the amount of phase rotation of the time domain signal from the correlation value calculated by the second correlation calculator 412, and adopts the calculated amount of phase rotation as the phase error of the time domain signal (step S435). The phase error detector 413 outputs the adopted phase error to the phase corrector 42.

[0110] 19 is a flowchart showing an example of the phase correction process according to the first embodiment. That is, the flowchart shown in Fig. 19 is the phase correction process of step S44 shown in Fig. 17.

[0111] The complex signal generation unit 420 of the phase correction unit 42 generates a complex signal having a specified argument and absolute value based on the phase error calculated by the phase error detection unit 413 of the phase error detection unit 41 (step S441). The complex signal generation unit 420 outputs the generated complex signal to the phase conversion unit 421.

[0112] The phase conversion unit 421 of the phase correction unit 42 converts the phase of the frequency axis signal by complex multiplying the frequency axis signal received from the FFT unit by the complex signal received from the complex signal generation unit 420 (step S442).

[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 determines whether or not it has received a notification of the completion of FFT processing (step S51). If it has not received a notification (step S51; No), the frequency waveform calculation unit 1005 ends the frequency waveform processing. On the other hand, if it has received a notification (step S51; Yes), the frequency waveform calculation unit 1005 executes the subsequent processing.

[0115] Next, the SSS detection unit 1016 executes the SSS detection process (step S52).

[0116] Next, the frequency waveform calculation unit 1005 determines whether a significant SSS has been detected (step S53). A significant SSS is determined here when the similarity to the SSS sequence calculated in the SSS detection process exceeds a predetermined threshold and is at its maximum. If no significant SSS exists (step S53; No), the frequency waveform calculation unit 1005 ends the frequency waveform processing. On the other hand, if a significant SSS exists (step S53; Yes), the frequency waveform calculation unit 1005 performs subsequent processing.

[0117] Next, the DMRS detector 1017 executes a DMRS detection process (step S54).

[0118] Next, the frequency waveform calculation unit 1005 determines whether a significant DMRS has been detected (step S55). Here, a significant DMRS is determined when the similarity to the DMRS sequence calculated in the DMRS detection process exceeds a predetermined threshold and is maximized. If a significant DMRS does not exist (step S55; No), the frequency waveform calculation unit 1005 ends the frequency waveform process. On the other hand, if a significant DMRS exists (step S55; Yes), the frequency waveform calculation unit 1005 performs subsequent processing.

[0119] Next, the frequency waveform calculation unit 1005 notifies the switching timing estimation process shown in step S7 of the completion of the frequency waveform processing (step S56).

[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 of step S52 shown in Fig. 20.

[0121] The SSS extraction unit 1161 extracts frequency components in which the SSS signals are allocated from the frequency axis waveform signal (step S521).

[0122] Next, the SSS generation unit 1162 reads out the NID2 stored in step S24 (step S522).

[0123] Next, the SSS generation unit 1162 generates a plurality of SSS sequences and SSS indices for identifying the SSS sequences based on NID2 (step S523).

[0124] Next, the comparison operation unit 1164 detects the SSS sequence that is most similar to the extracted SSS signal (step S524).

[0125] Next, the NID1 detection unit 1165 stores the SSS index corresponding to the most similar SSS sequence as NID1 (step S525).

[0126] Fig. 22 is a flowchart illustrating an example of the DMRS detection process according to the first embodiment. That is, the flowchart illustrated in Fig. 22 is the DMRS detection process of step S54 illustrated in Fig. 20 .

[0127] The DMRS extraction unit 1171 extracts the frequency component to which the DMRS signal is assigned from the frequency axis waveform signal (step S541).

[0128] Next, the DMRS generator 1172 reads out the NID1 stored in step S525 (step S542).

[0129] Next, the DMRS generating unit 1172 generates a plurality of DMRS sequences and an ibar_SSB index for identifying the DMRS sequences based on NID1 (step S543).

[0130] Next, the comparison operation unit 1174 detects the DMRS sequence that is most similar to the extracted DMRS signal (step S544).

[0131] Next, the ibar_SSB detector 1175 stores the ibar_SSB index corresponding to the DMRS sequence with the highest similarity as ibar_SSB (step S545).

[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. 14.

[0133] The switching timing estimation unit 1006 determines whether or not it has received a notification of the completion of frequency waveform processing (step S71). If it has not received a notification (step S71; No), the switching timing estimation unit 1006 ends the switching timing estimation process. On the other hand, if it has received a notification (step S71; 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 S25 (step S72).

[0135] Next, the switching timing estimation unit 1006 reads out the ibar_SSB stored in step S545 (step S73).

[0136] Next, the switching timing estimation unit 1006 estimates the position of the frame in which the currently detected SSB is located, based on the known SSB placement pattern and the ibar_SSB read out in step S72 (step S74).

[0137] Next, the switching timing estimation unit 1006 estimates the timing at which the next TDD switching will occur from the known TDD DL / UL configuration information, the PSS correlation detection time read in step S72, and the SSB frame position estimated in step S74 (step S75).

[0138] As described above, the switching timing generation unit 153 according to the first embodiment includes a signal receiving unit 1001, a time waveform calculation unit 1002, an FFT unit 1004, a frequency waveform phase correction unit 40, a frequency waveform calculation unit 1005, and a switching timing estimation unit 1006.

[0139] 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 portion of the time domain waveform signal that is the output of the signal receiving unit, and calculates the degree of similarity between the extracted signal and a known signal.

[0140] The FFT unit 1004 performs a Fourier transform on the time axis waveform signal from the signal receiving unit 1001. The frequency axis waveform phase correcting unit 40 corrects the phase of the frequency axis waveform signal that is the output of the FFT unit 1004.

[0141] The frequency waveform calculation unit 1005 extracts a portion of the frequency axis waveform signal that is the output of the frequency waveform phase correction unit 40, and calculates the degree of similarity between the extracted signal and a known signal. The switching timing estimation unit 1006 estimates the timing of switching between uplink and downlink communication in the own device based on the result of the frequency waveform calculation unit 1005.

[0142] According to the switching timing generator 153 of the first embodiment, the common phase error can be reduced by calculating a common phase error from the phase difference between a portion of a signal extracted from a time-domain waveform signal and a known signal, and correcting the phase of the frequency-domain waveform signal. Therefore, the common phase error can be reduced using a simple method that does not require a mechanism for controlling the frequency and phase of a local oscillator clock or a baseband system clock, or waveform equalization processing that estimates transmission path characteristics and corrects the waveform after FFT. As a result, even when a common phase error exists in the TDD system, the DL / UL switching timing can be estimated inexpensively and accurately.

[0143] Comparative Example 1 The effect of the switching timing generation unit 153 according to the first embodiment will be described in more detail with reference to a switching timing generation unit 153a according to a comparative example 1.

[0144] Fig. 24 is a diagram showing an example of the functional configuration of a switching timing generation unit 153a according to Comparative Example 1. As shown in Fig. 24, the switching timing generation unit 153a includes a signal receiving unit 1001, a time waveform calculation unit 1002, an FFT unit 1004, a frequency waveform calculation unit 1003, and a switching timing estimation unit 1006. That is, when Fig. 24 is compared with Fig. 7, the switching timing generation unit 153a according to Comparative Example 1 shown in Fig. 24 does not include the frequency waveform phase correction unit 40 shown in Fig. 7.

[0145] FIG. 25 is a diagram for explaining the constellation when there is a difference in the common phase error, using quadrature phase shift keying (QPSK) data as an example, when using the switching timing generation unit 153a according to comparative example 1.

[0146] Figure 25(a) shows an example of a constellation when there is no common phase error. As shown in Figure 25(a), when there is no common phase error, the data in the constellation converges to a single point in each of the four quadrants.

[0147] Figure 25(b) shows a case where the common phase error is 30 degrees. As shown in Figure 25(b), when the common phase error is 30 degrees, the constellation undergoes a 30-degree phase rotation in the counterclockwise direction. In the case of quadrature phase-shift keying, a 30-degree phase rotation does not result in data movement beyond the quadrant of the complex plane, and no data discrimination error occurs. However, in the case of phase-shift keying or quadrature amplitude modulation (QAM), which have a higher modulation index, data movement beyond the quadrant of the complex plane occurs, and this is discriminated as an erroneous value by the frequency waveform calculation unit 1003 located downstream of the FFT unit 1004.

[0148] 25(c) shows a case where the common phase error is 60 degrees. As shown in FIG. 25(c), when the common phase error is 60 degrees, the constellation undergoes a phase rotation of 60 degrees in the counterclockwise direction. With a phase rotation of 60 degrees, even in the case of quadrature phase shift keying, data moves beyond the quadrants of the complex plane, and is determined to be an erroneous value by the frequency waveform calculation unit 1003 located downstream of the FFT unit 1004.

[0149] As described above, when data modulated by phase shift keying (PSK) or quadrature amplitude modulation is judged in the presence of a phase error, the reception characteristics are significantly degraded. Therefore, data judgment is generally performed after correcting the phase error. In order to correct the phase error, a mechanism for controlling the frequency and phase of the local oscillator clock or the baseband system clock, or waveform equalization processing that estimates the transmission path characteristics and corrects the waveform after FFT, can be considered.

[0150] However, these processes are complex and expensive to implement, and in particular, controlling the clock frequency and phase requires collecting error information from many functional blocks located downstream of the AD converter and carefully changing the clock, which makes implementing the mechanism expensive.

[0151] Furthermore, due to the time restrictions imposed by the time division multiplexing system for switching between transmission and reception, there is a time restriction on the time from signal reception to completion of demodulation of the synchronization signal block, which also applies to the control of the clock frequency and phase and the waveform equalization process.

[0152] As a result, in order to correct the phase error, the processing circuits for demodulating the synchronization signal block, clock control, and waveform equalization must operate at high speed, which increases the cost of implementing the device.

[0153] In contrast, the switching timing generation unit 153 according to this embodiment can estimate the DL / UL switching timing inexpensively and accurately, even when a common phase error exists, without requiring the above-mentioned costs.

[0154] Second Embodiment Next, a description will be given of a switching timing generation unit 153 according to a second embodiment. The switching timing generation unit 153 according to the second embodiment executes a process of correcting a common phase error due to phase noise when executing a sampling phase conversion process for correcting a sampling phase that deviates from the original phase.

[0155] Fig. 26 is a diagram showing an example of the functional configuration of the switching timing generation unit 153 according to the second embodiment. When Fig. 26 is compared with Fig. 7 , the difference is that the switching timing generation unit 153 according to the second embodiment shown in Fig. 26 further includes a sampling phase conversion unit 30.

[0156] The sampling rate conversion unit 1012 of the signal receiving unit 1001 outputs the baseband time domain waveform signal to the PSS detection unit 1013 and the sampling phase conversion unit 30 .

[0157] The sampling phase converter 30 executes sampling phase conversion processing to convert 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.

[0158] The phase detector 31 detects the optimum phase at which the sampling phase of the time domain waveform signal is most favorable, based on the SSB timing and physical layer cell identifier NID2 output from the PSS detector 1013. That is, the phase detector 31 extracts a signal from the input baseband signal after sampling rate conversion, based on the input SSB timing, and detects the optimum phase from among a plurality of predetermined sampling phases, based on the input physical layer cell identifier NID2, and outputs the optimum phase to the phase converter 32.

[0159] 27 is a diagram showing an example of the functional configuration of the phase detection unit 31 in the second embodiment. Specifically, the phase detection unit 31 includes a PSS code sequence selection unit 310, a data holding unit 311, a phase conversion unit 312, a third correlation calculation unit 313, and a phase determination unit 314.

[0160] The PSS code sequence selection section 310 selects one of a plurality of PSS code sequences based on the input physical layer cell identifier NID 2 and outputs it to the third correlation calculation section 313 .

[0161] The data holding unit 311 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 312 .

[0162] The phase converter 312 converts the input baseband time domain signal into a plurality of predetermined sampling phases and outputs the phases to the third correlation calculator 313 .

[0163] 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 result to the phase determination unit 314 .

[0164] 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 optimum phase.

[0165] The phase converter 32 converts the sampling phase of the baseband time domain waveform signal received from the sampling rate converter 1012 based on the optimal phase that is output from the phase detector 31. That is, the phase converter 32 converts the sampling phase of the input baseband signal after sampling rate conversion to the optimal phase based on the input optimal phase, and outputs the converted phase to the FFT unit 1004.

[0166] 28 is a diagram showing an example of the functional configuration of the phase conversion unit 32 in the second embodiment. The phase conversion unit 32 includes a filter coefficient selection unit 320 and a filter calculation unit 321.

[0167] The filter coefficient selection unit 320 selects one of a plurality of filter coefficients based on the input optimum phase and outputs the selected one 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. 28 are merely an example, and the number of filter coefficients to be selected can be set arbitrarily.

[0168] 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.

[0169] 26 , based on the input SSB timing, the FFT unit 1004 extracts the SSB from the baseband time domain waveform signal after sampling phase conversion received from the phase conversion unit 32 and performs a Fourier transform on it. The FFT unit 1004 then outputs the SSB frequency domain waveform signal obtained by the Fourier transform to the phase correction unit 42 of the frequency waveform phase correction unit 40.

[0170] The frequency waveform phase correction unit 40 receives a baseband time axis waveform signal from the sampling rate conversion unit 1012 of the signal receiving unit 1001, a frequency axis waveform signal from the FFT unit 1004, and an SSB timing and physical layer cell identifier NID2 from the PSS detection unit 1013 of the time waveform calculation unit 1002, and performs phase correction processing on the frequency axis waveform signal.

[0171] Fig. 29 is a flowchart showing an example of TDD detection processing according to the second embodiment. Comparing Fig. 29 with Fig. 14, a difference is that sampling phase conversion processing (step S2a) is inserted before the FFT processing in step S3.

[0172] 30 is a flowchart showing an example of the sampling phase conversion process according to the second embodiment. That is, the flowchart shown in Fig. 30 is the sampling phase conversion process of step S2a shown in Fig. 29.

[0173] The phase detection unit 31 of the sampling phase conversion unit 30 determines whether or not the SSB timing has been notified from the time waveform calculation unit 1002 (step S21a). If the phase detection unit 31 has not received the notification, it exits from the sampling phase conversion process (No in step S21a), but if it has received the notification, it executes the process of the subsequent step S22a (Yes in step S21a).

[0174] Next, the phase detection unit 31 reads out the NID2 stored in step S24 (step S22a).

[0175] Next, the phase detection unit 31 executes a phase detection process (step S23a).

[0176] Next, the phase conversion unit 32 executes a phase conversion process (step S24a).

[0177] Next, the phase conversion unit 32 notifies the FFT unit 1004 of the SSB timing (step S25a).

[0178] The effect of the switching timing generator 153 according to the second embodiment will be described in more detail with reference to a switching timing generator 153b according to a second comparative example.

[0179] Fig. 31 is a diagram showing an example of the functional configuration of a switching timing generation unit 153b according to comparative example 2. When Fig. 31 is compared with Fig. 26 , the switching timing generation unit 153b according to comparative example 2 in Fig. 31 does not include the frequency waveform phase correction unit 40 shown in Fig. 26 .

[0180] FIG. 32 is a diagram illustrating a constellation when there is a difference in the common phase error and a difference in the sampling phase of the baseband time axis waveform signal, using data that has been subjected to quadrature phase shift keying as an example, when the switching timing generation unit 153b according to Comparative Example 2 is used.

[0181] The top part of Figure 32 shows an example of a constellation when there is only a common phase error and no deviation from the sampling phase at the time of transmission (corresponding to Figure 25). As shown in the top part of Figure 32, although phase rotation due to the common phase error can be seen, there is no effect related to deviation from the sampling phase.

[0182] The middle part of FIG. 32 shows an example of a constellation when the sampling phase deviates by 25% from that shown in the upper part.

[0183] The lower part of FIG. 32 shows an example of a constellation when the sampling phase deviates by 50% from that shown in the upper part.

[0184] As can be seen by comparing (a), (d), and (g) in the left column of Figure 32, 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. Focusing on the rotation in the phase direction in the center and right columns also shows the same tendency as in the left column.

[0185] When the signals in the middle and bottom rows of Figure 32 are provided to the switching timing generation unit 153b according to Comparative Example 2, the sampling phase conversion unit 30 suppresses phase rotation due to deviation in the sampling phase, correcting (d) and (g) in Figure 32 to a state close to (a), (e) and (h) to (b), and (f) and (j) to a state close to (c). However, the switching timing generation unit 153b according to Comparative Example 2 does not include the frequency waveform phase correction unit 40. Therefore, the phase rotation due to the phase error cannot be suppressed, and the phase rotation remains as it is, as shown in (b) and (c).

[0186] In contrast, the switching timing generator 153 according to the second embodiment, when performing sampling phase conversion processing to correct a sampling phase that deviates from the original phase, calculates a common phase error from the phase difference between a portion of a signal extracted from a time-domain waveform signal and a known signal, and corrects the phase of the frequency-domain waveform signal, thereby reducing the phase error. Therefore, the common phase error can be reduced using a simple method that does not require a mechanism for controlling the frequency and phase of a local oscillator clock or a baseband system clock, or waveform equalization processing that estimates transmission path characteristics and corrects the waveform after FFT. As a result, even when a common phase error exists in the TDD system, the DL / UL switching timing can be estimated inexpensively and accurately.

[0187] Third Embodiment Next, a description will be given of a switching timing generator 153 according to a third embodiment. The switching timing generator 153 according to the third embodiment executes a process of correcting a common phase error due to phase noise when a process of correcting a carrier frequency is executed to remove inter-carrier interference due to a carrier frequency error.

[0188] Fig. 33 is a diagram showing an example of the functional configuration of the switching timing generation unit 153 according to the third embodiment. When Fig. 33 is compared with Fig. 7 , the difference is that the switching timing generation unit 153 according to the third embodiment shown in Fig. 33 further includes a carrier frequency correction unit 20.

[0189] The sampling rate conversion unit 1012 of the signal receiving unit 1001 outputs the baseband time axis waveform signal to the PSS detection unit 1013 and the carrier frequency correction unit 20 .

[0190] 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 and the physical layer cell identifier NID2 from the PSS detection unit 1013, and performs carrier frequency correction processing. Specifically, the carrier frequency correction unit 20 includes a frequency error detection unit 21 and a frequency error correction unit 22.

[0191] 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 detected 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.

[0192] 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 baseband signal after sampling rate conversion, and outputs the result to the FFT unit 1004. The configuration of the frequency error correction unit 22 will be described in detail later.

[0193] 34 is a diagram showing an example of the functional configuration of the frequency error detection unit 21 according to the third embodiment. The frequency error detection unit 21 includes a PSS code sequence selection unit 210, a data holding unit 211, a fourth correlation calculation unit 212, and an error detection unit 213.

[0194] The PSS code sequence selection section 210 selects one of a plurality of PSS code sequences based on the input physical layer cell identifier NID 2 and outputs it to the fourth correlation calculation section 212 .

[0195] The data holding section 211 extracts and holds a signal from the input baseband time domain signal based on the input SSB timing, and outputs the signal to the fourth correlation calculation section 212 .

[0196] The fourth correlation calculation unit 212 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 213 .

[0197] The error detection section 213 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.

[0198] 35 is a diagram showing an example of the functional configuration of the frequency error correction unit 22 according to the third embodiment. The frequency error correction unit 22 includes a sine wave generation unit 220 and a frequency conversion unit 221.

[0199] The sine wave generating unit 220 generates a complex sine wave of a specified frequency based on the input frequency error, and outputs it to the frequency converting unit 221 .

[0200] The frequency conversion unit 221 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 .

[0201] 33 , based on the input SSB timing, FFT section 1004 extracts the SSB from the carrier frequency corrected baseband time domain waveform signal received from carrier frequency correction section 20 and performs a Fourier transform on it. Then, FFT section 1004 outputs the SSB frequency domain waveform signal obtained by the Fourier transform to phase correction section 42 of frequency waveform phase correction section 40.

[0202] The frequency waveform phase correction unit 40 receives a baseband time axis waveform signal from the sampling rate conversion unit 1012 of the signal receiving unit 1001, a frequency axis waveform signal from the FFT unit 1004, and an SSB timing and physical layer cell identifier NID2 from the PSS detection unit 1013 of the time waveform calculation unit 1002, and performs phase correction processing on the frequency axis waveform signal.

[0203] Fig. 36 is a flowchart showing an example of TDD detection processing according to the third embodiment. Comparing Fig. 36 with Fig. 14, a difference is that a carrier frequency correction processing (step S2b) is inserted before the FFT processing in step S3.

[0204] Fig. 37 is a flowchart showing an example of the carrier frequency correction process according to the third embodiment. That is, the flowchart shown in Fig. 37 is the carrier frequency correction process of step S2b shown in Fig. 36.

[0205] 37, the frequency error detection unit 21 of the carrier frequency correction unit 20 determines whether or not the SSB timing has been notified from the time waveform calculation unit 1002 (step S21b). If no notification has been received, the carrier frequency correction unit 20 exits the carrier frequency correction process (No in step S21b), and if notification has been received, the carrier frequency correction unit 20 executes the process of the subsequent step S22b (Yes in step S21b).

[0206] Next, the frequency error detection unit 21 reads out the NID2 stored in step S24 (step S22b).

[0207] Next, the frequency error detection unit 21 executes a frequency error detection process (step S23b).

[0208] Next, the frequency error correction unit 22 executes the frequency error correction process (step S24b).

[0209] Next, the frequency error correction unit 22 notifies the FFT processing of the SSB timing (step S25b).

[0210] The effect of the switching timing generation unit 153 according to the third embodiment will be described in more detail with reference to a switching timing generation unit 153c according to a third comparative example.

[0211] Fig. 38 is a diagram showing an example of the functional configuration of a switching timing generation unit 153c according to Comparative Example 3. When Fig. 38 is compared with Fig. 33 , the switching timing generation unit 153c according to Comparative Example 3 in Fig. 38 does not include the frequency waveform phase correction unit 40 shown in Fig. 33 .

[0212] FIG. 39 is a diagram illustrating a constellation when there is a difference in the common phase error and a difference in the carrier frequency error of the baseband time domain waveform signal, using data that has been quadrature phase-shift keyed as an example, when using the switching timing generation unit 153c according to Comparative Example 3.

[0213] The upper part of FIG. 39 shows an example of a constellation when there is only a common phase error and no carrier frequency error (corresponding to FIG. 25).

[0214] As shown in the upper part of FIG. 39, although phase rotation due to a common phase error is observed, when there is no carrier frequency error, the constellation data converges to a single point.

[0215] The middle part of FIG. 39 shows an example of a constellation when the carrier frequency error is 10% of the subcarrier spacing compared to the upper part.

[0216] The lower part of FIG. 39 shows an example of a constellation when the carrier frequency error is 20% of the subcarrier spacing compared to the upper part.

[0217] As can be seen by comparing the left columns (a), (d), and (g) of Figure 39, the presence of a carrier frequency error causes a phase rotation in the constellation, and data that had converged at a single point spreads. This data spread is caused by demodulation with the OFDM center frequency shifted by the amount of the carrier frequency error. Demodulation with a shifted center frequency destroys the orthogonality between OFDM subcarriers, causing inter-carrier interference and resulting in data spread. Furthermore, as the degree of carrier frequency error increases, the data spread becomes even greater. Focusing on the degree of data spread in the center and right columns also shows the same trend as in the left column.

[0218] When the signals in the middle and bottom rows of Figure 39 are provided to the switching timing generator 153c according to Comparative Example 3, the carrier frequency correction unit 20 removes inter-carrier interference, correcting (d) and (g) in Figure 39 to a state close to (a), (e) and (h) to (b), and (f) and (j) to a state close to (c). However, the switching timing generator 153c according to Comparative Example 3 does not include a frequency waveform phase correction unit 40. Therefore, the phase rotation caused by the phase error cannot be suppressed, and the phase rotation remains as it is, as shown in (b) and (c).

[0219] In contrast, when the switching timing generation unit 153 according to the third embodiment performs a carrier frequency correction process to remove inter-carrier interference due to a carrier frequency error, it calculates a common phase error from the phase difference between a part of a signal extracted from the time-domain waveform signal and a known signal, and corrects the phase of the frequency-domain waveform signal, thereby reducing the phase error.

[0220] Therefore, it is possible to reduce the common phase error using a simple method that does not require a mechanism for controlling the frequency and phase of the local oscillator clock or the baseband system clock, or waveform equalization processing that estimates transmission path characteristics and corrects the waveform after FFT.As a result, even if a common phase error exists in the TDD system, it is possible to estimate the DL / UL switching timing inexpensively and accurately.

[0221] Next, a switching timing generation unit 153 according to a fourth embodiment will be described. The switching timing generation unit 153 according to the fourth embodiment performs sampling phase conversion processing to correct a phase deviated from the original sampling phase, and also performs correction processing of a common phase error due to phase noise when performing carrier frequency correction processing to remove inter-carrier interference due to carrier frequency error.

[0222] Fig. 40 is a diagram showing an example of the functional configuration of the switching timing generation unit 153 according to the fourth embodiment. When Fig. 40 is compared with Fig. 7 , the difference is that the switching timing generation unit 153 according to the fourth embodiment shown in Fig. 40 further includes a sampling phase conversion unit 30 and a carrier frequency correction unit 20.

[0223] The sampling rate conversion unit 1012 of the signal receiving unit 1001 outputs the baseband time domain waveform signal to the PSS detection unit 1013 and the sampling phase conversion unit 30 .

[0224] The sampling phase converter 30 executes sampling phase conversion processing to convert 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.

[0225] The phase detector 31 detects the optimum phase that provides the best sampling phase for the time domain waveform signal based on the SSB timing and physical layer cell identifier NID2 output from the PSS detector 1013. That is, the phase detector 31 extracts a signal from the input baseband signal after sampling rate conversion based on the input SSB timing, detects the optimum phase from among a plurality of predetermined sampling phases based on the input physical layer cell identifier NID2, and outputs the optimum phase to the phase converter 32. The functional configuration of the phase detector 31 is as already described using FIG. 27 .

[0226] The phase converter 32 converts the sampling phase of the baseband time domain waveform signal received from the sampling rate converter 1012 based on the optimal phase that is output from the phase detector 31. That is, the phase converter 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 optimal phase to the frequency error corrector 22 of the carrier frequency corrector 20. The functional configuration of the phase converter 32 is as already described using FIG. 28 .

[0227] The carrier frequency correction unit 20 receives the baseband time domain signal from the sampling phase conversion unit 30 and the SSB timing and physical layer cell identifier NID2 from the PSS detection unit 1013, and performs carrier frequency correction processing. Specifically, the carrier frequency correction unit 20 includes a frequency error detection unit 21 and a frequency error correction unit 22.

[0228] 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 detected carrier frequency error to the frequency error correction unit 22. The functional configuration of the frequency error detection unit 21 is as already described using FIG.

[0229] 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 the generated signal by a signal obtained by converting the sampling phase of the input baseband signal after sampling rate conversion to an optimal phase, and outputs the corrected carrier frequency to the FFT unit 1004. The functional configuration of the frequency error correction unit 22 is as already described using FIG.

[0230] 40 , based on the input SSB timing, FFT section 1004 extracts the SSB from the carrier frequency corrected baseband time domain waveform signal received from carrier frequency correction section 20 and performs a Fourier transform on it. Then, FFT section 1004 outputs the SSB frequency domain waveform signal obtained by the Fourier transform to phase correction section 42 of frequency waveform phase correction section 40.

[0231] The frequency waveform phase correction unit 40 receives a baseband time axis waveform signal from the sampling rate conversion unit 1012 of the signal receiving unit 1001, a frequency axis waveform signal from the FFT unit 1004, and an SSB timing and physical layer cell identifier NID2 from the PSS detection unit 1013 of the time waveform calculation unit 1002, and performs phase correction processing on the frequency axis waveform signal.

[0232] Fig. 41 is a flowchart showing an example of TDD detection processing according to the fourth embodiment. Comparing Fig. 41 with Fig. 14, a difference is that sampling phase conversion processing (step S2c) and carrier frequency correction processing (step S2b) are inserted before the FFT processing in step S3.

[0233] Fig. 42 is a flowchart showing an example of the sampling phase conversion process according to the fourth embodiment. That is, the flowchart shown in Fig. 42 is the sampling phase conversion process of step S2c shown in Fig. 41.

[0234] 42, the phase detection unit 31 of the sampling phase conversion unit 30 determines whether or not the SSB timing has been notified from the time waveform calculation unit 1002 (step S21c). If no notification has been received, the phase detection unit 31 exits the sampling phase conversion process (No in step S21c), and if notification has been received, the phase detection unit 31 proceeds to the subsequent process of step S22c (Yes in step S21c).

[0235] Next, the phase detection unit 31 reads out the NID2 stored in step S24 (step S22c).

[0236] Next, the phase detection unit 31 executes a phase detection process (step S23c).

[0237] Next, the phase conversion unit 32 executes a phase conversion process (step S24c).

[0238] Next, the phase shifter 32 notifies the carrier frequency correction unit 20 of the SSB timing (step S25c). The carrier frequency correction unit 20 executes carrier frequency correction processing based on the SSB timing notified from the phase shifter 32. This carrier frequency correction processing is similar to the content described in FIG. 37.

[0239] The effect of the switching timing generator 153 according to the fourth embodiment will be described in more detail with reference to a switching timing generator 153d according to a fourth comparative example.

[0240] Fig. 43 is a diagram showing an example of the functional configuration of a switching timing generation unit 153d according to comparative example 4. When Fig. 43 is compared with Fig. 40 , the switching timing generation unit 153d according to comparative example 4 in Fig. 43 does not include the frequency waveform phase correction unit 40 shown in Fig. 40 .

[0241] FIG. 44 is a diagram illustrating a constellation when using the switching timing generation unit 153d according to Comparative Example 4, taking quadrature phase-shift keyed data as an example, in which there is a difference in the common phase error, a difference in the sampling phase of the baseband time domain waveform signal, and a difference in the carrier frequency error of the baseband time domain waveform signal.

[0242] The upper part of Figure 44 shows an example of a constellation when there is only a common phase error, no deviation from the sampling phase at the time of transmission, and no carrier frequency error (corresponding to Figure 25). As shown in the upper part of Figure 44, although phase rotation due to the common phase error is observed, there is no influence from deviation of the sampling phase, and there is also no influence from carrier frequency error, and the constellation data converges to a single point.

[0243] The middle part of FIG. 44 shows an example of a constellation when the sampling phase deviation from the upper part is 25% and the carrier frequency error is 10% of the subcarrier spacing.

[0244] The lower part of FIG. 44 shows an example of a constellation when the sampling phase deviation is 50% compared to the upper part and the carrier frequency error is 20% of the subcarrier spacing.

[0245] As can be seen by comparing the left columns (a), (d), and (g) in Figure 44, the deviation in sampling phase causes the constellation to rotate in the phase direction, and the carrier frequency error causes further phase rotation in the constellation, and the data that had converged at one point is now scattered.

[0246] As the deviation of the sampling phase and the degree of carrier frequency error increase, the amount of phase rotation and data spread become even larger. Looking at the amount of phase rotation and data spread in the center and right columns, we see the same trends as in the left column.

[0247] When the signals in the middle and bottom rows of Figure 44 are provided to the switching timing generation unit 153d according to comparative example 4, the sampling phase conversion unit 30 suppresses phase rotation due to deviation in sampling phase, and the carrier frequency correction unit 20 removes inter-carrier interference, correcting (d) and (g) in Figure 44 to a state close to (a), (e) and (h) to (b), and (f) and (j) to a state close to (c). However, the switching timing generation unit 153d according to comparative example 4 does not include the frequency waveform phase correction unit 40. Therefore, the phase rotation due to phase error cannot be suppressed, and the phase rotation remains as it is, as shown in (b) and (c).

[0248] In contrast, the switching timing generation unit 153 according to the fourth embodiment performs a sampling phase conversion process to correct a phase that deviates from the original sampling phase, and also performs a carrier frequency correction process to remove inter-carrier interference due to carrier frequency error. In this case, the switching timing generation unit 153 calculates a common phase error from the phase difference between a part of a signal extracted from the time-domain waveform signal and a known signal, and corrects the phase of the frequency-domain waveform signal, thereby reducing the phase error.

[0249] Therefore, it is possible to reduce the common phase error using a simple method that does not require a mechanism for controlling the frequency and phase of the local oscillator clock or the baseband system clock, or waveform equalization processing that estimates transmission path characteristics and corrects the waveform after FFT.As a result, even if a common phase error exists in the TDD system, it is possible to estimate the DL / UL switching timing inexpensively and accurately.

[0250] 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).

[0251] The program may also be configured to be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network, or to be provided or distributed via a network such as the Internet, or to be provided by being pre-installed in a ROM or the like.

[0252] 1...Distributed antenna system, 10...Master station unit (MU), 11...Upstream input / output unit, 12...Substream input / output unit, 13...Downlink processing unit, 14...Uplink processing unit, 15...Control unit, 20...Carrier frequency correction unit, 21...Frequency error detection unit, 22...Frequency error correction unit, 30...Sampling phase conversion unit, 31...Phase detection unit, 32...Phase conversion unit, 40...Frequency waveform phase correction unit, 41...Phase error detection unit, 42...Phase correction unit, 45...Relay unit (HU), 47...Slave station unit (RU), 50...Base station, 60...Terminal unit, 70...Antenna, 153...Switching timing generation unit, 80...Transmission path, 154...Switching unit, 210...P SS code sequence selection unit, 211...data holding unit, 212...fourth correlation calculation unit, 213...error detection unit, 220...sine wave generation unit, 221...frequency conversion unit, 310...PSS code sequence selection unit, 311...data holding unit, 312...phase conversion unit, 313...third correlation calculation unit, 314...phase determination unit, 320...filter coefficient selection unit, 321...filter calculation unit, 410...PSS code sequence selection unit, 411...data holding unit, 412...second correlation calculation unit, 413...phase error detection unit, 420...complex signal generation unit, 421...phase conversion unit, 1001...signal receiving unit, 1002...time waveform calculation unit, 1004...FFT (Fast Fourier Transform) Fourier Transform (Fourier Transform) 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... data determination unit, 1164... comparison calculation unit, 1165... NID1 detection unit, 1171... DMRS extraction unit, 1172... DMRS generation unit, 1173... data determination unit, 1174... comparison calculation unit, 1175... ibar_SSB detection unit

Claims

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

2. The communication device according to claim 1, wherein the signal receiving unit receives a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a synchronization signal block (SS / PBCH block) having a physical broadcast channel (PBCH) including a demodulation reference signal (DMRS).

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

4. The communications device according to claim 3, wherein the PSS detection unit comprises: a time signal extraction unit that extracts a portion of the time axis waveform signal; a PSS generation unit that outputs multiple 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 the time axis waveform signal that is the output of the time signal extraction unit and the PSS code sequence from the PSS generation unit and outputs the correlation value; and an NID2 detection unit that outputs the timing at which the correlation value is highest within a predetermined time range as the SSB timing, and outputs the PSS code sequence number corresponding to the PSS code sequence with the highest correlation value as a physical layer cell identifier NID2.

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

6. The communication device according to claim 5, wherein the signal receiving unit receives a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a synchronization signal block (SS / PBCH block) having a physical broadcast channel (PBCH) including a demodulation reference signal (DMRS).

7. The communication device according to claim 6, wherein the time waveform calculation unit includes a PSS detection unit that detects a PSS signal included in the time domain waveform signal.

8. The communications device according to claim 7, wherein the PSS detection unit comprises: a time signal extraction unit that extracts a portion of the time domain waveform signal; a PSS generation unit 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 a correlation calculation between the time domain waveform signal that is the output of the time signal extraction unit and the PSS code sequence from the PSS generation unit and outputs a correlation value; and an NID2 detection unit that outputs the timing at which the correlation value is highest within a predetermined time range as the SSB timing, and outputs the PSS code sequence number corresponding to the PSS code sequence with the highest correlation value as a physical layer cell identifier NID2.

9. The communication device according to claim 8, wherein the sampling phase conversion unit comprises: a phase detection unit that detects an optimum phase at which the sampling phase of the time domain waveform signal is most favorable based on the SSB timing and physical layer cell identifier NID2 that are the output of the PSS detection unit; and a phase conversion unit that converts the sampling phase of the time domain waveform signal based on the optimum phase that is the output of the phase detection unit.

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

11. The communication device according to claim 10, wherein the signal receiving unit receives a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a synchronization signal block (SS / PBCH block) having a physical broadcast channel (PBCH) including a demodulation reference signal (DMRS).

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

13. The communications device according to claim 12, wherein the PSS detection unit comprises: a time signal extraction unit that extracts a portion of the time domain waveform signal; a PSS generation unit that outputs a plurality of PSS code sequences of the PSS signal and a code sequence number that identifies the PSS code sequence; a first correlation calculation unit that performs a correlation calculation between the time domain waveform signal that is the output of the time signal extraction unit and the PSS code sequence from the PSS generation unit and outputs a correlation value; and an NID2 detection unit that outputs the timing at which the correlation value is highest within a predetermined time range as the SSB timing, and outputs the PSS code sequence number corresponding to the PSS code sequence with the highest correlation value as a physical layer cell identifier NID2.

14. The communications device of claim 13, wherein the carrier frequency correction unit comprises: a frequency error detection unit that detects a carrier frequency error of the time domain waveform signal based on the SSB timing and physical layer cell identifier NID2 that are outputs of the PSS detection unit; and a frequency error correction unit that corrects the carrier frequency of the time domain waveform signal based on the frequency error that is output from the frequency error detection unit.

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

16. The communication device according to claim 15, wherein the signal receiving unit receives a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a synchronization signal block (SS / PBCH block) having a physical broadcast channel (PBCH) including a demodulation reference signal (DMRS).

17. The communication device according to claim 16, wherein the time waveform calculation unit includes a PSS detection unit that detects a PSS signal included in the time domain waveform signal.

18. The communications device according to claim 17, wherein the PSS detection unit comprises: a time signal extraction unit that extracts a portion of the time domain waveform signal; a PSS generation unit that outputs a plurality of PSS code sequences of the PSS signal and a code sequence number that identifies the PSS code sequence; a first correlation calculation unit that performs a correlation calculation between the time domain waveform signal that is the output of the time signal extraction unit and the PSS code sequence from the PSS generation unit and outputs the correlation value; and an NID2 detection unit that outputs the timing at which the correlation value is highest within a predetermined time range as the SSB timing, and outputs the PSS code sequence number corresponding to the PSS code sequence with the highest correlation value as a physical layer cell identifier NID2.

19. The communication device according to claim 18, wherein the sampling phase conversion unit comprises: a phase detection unit that detects an optimum phase for the best sampling phase of the time domain waveform signal based on the SSB timing and physical layer cell identifier NID2 that are the output of the PSS detection unit; and a phase conversion unit that converts the sampling phase of the time domain waveform signal based on the optimum phase that is the output of the phase detection unit.

20. The communication device according to claim 19, wherein the carrier frequency correction unit comprises: a frequency error detection unit that detects a carrier frequency error of the time domain waveform signal based on the SSB timing and physical layer cell identifier NID2 that are the output of the PSS detection unit; and a frequency error correction unit that corrects the carrier frequency of the time domain waveform signal based on the frequency error that is the output of the frequency error detection unit.

21. A communication device as claimed in any one of claims 4, 9, 14 and 20, wherein the frequency waveform phase correction unit comprises: a phase error detection unit that detects a phase error of the time axis waveform signal based on the SSB timing and physical layer cell identifier NID2 that are the output of the PSS detection unit; and a phase correction unit that corrects the phase of the frequency axis waveform signal that is the output of the FFT unit based on the phase error that is the output of the phase error detection unit.

22. The communications device according to claim 21, wherein the phase error detection unit comprises: a data storage unit that stores a portion of the time-domain waveform signal based on the SSB timing output from 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 output from the PSS detection unit; a second correlation calculation unit that calculates a correlation value between the time-domain waveform signal stored in the data storage unit and the PSS code sequence selected by the PSS code sequence selection unit; and a phase error detection unit that calculates the amount of phase rotation on the time axis from the correlation value calculated by the second correlation calculation unit and detects a phase error in the time-domain waveform signal.

23. The communication device according to claim 22, wherein the phase correction unit comprises: a complex number generation unit that generates a complex number of an arbitrary argument based on the phase error that is the output of the phase error detection unit; and a phase correction unit that complex-multiplies the complex number that is the output of the complex number generation unit by the frequency axis waveform signal that is the output of the FFT unit, thereby correcting the phase of the frequency axis waveform signal.

24. In a distributed antenna system comprising a master station connected to a base station and one or more slave station devices that relay signals between terminal devices communicating with the base station and the master station, a control method for a communications device that functions as the master station or the slave station and receives Orthogonal Frequency Division Multiplexing (OFDM) signals transmitted using a time division multiplexing method, the control method comprising: receiving the OFDM signals and converting them to baseband OFDM signals; extracting a portion of a time-domain waveform signal and calculating a degree of similarity between the extracted signal and a known signal; performing a Fourier transform (FFT) on the time-domain waveform signal; correcting the phase of a frequency-domain waveform signal obtained by the Fourier transform based on the degree of similarity with the known signal; extracting a portion of the frequency-domain waveform signal after the correction and calculating a degree of similarity between the extracted signal and the known signal; and estimating a timing for switching between uplink and downlink communications within the communications device based on the degree of similarity.

25. A distributed antenna system comprising a master station connected to a base station and one or more slave station devices that relay signals between terminal devices that communicate with the base station and the master station, the computer included in a communication device that functions as the master station or the slave station and receives an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method comprises: a signal receiving unit that receives the OFDM signal and converts it into a baseband OFDM signal; a time waveform calculation unit that extracts a portion of a time domain waveform signal that is the output of the signal receiving unit and calculates the degree of similarity between the extracted signal and a known signal; an FFT unit that performs a Fourier transform (FFT) on the time domain waveform signal that is the output of the time waveform calculation unit; and a frequency waveform phase correction unit that corrects the phase of the frequency domain waveform signal that is the output of the FFT unit based on the degree of similarity with the known signal calculated by the time waveform calculation unit. A program for causing the device to function as a frequency waveform calculation unit that extracts a portion of the frequency axis waveform signal that is the output of the frequency waveform phase correction unit and calculates the degree of similarity between the extracted signal and a known signal, and a switching timing estimation unit that estimates the timing of switching between uplink communication and downlink communication in the device based on the result of the frequency waveform calculation unit.

26. In a distributed antenna system comprising a master station connected to a base station, and one or more slave stations that relay signals between terminal devices communicating with the base station and the master station, a control method for a communication device that functions as the master station or the slave station and receives an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method, the method comprising the steps of: receiving the OFDM signal and converting it to a baseband OFDM signal; extracting a portion of a time-domain waveform signal and calculating a degree of similarity between the extracted signal and a known signal; converting the sampling phase of the time-domain waveform signal based on the degree of similarity with the known signal; performing a Fourier transform (FFT) on the time-domain waveform signal after the sampling phase conversion; correcting the phase of the frequency-domain waveform signal obtained by the Fourier transform based on the degree of similarity with the known signal; extracting a portion of the corrected frequency-domain waveform signal and calculating a degree of similarity between the extracted signal and the known signal; and estimating a timing for switching between uplink communication and downlink communication in the communication device itself based on the degree of similarity.

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

28. In a distributed antenna system comprising a master station connected to a base station, and one or more slave stations that relay signals between terminal devices communicating with the base station and the master station, a control method for a communication device that functions as the master station or the slave station and receives an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method, the method includes the steps of: receiving the OFDM signal and converting it to a baseband OFDM signal; extracting a portion of a time-domain waveform signal and calculating a degree of similarity between the extracted signal and a known signal; correcting the carrier frequency of the time-domain waveform signal based on the degree of similarity with the known signal; performing a Fourier transform (FFT) on the corrected time-domain waveform signal; correcting the phase of the frequency-domain waveform signal obtained by the Fourier transform based on the degree of similarity with the known signal; extracting a portion of the frequency-domain waveform signal and calculating a degree of similarity between the extracted signal and the known signal; and estimating a timing for switching between uplink communication and downlink communication in the communication device itself based on the degree of similarity.

29. A distributed antenna system comprising a master station connected to a base station and one or more slave station devices that relay signals between terminal devices communicating with the base station and the master station, the computer included in a communication device that functions as the master station or the slave station and receives Orthogonal Frequency Division Multiplexing (OFDM) signals transmitted using a time division multiplexing method comprises: a signal receiving unit that receives the OFDM signals and converts them into baseband OFDM signals; a time waveform calculation unit that extracts a portion of a time domain waveform signal output by the signal receiving unit and calculates the degree of similarity between the extracted signal and a known signal; a carrier frequency correction unit that corrects the carrier frequency of the time waveform signal output by the signal receiving unit based on the degree of similarity between the extracted signal and a known signal calculated by the time waveform calculation unit; and an FFT unit that performs a Fourier transform (FFT) on the time waveform signal output by the carrier frequency correction unit. A program for causing the device to function as: a frequency waveform phase correction unit that corrects the phase of the frequency axis waveform signal that is the output of the FFT unit based on the degree of similarity with a known signal calculated by the time waveform calculation unit; a frequency waveform calculation unit that extracts a part of the frequency axis waveform signal that is the output of the frequency waveform phase correction unit and calculates the degree of similarity between the extracted signal and a known signal; and a switching timing estimation unit that estimates the timing of switching between uplink communication and downlink communication in the device based on the result of the frequency waveform calculation unit.

30. In a distributed antenna system comprising a master station connected to a base station, and one or more slave station devices that relay signals between terminal devices communicating with the base station and the master station, a control method for a communication device that functions as the master station or the slave station and receives an Orthogonal Frequency Division Multiplexing (OFDM) signal transmitted by a time division multiplexing method, the method comprising the steps of: receiving the OFDM signal and converting it to a baseband OFDM signal; extracting a portion of a time domain waveform signal and calculating a similarity between the extracted signal and a known signal; converting the sampling phase of the time domain waveform signal based on the similarity between the extracted signal and the known signal; correcting the carrier frequency of the time domain waveform signal after the sampling phase conversion based on the similarity between the known signal and the known signal; performing a Fourier transform (FFT) on the corrected time domain waveform signal; and correcting the phase of the frequency domain waveform signal obtained by the Fourier transform based on the similarity between the known signal and the known signal. extracting a portion of the frequency axis waveform signal, calculating a degree of similarity between the extracted signal and a known signal, and estimating a timing for switching between uplink communication and downlink communication in the communication device based on the degree of similarity.

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

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