Wireless communication system

Abstract

Provided is a wireless communication system that performs full-duplex wireless communication in which the OFDM symbol length of an uplink signal from a slave station to a master station is N times the OFDM symbol length of a downlink signal in the opposite direction. The wireless communication system makes it possible to appropriately deal with phase rotation which is caused by an FFT window on a master station side.　A master station 10 performs interference cancellation by setting, for a received signal, an FFT window of the OFDM symbol length of a downlink signal in accordance with the symbol timing of a downlink, performing FFT processing, and subtracting, from the received signal, an interference wave replica which is generated on the basis of the result of the FFT processing. The master station 10 further calculates an MER of a TMCC carrier in the received signal after the interference cancellation for all combinations of the timings of the FFT window and the number of correction rotations for correcting the phase rotation which is caused by the FFT window, and adopts a combination which maximizes the MER of the TMCC carrier to perform demodulation processing of the uplink signal.

Description

wireless communication system

[0001] The present invention relates to a wireless communication system that performs full-duplex wireless communication using Orthogonal Frequency Division Multiplexing (OFDM) as a modulation method.

[0002] As shown in Figure 1, full-duplex wireless communication, in which two-way wireless communication is performed between a master station and a slave station using the same frequency, time, and space, has recently attracted attention as a communication method that can achieve higher frequency utilization efficiency compared to frequency division multiplexing and time division multiplexing. In full-duplex wireless communication, both the master station and the slave station mix their own transmission signals into the received signals from the other station as interference waves, so this interference component must be canceled. Methods for canceling interference components are broadly divided into analog cancellation, which is performed in the analog domain, and digital cancellation, which is performed in the digital domain. This invention relates to digital cancellation, and the following explanation will focus on digital cancellation.

[0003] In order to easily perform digital cancellation in a wireless communication system that performs full-duplex wireless communication using OFDM as a modulation method, it is necessary to synchronize symbol timing during reception. The slave station transmits an uplink signal from the slave station to the master station in synchronization with the reception timing of a downlink signal from the master station, thereby synchronizing the symbol timing of the uplink that interferes with the reception of the downlink signal.

[0004] On the other hand, the master station receives the uplink signal transmitted from the slave station, but at that time, the downlink signal transmitted from the master station is mixed in as an interference wave. The master station receiver needs to accurately reproduce the interference wave in order to cancel it, and it is common to set an FFT (First Fourier Transform) window in the master station receiver based on the symbol timing of the interfering downlink signal.

[0005] However, this FFT window is not necessarily appropriate for an uplink signal that is delayed due to propagation. Therefore, the symbol switching timing of the uplink signal may exist within the FFT window. To avoid this problem, Patent Document 1 discloses an invention that selects an FFT window timing that prevents adjacent symbols from being captured within the FFT window of a slave station, regardless of the propagation path delay time, by making the symbol length of the uplink signal N times (N is an integer of 2 or more) the symbol length of the downlink signal.

[0006] Japanese Patent Application Laid-Open No. 2022-139409

[0007] The following describes the process performed when the main station receives an uplink signal when the symbol length of the uplink signal is N times (N is an integer equal to or greater than 2) the symbol length of the downlink signal. For example, when the main station receives an uplink signal with a doubled symbol length, the FFT window position for correctly generating a replica of an interference wave needs to be set based on the symbol timing of the downlink signal, as shown in Figure 2.

[0008] In the case of Fig. 2, if the FFT window position is set at timing A, the FFT window will include the boundary of the uplink symbol, causing inter-symbol interference. For this reason, in the case of Fig. 2, the FFT window position must be set at timing B. In this way, it is necessary to determine the FFT window timing at which inter-symbol interference does not occur.

[0009] However, even if the FFT window position is set at timing B, a shift (symbol d in the figure) occurs in the FFT window relative to the symbol timing of the uplink. This shift causes the signal to be observed as being advanced in time by the FFT window, which appears as a phase advance of each subcarrier in the frequency domain. The following equation (1) represents the OFDM signal when the d sample signal is advanced. Here, S is the OFDM time signal, M is the number of FFT points, m is the subcarrier number, and t is the sample time.

[0010] It can be seen that an advance in the phase occurs as the symbol timing of the uplink signal advances relative to the FFT window, as shown in the above equation (1). The phase advance differs depending on the subcarrier, and the amount of phase advance increases proportionally as the subcarrier number increases. Since the phase rotates when observed in the subcarrier direction, hereinafter this phenomenon will be referred to as "phase rotation due to the FFT window."

[0011] The phase rotation caused by the FFT window is similar to the phenomenon that occurs in conventional OFDM radio equipment due to the difficulty of precisely synchronizing the FFT window with the symbol timing. In a typical OFDM receiver, pilot carriers are used to estimate and correct the phase rotation. However, the insertion frequency of the pilot carriers is limited to improve transmission efficiency. For example, if the frequency of pilot carrier insertion in the frequency direction is one subcarrier per eight subcarriers, the maximum phase difference per subcarrier that can be estimated based on the sampling theorem is 2π / 16. When the symbol length is multiplied by N, a phase rotation exceeding 2π / 16 may occur. Therefore, the method using pilot carriers alone cannot accurately estimate the phase rotation caused by the FFT window, resulting in a problem of inaccurate demodulation and decoding of uplink signals.

[0012] The present invention has been made in view of the above-described conventional circumstances, and has an object to provide a wireless communication system that performs full-duplex wireless communication by setting the OFDM symbol length of an uplink signal from a slave station to a master station to N times the OFDM symbol length of a downlink signal in the reverse direction, so as to be able to appropriately deal with phase rotation caused by an FFT window on the master station side.

[0013] In order to achieve the above-mentioned object, the present invention has the following technical features in a wireless communication system that performs full-duplex wireless communication by setting the OFDM symbol length of an uplink signal from a slave station to a master station to N times the OFDM symbol length of a downlink signal in the reverse direction.

[0014] In a wireless communication system according to a first aspect, the main station performs FFT processing on a received signal including an uplink signal and an interference wave caused by a downlink signal by setting an FFT window of an OFDM symbol length of the downlink signal to match the symbol timing of the downlink, and subtracts an interference wave replica generated based on the result of the FFT processing from the received signal to perform interference cancellation. The main station further calculates the MER of the TMCC carrier in the received signal after interference cancellation for all combinations of the timing of the FFT window and the correction rotation number for correcting the phase rotation caused by the FFT window, and performs demodulation processing of the uplink signal by applying a combination in which the MER of the TMCC carrier is equal to or greater than a reference value or is at its maximum.

[0015] In a wireless communication system according to a second aspect, the main station performs FFT processing on a received signal including an uplink signal and an interference wave caused by a downlink signal by setting an FFT window of an OFDM symbol length of the downlink signal to match the symbol timing of the downlink, and subtracts an interference wave replica generated based on the result of the FFT processing from the received signal to perform interference cancellation. The main station further calculates the variance of all TMCC carriers in the received signal after interference cancellation for all combinations of the timing of the FFT window and the correction rotation number for correcting the phase rotation caused by the FFT window, and performs demodulation processing of the uplink signal by applying a combination in which the variance of all TMCC carriers is equal to or less than a reference value or is at a minimum.

[0016] In a wireless communication system according to a third aspect, the main station performs FFT processing on a received signal including an uplink signal and an interference wave caused by the downlink signal by setting an FFT window of an OFDM symbol length of the downlink signal to match the symbol timing of the downlink, and subtracts an interference wave replica generated based on the result of the FFT processing from the received signal to perform interference cancellation; the secondary station, before communication with the main station is established, transmits the uplink signal by including a predetermined known signal in a data carrier; and the main station further calculates, before communication with the secondary station is established, the MER of the data carrier in the received signal after interference cancellation for all combinations of the timing of the FFT window and the number of correction rotations for correcting the phase rotation caused by the FFT window; and after communication with the secondary station is established, performs demodulation processing of the uplink signal by applying a combination in which the MER of the data carrier is equal to or greater than a reference value or is at its maximum.

[0017] According to the present invention, in a wireless communication system for full-duplex wireless communication in which the OFDM symbol length of an uplink signal from a slave station to a master station is set to N times the OFDM symbol length of a downlink signal in the reverse direction, it is possible to appropriately deal with phase rotation caused by an FFT window on the master station side. Furthermore, since phase correction adapted to propagation delay can be performed automatically, it is possible to reduce the need to manually input propagation distance and delay, thereby contributing to improved user convenience.

[0018] 1 is a diagram illustrating an overview of a full-duplex wireless communication system. 2 is a diagram illustrating an example of an FFT window position of a master station in a full-duplex wireless communication system. 3 is a diagram illustrating an example of an interpolation pattern of a pilot carrier. 4 is a diagram illustrating an example of an interpolation pattern of a pilot carrier expressed on a time axis. 5 is a diagram illustrating an example of a phase change of an interpolation pattern. 6 is a diagram illustrating an example of a configuration of a wireless communication system according to the first embodiment, the second embodiment, and the third embodiment. 7 is a diagram illustrating an example of an OFDM symbol format when N = 1 and N = 2. 8 is a diagram illustrating an example of a configuration of a demodulation unit of a master station according to the first embodiment (first method). 9 is a diagram illustrating an example of a flowchart related to the processing of a window timing / correction rotation number control unit. 10 is a diagram illustrating simulation results of DATA-MER for each FFT window timing when the propagation delay time and the correction rotation number are changed. 11 is a diagram illustrating simulation results of TMCC-MER for each FFT window timing when the propagation delay time and the correction rotation number are changed. 12 is a diagram illustrating an example of a configuration of a demodulation unit of a master station according to the second embodiment (second method). 13 is a diagram illustrating an example of a configuration of a modulation unit of a slave station according to the third embodiment (third method). 14 is a diagram illustrating an example of a configuration of a demodulation unit of a master station according to the third embodiment (third method).

[0019] The present invention relates to a wireless communication system that performs full-duplex wireless communication by setting the length of an OFDM symbol of an uplink signal from a slave station to a master station to N times the length of an OFDM symbol of a downlink signal in the opposite direction. In such a wireless communication system, in order for the master station to accurately demodulate and decode the uplink signal, it is necessary to obtain a propagation path estimation result that reflects the phase rotation caused by the FFT window. Therefore, the present invention uses the three methods described below to search for the number of phase rotations (hereinafter referred to as the "phase rotation number") when observed in the subcarrier direction, and then performs an inverse rotation process on the received pilot carrier. This reduces the number of rotations of the pilot carrier in the subcarrier direction, allowing it to be interpolated in the frequency direction by an interpolation filter of a low-pass filter. By again performing the same phase rotation as the FFT window on the result, a correct propagation path estimation result can be obtained, enabling accurate equalization of the uplink signal. Hereinafter, the two above-mentioned rotation processes will be collectively referred to as the "correction rotation / inverse rotation process."

[0020] [First Method] In the first method, the MER (Modulation Error Ratio) (hereinafter referred to as "TMCC-MER") of a TMCC (Transmission and Multiplexing Configuration and Control) carrier after interference cancellation is measured for each combination of FFT window timing (two patterns of FFT window timing A and FFT window timing B in FIG. 2) and the number of rotations for the correction rotation / reverse rotation process (hereinafter referred to as "correction rotation number"), and the optimal FFT window timing and correction rotation number are searched for using the TMCC-MER as an index.

[0021] Generally, MER is calculated based on the error from the closest point among multiple ideal reception point candidates (64 points in the case of 64QAM), but TMCC-MER is calculated based on the error from the only ideal reception point obtained from a known signal or a signal equivalent thereto. For example, if the number of FFT points is 2048, the number of correction rotations will be anywhere from 0 to 2047. Therefore, 2048 patterns of correction rotations are performed for each of FFT window timing A and FFT window timing B, and the number of correction rotations at which TMCC-MER is equal to or greater than the reference value or at its maximum is selected.

[0022] The reason why TMCC-MER is used instead of the MER of the data carrier (hereinafter referred to as "DATA-MER") is that when calculating DATA-MER, the data transmission pattern is unknown, so it is necessary to calculate MER using the general method described above, and aliasing in propagation path estimation makes the contellation appear correct, resulting in a high DATA-MER value being calculated. This phenomenon will be explained using Figures 3, 4, and 5.

[0023] In Fig. 3, pilot carriers are inserted at intervals of eight, and eight types of interpolation patterns are shown for the case where the value of each pilot carrier is 1+0i. The interpolation pattern here refers to a pattern that can be estimated from the pilot carrier. In Fig. 4, the interpolation patterns in Fig. 3 are expressed on the time axis. For eight types of interpolation patterns (interpolation patterns A to H) including aliasing, the frequency characteristics of each interpolation pattern can be calculated by using a time limiting filter having a time passband for extracting the target interpolation pattern.

[0024] When explaining aliasing using the sampling theorem, it is common to sample on the time axis and then display the results on the frequency axis, but this relationship also holds true when time and frequency are reversed. Therefore, sampling is performed on the frequency axis and the results are displayed on the time axis in Figure 4.

[0025] 5 shows the phase change of each interpolation pattern when interpolation pattern A is used as a reference, and the phase of each subcarrier in interpolation patterns C, E, and G is a multiple of 2π / 4. The constellations are symmetrical on the I and Q axes, and phase changes of multiples of 2π / 4 result in the same apparent constellations. Therefore, it is not possible to determine which interpolation pattern is correct based on the pilot carriers alone.

[0026] In contrast, TMCC consists of 440 symbols per frame, transmitting a total of 440 bits. The first 16 bits of the frame transmit a predetermined bit string for frame synchronization on the receiving side. Data is modulated using differential BPSK (Binary Phase Shift Keying), and the same information is transmitted using multiple carriers in one symbol, enabling highly accurate transmission even if phase rotation occurs due to the FFT window. Furthermore, unlike pilot carriers, which are inserted at equal intervals, TMCC carriers are inserted at irregular intervals.

[0027] Since the information transmitted by TMCC is information that remains unchanged during transmission, such as wireless transmission parameters, it is possible to store the demodulation and decoding results and use them as known signals for the next frame and onward. Therefore, TMCC-MER can use a method of finding the MER from the error between the known signal and the only ideal reception point found from the known signal, and it is possible to calculate an accurate MER even if aliasing of the propagation path estimation result occurs.

[0028] [Method 2] In Method 2, the variance of all TMCC carriers is measured as an alternative to the TMCC-MER used in Method 1. That is, similar to Method 1, the variance of the TMCC carriers is measured for each combination of FFT window timing and the number of rotations in the correction rotation / reverse rotation process, and the variance of all TMCC carriers is used as an index to search for the optimal FFT window timing and correction rotation number.

[0029] All TMCC carriers within one symbol transmit the same data and have the same phase. Therefore, when measuring the dispersion of the TMCC carrier reception point after demodulation, if the demodulation is performed correctly, the dispersion will be a low value, and if the demodulation is performed incorrectly, the dispersion will be a high value. Therefore, the second method utilizes this characteristic to search for the optimal FFT window timing and correction rotation number.

[0030] [Method 3] Before communication from the slave station to the master station is established, the data carrier of the transmission signal from the slave station is set as a known signal, making it possible to calculate an accurate DATA-MER on the receiving side of the master station even with the apparently correct constellation described in Method 1. Therefore, in Method 3, before communication between the master station and slave station is established, DATA-MER is measured for each combination of FFT window timing and rotation number for the correction rotation / reverse rotation process, as in Method 1, and the FFT window timing and correction rotation number are searched for using DATA-MER as an index.

[0031] Hereinafter, a first embodiment to which the first method is applied, a second embodiment to which the second method is applied, and a third embodiment to which the third method is applied will be described with reference to the drawings.

[0032] [First Embodiment] Figure 6 shows an example configuration of a wireless communication system according to a first embodiment (first method). The configuration shown in Figure 6 is the same as that of a second embodiment (second method) and a third embodiment (third method) described later. The wireless communication system shown in the figure uses OFDM as the modulation method and is configured to perform full-duplex wireless communication at a higher transmission rate on the downlink from the master station 10 to the slave station 20 than on the uplink in the reverse direction. The present invention relates to the processing of the demodulator 15 of the master station 10 and the modulator 21 of the slave station 20. In order to explain the necessity of this processing, we will first briefly explain the contents of the aforementioned Patent Document 1 (Japanese Patent Laid-Open No. 2022-139409).

[0033] The master station 10 is a wireless communication device having a modulation unit 11, a high frequency transmission unit 12, a transmission / reception antenna 13, a high frequency reception unit 14, and a demodulation unit 15. Similarly, the slave station 20 is a wireless communication device having a modulation unit 21, a high frequency transmission unit 22, a transmission / reception antenna 23, a high frequency reception unit 24, and a demodulation unit 25.

[0034] The modulation unit 11 of the main station 10 receives transmission data on the downlink, performs processing such as error correction coding, and then modulates the data into an OFDM signal. The modulated signal generated by the modulation unit 11 is input to the high-frequency transmission unit 12, where it is converted to a desired carrier frequency and output to the transmission / reception antenna 13. The transmission / reception antenna 13 sends the transmission signal input from the high-frequency transmission unit 12 into space as radio waves. Here, the transmission / reception antenna 13 of the main station 10 may have a structure in which the transmission antenna and the reception antenna are integrated, or may have a structure in which they are separate.

[0035] In the case of an integrated antenna, a directional coupler called a circulator is often provided between the transmitting high frequency unit 12 and the receiving high frequency unit 14. In this case, the signal from the transmitting high frequency unit 12 is transmitted to the transmitting / receiving antenna 13 via the circulator. Furthermore, the signal received by the transmitting / receiving antenna 13 is transmitted to the receiving high frequency unit 14 via the circulator. At this time, a small amount of leakage component remains from the signal from the transmitting high frequency unit 12 to the receiving high frequency unit 14. Generally, the isolation between them is about 20 to 30 dB, and this leakage component becomes interference.

[0036] Furthermore, even when the transmitting and receiving antennas 13 are separate, interference occurs due to components that travel directly from the transmitting antenna to the receiving antenna via space. The isolation between these antennas is approximately 50 to 100 dB, depending on the directional gain of the antennas used and the distance between the antennas, ensuring higher isolation than with an integrated antenna.

[0037] The downlink signal sent from the transmitting / receiving antenna 13 of the master station 10 passes through the propagation path and is received by the transmitting / receiving antenna 23 of the opposing slave station 20, but as described above, a portion of the signal leaks or passes through space and is input as an interference wave to the receiving high frequency unit 14 of the master station 10. Note that, like the transmitting / receiving antenna 13 of the master station 10, the transmitting / receiving antenna 23 of the slave station 20 may have a structure in which the transmitting antenna and the receiving antenna are integrated, or a structure in which the transmitting antenna and the receiving antenna are separated.

[0038] The downlink signal received by the transmitting / receiving antenna 23 of the slave station 20 is converted from the carrier frequency to IF (Intermediate Frequency) by the receiving high frequency section 24 and output to the demodulation section 25. The demodulation section 25 performs interference wave cancellation processing and ODFM signal demodulation processing on the input signal to generate demodulated data for the downlink.

[0039] Next, the modulation unit 21 of the slave station 20 will be described. As mentioned above, if the signal timing of the downlink and the signal timing of the uplink are different, digital cancellation becomes difficult. Therefore, in the wireless communication system of this example, the OFDM symbol of the uplink signal generated by the modulation unit 21 of the slave station 20 is extended to N times its length (here, N is an integer equal to or greater than 2), and the symbol timing is made to coincide with the reception timing of the downlink from the master station 10.

[0040] First, we will explain how to lengthen the OFDM symbols of the uplink signal generated by modulation unit 21 of slave station 20 by N times. Fig. 7 shows examples of OFDM symbol formats when N = 1 and N = 2. When N = 1, the OFDM symbol format is the same as the conventional one. When N = 2, the effective symbols for N = 1 are copied and concatenated, and the latter half of the symbol, which is twice as long as the conventional one, is copied to the first half of the symbol as a guard interval.

[0041] ODFM symbols have waveform continuity between the beginning and end of the symbol, and even when concatenated, continuity at the concatenation timing is maintained. Similarly, there is continuity in the guard interval timing, so within the period of an ODFM symbol expanded by N = 2, there is continuity in the received waveform no matter at what timing the FFT window is set, and ODFM orthogonality that does not cause interference between subcarriers can be ensured.

[0042] Next, we will explain the symbol timing control in the modulation unit 21 of the slave station 20. The modulation unit 21 of the slave station 20 performs modulation processing on the transmission data of the uplink in the same manner as the modulation unit 11. The modulation timing at this time is controlled based on the timing from the demodulation unit 25. The demodulation unit 25 recovers the symbol timing from the received signal and transmits the recovered timing to the modulation unit 21.

[0043] The modulation unit 21 controls the transmission timing so that the timing of the received signal and the transmitted signal coincides, taking into account the delay occurring in the transmission high frequency unit 22. The modulated signal generated by the modulation unit 21 is sent out into space as a radio wave via the transmission high frequency unit 22 and the transmission / reception antenna 23, and is transmitted to the master station 10. At the same time, the modulated signal mixes with the received signal on the downlink of the slave station 20 as an interference wave.

[0044] By matching the timing of the received signal and the transmitted signal in the modulation unit 21, even if the demodulation unit 25 sets an FFT window based on the timing of the downlink signal, there is symbol continuity within the FFT window for the uplink as well. This ensures the orthogonality of the ODFM signal for both the downlink and uplink. As described above, the orthogonality of the ODFM signal is maintained in the demodulation unit 25 by symbol timing control, making it possible to easily perform digital cancellation.

[0045] Next, the reception processing of the master station 10 will be described. The uplink signal sent from the transmission / reception antenna 23 of the slave station 20 is delayed due to propagation delay, received by the transmission / reception antenna 13 of the master station 10, and input to the high-frequency reception unit 14. An example of the signal timing at this time is shown in Figure 1. The high-frequency reception unit 14 frequency-converts the received signal in the same way as the high-frequency reception unit 24 of the slave station 20, and outputs the converted signal to the demodulation unit 15.

[0046] The processing of the demodulation unit 15 of the main station 10 according to the first embodiment (first method) will be described below with reference to Fig. 8. Fig. 8 shows an example of the configuration of the demodulation unit 15 of the main station 10 according to the first embodiment (first method). The received signal input from the high frequency receiving unit 14 is input to the FFT unit 101. The FFT unit 101 converts the received signal into the frequency domain in accordance with a timing signal indicating the FFT window position input from the window timing / correction rotation number control unit 102, and outputs the converted signal to the TMCC demodulation / decoding unit 103, the adder 104, and the pilot separation unit 105. The timing signal indicating the FFT window position is a signal indicating FFT window timing A or FFT window timing B in Fig. 2.

[0047] The TMCC demodulation / decoding unit 103 demodulates and decodes the TMCC carrier, and outputs the decoded result to the frame synchronization unit 106 and the TMCC decoding result memory 107. The frame synchronization unit 106 detects frame timing from the decoding result by the TMCC demodulation / decoding unit 103 in accordance with a predetermined data periodicity, and outputs a timing signal indicating the frame timing to the TMCC decoding result memory 107.

[0048] The TMCC decoding result memory 107 stores the decoding result of the TMCC carrier in accordance with the frame timing, and simultaneously reads out the decoding result of the TMCC carrier one frame before in accordance with the frame timing and outputs it to the TMCC mapping unit 108. The TMCC mapping unit 108 maps the TMCC carrier based on the decoding result of the TMCC carrier one frame before, and outputs the result as an ideal reception point to the TMCC-MER calculation unit 109. The TMCC carrier after interference cancellation is input to the TMCC-MER calculation unit 109 from the TMCC extraction unit 115, and the calculation method for this signal will be described below.

[0049] Pilot separation section 105 separates the pilot signals of the uplink signal and the downlink signal in accordance with a pilot orthogonal method, outputs the pilot signal of the uplink signal to rotation section 110, and outputs the pilot signal of the downlink signal to interference wave propagation path estimation filter 111. Pilot orthogonal methods include code orthogonal and frequency orthogonal, but these are not the main focus of the present invention and therefore will not be described here.

[0050] Interference wave propagation path estimation filter 111 performs an interpolation process on the pilot signal of the downlink signal in the frequency direction to perform propagation path estimation, and outputs the result to interference replica generation unit 112. Interference replica generation unit 112 receives the frequency-domain transmission signal from modulation unit 11 for interference cancellation, generates an interference wave replica by multiplying the propagation path estimation result from interference wave propagation path estimation filter 111, and outputs the interference wave replica to adder 104. Adder 104 performs interference cancellation by subtracting the interference wave replica from the received signal, and outputs the interference-canceled received signal to equalization unit 113. Equalization unit 113 also receives the propagation path estimation result of the desired wave, which is an uplink signal, as input from derotation unit 114.

[0051] The propagation path estimation result of the desired wave is calculated through the following three processes. First, rotation section 110 performs rotation processing on the pilot signal of the uplink signal according to the correction rotation number input from window timing and correction rotation number control section 102, and outputs the result to desired wave propagation path estimation filter 116. Rotation section 110 corrects phase rotation caused by the FFT window. Next, desired wave propagation path estimation filter 116 performs interpolation processing in the frequency direction on the pilot signal of the uplink signal after the correction rotation, thereby performing propagation path estimation, and outputs the result to inverse rotation section 114. Thereafter, inverse rotation section 114 performs rotation processing on the pilot signal of the uplink signal after the correction rotation and interpolation processing, which is the inverse of the correction rotation number input from window timing and correction rotation number control section 102, and outputs the result of propagation path estimation of the desired wave to equalization section 113.

[0052] Since the received signal after interference cancellation has phase rotation due to the FFT window, the reverse rotation unit 114 performs a rotation opposite to that performed by the rotation unit 110 to make the phase rotation the same as that occurring in the data carrier, TMCC carrier, etc. of the received signal. By performing the above processing, it is possible to obtain a propagation path estimation result for the desired wave. The operation of the window timing and correction rotation number control unit 102 will be described separately.

[0053] The equalization unit 113 performs equalization processing on the received signal after interference cancellation using the propagation path estimation result of the desired wave, and outputs the result to the TMCC extraction unit 115 and the decoding unit 117. The decoding unit 117 performs error correction decoding on the equalized received signal, and outputs whether decoding was successful to the window timing and correction rotation number control unit 102. The TMCC extraction unit 115 extracts the TMCC carrier from the equalized received signal, and outputs it to the TMCC-MER calculation unit 109. The TMCC-MER calculation unit 109 receives the ideal reception point from the TMCC mapping unit 108, compares it with the TMCC carrier of the received signal, calculates the TMCC-MER, and outputs the result to the memory 118.

[0054] The memory 118 also receives corrected rotation speed information and FFT window timing information from the window timing and corrected rotation speed control unit 102, and stores the MER calculation result in association with the corrected rotation speed information and FFT window timing information. The optimal corrected rotation speed calculation unit 119 calculates the maximum value of the MER from the information stored in the memory 118, and outputs the FFT window timing and corrected rotation speed at that time as optimal values ​​to the window timing and corrected rotation speed control unit 102.

[0055] The operation of the window timing and correction rotation number control unit 102 will be described with reference to FIG. 9. FIG. 9 shows an example of a flowchart relating to the processing of the window timing and correction rotation number control unit 102. The window timing and correction rotation number control unit 102 first determines whether the decoding unit 117 is able to decode the signal (step S101). If decoding is possible (step S101; YES), the processing ends. If decoding is not possible (step S101; No), the FFT window timing signal to be output to the FFT unit 101 is set to timing A (step S102), the correction rotation number to be output to the rotation unit 110 and the counter rotation unit 114 is set to 0 (step S103), and one symbol is waited for (step S104). During this wait time, the TMCC-MER for one symbol is measured.

[0056] Thereafter, it is determined whether the number of corrected rotations is less than 2047 (step S105). If the number of corrected rotations is less than 2047 (step S105; YES), the number of corrected rotations is incremented by one (step S106), and the process returns to step S104 to wait for one symbol. By repeating the processes of steps S104 to S106, TMCC-MER is measured for each number of corrected rotations when the FFT window position is timing A.

[0057] If the corrected rotation number is 2047 or more (step S105; NO), it is determined whether or not the FFT window is set to timing A (step S107). If the FFT window is set to timing A (step S107; YES), the timing signal of the FFT window to be output to FFT unit 101 is set to timing B (step S108), and the process returns to step S103, where the corrected rotation number is set to 0. Thereafter, by repeating the processes of steps S104 to S106, TMCC-MER is measured for each corrected rotation number when the FFT window position is timing B. If the FFT window is not set to timing A (step S107; NO), the optimal FFT window timing and corrected rotation number input from optimal corrected rotation number calculation unit 119 are set, and the process returns to step S101.

[0058] By performing the above-described processing, TMCC-MER measurements are performed for all combinations of FFT window timing A, B, and 2048 patterns of correction rotation number, allowing the optimal FFT window timing and correction rotation number to be found. This makes it possible to determine the optimal FFT window timing and correction rotation number in the demodulator 15 of the master station 10, where symbol timing is shifted due to propagation path delay. Therefore, automatic and adaptive reception processing is possible regardless of propagation distance, making it possible to achieve bidirectional transmission at the same frequency.

[0059] Figure 10 shows the simulation results of DATA-MER for each FFT window timing when the propagation delay time and the correction rotation speed are changed. Figure 11 shows the simulation results of TMCC-MER for each FFT window timing when the propagation delay time and the correction rotation speed are changed.

[0060] As shown in Figure 10, in DATA-MER, there are multiple regions of the corrected rotation number where the MER is high when viewed at a certain delay time. In the example of Figure 10, when the delay time is approximately 2700 samples, the MER is high when the corrected rotation number is in region A, region C, region E, or region G at FFT window timing A. On the other hand, as shown in Figure 11, in TMCC-MER, the corrected rotation number where the MER is high when viewed at a certain delay time is limited to one region. In the example of Figure 11, when the delay time is approximately 2700 samples, the MER is high when the corrected rotation number is in region C at FFT window timing A. For this reason, it can be seen that using TMCC-MER is suitable as an index for searching for the corrected rotation number.

[0061] 11, it can be seen that if the delay time is in the range of 0 to 2303 samples, FFT window timing B should be selected, either window can be selected in the range of 2304 to 2559 samples, and FFT window timing A should be selected in the range of 2559 to 4607 samples. Even if the delay time exceeds this range, it can be seen that the same result will be obtained with a 4608 sample period.

[0062] As described above, in the wireless communication system according to the first embodiment, the main station 10 is configured to perform interference cancellation on a received signal including an uplink signal and an interference wave caused by a downlink signal by setting an FFT window of the OFDM symbol length of the downlink signal to match the symbol timing of the downlink, and to subtract an interference wave replica generated based on the result of the FFT processing from the received signal. The main station 10 is further configured to calculate the MER of the TMCC carrier in the received signal after interference cancellation for all combinations of the timing of the FFT window and the correction rotation number for correcting the phase rotation caused by the FFT window, and to perform demodulation processing of the uplink signal by applying the combination that maximizes the MER of the TMCC carrier.

[0063] This makes it possible to appropriately deal with phase rotation caused by the FFT window in the main station 10. Furthermore, since phase correction adapted to propagation delay can be automatically performed, manual input of propagation distance and delay can be eliminated, contributing to improved user convenience. In the first embodiment, the uplink signal is demodulated using a combination that maximizes the TMCC carrier MER. However, the uplink signal may be demodulated using a combination that maximizes the TMCC carrier MER. The reference value may be any value that ensures the accuracy of demodulation of the uplink signal. When multiple combinations exist that maximize or maximize the TMCC carrier MER, any combination may be selected. Alternatively, a combination with a larger correction rotation number may be preferentially selected, taking into account processing delays, etc.

[0064] [Second Embodiment] The processing of the demodulation unit 15 of the master station 10 according to the second embodiment (second method) will be described with reference to FIG. 12. FIG. 12 shows an example configuration of the demodulation unit 15 of the master station 10 according to the second embodiment (second method). The second method utilizes the fact that all TMCC carriers are in phase. Therefore, the second method does not require a circuit related to the calculation of TMCC-MER. The changes from the first method (FIG. 8) are the deletion of the TMCC demodulation / decoding unit 103, frame synchronization unit 106, TMCC decoding result memory 107, and TMCC mapping unit 108, and the replacement of the TMCC-MER calculation unit 109 with a TMCC carrier dispersion calculation unit 201.

[0065] The TMCC carrier variance calculation unit 201 calculates the variance of the equalized TMCC carrier input from the TMCC extraction unit 115 and outputs the result to the memory 118. When the correction rotation speed is correct, each TMCC carrier is in phase, and the variance value becomes large. On the other hand, when the correction rotation speed is incorrect, the phases of each TMCC carrier are not aligned, and the variance value becomes small. Utilizing this feature, the second method searches for the combination of FFT window timing and correction rotation speed that minimizes the TMCC-MER variance, and performs reception processing using this as the optimal value. The memory 118, optimal correction rotation speed calculation unit 119, and window timing / correction rotation speed control unit 102 use the TMCC carrier variance instead of TMCC-MER, but the specific processing content is the same as in the first method ( FIG. 6 ).

[0066] As described above, in the wireless communication system according to the second embodiment, the main station 10 is configured to perform interference cancellation on a received signal including an uplink signal and an interference wave caused by a downlink signal by setting an FFT window having an OFDM symbol length of the downlink signal to match the symbol timing of the downlink, and to subtract an interference wave replica generated based on the result of the FFT processing from the received signal. The main station 10 is further configured to calculate the variance of all TMCC carriers in the received signal after interference cancellation for all combinations of the timing of the FFT window and the correction rotation number for correcting the phase rotation caused by the FFT window, and to perform demodulation processing of the uplink signal by applying the combination that minimizes the variance of all TMCC carriers.

[0067] This makes it possible to appropriately deal with phase rotation caused by the FFT window in the main station 10. Furthermore, since phase correction adapted to propagation delay can be automatically performed, manual input of propagation distance and delay can be eliminated, contributing to improved user convenience. In the second embodiment, the uplink signal is demodulated using a combination that minimizes the variance of all TMCC carriers. However, the uplink signal may be demodulated using a combination that minimizes the variance of all TMCC carriers. The reference value may be any value that ensures the accuracy of demodulation of the uplink signal. When there are multiple combinations that minimize or minimize the variance of all TMCC carriers, any combination may be selected. Alternatively, a combination with a larger correction rotation number may be preferentially selected, taking into account processing delays, etc.

[0068] [Third Embodiment] In the third method, some changes are required to the processing of the modulation unit 21 of the slave station 20 and the demodulation unit 15 of the master station 10. First, the processing of the modulation unit 21 of the slave station 20 according to the third embodiment (third method) will be described with reference to Fig. 13. Fig. 13 shows an example of the configuration of the modulation unit 21 of the slave station 20 according to the third embodiment (third method).

[0069] Uplink transmission data is input from outside to coding section 301. Coding section 301 performs error correction coding on the uplink transmission data and outputs the resulting bit string to mapping section 302. Mapping section 302 maps the input bit string onto the IQ plane and outputs the result to switching section 303.

[0070] The switching unit 303 also receives a preset known signal from the known signal unit 304, and outputs the known signal to the multiplexing unit 305 before communication is established between the master station 10 and the slave station 20, and outputs the signal from the mapping unit 302 to the multiplexing unit 305 after communication is established. In order for the slave station 20 to determine whether communication with the master station 10 has been established, a means is required to notify the slave station 20 of the reception status of the master station 10 using unused bits of the TMCC carrier, etc.; however, this is not the main focus of the present invention and therefore will not be described here.

[0071] The multiplexing unit 305 multiplexes the signal input from the switching unit 303 and the pilot signal input from the pilot unit 306, and outputs the result to an IFFT (Inverse Fast Fourier Transform) unit 307. The IFFT unit 307 converts the signal input from the multiplexing unit 305 into a time domain signal and outputs it to the high frequency transmission unit 22. By the above processing, a known signal is transmitted from the slave station 20 to the master station 10 before communication between the master station 10 and the slave station 20 is established.

[0072] Next, the processing of the demodulation unit 15 of the main station 10 according to the third embodiment (third method) will be described with reference to Fig. 14. Fig. 14 shows an example of the configuration of the demodulation unit 15 of the main station 10 according to the third embodiment (third method). The processing on the receiving side of the uplink line is largely the same as that of the first embodiment (first method) shown in Fig. 8, so the following description will focus on the differences.

[0073] Before communication between the master station 10 and the slave station 20 is established, the master station 10 receives a known signal from the slave station 20, and the master station 10 can use the known signal to calculate the DATA-MER. The demodulation unit 15 according to the third method has a DATA-MER calculation unit 401 that calculates the DATA-MER. The equalized received signal from the equalization unit 113 and a predetermined known signal from the known signal unit 402 are input to the DATA-MER calculation unit 401. This known signal is the same as the known signal transmitted from the modulation unit 21 of the slave station 20. The DATA-MER calculation unit 401 calculates the DATA-MER using the known signal input from the known signal unit 402 as an ideal reception point, and outputs the DATA-MER to the memory 118.

[0074] In the third method, calculation of TMCC-MER is not required, and other operations are the same as in the first method. The demodulator 15 of the master station 10 in the third method searches for the combination of FFT window timing and correction rotation number that maximizes DATA-MER, and performs reception processing using this as the optimal value. This makes it possible to determine the optimal FFT window timing and correction rotation number, allowing automatic and adaptive reception processing at any propagation distance, and enabling bidirectional transmission at the same frequency.

[0075] As described above, in the wireless communication system according to the third embodiment, the main station 10 is configured to perform interference cancellation on a received signal including an uplink signal and an interference wave caused by the downlink signal by setting an FFT window having an OFDM symbol length of the downlink signal to coincide with the symbol timing of the downlink, and to subtract an interference wave replica generated based on the result of the FFT processing from the received signal. The slave station 20 is configured to transmit the uplink signal by including a predetermined known signal in a data carrier before communication with the main station 10 is established. The main station 10 is further configured to calculate, before communication with the slave station 20 is established, the MER of the data carrier in the received signal after interference cancellation for all combinations of the timing of the FFT window and the correction rotation number for correcting the phase rotation caused by the FFT window, and to perform demodulation processing of the uplink signal using the combination that maximizes the MER of the data carrier after communication with the slave station 20 is established.

[0076] This makes it possible to appropriately deal with phase rotation caused by the FFT window in the main station 10. Furthermore, since phase correction adapted to propagation delay can be automatically performed, manual input of propagation distance and delay can be eliminated, contributing to improved user convenience. In the third embodiment, the demodulation process for the uplink signal is performed using a combination that maximizes the MER of the data carrier. However, the demodulation process for the uplink signal may also be performed using a combination that maximizes the MER of the data carrier. The reference value may be any value that ensures the accuracy of demodulation of the uplink signal. If there are multiple combinations that maximize or maximize the MER of the data carrier, any combination may be selected, or a combination with a larger correction rotation number may be preferentially selected, taking into account processing delays, etc.

[0077] Although the embodiments of the present invention have been described above, these embodiments are merely illustrative and do not limit the technical scope of the present invention. The present invention can take on various other embodiments, and various modifications such as omissions and substitutions can be made without departing from the spirit of the present invention. These embodiments and modifications thereof are included in the scope and spirit of the invention described in this specification, etc., and are included in the invention described in the claims and their equivalents.

[0078] Furthermore, the present invention can be provided not only as devices such as those described above or as systems composed of these devices, but also as methods executed by these devices, programs for realizing the functions of these devices using a processor, and storage media for storing such programs in a computer-readable manner.

[0079] The present invention can be applied to a wireless communication system that performs full-duplex wireless communication using OFDM as a modulation method.

[0080] 10: master station, 20: slave station, 11, 21: modulator, 12, 22: transmitter high frequency section, 13, 23: transmitter / receiver antenna, 14, 24: receiver high frequency section, 15, 25: demodulator, 101: FFT section, 102: window timing / correction rotation number control section, 103: TMCC demodulation / decoding section, 104: adder, 105: pilot separation section, 106: frame synchronization section, 107: TMCC decoding result memory, 108: TMCC mapping section, 109: TMCC-MER calculation section, 110: rotation section, 111: interference wave propagation path estimation filter, 112: interference replica generation section, 113: equalization section, 114: reverse rotation section, 115: TMCC extraction section, 116: desired wave propagation path estimation filter 117: Decoding unit, 118: Memory, 119: Optimum correction rotation speed calculation unit, 201: TMCC carrier dispersion calculation unit, 301: Encoding unit, 302: Mapping unit, 303: Switching unit, 304: Known signal unit, 305: Multiplexing unit, 306: Pilot unit, 307: IFFT unit, 401: DATA-MER calculation unit, 402: Known signal unit

Claims

1. A wireless communication system for performing full-duplex wireless communication in which the OFDM symbol length of an uplink signal from a slave station to a master station is set to N times the OFDM symbol length of a downlink signal in the reverse direction, wherein the master station performs FFT processing on a received signal including the uplink signal and an interference wave caused by the downlink signal by setting an FFT window of the OFDM symbol length of the downlink signal to match the symbol timing of the downlink, and subtracts an interference wave replica generated based on the result of the FFT processing from the received signal to perform interference cancellation, wherein the master station further calculates the MER of the TMCC carrier in the received signal after interference cancellation for all combinations of the timing of the FFT window and the number of correction rotations for correcting the phase rotation caused by the FFT window, and performs demodulation processing of the uplink signal by applying a combination in which the MER of the TMCC carrier is equal to or greater than a reference value or is at its maximum.

2. A wireless communication system for performing full-duplex wireless communication in which the OFDM symbol length of an uplink signal from a slave station to a master station is set to N times the OFDM symbol length of a downlink signal in the reverse direction, wherein the master station performs FFT processing on a received signal including the uplink signal and an interference wave caused by the downlink signal by setting an FFT window of the OFDM symbol length of the downlink signal to match the symbol timing of the downlink, and subtracts an interference wave replica generated based on the result of the FFT processing from the received signal to perform interference cancellation, wherein the master station further calculates the variance of all TMCC carriers in the received signal after interference cancellation for all combinations of the timing of the FFT window and the number of correction rotations for correcting the phase rotation caused by the FFT window, and performs demodulation processing of the uplink signal by applying a combination in which the variance of all TMCC carriers is equal to or less than a reference value or is at a minimum.

3. A wireless communication system for performing full-duplex wireless communication in which the OFDM symbol length of an uplink signal from a slave station to a master station is set to N times the OFDM symbol length of a downlink signal in the reverse direction, wherein the master station performs FFT processing on a received signal including the uplink signal and an interference wave caused by the downlink signal by setting an FFT window of the OFDM symbol length of the downlink signal to match the symbol timing of the downlink, and subtracts an interference wave replica generated based on the result of the FFT processing from the received signal to perform interference cancellation, wherein the slave station transmits a predetermined known signal included in the data carrier of the uplink signal before communication is established with the master station, and the master station further calculates the MER of the data carrier in the received signal after interference cancellation for all combinations of FFT window timing and correction rotation numbers for correcting phase rotation caused by the FFT window before communication is established with the slave station, and after communication with the slave station is established, performs demodulation processing of the uplink signal using a combination that makes the MER of the data carrier equal to or greater than a reference value or is at its maximum.

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