Coordinated wireless device and its program

Abstract

To provide a cooperative wireless apparatus that performs phase variation compensation for a radio wave propagation path.SOLUTION: A base station 20 includes: a propagation estimation part 222 that estimates radio wave propagation characteristics between a terminal 10 and the base station 20 on the basis of a training signal received from the terminal 10; a phase compensation part 225 that compensates data, transmitted to the terminal 10, by phase rotation of a carrier wave exhibited by the radio wave propagation characteristics; and a frequency conversion part 21 that transmits the data, compensated by the phase compensation part 225, to the terminal 10.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a cooperative wireless device using a wireless bidirectional time synchronization technique and a program thereof.

Background Art

[0002] Conventionally, cooperative wireless communication based on synchronization between base stations using a cable such as an optical fiber has been proposed (Non-Patent Document 1). This cooperative wireless communication improves the communication performance (such as throughput) at the terminal by coordinating signal transmission between base stations arranged dispersedly. For example, by controlling the signal transmitted from the base station so that radio waves can be received in phase at the terminal, the received signal power at the terminal can be significantly improved.

[0003] A typical conventional method as cooperative wireless communication is CoMP (Coordinated Multi-Point access) standardized by 3GPP (Non-Patent Document 2). In CoMP, the master base station generates the signals of the data transmitted from each base station, and after the master base station performs synchronization with each base station via a cable, each base station transmits the signal. Note that the master base station is one base station selected in advance from among each base station.

[0004] In this CoMP, cable laying work between base stations is required, and the costs required for the work and maintenance increase. For example, when temporarily installing a base station at a construction site, CoMP is considered unsuitable because of the high cost. Therefore, it is considered that the costs of work and maintenance can be reduced by using a wireless bidirectional time synchronization technique instead of laying a cable such as an optical fiber.

[0005] Note that the wireless bidirectional time synchronization technique, also called Wi-Wi (Wireless two-way interferometry), accurately synchronizes the times of wireless devices located at remote locations (Non-Patent Documents 3 to 5).

Prior Art Documents

Non-Patent Documents

[0006] [Non-Patent Document 1] NTT DOCOMO, "Outdoor Experiment of Downlink CoMP Coherent Joint Transmission Using Remote Radio Head in LTE-Advanced," 2013. [Non-Patent Document 2] 3GPP TR 36.741 V14.0.0, "Study on further enhancements to Coordinated Multi-Point (CoMP) Operation for LTE," Release 14, 2017. [Non-Patent Document 3] "Wireless Bidirectional Time Comparison Technology", [online], [searched on February 5, 2021], Internet <URL:https: / / www2.nict.go.jp / sts / tft / rsc_wiwi.html> [Non-Patent Document 4] "Spatio-Temporal Authentication Infrastructure", [online], [searched on February 5, 2021], Internet <URL:https: / / shingi.jst.go.jp / var / rev0 / 0000 / 4254 / 2016_kisoken1_3.pdfl> [Non-Patent Document 5] "Aiming at the Social Implementation of 6 Spatio-Temporal Standard Technologies", [online], [searched on February 5, 2021], Internet <URL:https: / / www.nict.go.jp / publication / shuppan / kihou-journal / houkoku65-2_HTML / 2019S-06-01(05-01).pdf> [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] However, in the above-mentioned hubbub, although the phase synchronization of the carrier frequency can be established between base stations, since the phase fluctuation compensation in the radio propagation path is not performed, it is difficult to improve the received signal power at the terminal.

[0008] Therefore, an object of the present invention is to provide a cooperative wireless device that performs phase fluctuation compensation in a radio propagation path and a program thereof.

Means for Solving the Problems

[0009] To solve the above problems, a cooperative wireless device according to the present invention uses a wireless bidirectional time synchronization technique to A cooperative radio device serving as a base station and synchronize the frequency of the carrier wave synchronization with with time and with other cooperative wireless devices, and is a cooperative wireless device in which the synchronization is established, a terminal a receiving device in the uplink from the terminal to the cooperative radio device a propagation estimation unit that estimates the radio propagation characteristics between the receiving device and the cooperative wireless device based on the received training signal, from the cooperative radio device a receiving device in the downlink to a phase compensation unit that compensates the data to be transmitted by the phase rotation indicated by the radio propagation characteristics, and a transmission unit that transmits the data compensated by the phase compensation unit to radio propagation path the receiving device in the downlink and is configured to include a control unit that determines whether to participate in cooperative radio by performing threshold processing on the time difference between a selected master cooperative radio device and the cooperative radio device from among other cooperative radio devices, and threshold processing on the received power of the training signal; them. , the propagation estimation unit presets a reference training signal in a frequency band not affected by radio propagation characteristics, and estimates the radio propagation characteristics for the frequency at which the training signal was transmitted based on the ratio between the training signal in the frequency band affected by radio propagation characteristics and the reference training signal. The transmission unit transmits data to the receiving device when the control unit determines that the device participates in cooperative radio According to such a configuration, the cooperative wireless device can estimate the radio propagation characteristics between the receiving device and the cooperative wireless device and perform phase fluctuation compensation in the radio propagation path.

[0010] In addition, the present invention can also be realized by a program for causing a computer to function as the above-mentioned cooperative wireless device.

[0011] In addition, the present invention can also be realized by a program for causing a computer to function as the above-mentioned cooperative wireless device.

Effects of the Invention

[0012] According to the present invention, phase fluctuation compensation in a radio propagation path can be performed.

Brief Description of the Drawings

[0013]

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Modes for Carrying Out the Invention

[0014] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. However, each embodiment described below is for embodying the technical idea of the present invention, and the present invention is not limited to the following unless specifically described. Also, the same means may be denoted by the same reference numerals, and the description may be omitted.

[0015] (First Embodiment) [Overall Configuration of Cooperative Wireless Communication System] With reference to FIGS. 1 to 4, the overall configuration of the cooperative wireless communication system 1 according to the first embodiment will be described. As shown in FIG. 1, the cooperative wireless communication system 1 includes a terminal 10, a plurality of base stations 20 (20 1 ~20 i ), and a plurality of modules 30 (30 1 ~30 i ). (However, i is a natural number of 2 or more.) Note that the module 30 is illustrated as "WiWi".

[0016] Here, in the present embodiment, as an example, it is assumed that the terminal 10 is a "reception device" and the base station 20 is a "cooperative wireless device". Therefore, the terminal 10 transmits a training signal to the base station 20 (uplink), and the base station 20 transmits data to the terminal 10 (downlink). Also, in the cooperative wireless communication system 1, only the base stations 20 1 ~20 i synchronize with WiWi, and the terminal 10 does not synchronize with WiWi. Also, in the cooperative wireless communication system 1, the frequency f of the line α used for WiWi Wi-Wi(For example, 920 MHz) and the frequency f of line β used for cooperative wireless communication com (For example, 2.5 GHz) are different (f Wi-Wi ≠ f com ).

[0017] The terminal 10 receives data from each base station 20 i . Further, the terminal 10 transmits a training signal for estimating the radio wave propagation characteristics between the terminal 10 and each base station 20 i to each base station 20 i . This terminal 10 is not particularly limited as long as it has a wireless communication function, and is a general computer, tablet, or smartphone.

[0018] The base station 20 performs cooperative wireless communication by performing phase fluctuation compensation in the radio wave propagation path on the premise that the synchronization of the carrier frequency and time (clock) is established using Wi-Fi. Here, the synchronization by Wi-Fi is established for the base station 20 by the module 30 described later. Further, the base station 20 performs phase fluctuation compensation in the radio wave propagation path using the training signal received from the terminal 10 and transmits data to the terminal 10. At this time, one of each base station 20 i (for example, base station 20 1 ) is preselected as the master base station. Then, the data stored in this master base station or the data determined in advance to be used during cooperative wireless communication is transmitted by each base station 20 i to the terminal 10. Note that each base station 20 i has the same configuration, and the details will be described later.

[0019] The module 30 is provided for each base station 20 i and establishes the synchronization of the carrier time and frequency by Wi-Fi. Here, one of each module 30 (for example, module 30 1 ) is used as the master module, and the rest (for example, module 30 2 ~30 iUse as the slave module. First, compare the carrier phases of the master module and the slave module, and adjust the frequency of the internal clock of the slave module so that the leading edges of the carrier phases of both are aligned (phase lock). Next, in the state where phase lock is established, exchange time information between the master module and the slave module, and adjust the time difference between the two. After that, module 30 outputs a reference frequency (for example, 10 MHz) to oscillator 21a and BBU 22, and outputs a reference time (for example, 1 PPS) to BBU 22.

[0020] Note that the overall configuration of the cooperative wireless communication system 1 is not limited to the example in FIG. 1. As shown in FIG. 2, the cooperative wireless communication system 1 includes a module 40 on the side of the terminal 10, and the base station 20 1 ~10 i and the terminal 10 may be synchronized peer-to-peer. This module 40 is the same as module 30. Thereby, the preamble signal section necessary for synchronizing the frequency and time (clock) in cooperative wireless communication, such as frame synchronization and frequency pulling-in by PLL, can be shortened. Note that in the cooperative wireless communication system 1 of FIG. 2, the peer-to-peer frequency f Wi-Wi and the cooperative wireless communication frequency f com are different (f Wi-Wi ≠f com ).

[0021] Also, as shown in FIG. 3, in the cooperative wireless communication system 1, the peer-to-peer frequency f Wi-Wi and the cooperative wireless communication frequency f com may be the same (f Wi-Wi =f com ). That is, the peer-to-peer frequency channel and the cooperative wireless communication frequency channel are shared. In this case, the training signal and data are multiplexed by time division or frequency division. Note that in the cooperative wireless communication system 1 of FIG. 3, only the base station 20 1 ~20 i is synchronized peer-to-peer, while the terminal 10 is not synchronized peer-to-peer.

[0022] Furthermore, as shown in FIG. 4, in the cooperative wireless communication system 1, the frequency f of Wi-Fi Wi-Wi and the frequency f of cooperative wireless communication com are the same (f Wi-Wi = f com ), and the base stations 20 1 ~10 i and the terminals 10 may be synchronized in Wi-Fi. In FIGS. 1 and 2, the base station 20 and the module 30 are separately illustrated, but similar to FIGS. 3 and 4, the base station 20 may incorporate the module 30.

[0023] <Overview of Phase Variation Compensation> Hereinafter, phase variation compensation in the radio propagation path will be described. As described above, in the cooperative wireless communication system 1, using Wi-Fi, synchronization of the carrier frequency and time (clock) can be established at each of the distributed base stations 20 i . And in the cooperative wireless communication system 1, for performing cooperative wireless communication (amplitude-combined reception of radio waves at the terminal 10) using a plurality of base stations 20 i , each base station 20

[0024] First, each base station 20 i estimates the radio propagation characteristics using the training signal received from the terminal 10 in a wireless frame configuration in which the time and frequency are synchronized in Wi-Fi. The radio propagation characteristics H i (f) with respect to the frequency f is represented by the following equation (1). Therefore, the i-th base station 20 i calculates an estimated value H^ i (f) of the radio propagation characteristics H i (f) using the following equation (2). Note that a i (f) is the amplitude, e z is the exponential function with respect to z, j is the imaginary unit, p i (f) is the phase, and ^ represents the estimated value.

[0025]

Equation

Equation

[0026] Each base station 20 i transmits data X to the terminal 10 so that the terminal 10 can receive by amplitude synthesis D (f) with the radio wave propagation characteristic H i and the phase p of i (f). The compensated data X´ D,i (f) is represented by the following formula (3).

[0027] [Number]

[0028] Here, if p i (f) = p^ i (f), the received signal R(f) of the terminal 10 is represented by the following formula (4).

[0029] [Number]

[0030] Assuming |X D (f)| = 1 as in phase modulation, since the received signal power is represented by the following formula (5), it can be seen that amplitude synthesis reception is performed at the terminal 10 by this cooperative wireless communication.

[0031] [Number]

[0032] Thus, in order to perform amplitude synthesis reception at the terminal 10, it is sufficient that p i (f) = p^ i (f) holds. That is, it is sufficient to minimize the phase difference between the true value phase p i (f) and the estimated value phase p^ i (f).

[0033] [Configuration of Terminal] Referring to FIG. 5, the configuration of the terminal 10 will be described. As shown in FIG. 5, the terminal 10 includes a frequency conversion unit 11 and a BBU (Base Band Signal Processing Unit) 12. Further, when synchronizing with Wi-Fi, the terminal 10 may include a module 40 (not shown in FIG. 5).

[0034] The frequency conversion unit 11 converts a baseband signal used for communication with each base station 20 i into a carrier frequency band (at the time of transmission), or performs the inverse conversion (at the time of reception). For example, the frequency conversion unit 11 includes an oscillator 11a and a mixer unit 11b. Here, the oscillator 11a generates a carrier wave of frequency f com . Further, the mixer unit 11b transmits the training signal input from the training signal generation unit 120 by riding on the carrier wave. Furthermore, the frequency conversion unit 11 outputs the data signal received by each base station 20 i to the demodulation unit 121.

[0035] The BBU 12 processes baseband signals and includes a training signal generation unit 120 and a demodulation unit 121.

[0036] The training signal generation unit 120 generates a training signal x T (n) for the base station 20 to estimate the radio wave propagation characteristics. Here, n indicates time (time domain). Here, the training signal generation unit 120 may generate a commonly used training signal.

[0037] For example, as shown in FIG. 6, consider the case of single-carrier transmission capable of time-division multiplexing. In this case, the training signal generation unit 120 may generate a signal having a complex constant envelope waveform such as a Zadoff-Chu sequence as the training signal x T (n). In FIG. 6, "T" represents a training signal and "D" represents data. Further, for example, as shown in FIG. 7, consider the case of OFDM transmission capable of time-division multiplexing and frequency-division multiplexing. In this case, the training signal generation unit 120 is a training signal X TAs (n), a signal of a complex envelope waveform or a signal of a pseudo-random sequence such as an M-sequence may be generated.

[0038] Here, by the terminal 10 transmitting the same training signal x T (n) to all the base stations 20, the radio wave propagation characteristics H i (f) can be efficiently estimated. On the other hand, the terminal 10 may transmit the training signal x i for each base station 20 and estimate the radio wave propagation characteristics H T (f). i In the case of MIMO transmission using a plurality of antennas, in order to estimate the radio wave propagation characteristics between the plurality of antenna terminals, different training signals x T (n) may be transmitted for each antenna.

[0039] The demodulation unit 121 demodulates the data received by the frequency conversion unit 11 by a general method (for example, M-value QAM). Here, since amplitude synthesis reception is performed on the data input to the demodulation unit 121, it is represented by the following equation (6) as the signal obtained by converting the signal of equation (4) into the time domain. Then, the demodulation unit 121 outputs the data d~ D (k) by demodulating the data represented by equation (6). Note that c i (n) is the amplitude in the time domain, and k indicates the order of the bit sequence.

[0040]

Equation

[0041] [Configuration of Base Station] With reference to FIG. 5, the configuration of the base station 20 will be described. As shown in FIG. 5, the base station 20 includes a frequency conversion unit (transmission unit) 21, a BBU 22, and a control unit 23. As described above, it is assumed that the i base stations 20 i have the same configuration. Also, in FIG. 5, for ease of viewing the drawing, the illustration of the module 30 is omitted.

[0042] The frequency conversion unit 21 converts a baseband signal used in communication with the terminal 10 into a carrier frequency band (during transmission), or performs the reverse conversion (during reception). For example, it includes an oscillator 21a and a mixer unit 21b. Here, the oscillator 21a generates a carrier wave with a frequency f com according to the reference frequency input from the module 30. Also, the mixer unit 21b multiplies the data x D (n - δ i ) by the carrier wave and transmits it. Further, the frequency conversion unit 21 converts the training signal in the carrier wave band received by the terminal 10 into a baseband signal, and outputs it as the training signal x T,i (n) to the delay measurement unit 220.

[0043] The BBU 22 processes the baseband signal. For example, the BBU 22 includes a delay measurement unit 220, an FFT unit 221, a propagation estimation unit 222, a modulation unit 223, an FFT unit 224, a phase compensation unit 225, an IFFT unit 226, and a delay unit 227.

[0044] The delay measurement unit 220 measures the delay time Δ i including the propagation delay between the terminal 10 and each base station 20 T,i using the training signal x i (n) received at each base station 20 i . Here, since the time of each base station 20 i is synchronized by the module 30 of the base station, by presetting the measurement start time of the delay time Δ i among all the base stations 20 i , the difference in the time when the training signal x T,i (n) is received at each base station 20 i becomes the delay time Δ i . Then, the delay measurement unit 220 outputs the measured delay time Δ T,i to the delay unit 227, and outputs the training signal x

[0045] (n) from the frequency conversion unit 11 to the FFT unit 221.The FFT unit 221 converts the training signal x in the time domain into a training signal X in the frequency domain through a general time-frequency conversion process. T,i (n) is converted into a training signal X in the frequency domain. T,i (f). For example, as the time-frequency conversion process, the Fast Fourier Transform (FFT) can be mentioned. Then, the FFT unit 221 outputs the training signal X in the frequency domain. T,i (f) to the propagation estimation unit 222.

[0046] Based on the training signal X input from the FFT unit 221, the propagation estimation unit 222 estimates the radio wave propagation characteristics H between the terminal 10 and the base station 20i. T,i (f). Here, the propagation estimation unit 222 can estimate the radio wave propagation characteristics H by a general method, and an example will be described. i (f), and an example thereof will be described. i (f).

[0047] First, the propagation estimation unit 222 presets a reference training signal X that is not affected by the radio wave propagation characteristics H. i (f). Next, the propagation estimation unit 222 estimates the radio wave propagation characteristics H based on the ratio between the training signal X affected by the radio wave propagation characteristics H and the reference training signal X. T (f). i (f) and the reference training signal X. T,i (f). T (f). i (f).

[0048] As shown in FIG. 6, when the training signal X uses the entire frequency channel (in the case of time-division multiplexing), the propagation estimation unit 222 estimates the radio wave propagation characteristics H using the following equation (7). That is, for the frequency f at which the terminal 10 transmits the training signal X, the propagation estimation unit 222 estimates the radio wave propagation characteristics H from the ratio between the training signal X and the reference training signal X. T,i (f), the propagation estimation unit 222 estimates the radio wave propagation characteristics H using the following equation (7). That is, for the frequency f at which the terminal 10 transmits the training signal X. i (f), the propagation estimation unit 222 estimates the radio wave propagation characteristics H. T,i (f), the propagation estimation unit 222 estimates the radio wave propagation characteristics H from the ratio between the training signal X and the reference training signal X. T,i (f) and the reference training signal X. T (f). i (f), and the estimated value H of the radio wave propagation characteristics H. iObtain ^(f).

[0049]

Number

[0050] As shown in FIG. 7, for the training signal X T,i (f), when using a part of the frequency channels (in the case of frequency division multiplexing such as OFDM transmission), the propagation estimation unit 222 estimates the radio wave propagation characteristics H i (f) using the following formula (8). That is, for the frequency f T,i at which the terminal 10 transmits the training signal X S (f), the propagation estimation unit 222 obtains the estimated value H T,i (f) of the radio wave propagation characteristics H T (f) from the ratio between the training signal X i (f S ) and the reference training signal X i ^(f S ). Also, for the frequency f T,i at which the terminal 10 is not transmitting the training signal X G (f), the propagation estimation unit 222 linearly interpolates using the estimated values H i (f H ) and H i (f L ) of the radio wave propagation characteristics H i ^(f H ) and H i ^(f L ). Note that f H represents the lowest frequency among the frequencies at which the radio wave propagation characteristics H S (f) are estimated at frequencies higher than the frequency f i . Also, f L represents the highest frequency among the frequencies at which the radio wave propagation characteristics H S (f) are estimated at frequencies lower than the frequency f i .

[0051]

Number

[0052] After that, the propagation estimation unit 222 outputs the estimated radio wave propagation characteristics H i (f) to the phase compensation unit 225.

[0053] The modulation unit 223 modulates the data d D (k) to be transmitted to the terminal 10 by a general method (for example, M - value QAM) to generate the time - domain data x D (n). Then, the modulation unit 223 outputs the time - domain data x D (n) to the FFT unit 224.

[0054] The FFT unit 224 converts the time - domain data x D (n) input from the modulation unit 223 into the frequency - domain data X D (f) by a general time - frequency conversion process. For example, the time - frequency conversion process includes the above - mentioned FFT. Then, the FFT unit 224 outputs the frequency - domain data X D (f) to the phase compensation unit 225.

[0055] The phase compensation unit 225 compensates the data X D (f) input from the FFT unit 224 by the phase rotation in the radio wave propagation path indicated by the estimated value H i (f) of the radio wave propagation characteristics H i ^(f). Specifically, the phase compensation unit 225 substitutes the data X D (f) before compensation and the phase p i (f) of the estimated value H i ^(f) of the radio wave propagation characteristics H i ^(f) into the above - mentioned formula (3) to calculate the compensated data X´ D,i (f). That is, the phase compensation unit 225 uses the formula (3) to pre - cancel the phase rotation added by radio wave propagation to compensate the data X D (f). Then, the phase compensation unit 225 outputs the compensated data X´ D,i (f) to the IFFT unit 226.

[0056] The IFFT unit 226 converts the frequency domain data X' input from the phase compensation unit 225 into a digital signal by a general time-frequency inverse transform process. D,i (f) is the time domain data x´ D,i For example, the time-frequency inverse transform process may be an inverse fast Fourier transform (IFFT). The IFFT unit 226 converts the time domain data x' D,i (n) is output to the delay unit 227.

[0057] The delay unit 227 measures the delay time Δ i In response to the above, data x' input from the IFFT unit 226 D,i For example, the delay unit 227 delays the delay time Δ i Only data x' D,i (n) is delayed and the delayed data x' D,i (n-δ i ) to the frequency conversion unit 11. i =Δ-Δ i holds true.

[0058] As shown in FIG. 8, in the amplitude combining reception, the terminal 10 receives the i Each data x' from D,i To add (n), each data x´ D,i If the reception timing of (n) is shifted, a loss of reception power occurs. Therefore, the delay unit 227 delays each data x' D,i (n) reception timing is synchronized with time δ i (δ 1 , δ 2 ,…,δ i ), the loss of received power is suppressed. This allows the base station 20 to perform phase synchronization over the entire data signal even when transmitting a discrete data sequence.

[0059] Returning to FIG. 5, the description of the configuration of base station 20 will continue. The control unit 23 performs various controls on the BBU 22. Specifically, the control unit 23 determines whether to participate in cooperative radio through threshold processing of the time difference between the master base station and the base station 20 i and threshold processing of the received power of the training signal. Then, the control unit 13 controls the data transmission by the BBU 12 based on the determination result. Note that the details of the control unit 13 will be described later.

[0060] <Cooperative Radio Communication between Terminal and Base Station> With reference to FIGS. 10 to 12, the cooperative radio communication between the terminal 10 and the base station 20 will be described. Note that in FIGS. 10 to 12, "synchronization" is synchronization by Wi-Fi, "T" is a training signal, and "D" represents data.

[0061] In FIG. 10, it is assumed that the frequency f of Wi-Fi Wi-Wi is different from the frequency f of the cooperative radio communication. In this case, in the cooperative radio communication system 1, after the synchronization by Wi-Fi is completed, the terminal 10 transmits a training signal to each base station 20 com on the uplink, and each base station 20 i measures the radio wave propagation characteristics. Then, in the cooperative radio communication system 1, each base station 20 i transmits data to the terminal 10 on the downlink. i

[0062] In FIG. 11, it is assumed that the frequency f of Wi-Fi Wi-Wi is the same as the frequency f of the cooperative radio communication, and time-division multiplexing is performed. In this case, in the cooperative radio communication system 1, after the synchronization by Wi-Fi is completed, the terminal 10 transmits a training signal to each base station 20 com and each base station 20 i measures the radio wave propagation characteristics. Then, in the cooperative radio communication system 1, each base station 20 i transmits data to the terminal 10. i

[0063] In FIG. 12, it is assumed that the frequency f of Wi-Fi Wi-Wi is different from the frequency f of the cooperative radio communication. com ​​are the same, and frequency division multiplexing and time division multiplexing are to be performed. In this case, in the cooperative wireless communication system 1, simultaneously with the synchronization by Wi-Fi, each base station 20 i transmits data to the terminal 10. Thereafter, in the cooperative wireless communication system 1, the terminal 10 transmits a training signal to each base station 20 i , and each base station 20 i measures the radio wave propagation characteristics. Note that the cooperative wireless communication between the terminal 10 and the base station 20 is not limited to the examples in FIGS. 10 to 12.

[0064] [Operation of Cooperative Wireless Communication System] Referring to FIG. 13, the operation of the cooperative wireless communication system 1 will be described. In step S1, each base station 20 i establishes synchronization by Wi-Fi with reference to the master base station. Here, when the terminal 10 includes the module 40, the terminal 10 may also establish synchronization by Wi-Fi. In step S2, the terminal 10 transmits a training signal to each base station 20 i .

[0065] In step S3, each base station 20 i determines, by the control unit 23, whether synchronization by Wi-Fi has been established. Specifically, the control unit 23 determines whether the time difference between the master base station and each base station 20 i is less than a preset threshold. Note that the master base station does not have to perform the process of step S3.

[0066] When the time difference is equal to or greater than the threshold (No in step S3), the control unit 23 determines that synchronization by Wi-Fi has not been established, and proceeds to the process of step S6. When the time difference is less than the threshold (Yes in step S3), the control unit 23 determines that synchronization by Wi-Fi has been established, and proceeds to the process of step S4.

[0067] In step S4, each base station 20 iThe control unit 23 determines whether the estimation of the radio wave propagation characteristics has been successful. Specifically, the control unit 23 determines whether the received power of the training signal is equal to or greater than a preset threshold value.

[0068] If the received power of the training signal is less than the threshold value (No in step S4), the control unit 23 determines that the estimation of the radio wave propagation characteristics has not been successful, and proceeds to the process of step S6. If the received power of the training signal is equal to or greater than the threshold value (Yes in step S4), the control unit 23 determines that the estimation of the radio wave propagation characteristics has been successful, and proceeds to the process of step S5.

[0069] In step S5, each base station 20 i transmits data to the terminal 10 by the frequency conversion unit 21 in coordinated wireless communication, and ends the process. In step S6, each base station 20 i does not participate in the coordinated wireless communication, so it ends the process without transmitting data to the terminal 10.

[0070] [Operation and Effect] As described above, the coordinated wireless communication system 1 according to the first embodiment can estimate the radio wave propagation characteristics between the terminal 10 and the base station 20, and perform phase fluctuation compensation in the radio wave propagation path. Thereby, in the coordinated wireless communication system 1, laying of a cable such as an optical fiber becomes unnecessary, and the cost required for the construction and maintenance can be suppressed. For example, the coordinated wireless communication system 1 can provide stable coordinated wireless communication even in an environment where the radio wave propagation characteristics are likely to change, such as remote control of a robot moving near the ground.

[0071] (Second Embodiment) [Overall Configuration of the System] Referring to FIGS. 14 and 15, the differences from the first embodiment will be described with respect to the overall configuration of the coordinated wireless communication system 1B according to the first embodiment. In the cooperative wireless communication system 1B, it is different from the first embodiment in that the base station 50 transmits a training signal to the terminal 70 and the terminal 70 transmits data to the base station 50. In this embodiment, it is assumed that the base station 50 is a "reception device" and the terminal 70 is a "cooperative wireless device".

[0072] As shown in FIG. 14, the cooperative wireless communication system 1B includes a base station 50, a module 60, a plurality of terminals 70 (70 1 ~70 i ), and a plurality of modules 80 (80 1 ~80 i ), where i is a natural number of 2 or more.

[0073] Here, in the cooperative wireless communication system 1B, the base station 50 and the terminal 70 1 ~70 i are to be synchronized in a wireless manner. Also, in the cooperative wireless communication system 1B, the frequency f Wi-Wi of the line α used in the wireless connection and the frequency f com of the line β used in the cooperative wireless communication are different (f Wi-Wi ≠f com ). As a result, it is possible to shorten the preamble signal section necessary for synchronizing the frequency and time (clock) in the cooperative wireless communication, such as frame synchronization and frequency pulling-in by PLL.

[0074] The base station 50 receives data from each terminal 70 i . Also, the base station 50 transmits a training signal for estimating the radio wave propagation characteristics between the base station 50 and each terminal 70 i to each terminal 70 i .

[0075] The module 60 is provided to correspond to the base station 50 and establishes synchronization of the carrier frequency and time (clock) by wireless connection. Since the synchronization of the carrier frequency and time (clock) by wireless connection is the same as in the first embodiment, further explanation is omitted.

[0076] Assuming that the terminal 70 has established synchronization of the carrier frequency and time (clock) using WiWi, it performs phase fluctuation compensation in the radio propagation path to conduct cooperative wireless communication. Here, the synchronization by WiWi for the terminal 70 is established by the module 80. Also, the terminal 70 uses the training signal received from the base station 50 to perform phase fluctuation compensation in the radio propagation path and transmits data to the base station 50. At this time, among each terminal 70 i one unit (for example, terminal 70 1 ) is preselected as the master terminal. Then, the data stored in this master terminal or the data predetermined to be used during cooperative wireless communication is transmitted by each terminal 70 i to the base station 50. Note that each terminal 70 i is assumed to have the same configuration, and the details will be described later.

[0077] The module 80 is provided for each terminal 70 i and establishes synchronization of the carrier time and frequency by WiWi. Here, the module 60 provided in the base station 50 is used as the master module, and the module 80 provided in the terminal 70 is used as the slave module. Since the synchronization of the carrier frequency and time (clock) by WiWi is the same as that in the first embodiment, further description thereof is omitted.

[0078] In FIG. 14, the base station 50 and the module 60 are separately illustrated, but the base station 50 may incorporate the module 60. Also, in FIG. 14, the terminal 70 and the module 80 are separately illustrated, but the terminal 70 may incorporate the module 80.

[0079] The overall configuration of the cooperative wireless communication system 1B is not limited to the example in FIG. 14. As shown in FIG. 15, in the cooperative wireless communication system 1B, the frequency f of the line α used in WiWi Wi-Wi and the frequency f of the line β used in cooperative wireless communication com may be the same (f Wi-Wi = f com) That is, the frequency channels of Wi-Fi and the frequency channels of cooperative wireless communication are shared. In this case, training signals and data are multiplexed by time division or frequency division. In the cooperative wireless communication system 1B of FIG. 15, the base station 50 and the terminal 70 1 ~70 i are synchronized in Wi-Fi.

[0080] [Configuration of Base Station] Referring to FIG. 16, the configuration of the base station 50 will be described. In FIG. 16, for ease of viewing the drawing, the illustration of the modules 60 and 80 is omitted.

[0081] As shown in FIG. 16, the base station 50 includes a frequency conversion unit 51 and a BBU 52. The frequency conversion unit 51 converts a baseband signal used in communication with each terminal 70 i into a carrier frequency band (at the time of transmission), or performs the inverse conversion (at the time of reception). For example, it includes an oscillator 51a and a mixer unit 51b. The BBU 52 processes the baseband signal and includes a training signal generation unit 520 and a demodulation unit 521. Note that since each means of the base station 50 is the same as that of the terminal 10 in FIG. 5, further description is omitted.

[0082] [Configuration of Terminal] Referring to FIG. 16, the configuration of the terminal 70 will be described. As shown in FIG. 16, the terminal 70 includes a frequency conversion unit 71, a BBU 72, and a control unit 73. The frequency conversion unit 71 converts a baseband signal used in communication with the base station 50 into a carrier frequency band (at the time of transmission), or performs the inverse conversion (at the time of reception). For example, it includes an oscillator 71a and a mixer unit 71b. The BBU 72 processes the baseband signal. For example, the BBU 72 includes a delay measurement unit 720, an FFT unit 721, a propagation estimation unit 722, a modulation unit 723, an FFT unit 724, a phase compensation unit 725, an IFFT unit 726, and a delay unit 727. Note that since each means of the terminal 70 is the same as that of the base station 20 in FIG. 5, further description thereof will be omitted.

[0083] [Operation of Cooperative Wireless Communication System] Referring to FIG. 17, the operation of the cooperative wireless communication system 1B will be described. In step S10, each terminal 70 i establishes synchronization by WiWi with reference to the master module (module 60 provided in the base station 50). In step S11, the base station 50 transmits a training signal to each terminal 70 i .

[0084] In step S12, each terminal 70 i determines whether synchronization by WiWi has been established by the control unit 73. Specifically, the control unit 73 determines whether the time difference between the master terminal and each terminal 70 i is less than a preset threshold. Note that the master terminal does not necessarily need to perform the process of step S12.

[0085] When the time difference is equal to or greater than the threshold (No in step S12), the control unit 73 determines that synchronization by WiWi has not been established and proceeds to the process of step S15. When the time difference is less than the threshold (Yes in step S12), the control unit 73 determines that synchronization by WiWi has been established and proceeds to the process of step S13.

[0086] In step S13, each terminal 70 i determines whether the estimation of radio wave propagation characteristics has been successful by the control unit 73. Specifically, the control unit 73 determines whether the received power of the training signal is equal to or greater than a preset threshold.

[0087] When the received power of the training signal is less than the threshold (No in step S13), the control unit 73 determines that the estimation of radio wave propagation characteristics has not been successful and proceeds to the process of step S15. When the received power of the training signal is equal to or greater than the threshold value (Yes in step S13), the control unit 73 determines that the estimation of the radio wave propagation characteristics has been successful and proceeds to the process of step S14.

[0088] In step S14, each terminal 70 i transmits data to the base station 50 by means of cooperative wireless communication by the frequency conversion unit 71, and ends the process. In step S15, since each terminal 70 i does not participate in the cooperative wireless communication, it ends the process without transmitting data to the base station 50.

[0089] [Operation and Effect] As described above, the cooperative wireless communication system 1B according to the second embodiment can estimate the radio wave propagation characteristics between the base station 50 and the terminal 70 and perform phase fluctuation compensation in the radio wave propagation path. Thereby, in the cooperative wireless communication system 1B, laying of cables such as optical fibers becomes unnecessary, and the costs required for the construction and maintenance thereof can be suppressed. For example, the cooperative wireless communication system 1B can provide stable cooperative wireless communication even in an environment where the radio wave propagation characteristics are likely to change, such as remote control of a robot moving near the ground.

[0090] Although each embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiments, and also includes design changes and the like within the scope not departing from the gist of the present invention. In each of the above-described embodiments, it has been described as performing cooperative wireless communication, but the present invention is not limited thereto. For example, the present invention can be applied not only to wireless communication but also to wireless power transmission. In this case, since the present invention significantly improves the received signal power, it becomes a highly efficient wireless power transmission method, leading to the realization of a battery-less wireless terminal not found in the prior art.

[0091] In each of the above-described embodiments, the cooperative wireless device has been described as independent hardware, but the present invention is not limited thereto. For example, the cooperative wireless device can also be realized by a three-dimensional model generation program that causes hardware resources such as a CPU, a memory, and a hard disk included in a computer to cooperate as each of the above-described means. This program may be distributed via a communication line, or may be written on a recording medium such as a CD-ROM or a flash memory and distributed.

Example

[0092] Referring to FIG. 18, as an example, the result of simulating the received signal power of the cooperative wireless communication system according to the present invention will be described.

[0093] An evaluation by computer simulation was performed on a cooperative wireless communication system composed of three base stations. The radio wave propagation model was a free space model. The synchronization deviation (jitter) in Wi-Fi synchronization was based on measured values. A training signal of a cyclic extended Zadoff-Chu sequence and the protocol by time-division multiplexing in FIG. 10 were used. The frequency f of the cooperative wireless communication com was set to 2 GHz. Under these conditions, the received signal power of a terminal at an equal distance of 50 m from the base station was evaluated.

[0094] As shown in FIG. 18, the average value at the time of conventional power combination was -15.2 dBm. On the other hand, in the cooperative wireless communication system according to the present invention, the average value of the received signal power could be improved to -10.6 dBm. The difference between the two is 4.6 dB (= 2.88), and since the difference at the time of ideal amplitude combination is 4.8 dB (= 3.00), it was found that ideal characteristics can be obtained in the cooperative wireless communication system according to the present invention.

Explanation of Signs

[0095] 1,1B Cooperative wireless communication system 10 Terminal (reception device) 11 Frequency conversion unit 11a Oscillator 11b Mixer unit 12 Baseband Signal Processing Unit 120 Training Signal Generation Unit 121 Demodulation Unit 20 (20 1 ~20 i ) Base Station (Cooperative Radio Device) 21 Frequency Conversion Unit (Transmission Unit) 21a Oscillator 21b Mixer Unit 22 Baseband Signal Processing Unit 220 Delay Measurement Unit 221 FFT Unit 222 Propagation Estimation Unit 223 Modulation Unit 224 FFT Unit 225 Phase Compensation Unit 226 IFFT Unit 227 Delay Unit 23 Control Unit 30 (30 1 ~30 i ) Module 40 Module 50 Base Station (Receiving Device) 51 Frequency Conversion Unit 52 BBU 51a Oscillator 51b Mixer Unit 520 Training Signal Generation Unit 521 Demodulation Unit 60 Module 70 (70 1 ~70 i ) Terminal (Cooperative Radio Device) 71 Frequency Conversion Unit (Transmission Unit) 71a Oscillator 71b Mixer Unit 72 BBU 720 Delay Measurement Unit 721 FFT Unit 722 Propagation Estimation Unit 723 Modulation Unit 724 FFT Unit 725 Phase Compensation Unit 726 IFFT Unit 727 Delay Unit 73 Control Unit 80(80 1 ~80 i ) Module

Claims

1. A cooperative radio device in which frequency synchronization and time synchronization of a carrier wave are established between a cooperative radio device as a base station and other cooperative radio devices using a wireless bidirectional time synchronization technique, a propagation estimation unit that estimates radio wave propagation characteristics between the receiving device and the cooperative radio device based on a training signal received on an uplink from the receiving device, which is a terminal, to the cooperative radio device; a phase compensation unit that compensates data transmitted on a downlink from the cooperative radio device to the receiving device with a phase rotation of a radio wave propagation path indicated by the radio wave propagation characteristics; a transmission unit that transmits the data compensated by the phase compensation unit to the receiving device on the downlink; a control unit that determines whether to participate in cooperative radio by performing threshold processing on the time difference between one master cooperative radio device preselected from among the other cooperative radio devices and the cooperative radio device, and threshold processing on the received power of the training signal; comprising: the propagation estimation unit pre-sets a reference training signal in a frequency band not affected by the radio wave propagation characteristics, and estimates the radio wave propagation characteristics for the frequency at which the training signal was transmitted based on the ratio between the training signal in the frequency band affected by the radio wave propagation characteristics and the reference training signal; the transmission unit is characterized in that, when the control unit determines that the cooperative radio participates, the transmission unit transmits the data to the receiving device. A cooperative radio device.

2. a delay measurement unit that measures a delay time using the training signal; further comprising a delay unit that delays the data compensated by the phase compensation unit according to the delay time measured by the delay measurement unit, the transmission unit is characterized in that the transmission unit transmits the data delayed by the delay unit to the receiving device. The cooperative radio device according to claim 1.

3. A program for causing a computer to function as the cooperative radio device according to claim 1 or claim 2.

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