Communication control method and distributed antenna system

Abstract

Provided is a communication control method executed by a distributed antenna system that controls coherent transmission between a terminal and a plurality of distributed antennas that cooperatively execute coherent transmission, the terminal executing communication with a signal processing device or an upper-level signal processing device via the plurality of distributed antennas. The communication control method includes a step for estimating, for each of the plurality of distributed antennas: a propagation delay difference, at the terminal, for propagation between the signal processing device or the upper-level signal processing device and the terminal in accordance with a propagation delay between the signal processing device or the upper-level signal processing device and the terminal; or a propagation delay difference, at the terminal, for propagation between the plurality of distributed antennas and the terminal in accordance with a propagation delay between the signal processing device or the upper-level signal processing device and each of the plurality of distributed antennas, and a propagation delay between each of the plurality of distributed antennas and the terminal. The communication control method further includes a step for controlling a transmission time for each of the distributed antennas such that the propagation delay difference estimated for each of the distributed antennas is within an allowable delay difference.

Description

Communication control method and distributed antenna system

[0001] The present invention relates to a communication control method and a distributed antenna system.

[0002] In a cellular system, a base station may be located for each cell defined within a wireless communication area. Each base station includes a signal processing device and an antenna. Each base station communicates with terminals within the cell in which it is located, using the signal processing device and antenna. Here, wireless signals arriving at the base station's cell from other cells may cause interference, degrading the communication quality for terminals near the border of the base station's cell.

[0003] In contrast, in a distributed antenna system, multiple antennas (distributed antennas) connected to a signal processing device are distributed and placed in a wireless communication area. In a distributed antenna system, the distributed antennas cooperate to perform coherent transmission, which makes it possible to reduce interference between wireless signals between the distributed antennas.

[0004] When a terminal is equipped with multiple terminal antennas, the multiple distributed antennas cooperate to perform coherent transmission, and SU-MIMO (Single User-Multiple Input Multiple Output) is performed between the multiple distributed antennas and the multiple terminal antennas, thereby making it possible to improve the transmission speed. In addition, since wireless signals arrive at the terminal antenna from multiple distributed antennas, spatial correlation is reduced, and it is expected that the transmission speed will be further improved.

[0005] 16 is a diagram showing an example of the configuration of a distributed antenna system 100. The distributed antenna system 100 includes a communication control device 200, a signal processing device 300, N (N is an integer equal to or greater than 2) distributed antennas 400, and one or more terminals 500. The communication control device 200 includes a selection unit and a control unit. The terminal 500 includes M (M is an integer equal to or greater than 1) terminal antennas 501. The multiple distributed antennas 400 cooperate to perform coherent transmission.

[0006] 17 is a sequence diagram showing an example of operation of the distributed antenna system 100. The selection unit selects a terminal 500 that receives a coherently transmitted radio signal (step S11). The selection unit selects a plurality of distributed antennas 400 that perform coherent transmission from all of the distributed antennas 400 connected to the signal processing device 3 (step S12). The control unit coherently transmits the radio signal from the selected plurality of distributed antennas 400 to the terminal 500 (step S13). Furthermore, Non-Patent Document 1 discloses a distributed antenna system that communicates using radio signals in a high-frequency band.

[0007] In wireless communications, multipath interference such as reflected waves can cause delayed waves to occur relative to the direct wave. At a terminal receiving a delayed wave, inter-symbol interference degrades communication quality. To prevent this degradation in communication quality, a guard interval (GI) is sometimes added to the signal. Inter-symbol interference can be prevented within the time it takes for the guard interval to arrive.

[0008] Furthermore, even in an environment where a delayed wave arrives at a terminal later than the time it takes for the guard interval to arrive at the terminal, Orthogonal Frequency Dimension Modulation (OFDM) reduces the symbol rate to prevent degradation of communication quality due to inter-symbol interference. Thus, there exists an allowable delay time that satisfies a predetermined communication quality.

[0009] Daisei Uchida and 11 others, "A Study on High-Frequency Distributed Antenna Systems in Terminal-Dense / Shielded Environments," Institute of Electronics, Information and Communication Engineers General Conference, Proceedings of the Communications Lecture Series 1, B-5-87, p. 375, March 2020

[0010] In a distributed antenna system, multiple antennas are distributed and placed in a wireless communication area. Therefore, when multiple antennas cooperate to perform coherent transmission, the difference in propagation delay of wireless signals is larger than the difference in propagation delay of wireless signals in coherent transmission between one base station and one terminal.

[0011] The larger the propagation delay difference, the higher the possibility of inter-symbol interference, which deteriorates the quality of received communication. Thus, a distributed antenna system has the problem of being unable to suppress the deterioration of communication quality due to inter-symbol interference.

[0012] In view of the above circumstances, an object of the present invention is to provide a communication control method and a distributed antenna system that can suppress deterioration of communication quality due to inter-symbol interference.

[0013] One aspect of the present invention is a communication control method executed by a distributed antenna system that controls coherent transmission between a terminal that communicates with one or more signal processing devices or upper signal processing devices via a plurality of distributed antennas that cooperatively perform coherent transmission and the plurality of distributed antennas, the communication control method including the steps of: estimating, for each distributed antenna among the plurality of distributed antennas, a propagation delay difference at the terminal between one or more of the signal processing devices or the upper signal processing devices and the terminal, in accordance with a propagation delay between one or more of the signal processing devices or the upper signal processing devices and the terminal, or estimating a propagation delay difference at the terminal between the plurality of distributed antennas and the terminal, in accordance with a propagation delay between one or more of the signal processing devices or the upper signal processing devices and the terminal, and controlling a transmission time for each of the distributed antennas so that the propagation delay difference estimated for each of the distributed antennas is within a tolerable delay difference.

[0014] One aspect of the present invention is a distributed antenna system that controls coherent transmission between a terminal that communicates with one or more signal processing devices or upper signal processing devices via a plurality of distributed antennas that cooperatively perform coherent transmission and the plurality of distributed antennas, the distributed antenna system comprising: an estimation unit that estimates, for each distributed antenna among the plurality of distributed antennas, a propagation delay difference at the terminal between one or more of the signal processing devices or the upper signal processing devices and the terminal, in accordance with a propagation delay between one or more of the signal processing devices or the upper signal processing devices and the terminal, or a propagation delay difference at the terminal between the plurality of distributed antennas and the terminal, in accordance with a propagation delay between one or more of the signal processing devices or the upper signal processing devices and the terminal, and a control unit that controls a transmission time for each distributed antenna so that the propagation delay difference estimated for each distributed antenna is within a tolerable delay difference.

[0015] According to the present invention, it is possible to suppress the deterioration of communication quality due to inter-symbol interference.

[0016] 1 is a diagram illustrating an example of the configuration of a distributed antenna system in the first embodiment. FIG. 2 is a diagram illustrating an example of a propagation delay difference of signals received by a terminal in the first embodiment. FIG. 3 is a flowchart illustrating an example of the operation of a communication control device in the first embodiment. FIG. 4 is a flowchart illustrating an example of the operation of a communication control device in a modified example of the first embodiment. FIG. 5 is a diagram illustrating an example of the configuration of a distributed antenna system in the second embodiment. FIG. 6 is a diagram illustrating an example of the configuration of a distributed antenna system in the third embodiment. FIG. 7 is a diagram illustrating an example of the configuration of a distributed antenna system in the fourth embodiment. FIG. 8 is a sequence diagram illustrating an example of the operation of a distributed antenna system in the fourth embodiment. FIG. 9 is a diagram illustrating an example of the configuration of a distributed antenna system in the fifth embodiment. FIG. 10 is a sequence diagram illustrating an example of the operation of a distributed antenna system in the fifth embodiment. FIG. 11 is a diagram illustrating an example of the configuration of a distributed antenna system in the sixth embodiment. FIG. 12 is a sequence diagram illustrating an example of the operation of a distributed antenna system in the sixth embodiment. FIG. 13 is a diagram illustrating an example of the configuration of a distributed antenna system in the seventh embodiment. FIG. 14 is a sequence diagram illustrating an example of the operation of a distributed antenna system in the seventh embodiment. FIG. 15 is a diagram illustrating an example of the hardware configuration of a communication device in each embodiment. FIG. 16 is a diagram illustrating an example of the configuration of a distributed antenna system. FIG. 17 is a sequence diagram illustrating an example of the operation of a distributed antenna system.

[0017] Embodiments of the present invention will be described in detail with reference to the drawings. (First Embodiment) Fig. 1 is a diagram showing an example of the configuration of a distributed antenna system 1a in the first embodiment. The distributed antenna system 1a is a system in which a base station equipped with a signal processing device and terminals within a wireless communication area communicate with each other using multiple antennas distributed in the wireless communication area. In wireless communication, multipath such as reflected waves can cause delayed waves to occur relative to a direct wave.

[0018] The distributed antenna system 1a includes a communication control device 2a, a signal processing device 3, N (N is an integer equal to or greater than 2) distributed antennas 4, and one or more terminals 5a. The communication control device 2a includes an estimation unit 21a, a selection unit 22, and a control unit 23. The terminal 5a includes M (M is an integer equal to or greater than 1) terminal antennas 51.

[0019] The communication control device 2a and the signal processing device 3 are provided in a base station. Wired communication is possible between the communication control device 2a and the signal processing device 3. Wired communication is possible between the signal processing device 3 and each distributed antenna 4. Wireless communication is possible between each distributed antenna 4 and the terminal 5a in the wireless section.

[0020] The N distributed antennas 4 are distributed and placed in a predetermined wireless communication area. The terminal 5a is located within the wireless communication area. The terminal 5a can communicate with the communication control device 2a and the signal processing device 3 using one or more distributed antennas 4.

[0021] The estimation unit 21a or the terminal 5a estimates the propagation delay difference at the terminal 5a between the signal processing device 3 and the terminal 5a for each distributed antenna 4 using a propagation delay difference estimation method in accordance with the propagation delay (propagation time) between the signal processing device 3 and the terminal 5a. This estimation method is not limited to a specific estimation method. Several examples of estimation methods in a distributed antenna system will be described later in each of the fourth to seventh embodiments.

[0022] The selector 22 selects a terminal 5 a that receives the coherently transmitted radio signal (data signal) from one or more terminals 5 a. The selector 22 also selects a plurality of distributed antennas 4 from the N distributed antennas 4.

[0023] Here, the selector 22 selects multiple distributed antennas 4 so as to maximize the total system capacity of all terminals 5a in the distributed antenna system 1a. For example, the selector 22 may select multiple distributed antennas 4 using propagation channel information so as to increase the Shannon capacity. The selector 22 may preferentially select multiple distributed antennas 4 that increase the received power relative to interference power and noise power, such as the carrier to interference plus noise power ratio (CINR) or the signal to interference plus noise power ratio (SINR). The selector 22 may preferentially select multiple distributed antennas 4 that increase the received power. Furthermore, the selector 22 may preferentially select multiple distributed antennas 4 that can obtain a delay diversity effect from among the N distributed antennas 4 connected to the signal processing device 3.

[0024] 2 is a diagram showing an example of a propagation delay difference of a signal received by terminal 5a in the first embodiment. In FIG. 2, selector 22 selects a plurality of distributed antennas 4 including distributed antenna 4-1, distributed antenna 4-2, and distributed antenna 4-N from N distributed antennas 4. Estimator 21a or terminal 5a estimates the propagation delay difference at terminal 5a between signal processing device 3 and terminal 5a for each distributed antenna 4 in accordance with the propagation delay (propagation time) between signal processing device 3 and terminal 5a.

[0025] The control unit 23 controls the signal transmission time for each of the selected distributed antennas 4 so that the propagation delay difference estimated for each of the distributed antennas 4 falls within the allowable delay difference at the terminal 5a. For example, the control unit 23 may control the signal transmission time for each of the selected distributed antennas 4 so that the propagation delay difference estimated for each of the distributed antennas 4 disappears at the terminal 5a (so that the multiple wireless signals are received simultaneously at the terminal reception times at the terminal 5a). For example, the control unit 23 may shift the signal transmission time for each of the selected distributed antennas 4 so that the propagation delay difference estimated for each of the distributed antennas 4 intentionally occurs slightly at the terminal 5a (so that the terminal reception times of the multiple wireless signals differ for each of the distributed antennas 4 within the allowable delay time difference). This makes it possible to obtain a delay diversity effect. The signal transmission time may be the transmission time of a wired signal in the signal processing device 3 or the transmission time of a wireless signal from the distributed antenna 4.

[0026] 1, the description of the exemplary configuration of the distributed antenna system 1a continues. The control unit 23 controls the operation of the signal processing device 3 (for example, the signal transmission time) so that the selected distributed antennas 4 coherently transmit radio signals to the terminal 5a.

[0027] The signal processing device 3 (digital and analog signal processing device) outputs an electrical signal (analog signal) to a selected plurality of distributed antennas 4 at a transmission time controlled by the control unit 23. The plurality of distributed antennas 4 coherently transmits a radio signal in response to the electrical signal. The terminal 5a receives the radio signal from the plurality of distributed antennas 4 using one or more terminal antennas 51.

[0028] Next, an example of operation of the communication control device 2a will be described. Fig. 3 is a flowchart showing an example of operation of the communication control device 2a in the first embodiment. The communication control device 2a estimates the propagation delay difference at each terminal 5a in the distributed antenna system 1a for each of the N distributed antennas 4 (step S101). The communication control device 2a selects one terminal 5a that will receive the coherently transmitted radio signal (data signal) from one or more terminals 5a in the distributed antenna system 1a (step S102).

[0029] The communication control device 2a selects a plurality of distributed antennas 4 from among the N distributed antennas 4 (all distributed antennas 4) (step S103). The communication control device 2a coherently transmits radio signals from the plurality of distributed antennas 4 based on the transmission times controlled for each distributed antenna 4 so that the propagation delay difference at the selected terminal 5a is within the allowable delay difference (step S104).

[0030] As described above, the communication control device 2a (distributed antenna system) controls coherent transmission between the selected terminal 5a and the plurality of distributed antennas 4 that cooperate to perform coherent transmission.

[0031] The estimation unit 21a or the terminal 5a estimates the propagation delay difference at the terminal 5a between the signal processing device 3 (digital signal processing device) and the terminal 5a for each distributed antenna 4 among the multiple distributed antennas 4, depending on the propagation delay (propagation time) between the signal processing device 3 and the terminal 5a.

[0032] The control unit 23 controls the transmission time of the signal for each distributed antenna 4 so that the propagation delay difference estimated for each distributed antenna 4 falls within an allowable delay difference. The control unit 23 may control the transmission time of the wired signal transmitted from the signal processing device 3, or may control the transmission time of the wireless signal transmitted from the distributed antenna 4. The control unit 23 and the signal processing device 3 communicate with the terminal 5a using the selected plurality of distributed antennas 4. The terminal 5a communicates with the communication control device 2a and the signal processing device 3 via the selected plurality of distributed antennas 4.

[0033] This keeps the propagation delay difference within the allowable delay difference, making it possible to suppress deterioration of communication quality due to inter-symbol interference. Furthermore, if the transmission time of the radio signal is controlled for each distributed antenna 4 so that the propagation delay difference at terminal 5a is intentionally set within the allowable delay difference, a delay diversity effect can be obtained.

[0034] (Variation of First Embodiment) In the above-described first embodiment, the propagation delay difference is estimated for each distributed antenna 4 among the N distributed antennas 4. In contrast, in the variation of the first embodiment, the main difference from the first embodiment is that the propagation delay difference is estimated for each distributed antenna 4 among a selected plurality of distributed antennas 4. The variation of the first embodiment will be described mainly focusing on the difference from the first embodiment.

[0035] 4 is a flowchart showing an example of the operation of the communication control device 2a in a modification of the first embodiment. The communication control device 2a selects one terminal 5a that receives a coherently transmitted radio signal (data signal) from one or more terminals 5a in the distributed antenna system 1a (step S111). The communication control device 2a selects multiple distributed antennas 4 from N distributed antennas 4 (all distributed antennas 4) (step S112).

[0036] The communication control device 2a estimates the propagation delay difference at the selected terminal 5a for each of the selected distributed antennas 4 (step S113). The communication control device 2a coherently transmits radio signals from the distributed antennas 4 based on the transmission time controlled so that the propagation delay difference at the selected terminal 5a is within the allowable delay difference (step S114).

[0037] Second Embodiment The second embodiment is mainly different from the first embodiment in that the signal processing device 3 and each distributed antenna 4 can communicate using radio over fiber (RoF). The second embodiment will be described focusing on the differences from the first embodiment.

[0038] 5 is a diagram showing an example of the configuration of a distributed antenna system 1b in the second embodiment. The signal processing device 3 and each distributed antenna 4 can communicate using radio over fiber (RoF). That is, the signal processing device 3 and each distributed antenna 4 can communicate via wired communication using optical signals propagating through optical fibers in the RoF section (wired section).

[0039] In the RoF section, an optical signal propagates through the core of an optical fiber. Because the loss of an optical signal is smaller than the loss of a wireless signal, it is possible to extend the distributed antenna 4 to a position far from the signal processing device 3. Here, because the length of the optical fiber differs for each distributed antenna 4, the difference in propagation delay of the optical signal may become large in the RoF section. For this reason, the estimator 21b or the terminal 5b estimates the difference in propagation delay of each wireless signal arriving at the terminal 5b, taking into account the propagation delay (propagation time) of each optical signal in the RoF section.

[0040] For example, when the estimation unit 21b or the terminal 5b estimates the propagation delay difference in the section between the signal processing device 3 and the terminal 5b (the propagation delay difference taking into account the propagation delay (propagation time) in the RoF section), the control unit 23 controls the transmission time for each distributed antenna 4 based only on the propagation delay difference estimated for each distributed antenna 4 so that the propagation delay difference estimated for each distributed antenna 4 is within the allowable delay difference.

[0041] For example, when the estimation unit 21b or the terminal 5b estimates the propagation delay difference in the wireless section between the distributed antenna 4 and the terminal 5b (the propagation delay difference without taking into account the propagation delay (propagation time) in the RoF section), the selection unit 22 controls the transmission time for each distributed antenna 4 based on the propagation delay difference taking into account the propagation delay (propagation time) measured in advance for the RoF section, so that the propagation delay difference estimated for each distributed antenna 4 is within the allowable delay difference.

[0042] As described above, the communication control device 2b (distributed antenna system) controls coherent transmission between the selected terminal 5b and the plurality of distributed antennas 4 that cooperate to perform coherent transmission.

[0043] The estimation unit 21b or the terminal 5b estimates the propagation delay difference at the terminal 5b between the signal processing device 3 and the terminal 5b for each distributed antenna 4 in accordance with the propagation delay between the signal processing device 3 and the terminal 5b (propagation delay (propagation time) in the section including the RoF section).

[0044] The estimation unit 21b or the terminal 5b may estimate the propagation delay difference at the terminal 5b between the distributed antenna 4 and the terminal 5b for each distributed antenna 4, based on the propagation delay between the signal processing device 3 and the distributed antenna 4 (propagation delay measured in advance for each distributed antenna 4) and the propagation delay between the distributed antenna 4 and the terminal 5b (wireless section). That is, the estimation unit 21b or the terminal 5b may estimate the propagation delay difference between the distributed antenna 4 and the terminal 5b (wireless section) for each distributed antenna 4, taking into account the propagation delay (propagation time) in the wired section between the signal processing device 3 and the distributed antenna 4.

[0045] The control unit 23 controls the transmission time for each distributed antenna 4 so that the propagation delay difference estimated for each distributed antenna 4 falls within an allowable delay difference. The control unit 23 and the signal processing device 3 communicate with the terminal 5b using a plurality of distributed antennas 4 selected from the plurality of distributed antennas 4. The terminal 5b communicates with the communication control device 2b and the signal processing device 3 via the selected plurality of distributed antennas 4.

[0046] This makes it possible to suppress degradation of communication quality due to inter-symbol interference. Furthermore, if the transmission times of the radio signals are controlled for each distributed antenna 4 so that a difference in propagation delay is intentionally generated at terminal 5b within the allowable delay difference, a delay diversity effect can be obtained.

[0047] Third Embodiment The third embodiment is mainly different from the second embodiment in that the distributed antenna system includes an upper signal processing device and a plurality of signal processing devices 3. The third embodiment will be described focusing on the differences from the second embodiment.

[0048] 6 is a diagram showing an example of the configuration of a distributed antenna system 1c according to the third embodiment. The distributed antenna system 1c includes a communication control device 2c, K (K is an integer equal to or greater than 2) signal processing devices 3, N distributed antennas 4, and one or more terminals 5c. The communication control device 2c includes an estimation unit 21c, a selection unit 22, and a control unit 23. The terminal 5c includes M terminal antennas 51.

[0049] The distributed antenna system 1c may include an upper signal processing device 6 (signal aggregation device) above the signal processing devices 3. If the distributed antenna system 1c includes the upper signal processing device 6, the K signal processing devices 3 are connected to the upper signal processing device 6, for example, using optical fiber. If the distributed antenna system 1c does not include the upper signal processing device 6, the K signal processing devices 3 are connected to the communication control device 2c, for example, using optical fiber. In the following, the distributed antenna system 1c is described as including the upper signal processing device 6.

[0050] The communication control device 2c, each signal processing device 3, and the upper signal processing device 6 are provided in a base station. The communication control device 2c and each signal processing device 3 are capable of wired communication in a wired section. Each signal processing device 3 and the upper signal processing device 6 are capable of wired communication in a wired section (rear wired section) such as optical fiber. The signal processing device 3 and each subordinate distributed antenna 4 are capable of wired communication in a wired section. Each distributed antenna 4 and terminal 5c are capable of wireless communication in a wireless section.

[0051] The N distributed antennas 4 are distributed and placed in a predetermined wireless communication area. The terminal 5c is located within the wireless communication area. The terminal 5c can communicate with the communication control device 2c and the higher-level signal processing device 6 using the multiple signal processing devices 3 and the multiple distributed antennas 4.

[0052] The upper signal processing device 6 is a higher-level signal processing device (digital signal processing device) than the signal processing device 3. The upper signal processing device 6 performs predetermined digital signal processing so that the selected multiple distributed antennas 4 cooperate to perform coherent transmission. The upper signal processing device 6 outputs a digital signal generated by the digital signal processing to the subordinate signal processing device 3.

[0053] The signal processing device 3 converts the digital signal output from the higher-level signal processing device 6 into an analog signal, and outputs the converted analog signal to each of the distributed antennas 4 under its control.

[0054] In a wired section such as an optical fiber, the propagation delay difference of the optical signal may be large. Therefore, the estimation unit 21c or the terminal 5c estimates the propagation delay difference of the wireless signal arriving at the terminal 5c, taking into account the propagation delay (propagation time) of the signal in the wired section.

[0055] For example, when the estimation unit 21c or the terminal 5c estimates the propagation delay difference in the section between the signal processing device 3 and the terminal 5c (the propagation delay difference taking into account the propagation delay (propagation time) in the wired section), the control unit 23 controls the transmission time for each distributed antenna 4 based only on the propagation delay difference estimated for each distributed antenna 4 so that the propagation delay difference estimated for each distributed antenna 4 is within the allowable delay difference.

[0056] For example, when the estimation unit 21c or the terminal 5c estimates the propagation delay difference in the wireless section between the distributed antenna 4 and the terminal 5c (the propagation delay difference without taking into account the propagation delay (propagation time) in the wired section), the control unit 23 may control the transmission time for each distributed antenna 4 based on the propagation delay difference taking into account the propagation delay (propagation time) measured in advance for the wired section so that the propagation delay difference estimated for each distributed antenna 4 is within the allowable delay difference.

[0057] As described above, the communication control device 2c (distributed antenna system) controls coherent transmission between the selected terminal 5c and the plurality of distributed antennas 4 that cooperate to perform coherent transmission.

[0058] The estimation unit 21c or the terminal 5c estimates the propagation delay difference at the terminal 5c between one or more signal processing devices 3 or upper signal processing devices 6 and the terminal 5c for each distributed antenna 4 in accordance with the propagation delay between one or more signal processing devices 3 or upper signal processing devices 6 and the terminal 5c (propagation delay (propagation time) in a section including a wired section).

[0059] The estimation unit 21c or the terminal 5c may estimate the propagation delay difference at the terminal 5c between the distributed antenna 4 and the terminal 5c for each distributed antenna 4, based on the propagation delay between one or more signal processing devices 3 or upper signal processing devices 6 and the distributed antenna 4 (propagation delay measured in advance for each distributed antenna 4) and the propagation delay (propagation time) between the distributed antenna 4 and the terminal 5c (wireless section). That is, the estimation unit 21c or the terminal 5c may estimate the propagation delay difference between the distributed antenna 4 and the terminal 5c (wireless section) for each distributed antenna 4, taking into account the transmission delay (propagation time) in the wired section between the one or more signal processing devices 3 or upper signal processing devices 6 and the distributed antenna 4.

[0060] The control unit 23 controls the transmission time for each distributed antenna 4 so that the propagation delay difference estimated for each distributed antenna 4 falls within an allowable delay difference. The control unit 23 and the upper signal processing device 6 communicate with the terminal 5c using a plurality of distributed antennas 4 selected from the plurality of distributed antennas 4. The terminal 5c communicates with the communication control device 2c and the upper signal processing device 6 via the selected plurality of distributed antennas 4.

[0061] This makes it possible to suppress degradation of communication quality due to inter-symbol interference. Furthermore, if the transmission times of the radio signals are controlled for each distributed antenna 4 so that a difference in propagation delay is intentionally generated at terminal 5c within the allowable delay difference, a delay diversity effect can be obtained.

[0062] In each of the first to third embodiments, the communication control device may estimate a propagation delay difference using a known signal transmitted from a terminal. In the fourth embodiment, the differences from the first embodiment will be mainly described as an example of the first to third embodiments.

[0063] 7 is a diagram showing an example of the configuration of a distributed antenna system 1d according to the fourth embodiment. The distributed antenna system 1d includes a communication control device 2d, a signal processing device 3, N distributed antennas 4, and one or more terminals 5d. The communication control device 2d includes an estimation unit 21d, a selection unit 22, and a control unit 23. The terminal 5d includes M terminal antennas 51, a communication unit 52d, and a signal processing device 53. The terminal 5d and the signal processing device 53 may be separate entities.

[0064] The communication unit 52d transmits a known signal at a predetermined transmission time (transmission timing) using the signal processing device 53 and the M terminal antennas 51. Here, the communication unit 52d may transmit the known signal using a time resource that differs for each distributed antenna 4. The communication unit 52d may transmit the known signal using a frequency resource that differs for each distributed antenna 4. The communication unit 52d may transmit the known signal using a code that differs for each distributed antenna 4.

[0065] The signal processing device 53 converts the known signal (digital signal) output from the communication unit 52d into an analog signal, and outputs the analog signal to one or more terminal antennas 51.

[0066] The estimation unit 21d estimates the propagation delay difference based on the difference between the time when the known signal is scheduled to be received by the distributed antenna 4 (pre-scheduled timing) and the actual time when the known signal is received by the distributed antenna 4. The estimation unit 21d may estimate the propagation delay difference in the distributed antenna 4 in accordance with delay fluctuations of the known signal transmitted multiple times.

[0067] For example, the communication unit 52d transmits each known signal, and the estimation unit 21d estimates the cross-correlation of each received known signal, thereby estimating the actual time at which each known signal was received (the actual timing at which it was received).

[0068] For example, in the case of a known signal having periodicity, such as a signal to which a guard interval is added, the estimation unit 21d estimates the actual time at which the known signal was received by estimating the autocorrelation of the known signal. The guard interval may be a cyclic prefix (CP) to which a replicated signal is added, or a waveform signal transmitted during a period in which no data signal is transmitted.

[0069] For example, the estimation unit 21d estimates the actual time at which the known signal is received based on a delay profile estimated using the known signal. Here, the estimation unit 21d acquires the delay profile by, for example, performing an Inverse Fast Fourier Transform (IFFT) on the propagation channel in the frequency domain. Here, the actual time at which the known signal is received (actual reception timing) may be the actual time at which the known signal propagated through the path with the highest received power is received, or may be the median of the actual times at which the known signals propagated through paths with different propagation delays are received. Furthermore, the actual time at which the known signal is received may be a weighted average value weighted by the magnitude of the received power of the known signal with respect to the actual times at which the known signal propagated through paths with different propagation delays is received.

[0070] The time at which the known signal is scheduled to be received may be the time at which a known signal that is transmitted periodically is scheduled to be received, or the time at which a known signal that is transmitted periodically a specified number of times based on a trigger of the communication control device 2d or the terminal 5d is scheduled to be received, or the time at which a known signal that is transmitted only once based on a trigger of the communication control device or the terminal is scheduled to be received.

[0071] When the estimation unit 21d estimates the propagation delay difference in the section between the signal processing device 3 and the terminal 5d, the control unit 23 controls the transmission time for each distributed antenna 4 based only on the propagation delay difference estimated for each distributed antenna 4 so that the propagation delay difference estimated for each distributed antenna 4 falls within the allowable delay difference. The same applies to the second or third embodiment.

[0072] When the estimation unit 21d estimates the propagation delay difference in the wireless section between the distributed antenna 4 and the terminal 5d, the control unit 23 may control the transmission time for each distributed antenna 4 based on the propagation delay difference taking into account the propagation delay (propagation time) measured in advance for the wired section, so that the propagation delay difference estimated for each distributed antenna 4 falls within the allowable delay difference. The same applies to the second or third embodiment.

[0073] Next, an operation example of the distributed antenna system 1d will be described. Fig. 8 is a sequence diagram showing an operation example of the distributed antenna system 1d in the fourth embodiment. The terminal 5d transmits a known signal at a predetermined transmission time (transmission timing) (step S201).

[0074] The communication control device 2d records the actual times at which the known signals are received by the multiple distributed antennas (step S202). The communication control device 2d determines (calculates) the difference between the time at which the known signals are scheduled to be received and the actual time at which the known signals are received (step S203). The communication control device 2d estimates the propagation delay difference for each distributed antenna based on the determined difference (step S204).

[0075] As described above, in each of the first to third embodiments, the estimation unit 21 d estimates the propagation delay difference based on the difference between the time when the known signal is scheduled to be received and the actual time when the known signal is received, thereby making it possible to suppress degradation of communication quality due to inter-symbol interference.

[0076] Fifth Embodiment In each of the above-described first to third embodiments, a terminal may estimate a propagation delay difference using a known signal transmitted from a communication control device. In the fifth embodiment, the differences from the first embodiment will be mainly described as an example of the above-described first to third embodiments.

[0077] 9 is a diagram showing an example configuration of a distributed antenna system 1e according to the fifth embodiment. The distributed antenna system 1e includes a communication control device 2e, a signal processing device 3, N distributed antennas 4, and one or more terminals 5e. The communication control device 2e includes an estimation unit 21e, a selection unit 22, and a control unit 23. The terminal 5e includes M terminal antennas 51, a signal processing device 53, and an estimation unit 54e. The terminal 5e and the signal processing device 53 may be separate entities.

[0078] The estimation unit 21e transmits known signals from the plurality of distributed antennas 4 at predetermined transmission times using the signal processing device 3. Here, the estimation unit 21e may transmit the known signals using different time resources for each distributed antenna 4. The estimation unit 21e may transmit the known signals using different frequency resources for each distributed antenna 4. The estimation unit 21e may transmit the known signals using different codes for each distributed antenna 4. When a signal indicating a propagation delay difference for each distributed antenna 4 is acquired from the terminal 5e, the estimation unit 21e records the propagation delay difference for each distributed antenna 4.

[0079] The estimation unit 54e records the actual time when the known signal is received by the terminal antenna 51. The estimation unit 54e determines (calculates) the difference between the time when the known signal is scheduled to be received and the actual time when the known signal is received. The estimation unit 54e estimates the propagation delay difference based on the difference between the time when the known signal is scheduled to be received and the actual time when the known signal is received. The estimation unit 54e transmits a signal representing the propagation delay difference for each distributed antenna 4 to the estimation unit 21e using the terminal antenna 51. That is, the estimation unit 54e feeds back the propagation delay difference for each distributed antenna 4 to the estimation unit 21e.

[0080] Here, when a distributed antenna 4 that performs coordinated coherent transmission is selected, the estimation unit 54e may feed back the propagation delay difference at the terminal 5e between the distributed antenna 4 and the terminal 5e for the selected distributed antenna 4. When a distributed antenna 4 that performs coordinated coherent transmission is not selected, the estimation unit 54e may feed back the propagation delay difference at the terminal 5e between the distributed antenna 4 and the terminal 5e for all distributed antennas 4.

[0081] The signal representing the propagation delay difference for each distributed antenna 4 (signal used for feedback) is not limited to a specific uplink signal. For example, the signal representing the propagation delay difference may be a data signal of a higher layer or a signal of a predetermined format capable of carrying propagation delay difference information. For example, the signal representing the propagation delay difference may be a physical uplink shared channel (PUSCH), a sounding reference signal (SRS), or a physical uplink control channel (PUCCH). For example, the signal representing the propagation delay difference may be a data frame or a dedicated frame carrying propagation delay difference information.

[0082] When the estimation unit 54e estimates the propagation delay difference in the section between the signal processing device 3 and the terminal 5e, the control unit 23 controls the transmission time for each distributed antenna 4 based only on the propagation delay difference estimated for each distributed antenna 4 so that the propagation delay difference estimated for each distributed antenna 4 falls within the allowable delay difference. The same applies to the second or third embodiment.

[0083] When the estimation unit 54e estimates the propagation delay difference in the wireless section between the distributed antenna 4 and the terminal 5e, the control unit 23 may control the transmission time for each distributed antenna 4 based on the propagation delay difference taking into account the propagation delay (propagation time) measured in advance for the wired section, so that the propagation delay difference estimated for each distributed antenna 4 falls within the allowable delay difference. The same applies to the second or third embodiment.

[0084] Next, an example of the operation of the distributed antenna system 1e will be described. Fig. 10 is a sequence diagram showing an example of the operation of the distributed antenna system 1e in the fifth embodiment. The communication control device 2e transmits known signals from the multiple distributed antennas 4 at predetermined transmission times (step S301).

[0085] The terminal 5e records the actual time when the known signal is received by the terminal antenna 51 (step S302). The terminal 5e determines (calculates) the difference between the time when the known signal is scheduled to be received and the actual time when the known signal is received (step S303). The terminal 5e estimates the propagation delay difference for each distributed antenna 4 based on the determined difference (step S304). The terminal 5e transmits a signal representing the propagation delay difference for each distributed antenna 4 (step S305). The communication control device 2e records the propagation delay difference for each distributed antenna 4 (step S306).

[0086] As described above, in each of the first to third embodiments, the estimation unit 54e estimates the propagation delay difference based on the difference between the time when the known signal is scheduled to be received and the actual time when the known signal is received, thereby making it possible to suppress degradation of communication quality due to inter-symbol interference.

[0087] Sixth Embodiment In each of the first to third embodiments described above, a signal having transmission time information may be transmitted from a terminal, and a communication control device time-synchronized with the terminal may estimate a propagation delay difference using the transmission time information. In the sixth embodiment, the differences from the first embodiment will be mainly described as an example of the first to third embodiments described above.

[0088] 11 is a diagram showing an example of the configuration of a distributed antenna system 1f in the sixth embodiment. The distributed antenna system 1f includes a communication control device 2f, a signal processing device 3, N distributed antennas 4, and one or more terminals 5f. The communication control device 2f includes an estimation unit 21f, a selection unit 22, and a control unit 23. The terminal 5f includes M terminal antennas 51, a communication unit 52f, and a signal processing device 53. The terminal 5f and the signal processing device 53 may be separate entities.

[0089] The estimation unit 21f uses the signal processing device 3 to transmit a request signal from at least one distributed antenna 4. The estimation unit 21f records the actual times at which a signal having transmission time information is received by the multiple distributed antennas 4. The estimation unit 21f determines (calculates) the difference between the transmission time indicated by the transmission time information of the signal having transmission time information and the actual time at which the signal having transmission time information is received. The estimation unit 21f estimates the propagation delay difference for each distributed antenna 4 based on the determined difference.

[0090] When the communication unit 52f acquires the request signal, it transmits a signal having transmission time information to the plurality of distributed antennas 4. This transmission time information indicates the time at which the signal processing device 3 or the terminal antenna 51 transmits the signal having the transmission time information.

[0091] When the estimation unit 21f estimates the propagation delay difference in the section between the signal processing device 3 and the terminal 5f (the propagation delay difference taking into account the propagation delay (propagation time) in the wired section), the control unit 23 controls the transmission time for each distributed antenna 4 based only on the propagation delay difference estimated for each distributed antenna 4 so that the propagation delay difference estimated for each distributed antenna 4 falls within the allowable delay difference. The same applies to the second or third embodiment.

[0092] When the estimation unit 21f estimates the propagation delay difference in the wireless section between the distributed antenna 4 and the terminal 5f (the propagation delay difference without taking into account the propagation delay in the wired section), the control unit 23 may control the transmission time for each distributed antenna 4 based on the propagation delay difference taking into account the propagation delay measured in advance for the wired section, so that the propagation delay difference estimated for each distributed antenna 4 falls within the allowable delay difference. The same applies to the second or third embodiment.

[0093] Next, an operation example of the distributed antenna system 1f will be described. Fig. 12 is a sequence diagram showing an operation example of the distributed antenna system 1f in the sixth embodiment. The communication control device 2f transmits a request signal (step S401). The terminal 5f acquires the request signal (step S402). The terminal 5f transmits a signal having transmission time information (step S403).

[0094] The communication control device 2f records the actual times at which the signals having transmission time information were received by the multiple distributed antennas 4 (step S404). The communication control device 2f determines (calculates) the difference between the transmission time indicated by the transmission time information of the signals having transmission time information and the actual time at which the signals having transmission time information were received (step S405). The communication control device 2f estimates the propagation delay difference for each distributed antenna based on the determined difference (step S406).

[0095] As described above, the estimation unit 21f estimates the propagation delay difference based on the difference between the transmission time indicated by the transmission time information of the signal having the transmission time information and the actual time when the signal having the transmission time information was received, thereby making it possible to suppress deterioration of communication quality due to inter-symbol interference.

[0096] (Seventh embodiment) In each of the above first to third embodiments, a signal having transmission time information may be transmitted from a communication control device, and a terminal time-synchronized with the communication control device may estimate a propagation delay difference using the transmission time information. In the seventh embodiment, the differences from the first embodiment will be mainly described as an example of the above first to third embodiments.

[0097] 13 is a diagram showing an example configuration of a distributed antenna system 1g in the seventh embodiment. The distributed antenna system 1g includes a communication control device 2g, a signal processing device 3, N distributed antennas 4, and one or more terminals 5g. The communication control device 2g includes an estimation unit 21g, a selection unit 22, and a control unit 23. The terminal 5g includes M terminal antennas 51, a signal processing device 53, and an estimation unit 54g. The terminal 5g and the signal processing device 53 may be separate entities.

[0098] The estimation unit 21g transmits a signal having transmission time information from the multiple distributed antennas 4 using the signal processing device 3. The transmission time information may be the time at which the signal processing device 3 transmits the signal having the transmission time information, or may be an estimated time at which the signal is to be transmitted to the multiple distributed antennas 4. When a signal indicating the propagation delay difference for each distributed antenna 4 is acquired from the terminal 5g, the estimation unit 21g records the propagation delay difference for each distributed antenna 4.

[0099] The estimation unit 54g records the actual time at which a signal having transmission time information is received by the terminal antenna 51. The estimation unit 54g determines (calculates) the difference between the transmission time indicated by the transmission time information of the signal having transmission time information and the actual time at which the signal having transmission time information is received. The estimation unit 54g estimates the propagation delay difference for each distributed antenna 4 based on the determined difference. The estimation unit 54g transmits a signal indicating the propagation delay difference for each distributed antenna to the estimation unit 21g using the terminal antenna 51. That is, the estimation unit 54g feeds back the propagation delay difference for each distributed antenna 4 to the estimation unit 21g.

[0100] Here, when a distributed antenna 4 that performs coordinated coherent transmission is selected, the estimation unit 54g may feed back the propagation delay difference at the terminal 5g between the distributed antenna 4 and the terminal 5g for the selected distributed antenna 4. When a distributed antenna 4 that performs coordinated coherent transmission is not selected, the estimation unit 54g may feed back the propagation delay difference at the terminal 5g between the distributed antenna 4 and the terminal 5g for all distributed antennas 4.

[0101] The signal representing the propagation delay difference for each distributed antenna 4 (signal used for feedback) is not limited to a specific uplink signal. For example, the signal representing the propagation delay difference may be a data signal of a higher layer or a signal of a predetermined format capable of carrying propagation delay difference information. For example, the signal representing the propagation delay difference may be a physical uplink shared channel (PUSCH), a sounding reference signal (SRS), or a physical uplink control channel (PUCCH). For example, the signal representing the propagation delay difference may be a data frame or a dedicated frame carrying propagation delay difference information.

[0102] When the estimation unit 54g estimates the propagation delay difference (propagation delay difference taking into account the propagation delay (propagation time) in the wired section) in the section between the signal processing device 3 and the terminal 5g based on transmission time information indicating the time when the signal processing device 3 transmits a signal, the control unit 23 controls the transmission time for each distributed antenna 4 based only on the propagation delay difference estimated for each distributed antenna 4 so that the propagation delay difference estimated for each distributed antenna 4 falls within the allowable delay difference. The same applies to the second or third embodiment.

[0103] When the estimation unit 54g estimates the propagation delay difference in the wireless section between the distributed antenna 4 and the terminal 5g (the propagation delay difference without taking into account the propagation delay (propagation time) in the wired section) based on the transmission time information indicating the estimated time when the distributed antenna 4 will transmit a signal, the control unit 23 may control the transmission time for each distributed antenna 4 based on the propagation delay difference taking into account the propagation delay measured in advance for the wired section so that the propagation delay difference estimated for each distributed antenna 4 falls within the allowable delay difference. The same applies to the second or third embodiment.

[0104] Next, an example of the operation of the distributed antenna system 1g will be described. Fig. 14 is a sequence diagram showing an example of the operation of the distributed antenna system 1g in the seventh embodiment. The communication control device 2g transmits signals having transmission time information from the multiple distributed antennas 4 (step S501).

[0105] Terminal 5g records the actual time when the signal having the transmission time information is received by terminal antenna 51 (step S502). Terminal 5g determines (calculates) the difference between the transmission time indicated by the transmission time information of the signal having the transmission time information and the actual time when the signal having the transmission time information is received (step S503). Terminal 5g estimates the propagation delay difference for each distributed antenna 4 based on the determined difference (step S504). Terminal 5g transmits a signal indicating the propagation delay difference for each distributed antenna (step S505). Communication control device 2g records the propagation delay difference for each distributed antenna 4 (step S506).

[0106] As described above, the estimation unit 54g estimates the propagation delay difference based on the difference between the transmission time indicated by the transmission time information of the signal having the transmission time information and the actual time when the signal having the transmission time information was received, thereby making it possible to suppress deterioration of communication quality due to inter-symbol interference.

[0107] 15 is a diagram illustrating an example of the hardware configuration of a communication device in each embodiment. The example of the hardware configuration of the communication device 10 corresponds to the example of the hardware configuration of each communication device (communication control device, signal processing device, upper signal processing device, and terminal) in each embodiment.

[0108] The communication device 10 is realized as software by a processor 101, such as a CPU (Central Processing Unit), executing a program stored in a storage device 103 having a non-volatile recording medium (non-transitory recording medium) and a memory 102. The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), and a CD-ROM (Compact Disc Read Only Memory), and non-transitory recording media such as a hard disk or a solid-state drive (SSD) built into a computer system. The communication unit 104 executes predetermined communication processing.

[0109] The communication device 10 may be realized using hardware (accelerator) including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0110] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0111] The present invention is applicable to communication systems such as distributed antenna systems.

[0112] 1a, 1b, 1c, 1d, 1e, 1f... Distributed antenna system, 2a, 2b, 2c, 2d, 2e, 2f... Communication control device, 3... Signal processing device, 4... Distributed antenna, 5a, 5b, 5c, 5d, 5e, 5f... Terminal, 10... Communication device, 21a, 21b, 21c, 21d, 21e, 21f... Estimation unit, 22... Selection unit, 23... Control unit, 51... Terminal antenna, 52d, 52f... Communication unit, 53... Signal processing device, 54e, 54g... Estimation unit, 100... Distributed antenna system, 101... Processor, 102... Memory, 103... Storage device, 104... Communication unit, 200... Communication control device, 300... Signal processing device, 400... Distributed antenna, 500... Terminal, 501... Terminal antenna

Claims

1. A communication control method executed by a distributed antenna system that controls coherent transmission between a plurality of distributed antennas for performing coherent transmission in coordination and a terminal that communicates with one or more signal processing devices or a higher-level signal processing device, the method comprising: estimating a propagation delay difference at the terminal between one or more of the signal processing devices or the higher-level signal processing device and the terminal according to a propagation delay between one or more of the signal processing devices or the higher-level signal processing device and the terminal, or estimating a propagation delay difference at the terminal between the plurality of distributed antennas and the terminal according to a propagation delay between one or more of the signal processing devices or the higher-level signal processing device and the plurality of distributed antennas and a propagation delay between the plurality of distributed antennas and the terminal, for each of the distributed antennas among the plurality of distributed antennas; and controlling a transmission time for each of the distributed antennas such that the propagation delay difference estimated for each of the distributed antennas is within an allowable delay difference.

2. The communication control method according to claim 1, wherein the estimating step includes estimating the propagation delay difference based on a difference between a time when a known signal is expected to be received and an actual time when the known signal is received.

3. The communication control method according to claim 1, wherein the estimating step includes estimating the propagation delay difference based on a difference between a transmission time indicated by the transmission time information of a signal having transmission time information and an actual time when the signal having the transmission time information is received.

4. The communication control method according to claim 1, wherein the controlling step includes controlling a transmission time for each of the distributed antennas such that the propagation delay difference estimated for each of the distributed antennas becomes zero.

5. A terminal that communicates with one or more signal processing devices or a higher-level signal processing device via a plurality of distributed antennas that perform coherent transmission in a coordinated manner, and a distributed antenna system that controls the coherent transmission between the terminal and the plurality of distributed antennas, an estimation unit that estimates, for each distributed antenna among the plurality of distributed antennas, a propagation delay difference at the terminal between one or more of the signal processing devices or the higher-level signal processing device and the terminal according to a propagation delay between one or more of the signal processing devices or the higher-level signal processing device and the terminal, or estimates a propagation delay difference at the terminal between the plurality of distributed antennas and the terminal according to a propagation delay between one or more of the signal processing devices or the higher-level signal processing device and the plurality of distributed antennas and a propagation delay between the plurality of distributed antennas and the terminal; a control unit that controls a transmission time for each distributed antenna so that the propagation delay difference estimated for each distributed antenna is within an allowable delay difference. A distributed antenna system comprising the above.

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