Base station equipment, communication method, and program

Abstract

To provide better pre-compensation for at least one of the propagation delay and Doppler shift associated with the movement of wireless terminals. [Solution] A base station device is provided, which includes an acquisition unit that acquires information indicating the characteristics of at least one of propagation delay and Doppler shift at each wireless terminal, and a correction unit that corrects the phase of the signal to be transmitted to each wireless terminal in the frequency domain based on the characteristics of each wireless terminal.

Description

Technical Field

[0001] The present disclosure relates to a base station apparatus, a communication method, and a program.

Background Art

[0002] Patent Document 1 describes that a base station performs a Doppler pre-compensation scheme in transmitting a downlink (DL) signal / channel to a UE in an HST from a TRP.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the technique described in Patent Document 1, for example, there is room for improvement in pre-compensation of at least one of propagation delay and Doppler shift associated with the movement of a wireless terminal.

[0005] An object of the present disclosure is to provide a technique capable of more appropriately pre-compensating at least one of propagation delay and Doppler shift associated with the movement of a wireless terminal in view of the above problems.

Means for Solving the Problems

[0006] In a first aspect according to the present disclosure, there is provided a base station apparatus including an acquisition unit that acquires information indicating characteristics regarding at least one of propagation delay and Doppler shift at each wireless terminal, and a correction unit that corrects the phase of a signal transmitted to each wireless terminal in the frequency domain based on the characteristics at each wireless terminal.

[0007] A second aspect of the present disclosure provides a communication method that acquires information indicating characteristics of at least one of propagation delay and Doppler shift at each wireless terminal, and corrects the phase of a signal to be transmitted to each wireless terminal in the frequency domain based on the characteristics of each wireless terminal.

[0008] A third aspect of the present disclosure provides a program that causes a computer to perform a process of acquiring information indicating characteristics of at least one of propagation delay and Doppler shift at each wireless terminal, and correcting the phase of a signal to be transmitted to each wireless terminal in the frequency domain based on the characteristics of each wireless terminal. [Effects of the Invention]

[0009] In one respect, it is possible to more appropriately pre-compensate for at least one of the propagation delay and Doppler shift associated with the movement of wireless terminals. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows an example of the configuration of a base station device according to the embodiment. [Figure 2] This is a diagram showing an example configuration of a communication system according to the embodiment. [Figure 3] This figure shows an example of the hardware configuration of a base station device according to the embodiment. [Figure 4] This flowchart shows an example of processing by a base station device according to the embodiment. [Figure 5] This figure shows an example of processing by a base station device according to the embodiment. [Modes for carrying out the invention]

[0011] The principles of this disclosure will be described with reference to several exemplary embodiments. These embodiments are described for illustrative purposes only and should be understood as helping those skilled in the art to understand and implement this disclosure without implying any limitation on the scope of this disclosure. The disclosures described herein may be implemented in various ways other than those described below.

[0012] In the following description and claims, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which this disclosure belongs.

[0013] Embodiments of the present disclosure will be described below with reference to the drawings. Each drawing is merely illustrative for illustrating one or more embodiments. Each drawing may be associated not only with one specific embodiment but also with one or more other embodiments. As those skilled in the art will understand, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings, for example, to create embodiments not explicitly shown or described. Not all features or steps shown in any one drawing to illustrate an exemplary embodiment are necessarily required, and some features or steps may be omitted. The order of steps described in any of the drawings may be changed as appropriate.

[0014] (Embodiment 1) <Structure> Referring to Figure 1, the configuration of the base station device 10 according to the embodiment will be described. Figure 1 is a diagram showing an example of the configuration of the base station device 10 according to the embodiment. The base station device 10 has an acquisition unit 11 and a correction unit 12. Each of these units may be realized through the cooperation of one or more programs installed in the base station device 10 and hardware such as the processor and memory of the base station device 10.

[0015] The acquisition unit 11 acquires information for each of the multiple wireless terminals that shows the characteristics of at least one of the propagation delay and Doppler shift of the signal received from the base station equipment 10. The correction unit 12 corrects the phase of the signal transmitted to each wireless terminal in the frequency domain based on the characteristics of each wireless terminal. This makes it possible to more appropriately pre-compensate for at least one of the propagation delay and Doppler shift associated with the movement of the wireless terminal. As a result, it becomes possible to communicate appropriately with wireless terminals moving at high speed, for example, simultaneously with multiple base stations or while switching between multiple base stations.

[0016] The correction unit 12 of this disclosure is not limited to, for example, an example of correcting a signal in the frequency domain before modulation. Examples of wireless communication systems in which the signal before modulation is a frequency domain signal include, for example, orthogonal frequency division multiple access (OFDMA) and single-carrier frequency division multiple access (SC-FDMA).

[0017] If the wireless communication method is CDMA (Code Division Multiple Access), the correction unit 12 may correct the signal in the code domain. Also, if the wireless communication method is OTFS (Orthogonal Time Frequency Space), the correction unit 12 may correct the signal in the delay-Doppler domain.

[0018] (Embodiment 2) <System Configuration> Next, with reference to Figure 2, the configuration of the communication system 1 according to the embodiment will be described. Figure 2 is a diagram showing an example of the configuration of the communication system 1 according to the embodiment. In the example of Figure 2, the communication system 1 has base station equipment 10A, base station equipment 10B, and base station equipment 10C. In the following, when it is not necessary to distinguish between base station equipment 10A to 10C, they will simply be referred to as "base station equipment 10". The communication system 1 also has wireless terminals 20-1, wireless terminals 20-2, ... wireless terminals 20-N (where N is an integer of 2 or more). In the following, when it is not necessary to distinguish between wireless terminals 20-1 to 10-N, they will simply be referred to as "wireless terminal 20". Note that the number of base station equipment 10 and wireless terminals 20 is not limited to the example in Figure 2.

[0019] In the example shown in Figure 2, each base station device 10 is connected to enable communication via network N. Examples of network N include, for example, a core network, the internet, a LAN (Local Area Network), and a bus. It is also connected to enable communication via wireless communication of a mobile communication system (e.g., RAT (Radio Access Technology)). Examples of mobile communication systems include, for example, fifth-generation mobile communication systems (5G), sixth-generation mobile communication systems (6G, Beyond 5G), fourth-generation mobile communication systems (4G), and third-generation mobile communication systems (3G).

[0020] The base station device 10 transmits and receives radio waves and relays communication between the wireless terminal 20 and the network N. The base station device 10 may also be a virtualized base station (vRAN (virtual RAN)) in which the physical functions of the base station are separated by software.

[0021] The wireless terminal 20 may be, for example, an in-vehicle communication device installed in a vehicle, or a mobile terminal such as a smartphone owned by a user riding in the vehicle. Alternatively, the wireless terminal 20 may be, for example, a relay device (e.g., IAB (Integrated Access Backhaul), WAB (Wireless Access Backhaul)) that relays communication to a mobile terminal owned by a user riding in the vehicle.

[0022] <Hardware Configuration> Figure 3 shows an example of the hardware configuration of a base station device 10 according to an embodiment. In the example in Figure 3, the base station device 10 (computer 100) includes a processor 101, memory 102, and a communication interface 103. These parts may be connected by a bus or the like. The memory 102 stores at least a portion of the program 104. The communication interface 103 includes an interface necessary for communication with other network elements.

[0023] When program 104 is executed in cooperation with the processor 101 and memory 102, etc., the computer 100 performs at least some of the processing of embodiments of this disclosure. Memory 102 may be of any type. Memory 102 may, in non-limiting examples, be a non-temporary computer-readable storage medium. Memory 102 may also be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. Although only one memory 102 is shown for computer 100, computer 100 may have several physically different memory modules. Processor 101 may be of any type. Processor 101 may include one or more general-purpose computers, dedicated computers, microprocessors, digital signal processors (DSPs), and, in non-limiting examples, processors based on multicore processor architectures. Computer 100 may have multiple processors, such as application-specific integrated circuit chips that are time-dependent to a clock that synchronizes the main processor.

[0024] Embodiments of the present disclosure may be implemented in hardware or in dedicated circuitry, software, logic, or any combination thereof. Some embodiments may be implemented in hardware, while others may be implemented in firmware or software that can be executed by a controller, microprocessor, or other computing device.

[0025] This disclosure also provides at least one computer program product tangibly stored on a non-temporary computer-readable storage medium. The computer program product includes computer-executable instructions, such as instructions contained in a program module, and is executed on a device on a target real or virtual processor to perform the processes or methods of this disclosure. The program module includes routines, programs, libraries, objects, classes, components, data structures, etc., that perform a specific task or implement a specific abstract data type. The functionality of the program module may be combined or divided among the program module as desired in various embodiments. The machine-executable instructions of the program module can be executed on a local or distributed device. On a distributed device, the program module can reside on both local and remote storage media.

[0026] Program code for performing the methods of this disclosure may be written in any combination of one or more programming languages. These program codes are provided to a processor or controller of a general-purpose computer, a dedicated computer, or other programmable data processing device. When the program code is executed by the processor or controller, the functions / operations in the flowchart and / or block diagrams it implements are performed. The program code may run entirely on a machine, partially on a machine, partially as a standalone software package, partially on a machine, partially on a remote machine, or entirely on a remote machine or server.

[0027] The program, when loaded into a computer, includes a set of instructions (or software code) for causing the computer to perform one or more of the functions described in the embodiments. The program may be stored on a non-temporary computer-readable medium or a physical storage medium. Examples, but not limited to, include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disc (DVD), Blu-ray® disc or other optical disc storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage devices. The program may be transmitted over a temporary computer-readable medium or a communication medium. Examples, but not limited to, include temporary computer-readable medium or a communication medium that includes electrically, optically, acoustically or otherwise propagating signals.

[0028] <Processing> Next, an example of the processing of the base station device 10 according to the embodiment will be described with reference to Figures 4 and 5. Figure 4 is a flowchart showing an example of the processing of the base station device 10 according to the embodiment. Figure 5 is a diagram showing an example of the processing of the base station device 10 according to the embodiment. Note that the processing in Figure 4 may be executed at intervals such as periodic intervals.

[0029] In step S101, the acquisition unit 11 acquires information indicating the characteristics of at least one of the propagation delay and Doppler shift of the radio waves received by each wireless terminal 20 from each base station device 10. Here, the acquisition unit 11 may, for example, acquire (measure, estimate) the values ​​(characteristic values) of propagation delay and Doppler shift for each base station device 10 based on channel measurement information for one or more base station devices 10 (e.g., base station device 10A, base station device 10B, etc.) notified by the wireless terminal 20. In this case, the characteristic values ​​of each wireless terminal 20 may be calculated by the base station device 10 or the wireless terminal 20 based on a pilot signal transmitted from the base station device 10 and received by the wireless terminal 20. The pilot signal may be, for example, a signal known to both the base station device 10 and the wireless terminal 20.

[0030] Next, the correction unit 12 corrects the phase of the signal to be transmitted to each wireless terminal 20 in the frequency domain based on the characteristics of each wireless terminal 20 (step S102). Here, the correction unit 12 may perform phase correction, etc., on the frequency domain signal of each wireless terminal 20 before secondary modulation, according to the correction value (offset, pre-compensation amount) for each wireless terminal 20.

[0031] The correction unit 12 maps the transmission signal (complex symbol) x' to the subcarrier index k and symbol index l, which is transmitted to the wireless terminal 20-i (where i is an integer of 2 or more). i,l,l The phase can also be corrected as shown in equation (1) below.

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[0032] Here, x i,l,l k0 is the pre-phase-corrected transmitted signal (complex symbol) of the wireless terminal 20-i, mapped to subcarrier index k and symbol index l. l0 is the symbol index of an arbitrary reference resource element (RE). k0 is the subcarrier index of an arbitrary reference RE.

[0033] θ i= 2πΔf i T s is the phase rotation correction amount of the signal mapped to the RE shifted by one symbol from the symbol index of the reference RE during frequency correction. Φ i = 2πf0Δt i is the phase rotation correction amount of the signal mapped to the RE shifted by one subcarrier from the subcarrier index of the reference RE during timing correction. Δf i is the frequency offset [Hz] to be compensated for the wireless terminal 20-i. Δt i is the timing offset [sec] to be compensated for the wireless terminal 20-i. T s is the symbol interval [sec]. f0 is the subcarrier interval [Hz]. In Equation (1), exp{-jΦ i (k - k0)} is the term for correcting the transmission timing, and exp{-jθ i (l - l0)} is the term for correcting the transmission frequency.

[0034] The reference subcarrier index k0 and symbol index l0 can be arbitrary. The correction unit 12 may, for example, set (k0, l0) = (0, 0). Also, the correction unit 12 may commonly set the reference indices for each of the plurality of wireless terminals 20, or may set them for each wireless terminal 20. FIG. 5 shows an example of phase correction when the reference resource element has a subcarrier index l0 = 0 and a symbol index k0 = 0.

[0035] Hereinafter, in the OFDM system, the influence of the frequency offset caused by the Doppler shift or the like on the demodulation after reception will be described. However, for simplicity, the index of the wireless terminal 20 is omitted from the notation. x k,l represents the transmission symbol mapped to the subcarrier index k and symbol index l. Also, let the subcarrier interval be f0 and the number of subcarriers be K.

[0036] Focusing on the symbol index l. First, the frequency domain signal x k,l(k=0,···,K-1) is OFDM modulated by K-point IFFT (Inverse Fast Fourier Transform), and time-domain samples s l [n](k=0,···,K-1) is converted by the following equation (2).

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[0037] Then, based on each sample point, a time-domain continuous signal s l (t) is generated by the following equation (3).

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[0038] Next, assuming that a frequency offset of Δf [Hz] occurs in the receiver (wireless terminal 20) due to Doppler shift, etc., the received time-domain continuous signal s l RX (t) and the sampled received time-domain sample s l RX Each of [n] is expressed as shown in equations (4) and (5) below. However, channel fluctuations caused by phenomena other than frequency offset are omitted.

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[0039] Next, the received time domain sample s l RX For [n], OFDM demodulation is performed using K-point FFT (Fast Fourier Transform). The demodulated received frequency domain signal x k,l RX It can be expressed by the following equation (6).

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[0040] As described above, the orthogonality of OFDM is disrupted due to the effect of the frequency offset Δf, and after reception, the demodulated x k,l RX The actual transmitted signal x k,l In contrast, h k,l Attenuation and inter-subcarrier interference σ ICI These are added together and the balance is restored.

[0041] x k,l The x symbol is sent after l' minutes. k,l+l’ However, when subjected to a frequency offset Δf, the received frequency domain signal x k,l+l’ RX Similarly, this can be expressed as shown in equation (7) below.

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[0042] From the above, h k,l+l’ =h k,l e jθl’ Since the above holds true, it can be confirmed that the phase of the channel in the frequency domain rotates over time due to the frequency offset. In OFDM, the channel is estimated by mapping pilot symbols known to both the transmitter and receiver to a specific RE (Resource Element). Here, from the perspective of resource utilization efficiency, pilot symbols are often mapped somewhat sparsely, and the channel of an RE to which no pilot symbol is mapped is estimated and interpolated based on the channel estimate of the surrounding RE where pilot symbols are placed. Therefore, if the time variation of the channel due to the frequency offset cannot be accurately grasped, a large error occurs between the actual channel and the channel estimate, significantly degrading the demodulation performance.

[0043] As mentioned above, the reason the orthogonality of OFDM is broken is that each received time-domain sample s is affected by the frequency offset. l RX [n] is each transmission time domain sample s l For [n], e jθ’nThis is because a phase rotation occurs. Therefore, when transmitting, the time-domain sample is subjected to a phase rotation in the opposite direction of the expected phase rotation, s' l [n]=s l [n]e -jθ’n By transmitting this, it becomes possible to compensate for the effects of frequency offset, as shown in equation (8) below, and also to compensate for attenuation and inter-subcarrier interference.

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[0044] The above time-domain pre-compensation for frequency offset is applied to the transmitted time-domain samples s l A correction is applied to [n] according to the expected frequency offset. When frequency / spatial multiplexing signals from multiple wireless terminals, the transmission time-domain sample is generated by combining the signals from the multiple wireless terminals being multiplexed, making it extremely difficult to apply different corrections to each wireless terminal.

[0045] As shown in equation (7), another problem is that the phase of the frequency domain channel rotates over time due to the frequency offset. Therefore, at the time of transmission, the frequency domain symbol is subjected to x', which is the opposite of the expected phase rotation. k,l+l’ RX =x k,l+l’ e -jθl’ By transmitting this, it becomes possible to compensate for the rotation of the channel's phase in the frequency domain over time due to the frequency offset, as shown in equation (9) below.

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[0046] Thus, while frequency domain pre-compensation can compensate for the phase rotation of the frequency domain channel due to frequency offset, it does not compensate for the h due to frequency offset. k,l Attenuation and inter-subcarrier interference σ ICI It is impossible to eliminate this. On the other hand, frequency domain pre-compensation allows for different corrections to be applied to the transmission symbols of each wireless terminal in the frequency domain.

[0047] Similar to the case of frequency offset, the phase of the frequency domain channels rotates according to the frequency offset of each channel relative to the reference frequency (let's call it subcarrier k) as shown in equation (10) below, due to the timing offset (reception timing offset) Δt caused by propagation delay.

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[0048] Therefore, when transmitting, the frequency domain symbol is subjected to x', which is the opposite of the expected phase rotation. k+k’,l =x k+k’,l e -jΦk’ By transmitting this, it becomes possible to compensate for the rotation of the phase of the frequency domain channel due to the timing offset, as shown in equation (11) below.

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[0049] In 5G OFDM systems, cyclic prefixes (CPs) are assigned to each time-domain OFDM symbol to compensate for timing offsets caused by propagation delays, etc. k,l Attenuation and intersymbol interference σ ICI This occurs when the timing offset exceeds the CP length and cannot be compensated for by frequency domain pre-compensation. On the other hand, frequency domain pre-compensation allows for different corrections to be applied to the transmitted symbols of each wireless terminal in the frequency domain.

[0050] <<Regarding the process for determining the correction value>> The correction unit 12 may measure at least one of the frequency offset caused by Doppler shift and the timing offset caused by propagation delay, etc., and determine the measured offset value as the correction value.

[0051] As an example, we will explain how to measure each offset of the wireless terminal 20-i (where i is an integer of 2 or greater) using a pilot signal when the secondary modulation is orthogonal frequency-division multiplexing (OFDM). (Example of frequency offset calculation)

[0052] The correction unit 12 performs a phase rotation θ between multiple pilot signals. i,l,l’ means This can also be calculated using the following equation (12). Note that arg(z) is the argument of the complex number z.

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[0053] Then, the correction unit 12 performs a phase rotation θ between symbols according to the following equation (13). i means It can also be converted to this.

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[0054] Then, the correction unit 12 calculates the frequency offset Δf according to the following equation (14). i It can also be converted to this.

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[0055] The correction unit 12 performs a phase rotation φ between multiple pilot signals. i,k,k’ means This can also be calculated using the following formula (15).

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[0056] Then, the correction unit 12 performs the phase rotation φ between one subcarrier according to the following equation (16). i means It can also be converted to this.

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[0057] Then, the correction unit 12 calculates the timing offset Δt according to the following equation (17). i It can also be converted to this.

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[0058] The above is just one example, and frequency offset and timing offset may be measured by other methods. In this case, the correction unit 12 may determine each offset not only by the phase rotation between two channels, but also by the average of the phase rotations between multiple measurement channels, for example.

[0059] The correction unit 12 may, if necessary, multiply the signal to be mapped to any RE by a multi-antenna weight. When multiple frequency domain signals are mapped to the RE, the correction unit 12 may weight-combine the multiple frequency domain signals to be mapped according to the precoding weight to generate a signal to be mapped to the RE. When U frequency domain signals are mapped to RE(k,l), the correction unit 12 may calculate the precoded frequency domain signals xk,l as shown in equation (18) below. Here, w i This is the multi-antenna weight for the i-th frequency domain signal.

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[0060] (Example of correction in the time domain) The correction unit 12 may correct the phase of the signal transmitted to each wireless terminal in the frequency domain and time domain based on the characteristics of each wireless terminal 20. This allows, for example, that at least one of the frequency offset and timing offset specific to each wireless terminal, which cannot be fully compensated by a common time-domain pre-compensation among the wireless terminals 20, can be compensated by frequency-domain pre-compensation. More specifically, for example, it becomes possible to mitigate the effects of the breakdown of orthogonality of the second-order modulation by time-domain correction, while compensating for the effects of the frequency offset and timing offset specific to each wireless terminal 20, which cannot be fully compensated by time-domain correction, by frequency-domain pre-compensation.

[0061] The correction unit 12 may perform time-domain correction based on at least one of the correction values ​​of a frequency offset for time-domain correction and a timing offset. However, since it is difficult to apply different time-domain corrections to each wireless terminal 20, a common frequency offset correction value Δf is used for all wireless terminals 20. time , and timing offset correction value Δt time Time-domain correction may be performed based on this.

[0062] In this case, the correction unit 12 calculates, for example, the phase correction value θ for frequency offset compensation in the time domain using the following equation (19). time You may calculate this.

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[0063] Then, the correction unit 12 processes, for example, each transmission time domain sample s after secondary modulation. l [n] is corrected using the following formula (20) for the transmission time domain sample s', with sample index n0 as the reference. l [n] may be corrected.

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[0064] Furthermore, the correction unit 12 compensates for the timing offset in the time domain by, for example, adjusting the signal transmission timing by Δt from the original transmission timing. time You can just shift it by a little and send it.

[0065] Correcting in the time domain is difficult because it is difficult to use different correction values ​​for each wireless terminal 20. Therefore, the correction unit 12 may, for example, use the same (uniform) correction value for all wireless terminals 20. In this case, the correction unit 12 may, for example, use a representative value (e.g., mean, mode, or median) of the expected frequency offset for each of the multiple wireless terminals 20 that are the target of communication for the target wireless resource (e.g., per time frame). i Δf i This is the correction value Δf for the frequency offset in the time domain. time (:average i Δf i ) may also be used. In addition, the correction unit 12 may, for example, use the average of the expected timing offset of each of the multiple wireless terminals 20 that are to communicate with the target wireless resource. i Δt i This is the correction value Δt for the frequency offset in the time domain. time (:average i Δt i ) is also acceptable.

[0066] Furthermore, different corrections can be applied to each wireless terminal 20 in the frequency domain. Therefore, the correction unit 12 calculates the expected frequency offset Δf for each wireless terminal 20, for example, as shown in equation (21) below. i And the correction value Δf of the frequency offset in the time domain as described above. time The difference is the correction value Δf in the frequency domain. i freq This can be determined for each of the 20 wireless terminals.

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[0067] Further, the correction unit 12 may determine, for each wireless terminal 20, a difference between the assumed timing offset Δt of each wireless terminal 20 and the correction value Δt of the timing offset in the time domain described above as the correction value of Δt in the frequency domain, for example, as shown in the following formula (22). i and the correction value Δt of the timing offset in the above-described time domain time as the correction value of Δt in the frequency domain i freq for each wireless terminal 20.

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[0068] <Others> The present disclosure relates to a base station device for compensating at least one of a Doppler shift and a propagation delay associated with the movement of a wireless terminal in a wireless communication system that communicates with a wireless terminal moving at high speed, for example, simultaneously with a plurality of base stations or while switching between a plurality of base stations. Note that the present disclosure can be applied to, for example, cases where a plurality of base stations are connected to different control devices (for example, a CU (Central Unit) and a DU (Distributed Unit)), cases where a plurality of base stations are connected to and controlled by the same control device, cases where a plurality of base stations have different physical cell IDs, cases where a plurality of base stations have the same cell ID, and the like.

[0069] In order to achieve a larger capacity in a mobile communication system such as a cellular system, the importance of wireless communication using a high-frequency band such as a millimeter wave or a terahertz wave that can use a wide frequency bandwidth has been increasing. When using a high-frequency band for mobile communication, while large-capacity communication becomes possible by utilizing a wide frequency bandwidth, there are problems such as a large propagation loss depending on the frequency and a large influence by obstacles because of high directivity and difficulty of radio waves to penetrate.

[0070] One way to solve the former problem of propagation loss is beamforming technology, which strengthens the received level of radio signals transmitted in the direction of the communication target by performing appropriate phase control on the radio signals transmitted from multiple antenna elements. By using beamforming technology, it is possible to compensate for the large propagation loss in the high frequency band. Another way to solve the latter problem of straight-line propagation is a distributed antenna system (DAS). By extending the base station antenna and distributing multiple antennas, the probability of line-of-sight communication between the antenna and the radio terminal being blocked is reduced.

[0071] Furthermore, conventional macrocell systems have a large cell radius, and wireless terminals located at the cell edges suffer from reduced received power as they move further from the base station, as well as strong interference from adjacent cells, resulting in degraded communication quality. As one way to solve this problem, technologies that utilize and coordinate the operation of multiple base stations (also called antennas / cells / TRPs (Transmission Reception Points) / APs (Access Points), etc.) installed at relatively high density (e.g., Coordinated Multi-Point (CoMP), Multi-TRP, Single Frequency Network (SFN), Distributed MIMO) have been put into practical use or are under consideration.

[0072] In this context, for example, in the case of in-vehicle terminals that perform high-capacity communication by being mounted on high-speed moving objects such as trains and automobiles, or in wireless environments where wireless terminals move at high speeds, the movement of wireless terminals between the communication areas of multiple base stations becomes relatively frequent. Therefore, joint transmission (JT) and dynamic point selection (DPS) technologies between multiple base stations become particularly important.

[0073] On the other hand, when multiple base stations with different physical locations communicate with a wireless terminal, the wireless terminal is affected by different Doppler shifts and propagation delays for each base station. If the Doppler shift and propagation delay differ significantly from base station to base station, the communication quality may deteriorate during JT and DPS operation due to inter-subcarrier / inter-symbol interference in orthogonal frequency division multiplexing (OFDM), as well as phase rotation in the frequency / time direction of the channel.

[0074] In the case of DPS, in order to stabilize communication quality when switching base stations, it is necessary to compensate for sudden changes in Doppler shift and propagation delay. The same applies to JT, where the signals received by the wireless terminal from each base station antenna are subject to different Doppler shifts and propagation delays. It is difficult for the wireless terminal to simultaneously receive and compensate for the different Doppler shifts and propagation delays of multiple base station antennas, which can significantly degrade the communication quality of JT.

[0075] There are two methods for compensating for frequency offsets caused by Doppler shift and timing offsets caused by propagation delay at the base station transmitting the signal: "frequency domain pre-compensation" and "time domain pre-compensation." In wireless communication systems, when a signal is modulated, a process is often used to convert a signal mapped to the frequency domain into a time domain using OFDM modulation or the like. "Frequency domain pre-compensation" is the process of applying correction to the frequency domain signal before modulation, and "time domain pre-compensation" is the process of applying correction to the time domain signal after modulation.

[0076] Frequency domain pre-compensation is a process performed in the frequency domain where the signal transmitted to each wireless terminal is mapped, making it possible to apply different corrections to each wireless terminal. However, it is impossible to compensate for inter-symbol interference and inter-subcarrier interference caused by frequency offset and timing offset during received OFDM demodulation.

[0077] Time-domain pre-compensation can compensate for the effects of inter-symbol interference and inter-subcarrier interference. However, because this is a correction process applied to the time-domain signal after the signals from multiple wireless terminals have been combined by OFDM modulation, it is difficult to apply different corrections to each wireless terminal when communicating with multiple wireless terminals simultaneously.

[0078] On the other hand, according to this disclosure, at least one of the propagation delay and Doppler shift associated with the movement of wireless terminals can be more appropriately compensated in advance.

[0079] <Variation> The base station device 10 may be a device contained in a single enclosure, but the base station device 10 of this disclosure is not limited to this. Each part of the base station device 10 may be implemented by cloud computing, for example, consisting of one or more computers. Such a base station device 10 is also included as an example of a "base station device" in this disclosure.

[0080] Although the present disclosure has been described above with reference to embodiments, the present disclosure is not limited to the embodiments described above. Various modifications to the structure and details of the present disclosure can be made as can be understood by those skilled in the art within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0081] Some or all of the embodiments described above may also be described as follows, but are not limited to the following. Some or all of the elements (e.g., configuration and function) described in each appendix dependent on Appendix 1 may also be dependent on other independent appendices of other categories in a similar manner. Some or all of the elements described in any appendix may be applicable to various hardware, software, recording means, systems, and methods for recording software. (Note 1) An acquisition unit that acquires information indicating the characteristics of at least one of the propagation delay and Doppler shift at each wireless terminal, A correction unit that corrects the phase of the signal to be transmitted to each wireless terminal in the frequency domain based on the characteristics of each wireless terminal, A base station device having the following features. (Note 2) The acquisition unit acquires information indicating the characteristics of propagation delay at each wireless terminal, The correction unit corrects the phase of the signal transmitted to each wireless terminal in the frequency domain based on the timing offset caused by propagation delay at each wireless terminal. The base station equipment described in Appendix 1. (Note 3) The acquisition unit acquires information indicating the characteristics of Doppler shift at each of the wireless terminals, The correction unit corrects the phase of the signal transmitted to each wireless terminal in the frequency domain based on the frequency offset due to Doppler shift at each wireless terminal. Base station equipment as described in Appendix 1 or 2. (Note 4) The correction unit determines a correction value for the signal to be transmitted to each wireless terminal based on the phase rotation between the pilot signals transmitted from the base station device and received by each wireless terminal. Base station equipment as described in Appendix 1 or 2. (Note 5) The correction unit corrects the phase of the signal transmitted to each wireless terminal in the time domain and the frequency domain based on the characteristics of each wireless terminal. Base station equipment as described in Appendix 1 or 2. (Note 6) The correction unit corrects the phase of the signal transmitted to each wireless terminal in the time domain based on representative values ​​of the characteristics of each wireless terminal. Base station equipment as described in Appendix 5. (Note 7) The correction unit, Based on the representative values ​​of the characteristics of each wireless terminal, the phase of the signal transmitted to each wireless terminal is corrected in the time domain. Based on the difference between the characteristic value at each wireless terminal and the representative value, the phase of the signal transmitted to each wireless terminal is corrected in the frequency domain. Base station equipment as described in Appendix 6. (Note 8) The correction unit corrects the phase of the signal to be transmitted to each wireless terminal in the time domain for each time frame, based on a representative value of the characteristics of each wireless terminal. Base station equipment as described in Appendix 6. (Note 9) Information is obtained that shows the characteristics of at least one of the propagation delay and Doppler shift at each wireless terminal. Based on the characteristics of each wireless terminal, the phase of the signal transmitted to each wireless terminal is corrected in the frequency domain. Communication method. (Note 10) Information is obtained that shows the characteristics of at least one of the propagation delay and Doppler shift at each wireless terminal. Based on the characteristics of each wireless terminal, the phase of the signal transmitted to each wireless terminal is corrected in the frequency domain. A program that instructs a computer to perform a process. [Explanation of Symbols]

[0082] 1. Communication System 10 Base station equipment 11 Acquisition Department 12 Correction section 20 Wireless terminals

Claims

1. An acquisition unit that acquires information indicating the characteristics of at least one of the propagation delay and Doppler shift at each wireless terminal, A correction unit that corrects the phase of the signal to be transmitted to each wireless terminal in the frequency domain based on the characteristics of each wireless terminal, A base station device having the following features.

2. The acquisition unit acquires information indicating the characteristics of propagation delay at each wireless terminal, The correction unit corrects the phase of the signal transmitted to each wireless terminal in the frequency domain based on the timing offset caused by propagation delay at each wireless terminal. The base station device according to claim 1.

3. The acquisition unit acquires information indicating the characteristics of the Doppler shift at each of the wireless terminals. The correction unit corrects the phase of the signal transmitted to each wireless terminal in the frequency domain based on the frequency offset due to Doppler shift at each wireless terminal. The base station device according to claim 1 or 2.

4. The correction unit determines a correction value for the signal to be transmitted to each wireless terminal based on the phase rotation between the pilot signals transmitted from the base station device and received by each wireless terminal. The base station device according to claim 1 or 2.

5. The correction unit corrects the phase of the signal transmitted to each wireless terminal in the time domain and the frequency domain based on the characteristics of each wireless terminal. The base station device according to claim 1 or 2.

6. The correction unit corrects the phase of the signal transmitted to each wireless terminal in the time domain based on representative values ​​of the characteristics of each wireless terminal. The base station device according to claim 5.

7. The correction unit, Based on the representative values ​​of the characteristics of each wireless terminal, the phase of the signal transmitted to each wireless terminal is corrected in the time domain. Based on the difference between the characteristic value at each wireless terminal and the representative value, the phase of the signal transmitted to each wireless terminal is corrected in the frequency domain. The base station device according to claim 6.

8. The correction unit corrects the phase of the signal to be transmitted to each wireless terminal in the time domain for each time frame, based on a representative value of the characteristics of each wireless terminal. The base station device according to claim 6.

9. Information is obtained that shows the characteristics of at least one of the propagation delay and Doppler shift at each wireless terminal. Based on the characteristics of each wireless terminal, the phase of the signal transmitted to each wireless terminal is corrected in the frequency domain. Communication method.

10. Information is obtained that shows the characteristics of at least one of the propagation delay and Doppler shift at each wireless terminal. Based on the characteristics of each wireless terminal, the phase of the signal transmitted to each wireless terminal is corrected in the frequency domain. A program that instructs a computer to perform a process.

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