Terminal device, communication method, and computer program

Abstract

This terminal device comprises a radio reception unit that receives a multiplexed signal transmitted from a base station upon multiplexing an orthogonal frequency division multiplexing (OFDM) modulation signal of a base station transmission signal and an orthogonal time frequency space (OTFS) modulation signal of the base station transmission signal, a signal processing unit that demodulates the OTFS modulation system when demodulation of the OFDM modulation system fails for the received multiplexed signal, and a radio transmission unit that transmits a first terminal transmission signal for notifying the base station that demodulation of the OTFS modulation system is successful when demodulation of the OFDM modulation system fails for the received multiplexed signal.

Description

Terminal device, communication method, and computer program

[0001] This application claims priority to Japanese Patent Application No. 2023-138793, filed on August 29, 2023, the contents of which are incorporated herein by reference.

[0002] In a fifth-generation (5G) mobile communication system (hereinafter referred to as a 5G system), during initial access by a terminal (UE), a base station (gNB) uses a broadcast channel (PBCH (Physical Broadcast CHannel)) to broadcast broadcast information necessary for the terminal to perform a connection procedure to a cell. The broadcast information includes, for example, information on a common channel in the downlink direction (direction from the base station to the terminal) and information on a Random Access Channel (RACH), which is a common channel in the uplink direction (direction from the terminal to the base station).

[0003] Patent Document 1 describes a technology that uses different modulation methods for the uplink and downlink directions. For example, the uplink direction uses an Orthogonal Time Frequency Space (OTFS) modulation method, while the downlink direction uses an Orthogonal Frequency Division Multiplexing (OFDM) modulation method.

[0004] International Publication No. 2022 / 217536

[0005] The OFDM modulation method suffers from a degradation in communication performance due to the Doppler effect when a terminal is moving. The Doppler effect is particularly significant for terminals moving at high speeds, which significantly degrades the communication performance of the OFDM modulation method. One approach to address this problem is to use the OTFS modulation method, but how to utilize the OFDM modulation method and the OTFS modulation method has been an issue.

[0006] The present disclosure has been made in consideration of the above circumstances, and one example of its purpose is to improve the stability of communications between a base station and a terminal.

[0007] One aspect of the present disclosure is a terminal device including: a radio receiving unit that receives a multiplexed signal that is transmitted from a base station by multiplexing an OFDM (Orthogonal Frequency Division Multiplexing) modulated signal of a base station transmission signal and an OTFS (Orthogonal Time Frequency Space) modulated signal of the base station transmission signal; a signal processing unit that performs OTFS modulation demodulation on the received multiplexed signal when demodulation of the OFDM modulation scheme fails; and a radio transmitting unit that transmits a first terminal transmission signal that notifies the base station that demodulation of the OTFS modulation scheme has been successful when demodulation of the OFDM modulation scheme has been failed. Another aspect of the present disclosure is the terminal device described above, wherein the first terminal transmission signal is the OTFS modulated signal. Another aspect of the present disclosure is the terminal device described above, wherein the radio transmitting unit transmits a second terminal transmission signal that notifies the base station that demodulation of the OFDM modulation scheme has been successful on the received multiplexed signal. One aspect of the present disclosure is the above-mentioned terminal device, wherein the second terminal transmission signal is the OFDM modulated signal. Another aspect of the present disclosure is the above-mentioned terminal device, wherein the base station transmission signal is a PBCH (Physical Broadcast CHannel) signal. Another aspect of the present disclosure is the above-mentioned terminal device, wherein the first terminal transmission signal is the OTFS modulated signal of a RACH (Random Access CHannel) signal. Another aspect of the present disclosure is the above-mentioned terminal device, wherein the radio transmitting unit transmits the OFDM modulated signal of the RACH signal as a second terminal transmission signal that notifies the base station that demodulation of the received multiplexed signal using the OFDM modulation scheme has been successful.

[0008] One aspect of the present disclosure is a communication method executed by a terminal device, the communication method including: a wireless receiving step of receiving a multiplexed signal obtained by multiplexing an OFDM (Orthogonal Frequency Division Multiplexing) modulated signal of a base station transmission signal and an OTFS (Orthogonal Time Frequency Space) modulated signal of the base station transmission signal, the multiplexed signal being transmitted from a base station; a signal processing step of demodulating the received multiplexed signal using an OTFS modulation scheme when demodulation using the OFDM modulation scheme has failed; and a wireless transmitting step of transmitting a first terminal transmission signal notifying the base station that demodulation using the OTFS modulation scheme has succeeded when demodulation using the OFDM modulation scheme has failed.

[0009] One aspect of the present disclosure is a computer program causing a computer of a terminal device to execute the following steps: a wireless receiving step of receiving a multiplexed signal obtained by multiplexing an OFDM (Orthogonal Frequency Division Multiplexing) modulated signal of a base station transmission signal and an OTFS (Orthogonal Time Frequency Space) modulated signal of the base station transmission signal, the multiplexed signal being transmitted from a base station; a signal processing step of demodulating the received multiplexed signal using an OTFS modulation scheme when demodulation using the OFDM modulation scheme has failed; and a wireless transmitting step of transmitting a first terminal transmission signal to the base station, when demodulation using the OFDM modulation scheme has failed, notifying the base station that demodulation using the OTFS modulation scheme has succeeded. Another aspect of the present disclosure is the computer program, wherein the base station transmission signal is a PBCH (Physical Broadcast Channel) signal.

[0010] According to the present disclosure, as one example, an effect can be obtained in which the stability of communication between a base station and a terminal can be improved.

[0011] FIG. 1 is a block diagram showing an example of a schematic configuration of a terminal device according to an embodiment. FIG. 2 is a flowchart showing an example of the procedure of a communication method according to an embodiment. FIG. 3 is a sequence chart between a base station (gNB) and a terminal device (UE) showing an example of the procedure of a communication method according to an embodiment. FIG. 4 is a first diagram showing an example of a multiplexing method of an OFDM modulated signal and an OTFS modulated signal according to an embodiment. FIG. 5 is a second diagram showing an example of a multiplexing method of an OFDM modulated signal and an OTFS modulated signal according to an embodiment. FIG. 6 is a first diagram showing an example of a multiplexing method of an OFDM modulated signal and an OTFS modulated signal according to an embodiment. FIG. 7 is a second diagram showing an example of a multiplexing method of an OFDM modulated signal and an OTFS modulated signal according to an embodiment. FIG. 8 is a diagram showing an example of a multiplexing method of an OFDM modulated signal and an OTFS modulated signal according to an embodiment.

[0012] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Fig. 1 is a block diagram showing a schematic configuration example of a terminal device according to one embodiment. The terminal device 1 may be, for example, a terminal (UE) of a mobile communication system such as a 5G system, or may be a terminal of a wireless LAN system. Hereinafter, a terminal (UE) of a mobile communication system such as a 5G system will be described as an example of the terminal device 1 according to this embodiment.

[0013] In FIG. 1, the terminal device 1 includes a signal processing unit 10 , a radio unit 20 , an antenna 30 , a communication control unit 50 , and a transmission processing unit 60 .

[0014] Each part of the terminal device 1 may be realized by dedicated hardware, or may be composed of a CPU (Central Processing Unit) and memory, etc., and the functions of each part may be realized by the CPU executing a computer program for realizing the function of each part.

[0015] The radio unit 20 receives a radio signal transmitted from a base station device via the antenna 30. A received signal A, which is the radio signal transmitted from the base station device and received by the radio unit 20, is input to the signal processing unit 10. The received signal A is, for example, a broadcast signal broadcast to terminals. The received signal A is, for example, a PBCH (Physical Broadcast Channel) signal. The PBCH signal is a broadcast signal broadcast to terminals.

[0016] The signal processing unit 10 includes a CP (Cyclic Prefix) removal unit 101 , an OFDM (Orthogonal Frequency Division Multiplexing) demodulation unit 102 , an OTFS (Orthogonal Time Frequency Space) demodulation unit 103 , and a determination unit 104 .

[0017] The CP removal section 101 removes the CP from the received signal A.

[0018] The OFDM demodulation unit 102 performs OFDM demodulation on the CP-removed received signal B, which is obtained by removing the CP from the received signal A.

[0019] The OTFS demodulation unit 103 performs OTFS demodulation on the CP-removed received signal B obtained by removing the CP from the received signal A.

[0020] The determination unit 104 determines whether or not the OFDM demodulation of the OFDM modulation method has been successful for the OFDM demodulated signal C that is the result of the OFDM demodulation of the CP-removed received signal B.

[0021] The determination unit 104 determines whether or not the OTFS demodulation of the CP-removed received signal B, which is an OTFS demodulation signal D resulting from the OTFS demodulation, has been successful.

[0022] If the demodulation using the OFDM modulation method fails, the determination unit 104 outputs an OTFS demodulation control signal E instructing demodulation using the OTFS modulation method to the OTFS demodulation unit 103. In response to the OTFS demodulation control signal E instructing demodulation using the OTFS modulation method, the OTFS demodulation unit 103 starts OTFS demodulation on the CP-removed received signal B. If the OTFS demodulation control signal E does not instruct demodulation using the OTFS modulation method, the OTFS demodulation unit 103 does not demodulate the CP-removed received signal B using the OTFS modulation method.

[0023] If the demodulation using the OFDM modulation method is successful, the determination unit 104 outputs an OTFS demodulation control signal E instructing the OTFS demodulation method to be stopped to the OTFS demodulation unit 103. In response to the OTFS demodulation control signal E instructing the OTFS demodulation method to be stopped, the OTFS demodulation unit 103 stops the OTFS modulation method demodulation of the CP-removed received signal B.

[0024] The determination unit 104 outputs to the communication control unit 50 a demodulation status signal G indicating whether the demodulation of the OFDM modulation method and the demodulation of the OTFS modulation method have been successful.

[0025] If the demodulation of the OFDM modulation method is successful, the determination unit 104 outputs the OFDM demodulated signal C as the demodulated signal F. If the demodulation of the OFDM modulation method is unsuccessful but the demodulation of the OTFS modulation method is successful, the determination unit 104 outputs the OTFS demodulated signal D as the demodulated signal F.

[0026] The communication control unit 50 determines whether the OFDM modulation method or the OTFS modulation method should be used for transmission to the base station device based on the demodulation status signal G. When the demodulation status signal G indicates successful demodulation of the OFDM modulation method, the communication control unit 50 uses the OFDM modulation method for transmission to the base station device. When the demodulation status signal G indicates successful demodulation of the OTFS modulation method but indicates a failure in demodulation of the OFDM modulation method, the communication control unit 50 uses the OTFS modulation method for transmission to the base station device. The communication control unit 50 instructs the transmission processing unit 60 whether the OFDM modulation method or the OTFS modulation method should be used for transmission to the base station device.

[0027] The transmission processing unit 60 modulates a signal (terminal transmission signal) to be transmitted to the base station device using either the OFDM modulation method or the OTFS modulation method, as instructed by the communication control unit 50 .

[0028] The OFDM modulated signal obtained by converting the terminal transmission signal using the OFDM modulation method is wirelessly transmitted by the radio unit 20 via the antenna 30 and received by the base station device. The OTFS modulated signal obtained by converting the terminal transmission signal using the OTFS modulation method is wirelessly transmitted by the radio unit 20 via the antenna 30 and received by the base station device.

[0029] Next, an example of the operation of the terminal device 1 according to this embodiment will be described with reference to Figures 2 and 3. Figure 2 is a flowchart showing an example of the procedure of the communication method according to this embodiment. Here, the received signal A is a PBCH signal as an example.

[0030] (Step S1) The base station device periodically wirelessly transmits a multiplexed signal (OFDM-PBCH and OTFS-PBCH multiplexed signal) including an OFDM-modulated signal of a PBCH signal and an OTFS-modulated signal of the PBCH signal. The multiplexing method of the multiplexed signal may be TDM (Time Division Multiplexing) or FDM (Frequency Division Multiplexing).

[0031] Here, the PBCH signal has information (RACH information) of a RACH (Random Access Channel), which is an uplink common channel. The RACH information includes OFDM resource designation information that designates radio resources to be used for the OFDM modulation scheme and OTFS resource designation information that designates radio resources to be used for the OTFS modulation scheme. Note that the radio resources of the RACH used for the OFDM modulation scheme and the radio resources of the RACH used for the OTFS modulation scheme are set to different time-frequency resources, so that the RACH of the OFDM modulation scheme and the RACH of the OTFS modulation scheme do not interfere with each other, which is preferable from the viewpoint of correct RACH detection. In this case, the RACH information of the PBCH signal included in the OFDM modulated signal and the RACH information of the PBCH signal included in the OTFS modulated signal may be common information having both OFDM resource designation information and OTFS resource designation information, or may be separate information having only the respective resource designation information (only OFDM resource designation information for the OFDM modulated signal, and only OTFS resource designation information for the OTFS modulated signal).

[0032] The terminal device 1 receives a multiplexed signal of OFDM-PBCH and OTFS-PBCH periodically transmitted wirelessly from a base station device. The terminal device 1 removes the CP from the received multiplexed signal of OFDM-PBCH and OTFS-PBCH (received signal A).

[0033] (Step S2) The terminal device 1 performs OFDM modulation demodulation on the CP-removed received signal B, in which the CP has been removed from the received OFDM-PBCH and OTFS-PBCH multiplexed signal (received signal A). The terminal device 1 determines whether the OFDM modulation demodulation has been successful for the OFDM demodulated signal C, which is the result of the demodulation using the OFDM modulation method.

[0034] As an example of this determination method, CRC (Cyclic Redundancy Check) may be used. The base station device includes a CRC code of the PBCH signal in the multiplexed signal of OFDM-PBCH and OTFS-PBCH. The terminal device 1 determines whether or not a PBCH signal modulated by the OFDM modulation scheme has been received (whether demodulation of the OFDM modulation scheme has been successful) using the CRC code of the PBCH signal included in the multiplexed signal of OFDM-PBCH and OTFS-PBCH. Note that the terminal device 1 may perform a determination using the CRC for each multiplexed signal of OFDM-PBCH and OTFS-PBCH received multiple times, and determine whether or not a PBCH signal modulated by the OFDM modulation scheme has been received (whether demodulation of the OFDM modulation scheme has been successful) from the results of the multiple determinations.

[0035] If it is determined that a PBCH signal using the OFDM modulation method has been received (demodulation using the OFDM modulation method has been successful) (step S2, YES), the process proceeds to step S4. On the other hand, if it is determined that a PBCH signal using the OFDM modulation method has not been received (demodulation using the OFDM modulation method has failed) (step S2, NO), the process proceeds to step S3.

[0036] (Step S3) The terminal device 1 performs OTFS modulation demodulation on the CP-removed received signal B, which is obtained by removing the CP from the received OFDM-PBCH and OTFS-PBCH multiplexed signal (received signal A). The terminal device 1 determines whether or not the OTFS modulation demodulation has been successful for the OTFS demodulated signal D, which is the result of the demodulation using the OTFS modulation method. As an example of a method for this determination, CRC may be used, as in the case of the OFDM modulation method.

[0037] If it is determined that a PBCH signal using the OTFS modulation method has been received (demodulation using the OTFS modulation method has been successful) (step S3, YES), the process proceeds to step S7. On the other hand, if it is determined that a PBCH signal using the OTFS modulation method has not been received (demodulation using the OTFS modulation method has failed) (step S3, NO), the process returns to step S2.

[0038] (Step S4) Since the demodulation of the OFDM modulation scheme was successful, the terminal device 1 uses the OFDM modulation scheme for transmission to the base station device. If the demodulation of the OFDM-modulated signal of the PBCH signal was successful, the terminal device 1 transmits an uplink signal using the OFDM modulation scheme, using the radio resources specified by the OFDM resource designation information included in the PBCH signal. The terminal device 1 transmits an OFDM-modulated RACH signal (OFDM-RACH signal) obtained by converting the RACH signal using the OFDM modulation scheme, using the radio resources specified by the OFDM resource designation information.

[0039] When the base station device determines that it has received a RACH signal using the OFDM modulation method from the terminal device 1, it records that the transmitting terminal device 1 is moving at a low speed and that it is a terminal that transmits uplink signals using the OFDM modulation method. Note that low speed also includes stationary.

[0040] (Step S5) The terminal device 1 uses the radio resources specified by the OFDM resource specification information to complete initial access to the relevant base station using the OFDM modulation scheme in accordance with a predetermined random access procedure.

[0041] (Step S6) The terminal device 1 performs data communication with the base station device using OFDM modulated signals.

[0042] (Step S7) Since the demodulation of the OTFS modulation method was successful when the demodulation of the OFDM modulation method failed, the terminal device 1 uses the OTFS modulation method for transmission to the base station device. If the demodulation of the OTFS-modulated signal of the PBCH signal is successful, the terminal device 1 transmits an uplink signal by the OTFS modulation method using the radio resources specified by the OTFS resource designation information included in the PBCH signal. The terminal device 1 transmits an OTFS-modulated RACH signal (OTFS-RACH signal) obtained by converting the RACH signal by the OTFS modulation method using the radio resources specified by the OTFS resource designation information.

[0043] When the base station device determines that it has received a RACH signal of the OTFS modulation method from the terminal device 1, it records that the transmitting terminal device 1 is moving at high speed and that it is a terminal that transmits uplink signals using the OTFS modulation method. A terminal that has succeeded in demodulating the OTFS modulation method when demodulating the OFDM modulation method has failed is considered to be a terminal moving at high speed.

[0044] (Step S8) The terminal device 1 uses the radio resources specified by the OTFS resource specification information to complete initial access to the relevant base station using the OTFS modulation method in accordance with a predetermined random access procedure.

[0045] (Step S9) The terminal device 1 performs data communication with the base station device using an OTFS modulated signal.

[0046] The base station device may monitor a change in the modulation method used by the terminal device 1 (a change between the OFDM modulation method and the OTFS modulation method), determine an increase or decrease in the movement speed of the terminal device 1 from the monitoring result, and record the determination result of the increase or decrease in the movement speed of the terminal device 1. When the modulation method is changed from the OFDM modulation method to the OTFS modulation method, the base station device determines that the movement speed of the terminal device 1 has increased. On the other hand, when the modulation method is changed from the OTFS modulation method to the OFDM modulation signal, the base station device determines that the movement speed of the terminal device 1 has decreased.

[0047] Furthermore, a threshold value for the movement speed of the terminal device 1 when the modulation method is changed from the OFDM modulation method to the OTFS modulation method may be set in advance in the base station device, and the base station device may use this threshold value to estimate the movement speed of the terminal device 1. Furthermore, a threshold value for the movement speed of the terminal device 1 when the modulation method is changed from the OTFS modulation method to the OFDM modulation method may be set in advance in the base station device, and the base station device may use this threshold value to estimate the movement speed of the terminal device 1.

[0048] 3 is a sequence chart showing an example of a procedure of a communication method according to the present embodiment between a base station (gNB) and a terminal device 1 (UE). Here, a PBCH signal is used as an example of a received signal A.

[0049] (Step S101) The base station (gNB) periodically wirelessly transmits a multiplexed signal (OFDM-PBCH and OTFS-PBCH multiplexed signal) including an OFDM-modulated signal of a PBCH signal and an OTFS-modulated signal of the PBCH signal.

[0050] A terminal device 1 (UE) receives a multiplexed signal of OFDM-PBCH and OTFS-PBCH wirelessly transmitted from a base station device. Upon receiving the multiplexed signal of OFDM-PBCH and OTFS-PBCH, the terminal device 1 (UE) acquires the PBCH signal by successfully demodulating either the OFDM modulated signal of the PBCH signal or the OTFS modulated signal of the PBCH signal, acquires RACH information included in the acquired PBCH signal, and acquires OFDM resource designation information and OTFS resource designation information included in the acquired RACH information.

[0051] (Step S102) If the demodulation of the OFDM modulated signal of the PBCH signal is successful, the terminal device 1 (UE) transmits a RACH signal (OFDM-RACH signal) by the OFDM modulation method using the radio resource specified by the OFDM resource specification information.

[0052] On the other hand, if the demodulation of the OFDM modulated signal of the PBCH signal fails but the demodulation of the OTFS modulated signal of the PBCH signal is successful, the terminal device 1 (UE) transmits a RACH signal (OTFS-RACH signal) using the OTFS modulation method using the radio resource specified by the OTFS resource specification information.

[0053] The base station (gNB) receives a RACH signal using the OFDM modulation method or the OTFS modulation method from the terminal (UE).

[0054] The base station (gNB) uses a PBCH signal to specify the radio resources used by the terminal device 1 (UE) for the OFDM modulation method and the radio resources used for the OTFS modulation method as separate radio resources. As a result, the base station (gNB) can determine whether the transmitting terminal device 1 (UE) is a terminal using the OFDM modulation method (a terminal moving at a low speed) or a terminal using the OTFS modulation method (a terminal moving at a high speed) by detecting the radio resources used for the RACH signal transmitted from the terminal device 1 (UE).

[0055] When a base station (gNB) receives a RACH signal using the OFDM modulation method from a terminal device 1 (UE), it records that the transmitting terminal device 1 (UE) is moving at a low speed and is a terminal that transmits uplink signals using the OFDM modulation method. On the other hand, when a base station (gNB) receives a RACH signal using the OTFS modulation method from a terminal device 1 (UE), it records that the transmitting terminal device 1 (UE) is moving at a high speed and is a terminal that transmits uplink signals using the OTFS modulation method.

[0056] (Step S103) If the demodulation of the OFDM-modulated signal of the PBCH signal is successful, the terminal (UE) completes a predetermined initial access procedure using the OFDM modulation method. On the other hand, if the demodulation of the OFDM-modulated signal of the PBCH signal is unsuccessful but the demodulation of the OTFS-modulated signal of the PBCH signal is successful, the terminal (UE) completes a predetermined initial access procedure using the OTFS modulation method.

[0057] The base station (gNB) detects a reference signal using the OFDM modulation method or the OTFS modulation method transmitted from the terminal device 1 (UE).

[0058] (Step S104) The base station (gNB) performs data communication using an OFDM modulated signal with the terminal device 1 (terminal whose moving state is determined to be low speed) that transmits an uplink signal using the OFDM modulation method. On the other hand, the base station (gNB) performs data communication using the OTFS modulation method with the terminal device 1 (terminal whose moving state is determined to be high speed) that transmits an uplink signal using the OTFS modulation method.

[0059] Next, a method for multiplexing an OFDM modulated signal and an OTFS modulated signal according to this embodiment will be described below. Figures 4 to 6 are diagrams showing examples of a method for multiplexing an OFDM modulated signal and an OTFS modulated signal according to this embodiment.

[0060] Figure 4A shows an example of multiplexing an OFDM modulated signal and an OTFS modulated signal for a PBCH signal using the TDM method. Figure 4B shows an example of multiplexing an OFDM modulated signal and an OTFS modulated signal for a PBCH signal using the FDM method. The horizontal axis of Figures 4A and 4B represents time, and the vertical axis represents frequency.

[0061] Figure 5A shows another example of multiplexing an OFDM modulated signal and an OTFS modulated signal for a PBCH signal using the TDM method. Figure 5B shows another example of multiplexing an OFDM modulated signal and an OTFS modulated signal for a PBCH signal using the FDM method. The horizontal axis of Figures 5A and 5B represents frequency, and the vertical axis represents time.

[0062] FIG. 6 shows an example in which an OFDM modulated signal and an OTFS modulated signal are multiplexed using the TDM method and the FDM method for a PBCH signal.

[0063] According to this embodiment, a base station transmission signal, such as a PBCH signal, transmitted from the base station device to the terminal device 1 can be transmitted from the base station device using both the OFDM modulation method and the OTFS modulation method. As a result, even if the terminal device 1 moving at high speed fails to demodulate the OFDM modulation method, the terminal device 1 can correctly receive the base station transmission signal because the OTFS modulation method demodulation is successful. Furthermore, a terminal device 1 moving at low speed can correctly receive the base station transmission signal because the OFDM modulation method demodulation is successful. Therefore, according to this embodiment, whether the terminal device 1 is moving at high speed or at low speed, the base station transmission signal, such as a PBCH signal, can be correctly received. This has the effect of improving the stability of communication between the base station and the terminal.

[0064] Furthermore, since the terminal device 1 performs demodulation using the OTFS modulation method when demodulation using the OFDM modulation method fails, it is not necessary to perform demodulation using the OTFS modulation method all the time, which allows for a reduction in power consumption in the terminal device 1.

[0065] The base station device also receives a terminal transmission signal using the OFDM modulation method or the OTFS modulation method, which is transmitted from a terminal device 1 that has received an OFDM-modulated signal or an OTFS-modulated signal converted from the base station transmission signal. This makes it possible to determine whether the transmitting terminal device 1 is moving at a low speed or a high speed. This is because a terminal device 1 moving at a low speed will be successful in demodulating the OFDM modulation method, while a terminal device 1 moving at a high speed will be successful in demodulating the OTFS modulation method even if the OFDM modulation method demodulation fails.

[0066] In addition, a terminal device 1 determined to be moving at a low speed performs data communication using the OFDM modulation method, and a terminal device 1 determined to be moving at a high speed performs data communication using the OTFS modulation method, thereby contributing to realizing stable data communication between the base station and the terminal device 1.

[0067] This will enable, for example, improvements to the overall service quality of mobile communication systems, thereby contributing to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0068] The above has described in detail an embodiment of the present disclosure with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present disclosure.

[0069] Furthermore, a computer program for implementing the functions of each of the above-described devices may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read and executed by a computer system. Note that the term "computer system" may also include hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to a flexible disk, a magneto-optical disk, a ROM, a writable nonvolatile memory such as a flash memory, a portable medium such as a DVD (Digital Versatile Disc), or a storage device such as a hard disk built into a computer system.

[0070] Furthermore, the term "computer-readable recording medium" also includes a storage medium that stores a program for a certain period of time, such as a volatile memory (e.g., a dynamic random access memory (DRAM)) within a computer system that serves as a server or client when the program is transmitted via a network such as the Internet or a communication line such as a telephone line. The program may also be transmitted from a computer system that stores the program in a storage device or the like to another computer system via a transmission medium or by transmission waves within the transmission medium. Here, the "transmission medium" that transmits the program refers to a medium that has the function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may also be a program that realizes part of the aforementioned functions. Furthermore, the program may be a so-called differential file (differential program) that can realize the aforementioned functions in combination with a program already stored in the computer system.

[0071] According to the present disclosure, as one example, an effect can be obtained in which the stability of communication between a base station and a terminal can be improved.

[0072] 1... terminal device, 10... signal processing unit, 20... radio unit, 30... antenna, 50... communication control unit, 60... transmission processing unit, 101... CP removal unit, 102... OFDM demodulation unit, 103... OTFS demodulation unit, 104... determination unit

Claims

1. A terminal device comprising: a wireless receiving unit that receives a multiplexed signal transmitted from a base station by multiplexing an OFDM (Orthogonal Frequency Division Multiplexing) modulated signal of a base station transmission signal and an OTFS (Orthogonal Time Frequency Space) modulated signal of a base station transmission signal; a signal processing unit that performs OTFS modulation demodulation on the received multiplexed signal when demodulation of the OFDM modulation method fails; and a wireless transmitting unit that transmits a first terminal transmission signal notifying the base station that demodulation of the OTFS modulation method was successful when demodulation of the OFDM modulation method on the received multiplexed signal fails.

2. The terminal device according to claim 1, wherein the first terminal transmission signal is an OTFS modulated signal.

3. The terminal device according to claim 1 or 2, wherein the wireless transmitting unit transmits a second terminal transmission signal notifying the base station that demodulation of the received multiplexed signal using the OFDM modulation method has been successful.

4. The terminal device according to claim 3, wherein the second terminal transmission signal is the OFDM modulated signal.

5. The terminal device according to claim 1, wherein the base station transmission signal is a PBCH (Physical Broadcast CHannel) signal.

6. The terminal device according to claim 5, wherein the first terminal transmission signal is an OTFS modulated signal of a RACH (Random Access CHannel) signal.

7. The terminal device according to claim 5 or 6, wherein the radio transmitting unit transmits the OFDM modulated signal of a RACH signal as a second terminal transmission signal for notifying the base station that demodulation of the received multiplexed signal using the OFDM modulation method has been successful.

8. A communications method executed by a terminal device, comprising: a wireless receiving step of receiving a multiplexed signal transmitted from a base station by multiplexing an OFDM (Orthogonal Frequency Division Multiplexing) modulated signal of a base station transmission signal and an OTFS (Orthogonal Time Frequency Space) modulated signal of a base station transmission signal; a signal processing step of performing OTFS modulation demodulation on the received multiplexed signal when demodulation of the OFDM modulation method has failed; and a wireless transmitting step of transmitting a first terminal transmission signal notifying the base station that demodulation of the OTFS modulation method has been successful when demodulation of the OFDM modulation method has failed on the received multiplexed signal.

9. The communication method according to claim 8, wherein the base station transmission signal is a PBCH (Physical Broadcast CHannel) signal.

10. A computer program for causing a terminal device computer to execute the following steps: a wireless receiving step of receiving a multiplexed signal transmitted from a base station by multiplexing an OFDM (Orthogonal Frequency Division Multiplexing) modulated signal of a base station transmission signal and an OTFS (Orthogonal Time Frequency Space) modulated signal of a base station transmission signal; a signal processing step of demodulating the received multiplexed signal using an OTFS modulation method when demodulation using the OFDM modulation method has failed; and a wireless transmitting step of transmitting a first terminal transmission signal notifying the base station that demodulation using the OTFS modulation method has been successful when demodulation using the OFDM modulation method has failed for the received multiplexed signal.

11. The computer program product according to claim 10, wherein the base station transmission signal is a PBCH (Physical Broadcast CHannel) signal.

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