Link adaptation method and apparatus

Abstract

To provide link adaptation method and device that can appropriately set the MCS of a radio access link according to the moving speed of a radio terminal in a mobile communication system.SOLUTION: A link adaptation method includes transmitting an OFDM-CSI-RS from a radio base station to a radio terminal, transmitting an OTFS-CSI-RS from the radio base station to the radio terminal, receiving the OFDM-CSI-RS and determining a CQI by the radio terminal, receiving the OTFS-CSI-RS and estimating a Doppler shift by the radio terminal, feeding back information of the CQI and Doppler shift information from the radio terminal to the radio base station, receiving the CQI and Doppler shift information and determining an MCS by the radio base station, and notifying the radio terminal of the determined MCS.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a link adaptation method and apparatus in a mobile communication system, and particularly to a link adaptation method and apparatus for setting the MCS (Modulation and Coding Scheme) of a radio access link according to the signal quality and moving speed of a wireless terminal in a mobile communication system.

Background Art

[0002] The orthogonal frequency division multiplexing (OFDM: Orthogonal Frequency Division Multiplexing) method used in the 4th and 5th generation mobile communication services has high spectral efficiency and excellent resistance to multipath fading. Also, in the above services, link adaptation that switches the MCS according to the communication quality of a communication terminal is used, and the signal-to-interference and noise power ratio (SINR), or the CQI (Channel Quality Indicator) having a corresponding relationship with them, is used as an index of communication quality.

[0003] Orthogonal time frequency space (OTFS: Orthogonal Time Frequency Space) transmission has attracted attention as a transmission method capable of coping with temporal changes caused by different Doppler shifts.

[0004] Patent Document 1 discloses a technique related to the co-operation of an OTFS modulation communication system and an LTE system using OFDM.

[0005] Non-Patent Document 1 shows a fair comparison between OTFS and OFDM in an environment with sparsity.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] [Non-Patent Document 1] IEEE, OTFS vs. OFDM in the Presence of Sparsity: A FairComparison [Overview of the project] [Problems that the invention aims to solve]

[0008] Figure 2 compares the throughput of OFDM and OTFS modulation schemes for each Doppler frequency. OFDM has a problem in high-speed mobile environments where the Doppler shift causes unstable data communication quality and reduces communication reliability.

[0009] While it would be possible to improve performance if the MCS of the wireless access link could be adaptively switched not only according to the SINR but also according to the effect of Doppler shift, the OFDM modulation scheme does not include Doppler shift information in the CQI (Channel Quality Information). Therefore, it is necessary to periodically set an adaptive modulation scheme that corresponds to the Doppler shift.

[0010] The object of the present invention is to solve the above technical problems and to provide a link adaptation method and apparatus that can adaptively switch the MCS in response to the effects of Doppler shift. [Means for solving the problem]

[0011] To achieve the above objectives, the present invention provides a link adaptation method for a radio access link in a mobile communication system, wherein a radio base station transmits an OFDM-modulated reference signal (e.g., CSI-RS (OFDM-CSI-RS)) to a radio terminal, the radio base station transmits an OTFS-modulated reference signal (e.g., CSI-RS (OTFS-CSI-RS)) to the radio terminal, the radio terminal receives the OFDM-CSI-RS and determines channel quality information (e.g., CQI), the radio terminal receives the OTFS-CSI-RS and estimates the Doppler shift, the radio terminal feeds back the CQI and Doppler shift information to the radio base station, the radio base station receives the CQI and Doppler shift information and determines the MCS of the radio access link, and the radio base station notifies the radio terminal of the determined MCS determination result via a downlink control channel (e.g., PDCCH).

[0012] Furthermore, the present invention can be realized not only as a link adaptation method for a wireless access link that includes such characteristic procedures, but also as a link adaptation device that utilizes such characteristic procedures as a means. [Effects of the Invention]

[0013] According to the present invention, the MCS of the wireless access link in a mobile communication system can be adaptively set according to the movement speed of the wireless terminal, thereby improving the stability of OFDM transmission and enhancing the reliability of communication. [Brief explanation of the drawing]

[0014] [Figure 1] This is a sequence flow illustrating an example of a link adaptation method according to one embodiment of the present invention. [Figure 2] This figure compares the throughput of OFDM and OTFS modulation schemes for each Doppler frequency. [Figure 3] This figure shows an example of a lookup table that determines the MCS based on the CQI and Doppler Index. [Figure 4] FIG. is a diagram showing an example of a look-up table for determining a Doppler index based on a Doppler frequency. [Figure 5] FIG. is a diagram showing a specific example (Part 1) of determining MCS based on CQI and Doppler shift. [Figure 6] FIG. is a diagram showing a specific example (Part 2) of determining MCS based on CQI and Doppler shift. [Figure 7] FIG. is a diagram showing a specific example (Part 3) of determining MCS based on CQI and Doppler shift. [Figure 8] FIG. is a diagram showing a specific example (Part 4) of determining MCS based on CQI and Doppler shift.

MODE FOR CARRYING OUT THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sequence flow showing an example of a link adaptation method in a mobile communication system according to an embodiment of the present invention, and shows a communication sequence in a radio access link between a 5G base station (gNB) and a 5G terminal (UE).

[0016] Therefore, CSI-RS unique to 4G / 5G is adopted as a reference signal for downlink propagation path estimation / quality measurement, CQI is adopted as channel quality information in the same manner, and PDCCH is adopted as a downlink control channel. However, the present invention is not limited to this, and various reference signals, quality information, and control channels can be adopted according to the assumed radio communication system.

[0017] In this embodiment, an RRC configuration (OFDM CSI-RS config, OTFS CSI-RS Config) is periodically transmitted from the gNB to the UE, and the transmission conditions of the OFDM-modulated CSI-RS (OFDM CSI-RS) transmitted in subsequent step 1 and the OTFS-modulated CSI-RS (OTFS-CSI-RS) transmitted in step 2 are notified to the UE.

[0018] In step 1, OFDM-CSI-RS is transmitted from the gNB to the UE under the conditions notified to the UE. The UE calculates a CQI (Channel Quality Indicator) indicating the propagation quality of the downlink of the radio access link based on the OFDM-CSI-RS received from the gNB.

[0019] In step 2, OTFS-CSI-RS is transmitted from the gNB to the UE under the conditions notified to the UE. The UE estimates the Doppler shift based on the OTFS-CSI-RS received from the gNB.

[0020] In step 3, the CQI of the downlink is fed back from the UE to the gNB as OFDM-CSI. In step 4, information regarding the estimation result of the Doppler shift (Doppler shift information) is fed back from the UE to the gNB as OTFS-CSI.

[0021] The gNB determines the MCS to be adopted for the downlink of the radio access link based on the CQI and Doppler shift information fed back from the UE. Here, the MCS is information obtained by indexing combinations such as modulation schemes and coding rates.

[0022] FIG. 3 and FIG. 4 are diagrams showing an example of a method for determining the MCS of a radio access link based on the CQI and Doppler shift information fed back from the UE to the gNB.

[0023] In this embodiment, as shown in an example in FIG. 3, a look-up table (LUT1) defining the correspondence between CQI, Doppler index, and MCS is set in the gNB in advance. Further, as shown in an example in FIG. 4, a LUT2 defining the relationship between Doppler frequency and Doppler index is set in the gNB or the UE in advance.

[0024] If LUT2 is pre-configured in gNB, UE feeds back the Doppler frequency as Doppler shift information. gNB applies the fed-back Doppler frequency to its LUT2 to determine the corresponding Doppler index.

[0025] In contrast, if LUT2 is pre-configured on the UE, the UE applies the Doppler frequency to its LUT2 to determine the corresponding Doppler index and feeds this back to the gNB as Doppler shift information.

[0026] gNB can determine the MCS of the wireless access link by applying the CQI and Doppler index to LUT1 in Figure 3.

[0027] Figures 5-8 provide a more detailed explanation of the method for determining the MCS using gNB, showing the correspondence between the combination of "modulation scheme," "code rate x1024," and "efficiency" in the MCS for each CQI and the Doppler shift.

[0028] In the example of the correspondence shown in Figure 5 (Part 1), when the Doppler shift is 0.025 or greater, even if the CQI fed back from the UE is "3", the modulation scheme is converted from 64QAM to 16QAM, and the MCS of the radio access link is determined to be an MCS corresponding to 16QAM.

[0029] Similarly, if the Doppler shift is greater than 0.1, the MCS of the radio access link is determined to be the MCS corresponding to QPSK, so that the modulation scheme is converted from 16QAM to QPSK, even if the CQI index fed back from the UE is "2".

[0030] In the example of the correspondence shown in Figure 6 (part 2), when the Doppler shift is 0.1 or greater, even if the CQI index fed back from the UE is "3", the modulation scheme is converted from 64QAM to 16QAM, and the MCS of the radio access link is determined to be an MCS corresponding to 16QAM.

[0031] Similarly, if the Doppler shift is 0.175 or greater, the MCS of the radio access link is determined to be the MCS corresponding to QPSK, so that the modulation scheme is converted from 16QAM to QPSK, even if the CQI index fed back from the UE is "2".

[0032] In the example of the correspondence shown in Figure 7 (part 3), when the Doppler shift is 0.1 or greater, even if the CQI index fed back from the UE is "2", the MCS of the radio access link is determined to be the MCS corresponding to QPSK so that the modulation scheme is converted from 16QAM to QPSK.

[0033] In the example of the correspondence shown in Figure 8 (part 4), when the Doppler shift is 0.025 or greater, even if the CQI index fed back from the UE is "4", the modulation scheme is converted from 256QAM to 64QAM, and the MCS of the radio access link is determined to be an MCS corresponding to 64QAM.

[0034] Similarly, if the Doppler shift is greater than 0.125, the MCS of the radio access link is determined to be a 16QAM-compatible MCS, so that the modulation scheme is converted from 64QAM to 16QAM, even if the CQI index fed back from the UE is "3".

[0035] Similarly, if the Doppler shift is 0.175 or greater, the MCS of the radio access link is determined to be the MCS corresponding to QPSK, so that the modulation scheme is converted from 16QAM to QPSK, even if the CQI index fed back from the UE is "2".

[0036] Returning to Figure 1, once the MCS is determined based on the estimated CQI and Doppler shift as described above, in step 5, the gNB assigns the MCS determination result to the radio access link and notifies the UE via the downlink control channel (PDCCH) along with resource information. In step 6, the corresponding MCS transmits a shared channel (PDSCH). The UE receives and decodes the PDCCH and receives the PDSCH based on its control information.

[0037] In the embodiments described above, the present invention was explained using the application to the downlink channel of a wireless access link between a UE and a gNB as an example. However, the present invention is not limited to this, and can be similarly applied to the downlink channel of a wireless access link between a UE and a wireless access point (AP).

[0038] Furthermore, according to the above embodiment, the MCS of the wireless access link in the mobile communication system can be adaptively set according to the mobile speed of the wireless terminal, thereby improving the stability of OFDM transmission and enhancing the reliability of communication. Consequently, it becomes possible to contribute to Goal 9, "Build resilient infrastructure and promote inclusive and sustainable industrialization," and Goal 11, "Make cities inclusive, safe, resilient and sustainable." [Explanation of Symbols]

[0039] AP... Wireless access point, gNB... Wireless base station, UE... Wireless terminal

Claims

1. In a link adaptation method for a wireless access link in a mobile communication system, A reference signal modulated with OFDM is transmitted from the wireless base station to the wireless terminal. A reference signal modulated using OTFS is transmitted from the wireless base station to the wireless terminal. The wireless terminal receives the OFDM-modulated reference signal and determines the channel quality information of the wireless access link. The wireless terminal receives the OTFS-modulated reference signal and estimates the Doppler shift. The channel quality information and Doppler shift information are fed back from the wireless terminal to the wireless base station. The aforementioned wireless base station receives the channel quality information and Doppler shift information and determines the MCS of the wireless access link. A link adaptation method characterized in that the wireless base station notifies the wireless terminal of the determined MCS.

2. The aforementioned wireless base station is equipped with a lookup table that sets the correspondence between Doppler frequencies and Doppler indices, The wireless terminal transmits the Doppler frequency as the Doppler shift information. The link adaptation method according to claim 1, characterized in that the wireless base station applies the received Doppler frequency to the lookup table to determine the Doppler index.

3. The aforementioned wireless terminal is equipped with a lookup table that sets the correspondence between Doppler frequency and Doppler index, The link adaptation method according to claim 1, characterized in that the wireless terminal applies the Doppler frequency to the lookup table to determine the Doppler index and transmits the Doppler index as Doppler shift information.

4. The aforementioned wireless base station is equipped with a lookup table that sets the correspondence between channel quality information, Doppler index, and MCS, The link adaptation method according to claim 2, characterized in that the MCS is determined by applying the Doppler index to the lookup table.

5. The wireless base station comprises a lookup table for setting the correspondence between channel quality information, Doppler index, and MCS, The link adaptation method according to claim 3, characterized in that the MCS is determined by applying the Doppler index to the lookup table.

6. The aforementioned wireless base station is equipped with a lookup table that sets the correspondence between channel quality information, MCS, and Doppler shift reference values. The link adaptation method according to claim 1, characterized in that if the Doppler shift of the received Doppler shift information exceeds the Doppler shift reference value corresponding to the received channel quality information, the MCS corresponding to the received Doppler shift information is determined to be the MCS of the wireless access link.

7. The link adaptation method according to any one of claims 1 to 6, characterized in that the OFDM-modulated reference signal is OFDM-CSI-RS, the OTFS-modulated reference signal is OTFS-SRS, and the channel quality information is CQI.

8. In a link adaptation device for a wireless access link at a wireless base station of a mobile communication system, A means for transmitting an OFDM-modulated reference signal to a wireless terminal, A means for transmitting an OTFS-modulated reference signal to a wireless terminal, Means for receiving feedback of channel quality information determined by the receiving of the OFDM-modulated reference signal and Doppler shift estimated by receiving the OTFS-modulated reference signal, Means for determining the MCS of a wireless access link based on the channel quality information and Doppler shift, A link adaptation device characterized by comprising means for notifying the determined MCS to the wireless terminal.

9. The link adaptation device according to claim 8, characterized in that the OFDM-modulated reference signal is OFDM-CSI-RS, the OTFS-modulated reference signal is OTFS-SRS, and the channel quality information is CQI.

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