Link adaptation method and device

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-SRS from the radio terminal to the radio base station, receiving the OFDM-CSI-RS and determining a CQI by the radio terminal, receiving the OTFS-SRS and estimating a Doppler shift by the radio base station, feeding back the CQI from the radio terminal to the radio base station, determining an MCS for a radio access link on the basis of the fed back CQI and Doppler shift 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 device in a mobile communication system, and more particularly to a link adaptation method and device for setting the MCS (Modulation and Coding Scheme) of a radio access link in accordance with the moving speed of a radio terminal in a mobile communication system. [Background technology]

[0002] The Orthogonal Frequency Division Multiplexing (OFDM) method used in 4th and 5th generation mobile communication services has high spectral efficiency and excellent resistance to multipath fading. In addition, the above services use link adaptation to switch MCS according to the communication quality of the communication terminal, and use the signal-to-interference and noise power ratio (SINR) or its corresponding CQI (Channel Quality Indicator) as an indicator of communication quality.

[0003] Orthogonal time frequency space (OTFS) transmission has attracted attention as a transmission method that can accommodate time variations caused by different Doppler shifts.

[0004] Patent Document 1 discloses a technique for simultaneously operating an OTFS modulation communication system and an LTE system using OFDM.

[0005] Non-Patent Document 1 presents a fair comparison between OTFS and OFDM in a sparse environment. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] WO2019 / 241436 A1 [Non-patent literature]

[0007] [Non-Patent Document 1] IEEE, OTFS vs. OFDM in the Presence of Sparsity: A FairComparison Summary of the Invention [Problem to be solved by the invention]

[0008] Figure 2 compares the throughput of OFDM and OTFS for each modulation method at each Doppler frequency. OFDM has the problem that in high-speed moving environments, the Doppler shift can cause data communication quality to become unstable, reducing communication reliability.

[0009] In this case, there is a possibility of improvement if the MCS of the wireless access link can be adaptively switched according to the effect of the Doppler shift, but since the CQI does not include Doppler shift information in the OFDM modulation method, it is necessary to periodically set the MCS according to the Doppler shift.

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

[0011] In order to achieve the above object, the present invention provides a link adaptation method for a wireless access link in a mobile communication system, in which a wireless base station transmits an OFDM-CSI-RS to a wireless terminal, the wireless terminal transmits an OTFS-SRS to the wireless base station, the wireless terminal receives the OFDM-CSI-RS and determines a CQI, the wireless base station receives the OTFS-SRS and estimates a Doppler shift, the wireless terminal feeds back the CQI to the wireless base station, the wireless terminal determines an MCS for the wireless access link based on the fed back CQI and the estimated Doppler shift, the radio base station notifies the terminal of the determined MCS via a PDCCH, and a signal generated with the determined MCS is transmitted to the wireless terminal via a PDSCH.

[0012] The present invention can be realized not only as a link adaptation method for a wireless access link including such a characteristic procedure, but also as a link adaptation device using such a characteristic procedure as means. Effect of the Invention

[0013] According to the present invention, since the MCS of a wireless access link in a mobile communication system can be adaptively set according to the moving speed of a wireless terminal, it is possible to improve the quality of data communication by OFDM and increase the stability of communication. [Brief description of the drawings]

[0014] [Figure 1] 1 is a sequence flow diagram illustrating an example of a link adaptation method according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram comparing the throughput of each modulation scheme of OFDM and OTFS for each Doppler frequency. [Diagram 3] FIG. 13 is a diagram showing an example of a lookup table for determining MCS based on CQI and Doppler index. [Figure 4] FIG. 13 is a diagram showing an example of a lookup table for determining a Doppler index based on a Doppler frequency. [Diagram 5] FIG. 13 is a diagram showing a specific example (part 1) of determining MCS based on CQI and Doppler shift. [Figure 6] FIG. 13 is a diagram showing a specific example (part 2) of determining MCS based on CQI and Doppler shift. [Figure 7] FIG. 11 is a diagram showing a specific example (part 3) of determining MCS based on CQI and Doppler shift. [Figure 8] FIG. 11 is a diagram showing a specific example (part 4) of determining MCS based on CQI and Doppler shift. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment 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, the CSI-RS specific to 4G / 5G is adopted as a reference signal for downlink propagation path estimation and quality measurement, and similarly, CQI is adopted as channel quality information, 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 depending on the assumed wireless communication system.

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

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

[0019] In step 2, the UE transmits an OTFS-SRS to the gNB under the notified conditions. The gNB estimates the Doppler shift based on the OTFS-SRS received from the UE. In step 3, the UE feeds back the downlink CQI to the gNB as OFDM-CSI.

[0020] The gNB determines the MCS to be adopted for the downlink of the radio access link based on the CQI fed back from the UE and the Doppler shift estimated by itself. Here, MCS is information that indexes the combination of modulation scheme, coding rate, etc.

[0021] 3 and 4 are diagrams showing examples of a method in which a gNB determines the MCS of a radio access link based on the CQI fed back from the UE and Doppler shift information estimated by the gNB.

[0022] In this embodiment, a lookup table (LUT1) that defines the correspondence between CQI, Doppler index, and MCS is set in advance in the gNB, as shown in an example in Fig. 3. Furthermore, a LUT2 that defines the relationship between Doppler frequency and Doppler index is set in advance in the gNB, as shown in an example in Fig. 4. The gNB applies a Doppler shift frequency estimated by itself to its own LUT2 to determine the corresponding Doppler index.

[0023] 5 to 8 are diagrams showing in more detail how the gNB determines the MCS, and show the correspondence between the combination of "modulation scheme," "code rate x1024," and "efficiency" in the MCS for each CQI and the Doppler shift.

[0024] In the example of the correspondence relationship (part 1) shown in FIG. 5, when the Doppler shift is 0.025 or more, even if the CQI fed back from the UE is “3”, the MCS of the wireless access link is determined to be the MCS corresponding to 16QAM so that the modulation scheme is converted from 64QAM to 16QAM.

[0025] Similarly, when the Doppler shift is 0.1 or more, 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.

[0026] In the example of the correspondence relationship (part 2) shown in FIG. 6, when the Doppler shift is 0.1 or more, even if the CQI index fed back from the UE is “3”, the MCS of the radio access link is determined to be the MCS corresponding to 16QAM so that the modulation scheme is converted from 64QAM to 16QAM.

[0027] Similarly, when the Doppler shift is 0.175 or more, 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.

[0028] In the example (third) of the correspondence relationship shown in FIG. 7, when the Doppler shift is 0.1 or more, even if the CQI index fed back from the UE is “2”, the MCS of the wireless access link is determined to be the MCS corresponding to QPSK so that the modulation scheme is converted from 16QAM to QPSK.

[0029] In the correspondence relationship example (part 4) shown in FIG. 8, when the Doppler shift is 0.025 or more, even if the CQI index fed back from the UE is “4”, the MCS of the radio access link is determined to be the MCS corresponding to 64QAM so that the modulation scheme is converted from 256QAM to 64QAM.

[0030] Similarly, when the Doppler shift is 0.125 or more, even if the CQI index fed back from the UE is “3”, the MCS of the radio access link is determined to be the MCS compatible with 16QAM so that the modulation scheme is converted from 64QAM to 16QAM.

[0031] Similarly, when the Doppler shift is 0.175 or more, 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.

[0032] Returning to Fig. 1, once the MCS is determined based on the estimation results of the CQI and Doppler shift as described above, in step 4, the gNB allocates a downlink control channel (PDCCH: Physical Downlink Control CHannel) to the radio access link and notifies the radio terminal of the MCS. In step 5, a signal generated with the determined MCS is transmitted to the radio terminal via the PDSCH.

[0033] In the above embodiment, the present invention has been described using an example of application to the downlink channel of a wireless access link between a UE and a gNB, but 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).

[0034] According to the above embodiment, the MCS of the wireless access link in the mobile communication system can be adaptively set according to the moving speed of the wireless terminal, so that the stability of OFDM transmission can be improved and the reliability of communication can be enhanced. Therefore, it is 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" of the Sustainable Development Goals (SDGs) led by the United Nations. [Explanation of symbols]

[0035] AP: wireless access point, gNB: wireless base station, UE: wireless terminal

Claims

1. A link adaptation method for a wireless access link in a mobile communication system, comprising: A wireless base station transmits an OFDM modulated reference signal to a wireless terminal; A reference signal modulated by OTFS is transmitted from the wireless terminal to the wireless base station. A wireless terminal receives the OFDM modulated reference signal and determines channel quality information of a wireless access link; A radio base station receives the OTFS modulated reference signal and estimates a Doppler shift; feeding back the channel quality information from the wireless terminal to the wireless base station; The radio base station determines an MCS of a radio access link based on the fed-back channel quality information and an estimated result of a Doppler shift; A link adaptation method, comprising the step of: notifying the wireless terminal of the determined MCS by the wireless base station.

2. the wireless base station includes a lookup table in which a correspondence relationship between a Doppler frequency and a Doppler index is set; The radio base station estimates a Doppler frequency as the Doppler shift; 2. The method of claim 1, wherein the radio base station applies the estimated Doppler frequency to the look-up table to determine a Doppler index.

3. the radio base station includes a look-up table that sets a correspondence relationship between channel quality information, a Doppler index, and an MCS; 3. The method of claim 2, further comprising applying the Doppler index to the lookup table to determine an MCS.

4. the radio base station includes a look-up table in which a correspondence relationship between channel quality information, an MCS, and a Doppler shift reference value is set; 2. The link adaptation method according to claim 1, further comprising determining, when the estimated Doppler shift exceeds a Doppler shift reference value corresponding to the received channel quality information, an MCS corresponding to the estimated Doppler shift as an MCS for a wireless access link.

5. 5. The link adaptation method according to claim 1, wherein the OFDM modulated reference signal is OFDM-CSI-RS, the OTFS modulated reference signal is OTFS-SRS, and the channel quality information is CQI.

6. A link adaptation device for a radio access link in a radio base station of a mobile communication system, comprising: means for transmitting an OFDM modulated reference signal to a wireless terminal; means for receiving an OTFS modulated reference signal from a wireless terminal; a means for receiving feedback of channel quality information determined by a wireless terminal receiving the OFDM modulated reference signal; means for receiving the OTFS modulated reference signal and estimating a Doppler shift; means for determining an MCS of a wireless access link based on the fed back channel quality information and an estimated Doppler shift; and means for notifying the wireless terminal of the determined MCS.

7. The link adaptation device according to claim 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.

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