Reference signal setting method and device

Abstract

To provide reference signal setting method and device that can adaptively map a reference signal (RS) transmitted and received in an access link in accordance with the effects of Doppler shift.SOLUTION: A reference signal setting method includes transmitting OFDM-CSI-RS to a radio terminal by a radio base station, transmitting OTFS-CSI-RS to the radio terminal by the radio base station, receiving the OTFS-CSI-RS and estimating a Doppler shift by the radio terminal, feeding back the Doppler shift to the radio base station by the radio terminal, setting a reference signal on the basis of the Doppler shift by the radio base station, and notifying the radio terminal of the setting result by the radio base station. The radio base station sets the period of the reference signal to be shorter as the Doppler shift increases.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method and device for setting a reference signal transmitted and received over a radio access link in a mobile communication system, and more particularly to a method and device for adaptively setting or resetting a reference signal in accordance with the moving speed of a radio terminal. [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.

[0003] Orthogonal time frequency space (OTFS) transmission has attracted attention as a transmission method that can deal with time-varying propagation paths caused by Doppler shifts associated with high-speed movement.

[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] The recent explosive increase in the number of wireless terminals has posed a technical challenge in that it increases the overhead caused by reference signals (RS: Reference Signals) used for channel estimation and quality measurement, such as Sounding Reference Signal (SRS) and Channel State Information Reference Signal (CSI-RS), which are transmitted and received over wireless access links between wireless terminals and base stations or wireless access points.

[0009] In this case, if the RS of the wireless access link could be set to a long cycle for users who are less affected by the Doppler shift and set to a short cycle for users who are more affected, it may be possible to reduce overhead, but the wireless base station cannot accurately grasp the Doppler shift of the wireless terminal, and therefore cannot adaptively set the RS according to the effect of the Doppler shift.

[0010] An object of the present invention is to solve the above technical problems and to provide a method and device capable of adaptively setting an RS transmitted and received over a wireless access link in accordance with the influence of the Doppler shift. [Means for solving the problem]

[0011] In order to achieve the above object, the present invention is characterized in that a method for setting a reference signal transmitted and received over a radio access link in a mobile communication system has the following configuration.

[0012] (1) A wireless base station transmits an OTFS modulated reference signal to a wireless terminal, the wireless terminal receives the OTFS modulated reference signal and estimates a Doppler shift, the wireless terminal feeds back the Doppler shift to the wireless base station, the wireless base station sets or reconfigures an OFDM modulated reference signal based on the Doppler shift, and the wireless base station notifies the wireless terminal of the setting or reconfiguration of the reference signal.

[0013] (2) A setting is adopted in which the period of the reference signal becomes shorter as the Doppler shift becomes larger.

[0014] The present invention can be realized not only as a reference signal setting method having such a characteristic procedure, but also as a reference signal setting device configured with such a characteristic procedure. Effect of the Invention

[0015] According to the present invention, the following effects can be achieved.

[0016] (1) Reference signals (SRS and CSI-RS) transmitted and received over the wireless access link of a mobile communication system can be adaptively mapped according to the moving speed of a wireless terminal, thereby making it possible to prevent the overhead of reference signals from increasing as the number of wireless terminals increases.

[0017] (2) Since the increase in overhead of reference signals, especially CSI-RS, can be suppressed, the overhead of feedback of the reference signals can also be reduced. [Brief description of the drawings]

[0018] [Figure 1] 4 is a sequence flow showing a method for setting a reference signal according to an embodiment of the present invention. [Diagram 2] 1 is a diagram showing an example of mapping of an SRS, which is a type of reference signal. [Diagram 3]FIG. 13 is a diagram showing a method for determining the block length mSRS of an SRS block based on the estimation result of the Doppler shift. [Figure 4] FIG. 13 is a diagram showing a method for determining a transmission period TSRS of an SRS block based on an estimated result of a Doppler shift. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a sequence flow showing a reference signal mapping method according to an embodiment of the present invention, and shows a communication sequence in a radio access link between a 5G base station gNB (eNodeB) and a 5G terminal UE.

[0020] 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.

[0021] In this embodiment, the gNB transmits an RRC configuration (OFDM CSI-RS config, OTFS CSI-RS config, OFDM SRS-config) to the UE, and then notifies the UE of the transmission conditions for the OFDM modulated CSI-RS (OFDM CSI-RS) transmitted in step 1 and the OTFS modulated CSI-RS (OTFS-CSI-RS) transmitted in step 2.

[0022] In step 1, the gNB transmits OFDM-CSI-RS to the UE under the conditions notified to the UE. The UE sets a CQI (Channel Quality Indicator) indicating the propagation quality of the downlink of the wireless access link based on the OFDM-CSI-RS received from the gNB.

[0023] In step 2, the gNB transmits the OTFS-CSI-RS to the UE under the conditions notified to the EU. The UE estimates the Doppler shift based on the OTFS-CSI-RS received from the gNB.

[0024] In step 3, the downlink CQI is fed back as OFDM-CSI from the UE to the gNB. In step 4, the Doppler shift estimation result is fed back as OTFS-CSI from the UE to the gNB.

[0025] Based on the Doppler shift fed back from the UE, the gNB maps the RS transmitted and received over the wireless access link so that the period of the reference signal becomes shorter as the Doppler shift becomes larger.

[0026] FIG. 2 shows an example of a setting of a sounding reference signal (SRS), which is a type of RS that a gNB refers to in order to estimate the quality of an uplink channel. The SRS is divided into multiple blocks (SRS blocks), and each SRS block is transmitted at a predetermined transmission period T SRS is sent.

[0027] SRS is a block of length m for each SRS block. SRS and the transmission period T SRS In this embodiment, the block length m of the SRS block is determined based on the Doppler shift fed back from the UE. SRS and transmission period T SRS is set adaptively.

[0028] Figure 1(a) shows the SRS block length m SRS The figure shows an example of the setting when m = 2. The allocation of frequency resources to the SRS is SRS The frequency resources are 10 and m SRS If = 2, 5 hops are required, so the SRS period after mapping is 5 × T SRS become.

[0029] Figure 2(b) shows the SRS block length m SRS A diagram showing a mapping example when m = 3. SRS If = 3, three hops are required, so the SRS period after setting is 3 × T SRS That is, the SRS block length m SRS The larger the number of hops can be reduced, so the SRS period can be shortened.

[0030] Returning to FIG. 1, once the SRS is configured based on the Doppler shift estimation result as described above, in step 4, the gNB notifies the UE of the SRS configuration result via a downlink control channel (PDCCH: Physical Downlink Control CHannel) or RRC Reconfiguration.

[0031] Fig. 3 shows the block length m of each block of the SRS based on the Doppler shift. SRS and the transmission period T SRS FIG. 13 is a diagram showing an example of the first embodiment in which the following is set:

[0032] In this embodiment, the gNB selects a set of SRS bandwidth configurations C SRS In SRS block length m SRS A table that specifies the appropriate correspondence between the SRS block length m and the Doppler shift is preset, and the Doppler shift fed back from the UE is applied to the table to obtain the corresponding SRS block length m SRS Determine.

[0033] In this embodiment, the SRS block length m of a UE with a faster moving speed and a higher Doppler shift is SRS By setting T longer, the faster the UE moves, the faster the T SRS Since the number of hoppings can be reduced, the SRS period can be shortened.

[0034] Figure 4 shows the SRS block transmission period T SRS FIG. 13 is a diagram showing an example of the second embodiment in which the above-mentioned is set.

[0035] In this embodiment, the gNB is T SRS A table is set in advance that defines the relationship between the Doppler frequency and the time. Here, sl1 to sL40 are T SRS This is a command to set the resource limit of SRS, which is used to adjust the period of T SRS is T SRS (sl1) <T SRS (sl2)<… <T SRS (sln). Therefore, the higher the Doppler frequency, the higher the T SRS is set to a large value.

[0036] In this embodiment, the Doppler frequency corresponding to the Doppler shift fed back from the UE is applied to the table, so that the transmission period T SRS In this case, the transmission period T SRS By setting the SRS period shorter, the faster the UE is moving, the shorter the SRS period can be.

[0037] According to this embodiment, the RS transmitted and received over the wireless access link of a mobile communication system can be adaptively mapped according to the moving speed of the wireless terminal, thereby making it possible to prevent the RS overhead from increasing as the number of wireless terminals increases.

[0038] In the above embodiment, the reference signal to be mapped is an SRS used for estimating the quality of an uplink channel, but the present invention is not limited to this and can be similarly applied to the case where the reference signal is a CSI-RS used for estimating the quality of a downlink channel.

[0039] In addition, in the above embodiment, the present invention has been described using an example of application to 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 a wireless access link between a UE and a wireless access point (AP).

[0040] According to the above embodiment, the RS transmitted and received through the wireless access link of the mobile communication system can be adaptively set according to the moving speed of the wireless terminal, and as a result, the overhead of the RS can be prevented from increasing with an increase in the number of terminals. 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]

[0041] AP: wireless access point, gNB: wireless base station, UE: wireless terminal

Claims

1. A method for configuring a reference signal transmitted and received in a radio access link of a mobile communication system, comprising: A reference signal modulated by OTFS is transmitted from the wireless base station to the wireless terminal. A wireless terminal receives the OTFS modulated reference signal and estimates a Doppler shift; feeding back the Doppler shift from the wireless terminal to a wireless base station; the radio base station sets a reference signal to be OFDM modulated based on the Doppler shift; A reference signal configuration method, characterized in that the radio base station notifies a radio terminal of a result of the configuration.

2. 2. The method of claim 1, wherein the radio base station performs mapping such that the period of the reference signal becomes shorter as the Doppler shift increases.

3. The radio base station divides a reference signal into a plurality of blocks and transmits each block at a predetermined transmission period; 3. The method for setting a reference signal according to claim 1, further comprising the steps of: lengthening a block length of each block to reduce the number of times each block is transmitted as the Doppler shift increases, thereby shortening a transmission period of the reference signal.

4. The radio base station divides a reference signal into a plurality of blocks and transmits each block at a predetermined transmission period; 3. The method of claim 1, wherein the wireless base station shortens the transmission period of each block as the Doppler shift increases, thereby shortening the transmission period of the reference signal.

5. the OFDM-modulated reference signal to be set is a CSI-RS, 5. The method for configuring a reference signal according to claim 1, wherein the smaller the Doppler shift is, the longer the transmission period and the transmission period of the corresponding CSI Feedback are set by RRC Configuration.

6. the OFDM-modulated reference signal to be set is an SRS, 5. The method for configuring a reference signal according to claim 1, further comprising: setting a signal transmission period longer by RRC configuration as the Doppler shift becomes smaller.

7. 1. An apparatus for setting a reference signal for a radio access link in a radio base station of a mobile communication system, comprising: A means for transmitting an OTFS modulated reference signal to a wireless terminal; means for receiving feedback of a Doppler shift estimated by the wireless terminal based on the OTFS modulated reference signal; A means for setting a reference signal to be OFDM modulated based on the Doppler shift fed back by the wireless terminal; and means for notifying a wireless terminal of the result of said setting.

8. 8. The reference signal setting device according to claim 7, wherein said setting means performs mapping so that the period of the reference signal becomes shorter as the Doppler shift increases.

9. the OFDM-modulated reference signal to be set is a CSI-RS, 9. The reference signal setting device according to claim 7, wherein the setting means sets the transmission period and the corresponding CSI Feedback transmission period according to an RRC configuration to be longer as the Doppler shift is smaller.

10. the OFDM-modulated reference signal to be set is an SRS, 9. The reference signal setting device according to claim 7, wherein the setting means sets a signal transmission period to be longer according to an RRC configuration as the Doppler shift becomes smaller.

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