Method and device for configuring reference signal

Abstract

In the present invention, an OFDM-CSI-RS is transmitted from a wireless base station to a wireless terminal, an OTFS-CSI-RS is transmitted from the wireless base station to the wireless terminal, the wireless terminal receives the OTFS-CSI-RS and estimates Doppler shift, the Doppler shift is provided as feedback from the wireless terminal to the wireless base station, the wireless base station configures a reference signal on the basis of the Doppler shift, and the wireless base station notifies the wireless terminal of the result of the configuration. The wireless base station configures the reference signal such that the greater the Doppler shift, the shorter the period of the reference signal.

Description

Reference signal setting method and device

[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 according to the moving speed of a radio terminal.

[0002] The orthogonal frequency division multiplexing (OFDM) method used in fourth and fifth 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 cope with the time variations in propagation paths caused by Doppler shifts associated with high-speed movement.

[0004] Patent Document 1 discloses a technique for simultaneous operation of 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 sparsity environment.

[0006] International Publication No. 2019 / 241436

[0007] IEEE, OTFS vs. OFDM in the Presence of Sparsity: A Fair Comparison

[0008] The explosive increase in the number of wireless terminals in recent years has posed a technical challenge: increasing overhead due to reference signals (RS) 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, it may be possible to reduce overhead if the RS of the wireless access link can be set to a long cycle for users who are less affected by Doppler shift and to a short cycle for users who are more affected, but the wireless base station cannot accurately grasp the Doppler shift of the wireless terminal, and therefore it is not possible to adaptively set the RS according to the effect of Doppler shift.

[0010] The present invention provides a method and apparatus that can adaptively set an RS transmitted and received over a wireless access link in accordance with the influence of Doppler shift.

[0011] The present invention is characterized in that it is a method for setting a reference signal transmitted and received over a radio access link in a mobile communication system, and 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 the Doppler shift, the wireless terminal feeds back the Doppler shift to the wireless base station, the wireless base station sets or resets an OFDM-modulated reference signal based on the Doppler shift, and the wireless base station notifies the wireless terminal of the setting or resetting 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.

[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 movement speed of the wireless terminal, thereby preventing the overhead of reference signals from increasing as the number of wireless terminals increases.

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

[0018] Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which the same or similar elements are designated by the same reference numerals.

[0019] The accompanying drawings are incorporated in and constitute a part of the specification, illustrate embodiments of the present invention, and together with the description are used to explain the principles of the present invention. Figure 1 is a sequence flow showing a method for setting a reference signal according to an embodiment of the present invention. Figure 2A is a diagram showing an example of mapping of an SRS, which is a type of reference signal. Figure 2B is a diagram showing an example of mapping of an SRS, which is a type of reference signal. Figure 3 is a diagram showing a method for setting a block length m of an SRS block based on an estimated Doppler shift. SRS 4 shows a method for determining the transmission period T of the SRS block based on the estimated Doppler shift. SRS 5 is a sequence flow diagram showing a method for determining a reference signal according to another embodiment of the present invention.

[0020] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. Furthermore, the same reference numerals are used to designate identical or similar components, and redundant descriptions will be omitted.

[0021] FIG. 1 is a sequence flow showing a reference signal mapping method according to one 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.

[0022] Here, the CSI-RS specific to 4G / 5G is adopted as a reference signal for downlink propagation path estimation and quality measurement, and similarly, the CQI (Channel Quality Indicator) is adopted as channel quality information, and the PDCCH (Physical Downlink Control Channel) 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.

[0023] 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 procedure 1 and the OTFS-modulated CSI-RS (OTFS-CSI-RS) transmitted in procedure 2. RRC is an abbreviation for Radio Resource Control.

[0024] In step 1, the gNB transmits OFDM-CSI-RS to the UE under the conditions (e.g., OFDM CSI-RS config) notified to the UE. Based on the OFDM-CSI-RS received from the gNB, the UE sets a CQI indicating the downlink propagation quality of the radio access link.

[0025] In step 2, the gNB transmits the OTFS-CSI-RS to the UE under the conditions (e.g., OTFS CSI-RS Config) notified to the UE. The UE estimates the Doppler shift based on the OTFS-CSI-RS received from the gNB.

[0026] In step 3, the UE feeds back downlink CQI as OFDM-CSI to the gNB. In step 4, the UE feeds back the Doppler shift estimation result as OTFS-CSI to the gNB.

[0027] Based on the Doppler shift fed back from the UE, the gNB maps the RS transmitted and received over the radio access link so that the larger the Doppler shift, the shorter the period of the reference signal. Then, in step 5, the gNB notifies the UE of the mapping result.

[0028] 2A and 2B are diagrams showing examples of setting 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.

[0029] The SRS is a block of length m SRS and 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.

[0030] FIG. 2A shows the SRS block length m SRS 10 shows an example of the setting when m = 2. The allocation of frequency resources to SRS is SRS The frequency resource is 10 and the frequency resource is m SRS If = 2, 5 hops are required, so the SRS period after mapping is 5 × T SRS become.

[0031] FIG. 2B shows the SRS block length m SRS 10 shows an example of mapping 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 value, the more the number of hops can be reduced, and the shorter the SRS period can be.

[0032] Returning to Figure 1, once the SRS is configured based on the Doppler shift estimation result as described above, in procedure 4, the gNB notifies the UE of the SRS configuration result via the downlink control channel (PDCCH) or RRC Reconfiguration.

[0033] FIG. 3 shows the block length m of each block of the SRS based on the Doppler shift. SRS and transmission period T SRS 10 is a diagram showing an example of the first embodiment in which the following is set:

[0034] In this embodiment, the gNB uses a set of SRS bandwidth configurations C SRS In SRS block length m SRS A table specifying the appropriate correspondence between the SRS block length m and the Doppler shift is prepared in advance, and the Doppler shift fed back from the UE is applied to the table to obtain the corresponding SRS block length m SRS Determine.

[0035] In this embodiment, the SRS block length m SRS By setting T longer, the faster the UE moves, the faster the T SRS Since the number of hopping times can be reduced, the SRS period can be shortened.

[0036] FIG. 4 shows the SRS block transmission period T SRS 10 is a diagram illustrating an example of a second embodiment in which the following is set:

[0037] In this embodiment, the gNB is T SRS A table is set in advance that defines the correspondence between the Doppler frequency and the time. 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 greater the T SRS is set to a large value.

[0038] In this embodiment, the Doppler frequency corresponding to the Doppler shift fed back from the UE is applied to the table, thereby adjusting 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.

[0039] In the above embodiment, an example in which the UE measures the Doppler shift has been described. Alternatively, for example, the UE may transmit an OTFS-modulated reference signal, and the gNB may measure the Doppler shift. An example of the processing flow in this case is shown in FIG. 5.

[0040] In the process of Figure 5, the gNB transmits an RRC configuration (OFDM CSI-RS config, OTFS SRS 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) to be transmitted in step 1 and the OTFS-modulated SRS (OTFS-SRS) to be transmitted in step 2.

[0041] Step 1 is the same as step 1 in Figure 1. Meanwhile, in step 2, the UE transmits an OTFS-SRS to the gNB under the conditions (e.g., OTFS SRS Config) notified to the UE. The gNB estimates the Doppler shift based on the OTFS-SRS received from the UE. Furthermore, the UE periodically transmits an OFDM SRS to the gNB under the conditions (e.g., OFDM SRS-config) notified to the UE.

[0042] Since Doppler shift fluctuations are unlikely to occur in short cycles, the OTFS SRS can be transmitted in very long cycles or a number of times specified in advance for the RRC configuration.

[0043] In the example of Fig. 5, the gNB maps the RS transmitted and received over the radio access link based on the Doppler shift estimated by itself so that the larger the Doppler shift, the shorter the period of the reference signal. Regarding the method of setting the reference signal, the examples described using Figs. 2 to 4 can be applied as is.

[0044] According to each of the above-described embodiments, RSs transmitted and received over the wireless access link of a mobile communication system can be adaptively mapped according to the movement speed of the wireless terminal, thereby preventing the RS overhead from increasing as the number of wireless terminals increases.

[0045] 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 a case where the reference signal is a CSI-RS used for estimating the quality of a downlink channel.

[0046] In addition, in the above embodiment, the present invention has been described using an example of applying it to a wireless access link between a UE and a gNB, but the present invention is not limited to this and can also be applied to a wireless access link between a UE and a wireless access point (AP).

[0047] According to the above embodiment, the RS transmitted and received over the wireless access link of the mobile communication system can be adaptively set according to the moving speed of the wireless terminal, thereby suppressing the increase in RS overhead caused by an increase in the number of terminals. This makes it 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.

[0048] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

[0049] This application claims priority based on Japanese Patent Application No. 2023-170107 filed on September 29, 2023 and Japanese Patent Application No. 2023-170110 filed on September 29, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A method for setting a reference signal transmitted and received over a wireless access link in a mobile communication system, comprising the steps of: transmitting an OTFS modulated reference signal from a wireless base station to a wireless terminal; the wireless terminal receiving the OTFS modulated reference signal and estimating a Doppler shift; feeding back the Doppler shift from the wireless terminal to the wireless base station; the wireless base station setting an OFDM modulated reference signal based on the Doppler shift; and notifying the wireless terminal of the setting result.

2. The method for setting a reference signal according to claim 1, characterized in that the radio base station performs mapping so that the period of the reference signal becomes shorter as the Doppler shift becomes larger.

3. The method for setting a reference signal according to claim 1 or 2, characterized in that the radio base station divides the reference signal into a plurality of blocks and transmits each block at a predetermined transmission period, and shortens the transmission period of the reference signal by lengthening the block length of each block as the Doppler shift increases and reducing the number of times the block is transmitted.

4. The method for setting a reference signal according to claim 1 or 2, characterized in that the radio base station divides the reference signal into a plurality of blocks and transmits each block at a predetermined transmission period, and the radio base station shortens the transmission period of each block as the Doppler shift increases, thereby shortening the transmission period of the reference signal.

5. A reference signal configuration method according to any one of claims 1 to 4, characterized in that the OFDM modulated reference signal to be configured is a CSI-RS, and the smaller the Doppler shift, the longer the transmission period and the corresponding CSI Feedback transmission period are set by RRC Configuration.

6. A reference signal configuration method according to any one of claims 1 and 4, characterized in that the OFDM-modulated reference signal to be configured is an SRS, and the smaller the Doppler shift, the longer the signal transmission period is set by the RRC configuration.

7. An apparatus for setting a reference signal for a wireless access link in a wireless base station of a mobile communication system, comprising: 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; means for setting an OFDM modulated reference signal based on the Doppler shift fed back by the wireless terminal; and means for notifying the wireless terminal of the setting result.

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 reference signal setting device according to claim 7 or 8, characterized in that the OFDM modulated reference signal to be set is CSI-RS, and the setting means sets the transmission period and the corresponding CSI feedback transmission period longer according to RRC configuration as the Doppler shift becomes smaller.

10. The reference signal setting device according to claim 7 or 8, characterized in that the OFDM modulated reference signal to be set is an SRS, and the setting means sets the signal transmission period to be longer according to an RRC configuration as the Doppler shift becomes smaller.

Images