Circular shift estimation technique in OFDM-based communication systems

Abstract

To provide a circular shift estimation technique in OFDM-based communication systems.SOLUTION: Various embodiments are disclosed for a received signal processing technique in OFDM-based communication systems. In one embodiment, an operation method for a receiver in a communication system in which at least one OFDM symbol is transmitted includes generating at least one received reference signal group corresponding to a first subchannel based on a received signal, calculating a channel impulse response of the first subchannel based on the generated at least one received reference signal group corresponding to the first subchannel, and estimating a circular shift corresponding to the first subchannel based on the calculated channel impulse response of the first subchannel.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present disclosure relates to receive signal processing techniques in communication systems, and more particularly, some embodiments relate to techniques for efficiently detecting a Cellular Vehicle-to-Everything (C-V2X) Physical Sidelink Control Channel (PSCCH) via Inverse Discrete Fourier Transform (IDFT)-based cyclic shift estimation. [Background technology]

[0002] To realize autonomous vehicles, it is necessary to accurately collect information about the vehicle's surroundings and control the vehicle based on this information. Methods for collecting information include direct sensing of the surroundings using cameras, radar, and lidar, which belong to Advanced Driver Assistance Systems (ADAS), as well as Vehicle-to-Everything communication (V2X), which shares collected information with nearby vehicles via wireless communication. To achieve this, international standards such as IEEE 802.11p, also known as dedicated short range communication (DSRC), 3GPP Long Term Evolution (LTE) sidelink (hereinafter referred to as "SL"), and New Radio (NR) sidelink have been established, and related research and implementation are actively underway.

[0003] The LTE SL and NR SL standards define the total bandwidth as divided into up to 20 and 27 subchannels, respectively, and define each subchannel to enable peer-to-peer communication between different vehicles. Each subchannel consists of a PSCCH containing control information and a Physical Sidelink Shared Channel (PSSCH) containing transport blocks (TBs). Each terminal is defined to attempt to receive all PSCCH candidates as much as possible and to receive only the PSSCH corresponding to the PSCCH that is successfully received.

[0004] Therefore, there is a demand for efficient received signal processing techniques, such as techniques for efficiently detecting PSCCH candidates. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, an efficient received signal processing technique (for example, a technique for efficiently detecting a large number of PSCCH candidates) is required. [Means for solving the problem]

[0006] One aspect of the present disclosure provides a method for operating a receiver in a communication system in which at least one OFDM symbol is transmitted - a reference signal group for each of 1st to Mth subchannels (M is a natural number greater than or equal to 2), wherein the reference signal group includes a plurality of reference signals to which a cyclic shift corresponding to the subchannel is applied - the method including the steps of: generating, based on a received signal, at least one received reference signal group corresponding to the first subchannel - each received reference signal group including a received reference signal received via the OFDM symbol and the first subchannel; calculating a channel impulse response of the first subchannel based on the generated at least one received reference signal group corresponding to the first subchannel; and estimating a cyclic shift corresponding to the first subchannel based on the calculated channel impulse response of the first subchannel.

[0007] In some embodiments, the step of generating the at least one received reference signal group may include the steps of: extracting at least one sample group from the received signal corresponding to a symbol body of each of the at least one OFDM symbol; applying a Discrete Fourier Transform (hereinafter referred to as "DFT") to each of the extracted at least one sample group to generate at least one frequency domain signal; and extracting the received reference signals included in each of the at least one received reference signal group corresponding to the first subchannel from the generated at least one frequency domain signal.

[0008] In some embodiments, the step of calculating the channel impulse response may include generating a time-domain signal corresponding to each of the at least one received reference signal group, and calculating the channel impulse response based on the generated at least one time-domain signal.

[0009] In some embodiments, generating at least one time-domain signal may include applying descrambling to each of the at least one received reference signal group to generate at least one descrambled symbol group, and applying an inverse discrete Fourier transform (IDFT) to each of the generated at least one descrambled symbol group to generate the at least one time-domain signal. In some embodiments, the size of the IDFT may be four times the size of the descrambled symbol group to be subjected to the IDFT. In some embodiments, the size of the IDFT may be equal to or larger than the size of the descrambled symbol group to be subjected to the IDFT, and applying the IDFT may include applying the IDFT by positioning the center of the descrambled symbol group to be subjected to the IDFT at the center of an IDFT window.

[0010] In some embodiments, the reference signal group of the first subchannel may be transmitted via one OFDM symbol, the step of generating at least one received reference signal group may include generating one received reference signal group corresponding to the first subchannel, the step of generating at least one time-domain signal may include generating a time-domain signal corresponding to the generated one received reference signal group, and the step of calculating the channel impulse response may include determining the generated one time-domain signal as the channel impulse response.

[0011] In some embodiments, the reference signal group of the first subchannel may be transmitted via a plurality of OFDM symbols, and the step of generating the at least one received reference signal group may include generating a plurality of received reference signal groups corresponding to the first subchannel, the step of generating the at least one time-domain signal may include generating a time-domain signal corresponding to each of the generated plurality of received reference signal groups, and the step of calculating the channel impulse response may include calculating the channel impulse response by summing time-domain samples included in each of the generated plurality of time-domain signals by the same time index.

[0012] In some embodiments, estimating the cyclic shift may include detecting a time index having a maximum value among time-domain samples of the channel impulse response, and estimating a cyclic shift corresponding to each of the at least one subchannel based on the detected time index. In some embodiments, estimating the cyclic shift may include estimating the cyclic shift based on a time index having a maximum value of the channel impulse response among a plurality of intervals, the time index being included in the time-domain samples of the channel impulse response, and the plurality of intervals may be obtained by dividing a time-domain interval of the channel impulse response based on statistical characteristics of the channel impulse response when a cyclic shift corresponding to each of the M subchannels is applied. In some embodiments, the statistical characteristics of the channel impulse response may form a sinc function centered on each of the plurality of intervals.

[0013] In some embodiments, the method may further include estimating a timing offset based on the estimated channel impulse response. In some embodiments, estimating the cyclic shift may include estimating a cyclic shift corresponding to each of the at least one subchannel based on a time index having a maximum value among time-domain samples of the channel impulse response, and estimating the timing offset may include estimating the timing offset based on a ratio between a size of a DFT used to generate the at least one received reference signal group and a size of an IDFT used to calculate the channel impulse response, the time index having the maximum value, and the estimated cyclic shift.

[0014] In some embodiments, the method may further include, for each m (m having a value from 2 to M), generating, based on the received signals, at least one received reference signal group corresponding to the m subchannel, where each received reference signal group includes a corresponding OFDM symbol and a received reference signal received via the m subchannel; calculating, based on the generated at least one received reference signal group corresponding to the m subchannel, a channel impulse response of the m subchannel; and estimating, based on the calculated channel impulse response of the m subchannel, a cyclic shift corresponding to the m subchannel.

[0015] In some embodiments, each of the first to M subchannels includes a PSCCH and a PSSCH of an LTE sidelink, and the reference signal group of each of the first to M subchannels includes a reference signal group of the PSCCH included in that subchannel.

[0016] In some embodiments, each of the first to M subchannels includes a PSCCH and a PSSCH of an NR sidelink, and the reference signal group of each of the first to M subchannels includes a reference signal group of the PSCCH included in that subchannel.

[0017] Another aspect of the present disclosure provides a receiving device in a communication system in which at least one OFDM symbol is transmitted, where a reference signal group for each of 1st to Mth subchannels (M is a natural number equal to or greater than 2) is transmitted by at least one of the at least one OFDM symbol, and the reference signal group includes a plurality of reference signals to which a cyclic shift corresponding to the subchannel has been applied, the receiving device including: a received reference signal group generation block that generates at least one received reference signal group corresponding to the first subchannel based on a received signal, where each received reference signal group includes a received reference signal received via the OFDM symbol and the first subchannel; a channel impulse response calculation block that calculates a channel impulse response of the first subchannel based on the generated at least one received reference signal group corresponding to the first subchannel; and a cyclic shift estimation block that estimates a cyclic shift corresponding to the first subchannel based on the calculated channel impulse response of the first subchannel.

[0018] In some embodiments, the received reference signal group generation block may include a sample group extraction block that extracts at least one sample group corresponding to a symbol body of each of the at least one OFDM symbol from the received signal, a DFT block that applies a DFT to each of the extracted at least one sample group to generate at least one frequency domain signal, and a received reference signal extraction block that extracts the received reference signal included in each of the at least one received reference signal group corresponding to the first subchannel from the generated at least one frequency domain signal.

[0019] In some embodiments, the channel impulse response calculation block may include a time domain signal generation block that generates a time domain signal corresponding to each of the at least one received reference signal group, and a calculation block that calculates the channel impulse response based on the generated at least one time domain signal.

[0020] In some embodiments, the time-domain signal generation block may include a descrambling block that applies descrambling to each of the at least one received reference signal group to generate at least one descrambled result symbol group, and an IDFT block that applies IDFT to each of the generated at least one descrambled result symbol group to generate the at least one time-domain signal.

[0021] In some embodiments, the cyclic shift estimation block may include a detection block that detects a time index having a maximum value among the time domain samples of the channel impulse response, and an estimation block that estimates a cyclic shift corresponding to each of the at least one subchannel based on the detected time index.

[0022] In some embodiments, the receiving device may further include a timing offset estimation block that estimates a timing offset based on the estimated channel impulse response.

[0023] In some embodiments, the received reference signal group generation block generates, for each m (m has a value from 2 to M), at least one received reference signal group corresponding to the m subchannel based on the received signal, each of the received reference signal groups including a received reference signal received via the corresponding OFDM symbol and the m subchannel; the channel impulse response calculation block calculates a channel impulse response of the m subchannel based on the generated at least one received reference signal group corresponding to the m subchannel; and the cyclic shift estimation block can estimate a cyclic shift corresponding to the m subchannel based on the calculated channel impulse response of the m subchannel.

[0024] In some embodiments, each of the first to M subchannels includes a PSCCH and a PSSCH of an LTE sidelink, and the reference signal group of each of the first to M subchannels includes a reference signal group of the PSCCH included in that subchannel.

[0025] In some embodiments, each of the first to M subchannels includes a PSCCH and a PSSCH of an NR sidelink, and the reference signal group of each of the first to M subchannels includes a reference signal group of the PSCCH included in that subchannel.

[0026] Another aspect of the present disclosure provides a non-transitory storage medium storing instructions readable by a processor of an electronic device, the instructions causing the processor to perform embodiments of the present disclosure.

[0027] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Moreover, the claimed subject matter is not limited to only embodiments that solve some or all of the problems addressed in any portion of this specification. In addition to the exemplary aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent with reference to the following Detailed Description and drawings. [Effects of the Invention]

[0028] Some embodiments of the present disclosure may have effects including the following advantages, however, this does not mean that all embodiments must include all of these, and the scope of the present invention should not be understood as being limited thereby.

[0029] According to some embodiments, the cyclic shift and timing offset can be calculated simultaneously using the IDFT for the PSCCH DMRS.

[0030] According to some embodiments, a cyclic shift estimation technique can be provided that provides excellent cyclic shift estimation performance even in an environment where the timing offset is large.

[0031] According to some embodiments, by reusing existing logic (eg, logic for determining timing offsets), a cyclic shift estimation technique can be provided with minimal additional logic.

[0032] According to some embodiments, reception attempts for many PSCCH candidates can be effectively reduced through superior cyclic shift detection performance. [Brief explanation of the drawings]

[0033] [Figure 1]1 illustrates an OFDM symbol generation block. [Figure 2] 1 illustrates an example OFDM symbol. [Figure 3] 1 illustrates a 3GPP LTE frame structure. [Figure 4] 1 illustrates an example of a resource grid for LTE sidelink. [Figure 5] 1 illustrates an example of a resource grid for NR SL. [Figure 6] 1 illustrates an LTE SL subframe structure and an NR SL subframe structure. [Figure 7] 1 illustrates an LTE SL subframe structure and an NR SL subframe structure. [Figure 8] FIG. 10 is a diagram illustrating DMRS RE included in a PSCCH of an NR SL. [Figure 9] FIG. 2 is a block diagram illustrating some embodiments for receiving signal processing. [Figure 10] 10 is pseudocode for illustrating some embodiments of estimating the cyclic shift applied to the PSCCH DMRS from the IDFT result. [Figure 11] 1 illustrates the CIR when there is no timing offset in LTE SL. [Figure 12] 1 illustrates an example of CIR when there is a timing offset in LTE SL. [Figure 13] 1 illustrates the CIR when there is no timing offset in NR SL. [Figure 14] 1 illustrates the CIR when there is a timing offset in NR SL. [Figure 15] 10 is a graph illustrating the performance of the cyclic shift estimation technique of the present disclosure in LTE SL. [Figure 16] Table 14.2-1 of the 3GPP standard document (3GPP 36.101) is shown, which specifies the performance requirements related to timing offset and frequency offset in LTE SL. [Figure 17]Table 14.2-2 of the 3GPP standard document (3GPP 36.101) that specifies the performance requirements in LTE SL is shown below. [Figure 18] 10 is a graph illustrating the performance of the cyclic shift estimation technique of the present disclosure in NR SL. [Figure 19] The performance requirements for NR SL are shown below. DETAILED DESCRIPTION OF THE INVENTION

[0034] The description of the present invention is merely an embodiment for the purpose of structural or functional explanation, and therefore the scope of the present invention should not be construed as being limited by the embodiments described herein. In other words, since the embodiments can be modified in various ways and can have various forms, the scope of the present invention should be understood to include equivalents that can realize the technical idea. Furthermore, the objectives or effects presented in the present invention do not mean that a particular embodiment must include all of these or only such effects, and therefore the scope of the present invention should not be understood as being limited thereby.

[0035] Meanwhile, the meanings of terms used in this disclosure should be understood as follows: Terms such as "first" and "second" are used to distinguish one component from another, and should not be used to limit the scope of rights. For example, a first component can be named a second component, and similarly, a second component can be named a first component.

[0036] When a component is said to be "connected" to another component, it should be understood that it may be directly connected to the other component, or that there may be other components between them. Conversely, when a component is said to be "directly connected" to another component, it should be understood that there are no other components between them. Meanwhile, other expressions describing the relationship between components, such as "between" and "immediately between," or "adjacent to" and "directly adjacent to," should be interpreted similarly.

[0037] Singular expressions should be understood to include plural expressions unless the context clearly indicates otherwise, and terms such as "comprise" or "have" are intended to specify the presence of embodied features, numbers, steps, operations, components, parts, or combinations thereof, and should be understood not to preclude the presence or possible addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0038] The designations (e.g., a, b, c, etc.) used in each step are for convenience of explanation, and do not describe the order of the steps. The steps may be performed in an order different from that specified unless the context clearly dictates a particular order. That is, the steps may be performed in the same order as specified, substantially simultaneously, or in the reverse order.

[0039] FIG. 1 illustrates an OFDM symbol generation block.

[0040] Orthogonal Frequency Division Multiplexing (OFDM) is a method of dividing data to be transmitted into multiple small pieces of data, modulating them into mutually orthogonal subcarriers through an inverse fast Fourier transform (IFFT), and transmitting them simultaneously, as shown in Figure 1.

[0041] FIG. 2 illustrates an OFDM symbol.

[0042] As shown in Figure 2, an OFDM symbol can be composed of a cyclic prefix (hereinafter referred to as "CP") and a transmission signal body. Multipath interference can be mitigated by adding a certain portion of the rear of the multi-carrier transmission signal (i.e., a section corresponding to the cyclic prefix section in the symbol body, hereinafter referred to as the "cyclic prefix corresponding section") to the front. In 3GPP LTE / NR, the basic time unit T s Based on this, symbol body section N c =2048T s In normal CP, N g =144T s or 160T s , and N in extended CP g =512T s It is stipulated that only

[0043] The combination of CP and symbol body is called CP-OFDM, and 3GPP LTE / NR sidelink uses this CP-OFDM.

[0044] FIG. 3 illustrates a 3GPP LTE frame structure.

[0045] In 3GPP LTE / NR, as shown in FIG. 3, a frame can be composed of a time unit (e.g., a subframe or a slot) consisting of multiple OFDM symbols on the time axis, and can be composed of a resource block (hereinafter referred to as "RB") consisting of multiple (e.g., 12) subcarriers on the frequency axis.

[0046] FIG. 4 illustrates an example of a resource grid for an LTE sidelink (hereinafter referred to as "SL").

[0047] In LTE SL, as shown in FIG. 4, a PSCCH including sidelink control information (hereinafter referred to as "SCI") consisting of two RBs is used.

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[0048] Figure 5 illustrates an example resource grid for NR SL.

[0049] In NR SL, as shown in Figure 5, a PSCCH and a PSSCH may be allocated to one or more subchannels, respectively. However, unlike LTE, a two-stage SCI is configured, and the PSCCH and the PSSCH are attached to each other. For example, in Figure 5, the white box formed by dashed lines is a one-stage SCI and is included in the PSCCH, the shaded box formed by dashed lines is a two-stage SCI and is included in the PSSCH, and the solid-line box including the white box formed by dashed lines and the shaded box formed by dashed lines can include PSSCH data in the remaining resource elements excluding the white box formed by dashed lines and the shaded box formed by dashed lines.

[0050] 6 and 7 illustrate an LTE SL subframe structure and an NR SL subframe structure, respectively.

[0051] FIG. 8 is a diagram illustrating DMRS REs included in the PSCCH of an NR SL.

[0052] In LTE SL, one subframe is an OFDM symbol and can include four demodulation reference signal (DMRS) symbols and data symbols, as shown in Figure 6. Referring to Figure 6, it can be seen that an OFDM symbol corresponding to a DMRS symbol is composed of a PSSCH DMRS and a PSCCH DMRS in the frequency domain. Also, referring to Figure 6, it can be seen that an OFDM symbol corresponding to a data symbol is composed of a PSCCH data signal and a PSSCH data signal in the frequency domain.

[0053] In NR SL, the number of DMRS symbols can be variably changed via an upper control signal. Referring to Fig. 7, the second to fourth OFDM symbols include a PSCCH, and the PSCCH can include a PSCCH data signal and a PSCCH DMRS in the frequency domain as shown in Fig. 8. Referring to Fig. 7, the OFDM symbol denoted as PSSCH DMRS can include a PSSCH DMRS and a PSSCH data signal in the frequency domain.

[0054] In common with LTE SL and NR SL, the last symbol of a subframe is a guard period, during which no signal is transmitted.

[0055] As shown in Figures 4 and 5, the LTE sidelink and the NR sidelink have a total bandwidth of multiple (e.g., M = N sub The vehicle-to-vehicle communication is performed through one or more of the sub-channels. subis a symbol representing the number of subchannels, and for convenience, these are used interchangeably (for example, M is used in descriptive expressions, and N is used in expressions related to mathematical expressions). sub (using ) and try to use it.

[0056] As shown in FIGS. 4 to 8, each subchannel can be configured with a PSCCH having control information and a PSSCH having a TB.

[0057] The DMRS used for PSCCH channel estimation is a known signal having a constant amplitude but a different phase in the frequency domain. In LTE SL and NR SL, the DMRS is defined differently as follows:

[0058] As shown in Figure 6, the LTE SL DMRS exists on four OFDM symbols and two RBs, and all resource elements (hereinafter referred to as "RE") in the RB are DMRSs. The LTE SL DMRS is a DMRS that is generated by applying a cyclic shift n to a basic reference signal d(k) as shown in Equation 1. cs The linear phase can be multiplied by the cyclic shift n cs can have a value of 0, 3, 6, or 9, and can be arbitrarily selected by the transmitting user equipment (UE).

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[0059] The NR SL DMRS is transmitted over two or three OFDM symbols and

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[0060] Since the receiving UE does not know in advance which cyclic shift the transmitting UE will use for transmission, it must try receiving each PSCCH using each cyclic shift candidate. sub There are 3N PSCCH candidates, and in NR SL, sub There can be PSCCH candidates.

[0061] Some embodiments of the present disclosure relate to a technique in which a receiving UE estimates a cyclic shift before receiving a PSCCH to reduce the number of reception attempts.

[0062] When the discrete Fourier transform (DFT) result of the CP-OFDM time domain signal x[n] is X[k], there is a timing offset τ, x[((n-τ)) N ], the DFT result is

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[0063] As described above, in V2X SL, a receiving UE must perform reception attempts for a large number of PSCCH candidates. Meanwhile, V2X communication requires low processing delay for urgent data transmission, such as collision prevention between vehicles. Therefore, a technique for reducing reception attempts for a large number of PSCCH candidates may be necessary to meet the low processing delay requirement. Some embodiments of the present disclosure relate to a technique for reducing reception attempts for a large number of PSCCH candidates to meet the low processing delay requirement.

[0064] On the other hand, in V2X communication, since direct peer-to-peer communication is performed between vehicles, synchronization errors (or timing offsets) and frequency errors (or frequency offsets) may occur in each peer-to-peer communication due to imperfect local oscillators in the vehicle transmitters themselves, and correction for these errors may be necessary for each peer-to-peer communication. 3GPP standard documents (3GPP 36.101 and 38.101) specify the maximum timing offset between vehicles as a performance requirement. g / 2-12T S It is defined so that up to 1 / 2,0 .... In this specification, even in such an environment where the timing offset is large, a technique capable of effectively estimating a cyclic shift applied to a DMRS may be needed to reduce the number of PSCCH candidates for which reception attempts should be made. Some embodiments of the present disclosure relate to a technique capable of effectively estimating a cyclic shift even in an environment where the timing offset is large.

[0065] Previous studies to reduce the number of PSCCH reception attempts include blind decoding (BD) and sensing-based algorithms (SALG). The BD technique measures Reference Signals Received Power (RSRP) for each cyclic shift and first attempts reception for a cyclic shift with a superior RSRP. If a signal processed according to the first attempted cyclic shift passes a subsequent check (e.g., a Cyclic Redundancy Check (CRC)), reception attempts for a lower priority cyclic shift (e.g., a cyclic shift with a lower RSRP) can be omitted, potentially reducing the overall number of reception attempts.

[0066] The SALG technique is a technique that obtains a correlation between the phase of each cyclic shift and the received DMRS, and performs reception attempts for the PSCCH based on a signal processed according to the cyclic shift with the largest correlation value.

[0067] However, both of these techniques rely on the correlation between the linear phase and the DMRS due to the cyclic shift, and therefore can have the drawback that when the timing offset is large, the correlation becomes small, leading to an incorrect estimation of the cyclic shift.

[0068] FIG. 9 is a block diagram illustrating some embodiments for receiving signal processing.

[0069] 10 is pseudocode for illustrating some embodiments for estimating the cyclic shift applied to the PSCCH DMRS from the IDFT result. As an example, some embodiments of FIG. 10 include a five-step embodiment for estimating the cyclic shift applied to the PSCCH DMRS from the IDFT result used to estimate the timing offset.

[0070] In some embodiments, as shown in FIG. 9, the receiving apparatus 900 may include at least some of a received reference signal group generation block 910, a CIR calculation block 920, a cyclic shift estimation block 930, and a timing offset estimation block 940.

[0071] In some embodiments, the receiving apparatus 900 may further include blocks (e.g., a receiving antenna, an RF circuit, a channel decoder, etc.) that are not shown in Fig. 9. As an example, the receiving apparatus 900 may further include a module that performs a reception attempt (e.g., a CRC test) on the PSCCH based on the estimation information obtained via the cyclic shift estimation block 930 and / or the timing offset estimation block 940.

[0072] In some embodiments, the receiving device 900 may correspond to a receiver of an OFDM symbol-based communication system. As an example, the receiving device 900 may correspond to a V2X receiving UE.

[0073] In some embodiments, an OFDM symbol-based communication system may transmit at least one OFDM symbol over a wireless channel and receive it via the wireless channel by a receiver. In some embodiments, a reference signal group for each of first to Mth subchannels (M is a natural number equal to or greater than 2) may be transmitted by at least one of the at least one OFDM symbol. In some embodiments, the reference signal group may include a plurality of cyclically shifted reference signals corresponding to the subchannel.

[0074] In some embodiments, the plurality of subchannels may include a plurality of PSCCHs of an LTE sidelink, and the reference signal may include a demodulation reference signal for each of the plurality of PSCCHs.

[0075] In some embodiments, the plurality of subchannels may include a plurality of PSCCHs for the NR sidelink, and the reference signal may include a demodulation reference signal for each of the plurality of PSCCHs.

[0076] In some embodiments, the first to Mth subchannels are represented by subchannel indexes c=0 to N in FIG. sub It can correspond to the subchannel corresponding to -1.

[0077] In some embodiments, the at least one OFDM symbol may be a plurality of OFDM symbols. As an example, the plurality of OFDM symbols may be represented by the symbol indexes of FIG.

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[0078] In some other embodiments, the at least one OFDM symbol may be one OFDM symbol. As an example, at least one of the first to Mth subchannels may transmit a demodulation reference signal for that subchannel via one OFDM symbol, or the receiver may perform a received signal processing operation for some embodiments of the present disclosure using only one of the at least one OFDM symbol. In this case, as will be described later, cyclic shift estimation may be performed based on a signal corresponding to one OFDM symbol without a summation operation (e.g., Step 3 in FIG. 10).

[0079] Although some of the following description discloses some embodiments focusing on the processing steps for the first subchannel, the embodiments can be similarly applied to the processing steps for other subchannels (e.g., the second to Mth subchannels). For example, as shown in FIG. 10, the operations are performed for subchannels with subchannel index c ranging from 0 to N. sub This can be repeated until it reaches -1.

[0080] In some embodiments, the received reference signal group generation block 910 may generate at least one received reference signal group corresponding to a first subchannel based on the received signal, where each of the at least one received reference signal group may include a received reference signal received via the corresponding OFDM symbol and the first subchannel.

[0081] In some embodiments, the CIR calculation block 920 can calculate a channel impulse response (hereinafter referred to as "CIR") of the first subchannel based on at least one received reference signal group corresponding to the first subchannel generated in the received reference signal group generation block 910.

[0082] In some embodiments, the cyclic shift estimation block 930 can estimate a cyclic shift corresponding to the first subchannel based on the channel impulse response of the first subchannel calculated in the CIR calculation block 920 .

[0083] In some embodiments, as shown in FIG. 9, the received reference signal group generation block 910 may include a sample group extraction block 912, a DFT block 914, and a received reference signal extraction block 916.

[0084] In some embodiments, the sample group extraction block 912 can extract at least one sample group corresponding to a symbol body of each of at least one OFDM symbol from the received signal.

[0085] In some embodiments, the DFT block 914 may apply a DFT to each of the at least one sample group extracted from the sample group extraction block 912 to generate at least one frequency domain signal.

[0086] Each frequency domain signal resulting from the DFT application can include a received demodulation reference symbol r(k) expressed by Equation 4. Equation 4 can be derived from Equation 1, Equation 2, and a linear phase due to a timing offset.

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[0087] In Equation 4, H is a channel response. For clarity of the equation, the channel response is assumed to be a one-tap response, but some embodiments of the present disclosure can be applied to a channel response other than the one-tap response in a similar principle.

[0088] In Equation 4, ε represents the cyclic shift scaled with respect to the IFFT size N, and τ represents the timing offset scaled with respect to the IFFT size N.

[0089] In some embodiments, the received reference signal extraction block 916 can extract received reference signals included in at least one received reference signal group corresponding to the first subchannel from at least one frequency domain signal generated by the DFT block 914.

[0090] In some embodiments, as shown in FIG. 9, the CIR calculation block 920 may include a time domain signal generation block 922 and a calculation block 928.

[0091] In some embodiments, the time domain signal generation block 922 can generate a time domain signal corresponding to each of at least one received reference signal group corresponding to the first subchannel generated in the received reference signal group generation block 910.

[0092] In some embodiments, the calculation block 928 can calculate a channel impulse response of the first subchannel based on at least one time domain signal generated in the time domain signal generation block 922 .

[0093] In some embodiments, as shown in FIG. 9, the time domain signal generation block 922 may include a descrambling block 924 and an IDFT block 926 .

[0094] In some embodiments, the descrambling block 924 can apply descrambling to each of at least one received reference signal group corresponding to the first subchannel generated in the received reference signal group generation block 910 to generate at least one descrambling result symbol group.

[0095] As described above, since the DMRSs are known signals with a constant amplitude, although the phase may differ for each DMRS, the receiving end can compensate for the phase of the DMRSs to convert them to have a constant amplitude and phase, and use them for channel estimation. Similarly, the descrambling block 924 multiplies each received reference signal by the complex conjugate of the corresponding basic reference signal d(k) according to Step 1) of FIG. 10 to generate a descrambling result signal x c,i can be generated.

[0096] For example, the number of REs of the PSCCH corresponding to the subchannel index c in LTE SL is

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[0097] As another example, since there is one DMRS RE per four REs in the NR SL, the descrambling block 924 may generate a descrambling result symbol group expressed by Equation 6. The descrambling result symbol group includes a descrambling result signal x corresponding to a received reference signal group of a corresponding subchannel (subchannel index c) included in a corresponding OFDM symbol (symbol index l). c,l (k) may be included.

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[0098] In some embodiments, the IDFT block 926 may apply an IDFT to each of the at least one descrambling result symbol group generated by the descrambling block 924 to generate the at least one time-domain signal.

[0099] In some embodiments, the size of the IDFT is equal to or larger than the size of the descrambling result symbol group that is the subject of the IDFT, and the IDFT block 926 can apply the IDFT by positioning the center of the descrambling result symbol group that is the subject of the IDFT at the center of the IDFT window.

[0100] In some embodiments, the size of the IDFT may be four times the size of the descrambling result symbol group that is the subject of the IDFT.

[0101] The operation of the IDFT block 926 according to some embodiments may correspond to Step 2 in FIG. 10. Generally, a timing offset is corrected during the channel estimation process, but a linear phase may still exist after the correction due to a timing offset estimation error. In some embodiments, an IDFT size that is four times the number of PSCCH DMRS REs may be selected so that the linear phase between both ends of the DMRS RE due to the estimation error is π / 4 or less. As an example, in LTE SL, since all REs in each DMRS symbol are DMRS REs, the IDFT size may be set to π / 4.

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[0102] For example, in LTE SL, when the center of the PSCCH DMRS RE is positioned as the center of the IDFT and an IDFT of size N′ is performed, CIRix is ​​calculated as shown in Equation 7. c,l (n) can be obtained.

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[0103] Referring to Equation 7, CIRix c,l (n) is the sinc function

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[0104] As another example, in NR SL, only one DMRS RE is extracted per four REs and IDFT is applied, so CIRix c,l (n) is the sinc function

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[0105] As described above, the calculation block 928 can calculate the channel impulse response of the first subchannel based on at least one time-domain signal generated by the time-domain signal generation block 922 .

[0106] In some embodiments, one time-domain signal (e.g., ix where l=0) c,l ) is generated or utilized, the calculation block 928 can determine the time domain signal as the CIR.

[0107] In some other embodiments, multiple time domain signals (e.g., ix c,l , l=0, 1, …,

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[0108] For example, the calculation block 928 may calculate the CIR by summing time-domain samples included in each of the plurality of time-domain signals for the same time index. That is, some embodiments of the calculation block 928 may correspond to Step 3 of FIG. 10. For example, the calculation block 928 may perform accumulation for the PSCCH DMRS symbols as in Step 3 of FIG. 10 to calculate the CIR. c Since noise is reduced by such accumulation calculation, the accuracy of estimating the cyclic shift and timing offset can be improved.

[0109] In some embodiments, as shown in FIG. 9, the cyclic shift estimation block 930 may include a detection block 932 and an estimation block 934 .

[0110] In some embodiments, the detection block 932 can detect the time index having the maximum value among the time domain samples of the channel impulse response calculated in the CIR calculation block 920 .

[0111] Some embodiments of the detection block 932 may correspond to Step 4 in FIG.

[0112] As an example, the detection block 932 detects ix c The time index k with the largest value among (n) max、C This time index k max、C can be expressed by Equation 8 and Equation 9 in LTE SL and NR SL, respectively.

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[0113] On the other hand, in LTE SL, cs The linear phase and ε are

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[0114] In some embodiments, the estimation block 934 can estimate a cyclic shift corresponding to each of the at least one subchannel based on the time index detected in the detection block 932 .

[0115] Some embodiments of the detection block 932 may correspond to Step 5 in FIG.

[0116] For example, the estimation block 934 may estimate the cyclic shift based on a time index of the plurality of intervals that has a maximum value of the channel impulse response. In some embodiments, the plurality of intervals may be obtained by dividing a time domain interval of the channel impulse response based on statistical characteristics of the channel impulse response when a cyclic shift corresponding to each of the M subchannels is applied. For example, the statistical characteristics of the channel impulse response may form a sinc function centered on each of the plurality of intervals.

[0117] FIG. 11 illustrates the CIR when there is no timing offset in LTE SL.

[0118] More specifically, FIG.

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[0119] As an example,

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[0120] After the cyclic shift is determined, the timing offset is calculated based on the determined cyclic shift, as will be described later.

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[0121] The SALG technique obtains the CIR value at the center of the Rice window, represented by the black arrow in Figure 11, and compares these CIR values ​​to estimate the cyclic shift. When there is no timing offset as in Figure 11, the CIR peak (i.e., the maximum value of the CIR) is detected, so the cyclic shift estimation performance may be at a level similar to that of some embodiments of the present disclosure. However, the estimation performance of the SALG technique may be significantly degraded in a channel environment where there is a timing offset and multipath and noise are present, as shown in Figure 12.

[0122] FIG. 12 illustrates the CIR when there is a timing offset in LTE SL.

[0123] More specifically, FIG. 12 differs from FIG. 11 in that there is a timing offset (

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[0124] In NR SL, the DMRS RE index k□ exists per 4 REs, so the linear phase with i is

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[0125] FIG. 13 illustrates the CIR when there is no timing offset in NR SL.

[0126] More specifically, FIG.

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[0127] As an example,

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[0128] On the other hand, the SALG technique, similar to the description of Fig. 11, obtains the CIR value at the center of the slice window, represented by the black arrow in Fig. 13, and compares these CIR values ​​to estimate the cyclic shift. When there is no timing offset as in Fig. 13, the CIR peak (i.e., the maximum value of the CIR) is detected, so the cyclic shift estimation performance may be at a level similar to that of some embodiments of the present disclosure. However, the estimation performance of the SALG technique may be significantly degraded in a channel environment where there is a timing offset and multipath and noise are present, as in Fig. 14.

[0129] FIG. 14 illustrates the CIR when there is a timing offset in NR SL.

[0130] More specifically, FIG. 14 differs from FIG. 13 in that there is a timing offset (

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[0131] In some embodiments, the timing offset estimation block 940 can estimate the timing offset based on the channel impulse response estimated in the cyclic shift estimation block 930 .

[0132] In some embodiments, the timing offset estimation block 940 is configured to estimate the time index k of the maximum value detected in the detection block 932, based on the ratio of the size N of the DFT used to generate the at least one received reference signal group in the DFT block 914 to the size N□ of the IDFT used to calculate the channel impulse response in the IDFT block 926. max、C , and the cyclic shift estimated in estimation block 934 (e.g., n cs ;For NR SL, the timing offset can be estimated based on i).

[0133] As an example, for LTE SL, the timing offset estimation block 940 calculates the timing offset as

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[0134] As another example, in the case of NR SL, the timing offset estimation block 940 calculates the timing offset as

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[0135] 15 is a graph illustrating the performance of the cyclic shift estimation technique of the present disclosure in LTE SL. More specifically, FIG. 15 illustrates the cyclic shift estimation performance of the technique of the present disclosure and the SALG technique.

[0136] The simulation environment used was PSSCH requirement test num. 4 defined in section 14.2 of the 3GPP standard document TS 36.101.

[0137] FIG. 16 shows Table 14.2-1 of the 3GPP standard document (3GPP36.101) that specifies performance requirements related to timing offset and frequency offset in LTE SL.

[0138] FIG. 17 shows Table 14.2-2 of the 3GPP standard document (3GPP 36.101) which specifies the performance requirements in LTE SL.

[0139] The simulation environment values ​​are: frequency offset set to 600Hz, channel condition is EVA2700, timing offset is 0 to 30T s The technique of the present disclosure and the SALG technique were compared in terms of cyclic shift estimation performance while varying the SNR from 2.8 dB to 0.0 dB as defined in the standard document.

[0140] 15, it can be seen that both techniques accurately estimate the cyclic shift when the timing offset is small. However, the timing offset CP / 2-12T specified in the performance requirements is s =24T s,It can be seen that the SALG technique has an estimation error with accuracies of 0.941 and 0.983 when SNR=0 dB and 2.8 dB, respectively, as shown in FIG.

[0141] 18 is a graph illustrating the performance of the cyclic shift estimation technique of the present disclosure in NR SL. More specifically, FIG. 18 illustrates the cyclic shift estimation performance of the technique of the present disclosure and the SALG technique.

[0142] The simulation environment used was PSSCH requirement test num. 1 defined in section 11.1.3 of 3GPP standard document TS 38.101-4.

[0143] Figure 19 illustrates the performance requirements for NR SL (minimum required performance described in Section 11.1.3 of TS 38.101-4).

[0144] The simulation environment values ​​are set as follows: frequency offset is set to 600Hz, channel condition is TDLA30-1400, timing offset is set from 0 to 30T s The technique of the present disclosure and the SALG technique were compared in terms of cyclic shift estimation performance while varying the SNR from 4.7 dB to 0.0 dB as defined in the standard document.

[0145] 18, it can be seen that both techniques accurately estimate the cyclic shift when the timing offset is small. However, the timing offset P / 2-12T specified in the performance requirements is too small. s =24T s As shown in FIG. 18, the accuracy of the SALG technique is 0.421 and 0.372 when SNR=0 dB and 4.7 dB, respectively, and it can be seen that the estimation error increases rapidly.

[0146] As described above, in the SALG technique, the accuracy performance fluctuates depending on the timing offset outside the peak main lobe, as can be seen from Figure 18. On the other hand, in the technique of the present disclosure, the lowest accuracy performance is 0.996, and it can be seen from Figure 18 that accurate estimation is maintained even when the timing offset is large.

[0147] The devices described above may be implemented using hardware components, software components, and / or a combination of hardware and software components. For example, the devices and components described in the embodiments may be implemented using one or more general-purpose or special-purpose computers, such as a processor, controller, arithmetic logic unit (ALU), digital signal processor, microcomputer, field programmable gate array (FPGA), programmable logic unit (PLU), microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications that run on the operating system. The processing device may also access, store, manipulate, process, and generate data in response to the execution of software. For ease of understanding, the processing device may be described as being a single processing element. However, those skilled in the art will recognize that the processing device may include multiple processing elements and / or multiple types of processing elements. For example, the processing device may include multiple processors or one processor and one controller. Other processing configurations are also possible, such as parallel processors.

[0148] Software may include computer programs, code, instructions, or a combination of one or more of these, capable of configuring or individually or collectively instructing a processing device to operate in a desired manner. The software and / or data may be embodied in any type of machine, component, physical device, computer storage medium, or device to be interpreted by or provide instructions or data to a processing device. The software may also be distributed across network-coupled computer systems, stored or executed in a distributed manner. The software and data may be stored on one or more computer-readable storage media.

[0149] Methods according to embodiments may be implemented in the form of program instructions that can be executed by various computer means and recorded on a computer-readable medium. In this case, the medium may continuously store a computer-executable program or may temporarily store the program for execution or download. Furthermore, the medium may be various recording or storage means in the form of a single or multiple pieces of hardware combined together. The medium is not limited to media directly connected to a computer system but may also be distributed over a network. Examples of media configured to store program instructions include magnetic media such as hard disks, floppy disks, and magnetic tapes; optical recording media such as CD-ROMs and DVDs; magneto-optical media such as floptical disks; and ROM, RAM, flash memory, and the like. Other examples of media include recording media or storage media managed by app stores that distribute applications, or by sites or servers that provide or distribute various other software.

[0150] Although the embodiments have been described above with reference to limited embodiments and drawings, those skilled in the art will appreciate that various modifications and variations may be made from the above description. For example, the described techniques may be performed in a different order than described, and / or the components of the described systems, structures, devices, circuits, etc. may be combined or combined in a different manner than described, or may be replaced or substituted with other components or equivalents, and still achieve suitable results.

[0151] Accordingly, other implementations, embodiments, and equivalents of the claims are within the scope of the following claims.

Claims

1. 1. A method for operating a receiver in a communication system in which at least one OFDM symbol is transmitted, wherein a reference signal group for each of 1st to Mth subchannels (M is a natural number equal to or greater than 2) is transmitted by at least one of the at least one OFDM symbol, and the reference signal group includes a plurality of reference signals to which cyclic shifts corresponding to the subchannels have been applied, comprising: generating at least one received reference signal group corresponding to the first subchannel based on the received signal, each of the received reference signal groups including a corresponding OFDM symbol and a received reference signal received through the first subchannel; calculating a channel impulse response of the first subchannel based on at least one received reference signal group corresponding to the generated first subchannel; and estimating a cyclic shift corresponding to the first subchannel based on the calculated channel impulse response of the first subchannel.

2. The step of generating at least one received reference signal group comprises: extracting at least one sample group corresponding to a symbol body of each of the at least one OFDM symbol from the received signal; applying a Discrete Fourier Transform (DFT) to each of the at least one extracted sample group to generate at least one frequency domain signal; and extracting the received reference signals included in at least one received reference signal group corresponding to the first subchannel from the generated at least one frequency domain signal.

3. The step of calculating a channel impulse response comprises: generating time domain signals corresponding to each of the at least one received reference signal group; and calculating the channel impulse response based on the generated at least one time-domain signal.

4. The step of generating at least one time domain signal comprises: applying descrambling to each of the at least one received reference signal group to generate at least one descrambled resultant symbol group; and applying an Inverse Discrete Fourier Transform (IDFT) to each of the at least one descrambling result symbol group to generate the at least one time-domain signal.

5. 5. The method of claim 4, wherein the size of the IDFT is four times the size of the descrambling result symbol group that is subject to the IDFT.

6. the size of the IDFT is equal to or larger than the size of the descrambling result symbol group that is the target of the IDFT; 5. The method of claim 4, wherein the step of applying the IDFT includes the step of positioning the center of a descrambling result symbol group to be subjected to the IDFT at the center of a window of the IDFT and applying the IDFT.

7. The reference signal group of the first subchannel is transmitted via one OFDM symbol; generating at least one received reference signal group includes generating one received reference signal group corresponding to the first subchannel; generating at least one time domain signal includes generating a time domain signal corresponding to the generated one received reference signal group; 4. The method of claim 3, wherein the step of calculating the channel impulse response comprises determining the generated one time domain signal as the channel impulse response.

8. The reference signal group of the first subchannel is transmitted via a plurality of OFDM symbols; generating at least one received reference signal group includes generating a plurality of received reference signal groups corresponding to the first subchannel; generating at least one time domain signal includes generating a time domain signal corresponding to each of the plurality of generated received reference signal groups; 4. The method of claim 3, wherein the calculating the channel impulse response comprises: calculating the channel impulse response by summing time-domain samples included in each of the generated time-domain signals by the same time index.

9. The step of estimating a cyclic shift comprises: detecting a time index having a maximum value among the time domain samples of the channel impulse response; and estimating a cyclic shift corresponding to each of the at least one subchannel based on the detected time index.

10. the step of estimating the cyclic shift includes a step of estimating the cyclic shift based on a time index having a maximum value of the channel impulse response among a plurality of time intervals; 10. The method of claim 9, wherein the plurality of intervals are obtained by dividing a time domain interval of the channel impulse response based on statistical characteristics of the channel impulse response when a cyclic shift corresponding to each of the M subchannels is applied.

11. 11. The method of claim 10, wherein the statistical characteristics of the channel impulse response form a sinc function centered on each of the plurality of intervals.

12. 2. The method of claim 1, further comprising the step of estimating a timing offset based on the estimated channel impulse response.

13. estimating the cyclic shift includes estimating a cyclic shift corresponding to each of the at least one subchannel based on a time index having a maximum value among time-domain samples of the channel impulse response; 13. The method of claim 12, wherein estimating the timing offset comprises estimating the timing offset based on a ratio of a size of a DFT used to generate the at least one received reference signal group to a size of an IDFT used to calculate the channel impulse response, a time index having the maximum value, and the estimated cyclic shift.

14. For each m (m has a value from 2 to M), generating at least one received reference signal group corresponding to the m subchannel based on the received signal, each of the received reference signal groups including a corresponding OFDM symbol and a received reference signal received through the m subchannel; calculating a channel impulse response of the mth subchannel based on the generated at least one received reference signal group corresponding to the mth subchannel; 2. The method of claim 1, further comprising: estimating a cyclic shift corresponding to the mth subchannel based on the calculated channel impulse response of the mth subchannel.

15. The first to M subchannels each include a PSCCH and a PSSCH of an LTE side link; The method of claim 1, wherein the reference signal group for each of the first to M-th subchannels includes a reference signal group for a PSCCH included in the corresponding subchannel.

16. Each of the first to M subchannels includes a PSCCH and a PSSCH of an NR sidelink, The method of claim 1, wherein the reference signal group for each of the first to M-th subchannels includes a reference signal group for a PSCCH included in the corresponding subchannel.

17. A receiving device in a communication system in which at least one OFDM symbol is transmitted, wherein a reference signal group for each of 1st to Mth subchannels (M is a natural number equal to or greater than 2) is transmitted by at least one of the at least one OFDM symbol, and the reference signal group includes a plurality of reference signals to which cyclic shifts corresponding to the subchannels are applied, a received reference signal group generation block that generates at least one received reference signal group corresponding to the first subchannel based on the received signal, each of the received reference signal groups including a corresponding OFDM symbol and a received reference signal received through the first subchannel; a channel impulse response calculation block that calculates a channel impulse response of the first subchannel based on at least one received reference signal group corresponding to the generated first subchannel; a cyclic shift estimation block that estimates a cyclic shift corresponding to the first subchannel based on the calculated channel impulse response of the first subchannel.

18. The received reference signal group generation block: a sample group extraction block for extracting at least one sample group corresponding to a symbol body of each of the at least one OFDM symbol from the received signal; a DFT block for applying a DFT to each of the at least one extracted group of samples to generate at least one frequency domain signal; 18. The receiving device of claim 17, further comprising: a receiving reference signal extraction block that extracts the receiving reference signals included in at least one receiving reference signal group corresponding to the first subchannel from the generated at least one frequency domain signal.

19. The channel impulse response calculation block a time domain signal generating block for generating time domain signals corresponding to each of the at least one received reference signal group; 18. The receiving device of claim 17, further comprising: a calculation block for calculating the channel impulse response based on the generated at least one time domain signal.

20. The time domain signal generation block comprises: a descrambling block for applying descrambling to each of the at least one received reference signal group to generate at least one descrambling result symbol group; and an IDFT block that applies an IDFT to each of the generated at least one descrambling result symbol group to generate the at least one time domain signal.

21. The cyclic shift estimation block a detection block for detecting a time index having a maximum value among the time domain samples of the channel impulse response; 18. The receiving apparatus of claim 17, further comprising: an estimation block that estimates a cyclic shift corresponding to each of the at least one subchannel based on the detected time index.

22. The receiving apparatus of claim 17, further comprising a timing offset estimation block for estimating a timing offset based on the estimated channel impulse response.

23. For each m (m has a value from 2 to M), the received reference signal group generation block generates, based on the received signal, at least one received reference signal group corresponding to the m subchannel, each of the received reference signal groups including a corresponding OFDM symbol and a received reference signal received through the m subchannel; the channel impulse response calculation block calculates a channel impulse response of the mth subchannel based on at least one received reference signal group corresponding to the generated mth subchannel; The receiving apparatus of claim 17 , wherein the cyclic shift estimation block estimates a cyclic shift corresponding to the mth subchannel based on the calculated channel impulse response of the mth subchannel.

24. The first to M subchannels each include a PSCCH and a PSSCH of an LTE side link; The receiving apparatus of claim 17, wherein the reference signal group for each of the first to M-th subchannels includes a reference signal group for a PSCCH included in the corresponding subchannel.

25. Each of the first to M subchannels includes a PSCCH and a PSSCH of an NR sidelink, The receiving apparatus of claim 17, wherein the reference signal group for each of the first to M-th subchannels includes a reference signal group for a PSCCH included in the corresponding subchannel.

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