Frequency Error Estimation and Compensation Techniques in OFDM-Based Communication Systems

Abstract

To provide frequency error estimation and compensation techniques 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, -each OFDM symbol including a cyclic prefix and a symbol body- is transmitted includes generating first, second, and third FFT signals for a specific OFDM symbol by performing FFT on an interval from each of first, second, and third start positions included in a received signal to the length of the symbol body, and estimating a frequency offset for the specific OFDM symbol based on the first to third FFT signals.SELECTED DRAWING: Figure 15

Description

[Technical Field]

[0001] This disclosure relates to received signal processing techniques in communication systems, and more specifically, some embodiments relate to frequency error estimation and compensation techniques in OFDM-based communication systems. [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 methods such as cameras, radar, and lidar, which belong to ADAS (Advanced Driver Assistance System), as well as V2X (Vehicle to Everything communication), which shares the collected information with surrounding vehicles via wireless communication, and these are considered essential technologies. For this purpose, international standards such as IEEE 802.11p, 3GPP LTE (Long Term Evolution) sidelink, and NR (New Radio) sidelink, known as DSRC (dedicated short-range communication), have been established, and research and implementation related to these standards are actively progressing. In particular, communication between vehicles traveling at high speeds presents the challenge of enabling communication in channel conditions that change rapidly over time due to Doppler spread. [Overview of the Initiative] [Problems that the invention aims to solve]

[0003] Therefore, there is a need for received signal processing techniques (for example, frequency offset estimation and / or compensation techniques, or timing offset estimation and / or compensation techniques) that can overcome these difficulties. [Means for solving the problem]

[0004] One aspect of the present disclosure provides a method for processing a received signal including at least one OFDM symbol—each OFDM symbol including a cyclic prefix and a symbol body—the method comprising the steps of generating a first FFT signal, a second FFT signal, and a third FFT signal for a particular OFDM symbol by performing an FFT on intervals from a first start position, a second start position, and a third start position included in the received signal to the length of the symbol body, and estimating a frequency offset for the particular OFDM symbol based on the first to third FFT signals.

[0005] In some embodiments, the first start position may include an estimated start position where the particular OFDM symbol is located in the received signal, the second start position may include a position that precedes the estimated start position by a predetermined time length, and the third start position may include a position that follows the estimated start position by a predetermined time length. In some embodiments, the predetermined time length may include the length of the cyclic prefix.

[0006] In some embodiments, the step of estimating the frequency offset may include the steps of generating first to third IFFT signals by performing an IFFT on each of the first to third FFT signals only on resource blocks belonging to a specific subchannel of the FFT signal, and estimating the frequency offset based on the first to third IFFT signals.

[0007] In some embodiments, the step of estimating the frequency offset based on the first to third IFFT signals may include the step of estimating the frequency offset using, in at least a portion of the first to third IFFT signals, a cyclic prefix section of the particular OFDM symbol and a section of the symbol body of the particular OFDM symbol corresponding to the cyclic prefix section (hereinafter referred to as the cyclic prefix corresponding section).

[0008] In some embodiments, the method further includes estimating a timing offset for the received signal, and the step of estimating a frequency offset using the cyclic prefix section and the cyclic prefix corresponding section includes taking samples belonging to the cyclic prefix section and samples belonging to the cyclic prefix corresponding section from the second IFFT signal and the third IFFT signal respectively based on the estimated timing offset.

[0009] In some embodiments, the step of estimating a frequency offset using the cyclic prefix section and the cyclic prefix corresponding section may include performing a cross-correlation on the cyclic prefix section and the cyclic prefix corresponding section, and estimating the frequency offset based on the result of the cross-correlation.

[0010] In some embodiments, the method may further include compensating the estimated frequency offset for the first IFFT signal. In some embodiments, the method may further include performing an FFT on the first IFFT signal with the frequency offset compensated to obtain resource blocks of sub-channels. In some embodiments, the method may further include performing resource demapping on the obtained resource blocks.

[0011] In some embodiments, the method may further include estimating a timing offset for the received signal, and compensating the estimated timing offset for the first IFFT signal with the frequency offset compensated.

[0012] In some embodiments, the method may further include performing an FFT on the first IFFT signal with the timing offset compensated to obtain resource blocks of sub-channels.

[0013] In some embodiments, the size of the FFT performed on the first IFFT signal may be smaller than the size of the FFT used to generate the first FFT signal.

[0014] In some embodiments, the method may further include the step of estimating a timing offset with respect to the received signal.

[0015] In some embodiments, the step of estimating the timing offset may include the step of estimating the timing offset based on at least a portion of the first to third FFT signals.

[0016] In some embodiments, the step of estimating the timing offset may include the step of estimating the timing offset based on a demodulated reference signal included in the received signal.

[0017] Another aspect of the present disclosure provides a receiving device for processing a received signal including at least one OFDM symbol—each OFDM symbol including a cyclic prefix and a symbol body—the receiving device comprising: an FFT block for generating a first FFT signal, a second FFT signal, and a third FFT signal for a particular OFDM symbol by performing an FFT on intervals from a first start position, a second start position, and a third start position included in the received signal to the length of the symbol body; and a frequency offset estimation block for estimating a frequency offset for the particular OFDM symbol based on the first to third FFT signals.

[0018] In some embodiments, the first start position includes an estimated start position where the particular OFDM symbol is located in the received signal, the second start position includes a position that precedes the estimated start position by a predetermined time length, and the third start position includes a position that follows the estimated start position by a predetermined time length.

[0019] In some embodiments, the receiving device may further include a timing offset estimation block for estimating a timing offset with respect to the received signal.

[0020] In some embodiments, the frequency offset estimation block may include an IFFT block that generates the first to third FFT signals by performing an IFFT on resource blocks belonging to a specific subchannel of each of the first to third FFT signals, and a frequency offset calculation block that estimates the frequency offset based on the first to third IFFT signals.

[0021] In some embodiments, the frequency offset calculation block may estimate the frequency offset using the cyclic prefix interval of the specific OFDM symbol and the cyclic prefix corresponding interval of the specific OFDM symbol in at least a portion of the first to third IFFT signals.

[0022] The frequency offset calculation block may include a section extraction block that takes samples belonging to the cyclic prefix section and samples belonging to the cyclic prefix corresponding section from the second IFFT signal and the third IFFT signal, respectively, based on the estimated timing offset, and a frequency offset determination block that performs cross-correlation between the samples belonging to the cyclic prefix section and the samples belonging to the cyclic prefix corresponding section, and determines the frequency offset based on the obtained cross-correlation result.

[0023] In some embodiments, the receiving device may further include a frequency offset compensation block that compensates the estimated frequency offset for the first IFFT signal.

[0024] In some embodiments, the receiving device may further include a timing offset compensation block that compensates for the estimated timing offset with respect to the first IFFT signal from which the frequency offset has been compensated.

[0025] Another aspect of the present disclosure provides a non-temporary recording medium for storing instructions readable by a processor of an electronic device, wherein the instructions cause the processor to perform an embodiment of the present disclosure.

[0026] This summary is provided to introduce, in a simplified form, selected concepts from those further described in the detailed description below. This summary is not intended to identify any important or essential features of the subject matter of the claimed invention, nor is it intended to be used to limit the scope of the subject matter of the claimed invention. Furthermore, the subject matter of the claimed invention is not limited to embodiments that solve some or all of the problems mentioned in any part of this specification. In addition to the exemplary aspects, embodiments, and features described above, additional aspects, embodiments, and features will become clear with reference to the detailed description and drawings below. [Effects of the Invention]

[0027] Some embodiments of this disclosure may have the following advantages; however, this does not mean that all embodiments must include all of these advantages, and the scope of the invention should not be understood to be limited by this.

[0028] According to some embodiments, estimation and compensation can be performed with excellent performance even in environments with large timing offsets and / or large frequency offsets.

[0029] According to some embodiments, estimation and compensation with excellent performance can be performed even when multiple peer-to-peer communications coexist.

[0030] According to some embodiments, frequency offset estimation and compensation can be performed on a sub-channel basis rather than across the entire bandwidth.

[0031] According to some embodiments, by measuring the frequency offset for each symbol, it is possible to measure up to half the subcarrier interval, thus enabling excellent performance estimation and compensation even in large Doppler environments.

[0032] According to some embodiments, the complexity of the receiver can be reduced by generating a decimated time-domain signal using FFT and IFFT corresponding to the size of the subchannels, rather than the entire bandwidth. [Brief explanation of the drawing]

[0033] [Figure 1] An example of an OFDM symbol generation block is shown. [Figure 2] Examples of OFDM symbols are shown. [Figure 3] The 3GPP LTE frame structure is illustrated as an example. [Figure 4] This example illustrates the resource grid for LTE sidelink (SL). [Figure 5] An example of an NR SL resource grid is shown. [Figure 6] Examples of LTE SL subframe structures and NR SL subframe structures are provided. [Figure 7] Examples of LTE SL subframe structures and NR SL subframe structures are provided. [Figure 8] Table 14.2-1 of the 3GPP standard document (3GPP 36.101), which specifies the performance requirements related to timing offset and frequency offset in LTE SL, is shown below. [Figure 9]Table 11.1.2.1.1-1 of the 3GPP standard document (3GPP 38.101), which specifies the performance requirements related to timing offset and frequency offset in 5G SL, is shown below. [Figure 10] Table 14.2-2 of the 3GPP standard document (3GPP 36.101), which specifies the performance requirements related to Doppler spread in LTE SL, is shown below. [Figure 11] Table 11.1.2.1.1-2 of the 3GPP standard document (3GPP 38.101), which specifies the performance requirements related to Doppler spread in 5G SL, is shown below. [Figure 12] This paper illustrates the limitations of various frequency offset estimation and channel estimation techniques. [Figure 13] Several embodiments of the received signal processing method are illustrated as examples of communication systems in which they can be used. [Figure 14] This is a flowchart illustrating several embodiments of received signal processing. [Figure 15] Pseudocode is provided to illustrate several embodiments of the received signal processing algorithm. [Figure 16] This is a block diagram illustrating several embodiments of the received signal processing module. [Figure 17] This shows the FFT window when the OFDM symbol has a timing offset. [Figure 18] This is a diagram illustrating the DMRS RE included in the LTE SL PSCCH. [Figure 19] This is a diagram illustrating the DMRS RE included in NR SL's PSCCH. [Figure 20] This figure illustrates an embodiment for regenerating time-domain signals for symbols and subchannels. [Figure 21] This diagram illustrates the cyclic prefix interval and the cyclic prefix corresponding interval of the regenerated time-domain signal. [Figure 22]This diagram illustrates the timing sample offset between the cyclic prefix interval and the corresponding cyclic prefix interval of the regenerated time-domain signal. [Figure 23] This is pseudocode to illustrate several embodiments of frequency offset compensation. [Figure 24] An example of θacc given by θi,l is shown. [Figure 25] A cyclic shift for timing offset compensation is illustrated as an example. [Figure 26] This graph illustrates the performance of the frequency offset estimation and compensation techniques of this disclosure. [Modes for carrying out the invention]

[0034] The descriptions relating to the present invention are merely embodiments for structural or functional explanation; therefore, the scope of the present invention should not be construed as being limited by the embodiments described herein. That is, since embodiments can be modified in various ways and can take on various forms, the scope of the present invention should be understood to include equivalents that can realize the technical idea. Furthermore, the purposes or effects presented in the present invention do not mean that a particular embodiment must include all of them or only such effects; therefore, the scope of the present invention should not be understood as being limited by them.

[0035] On the other hand, the meaning of the terms used in this disclosure should be understood as follows: Terms such as "First," "Second," etc., are used to distinguish one component from another, and these terms should not limit the scope of rights. For example, the first component may be named the second component, and similarly, the second component may be named the first component.

[0036] When it is mentioned that one component is "connected" to another, it should be understood that it may be directly connected to that other component, or another component may be intervening between them. Conversely, when it is mentioned that one component is "directly connected" to another, it should be understood that no other component is intervening between them. On the other hand, 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] A singular expression should be understood to include multiple expressions unless the context clearly indicates otherwise, and terms such as “includes” or “possesses” should be understood to indicate the presence of a particular feature, number, stage, action, component, part, or combination thereof, without prejudice against the existence or possibility of adding one or more other features, numbers, stages, actions, components, parts, or combinations thereof.

[0038] In each stage, identification codes (e.g., a, b, c, etc.) are used for explanatory purposes only and do not indicate the order of the stages. The stages may be performed in an order different from the one specified unless the context clearly indicates a specific order. That is, the stages may be performed in the same order as specified, substantially simultaneously, or in reverse order.

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

[0040] Orthogonal Frequency Division Multiplexing (OFDM), as shown in Figure 1, is a method that divides the data to be transmitted into multiple smaller data units, modulates these into mutually orthogonal subcarriers via the inverse fast Fourier transform (IFFT), and transmits them simultaneously.

[0041] Figure 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 (symbol body). Multipath interference can be mitigated through the CP that adds a certain part at the rear of the multi-carrier transmission signal (i.e., the 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, based on the basic time unit T with respect to, for the symbol body section N c = 2048T s when, for normal CP, N g = 144T s or 160T s and for extended CP, N g = 512T s is only specified to be placed.

[0043] Thus, the combination of the CP and the symbol body is called CP-OFDM, and this CP-OFDM is used in 3GPP LTE / NR side links.

[0044] When the number of subcarriers is N u , the CP-OFDM signal s(k) at the transmitter can be expressed by Equation (1).

[0045]

Equation

[0046] Some embodiments of this disclosure relate to a technique for estimating frequency errors due to the Doppler effect occurring during high-speed driving using CP in CP-OFDM. For convenience, some embodiments are described herein based on a 3GPP LTE / NR environment, but some embodiments of this disclosure can be directly applied to general CP-OFDM-based systems.

[0047] Figure 3 illustrates the 3GPP LTE frame structure.

[0048] In 3GPP LTE / NR, as shown in Figure 3, a frame can consist of time units (e.g., subframes or slots) made up of multiple OFDM symbols on the time axis, and resource blocks (RBs) made up of multiple (e.g., 12) subcarriers on the frequency axis.

[0049] Figure 4 illustrates a resource grid for an LTE sidelink (hereinafter referred to as "SL").

[0050] In LTE SL, as shown in Figure 4, there is a Physical Sidelink Control Channel (PSCCH) which contains sidelink control information (SCI) consisting of two RBs,

number

[0051] Figure 5 illustrates the resource grid of NR SL.

[0052] In NR SL as well, as shown in Figure 5, one or more subchannels can be assigned PSCCH and PSSCH respectively. However, unlike LTE, it consists of two stages of SCI, with PSCCH and PSSCH adhering to each other. For example, the white box with dashed lines in Figure 5 is a single-stage SCI included in PSCCH, the shaded box with dashed lines is a two-stage SCI included in PSSCH, and the solid box containing the white box with dashed lines and the shaded box with dashed lines can include PSSCH data in the remaining resource elements excluding the white box with dashed lines and the shaded box with dashed lines.

[0053] Figures 6 and 7 illustrate the LTE SL subframe structure and the NR SL subframe structure, respectively.

[0054] In LTE SL, as shown in Figure 6, a single subframe can contain four demodulation reference signal (DMRS) symbols and multiple data symbols as an OFDM symbol. Referring to Figure 6, it can be seen that the OFDM symbol corresponding to the DMRS symbol consists of PSSCH DMRS and PSCCH DMRS in the frequency domain. Similarly, referring to Figure 6, it can be seen that the OFDM symbol corresponding to the data symbol consists of a PSCCH data signal and a PSSCH data signal in the frequency domain.

[0055] In NR SL, the number of DMRS symbols can be variably changed via higher-level control signals. Referring to Figure 7, the second to fourth OFDM symbols include PSCCH, and the PSCCH can include PSCCH data signals and PSCCH DMRS in the frequency domain, as shown in Figure 19. Referring to Figure 7, the OFDM symbol labeled PSSCH DMRS can include PSSCH DMRS and PSSCH data signals in the frequency domain.

[0056] In both LTE SL and NR SL, the last symbol of a subframe is the guard period, during which no signal is transmitted.

[0057] On the other hand, when the result of the Discrete Fourier Transform (DFT) of a time-domain signal x[k] is X[n], the circular shift is x[((km)) N The DFT result for ] is:

number

number

[0058] On the other hand, when the aforementioned transmitted signal S(k) passes through the L-taph(τ;k) channel and the n(k) noise channel, the L-taph(τ;k) channel and the received signal x(k) after passing through the channel can be expressed by equations 2 and 3, respectively.

number

number

[0059] In this case, if there is a normalized frequency offset ε0 between the transmitting and receiving ends, the received signal x(k) in the cyclic prefix section can be expressed as shown in equations 1 and 3, and then equation 4.

number

[0060] The corresponding cyclic prefix interval can be expressed as shown in equation 5.

number

[0061] The magnitude (amplitude) of each tap l due to the Doppler effect (β) l The difference between this and the normalized phase ε l It can be changed independently, and the size change amount within the symbol

number

number

[0062] Applying the result of equation 6 to equation 5, the cyclic prefix corresponding interval can be expressed as shown in equation 7.

number

[0063] In other words, between the cyclic prefix section and the cyclic prefix corresponding section,

number

[0064] As mentioned above, timing offset can cause linear phase from a frequency domain signal, and frequency offset can cause linear phase from a time domain signal.

[0065] On the other hand, the following are examples of difficulties in V2X systems to which some embodiments of this disclosure may apply:

[0066] Firstly, V2X systems can have the difficulty of having large transmission / reception synchronization and frequency errors (hereinafter referred to as the "P1 problem"). In LTE / NR systems where user equipment (UE) communicates with a base station, 1-to-N communication is performed where each UE only needs to match the transmission / reception synchronization and frequency to the base station, making it easy to correct each error at the receiving end. However, in V2X systems where vehicles communicate directly peer to peer, it becomes N-to-N communication where the synchronization and frequency errors due to the imperfect local oscillators of the vehicle's transceiver itself must be matched separately, which can make it difficult to correct each error. In the relevant 3GPP standard documents (e.g., 3GPP 36.101 and 38.101), the performance requirement is that the timing offset between vehicles should be limited to a maximum of T g / 2-12T S The regulations stipulate that a frequency offset between vehicles can be tolerated up to a maximum of 600 Hz.

[0067] Figure 8 shows Table 14.2-1 of the 3GPP standard document (3GPP 36.101) which specifies the performance requirements related to timing offset and frequency offset in LTE SL.

[0068] Figure 9 shows Table 11.1.2.1.1-1 of the 3GPP standard document (3GPP 38.101) which specifies the performance requirements related to timing offset and frequency offset in 5G SL.

[0069] Referring to Figures 8 and 9, the requirements for timing offset (i.e., synchronization error) and frequency offset (i.e., frequency error) in each system can be confirmed.

[0070] Secondly, a V2X system may face the challenge of having different frequency and timing offsets for each subchannel (hereinafter referred to as the "P2 problem"). This is because each subchannel may have different vehicle-to-vehicle communications. Therefore, the estimation and / or compensation of offsets (frequency offset and / or timing offset) in a V2X system must be handled independently for each subchannel.

[0071] Thirdly, V2X systems may have the difficulty of having large Doppler spread (hereinafter referred to as the "P3 problem"). In vehicle-to-vehicle communication at high speeds, the channel response changes rapidly in time due to large Doppler spread, but transmission and reception must be smooth even on such channels. In addition, V2X systems may experience interference (inter-carrier interference, hereinafter referred to as "ICI") caused by the orthogonality between OFDM subcarriers being broken due to Doppler spread and frequency offset, and such ICI problems also need to be effectively resolved. Relevant 3GPP standard documents (e.g., 3GPP 36.101 and 38.101) explicitly state as a performance requirement that support up to a maximum Doppler frequency of 2700 Hz be provided.

[0072] Figure 10 shows Table 14.2-2 of the 3GPP standard document (3GPP 36.101) which specifies the performance requirements related to Doppler spread in LTE SL.

[0073] For example, the propagation condition EVA2700 explicitly shown in Test num. 4 in Figure 10 refers to the multi-path condition EVA (extended vehicular A model) and a maximum Doppler diffusion of 2700 Hz.

[0074] Figure 11 shows Table 11.1.2.1.1-2 of the 3GPP standard document (3GPP 38.101) which specifies the performance requirements related to Doppler diffusion in 5G SL.

[0075] For example, the propagation condition TDLA30-2700 explicitly shown in Test num.1 of Figure 11 refers to the multipath condition TDLA30 (Tapped delay line A) and a maximum Doppler spread of 2700 Hz.

[0076] Fourthly, V2X systems may face the challenge of ensuring low implementation complexity and low processing latency (hereinafter referred to as the "P4 problem"). Low processing latency must be guaranteed for urgent data transmission, such as collision prevention between vehicles. Furthermore, low-complexity algorithms may be necessary to achieve the proposed chip size and heat generation requirements.

[0077] Various studies have been conducted on frequency offset and channel estimation to address the temporal changes in channels due to Doppler diffusion.

[0078] Firstly, there is a technique for measuring frequency offset using CP in the time domain (hereinafter referred to as the time domain CP-FOE (Frequency Offset Estimation) technique). As mentioned above, in time domain signals, a linear phase proportional to the frequency offset occurs, so this technique can measure the phase difference and the resulting frequency offset by determining the cross-correlation between the CP signal and its corresponding symbol body signal. However, as stated in problem P2, each received signal in the sidelink consists of N-to-N communication signals, each with a different frequency offset for each subchannel, making it difficult to find only the frequency offset corresponding to itself in the time domain signal.

[0079] Secondly, there is a technique that measures the phase difference and the resulting frequency offset by determining the cross-correlation between symbols with reference signals (hereinafter referred to as the "frequency domain FOE technique"). The frequency offset measured in this way can be used to estimate the frequency offset in data symbols via interpolation. This technique can be a solution to the P2 problem because it can measure the frequency offset in the frequency domain assigned to it. However, as mentioned in the P3 problem, when the frequency offset is large in addition to Doppler spread, it has the disadvantage that the error due to interpolation becomes large, and in the case of data symbols outside subframes where interpolation is impossible, performance degradation due to extrapolation errors becomes unavoidable. Adding a frequency offset of 600 Hz to the aforementioned Doppler spread of 2700 Hz can generate up to 3300 Hz, but in LTE SL, the distance between DMRS symbols is 3 symbols, and with a subcarrier spacing (SCS) of 15 kHz, the measurable frequency offset is

number

[0080] Thirdly, focusing on the fact that channels can be modeled with even smaller parameters in the transform domain, there is a technique (hereinafter referred to as "BEM-based channel estimation technique") that detects the characteristics of reference symbols using a basis expansion model (BEM) and extends them to data symbols through interpolation or Kalman filtering. However, this technique has a complexity of O(N). u *N sym ) 3 Because it requires large-sized matrix operations, it cannot satisfy the low complexity requirements (i.e., the P4 problem), and it has the disadvantage of performance degradation under the large Doppler diffusion described in the P3 problem due to interpolation errors.

[0081] Fourthly, there is a technique that applies deep learning-based channel estimation to channels that change on the time and frequency axes, like sidelinks (hereinafter referred to as "deep learning-based channel estimation technique"). However, this technique has an implementation complexity of O(h*w*l*N) when the height of the convolutional filter is h, the width is w, and the number of layers is l. u *N sym Therefore, it has the disadvantage of high implementation complexity and the use of only reference symbols as input. Furthermore, techniques such as the long short-term memory model (LSTM), which have relatively low implementation complexity, require that reference symbols accompany the symbols to be estimated. However, unlike LTE, where reference signals are continuously present, LTR / NR SL has the disadvantage that data transmission is difficult to apply on a subframe basis, and processing delays occur, making it impossible to solve the P4 problem.

[0082] Figure 12 illustrates the limitations of various frequency offset estimation and channel estimation techniques. Referring to Figure 12, the limitations of the techniques described above are illustrated. For example, the time-domain CP-FOE technique may have limitations in solving the P2 problem.

[0083] Figure 13 illustrates a communication system in which several embodiments of the received signal processing method can be used.

[0084] Figure 13 illustrates a typical configuration of a CP-OFDM communication system, but some embodiments of this disclosure can also be applied to CP-OFDM communication systems with configurations different from those shown in Figure 13.

[0085] Referring to Figure 13, the CP-OFDM communication system 1300 may include a transmitter 1310, a channel 1350, and a receiver 1360.

[0086] In some embodiments, the transmitter 1310 and the receiver 1360 may each be a UE (e.g., a V2X-based UE performing a sidelink). In some other embodiments, the transmitter 1310 and the receiver 1360 may be a base station and a UE, or a UE and a base station.

[0087] Referring to Figure 13, the transmitter 1310 may include an encoder block 1315, a modulation block 1320, a resource mapping block 1325, an IFFT block 1330, a CP insertion block 1335, a D / A block 1340, and an upconverter block 1345.

[0088] The encoder block 1315 can encode the input data (for example, channel coding) and output the encoded data.

[0089] The modulation block 1320 can map each encoded data (e.g., binary bits) or a bundle of encoded data to a modulation symbol (e.g., a QPSK symbol).

[0090] The resource mapping block 1325 can provide modulation symbols to the IFFT block 1330 so that each modulation symbol can be positioned on its respective resource (e.g., a subcarrier).

[0091] The IFFT block 1330 can generate the symbol body for each OFDM symbol by performing an IFFT transformation on the input modulation symbols.

[0092] The CP insertion block 1335 can insert the CP before the symbol body of each input OFDM symbol.

[0093] An OFDM symbol with a CP inserted (i.e., a CP-OFDM symbol) can be converted to an analog signal via the D / A block 1340 and transmitted to the radio communication channel 1350 via the upconverter block 1345 and at least one transmitting antenna (not shown).

[0094] Referring to Figure 13, the receiver 1360 may include a downconverter block 1365, an A / D block 1370, a CP rejection and offset estimation / compensation block 1375, a channel estimation block 1380, a resource demapping block 1385, a demodulation block 1390, and a decoder 1395.

[0095] The downconverter block 1365 can downconvert a signal received via at least one receiving antenna (not shown) to the baseband frequency to generate a baseband signal.

[0096] The A / D block 1370 can receive an analog baseband signal input from the downconverter block 1365 and convert it into a digital baseband signal.

[0097] The CP rejection and offset estimation / compensation block 1375 receives a digital baseband signal as input, performs CP rejection and offset estimation / compensation, and provides the resulting signal to the channel estimation block 1380 and the resource demapping block 1385. An example of a digital baseband signal input to the CP rejection and frequency offset estimation / compensation block 1375 is a signal that can be approximated by Equation 3.

[0098] The channel estimation block 1380 performs channel estimation based on the output of the CP rejection and frequency offset estimation / compensation block 1375 (e.g., sample values ​​corresponding to pilot symbols for channel estimation), and the resource demapping block 1385 can extract demodulation symbols contained in the resource (e.g., the subcarrier position of the subchannel) based on the channel estimation result and the offset-compensated signal and provide them to the demodulation block 1390.

[0099] The demodulation block 1390 can detect (i.e., demaplate) the data corresponding to each input demodulation symbol and provide it to the decoder 1395.

[0100] The decoder 1395 can decode the input data stream (for example, channel decoding) to recover the data transmitted by the transmitter 1310.

[0101] Figure 14 is a flowchart illustrating several embodiments of received signal processing.

[0102] Some embodiments of the received signal processing illustrated in Figure 14 can be performed by a receiver receiving the CP-OFDM signal (e.g., a UE, a base station, or the receiver in Figure 13) or by a detailed block of said receiver (e.g., a baseband processing module, or the CP rejection and offset estimation / compensation block in Figure 13).

[0103] In the following, we assume that the CP removal and offset estimation / compensation block 1375 in Figure 13 performs several embodiments of the received signal processing illustrated in Figure 14, but we will describe several embodiments by representing the CP removal and offset estimation / compensation block 1375 as a received signal processing module.

[0104] In some embodiments, as shown in Figure 14, the received signal processing module may include an FFT block (S1410), a timing offset estimation block (S1420), a frequency offset estimation block (S1430), a frequency offset compensation block (S1440), and a timing offset compensation block (S1450). In other embodiments, the received signal processing module may include only a portion of the FFT block (S1410), the timing offset estimation block (S1420), the frequency offset estimation block (S1430), the frequency offset compensation block (S1440), and the timing offset compensation block (S1450).

[0105] Figure 15 shows pseudocode to illustrate several embodiments of the received signal processing algorithm.

[0106] The pseudocode in Figure 15 is such that the received signal is at least N sym The number of OFDM symbols (OFDM symbol indices 0, 1, ..., N) sym -l) is a pseudocode consisting of a subframe, which is expressed assuming that the subframe may contain subchannel i in the frequency domain. For example, a received signal processing module can estimate and / or compensate for the offset (timing offset and / or frequency offset) of the signal associated with subchannel i to be received by the receiver, according to the pseudocode illustrated in Figure 15.

[0107] Steps 1, 2, 3, 4, 5, 6, and 7 in Figure 15 can correspond to S1410, S1420, S1432, S1435, S1436, S1440, and S1450 described later in several embodiments.

[0108] Figure 16 is a block diagram illustrating several embodiments of the received signal processing module.

[0109] Referring to Figure 16, the received signal processing module 1600 may include first to third FFT target sample extraction blocks 1610_1, 1610_2, 1610_3, first to third FFT blocks 1620_1, 1620_2, 1620_3, and offset estimation / compensation block 1630.

[0110] In some embodiments, the first to third FFT target sample extraction blocks 1610_1, 1610_2, 1610_3 and the first to third FFT blocks 1620_1, 1620_2, 1620_3 in Figure 16 can correspond to the FFT block (S1410) in Figure 14. In some embodiments, the offset estimation / compensation block 1630 in Figure 16 can correspond to at least some of the timing offset estimation block (S1420), frequency offset estimation block (S1430), frequency offset compensation block (S1440), and timing offset compensation block (S1450) in Figure 14.

[0111] In some embodiments, the FFT block (S1410) can generate a first FFT signal, a second FFT signal, and a third FFT signal for a specific OFDM symbol by performing an FFT on the intervals from the first, second, and third start positions included in the received signal to the length of the symbol body.

[0112] In some embodiments, the FFT block (S1410) may include first to third FFT target sample extraction blocks 1610_1, 1610_2, 1610_3 and first to third FFT blocks 1620_1, 1620_2, 1620_3.

[0113] In some embodiments, the first start position may include an estimated start position where the particular OFDM symbol is located in the received signal, the second start position may include a position that precedes the estimated start position by a predetermined time length, and the third start position may include a position that follows the estimated start position by a predetermined time length.

[0114] In some embodiments, the preset time length may include the length of the cyclic prefix.

[0115] In typical OFDM receivers, only the FFT is performed on the symbol body with the CP removed. However, in sidelinks, the timing offset between vehicles is up to ±CP / 2-12T. S Because only certain actions are permissible, corresponding measures may be necessary.

[0116] Figure 17 illustrates the FFT window when the OFDM symbol has a timing offset.

[0117] Figure 17 shows the timing offset τ in OFDM symbol l. l When is 0, timing offset τ l is N g When it is / 2, the timing offset τ l is N g When this is the case, coincidence FFT window FFT 0 , preceding (leading) FFT window FFT - and subsequent (lagging) FFT window FFT + This is shown.

[0118] Timing offset is up to ±CP / 2-12T S Because this can occur up to a certain point, matching FFT window FFT 0 The system is operated so that it is positioned in the middle of the CP, so that even if a timing offset occurs, it does not deviate from the CP. Furthermore, in the proposed technique, the FET 0 Based on N g Just pull and take the FFT window FFT - And, N g Press only this button to take the FFT window. +An additional FFT is performed using this method, in order to include the cyclic prefix interval and the cyclic prefix corresponding interval used to estimate the frequency offset, even if a timing offset occurs.

[0119] The three FFT results thus obtained can be used in the offset estimation / compensation block 1630 to estimate and compensate for frequency offsets, including timing offsets and Doppler spread. For convenience, in this specification, we will describe some embodiments assuming that timing offsets do not change within a subframe and that frequency offsets change per symbol. As an example, under such assumptions, in some embodiments, frequency offsets can be performed per OFDM symbol.

[0120] Referring again to Figure 14, in some embodiments, as shown in Figure 14, the timing offset estimation block (S1420) can estimate the timing offset relative to the received signal.

[0121] In some embodiments, the timing offset estimation block (S1420) may be included in the offset estimation / compensation block 1630 in Figure 16.

[0122] In some embodiments, the timing offset estimation block (S1420) can estimate the timing offset based on at least a portion of the first to third FFT signals.

[0123] In some embodiments, the timing offset estimation block (S1420) can estimate the timing offset based on the demodulated reference signal included in the received signal. For example, the timing offset estimation block (S1420) can estimate the timing offset using the PSCCH DMRS belonging to subchannel i in the sidelink system.

[0124] Figure 18 is a diagram illustrating the DMRS RE included in the LTE SL PSCCH.

[0125] Figure 19 is a diagram illustrating the DMRS RE included in the PSCCH of NR SL.

[0126] As mentioned earlier, when taking the FFT window, if a timing offset of τ occurs, in the frequency domain, for RE with an RE index of k,

number

[0127] In the case of LTE SL, as shown in Figure 18, it consists of 24 DMRS REs within 4 DMRS symbols, and in the case of NR SL, within 2 or 3 PSCCH symbols (as shown in Figure 19).

number

[0128] In some embodiments, the received signal processing module can perform the smallest possible IFFT for each subchannel. This can lead to the effect of reducing implementation complexity. For example, the number of REs belonging to subchannel i

number

number

number

[0129] In other words, the smallest of the two exponents greater than the number of REs in the subchannel is the IFFT size.

number

[0130] As shown in Figure 17, when an FFT window is taken for the received signal, τ i Assuming that only a timing offset occurs, the timing offset of the resulting signal after performing an IFFT on the FFT result signal.

number

number

[0131] In other words,

number

number

[0132] Referring again to Figure 14, in some embodiments, as shown in Figure 14, the frequency offset estimation block (S1430) can estimate the frequency offset for a particular OFDM symbol based on the first to third FFT signals.

[0133] In some embodiments, as shown in Figure 14, the frequency offset estimation block (S1430) may include an IFFT block (S1432) and a frequency offset calculation block (S1434).

[0134] In some embodiments, the IFFT block (S1432) can generate the first to third IFFT signals by performing an IFFT on each of the first to third FFT signals only on resource blocks belonging to a specific subchannel of the FFT signal. As an example, a time-domain signal for a specific subchannel (e.g., subchannel i) of a specific OFDM symbol (e.g., OFDM symbol l) can be regenerated via the IFFT block (S1432).

[0135] In some embodiments, the IFFT block (S1432) is obtained in the S1410 block for the OFDM symbol l.

number

number

[0136] In some embodiments, the received signal processing module uses the IFFT size at this time, which is calculated by Equation 8.

number

[0137] Figure 20 illustrates an embodiment for regenerating time-domain signals for symbols and subchannels.

[0138] As shown in Figure 20,

number

number

number

[0139] This is how it was requested.

number

number

number

[0140] Referring again to Figure 14, in some embodiments, as shown in Figure 14, the frequency offset calculation block (S1434) can estimate the frequency offset using the cyclic prefix interval of the specific OFDM symbol and the cyclic prefix corresponding interval of the specific OFDM symbol in at least a portion of the first to third IFFT signals.

[0141] In some embodiments, as shown in Figure 14, the frequency offset calculation block (S1434) may include an interval extraction block (S1435) and a frequency offset determination block (S1436).

[0142] In some embodiments, the interval extraction block (S1435) can take samples belonging to the cyclic prefix interval and samples belonging to the cyclic prefix corresponding interval from the second IFFT signal and the third IFFT signal, respectively, based on the estimated timing offset.

[0143] Figure 21 is a diagram illustrating the cyclic prefix interval and the cyclic prefix corresponding interval of the regenerated time-domain signal.

[0144] Figure 21 shows the timing offset obtained in block S1420.

number

number

[0145] The cyclic prefix interval of the time-domain signal regenerated in Figure 21 is:

number

number

[0146] As mentioned above, time-domain signals

number

number

number

number

number

number

[0147] Circular prefix section

number

number

number

number

[0148] The relevant cyclic prefix section

number

number

number

number

number

[0149] Referring again to Figure 14, in some embodiments, as shown in Figure 14, the frequency offset determination block (S1436) can determine the frequency offset based on the obtained cross-correlation results, by performing cross-correlation between samples belonging to the cyclic prefix interval and samples belonging to the cyclic prefix corresponding interval.

[0150] In some embodiments, the received signal processing module is of the symbol l

number

number

[0151] In some embodiments, the received signal processing module uses Equation 12 to obtain the phase Θ from the cross-correlation value. i,l It is possible to find this.

number

[0152] In equations 11 and 12, re(a) and im(a) represent the real and imaginary parts of a, respectively. * This means a conjugate.

[0153] Phase Θ i,l This is the difference between the DC positions of the FFT and IFFT described in block S1432.

number

number

Number

[0154] ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Referring again to Figure 14, in some embodiments, as shown in Figure 14, the frequency offset compensation block (S1440) can perform frequency offset compensation on the received signal based on the estimated frequency offset.

[0158] In some embodiments, a frequency offset compensation block (S1440) can compensate the estimated frequency offset with respect to the first IFFT signal.

[0159] As mentioned earlier, frequency offset appears as a linear phase rotation in the time domain, and this can be compensated for by rotating the phase in the opposite direction.

[0160] Figure 23 is pseudocode to illustrate several embodiments of frequency offset compensation.

[0161] As an example, the pseudocode in Figure 23 is:

number

number

[0162] As shown above in Figure 21, in the time domain

number

number

[0163] In addition, since the linear phase rotation also occurs in the cyclic prefix section, it must be considered as in line 4 of the pseudo code in FIG. 23.

[0164] FIG. 24 shows an example of θ i,l by θ acc of.

[0165] Referring again to FIG. 14, in some embodiments, as shown in FIG. 14, the timing offset compensation block (S1450) can compensate the timing offset for the received signal. In some embodiments, the timing offset compensation block (S1450) can compensate the estimated timing offset for the first IFFT signal with the frequency offset compensated.

[0166] In some embodiments, the received signal processing module performs a cyclic shift in the opposite direction as in Equation 15 only for the timing offset obtained by the S1410 block for

Number

Number

Number

Number

[0167] FIG. 25 illustrates the cyclic shift for timing offset compensation.

[0168] In some embodiments, for the [number] with the timing offset compensated

Number

number

[0169] In some embodiments, the resulting RB can be used as input to a subsequent signal processing block (e.g., the channel estimation block and / or resource demapping block in Figure 13).

[0170] Figure 26 is a graph illustrating the performance of the frequency offset estimation and compensation techniques of this disclosure.

[0171] More specifically, Figure 26 shows the results of simulating PSSCH BLER (Block Error Rate) performance for six cases, including the technique described herein ("Proposed," "Interpolation," etc.).

[0172] As the simulation environment, we used PSSCH requirement test num.4 as defined in 3GPP standard document TS 38.104 section 14.2. The timing offset and frequency offset were CP / 2-12Ts and 600Hz, respectively, and the channel conditions were EVA2700 with reference channel cd.14.

[0173] In the channel estimation method, a moving average of 12RE was used for the frequency axis, and linear interpolation was used for the time axis.

[0174] In Figure 26, "Ideal" shows the case where the frequency offset, including Doppler spread, is estimated from an ideal channel without added noise, and the frequency offset and timing offset are compensated, as in the S1440 and S1450 blocks.

[0175] Furthermore, in Figure 26, "Proposed" shows the case where the offset estimation and compensation techniques of this disclosure are used, and "CP-FOE" shows the case where the frequency offset is estimated from a time-domain based CP-FOE, but the frequency offset and timing offset are compensated, as in the S1440 and S1450 blocks.

[0176] Furthermore, in Figure 26, "Interpolation" shows the case where frequency offset estimation and compensation are not performed, while "FD-FOE" shows the case where the frequency offset is estimated from four DMRS symbols in the frequency domain and the frequency offset and timing offset are compensated, as in the S1440 and S1450 blocks.

[0177] Furthermore, in Figure 26, "Matlab" shows the result when the LTE SL simulation model included in Mathworks' Matlab™ is changed to test num. 4 and a frequency offset of 600 Hz is added.

[0178] Referring to Figure 26, it can be seen that only "Ideal," "Proposed," and "CP-FOE" satisfy the Target SNR of 2.8dB and the PSSCH BLER of 10% with margins of 5.4dB, 2.5dB, and 0.1dB, respectively.

[0179] Comparing "Proposed" and "CP-FOE," "Proposed" can remove noise belonging to RBs that are not included in the subchannels, while "CP-FOE" estimates the frequency offset by including noise belonging to all RBs, which can lead to such performance differences.

[0180] Comparing "Proposed" and "FD-FOE," "Proposed" estimates the frequency offset for each symbol, while FD-FOE only estimates between {symbol 2, symbol 5}, {symbol 5, symbol 8}, and {symbol 8, symbol 11}, resulting in a larger estimation error. Therefore, compensation using FD-FOE can actually perform worse than "Interpolation."

[0181] Comparing "Proposed," "Interpolation," and "Matlab," when the frequency offset is large, not only is there a channel estimation error due to the frequency offset, but the orthogonality between subcarriers is broken, causing ICI. However, "Interpolation" and "Matlab" cannot compensate for this, so as shown in Figure 26, even if the SNR is high, the BLER does not drop to an appropriate level, and thus the performance requirements are not met.

[0182] The devices described above can be realized by hardware components, software components, and / or combinations of hardware and software components. For example, the devices and components described in the embodiments can be realized using one or more general-purpose or special-purpose computers, such as a processor, controller, ALU (arithmetic logic unit), digital signal processor, microcomputer, FPGA (field programmable gate array), PLU (programmable logic unit), microprocessor, or any other device capable of executing and responding to instructions. The processing device can run an operating system (OS) and one or more software applications run on the OS. The processing device can also access, store, manipulate, process, and generate data in response to software execution. For convenience of understanding, the processing device has sometimes been described as being used by one, but a person with ordinary skill in the art will see that the processing device can include multiple processing elements and / or multiple types of processing elements. For example, the processing device can include multiple processors or one processor and one controller. Furthermore, other processing configurations, such as parallel processors, are also possible.

[0183] Software may include computer programs, code, instructions, or a combination of one or more of these, which can configure a processing unit to operate as desired, or which can independently or collectively instruct a processing unit. Software and / or data can be embodyed in any type of machine, component, physical device, computer storage medium, or device in order to be interpreted by a processing unit or to provide instructions or data to a processing unit. Software can also be distributed on a networked computer system and stored or executed in a distributed manner. Software and data can be stored on one or more computer-readable recording media.

[0184] The methods according to the embodiments can be implemented in the form of program instructions that can be delivered via various computer means and recorded on a computer-readable medium. In this case, the medium can either continuously store programs that can be executed by a computer or temporarily store them for execution or download. The medium can be various recording or storage means in the form of a combination of one or more hardware components, and is not limited to a medium directly connected to a computer system, but may be distributed on a network. Examples of mediums include magnetic media such as hard disks, floppy disks and magnetic tapes, optical recording media such as CD-ROMs and DVDs, magneto-optical mediums such as floptical disks, and ROMs, RAMs, flash memories, etc., that are configured to store program instructions. Other examples of mediums include recording media or storage media managed by app stores that distribute applications and other sites, servers that supply or distribute various software.

[0185] Although embodiments have been described above with reference to limited embodiments and drawings, various modifications and variations can be made from the above description by a person with ordinary skill in the art. For example, the described technique may be performed in a different order than described, and / or the components of the described system, structure, apparatus, circuit, etc. may be combined or assembled in a different manner than described, or replaced or substituted by other components or equivalents, and the appropriate results may still be achieved.

[0186] Therefore, other realizations, other embodiments, and claims equivalent to those described below also fall within the scope of the claims.

Claims

1. A method for operating a receiver in a communication system in which at least one OFDM symbol—each OFDM symbol including a circular prefix and a symbol body—is transmitted, The steps include generating a first FFT signal, a second FFT signal, and a third FFT signal for a specific OFDM symbol by performing an FFT on the interval from each of the first, second, and third start positions included in the received signal to the length of the symbol body, The process includes the step of estimating a frequency offset for a particular OFDM symbol based on the first to third FFT signals, The step of estimating the frequency offset is: The steps include generating the first to third IFFT signals by performing IFFT only on resource blocks belonging to a specific subchannel of each of the first to third FFT signals, The process includes the step of estimating the frequency offset based on the first to third IFFT signals, The step of estimating the frequency offset based on the first to third IFFT signals is as follows: The process includes a step of estimating a frequency offset using a cyclic prefix section of the specific OFDM symbol and a section of the symbol body of the specific OFDM symbol corresponding to the cyclic prefix section (hereinafter referred to as the cyclic prefix corresponding section) in at least a portion of the first to third IFFT signals, The process further includes the step of estimating a timing offset for the received signal, The first starting position includes an estimated starting position where the specific OFDM symbol is located in the received signal. The second starting position includes a position that precedes the estimated starting position by a predetermined time length, The third starting position includes a position that is a predetermined time length behind the estimated starting position, The step of estimating the frequency offset using the cyclic prefix section and the cyclic prefix corresponding section is as follows: A method for operating a receiver, comprising the step of taking samples belonging to the cyclic prefix interval and samples belonging to the cyclic prefix corresponding interval from the second IFFT signal and the third IFFT signal, respectively, based on the estimated timing offset.

2. The method for operating a receiver according to claim 1, wherein the preset time length includes the length of the cyclic prefix.

3. The step of estimating the frequency offset using the cyclic prefix section and the cyclic prefix corresponding section is as follows: The steps include performing a cross-correlation between the cyclic prefix interval and the cyclic prefix corresponding interval, A method for operating a receiver according to claim 1, comprising the step of estimating the frequency offset based on the results of the cross-correlation.

4. The method for operating a receiver according to claim 1, further comprising the step of compensating the estimated frequency offset with respect to the first IFFT signal.

5. The method for operating a receiver according to claim 4, further comprising the step of performing an FFT on a first IFFT signal with the frequency offset compensated to obtain a subchannel resource block.

6. The receiver operation method according to claim 5, wherein the size of the FFT performed on the first IFFT signal is smaller than the size of the FFT used to generate the first FFT signal.

7. The receiver operation method according to claim 5, further comprising the step of performing resource demapping on the acquired resource block.

8. The method of operating a receiver according to claim 4, further comprising the step of compensating for the estimated timing offset with respect to the first IFFT signal whose frequency offset has been compensated.

9. The receiver operation method according to claim 8, further comprising the step of performing an FFT on a first IFFT signal with the timing offset compensated to obtain a subchannel resource block.

10. The step of estimating the timing offset is: A method for operating a receiver according to claim 1, comprising the step of estimating the timing offset based on at least a portion of the first to third FFT signals.

11. The step of estimating the timing offset is: A method for operating a receiver according to claim 1, comprising the step of estimating the timing offset based on a demodulation reference signal included in the received signal.

12. A receiving device in a communication system in which at least one OFDM symbol—each OFDM symbol including a circular prefix and a symbol body—is transmitted, An FFT block that generates a first FFT signal, a second FFT signal, and a third FFT signal for a specific OFDM symbol by performing an FFT on the interval from the first start position, the second start position, and the third start position included in the received signal to the length of the symbol body, The system includes a frequency offset estimation block that estimates the frequency offset for a specific OFDM symbol based on the first to third FFT signals, The frequency offset estimation block is, An IFFT block that generates the first to third IFFT signals by performing IFFT only on resource blocks belonging to a specific subchannel of each of the first to third FFT signals, The system includes a frequency offset calculation block that estimates the frequency offset based on the first to third IFFT signals, The frequency offset calculation block described above is: The frequency offset is estimated using the cyclic prefix section of the specific OFDM symbol and the cyclic prefix corresponding section of the specific OFDM symbol in at least a portion of the first to third IFFT signals. The system further includes a timing offset estimation unit that estimates the timing offset for the received signal, The first starting position includes an estimated starting position where the specific OFDM symbol is located in the received signal. The second starting position includes a position that precedes the estimated starting position by a predetermined time length, The third starting position includes a position that is a predetermined time length behind the estimated starting position, The frequency offset calculation block described above is: A section extraction block that takes samples belonging to the cyclic prefix section and samples belonging to the cyclic prefix corresponding section from the second IFFT signal and the third IFFT signal, respectively, based on the estimated timing offset, A receiving device comprising: a frequency offset determination block that performs cross-correlation between a sample belonging to the cyclic prefix section and a sample belonging to the cyclic prefix corresponding section, and determines the frequency offset based on the obtained cross-correlation result.

13. The receiving device according to claim 12, further comprising a frequency offset compensation block for compensating the estimated frequency offset with respect to the first IFFT signal.

14. The receiving device according to claim 13, further comprising a timing offset compensation block for compensating the estimated timing offset with respect to the first IFFT signal whose frequency offset has been compensated.

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