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] The present disclosure relates to receive signal processing techniques in communication systems, and more particularly, 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 that information. Methods for collecting information include direct sensing of the surroundings using cameras, radar, and lidar, which are part of the Advanced Driver Assistance System (ADAS), as well as vehicle-to-everything communication (V2X), which wirelessly shares collected information with nearby vehicles. To achieve this, international standards such as IEEE 802.11p (also known as dedicated short range communication), 3GPP LTE (Long Term Evolution) sidelink, and NR (New Radio) sidelink have been established, and research and implementation of these standards is actively underway. Communication between vehicles traveling at high speeds presents particular challenges, as communication must be possible under rapidly changing channel conditions due to Doppler spread. Summary of the Invention [Problem to be solved by the invention]

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

[0004] One aspect of the present disclosure provides a method for operating a receiver, which is 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 including: generating a first FFT signal, a second FFT signal, and a third FFT signal for a specific OFDM symbol by performing an FFT on an interval from a first start position, a second start position, and a third start position included in the received signal, respectively, 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.

[0005] In some embodiments, the first starting position may comprise a starting position estimate where the particular OFDM symbol is located in the received signal, the second starting position may comprise a position preceding the starting position estimate by a predetermined amount of time, and the third starting position may comprise a position following the starting position estimate by a predetermined amount of time. In some embodiments, the predetermined amount of time may comprise a 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 IFFT on only resource blocks belonging to specific subchannels of the first to third FFT signals, respectively; 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 a step of estimating the frequency offset in at least a part of the first to third IFFT signals using a cyclic prefix interval of the specific OFDM symbol and an interval in a symbol body of the specific OFDM symbol corresponding to the cyclic prefix interval (hereinafter referred to as a cyclic prefix corresponding interval).

[0008] In some embodiments, the method further includes estimating a timing offset for the received signal, and estimating a frequency offset using the cyclic prefix interval and the cyclic prefix corresponding interval may include 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.

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

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

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

[0013] In some embodiments, the size of the FFT performed on the first FFT 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 estimating a timing offset for the received signal.

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

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

[0017] Another aspect of the present disclosure provides a receiving device that processes a received signal including at least one OFDM symbol, each OFDM symbol including a cyclic prefix and a symbol body, the receiving device including: 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 an interval 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, respectively; and a frequency offset estimation block that estimates a frequency offset for the specific OFDM symbol based on the first to third FFT signals.

[0018] In some embodiments, the first start position may comprise a start position estimate where the particular OFDM symbol is located in the received signal, the second start position may comprise a position preceding the start position estimate by a predetermined amount of time, and the third start position may comprise a position following the start position estimate by a predetermined amount of time.

[0019] In some embodiments, the receiving device may further include a timing offset estimation block that estimates a timing offset for the received signal.

[0020] In some embodiments, the frequency offset estimation block may include an IFFT block that generates first to third FFT signals by performing IFFT on only resource blocks that belong to specific subchannels of the first to third FFT signals, respectively, 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 a frequency offset in at least some of the first to third IFFT signals using a cyclic prefix interval of the specific OFDM symbol and a cyclic prefix corresponding interval of the specific OFDM symbol.

[0022] The frequency offset calculation block may include: a section extraction block that extracts 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 receiver may further include a frequency offset compensation block that compensates the first IFFT signal for the estimated frequency offset.

[0024] In some embodiments, the receiver may further include a timing offset compensation block that compensates the estimated timing offset for the frequency offset-compensated first IFFT signal.

[0025] 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.

[0026] 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]

[0027] Some embodiments of the present disclosure may have the following advantages, including the following: However, this does not mean that all embodiments must include all of these advantages, and the scope of the present invention should not be understood as being limited thereby.

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

[0029] According to some embodiments, estimation and compensation with superior performance can be achieved 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 every symbol, it is possible to measure up to half the subcarrier spacing, allowing for excellent estimation and compensation performance even in large Doppler environments.

[0032] According to some embodiments, receiver complexity can be reduced by generating a decimated time domain signal using FFT and IFFT depending on the size of the sub-channel rather than the full bandwidth. [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 an LTE sidelink (hereinafter referred to as "SL"). [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] 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 9]Table 11.1.2.1.1-1 of the 3GPP standard document (3GPP 38.101) is shown, which specifies the performance requirements related to timing offset and frequency offset in 5G SL. [Figure 10] Table 14.2-2 of the 3GPP standard document (3GPP 36.101) is shown, which specifies the performance requirements related to Doppler spread in LTE SL. [Figure 11] Table 11.1.2.1.1-2 of the 3GPP standard document (3GPP 38.101) is shown, which specifies the performance requirements related to Doppler spread in 5G SL. [Figure 12] 1 illustrates the limitations of various frequency offset estimation and channel estimation techniques. [Figure 13] 1 illustrates a communication system in which some embodiments of the received signal processing method can be used. [Figure 14] 1 is a flowchart illustrating some embodiments for received signal processing. [Figure 15] 1 shows pseudocode to illustrate some embodiments for a receive signal processing algorithm. [Figure 16] 1 is a block diagram illustrating some embodiments of a receive signal processing module. [Figure 17] 1 shows the FFT window when there is a timing offset in the OFDM symbol. [Figure 18] FIG. 10 is a diagram illustrating DMRS RE included in a PSCCH of LTE SL. [Figure 19] FIG. 10 is a diagram illustrating DMRS RE included in a PSCCH of an NR SL. [Figure 20] FIG. 1 illustrates an embodiment for regenerating time domain signals for symbols and subchannels. [Figure 21] 10A and 10B are diagrams illustrating a cyclic prefix section and a cyclic prefix corresponding section of a regenerated time domain signal. [Figure 22]10A and 10B are diagrams illustrating timing sample offsets between a cyclic prefix section and a cyclic prefix corresponding section of a regenerated time domain signal. [Figure 23] 1 is a pseudo code for illustrating some embodiments of frequency offset compensation. [Figure 24] An example of θacc using θi,l is shown below. [Figure 25] 1 illustrates a cyclic shift for timing offset compensation. [Figure 26] 10 is a graph illustrating the performance of the frequency offset estimation and compensation technique of the present disclosure. 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, a 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] The number of subcarriers is N u Then, the CP-OFDM signal s(k) at the transmitting end can be expressed by Equation (1).

[0045]

number

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

[0047] FIG. 3 illustrates a 3GPP LTE frame structure.

[0048] In 3GPP LTE / NR, as shown in FIG. 3, a frame can be configured on the time axis as a time unit (e.g., a subframe or a slot) consisting of multiple OFDM symbols, and on the frequency axis as a resource block (RB) consisting of multiple (e.g., 12) subcarriers.

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

[0050] In LTE SL, as shown in Figure 4, a physical sidelink control channel (PSCCH) containing sidelink control information (SCI) consisting of two RBs is used.

number

[0051] Figure 5 illustrates an example resource grid for NR SL.

[0052] 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.

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

[0054] In LTE SL, one subframe can include four demodulation reference signal (DMRS) symbols and a plurality of data symbols as OFDM 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.

[0055] 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. 19. 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.

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

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

number

number

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

number

number

[0059] In this case, if there is a normalized frequency offset ε between the transmitting end and the receiving end, the received signal x(k) of the cyclic prefix section can be expressed as Equations 1, 3, and 4.

number

[0060] The corresponding cyclic prefix corresponding section can be expressed as in Equation 5.

number

[0061] The amplitude of each tap l due to Doppler β l and the normalized phase difference ε l can be changed independently, and the magnitude of the change within the symbol

number

number

[0062] By applying the result of Equation 6 to Equation 5, the cyclic prefix corresponding section can be expressed as Equation 7.

number

[0063] That is, between the cyclic prefix section and the cyclic prefix corresponding section,

number

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

[0065] Meanwhile, examples of difficulties in V2X systems to which some embodiments of the present disclosure can be applied are as follows.

[0066] First, V2X systems can have the difficulty of large timing and frequency offsets (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, in which each UE simply adjusts its transmission and reception synchronization and frequency to that of 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, N-to-N communication is performed, in which synchronization and frequency errors caused by the imperfect local oscillators of the vehicle's transceiver must be adjusted separately, making it difficult to correct each error. Related 3GPP standard documents (e.g., 3GPP 36.101 and 38.101) specify, as performance requirements, a maximum timing offset between vehicles of T g / 2-12T S The standard specifies that a maximum frequency offset between vehicles can be tolerated up to 600 Hz.

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

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

[0069] 8 and 9, the timing offset (ie, synchronization error) requirements and frequency offset (ie, frequency error) requirements in each system can be seen.

[0070] Second, a V2X system may have a difficulty in that each subchannel may have a different frequency offset and timing offset (hereinafter referred to as the "P2 problem"), because each subchannel may have different inter-vehicle communications. Therefore, to estimate and / or compensate for offsets (frequency offset and / or timing offset) in a V2X system, each subchannel must be processed independently.

[0071] Third, V2X systems can face the challenge of large Doppler spread (hereinafter referred to as the "P3 problem"). In vehicle-to-vehicle communications at high speeds, the channel response changes rapidly over time due to large Doppler spread, but transmission and reception must be smooth even in such a channel. In addition, V2X systems can experience inter-carrier interference (hereinafter referred to as "ICI") due to the breakdown of orthogonality between OFDM subcarriers depending on Doppler spread and frequency offset. This ICI problem must also be effectively addressed. Related 3GPP standard documents (e.g., 3GPP 36.101 and 38.101) specify performance requirements requiring support for a maximum Doppler frequency of 2700 Hz.

[0072] FIG. 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] As an example, the propagation condition EVA2700 specified in Test number 4 in FIG. 10 means the multi-path condition EVA (extended vehicular A model) and a maximum Doppler spread of 2700 Hz.

[0074] FIG. 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 spread in 5G SL.

[0075] As an example, the propagation condition TDLA30-2700 specified in Test number 1 in FIG. 11 means a multipath condition TDLA30 (Tapped delay line A) and a maximum Doppler spread of 2700 Hz.

[0076] Fourth, 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 is required for urgent data transmission, such as collision prevention between vehicles. Furthermore, low-complexity algorithms may be required to achieve the proposed chip's heat dissipation and size.

[0077] To deal with the time-varying channel due to Doppler spread, various studies have been carried out on frequency offset and channel estimation.

[0078] First, there is a technique for measuring frequency offset using CP in the time domain (hereinafter referred to as time-domain CP-FOE (Frequency Offset Estimation) technique). As mentioned above, a linear phase proportional to the frequency offset occurs in a time-domain signal. This technique can measure the phase difference and the resulting frequency offset by calculating the cross-correlation between the CP signal and the corresponding symbol body signal. However, as described in Problem P2, each received signal in the sidelink is composed 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] A second technique (hereinafter referred to as the "frequency-domain FOE technique") involves calculating the cross-correlation between symbols with reference signals to measure the phase difference and the resulting frequency offset. The frequency offset measured in this way can be used to estimate the frequency offset in data symbols through interpolation. This technique can solve the P2 problem because it can measure the frequency offset in its assigned frequency domain. However, as mentioned in the P3 problem, when the frequency offset is large in addition to the Doppler spread, performance degradation is unavoidable due to errors caused by extrapolation in the case of data symbols outside the subframe where interpolation is not possible. Adding a 600 Hz frequency offset to the aforementioned 2700 Hz Doppler spread can produce a maximum of 3300 Hz. However, in LTE SL, when the distance between DMRS symbols is three symbols and the subcarrier spacing (hereinafter referred to as "SCS") is 15 kHz, the measurable frequency offset is

number

[0080] Third, 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 a Kalman filter, focusing on the fact that the channel can be modeled with even smaller parameters in the transform domain. However, this technique has a complexity of O((N u *N sym ) 3 ), it is necessary to perform large-size matrix operations, which means that it cannot meet the low complexity requirement (i.e., the P4 problem), and there is a drawback in that the performance deteriorates under the large Doppler spread described in the P3 problem due to errors caused by interpolation.

[0081] Fourth, there is a technique (hereinafter referred to as "deep learning-based channel estimation technique") that applies deep learning-based channel estimation to a channel that varies on the time and frequency axes, such as a sidelink. However, this technique has an implementation complexity of O(h*w*l*N) when the height of the convolution filter is h, the width is w, and the number of layers is l. u *N sym ), it has the disadvantages of being highly complex to implement and using only reference symbols as input. In addition, techniques such as the long short-term memory model (LSTM), which have relatively low implementation complexity, require that a reference symbol be added after the symbol to be estimated. However, unlike LTE, which uses a continuous reference signal, LTR / NR SL has the disadvantages of being unable to apply data transmission in subframe units and generating processing delays, making it impossible to solve the P4 problem.

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

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

[0084] FIG. 13 illustrates a typical configuration of a CP-OFDM communication system, but some embodiments of the present disclosure may also be applied to a CP-OFDM communication system with a configuration different from that of FIG.

[0085] Referring to FIG. 13, a 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), while in 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 FIG. 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 may encode (eg, channel code) the input data and output the encoded data.

[0089] The modulation block 1320 can map each coded data (eg, binary bits) or bundles of coded data to modulation symbols (eg, QPSK symbols).

[0090] The resource mapping block 1325 can provide the modulation symbols to the IFFT block 1330 so that each modulation symbol can be located on a corresponding resource (eg, subcarrier).

[0091] The IFFT block 1330 can generate a symbol body for each OFDM symbol by performing 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] The OFDM symbol with a CP inserted (i.e., a CP-OFDM symbol) can be converted to an analog signal via a D / A block 1340 and transmitted to the wireless communication channel 1350 via an upconverter block 1345 and at least one transmit antenna (not shown).

[0094] Referring to FIG. 13, the receiver 1360 may comprise a downconverter block 1365, an A / D block 1370, a CP removal 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 frequency downconvert a signal received via at least one receiving antenna (not shown) to a baseband to generate a baseband signal.

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

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

[0098] The channel estimation block 1380 performs channel estimation based on the output of the CP removal 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 included 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 (ie, demap) data corresponding to each input demodulation symbol and provide the data to a decoder 1395 .

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

[0101] FIG. 14 is a flow chart illustrating some embodiments for receiving signal processing.

[0102] Some embodiments for the received signal processing illustrated in FIG. 14 may be performed by a receiver (e.g., a UE, a base station, or the receiver of FIG. 13) that receives the CP-OFDM signal or by a detailed block of the receiver (e.g., a baseband processing module, or the CP removal and offset estimation / compensation block of FIG. 13).

[0103] In the following, it is assumed that the CP removal and offset estimation / compensation block 1375 in FIG. 13 performs some embodiments of the received signal processing illustrated in FIG. 14, but some embodiments will be described by representing the CP removal and offset estimation / compensation block 1375 as a received signal processing module.

[0104] In some embodiments, the receive 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), as shown in Figure 14. In other embodiments, the receive signal processing module may include only some 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] FIG. 15 shows pseudocode to illustrate some embodiments for the receive signal processing algorithm.

[0106] The pseudocode in Figure 15 is used to verify that the received signal is at least N sym OFDM symbols (OFDM symbol index 0, 1, ..., N sym 15 is pseudocode expressed on the assumption that the subframe is composed of subframes including subchannel i (i-l), and the subframes can include subchannel i in the frequency domain. As an example, the receiving signal processing module can estimate and / or compensate for offsets (timing offsets and / or frequency offsets) for signals associated with subchannel i to be received by the receiver, according to the pseudocode illustrated in FIG.

[0107] Steps 1, 2, 3, 4, 5, 6, and 7 in FIG. 15 may correspond to steps S1410, S1420, S1432, S1435, S1436, S1440, and S1450 described below in accordance with some embodiments.

[0108] FIG. 16 is a block diagram illustrating some embodiments of the receive signal processing module.

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

[0110] In some embodiments, first to third FFT target sample extraction blocks 1610_1, 1610_2, and 1610_3 and first to third FFT blocks 1620_1, 1620_2, and 1620_3 in Figure 16 may correspond to the FFT block (S1410) in Figure 14. In some embodiments, offset estimation / compensation block 1630 in Figure 16 may correspond to at least a portion of 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) 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 interval from each of 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.

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

[0113] In some embodiments, the first start position may comprise a start position estimate where the particular OFDM symbol is located in the received signal, the second start position may comprise a position preceding the start position estimate by a predetermined amount of time, and the third start position may comprise a position following the start position estimate by a predetermined amount of time.

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

[0115] In a typical OFDM receiver, only the FFT is performed on the symbol body from which the CP has been removed. However, in the sidelink, the timing offset between vehicles can be reduced to a maximum of ±CP / 2-12T. S Only a limited number of cases can be tolerated and appropriate measures may be required.

[0116] FIG. 17 illustrates an FFT window when there is a timing offset in the OFDM symbols.

[0117] FIG. 17 shows the timing offset τ l When is 0, the timing offset τ l N g / 2, the timing offset τ l N g When , the coincident FFT window FFT 0 , leading FFT window FFT - and lagging FFT window FFT + is shown.

[0118] Timing offset up to ±CP / 2-12T S Since up to 0 The proposed technique is to operate the FET so that it is located in the middle of the CP, so that it does not deviate from the CP even if a timing offset occurs. 0 Based on N g Just pull the FFT window and take the FFT - And, N g Just press FFT to take the FFT window +This is to enable the inclusion of a cyclic prefix section and a cyclic prefix corresponding section used for estimating a frequency offset even when a timing offset occurs.

[0119] The three FFT results thus obtained can be used in offset estimation / compensation block 1630 to estimate and compensate for the timing offset and frequency offset, including Doppler spread. For convenience, some embodiments will be described herein assuming that the timing offset does not change within a subframe and that the frequency offset changes for each symbol. As an example, under this assumption, in some embodiments, the frequency offset can be performed for each OFDM symbol.

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

[0121] In some embodiments, the timing offset estimation block (S1420) can be included in the offset estimation / compensation block 1630 of FIG.

[0122] In some embodiments, the timing offset estimation block (S1420) can estimate a 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 a demodulation reference signal included in the received signal. For example, the timing offset estimation block (S1420) can estimate the timing offset using a PSCCH DMRS belonging to subchannel i in a sidelink system.

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

[0125] FIG. 19 is a diagram illustrating DMRS REs included in the PSCCH of an NR SL.

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

number

[0127] For LTE SL, 24 DMRS REs are arranged in four DMRS symbols as shown in Figure 18, and for NR SL, 24 DMRS REs are arranged in two or three PSCCH symbols (as shown in Figure 19).

number

[0128] In some embodiments, the receiving signal processing module can perform an IFFT of as small a size as possible for each subchannel, which can lead to an effect of reducing the implementation complexity. For example, the number of REs belonging to subchannel i can be set as

number

number

number

[0129] That is, the smallest exponent of 2 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 applied to the received signal, τ i When a timing offset occurs, the timing offset of the result signal obtained by performing IFFT on the FFT result signal is

number

number

[0131] That is,

number

number

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

[0133] In some embodiments, as shown in FIG. 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 IFFT only on resource blocks belonging to a specific subchannel of each of the first to third FFT signals. As an example, the IFFT block (S1432) can regenerate a time domain signal for a specific subchannel (e.g., subchannel i) of a specific OFDM symbol (e.g., OFDM symbol l).

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

number

number

[0136] In some embodiments, the receiving signal processing module uses the IFFT size calculated by Equation 8.

number

[0137] FIG. 20 is a diagram illustrating an embodiment of regenerating time domain signals for symbols and subchannels.

[0138] As shown in Figure 20,

number

number

number

[0139] This is how I asked for it.

number

number

number

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

[0141] In some embodiments, as shown in FIG. 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 extract 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] FIG. 21 is a diagram illustrating a cyclic prefix section and a cyclic prefix corresponding section of a regenerated time domain signal.

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

number

number

[0145] The cyclic prefix section of the time domain signal reproduced in Figure 21 is

number

number

[0146] As mentioned above, the time domain signal

number

number

number

number

number

number

[0147] Circular prefix section

number

number

number

number

[0148] The cyclic prefix section

number

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number

number

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[0149] Referring again to FIG. 14, in some embodiments, as shown in FIG. 14, the frequency offset determination block (S1436) may determine the frequency offset based on the cross-correlation result obtained 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 receive signal processing module

number

number

[0151] In some embodiments, the receive signal processing module calculates the phase Θ from the cross-correlation value using Equation 12. i,l can be obtained.

number

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

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

number

number

number

[0154] FIG. 22 is a diagram illustrating a time sample offset between a cyclic prefix section and a cyclic prefix corresponding section of a regenerated time domain signal.

[0155] As mentioned above,

number

number

number

number

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[0156] θ i,l can be obtained from the result of Equation 13 and Equation 14.

number

[0157] Referring again to FIG. 14, in some embodiments, as shown in FIG. 14, a 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 first IFFT signal for the estimated frequency offset.

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

[0160] FIG. 23 is pseudo code for explaining some embodiments of frequency offset compensation.

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

number

number

[0162] As mentioned above in Figure 21,

number

number

[0163] Furthermore, since linear phase rotation also occurs in the cyclic prefix section, it must be taken into account as shown in line 4 of the pseudocode in FIG.

[0164] Figure 24 shows θ i,l θ by acc Here is an example:

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

[0166] In some embodiments, the receive signal processing module compensates for frequency offset.

number

number

number

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

[0168] In some embodiments, the timing offset is compensated for.

number

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[0169] In some embodiments, the resulting RBs can be used as input to subsequent signal processing blocks (eg, the channel estimation block and / or the resource demapping block in FIG. 13).

[0170] FIG. 26 is a graph illustrating the performance of the frequency offset estimation and compensation technique of the present disclosure.

[0171] More specifically, FIG. 26 shows simulated results of PSSCH Block Error Rate (BLER) performance for six cases (eg, "Proposed," "Interpolation") that include the techniques of this disclosure.

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

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

[0174] In FIG. 26, "Ideal" indicates the case where the frequency offset including Doppler spread is estimated from an ideal channel with no added noise, and the frequency offset and timing offset are compensated for as in blocks S1440 and S1450.

[0175] Also, in Figure 26, "Proposed" indicates the case where the offset estimation and compensation technique of the present disclosure is used, and "CP-FOE" indicates the case where the frequency offset is estimated from the time-domain based CP-FOE, but the frequency offset and timing offset are compensated as in the S1440 block and the S1450 block.

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

[0177] In addition, in FIG. 26, "Matlab" indicates a case where the LTE SL simulation model included in Matlab™ by Mathworks Inc. is changed to test num. 4 and a frequency offset of 600 Hz is added.

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

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

[0180] Comparing "Proposed" and "FD-FOE," "Proposed" estimates the frequency offset for each symbol, while FD-FOE estimates only between {symbol 2, symbol 5}, {symbol 5, symbol 8}, and {symbol 8, symbol 11}, resulting in a large estimation error. Therefore, compensation using this may actually show inferior performance to "Interpolation."

[0181] Comparing "Proposed", "Interpolation" and "Matlab", when the frequency offset is large, not only does it cause channel estimation errors due to the frequency offset, but it also causes ICI due to the loss of orthogonality between subcarriers. However, "Interpolation" and "Matlab" cannot compensate for this, and as shown in Figure 26, even if the SNR increases, the BLER does not decrease to an appropriate level, and therefore the performance requirements are not met.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] Accordingly, other implementations, embodiments, and equivalents of the claims are within the scope of the following claims.

Claims

1. 1. A method of operating a receiver in a communication system in which at least one OFDM symbol is transmitted, each OFDM symbol including a cyclic prefix and a symbol body, comprising: generating a first FFT signal, a second FFT signal, and a third FFT signal for a specific OFDM symbol by performing an FFT on an interval from a first start position, a second start position, and a third start position included in the received signal to a length of the symbol body; and estimating a frequency offset for the particular OFDM symbol based on the first to third FFT signals.

2. the first starting position comprises a starting position estimate where the particular OFDM symbol is located in the received signal; the second starting position includes a position preceding the starting position estimate by a predetermined length of time; 2. The method of claim 1, wherein the third starting position comprises a position that is a predetermined amount of time later than the starting position estimate.

3. The method of claim 2 , wherein the predetermined length of time comprises the length of the cyclic prefix.

4. The step of estimating a frequency offset comprises: generating first to third IFFT signals by performing IFFT on only resource blocks belonging to specific subchannels of the first to third FFT signals, respectively; and estimating the frequency offset based on the first to third IFFT signals.

5. The step of estimating the frequency offset based on the first to third IFFT signals includes:

5. The method of claim 4, further comprising: estimating a frequency offset in at least a portion of the first, second, third IFFT signals using a cyclic prefix interval of the specific OFDM symbol and an interval of a symbol body of the specific OFDM symbol corresponding to the cyclic prefix interval (hereinafter referred to as a cyclic prefix-corresponding interval).

6. estimating a timing offset for the received signal; the first starting position comprises a starting position estimate where the particular OFDM symbol is located in the received signal; the second starting position includes a position preceding the starting position estimate by a predetermined length of time; the third start position includes a position that is later than the start position estimate by a predetermined time length, estimating a frequency offset using the cyclic prefix section and the cyclic prefix corresponding section, 6. The method of claim 5, further comprising: obtaining 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.

7. estimating a frequency offset using the cyclic prefix section and the cyclic prefix corresponding section, performing a cross-correlation between the cyclic prefix section and the cyclic prefix corresponding section; and estimating the frequency offset based on the cross-correlation results.

8. 5. The method of claim 4, further comprising the step of compensating the first IFFT signal for the estimated frequency offset.

9. 9. The method of claim 8, further comprising performing an FFT on the frequency offset compensated first IFFT signal to obtain resource blocks of subchannels.

10. 10. The method of claim 9, 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.

11. The method of claim 9, further comprising the step of performing resource demapping on the obtained resource blocks.

12. estimating a timing offset for the received signal; 9. The method of claim 8, further comprising the step of: compensating the estimated timing offset for the frequency offset-compensated first IFFT signal.

13. The method of claim 12, further comprising performing an FFT on the timing offset compensated first IFFT signal to obtain resource blocks of subchannels.

14. 2. The method of claim 1 further comprising the step of estimating a timing offset for the received signal.

15. The step of estimating a timing offset comprises:

15. The method of claim 14, further comprising estimating the timing offset based at least in part on the first through third FFT signals.

16. The step of estimating a timing offset comprises:

15. A method of operating a receiver as claimed in claim 14, comprising estimating the timing offset based on a demodulation reference signal included in the received signal.

17. 1. A receiver in a communication system in which at least one OFDM symbol is transmitted, each OFDM symbol including a cyclic prefix and a symbol body, comprising: 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 an interval from a first start position, a second start position, and a third start position included in the received signal to a length of the symbol body; a frequency offset estimation block that estimates a frequency offset for the specific OFDM symbol based on the first to third FFT signals.

18. the first starting position comprises a starting position estimate where the particular OFDM symbol is located in the received signal; the second starting position includes a position preceding the starting position estimate by a predetermined length of time; The receiving device of claim 17 , wherein the third start position comprises a position that is a predetermined length of time behind the start position estimate.

19. The frequency offset estimation block an IFFT block that generates first to third FFT signals by performing IFFT on only resource blocks that belong to specific subchannels of the first to third FFT signals, respectively; a frequency offset calculation block that estimates the frequency offset based on the first to third IFFT signals.

20. The frequency offset calculation block The receiving device according to claim 19, wherein a frequency offset is estimated using a cyclic prefix section of the specific OFDM symbol and a cyclic prefix corresponding section of the specific OFDM symbol in at least a portion of the first to third IFFT signals.

21. a timing offset estimator configured to estimate a timing offset for the received signal; the first starting position comprises a starting position estimate where the particular OFDM symbol is located in the received signal; the second starting position includes a position preceding the starting position estimate by a predetermined length of time; the third start position includes a position that is later than the start position estimate by a predetermined time length, The frequency offset calculation block a section extraction block that extracts 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 frequency offset determination block that performs cross-correlation between samples belonging to the cyclic prefix interval and samples belonging to the cyclic prefix corresponding interval and determines the frequency offset based on the obtained cross-correlation result.

22. 20. The receiving apparatus of claim 19, further comprising a frequency offset compensation block that compensates the first IFFT signal for the estimated frequency offset.

23. 23. The receiving apparatus of claim 22, further comprising: a timing offset estimation block that estimates a timing offset for the received signal; and a timing offset compensation block that compensates for the estimated timing offset for the first IFFT signal that has been compensated for the frequency offset.

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