Receiver and operation method of receiver

Abstract

A receiver and an operation method of the receiver are provided. The operation method of the receiver includes: detecting a signal received from a transmitter at a plurality of sub-bands constituting a frequency band; determining a first frequency offset of the signal at a receiving sub-band of the plurality of sub-bands from which the signal has been detected; and determining a second frequency offset by calibrating the carrier frequency offset based on a distance of each of the received sub-bands from a center frequency of the frequency band.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on and claims the benefit of priority from Korean Patent Application No. 10-2023-0087400 filed in the Korean Intellectual Property Office on July 5, 2023, and Korean Patent Application No. 10-2023-0133696 filed in the Korean Intellectual Property Office on October 6, 2023, the disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0003] Aspects of the inventive concept relate to methods and apparatuses for determining a frequency offset to improve communication performance. Background Art

[0004] As an example of wireless communication, a wireless local area network (WLAN) is a technology that connects two or more devices by using a wireless signal transmission method. WLAN can be based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. The 802.11 standard has been developed into 802.11b, 802.11a, 802.11g, 802.11n, 802.11ac, 802.11ax, etc., and can support a transmission rate of up to 1 Gbyte / second based on orthogonal frequency division multiplexing (OFDM).

[0005] In 802.11ac, data can be sent to multiple users simultaneously through Multi-User Multiple Input Multiple Output (MU-MIMO). In 802.11ax, also known as High Efficiency (HE), Orthogonal Frequency Division Multiple Access (OFDMA) and MU-MIMO are also applied to achieve multiple access by dividing available subcarriers and providing the divided subcarriers to users. Therefore, a WLAN system applying 802.11ax can effectively support communications in dense areas and outdoors.

[0006] 802.11be, also known as Extremely High Throughput (EHT), seeks to support the 6 GHz unlicensed band, supports various bandwidths per channel, introduces Hybrid Automatic Repeat and Request (HARQ), and supports up to 16×16 MIMO. Therefore, it is expected that the next generation WLAN system effectively supports low latency and high-speed transmission, such as New Radio (NR) as the 5th generation (5G) technology. Recently, new technologies capable of supporting bandwidths of up to 640 MHz per channel in 802.11 have been proposed to improve spectrum efficiency and transmission rate.

[0007] In a wireless communication system, a difference may occur between the carrier frequency of a transmission signal sent by a transmitter and the carrier frequency of a received signal recognized by a receiver. Due to this difference, the receiver can calculate a frequency offset and match the carrier frequency of the transmission signal with the carrier frequency of the received signal.

[0008] In a broadband wireless communication system, a difference may occur between a carrier frequency of a transmission signal transmitted by a transmitter and a carrier frequency of a reception signal recognized by a receiver due to various factors. Therefore, a method of determining a frequency offset by considering various factors is required. Summary of the invention

[0009] Aspects of the present inventive concept provide a method and apparatus for determining a frequency offset to improve communication performance.

[0010] According to one aspect of the inventive concept, there is provided an operating method of a receiver, the operating method comprising: detecting a signal received from a transmitter at a plurality of sub-bands constituting a frequency band; determining a first frequency offset of the signal at a receiving sub-band in which the signal has been detected among the plurality of sub-bands; and determining a second frequency offset by calibrating the carrier frequency offset based on the distance of each of the receiving sub-bands from a center frequency of the frequency band.

[0011] According to another aspect of the present invention, there is provided a receiver for communicating with a transmitter via a frequency band, the receiver comprising: a radio frequency integrated circuit (RFIC); and a processor configured to: detect a signal received from the transmitter via the RFIC at a plurality of sub-bands constituting the frequency band; determine a first frequency offset of the signal at a receiving sub-band in which the signal has been detected among the plurality of sub-bands; determine a second frequency offset by calibrating the carrier frequency offset based on the distance of each of the receiving sub-bands from the center frequency of the frequency band; and determine a third frequency offset of the frequency band based on the second frequency offset.

[0012] According to another aspect of the inventive concept, a method for operating a receiver is provided, the method comprising: dividing a frequency band of a received signal into a first sub-band; detecting the received signal at a second sub-band in the first sub-band; determining a first frequency offset of the received signal at the second sub-band; determining a second frequency offset by calibrating the first frequency offset based on a distance of each of the second sub-bands from a center frequency of the frequency band; and determining a third frequency offset of the frequency band by using the second frequency offset of each of the second sub-bands. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0014] Figure 1 is a diagram showing a wireless communication system according to an embodiment;

[0015] Figure 2 A block diagram of a wireless communication device according to an embodiment is shown;

[0016] Figure 3AA block diagram of a wireless communication device according to an embodiment is shown;

[0017] Figure 3B is a diagram for describing sampling clock offset (SCO);

[0018] Figure 3C The carrier frequency offset (CFO) and SCO in the frequency domain are shown;

[0019] Figure 3D An embodiment of calibrating a deviation due to the SCO effect from a CFO for each of 16 sub-bands with respect to a received signal having a bandwidth of 320 MHz in a wideband channel is shown;

[0020] Figure 4 The operation process of the wireless communication device according to the embodiment is shown;

[0021] Figure 5A The operation process of the wireless communication device according to the embodiment is shown;

[0022] Figure 5B The operation process of the wireless communication device at the mth sub-band according to the embodiment is shown;

[0023] Figure 5C An operation of a wireless communication device at each sub-band and a method of combining a plurality of sub-bands according to an embodiment are shown;

[0024] Figure 6 A method of detecting a received signal at a subband, obtaining a synchronization timing, and determining a frequency offset based on the synchronization timing and the received signal according to an embodiment is shown;

[0025] Figure 7 The operation process of the wireless communication device according to the embodiment is shown;

[0026] Figure 8 shows signals processed by a wireless communication device according to an embodiment;

[0027] Fig.9A and Fig. 9B The frequency offset of the uncalibrated SCO effect in an additive white Gaussian noise (AWGN) channel is shown;

[0028] Fig. 9C and Fig.9D shows the frequency offset in an AWGN channel calibrated for SCO effect according to an embodiment;

[0029] Fig.9E and Fig.9F shows the frequency offset of the uncalibrated SCO effect in a fading channel according to an embodiment;

[0030] Figure 9G and Figure 9H shows a frequency offset in a fading channel calibrated for SCO effect according to an embodiment;

[0031] Fig.10 shows the "frequency offset of the frequency band" without SCO effect correction and the "frequency offset of the frequency band" with SCO effect correction in a fading channel; and

[0032] Fig.11 is a diagram illustrating an example of an apparatus for wireless communication according to an embodiment. DETAILED DESCRIPTION

[0033] Figure 1 is a diagram showing a wireless communication system 10 according to the embodiment.

[0034] Specifically, Figure 1 A wireless local area network (WLAN) system is shown as an example of a wireless communication system 10. The detailed description of the embodiment focuses on a wireless communication system based on orthogonal frequency division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA), especially the IEEE 802.11 standard. However, the various aspects of the inventive concept can also be applied to other communication systems with similar technical backgrounds and channel forms (e.g., cellular communication systems such as long term evolution (LTE), advanced LTE (LTE-A), new radio (NR), wireless broadband (WiBro) and global mobile communication system (GSM), or short-range communication systems such as Bluetooth and near field communication (NFC)) by slight modifications without significantly departing from the scope of the inventive concept. This can be achieved by determination of a person of ordinary skill in the art.

[0035] In addition, the various functions described below can be implemented or supported by artificial intelligence technology or one or more computer programs, each of which can be implemented as a computer-readable program code and can be executed on a computer-readable recording medium. The terms "application" and "program" refer to one or more computer programs, software components, instruction sets, processes, functions, objects, classes, instances, related data or a part thereof suitable for implementing suitable computer-readable program codes. The term "computer-readable program code" includes any type of computer code, including source code, object code and executable code. The term "computer-readable recording medium" includes any type of memory accessible by a computer, such as a read-only memory (ROM), a random access memory (RAM), a hard drive, a compact disc (CD), a digital video disc (DVD) or any other type of memory. "Non-transitory" computer-readable recording media exclude wired, wireless, optical or other communication links that send temporary electrical signals or other signals. Non-transitory computer-readable recording media include media that allow data to be permanently stored and media that allow data to be stored and subsequently rewritten, such as rewritable optical discs or erasable memory devices.

[0036] In various embodiments described below, hardware methods are described as examples. However, since various embodiments include techniques using both hardware and software, various embodiments do not exclude software-based methods.

[0037] In addition, for the convenience of explanation, terms related to control information, terms related to items, terms related to network entities, terms related to messages, terms related to elements of devices, etc. are exemplified. Therefore, the inventive concept is not limited to the terms to be described below, and other terms related to equivalent technical meanings may be used.

[0038] Reference Figure 1, the wireless communication system 10 may include a first access point AP1 and a second access point AP2, a first station STA1, a second station STA2, a third station STA3, and a fourth station STA4. The first access point AP1 and the second access point AP2 may be connected to a network 13 including the Internet, an Internet Protocol (IP) network, or any other network. The first access point AP1 may provide access to the network 13 to the first station STA1, the second station STA2, the third station STA3, and the fourth station STA4 within the first coverage area 11, and the second access point AP2 may provide access to the network 13 to the third station STA3 and the fourth station STA4 within the second coverage area 12. In some embodiments, the first access point AP1 and the second access point AP2 may communicate with at least one of the first station STA1, the second station STA2, the third station STA3, and the fourth station STA4 based on Wireless Fidelity (Wi-Fi) or any other WLAN access technology.

[0039] Access points may be referred to as routers, gateways, etc., and stations may be referred to as mobile stations, user stations, terminals, mobile terminals, wireless terminals, user equipment, users, etc. A station may be a mobile device such as a mobile phone, a laptop computer, a wearable device, etc., or may be a fixed device such as a desktop computer, a smart television (TV), etc.

[0040] The access point may determine the channel bandwidth used to communicate with the station as one of a plurality of channel bandwidths. According to aspects of the inventive concept, the channel bandwidth may be referred to as bandwidth. In an embodiment, the channel bandwidth may include 20 MHz, 40 MHz, 80 MHz, 160 MHz, 320 MHz, and 640 MHz.

[0041] According to an embodiment, the access point and the station may detect a signal received from another device at a plurality of sub-bands constituting a frequency band. The access point and the station may determine a first frequency offset of a signal at a reception sub-band in which the signal has been detected in the sub-band. The access point and the station may determine a second frequency offset by calibrating the first frequency offset based on the distance of each of the reception sub-bands from the center frequency of the frequency band. The access point and the station may determine a third frequency offset of the frequency band based on the second frequency offset.

[0042] According to an embodiment, the access point and the station may determine the frequency offset by considering the difference between the frequency of a sampling clock of an analog-to-digital converter (ADC) and the frequency of a sampling clock of a digital-to-analog converter (DAC) and the difference between the frequency of a clock generated by a local oscillator (LO) of a transmitter and the frequency of a clock generated by a LO of a receiver.

[0043] According to an embodiment, the access point and the station may calibrate the carrier frequency offset deviation of the received signal according to the frequency position within the wideband channel.

[0044] According to an embodiment, the access point and the station may determine a frequency offset that is not affected by a frequency band and a bandwidth of a received signal.

[0045] According to an embodiment, the access point and the station may determine a frequency offset reflecting the channel quality of each subband by combining calibrated carrier frequency offsets of respective subbands in an in-phase and quadrature (I / Q) region.

[0046] According to an embodiment, an access point and a station may have a diversity gain by combining calibrated carrier frequency offsets of respective subbands in an I / Q region.

[0047] For example, according to an embodiment, the access point and the station may consider the sampling clock offset (SCO) and carrier frequency offset (CFO) coupling effects that behave differently at each subband constituting a wideband channel depending on the position away from the center frequency, and may determine an accurate frequency offset value for each subband regardless of the frequency position within the channel. In addition, the access point and the station may perform appropriate coherent combination of the frequency offset values ​​of all subbands in which a received signal in a wideband channel is detected among the frequency offset values ​​determined for each subband by reflecting the SCO and CFO coupling effects, and may determine an accurate frequency offset value regardless of the occupied frequency band and bandwidth of the frame finally transmitted.

[0048] Figure 2 A block diagram of a wireless communication device 100 according to an embodiment is shown.

[0049] In wireless communication systems, the clock frequencies of local oscillators (LOs) driven by transmitters and receivers, respectively, are difficult to accurately match each other. As a result, a difference may occur between the carrier frequency of a transmit signal sent by the transmitter and the carrier frequency of a received signal identified by the receiver. According to various aspects of the inventive concept described herein, the frequency offset that occurs for this reason is referred to as CFO. When CFO exists, the receiver identifies the subcarriers of the transmit signal as offset by a specific frequency interval.

[0050] On the other hand, the difference in the frequency of the sampling clock applied to the analog-to-digital signal conversion may cause a frequency offset. In other words, the difference in the frequency of the sampling clock between the transmitter and the receiver may also cause a frequency offset. Specifically, the difference between the frequency of the sampling clock of the ADC and the frequency of the sampling clock of the DAC may cause a frequency offset between the transmitter and the receiver. According to various aspects of the inventive concept described herein, such a frequency offset is referred to as SCO. SCO can occur in conjunction with CFO. Specifically, the presence of SCO can affect the degree of CFO. For example, the presence of SCO can have different degrees of influence on CFO depending on the frequency band of the signal, and CFO can have different deviations at sub-bands with different frequency positions.

[0051] The wireless communication device 100 according to aspects of the inventive concept may determine a frequency offset by considering both CFO and SCO. That is, the wireless communication device 100 may consider that the CFO of the received signal has different deviations for each subband due to the SCO effect.

[0052] Reference Figure 2 , the wireless communication device 100 may include a processor 110, a radio frequency integrated circuit (RFIC) 120, and an antenna 130. The wireless communication device 100 may also include components for sending and receiving signals and data. For example, the wireless communication device 100 may also include a LO, etc.

[0053] The wireless communication device 100 may transmit or receive signals through the processor 110, the RFIC 120, and the antenna 130. When the wireless communication device 100 transmits a signal, the wireless communication device 100 may operate as a transmitter, and when the wireless communication device 100 receives a signal, the wireless communication device 100 may operate as a receiver.

[0054] The processor 110 according to the embodiment may detect a signal received from a transmitter through the RFIC 120 at a plurality of sub-bands constituting a frequency band. The processor 110 may determine a first frequency offset of a signal at a receiving sub-band in which a signal has been detected in the sub-band. For example, the received signal may include a training sequence that is periodically repeated in the time domain. The processor 110 may determine the first frequency offset based on the training sequence. In addition, the processor 110 may determine the first frequency offset by extracting phase information of each sub-band using an autocorrelation function (ACF).

[0055] The processor 110 can determine the second frequency offset by calibrating the CFO based on the distance of each of the receiving subbands from the center frequency of the frequency band. The presence of SCO can affect the degree of CFO of the frequency components within the channel. Specifically, SCO can make the CFO behave differently depending on how far the subcarrier is from the center frequency of the frequency band. Therefore, the second frequency offset generated by calibrating the first frequency offset based on the distance of each of the subbands from the center frequency of the frequency band can be the CFO from which the SCO effect is removed. On the other hand, the distance of each of the receiving subbands from the center frequency of the frequency band can correspond to the size of the index of each of the receiving subbands.

[0056] The processor 110 may determine a third frequency offset of the frequency band based on the second frequency offset.

[0057] For example, the processor 110 may determine the third frequency offset by performing weighted averaging on the second frequency offset based on a weight corresponding to the amplitude of the signal measured at each of the reception subbands.

[0058] For example, the processor 110 may reconstruct the I / Q vector of each of the reception subbands by using the amplitude of the signal measured at each of the reception subbands and the second frequency offset. The processor 110 may obtain the vector of the frequency band by combining the I / Q vectors. The processor 110 may determine the third frequency offset by calculating the phase of the vector of the frequency band.

[0059] The processor 110 may receive data from the transmitter via the RFIC 120 by using the third frequency offset.

[0060] Figure 3A A block diagram of a wireless communication device 200 according to an embodiment is shown.

[0061] Reference Figure 3A , the wireless communication device 200 may include a band segmentation circuit 210, a CFO estimator 220, a calibration circuit 230, and a sub-band combiner 240. The wireless communication device 200 may also include components for transmitting and receiving signals and data.

[0062] The band splitting circuit 210 may split the channel of the received signal. For example, when the wireless communication device 200 operates at a broadband of 320 MHz or more, the band splitting circuit 210 may split the channel into a plurality of sub-band units having a bandwidth of 20 MHz. For example, the band splitting circuit 210 may split the wideband channel signal into sub-band units based on band splitting filtering.

[0063] Figure 3A The wireless communication device 200 is Figure 2 The processor 110 may include a band segmentation circuit 210, a carrier frequency offset estimator 220, a calibration circuit 230, and a sub-band combiner 240.

[0064] The CFO estimator 220 may determine the CFO for each of the subbands. For example, the CFO estimator 220 may determine the CFO by using the periodicity of the received signal. As a specific example, the CFO estimator 220 may calculate the phase information for each of the subbands by using the ACF.

[0065] When SCO exists, the calibration circuit 230 can calibrate the CFO. The degree to which the CFO is affected by SCO may vary depending on the position of the subband in the frequency domain. The calibration circuit 230 can remove the SCO effect from the CFO.

[0066] The subband combiner 240 may combine the calibrated CFOs corresponding to the respective subbands. The subband combiner 240 may obtain a frequency offset of a frequency band of a received signal by combining the calibrated CFOs corresponding to the respective subbands.

[0067] Figure 3BIt is a diagram used to describe SCO. Figure 3C CFO and SCO in the frequency domain are shown. Figure 3D An embodiment of calibrating a deviation due to the SCO effect from a CFO for each of 16 sub-bands with respect to a received signal having a bandwidth of 320 MHz in a wideband channel is shown.

[0068] Due to LO clock mismatch, there may be a frequency offset between the transmitter and the receiver. This can be expressed in parts per million (ppm). (ppm) The resulting CFO size of the received signal is f CFO can depend on the center frequency f of the wideband channel in which the receiver operates c , and can be expressed in Hz as shown in Equation 1 below.

[0069] [Equation 1]

[0070]

[0071] Frequency Offset FO (ppm) This causes an offset in the sampling rate of the analog-to-digital signal conversion performed between transmit and receive. Figure 3B , the sampling period of the transmitter (Tx sampling) is T s , and the sampling period of the receiver (Rx sampling) is T s '. T s With T s The difference between ' is ε.

[0072] This is called SCO or sampling frequency offset (SFO). The size of the SCO may depend on the bandwidth of the channel in which the receiver operates and may be expressed in Hz as follows.

[0073] [Equation 2]

[0074]

[0075] T s and T s 'represent the sampling period of the transmitter and the sampling period of the receiver respectively, and f BW and f′ BW is the reciprocal of Ts and Ts', and represents the sampling frequency and bandwidth of the transmitting end and the receiving end, respectively. As such, when SCO exists, the bandwidths recognized between the transmitter and the receiver in the frequency domain are different from each other, and therefore, a difference may also occur in the subcarrier spacing. When the wideband channel in which the receiver operates includes a total of N subcarriers, the deviation Δf of the subcarrier spacing due to SCO is subcarrier as follows.

[0076] [Equation 3]

[0077]

[0078] By wireless communication device (see Figure 2 100) deviates from the actual degree of CFO experienced by the received signal f CFO , because Δf subcarrier Each subcarrier is accumulated according to its distance from the center frequency in the frequency domain.

[0079] Reference Figure 3C , when there is no SCO effect, the difference between the first subcarrier TSC_1 of the transmitted signal and the first subcarrier RSC_1 identified by the receiver is CFO. Similarly, when there is no SCO effect, the difference between the second subcarrier TSC_2 of the transmitted signal and the second subcarrier RSC_2 identified by the receiver is CFO. In this way, when there is no SCO effect, the difference between the third subcarrier TSC_3 to the sixth subcarrier TSC_6 of the transmitted signal and the third subcarrier RSC_3 to the sixth subcarrier RSC_6 identified by the receiver is CFO.

[0080] A difference occurs between the frequency position of the first subcarrier RSC_1' identified by the receiver when the SCO effect is present and the frequency position of the first subcarrier RSC_1 identified by the receiver when the SCO effect is not present. The difference is based on the distance from the center frequency SCO_1. That is, the difference between the frequency positions of the second subcarrier RSC_2' to the sixth subcarrier RSC_6' identified by the receiver when the SCO effect is present and the frequency positions of the second subcarrier RSC_2 to the sixth subcarrier RSC_6 identified by the receiver when the SCO effect is not present can be changed according to the distance from their center frequencies SCO_2 to SCO_6, respectively. For example, as the distance from the center frequency increases, the difference between the position of the subcarrier identified by the receiver when the SCO effect is present and the position of the subcarrier identified by the receiver when the SCO effect is not present may increase.

[0081] On the other hand, when the frequency index of each subcarrier is k, the subcarrier exists within the range of -N / 2≤k<N / 2 within the channel, and the center frequency corresponds to k=0. The CFO deviation due to SCO behaves differently for each subcarrier depending on the position away from the center frequency of the entire channel according to a specific rule. The mathematical relationship is derived as follows.

[0082] [Equation 4]

[0083]

[0084] In equation 4, f CFO，krepresents the size of the CFO of the subcarrier at index k.

[0085] This is expressed in ppm as follows.

[0086] [Equation 5]

[0087]

[0088] This can also be expressed as follows.

[0089] [Equation 6]

[0090]

[0091] In Equation 6, α and δ are constants that depend on the system environment. CF and SCOf SCO Both are related to the frequency offset FO caused by LO mismatch between transmitter and receiver. (ppm) So the degree of CFO experienced at any subcarrier position k is CFO，k with FO (ppm) is proportional to, and increases or decreases linearly as a linear function of the frequency index k. When the determined CFO value for each subband and the frequency index according to the subband position are substituted into Equation 6, the SCO effect can be inverted and calibrated, and the basic frequency offset FO can be obtained (ppm) .

[0092] Reference Figure 3D , assuming there is a frequency offset FO between the transmit and receive (ppm) 20ppm and BW=320MHz&N=1024&f c =6GHz wideband channel operation. The CFO value experienced by each 20MHz subband within the 320MHz channel (CFO per subcarrier) exhibits a linear deviation according to the subcarrier index relative to 20ppm at the center band. By the above relationship, Figure 3D As shown in the direction of the arrow in , when the SCO effect is calibrated so as not to be affected, a frequency offset corresponding to 20 ppm can always be obtained regardless of the position of the sub-band.

[0093] The various points in the graph indicate the CFO of the subcarrier at the center frequency position of each of the 16 20 MHz subbands in the 320 MHz wideband channel. The index k of the subcarrier corresponding to the center frequency at any subband index m is m The definitions are as follows.

[0094] [Equation 7]

[0095]

[0096] in

[0097] The value obtained when CFO is determined for each subband The CFO at the center frequency can be approximated by the average value of the subcarriers within the subband as shown below.

[0098] [Equation 8]

[0099]

[0100] In contrast, when the equation is modified to obtain the frequency offset FO from the CFO determined for each subband (ppm) When the frequency offset FO is determined at the subband with index m (ppm)，m It can be expressed as follows.

[0101] [Equation 9]

[0102]

[0103] By substituting the index of the subcarrier into Equation 9, the frequency offset is expressed as follows.

[0104] [Equation 10]

[0105]

[0106] Among them, Or for

[0107] Figure 4 The operation process of the wireless communication device according to the embodiment is shown. Figure 3A To describe Figure 4 .

[0108] Reference Figure 4 In operation S101, the wireless communication device 200 may detect a signal received from a transmitter at a plurality of sub-bands constituting a frequency band. For example, the bandwidth of the frequency band is 320 MHz, and the bandwidth of each of the sub-bands is 20 MHz. The bandwidths of the frequency band and the sub-bands may be changed variously and are not limited to the above-described embodiments.

[0109] In operation S103, the wireless communication device 200 may determine a first frequency offset of a signal at a reception subband in which a signal has been detected. The first frequency offset may be the above-mentioned CFO, and the reception subband refers to a subband in which a signal has been detected in subbands constituting a frequency band.

[0110] For example, the signal received by the wireless communication device 200 may include a training sequence that is periodically repeated in the time domain, and the wireless communication device 200 may determine the first frequency offset based on the periodicity of the training sequence. In addition, the wireless communication device 200 may determine the first frequency offset by extracting phase information of each of the subbands from the training sequence using ACF.

[0111] In addition, in operation S105, the wireless communication device 200 can determine the second frequency offset by calibrating the first frequency offset based on the distance of each of the receiving subbands from the center frequency of the frequency band. That is, the second frequency offset is a frequency offset calibrated in a direction to remove the SCO effect relative to the first frequency offset.

[0112] As an example, the distance of each of the reception sub-bands from the center frequency of the frequency band may correspond to the size of the index of each of the reception sub-bands.

[0113] In operation S107, the wireless communication device 200 may determine a third frequency offset of the frequency band based on the second frequency offset.

[0114] For example, the wireless communication device 200 may determine the third frequency offset by performing weighted averaging on the second frequency offset based on a weight corresponding to the amplitude of the signal measured at each of the reception subbands.

[0115] For example, the wireless communication device 200 can reconstruct the I / Q vector of each of the receiving subbands by using the amplitude of the signal measured at each of the receiving subbands and the second frequency offset to obtain the vector of the frequency band by combining the I / Q vectors, and can determine the third frequency offset by calculating the phase of the vector of the frequency band.

[0116] The wireless communication device 200 may receive data from the transmitter by using the third frequency offset. For example, the wireless communication device 200 may receive data by calibrating the frequency of the LO by using the third frequency offset. As another example, the wireless communication device 200 may receive data by calibrating the modulation of the received signal by using the third frequency offset. The wireless communication device 200 may receive data from the transmitter by using the third frequency offset in various methods, and is not limited to the above-described embodiments.

[0117] Figure 5A The operation process of the wireless communication device according to the embodiment is shown. Figure 2 To describe Figure 5A .

[0118] Reference Figure 5AIn operation S201, the wireless communication device 100 may detect a received signal of each sub-band based on an ACF and a cross-correlation function (CCF). For example, the wireless communication device 100 may divide a wideband channel into sub-bands each having a bandwidth of 20 MHz, and may calculate and update the ACF and CCF of each sub-band. When the ACF value and the CCF value exceed a specific threshold, the wireless communication device 100 may consider that a received signal has been detected at the corresponding sub-band, and may start a frame reception process through synchronization timing determination and frequency offset estimation.

[0119] In operation S203, the wireless communication device 100 may calculate phase information (CFO) based on the ACF result of each subband. That is, the wireless communication device 100 does not combine the ACF of each subband, but the wireless communication device 100 first calculates the CFO value of each subband by extracting phase information from each ACF.

[0120] In operation S205 , the wireless communication device 100 may calibrate phase information (CFO) based on the frequency position of the sub-band.

[0121] In operation S207 , the wireless communication device 100 may reconstruct an I / Q vector based on the absolute value of the AFC and the calibrated CFO.

[0122] In operation S209, the wireless communication device 100 may combine I / Q vectors of the subbands in which the reception signal has been detected.

[0123] In operation S211, the wireless communication device 100 may determine a frequency offset by calculating phase information of one combined vector.

[0124] Figure 5B FIG. 4 shows the operation process of the wireless communication device at the mth subband according to the embodiment. Figure 5A To describe Figure 5B .

[0125] Operations S203', S205' and S207' may correspond to Figure 5A Operations S203, S205 and S207 in .

[0126] The wireless communication device 100 may divide the frequency band of the received signal. For example, the wireless communication device 100 may divide the frequency band into sub-bands each having a bandwidth of 20 MHz.

[0127] Reference Figure 5B In operation S203', the wireless communication device 100 may calculate the ACF result (ACF 20M,m ) calculates the phase information of the mth subband (∠(ACF 20M,m )).

[0128] The wireless communication device 100 may obtain the amplitude and phase of the received signal as an ACF result. For example, the wireless communication device 100 may extract a synchronization timing from the received signal including the training sequence, and may calculate the phase information (CFO) of the mth subband by using the synchronization timing.

[0129] In operation S205′, the wireless communication device 100 may convert the phase information (∠(ACF 20M,m )) is calibrated to phase information (∠(ACF 20M,m ) calib ).

[0130] In operation S207′, the wireless communication device 100 may calculate the amplitude of the received signal and the calibrated phase information (∠(ACF 20M,m ) calib )) to reconstruct the phasor vector (|ACF20M, m|*e) in the I / Q region j2π{∠(ACF20M，m)calib} ).

[0131] Figure 5C The operation of the wireless communication device at each sub-band and the method of combining multiple sub-bands according to the embodiment are shown. Figure 5A and Figure 5B To describe Figure 5C , and redundant descriptions can be omitted.

[0132] Reference Figure 5C , operations S203a, S203b, and S203c may correspond to operation S203'. Operations S205a, S205b, and S205c may correspond to operation S205'. Operations S207a, S207b, and S207c may correspond to operation S207'. Operations S201a, S201b, and S201c may correspond to operation S201.

[0133] In operation S201a, the wireless communication device 100 may detect a received signal at the 0th sub-band. For example, the wireless communication device 100 may detect a received signal at the 0th sub-band based on the ACF and the CCF.

[0134] In operation S201b, the wireless communication device 100 may detect a received signal at the first sub-band. For example, the wireless communication device 100 may detect a received signal at the first sub-band based on the ACF and the CCF.

[0135] In operation S201c, the wireless communication device 100 may detect a received signal at the mth subband. For example, the wireless communication device 100 may detect a received signal at the mth subband based on the ACF and the CCF.

[0136] In operation S209a, the wireless communication device 100 may combine the I / Q vectors of the subbands where the received signal has been detected. For example, when a received signal is detected at the zeroth subband, the wireless communication device 100 may use the first multiplexer MUX_0 to select the phasor vector (|ACF20M, 0|*e) of the I / Q region of the zeroth subband. j2π{∠(ACF20M，0)calib} ). In this way, the wireless communication device 100 can select the phasor vector of the subband in which the received signal has been detected. The wireless communication device 100 can generate one phasor vector by combining all the selected phasor vectors.

[0137] In operation S211a, the wireless communication device 100 may determine a frequency offset of a frequency band by calculating phase information of one combined vector.

[0138] Figure 6 A method for detecting a received signal at a subband, obtaining a synchronization timing, and determining a frequency offset based on the synchronization timing and the received signal according to an embodiment is shown. Figure 2 To describe Figure 6 .

[0139] Reference Figure 6 , in operation S301, the wireless communication device 100 can receive a signal.

[0140] In operation S303, the wireless communication device 100 may divide the frequency band of the received signal into sub-bands each having a bandwidth of 20 MHz.

[0141] In operation S305, the wireless communication device 100 can detect the received signal at the subband by using CCF and can obtain the synchronization timing of the received signal. For example, in operation S307, the received signal can be detected by detecting the peak of the periodic received signal and can obtain the synchronization timing of the received signal.

[0142] In operation S309, the wireless communication device 100 may extract phase information of each of the sub-bands by using ACF. For example, in operation S311, the phase information of each of the sub-bands may be extracted by using the ACF result and the ARCTAN function based on the synchronization timing. That is, the wireless communication device 100 may calculate the ACF value of each sub-band corresponding to the synchronization time point.

[0143] In operation S313, the wireless communication device 100 may calibrate the extracted phase information by considering the SCO effect. When the wireless communication device 100 calibrates the deviation caused by the SCO from the measured CFO value according to the position of each subband from the center frequency within the channel, the wireless communication device 100 may determine the correct frequency offset regardless of the position of the subband and the bandwidth of the received signal.

[0144] In operation S315, the wireless communication device 100 may perform I / Q reconstruction and subband combining. In operation S317, the wireless communication device 100 may extract phase information of the frequency offset through the combined I / Q region phasor vector of the subband and the ARCTAN function.

[0145] Figure 7 The operation process of the wireless communication device according to the embodiment is shown. Figure 2 To describe Figure 7 .

[0146] Reference Figure 7 In operation S401, the wireless communication device 100 may divide a frequency band of a received signal into a first sub-band.

[0147] In operation S403 , the wireless communication device 100 may detect a reception signal at a second sub-band in the first sub-band.

[0148] In operation S405 , the wireless communication device 100 may determine a first frequency offset of a received signal at the second sub-band.

[0149] For example, the received signal may include a training sequence that is periodically repeated in the time domain, and the wireless communication device 200 may determine the first frequency offset based on the periodicity of the training sequence. The wireless communication device 100 may determine the first frequency offset by extracting phase information of each of the second subbands from the training sequence based on the ACF.

[0150] For example, the wireless communication device 100 may obtain the synchronization timing of the received signal of each of the second sub-bands, and may also determine the first frequency offset by extracting phase information of each of the second sub-bands from the training sequence based on the synchronization timing.

[0151] In operation S407, the wireless communication device 100 may determine the second frequency offset by calibrating the first frequency offset based on a distance of each of the second sub-bands from the center frequency of the frequency band.

[0152] In operation S409, the wireless communication device 100 may determine a third frequency offset of the frequency band by using the second frequency offset of each of the second sub-bands. For example, the wireless communication device 100 may determine the third frequency offset by performing weighted averaging on the second frequency offset according to the amplitude of the received signal of each of the second sub-bands.

[0153] For example, the wireless communication device 100 can reconstruct multiple I / Q vectors corresponding to the second subband by using the amplitude of the received signal of each of the second subbands and the second frequency offset to obtain one vector by combining the I / Q vectors, and can determine the third frequency offset by calculating the phase of this one vector.

[0154] Figure 8 2 shows a signal processed by a wireless communication device according to an embodiment. Figure 2 To describe Figure 8 .

[0155] The wireless communication device 100 can perform synchronization by detecting a preamble of a frame signal for a signal receiving operation and determining a frequency offset. The preamble of the frame signal may include a training sequence of a sample array of a specific length periodically repeated in the time domain. When s(n) represents N defined by the WLAN standard, L When receiving a signal of a training sequence repeated at sampling intervals, the relationship shown in the following equation 11 can be established in an ideal channel environment.

[0156] [Equation 11]

[0157] s(n)=s(nN L )

[0158] CFO CFO An actual received signal existing between transmission and reception and considering an additive white Gaussian noise (AWGN) channel can be expressed as in the following Equation 12.

[0159] [Equation 12]

[0160]

[0161] In Equation 12, s(n) represents the ideal received signal, f CFO represents CFO, η(n) represents noise, and T s Indicates the sampling period.

[0162] Reference Figure 8In operation S501, the wireless communication device 100 may divide a wideband channel into subbands. The wireless communication device 100 may divide a channel of a received signal r(n) into m subbands. For example, the wireless communication device 100 may divide the received signal r(n) into units of 20 MHz by filtering the received signal r(n) in the time domain. The signal r corresponding to the mth subband m (n) can be expressed as in the following equation 13.

[0163] [Equation 13]

[0164]

[0165] In Equation 13, f CFO,m ∝ represents the CFO experienced by the wireless communication apparatus 100 for the signal of the m-th subband.

[0166] In operation S503, the wireless communication device 100 may process a signal r corresponding to the m-th subband by using the ACF. m (n). For example, the wireless communication device 100 may calculate the ACF corresponding to a delay equal to the sampling repetition period NL of the training sequence. The ACF may be expressed as in the following equation 14.

[0167] [Equation 14]

[0168]

[0169] In Equation 14, L auto Represents the buffer (window) length of accumulated samples over which the ACF is calculated.

[0170] In operation S505, the wireless communication device 100 may extract phase information (CFO) corresponding to the m-th subband from the ACF. For example, the wireless communication device 100 may extract phase information (CFO) corresponding to the m-th subband from the synchronization time point n=n SYNC The corresponding ACF value determines the CFO of the sub-band as shown below.

[0171] [Equation 15]

[0172]

[0173] In Equation 15, represents the CFO of the m-th subband, This includes a certain proportion of deviation due to SCO depending on the position of the sub-band away from the center frequency within the entire wideband channel.

[0174] In operation S507, the wireless communication device 100 may calibrate the SCO effect. The wireless communication device 100 may obtain a CFO value determined in an environment without SCO by reversely calibrating the SCO effect, as shown in the following Equation 16.

[0175] [Equation 16]

[0176]

[0177] Among them, Or for

[0178] In Equation 16, m may represent an index according to the location of each 20 MHz subband within a wideband channel. Indicates the calibrated CFO value. It can be the CFO of the channel center frequency caused by the fundamental frequency offset due to LO mismatch at the transmitting and receiving ends, regardless of the bandwidth of the received signal and the position of the sub-band.

[0179] In operation S509, the wireless communication device 100 may reconstruct the I / Q value of each subband by using the calibrated CFO value. The reconstructed phasor vector of each subband may be expressed as in Equation 17 below.

[0180] [Equation 17]

[0181]

[0182] In operation S511, the wireless communication device 100 may combine the calibrated CFOs of each subband. For example, when the received signal is a broadband signal occupying multiple 20MHz subbands, a more accurate CFO value may be obtained by combining the calibrated CFOs of each subband. In order to reflect the influence of different channel qualities of each subband, instead of simply performing arithmetic averaging on the CFO value of each subband, the wireless communication device 100 may reconstruct and combine phasor vectors in the I / Q region. That is, the wireless communication device 100 may obtain a phasor vector for all subbands within the channel by coherently combining vectors in the complex dimension.

[0183] In operation S513, the wireless communication device 100 may extract phase information from the phasor vector. That is, the wireless communication device 100 may determine the CFO obtained as an average value of the entire channel band as follows.

[0184] [Equation 18]

[0185]

[0186] represents the offset of the pure carrier whose influence due to SCO has been calibrated, and the wireless communication device 100 can determine the frequency offset as shown in Equation 19 below.

[0187] [Equation 19]

[0188]

[0189] f c Indicates the center frequency of the frequency band.

[0190] Fig.9A and Fig. 9B The frequency offset in an AWGN channel without correction for the SCO effect is shown. Fig. 9C and Fig.9D The frequency offset in an AWGN channel corrected for the SCO effect is shown according to an embodiment.

[0191] When determining the frequency offset of a received signal in a wideband channel, the wireless communication device according to the present invention (see Figure 2 The wireless communication device 100 can determine an accurate frequency offset value by calibrating the deviation of the CFO caused by the CFO and SCO coupling effect. The wireless communication device 100 can accurately predict and calibrate the deviation that occurs linearly due to the distance away from the center frequency of the wideband channel, and thus can always determine a consistent frequency offset value of the signal received on all or some of the subbands in the subband, regardless of the bandwidth and frequency position. Therefore, the wireless communication device 100 can ensure correct synchronization and reception performance.

[0192] exist 9A to 9D In the example, it is assumed that the received signal exists only at a specific 20 MHz sub-band in a 320 MHz wideband channel and there is a 20 ppm frequency offset between transmission and reception.

[0193] Fig.9A and Fig. 9B The distribution of CFO without considering the SCO effect in an AWGN channel is shown as a cumulative distribution function (CDF). That is, this represents the case where the CFO is not calibrated. According to the CH_OFFSET value, the position of the 20 MHz sub-band where the received signal exists has one of the values ​​within the range of -8 ≤ CH_OFFSET ≤ -1 and +1 ≤ CH_OFFSET ≤ +8 relative to the center frequency of the 320 MHz channel. Fig.9A shows the case where -8≤CH_OFFSET≤-1, and Fig. 9B The case where +1≤CH_OFFSET≤+8 is shown.

[0194] Fig. 9C and 9DThe distribution of CFO in the case of considering the SCO effect in the AWGN channel is shown as CDF. That is, this shows the case of calibrating CFO. Fig. 9C shows the case where -8≤CH_OFFSET≤-1, and Fig.9D The case where +1≤CH_OFFSET≤+8 is shown.

[0195] Reference 9A to 9D , when CFO is not calibrated, the frequency offset gradually moves away from 20ppm according to the frequency position. Specifically, in an environment where there is a frequency offset of 20ppm, due to the CFO and SCO coupling effect, the CFO measured from the received signal of each subband shows a specific deviation according to the position CH_OFFSET of the frequency band. The wireless communication device 100 can calibrate the deviation by using the mathematical relationship between the frequency offset and CFO and SCO.

[0196] It can be confirmed that when the CFO is calibrated by considering the SCO effect, the frequency offsets are all unified around 20 ppm. That is, the wireless communication device 100 can calibrate the CFO to accurately determine the original frequency offset of 20 ppm between transmission and reception regardless of the frequency band position of the subband of the received signal.

[0197] Fig.9E and Fig.9F The frequency offset of the uncalibrated SCO effect in a fading channel according to an embodiment is shown. Figure 9G and 9H The frequency offset corrected for the SCO effect in a fading channel according to an embodiment is shown.

[0198] exist FIG. 9E to FIG. 9H In the example, it is assumed that the received signal exists only at a specific 20 MHz sub-band in a 320 MHz wideband channel and there is a 20 ppm frequency offset between transmission and reception.

[0199] Fig.9E and Fig.9F The distribution of CFO without considering the SCO effect in a fading channel is shown as a CDF. That is, this represents the case where the CFO is not calibrated. According to the CH_OFFSET value, the position of the 20 MHz sub-band where the received signal exists has one of the values ​​within the range of -8 ≤ CH_OFFSET ≤ -1 and +1 ≤ CH_OFFSET ≤ +8 relative to the center frequency of the 320 MHz channel. Fig.9E shows the case where -8≤CH_OFFSET≤-1, and Fig.9F The case where +1≤CH_OFFSET≤+8 is shown.

[0200] Figure 9G and Figure 9H The distribution of CFO in the case of considering the SCO effect in a fading channel is shown as CDF. That is, this shows the case where the CFO is calibrated. Figure 9G shows the case where -8≤CH_OFFSET≤-1, and Figure 9H The case where +1≤CH_OFFSET≤+8 is shown.

[0201] Reference Fig.9E and Fig.9F , in an environment where there is a 20ppm frequency offset, due to the CFO and SCO coupling effect, the CFO measured from the received signal of each sub-band shows a specific deviation depending on the position of the frequency band CH_OFFSET. Figure 9G and Figure 9H , it can be confirmed that when the CFO is calibrated by taking the SCO effect into account, the frequency offsets are all unified around 20ppm.

[0202] Fig.10 The frequency offset of a frequency band in a fading channel without SCO effect correction and the frequency offset of a frequency band in which SCO effect correction are made are shown.

[0203] When the received signal exists over the entire 320 MHz wideband channel between transmission and reception with a frequency offset of 20 ppm, the CFO deviation due to the SCO effect appears differently for each subband. Even when the CFO of each subband is not calibrated (baseline), the average frequency offset can be approximated to 20 ppm. However, since the channel quality of each subband is different in a fading channel, the CFO deviation in a specific frequency band undergoes weighted averaging at a higher ratio, which may cause the determined frequency offset value to be biased. Because the wireless communication device (see Figure 2 100) calibrates the CFO deviation due to SCO for each subband, and vector combines the calibrated CFO deviations in the I / Q region to determine the average frequency offset, so that a more accurate result can be obtained regardless of the influence of different channel qualities of each frequency.

[0204] Reference Fig.10 , for a received signal with a frequency offset of 20 ppm and a bandwidth of 320 MHz, in a fading channel, the (proposed) frequency offset value when the CFO is calibrated has a smaller standard deviation than the baseline.

[0205] Fig.11 is a diagram illustrating an example of an apparatus for wireless communication according to an embodiment.

[0206] Specifically, Fig.11 An Internet of Things (IoT) network system including a home appliance 241 , a home appliance 242 , an entertainment device 243 , and an access point 245 is shown.

[0207] In some embodiments, as described above, Fig.10 The device for wireless communication shown in can take into account the SCO and CFO coupling effects that behave differently at each sub-band constituting a wideband channel depending on the position away from the center frequency, and can determine the accurate frequency offset value of each sub-band regardless of the frequency position within the channel.

[0208] in addition, Fig.10 The device for wireless communication shown in can perform appropriate coherent combination of the frequency offset values ​​of all subbands of the received signal detected in the wideband channel among the frequency offset values ​​determined for each subband by reflecting the SCO and CFO coupling effects, and can determine the accurate frequency offset value regardless of the occupied frequency band and bandwidth of the frame finally transmitted.

[0209] While aspects of the inventive concept have been particularly shown and described with reference to aspects thereof, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the appended claims.

Claims

1. A method for operating a receiver that communicates with a transmitter via a frequency band, the method comprising: detecting a signal received from the transmitter at a plurality of sub-bands constituting the frequency band; determining a first frequency offset of the signal at a receive subband of the plurality of subbands in which the signal has been detected; as well as The second frequency offset is determined by calibrating the carrier frequency offset based on a distance of each of the receive subbands from a center frequency of the frequency band.

2. The operating method according to claim 1, wherein: The signal comprises a training sequence that is repeated periodically in the time domain, and Determining the first frequency offset includes determining the first frequency offset based on a periodicity of the training sequence.

3. The operating method according to claim 2, wherein: Determining the first frequency offset includes determining the first frequency offset by extracting phase information of each of the plurality of subbands from the training sequence using an autocorrelation function.

4. The operating method according to claim 1, wherein: The distance of each of the reception sub-bands from the center frequency of the frequency band corresponds to the size of the index of each of the reception sub-bands.

5. The operating method according to claim 1, further comprising determining a third frequency offset of the frequency band based on the second frequency offset, in, Determining the third frequency offset includes determining the third frequency offset by performing a weighted average on the second frequency offset based on a weight corresponding to an amplitude of the signal measured at each of the reception subbands.

6. The operating method according to claim 1, further comprising determining a third frequency offset of the frequency band based on the second frequency offset, in, Determining the third frequency offset includes: reconstructing an in-phase / quadrature vector for each of the receive subbands by using the amplitude of the signal measured at each of the receive subbands and the second frequency offset; obtaining a vector of the frequency band by combining the in-phase / orthogonal vectors; and The third frequency offset is determined by calculating a phase of a vector of the frequency band.

7. The operating method according to claim 1, further comprising: determining a third frequency offset for the frequency band based on the second frequency offset; as well as Data is received from the transmitter by using the third frequency offset.

8. The operating method according to claim 1, wherein: The bandwidth of the frequency band is 320 MHz, and A bandwidth of each of the plurality of sub-bands is 20 MHz.

9. A receiver for communicating with a transmitter via a frequency band, the receiver comprising: Radio frequency integrated circuits; as well as A processor configured to: detecting a signal received from the transmitter via the radio frequency integrated circuit at a plurality of sub-bands constituting the frequency band; determining a first frequency offset of the signal at a receive subband of the plurality of subbands in which the signal has been detected; determining a second frequency offset by calibrating a carrier frequency offset based on a distance of each of the receive subbands from a center frequency of the frequency band; as well as A third frequency offset for the frequency band is determined based on the second frequency offset.

10. The receiver according to claim 9, wherein: The signal comprises a training sequence that is repeated periodically in the time domain, and The processor is further configured to determine the first frequency offset based on a periodicity of the training sequence.

11. The receiver according to claim 10, wherein: The processor is further configured to determine the first frequency offset by extracting phase information of each of the plurality of subbands from the training sequence using an autocorrelation function.

12. The receiver according to claim 9, wherein: The distance of each of the reception sub-bands from the center frequency of the frequency band corresponds to the size of the index of each of the reception sub-bands.

13. The receiver according to claim 9, wherein: The processor is further configured to determine the third frequency offset by performing weighted averaging on the second frequency offset based on a weight corresponding to a magnitude of the signal measured at each of the reception subbands.

14. The receiver according to claim 9, wherein: The processor is further configured to: reconstructing an in-phase / quadrature vector for each of the receive subbands by using the magnitude of the signal measured at each of the receive subbands and the second frequency offset; Obtaining a vector of the frequency band by combining the in-phase / orthogonal vectors; as well as The third frequency offset is determined by calculating a phase of a vector of the frequency band.

15. The receiver according to claim 9, wherein: The processor is also configured to receive data from the transmitter by using the third frequency offset.

16. The receiver according to claim 9, wherein: The bandwidth of the frequency band is 320 MHz, and A bandwidth of each of the plurality of sub-bands is 20 MHz.

17. A method of operating a receiver that communicates with a transmitter via a frequency band, the method comprising: dividing a frequency band of a received signal into a first sub-band; detecting the received signal at a second sub-band in the first sub-band; determining a first frequency offset of the received signal at the second sub-band; determining a second frequency offset by calibrating the first frequency offset based on a distance of each of the second sub-bands from a center frequency of the frequency band; as well as A third frequency offset of the frequency band is determined by using the second frequency offset of each of the second sub-bands.

18. The operating method according to claim 17, wherein: The received signal includes a training sequence that is repeated periodically in the time domain, and Determining the first frequency offset includes determining the first frequency offset based on a periodicity of the training sequence.

19. The operating method according to claim 18, wherein: Determining the first frequency offset includes determining the first frequency offset by extracting phase information of each of the second subbands from the training sequence based on an autocorrelation function.

20. The operating method according to claim 19, wherein: detecting the received signal at the second sub-band comprises obtaining synchronization timing of the received signal for each of the second sub-bands, and Determining the first frequency offset further includes determining the first frequency offset by extracting phase information of each of the second sub-bands from the training sequence based on the synchronization timing.

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