JP2008104015A - Automatic frequency control apparatus, receiver, communication apparatus, and communicating system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an automatic frequency control apparatus which compensates the frequency error of a low CNR (Carrier to Noise Ratio) receiving signal in high precision. <P>SOLUTION: The automatic frequency control apparatus which compensates the frequency error of the receiving signal using a known symbol included in the receiving signal is provided with: a same phase acquisition processing unit (11) which multiplies a complex conjugate of the known symbol to the known symbol, and removes a modulation component; a frequency error estimation unit (12) which uses the known symbol after removing the modulation component in the same phase acquisition processing unit (11), and estimates the frequency error; and a frequency error compensation means (a complex information conversion unit (13) and a complex multiplication unit (14)) which correct the frequency error of the receiving signal based on the frequency error estimated in the frequency error estimation unit (12). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a receiver that constitutes a digital wireless communication device, and more particularly to an AFC (Automatic Frequency Control) that compensates a frequency error between a transmission side and a reception side.

  In digital data transmission, the frequency deviation between oscillators used in the modulation circuit in the communication device (transmitter) on the transmission side and the demodulation circuit in the communication device (receiver) on the reception side, or the Doppler shift added in the transmission path A frequency error occurs between the reception side and the transmission side. If this frequency error exists, the phase of the received signal rotates on the phase plane with time. As a result, there is a risk of erroneous determination of transmission data in the demodulation circuit on the reception side. Therefore, the receiving side needs to estimate the frequency error and compensate for the estimated frequency error.

  Further, for example, in power limited wireless communication such as satellite communication, improvement of communication quality in a low CNR (Carrier to Noise Ratio) environment is a problem. That is, since the estimation accuracy of the frequency error deteriorates in a low CNR environment and a determination error due to cycle slip or the like occurs, research for estimating the frequency error with high accuracy in a low CNR environment has been actively conducted.

  Here, a frequency error estimation device that estimates a frequency error with high accuracy is described in Patent Document 1 below. In the frequency error estimation device described in Patent Document 1 below, the frequency error of a received signal is estimated based on the result of delay detection of a plurality of received signals with different numbers of delayed detection symbols. As a result, the frequency error estimation accuracy is improved while maintaining a wide supplemental range of phase shift (frequency error).

Japanese Patent No. 3789157

  As described above, the conventional frequency error estimation apparatus can estimate the frequency error with high accuracy. However, since the frequency error is estimated using random modulation data, the modulation data is multiplied by M (M is used). Processing that removes the modulation component (depending on the modulation method) is required. When the multiplication process is executed, the noise component included in the modulation data increases (multiplication loss), so that the threshold CNR of the frequency error estimation operation (the limit point of CNR capable of estimating the frequency error with high accuracy) increases. There was a problem.

  FIG. 16 is a diagram showing the relationship between the CNR of the received signal and the phase estimation error when the conventional frequency error estimation device is used. As shown in FIG. 16, when the CNR falls below the threshold CNR, the phase error (frequency error) estimation accuracy deteriorates rapidly.

  The present invention has been made in view of the above, and in a receiver or the like included in a communication apparatus that transmits and receives a digital modulation signal, it is difficult to estimate a frequency error with high accuracy in the past because of a low CNR. An object of the present invention is to obtain an automatic frequency control device that estimates a frequency error of a received signal with high accuracy and compensates the estimated frequency error.

  In order to solve the above-described problems and achieve the object, the present invention provides an automatic frequency control device that compensates for a frequency error of a received signal using a known symbol included in the received signal, A modulation component removing unit that multiplies the complex conjugate of the known symbol to remove the modulation component from the known symbol, and a frequency error using the known symbol after the modulation component is removed by the modulation component removing unit. And a frequency error correcting unit that corrects the frequency error of the received signal based on the frequency error estimated by the frequency error estimating unit.

  According to the present invention, since the frequency error is estimated using the known symbol included in the received signal, the M-multiplication process of the modulation data accompanied by an increase in the noise component is not necessary, and the conventional method has a high-accuracy frequency. Even when a signal having a low CNR is received to such an extent that it is difficult to estimate the error, the frequency error can be estimated with high accuracy and the estimated frequency error can be compensated, that is, the reception performance can be improved. There is an effect that can be.

  Embodiments of an automatic frequency control device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram illustrating a configuration example of a first embodiment of a receiver including an automatic frequency control device according to the present invention. This receiver corresponds to an automatic frequency control device according to the present invention, 1 for extracting a desired component from the received signal, BTR unit 2 for reproducing the bit timing of the received signal output from the filter unit 1, and BTR. The AFC unit 3 that compensates for the frequency error of the received signal whose bit timing has been recovered by the unit 2 and the synchronous detection unit 4 that performs carrier recovery based on the received signal whose frequency error has been compensated for by the AFC unit 3 are provided.

  FIG. 2 is a diagram illustrating an example of a frame configuration of a signal transmitted from the transmitter to the receiver, that is, a signal received by the receiver. This received signal frame has a configuration in which a known symbol is inserted into a data (data symbol) string. The automatic frequency control device (AFC unit 3) according to the present invention uses this known symbol to estimate and compensate for the frequency error of the received signal. The ratio between the known symbol and the data symbol (the ratio between the data symbol and the known symbol included in one frame) is defined in advance so as to satisfy the communication quality (reception error rate, transmission rate, etc.) required by the system. And

  FIG. 3 is a diagram illustrating a configuration example of the AFC unit 3 according to the first embodiment. The AFC unit 3 includes an in-phase processing unit 11, which is a modulation component removing unit, a frequency error estimation unit 12, and a complex information conversion unit. 13 and the complex multiplier 14. The complex information conversion unit 13 and the complex multiplication unit 14 constitute a frequency error correction unit.

  Next, the frequency error estimation operation in the AFC unit 3 will be described with reference to FIG. When a received signal is input to the AFC 3 unit, the in-phase processing unit 11 serving as a modulation component removing unit performs in-phase processing of a known symbol (a known signal in a modulated state) included in the received signal. Specifically, as shown in FIG. 4, the complex conjugate of the known modulation signal (the signal obtained by modulating the known signal) generated by the known modulation signal generation unit 21 in the in-phase processing unit 11 is complex conjugate. The generation unit 22 generates and multiplies the generated complex conjugate by the received known signal (the modulated known signal). As a result, the modulation component of the received known signal is removed, and an in-phase known symbol is obtained. The in-phase known symbol is output to the frequency error estimator 12.

  FIG. 5 is a diagram illustrating a configuration example of the frequency error estimator 12. The frequency error estimator 12 includes a plurality of frequency error detectors 31-1, 31-2,. 32. Each frequency error detection unit (frequency error detection units 31-1, 31-2,..., 31-n) is defined in advance using a known symbol that has been in-phased by the in-phase processing unit 11. A frequency error is detected at every processing interval (time). Here, the predetermined processing interval is an integral multiple of the interval at which the known symbol is inserted into the received signal frame (known symbol insertion interval). In addition, the processing interval in each frequency error detection unit is different. For example, as shown in FIG. 6, the processing interval of the frequency error detector 31-1 is the known symbol insertion interval (1 unit), and the processing interval of the frequency error detector 31-2 is twice the known symbol insertion interval (2 Unit).

  In the frequency error detection operation performed by each frequency error detection unit, first, delayed detection of the in-phase known symbol that is an input signal is performed. Specifically, a complex conjugate is generated while delaying an input known symbol (first input signal), and the generated complex conjugate is different from the first input signal. Complex multiplication is performed on (input signal not given a delay). The delay time used at this time (the time for generating the complex conjugate while giving a delay to the input signal) is the interval between the time when the first input signal is input and the time when the second input signal is input. The delay time is set to the above-mentioned “different processing interval for each frequency error detection unit”. Next, the phase difference (complex number) that is the result of the delay detection is averaged to suppress the noise component, and the averaged phase difference is subjected to polar coordinate conversion. Then, the frequency error is calculated based on the phase difference after the polar coordinate conversion and the processing interval (delay time).

  As described in Patent Document 1, it is known that if the delay time applied to the input signal in the delay detection process is changed, the phase shift capturing range and the frequency error estimation accuracy in the frequency error detection process also change. ing. That is, the shorter the delay time, the wider the phase shift capture range, while the longer the delay time, the narrower the phase shift capture range, but the frequency error estimation accuracy increases. Therefore, the frequency errors output from the frequency error detectors 31-1, 31-2,..., 31-n are calculated by applying different conditions (phase shift capturing range, frequency error estimation accuracy). Is. Each frequency error detection unit calculates the number of frequency errors corresponding to the delay time used in the calculation process (delay detection process), and calculates more frequency errors as the frequency error estimation accuracy increases. For example, when the delay time is 1 symbol time, the frequency error detector calculates only one frequency error, but when the delay time is 2 symbol times, it calculates two frequency errors. However, each frequency error detection unit, when calculating a plurality of frequency errors, cannot independently determine which one is the most accurate frequency error.

  Therefore, the frequency error specifying unit 32 finally compares the calculation results in the frequency error detecting units 31-1, 31-2,... The frequency error output as the frequency error estimation result is specified. For example, the frequency error specifying unit 32 selects a frequency error calculated by a certain frequency error detection unit as the first frequency error detection result. The first frequency error detection result is preferably calculated using the shortest possible delay time so as to widen the phase shift capturing range, but is not necessarily calculated using the shortest delay time. You don't have to. Then, a plurality of frequency errors calculated by the frequency error detection unit that performs processing with a delay time longer than the delay time for calculating the first frequency error detection result are compared with the first frequency error detection result as a comparison target. Then, the comparison target closest to the first frequency error detection result is selected as the second frequency error detection result. Further, if there is a frequency error detection unit that calculates a frequency error with a longer delay time than the frequency error detection for which the second frequency error detection result is calculated, the second frequency is compared with the plurality of frequency errors calculated by the frequency error detection unit. Compared with the error detection result, the one closest to the second frequency error detection result is selected from the comparison targets as the third frequency error detection result.

  The frequency error specifying unit 32 repeatedly executes the comparison processing of the frequency error calculation results in the respective frequency error detection units as described above, from the frequency errors calculated in the frequency error detection unit that performs the processing with the longest delay time. The frequency error estimation unit 12 specifies what is output as the final frequency error estimation result.

  By estimating the frequency error in such a procedure, the frequency error estimation unit keeps the phase shift capturing range wide (while maintaining the capturing range when the first frequency error detection result is calculated), and the frequency error. The estimation accuracy can be increased.

  The complex information conversion unit 13 converts the frequency error estimation result (phase) received from the frequency error estimation unit 12 into a complex number, and generates and outputs the complex conjugate. The complex multiplier 14 multiplies the output from the complex information converter 13 and the received signal that is the input signal to the AFC 3 unit, and outputs the result to the CR unit 4.

  In the above description, the signal transmission side (transmitter or communication device) is not mentioned. However, the transmission side is limited to transmission conditions defined in advance (for example, bit patterns of known symbols, transmission intervals of known symbols, etc.) ) To transmit a known symbol. Also, a plurality of transmission conditions may be defined in advance, and the transmission side may transmit known symbols according to the transmission conditions specified by the reception side at the start of data transmission and / or during data transmission. As a result, for example, when the CNR is sufficiently high and the communication quality is good, a flexible operation according to the situation is possible, such as decreasing the transmission frequency of known symbols and increasing the transmission rate.

  As described above, in the present embodiment, by executing the delayed detection results using different delay times for the known information (known symbols) included in the received signal, each of the plurality of pieces of information is detected with different detection accuracy. The frequency error is detected, and the frequency error detected with different accuracy is compared to estimate the frequency error with high accuracy. This eliminates the need for M-multiplication processing of modulated data that accompanies an increase in noise components in frequency error estimation processing, and as compared with the case where a conventional method requiring M-multiplication processing is applied, as shown in FIG. Thus, the threshold CNR at which the error (phase estimation error) estimation accuracy rapidly deteriorates becomes low. That is, compared with the conventional method, it is possible to better estimate the frequency error and compensate the estimated frequency error even in an environment where the reception CNR is lower. In FIG. 7, the relationship between the phase estimation error and the CNR when the present invention is applied is shown as “method 1”.

  In addition, the transmission power required to ensure the same communication quality as in the past can be made lower than in the past, and the apparatus can be reduced in size and power consumption.

Embodiment 2. FIG.
Next, the automatic frequency control device according to the second embodiment will be described. In the present embodiment, an automatic frequency control apparatus that estimates and compensates for a frequency error satisfactorily in an environment where the CNR is lower than that of the automatic frequency control apparatus of the first embodiment will be described. The configuration of the receiver provided with the automatic frequency control device of the present embodiment is the same as that of the receiver of the first embodiment.

  FIG. 8 is a diagram illustrating an example of a frame configuration of a signal received by the receiver according to the second embodiment. This received signal frame is different from the frame configuration of the first embodiment in that a plurality of continuous known symbol sequences are inserted in the data symbol sequence. In FIG. 8, two known symbols are continuously arranged. However, the number of consecutive symbols may be three or more.

  FIG. 9 is a diagram illustrating a configuration example of the AFC unit according to the second embodiment. The AFC unit 3a has a configuration in which an adjacent symbol adding unit 15 is added to the AFC unit 3 (see FIG. 3) of the first embodiment described above. Since portions other than the adjacent symbol adding unit 15 are the same as those of the AFC unit 3 of the first embodiment described above, the same reference numerals are given and detailed description thereof is omitted.

  The frequency error estimation operation in the AFC unit 3a will be described with reference to FIGS. FIG. 10 is a diagram illustrating the concept of the frequency error estimation operation performed by the automatic frequency control device (AFC unit 3a) according to the second embodiment. The adjacent symbol adding unit 15 of the AFC unit 3a adds a plurality of adjacent known symbols when there are a plurality of known symbols that are in-phased by the in-phase processing unit 11 and adjacent to each other. A known symbol after addition is obtained. Then, the known symbol after addition is output to the frequency error estimator 12. Next, the frequency error estimator 12 executes the same frequency error estimation operation as that of the first embodiment using the post-addition known symbols output from the adjacent symbol adder 15.

  The number of consecutive known symbols is determined in advance so as to satisfy the communication quality required by the system including the receiver by performing simulation or the like. In addition, the number of consecutive known symbols does not necessarily need to match the number of symbols added by the adjacent symbol adding unit 15. For example, when the number of consecutive known symbols is 3, only the first and second known symbols may be added, and the frequency error may be estimated using the added known symbols.

  As described above, in this embodiment, adjacent known symbols included in the received signal are in-phased and then added to improve the CNR, and the known symbol with the improved CNR (known symbol obtained by addition) ) Was used to estimate the frequency error. As a result, as shown in FIG. 11, the threshold CNR becomes even lower than when the method of the first embodiment is applied (method 1). In FIG. 11, the relationship between the phase estimation error and the CNR when the method of the first embodiment is applied and when the method of the present embodiment is applied is referred to as “method 1” and “method 2”, respectively. Show.

Embodiment 3 FIG.
Next, the automatic frequency control apparatus according to the third embodiment will be described. In the present embodiment, a method for improving the efficiency of the frequency error estimation operation described in the first or second embodiment by devising the frame configuration of the received signal will be described. Note that the configuration of the receiver of this embodiment is the same as that of the receiver of Embodiment 1. The configuration of the automatic frequency control device is the same as that in the first or second embodiment. The configuration of the automatic frequency control device is determined according to the configuration of the received signal frame to be employed.

  12A to 12D are diagrams illustrating an example of a frame configuration of a reception signal used in the third embodiment. The portion described as “ALL0” indicates a symbol in which all bits are “0” (hereinafter referred to as “zero symbol”), while the portion described as “known pattern” includes at least one bit. A symbol “1” (hereinafter referred to as “non-zero symbol”) is shown.

  For example, when a configuration in which non-zero symbols and zero symbols are mixed as shown in FIG. 12-1 or FIG. 12-2 is adopted, first, in the receiver of the present embodiment, the BTR unit 2 uses non-zero symbols. Then, bit timing recovery processing (BTR (Bit Timing Recovery) processing) and frame timing detection processing of the received signal are performed, and then the AFC unit 3 performs frequency error estimation using zero symbols. As a result, the bit timing reproduction accuracy can be improved, and in the frequency error estimation process, the known symbol in-phase process required in the processes of the first and second embodiments is not required. Further, the influence of intersymbol interference due to the delayed wave can be suppressed, and the frequency error can be estimated with higher accuracy. If the non-zero symbol has a bit pattern similar to that of the pilot symbol, the effect of improving the bit timing reproduction accuracy is increased.

  In the case of a frame configuration including only zero symbols as shown in FIG. 12C, the in-phase processing of the known symbols (that is, the in-phase unit 11) in the frequency error estimation operation is unnecessary, and the apparatus can be downsized. Also, in the case of a frame configuration including only non-zero symbols as shown in FIG. 12-4 (corresponding to the case of Embodiment 1), it is possible to improve frame timing detection accuracy and frequency error estimation accuracy. it can.

  As in the second embodiment, a frame configuration in which a plurality of known symbols (non-zero symbols, zero symbols) are continuous is adopted, and a plurality of adjacent known symbols are added before frame timing detection and frequency error. You may make it perform estimation. Thereby, CNR can be improved.

Embodiment 4 FIG.
Next, the automatic frequency control apparatus according to the fourth embodiment will be described. In the present embodiment, unlike the first to third embodiments, an automatic frequency control device that estimates and compensates for a frequency error without using a known symbol will be described. That is, an automatic frequency control apparatus that estimates and compensates for a frequency error using data symbols will be described. The configuration of the receiver provided with the automatic frequency control device of the present embodiment is the same as that of the receiver of the first embodiment.

  FIG. 13 is a diagram illustrating a configuration example of the AFC unit according to the fourth embodiment. The AFC unit 3b includes an in-phase processing unit 11b and a frequency error estimation unit 12b instead of the in-phase processing unit 11 and the frequency error estimation unit 12 of the AFC unit 3 (see FIG. 3) of the first embodiment described above. Further, a configuration in which an adjacent symbol adding unit 15b is added is adopted. Since the other parts are the same as those of the AFC unit 3 of the first embodiment, the same reference numerals are given and detailed description thereof is omitted.

  The frequency error estimation operation in the AFC unit 3b will be described with reference to FIGS. FIG. 14 is a diagram showing the concept of the frequency error estimation operation performed by the automatic frequency control device (AFC unit 3b) according to the fourth embodiment. When a reception signal (data symbol) is input to the AFC unit 3b, the in-phase processing unit 11b performs in-phase processing on the data symbols. Unlike the first to third embodiments, the in-phase processing at this time multiplies the data symbol by M to remove the modulation component and obtain the in-phase data symbol. The in-phase data symbol is input to the adjacent symbol adding unit 15b.

  The adjacent symbol adding unit 15b that has received the in-phase data symbol adds three adjacent data symbols, for example, as shown in FIG. 14, and obtains the added data symbol. Then, the data symbol after addition is output to the frequency error estimator 12b. The frequency error estimator 12b estimates the frequency error using the data symbol received from the adjacent symbol adder 15b. The configuration of the frequency error estimator 12b is the same as that of the frequency error estimator 12 of the first embodiment described above. The frequency error estimation operation performed by the frequency error estimation unit 12b is the same as the frequency error estimation operation in the frequency error estimation unit 12 of Embodiment 1 except that an input signal generated based on the data symbol is used. It is. That is, since the process itself performed on the input signal is the same, the description of the frequency error estimation operation is omitted.

  Thus, in the present embodiment, the CNR is improved by adding adjacent data symbols after making them in-phase, and data symbols with improved CNR (data symbols obtained by addition) are used. The frequency error is detected (estimated) under a plurality of different conditions, and the most accurate one of the plurality of detection results is treated as the final frequency error estimation result. Thereby, since the CNR once deteriorated can be improved by executing the in-phase processing (multiplication processing) of the data symbols, as shown in FIG. 15, compared with the case where the conventional method is applied, The threshold CNR is lowered. That is, compared with the conventional method, it is possible to estimate the frequency error better and compensate for the estimated frequency error even in an environment where the CNR of the received signal is lower. In FIG. 15, the relationship between the phase estimation error and the CNR when the present invention is applied is shown as “method 4”.

  As described above, the automatic frequency control device according to the present invention is useful for a digital signal receiver, and is particularly suitable for a receiver that receives a digital signal in a low CNR environment.

It is a figure which shows the structural example of the receiver provided with the automatic frequency control apparatus concerning this invention. 6 is a diagram illustrating an example of a frame configuration of a reception signal used in Embodiment 1. FIG. 3 is a diagram illustrating a configuration example of an AFC unit included in the receiver according to Embodiment 1. FIG. It is a figure which shows the structural example of an in-phase processing part. It is a figure which shows the structural example of a frequency error estimation part. It is the figure which showed the concept of the frequency error estimation operation | movement which the automatic frequency control apparatus of Embodiment 1 performs. FIG. 6 is a diagram showing a relationship between a CNR of a received signal and a phase estimation error when the frequency error estimation operation of Embodiment 1 is used. 6 is a diagram illustrating an example of a frame configuration of a reception signal used in Embodiment 2. FIG. 6 is a diagram illustrating a configuration example of an AFC unit according to Embodiment 2. FIG. It is the figure which showed the concept of the frequency error estimation operation | movement which the automatic frequency control apparatus of Embodiment 2 performs. FIG. 10 is a diagram illustrating a relationship between a CNR of a received signal and a phase estimation error when the frequency error estimation operation of the second embodiment is used. 10 is a diagram illustrating a frame configuration example of a reception signal used in Embodiment 3. FIG. 10 is a diagram illustrating a frame configuration example of a reception signal used in Embodiment 3. FIG. 10 is a diagram illustrating a frame configuration example of a reception signal used in Embodiment 3. FIG. 10 is a diagram illustrating a frame configuration example of a reception signal used in Embodiment 3. FIG. FIG. 10 is a diagram illustrating a configuration example of an AFC unit according to a fourth embodiment. It is the figure which showed the concept of the frequency error estimation operation | movement which the automatic frequency control apparatus of Embodiment 4 performs. FIG. 10 is a diagram illustrating a relationship between a CNR of a received signal and a phase estimation error when the frequency error estimation operation of the fourth embodiment is used. It is the figure which showed the relationship between CNR of a received signal at the time of using the conventional frequency error estimation apparatus, and a phase estimation error.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Filter part 2 BTR part 3, 3a, 3b AFC part 4 Synchronous detection part 11, 11b In-phase processing part 12, 12b Frequency error estimation part 13 Complex information conversion part 14 Complex multiplication part 15, 15b Adjacent symbol addition part 21 known modulation signal generation unit 22 complex conjugate generation unit 31-1, 31-2, 32-n frequency error detection unit 32 frequency error identification unit

Claims (14)

An automatic frequency control device that compensates for a frequency error of the received signal using a known symbol included in the received signal,
A modulation component removing means for multiplying the known symbol by a complex conjugate of the known symbol and removing a modulation component from the known symbol;
A frequency error estimating means for estimating a frequency error using a known symbol after the modulation component is removed in the modulation component removing means;
A frequency error correcting means for correcting a frequency error of the received signal based on the frequency error estimated by the frequency error estimating means;
An automatic frequency control device comprising: The frequency error estimating means includes
A first frequency error detector for delay-detecting a known symbol with an arbitrary delay time and detecting a frequency error of the received signal based on the detection result;
At least one second frequency error detection unit that delay-detects a known symbol with a delay time (number of delay detection symbols) larger than that of the first frequency error detection unit and detects a frequency error of the received signal based on the detection result. When,
The frequency error detected by the first frequency error detection unit and the frequency error detected by the second frequency error detection unit are compared, and based on the comparison result, the second frequency error detection unit A frequency error specifying unit for specifying what is output as a frequency error estimation result from the detected frequency errors;
The automatic frequency control apparatus according to claim 1, further comprising: The frequency error specifying unit compares the frequency error detected by the first frequency error detection unit and the frequency error detected by the second frequency error detection unit with each other in ascending order of delay time. The frequency error detected by the frequency error detection unit of
The frequency error detected by the first frequency error detection unit or the frequency error obtained as a result of the comparison that has already been performed, and the frequency error detected by the second frequency error detection unit that has not been compared yet, one after another. The automatic frequency control device according to claim 2, wherein the comparison is performed.   The frequency error specifying unit estimates a plurality of frequency error candidates based on a result obtained by the second frequency error detection unit according to a delay time used in the delay detection process, and a first frequency error detection unit 4. The automatic frequency control apparatus according to claim 2, wherein a frequency error estimation result is specified by selecting a frequency error from frequency error candidates based on the result obtained in step (5). If a known symbol contains a known symbol with all bits “0”,
The frequency error estimation means performs a frequency error detection process using a known symbol whose bits are all “0” instead of the known symbol after the modulation component is removed by the modulation component removal means. The automatic frequency control device according to any one of claims 1 to 4. further,
When a plurality of known symbols are continuously included in the data symbol sequence, the adjacent known symbols after the modulation component is removed by the modulation component removal means are added,
The automatic frequency error estimation unit according to any one of claims 1 to 5, wherein the frequency error estimation unit performs the frequency error estimation process using the added adjacent symbol obtained as a result of the addition process. Frequency control device.   7. The automatic frequency control apparatus according to claim 6, wherein in the addition processing of adjacent known symbols, when three or more known symbols are continuous, at least two adjacent known symbols are added. A modulation component removing unit that performs multiplication processing on the received signal and removes the modulation component from the received signal;
Adjacent symbol addition means for receiving a received signal from which a modulation component has been removed by the modulation component removal means as an input, and adding a plurality of received signals after removal of the modulation component for each adjacent data symbol;
A frequency error estimating means for estimating a frequency error using the added data symbol obtained as a result of the adding process in the adjacent symbol adding means;
A frequency error correcting means for correcting a frequency error of the received signal based on the frequency error estimated by the frequency error estimating means;
An automatic frequency control device comprising: The frequency error estimating means includes
A first frequency error detector for delay-detecting the added data symbol at an arbitrary delay time (number of delay detection symbols) and detecting a frequency error of the received signal based on the detection result;
At least one second frequency error for delay-detecting the added data symbol with a delay time (number of delay detection symbols) larger than that of the first frequency error detection unit and detecting the frequency error of the received signal based on the detection result A detection unit;
The frequency error detected by the first frequency error detection unit and the frequency error detected by the second frequency error detection unit are compared, and based on the comparison result, the second frequency error detection unit A frequency error specifying unit for specifying what is output as a frequency error estimation result from the detected frequency errors;
The automatic frequency control apparatus according to claim 8, further comprising: The frequency error specifying unit compares the frequency error detected by the first frequency error detection unit and the frequency error detected by the second frequency error detection unit with each other in ascending order of delay time. The frequency error detected by the frequency error detection unit of
The frequency error detected by the first frequency error detection unit or the frequency error obtained as a result of the comparison that has already been performed, and the frequency error detected by the second frequency error detection unit that has not been compared yet, one after another. The automatic frequency control device according to claim 9, wherein the comparison is performed.   The frequency error specifying unit estimates a plurality of frequency error candidates based on a result obtained by the second frequency error detection unit according to a delay time used in the delay detection process, and performs the first frequency error detection. 11. The automatic frequency control apparatus according to claim 9, wherein a frequency error estimation result is specified by selecting a frequency error from frequency error candidates based on a result obtained by the unit.   A receiver comprising the automatic frequency control device according to claim 1.   A communication apparatus comprising the receiver according to claim 12. A receiver according to claim 12;
A transmitter for transmitting a signal including a predetermined known signal to the receiver;
A communication system comprising:

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