JP4796213B1 - Equalizer and equalization method - Google Patents

Abstract

Frequency offset compensation is performed using an appropriate frequency offset estimation value in forward equalization and reverse equalization, and deterioration in equalization performance is suppressed.
An RSSI minimum position determination unit 106 includes RSSI value minimum position information of each synchronization word section of a current frame and a next frame, and an RSSI comparison unit 107 includes RSSI threshold comparison information obtained by comparing an RSSI value and a threshold. Output to frequency offset estimated value selection section 108. The frequency offset estimated value selection unit 108 is more correct among the frequency offset estimated values obtained by the forward equalization processing unit 103 and the reverse equalization processing unit 104 based on the RSSI value minimum position information and the RSSI threshold comparison information. The estimated frequency offset value is the frequency offset estimate value of the current frame. The frequency offset compensation unit 101 calculates the frequency offset compensation amount of the next frame from the estimated frequency offset value of the current frame and the frequency offset compensation amount.
[Selection] Figure 1

Description

  The present invention relates to a decision feedback type equalization apparatus and equalization method for performing forward equalization and reverse equalization on a received signal.

0. Technical background and issues 0.1. Conventional Device Configuration In a wireless communication system, radio signals are reflected by buildings and affected by multipaths that follow a number of propagation paths, causing intersymbol interference in communication signals, thereby degrading communication quality. Are known. Therefore, a delay equalizer (equalizer) is used to reduce the influence of multipath.

  The delay equalizer is composed of two FIR (Finite Impulse Response) filters composed of digital filters, and an error (equalization error) between the equalization result of the equalization processing unit and the known symbol by training using the known symbol. The tap coefficients are converged so that is minimized. The delay equalizer with converged tap coefficients performs forward equalization on data located in the code string behind the known symbol, and reverse equalization on data located in the code string in front of the known symbol. Yes. The delay equalizer estimates the propagation path state by training using known symbols, initializes the estimated information, and performs an optimal equalization process.

  On the other hand, wireless communication systems are susceptible to frequency offsets caused by deviations in the oscillation frequency of local oscillators in transmitters and receivers, Doppler shifts caused by movement of terminal equipment, and the like. In particular, a delay equalizer (equalization device) used in a wireless communication system has a remarkable characteristic deterioration with respect to a frequency offset.

  For example, a decision feedback equalizer (DFE) will be described as an example. In the course of training of the equalizer, the tap coefficient becomes an inverse characteristic of an impulse response due to frequency selective fading. It is formed. However, when there is a frequency offset, the tap coefficient rotates in phase so as to compensate for the frequency offset. Therefore, it is necessary to compensate for the frequency offset with high accuracy.

  In general, frequency offset estimation accuracy tends to deteriorate due to the influence of intersymbol interference. That is, in an environment of frequency selective fading or in an environment where signals are simultaneously transmitted from a plurality of base stations with transmission timing offsets, the accuracy of frequency offset estimation is significantly degraded due to intersymbol interference. Therefore, it is necessary to compensate the frequency offset with high accuracy also from such a side. Thus, as a technique for solving such a problem of frequency offset, for example, Patent Document 1 or Patent Document 2 discloses related techniques.

0.2. Technology disclosed in Patent Document 1 In the technology disclosed in Patent Document 1, channel impulse characteristics are estimated by a matched filter and an equalizer, respectively, and a frequency offset is obtained from the result of passing through the matched filter. Then, the equalizer performs equalization processing based on the received signal and information on the frequency offset obtained by the matched filter. As a result, when a digital signal is transmitted via a communication path in which intersymbol interference occurs, even if there is a frequency offset, the digital signal can be properly demodulated, and high-quality communication can be realized. it can.

0.3. Technology disclosed in Patent Document 2 In addition, in the technology disclosed in Patent Document 2, frequency offset estimation values estimated from two sets of fixed patterns used for frequency offset estimation processing are selected according to the state of the transmission path. Yes. Then, the received signal whose frequency offset amount is corrected by the selected estimated frequency offset value is input to the equalizer to perform equalization processing. That is, the frequency offset estimation value to be used is selected according to the state of the transmission path, and the signal distortion depending on the frequency offset in the received signal is corrected based on the selected frequency offset estimation value. As a result, good communication quality can be maintained even in a communication environment where intersymbol interference due to multipath exists.

JP-A-3-133218 JP 2002-44176 A

0.4. However, in the technique disclosed in Patent Document 1 described above, when performing processing using a matched filter from estimation of channel impulse characteristics, it is necessary to perform processing at the same level as when performing equalization processing. For this reason, the circuit scale of the entire equalizer (equalization apparatus) increases, and the amount of computation during processing increases. In addition, when the received power in the training period in the equalization process is small, there is a possibility that sufficient training cannot be performed, and the equalization result (equalization signal) of the frame may be deteriorated.

  Further, in the technique disclosed in Patent Document 2 described above, two types and two sets of fixed patterns are required to perform the frequency offset estimation process. Therefore, the transmission efficiency is determined from the ratio of the fixed pattern to the data. May decrease. Furthermore, since the processing for estimating the transmission path state requires delay amount estimation and noise power estimation of the delayed wave, the circuit scale of the equalizer (equalization device) increases and the amount of computation during processing Will increase.

0.5. SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and in an equalization apparatus that performs forward equalization and reverse equalization, it is possible to reduce frequency offset while suppressing the overall circuit scale and calculation amount. It is an object of the present invention to provide an equalization apparatus and an equalization method that can suppress degradation of equalization performance caused by the equalization performance.

  The equalization apparatus of the present invention uses the synchronization word of the current frame to perform forward equalization that performs training and tracking over time, and uses the synchronization word of the next frame to train backward in time. A decision feedback type equalization apparatus that performs delay equalization processing by reverse direction equalization that performs tracking, an RSSI measurement unit that measures an RSSI value of a received signal, and an RSSI that is measured by the RSSI measurement unit RSSI minimum position determination means for determining the minimum position of the RSSI value in each of the synchronization word section of the current frame and the synchronization word section of the next frame based on the value, and outputting RSSI minimum position information indicating the determination result; RSS that compares the RSSI value measured by the RSSI measuring means with a predetermined threshold and outputs RSSI threshold comparison information indicating the comparison result Comparison means, forward frequency offset estimation value obtained by the forward equalization, reverse frequency offset estimation value obtained by the backward equalization, RSSI minimum position information output from the RSSI minimum position determination means And, based on the RSSI threshold comparison information output from the RSSI comparison means, a frequency offset estimation value selection means for selecting and outputting the frequency offset estimation value of the current frame, and an output from the frequency offset estimation value selection means Frequency offset compensation means for calculating the frequency offset compensation amount of the next frame based on the estimated frequency offset value of the current frame and the frequency offset compensation amount of the current frame obtained from the received signal. Take the configuration.

  The equalization method of the present invention includes forward equalization that performs training and tracking over time using the synchronization word of the current frame, and training backwards using the synchronization word of the next frame. An equalization method applied to a decision feedback equalizer that performs delay equalization processing by backward equalization for tracking, an RSSI measurement step of measuring an RSSI value of a received signal, and the RSSI measurement Based on the RSSI value measured in the process, the minimum position of the RSSI value in each of the synchronization word section of the current frame and the synchronization word section of the next frame is determined, and RSSI minimum position information indicating the determination result is output. An RSSI threshold comparison that compares the minimum position determination step and the RSSI value measured in the RSSI measurement step with a predetermined threshold and indicates a comparison result Obtained in the RSSI comparison step, the forward frequency offset estimation value obtained by the forward equalization, the reverse frequency offset estimation value obtained by the backward equalization, and the RSSI minimum position determination step. A frequency offset estimation value selection step of selecting and outputting a frequency offset estimation value of the current frame based on the RSSI minimum position information and the RSSI threshold comparison information obtained in the RSSI comparison step; and the frequency offset estimation Frequency offset compensation for calculating the frequency offset compensation amount of the next frame based on the frequency offset estimation value of the current frame selected in the value selection step and the frequency offset compensation amount of the current frame obtained from the received signal Process.

  According to the present invention, frequency offset compensation is performed using a frequency offset estimated value estimated to be more correct among frequency offset estimated values obtained from two types of training results during forward equalization and backward equalization. As a result, the frequency offset can be compensated accurately even in an environment where there is intersymbol interference, and the degradation of equalization performance due to the frequency offset is suppressed while suppressing the overall circuit scale and the calculation amount. Can do.

The block diagram which shows the structure of the radio | wireless receiver which concerns on one embodiment of this invention The figure which shows the structure of the equalization apparatus applied to one embodiment of this invention The figure which shows the flame | frame structure which concerns on one embodiment of this invention Diagram for explaining general frame structure and equalization processing Explanatory drawing which calculates | requires a frequency offset estimated value from the training result of a reverse direction in the 1st frequency offset compensation method in this Embodiment. Explanatory drawing which calculates | requires a frequency offset estimated value from the training result of a forward direction in the 1st frequency offset compensation method in this Embodiment. Explanatory drawing which shows the 2nd frequency offset compensation method in this Embodiment. The flowchart which shows the 3rd frequency offset compensation method in this Embodiment. The flowchart which shows the 4th frequency offset compensation method in this Embodiment. Explanatory drawing which shows the 5th frequency offset compensation method in this Embodiment. Explanatory drawing which shows the 6th frequency offset compensation method in this Embodiment. Block diagram showing a seventh frequency offset compensation method in the present embodiment

1. Overview 1.1. Outline of an embodiment of the present invention An equalization apparatus according to an embodiment of the present invention is an equalization apparatus that performs delay equalization by forward equalization and reverse equalization, and at the time of forward equalization. The frequency offset compensation is performed using the frequency offset estimated value estimated to be more correct among the frequency offset estimated values obtained from two kinds of training results at the time of reverse equalization. Thereby, degradation of equalization performance due to frequency offset can be suppressed. Specifically, frequency offset compensation is performed by the following method.

(1) In two sync word sections (known symbol sections) before and after the same data section, forward training is performed using the sync word section of the current frame, and reverse training is performed using the sync word section of the next frame. .
(2) For each of the forward training and the backward training, after completion of the training, a complex correlation operation is performed between the data in the synchronization word section and the replica of the synchronization word to estimate the frequency offset.
(3) Further calculation from either or both of the two frequency offset estimation values obtained in (2) above, based on the symbol position where RSSI (Received Signal Strength Indicator) is minimized and the RSSI value at that time. Frequency offset compensation is performed using the obtained value.

  Hereinafter, an embodiment of an equalization apparatus according to the present invention will be described in detail with reference to the drawings.

2. Embodiment 2.1. Configuration of Radio Reception Device According to One Embodiment FIG. 1 is a block diagram showing a configuration of a radio reception device according to an embodiment of the present invention. In FIG. 1, a radio receiving apparatus 100 includes a frequency offset compensation unit 101, a received signal buffer 102, a forward equalization processing unit 103, a reverse equalization processing unit 104, an RSSI measurement unit 105, and an RSSI minimum position. The determination unit 106, the RSSI comparison unit 107, the frequency offset estimated value selection unit 108, a multiplier 109, an adder 110, and a delay circuit (T) 111 are mainly configured.

  The forward equalization processing unit 103 includes a training unit 103a, a tracking unit 103b, and a frequency offset estimation unit 103c. The backward equalization processing unit 104 has the same configuration as the forward equalization processing unit 103, and includes a training unit 104a, a tracking unit 104b, and a frequency offset estimation unit 104c.

  The frequency offset compensation unit 101 performs frequency offset compensation on the received signal based on the frequency offset compensation amount output from the frequency offset estimated value selection unit 108.

  The reception signal buffer 102 receives and temporarily stores the reception signal after frequency offset compensation output from the frequency offset compensation unit 101, and forwards the forward data and the backward data in accordance with the equalization processing speed. Output to the direction equalization processing unit 103 and the reverse direction equalization processing unit 104.

  In the forward equalization processing unit 103, the training unit 103a performs training by inputting the forward direction synchronous word replica and the forward direction data output from the received signal buffer 102, and the tap coefficient initial value is determined as the tracking unit 103b. And the synchronized word (known symbol) after training is output to the frequency offset estimator 103c. The tracking unit 103b performs tracking based on the forward data output from the reception buffer 102 and the tap coefficient initial value output from the training unit 103a, and outputs the generated forward equalization result to the outside. The frequency offset estimation unit 103c estimates a frequency offset based on the forward synchronization word replica and the post-training synchronization word output from the training unit 103a, and uses the forward frequency offset estimation value as the frequency offset estimation value selection unit 108. Output to.

  In the reverse equalization processing unit 104, the training unit 104a inputs the reverse direction synchronous word replica and the reverse direction data output from the reception signal buffer 102 to perform training, and the tap coefficient initial value is determined as the tracking unit 104b. And the synchronized word after training is output to the frequency offset estimator 104c. The tracking unit 104b performs tracking based on the backward data output from the reception buffer 102 and the tap coefficient initial value output from the training unit 104a, and outputs the generated backward equalization result to the outside. The frequency offset estimation unit 104c estimates the frequency offset based on the backward synchronization word replica and the training synchronization word output from the training unit 104a, and the backward frequency offset estimation value is used as the frequency offset estimation value selection unit 108. Output to.

  The RSSI measurement unit 105 measures the RSSI (reception signal strength) of the received signal, and outputs the measured RSSI value to the RSSI minimum position determination unit 106 and the RSSI comparison unit 107.

  The RSSI minimum position determination unit 106 receives the RSSI value measured by the RSSI measurement unit 105 and determines the position where the RSSI is minimum in each of the synchronization word period (known symbol period) of the current frame and the next frame, The RSSI minimum position information indicating the determination result is output to the frequency offset estimated value selection unit 108.

  The RSSI comparison unit 107 inputs the RSSI value measured by the RSSI measurement unit 105, compares the input RSSI value with a predetermined threshold value, and displays RSSI threshold comparison information indicating the comparison result as a frequency offset estimated value selection unit. To 108. The predetermined threshold is an RSSI threshold for compensating the frequency offset, and is a limit RSSI value at which it is determined that the accuracy of the estimated frequency offset is poor.

  The frequency offset estimated value selection unit 108 includes a reverse frequency offset estimated value output from the reverse equalization processing unit 104, a forward frequency offset estimated value output from the forward equalization processing unit 103, and an RSSI minimum position. The RSSI minimum position information output from the determination unit 106 and the RSSI threshold comparison information output from the RSSI comparison unit 107 are input, and the optimum frequency offset estimation value is selected and output as the frequency offset estimation value of the current frame. To do.

  Specifically, (1) First, the frequency offset estimated value selection unit 108 acquires the RSSI minimum position of the synchronization word section of the current frame based on the RSSI minimum position information output from the RSSI minimum position determination unit 106. The RSSI threshold value comparison information at the RSSI minimum position is obtained. (2) Next, the frequency offset estimated value selection unit 108 acquires the RSSI minimum position of the synchronization word section of the next frame from the RSSI minimum position information, and obtains RSSI threshold comparison information at the RSSI minimum position.

  (3-1) Next, the frequency offset estimated value selection unit 108 performs the RSSI threshold comparison information at the RSSI minimum position in the synchronization word section of the current frame obtained in (1) and the next frame obtained in (2). Of the RSSI threshold comparison information at the RSSI minimum position in the synchronization word section, if any RSSI value is less than the threshold, the following processing is performed. That is, when the RSSI minimum value in the synchronization word section of the current frame is less than the threshold, the frequency offset estimation value from the synchronization word of the next frame is set as the frequency offset estimation value of the current frame, and the RSSI of the synchronization word section of the next frame is set. When the minimum value is less than the threshold value, the frequency offset estimated value from the synchronization word of the current frame is set as the frequency offset estimated value of the current frame.

(3-2) The frequency offset estimated value selection unit 108 includes the RSSI threshold comparison information at the RSSI minimum position in the synchronization word section of the current frame obtained in (1), and the synchronization word of the next frame obtained in (2). In the RSSI threshold comparison information at the RSSI minimum position in the section, when both RSSI values are equal to or greater than the threshold, the following processing is performed.

  That is, if both RSSI minimum values in the synchronization word section of the current frame and the next frame are equal to or greater than the threshold value, the average value of the frequency offset estimation values obtained in each of the two synchronization word sections of the current frame and the next frame is calculated. This is the estimated frequency offset of the frame.

(3-3) The frequency offset estimated value selection unit 108 includes the RSSI threshold comparison information at the RSSI minimum position in the synchronization word section of the current frame obtained in (1), and the synchronization word of the next frame obtained in (2). Of the RSSI threshold comparison information at the RSSI minimum position in the section, when both RSSI values are less than the threshold, the following processing is performed.

  That is, when both RSSI minimum values of two synchronization word sections sandwiching the data section are less than the threshold value, the frequency offset estimated value estimated in the previous frame is set as the frequency offset estimated value of the current frame. Alternatively, the estimated frequency offset value of the current frame is set to zero.

  Further, when the frequency offset estimated value obtained as described above is equal to or greater than a predetermined estimated value threshold, the frequency offset estimated value selecting unit 108 uses the frequency offset estimated value estimated in the previous frame as the frequency of the current frame. The estimated offset value. Alternatively, the estimated frequency offset value of the current frame is set to zero.

  Multiplier 109 multiplies the frequency offset estimation value of the current frame output from frequency offset estimation value selection section 108 by a forgetting factor and outputs the result. The adder 110 adds the value output from the multiplier 109 and the frequency offset compensation amount of the current frame, and outputs the frequency offset compensation amount of the next frame as the addition result. The delay circuit 111 holds the frequency offset compensation amount of the next frame output from the adder 110 for one frame time before outputting. As a result, the output of the delay circuit 111 becomes the frequency offset compensation amount of the current frame. The frequency offset compensation amount of the current frame output from the delay circuit 111 is input to the adder 110 and the frequency offset compensation unit 101.

2.2. Preconditions of an embodiment of the present invention 2.2.1. Configuration of Equalizer of One Embodiment Before describing a specific example of a frequency offset compensation method by the equalizer of this embodiment, preconditions for realizing this embodiment will be described. FIG. 2 is a diagram showing a configuration of an equalization apparatus applied to one embodiment of the present invention. As shown in FIG. 2, the equalization apparatus 200 is configured as a decision feedback equalizer (DFE), and includes an FF (feed forward) tap unit 201, an FB (feedback) tap unit 202, and data determination. A unit 203, an error estimation unit 204, a tap coefficient update unit 205, and a changeover switch 206 are provided.

  The FF tap unit 201 receives the received signal and synthesizes current or future data as viewed from the rightmost tap (center tap) of the FF tap unit 201. Further, the FB tap unit 202 inputs a determination value of the soft determination result output from the data determination unit 203 described later, and combines past data as viewed from the center tap. However, when setting an initial value, the FB tap unit 202 inputs a training signal (synchronization word) that is a signal sequence of known symbols and is used to check the line state during training.

  The data determination unit 203 receives the addition result of the output signal of the FF tap unit 201 and the output signal of the FB tap unit 202, and estimates a transmission symbol. The estimation result of the transmission symbol is output from the data determination unit 203 as a hard decision result (equalized signal), and is output to the FB tap unit 202 and the error estimation unit 204 as a soft decision result.

  The error estimation unit 204 is the difference between the addition result of the output signal of the FF tap unit 201 and the output signal of the FB tap unit 202 and the transmission symbol estimation result (soft decision result) output from the data determination unit 203, that is, The error is estimated and output to the tap coefficient updating unit 205. However, when the equalization apparatus 200 sets an initial value, the training signal (synchronization word) is input to the error estimation unit 204 by switching the changeover switch 206, and the training signal, the output signal of the FF tap unit 201, and the FB A difference from the addition result of the output signal of the tap unit 202 is estimated as an error.

  The tap coefficient update unit 205 uses the error output from the error estimation unit 204, the number of taps (FF tap number and FB tap number) output from the parameter set selection unit (not shown), and the forgetting coefficient. The tap coefficient is updated, and the updated tap coefficient is output to the FB tap unit 202 and the FF tap unit 201.

  The changeover switch 206 appropriately switches between the soft decision result output from the data determination unit 203 and the training signal, and outputs the switched soft decision result or training signal to the FB tap unit 202 and the error estimation unit 204. It is a switch for. Further, F of the tap (T / F) shown in FIG. 2 is a fractional number, and F = 1 for symbol interval equalization, and F is an arbitrary integer for fractional interval equalization. However, F> 1.

  That is, as shown in FIG. 2, the equalization apparatus 200 according to the present embodiment has a configuration of a decision feedback equalization apparatus (DFE), and an FF tap unit is obtained by training using a synchronization word (known symbol). The tap coefficients of the (FF filter) 201 and the FB tap unit (FB filter) 202 are brought close to the inverse characteristics of the channel frequency characteristics. Then, an equalization result (equalization signal) of the synchronization word is obtained according to the training result. In addition, since the inter-code interference is removed (that is, equalized) in the soft decision value of the synchronization word obtained by training, it is possible to estimate the frequency offset amount with high accuracy from this soft decision value. it can.

2.2.2. Equalized Signal Frame Configuration FIG. 3 is a diagram showing a frame configuration of the equalized signal according to an embodiment of the present invention, and the right direction on the horizontal axis is the direction in which time passes. In the frame configuration shown in FIG. 3, a code string of a synchronization word (known symbol) is arranged at the head of the frame, and a code string of data is arranged following the code string of the synchronization word. In such a frame configuration, when performing forward equalization processing, training is performed in the forward direction (along the time axis) from the beginning to the rear end using the code string of the synchronization word of the current frame, Tracking is performed in the forward direction for the code string in the data section of the frame.

  In addition, when performing reverse equalization processing, training is performed in the reverse direction from the rear end toward the top using the code string of the synchronization word of the next frame (back in the time axis), and the data section of the current frame The code string is tracked in the reverse direction. Thereby, two equalization results of the forward equalization result and the reverse equalization result can be obtained with the code string in the same data section. Then, the forward equalization result is selected as an equalization result (equalization signal) after the RSSI minimum position and the reverse equalization result is output from the equalization apparatus before the RSSI minimum position.

  That is, as shown in FIG. 3, when a synchronization word (known symbol) is placed at the beginning of a frame and forward equalization is performed, training is performed using the synchronization word of the current frame, and the backward movement of the current frame is performed. Tracking. When performing reverse equalization, training is performed using the synchronization word (known symbol) of the next frame, and tracking is performed toward the front of the current frame. Since two training results (equalization results) are obtained in this way, even if the reception state of the synchronization word section (known symbol section) of the current frame is poor and the accuracy of forward training is low, the synchronization of the next frame is performed. Since there is a possibility that the accuracy of backward training using words (known symbols) may be good, a good equalization signal (equalization result) can be obtained as a result.

2.2.3. General Frame Configuration and Equalization Processing FIG. 4 is a diagram for explaining a general frame configuration and equalization processing, and the right direction on the horizontal axis is the direction in which time passes. As shown in FIG. 4, synchronization words (known symbols) are arranged at positions other than the beginning and end of the frame. In general, the synchronization word is often arranged at the center position of the frame. Then, forward equalization is performed from the synchronization word toward the end of the frame. Further, backward equalization is performed from the synchronization word to the head of the frame. At this time, when the frequency offset amount is estimated by a complex operation of the received synchronization word (known symbol) and a replica of the synchronization word (known symbol), the received signal level (in the known symbol period) of the synchronization word period (known symbol period) by fading or the like. If the RSSI is depressed, the frequency offset cannot be compensated with high accuracy in the frame. Therefore, in the embodiment of the present invention, the frequency offset is compensated by the method described below.

2.2.4. Preconditions for frequency offset compensation For estimation of frequency offset amount and frequency offset compensation, first, the synchronization word soft decision value obtained by training and the complex conjugate of the synchronization word replica are complex multiplied by the complex multiplication of the synchronization word interval. The phase rotation amount is calculated. Then, the amount of phase rotation per sample is obtained, and the received signal is reversely rotated to compensate for the frequency offset.

  Also, for the soft decision value (soft decision result) output from the data decision unit 203 of the equalization apparatus 200 of FIG. 2, the equalization apparatus 200 performs FF tap unit (FF filter) 201 by training using a synchronization word. And the tap coefficient of the FB tap unit (FB filter) 202 can be made close to the inverse characteristic of the propagation path frequency characteristic. However, if there is a frequency offset, the tap coefficient is phase rotated to compensate for the frequency offset.

  Therefore, since the soft decision value after training is in a state where the frequency offset is slightly compensated, the frequency offset estimated value obtained from this soft decision value is slightly smaller than the actual frequency offset amount. . However, this can be considered equivalent to reducing the amount of compensation for the frequency offset per control period by multiplying the estimated frequency offset value obtained from the soft decision value by a forgetting factor for weighting. .

Regarding the RSSI calculation method, the RSSI can be obtained from the power (I ² + Q ² ) of each symbol. On the other hand, in an environment of multipath fading, since the instantaneous RSSI for each symbol of the frame fluctuates drastically, the RSSI is preferably an average RSSI for several symbols before and after the symbol. For example, it is set as the average RSSI in three symbols before and after the symbol.

2.3. First Frequency Offset Compensation Method in the Present Embodiment FIG. 5 is an explanatory diagram for obtaining a frequency offset estimated value from a reverse training result in the first frequency offset compensation method in the present embodiment.

  As shown in FIG. 5, when the RSSI minimum value in the synchronization word section of the current frame is less than the threshold value, the result of the backward training synchronization word section (that is, the synchronization word and the synchronization word replica after the backward training). From this, a frequency offset estimated value is obtained (step S1a). Then, this is selected as a frequency offset estimation value of the current frame (step S2a). Next, the frequency offset compensation amount of the next frame is calculated based on the selected frequency offset estimation value (S2a) of the current frame and the frequency offset compensation amount (S3a) of the current frame (step S4a). Then, the calculated frequency offset compensation amount of the next frame is set as the final frequency offset compensation amount of the next frame (step S5a).

  FIG. 6 is an explanatory diagram for obtaining an estimated frequency offset value from a training result in the forward direction in the first frequency offset compensation method according to the present embodiment.

  As shown in FIG. 6, when the RSSI minimum value in the synchronization word section of the next frame is less than the threshold value, from the result of the synchronization word section of the forward training (that is, the synchronization word and the synchronization word replica after the forward training) From this, a frequency offset estimated value is obtained (step S1b). Then, this is selected as the frequency offset estimation value of the current frame (step S2b). Next, the frequency offset compensation amount of the next frame is calculated based on the selected frequency offset estimation value (S2b) of the current frame and the frequency offset compensation amount (S3b) of the current frame (step S4b). Then, the calculated frequency offset compensation amount of the next frame is set as the final frequency offset compensation amount of the next frame (step S5b).

  That is, in the first frequency offset compensation method in the present embodiment, the forward or backward frequency offset estimation value is obtained from the synchronization word and the synchronization word replica after forward training or backward training. At this time, if the RSSI minimum value in the synchronization word section of the current frame is less than the threshold, the frequency offset estimation value from the synchronization word of the next frame is selected as the frequency offset estimation value of the current frame. Further, when the RSSI minimum value in the synchronization word section of the next frame is less than the threshold value, the frequency offset estimation value from the synchronization word of the current frame is selected as the frequency offset estimation value of the current frame.

  Then, the frequency offset compensation amount of the next frame is calculated based on the selected frequency offset estimation value of the current frame and the frequency offset compensation amount of the current frame, and this is used as the final frequency offset compensation amount.

  According to such a frequency offset compensation method, since it is possible to select a frequency offset amount that seems to be more correct, it is possible to maintain the equalization performance of the equalizer at a high level. That is, in general, when the RSSI value in the synchronization word interval is lower than the threshold value, the accuracy of training using the synchronization word may be reduced, so the accuracy of the frequency offset amount estimated from the training result Is also likely to be low. Therefore, as in this embodiment, the frequency offset is corrected by using the frequency offset estimation value of the synchronization word that holds sufficient RSSI in the synchronization word section, and thus the frequency offset that seems to be more correct. Therefore, it is possible to suppress deterioration of equalization performance of the equalization apparatus.

2.4. Second Frequency Offset Compensation Method in the Present Embodiment FIG. 7 is an explanatory diagram showing a second frequency offset compensation method in the present embodiment. As shown in FIG. 7, first, a frequency offset estimation value in the forward direction is obtained from the result of forward training (that is, from the synchronized word and the synchronized word replica after forward training) (step S1c). Next, from the reverse training result (that is, from the sync word and the sync word replica after the reverse training), a reverse frequency offset estimate is obtained (step S2c).

  At this time, if the RSSI minimum value in the synchronization word section of the current frame and the RSSI minimum value in the synchronization word section of the next frame are both equal to or greater than the threshold value, the frequency offset estimation values obtained in the two synchronization word sections are An average value is obtained (step S3c), and the average value of the frequency offset estimated values is set as the frequency offset estimated value of the current frame (step S4c). Then, the frequency offset compensation amount of the next frame is calculated based on the estimated frequency offset value (S4c) of the current frame and the frequency offset compensation amount (S5c) of the current frame (step S6c). Then, the calculated frequency offset compensation amount of the next frame is set as the final frequency offset compensation amount of the next frame (step S7c).

  That is, in the second frequency offset compensation method according to the present embodiment, the forward frequency offset estimation value and the backward frequency offset estimation value are obtained from the synchronization word and the synchronization word replica after forward training and backward training. ing. At this time, if the RSSI minimum value in the synchronization word section of the current frame and the RSSI minimum value in the synchronization word section of the next frame are both equal to or greater than the threshold value, the frequency offset estimation values obtained in the two synchronization word sections are The average value is the estimated frequency offset value of the current frame. Further, the frequency offset compensation amount of the next frame is calculated from the estimated frequency offset value of the current frame and the frequency offset compensation amount of the current frame.

  According to such a frequency offset compensation method, it is possible to compensate for the frequency offset by estimating a highly accurate frequency offset amount. That is, in order to estimate the amount of frequency offset, the reliability is higher when the synchronization word (known symbol) maintains a sufficient RSSI level. At this time, if the RSSI level of both the synchronization word of the current frame and the synchronization word of the next frame is higher than the threshold value, the frequency offset estimation error due to noise or the like is reduced by taking the average value of the two frequency offset estimation values. Can be made. As a result, good frequency offset correction can be performed, and deterioration of equalization performance of the equalization apparatus can be suppressed.

2.5. Third Frequency Offset Compensation Method in Present Embodiment FIG. 8 is a flowchart showing a third frequency offset compensation method in the present embodiment. In the third frequency offset compensation method, as described in the first frequency offset compensation method, the frequency offset estimation value obtained in the synchronization word section in which the RSSI minimum value is higher than the threshold value, or the second frequency offset compensation method described above. As described in the frequency offset compensation method, when the RSSI minimum value is higher than the threshold value in any synchronization word section, the frequency offset estimated value obtained by the average value of both is used as the frequency offset estimated value foff of the current frame. (Step S11).

  Then, it is determined whether or not the frequency offset estimated value foff of the current frame obtained as described above is higher than a predetermined threshold (step S12). If the estimated frequency offset value foff of the current frame is higher than a predetermined estimated value threshold value (YES in step S12), the estimated frequency offset value of the previous frame is used as the estimated frequency offset value of the current frame (step S12). S13). Then, the frequency offset compensation amount for the next frame is calculated based on the frequency offset estimate value for the current frame (actually, the frequency offset estimate value for the previous frame (S13)) and the frequency offset compensation amount for the current frame (S14). (Step S15). Then, the calculated frequency offset compensation amount of the next frame is determined as the frequency offset compensation amount of the next frame (step S16).

  When the estimated frequency offset value foff of the current frame is lower than the predetermined estimated value threshold (NO in step S12), the estimated frequency offset value (S11) of the current frame obtained in step S11 and the frequency offset compensation of the current frame. Based on the amount (S14), the frequency offset compensation amount of the next frame is calculated (step S15). Then, the calculated frequency offset compensation amount of the next frame is determined as the frequency offset compensation amount of the next frame (step S16).

  That is, in the third frequency offset compensation method according to the present embodiment, the frequency offset estimated value obtained by the first frequency offset compensating method or the second frequency offset compensating method is a predetermined estimated value. If it is greater than or equal to the threshold, the frequency offset estimate estimated in the previous frame is selected as the frequency offset estimate for the current frame, and the frequency offset for the next frame is compensated.

  According to such a frequency offset compensation method, when a large error is included in the frequency offset estimation value due to the influence of noise or the like, the frequency offset of the previous frame is not included in the calculation of the frequency offset compensation amount. A frequency offset compensation amount is calculated using the offset estimation value. Therefore, since an abnormal frequency offset estimation value caused by the influence of noise or the like can be excluded, it is possible to suppress deterioration in equalization performance of the equalization apparatus.

2.6. Fourth Frequency Offset Compensation Method in Present Embodiment FIG. 9 is a flowchart showing a fourth frequency offset compensation method in the present embodiment. In the fourth frequency offset compensation method, as described in the first frequency offset compensation method, the frequency offset estimation value obtained in the synchronization word section in which the RSSI minimum value is higher than the threshold value or the second frequency offset compensation method described above. As described in the frequency offset compensation method, when the RSSI minimum value is higher than the threshold value in any synchronization word section, the frequency offset estimated value obtained by the average value of both is used as the frequency offset estimated value foff of the current frame. (Step S21).

  Then, it is determined whether or not the frequency offset estimated value foff of the current frame obtained as described above is higher than a predetermined estimated value threshold value (step S22). If the estimated frequency offset value foff of the current frame is higher than a predetermined threshold (YES in step S22), the estimated frequency offset value foff of the current frame is set to 0 (step S23). Then, the frequency offset compensation amount of the next frame is calculated based on the estimated frequency offset value (= 0) of the current frame and the frequency offset compensation amount (S24) of the current frame (step S25). Then, the calculated frequency offset compensation amount of the next frame is determined as the frequency offset compensation amount of the next frame (step S26).

  When the estimated frequency offset value foff of the current frame is lower than the predetermined estimated value threshold (NO in step S22), the estimated frequency offset value (S21) of the current frame obtained in step S21 and the frequency offset compensation of the current frame. Based on the amount (S24), the frequency offset compensation amount of the next frame is calculated (step S25). Then, the calculated frequency offset compensation amount of the next frame is determined as the frequency offset compensation amount of the next frame (step S26).

That is, in the fourth frequency offset compensation method according to the present embodiment, the frequency offset estimated value obtained by the first frequency offset compensating method or the second frequency offset compensating method is a predetermined estimated value. If it is equal to or greater than the threshold, the frequency offset estimation value of the current frame is set to 0, and the frequency offset of the next frame is compensated.
Yes.

  According to such a frequency offset compensation method, if a large error is included in the estimated frequency offset value due to noise or the like, the frequency offset of the current frame is not included in the calculation of the frequency offset compensation amount. The frequency offset compensation amount is calculated by setting the offset estimated value to 0. Therefore, since an abnormal frequency offset estimation value caused by the influence of noise or the like can be excluded, it is possible to suppress deterioration in equalization performance of the equalization apparatus.

2.7. Fifth Frequency Offset Compensation Method in the Present Embodiment FIG. 10 is an explanatory diagram showing a fifth frequency offset compensation method in the present embodiment. First, from the forward training results (ie, from the sync word and sync word replica after the forward training), the forward frequency offset estimate is obtained and from the reverse training results (ie, after the reverse training) From the sync word and sync word replica), find the frequency offset estimate in the reverse direction.

  At this time, when the RSSI minimum values of the two synchronization word sections sandwiching the data section are both less than the threshold value, the frequency offset estimated value of the previous frame estimated in the previous frame is set as the frequency offset estimated value of the current frame (step S1d). Based on the estimated frequency offset value (S1d) of the current frame and the frequency offset compensation amount (S2d) of the current frame, the frequency offset compensation amount of the next frame is calculated (S3d). Then, the calculated frequency offset compensation amount of the next frame is set as the final frequency offset compensation amount of the next frame (step S4d).

  That is, according to the fifth frequency offset compensation method in the present embodiment, when both RSSI minimum values of two synchronization word sections sandwiching the data section are less than the threshold, the frequency offset estimation estimated in the previous frame is performed. Using the value as the frequency offset estimation value of the current frame, the frequency offset of the next frame is compensated.

  According to such a frequency offset compensation method, when both RSSIs of the synchronization word sections on both sides of the data section are less than the threshold value, the frequency offset estimation value of any synchronization word section is low in reliability. Is not included in the frequency offset compensation amount calculation, and the frequency offset compensation amount is calculated using the frequency offset estimation value of the previous frame. Therefore, since the frequency offset estimation value with low reliability is not used, it is possible to suppress deterioration in equalization performance of the equalization apparatus.

2.8. Sixth Frequency Offset Compensation Method in the Present Embodiment FIG. 11 is an explanatory diagram showing a sixth frequency offset compensation method in the present embodiment. First, from the forward training results (ie, from the sync word and sync word replica after the forward training), the forward frequency offset estimate is obtained and from the reverse training results (ie, after the reverse training) From the sync word and sync word replica), find the frequency offset estimate in the reverse direction.

  At this time, if both of the RSSI minimum values of the two synchronization word sections sandwiching the data section are less than the threshold value, the frequency offset estimation value of the current frame is set to 0 (step S1e). Then, the frequency offset compensation amount of the next frame is calculated based on the estimated frequency offset value (S1e) of the current frame and the frequency offset compensation amount (S2e) of the current frame (S3e). Then, the calculated frequency offset compensation amount of the next frame is set as the final frequency offset compensation amount of the next frame (step S4e).

  That is, according to the sixth frequency offset compensation method of the present embodiment, when the RSSI minimum value of two synchronization word sections sandwiching the data section is less than the threshold, the frequency offset estimation value of the current frame is calculated. As 0, the frequency offset of the next frame is compensated.

  According to such a frequency offset compensation method, when both RSSIs of the synchronization word sections on both sides of the data section are less than the threshold, the frequency offset estimation value of any synchronization word section is low in reliability. Without being included in the frequency offset compensation amount calculation, the frequency offset compensation amount is calculated by setting the estimated frequency offset value of the current frame to zero. Therefore, since the frequency offset estimation value with low reliability is not used, it is possible to suppress deterioration in equalization performance of the equalization apparatus.

2.9. Seventh Frequency Offset Compensation Method in the Present Embodiment FIG. 12 is a block diagram showing a seventh frequency offset compensation method in the present embodiment. That is, this figure shows a sequence when the frequency offset compensation amount of the next frame is calculated from the frequency offset estimation value of the current frame and the frequency offset compensation amount.

  That is, in the seventh frequency offset compensation method, as described in the first frequency offset compensation method, the frequency offset estimation value obtained in the synchronization word interval in which the RSSI minimum value is higher than the threshold value, As described in the second frequency offset compensation method, when the RSSI minimum value is higher than the threshold value in any synchronization word section, the frequency offset estimated value obtained by the average value of both is used as the frequency offset estimated value of the current frame. Basically, the frequency offset compensation method is switched according to the operation status of the equalizer. In other words, based on the first frequency offset compensation and the second frequency offset compensation described above, the third frequency offset compensation method described above according to the reception (equalization processing) start / steady (stable) state, The fourth frequency offset compensation method, the fifth frequency offset compensation method, and the sixth frequency offset compensation method are properly used.

  Specifically, as shown in FIG. 12, reception (equalization processing) is started for the frequency offset estimated value A obtained by the first frequency offset compensation method or the second frequency offset compensation method described above. Is multiplied by the forgetting factor k weighted according to the convergence condition until the frequency offset to be originally compensated, and based on the weighted frequency offset estimation value and the frequency offset compensation amount of the current frame, The frequency offset compensation amount B is calculated. The forgetting factor K is 0 ≦ K <1.

  According to such a frequency offset compensation method, for example, a value close to 1 is used as a forgetting factor at the start of reception of wireless communication, and the frequency offset compensation amount can be set up early based on the estimated frequency offset value. Try to raise. However, if the estimated frequency offset value includes a large error due to noise or the like, the correct frequency offset compensation result cannot be obtained, and the error also affects the frequency offset compensation amount for the subsequent frame. Resulting in. In such a case, the influence of the estimation error on the subsequent frame is set by setting the frequency offset estimation value to 0 as in the above-described fourth frequency offset compensation method or the above-described sixth frequency offset compensation method. Can be suppressed.

  In addition, in order to stabilize the frequency offset compensation amount from the error in the estimated frequency offset value due to noise and calculation error of the frequency offset amount in a steady state (a state close to the frequency offset that should be compensated originally) The forgetting factor is a value close to 0. In this case, it takes some time to reach the required frequency offset compensation amount.

  At this time, even when the frequency offset estimation value is low or an abnormal frequency offset estimation value, as in the third frequency offset compensation method or the fifth frequency offset compensation method described above, By using the estimated frequency offset value of the previous frame, it is possible to suppress an increase in the time required to reach the required frequency offset compensation amount without impairing the stability of the equalization performance. In this way, frequency offset compensation can be stabilized.

  That is, in the seventh frequency offset compensation method in the present embodiment, the frequency offset estimated value of the current frame multiplied by the forgetting factor and added to the frequency offset compensation amount of the current frame is used as the frequency offset compensation amount of the next frame. It is said. Therefore, stable frequency offset compensation can be performed by properly using the forgetting factor according to the convergence state from the start of reception (equalization processing) to the frequency offset that should be compensated originally. At this time, since the convergence state up to the correct frequency offset is actually unknown, for example, the forgetting factor is temporarily reduced from 1 depending on the time from the start of reception (equalization process) or the number of equalization processes. The forgetting factor is set to a value close to 0 after a certain time or a certain number of processing times.

  Note that the threshold value in the third frequency offset compensation method or the fourth frequency offset compensation method described above may be a fixed value determined from the design condition or the use condition, or may be determined from the frequency offset estimation value of the previous frame. You may prescribe | regulate as a difference (or change rate). Or it is good also as a difference (or change rate) from the average value of the frequency offset estimated value to a previous frame.

2.10. Effects of this Embodiment As described above, according to this embodiment, in the equalization apparatus that performs delay equalization by forward equalization and reverse equalization, the equalization during the forward equalization and the reverse equalization are performed. Frequency offset compensation is performed using a frequency offset estimated value that is estimated to be more correct among the frequency offset estimated values obtained from two kinds of training results. Therefore, since the frequency offset can be accurately compensated even in an environment where there is intersymbol interference, it is possible to prevent deterioration of equalization performance in the equalization apparatus. Further, according to the present embodiment, it is not necessary to prepare a matched filter for equalization processing or to prepare two sets of fixed patterns, so that the circuit scale and the calculation amount of the entire equalization apparatus are suppressed. be able to.

  That is, when the RSSI minimum value in the synchronization word section of the current frame is less than the threshold, the frequency offset estimation value from the synchronization word of the next frame is selected as the frequency offset estimation value of the current frame, and the synchronization word section of the next frame is selected. When the RSSI minimum value is less than the threshold, the frequency offset estimated value from the synchronization word of the current frame is selected as the frequency offset estimated value of the current frame, and the frequency offset of the next frame is compensated. As a result, frequency offset compensation can be performed using the frequency offset estimation value on the side of the synchronization word section maintaining a sufficient RSSI level, so that degradation of equalization performance of the equalizer can be suppressed. .

  When the RSSI minimum value in the synchronization word period of the current frame and the RSSI minimum value in the synchronization word period of the next frame are both equal to or greater than the threshold value, the average of the frequency offset estimation values obtained in each of the two synchronization word periods The value is selected as the frequency offset estimation value of the current frame to compensate for the frequency offset of the next frame. By taking the average value of the two frequency offset estimated values in this way, it is possible to compensate for the frequency offset by reducing the error of the frequency offset estimated value due to noise or the like. Deterioration can be suppressed.

  If the frequency offset estimated value obtained as described above is equal to or greater than a predetermined estimated value threshold, the frequency offset estimated value estimated in the previous frame is selected as the frequency offset estimated value of the current frame, and the next frame The frequency offset is compensated. As a result, it is possible to compensate for the frequency offset by eliminating the influence of noise, so that it is possible to suppress deterioration in equalization performance of the equalization apparatus.

  Further, when the frequency offset estimated value obtained as described above is equal to or greater than a predetermined estimated value threshold, the frequency offset estimated value of the current frame is set to 0 and the frequency offset of the next frame is compensated. As a result, it is possible to compensate for the frequency offset by eliminating the influence of noise, so that it is possible to suppress deterioration in equalization performance of the equalization apparatus.

  When the RSSI minimum values of the two synchronization word sections sandwiching the data section are both less than the threshold value, the frequency offset estimated value estimated in the previous frame is set as the current frame frequency offset estimated value, and the frequency offset of the next frame is set. Is compensated. That is, when the reliability of the frequency offset estimation value in the two synchronization word intervals is low, the equalization performance of the equalization apparatus is obtained by performing frequency offset compensation using the frequency offset estimation value in the synchronization word interval of the previous frame. Can be prevented.

  When the RSSI minimum values of the two synchronization word sections sandwiching the data section are both less than the threshold value, the frequency offset estimated value of the current frame is set to 0 and the frequency offset of the next frame is compensated. In other words, when the reliability of the frequency offset estimation values in the two synchronization word sections is low, it is possible to compensate for the frequency offset without including these frequency offset estimation values, thereby suppressing degradation of the equalization performance of the equalizer. can do.

  Also, stable frequency offset compensation can be performed by performing frequency offset compensation using the frequency offset estimated value obtained as described above multiplied by the forgetting factor as the frequency offset estimated value of the current frame.

  The equalization apparatus and equalization method according to the present invention can be applied to, for example, a wireless communication apparatus.

DESCRIPTION OF SYMBOLS 100 Radio | wireless receiver 101 Frequency offset compensation part 102 Reception signal buffer 103 Forward direction equalization process part 104 Reverse direction equalization process part 105 RSSI measurement part 106 RSSI minimum position determination part 107 RSSI comparison part 108 Frequency offset estimated value selection part 109 Multiplication 110 Adder 111 Delay circuit (T)
201 FF tap section 202 FB tap section 203 Data determination section 204 Error estimation section 205 Tap coefficient update section 206 Changeover switch

Claims (9)

Forward equalization with training and tracking over time using the sync word of the current frame, and reverse equalization with training and tracking going back in time using the sync word of the next frame A decision feedback type equalization apparatus that performs delay equalization processing by
RSSI measuring means for measuring the RSSI value of the received signal;
Based on the RSSI value measured by the RSSI measuring means, the minimum position of the RSSI value in each of the synchronization word section of the current frame and the synchronization word section of the next frame is determined, and RSSI minimum position information indicating the determination result is output. RSSI minimum position determining means to perform,
An RSSI comparing means for comparing the RSSI value measured by the RSSI measuring means with a predetermined threshold and outputting RSSI threshold comparison information indicating a comparison result;
A forward frequency offset estimate obtained by the forward equalization, a reverse frequency offset estimate obtained by the backward equalization, the RSSI minimum position information output from the RSSI minimum position determination means, and Frequency offset estimation value selection means for selecting and outputting the frequency offset estimation value of the current frame based on the RSSI threshold comparison information output from the RSSI comparison means;
A frequency offset compensation amount for the next frame is calculated based on the frequency offset estimate value for the current frame output from the frequency offset estimate value selection means and the frequency offset compensation amount for the current frame obtained from the received signal. An equalization apparatus comprising: frequency offset compensation means for performing The frequency offset estimated value selection means includes
If the RSSI minimum value in the synchronization word section of the current frame is less than a threshold, select a frequency offset estimate from the synchronization word of the next frame as the frequency offset estimate of the current frame;
The frequency offset estimation value from the synchronization word of the current frame is selected as the frequency offset estimation value of the current frame when the RSSI minimum value in the synchronization word section of the next frame is less than a threshold value. Item 4. The equalizer according to Item 1. The frequency offset estimated value selection means includes
When the RSSI minimum value in the synchronization word period of the current frame and the RSSI minimum value in the synchronization word period of the next frame are both equal to or greater than a threshold value, each of the synchronization word period of the current frame and the synchronization word period of the next frame 3. The equalization apparatus according to claim 1, wherein an average value of the frequency offset estimation values obtained in step 1 is selected as the frequency offset estimation value of the current frame. The frequency offset estimated value selection means includes
When the frequency offset estimated value obtained in the synchronization word section is equal to or greater than a predetermined estimated value threshold, the frequency offset estimated value estimated in the previous frame is selected as the frequency offset estimated value of the current frame. The equalization apparatus according to any one of claims 1 to 3. The frequency offset estimated value selection means includes
The frequency offset estimation value of the current frame is set to 0 when the frequency offset estimation value obtained in the synchronization word interval is equal to or greater than a predetermined estimation value threshold. The equalization apparatus in any one. The frequency offset estimated value selection means includes
If the RSSI minimum value in the synchronization word section of the current frame and the RSSI minimum value in the synchronization word section of the next frame are both less than the threshold, the frequency offset estimation value estimated in the previous frame is used as the frequency offset estimation value in the current frame. The equalizer according to claim 1, wherein the equalizer is selected as a value. The frequency offset estimated value selection means includes
When the RSSI minimum value in the synchronization word section of the current frame and the RSSI minimum value in the synchronization word section of the next frame are both less than a threshold value, the frequency offset estimation value of the current frame is set to 0. The equalization apparatus according to claim 1.   The frequency offset compensation means is a forgetting factor k (where 0 ≦ k < 1) is changed, and the frequency offset compensation amount of the next frame is calculated based on the value obtained by multiplying the forgetting factor and the frequency offset compensation amount of the current frame obtained from the received signal. The equalization apparatus in any one of Claims 1-7. Forward equalization with training and tracking over time using the sync word of the current frame, and reverse equalization with training and tracking going back in time using the sync word of the next frame An equalization method applied to a decision feedback equalizer that performs delay equalization processing with
An RSSI measurement step of measuring the RSSI value of the received signal;
Based on the RSSI value measured in the RSSI measurement step, the minimum position of the RSSI value in each of the synchronization word section of the current frame and the synchronization word section of the next frame is determined, and RSSI minimum position information indicating a determination result is determined. An RSSI minimum position determination step to output;
An RSSI comparison step of comparing the RSSI value measured in the RSSI measurement step with a predetermined threshold and outputting RSSI threshold comparison information indicating a comparison result;
Forward frequency offset estimate obtained by the forward equalization, reverse frequency offset estimate obtained by the reverse equalization, RSSI minimum position information obtained in the RSSI minimum position determination step, and Based on the RSSI threshold comparison information obtained in the RSSI comparison step, a frequency offset estimation value selection step of selecting and outputting the frequency offset estimation value of the current frame;
A frequency offset compensation amount for the next frame is calculated based on the frequency offset estimate value for the current frame selected in the frequency offset estimate selection step and the frequency offset compensation amount for the current frame obtained from the received signal. A frequency offset compensation step.

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