JP2004112218A - Nonlinear compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adaptively compensate nonlinear characteristics even when the amount of level change of an output average power in a time base direction in a device to be compensated becomes large. <P>SOLUTION: A signal processing section captures the input/output signals of the device to be compensated, detects the time difference and phase difference of both signals, and obtains a distortion component from the amplitude and phase errors of both signals while matching the synchronization and the phases. A distortion correction section D sequentially selects the amount of compensation corresponding to the amplitude from the amounts of compensation which are registered in a compensation table in an initial stage and adaptively updated, adds the amount of the compensation to the input signal to compensate the distortion component and outputs the resultant signal to the device to be compensated. Through this configuration, a transient characteristic detection section H obtains the transient characteristic of the device to be compensated, and the distortion correction section D uses an adaptive filter I to give the inverse characteristic of the transient characteristic to the input amplitude and performs bank switching of the compensation table. Thus, the compensator can adaptively compensate the nonlinear characteristic by following a change in the nonlinear characteristic due to variations in the operating point of the device to be compensated. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-linear compensator which is used in transmission devices such as medium-wave, short-wave, terrestrial / satellite / cable television, and compensates for non-linear characteristics generated in an amplifier of a transmission device, for example.
[0002]
[Prior art]
At present, in analog television broadcasting, nonlinear compensation is performed by a pre-compensator having characteristics opposite to those produced by an amplifier. In particular, since the non-linear characteristics of the amplifier change depending on the operating temperature of the amplifier, the compensation characteristics are switched according to the operating conditions of the amplifier.
[0003]
By the way, in the case of analog television broadcasting, the signal peak value is almost constant because it is defined by the synchronization peak value. Further, since the vicinity of the clip value is synchronous, there is no need to consider phase distortion occurring near the clip level, and only the synchronization amplitude needs to be corrected so that the synchronization length is the same. Further, since the peak factor (peak value / average value) is relatively small, the linearity of the low-level signal region is not so much required.
[0004]
On the other hand, in next-generation digital television broadcasting, the adoption of the OFDM (orthogonal frequency division multiplexing) system has been decided, and various developments have been made for practical use. Here, in the OFDM system, since the peak factor is extremely large compared to the analog system due to the nature of the OFDM signal, linearity from a low level to a high level is required. In addition, since the phase of each carrier is the point of information transmission, even a slight disturbance in phase rotation leads to deterioration of characteristics. For this reason, accurate compensation for the non-linear characteristics and phase rotation is required.
[0005]
Based on the above requirements, conventionally, when the average power of the transmission signal fluctuates, attention is paid to the fact that the operating point of the amplifier fluctuates and the nonlinear characteristic changes, and by sequentially updating the nonlinear characteristic, this temporal direction is updated. There has been proposed a nonlinear amplifier adapted to a change in nonlinear characteristics (for example, see Patent Document 1).
[0006]
This nonlinear amplifier can exhibit sufficient performance in an environment in which the average power of a transmission signal changes relatively slowly. However, as the level change amount of the average power in the time axis direction increases, the tracking of the nonlinear compensation by the successive update cannot be performed in time, and the optimal compensation cannot be performed.
[0007]
[Patent Document 1]
JP-A-2001-168774.
[0008]
[Problems to be solved by the invention]
As described above, in digital signal transmission such as OFDM, accurate compensation of nonlinear characteristics is required. However, in a conventional nonlinear compensator, the average output power of the compensated electronic device in the time axis direction is required. However, as the level change amount increases, there is a problem that the tracking of the nonlinear compensation by the successive update cannot be performed in time, and the optimum compensation cannot be performed.
The present invention has been made in view of the above circumstances, and provides a non-linear compensator capable of adaptively compensating for non-linear characteristics even when the level change amount in the time axis direction of the output average power in the compensated electronic device is large. The purpose is to provide.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a nonlinear compensator according to the present invention has the following characteristic configuration.
(1) In a non-linear compensator for compensating for non-linear characteristics of a compensated electronic device that handles a transmission signal,
After capturing the input signal and output signal of the compensated electronic device, suitably demodulating and matching the same signal format, the time difference and the phase difference between the two signals were detected by taking the correlation between the two signals, and were detected. A signal processing unit that performs synchronization and phase adjustment of both signals based on the time difference and the phase difference, and an amplitude error and a phase error of an input signal and an output signal of the compensated electronic device whose synchronization and phase are adjusted by the signal processing unit. A distortion detector that detects a distortion component, a transient characteristic detector that compares an input signal and an output signal of the compensated electronic device to detect a transient characteristic of the compensated electronic device, and a transient characteristic detector that detects the transient characteristic. An adaptive filter for applying an inverse characteristic of the transient characteristic to an input signal of the compensated electronic device, a distortion component detected in advance by the distortion detection unit, and a non-linear distortion compensation for compensating the distortion component Are stored in a plurality of memory banks according to the magnitude of the distortion component, and the memory banks are selectively switched according to the output level of the adaptive filter to read the distortion compensation amount stored in the selected memory bank. And a distortion correction unit for compensating an input signal of the compensated electronic device with the distortion compensation amount.
[0010]
(2) In a non-linear compensator for compensating for non-linear characteristics of a compensated electronic device handling a transmission signal, an input signal and an output signal of the compensated electronic device are fetched, appropriately demodulated, and adjusted to the same signal format. A signal processing unit that detects a time difference and a phase difference between the two signals by calculating a correlation between the two signals, and performs synchronization and phase adjustment of the two signals based on the detected time difference and the phase difference. A distortion detection unit that detects, as a distortion component, an amplitude error and a phase error of an input signal and an output signal of the compensated electronic device whose phases are matched, and an average power detection unit that determines an average power of the input signal of the compensated electronic device. And a distortion component detected in advance by the distortion detection unit and a nonlinear distortion compensation amount for compensating the distortion component are stored in a plurality of memory banks for each average power, and The memory bank is selectively switched in accordance with the detection level of the equalizing power detection unit, a distortion compensation amount stored in the selected memory bank is read, and the distortion compensation amount compensates an input signal of the compensated electronic device with the distortion compensation amount. And a correction unit.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows the configuration of an OFDM transmission apparatus to which the present invention is applied. An OFDM signal is output from a modulator 1 and power is amplified by an RF amplifier 3 via a nonlinear compensator 2 according to the present invention. And outputs it as a transmission signal. The output of the RF amplifier 3 is partially distributed by a distributor (directional coupler) 4 and supplied to the nonlinear compensator 2.
[0012]
(1st Embodiment)
FIG. 2 is a block diagram showing the configuration of the first embodiment when the present invention is applied to the nonlinear compensator 2. In FIG. 2, an analog RF input terminal 11 is supplied with an RF signal from the modulator 1. The RF signal supplied to this terminal 11 is converted by a first down converter (D / C1) 12 into an IF signal based on a local signal from a local oscillator 13, and is given a predetermined amplitude by an AGC (automatic gain control) circuit 14. Stabilized to a level. The output of the AGC circuit 14 is discriminated by a squelch (SQ) circuit 15 to determine the presence or absence of a signal, is converted to a digital IF signal by a first analog-to-digital converter (ADC1) 16, and then is converted to a first quadrature demodulation circuit (Q- DEM1) 17 performs quadrature demodulation to obtain complex digital baseband signals I1 and Q1. The I1 and Q1 signals obtained here are down-sampled by FIR filters (or LPFs) 18 and 19 as necessary. Thus, the input demodulation unit A is configured.
[0013]
On the other hand, an analog PA input terminal 21 is supplied with an RF signal output from the RF amplifier 3. The RF signal supplied to the terminal 21 is converted to an IF signal by a second down converter (D / C2) 22 based on the local signal whose phase has been adjusted by the phase shifter 23. This IF signal is stabilized by the AGC circuit 24 to a predetermined amplitude level. The output of the AGC circuit 24 is discriminated by a squelch (SQ) circuit 25 to determine the presence or absence of a signal, and is converted to a digital IF signal by a second analog-to-digital converter (ADC2) 26. DEM2) 27 performs quadrature demodulation to obtain complex digital baseband signals I2 and Q2. The I2 and Q2 signals obtained here are down-sampled by FIR filters (or LPFs) 28 and 29 as necessary. As described above, the output demodulation unit B is formed.
[0014]
The digital baseband signals I1 and Q1 output from the input demodulation unit A are supplied to a delay adjustment unit C and a distortion correction unit D. Here, the delay adjustment unit C includes RAM delay units 31 and 32 for respectively delaying the digital baseband signals I1 and Q1 from the input demodulation unit A for a predetermined time. The digital baseband signals I3 and Q3 delayed by the RAM delay units 31 and 32 are supplied to a delay detection unit E and a distortion detection unit F together with the digital baseband signals I2 and Q2 output from the output demodulation unit B. .
[0015]
In the delay detector E, the baseband signals I3 and Q3 from the delay adjuster C and the baseband signals I2 and Q2 from the output demodulator B are supplied to the complex multiplier 41. The complex multiplier 41 obtains a REAL (real part) signal and an IMAG (imaginary part) signal by complexly multiplying both input signals to obtain a complex correlation between them. The obtained REAL signal and IMAG signal are supplied to a REAL integrator 42 and an IMAG integrator 43, respectively.
[0016]
The integrators 42 and 43 remove the influence of noise and the like by performing, for example, section integration for obtaining the cumulative value / cumulative time. The outputs of the integrators 42 and 43 are supplied to a Pythagoras converter 44, which converts the Cartesian coordinates into polar coordinates. Among the outputs of the Pythagorean converter 44, the amplitude value is supplied to the correlation peak detector 45. The correlation peak detector 45 determines a peak position in a correlation output between two input signals. The peak position information detected by the correlation peak detector 45 is supplied to the delay / angle detector 46 together with the angle value (phase value) output from the Pythagoras converter 44.
[0017]
The delay / angle detector 46 calculates a time difference and a phase difference (angle) between the digital baseband signals I3 and Q3 on the amplifier input side and the digital baseband signals I2 and Q2 on the amplifier output side from the peak position information. The obtained time difference is supplied to a delay controller 47, and the phase difference is supplied to a phase controller 48. The delay controller 47 sets the delay amounts of the RAM delay units 31 and 32 of the delay adjustment unit C according to the given time difference, performs coarse synchronization, and furthermore, sets the coefficient values of the FIR filters 28 and 29 of the output demodulation unit B. For precise synchronization. As a result, the digital baseband signals I3 and Q3 on the amplifier input side are synchronized with the digital baseband signals I2 and Q2 on the amplifier output side. Further, the phase controller 48 adjusts the phase shift amount of the phase shifter 23 of the output demodulation unit B according to the given phase difference. Thus, the phases of the amplifier input side and the amplifier output side are matched.
[0018]
Note that the delay controller 47 and the phase controller 48 cannot obtain a time difference and a phase difference when no signal component is included in the digital baseband signal, so that the control becomes impossible and a malfunction may occur. . Therefore, the presence or absence of a signal component is determined from the outputs of the squelch circuits 15 and 25 provided in the input demodulation unit A and the output demodulation unit B, and control is performed only when there is a signal component.
[0019]
The distortion detecting unit F converts the digital baseband signals I3 and Q3 from the delay adjusting unit C and the digital baseband signals I2 and Q2 from the output demodulating unit B into Cartesian coordinates (I3 and Q3) by the Pythagoras converters 51 and 52, respectively. , (I2, Q2) are converted into polar coordinates (R3, θ3) and (R2, θ2), and the error calculator 53 obtains the amplitude error ΔR and the phase error Δθ of both.
ΔR = R3-R2
Δθ = θ3-θ2
The obtained amplitude error ΔR and phase error Δθ are supplied to the distortion correction unit D.
[0020]
In the distortion correction unit D, the amplitude error ΔR and the phase error Δθ from the distortion detection unit F are each section-integrated by the integrator 61, and the integration result is registered in the RAM table 62 as a distortion compensation amount. On the other hand, after the digital baseband signals I1 and Q1 from the input demodulation unit A are converted from the Cartesian coordinates (I1, Q1) to the polar coordinates (R1, θ1) by the Pythagoras converter 63, the distortion compensation amount (R1) according to the value of R1 ΔR, Δθ) are read from the RAM table 62, the compensation amount is added by the distortion compensation amount adding section 64, and the inverse Pythagoras converter 65 returns the original Cartesian coordinates (I1 ′, Q1 ′) and outputs the original Cartesian coordinates (I1 ′, Q1 ′).
[0021]
The digital baseband signal output from the distortion correction unit D is supplied to an output conversion unit G. The output conversion unit G returns the input digital baseband signal to the original bit rate by FIR filters (or LPFs) 71 and 72 (oversampling), and performs quadrature modulation by a quadrature modulation (Q-MOD) circuit 73 to obtain an IF signal. After being converted into an analog signal by a digital / analog converter (DAC) 74, the signal is converted into an RF signal by an up-converter (U / C) 75 based on a local signal from the local oscillator 13, and distortion is compensated from an RF output terminal 76. Output as a signal.
[0022]
The feature of the first embodiment according to the present invention in the nonlinear compensator having the above configuration lies in the following configuration.
[0023]
In FIG. 1, a transient characteristic detecting unit H includes a digital baseband signal (input to the RF amplifier 3) I3, Q3 from the delay adjusting unit C and a digital baseband signal (output from the RF amplifier 3) from the output demodulating unit B. The transient characteristic of the RF amplifier 3 is detected by comparing I2 and Q2, and the detection result is supplied as a coefficient to the adaptive filter I provided in the distortion correction unit D.
[0024]
On the other hand, as shown in FIG. 3, the RAM table 62 provided in the distortion correction unit D includes n bank memories M1 to Mn for storing distortion compensation amounts for respective integrated output levels, and reading of the bank memories M1 to Mn. And a selector SEL for selectively deriving an output. The addresses of the bank memories M1 to Mn are controlled by the amplitude value R1 output from the Pythagorean converter 63. As a result, the distortion compensation amount corresponding to the amplitude value of R1 is read out and output from each of the bank memories M1 to Mn, and is selectively derived by the selector SEL. The selector SEL selectively derives the read output of the bank memories M1 to Mn according to the output level of the adaptive filter I.
[0025]
The adaptive filter I gives the amplitude value R1 output from the Pythagorean converter 63 a characteristic opposite to the transient characteristic obtained by the transient characteristic detector H. Specifically, the amplitude value R1 is multiplied and output by the reciprocal of the coefficient indicating the transient characteristic. Therefore, as the transient characteristics of the RF amplifier 3 become steeper, the level change of the amplitude value R1 output from the adaptive filter I becomes gentler, and the switching speed of the selector SEL becomes slower. Conversely, as the transient characteristics of the RF amplifier 4 become gentler, the level change of the amplitude value R1 output from the adaptive filter I becomes faster.
Thus, even if the operating point of the RF amplifier 3 fluctuates and its non-linear characteristic changes, the non-linear compensation characteristic is sequentially updated following the change in the non-linear characteristic in the time direction.
[0026]
(Second embodiment)
FIG. 4 is a block diagram showing a configuration of the second embodiment in which the present invention is applied to the nonlinear compensator 2. In FIG. 4, the same parts as those in FIG. 2 are denoted by the same reference numerals, and different parts will be described in detail.
[0027]
That is, the feature of the second embodiment according to the present invention lies in the following configuration.
In FIG. 4, the average power detection unit K receives the amplitude value R1 output from the Pythagoras converter 63 of the distortion correction unit D, and obtains the average power by an integration process using a non-recursive digital filter (IIR). . The RAM table 62 has the configuration shown in FIG. 3 except for the aforementioned adaptive filter I, and includes bank memories M1 to Mn and a selector SEL. However, in the case of the present embodiment, the read output of the bank memories M1 to Mn is switch-controlled based on the detection result of the average power detection unit K.
[0028]
According to the above configuration, although the accuracy is lower than that of the first embodiment, it can be realized with a simple configuration, and it can be considered that the fluctuation of the operating point of the RF amplifier 3 follows the change of the average power. In such a case, the function can be sufficiently exhibited, so that it can be said that the cost performance is excellent.
[0029]
As described above, in the non-linear compensator 2 of the present embodiment, the input demodulation unit A and the output demodulation unit B extract the digital baseband signals of the RF input and the RF output of the RF amplifier 3 and determine the time difference between the two signals. The phase difference is detected by the correlation calculation in the delay detection unit E, and the synchronization of the two signals is performed by the delay adjustment unit C. In addition, the phase shifter 23 adjusts the phase of both signals. In this state, the amplitude error and the phase error of both signals are obtained by the distortion detection unit F, and input to the distortion correction unit D as distortion components. In the distortion correction unit D, a compensation amount corresponding to the amplitude value is sequentially selected from the compensation amounts registered by the means, and the compensation amount is added to the digital baseband signal obtained in the input demodulation unit A. The distortion component is compensated, the output signal is converted to the original signal format by the output conversion unit G, and output to the RF amplifier 3. As a result, the RF signal can be input to the RF amplifier 3 with the opposite characteristic to the nonlinear characteristic of the RF amplifier 3, and the distortion component due to the nonlinear characteristic of the RF output can be compensated.
[0030]
Here, in the first embodiment, the transient characteristic of the RF amplifier 3 is obtained, and the distortion correction unit D gives the inverse characteristic to the input amplitude value to switch the bank of the compensation table. Even when the level change amount of the average power becomes large and the operating point of the RF amplifier 3 fluctuates and its non-linear characteristic changes, it is possible to sequentially update the non-linear compensation characteristic following the change in the non-linear characteristic in the time direction. it can.
[0031]
Further, in the second embodiment, the average power is obtained from the input amplitude value of the distortion correction unit D, and the bank switching of the compensation table is performed based on the result, so that the operating point of the RF amplifier 3 varies. Even if the non-linear characteristic changes, the non-linear compensation characteristic can be successively updated by following a change in the non-linear characteristic of the transmission average power in the time direction with a simple configuration.
[0032]
Note that the present invention is not limited to the above embodiment.
For example, in the above embodiment, the coefficient values of the FIR filters 28 and 29 of the output demodulation unit B are controlled to achieve precise synchronization. However, the coefficient values of the FIR filters 18 and 19 of the input demodulation unit A are controlled. It is also possible to achieve precise synchronization.
[0033]
In the above embodiment, the phase is adjusted by adjusting the phase shift amount of the phase shifter 23 of the output demodulation unit B. However, the local signal supplied to the down converter 12 of the input demodulation unit A is adjusted. Even if the phase is adjusted by the phase shifter, the phase can be adjusted similarly.
[0034]
Furthermore, in the above embodiment, the case where the analog RF signal is input from the modulator 1 has been described. However, when the modulator 1 directly outputs the digital baseband signal, the digital baseband signal is input and the input is performed. If the output of the demodulation unit A is directly supplied to the delay adjustment unit C and the distortion correction unit D instead of the output of the demodulation unit A, the same effect as the above embodiment can be obtained.
[0035]
Although the above embodiment is applied to the OFDM transmission apparatus, the present invention is not limited to this. Other electronic circuits of analog communication system and digital communication system, for example, analog television signal by NTSC system The present invention can also be applied to compensation of non-linear characteristics and phase rotation in a transmission device of the above, a transmission device of a digital television signal according to the ATSC system, and the like. Further, in the above embodiment, the distortion correction is performed by adding the polar coordinates (R, θ). However, the distortion correction may be performed by multiplication by the Cartesian coordinates (I, Q).
[0036]
Further, in the above embodiment, the non-linear characteristic and the phase rotation are adaptively compensated by the automatic adjustment and the automatic control by making all the loops. However, the detection results of the respective detection units are appropriately displayed, and the display contents are displayed. It is needless to say that the adjustment and the correction may be manually performed while watching.
Further, in the above embodiment, the case where the non-linear characteristic of the RF amplifier is compensated has been described. However, the present invention can be similarly applied to other electronic devices that require compensation of the non-linear characteristic.
[0037]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a non-linear compensator capable of adaptively compensating for non-linear characteristics even when the amount of level change of the transmission average power in the time axis direction is large.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an OFDM transmitting apparatus to which the present invention is applied.
FIG. 2 is a block diagram showing a configuration of a non-linear compensator for compensating for non-linear characteristics of the RF amplifier of FIG. 1 as a first embodiment of the present invention;
FIG. 3 is a block diagram showing a specific configuration of a distortion correction unit of the embodiment shown in FIG.
FIG. 4 is a block diagram showing a configuration of a second embodiment of the nonlinear compensator according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Modulator 2 ... Nonlinear compensator 3 ... RF amplifier 4 ... Distributor A ... Input demodulation part B ... Output demodulation part C ... Delay control part D ... Distortion correction part E ... Delay detection part F ... Distortion detection part G ... Output Converter H Transient characteristic detector I Adaptive filter K Average power detectors M1 to Mn Bank memory SEL Selector 11 Analog RF input terminal 12 First down converter (D / C1)
13 local oscillator 14 AGC circuit 15 squelch circuit (SQ)
16 First analog-to-digital converter (ADC1)
17 1st quadrature demodulation circuit (Q-DEM1)
18, 19 ... FIR filter 21 ... analog PA input terminal 22 ... second down converter (D / C2)
23 phase shifter 24 AGC circuit 25 squelch circuit (SQ)
26 Second analog-to-digital converter (ADC2)
27: second quadrature demodulation circuit (Q-DEM2)
28, 29 FIR filter 30 Local oscillator 31, 32 RAM delay 41 Complex multiplier 42 REAL integrator 43 IMAG integrator 44 Pythagoras converter 45 Autocorrelation peak detector 46 Delay / angle detection Device 47 delay controller 48 phase controller 49 carrier synchronization circuit 491 differentiator 492 loop filter 493 adder 494 loop filters 51 and 52 Pythagoras converter 53 error calculator 61 integrator 62 RAM table 621... Working area 622... Reserve area 623... Address timing control unit 63.
74 Digital-to-analog converter (ADC)
75 ... Up converter (U / C)
76: RF output terminal 77: Local oscillator

Claims (2)

In a non-linear compensator for compensating for non-linear characteristics of a compensated electronic device that handles a transmission signal,
After capturing the input signal and output signal of the compensated electronic device, suitably demodulating and matching the same signal format, the time difference and the phase difference between the two signals were detected by taking the correlation between the two signals, and were detected. A signal processing unit that performs synchronization and phase adjustment of both signals based on the time difference and the phase difference,
A distortion detection unit that detects, as a distortion component, an amplitude error and a phase error of an input signal and an output signal of the compensated electronic device whose synchronization and phase are adjusted by the signal processing unit;
A transient characteristic detecting unit that compares an input signal and an output signal of the compensated electronic device and detects a transient characteristic of the compensated electronic device;
An adaptive filter that applies an inverse characteristic of the transient characteristic detected by the transient characteristic detection unit to an input signal of the compensated electronic device;
The distortion component detected in advance by the distortion detection unit and a nonlinear distortion compensation amount for compensating the distortion component are stored in a plurality of memory banks for each magnitude of the distortion component, and the output level of the adaptive filter is And a distortion correction unit for selectively switching the memory bank in response to the distortion compensation amount stored in the selected memory bank, and for compensating the input signal of the compensated electronic device with the distortion compensation amount. Characteristic non-linear compensator. In a non-linear compensator for compensating for non-linear characteristics of a compensated electronic device that handles a transmission signal,
After capturing the input signal and output signal of the compensated electronic device, suitably demodulating and matching the same signal format, the time difference and the phase difference between the two signals were detected by taking the correlation between the two signals, and were detected. A signal processing unit that performs synchronization and phase adjustment of both signals based on the time difference and the phase difference,
A distortion detection unit that detects, as a distortion component, an amplitude error and a phase error of an input signal and an output signal of the compensated electronic device whose synchronization and phase are adjusted by the signal processing unit;
An average power detection unit that determines an average power of an input signal of the compensated electronic device;
The distortion component detected by the distortion detection unit and the nonlinear distortion compensation amount for compensating the distortion component are previously stored in a plurality of memory banks for each average power, and the detection level of the average power detection unit is And a distortion correction unit for selectively switching the memory bank in response to the distortion compensation amount stored in the selected memory bank, and for compensating the input signal of the compensated electronic device with the distortion compensation amount. Characteristic non-linear compensator.

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