JP2009118454A - Wireless transmission equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide wireless transmission equipment which reduces an error of a distortion correction coefficient and shortens a convergent time of the distortion correction coefficient. <P>SOLUTION: The wireless transmission equipment does not renew the distortion correction coefficient during a fixed term shorter than a transmission term from the starting of the transmission term, and after a fixed term passed from the starting, the equipment carries out the renewal operation of the distortion correction coefficient. During a fixed term from the transmission starting for which the renewal operation of the distortion correction coefficient is not carried out, an distortion correction operation is carried out on a transmission signal. The wireless transmission equipment carries out the interpolating processing of the distortion correction coefficient in order to shorten the convergent time of the distortion correction coefficient. The distortion correction coefficient is given to the two-dimensional coordinates (address) which is shown by an electric power level of the transmission signal to be inputted and a difference of electric power between the transmission signal and a feedback signal, and the distortion correction coefficient of the fixed coordinate is renewed to an interpolating value which is obtained by an interpolating operation using the distortion correction coefficient of coordinate adjacent to the fixed coordinate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wireless transmission device that performs distortion compensation processing using a distortion compensation coefficient, and more particularly to a wireless transmission device that performs distortion compensation processing on a transmission signal in a time division duplex (TDD).

  As a power amplifier for amplifying a linear modulation signal and a low noise amplifier used for a receiver of a linear modulation signal, an amplifier with high linearity is required to suppress deterioration of transmission characteristics due to spectrum characteristics and signal distortion.

  In particular, when a multi-value amplitude modulation method is applied to wireless communication, a technique is required on the transmission side to linearize the amplification characteristics of the power amplifier to suppress nonlinear distortion and reduce adjacent channel leakage power. In general, amplifiers are always required to have high power efficiency. However, the linearity and efficiency of amplifiers are generally contradictory characteristics. When an amplifier with inferior linearity is used to improve power efficiency, the distortion caused by the same Technology to compensate for this is essential.

  As one of such distortion compensation methods, a predistortion method is known. The principle of the predistortion method is a method of obtaining a desired signal without distortion at the output of the amplifier by adding in advance a characteristic opposite to the distortion characteristic of the amplifier to the input signal of the amplifier. The predistortion method is described in detail in the following Patent Documents 1, 2, 3, and 4, for example.

The transmission signal before distortion compensation is compared with the demodulated feedback signal, and the distortion compensation coefficient is calculated and updated using the error. The distortion compensation coefficient is stored in the memory using the amplitude, power, or a function thereof of the transmission signal as an address. Then, predistortion processing is performed using the updated distortion compensation coefficient for the next transmission signal to be transmitted, and output. By repeating this operation, it finally converges to the optimum distortion compensation coefficient, and the distortion of the transmission power amplifier is compensated.
JP 9-153849 A JP 2002-223171 A JP 2006-197537 A JP 2006-74539 A

  On the other hand, in recent years, in wireless communication, a TDD (Time Division Duplex) system such as WiMAX has been put into practical use in addition to the current mainstream 3G system that realizes simultaneous transmission and reception by FDD (Frequency Division Duplex).

  When the conventional predistortion processing is performed on the transmission signal of the TDD wireless communication system, a rapid bias current flows through the power amplifier immediately after the transmission period starts, so that transmission and reception are switched at high speed. The amplitude and phase components fluctuate, and the distortion compensation coefficient to be updated contains a relatively large error, so that a normal distortion compensation coefficient cannot be calculated and a sufficient distortion compensation effect cannot be obtained. Occurs.

  Also, in the WiMAX system using TDD, when the transmission level of the first symbol (preamble) of the transmission signal is transmitted with full subcarriers, the transmission level in the data symbol period is about 3 dB higher, and the linear region is further reduced. The error of the distortion compensation coefficient becomes large, and normal distortion compensation operation is not performed.

  In addition, in the case of the TDD scheme, the transmission period and the reception period are alternately switched, and the distortion compensation coefficient is not updated in the reception period, and the distortion compensation coefficient is updated only in the transmission period as compared with the case of the FDD scheme. Therefore, it takes time to converge the distortion compensation coefficient.

  Furthermore, in the case of the TDD scheme, the number of transmission subcarriers in the transmission signal of the WiMAX system increases or decreases in units of symbols, thereby changing the transmission power level for each symbol period. The transmission level may change after calculating the distortion compensation coefficient at a certain transmission level, and it is difficult to always obtain an optimal distortion compensation coefficient. For this reason, it is necessary to further shorten and speed up the convergence time of the distortion compensation coefficient.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a radio transmission apparatus that reduces an error of a distortion compensation coefficient and shortens a convergence time of the distortion compensation coefficient.

  Immediately after the start timing of the transmission period in time division duplex (TDD), the amplitude and phase components vary greatly, and a normal distortion compensation coefficient cannot be calculated. The distortion compensation coefficient is not updated for a certain period shorter than the transmission period, and the distortion compensation coefficient is updated after a certain period from the start timing. Note that the distortion compensation operation for the transmission signal is performed for a certain period from the transmission period start timing when the distortion compensation coefficient update operation is not performed.

  Further, the wireless transmission device performs distortion compensation coefficient interpolation processing in order to shorten the convergence time of the distortion compensation coefficient. The distortion compensation coefficient is given to the two-dimensional coordinate (address) of the power level of the input transmission signal and the power difference between the input transmission signal and the feedback signal, and the distortion compensation coefficient of the predetermined coordinate is set to the predetermined coordinate. The value is updated to the interpolation value obtained by the interpolation calculation using the distortion compensation coefficient of the adjacent coordinates.

  In addition, the wireless transmission device changes a predetermined timing for starting the distortion compensation coefficient update processing for each transmission period within the transmission period.

  Distortion compensation coefficient update processing is not performed for a certain period from the start timing of the transmission period in time division duplex (TDD), and the distortion compensation coefficient is updated after a certain period of time, so that the amplitude and phase of the transmission signal It is possible to avoid updating the distortion compensation coefficient during a period in which the fluctuation is large, to prevent an error in the distortion compensation coefficient from increasing, and to maintain a normal distortion compensation operation.

  In addition, a predetermined distortion compensation coefficient stored in the memory is interpolated using the distortion compensation coefficient adjacent to the distortion compensation coefficient in the memory, an interpolation value of the predetermined distortion compensation coefficient is obtained, and the interpolation value By updating to, the convergence time of the distortion compensation coefficient can be shortened.

  Embodiments of the present invention will be described below with reference to the drawings. However, such an embodiment does not limit the technical scope of the present invention.

  FIG. 1 is a diagram illustrating a first configuration example of a wireless transmission device according to the present embodiment. The transmission signal generator 1 sends out a serial digital data string. The serial / parallel converter (S / P) 2 performs serial / parallel conversion on the serial digital data string to convert it into parallel data strings of I and Q signals.

  The timing generation unit 3 generates a timing for starting the update of the distortion compensation coefficient at a timing when a certain period has elapsed from the transmission period start timing, and generates a timing for ending the update of the distortion compensation coefficient at the transmission period end timing. To do. Specifically, the signal information detection unit 31 of the timing generation unit 3 detects map information (information indicating the data position) of the transmission signal from the parallel data string. The preamble detector 32 obtains the transmission period of the first symbol (preamble) in the transmission signal from the map information and the previously stored transmission period and reception period switching timing. Then, the distortion compensation timing control unit 33 outputs the distortion compensation update timing signal to the distortion compensation unit 4 at the preamble transmission end timing (distortion compensation update timing signal ON), and ends the distortion compensation update at the transmission period end timing. Therefore, the distortion compensation update timing signal is set to OFF. On the other hand, for the distortion compensation operation, the distortion compensation timing control unit 33 outputs a timing signal for starting the distortion compensation operation to the distortion compensation unit 4 at the start timing of the transmission period (distortion compensation operation timing signal ON), and transmission. The distortion compensation operation timing signal is turned OFF at the end of the period. In other words, the distortion compensation operation is performed from the transmission period start timing to the preamble transmission end timing, but since the fluctuation of the amplitude and phase of the transmission signal is large, the distortion compensation update is not performed. The period in which the distortion compensation update is not performed is not limited to the period from the transmission period start timing to the preamble transmission end timing, and can be changed as appropriate according to the state of fluctuation of the amplitude and phase of the transmission signal. In the WiMAX system using TDD, the transmission level of the first symbol (preamble) of the transmission signal is about 3 dB larger than the transmission level of the data symbol period, and a significant error is likely to occur. For example, distortion compensation update is not performed. As the period, the preamble transmission end timing is illustrated from the transmission period start timing.

  FIG. 2 is a timing chart of the distortion compensation timing control unit 33. The distortion compensation timing control unit 33 outputs a distortion compensation operation timing signal at the transmission period start timing. The distortion compensation update timing signal for starting the distortion compensation update is a timing (preamble) after a certain period has elapsed from the transmission period start timing. Output at transmission end timing). As a result, the distortion compensation coefficient is not obtained during a period in which the amplitude and phase of the transmission signal fluctuate greatly immediately after the start of the transmission period. It is possible to exclude the period in which the occurrence of the distortion from the distortion compensation coefficient update period. Since the distortion compensation coefficient is obtained and updated when the amplitude and phase of the transmission signal are stabilized, a normal distortion compensation coefficient is obtained, and distortion characteristic deterioration of the transmission signal can be minimized. Further, the distortion compensation timing control unit 33 turns off the distortion compensation operation timing signal at the transmission period end timing and also turns off the distortion compensation coefficient update timing signal, and stops updating the distortion compensation coefficient in the reception period. The destruction of the compensation factor is prevented.

  Returning to FIG. 1, the distortion compensation unit 4 performs a distortion compensation operation on the parallel data string (transmission signal) composed of the I signal and the Q signal by the above-described distortion compensation operation start timing signal, and by the distortion compensation operation end timing signal, The distortion compensation operation ends. Also, the update of the distortion compensation coefficient is started by the distortion compensation update start timing signal, and the update of the distortion compensation coefficient is stopped by the distortion compensation update end timing signal. The distortion compensation calculation unit 41 reads the distortion compensation coefficient corresponding to the power level of the input transmission signal from the memory (LUT) 42, and performs a predetermined calculation process using the read distortion compensation coefficient on the transmission signal. Output. The memory (LUT) 42 has a distortion compensation coefficient corresponding to a two-dimensional coordinate between the power level of the transmission signal and the power difference between the transmission signal and the feedback signal (for example, the feedback signal of the current transmission signal and the previous transmission signal). Remember. The distortion compensation calculation unit 41 calculates a distortion compensation coefficient corresponding to the power of the input transmission signal based on the power difference between the transmission signal and the feedback signal, and stores the distortion compensation stored in the memory (LUT) 42. Update the coefficient. In the embodiment of the present invention, the interpolation processing unit 43 performs an interpolation operation on the distortion compensation coefficient obtained by the distortion compensation operation unit 41, and the distortion compensation coefficient obtained by the interpolation operation is written in the memory (LUT) 42. . Details of the interpolation calculation will be described later.

  The distortion-compensated transmission signal output from the distortion compensator 4 is input to the quadrature modulator 6 via the D / A converter 5, and the quadrature modulator 6 applies a reference carrier wave generator to each of the input transmission signals. 7 is multiplied by the reference carrier wave from 7 and the transmission signal shifted in phase by 90 ° to perform quadrature modulation and output.

  The frequency converter 8 mixes the quadrature modulation signal and the local oscillation signal to convert the transmission signal into a radio frequency signal, amplifies it by the power amplifier 9 and transmits it by time division duplex, and the transmission signal is directionally coupled. The signal is folded back in the wireless transmission device via the converter, converted into an IF signal by the frequency converter 11 and the quadrature detector 12, and then fed back to the distortion compensation unit 4 as a feedback signal via the A / D converter 13. .

  The distortion compensation update process performed by the distortion compensation unit 4 performs an arithmetic process based on the transmission signal and the feedback signal, calculates a distortion compensation coefficient, and periodically performs the update process. In the TDD system, the transmission period and the reception period are alternately switched, so that there is little time available for updating the distortion compensation coefficient, and a large time is required for coefficient convergence. Therefore, the interpolation processing unit 43 of the distortion compensation unit 4 performs an interpolation calculation process of the distortion compensation coefficient, thereby speeding up the convergence time and stabilizing the coefficient. The distortion compensation coefficient interpolation calculation process will be described.

  3 and 4 are diagrams for explaining the interpolation processing of the distortion compensation coefficient. In the interpolation processing, the distortion compensation coefficient at each coordinate stored in the memory (LUT) 42 is updated by performing an interpolation operation using the distortion compensation coefficient at an adjacent coordinate. The coordinates of the memory are synonymous with the address specifying the position in the memory. FIGS. 3A and 3B are diagrams illustrating the interpolation process in the one-dimensional direction, and FIGS. 4A and 4B are diagrams illustrating the interpolation process in the two-dimensional direction. 3A and 4A are diagrams showing a mapping configuration of distortion compensation coefficients stored in the memory (LUT) 42. A variable in a one-dimensional direction represents a power value of a transmission signal, and is two-dimensional. The direction variable represents the power difference between the transmission signal and the feedback signal. “Slope 0” in the two-dimensional direction variable represents a case where the power difference is 0, that is, the power values of the transmission signal and the feedback signal (for example, the feedback signal of the current transmission signal and the previous transmission signal) are the same, From the coordinates of the row with the slope 0, one of the upper side and the lower side of the figure indicates that the power difference is in the plus (+) direction (power of the transmission signal> power of the feedback signal), and the other is in the minus (−) direction (of the transmission signal). Power <feedback signal power). FIG. 3B shows a distortion compensation coefficient corresponding to the one-dimensional variable when the two-dimensional variable (power difference) is a predetermined value, and FIG. 4B shows the one-dimensional variable (transmission). The distortion compensation coefficient corresponding to the variable in the two-dimensional direction when the signal power value is a predetermined value. The initial value of the distortion compensation coefficient is “1 + j0” (complex display).

  In the interpolation process in one-dimensional direction, the distortion compensation coefficient of the coordinates to be interpolated (for example, B in FIG. 3A) is calculated by using the distortion compensation coefficient before interpolation of the coordinates and the coordinates adjacent to the coordinates in the one-dimensional direction. Interpolation is performed using the distortion compensation coefficients (A and C in FIG. 3A), and the distortion compensation coefficient subjected to the interpolation is obtained for the coordinates to be interpolated. The interpolation calculation formula is given by, for example, the following formula (1). In the equation (1), the distortion compensation coefficients at the coordinates A, B, and C are also expressed as A, B, and C.

B ′: Distortion compensation coefficient of coordinate B subjected to interpolation calculation (also referred to as interpolation value)
B: Distortion compensation coefficient of coordinate B before interpolation calculation A: Distortion compensation coefficient of coordinate A adjacent to coordinate B in one-dimensional direction C: Distortion compensation coefficient of coordinate C adjacent to coordinate B in one-dimensional direction M: Interpolation coefficient For example, if the interpolation coefficient M = 3,
B ′ = (4B + A + C) / 6
Thus, the distortion compensation coefficient at coordinate B has the ratio 2/3 of the distortion compensation coefficient at coordinate B before the interpolation calculation, the ratio 1/6 of the distortion compensation coefficient at coordinate A, and the ratio 1/6 of the distortion compensation coefficient at coordinate C. It is obtained by interpolation calculation.

  Subsequent to the coordinate B, the coordinate C is interpolated in the one-dimensional direction by the above equation (1) using the distortion compensation coefficients of the adjacent coordinates B and D adjacent to each other, and the interpolated value of the coordinate C is obtained. Then, interpolation calculation is sequentially performed on the right adjacent coordinate.

  When the distortion compensation coefficient of the adjacent coordinate is the initial value, the coefficient is not used, and the distortion compensation coefficient of the coordinate whose distortion compensation coefficient is not the initial value is used in the one-dimensional direction. For example, in FIG. 3A, when the interpolation value of the coordinate C is obtained, the distortion compensation coefficient of the coordinate D is the initial value, and the distortion compensation coefficient of the coordinate E adjacent to the coordinate D in the one-dimensional direction is not the initial value. , Instead of the distortion compensation coefficient at the coordinate D, the distortion compensation coefficient at the coordinate E is used. In other words, the “adjacent coordinates” in the equation (1) are the most in the coordinates of the interpolation target on both sides of the coordinates of the interpolation target in the one-dimensional direction among the coordinates having the distortion compensation coefficient that is not the initial value in the one-dimensional direction. Means close coordinates. However, the coordinates at both ends in the one-dimensional direction (coordinates A and H in FIG. 3A) are used as they are even if they are the initial values (as described above, in the coordinate B interpolation operation, the coordinates C Even if is an initial value, the interpolated value of coordinate B is calculated using the initial value). Also, the coordinates at both ends in the one-dimensional direction (coordinates A, H, etc. in FIG. 3A) are not interpolated in the one-dimensional direction.

  For example, the interpolation calculation in the one-dimensional direction is sequentially performed from the left end side (excluding the coordinates at both ends) of the row in which the value in the two-dimensional direction is 0 (slope 0). That is, when the interpolation calculation is performed from the coordinate B in the right end direction to the coordinate (G) immediately before the right end coordinate (H), next, the row immediately below the row with the slope 0 is viewed from the left end side. Interpolation calculation is performed on the right end side, and then, the interpolation calculation is performed by moving to a line that is one level higher than the line with the slope 0. As described above, the interpolation calculation is alternately performed on the plus direction and minus direction rows in the two-dimensional direction around the row having the slope 0.

  FIG. 3B shows a one-dimensional distortion compensation coefficient in a predetermined two-dimensional value and its interpolation value (distortion compensation coefficient after interpolation). As shown in FIG. The distortion compensation coefficient that is likely to include a large error that protrudes compared to the distortion compensation coefficient of the coordinates to be smoothed is processed, and a value closer to the convergence value is obtained.

  Also in the two-dimensional direction, the same interpolation process as the one-dimensional direction is performed. In FIG. 4A, the distortion compensation coefficient of the coordinates to be interpolated (for example, P in FIG. 4A) is the distortion compensation coefficient before interpolation of the coordinates and coordinates adjacent to the coordinates in the two-dimensional direction (see FIG. Interpolation is performed using the distortion compensation coefficients A, Q) of 4 (a), and the interpolation compensation distortion compensation coefficients for the interpolation target coordinates are obtained. The interpolation calculation formula is given by the following formula (2), for example. In the equation (2), distortion compensation coefficients at the coordinates A, P, and Q are also expressed as A, P, and Q.

P ′: Distortion compensation coefficient of coordinate B subjected to interpolation calculation (also referred to as interpolation value)
P: Distortion compensation coefficient of coordinate B before interpolation calculation A: Distortion compensation coefficient of coordinate A adjacent to coordinate B in one-dimensional direction Q: Distortion compensation coefficient of coordinate C adjacent to coordinate B in one-dimensional direction N: Interpolation coefficient For example, if the interpolation coefficient N = 3,
P ′ = (4P + A + Q) / 6
Thus, the distortion compensation coefficient at the coordinate P has the ratio 2/3 of the distortion compensation coefficient at the coordinate P before the interpolation calculation, the ratio 1/6 of the distortion compensation coefficient at the coordinate A, and the ratio 1/6 of the distortion compensation coefficient at the coordinate Q. It is obtained by interpolation calculation.

  Following the coordinate P, the coordinate Q is interpolated in the two-dimensional direction according to the above equation (2) using the distortion compensation coefficients of the adjacent coordinates P and R adjacent to each other to obtain the interpolated value of the coordinate Q. Then, interpolation calculation is sequentially performed on the lower adjacent coordinates.

  As in the one-dimensional direction interpolation processing, when the distortion compensation coefficient of the adjacent coordinate is the initial value, the coefficient is not used, and the coordinate of the distortion compensation coefficient is not the initial value in the two-dimensional direction. A distortion compensation coefficient is used. For example, in FIG. 4A, when obtaining the interpolation value of the coordinate Q, the distortion compensation coefficient of the coordinate R is the initial value, and the distortion compensation coefficient of the coordinate S adjacent to the coordinate R in the two-dimensional direction is not the initial value. Uses a distortion compensation coefficient at coordinates S instead of a distortion compensation coefficient at coordinates R. Therefore, also in the formula (2), “adjacent coordinates” are the coordinates of the interpolation target on both sides of the coordinates of the interpolation target in the two-dimensional direction among the coordinates having the distortion compensation coefficient that is not the initial value in the two-dimensional direction. Means the coordinates closest to. However, the coordinates at both ends in the two-dimensional direction (coordinates T, U, Z, etc. in FIG. 4A) are used as they are even if they remain at the initial values. Further, the coordinates of the row with the inclination 0 are also used as they are even if the initial values are maintained. In the interpolation process in the two-dimensional direction, the coordinates at the two ends in the two-dimensional direction (coordinates T, U, Z, etc. in FIG. 4A) and the coordinates in the row with the gradient 0 (one-dimensional direction) are No operation is performed.

  The interpolation calculation in the two-dimensional direction proceeds from the column on the left end side, for example, from the coordinate P on the lower left end to the lower end direction centering on the row with the slope 0, and to the coordinate S just before the lower end coordinate T. Then, the interpolation operation is performed from the upper left coordinate V to the upper end direction to the coordinate Y immediately before the upper end coordinate Z, and then the sequence moves to the right column in the same manner. The lower end side column and the upper end side column are alternately interpolated around the 0 row.

  In one interpolation process, the above-described one-dimensional interpolation calculation and two-dimensional interpolation calculation are preferably performed, but only one of them may be performed. When only the two-dimensional direction interpolation calculation is performed, first, the one-dimensional direction interpolation calculation is performed only for the row with the slope 0, and then the two-dimensional direction interpolation calculation is performed. This is because the distortion compensation coefficient in the row with zero inclination is the reference.

  FIG. 5 is a diagram schematically illustrating the interpolation value of the distortion compensation coefficient obtained by the interpolation calculation. FIG. 5A shows the distortion compensation coefficient before interpolation stored in the memory (LUT) 42, and FIG. 5B shows the distortion compensation coefficient after interpolation stored in the memory (LUT) 42. 5A and 5B, the one-dimensional direction represents the power value of the transmission signal, the two-dimensional direction represents the power difference between the transmission signal and the feedback signal, and the Z direction (vertical axis) represents the distortion compensation coefficient. Represents a value.

  Since the distortion compensation coefficient has a high correlation with the adjacent coefficient, the distortion compensation coefficient is significantly larger than the distortion compensation coefficient value of the adjacent surrounding coordinates (for example, the reference symbol a in FIG. 5A). Is a distortion compensation coefficient that has a high possibility of containing a large error. However, by performing an interpolation operation, as shown in FIG. Shortening can be achieved.

  FIG. 6 is a timing chart of distortion compensation coefficient update processing and interpolation processing in the TDD scheme. In the TDD scheme in which the transmission period and the reception period are alternately switched, in the transmission period, the distortion compensation calculation unit 41 calculates a distortion compensation coefficient based on the transmission signal and the feedback signal, and is stored in the memory (LUT) 42. Update distortion compensation coefficient. In the reception period, the transmission signal is not transmitted, and the distortion compensation coefficient based on the transmission signal and the feedback signal is not calculated. Therefore, the above interpolation calculation is performed using the reception period.

  When the interpolation calculation for the distortion compensation coefficients of all coordinates in the memory (LUT) 42 is not completed within one reception period, the remaining part is performed in the next reception period.

  Also, the interpolation process is not always repeated. When one interpolation process, that is, an interpolation operation for the distortion compensation coefficients of all coordinates in the memory (LUT) 42 is completed once, the interpolation process is not performed for a certain period thereafter. This is because the distortion compensation coefficient is excessively smoothed and the distortion characteristic is deteriorated if it is always repeated. For example, only one interpolation process is performed in the first reception period when communication is started (if necessary, the second and subsequent reception periods). Alternatively, the interpolation process is executed intermittently. As described above, the first interpolation process is performed during the first reception period when communication is started (if necessary, the second and subsequent reception periods). When the second interpolation process is performed, for example, a distortion compensation coefficient is used. Is carried out after the convergence state, and after that, it is carried out after a certain period of time. By carrying out after convergence, the stability of the distortion compensation coefficient can be further improved.

  The above-described distortion compensation coefficient interpolation processing in the present embodiment is not limited to a TDD wireless transmission apparatus, but is a method in which transmission and reception are performed simultaneously at the same time, for example, by changing the transmission and reception frequencies simultaneously. The present invention can also be applied to an FDD system that realizes transmission and reception.

  FIG. 7 is a timing chart of distortion compensation coefficient update processing and interpolation processing in the FDD scheme in which transmission is performed continuously. In the update process and the interpolation process, the update process period and the interpolation process period are alternately switched within a transmission period of predetermined symbols (symbols 2, 3, and 6 in FIG. 7). Thereby, both the update process and the interpolation process can be performed within the transmission period of one symbol. Since there may be a difference in the level (power value) of the transmission signal for each symbol, it is preferable to perform the update process in all symbol periods. However, during one symbol period, the update process period and the interpolation process period By alternately performing the steps, necessary update processing and interpolation processing can be performed.

  In FIG. 7, the update process and the interpolation process are switched by dividing one symbol period into six. However, the number of divisions is not limited to six, and may be an arbitrary number of divisions such as two or four. Further, the symbol period for performing the interpolation processing is provided intermittently. For example, in the example of FIG. 7, interpolation processing is performed in two consecutive symbol periods (symbols 2 and 3) of four symbol periods (symbols 2-5), and in the next two symbol periods (symbols 4 and 5). Interpolation processing is not performed. Further, the next two consecutive symbol periods (symbols 6 and 7 (not shown)) are symbol periods in which interpolation processing is performed again.

  FIG. 8 is a diagram illustrating a second configuration example of the wireless transmission device according to the present embodiment, which is a configuration example corresponding to the timing chart of FIG. Compared with the first configuration example in FIG. 1, the timing generation unit 3 does not need to detect the switching timing and the preamble period between the transmission period and the reception period, and the symbol timing detection unit 34 detects each symbol timing, When the update / interpolation timing control unit 35 determines whether the detected symbol timing is a symbol period for performing the interpolation process according to the preset period information for performing the interpolation process, Then, a switching signal obtained by dividing the symbol period is output according to a preset number of divisions. That is, during the update processing period, the distortion compensation calculation unit 41 performs a distortion compensation coefficient update process based on the transmission signal (symbol) and the feedback signal, and the interpolation processing unit 43 stops the distortion compensation coefficient interpolation process. During the interpolation processing period, the distortion compensation calculation unit 41 stops the distortion compensation coefficient updating process, and the interpolation processing unit 43 performs the distortion compensation coefficient interpolation process.

  FIG. 9 is a diagram illustrating a third configuration example of the wireless transmission device according to the present embodiment. Compared to the first configuration example of FIG. 1, the third configuration example further includes a timing adjustment unit 14 that adjusts the output timing of the distortion compensation coefficient update timing signal. The timing adjustment unit 14 performs control to shift the output timing (ON timing) of the distortion compensation coefficient update timing signal by a certain interval width for each transmission period, and the timing (preamble transmission end timing) after a certain period has elapsed from the start timing of the transmission period. ), The distortion compensation coefficient update timing signal can be output at a later timing. By shifting the output timing of the distortion compensation coefficient update timing signal by a fixed interval for each transmission period, the growth of the error component of the distortion compensation coefficient is suppressed, and the unwanted spurious caused by the error component and the lifting phenomenon of the entire noise floor are suppressed. Therefore, better distortion compensation is possible. The procedure of the timing adjustment process by the timing adjustment unit 14 will be described later.

  When a coefficient update transmission signal is always acquired at the same timing after a certain period of time has elapsed from the start timing of the transmission period (after the preamble transmission ends), the transmission signal is pattern data (for example, synchronization pattern, test data, dummy data, etc.) If it is, it will continue to acquire the same data with almost no amplitude and phase change, and when updating the distortion compensation coefficient with almost the same data, error components accumulate in the distortion compensation coefficient in a specific range, As a result, unnecessary spurious is generated and the distortion compensation characteristic is deteriorated. Moreover, the phenomenon of lifting of the entire noise floor occurs due to the characteristic deterioration. In particular, it appears remarkably in the portion corresponding to the low power of the LUT. By using transmission signals having various amplitudes and phases for the distortion compensation update process, the distortion compensation coefficient is updated randomly and on average, so that unnecessary spurious generation can be suppressed.

  Note that the distortion compensation coefficient can also be smoothed by performing the above-described interpolation processing on the distortion compensation coefficient so as to suppress the error component, and the unnecessary spurious and the entire noise floor are suppressed by the smoothed amount. be able to. Therefore, the error component can be more effectively suppressed by using the interpolation processing and the timing adjustment processing together.

  As described above, if an excessive amount of interpolation processing is performed, the distortion compensation coefficient corresponding to the peak point will be smoothed, so the high-power transmission function as a transmission amplifier may be reduced. It is particularly effective to apply this timing adjustment processing when unnecessary spurious generated by data cannot be sufficiently removed.

  In the third configuration example, by the timing adjustment processing by the timing adjustment unit 14, the output timing of the distortion compensation coefficient update timing signal is shifted by a constant interval for each transmission period, and the acquisition timing of data used for the distortion compensation coefficient update is acquired. To change. As a result, transmission signals with various (moderately varying) amplitudes and phases can be acquired, distortion compensation coefficients can be updated randomly and on average, the growth of error components can be suppressed, and unnecessary spurious generation can be suppressed. it can.

  FIG. 10 is a timing chart for explaining the timing adjustment processing in the third configuration example. The distortion compensation coefficient update process includes, for example, each element process of process A, process B, coefficient update process, and process C in the order of processing, and transmission signal data is acquired at the start timing of the coefficient update process.

  10A shows the distortion compensation coefficient update processing timing when the timing adjustment processing by the timing adjustment unit 14 is not performed, and FIG. 10B shows distortion compensation when the timing adjustment processing by the timing adjustment unit 14 is performed. The coefficient update processing timing is shown. In FIG. 10A, the distortion compensation coefficient update process is always started at the same timing after a fixed time has elapsed from the start of the transmission period (after the end of the first symbol transmission) in all transmission periods. Process B, “coefficient update”, and process C are completed within one transmission period, and each process is performed at the same timing in any transmission period. Processes A, B, and C are processes related to the distortion compensation coefficient update process, and “coefficient update” is a process for obtaining and updating the distortion compensation coefficient by calculation based on data acquired from the transmission signal at the start timing. is there. Accordingly, the calculation data acquisition timing performed in the “coefficient update” is also the same timing in each transmission period.

  On the other hand, in FIG. 10B, in order to shift the start timing of the distortion compensation coefficient update process for each transmission period, the predetermined timing after the lapse of a certain time from the transmission period start timing (after the end of the first symbol transmission) is further increased. A predetermined stop time is provided, and the distortion compensation coefficient update process is started at a timing after the stop time has elapsed.

  The stop time is changed every transmission period (including no stop time), and when one unit time of the stop time is α, as shown in the figure, there is no stop time in the transmission period 1 and stop time in the transmission period 2 as shown in the figure. By setting α to a stop time 2α in the transmission period 3 and a stop time 3α in the transmission period 4, the start timing of the distortion compensation coefficient update process is shifted by a time α for each transmission period. Thereby, the data acquisition timing within the transmission period is also shifted for each transmission period. In the transmission period 5, it returns again without a stop time. The number of possible shifts is determined in advance from the length of the transmission period and the stop time, the start timing is shifted for each transmission period, and when the number of shifts is reached, the stop time is repeated again for each unit time α without any stop time. . The length of the time α can be appropriately set to such an extent that the amplitude change of the acquired data varies randomly.

  If the start timing of the distortion compensation coefficient update process is delayed due to the insertion of the stop time, for example, as in the transmission period 3, the entire process of the distortion compensation coefficient update process may not end at the transmission period end timing. In such a case, the remaining process (process C) is processed in the next transmission period (transmission period 4). Further, as shown in the transmission period 3, the process (coefficient update process) being processed at the transmission period end timing is continued over the reception period.

  FIG. 11 is a process flowchart of the timing adjustment unit 14. The timing adjustment unit 14 acquires transmission (Tx) symbol information detected by the signal information detection unit 31 (S100), obtains the length of the transmission period based on the information, and sets a unit time α of a preset stop time. The number of possible insertions (number of possible shifts) n is calculated (S102). Then, an insertion count number within one transmission period (CNT1) (hereinafter referred to as count number CNT1) and an actual insertion count number during one transmission period (CNT2) (hereinafter referred to as actual count number CNT2) are initialized to 0 (S104, S106). The count number CNT1 is the number of unit times α set in each transmission period. The larger the count number CNT1, the longer the stop time, and the start of the distortion compensation coefficient update process is delayed. CNT1 = 0 is when there is no stop time.

  When the timing adjustment unit 14 acquires preamble transmission end timing information from the preamble detection unit 32 for each transmission period (S108), the timing adjustment unit 14 determines whether the count number CNT1 = 0 (S110). If Yes, step S120 described later is performed. Proceed to the subsequent processing. If No, the unit time α is measured (S112), and the actual count CNT2 is incremented every time the unit time α elapses (S114). The count number CNT1 is compared with the actual count number CNT2 (S116). If the counted up CNT2 is less than the set CNT1, the unit time α is measured again (S112), and the actual count number CNT2 is the count number. The unit time α is repeatedly measured until CNT1 is reached. The start timing of the distortion compensation coefficient update process is shifted by the measurement time of the unit time α.

  When the actual count number CNT2 reaches the count number CNT1, an update processing start signal is transmitted to the distortion compensation timing control unit 33 (S118). When receiving the update processing start signal, the distortion compensation timing control unit 33 outputs a distortion compensation coefficient update timing signal, thereby starting the distortion compensation coefficient update process. Thereafter, when the transmission period end timing information is acquired from the preamble detector 32 (S120), the count number CNT1 is incremented by 1 (S122). By counting up the count number CNT1, the start timing of the distortion compensation coefficient update process in the next transmission period is further delayed by the unit time α.

  If the counted count number CNT1 is less than or equal to the insertable number of times n (S128), in the next transmission period, the process returns to step S106, the actual count number CNT2 is initialized, and preamble transmission end timing information is acquired ( After S108), the operations of Steps S110 to S128 are repeated. If the counted number CNT1 exceeds the insertable number of times n (S128), both the count number CNT1 and the actual count number CNT2 are initialized in the next transmission period (S104, S106), and the preamble transmission ends. After the timing information is acquired (S108), the operations in steps S110 to S128 are repeated.

  Note that the processing of steps S124 and S126 acquires transmission (Tx) symbol information for each transmission period (S124), confirms the length of the transmission period, and if the length of the transmission period has changed (S126 ), The process returns to step S102, re-calculates the insertable number of times n, and proceeds to the processing after step S104. However, the length of the transmission period is not usually changed halfway.

  FIG. 12 is a diagram illustrating distortion compensation coefficients that are updated by the third configuration example. FIG. 12A shows the distortion compensation coefficient before interpolation stored in the memory (LUT) 42 as in FIG. 5A. When the number of updates is small or the operation of the RF circuit is unstable, the distortion compensation coefficient (hereinafter referred to as an error component) having a significantly larger value than the distortion compensation coefficient values of adjacent surrounding coordinates (hereinafter referred to as an error component) (for example, FIG. 12). Reference symbol a) of (a) grows, and as a result, this error component causes unwanted spurious and lifting of the entire noise floor.

  FIGS. 12B and 12C show the distortion compensation coefficients after the interpolation processing, as in FIG. 5B. In both cases, an appropriate number of interpolation processes are performed, and the error component (reference symbol a) is greatly suppressed. However, in FIG. 12C, a part of the error component larger than that in FIG. Remaining. When the number of interpolation processes is too small, or when pattern data with a small amplitude change is used for the update process, a relatively large error may remain as shown in FIG. If excessive interpolation processing is performed in order to suppress the error component, the distortion compensation coefficient is excessively smoothed as shown in FIG. 12D, resulting in deterioration of distortion characteristics. In this case, since the distortion compensation coefficient corresponding to the peak point is smoothed, the high output transmission function as a transmission amplifier is deteriorated.

  FIG. 12E shows a distortion compensation coefficient that has been updated by applying the process of the timing adjustment unit 14 in the third configuration example. Compared with FIGS. 12B and 12C, the error component is smaller. It is almost suppressed. By shifting the start timing of the distortion compensation coefficient update processing for each transmission period by the processing of the timing adjustment unit 14, the growth of error components can be suppressed, and the generated error components can be substantially suppressed by appropriate interpolation processing. .

  The radio transmission apparatus of the present invention can be applied to either a base station or a mobile station in a mobile communication system.

  The main technical features of the embodiment described above are as follows.

(Appendix 1)
In a radio transmission apparatus that amplifies a transmission signal with an amplifier and transmits it in a transmission period that is alternately switched with a reception period,
A timing detector that detects the start timing and end timing of the transmission period;
A memory for storing a distortion compensation coefficient for compensating a distortion characteristic of the amplifier;
Based on a distortion compensation coefficient stored in the memory, a distortion compensation process is performed on a transmission signal from the start timing to the end timing, and the end timing is reached from a predetermined timing after a certain time has elapsed from the start timing. Until a distortion compensation coefficient is calculated based on the distortion-compensated transmission signal input to the amplifier and a feedback signal from the amplifier, and the distortion compensation coefficient stored in the memory is calculated as the calculated distortion A radio transmission apparatus comprising: a distortion compensation unit that updates a compensation coefficient.

(Appendix 2)
In Appendix 1,
The wireless transmission apparatus according to claim 1, wherein the predetermined timing after a predetermined time has elapsed after transmission of a preamble signal included at the head of the transmission signal.

(Appendix 3)
In Appendix 1,
The memory stores the distortion compensation coefficient in association with a variable related to a transmission signal,
Interpolation using the distortion compensation coefficient corresponding to the predetermined variable value and the distortion compensation coefficient corresponding to the variable value adjacent to the predetermined variable value, and the interpolation value of the distortion compensation coefficient corresponding to the predetermined variable value And a interpolation processing unit that executes an interpolation process for updating a distortion compensation coefficient corresponding to the predetermined variable value stored in the memory to the interpolation value.

(Appendix 4)
In Appendix 3,
The wireless transmission device according to claim 1, wherein the interpolation processing unit performs an operation for executing the interpolation processing only during a reception period.

(Appendix 5)
In Appendix 3,
The wireless transmission device, wherein the interpolation processing unit intermittently executes the interpolation processing during a reception period.

(Appendix 6)
In Appendix 3,
The variables include a first variable that is a power value of the transmission signal and a second variable that is a power difference between the transmission signal and the feedback signal,
The wireless transmission device, wherein the interpolation processing unit executes an interpolation process for one or both of the first variable and the second variable.

(Appendix 7)
In a radio transmission apparatus that amplifies a transmission signal with an amplifier and transmits it in a transmission period that is alternately switched with a reception period,
A timing detector that detects the start timing and end timing of the transmission period;
A memory for storing a distortion compensation coefficient for compensating for a distortion characteristic of the amplifier in association with a variable related to a transmission signal;
Based on a distortion compensation coefficient stored in the memory, a distortion compensation process is performed on a transmission signal from the start timing to the end timing, and the distortion-compensated transmission signal input to the amplifier A distortion compensation coefficient that calculates a distortion compensation coefficient based on the feedback signal from the amplifier and updates the distortion compensation coefficient stored in the memory to the calculated distortion compensation coefficient;
Interpolation using the distortion compensation coefficient corresponding to the predetermined variable value and the distortion compensation coefficient corresponding to the variable value adjacent to the predetermined variable value, and the interpolation value of the distortion compensation coefficient corresponding to the predetermined variable value And a interpolation processing unit that executes an interpolation process for updating a distortion compensation coefficient corresponding to the predetermined variable value stored in the memory to the interpolation value.

(Appendix 8)
In Appendix 7,
The wireless transmission device according to claim 1, wherein the interpolation processing unit performs an operation for executing the interpolation processing only during a reception period.

(Appendix 9)
In Appendix 7,
The variables include a first variable that is a power value of the transmission signal, and a second variable that is a power difference between the transmission signal and the feedback signal.
The wireless transmission device, wherein the interpolation processing unit executes an interpolation process for each of the first variable and the second variable.

(Appendix 10)
In Appendix 7,
The wireless transmission device, wherein the interpolation processing unit intermittently executes the interpolation processing.

(Appendix 11)
In a wireless transmission device that amplifies a transmission signal with an amplifier and transmits it,
A memory for storing a distortion compensation coefficient for compensating for a distortion characteristic of the amplifier in association with a variable related to a transmission signal;
Based on the distortion compensation coefficient stored in the memory, distortion compensation processing is performed on the transmission signal, and distortion is performed based on the distortion-compensated transmission signal input to the amplifier and the feedback signal from the amplifier. A distortion compensation unit that calculates a compensation coefficient and executes an update process for updating the distortion compensation coefficient stored in the memory to the calculated distortion compensation coefficient;
Interpolation using the distortion compensation coefficient corresponding to the predetermined variable value and the distortion compensation coefficient corresponding to the variable value adjacent to the predetermined variable value, and the interpolation value of the distortion compensation coefficient corresponding to the predetermined variable value And a interpolation processing unit that executes an interpolation process for updating a distortion compensation coefficient corresponding to the predetermined variable value stored in the memory to the interpolation value.

(Appendix 12)
In Appendix 11,
The wireless transmission apparatus, wherein the update processing by the distortion compensation unit and the interpolation processing unit by the interpolation processing unit are alternately switched and executed within one symbol period of a transmission signal in symbol units.

(Appendix 13)
In a radio transmission apparatus that amplifies a transmission signal with an amplifier and transmits it in a transmission period that is alternately switched with a reception period,
A timing detector that detects the start timing and end timing of the transmission period;
A memory for storing a distortion compensation coefficient for compensating for a distortion characteristic of the amplifier in association with a variable related to a transmission signal;
Based on a distortion compensation coefficient stored in the memory, a distortion compensation process is performed on a transmission signal from the start timing to the end timing, and the distortion-compensated transmission signal input to the amplifier A distortion compensation unit that calculates a distortion compensation coefficient based on the feedback signal from the amplifier and executes an update process for updating the distortion compensation coefficient stored in the memory to the calculated distortion compensation coefficient;
A radio transmission apparatus comprising: a timing adjustment unit that changes a predetermined timing at which the distortion compensator starts the update process within a transmission period for each transmission period.

(Appendix 14)
In Appendix 13,
The timing adjustment unit delays a predetermined timing for each transmission period by a unit time from an initial setting timing, delays a predetermined number of times, then returns to the initial setting timing, and repeats a delay by a unit time from the initial setting timing again. A wireless transmitter characterized by the above.

(Appendix 15)
In Appendix 13,
The wireless transmission device according to claim 1, wherein the predetermined timing is after a predetermined time has elapsed from the start timing.

(Appendix 16)
In Appendix 14,
The memory stores the distortion compensation coefficient in association with a variable related to a transmission signal,
Interpolation using the distortion compensation coefficient corresponding to the predetermined variable value and the distortion compensation coefficient corresponding to the variable value adjacent to the predetermined variable value, and the interpolation value of the distortion compensation coefficient corresponding to the predetermined variable value And a interpolation processing unit that executes an interpolation process for updating a distortion compensation coefficient corresponding to the predetermined variable value stored in the memory to the interpolation value.

It is a figure which shows the 1st structural example of the radio | wireless transmitter in this Embodiment. 4 is a timing chart of a distortion compensation timing control unit 33. It is a figure explaining the interpolation process of a distortion compensation coefficient. It is a figure explaining the interpolation process of a distortion compensation coefficient. It is a figure which illustrates typically the interpolation value of the distortion compensation coefficient calculated | required by the interpolation calculation. It is a figure which shows the timing chart of the update process of a distortion compensation coefficient in a TDD system, and an interpolation process. It is a figure which shows the timing chart of the update process and the interpolation process of a distortion compensation coefficient in the FDD system in which transmission is performed continuously. It is a figure which shows the 2nd structural example of the radio | wireless transmitter in this Embodiment. It is a figure which shows the 3rd structural example of the radio | wireless transmitter in this Embodiment. It is a timing chart for demonstrating the timing adjustment process in the 3rd structural example. 5 is a process flowchart of the timing adjustment unit 14. It is a figure explaining the distortion compensation coefficient updated by a 3rd structural example.

Explanation of symbols

1: transmission signal generation unit, 2: serial / parallel conversion unit, 3: timing generation unit, 4: distortion compensation unit, 5: D / A, 6: quadrature modulator, 7: reference carrier generation unit, 8: frequency conversion 9: power amplifier, 10: antenna, 11: frequency converter, 12: quadrature detector, 13: A / D, 14: timing adjustment unit, 31: signal information detection unit, 32: preamble detection unit, 33: Distortion compensation timing control unit 34: Symbol timing detection unit 35: Update / interpolation timing control unit 41: Distortion compensation calculation unit 42: Memory (LUT) 43: Interpolation processing unit

Claims (10)

In a radio transmission apparatus that amplifies a transmission signal with an amplifier and transmits it in a transmission period that is alternately switched with a reception period,
A timing detector that detects the start timing and end timing of the transmission period;
A memory for storing a distortion compensation coefficient for compensating a distortion characteristic of the amplifier;
Based on a distortion compensation coefficient stored in the memory, a distortion compensation process is performed on a transmission signal from the start timing to the end timing, and the end timing is reached from a predetermined timing after a certain time has elapsed from the start timing. Until a distortion compensation coefficient is calculated based on the distortion-compensated transmission signal input to the amplifier and a feedback signal from the amplifier, and the distortion compensation coefficient stored in the memory is calculated as the calculated distortion A radio transmission apparatus comprising: a distortion compensation unit that updates a compensation coefficient. In claim 1,
The wireless transmission apparatus according to claim 1, wherein the predetermined timing after a predetermined time has elapsed after transmission of a preamble signal included at the head of the transmission signal. In claim 1,
The memory stores the distortion compensation coefficient in association with a variable related to a transmission signal,
Interpolation using the distortion compensation coefficient corresponding to the predetermined variable value and the distortion compensation coefficient corresponding to the variable value adjacent to the predetermined variable value, and the interpolation value of the distortion compensation coefficient corresponding to the predetermined variable value And a interpolation processing unit that executes an interpolation process for updating a distortion compensation coefficient corresponding to the predetermined variable value stored in the memory to the interpolation value. In claim 3,
The wireless transmission device according to claim 1, wherein the interpolation processing unit performs an operation for executing the interpolation processing only during a reception period. In claim 3,
The wireless transmission device, wherein the interpolation processing unit intermittently executes the interpolation processing during a reception period. In a radio transmission apparatus that amplifies a transmission signal with an amplifier and transmits it in a transmission period that is alternately switched with a reception period,
A timing detector that detects the start timing and end timing of the transmission period;
A memory for storing a distortion compensation coefficient for compensating for a distortion characteristic of the amplifier in association with a variable related to a transmission signal;
Based on a distortion compensation coefficient stored in the memory, a distortion compensation process is performed on a transmission signal from the start timing to the end timing, and the distortion-compensated transmission signal input to the amplifier A distortion compensation coefficient that calculates a distortion compensation coefficient based on the feedback signal from the amplifier and updates the distortion compensation coefficient stored in the memory to the calculated distortion compensation coefficient;
Interpolation using the distortion compensation coefficient corresponding to the predetermined variable value and the distortion compensation coefficient corresponding to the variable value adjacent to the predetermined variable value, and the interpolation value of the distortion compensation coefficient corresponding to the predetermined variable value And a interpolation processing unit that executes an interpolation process for updating a distortion compensation coefficient corresponding to the predetermined variable value stored in the memory to the interpolation value. In a radio transmission apparatus that amplifies a transmission signal with an amplifier and transmits it in a transmission period that is alternately switched with a reception period,
A timing detector that detects the start timing and end timing of the transmission period;
A memory for storing a distortion compensation coefficient for compensating for a distortion characteristic of the amplifier in association with a variable related to a transmission signal;
Based on a distortion compensation coefficient stored in the memory, a distortion compensation process is performed on a transmission signal from the start timing to the end timing, and the distortion-compensated transmission signal input to the amplifier A distortion compensation unit that calculates a distortion compensation coefficient based on the feedback signal from the amplifier and executes an update process for updating the distortion compensation coefficient stored in the memory to the calculated distortion compensation coefficient;
A radio transmission apparatus comprising: a timing adjustment unit that changes a predetermined timing at which the distortion compensator starts the update process within a transmission period for each transmission period. In claim 7,
The timing adjustment unit delays a predetermined timing for each transmission period by a unit time from an initial setting timing, delays a predetermined number of times, then returns to the initial setting timing, and repeats a delay by a unit time from the initial setting timing again. A wireless transmitter characterized by the above. In claim 7,
The wireless transmission device according to claim 1, wherein the predetermined timing is after a predetermined time has elapsed from the start timing. In claim 8,
The memory stores the distortion compensation coefficient in association with a variable related to a transmission signal,
Interpolation using the distortion compensation coefficient corresponding to the predetermined variable value and the distortion compensation coefficient corresponding to the variable value adjacent to the predetermined variable value, and the interpolation value of the distortion compensation coefficient corresponding to the predetermined variable value And a interpolation processing unit that executes an interpolation process for updating a distortion compensation coefficient corresponding to the predetermined variable value stored in the memory to the interpolation value.