JP2010093697A - Multi-carrier radio transmission device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-carrier radio transmission device which controls transmission power uniformly regardless of a carrier number in a multi-carrier radio system. <P>SOLUTION: The multi-carrier radio transmission device includes: a means for determining a number of a carrier in a symbol to be transmitted; a digital baseband part for performing orthogonal frequency division multiplexing to the determined carrier data; and an RF part in which the output of the digital baseband part is converted into a desired frequency and amplified by an amplifier so as to be radiated. The multi-carrier radio transmission device includes: a memory for storing a multiplier to make both the number of times of normalization calculated statistically in the case of overflowing by IFFT operation and the IFFT resulted from the above number of times of normalization into a uniform value, with respect to a required power corresponding to a number of carrier in the above symbol for carrying out transmission; a shift amount adjustment circuit for performing adjusting the number of times of normalization according to the difference between an actual number of times of normalization in the IFFT operation process and the number of times of normalization memorized by the memory and determined statistically; and a correction circuit for multiplying the multiplier to the output of the shift amount adjustment circuit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multicarrier radio transmission apparatus.

  In a multi-carrier wireless system such as mobile WiMAX (World Interoperability Microwave Access), the number of carriers to be transmitted may be controlled according to the amount of data to be transmitted. At that time, a mechanism for keeping the transmission power constant is necessary, and is generally performed by an RF unit (analog circuit). FIG. 1 is a diagram illustrating a schematic configuration of a wireless transmission device of a multicarrier wireless system.

  The transmission data is generated by the processor (101), stored in the memory (102), and then subjected to error correction coding processing in the error correction unit (103). In WiMAX, a turbo code (Convolutional Turbo Coding) or a convolutional (Convolutional Coding) code is used.

  In the mapping unit (104), the data subjected to error correction processing is modulated by a modulation scheme corresponding to the required communication quality, for example, PSK (phase variation modulation) or transmission capacity that can be received even in a poor environment with a small transmission capacity. However, carrier mapping corresponding to QAM (Quadrature Amplitude Modulation) used when the environment is good is performed.

  The carrier-mapped data is IFFTed by an IFFT (Inverse Fourier Transform) block (105), and a cyclic prefix is added (106) to generate an OFDMA digital baseband signal.

  The digital baseband signal is converted into an analog baseband signal through the ADC (107) and input to the RF unit. After passing through the VGA (108) and the filter (109) and being up-converted to a desired frequency band by the QMOD (110), the signal is output from the antenna as an RF signal through the VGA (111).

  Here, in the configuration of the wireless transmission device of FIG. 1, the transmission power is controlled by varying the voltage of the VGA (108, 111) of the RF unit exclusively. In a communication system using OFDMA, the number of carriers to be used is increased or decreased according to an increase or decrease in the amount of information. When the amount of information decreases, the analog baseband signal decreases accordingly. In such a state, in order to keep the average transmission power constant, the VGA gain of the RF unit is controlled. However, if the analog baseband signal becomes small, the quality of the RF block VGA can be controlled with sufficient quality. In addition, an RF signal with sufficient power may not be obtained.

  FIG. 2 is a diagram for explaining an IFFT processing operation based on a fixed point, which is assumed as a circuit for performing transmission power control with a digital baseband signal in the IFFT block (105) of FIG.

  In the IFFT process, data from the mapping unit (104) is first stored in the memory (201). The data is read from the memory, the calculation is performed by the butterfly calculator (202), and the result is stored in the butterfly calculation memory (204). Next, data is read from the butterfly computation memory (204), butterfly computation is performed, and the result is stored in the butterfly computation memory (204). This calculation is repeated as many times as necessary, but the result of the calculation increases in the butterfly calculation and exceeds the number of effective bits. Therefore, normalization (division) (203) is performed and the result is stored within the number of effective bits. It needs to be stored in the memory (204). The number of times of normalization and the timing to perform are set so that the IFFT output value becomes an optimum value when all carriers are present. If the number of normalizations is fixed, the IFFT output value decreases as the number of effective carriers decreases. Even if transmission power control is performed by VGA control of the RF unit in such a state, a sufficient RF output signal cannot be obtained.

  Therefore, an output multiplier (205) of IFFT can be placed to increase the output by obtaining the coefficient in advance by the processor (206) or the like. However, if the calculation is performed in a fixed point, the rounding error is simultaneously increased. There is a growing problem.

  3A is a frequency spectrum of the output of the ADC 107 in FIG. Here, the signal component is main and there is almost no noise component. (B) is a frequency spectrum obtained as a result of amplification in the RF section, and the signal component increases, but at the same time the noise increases.

  In order to avoid such an inconvenience, it is assumed that the IFFT block shown in FIG. 2 is processed not by a fixed point but by a floating point.

  When IFFT is performed using a floating point, the influence of rounding errors is small, and the noise component does not increase. When a floating point is used instead of a fixed point, the circuit becomes complicated and the circuit scale is two to three times, which is against the miniaturization of the apparatus.

  As a conventional technique, Patent Document 1 describes an invention in which transmission power is controlled according to the number of detected multicarriers and transmission output per carrier wave is constant.

  Patent Document 2 describes an invention in which the number n of multicarriers is detected from an input signal, and transmission power is controlled according to n to obtain an output signal of a predetermined level.

Patent Document 2 describes an invention in which block floating-point is used for IFFT calculation and data is adjusted to the same scale depending on the characteristics of input data.
Japanese Unexamined Patent Publication No. 02-143719 Japanese Unexamined Patent Publication No. 02-013136 Japanese Patent Laid-Open No. 2001-313545

  An object of the present invention is to provide a multicarrier radio transmission apparatus that controls transmission power to be constant regardless of the number of carriers in a multicarrier radio system.

  In response to the above problem, the multicarrier wireless transmission apparatus provides statistics when there is a possibility that the digital baseband unit may overflow due to IFFT computation with respect to desired power corresponding to the number of carriers in the symbol to be transmitted. Memory for storing the normalized number of times automatically obtained, a multiplier for making the IFFT result based on the normalized number of times a constant value, the actual number of times of normalization in the IFFT calculation process, and the statistical data stored in the memory The shift amount adjusting circuit corrects the number of times of normalization corresponding to the difference from the number of times of normalization obtained in step (b), and the correction circuit that multiplies the multiplier by the output of the digit alignment circuit.

  That is, the number of carriers adaptively normalized in IFFT processing with respect to the number of carriers, an appropriate number of normalizations for the number of carriers obtained in advance, and a coefficient table that is a fraction less than the normalization are used.

  As a result, even if the number of carriers decreases, the output level of the digital baseband unit can be kept constant without degrading the S / N of the transmission signal, and the circuit can cope with a slight increase. .

  Embodiments will be described below with reference to the drawings.

  FIG. 4 is a block diagram of an embodiment of a transmission circuit including a transmission power control function in digital baseband signal processing.

  Characteristically, the normalization processing in the IFFT block is adaptive normalization in the adaptive normalization unit (408), and the shift amount adjustment unit (410) and multiplier (411) of the IFFT calculation result are newly provided. It will be added.

  In addition, the processor (402) adds a table and an instruction function for setting appropriate values to the shift amount adjustment unit (410) and the multiplier (411) according to the number of carriers of transmission data.

  Transmission data memory (403), error correction unit (404), mapping unit (405), memory in IFFT block (406), butterfly calculator (407), butterfly calculation memory (409), cyclic prefix addition unit (412) ), ADC (413) has the same function as the IFFT block (105) of FIG. 2 described above.

  In FIG. 4, the processor (402) holds in the program memory (401) a table for storing the number of carriers I, the number of times of IFFT execution statistically obtained for the number of carriers I, and the corresponding multipliers. is doing.

FIG. 6 is an example of a held table. The number of normalizations is the number of normalizations that would occur ideally for a certain number of carriers, and the multiplier is a value of ²ⁿ or less that cannot be normalized.

Adaptive normalization unit (408) obtains the maximum value of the result of the butterfly operation, when it is expected to overflow at the next butterfly operation, a function of 1/2 ⁿ all values butterfly operation result, the IFFT The number of times of normalization performed in the middle is stored, and the function of notifying the number of shifts to the shift amount adjustment unit (410) is provided.

  As the value of n, an optimal value is selected in advance when the system is constructed, depending on the radix of the butterfly calculation and the number of points of IFFT. The shift amount adjustment unit (410) compares the normalized number of times passed from the adaptive normalization unit (408) with the number of normalizations that should have been set in advance from the processor (402).

FIG. 5 shows the operation. The number of times of normalization from the adaptive normalization unit (408) is (a), and the number of times of normalization in the number of transmitted carriers stored in the program memory (401) from the processor (402) is (b) ), IFFT result from the butterfly operation memory (409) is input id, (a), (b) If the difference between the two values is m, and the absolute value is m _ABS , The IFFT result read from the butterfly computation memory (409) is multiplied by 1 / (2 ⁿ × m _ABS ), and when the number of normalization is large, 2 ⁿ × m _ABS is multiplied. If m is 0, nothing is done. The multiplier (412) performs multiplication of coefficients instructed by the processor.

  When transmitting, the processor (402) creates transmission data and writes the created transmission data in the memory (403).

  At this time, a normalization number and a multiplier for the number of transmission carriers are obtained by referring to the table of the program memory (401), the normalization number is set in the shift amount adjustment (410), and the corresponding multiplier is set in the multiplier (412). To do. For example, when the number of transmission carriers is 750, a numerical value is set such that the normalization is 4 times and the multiplier is 1.06667 from the table held in the program memory (401).

  Transmission data held in the memory (403) is subjected to error correction and mapping, and a butterfly operation is performed as many times as necessary in the IFFT block. In the repeated butterfly calculation, the adaptive normalization unit (408) adaptively normalizes so that the calculation result does not overflow.

The number of times of adaptive normalization together with the IFFT result is sent to the subsequent shift amount adjustment (410). Here, the number of times of normalization in a certain number of carriers set in advance by the processor (402) is set. As a result of comparison with this value, if the absolute value of the difference between the two values is m _ABS , the normalization number When the number of times is small, the read data from the butterfly calculation memory (409) is multiplied by 1 / (2 ⁿ × m _ABS ), and when the number of normalization is large, 2 ⁿ × m _ABS Perform multiplication.

  A multiplier (411) multiplies the output of the shift amount adjustment unit (410) by a coefficient instructed by the processor (402). By performing the processing as described above, the transmission power can be controlled without degrading the transmission S / N.

  FIG. 7 is a diagram comparing the IFFT result in which the number of normalizations in the conventional method is fixed with the case of the example method. That is, this is an example in which the output of the shift amount adjustment unit (410) and the output of the multiplier (411) are compared. In the case of 150 carriers, the conventional method requires about 5.3 times the power to obtain 750 power, but the embodiment method only requires about 1.3 times multiplication. The noise component is suppressed to about 1/4.

It is a figure which shows schematic structure of the radio | wireless transmission apparatus of a multicarrier radio | wireless system. It is a figure explaining IFFT processing operation by a fixed point assumed as a circuit which performs transmission power control in the IFFT block in the digital baseband part of FIG. It is a figure explaining a noise level becoming large by the power control using the IFFT processing circuit performed by a fixed point. It is an Example block diagram of the transmission power control circuit by the proposed method in a digital baseband part. It is a figure explaining operation | movement of shift amount adjustment. It is a figure which shows an example of the table hold | maintained at the program memory. It is a figure showing the difference of the IFFT result by a conventional method and an Example method.

Explanation of symbols

105 IFFT block 201 Memory 202 Butterfly computing unit 203 Normalization unit 204 Butterfly computing 205 Multiplier 206 Processor

Claims (4)

A fixed-point IFFT arithmetic circuit,
A memory for storing a statistically obtained number of times of normalization when there is a possibility of overflow due to an IFFT operation on a predetermined value, and a multiplier for making the IFFT result of the number of times of normalization a constant value;
A normalization circuit that adjusts the number of normalizations corresponding to the difference between the actual number of normalizations in the IFFT calculation process for the predetermined value and the statistically obtained number of normalizations stored in the memory;
A correction circuit that multiplies the multiplier by the multiplier output;
An IFFT arithmetic circuit comprising: In claim 1,
The IFFT operation circuit, wherein the normalization circuit is a ²ⁿ division circuit (n is 0 or more), and the multiplier is a numerical value less than ²ⁿ . Means for obtaining the number of carriers in a symbol to be transmitted, a digital baseband unit that performs orthogonal frequency division multiplexing on the obtained carrier data, and an output of the digital baseband unit at a desired frequency In a multi-carrier radio transmission apparatus that converts the signal into
In the digital baseband part,
When the desired power corresponding to the number of carriers in the symbol to be transmitted may overflow due to IFFT computation, the number of times of normalization obtained statistically, and the IFFT result based on the number of times of normalization as a constant value A memory for storing a multiplier for
A shift amount adjustment circuit that adjusts the number of normalizations corresponding to the difference between the actual number of normalizations in the IFFT calculation process and the statistically obtained number of normalizations stored in the memory;
A correction circuit that multiplies the multiplier by the output of the shift amount adjustment circuit;
A multi-carrier radio transmission apparatus comprising: In claim 2,
2. The multicarrier radio transmission apparatus according to claim 1, wherein the normalization circuit is a ²ⁿ division circuit, and the multiplier is a numerical value less than ²ⁿ .

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