JP4784226B2 - Diversity receiver - Google Patents

Description

  The present invention relates to a diversity reception method and apparatus. The present invention is particularly effective when mounted on a vehicle and receiving terrestrial digital television broadcasting.

  Terrestrial digital television broadcasting is digital broadcasting using OFDM, which is multicarrier modulation. With this OFDM reception, a high-quality image or the like can be easily obtained at a fixed point. However, in a mobile object, frequency fading due to multipath always varies, and therefore application of diversity and other techniques is being studied. Also, if the electric field strength is low, the dynamic range cannot be used effectively during A / D conversion, so that the auto gain controller (AGC) amplifies the signal to have a predetermined amplitude in the state of the intermediate frequency signal (IF). Technology is also used.

  When AGC is used, the amplitude of the desired wave is small compared to other branches, and even a signal of a branch with a poor S / N is amplified to a predetermined amplitude, so noise is inadvertently amplified. Result. In this case, there was a problem that diversity synthesis was not performed properly.

  The present invention has been made to solve the above-described problems, and an object thereof is to suppress noise from being mixed into a combined signal in diversity combining of a plurality of signals using AGC.

In order to solve the above-described problem, according to the means of claim 1, in a diversity receiving apparatus that has a plurality of antennas and combines a plurality of received signals into one to perform signal processing, Provided for each of the plurality of antennas, which is provided for each of the plurality of antennas, and for each of the plurality of antennas, which can control the amplification factor by a control voltage, and each output signal output from each variable amplification factor amplifier is multiplied by a weighting factor. a multiplier which is an adder for combining the output signals of the multipliers, the respective control voltage for controlling the target value the output level of the amplification factor variable analog amplifier for each antenna, each amplification factor variable analog amplifier a control voltage generation unit for outputting the pre-correction weighting coefficient from the correlation between the output signals output from the composite signal and the amplification factor variable analog amplifier to output of the adder required in the control An arithmetic unit for inputting each control voltage output from the pressure generator, and multiplying the pre-correction weighting coefficient by a value that decreases as each gain of each gain variable analog amplifier indicated by each control voltage increases. A diversity receiving apparatus comprising a weighting factor calculator that outputs a value to a multiplier as a weighting factor after correction .

According to a second aspect of the present invention, in the first aspect of the present invention, the pre-correction weighting factor includes a composite signal that is a complex signal and an output signal of the variable gain analog amplifier that performs quadrature demodulation and analog / digital conversion. The corrected weighting coefficient is a value obtained by multiplying the complex correlation coefficient by the inverse of each amplification factor.

  Since the amplification factor information in AGC can be reflected in the weighting factor at the time of diversity combining, for example, for a branch with a large amplification factor, the weighting factor (the absolute value in the case of complex numbers) is set according to the amplification factor. It can be made smaller. Thereby, the magnitude of noise mixed in the combined signal of the branch having a large amplification factor can be suppressed. As a method of decreasing the weighting factor (absolute value in the case of complex numbers) in accordance with the amplification factor (control voltage), a threshold value is provided for the amplification factor, and the weighting factor of the branch that exceeds the threshold value (in the case of complex numbers, the absolute value thereof) ) Is higher than a predetermined value, a method for obtaining the predetermined value, a method for determining a weighting factor by multiplying the reciprocal of the amplification factor, and a weighting factor for the amplification factor (or its absolute value in the case of complex numbers) Can be a monotonically decreasing function in a broad sense.

  The present invention is arbitrary for the modulation signal, but is particularly effective as a diversity receiver for receiving multicarrier modulation, particularly OFDM modulation signal.

  For diversity combining, maximum ratio combining, equal gain combining or any other means can be used. When updating the weighting factor sequentially, smoothing processing is performed, and the new weighting factor obtained by calculation and the weighting factor before updating are multiplied by α and 1−α to add, thereby changing the weighting factor. The amount can be suppressed. The weighting coefficient for phase control is calculated using complex correlation calculation. At this time, the value of the integration interval of the correlation calculation is arbitrary by design. It is possible to align the phases of the branches by complex correlation calculation.

  FIG. 1 is a block diagram showing a configuration of a diversity receiving apparatus 100 according to a specific embodiment of the present invention. Diversity receiving apparatus 100 has four antennas and is placed in front of a signal processing unit such as FFT and error correction of an apparatus that receives OFDM signals.

  The configuration of the diversity receiver 100 includes four antennas A1, A2, A3, and A4, multipliers (downconverters) 21, 22, 23, and 24, and variable analog amplifiers 31, 32 provided corresponding to the antennas. 33 and 34, analog / digital converters (A / D) 41, 42, 43 and 44, complex multipliers 71, 72, 73 and 74, local oscillator 10, auto gain controller (AGC) 30, and quadrature demodulator 50, a weight coefficient calculator 70 and an adder 80. The AGC 30 corresponds to the control voltage generation unit described in the claims.

  Signal processing in the diversity receiver 100 is as follows. A high frequency of, for example, a 500 MHz band received by the antenna A1 is multiplied by a sine wave generated by the local oscillator 10 in a multiplier (down converter) 21 and converted into an intermediate frequency signal (IF). This is amplified by the variable analog amplifier 31 controlled by the AGC 30, converted into a digital signal by the A / D 41, and output as a baseband digital complex signal by the orthogonal demodulator 50. The AGC 30 controls the amplification factor in the variable analog amplifier 31 in accordance with the output of the quadrature demodulator 50. In exactly the same manner, the reception signals of the antennas A2, A3, and A4 are also output from the orthogonal demodulator 50 as baseband digital complex signals. In FIG. 1, the quadrature demodulation unit 50 is described as one device, but four quadrature demodulation units that share a digital oscillator may be provided. The output of the control voltage of the AGC 30 is also output to the weight calculator 70.

  The four baseband band digital complex signals, which are the outputs of the quadrature demodulator 50, are input to the weight coefficient calculator 70, and complex correlation calculations are performed with the outputs of the adders 80, respectively. From these results, the weight coefficients (complex numbers) of the four baseband digital complex signals are determined and output to the complex multipliers 71, 72, 73 and 74, respectively. In the complex multipliers 71, 72, 73 and 74, signal processing is performed by complex calculation and the result is output to the adder 80. The adder 80 performs simple addition of the outputs of the complex multipliers 71, 72, 73, and 74, and outputs the result to subsequent signal processing.

  In the calculation of the weighting factor, each gain is calculated from the AGC control voltage with respect to a new weighting factor that does not reflect the AGC control voltage, and a new weighting factor is calculated by multiplying the reciprocal of the gain. Output to the multipliers 71, 72, 73 and 74. Accordingly, it is possible to reduce the magnitude of noise mixed in the synthesized signal by suppressing the influence of the branch having a large AGC control voltage and a high amplification factor in the variable analog amplifiers 31 to 34.

  FIG. 2 is a block diagram showing the configuration of a diversity receiver 200 according to another specific embodiment of the present invention. The configuration of FIG. 2 is a combination of the configuration of the first embodiment described in Japanese Patent Application Laid-Open No. 2004-221808.

  The configuration of the diversity receiving apparatus 200 includes four antennas A1, A2, A3, and A4, multipliers (downconverters) 21, 22, 23, and 24, and variable analog amplifiers 31, 32 that are provided corresponding to the antennas. 33 and 34, analog / digital converters (A / D) 41, 42, 43 and 44, band division filters 61, 62, 63 and 64, complex multipliers 71L, 72L, 73L and 74L, and a local oscillator 10, The AGC 30 includes an orthogonal demodulator 50, a weighting factor calculator 70L, an adder 80L, and a combiner 90. Although not shown in the figure, corresponding to the configuration shown as Low-Band, Mid-Band includes complex multipliers 71M, 72M, 73M and 74M, weight coefficient calculator 70M and adder 80M, and High-Band. Are provided with complex multipliers 71H, 72H, 73H and 74H, a weight coefficient calculator 70H and an adder 80H.

  The configuration of the diversity receiving device 200 is different from the configuration of the diversity receiving device in FIG. 1 in that each branch is divided by a band dividing filter, diversity combining is performed for each band, and these are combined by a combiner 90. is there. The contents of the combiner 90 include, for example, performing a complex correlation operation on the outputs of the adders 80L, 80M, and 80H with the outputs of the adders 80L and 80H on the basis of the output of the adder 80M to calculate a phase shift, By calculating the respective complex weights for phase compensation for the outputs of the adders 80L and 80H, and adding the outputs of the adders 80L and 80H and the respective complex weights to the outputs of the adder 80M, A band diversity combined signal is obtained. The obtained diversity combined signal of the entire band is output to the subsequent signal processing.

  Also in the present embodiment, similarly to the first embodiment, by suppressing the influence of a branch having a large AGC control voltage and a high amplification factor in the variable analog amplifiers 31 to 34, the magnitude of noise mixed in the synthesized signal can be reduced. It can be made smaller.

[Details of AGC 30 and Weight Coefficient Calculator 70]
Hereinafter, an example of the details of the AGC 30 and the weighting factor calculator 70 of the diversity receiver 100 according to the first embodiment will be described with reference to FIGS. 3 and 4. Note that the details of the AGC 30 and the weighting factor calculators 70L, 70M, and 70H of the diversity receiver 200 of the second embodiment may be configured almost exactly the same.

  As shown in FIG. 3, the AGC 30 has an average amplitude calculator 35i, an adder (subtracter) 36i, a sign determiner 37i, and an adder 38i for each branch i corresponding to four antennas Ai (i = 1 to 4). And a delay memory 38iM and a branch of AGC-ROM 39i which is a lookup table.

  As shown in FIG. 3, the weighting factor calculator 70 includes an offset value adder 710 having a memory (not shown), a difference calculator 720, a weighting factor suppression amount determiner 730, and a normalizing unit 760, and includes four antennas. Each branch i corresponding to Ai (i = 1 to 4) includes a complex correlation calculator 74i, a complex multiplier 75i (double multiplier), and a smoother 77i.

  The operation of each branch of the AGC 30 is as follows. A branch with i = 1 is shown as a representative. A baseband signal (complex signal) based on the signal received by the antenna A1 is output from the orthogonal demodulator 50 to the average amplitude calculator 351. The average amplitude calculator 351 calculates the average amplitude (positive real number or 0) for a predetermined time and outputs it to the adder (subtracter) 361. The adder (subtracter) 361 calculates the difference between the amplitude of the baseband signal output from the predetermined memory and the target value. At this time, if the output of the average amplitude calculator 351 is larger than the target value, a positive value is output to the sign determiner 371, and if the output of the average amplitude calculator 351 is smaller than the target value, a negative value is the sign determiner. 371 is output. When a positive value is input to the sign determination unit 371, 1 is output to the adder 381, and when a negative value is input to the sign determination unit 371, −1 is output to the adder 381. The adder 381 adds the “cumulative value” stored in the delay memory 381M before the predetermined time interval and the output of the sign determination unit 371, and the output of the adder 381 is stored in the delay memory 381M while being sequentially updated. . Note that the output of the adder 381 is, for example, 1024 stages from 0 to 1023 so that other values cannot be taken, and for example, the initial value stored in the delay memory 381M is 511. The output of the adder 381 is separately output to the AGC-ROM 391 that is a lookup table. In the AGC-ROM 391 that is a lookup table, the stored AGC voltage is output to the variable analog amplifier 31 with the “cumulative value” that is the output of the adder 381 as an address.

  As can be easily understood, in the adder (subtracter) 361, the output of the adder 381 increases or decreases until the difference between the target value and the output of the average amplitude calculator 351 becomes zero, and the target value and the average amplitude are calculated. The output of the adder 381 converges when the difference in the output of the adder 351 becomes near zero. Actually, if the reception signal amplified by the AGC voltage stored in the AGC-ROM 391 having the initial value 511 of the delay memory 381M as an address is smaller than the target value, the output of the adder 381 becomes small. Conversely, if the received signal amplified by the AGC voltage stored in the AGC-ROM 391 with the initial value 511 of the delay memory 381M as the address is larger than the target value, the output of the adder 381 becomes larger. Thus, the stored AGC voltage is output to the variable analog amplifier 31 by using the output of the converged adder 381 as an address. Thus, the AGC voltage output to the variable analog amplifier 3i is controlled for each branch i so that the amplitude of the baseband signal output from the quadrature demodulator 50 becomes the target value.

Regarding the weighting factor calculator 70, the operation of the weighting factor suppression amount determiner 730 and the following will be described first. A baseband signal (complex signal) based on the signal received by the antenna Ai is output from the orthogonal demodulator 50 to the complex correlation calculator 74i, and a synthesized signal is output from the adder 80. In the complex correlation calculator 74i, the correlation coefficient of these two signals is obtained and output to the complex multiplier 75i. Now, assuming that the outputs of the weight coefficient suppression amount determiner 730 and the complex multipliers 751 to 754 are all 1, the complex multiplier 75i outputs the input value to the normalization unit 760 as it is. In the normalization unit 760, the four values from the complex multipliers 751 to 754 are normalized by a desired normalization method and output to the smoothers 771 to 774. In the smoothers 771 to 774, the complex weight coefficients, in which fluctuations in the input value are suppressed, are output to the complex multipliers 71 to 74 based on the predetermined forgetting coefficient α. In the smoothing based on the forgetting factor α, ω _{n + 1} = αω ′ + (1−α) where ω _n is the previous weight, ω _{n + 1} is the updated weight, and ω ′ is the output of the normalization unit 760. ω _{n + 1} is calculated from ω _n .

  Next, the operation of the difference calculator 720 and the weight coefficient suppression amount determiner 730 of the weight coefficient calculator 70 will be described. The case where the input value is output as it is from the offset calculator 710 will be described first. That is, the outputs of the adders 381 to 384 of the AGC 30 are directly output to the difference calculator 720 via the offset calculator 710. The difference calculator 720 selects the maximum value of the four “cumulative values” corresponding to each antenna Ai, and calculates the difference between the other three “cumulative values” and the maximum value. Note that the maximum value of the “cumulative value” is also calculated as 0, and these four differences are output to the weighting coefficient suppression amount determiner 730. As described above, a large “cumulative value” means that the amplification factor is small, that is, the power of the received signal before amplification is large.

  In the weight coefficient suppression amount determiner 730, the suppression amount is calculated based on the difference between the maximum value of the four “cumulative values” corresponding to each antenna Ai, and a complex multiplier (double multiplier) 751 is obtained. To 754, respectively. In this way, the influence of the correlation value is reduced when calculating the weighting coefficient for the branch in which the amplitude of the baseband signal is further amplified by AGC. For example, when the “cumulative value” is the largest, that is, when the amplification factor is the smallest, the correlation value is left as it is, and the smaller the “cumulative value”, that is, the larger the amplification factor, the smaller the correlation value is less than 1. Multiplication is performed by multipliers (double multipliers) 751 to 754.

The suppression amount based on the difference from the maximum value of the “cumulative value” of the weight coefficient suppression amount determiner 730 may be calculated as follows. For example, when the “cumulative value” is represented by 10 bits, that is, in 1024 steps from 0 to 1023, the gain is 1 to 0 (1 to 0 times, Alternatively, for example, coefficients from 0 dB to -70 dB) are stored in the ROM. Alternatively, the “cumulative value” is divided into 11 stages, and the gain is set to 1, 2 ⁻¹ , 2 ⁻² , 2 ⁻³ ,..., 2 ⁻⁹ , 2 ⁻¹⁰ . Multiplication may be realized. When storing 1024 stages of linear coefficients in the ROM, the accuracy is good, but a more complicated circuit is required as the complex multiplier 75i. When bit shifting is performed, the complex multiplier 75i can be configured by a shift register, which is extremely simple, but the accuracy is deteriorated.

  Next, the function of the offset calculator 710 will be described. As apparent from the above description, the offset calculator 710 can be omitted depending on the design. This is the case when the signals of the four antennas have the same amount of noise. This is shown in FIG. Shown as A. FIG. In A, the power of the received signal of each branch is shown. FIG. In A, the received signal is the largest in branch 4, and the power of the received signal decreases in the order of branch 1, branch 3, and branch 2. As described above, the larger the received signal before amplification, the larger the “cumulative value”. In this case, by amplifying each branch by AGC, the signal of each branch is amplified so as to be equal to the received power of (amplified by) branch 4. Then, when obtaining the weighting coefficient for diversity combining, the correlation coefficient calculated based on “the signal of each branch amplified by AGC” is shown in FIG. It is necessary to reduce the correlation coefficient of each branch by the amount indicated as “difference from the largest branch” in A. FIG. In A, since the signals of the four antennas have the same amount of noise, there is no need to provide an “offset” between the branches.

  On the other hand, when there is a difference in noise level, for example, in an in-vehicle receiver, when antennas A1 and A2 are installed on a windshield and antennas A3 and A4 are installed on a rear bumper, antennas A3 and A4 close to the road surface The received signal generally has a lower noise level than the received signals of antennas A1 and A2. Then, even when the power of the received signals of the antennas A3 and A4 is smaller than the power of the received signals of the antennas A1 and A2, the weights of the antennas A3 and A4 are increased as the weights for diversity reception. The influence of noise should be suppressed by reducing the weight (FIG. 4.B). That is, even if the reception signals of the antennas A3 and A4 are amplified by AGC, they should not be suppressed by weighting. Therefore, FIG. As shown in C, the offset calculator 710 provides an offset to the “cumulative value” of the branches that should not be suppressed in the weighting, and provides an offset to the weight between the branches. Thus, even if the branch having a low noise level is amplified by AGC, that is, even if the “cumulative value” is small, the “cumulative value” can be increased so that it is not suppressed by weighting.

[Modification]
In each of the above embodiments, in the calculation of the weighting factor, the amplification factor is calculated from the AGC control voltage for the new weighting factor not reflecting the AGC control voltage, and multiplied by the inverse of the amplification factor. A method may be used in which the weight coefficient of the branch having a large AGC control voltage is reduced. For example, if the AGC control voltage is a branch that exceeds a certain threshold and a new weighting factor (absolute value in the case of a complex number) that does not reflect the AGC control voltage exceeds a predetermined value, the weighting factor (complex number) In this case, the absolute value) is set as the predetermined value.

  The present invention can be combined with various other diversity combining techniques. The weighting factor may be equal gain combining with an absolute value of 1 for all branches, or maximum ratio combining with different absolute values for each branch.

  The present invention can be applied to a device for receiving terrestrial digital television broadcasting in a vehicle or the like.

The block diagram which showed the structure of the diversity receiver 100 which concerns on one specific Example of this invention. The block diagram which showed the structure of the diversity receiver 200 which concerns on another specific Example of this invention. FIG. 3 is a block diagram showing details of configurations of an auto gain controller (AGC) 30 and a weighting factor calculator 70. The conceptual diagram which shows the effect | action of the offset calculator 710. FIG.

100, 200: Diversity receiver A1, A2, A3, A4: Antenna 10: Local oscillator 21, 22, 23, 24: Multiplier 30: Auto gain controller (AGC)
31, 32, 33, 34: Variable analog amplifier 41, 42, 43, 44: Analog / digital converter (A / D)
50: Quadrature demodulator 61, 62, 63, 64: Band division filter (3 bands)
70, 70L, 70M, 70H: Weight coefficient calculators 71, 72, 73, 74, 71L, 72L, 73L, 74L, 71M, 72M, 73M, 74M, 71H, 72H, 73H, 74H: Complex multipliers 80, 80L , 80M, 80H: adder 90: coupler

Claims (2)

In a diversity receiving apparatus that has a plurality of antennas and performs signal processing by combining a plurality of reception signals received thereby,
An amplification factor variable analog amplifier provided for each of the plurality of antennas, the amplification factor being controllable by a control voltage;
A multiplier provided for each of the plurality of antennas, which multiplies each output signal output from each variable gain analog amplifier by a weighting factor ;
An adder for combining the output signals of the multipliers;
A control voltage generator for outputting each control voltage for controlling the output level of the variable gain analog amplifier for each antenna to a target value to each variable gain analog amplifier ;
An arithmetic unit that obtains a pre-correction weighting factor from each correlation between the combined signal output from the adder and each output signal output from each gain variable analog amplifier, and inputs each control voltage output from the control voltage generator And, as each amplification factor of each amplification factor variable analog amplifier indicated by each control voltage becomes larger, a value obtained by multiplying the pre-correction weighting factor by a smaller value is used as the weighting factor after correction, A diversity receiver comprising: a weighting factor calculator for outputting to a multiplier . The uncorrected weighting factor, the combined signal and a complex signal, a complex correlation coefficient between the orthogonal demodulation, and analog / digital converted complex signal to an output signal of the amplification factor variable analog amplifier, the weight after correction The diversity receiving apparatus according to claim 1, wherein the coefficient is a value obtained by multiplying the complex correlation coefficient by an inverse number of each amplification factor.