JP2006253866A - Diversity receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a band split diversity receiver the circuit scale of which is decreased. <P>SOLUTION: Multipliers 2i convert high frequency signals received by antennas Ai (i=1 to 4) into intermediate frequency signals, variable analog amplifiers 3i amplify the intermediate frequency signals, A/D converters 4i converts the amplified signals into digital signals, and an orthogonal demodulation section 50 receiving outputs of the A/D converters 4i outputs baseband digital complex signals. The phases of the four baseband digital complex signals are arranged at a phase control section 60 by multiplying complex weight coefficients, determined by four sets of complex correlation arithmetic operations receiving an output of an adder 90, with the four baseband digital complex signals. Thereafter, band split filters 6i split the four baseband digital complex signals into three bands, double multipliers 8iL, 8iM, 8iH apply weighting to the three band signals, adders 85L, 85M, 85H summate the weighted signals, and an adder 90 summates outputs of the adders 85L, 85M, 85H. The weighting coefficients applied to the double multipliers 8iL, 8iM, 8iH are determined from amplitudes of each branch by each of bands of amplitude coefficient calculation units 80L, 80M, 80H. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a diversity receiver, and more particularly to a diversity receiver for reducing the influence of frequency selective fading due to multipath.

In diversity reception of a multicarrier modulation signal, the received signal is stochastically degraded at a certain frequency component due to frequency selective fading due to multipath. This phenomenon occurs independently for each antenna. Therefore, the present inventors invented the technique described in Patent Document 1 below. In this method, a multicarrier modulation signal is divided into bands and diversity combined, and the combined signals in each band are aligned and combined to perform subsequent signal processing. As a result, the synthesis means for each frequency band can calculate a more accurate weighting factor with reduced influence of deteriorated signal components existing in other bands, and the signal level for each frequency band can be equalized. It becomes. In addition, it is possible to reduce the influence of frequency selective fading due to multipath.
JP2004-221808

  FIG. 2 shows the configuration of the diversity receiver 100 of Patent Document 1. The configuration of the diversity receiver 900 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 71, 72, 73 and 74, complex multipliers 91L, 92L, 93L and 94L, and a local oscillator 10, An auto gain controller (AGC) 30, an orthogonal demodulator 50, a weighting factor calculator 95 </ b> L, an adder 85 </ b> L, and a combiner 99 are included. Although omitted in the figure, corresponding to the configuration shown as Low-Band, Mid-Band includes complex multipliers 91M, 92M, 93M and 94M, weight coefficient calculator 95M and adder 85M, and High-Band. Are provided with complex multipliers 91H, 92H, 93H and 94H, a weight coefficient calculator 95H and an adder 85H.

  Signal processing in the diversity receiver 900 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.

  The four baseband digital complex signals, which are the outputs of the quadrature demodulator 50, are divided into three bands, Low-Band, Mid-Band, and High-Band, by band division filters 71, 72, 73, and 74. The complex multipliers 91 to 94L and the weight coefficient calculator 95L, the complex multipliers 91 to 94M, the weight coefficient calculator 95M, the complex multipliers 91 to 94H, and the weight coefficient calculator 95H, respectively.

  First, the components indicated as Low-Band will be described. The four low-band baseband digital complex signals input to the weighting factor calculator 95L are each subjected to complex correlation calculation with the output of the adder 85L. From these results, the weight coefficients (complex numbers) of the four baseband digital complex signals are determined and output to the complex multipliers 91L, 92L, 93L and 94L, respectively. The complex multipliers 91L, 92L, 93L, and 94L perform signal processing by complex calculation and output to the adder 85L. The adder 85L performs simple addition of the outputs of the complex multipliers 91L, 92L, 93L, and 94L and outputs the result to the combiner 99. In this way, four sets of low-band baseband digital complex signals are diversity-combined.

  In exactly the same way, in Mid-Band and High-Band, four baseband band digital complex signals are subjected to complex correlation operation with the outputs of adders 85M and 85H, respectively, to determine weight coefficients (complex numbers), and complex multiplication is performed. The four baseband digital complex signals are weighted by the units 91M to 94M and the complex multipliers 91H to 94H, added by the adders 85M and 85H, respectively, and output to the combiner 99. In this way, each of the four baseband digital complex signals of Mid and High-Band is diversity-combined.

  The combiner 99 performs a complex correlation operation on the outputs of the adders 85L, 85M, and 85H, for example, with the outputs of the adders 85L and 85H on the basis of the output of the adder 85M to calculate a phase shift, and the adder By calculating the respective complex weights for phase compensation for the outputs of 85L and 85H, and adding the outputs of the adders 85L and 85H and the respective complex weights and the output of the adder 85M, A diversity combined signal is obtained and output to the subsequent signal processing.

  In the technique in Patent Document 1, since the frequency characteristic of the band division filter cannot be a strict step function, an overlap of the frequency bands is provided at the band boundary. That is, the two adjacent band filters are designed such that the frequency characteristic has an intensity of −6 dB at the boundary frequency. As described above, since the frequency band overlaps at the boundary portion of the divided bands, the signal after the combination is distorted in the overlapped portion unless the phases are matched after the diversity combining for each band. . In Patent Document 1, for this phase matching, a complex correlation operation is performed on the basis of one of the outputs of the adders 85L, 85M, and 85H. That is, the correlation operation between the combined signal for each band and the received signal in that band for calculating the weighting factor forming the combined signal for each band, and the overlapping part of the frequency band of the combined signal for each band Therefore, a two-stage correlation calculation with a correlation calculation between synthesized signals for aligning the phases of the two signals is necessary.

  The inventors have improved the configuration of Patent Document 1 and invented a configuration that enables addition between bands after diversity combining for each band with a smaller circuit scale.

  According to a first aspect of the present invention, there is provided a diversity receiver in communication using multi-carrier modulation, wherein a plurality of antennas and a division that divides the signals received by the plurality of antennas into a plurality of frequency bands after orthogonal demodulation. Means, weighting each signal of the plurality of antennas divided for each of the plurality of frequency bands and outputting a combined signal, and combining for each frequency band that is an output of the in-band combining means Interband synthesizing means for adding signals; phase control means for controlling the phase of the signal received by each antenna by a complex correlation with the output of the interband synthesizing means; An amplitude coefficient calculator that calculates an amplitude coefficient that is a real number for weighting in accordance with an average amplitude of each signal, That.

In Patent Document 1, assuming that the number of antennas is N _A and the number of bands is N _B , N _A N _B complex correlation operations and N _B synthesized for each band are used for diversity combining within the band. the complex correlation calculating -1 N _B of for binding pieces of the composite signal, the sum (N _a +1) N _B -1 of the complex correlation operation was necessary. According to the present invention, since the phase is compensated before the band division, the number of complex correlation operations may be N _A , and the diversity combining after the band division is processed on the basis of the amplitude that is a real number. No computation is necessary. Therefore, when the number of antennas is N _A and the number of divided bands is N _B , the present invention omits (N _A +1) (N _B −1) complex correlation operations compared to the configuration of Patent Document 1. Therefore, the circuit scale can be reduced. Similarly, multiple multiplications are necessary only in the phase control means before dividing the band, and the number of branches can be reduced from N _A N _B performed after dividing the conventional branch to N _A.

  The present invention can be used for vehicles, ships, airplanes, and other mobile objects. The number of antennas is arbitrary. When using four antennas, it is preferable to provide the moving direction in front, for example, the left front, right front, left rear, and right rear of the moving body.

  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.

  Any bandpass filter can be used for band division, but a digital filter is preferably used after analog / digital conversion and orthogonal demodulation. The frequency characteristic of the digital filter is desirably steep, but it is desirable to design the gain so as to have a gain of −6 dB at the boundary frequency with the adjacent bandpass filter.

  FIG. 1 is a block diagram showing a configuration of a diversity receiver 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, and is mounted on a vehicle.

  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, phase control unit 60, band division filters 71, 72, 73 and 74, double multipliers 81L, 82L, 83L and 84L And a local oscillator 10, an auto gain controller (AGC) 30, an orthogonal demodulator 50, an amplitude coefficient calculator 80L, and adders 85L and 90. Although not shown in the figure, corresponding to the configuration shown as Low-Band, Mid-Band includes double multipliers 81M, 82M, 83M and 84M, amplitude coefficient calculator 80M and adder 85M, and High-Band. Band includes double multipliers 81H, 82H, 83H and 84H, an amplitude coefficient calculator 80H and an adder 85H. The configurations indicated as Low-Band, Mid-Band, and High-Band correspond to the in-band synthesizing means described in the claims, and the adder 90 corresponds to the inter-band synthesizing means 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.

  The phases of the four sets of baseband digital complex signals, which are the outputs of the quadrature demodulator 50, are aligned by the complex calculation processing in the phase controller 60. Based on the output of the adder 90, four complex weight coefficients having an absolute value of 1 are calculated by a complex correlation operation with four sets of base band digital complex signals, and each of the four sets of base band digital The signal is multiplied by the complex signal and output to the band division filters 71, 72, 73 and 74. These are divided into three parts of Low-Band, Mid-Band, and High-Band by band division filters 71, 72, 73, and 74, respectively, and double multipliers 81 to 84L, amplitude coefficient calculator 80L, and double multiplication. Are input to the multipliers 81 to 84M, the amplitude coefficient calculator 80M, the double multipliers 81 to 84H, and the amplitude coefficient calculator 80H.

  First, the components indicated as Low-Band will be described. With respect to the four baseband digital complex signals of Low-Band inputted to the amplitude coefficient calculator 80L, real amplitude coefficients are determined as shown below and multiplied by the double multipliers 81L to 84L. . The double multipliers 81 to 84L are multipliers for multiplying two real numbers of a real part and an imaginary part, which do not substantially perform a complex operation because they simply multiply a complex signal by a real number. The four baseband band digital complex signals multiplied by the real number are output to the adder 85L, and the real part and the imaginary part are simply added and output to the adder 90. In this way, four sets of low-band baseband digital complex signals are subjected to diversity combining by determining amplitude coefficients.

  Exactly in the same manner, in Mid-Band and High-Band, for the four baseband band digital complex signals, the amplitude coefficient calculators 80M and 80H determine the real amplitude coefficient, and double multipliers 81M to 84M and 81H to 84H. The four sets of baseband digital complex signals are weighted, added by the adders 85M and 85H, and output to the adder 90. In this way, each of the four baseband digital complex signals of Mid and High-Band is diversity-combined. The adder 90 simply adds the outputs of the adders 85L, 85M, and 85H, and outputs the result to subsequent signal processing.

  Here, before the band division, the phase control unit 60 determines the complex weight coefficient (each absolute value is 1) by complex correlation calculation based on the output of the adder 90 and controls the phase. Even when the diversity combining is performed, the phases of the subcarriers in the overlapping portions of the bands of the output signals of the adder 90 are also aligned. That is, there is no drop at the junction of each band in the frequency space. Therefore, since there are no subcarriers whose phases are not aligned, there is no subcarrier whose gain by the subsequent diversity combining is negative. Therefore, by performing FFT, error correction, and other signal processing on the output of the adder 90, a receiver that is resistant to multipath fading can be obtained.

For example, any of the following methods can be used as the method of determining the amplitude by the amplitude coefficient calculators 80L, 80M, and 80H. Hereinafter, the average amplitude of the baseband signal before band division is represented by B _i (i indicates a branch corresponding to the antenna Ai (i = 1, 2, 3, 4)), the average amplitude after band division is represented by Low-Band, Mid-Band, High-Band each L _i, M _i, and H _i put. Further, unless otherwise specified, Σ represents the sum of i = 1, 2, 3, and 4.

[Method for determining amplitude coefficient 1]
Diversity combining in each band is set as maximum ratio combining, and the average amplitude of the combined signals in each band, which is the output of the adders 85L, 85M, and 85H, is set to N in advance. In this case, the amplitude coefficient is NL _i / ΣL _i ² for the signal of the average amplitude L _i of the Low-Band branch i. Similarly, NM _i / ΣM _i ² for Mid-Band and NH _i / ΣH _i ² for High-Band.

[Method for determining amplitude coefficient 2]
With diversity combining in each band as maximum ratio combining, the average amplitude of the combined signal in each band, which is the output of the adders 85L, 85M, and 85H, becomes 1/3 of the average amplitude of the four branches before band division. To. This may be achieved by setting N to ΣB _i / 12 in the method 1 for determining the amplitude coefficient. Therefore to branch i, and ^{_{L i ΣB i / 12ΣL i 2}} , Mid-Band in ^{_{M i ΣB i / 12ΣM i 2}} , the _{High-Band H i ΣB i /} 12ΣH i 2 In Low-Band.

[Method 3 for determining amplitude coefficient]
In the determination method 1 of the amplitude coefficient, N is set as the sum ΣL _i , ΣM _i, and ΣH _i of the average amplitudes of the branches of the input band. To branch i, Low-Band in _{L i / ΣL i, Mid-} Band in M _i / ΣM _i, and H _i / ΣH _i in High-Band to.

[About smoothing coefficients]
Signal distortion can be suppressed by performing smoothing on the complex weights in the phase control unit 60 and the amplitude coefficients in the amplitude coefficient calculators 80L, 80M, and 80H. The new weighting coefficient obtained by the calculation and the weighting coefficient before update are multiplied by α and 1−α and added. In order to perform digital processing easily, the value of α is, for example, 0, 1/256, 1/128, 1/64, 1/32, 1/16, 1/8, 1/4, 1/2, 1 Ten pieces should be prepared. α = 0 means that the coefficient is fixed and is not updated, and α = 1 means that smoothing is not performed and the calculated coefficient is sequentially updated.

  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 900 of patent document 1. FIG.

Explanation of symbols

100: 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 60: Phase controller 61, 62, 63, 64: Band division filter (3 bands)
80L, 80M, 80H: (Real number) amplitude coefficient calculator 81L, 82L, 83L, 84L, 81M, 82M, 83M, 84M, 81H, 82H, 83H, 84H: Double multiplier 85L, 85M, 85H, 90: Addition Units 91L, 92L, 93L, 94L, 91M, 92M, 93M, 94M, 91H, 92H, 93H, 94H: Complex multipliers 95L, 95M, 95H: (complex) weight coefficient calculator 99: Combiner

Claims (1)

In a diversity receiver in communication using multicarrier modulation,
Multiple antennas,
Division means for dividing the signals received by the plurality of antennas into a plurality of frequency bands after orthogonal demodulation;
In-band combining means for weighting each signal of the plurality of antennas divided for each of the plurality of frequency bands and outputting a combined signal;
An interband synthesizing unit that adds a synthesized signal for each frequency band that is an output of the in-band synthesizing unit;
Phase control means for controlling the phase of the signal received by each antenna by the complex correlation with the output of the interband combining means, in the preceding stage of the dividing means,
A diversity receiving apparatus, comprising: an amplitude coefficient computing unit that weights an amplitude coefficient that is a real number for weighting in an in-band combining unit based on an average amplitude of each signal.