JP4760068B2 - Diversity receiving method and diversity receiving apparatus - Google Patents

Description

  The present invention relates to a diversity reception method and apparatus in a moving object. 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. In addition, when mounted on a vehicle, the received power on the road on which the vehicle travels also changes. Actually, the received power is large in the suburbs where there are few obstacles in the vicinity, such as a high-rise building, and the received power is small when traveling on the road surface of an urban building.

For example, Patent Document 1 below describes a technique for switching antenna elements for diversity combining after OFDM demodulation.
JP 2003-283405 A

  In the study of an OFDM reception diversity receiver mounted on a vehicle, the present inventors, for example, for diversity synthesis when antennas are arranged at four points on the front left, right front, left rear, and right rear of a private car. The optimum values of various parameters were studied. Then, as shown below, when diversity combining is performed by dividing the received signals at the four points of the left front, right front, left rear, and right rear into two groups, the grouping is switched according to the traveling speed of the vehicle and the received radio wave intensity. The present invention was completed by finding the fact that this is appropriate. That is, an object of the present invention is to select an optimum combined antenna in a weak electric field area and expand a receivable area in diversity reception.

According to the first aspect of the present invention, in the diversity receiver mounted on the moving body, the left front antenna provided on the left front, the right front antenna provided on the right front, and the left rear are provided with the moving direction of the moving body as the front. The left rear antenna, the right rear antenna provided on the right rear, and the received signal of the left front antenna and the left rear when the received radio wave is smaller than a predetermined intensity and the speed of the moving body is smaller than the predetermined speed. When the received signal set of the antenna, the received signal of the right rear antenna and the received signal of the right front antenna, and the received radio wave is larger than the predetermined intensity or the speed of the moving body is larger than the predetermined speed, the front left A switching control unit that selects and switches between a combination of the reception signal of the antenna and the reception signal of the right front antenna and a combination of the reception signal of the left rear antenna and the reception signal of the right rear antenna is switched by the switching control unit. For each set of received signals which are, in diversity combining, and having a switching combining unit for outputting each set of combined signal.

The present invention performs diversity combining before demodulation.

According to a second aspect of the present invention, in the diversity reception method mounted on a moving body, four antennas are provided in front of the left, front right, left rear, and right rear with respect to the moving direction of the moving body, and a received radio wave is predetermined When the moving body speed is smaller than a predetermined speed, the set of the reception signal of the left front antenna and the reception signal of the left rear antenna, the reception signal of the right rear antenna, and the right front antenna When the received radio wave is larger than a predetermined intensity or the speed of the moving body is larger than a predetermined speed, the received signal of the left front antenna and Each combined signal formed by a set of received signals from the right front antenna, a set of received signals from the left rear antenna, and a set of received signals from the right rear antenna is output. The present invention performs diversity combining before demodulation.

  As described below, the present inventors have found that more appropriate diversity combining is possible by switching the combination of antennas provided in the moving body according to the speed of the moving body and the intensity of the received radio wave. . This is because, when the moving body is vertically long with respect to the main moving direction of the moving body, the received radio waves of the two antennas provided apart in the longitudinal direction are divided between the traveling direction of the moving body and the traveling direction of the received radio waves. This is due to the fact that the frequency, phase, and multipath fading are often different because they are reversed. That is, when the speed of the moving body is high or the intensity of the received radio wave is high, it is more than diversity combining the received signals of the two antennas provided apart in the longitudinal direction of the longitudinally moving body in such a moving direction. For example, it is appropriate to combine the received signals of two antennas separated from each other by the width in the horizontal direction of the moving body on the front surface. In this case, the reason is that it is difficult to follow the change in the radio wave environment accompanying the movement of the moving body between the antennas having a large distance.

  On the other hand, when the moving speed of the moving body is low and the intensity of the received radio wave is small, the change in the radio wave environment itself is small, so that it is easy to follow the change in the radio wave environment even between distant antennas. If the intensity of the received radio wave is small, diversity combining between antennas farther away can realize combining with few errors.

The present invention uses four antennas, two each on a vertical position and a position parallel to the direction of movement of the moving body performs two sets of d'Ibashichi synthesized by the speed and intensity of the received radio wave of mobile This can be achieved. In addition, when receiving a modulated signal having an error correction code, etc., two sets of diversity combining are performed to check the error correction state after demodulation, and the error can be corrected while using the demodulated signal from the main combined signal. If the part which is not replaced is replaced with a demodulated signal from another synthesized signal, the antenna usage efficiency increases. Also, since two sets of diversity combined signals are obtained , they are combined before demodulation to further improve diversity gain .

  The present invention can be used for a moving body that is vertically long in the moving direction, for example, a moving body such as a vehicle, a ship, an aircraft, or the like. The number of antennas is three or more, two are arranged in the moving direction of the moving body, that is, the vertical direction of the vertically long moving body, and the other one is arranged in the horizontal direction. In the case of using four antennas, it is preferable to provide the moving direction in front, for example, left front, right front, left rear, and right rear of the moving body.

  When receiving a modulated signal having an error correction code, etc., two or more sets of diversity combining are performed, the error correction state after demodulation is confirmed, and the error can be corrected while using the demodulated signal from the main combined signal. It is preferable to replace the missing portion with a demodulated signal from another synthesized signal. When receiving an OFDM-modulated signal, two or more sets of fast Fourier transformers and error correctors are required, but the error correction function can be supplemented.

  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. For the weighting coefficient, for example, (complex) correlation calculation can be used. 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. Also, the weighting factor may be determined based solely on the average amplitude of each branch.

  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 signal processing units such as two sets of FFT and error correction in an apparatus that receives an OFDM signal, and is mounted on a vehicle. .

  The configuration of the diversity receiver 100 includes four antennas A1, A2, A3, and A4 provided on the right front, left front, right rear, and left rear of the vehicle, and a multiplier (down converter) provided corresponding to each antenna. ) 21, 22, 23 and 24, variable analog amplifiers 31, 32, 33 and 34, analog / digital converters (A / D) 41, 42, 43 and 44, complex multipliers 71, 72, 73 and 74, It comprises a local oscillator 10, an auto gain controller (AGC) 30, an orthogonal demodulator 50, a switching controller 60, a weighting factor calculator 70 and a switching adder 80. Here, the complex multipliers 71, 72, 73 and 74, the weighting factor calculator 70, and the switching adder 80 constitute a switching composition unit as claimed.

  Signal processing in the diversity receiver 100 is as follows. A high frequency of, for example, a 500 MHz band received by the right front 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 left front antenna A2, the right rear antenna A3, and the left rear antenna A4 are also output as baseband digital complex signals from the orthogonal demodulation unit 50. 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.

  Four sets of baseband digital complex signals, which are outputs of the orthogonal demodulator 50, are input to the weight coefficient calculator 70, and complex correlation calculation is performed with one of the two outputs of the switching adder 80. 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 switching adder 80. In the switching adder 80, the addition of the outputs of the complex multipliers 71 and 72 is set as the master combined signal M, the addition of the outputs of the complex multipliers 73 and 74 is output as the slave combined signal S, and the complex multipliers 71 and 73 are output. Of the outputs of the complex multipliers 72 and 74 may be output as the slave combined signal S.

  In the weighting factor calculator 70, each of the four sets of baseband digital complex signals is switched with which of the two outputs of the switching adder 80 is subjected to complex correlation calculation, and the master synthesis in the switching adder 80 The switching control unit 60 controls switching of which complex multiplier outputs the signal M and the slave combined signal S are added to.

  The switching control unit 60 is a combination of two sets of diversity combining of four branches based on the vehicle speed obtained from an unillustrated sensor and the received radio wave intensity calculated from the amplification factors of the variable analog amplifiers 31 to 34 obtained from the AGC 30. Switch.

  When the vehicle speed is lower than the predetermined speed and the received radio wave intensity is lower than the predetermined intensity, diversity combining by the right front branch and the right rear branch is performed as a master combined signal, and the left front branch and the left rear branch are combined as slave combined signals. Diversity synthesis with. That is, in the weighting factor calculator 70, the weighting factors output to the complex multipliers 71 and 73 are calculated by complex correlation calculations between the right front branch and the right rear branch and the master composite signal M, respectively. On the other hand, the weighting coefficients output to the complex multipliers 72 and 74 are calculated by complex correlation operations between the left front branch and the left rear branch and the slave combined signal S, respectively. On the other hand, the switching adder 80 outputs the addition of the outputs of the complex multipliers 71 and 73 as the master combined signal M, and outputs the addition of the outputs of the complex multipliers 72 and 74 as the slave combined signal S. When the vehicle speed is lower than the predetermined speed and the received radio wave intensity is lower than the predetermined intensity, the switching control unit 60 controls the weighting coefficient calculator 70 and the switching adder 80 in this way.

  When the vehicle speed is higher than the predetermined speed or the received radio wave intensity is higher than the predetermined intensity, diversity combining is performed by using the right front branch and the left front branch as the master combined signal, and the right rear branch and the left rear branch are used as the slave combined signal. Diversity synthesis with. That is, in the weighting coefficient calculator 70, the weighting coefficients output to the complex multipliers 71 and 72 are calculated by complex correlation calculations of the right front branch and the left front branch and the master composite signal M, respectively. On the other hand, the weighting coefficients output to the complex multipliers 73 and 74 are calculated by complex correlation operations between the right rear branch and the left rear branch and the slave combined signal S, respectively. On the other hand, the switching adder 80 outputs the addition of the outputs of the complex multipliers 71 and 72 as the master combined signal M, and outputs the addition of the outputs of the complex multipliers 73 and 74 as the slave combined signal S. When the vehicle speed is lower than the predetermined speed and the received radio wave intensity is lower than the predetermined intensity, the switching control unit 60 controls the weighting coefficient calculator 70 and the switching adder 80 in this way.

  This switching and the subsequent processing are shown in FIG. FIG. The antennas A1, A2, A3, and A4 are arranged on the right front, left front, right rear, and left rear of the wagon type vehicle whose movement direction is indicated by an arrow as in A, and the front right and left front diversity as indicated by the broken line. The synthesis (master synthesis signal) is fast Fourier transformed (FFT) to obtain a master signal. On the other hand, the right rear and left rear diversity combining (slave combined signal) is fast Fourier transformed (FFT) to obtain a slave signal. By combining these for each carrier, a signal with higher reliability is obtained and processing such as error correction processing is performed. FIG. A corresponds to the case where the vehicle speed is higher than a predetermined speed or the received radio wave intensity is higher than a predetermined intensity.

  On the other hand, FIG. The antenna antennas A1, A2, A3, and A4 are arranged on the right front, left front, right rear, and left rear of the wagon type vehicle whose movement direction is indicated by arrows as shown in B, and the front right and right rear as shown by the broken lines. The diversity synthesis (master synthesis signal) is fast Fourier transformed (FFT) to obtain a master signal. On the other hand, diversity synthesis (slave synthesis signal) on the left front and left rear is fast Fourier transformed (FFT) to obtain a slave signal. By combining these for each carrier, a signal with higher reliability is obtained and processing such as error correction processing is performed. FIG. B corresponds to a case where the vehicle speed is lower than a predetermined speed and the received radio wave intensity is lower than a predetermined intensity.

  When the vehicle speed is higher than the predetermined speed or the received radio wave intensity is higher than the predetermined intensity as described above, FIG. The configuration of A is shown in FIG. FIG. 3 shows that it is more appropriate than the configuration of B. FIG. A is shown in FIG. FIG. 3 shows a change in the reception rate when the diversity combining of A is performed (the master is front right and front left) in a hatched area. B is FIG. The change of the reception rate when the diversity combining of B (the master is front right and rear right) is shown by the hatched area. The electric field strength was 60-80 μV / m, and the moving speed was 90 km / h. FIG. When the diversity combining of A (the master is front right and front left), the reception rate is 100% in most of all the sections, and the average is 99.7%. FIG. When the diversity combining of B is performed (the master is front right and rear right), there are only a few portions indicating 100%, there is a section where the reception ratio is 0%, and the average in all the sections is 83.6. % Remained.

  When the vehicle speed is lower than the predetermined speed and the received radio wave intensity is lower than the predetermined intensity, FIG. The configuration of B is shown in FIG. FIG. 4 shows that it is more appropriate than the configuration of A. FIG. A is shown in FIG. FIG. 4 shows the change in the reception rate when the diversity combining of A is performed (the master is front right and front left) in a hatched area. B is FIG. The change of the reception rate when the diversity combining of B (the master is front right and rear right) is shown by the hatched area. Although the electric field strength partially reached 80 μV / m, it was 65 μV / m or less in most sections, and the moving speed was 40 km / h or less including stopping. FIG. The reception rate when diversity combining of A is performed (master front right and left front) is 100% in almost all sections, but there is a section where the field strength becomes 0% when the electric field strength falls below 50 μV / m. The average was 92.8%. FIG. Although the reception rate when diversity combining of B (master is on the right front and right rear) is 100% in almost all the sections, there is a section where the field intensity becomes 0% when the electric field strength falls below 50 μV / m. Occurred in part, average 94.5%

  FIG. In A, carrier synthesis is performed after FFT conversion, but the following may be used. The right front and left front diversity combining (master combined signal) is OFDM demodulated into a master demodulated signal. On the other hand, diversity combining (slave combining signal) of the right rear and left rear is OFDM demodulated to obtain a slave demodulated signal. Each of these is subjected to error correction processing or the like, and the portion where the error cannot be corrected by the master demodulated signal is replaced with a slave demodulated signal. This case is also appropriate when the vehicle speed is higher than the predetermined speed or the received radio wave intensity is higher than the predetermined intensity.

  Similarly, FIG. Although carrier synthesis was performed after FFT conversion in B, the following may be used. The right front and right rear diversity combining (master combined signal) is OFDM demodulated into a master demodulated signal. On the other hand, diversity combining (slave combined signal) of the left front and left rear is OFDM demodulated to obtain a slave demodulated signal. Each of these is subjected to error correction processing or the like, and the portion where the error cannot be corrected by the master demodulated signal is replaced with a slave demodulated signal. This case is also appropriate when the vehicle speed is lower than the predetermined speed and the received radio wave intensity is lower than the predetermined intensity.

[Modification]
The present invention can be combined with various other diversity combining techniques. For example, as disclosed in Japanese Patent Application Laid-Open No. 2004-221808 by the present inventors, the received signal of each antenna is divided into three bands, and the diversity combining is performed for each band, and then combined in phase and the above-described implementation Examples may be combined.

  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 shows the structure of the diversity receiver 100 which is one specific Example of this invention. 2. A is an explanatory diagram of diversity combining when the vehicle speed is higher than a predetermined speed or the received radio wave intensity is higher than a predetermined intensity. B is an explanatory diagram of diversity combining when the vehicle speed is lower than a predetermined speed and the received radio wave intensity is lower than a predetermined intensity. 2. When the vehicle speed is higher than a predetermined speed or the received radio wave intensity is higher than a predetermined intensity, A is shown in FIG. 2. A change in the reception rate in the case of performing A diversity combining (master is front right and left front) is indicated by a hatched area. B is shown in FIG. The hatched area indicates the change in the reception rate when the diversity combining of B (right front and right after the master) is performed. 3. When the vehicle speed is lower than the predetermined speed and the received radio wave intensity is lower than the predetermined intensity, A is shown in FIG. 3. A change in the reception rate when the diversity combining of A (the master is front right and front left) is indicated by a hatched area. B is shown in FIG. The hatched area indicates the change in the reception rate when the diversity combining of B (right front and right after the master) is performed.

100: Diversity receiver A1, A2, A3, A4: Front right, left front, right rear, and left rear 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: Orthogonal demodulator 60: Switch controller 70: Weight coefficient calculator 71, 72, 73, 74: Complex multiplier 80: Switch adder

Claims (2)

In a diversity receiver mounted on a moving body,
With the moving direction of the moving body as the front, the left front antenna provided at the left front, the right front antenna provided at the right front, the left rear antenna provided at the left rear, and the right rear antenna provided at the right rear,
When the received radio wave is smaller than a predetermined intensity and the speed of the moving body is lower than the predetermined speed, the set of the reception signal of the left front antenna and the reception signal of the left rear antenna and the reception signal of the right rear antenna When the received signal set of the right front antenna and the received radio wave are larger than a predetermined intensity or the speed of the moving body is larger than the predetermined speed, the received signal of the left front antenna and the received signal of the right front antenna A switching control unit that switches and selects a set and a set of the reception signal of the left rear antenna and the reception signal of the right rear antenna;
A diversity receiving apparatus comprising: a switching combining unit that performs diversity combining on each set of reception signals switched by the switching control unit and outputs a combined signal of each set . In a diversity reception method in a mobile object,
Four antennas are provided in front of the moving direction of the moving body, left front, right front, left rear, right rear,
When the received radio wave is lower than the predetermined intensity and the speed of the moving body is lower than the predetermined speed, a set of the reception signal of the left front antenna and the reception signal of the left rear antenna and the reception signal of the right rear antenna And each combined signal formed by the set of received signals of the right front antenna,
When the received radio wave is larger than a predetermined intensity or the speed of the moving body is larger than a predetermined speed, a set of the reception signal of the left front antenna and the reception signal of the right front antenna, the reception signal of the left rear antenna, and A diversity reception method, comprising: outputting combined signals formed by a set of reception signals of the right rear antenna.