JP2003283405A - On-vehicle digital communication receiver and antenna - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an on-vehicle digital communication receiver for decreasing the number of wireless detection sections in use in comparison with the number of antennas and to provide the on-vehicle mount antennas capable of easily obtaining the directivity. <P>SOLUTION: A forward beam antenna 22A (backward beam antenna 22B) is mounted in front (at the back) of a vehicle, an antenna selection circuit 29 switches a changeover switch 23, and the receiver receives a radio wave signal of the OFDM system to reduce the inter-carrier interference ICI due to multi-path fading or the like. The antenna selection circuit 29 discriminates whether or not the switching is to be performed on the basis of received power information and error rate information. The forward beam antenna 22A and the backward beam antenna 22B realize their reflectors by using the metallic body of the vehicle. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is mounted on a vehicle,
Orthogonal Frequency Divi
The present invention relates to an in-vehicle digital signal receiving device and an antenna for receiving a digital signal such as a radio wave modulated by a sion multiplex (sometimes abbreviated as “OFDM”) system.

[0002]

2. Description of the Related Art Conventionally, an OFDM system has been developed as a transmission system for terrestrial digital television broadcasting. The OFDM system is a form of a multi-carrier transmission system, and is, for example, 530 arranged at 1 kHz intervals.
Amplitude and phase modulation (QA
M) is applied and the signal is transmitted. The multi-carrier method is generally known as a modulation method having excellent resistance to frequency selective fading. Frequency selective fading poses a problem of degrading the line quality in broadband wireless communication. In terrestrial digital television broadcasting, it is necessary to transmit high-quality images, so
OFD in a frequency band of about 500 MHz to 800 MHz
Adopt M method. In a modulated signal of the OFDM system, although the frequency bands of modulated waves overlap between adjacent subcarriers, orthogonality such that the correlation of modulated wave band signals becomes zero is secured by batch modulation / demodulation by fast Fourier transform (FFT). be able to. Furthermore, by adding a guard interval signal on the transmission side, inter-symbol interference (Inter-Symbol Interfer
ence: ISI) can be removed.

FIG. 29 shows the structure of the transmission side and the frequency band arrangement of subcarriers according to the OFDM method. FIG. 29
As shown in (a), first, in the baseband, serial data to be transmitted is converted by the serial / parallel conversion unit (S / P) 5 into parallel data composed of a plurality of, for example, N complex number symbols. IFFT (Inverse Fast FourierTransf
The orm) calculation unit 6 performs an inverse fast Fourier transform (IFFT) on the frequency data so that each symbol is transmitted by subcarriers having frequencies at intervals shown in FIG.
As a result, the frequency components of the subcarriers are converted into a multiplexed time signal. The real part Re and the imaginary part of the time signal Im are LPF (Low Pass Filter) 7a,
It is input to the quadrature modulator 8 as I-ch and Q-ch through 7b. The quadrature modulator 8 performs quadrature modulation on the input data, and up-converts it into a high-frequency signal and transmits it by a transmission unit on the latter stage side (not shown).
On the receiving side, the FFT is performed as the inverse operation of the IFFT on the transmitting side.
To time-frequency conversion, demodulate and output N symbols transmitted on N subcarriers.

FIG. 30 shows a guard interval. The OFDM signal constitutes one symbol in the guard period GI and the effective symbol period. In the guard period GI, the signal after the effective symbol period is cyclically copied. The guard period GI is inserted in order to prevent interference due to a delayed signal. The concept of performing frequency synchronization using a signal in the guard period GI is, for example, October 1, 1996.
Technical Report of Television Society announced on 7th (ITE Technical
Page 61 to 66 of Report Vol.20 No.53), "ODF
Of frequency synchronization in M demodulation ".

When a moving vehicle receives a radio wave modulated by the OFDM system, a Doppler shift, which is a frequency shift based on the Doppler effect, becomes an obstacle. The Doppler shift is particularly likely to cause deterioration of reception characteristics when the multipath in which radio waves propagate through a plurality of paths have frequency selectivity. If frequency fluctuations occur independently for each subcarrier, synchronization between subcarriers on the receiving side becomes difficult, orthogonality is lost, and inter-carrier interference (inter-carrier interference) occurs.
This is because Interference (ICI) occurs. Since the frequency shift caused by the Doppler shift is proportional to the speed of the vehicle, the inter-carrier interference becomes remarkable especially during traveling at high speed. In order to suppress inter-carrier interference in a multipath environment, each path must be estimated and its fluctuation component must be equalized. The applicant of the present application filed Japanese Patent Application No. 2001-27
As 9292, a concept is proposed in which a plurality of directional antennas having different directing directions are provided in a moving body and the directivity is switched to improve characteristic deterioration due to inter-carrier interference in a multipath environment.

FIG. 31 shows a patent application 20 as a basis of the present invention.
01-279292 shows a configuration basically equivalent to the OFDM receiving apparatus according to the first embodiment attached as FIG. It should be noted that the above-mentioned FIG. 29 and FIG.
-279292 is basically equivalent to the drawings attached as FIGS. 24 and 25, respectively. However, for convenience of description, some reference numerals and the like are changed.

In FIG. 31, the area 3 around the automobile, which is a moving body, is shown.
The range of 60 ° is divided into four sectors of 90 °, and the directional antennas 11a, 11b, 11c, 11 are provided in each sector.
d is provided. The antennas 11a and 11d have directivities in the front and rear directions of the vehicle, respectively, and the antennas 11b and 11c have directivity in the left and right directions of the vehicle. Radio receiver (RV) 12a, 1
2b, 12c, 12d are antennas 11a, 11b,
The radio signals received by 11c and 11d are amplified, frequency-converted into a baseband signal, and input to the antenna switching unit 13. The received power measuring unit 14 receives the received signal strength of each of the wireless receiving units 12a, 12b, 12c, 12d, for example, RSSI (Received Signal Strength Indicato).
The received power is measured by measuring r). The antenna selection unit 15 selects the antennas 11a to 11d having the maximum received power based on the received power. The reception signal of the selected antenna is input to the quadrature demodulation unit 16 which constitutes the demodulation unit DEM (DE Modulator). The quadrature demodulator 16
The received signal is subjected to quadrature demodulation processing. The demodulated signal is G
The I removing unit 17 synchronizes the timing, removes the guard period (GI), and outputs the signal.

The variable average shift amount calculating section 18 calculates the variable average shift amount Δθ per symbol of multipath fading by calculating the correlation between the known pilot signal and the received signal. The fading compensation unit 19
The received signal is multiplied by exp (-jΔθ) to compensate for multipath fading. The FFT calculator 20 transforms the time domain signal into N carrier signals. An error detection / correction decoding unit (not shown) performs error detection / correction and decoding processing on the N carrier signals.

A prior art relating to receiving a radio wave of a digital signal such as OFDM by switching a plurality of antennas is disclosed in, for example, Japanese Patent Laid-Open No. 11-205290 and Japanese Patent Laid-Open No. 2290290.
000-174726, JP 2000-2782.
No. 43 and Japanese Patent Laid-Open No. 2001-86091. In Japanese Patent Application Laid-Open No. 11-205290, in order to improve the deterioration of the reception characteristics that occurs in a multiple reflection radio wave propagation environment or a mobile reception environment, O from a plurality of antennas is used.
Disclosed is a prior art in which an FDM received signal is delayed in time, an antenna having a maximum correlation value of the OFDM received signal before and after the delay is selected, and an OFDM signal from the selected antenna is demodulated. Japanese Patent Laid-Open No. 2000-17472
Japanese Patent Publication No. 6 discloses a prior art in which a subcarrier level or the like is detected and antenna switching is performed so that a sufficient diversity effect can be obtained even in the case of a frequency selective fading propagation path. Japanese Patent Laid-Open No. 2000-278243 discloses a prior art in which received signals from a plurality of antennas are combined in order to improve anti-multipath fading characteristics. Japanese Patent Laid-Open No. 2001-86091 discloses a prior art in which signals received by a plurality of antennas are combined before OFDM demodulation to improve the characteristics of the received signal.

[0010]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention In the above-mentioned respective prior arts, a diversity system for receiving a digital signal radio wave such as OFDM is provided by installing an antenna having a directional characteristic of a vehicle traveling direction and an antenna having a reverse directional characteristic of a vehicle. There is no specific disclosure regarding an antenna arrangement suitable for the above.

In FIG. 31, the directivity of the antennas 11a to 11d is used to limit the range for compensating for multipath fading to the direction in which the received power is large. Since this direction changes as the vehicle moves, it is switched so that the received power becomes maximum. Whether the received power is maximum or not,
Since it is necessary to compare the received powers from the antennas 11a to 11d, the wireless reception units 12a to 12d are provided for the antennas 11a to 11d, respectively. However, as described above, the wireless reception units 12a to 12d that amplify the high frequency signal and convert the high frequency signal to the base band are 500M.
Since a high frequency signal of about Hz is handled, it is expensive, and if the same number as the plurality of antennas 11a to 11d is used, the vehicle-mounted OFD is used.
This increases the manufacturing cost of the M receiver.

An object of the present invention is to provide an on-vehicle digital signal receiving apparatus which can reduce the number of radio receiving units used as compared with the number of antennas, and an antenna which can be easily mounted on a vehicle to obtain directivity. Is to provide.

[0013]

SUMMARY OF THE INVENTION The present invention is a vehicle-mounted digital signal receiving apparatus for receiving a radio wave modulated by an orthogonal frequency division multiplexing system, which is mounted on a vehicle, and which is unidirectionally predetermined for the vehicle. The orthogonal frequency division multiplexing system is switched to select one of a plurality of directivities including a directivity in which the gain is increased on the side of one side and a directivity in which the gain is increased in the direction opposite to the one direction. The antenna means capable of receiving the radio wave modulated by, and the demodulation means for inputting the electric signal corresponding to the received radio wave by switching the directivity from the antenna means, amplifying and demodulating it, and for running the predetermined vehicle An in-vehicle digital signal receiving device, comprising: directivity selecting means for detecting accompanying information and controlling the antenna means by switching the antenna means in accordance with the detected information.

According to the present invention, the on-vehicle digital signal receiving device is mounted on a vehicle and has an antenna means, a demodulating means, and a directivity selecting means for receiving a radio wave modulated by the orthogonal frequency division multiplexing method. including. The antenna means has one of a plurality of directivities including a directivity in which a gain is increased in a predetermined one direction side with respect to the vehicle and a directivity in which a gain is increased in a reverse direction of the one direction side. It is possible to receive the electric wave of the digital signal modulated by the orthogonal frequency division multiplexing method or the like by switching the selection. Therefore,
Even if the radio wave of the received digital signal is affected by multipath fading, the directivity can be switched to narrow the arrival direction of the received radio wave. The demodulation means inputs the electric signal corresponding to the electric wave received by switching the directivity from the antenna means, amplifies and demodulates the electric signal. The directivity selecting means detects information associated with traveling of a predetermined vehicle, and switches the antenna means according to the detected information to control the directivity. Therefore, when the vehicle travels and the direction of the incoming radio wave changes, the directivity of the antenna means can be switched to receive the radio wave under the condition that the influence of multipath fading is easily removed. Since a plurality of directivities can be switched by the directivity selection means and input to the demodulation means, it is possible to reduce the number of demodulation means, particularly the number of parts for performing high frequency amplification and frequency conversion to baseband, and to reduce the terrestrial wave. OF for television broadcasting
It is possible to satisfactorily receive a DM signal and a large-capacity high-speed data signal.

Further, in the present invention, the directivity selection means switches the directivity of the antenna means for each predetermined short time, and selects the directivity depending on the superiority or inferiority of the reception state.

According to the present invention, directivities in a plurality of directions are
Since the switching is performed for each predetermined short time, it is possible to easily compare the superiority and inferiority of the reception state between the directivities and judge the superiority or inferiority without receiving a plurality of directivities at the same time.

Further, in the invention it is preferable that the directivity selecting means determines the superiority or inferiority of the reception state based on the reception power information.

According to the present invention, since the superiority or inferiority of the reception state is judged from the received power information, the directivity of the antenna means can be switched to the direction in which the received power is high.

Further, in the invention it is preferable that the directivity selecting means determines the superiority or inferiority of the reception state based on the reception error rate information.

According to the present invention, since the superiority or inferiority of the reception state is judged from the reception error rate information, the directivity of the antenna means can be switched to the direction in which the reception error rate is small.

Further, in the present invention, the directivity selecting means selects the directivity of the antenna means based on the information about the arrival direction of the received radio wave.

According to the present invention, the radio wave is received under the condition that the influence of the multipath fading is easily removed by adjusting the directionality of the antenna to the arrival direction based on the information about the arrival direction of the received radio wave. It can be performed.

Also, in the present invention, the directivity selecting means determines the arrival direction of the received radio wave based on information about the direction of Doppler shift with respect to the frequency of the received radio wave and information about the traveling speed of the vehicle. It is characterized by

According to the present invention, when the traveling direction of the vehicle approaches the arrival direction of the received radio wave, the Doppler shift shifts to the direction in which the frequency increases, and when the traveling direction moves away from the arrival direction, the Doppler shift decreases in the frequency. It shifts in the direction. The frequency shift due to Doppler shift can be considered to be proportional to the traveling speed. Therefore, it is possible to know the arrival direction of the received radio wave based on the information about the Doppler shift and the information about the traveling speed of the vehicle, and to select the direction of the directivity of the antenna means according to the arrival direction of the received radio wave. You can

Further, in the present invention, the directivity selecting means detects the information about the traveling speed of the vehicle based on the detection of the change of the traveling direction by the gyro and the detection of the speed.

According to the present invention, since the information about the traveling speed of the vehicle is detected based on the change of the traveling direction by the gyro and the speed, the influence of the Doppler shift is evaluated by the speed and the traveling direction is evaluated according to the traveling direction. The directivity can be appropriately selected.

Further, in the present invention, the directivity selecting means determines the arrival direction of the received radio wave based on the detection information of the current position of the vehicle and the geographical information about the location of the broadcasting station. And

According to the present invention, it is possible to geographically determine the arrival direction of the received radio wave transmitted from the transmitting antenna of the broadcasting station and arriving at the vehicle, and select an appropriate directivity direction.

Further, in the present invention, the directivity selecting means selects the directivity of the antenna means when a predetermined switching start condition is satisfied.

According to the present invention, the directivity of the antenna means is selected when a predetermined switching start condition is satisfied. Therefore, the high frequency amplification and frequency of the received signal are compared with the number of selectable directivity directions. Even if the number of parts to be converted is small,
If it is necessary to switch the directivity, the directivity of the antenna means can be switched to receive the radio wave of the digital signal under appropriate conditions.

Further, in the invention, it is preferable that the directivity selecting means determines a time point at which the received power falls below a predetermined standard as a time when the predetermined switching start condition is satisfied.

According to the present invention, if the deviation between the arrival direction of the received radio wave and the directivity of the antenna means becomes large, the reception power decreases. Since it is determined that the switching start condition is satisfied when the received power falls below a predetermined standard,
The directivity of the antenna means can be matched with the arrival direction of the received radio wave, and the deviation of the direction can be appropriately eliminated.

Further, in the invention it is preferable that the directivity selecting means determines a time point at which the reception error rate rises above a predetermined standard as the time when the predetermined switching start condition is satisfied.

According to the present invention, if the difference between the arrival direction of the received radio wave and the direction of the directivity of the antenna means becomes large, the reception power is lowered and is easily affected by noise and the reception error rate is increased. Since the time when the reception error rate rises above the predetermined standard is determined as the time when the switching start condition is satisfied, the directivity of the antenna means can be adjusted to the arrival direction of the received radio wave, and the deviation of the direction can be appropriately eliminated. be able to.

Further, in the invention, it is preferable that the directivity selecting means determines a time point at which the traveling speed rises above a predetermined reference as a time when the predetermined switching start condition is satisfied.

According to the present invention, as the traveling speed of the vehicle increases, the influence of Doppler shift increases, and it becomes necessary to match the arrival direction of the received radio wave with the directivity of the antenna means. Since the time when the traveling speed rises above the predetermined standard is judged as the time when the switching start condition is satisfied, it is possible to perform radio wave reception under appropriate conditions by adjusting the directivity of the antenna means to the arrival direction of the received radio wave. .

Further, in the invention, it is characterized in that the directivity selecting means always selects the directivity of the antenna means.

According to the present invention, since the directivity selecting means always selects the directivity of the antenna means, it is possible to always receive radio waves under appropriate conditions even when the vehicle moves.

Further, in the present invention, the antenna means and the demodulation means are provided with two systems capable of receiving radio waves independently of each other, and the directivity selection means is an antenna means and a demodulation system of either one of the systems. Regarding the means, the directivity is selected.

According to the present invention, since the antenna means and the demodulating means are used in two systems and the directivity is selected in either one of the systems, while the directivity is selected, only the other system receives the signal. Can be continued, and smooth reception can be performed even if the number of portions performing high-frequency amplification or frequency conversion is smaller than the number of directivity directions selectable by the antenna means in each system.

Further, in the present invention, the directivity selecting means adjusts the directivity of the antenna means of a system different from the one of the two systems to the directivity of the antenna means of the one system. It is characterized in that they are selected and a time lag is provided for switching.

According to the present invention, when an appropriate directivity direction is selected by using the antenna means and demodulation means of one system, the directivity directions of the antenna means of the other system are also made to coincide with each other. Thus, it is possible to receive radio waves by the diversity method by matching the directivity directions.
Since the operation of matching the directivity of the other system with the directivity of the one system is performed with a time difference, the directivity of the other system is switched while receiving the directivity of the other system that has switched the directivity first. be able to.

In the present invention, the received signals from the antenna means of the two systems are used as frequency synthesis diversity.
It is characterized by further including a synthesizing unit for synthesizing by receiving weighting based on the superiority or inferiority of the receiving state of each frequency component, synthesizing and receiving, and switching the antenna directivity.

According to the present invention, since the receiving means from the antenna means of the system is combined and received by the combining means as frequency combining diversity with weighting based on the superiority or inferiority of the receiving condition of each frequency component, It is possible to perform reception by appropriately allocating antenna sequences according to the arrival state of. In the system in which the directivity of the antenna is switched, the reception state fluctuates greatly, so the weighting can be lowered (it is also possible to set it to 0), and the deterioration of the reception performance can be prevented.

In the present invention, the antenna means and the demodulation means are provided with two systems capable of receiving radio waves independently of each other, and the directivity selecting means controls the directivity of the two systems of antenna means. , Are selected so as to be different from each other, and frequency band division diversity system reception is performed between the two systems.

According to the present invention, in multipath fading, it may be preferable to receive on different paths depending on the frequency band. Since the directivities of the antenna means of the two systems in different directions are selected to be different from each other and the frequency band division diversity system reception is performed between the two systems, it is possible to comprehensively receive under the appropriate conditions.

In the present invention, the antenna means includes an antenna having directivity toward the front of the vehicle, an antenna having directivity toward the rear, and an antenna having directivity toward the side of the vehicle. And

According to the present invention, by switching the directivity to the front and the rear of the vehicle, it is possible to easily compensate the deviation of the reception frequency due to the Doppler shift when the vehicle is traveling at high speed. By switching to the directivity to the side of the vehicle, it is possible to receive radio waves coming from the side of the vehicle under appropriate conditions.

In the present invention, the antenna means includes an antenna having directivity to the front of the vehicle and an antenna having directivity to the rear, and the antenna having the directivity to the front or the directivity to the rear. At least one of the effective antennas is characterized in that the lateral gain of the vehicle is also improved.

According to the present invention, the antenna having the directivity toward the side of the vehicle is also used as the antenna having the directivity toward the front or the rear of the vehicle to reduce the space required for installation in the vehicle. Thus, cost reduction can be achieved.

In the present invention, the lateral gain of the vehicle is improved by adding an antenna element.

According to the present invention, the gain to the side of the vehicle can be improved only by adding the antenna element to the antenna having directivity in front of or behind the vehicle.

Further, in the invention, it is characterized in that the antenna means includes a directional antenna having a reflector made of a metal body of the vehicle.

According to the present invention, since the antenna means includes the directional antenna using the metal body of the vehicle as a reflector, the metal body of the vehicle can be effectively used and the directional antenna can be realized at low cost. it can.

Further, in the invention, it is preferable that the antenna means includes a directional antenna that operates one of the two antenna elements as a reflector.

According to the present invention, a two-element Yagi type antenna or the like in which one of the two element antenna elements operates as a reflector is used as a directional antenna, and an antenna required in a plurality of directional directions is easily formed. Can be mounted on a vehicle.

Further, in the invention, it is characterized in that the two-element antenna element is a pole antenna element which is erected vertically from the vehicle.

According to the present invention, it is possible to provide a reflector on a pole antenna element which has no directivity at least in a horizontal plane, and can be used as a directional antenna mounted on a vehicle.

The present invention also relates to the digital signal,
The directivity selecting means further includes a correcting means for correcting in the time axis direction, and the directivity selecting means takes a predetermined time by switching the antenna so that the correction by the correcting means can follow.
It is characterized in that the attenuation rate of the reception signal from one antenna means is increased and the attenuation rate of the reception signal from the other antenna means is decreased.

According to the present invention, the correction means performs the correction in the time axis direction. For example, in an OFDM signal, a scattered pilot (SP) signal is used to predict the reception state, and the signal is received while performing correction based on the prediction. However, when the antenna is switched rapidly, the reception state fluctuates. May fall outside the range of prediction. The switching of the antenna means is performed by a fade-in / fade-out method that increases the attenuation rate of one side and decreases the attenuation rate of the other side over a certain period of time. It is possible to reduce performance deterioration.

Further, in the present invention, the directivity selecting means is provided in a weak electric field area where the reception state does not reach a predetermined standard.
It is characterized in that the outputs from the plurality of antenna means are combined and controlled to be received.

According to the present invention, the deterioration of the reception performance due to the decrease of the reception power becomes dominant in the weak electric field area, but since the outputs from the plurality of antenna means are combined and received,
It is possible to receive radio waves coming from many directions and increase the received electric field strength.

Further, in the present invention, the directivity selecting means is controlled so that the outputs from the plurality of antenna means are combined and received at the time of searching or tuning the received signal.

According to the present invention, the received signal cannot be specified when the received signal is searched or selected, and its arrival direction cannot be accurately known. If the antenna means is switched before the reception signal is specified, the state in which the OFMD signal is not synchronized, such as TMCC, continues for a long time, and it takes time to achieve stable reception.

Further, the present invention is an antenna mounted on a vehicle, which is arranged between a dipole element which is linearly arranged and has a power feeding portion in the center, and a metal body of the vehicle and one power feeding portion of the dipole element. Has a impedance matching the power feeding portion of the dipole element, and the first power feeding line electrically connecting with the first power feeding line and the metal body at the tip for power feeding. A coaxial cable in which the outer conductor is connected to the connection portion, the center conductor at the tip of the coaxial cable for feeding power, and the other feeding portion of the dipole element are electrically connected at the length of the quarter wavelength. And a second feed line kept in parallel with the first feed line.

According to the present invention, the metallic body of the vehicle and the feeding point of the dipole element are connected by the first and second feeding lines having a length of ¼ wavelength, and the metallic body operates as a reflector. Can be made. A dipole-type antenna mounted on a vehicle that allows a metallic vehicle body to act as a reflector to provide directivity. Since the tip of the coaxial cable has only to reach the connection part to the metal body, it can be hidden so that it cannot be seen from the outside.

Further, in the invention, it is characterized in that the dipole element, the first feeder line and the second feeder line are formed as a conductor pattern on an electrically insulating synthetic resin film.

According to the invention, a dipole element,
Since the first and second power supply lines are formed as conductor patterns on the electrically insulating synthetic resin film, the first and second power supply lines are formed.
It can be handled in a state where the power feeding line of is connected to the power feeding portion in the center of the dipole element.

Further, in the present invention, the metal vehicle body is a roof of a vehicle, and the synthetic resin film is attached on a window glass of the vehicle.

According to the present invention, a synthetic resin film having a dipole element and first and second power feed lines formed as conductor patterns is attached on a window glass of a vehicle, and a metal car body is used as a reflector for directing. It is possible to easily realize the antenna having the property.

[0071]

BEST MODE FOR CARRYING OUT THE INVENTION An on-vehicle OFDM receiver as an embodiment of the present invention will be described below with reference to FIGS. 16 to 24, an antenna according to each embodiment of the present invention will be described. In addition, FIGS.
8, antenna switching according to yet another embodiment of the present invention will be described. In each embodiment, the same reference numerals are given to portions corresponding to the embodiments described above,
A duplicate description will be omitted. Further, although a case of receiving an OFDM terrestrial digital television broadcast will be described, the present invention can be applied to a case of receiving a large-capacity digital signal in general.

FIG. 1 shows a schematic configuration of an in-vehicle OFDM receiver 21 according to the first embodiment of the present invention. In-vehicle O
The FDM receiver 21 is mounted on a vehicle, and receives a radio wave modulated by the orthogonal frequency division multiplexing system. The front beam antenna 22A, the rear beam antenna 22B,
Changeover switch 23, RF / IF unit 24, OFDM demodulation unit 25, level detection unit 26, error correction unit 27, AGC unit 2
8 and an antenna selection circuit 29.

The forward beam antenna 22A, the backward beam antenna 22B, and the changeover switch 23 have directivity such that the gain is high in the forward direction, which is a predetermined one-direction side with respect to the vehicle, and the reverse direction of the one-direction side. Is selected by the change-over switch 23 so as to select one of a plurality of directivities including a directivity in which the gain is increased in the rear direction.
An antenna means capable of receiving a radio wave modulated by the orthogonal frequency division multiplexing method is configured.

RF / IF section 24, OFDM demodulation, OFD
The M demodulation unit 25, the level detection unit 26, the error correction unit 27, and the AGC unit 28 are OFDM demodulation means for inputting, from the antenna means, an electric signal corresponding to a radio wave received by switching the directivity, and amplifying and demodulating the electric signal. Function as. RF /
The IF unit 24 amplifies a high frequency signal, converts it into an intermediate frequency, and further amplifies it. O for demodulating intermediate frequency signals
The FDM demodulation unit 25 includes a level detection unit 26 and an error correction unit 27 and demodulates and outputs an effective symbol (TS). The level detection unit 26 outputs the received power information, and the AG
The gain of the RF / IF unit 24 is adjusted via the C unit 28. The error correction unit 27 uses the error correction information included in the demodulated signal to detect an error and correct the error within a possible range, and outputs error rate information (Bit Error Rate: BER). The received power information and the error rate information are input to the antenna selection circuit 29. The antenna selection circuit 29 is
It functions as directivity selecting means for detecting information associated with traveling of a predetermined vehicle and controlling the antenna means by switching the antenna means in accordance with the detected information.

FIG. 2 shows an on-board OFDM receiver 21 of FIG.
The procedure of the antenna directivity switching control performed by the antenna selection circuit 29 will be described below. In step a1, it waits until the reception error rate becomes larger than a predetermined standard. That is, the reception error rate may exceed the standard and increase.
This is the condition for starting the antenna directivity switching. If the reception error rate is smaller than the standard, error correction is possible,
There is no need to switch the directivity of the antenna because the effect of errors is inconspicuous. When the error rate exceeds the reference in step a1 and becomes large, in step a2, the average reception level of the forward beam antenna 22A is set to, for example, several hundred meters.
Detect over a period of seconds. In step a3, the changeover switch 23 is switched to the backward beam antenna 22B side, and the average reception level of the backward beam antenna 22B is detected over a time period of, for example, several hundred milliseconds.
At step a4, the forward beam antenna 22A and the backward beam antenna 22B are compared at the average reception level. In step a5, based on the comparison result in step a4, the higher average reception level is held for a certain period of time, for example, several seconds to several tens seconds, and the process returns to step a1.

In steps a2 to a4, the antenna selection circuit 29 switches a plurality of directivities of the antenna means for each predetermined short time, and selects the directivity depending on the superiority or inferiority of the reception state. Since the directivities of multiple directions are switched for a predetermined short time, it is possible to easily compare the superiority and inferiority of the reception state between the directivities and judge the superiority or inferiority even if the multiple directivities are not simultaneously received. it can. Further, the superiority or inferiority of the reception state is determined based on the received power information. Since the superiority or inferiority of the reception state is determined by the received power information, it is possible to switch the directivity of the antenna means in the direction in which the received power is high.
The determination of the superiority or inferiority of the reception state can be made based on the reception error rate information.

FIG. 3 shows a schematic structure of an in-vehicle OFDM receiver 31 according to the second embodiment of the present invention. In-vehicle O
The FDM receiver 31 has two systems of antenna means and O.
Equipped with FDM demodulation means, it is possible to perform reception by the frequency division diversity system. One system is a forward beam antenna 22A1 and a backward beam antenna 22B.
1, a changeover switch 23, an RF / IF unit 24, an OFDM demodulation unit 35, a level detection unit 36, and an AGC unit 28. The other system includes the forward beam antenna 22A2, the backward beam antenna 22B2, the changeover switch 43, and the RF.
/ IF unit 44, OFDM demodulation unit 45, level detection unit 46
And an AGC section 48. OFDM demodulators 35 and 45
Is basically the same as the OFDM demodulation unit 25 of the embodiment of FIG. 1 except that it includes only the level detection units 36 and 46 and does not include the error correction unit 37. Two systems of forward beam antennas 22A1, 22A2, backward beam antennas 22B1, 22B2, changeover switch 23,
43, RF / IF section 24, 44, level detection section 36, 4
6 and the AGC units 28 and 48 are equivalent.

The outputs of the two OFDM demodulation units 35 and 45 are combined by the diversity combining unit 38, the combined output is input to the error correction unit 37, and the error rate information is input to the antenna selection circuit 39. Received power information from the level detectors 36 and 46 is also input to the antenna selection circuit 39,
It is used to control the changeover switches 23 and 43.

FIG. 4 shows the vehicle-mounted OFDM receiver 31 of FIG.
The procedure of antenna directivity switching control performed by the antenna selection circuit 39 will be described below. Step b1 waits until the reception error rate becomes larger than a predetermined standard. If the error rate exceeds the standard in step b1, the forward beam antenna 22A of one system is processed in step b2.
An average reception level of 1 is detected over a time period of, for example, several hundred milliseconds. In step b3, the changeover switch 23 is switched to the backward beam antenna 22B1 side, and the average reception level of the backward beam antenna 22B1 is detected over a time period of, for example, several hundred milliseconds. In step b4, the front beam antenna 22A1 and the rear beam antenna 22B1 are compared at the average reception level,
Switch to a higher average reception level. Step b5
Then, it waits for a fixed time, for example, a few hundred milliseconds.
In step b6, based on the comparison result in step b4, the other system is also switched to the one in which it is determined that the average reception level is higher in one system. For example, in the comparison result of step b4, the forward beam antenna 22A
1 average reception level> rearward beam antenna 22B1 average reception level, the forward beam antenna 22
A2 is selected. When the average reception level of the backward beam antenna 22B1> the average reception level of the forward beam antenna 22A1, the backward beam antenna 22B2 is selected. In step b7, a certain period of time, for example, several seconds to several tens seconds is held, and the process returns to step b1.

FIG. 5 shows a schematic configuration of an in-vehicle OFDM receiver 51 according to the third embodiment of the present invention. In-vehicle O
Although the FDM receiver 51 is provided with one system of antenna means and OFDM demodulation means as in the embodiment of FIG. 1, the OFDM demodulation section 55 includes the frequency detection circuit 26, the error correction section 27, and the frequency synchronization circuit 56. including. Further, the antenna selection circuit 59 inputs the error rate information from the error correction unit 27, the frequency shift information from the frequency synchronization circuit 56, and the vehicle speed pulse from the vehicle, detects the Doppler shift direction, and detects the Doppler shift direction. Switch over. Note that the OFDM demodulation units 25, 35, 45 of the embodiments of FIGS. 1 and 3 also include the same configuration as the frequency synchronization circuit.

As described above, in the present embodiment, the antenna selection circuit 49 as the directivity selecting means determines the arrival direction of the received radio wave, the information about the Doppler shift direction with respect to the frequency of the received radio wave, and the traveling speed of the vehicle. Make a decision based on the information. When the traveling direction of the vehicle approaches the arrival direction of the received radio wave, the Doppler shift shifts to the direction in which the frequency increases, and when the traveling direction moves away from the arrival direction, the Doppler shift shifts to the direction in which the frequency decreases. The frequency shift due to Doppler shift can be considered to be proportional to the traveling speed. Therefore, it is possible to know the arrival direction of the received radio wave based on the information about the Doppler shift and the information about the traveling speed of the vehicle, and to select the direction of the directivity of the antenna means according to the arrival direction of the received radio wave. You can

FIG. 6 shows the concept of detecting the Doppler shift direction in the embodiment of FIG. The traveling direction of the vehicle can be considered as a vector having the length of the traveling speed V. The angle formed by the traveling speed direction and the radio wave arrival direction is θ. When the Doppler shift frequency fd is positive, the angle θ is in the range of −90 ° to + 90 °. When the Doppler shift frequency fd is negative, θ is + 90 ° to +1.
It is in the range of 80 ° and −90 ° to −180 °. The Doppler shift frequency fd can be expressed by the following equation (1), where fc is the broadcast frequency and C is the radio wave propagation speed.

[0083]

[Equation 1]

Therefore, the angle θ can be calculated by the following equation (2).

[Equation 2]

Thus, when the angle θ is strictly calculated,
The arrival direction of radio waves can be calculated. However, there is no distinction between left and right directions with respect to the traveling direction of the vehicle. The lateral direction can be detected. The error increases when the traveling speed V is low. From equation (1), fc = 470 MH
When z = V = 100 km / h, fd = 44 Hz.

FIG. 7 shows an on-vehicle OFDM receiver 51 of FIG.
The procedure of antenna directivity switching control performed by the antenna selection circuit 59 will be described below. In step c1, it waits until the reception error rate becomes larger than a predetermined standard. When the error rate exceeds the standard in step c1, the average value of the Doppler shift frequency fd is detected in step c2 over a time period of several seconds, for example. In step c3, it is determined whether the Doppler shift frequency fd is higher than the threshold frequency fth and the traveling speed V is higher than the threshold speed Vth. When it is determined that both conditions are satisfied, the antenna selection circuit 59 switches the changeover switch 23 so as to select the forward beam antenna 22A in step c4. If the condition is not satisfied in step c3, it is determined in step c5 whether the Doppler shift frequency fd is lower than the threshold frequency −fth and the traveling speed V is higher than the threshold speed Vth. When it is determined that both conditions are satisfied, the antenna selection circuit 59 switches the changeover switch 23 so as to select the backward beam antenna 22B in step c6. If the condition is not satisfied in step c5, selection of the currently selected antenna is continued in step c7. Step c4,
After step c6 and step c7, step c1
Return to.

FIG. 8 shows a schematic configuration of an in-vehicle OFDM receiver 61 according to the fourth embodiment of the present invention. In-vehicle O
The FDM receiver 61 is provided with two systems of antenna means and OFDM demodulation means as in the embodiment of FIG. 3, and can perform reception by the frequency division diversity system. One system includes a front beam antenna 22A1, a rear beam antenna 22B1, a changeover switch 23, and an RF.
/ IF unit 24, OFDM demodulation unit 65, level detection unit 36
And an AGC unit 28. The other system is a front beam antenna 22A2, a rear beam antenna 22B2,
A changeover switch 43, an RF / IF unit 44, an OFDM demodulation unit 66, a level detection unit 46, and an AGC unit 48 are included. O
The FDM demodulation units 65 and 66 include only the level detection units 36 and 46, respectively, and further include the same configuration as the frequency synchronization circuit 56 of FIG. 5, and output the frequency shift information.

Similar to the embodiment of FIG. 3, two OFDM
The outputs of the demodulators 65 and 66 are output to the diversity combiner 38.
The combined output is input to the error correction unit 37, and the error rate information is input to the antenna selection circuit 69. Frequency shift information and vehicle speed pulses from the OFDM demodulators 65 and 66 are also input to the antenna selection circuit 69, and are used to control the changeover switches 23 and 43. The directivity switching of the antenna in this embodiment can also be performed in the same manner as in FIG. 7. However, in steps c4 and c6, both systems are switched to directivity in the same direction.

Further, the antenna selection circuit 69 can obtain the information about the traveling speed of the vehicle by detecting the change of the traveling direction by the gyro. Since the information about the traveling speed of the vehicle is detected based on the change of the course direction by the gyro and the vehicle speed pulse, the influence of the Doppler shift is evaluated by the speed and the directivity is appropriately selected according to the course direction. be able to.

FIG. 9 shows a configuration for performing lateral directivity control in the first to fourth embodiments of the present invention. The vehicle body 70 includes a front beam 71, a rear beam 72, and a lateral beam 7.
An antenna having directivity of 3,74 is mounted. By combining the lateral beams 73 and 74, lateral directivity can be realized. When two-way reception is performed as shown in FIGS. 3 and 8, two pairs of the configuration shown in FIG. 9 may be provided.

FIG. 10 shows a control procedure in the case of performing the Doppler shift direction detection and lateral direction directivity control with the configuration shown in FIG. The steps d1 to d6 are the same as the steps c1 to c6 in FIG. 7, respectively. At step d7, as shown in FIG.
A lateral directivity state by synthesis as shown in is selected and switched. After step d4, step d6 and step d7, the process returns to step d1.

Note that step c3 in FIG. 7 and FIG.
Although one of the judgment conditions is that the traveling speed V is higher than the threshold speed Vth in step c5, step d3 and step d5, this judgment is not essential. As the traveling speed of the vehicle increases, the influence of Doppler shift increases, and it becomes necessary to match the arrival direction of the received radio wave with the directivity of the antenna means. If the time point at which the traveling speed rises above the predetermined reference is determined as the time when the switching start condition is satisfied, it is possible to perform radio wave reception under appropriate conditions by adjusting the directivity to the arrival direction of the received radio wave.

In the procedures of FIGS. 2, 4, 7 and 10, the control procedure start condition is that the reception error rate is large in step a1, step b1, step c1 and step d1, but it is unconditional. Therefore, the control procedure can be always executed. Further, instead of the reception error rate, the start condition may be that the reception power becomes smaller than the reference, or both the conditions of the reception error rate and the reception power may be the start conditions.

FIG. 11 shows a schematic structure of an in-vehicle OFDM receiver 80 according to the fifth embodiment of the present invention. The vehicle-mounted OFDM receiver 80 includes a DTV receiver 81 that receives digital television broadcasts, an antenna selection circuit 82, a navigation device 83, and an antenna directivity control device 8.
Including 4. The antenna selection circuit 82 obtains the direction of the broadcasting station from the broadcasting station position table, the current position information, and the vehicle direction information, and selects the antenna directivity. Current location information is
GPS (Global Posit) included in the navigation device 83
ioning System)) function, etc.

FIG. 12 shows an outline of a test section for confirming the effect of frequency division diversity. The length of section A is about 2 km, and the entire circumference is about 8 km. 13 is the same as FIG.
In the second test section, a comparison was made between the case of performing diversity using a bidirectional beam antenna such as a standard dipole antenna, the case of performing diversity using a directional antenna, and the case of not performing diversity. The results are shown. In section A of FIG. 12, the rear of the traveling direction is the radio wave arrival direction. From FIG. 13, it can be seen that the diversity method in which directivity is provided in front of and behind the vehicle has the highest reception rate and is favorable. This confirms the effectiveness of having bidirectionality in the front and rear of the vehicle even in the test using the actual vehicle.

14 and 15 show a vehicle body 70 of a passenger car.
The mounting position of the directional antenna in consideration of mountability to the antenna is shown. As shown in FIG. 14, in the front of the vehicle body 70, a form of a windshield-attached film antenna can be considered. Behind the vehicle body 70, a rear bumper-attached film antenna can be considered. As shown in FIG. 15, the front beam 71 is obtained in front of the vehicle body 70, and the rear beam 72 is obtained in the rear of the vehicle body 70. Given such an arrangement, it is conceivable to use the metal body of the vehicle body 70 as a reflector to provide directivity.

FIG. 16 shows, as an embodiment of the antenna according to the present invention, a basic structure of a directional antenna 90 which uses a metal car body of a vehicle as a reflector. The directional antenna 90 includes a pair of dipole elements 90.
One ends of the first power supply line 91 and the second power supply line 92 are connected to the center power supply parts of a and 90b. First power supply line 91
The second feed line 92 is parallel and has a length of ¼ of the wavelength λ in consideration of the shortening rate. The other end of the first power supply line 91 is connected to a ground 93 to the metal body. The other end of the second power supply line 92 is connected to the core wire at the tip of the coaxial cable 94. The outer skin of the tip of the coaxial cable 94 is connected to the ground 93 to the body.

The directional antenna 90 includes first and second feeder lines 91 and 92 having a length of ¼ wavelength between the metal body of the vehicle and the feeding points of the dipole elements 90a and 90b.
And the metal car body can be operated as a reflector. A dipole-type antenna mounted on a vehicle that allows a metallic vehicle body to act as a reflector to provide directivity. Since the tip of the coaxial cable 94 has only to reach the connecting portion to the metal body, it can be hidden so that it cannot be seen from the outside.

FIG. 17 shows a state in which the directional antenna 90 of FIG. 16 is attached to the windshield 95 in (a), and shows the directivity in the horizontal plane obtained in (b). FIG. 17
As shown in (a), the length of the dipole elements 90a and 90b when attached to the windshield 95 is shortened by the dielectric constant of the glass, and the element length 90 mm × 2 becomes 140 mm × 2 in free space. Equivalent to.
FIG. 18 shows the results of examining the frequency characteristics by using the roof 96 as a metal body for grounding and varying the distance Y from the roof 96 at the mounting position. FIG. 18A shows forward gains at three frequencies, and FIG.
Shows the F / B ratio which is the ratio of the forward gain and the backward gain. It is desirable that the F / B ratio be 10 dB or more.

19 and 20 show the directional antenna 9
0 is pasted on the windshield of the vehicle and the front beam 71
Shows the state in which 19 shows a plan view and FIG. 20 shows a perspective view. With such a directional antenna 90, the dipole elements 90a, 90b, the first
The power supply line 91 and the second power supply line 92 can be formed as a conductor pattern on an electrically insulating synthetic resin film. As a result, the first and second power supply lines 91,
92 can be handled in a state where it is connected to the power feeding portion in the center of the dipole elements 90a and 90b.

FIG. 21 (a) shows a schematic structure of a directional antenna 100 having improved lateral directivity,
A method of feeding power to the directional antenna 100 is shown in (b). The directional antenna 100 is realized by a configuration in which the dipole elements 90a and 90b of FIG. 16 are installed in a state in which the directivity is oriented in the front or rear of the vehicle, and an additional element 100a in the horizontal direction is added to improve the directivity in the horizontal direction. Sex 10
1 is obtained. As shown in FIG. 20B, the dipole elements 90a and 90b are fed through the coupling circuit 102, and the additional element 100a is fed through the 90 ° phaser 103.

FIG. 22 shows the structure of a directional antenna 104 as another embodiment of the antenna according to the present invention.
FIG. 22A shows the dipole element 100 of FIG.
a and 100b, a dipole element 105 having a length of ¼ of the wavelength λ used in combination with a reflector,
The dipole antenna by 106 shows a state where the dipole elements 105 and 106 are bent 90 ° on the way. FIG. 22B shows the dipole element 105,
The total length of each 106 is 100 mm, and the tip 30
The state where the mm portion is bent is shown. By bending the tip in this manner, the directivity in the lateral direction can be improved.

FIG. 23 shows the configuration of a directional antenna as still another embodiment of the antenna according to the present invention.
FIG. 23A shows a state in which a single pole antenna 107 is erected on the trunk 108 of the vehicle. Even if the pole antenna 107 is set up behind the rear glass, the directivity 11
0 indicates omnidirectionality in the horizontal plane. As shown in FIG. 23 (b), if one pole antenna 107b is added and operated as a reflector, it can be used as a directional antenna 111 that has directivity in the direction of the reflector 107a. Such directivity can also be obtained with a 2-element Yagi antenna.

FIG. 24 shows an example of combinations of antenna directivities that can be adopted in the on-vehicle OFDM receiver described above.
The switching method is shown. It also shows how to implement the antenna element. In addition, the installation location is also shown.

In each of the embodiments described above, it is possible to switch to select one of a plurality of directivities and receive the radio wave modulated by the orthogonal frequency division multiplexing method. Therefore, even if the received radio wave modulated by the orthogonal frequency division multiplexing system is affected by the multipath fading, the directivity can be switched and the arrival direction of the received radio wave can be narrowed. Since a plurality of directivities can be switched and input, it is possible to reduce the number of parts used for high frequency amplification and frequency conversion to baseband.

FIG. 25A shows a partial structure of the vehicle-mounted OFDM receiver 121 as the sixth embodiment of the present invention, and FIG. 25B shows a switching transition state. In the present embodiment, this is done via the selector 123 of the antennas 22A and 22B. The selector 123 includes the antenna directivity control device 1
A pair of digital / analog conversion outputs (hereinafter referred to as "D / A") whose voltage level changes from 24 to 24
Output)). The output switched by the selector 123 is input to the tuner 125 and subjected to processing such as demodulation.

The selector 123 includes diodes 130A,
130B, NPN type transistors 131A and 131
B, coils 132A and 132B, coils 133A and 13
A DC circuit is formed by 3B and resistors 134A and 134B, respectively. D / applied from the antenna directivity control device 124 to the bases of the transistors 131A and 131B
The value of the direct current flowing through the diodes 130A, 130B changes according to the A output, and the diodes 130A, 130B
Impedance changes according to the current value. The diodes 130A and 130B have capacitors 135A and 1
Signals from the antennas 22A and 22B are input via the antenna 35B and output to the tuner 125 via the capacitors 136A and 136B.

By changing one of the pair of D / A output from the antenna directivity control device 124 so as to lower and the other to rise, as shown in FIG. 25B, the impedance of one diode 130A is changed. To increase the attenuation rate, decrease the reception level to fade out, and decrease the impedance of the other diode 130B to decrease the attenuation rate and increase the reception level to fade in. It can be carried out.

When the radio wave of the OFDM system is received, although the frequency component of the scattered pilot signal changes about every 1 msec, a periodicity is given to make a cycle every about 4 msec. By utilizing this periodicity, the received signal level in the time axis direction can be predicted and corrected. However, if the antennas 22A and 22B are switched,
The prediction is wrong and the reception performance is deteriorated. In this embodiment, the tuner 1 is provided with a time constant of about 200 msec.
Switch slowly so that the correction in the time axis direction by 25 can follow.

The concept of this embodiment can be similarly applied to each of the above-described embodiments. Further, it is preferable that the capacitors 134A and 134B are not directly connected to the antennas 22A and 22B but are connected via a buffer amplifier because the influence of impedance change can be avoided.

FIG. 26 shows a schematic structure of an in-vehicle OFDM receiver 141 according to the seventh embodiment of the present invention.
In this embodiment, the selector 123A and the tuner 125A are used as the branch A, and the selector 1 is used as the branch B.
23B and tuner 125B, and diversity frequency synthesizer 148 between branch A and branch B
Frequency synthesis is performed with. Note that the selectors 123A, 123
B and tuners 125A and 125B are equivalent to the selector 123 and tuner 125 of FIG. 25, respectively. The diversity frequency synthesizer 148 has an OF
DM demodulators 25A and 25B, a weighting circuit 150,
A weight changing circuit 151 and a synthesizing circuit 152 are included. The OFDM demodulators 25A and 25B are the OFDM demodulators of FIG.
It is equivalent to the demodulation unit 25. The weighting circuit 150 has an OF
The OFDM demodulation unit 25 for each carrier forming the DM signal
In the output of branch A and branch B from A, 25B,
Weighting is set according to the received signal level, and the synthesis circuit 1
It synthesizes with 52. However, the antenna directivity control device 14
When 4 is switching the antenna on either branch A or branch B, the weighting on the branch side that is switching is halved, for example, and the weighting on the branch side that is not switching is increased accordingly. Weighting is changed by the weighting change circuit 151.

When frequency synthesis diversity is used by the diversity frequency synthesizer 148, weighting synthesis of two branches is performed, and at the time of switching the directivity of the antenna, the weighting of the branch that is switching is lowered to achieve switching It is possible to reduce deterioration of reception performance.
For example, when switching the antenna of the branch A, the weight of the branch A is reduced by about 50% and the weight of the branch B is increased accordingly. When switching the antenna of branch B,
The weight of branch B is reduced by about 50%, and the weight of branch A is increased accordingly. For example, when switching the branch A, if the weight of the original branch A is 60%,
This is reduced to about 30% and the weight of branch B is set to 70.
Increase to about%. Also, the weighting of the one that is switching is 0
It is also possible to

FIG. 27 shows, as an eighth embodiment of the present invention, a procedure for switching between the control for switching the antennas according to the reception level and the control for combining the front and rear antennas in each of the above-described embodiments. . The procedure is started from step e0, and the reception level is acquired in step e1. In step e2, it is determined whether or not the electric field is weak based on the acquired reception level. When the reception level is lower than the reference and it is determined that the electric field is weak, the front and rear antennas are combined in step e3. That is, both the diodes 130A and 130B are put into the low impedance state by the selector 123 of FIG. 25, and the outputs of the two antennas 22A and 22B are combined. When it is determined in step e2 that the electric field is not a weak electric field, the antenna switching control of each embodiment is performed in step e4. After step e3 or step e4, the process returns to step e1 at regular intervals and the procedure is repeated.

The determination as to whether or not the electric field is weak can be made by directly measuring the reception level or converting the AGC voltage level. The error correction function included in the digital signal can be used to make the determination based on the BER. When a directional antenna is used, the reception power is reduced by narrowing the directivity, and the reception performance deterioration due to the reduction of the reception power becomes dominant in the weak electric field area. In the present embodiment, in a weak electric field area, it is possible to improve the reception performance by combining the reception signals from the antennas in which the directional beam is directed in a plurality of directions, such as front and back, to increase the reception power.

FIG. 28 shows, as a ninth embodiment of the present invention, a control procedure in which the antennas are not switched at the time of a search or a channel selection and the front and rear are combined in each of the above embodiments. The procedure is started from step f0, and in step f1, it is judged whether or not a search for a signal to be received and a channel selection for selecting a broadcasting station to be received are being performed. When it is determined that the search or the channel selection is being performed, in step f2, as shown in FIG.
Similar to step e3 in (1), the directional beam is combined with the reception signals from the antennas pointing in a plurality of directions such as front and back to be received. When it is determined in step f1 that the search or tuning is not in progress, the antenna switching control in each embodiment is performed in step f3. After step f2 or step f3, the process returns to step f1 and the procedure is repeated at a constant cycle. The signal to be received is not determined during searching or tuning, so various synchronizations are not achieved, and switching the antennas promotes fluctuations in the reception status and makes stable reception difficult. turn into.

[0116]

As described above, according to the present invention, even if the received radio wave modulated by the orthogonal frequency division multiplexing system is affected by multipath fading, the directivity of the antenna means is switched to receive the radio wave. The direction of arrival can be narrowed down. The directivity selection means detects information associated with traveling of a predetermined vehicle and controls the antenna means to switch the antenna means in accordance with the detected information so as to select the directivity. In such a case, the directivity of the antenna means can be switched to receive the radio wave under the condition that the influence of multipath fading is easily removed. Since a plurality of directivities can be switched by the directivity selecting means and input to the demodulating means, it is possible to reduce the number of demodulating means, particularly the number of parts for performing high frequency amplification and frequency conversion to baseband.

Further, according to the present invention, it is possible to easily judge the superiority or inferiority of the reception state between the directivities by switching the directivities of the antenna means without receiving a plurality of directivities at the same time.

Further, according to the present invention, the directivity of the antenna means can be switched to the direction in which the received power is high based on the received power information.

Further, according to the present invention, it is possible to switch the directivity of the antenna means in the direction in which the reception error rate is small based on the reception error rate information.

Further, according to the present invention, radio waves can be received under the condition that the influence of multipath fading can be easily removed based on the information about the arrival direction of the received radio waves.

Further, according to the present invention, the arrival direction of the received radio wave can be known based on the information about the Doppler shift and the information about the traveling speed of the vehicle, and the antenna means of the antenna means can be adjusted according to the arrival direction of the received radio wave. The direction of directivity can be selected.

Further, according to the present invention, the influence of the Doppler shift can be evaluated by the speed, and the directivity can be appropriately selected according to the course direction.

Further, according to the present invention, it is possible to geographically determine the arrival direction of the radio wave transmitted from the broadcasting station and select the appropriate directivity direction.

Further, according to the present invention, the directivity of the antenna means may be adjusted as necessary even if the number of portions for high-frequency amplification or frequency conversion of the received signal is smaller than the number of selectable directivity directions. , And it is possible to receive radio waves of digital signals under appropriate conditions.

Further, according to the present invention, when the deviation between the arrival direction of the received radio wave and the direction of the directivity of the antenna means increases, the received power decreases, so that the directivity of the antenna means is received so that the received power does not decrease. It is possible to appropriately eliminate the deviation of the direction according to the arrival direction of the radio wave.

Further, according to the present invention, if the deviation between the arrival direction of the received radio wave and the direction of the directivity of the antenna means becomes large, the reception power is lowered and is easily affected by noise and the reception error rate is increased. Therefore, the directivity of the antenna means can be adjusted to the arrival direction of the received radio wave so that the reception error rate does not increase, and the deviation of the direction can be appropriately eliminated.

Further, according to the present invention, when the traveling speed of the vehicle is increased and the influence of the Doppler shift is increased, the directivity of the antenna means is adjusted to the arrival direction of the received radio wave to perform radio wave reception under appropriate conditions. be able to.

Further, according to the present invention, by always selecting the directivity of the antenna means, it is possible to always receive radio waves under appropriate conditions even when the vehicle moves.

Further, according to the present invention, since two systems of the antenna means and the demodulation means are used and the directivity can be selected by either one of the systems, the reception can be continued by the other system, the antennas can be used in each system. Even if the number of parts performing high frequency amplification or frequency conversion is smaller than the number of directivity directions selectable by the means, smooth reception can be performed.

Further, according to the present invention, when an appropriate directivity direction is selected using the antenna means and demodulation means of one system, the directivity directions of the antenna means of the other system are also made to coincide with each other. The radio wave can be received by the diversity method by adjusting the directivity direction. Since there is a time difference in switching to match the directivities of the two systems, the directivity of the other system can be switched while receiving the directivity of the other system that has switched the directivity first.

According to the present invention, the received signals from the antenna means of the two systems are combined and received as frequency combining diversity with weighting based on the superiority or inferiority of the receiving condition for each frequency component, and thus the appropriate antenna is received. It is possible to perform reception by distributing the streams, and in a system in which the directivity of the antenna is switched, the reception state fluctuates greatly, so weighting can be reduced and deterioration of reception performance can be prevented.

Further, according to the present invention, even if multipath fading occurs, the directivity of the antenna means of the two systems is selected to be different from each other, and the frequency band division diversity system reception is performed between the two systems. It can be received under comprehensively appropriate conditions.

Further, according to the present invention, the shift of the reception frequency due to the Doppler shift can be easily compensated by switching the directivity to the front and the rear of the vehicle. By changing the directivity to the side of the vehicle, it is possible to receive radio waves coming from the side of the vehicle under appropriate conditions.

Further, according to the present invention, the antenna having the directivity to the side of the vehicle is also used as the antenna having the directivity to the front or rear of the vehicle to reduce the space and cost required for installation. be able to.

Further, according to the present invention, an antenna element can be added to the directional antenna in front of or behind the vehicle to improve the gain to the side of the vehicle.

Further, according to the present invention, the directional antenna can be realized at low cost by effectively utilizing the metallic vehicle body of the vehicle as the reflector.

Further, according to the present invention, one of the two antenna elements operates as a reflector.
By using the directional antenna of the element, the directional antennas in a plurality of directions can be easily mounted on the vehicle.

Further, according to the present invention, the unidirectional pole antenna element can be used as a directional antenna mounted on a vehicle by providing a reflector on the pole antenna element.

Further, according to the present invention, when the antenna is switched abruptly when a signal is received while predicting the reception state by the correction means and performing the correction based on the prediction, the variation of the reception state is within the prediction range. There is a possibility that it may come off from
It is possible to reduce deterioration of reception performance at the time of switching by performing switching so that one attenuation rate increases and the other attenuation rate decreases over a certain period of time.

Further, according to the present invention, in the weak electric field area,
Since the outputs from the plurality of antenna means are combined and received, the received electric field strength can be increased by the radio waves coming from many directions.

Further, according to the present invention, when the received signal is searched or selected, the antenna means is not switched until the received signal is specified, so that stable reception does not take time. You can

Further, according to the present invention, a dipole type antenna mounted on a vehicle can be used to operate a metal vehicle body as a reflector to provide directivity. The coaxial cable that supplies power can be hidden so that it cannot be seen from the outside.

Further, according to the present invention, the conductor pattern can be formed on the electrically insulating synthetic resin film, and the first and second feeder lines can be handled in a state of being connected to the feeder portion at the center of the dipole element.

Further, according to the present invention, a synthetic resin film having a dipole element or the like is attached to a window glass of a vehicle, and a metal body is used as a reflector to easily realize an antenna having directivity. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an in-vehicle OFDM receiver 21 according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a directivity switching procedure in the vehicle-mounted OFDM receiver 21 of FIG.

FIG. 3 is a block diagram showing a configuration of an in-vehicle OFDM receiver 31 according to a second embodiment of the present invention.

4 is a flowchart showing a directivity switching procedure in the vehicle-mounted OFDM receiver 31 of FIG.

FIG. 5 is a block diagram showing a configuration of an in-vehicle OFDM receiver 51 according to a third embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between a traveling direction of a vehicle and a radio wave arrival direction.

7 is a flowchart showing a directivity switching procedure in the vehicle-mounted OFDM receiver 51 of FIG.

FIG. 8 is a block diagram showing a configuration of an in-vehicle OFDM receiver 61 according to a fourth embodiment of the present invention.

FIG. 9 is a plan view showing a simplified configuration in the case of performing lateral directivity control in each of the embodiments of the present invention.

FIG. 10 is a flowchart showing a control procedure when performing Doppler shift direction detection and lateral directionality control in each of the embodiments of the present invention.

FIG. 11 is a vehicle-mounted OFDM system according to a fifth embodiment of the present invention.
It is a block diagram showing a configuration of a receiving device 80.

FIG. 12 is a diagram showing an example of a section in which each embodiment of the present invention is tested.

FIG. 13 is a chart showing test results in the test section of FIG.

FIG. 14 is a perspective view showing a position where a directional antenna is mounted on a vehicle body 70 of a vehicle.

FIG. 15 is a simplified plan view showing a state in which directional antennas are mounted in front of and behind a vehicle body 70.

FIG. 16 is a diagram showing a configuration of a directional antenna 90 that is an embodiment of the present invention.

FIG. 17 is a diagram showing a state in which the directional antenna 90 of FIG. 16 is attached to a windshield 95 of a vehicle and the resulting directivity.

FIG. 18 is a graph showing changes in the characteristics of the front gain and the F / B ratio when the mounting position Y in FIG. 17 is changed.

FIG. 19 is a simplified plan view showing a state in which the directional antenna 90 of FIG. 16 is attached to a windshield 95 of a vehicle.

20 is a simplified perspective view showing a state in which the directional antenna 90 of FIG. 16 is attached to a windshield 95 of a vehicle.

FIG. 21 is a diagram showing a configuration and a power feeding method of a directional antenna 100 according to another embodiment of the present invention.

FIG. 22 is a diagram showing the configuration of a directional antenna 104 that is still another embodiment of the present invention.

FIG. 23 is a diagram showing a configuration of a directional antenna 111 which is still another embodiment of the present invention.

FIG. 24 is a chart showing directivity combinations obtained in each embodiment of the present invention, switching methods, element configurations, and mounting locations.

FIG. 25 is an in-vehicle OFDM system according to a sixth embodiment of the present invention.
It is a block diagram which shows the partial structure of the receiver 121.

FIG. 26 is an in-vehicle OFDM system according to a seventh embodiment of the present invention.
It is a block diagram which shows the schematic structure of the receiver 141.

FIG. 27 is a flowchart showing a schematic control procedure as an eighth embodiment of the invention.

FIG. 28 is a flowchart showing a schematic control procedure as a ninth embodiment of the invention.

[Fig. 29] Fig. 29 is a block diagram showing a configuration on the transmission side of the OFDM system and a graph showing a part of subcarriers.

[Fig. 30] Fig. 30 is a diagram illustrating an insertion state of a guard period GI of an OFDM signal.

FIG. 31 is a block diagram showing the configuration of an in-vehicle OFDM receiver that is the basis of the present invention.

[Explanation of symbols]

21, 31, 51, 61, 80, 121, 141 In-vehicle OFDM receivers 22A, 22A1, 22A2 Forward beam antennas 22B, 22B1, 22B2 Rear beam antennas 23, 43 Changeover switch 24, 44 RF / IF section 25, 25A , 25B, 35, 45, 55, 65, 66
OFDM demodulation unit 26, 36, 46 Level detection unit 27, 37 Error correction unit 29, 39, 59, 69, 82 Antenna selection circuit 38 Diversity combination unit 56 Frequency synchronization circuit 70 Car body 83 Navigation device 84, 124, 144 Antenna directivity Control device 90, 100, 104, 111 Directional antenna 90a, 90b, 105, 106 Dipole element 91 First feeding line 92 Second feeding line 93 Installation on body 94 Coaxial cable 95 Windshield 96 Roof 100a Additional element 107a , 107b Pole antennas 123, 123A, 123B Selectors 125, 125A, 125B Tuner 148 Diversity frequency synthesizer 150 Weighting circuit 151 Weighting change circuit 152 Synthesis circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masaaki Nagami             1-228 Goshodori, Hyogo-ku, Kobe-shi, Hyogo               Within Fujitsu Ten Limited (72) Inventor Ken Miyano             1-228 Goshodori, Hyogo-ku, Kobe-shi, Hyogo               Within Fujitsu Ten Limited (72) Inventor Kazushi Ogino             1-228 Goshodori, Hyogo-ku, Kobe-shi, Hyogo               Within Fujitsu Ten Limited F term (reference) 5K022 DD01 DD19 DD31                 5K059 CC03 CC04 DD02 DD05 DD09                       DD10 DD27 DD32 DD35 EE01

Claims (29)

[Claims] 1. An on-vehicle digital communication receiving device for receiving a radio wave modulated by a digital signal, which is mounted on a vehicle, wherein the directivity is such that a gain is increased on a predetermined one side with respect to the vehicle, And antenna means capable of receiving radio waves modulated by the orthogonal frequency division multiplexing method by switching to select one of a plurality of directivities including a directivity in which the gain is increased in the opposite direction of the one direction side. And a demodulation means for inputting an electric signal corresponding to the received radio wave by switching the directivity from the antenna means, amplifying and demodulating it, and detecting information associated with traveling of a predetermined vehicle, and following the detected information. An in-vehicle digital signal receiving device, comprising: a directivity selecting unit that controls the antenna unit by switching to select a directivity. 2. The directivity selecting means switches a plurality of directivities of the antenna means by a predetermined short time, and selects the directivity depending on the superiority or inferiority of the reception state. In-vehicle digital signal receiver. 3. The vehicle-mounted digital signal receiving apparatus according to claim 2, wherein the directivity selecting unit determines the superiority or inferiority of the reception state based on received power information. 4. The vehicle-mounted digital signal receiving apparatus according to claim 2, wherein the directivity selecting means determines superiority or inferiority of the reception state based on reception error rate information. 5. The vehicle-mounted digital signal receiving apparatus according to claim 1, wherein the directivity selecting means selects the directivity of the antenna means based on information about a direction of arrival of a received radio wave. 6. The directivity selection means determines the arrival direction of the received radio wave based on information about the Doppler shift direction with respect to the frequency of the received radio wave and information about the traveling speed of the vehicle. The vehicle-mounted digital signal receiving device according to claim 5. 7. The directivity selecting means detects the information about the traveling speed of the vehicle based on the detection of the change of the traveling direction by the gyro and the detection of the speed. In-vehicle digital signal receiver. 8. The directivity selecting means determines the arrival direction of the received radio wave based on detection information of the current position of the vehicle and geographical information about the location of the broadcasting station. Item 5. The vehicle-mounted digital signal receiving device according to any one of items 5 to 7. 9. The in-vehicle digital apparatus according to claim 1, wherein the directivity selecting unit selects the directivity of the antenna unit when a predetermined switching start condition is satisfied. Signal receiving device. 10. The vehicle-mounted digital signal according to claim 9, wherein the directivity selecting means determines a time point at which the received power falls below a predetermined standard as a time when the predetermined switching start condition is satisfied. Receiver. 11. The directivity selecting means determines a time point at which the reception error rate rises above a predetermined standard as the time when the predetermined switching start condition is satisfied. In-vehicle digital signal receiver. 12. The directivity selecting means determines a time point at which the traveling speed rises above a predetermined reference as a time point when the predetermined switching start condition is satisfied. The in-vehicle digital signal receiving device according to [4]. 13. The in-vehicle digital signal receiving apparatus according to claim 1, wherein the directivity selecting unit always selects the directivity of the antenna unit. 14. The antenna means and the demodulation means are provided with two systems capable of receiving radio waves independently of each other, and the directivity selection means includes an antenna means and a demodulation means of either one of the systems. 14. The vehicle-mounted digital signal receiving device according to claim 1, wherein the directivity is selected. 15. The directivity selecting means selects the directivity of an antenna means of a system different from the one of the two systems so as to match the directivity of the antenna means of the one system, 15. The vehicle-mounted digital signal receiving apparatus according to claim 14, wherein the switching is performed by providing a time difference. 16. A system for switching the directivity of an antenna by receiving the received signals from the antenna means of the two systems as frequency combining diversity with weighting based on the superiority or inferiority of the receiving state of each frequency component for reception. 16. The vehicle-mounted digital signal receiving apparatus according to claim 14 or 15, further comprising a synthesizing unit for synthesizing with a low weight. 17. The antenna means and the demodulation means are provided with two systems capable of receiving radio waves independently of each other, and the directivity selection means provides mutual directivity of the two systems of antenna means. The in-vehicle digital signal receiving apparatus according to claim 1, wherein the signals are selected differently and frequency band division diversity system reception is performed between the two systems. 18. The antenna means includes an antenna having directivity toward the front of the vehicle, an antenna having directivity toward the rear, and an antenna having directivity toward the side of the vehicle. Item 18. The vehicle-mounted digital signal receiving device according to any one of items 1 to 17. 19. The antenna means includes an antenna having directivity toward the front of the vehicle and an antenna having directivity toward the rear, and has the antenna having the directivity toward the front or the directivity toward the rear. 18. The in-vehicle digital signal receiving device according to claim 1, wherein at least one of the antennas also improves a lateral gain of the vehicle. 20. The vehicle-mounted digital signal receiving apparatus according to claim 19, wherein the lateral gain of the vehicle is improved by adding an antenna element. 21. The vehicle-mounted digital signal receiving apparatus according to claim 1, wherein the antenna means includes a directional antenna having a metal car body of the vehicle as a reflector. 22. The antenna means includes a directional antenna for operating one of two antenna elements as a reflector.
1. The in-vehicle digital signal receiving device according to any one of 1. 23. The two-element antenna element comprises:
23. The vehicle-mounted digital signal receiving device according to claim 22, wherein the on-vehicle digital signal receiving device is a pole antenna element that is vertically provided upright from the vehicle. 24. The digital signal further includes a correction unit for correcting the digital signal in a time axis direction, and the directivity selection unit switches the antenna for a predetermined time so that the correction by the correction unit can follow. The control is performed such that the attenuation rate of the reception signal from one antenna means is increased and the attenuation rate of the reception signal from the other antenna means is decreased by multiplying by.
23. The in-vehicle digital signal receiving device according to any of 23. 25. The directivity selecting means controls so that outputs from a plurality of antenna means are combined and received in a weak electric field area in which a reception state does not reach a predetermined reference. The vehicle-mounted digital signal receiving device according to any one of 1 to 24. 26. The directivity selecting means controls so that outputs from a plurality of antenna means are combined and received at the time of searching or tuning a received signal. The vehicle-mounted digital signal receiving device according to any one of claims. 27. An antenna mounted on a vehicle, wherein a dipole element that is linearly arranged and has a power feeding portion in the center, and a metal body of the vehicle and one power feeding portion of the dipole element / 4 length of the first power supply line that is electrically connected to the power supply part of the dipole element, and an impedance matching the power supply part of the dipole element, and the connection part between the first power supply line and the metal body at the power supply end. A coaxial cable to which the outer conductor is connected, a central conductor for feeding the coaxial cable, and the other feeding portion of the dipole element are electrically connected at a length of the quarter wavelength, and An antenna, characterized in that it comprises a second feed line kept parallel to the first feed line. 28. The dipole element, the first
28. The antenna according to claim 27, wherein the power supply line and the second power supply line are formed as conductor patterns on an electrically insulating synthetic resin film. 29. The antenna according to claim 28, wherein the metal vehicle body is a roof of a vehicle, and the synthetic resin film is attached on a window glass of the vehicle.