JP2005236678A - Receiver for mobile object - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver for a mobile object which reduces the influence of Doppler variation, using simple processings. <P>SOLUTION: This receiver 1, for a mobile object which is mounted on a mobile object and receives modulated radio waves, is provided with a first antenna 2 having directivity in a moving direction of the mobile object, a second antenna 3 having directivity in a direction reverse to the moving direction of the mobile object, a correction means 7 for correcting a reception signal received by the first antenna 2 and also correcting a reception signal received by the second antenna 3, and a combining means 7 for combining two correction signals which have been corrected by the correction means 7. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a mobile receiver for receiving modulated radio waves.

  Terrestrial digital broadcasting has also begun, and development of receivers that receive modulated radio waves in a moving body such as an automobile is underway. An orthogonal wave frequency division multiplexing (hereinafter referred to as OFDM [Orthogonal Frequency Division Multiplexing]) method is used as a transmission method for terrestrial digital broadcasting. The OFDM scheme is a digital modulation scheme used for radio and the like, and is suitable for wideband transmission that efficiently utilizes a narrow frequency range.

When a radio wave is received by a mobile body, the shift of the reception frequency (Doppler shift) due to the Doppler effect increases as the mobile body becomes faster. In particular, in the case of the OFDM system, it is easily affected by Doppler dispersion having a spread on both the plus side and the minus side with respect to the frequency of the carrier wave, and the line quality deteriorates due to the influence of Doppler dispersion. Therefore, some mobile receivers suppress the influence of Doppler dispersion by using a plurality of antennas having directivity (see Patent Document 1). In this mobile receiver, for example, a cross-correlation vector between a received signal by a directional antenna and a known signal is calculated, an average value of fading fluctuation is calculated based on the cross-correlation vector, and Doppler is calculated based on the average value. There is something that corrects the shift.
JP 2003-87213 A JP 2003-283405 A

  However, since the conventional mobile receiver has to calculate a cross-correlation vector and an average value of fading fluctuations in order to reduce the influence of Doppler dispersion, the processing becomes complicated. Therefore, the configuration of the mobile receiver is complicated and expensive.

  Therefore, an object of the present invention is to provide a mobile receiver that reduces the influence of Doppler dispersion by simple processing.

  A mobile receiver according to the present invention is a mobile receiver for receiving a modulated radio wave mounted on a mobile, the first antenna having directivity on the moving direction side of the mobile, A second antenna having directivity in the direction opposite to the moving direction of the moving body, a correction means for correcting the received signal received by the first antenna and correcting the received signal received by the second antenna, and a correcting means And a synthesizing unit for synthesizing the two correction signals corrected in (1).

  In this mobile receiver, the first antenna receives radio waves from the moving direction side of the moving body, and the second antenna receives radio waves from the direction opposite to the moving direction. In the mobile receiver, the correcting means corrects the Doppler shift in the received signal received by the first antenna and corrects the Doppler shift in the received signal received by the second antenna. Further, in the mobile receiver, two correction signals subjected to the correction by the combining unit are combined. Since this combined signal is a signal obtained by combining signals obtained by correcting the plus side Doppler shift and the minus side Doppler shift, the Doppler dispersion is suppressed. As described above, the mobile receiver can reduce the influence of Doppler dispersion by a simple process of combining two received signals after correction. Therefore, the mobile receiver can be configured at a low cost with a simple configuration. Note that the modulated radio wave is not particularly limited, and may be analog modulation or digital modulation.

  In the mobile receiver according to the present invention, the correcting means may correct the frequency using a frequency that balances the power distribution of the received signal.

  In this mobile receiver, each received signal has a power distribution having a predetermined spread with respect to the frequency of the carrier wave by Doppler shift. Therefore, a frequency at which the power distribution of each received signal is balanced is obtained, Each received signal is corrected using each frequency. As described above, by using the frequency at which the power distribution is balanced, even if the power distribution is biased, appropriate correction reflecting the bias can be performed, so that the effect of reducing Doppler dispersion can be improved.

  In the moving body receiving apparatus of the present invention, the correcting means may be configured to obtain a frequency at which the power distribution is balanced based on the speed of the moving body.

  In this mobile receiver, since the power distribution of the received signal is determined by the speed of the mobile body, the frequency at which the power distribution is balanced can be easily obtained from the speed of the mobile body.

  According to the present invention, the influence of Doppler dispersion can be reduced by a simple process.

  Embodiments of a mobile receiver according to the present invention will be described below with reference to the drawings.

  In the present embodiment, the mobile receiver according to the present invention is applied to an in-vehicle receiver that is mounted on an automobile and receives radio waves modulated by the OFDM method. The in-vehicle receiving apparatus according to the present embodiment includes two antennas having directivity in the front-rear direction of the automobile, and receives radio waves with these two antennas.

  With reference to FIGS. 1-3, the structure of the vehicle-mounted receiving apparatus 1 is demonstrated. FIG. 1 is a configuration diagram of a vehicle-mounted receiving device according to the present embodiment. FIG. 2 is an explanatory diagram of processing in the Doppler correction / synthesis unit of FIG. FIG. 3 is a diagram showing the power distribution of the received signal and the power distribution of the correction signal by the two directional antennas of FIG.

  The in-vehicle receiving device 1 is mounted on an automobile and is a receiving device for terrestrial digital television broadcasting. The in-vehicle receiver 1 receives a radio wave modulated with a digital signal by the OFDM method and demodulates the received radio wave. In particular, the in-vehicle receiver 1 reduces the influence of Doppler dispersion accompanying the movement of the automobile and ensures high line quality. For this purpose, the in-vehicle receiver 1 includes a front antenna 2, a rear antenna 3, RF / IF units 4 and 5, a vehicle speed sensor 6, a Doppler correction / synthesis unit 7, and an OFDM demodulation unit 8.

  In this embodiment, the forward antenna 2 corresponds to the first antenna described in the claims, the rear antenna 3 corresponds to the second antenna described in the claims, and Doppler correction / synthesis is performed. The unit 7 corresponds to correction means and synthesis means described in the claims.

  The forward antenna 2 is an antenna having directivity (directivity illustrated by reference sign FA in FIG. 2) such that the gain is increased on the front side (moving direction) side of the automobile. The forward antenna 2 receives radio waves from the front side of the automobile and outputs an electrical signal (reception signal) FR corresponding to the received radio waves to the RF / IF unit 4. The rear antenna 3 is an antenna having a directivity (directivity illustrated by the symbol RA in FIG. 2) such that the gain is increased on the rear side (the direction opposite to the moving direction) of the automobile. The rear antenna 3 receives radio waves from the rear side of the automobile and outputs an electrical signal (reception signal) RR corresponding to the received radio waves to the RF / IF unit 5. Thus, the front antenna 2 and the rear antenna 3 are antennas spatially separated by the directivity in the reverse direction.

  The RF / IF units 4 and 5 receive the received signals FR and RR, which are RF [Radio Frequency] (high frequency), from the directional antennas 2 and 3, and receive signals FR ′ and RR of IF [Intermidiate Frequency] (intermediate frequency). It is a frequency down converter that converts each to '. Depending on the specifications, there is a case where it is not necessary to reduce the frequency to an intermediate frequency. In this case, the RF / IF unit is not necessary.

  Since the automobile moves with respect to the radio tower, the radio wave received by the forward antenna 2 and the radio wave received by the backward antenna 3 are opposite in an environment where radio waves coming from the front direction and radio waves coming from the rear direction exist at the same time. Doppler shift in each direction. Therefore, the received signal FR ′ has a frequency offset on the plus side of the signal having the carrier frequency (f), and the received signal RR ′ has a frequency offset on the minus side of the signal having the carrier frequency (f) (in FIG. 3, a solid line). See the graph). FIG. 3 shows the power distribution of the received signals FR ′ and RR ′ corresponding to the radio waves received by the directional antennas 2 and 3, where the horizontal axis is frequency and the vertical axis is power. As can be seen from FIG. 3, the power distribution of the received radio waves spreads up to the maximum Doppler frequencies + fd and −fd, and the power distribution amount increases as it approaches + fd and −fd. This power distribution S (t) is expressed by equation (1).

式（１）において、Ｓ（ｆ）は周囲３６０°から均一に到来波が分布していると仮定したときの周波数ｆの電力の分布を示し（但し、ｆはドップラシフトがないときの周波数が０となるようにオフセットしている）、Ｐは送信電力及び送信側や受信側のアンテナ利得で決まる定数であり、ｆｄは最大ドップラ周波数（最大周波数オフセット、ドップラ分散幅）である。ｆｄは、車速Ｖに比例するので、車速Ｖが判れば求めることができる。したがって、高速になるほど、最大ドップラ周波数が増加し、ドップラ分散幅が拡大する。

In equation (1), S (f) indicates the distribution of power at frequency f when it is assumed that the incoming waves are uniformly distributed from the surrounding 360 ° (where f is the frequency when there is no Doppler shift). P is a constant determined by the transmission power and the antenna gain on the transmission side and the reception side, and fd is the maximum Doppler frequency (maximum frequency offset, Doppler dispersion width). Since fd is proportional to the vehicle speed V, it can be obtained if the vehicle speed V is known. Therefore, as the speed increases, the maximum Doppler frequency increases and the Doppler dispersion width increases.

  The vehicle speed sensor 6 is a sensor that detects the speed of the automobile, for example, a wheel speed sensor that detects the rotational speed of the wheel. The vehicle speed sensor 6 transmits the detected value to the Doppler correction / synthesis unit 7 as a vehicle speed signal SS. The vehicle speed sensor 6 is not a sensor dedicated to the in-vehicle receiver 1 but is shared with other devices such as a power steering device.

  The Doppler correction / synthesis unit 7 individually corrects the reception signals FR ′ and RR ′ from the RF / IF units 4 and 5 and synthesizes the corrected reception signals. As described above, when radio waves are received by the antennas 2 and 3 having the directivity in the reverse direction, the frequency offset is received in the reverse direction on the plus side and the minus side, respectively, thus reducing the effect of Doppler shift (Doppler dispersion). In order to do this, it is necessary to correct each frequency offset. Therefore, the Doppler correction / synthesis unit 7 corrects the reception signal FR ′ that has received the frequency offset on the plus side in the minus direction, and corrects the reception signal RR ′ that has received the frequency offset on the minus side in the plus direction. As shown in FIG. 3, the received power of the received signals FR ′ and RR ′ is distributed to the maximum Doppler frequency + fd, −fd side. Therefore, if the frequency to be corrected is simply set to half the maximum Doppler frequency (fd / 2), an imbalance is generated in the power distribution, and the effect of reducing the influence of Doppler dispersion cannot be sufficiently obtained. Therefore, the Doppler correction / combination unit 7 obtains a frequency indicating a half of the power distribution from 0 to + fd (−fd to 0), and performs correction at a frequency that balances the power distribution. Specifically, the Doppler correction / synthesis unit 7 obtains the value of x from Expression (2).

式（２）では、図３に示すＦＲ’（ＲＲ’）の電力分布において、０〜＋ｆｄ（−ｆｄ〜０）における面積の２分の１の面積となる周波数をｘとしている。このｘは、車速Ｖが判れば一意的に求めることができる。そこで、ドップラ補正／合成部７では、車速センサ６からの車速信号ＳＳに基づいて、式（２）にから周波数ｘを求める。さらに、ドップラ補正／合成部７では、この周波数ｘを用いて、式（３）により受信信号ＦＲ’をマイナス方向に補正した補正信号ＦＨを求め、式（４）により受信信号ＲＲ’をプラス方向に補正した補正信号ＲＨを求める（図２参照）。

In Expression (2), in the power distribution of FR ′ (RR ′) shown in FIG. 3, x is a frequency that is an area that is a half of the area in 0 to + fd (−fd to 0). This x can be uniquely determined if the vehicle speed V is known. Therefore, the Doppler correction / synthesis unit 7 obtains the frequency x from Equation (2) based on the vehicle speed signal SS from the vehicle speed sensor 6. Further, the Doppler correction / synthesis unit 7 uses this frequency x to obtain a correction signal FH obtained by correcting the reception signal FR ′ in the minus direction by Expression (3), and sets the reception signal RR ′ in the plus direction by Expression (4). The correction signal RH corrected to (1) is obtained (see FIG. 2).

この補正により、補正信号ＦＨの電力分布は受信信号ＦＲ’の電力分布から周波数ｘ分マイナス方向にシフトし、補正信号ＲＨの電力分布は受信信号ＲＲ’の電力分布から周波数ｘ分プラス方向に移動する（図３に一点鎖線で示すグラフ参照）。さらに、ドップラ補正／合成部７では、式（５）により、個々に補正を施した補正信号ＦＨと補正信号ＲＨとを加算し、合成信号Ｃを求める（図２参照）。そして、ドップラ補正／合成部７では、求めた合成信号ＣをＯＦＤＭ復調部８に出力する。

By this correction, the power distribution of the correction signal FH is shifted in the minus direction by the frequency x from the power distribution of the reception signal FR ′, and the power distribution of the correction signal RH is moved in the plus direction by the frequency x from the power distribution of the reception signal RR ′. (Refer to the graph indicated by the alternate long and short dash line in FIG. 3). Further, the Doppler correction / synthesis unit 7 adds the correction signal FH and the correction signal RH that have been individually corrected by the equation (5) to obtain a combined signal C (see FIG. 2). Then, the Doppler correction / synthesis unit 7 outputs the obtained synthesized signal C to the OFDM demodulation unit 8.

この合成信号Ｃは、プラス側とマイナス側のドップラシフトの影響がそれぞれ軽減した信号を足し合わせた信号なので、ドップラ分散の影響を極力取り除いた信号となっている。

The composite signal C is a signal obtained by adding the signals that have been reduced by the effects of the Doppler shift on the plus side and the minus side, and thus is a signal that eliminates the influence of Doppler dispersion as much as possible.

  The OFDM demodulator 8 demodulates the combined signal C from the Doppler correction / synthesis unit 7 and extracts an original signal (information) before modulation. Then, the OFDM demodulator 8 outputs the demodulated signal D to the playback device.

  The operation of the in-vehicle receiving device 1 will be described with reference to FIG. In the vehicle-mounted receiving device 1, the front antenna 2 receives the front side radio wave and the rear antenna 3 receives the rear side radio wave. In the in-vehicle receiving apparatus 1, the received signals FR and RR are converted into received signals FR ′ and RR ′ that are reduced to an intermediate frequency, respectively. Further, the in-vehicle receiving apparatus 1 obtains the frequency x at which the power distributions of the received signals FR ′ and RR ′ are balanced based on the vehicle speed signal SS by the equation (2). Subsequently, the in-vehicle receiving apparatus 1 uses the frequency x to shift the frequency of the reception signal FR ′ and the reception signal RR ′ according to the equations (3) and (4), respectively, and the two directional antennas 2 and 3. Correct the signals corresponding to the radio waves received at. Further, the in-vehicle receiver 1 adds the corrected correction signal FH and the correction signal RH, and synthesizes individually corrected signals. Finally, the in-vehicle receiver 1 demodulates the synthesized signal C and extracts the original signal.

  According to the in-vehicle receiver 1, the influence of Doppler dispersion is reduced by a simple process of correcting the radio waves received by the two directional antennas 2 and 3 individually and synthesizing the corrected signals. And the line quality can be ensured. Therefore, the vehicle-mounted receiving device 1 can be simplified in configuration and can be configured at low cost. Furthermore, since the in-vehicle receiving apparatus 1 performs correction with the frequency at which the power distribution of the received radio wave balances, the effect of reducing Doppler dispersion is very high.

  As mentioned above, although embodiment which concerns on this invention was described, this invention is implemented in various forms, without being limited to the said embodiment.

  For example, in the present embodiment, the present invention is applied to a receiving device mounted on an automobile, but the present invention can also be applied to a receiving device mounted on another moving body such as a train, a ship, and an airplane.

  In this embodiment, the present invention is applied when receiving radio waves modulated by the OFDM method. However, when receiving radio waves modulated by another digital modulation method or receiving radio waves modulated by the analog modulation method. It is also applicable to.

  In this embodiment, the Doppler correction / synthesis unit is configured, but the correction unit and the synthesis unit may be configured separately.

  In this embodiment, the correction is performed using the frequency that balances the power distribution of the received signal. However, the correction may be performed using another frequency such as the median value (fd / 2) of the maximum Doppler frequency.

It is a block diagram of the vehicle-mounted receiving apparatus which concerns on this Embodiment. It is explanatory drawing of the process in the Doppler correction | amendment / synthetic | combination part of FIG. It is a figure which shows the power distribution of the received signal by the two directional antennas of FIG. 1, and the power distribution of a correction signal.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... In-vehicle receiver, 2 ... Forward antenna, 3 ... Backward antenna, 4, 5 ... RF / IF part, 6 ... Vehicle speed sensor, 7 ... Doppler correction / synthesis part, 8 ... OFDM demodulation part

Claims (3)

A mobile receiver for receiving a modulated radio wave mounted on a mobile,
A first antenna having directivity on the moving direction side of the moving body;
A second antenna having directivity on the side opposite to the moving direction of the moving body;
Correcting means for correcting the received signal received by the first antenna and correcting the received signal received by the second antenna;
And a combining unit that combines the two correction signals corrected by the correcting unit.   2. The mobile receiver according to claim 1, wherein the correction unit performs correction using a frequency at which a power distribution of the reception signal is balanced.   3. The mobile receiver according to claim 2, wherein the correction unit obtains a frequency at which the power distribution balances based on a speed of the mobile body.

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