JP4260051B2 - In-vehicle digital communication receiver - Google Patents

Description

  The present invention relates to a digital communication receiver, and more particularly to an in-vehicle digital communication receiver that is mounted on a vehicle and receives a digital signal such as a radio wave modulated by an orthogonal frequency division multiplex (OFDM) method. is there.

  The OFDM system is used for terrestrial digital television broadcasting. The OFDM system is a form of multi-carrier transmission system, and transmits, for example, 5300 subcarriers arranged at 1 KHz intervals, respectively, by amplitude-phase modulation (QAM).

  In the OFDM scheme, the frequency bands of the modulated waves overlap with each other between adjacent subcarriers, but using the orthogonality at which the correlation of the modulated wave band signals becomes zero, a batch using Fast Fourier Transform (FFT) Modulate and demodulate. Further, by adding a guard interval signal on the transmission side, inter-symbol interference (ISI) due to multipath delay waves is removed.

  Conventionally, the current reception state is first acquired using an omnidirectional antenna, and a plurality of antennas having different directivities are sequentially switched every predetermined period according to the reception state to detect each average reception level. From the comparison result, the directional antenna having the highest reception level was switched.

  As a result, the influence of multipath fading and Doppler shift when a traveling vehicle receives a digital television broadcast signal has been reduced (see FIGS. 1 and 2 of Patent Document 1).

Japanese Patent Application No. 2002-231611

  However, as in the conventional example described above, a plurality of directional antennas are sequentially switched every predetermined period to detect each average reception level, and are simply switched to an antenna having the best directivity by comparing them. There was a case where the reception level before and after the antenna switching fluctuated greatly.

  Therefore, the AGC circuit in the receiver cannot follow the level fluctuation before and after the switching, and the transient response characteristic of the subsequent RF / IF filter causes impulsive noise and a time delay until the reception level is stabilized. There is a problem that the reception state is deteriorated and a bit error is caused by various factors such as a sharp level change of the reception signal exceeding the allowable level difference value of the sampling of the A / D converter.

  In view of the above problems, an object of the present invention is to provide an in-vehicle digital communication receiving device that reduces the influence of antenna switching on the receiving device by providing the receiving device with a means for suppressing reception level fluctuation before and after antenna switching. There is to do.

According to the present invention, there is provided a receiving device for receiving radio waves modulated with digital signals, a selection unit that receives a plurality of received signals and selects at least one received signal, and a selection switching of the received signals. Provided is a receiving device including an adjusting unit for adjusting timing.

According to the invention, the antenna unit includes a plurality of directional antennas, and the selection unit selects the at least one received signal by selecting at least one antenna of the antenna group, and The adjustment unit is provided with the reception device that adjusts the selection switching timing of the reception signal by adjusting the selection switching timing of the antenna.

  According to the present invention, since reception level fluctuations before and after antenna switching are suppressed, deterioration of the reception state due to antenna switching can be prevented and a good reception state can be maintained.

FIG. 1 shows a configuration example of an OFDM receiving apparatus to which the present invention is applied.
1 includes two systems of antenna means and OFDM demodulation means that operate independently of each other, a diversity combining unit shared by them, and an antenna switching / combining control unit that controls switching and combining of the antennas. And. The system 1 will be mainly described below, but the system 2 is the same.

  The antenna means of system 1 switches and outputs either the front directional antenna (FR) 11A and the rear directional antenna (RR) 11B mounted on the right side of the vehicle and the reception signal of the antenna 11A or 11B, or And a switching / synthesizing unit 13-1 for outputting the synthesized signal. By such a combination of antennas, antenna characteristics suitable for a vehicle situation such as “omnidirectional (front and rear)” and “directivity (front or rear)” are realized.

  The tuner 1 (14-1) amplifies the radio signal (RF signal) from the switching / synthesis unit 13-1 and converts it to an intermediate frequency signal (IF signal). This can include a level detection unit that outputs received power information and an AGC unit that adjusts the gain of RF / IF.

  The OFDM demodulator 15-1 demodulates and outputs an effective symbol (TS) for each subcarrier from the intermediate frequency signal. Here, instead of providing the tuner 1, a level detection unit that outputs received power information and an AGC unit that adjusts the gain of the RF / IF can be included.

  The diversity combining unit 16 performs frequency division diversity for each subcarrier from each of the OFDM demodulation units 15-1 and 15-2 of the systems 1 and 2, thereby reducing inter-carrier interference (ICI). Here, an error correction unit that detects an error included in the demodulated signal and corrects the error within a possible range to output error rate information can be included.

  The antenna switching / combination control unit 17 receives received power information, error rate information, and / or Doppler shift obtained from the tuners 14-1 and 14-2, the OFDM demodulation units 15-1, 15-2, and / or the diversity combining unit 16. The state of reception degradation is determined based on the frequency shift information and the like, and the switching / combining of the antennas is instructed corresponding to the switching / combining units 13-1 and 13-2.

The system 2 has the same configuration as described above. From this, for example, the following combinations of directional antennas and tuners are possible.
(1) Tuner 1 for connecting FL and / or RL
(2) Tuner 2 connecting FR and / or RR
(3) Diversity tuner using FR and FL forward directional antennas (4) Diversity tuner using RR and RL backward directional antennas (5) No synthesis by combining FR and RR and FL and RL Diversity tuner using directional antenna

FIG. 2 shows an example of a specific configuration for easy understanding of FIG.
In FIG. 2, the in-vehicle OFDM receiver 20 includes two systems of a switching / combining unit, a tuner, and an OFDM demodulating unit, and can perform reception using a frequency division diversity system. One system 1 includes a switching / synthesizing unit including a forward directional antenna 21A, a rear directional antenna 21B, and a switch 23 for performing switching / combining connection therebetween, and a tuner including an RF / IF unit 24 and an AGC unit 28. 1 and an OFDM demodulator 25 including a level detector 26. The level detector 26 may be included on the tuner 1 side.

  Similarly, the other system 2 includes a switching / synthesizing unit including a forward directional antenna 32A, a backward directional antenna 32B, and a switch 33 for switching / combining them, and an RF / IF unit 34 and an AGC unit 38. A tuner 2 and an OFDM demodulator 35 including a level detector 36 are included. Again, the level detector 36 may be included on the tuner 2 side.

  The outputs from the two OFDM demodulation units 25 and 35 are combined for each subcarrier demodulated by the diversity combining unit 46, and the combined output is input to the error correction unit 48. The error correction unit 48 performs error correction as much as possible and outputs error rate information.

  The antenna switching / combining circuit 47 receives received power information from the level detection units 26 and 36, error rate information from the error correction unit 48, and / or frequency shift information by Doppler shift detected by the OFDM demodulation units 25 and 35, and the like. Based on this, the reception deterioration state is determined, and antenna switching / combination is instructed corresponding to the switches 23 and 33.

  Here, in order to facilitate understanding of the present invention, a configuration example of the conventional switch 23 will be described first. The switch 33 is the same. 3A shows an example of a circuit configuration inside the switch 23, and FIG. 3B shows an example of the operation timing.

  In FIG. 3A, received signals from the front directional antenna 21A (antenna A) and the rear directional antenna 21B (antenna B) are combined through switches 51 and 52 that are on / off controlled by a control circuit 54. 53 and the switching / combining output is output to the RF / IF unit 24 in the next stage.

  The control unit 54 controls switching of the switches 51 and 52 at the same time. In FIG. 3B, the antenna A is turned on (connected) from off (disconnected), and the antenna B is turned off (disconnected) on (connected). It is switched at the same time.

  In such a conventional configuration, as described above, the AGC circuit in the receiver cannot follow the level fluctuation before and after the switching, and the impulsive noise and the reception level are stabilized by the transient response characteristic of the subsequent RF / IF filter. In this case, the reception state deteriorates and bit errors occur due to various factors such as a time delay until the signal is received and a steep level change of the received signal exceeds the allowable level difference value of sampling of the A / D converter.

  Hereinafter, various embodiments of the present invention that solve the above-described problems will be described in detail. In this case, the configuration of the present invention will be described by taking the switch 23 of FIG. 3 as an example, but it is obvious that the present invention can be similarly applied to the switch 33.

FIG. 4 shows a first embodiment of the present invention. FIG. 5 shows an example of the basic switch operation of FIG.
In this example, a delay device 61 is newly added to the controller 54. Others are the same as FIG. The operation of the delay unit 61 will be described with reference to FIG. 5. First, the controller is controlled by an antenna switching request signal from the antenna switching / combining circuit 47 (in this example, switching from antenna A (21A) to antenna B (21B)). Inside 54, the on / off control signals for the switches 51 and 52 shown in FIG. 3B are generated.

  In the case of FIG. 5A, the control signal on the side for switching the antenna 21 </ b> A from on to off is delayed by the delay device 61 by a predetermined time t. As a result, during the delay time t, the reception signals of the antennas 21A and 21B are input to the combiner 53, and the combined signals are output. Such processing is advantageous when the reception power of the antenna 21B that receives the radio wave from the rear is larger than the reception power of the antenna 21A that receives the radio wave from the front.

  That is, by generating the composite signal only during the delay time t, the time until the reception power of the AGC circuit is increased and the rising transient response characteristic of the subsequent RF / IF filter is stabilized is further increased. Control is performed in a direction in which the difference in reception level before and after switching is reduced in a short time. As a result, after the delay time t has elapsed, a smooth transition from a small received power of the antenna 21A to a large received power of the antenna 21B becomes possible.

  On the other hand, in the case of FIG. 5B, the control signal on the side for switching the antenna 21B from OFF to ON is delayed by the delay device 61 by a predetermined time t. Thereby, during the delay time t, the input to the synthesizer 53 is cut off for both the reception signals of the antennas 21A and 21B. Such processing is advantageous when the reception power of the antenna 21B that receives the radio waves from the rear is smaller than the reception power of the antenna 21A that receives the radio waves from the front.

  That is, by making the output from the synthesizer 53 no signal only during the delay time t, the control in the direction in which the reception power of the AGC circuit is reduced and the falling transient response characteristic of the subsequent RF / IF filter is stabilized. It is controlled in such a manner that the time until this is done is shorter and the difference in reception level before and after switching becomes smaller. As a result, after the delay time t has elapsed, a smooth transition from a large received power of the antenna 21A to a small received power of the antenna 21B becomes possible.

FIG. 6 shows another example of the first embodiment of the present invention.
In this example, the amount of delay time at the time of combining described above is switched according to the level of reception level before and after antenna switching. Here, the case of switching from the antenna 21A to the antenna 21B will be described, but the same applies to switching in the opposite direction.

  In this example, when switching from the antenna 21A to the antenna 21B (S01), a level difference | α−β | between the reception level (α) of the antenna 21A before switching and the reception level (β) of the antenna 21B after switching is obtained. (S02). When the level difference is smaller than a predetermined reference value, the delay time of the delay device 61 is set short (S03), and when the difference is large, the delay time of the delay device 61 is set large (S04). After the set delay time has elapsed, the antenna 21A is disconnected (S05).

  When the level difference before and after the antenna switching is small, the combined output becomes larger, the control until the received power of the AGC circuit is increased, and the time until the rising transient response characteristic of the subsequent RF / IF filter is stabilized is Further shortened. On the other hand, if the delay time t is set longer than necessary, the reception level difference before and after switching is increased.

  Therefore, when the level difference is smaller than the predetermined reference value, the delay time is set short, and when the level difference is large, the delay time is set large to adjust the time appropriately. Note that the delay time may be simply switched, or a delay time corresponding to each reception level difference may be set.

  In this example and the next example (FIG. 7), only the combination is described. This is because, in actual use, antenna switching / combination control is performed so that the reception level after switching is increased. . However, the reception level may be searched in advance for each of the antennas 21A and 21B, and the delay time of disconnection ((b) in FIG. 5) may be set similarly to this example based on the reception level difference (predicted value). it can.

FIG. 7 shows still another example of the first embodiment of the present invention.
In this example, the signal modulation method is identified from the broadcast parameters included in the received radio wave, and a delay time corresponding to the signal modulation method is set.

  First, when switching from the antenna 21A to the antenna 21B (S11), the signal modulation method after switching is identified (S12). When the signal modulation method is DQPSK that is strong against noise and can detect synchronization in a short time, the delay time of the delay unit 61 is set short (S13). Conversely, in the case of a 64QAM signal that is weak against noise and takes time to detect synchronization. Sets a larger delay time (S14). After the set delay time has elapsed, the antenna 21A is disconnected (S15). This example can also be used in combination with the previous example.

FIG. 8 shows a second embodiment of the present invention. FIG. 9 shows a basic operation example of FIG.
In FIG. 8, an amplifier A (71A) and an attenuator A (72A) are inserted in the communication path of the antenna 21A. An amplifier B (71B) and an attenuator B (72B) are inserted in the communication path of the antenna 21B. Further, the control unit 54 controls the amplification controller 62 that controls the amplification factors of the amplifiers 71A and 71B, the attenuation controller 64 that controls the attenuation factors of the attenuators 72A and 72B, and further controls the combination ratio of the combiner 53. A synthesis controller 64 is provided.

  In this example, at least one of an amplifier, an attenuator, and a synthesizer provided in each communication path is used instead of the switches 51 and 52 and the delay unit 61 that controls the switching time in the first embodiment. Thus, a gradual level change (gradual switching of the received signal) of the received signal on each communication path is realized.

  FIG. 9A shows an example in which both antenna A (21A) and antenna B (21B) are gently switched simultaneously. This operation will be described with reference to the configuration of FIG. 8. While the amplification controller 62 gradually decreases the amplification factor of the amplifier 71A on the antenna 21A side, it simultaneously increases the amplification factor of the amplifier 71B on the antenna 21B side. I will do it.

  Further, the attenuation controller 63 gradually increases the attenuation rate of the attenuator 72A on the antenna 21A side, and at the same time, gradually decreases the attenuation rate of the attenuator 72B on the antenna 21B side. In addition, the synthesis controller 64 gradually decreases the synthesis ratio of the reception signal on the antenna 21A side, and at the same time, gradually increases the synthesis ratio of the reception signal on the antenna 21B side.

  These operations can be realized by controlling any one of an amplification factor, an attenuation factor, and a synthesis ratio, but these may be combined as appropriate in order to obtain an optimum S / N. The amplification controller 62, the attenuation controller 63, and the synthesis controller 64 can also be realized by software using a CPU circuit of the control unit 54.

  The combination shown in (b) of FIG. 9 and the disconnection shown in (c) of FIG. 9 can be realized by giving a time difference to the control of the amplification factor, attenuation factor, and combination rate on each communication path described above. In the synthesis of FIG. 9B, the control on the antenna 21A side is delayed for a predetermined time, and in the disconnection of FIG. 9C, the control on the antenna 21B side is delayed for a predetermined time.

  In this way, in this example, the follow-up performance of the AGC circuit is improved by gently changing the received power level including the vicinity (transient region) before and after antenna switching, and the transient response of the RF / IF filter. The generation of impulsive noise at the time is significantly reduced. Furthermore, by appropriately adjusting / variing the amount of gradual change in received power, smooth transition of received power before and after antenna switching can be ensured.

FIG. 10 shows another example of the second embodiment.
In FIG. 10A, the amplification factor, the attenuation factor, and / or the synthesis is performed by software control using the CPU circuit of the control unit 54 or the stepwise control data given from the external antenna switching / combination circuit 47. The ratio is changed in steps. In this example, it is possible to control the reception level more precisely by using a digital amplifier or a digital attenuator whose gain and attenuation can be controlled stepwise by setting data. In FIG. 10A, the antennas 21A and 21B are controlled at the same timing for each step, but the antenna 21A side and 21B may be controlled alternately for each step.

FIG. 10B corresponds to another example of FIG. 10A, and FIG. 11 shows an example of the control flow.
In this example, the antenna switching control is executed as appropriate while monitoring the gradually changing reception level in real time. In FIG. 11, the reception level (α) of each antenna 21A and the reception level (β) of the antenna 21B are acquired by monitoring a predetermined period (Δt) (S21).

  If the amount of variation in reception level (Δα, Δβ or Δ | α−β |) is equal to or greater than a predetermined reference value, it is determined that the signal is abnormal due to noise or the like, and monitoring of the reception level is continued (S22). And 21). On the other hand, when the reception level difference becomes smaller than the predetermined reference value, it is determined that the signal is received normally, and various antenna controls as shown in FIG. 9 are executed (S23-24).

  In step S24, when the antenna switching is performed when the received reception level difference (| α−β |) between the antenna 21A and the antenna 21B becomes smaller than the predetermined reference value, the reception power is surely and smoothly increased. Can be migrated.

  As described above, in this example, the antenna switching control is appropriately performed while monitoring the reception level that changes gently or stepwise in real time, so that it is possible to reliably prevent deterioration of the reception affection at the time of antenna switching. .

FIG. 12 shows still another example of the second embodiment.
In this example, an example of a flow for determining which waveform (b) or (c) in FIG. 9 is used is shown. As mentioned before, if the reception level after antenna switching is higher, use synthesis, and if the reception level after antenna switching is lower, use cutting to make antenna switching smoother Is realized.

  Therefore, in this example, the reception level (α) of the antenna 21A and the reception level (β) of the antenna 21B are compared (S31 and 32), and the reception level after antenna switching is higher (α <β). In FIG. 9, the switching waveform (switching waveform (b)) of FIG. 9B to be combined is used (S33). On the other hand, when the reception level after the antenna switching is smaller (α> β), the switching waveform (switching waveform (c)) of FIG. 9C for cutting is used (S34).

13 and 14 show control flow examples of delay time (switching time) applied to the switching waveform of FIG.
13 and 14 respectively correspond to FIGS. 6 and 7 of the first embodiment described above, and the delay time (switching time) determined in FIGS. 13 and 14 is the switching waveform (b) or ( The same as described in the first embodiment except that it is used for the time delay of the reception level control on one side of c). Therefore, they will not be further described here.

It is the figure which showed the example of 1 structure of the OFDM receiver. It is the figure which showed the more specific structural example of FIG. It is the figure which showed the example of 1 structure of the conventional switch. It is the figure which showed the 1st Example of this invention. It is the figure which showed an example of the switch operation | movement of FIG. It is the figure which showed an example (1) of the switch control flow of FIG. It is the figure which showed an example (2) of the switch control flow of FIG. It is the figure which showed the 2nd Example of this invention. It is the figure which showed an example of the operation | movement of FIG. It is the figure which showed another example of the operation | movement of FIG. It is the figure which showed an example of the control flow of FIG. It is the figure which showed an example of the switching waveform control flow. It is the figure which showed an example (1) of the control flow of FIG. It is the figure which showed an example (2) of the control flow of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 20 ... OFDM receiver 11A, 12A, 21A, 32A ... Forward directional antenna 11B, 12B, 21B, 32B ... Back directional antenna 13-1, 13-2 ... Switching and combining unit 23, 33, 51, 52 ... Switches 26, 36 ... Level detector 48 ... Error correction part 47 ... Antenna switching / combining circuit 53 ... Synthesizer 54 ... Controller 61 ... Delay devices 71A, 71B ... Amplifiers 72A, 72B ... Attenuator 62 ... Amplification controller 63 ... Attenuation controller 64 ... Composition controller

Claims (2)

A receiving device for receiving radio waves modulated with a digital signal,
A selection unit that receives a plurality of reception signals and selects at least one reception signal;
An antenna switching / synthesis controller that adjusts the selection switching timing of the received signal , and
The antenna switching / combination control unit includes a connection timing for switching one of the plurality of antennas from non-selection to selection, and a disconnection timing for switching another antenna of the plurality of antennas from selection to non-selection. The receiving apparatus adjusts the amount of shifting the connection timing and the disconnection timing based on a broadcast parameter included in the received radio wave . A receiving device for receiving radio waves modulated with a digital signal,
A selection unit that receives a plurality of reception signals and selects at least one reception signal;
An antenna switching / synthesis controller that adjusts the selection switching timing of the received signal, and
The antenna switching / synthesizing control unit synthesizes the plurality of received signals by delaying control for switching the antenna from on to off when the reception level after the antenna switching is larger, and receives after the antenna switching. A receiving apparatus characterized in that when the level is smaller, the plurality of received signals are disconnected by delaying control for switching the antenna from off to on .

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