JP2011101108A - Device, method and processor for receiving radio signal, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely receive a necessary normal signal even when more strong normal signals continuously arrive after a weak normal signal or noise arrives. <P>SOLUTION: A receiving device 1R of a radio signal is provided with a plurality of reception systems 1A, 1B, a detection unit 110A which can detect the arrival of the reception signal by raising a receiving signal level in the plurality of receiving systems 1A, 1B, a discrimination unit 110C which discriminates whether or not the receiving signal subjected to arrival detection, is a normal PDU (Protocol Data Unit), and a decoding unit 110D which performs data decoding of the PDU discriminated as the normal one. The detection unit 110A can detect the arrival of the plurality of radio signals whose levels are different owing to plural times of raise of the receiving signal level. Moreover, the discrimination unit 110C discriminates whether or not the receiving signals are respectively normal PDUs when the arrival of the plurality of the receiving signals is detected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radio signal receiver, a reception method, a radio signal reception processor, and a program which are mounted on the receiver, for example, suitable in the field of Intelligent Transport System (ITS).

In wireless communication, even if the signal power transmitted from the transmitter is constant, the signal level received by the receiver varies depending on the distance and the propagation path of the radio wave. Therefore, an AGC (Automatic Gain Control) circuit is used to keep the signal level at the receiver side constant (see, for example, Patent Document 1).
On the other hand, in the field of intelligent road traffic systems (ITS), road traffic is achieved by communicating between in-vehicle communication devices installed in vehicles and roadside communication devices installed in infrastructure equipment on the road side. Technology to improve safety of the device is being studied.

For example, if each vehicle's in-vehicle communication device can exchange vehicle information including the current position of the vehicle for each vehicle where an accident such as a head-on collision or a right-hand collision is expected, the risk of the collision can be determined by the driver of the vehicle. Can be warned, and in some cases, driving intervention can be performed automatically, which can be useful for preventing accidents.
In particular, there is a high need to prevent accidents such as those described above, since encounter collisions between vehicles tend to occur near intersections.

However, high-rise buildings stand near intersections in urban areas, so that radio wave visibility is often not good between vehicles, and it is difficult to exchange information between in-vehicle communication devices.
For this reason, if the roadside communication device acts as an intermediary for vehicle information and transmits vehicle information such as the current position of the vehicle collected from a number of in-vehicle communication devices near the intersection to each in-vehicle communication device, each vehicle The vehicle information of the vehicle can be sensed almost in real time, and the safety of road traffic can be improved.

In this case, it is estimated that CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) is used as an access control method between the in-vehicle communication devices. That is, each in-vehicle communication device transmits a radio signal to the outside in order after confirming that no other in-vehicle communication device transmits a radio signal.
For this reason, if there is no problem such as a so-called hidden terminal in which transmission of a regular in-vehicle communication device is hindered by a transmission request from a non-existent terminal, a radio signal (radio signal) transmitted from each in-vehicle communication device Are transmitted in chronological order without overlapping each other.

  For example, when the wireless signal used in the above-mentioned intelligent road traffic system conforms to the standard of IEEE802.11a / g / p, it is a protocol data unit (Protocol Data Unit: hereinafter referred to as “PDU”). Sent in units. One frame length of the PDU is about 1 msec, and a time gap (guard time) of about 40 μsec is provided between the frames.

JP 2002-84153 A

In the above-mentioned intelligent road traffic system, it is necessary for one roadside communication device to reliably receive radio signals transmitted from a large number of in-vehicle communication devices with different positions. Vastly different.
For example, the intensity of radio waves is said to be inversely proportional to the square of distance in rural areas close to free space, and attenuated in inverse proportion to the fourth power of distance in urban areas with many buildings. Radio wave attenuation in urban areas is mainly caused by reflection of radio waves by buildings.

  In addition, since the radio signal transmitted by each in-vehicle communication device becomes a multipath state due to the reflection of radio waves and fading may occur, even a radio signal transmitted from the same in-vehicle communication device has a slight difference in conditions. It is assumed that the signal level received by the roadside communication device rapidly decreases. It has been confirmed that the degree of this reduction reaches, for example, 32 dB.

In this regard, since the AGC circuit is mounted on the receiver of the roadside communication device, the reception level can be made uniform by the gain control function even for a radio signal having a large level difference.
That is, when the receiver of the roadside communication device detects arrival of a radio signal due to an increase in received signal strength, the gain of the AGC circuit is set according to the level of the input signal (received signal strength), and the radio signal is noise. It is determined whether there is a regular PDU to be demodulated (hereinafter sometimes referred to as “regular packet”).

However, in the case of a roadside communication device used in an intelligent road traffic system, a relatively weak radio signal (not only a regular signal but also noise) due to the noisy environment and the peculiarity that a hidden terminal may exist. Including the meaning of “radio waves”.) After the arrival of a), a stronger regular radio signal may arrive continuously.
In this case, if the next radio signal arrives while determining whether the previous radio signal is a regular packet, the process for determining whether the next radio signal is a regular packet is not in time. There is a risk of missing a regular packet included in the next radio signal.

Further, in order to determine whether or not the next radio signal is a regular packet, it is necessary to match the gain in the AGC circuit with the next radio signal.
In this case, in the conventional receiver, while determining whether or not a certain radio signal is a regular packet, the gain of the AGC circuit is maintained until the determination is completed. When a strong next radio signal arrives, the gain in the AGC circuit may be too high and the next radio signal may be saturated (saturation).

In this way, if the wireless signal that arrives later is saturated, it is impossible to determine whether or not this wireless signal is a regular packet, and even if it is a regular packet, it is determined to be noise, and the subsequent wireless signal Contain useful regular packets cannot be captured.
On the other hand, assuming an intelligent road traffic system, vehicle information from a vehicle closer to a roadside communication device installed near an intersection is considered to be more useful, so it reliably receives a high-intensity radio signal that arrives later. That is extremely important.

  In view of the above problems, the present invention is a wireless signal that can reliably receive a necessary regular signal even when a weak regular signal or noise arrives and a stronger regular signal arrives continuously. The purpose is to provide a receiver and the like.

  (1) A receiver according to the present invention includes a plurality of reception systems, a detection unit capable of detecting arrival of a reception signal by an increase in reception level in the plurality of reception systems, and the reception signal from which arrival has been detected is normal. A radio signal receiver comprising: a determination unit that determines whether or not a PDU is present; and a demodulation unit that performs data demodulation of the PDU determined to be legitimate, wherein the detection unit includes the reception level When the arrival of the received signals from a plurality of transmission sources with different levels is detected, and the determination unit detects arrival of a plurality of consecutive received signals, It is determined whether each of the received signals is the regular PDU.

According to the receiver of the present invention, the detection unit can detect the arrival of different reception signals from a plurality of transmission sources having different levels, and the determination unit detects the arrival of a plurality of reception signals. Since it is determined whether or not each of the received signals is a regular PDU, any of the plurality of received signals is a regular PDU, and this is not missed.
For this reason, even if a weaker normal signal (meaning “radio wave including noise”) arrives after a stronger normal signal continuously, the normal PDU included in the subsequent normal signal can be demodulated, The subsequent regular signal can be reliably received.

(2) Here, when the weaker received signal is the first radio signal and the subsequent strong received signal is the second radio signal, the demodulator in the receiver of the present invention is When it is determined that the second radio signal is the regular PDU, it is preferable that the second radio signal is a demodulation target regardless of the determination result of the first radio signal.
The reason is that, for example, in an intelligent road traffic system, vehicle information closer to the receiver of the present invention mounted on a roadside communication device is more useful, so it arrived later than the weaker radio signal that reached earlier This is because the stronger regular signal should be received reliably.

(3) In the receiver according to the present invention, an amplification circuit provided for each of the plurality of reception systems can be variably set, and the amplification factor of the amplification circuit is controlled in accordance with the reception level. It is preferable to further include a gain control unit.
In this case, when the arrival of the first radio signal is detected, the gain control unit adjusts only the gain of the first reception system, which is one of the plurality of reception systems, to the reception level. When the arrival of the second radio signal is detected, it is preferable to change only the amplification factor of the second reception system other than the first reception system in accordance with the reception level.
In this case, saturation of the second radio signal can be prevented even when the second radio signal arrives continuously after the first radio signal.
For this reason, when the stronger wireless signal is a regular packet, it is not determined as noise, and the subsequent regular signal can be reliably received as a regular packet.

(4) In the receiver according to the present invention, when the arrival of the second radio signal is detected while demodulating the PDU with respect to the first radio signal, the second radio signal is normal. When it is determined that it is not the PDU, the demodulation of the PDU with respect to the first radio signal can be continued.
Here, the second radio signal includes one detected as arrival of a different radio signal when the level of the first radio signal increases due to fading. In such a case, more appropriate demodulation can be performed by continuing demodulation of the first radio signal than by stopping demodulation of the first radio signal and demodulating the second radio signal.

(5) In the receiver of the present invention, the demodulator determines the regular PDU to be demodulated, and then performs data demodulation on the combined signal obtained by combining the output signals of the plurality of receiving systems. Preferably it is done.
In this case, since the control unit performs data demodulation on the combined signal obtained by combining the output signals of the plurality of reception systems after determining the normal PDU, it is possible to accurately perform data demodulation on the normal PDU.

(6) The reception method of the present invention is a radio signal reception method performed by the receiver of the present invention, and has the same operational effects as the receiver.
(7) The receiving processor of the present invention is a wireless signal receiving processor mounted on the receiver of the present invention, and has the same effects as the receiver.
(8) The program of the present invention is a program executed by the receiving processor of the present invention, and has the same effects as the receiving processor.

  As described above, according to the present invention, when arrival of a plurality of received signals is detected, it is determined whether or not each received signal is a regular PDU. Even when a stronger regular signal arrives continuously, the subsequent regular signal can be reliably received.

It is a road top view for showing the whole structure of an intelligent road traffic system. It is a block diagram which shows the internal structure of the receiver which concerns on embodiment of this invention mounted in the roadside communication apparatus. It is a flowchart which shows the specific example of the processing content by the processor for reception. (A) is a road side view when two vehicles at different positions transmit radio signals, (b) and (c) are radio signal frames transmitted by the respective vehicles, and the radio signals It is a figure which shows the input waveform to a variable amplifier (AGC circuit), (d) is explanatory drawing in case a receiver receives noise from a mobile telephone etc. FIG. It is a time chart when the conventional receiver receives noise before arrival of a strong regular packet, (a) is an input waveform of a variable amplifier, (b) is a time change of RSSI, (c) is a variable amplifier. (D) shows the output waveform of the variable amplifier, and (e) shows the time change of the autocorrelation signal.

It is a time chart when the receiver which concerns on embodiment of this invention receives noise before arrival of a strong regular packet, (a) is an input waveform of a variable amplifier, (b) is a time change of RSSI, ( c) is a temporal change of the gain of the variable amplifier of the first reception system, (d) is an output waveform of the variable amplifier of the first reception system, (e) is a temporal change of the gain of the variable amplifier of the second reception system, (F) shows the output waveform of the variable amplifier of the second receiving system. 4 is a time chart when a receiver according to an embodiment of the present invention receives a regular packet whose level gradually increases due to fading, (a) is an input waveform of a variable amplifier, (b) is a change in RSSI with time, ( c) is a temporal change of the gain of the variable amplifier of the first reception system, (d) is an output waveform of the variable amplifier of the first reception system, (e) is a temporal change of the gain of the variable amplifier of the second reception system, (F) shows the output waveform of the variable amplifier of the second receiving system.

[Overall system configuration]
FIG. 1 is a road plan view showing the overall configuration of an intelligent road traffic system.
As shown in FIG. 1, the intelligent road traffic system of the present embodiment is composed of a roadside communication device 1 provided near an intersection and a plurality of in-vehicle communication devices 3 that can communicate with the device 1. A roadside communication device 1 shown in the vicinity of the center of 1 is installed, for example, on a column of a traffic light 2 at an intersection.

Each vehicle traveling on the road is equipped with an in-vehicle communication device 3 that can communicate with the roadside communication device 1. The roadside communication device 1 can communicate with a large number (for example, about 200) of the vehicle-mounted communication devices 3 in the communicable area.
The roadside communication device 1 is connected to the central device 4 of the traffic control center, and the central device 4 and the roadside communication device 1 are connected by wire (or wirelessly). Moreover, the road-to-road communication between the roadside communication apparatuses 1 located at each intersection, the road-to-vehicle and road-to-vehicle communication between the roadside communication apparatus 1 and the in-vehicle communication apparatus 3, and the inter-vehicle communication between the in-vehicle communication apparatuses 3 For this, wireless communication is used. Among these, it is presumed that CSMA / CA is used for inter-vehicle communication between the in-vehicle communication devices 3.

In the present embodiment, an Orthogonal Frequency-Division Multiplexing (OFDM) is adopted as a modulation method for wireless communication between the communication apparatuses 1 and 3.
This method is a multi-carrier digital modulation method in which transmission data is carried on a large number of carrier waves (subcarriers). Since the subcarriers are orthogonal to each other, the data can be arranged so densely as to overlap on the frequency axis. There are advantages.

Furthermore, the in-vehicle communication device 3 of the present embodiment transmits a radio signal in a format compliant with IEEE 802.11a / g / p using an access control method based on CSMA / CA.
For this reason, the regular frames (for example, about 1 msec in length) transmitted by each in-vehicle communication device 3 are transmitted in time series without overlapping each other, and for example, about 40 μsec is transmitted between the frames. There is a time gap. In principle, the number of frames transmitted from the transmitter of each in-vehicle communication device 3 is one except in the so-called burst mode.

Usually, “frame” is a PDU name used in layer 2 communication, and “packet” is often a name used in layer 3 communication. Both “packets” and “frames” are used in combination as simple PDUs.
In addition, simply speaking “signal” generally means a “narrow sense signal” including necessary information, and is used to distinguish it from “noise” that interferes with this narrow sense signal. In the book, “signal” simply means “a signal in a broad sense” including both “a signal in a narrow sense” and “noise”. Therefore, in the “reception signal” and “radio signal” in this specification, both a narrowly defined signal (regular PDU) having information carried by the transmission side and noise that does not have the information or the information is corrupted. Is included.

[Receiver of roadside communication device]
Next, the internal configuration of the receiver mounted on the roadside communication device 1 will be described.
FIG. 2 is a block diagram showing an internal configuration of the receiver 1R in the roadside communication apparatus 1.
In addition, this invention proposes the new policy for the roadside communication apparatus 1 to receive appropriately the transmission signal of the stronger in-vehicle communication apparatus 3 which arrives continuously after the radio | wireless signal before including a noise. Therefore, in the following, the roadside communication device 1 will be described as “receiver 1R”, and the in-vehicle communication device 3 will be described as “transmitter 3S”.

The receiver 1R in the roadside communication apparatus 1 includes two systems of reception systems 1A and 1B and a reception processor 110 that performs reception control on these systems, and each of the reception systems 1A and 1B includes each component shown in FIG. Are connected as shown in the figure.
That is, each of the receiving systems 1A and 1B of the receiver 1R includes an antenna 101, a band-pass filter 102, a low noise amplifier 103, an attenuator 104, a low noise amplifier 105, a variable amplifier 106 including an AGC circuit, and a quadrature demodulator in order from the left side. 107, an A / D converter 108, and a detection circuit 109.

First, the radio signal transmitted from each transmitter 3S is received by the antenna 101, and a signal in a predetermined band is extracted by the band pass filter 102 from the received signal.
The extracted signal is amplified as a whole by a low noise amplifier 103, an attenuator 104, a low noise amplifier 105, and a variable amplifier 106 which is an amplifier circuit having an automatic gain control function.

The output signal of the variable amplifier 106 is demodulated into an in-phase component I signal and a quadrature component Q signal by a quadrature demodulator 107, and each component signal is digitized by an A / D converter 108 in the next stage. And input to the receiving processor 110.
Further, the output signal of the low noise amplifier 105, that is, the input signal to the variable amplifier (AGC circuit) 106 is envelope-detected by the detection circuit 109, and the received signal strength (RSSI: Received Signal Strength Indication) which is the signal level of the envelope. Hereinafter, in this specification, it may also be referred to as “reception level”) is also input to the reception processor 110.

That is, each receiving system 1A, 1B is controlled by one receiving processor 110, and the output signals of the A / D converter 108 and the detection circuit 109 of each receiving system 1A, 1B are both Input to one receiving processor 110.
The receiving processor 110 according to the present embodiment includes, for example, an FPGA (Field Programmable Gate Array) that stores a control program for a plurality of receiving systems, and includes a detection unit 110A and a gain as functional units realized by executing the control program. A control unit 110B, a determination unit 110C, and a demodulation unit 110D are provided.

Among these, the detection unit 110A constantly monitors an increase in the level (RSSI) of the input signal to the variable amplifier 106 of both reception systems 1A and 1B, and whether or not the RSSI has exceeded the first threshold Th1 with the smaller RSSI. Accordingly, the arrival of the weaker radio signal (hereinafter sometimes referred to as “first radio signal”) is detected.
In addition, the detection unit 110A detects the arrival of a stronger radio signal (hereinafter also referred to as “second radio signal”) depending on whether or not the second threshold Th2 having a larger RSSI is exceeded.

That is, the detection unit 110A of the reception processor 110 can continuously reach the radio signal in addition to the first threshold Th1 for detecting the arrival of the first radio signal (first radio signal). A second threshold Th2 for detecting a strong wireless signal (second wireless signal) is further held.
For example, Th1 = −85 dBM and Th2 = Th1 + 5 dBM are set depending on the installation location of the roadside communication device 1.

As described above, the receiver 1R of the present embodiment can detect continuous arrival of two types of strong and weak radio signals (first and second radio signals) in a default state before an undetected radio signal arrives. It is in a receiving position.
On the other hand, the gain control unit 110B independently varies the attenuation factor of the attenuator 104 of each reception system 1A, 1B and the amplification factor of the variable amplifier 106 in accordance with the RSSI value in each reception system 1A, 1B. Can be set.

Then, when the arrival of the first radio signal is detected, the gain control unit 110B tracks only the gain of the first reception system 1A in accordance with the RSSI value, and the arrival of the second radio signal is detected. In this case, only the amplification factor of the second reception system 1B is made to follow the RSSI value.
In this case, since the intensity of the second radio signal is greater than that of the first radio signal, the gain setting for the variable amplifier 106 is set lower in the second reception system 1B than in the first reception system 1A. It will be.

In addition, when the detection unit 110A detects the arrival of the continuous first and second radio signals, the determination unit 110C applies to the digitized I signal and Q signal output from the reception systems 1A and 1B. To determine whether each of the signals is a regular packet.
Specifically, the control unit 110B determines whether or not the packet is a regular packet, depending on whether or not the autocorrelation value for the preamble (see FIG. 4B) at the beginning of the received frame exceeds a predetermined threshold. Is called.

However, as a method of discriminating regular packets using the preamble, not only autocorrelation values but also judgments based on calculation results such as RSSI difference values (differential values) and addition values (integration values), and judgments based on pattern recognition methods are used. It can also be adopted.
Then, the demodulation unit 110D performs data demodulation on the packet (I signal and Q signal) determined by the determination unit 110C as normal, and extracts the header and data information included in the normal packet.

If the determination unit 110C determines that the second wireless signal, which is the stronger wireless signal, is a regular packet, the second wireless signal is unconditionally transmitted regardless of the determination result of the first wireless signal. It is intended to be judged.
The reason is that, as described above, in ITS, the vehicle information closer to the roadside communication device 1 is more useful, so the stronger second radio signal that arrived later than the weaker first radio signal that arrived earlier This is because it should be received reliably.

Furthermore, when the arrival of a radio signal is detected, the gain control unit 110B changes the amplification factor of the variable amplifier 106 of either one of the reception systems 1A and 1B at high speed, but the variable amplifier during the other periods The gain of 106 is kept substantially constant.
As described above, since the amplification factor of the variable amplifier 106 is maintained substantially constant during a period other than when the arrival of the radio signal is detected, for example, when determining whether the packet is a regular packet based on the autocorrelation value for the preamble, The autocorrelation value can be stabilized, and there is an advantage that regular packet determination processing can be performed reliably.

[Specific example of processing contents of receiving processor]
FIG. 3 is a flowchart illustrating a specific example of processing contents of the reception processor 110.
As shown in FIG. 3, the reception processing in the reception processor 110 is largely divided into a “preamble search mode” in the first half and a “data demodulation mode” in the second half. In the “preamble search mode”, the first or second (2) The presence / absence of a regular packet is determined using the preamble of the radio signal.

The “data demodulation mode” is a mode that is executed for subsequent data reception on the condition that synchronization is established by a preamble. In this mode, data demodulation is performed on a combined signal obtained by combining the output signals (I signal and Q signal) of the receiving systems 1A and 1B by, for example, the maximum ratio combining method.
As a method for combining the output signals of the receiving systems 1A and 1B, a selective combining method or an equal gain combining method may be employed in addition to the maximum ratio combining method. Hereinafter, the radio signal reception processing by the reception processor 110 will be described in more detail with reference to the flowchart of FIG.

As shown in FIG. 3, the receiving processor 110 first executes a preamble search mode (step ST1 in FIG. 3).
In this preamble search mode, when the detection unit 110A detects an increase in RSSI exceeding the first threshold Th1, the gain control unit 110B of the reception processor 110 adjusts the variable amplifier of the first reception system 1A according to the RSSI value. The gain of 106 is made to follow.

Further, when the detection unit 110A detects an increase in RSSI exceeding the second threshold Th2, the gain control unit 110B of the reception processor 110 adjusts the amplification factor of the variable amplifier 106 of the second reception system 1B according to the RSSI value. To follow.
As described above, in the preamble search mode, the reception processor 110 sets the amplification factor (gain) independently for each of the variable amplifiers 106 included in the reception systems 1A and 1B (step ST2 in FIG. 3). ).

Next, the determination unit 110C of the reception processor 110 searches the preamble for the radio signals received by the reception systems 1A and 1B by calculating an autocorrelation value or the like, thereby determining the presence or absence of a regular packet ( Step ST3 in FIG.
In the above determination, when the preamble is not found, the determination unit 110C repeatedly executes the preamble search mode. When the preamble is found, the determination unit 110C shifts to the next data demodulation mode (step ST4 in FIG. 3).

On the other hand, in the data demodulation mode, the gain determination unit 110B of the receiving processor 110 resets the gains of the variable amplifiers of the receiving systems 1A and 1B to a common value (step ST5 in FIG. 3). Demodulation section 110D combines the output signals from both reception systems 1A and 1B by a maximum ratio combining method or the like, and performs data demodulation (step ST6 in FIG. 3).
Next, demodulation section 110D determines whether or not a series of frame reception has been completed by CRC detection or the like (step ST7 in FIG. 3), and if it is determined to be complete, the operation mode is set to the first preamble search mode. If it is determined that the data demodulation is incomplete, the data demodulation mode is repeatedly executed.

[Transmission signal of each vehicle and its input waveform]
FIG. 4A is a side view of a road when two vehicles A and B at different positions transmit radio signals. FIGS. 4B and 4C show the vehicles A and B, respectively. It is a figure which shows the flame | frame of the radio signal to transmit, and the input waveform to the variable amplifier (AGC circuit) 106 of the radio signal, and FIG.4 (d) is a case where a receiver receives noise from a mobile telephone etc. It is explanatory drawing.
In the example shown in FIG. 4, the transmission time at the vehicle B (or mobile phone or the like) B far from the receiver 1R is t1, and the transmission time at the near vehicle A is t2 (> t1). Is assumed to arrive later than the radio signal from the vehicle B.

As shown in FIG. 4B, the frames of the transmission signals of the vehicles A and B include a preamble, a header, data, and a CRC (Cyclic Redundancy Code) in order from the top. The CRC is code data for error detection included at the end of a digital signal frame in the IEEE802.11a / g / p format.
Therefore, by detecting the CRC at the end of the frame, it is possible to detect the end of reception of each frame.

On the other hand, as shown in FIG. 4B, there is a large signal level difference in the input waveform to the variable amplifier 106 of the transmission signals of the vehicles A and B at different positions. The level fluctuates.
Further, since the transmitter 3S transmits a frame by the CSMA / CA method, both the vehicles A and B are equipped with the regular in-vehicle communication device 3, and the vehicle A appropriately receives the radio wave from the vehicle B. Then, the frames transmitted by these vehicles A and B do not overlap each other, and as shown in FIG. 4B, a predetermined guard time Δt is provided between the frames of the vehicles A and B that reach the receiver 1R. (For example, 40 microseconds) exists.

However, when vehicle A is not properly receiving radio waves from vehicle B (when vehicle B is a “hidden terminal”), for example, as shown in FIG. After a relatively weak regular signal reaches the receiver 1R first, a stronger regular signal from the vehicle A may continuously reach the receiver 1R in a state where it overlaps with the regular signal from the vehicle B. is there.
In addition, as shown in FIG. 4 (d), a part of radio waves emitted from a device using another frequency band such as a mobile phone reaches the receiver 1R first as relatively weak noise, A stronger regular signal of the vehicle A may reach the receiver continuously with its noise superimposed.
Thus, before the arrival of the strong regular packet (vehicle A in FIG. 4), the weak regular packet (vehicle B in FIG. 4) or noise arrives, so that the antenna of the receiver 1R is superposed on both of them. 101 may arrive continuously.

[Continuous arrival of wireless signals and its problems]
FIG. 5 is a time chart when a conventional receiver receives weak noise before arrival of a strong regular packet, and when a strong next wireless signal arrives continuously after arrival of a weak wireless signal, The subject of the conventional receiver is shown.
5A shows the input waveform of the variable amplifier 106 in the above case, FIG. 5B shows the time change of RSSI, and FIG. 5C shows the time change of the gain of the variable amplifier 106, respectively. Show.

As shown in FIGS. 5A and 5B, in this case, RSSI (reception level) once rises due to noise that has reached the receiver first, and then RSSI further rises due to regular packets that arrive continuously thereafter. is doing.
At this time, when the RSSI exceeds a predetermined threshold Th1 due to the first noise, and the arrival of any wireless signal is detected by this, the gain of the variable amplifier 106 is set corresponding to the RSSI value (FIG. 5 (c)). )), A process of determining whether or not the packet is a regular packet is performed with respect to the wireless signal that has arrived first (in this case, noise).

As described above, even if the received signal that has arrived first is noise as a result, the determination process (for example, using an autocorrelation value) takes a predetermined time, but during the determination process for the noise. In addition, when the next regular packet arrives, the determination process for the next regular packet may not be in time.
Therefore, as in the case assumed in FIG. 5, although the radio signal that has arrived after the noise is actually a regular packet, the preamble cannot be determined for the regular packet, and the regular packet may be missed. is there.

On the other hand, in order to determine whether or not the next radio signal is a regular packet, it is necessary to match the gain of the variable amplifier 106 to the next radio signal. However, in a conventional receiver, a certain radio signal is a regular packet. During the determination of whether or not, the gain of the variable amplifier 106 is fixed and maintained until the determination is completed.
For this reason, as shown in FIG. 5D, when a stronger next regular packet arrives during the determination process for the previous radio signal (in this case, noise), the variable amplifier 106 is used for this regular packet. The gain at may be too high and saturate.

Thus, when the next regular packet is saturated, as shown in FIG. 5E, the autocorrelation signal of the regular packet is also destroyed. Therefore, it is possible to appropriately determine whether or not the next radio signal is a regular packet. Cannot be executed.
Therefore, even if the later radio signal is a regular packet, it is determined as noise, and a useful regular packet included in the later radio signal cannot be captured.
Note that the same phenomenon as described above also occurs when the weak noise that reaches first in FIG. 4 is replaced with a weak normal signal (a normal packet from vehicle B in FIG. 4C).

Assuming an intelligent road traffic system like this embodiment, as shown in FIG. 4 (a), the one closer to the device 1 than the vehicle B far from the roadside communication device 1 installed near the intersection. Vehicle information from vehicle A is considered to be more useful.
Therefore, in the case of the receiver 1R of the roadside communication device 1 configuring the intelligent road traffic system, it can be said that it is an extremely important issue to reliably receive a radio signal having a higher strength that has arrived later.

[Effects of this embodiment (1)]
FIG. 6 is a time chart when the receiver 1R of the present embodiment receives weak noise before arrival of a strong regular packet, and the next stronger wireless signal arrives continuously after the arrival of the weak wireless signal. In this case, the effect of the receiver 1R of the present embodiment is shown.
FIG. 6A shows the input waveform of the variable amplifier in the above case, and FIG. 6B shows the time change of RSSI.

FIG. 6C shows a temporal change in gain of the variable amplifier 106 of the first reception system 1A, and FIG. 6D shows an output waveform of the variable amplifier 106 of the first reception system 1A.
Further, FIG. 6E shows a temporal change in gain of the variable amplifier 106 of the second reception system 1B, and FIG. 6F shows an output waveform of the variable amplifier 106 of the second reception system 1B.
As shown in FIG. 6B, when the RSSI exceeds the first threshold value Th1 due to noise that has reached the receiver 1R first, the detection unit 110A of the reception processor 110 causes the weaker first radio signal to reach. To detect.

At this time, as shown in FIG. 6C, the gain control unit 110B of the reception processor 110 reduces the gain of the variable amplifier 106 included in the first reception system 1A in accordance with the RSSI value. The gain in 1 reception system 1A is made to follow RSSI.
The gain operation performed by the gain control unit 110B on the first reception system 1A is only when the first wireless signal that has arrived first is detected, and even if a stronger regular packet arrives later, the first reception is performed. The gain of the system 1A is maintained as it is.
For this reason, as shown in FIG. 6D, a regular packet that arrives later may be saturated with respect to the variable amplifier 106 of the first reception system 1A.

On the other hand, as shown in FIG. 6 (b), when the RSSI exceeds the second threshold Th1 due to regular packets that subsequently arrive at the receiver 1R, the detection unit 110A detects that the stronger second radio signal has arrived. To detect.
At this time, the gain control unit 110B of the reception processor 110 reduces the gain of the variable amplifier 106 included in the second reception system 1B in accordance with the RSSI value, as shown in FIG. 2 The gain in the receiving system 1B is made to follow RSSI.

For this reason, as shown in FIG. 6 (d), the regular packet that arrives later does not saturate with respect to the variable amplifier 106 of the second reception system 1B. Therefore, based on the output waveform of the second reception system 1B. Then, a process for determining whether or not the packet is a regular packet using the preamble is performed.
After that, using the output signals (I signal and Q signal) of the second reception system 1B, the demodulation unit 110D of the reception processor 110 performs data demodulation on the normal packet in the data demodulation mode (FIG. 3). Will do.

As described above, according to the receiver 1R and the reception processor 110 of the present embodiment, the detection unit 110A receives subsequent reception signals with different transmission sources that are continuous with the reception signal that has already reached due to further increase in RSSI. The arrival of the signal can be detected, and when the determination unit 110C detects the arrival of the subsequent reception signal, the determination is made for the subsequent reception signal.
For this reason, if a later received signal is a regular packet, it will not be missed, and even if a stronger regular signal arrives continuously after arrival of a weak radio signal consisting of noise or a regular signal, It is possible to demodulate the normal packet of the normal signal.

In the present embodiment, the gain control unit 110B can set the amplification factor (gain) independently for the variable amplifiers 106 included in the reception systems 1A and 1B, and the arrival of the first radio signal is detected. In this case, only the amplification factor of the first reception system 1A is changed, and when the arrival of the second reception signal is detected, only the amplification factor of the second reception system 1B is changed. Even if the second radio signal arrives continuously, saturation of the second radio signal can be prevented.
For this reason, when the stronger next radio signal is a regular packet, it is not determined as noise, and the next radio signal can be reliably received as a regular packet.

As described above, according to the receiver 1R and the reception processor 110 of this embodiment, even when used in a communication apparatus installed in a noisy environment such as the roadside communication apparatus 1 in FIG. Can be received.
In contrast to the case of FIG. 6, it is conceivable that the previous weak radio signal is a regular packet and the next stronger radio signal is noise, but in this case, the strong noise that arrived later Since it is considered that demodulation of regular packets is difficult in the first place due to superposition, this is not a big problem.

[Effect (2) of this embodiment]
FIG. 7 is a time chart when the receiver 1R according to the present embodiment receives a regular packet whose level gradually increases due to fading, and shows another effect of the receiver 1R according to the present embodiment.
FIG. 7A shows the input waveform of the variable amplifier in the above case, and FIG. 7B shows the temporal change of RSSI.

FIG. 7C shows a temporal change in gain of the variable amplifier 106 of the first reception system 1A, and FIG. 7D shows an output waveform of the variable amplifier 106 of the first reception system 1A.
Further, FIG. 7E shows a temporal change in gain of the variable amplifier 106 of the second reception system 1B, and FIG. 7F shows an output waveform of the variable amplifier 106 of the second reception system 1B.
As shown in FIG. 7A, the level of the regular packet gradually increases due to fading, and as a result, the RSSI exceeds the first and second threshold values Th1 and Th2 in stages (see FIG. 7B). .

At this time, when the RSSI value exceeds the first threshold Th1, the gain control unit 110B of the reception processor 110 decreases the gain of the variable amplifier 106 included in the first reception system 1A, and the gain in the first reception system 1A. Is made to follow RSSI (see FIG. 7C).
When the RSSI value exceeds the second threshold Th2 (and is detected as the arrival of a radio signal with a different level increase due to fading), the gain control unit 110B includes the variable amplifier included in the second reception system 1B. The gain of 106 is lowered, and the gain in the second reception system 1B is made to follow RSSI (see FIG. 7E).

In the example shown in FIG. 7, it is assumed that the amplification factor of the variable amplifier 106 of the first reception system 1A is more appropriate even if the level increases due to fading. For this reason, as shown in FIG. 7 (d), it is possible to perform determination processing and data demodulation on a regular packet by using the output waveform of the first reception system 1A.
On the other hand, as shown in FIG. 7F, the output waveform in the second reception system 1B has insufficient power, and there is a possibility that determination processing and data demodulation for a regular packet cannot be performed.

Therefore, in this case, the determination unit 110C of the reception processor 110 determines that the output waveform in the first reception system 1A is a normal packet.
Therefore, the demodulation unit 110D performs data demodulation on the packet (I signal and Q signal) from the first reception system 1A determined to be normal, and extracts the header and data information included in the normal packet. Will be.

Thus, according to the receiver 1R of the present embodiment, the two reception systems 1A and 1B are provided, and it is determined whether the received signals received by the reception systems 1A and 1B are regular packets. Therefore, when the weak wireless signal is a regular packet, this wireless signal can also be selected as a determination target.
For this reason, according to the receiver 1R of the present embodiment, even if it is a series of regular packets whose levels are increased by fading as shown in FIG. 7, the regular packets can be effectively demodulated. it can.

  Further, in the receiver 1R of the present embodiment, after capturing a synchronization signal for a regular packet and determining a signal to be demodulated, the receiver 1R switches to diversity reception and performs data demodulation by the maximum ratio combining method or the like (FIG. 3). (See also), and there is an advantage that data demodulation can be performed with high accuracy.

[Other variations]
The embodiment disclosed this time is illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, and includes all modifications that are within the scope of the claims and equivalents.

For example, in the above-described embodiment, three or more reception systems may be provided, and the detection unit 110A may detect an increase in RSSI in three or more stages to detect arrival of wireless signals of three or more types.
In this case, the determination unit 110C determines whether each output signal output by three or more reception systems is a regular packet.

DESCRIPTION OF SYMBOLS 1 Roadside communication apparatus 1R Receiver 1A 1st receiving system 1B 2nd receiving system 3 In-vehicle communication apparatus 3S Transmitter 101 Antenna 102 Band pass filter 103 Low noise amplifier 104 Attenuator 105 Low noise amplifier 106 AGC circuit (variable amplifier: amplification circuit)
107 quadrature demodulator 108 A / D converter 109 detection circuit 110 receiving processor 110A detection unit 110B gain control unit 110C determination unit 110C demodulation unit

Claims (8)

A plurality of reception systems, a detection unit capable of detecting arrival of a reception signal by an increase in reception level in the plurality of reception systems, and the reception signal from which arrival has been detected is a normal protocol data unit (Protocol Data Unit: A radio signal receiver comprising: a determination unit that determines whether or not the signal is “PDU”), and a demodulation unit that performs data demodulation of the PDU determined to be legitimate,
The detection unit is capable of detecting arrival of a plurality of reception signals having different levels by increasing the reception level multiple times.
The determination unit determines whether or not each of the received signals is the regular PDU when the arrival of a plurality of the received signals is detected. When the weaker received signal is the first radio signal, and the stronger continuous signal after this is the second radio signal,
The demodulation unit, when it is determined that the second wireless signal is the regular PDU, the second wireless signal is a demodulation target regardless of the determination result of the first wireless signal. A radio signal receiver as described in 1. An amplification circuit that can variably set the amplification factor provided for each of the plurality of reception systems; and a gain control unit that controls the amplification factor of the amplification circuit corresponding to the reception level;
When the arrival of the first radio signal is detected, the gain control unit changes only the gain of the first reception system, which is one of the plurality of reception systems, according to the reception level. ,
3. The radio signal receiver according to claim 2, wherein, when arrival of the second radio signal is detected, only an amplification factor of a second reception system other than the first reception system is changed in accordance with the reception level. 4. .   The demodulation unit determines that the second radio signal is not the regular PDU when the arrival of the second radio signal is detected while demodulating the PDU with respect to the first radio signal. The radio signal receiver according to claim 2 or 3, wherein the demodulation of the PDU with respect to the first radio signal is continued.   The demodulation unit according to any one of claims 1 to 4, wherein the demodulation unit performs data demodulation on a combined signal obtained by combining a plurality of output signals of the reception system after determining the regular PDU to be demodulated. A receiver of the described radio signal. Detection of arrival of a received signal by an increase in reception level in a plurality of receiving systems, determination of whether or not the received signal whose arrival has been detected is a normal PDU, and data demodulation of the PDU determined to be normal A wireless signal receiving method for performing
Detecting the arrival of a plurality of received signals having different levels due to a plurality of rises in the received level;
And a step of determining whether or not each of the received signals is a regular PDU when arrival of a plurality of the received signals is detected. A detection unit capable of detecting arrival of a reception signal by an increase in reception level in a plurality of reception systems, a determination unit for determining whether or not the reception signal for which arrival has been detected is a normal PDU, and determination as normal A radio signal receiving processor comprising: a demodulator that demodulates data of the PDU,
The detection unit is capable of detecting arrival of a plurality of reception signals having different levels by increasing the reception level multiple times.
The processor for receiving a radio signal, wherein the determination unit determines whether or not each of the received signals is a regular PDU when arrival of a plurality of the received signals is detected. A detection unit capable of detecting arrival of a reception signal by an increase in reception level in a plurality of reception systems, a determination unit for determining whether or not the reception signal for which arrival has been detected is a normal PDU, and determination as normal A program executed by a radio signal reception processor comprising: a demodulator that demodulates data of the PDU,
Detecting the arrival of a plurality of received signals having different levels due to a plurality of rises in the received level;
A program for causing the receiving processor to execute a step of determining whether or not each of the received signals is a regular PDU when the arrival of a plurality of the received signals is detected.