JP2011259403A - Receiver, reception method, processor for reception, and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect arrival of a packet while the radio signals of a former packet are received.SOLUTION: A road-side communication device which receives radio signals stores the reception level of the preamble part of packet signals as a reference signal in advance. While radio signals following the preamble part are received, the arrival of another radio signal from a different origination source is detected on the basis of the rising of the reception level.

Description

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

  In the field of intelligent road traffic systems (ITS), road traffic safety is achieved by communicating between in-vehicle communication devices installed in vehicles and roadside communication devices installed in infrastructure equipment on the road side. A technique for improving the property has been studied (for example, see Patent Document 1).

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. In this case, ideally, the radio signals transmitted from the in-vehicle communication devices are transmitted side by side in time series without overlapping each other.

Here, the roadside communication device is required to receive as many packets as possible transmitted one after another from many in-vehicle communication devices. However, since the reception timing and reception level of the radio signal to be received by the roadside communication device are not constant, reception is not always easy.
Moreover, the roadside communication device needs to receive a radio signal transmitted unilaterally from the in-vehicle communication device, instead of establishing a connection channel by exchanging ACK or the like with the in-vehicle communication device. Even if reception fails, retransmission processing is not performed.
Thus, reception by the roadside communication device is performed under severe conditions.

Japanese Patent No. 2806801

  Moreover, the so-called hidden terminal problem makes reception by the roadside communication device more difficult. Here, the hidden terminal problem is that a plurality of in-vehicle communication devices (terminals) are shielded from each other by a building or the like and are hidden from each other. That happens.

For example, while a roadside communication device is receiving a radio signal (first packet) from one in-vehicle communication device, it overlaps with another radio signal (later Packet) may reach the roadside communication device.
When viewed from the radio signal of the previous packet being received, the radio signal of the subsequent packet is noise, and if the radio signal of the subsequent packet that causes noise is stronger, the demodulation of the previous packet is almost impossible. Is possible. As a result, reception of both the previous packet and the subsequent packet fails. That is, when the subsequent packet arrives, the previous packet is already being demodulated, so that the subsequent packet is also considered to be part of the previous packet, and the demodulation processing as the previous packet is continued. However, the demodulation of the previous packet is likely to fail due to the presence of the later packet as a large noise. Further, since the subsequent packet is treated as noise and is not recognized as a regular packet, it cannot be demodulated.

  However, from the viewpoint of acquiring as many packets as possible, it is desirable to demodulate and acquire the subsequent packets even if the demodulation of the earlier packets that cannot be demodulated is abandoned. This is because if the wireless signal of the subsequent packet is a signal stronger than the wireless signal of the previous packet, the subsequent packet can be demodulated even if the wireless signal of the previous packet becomes noise.

  Accordingly, an object of the present invention is to detect the arrival of another wireless signal when the wireless signal (regular wireless signal) of the previous packet is received.

(1) The present invention is a receiver that receives a radio signal, and includes a detection unit that detects arrival of another radio signal having a different transmission source based on an increase in reception level during packet reception. It is the receiver characterized by this.
When another radio signal with a different source arrives while receiving the radio signal of the previous packet, if the reception level of the other radio signal with a different source is higher than the reception level of the previous packet, it is being received. The arrival of another radio signal with a different source can be detected based on the increase in the reception level at.

(2) The present invention from another viewpoint is a receiver that receives a radio signal of a packet having a preamble portion added to the head, and stores a reception level of the preamble portion as a reference level; A detection unit that detects arrival of another radio signal having a different transmission source when the reception level rises above a predetermined threshold value above a reference level during reception of the radio signal following the preamble unit; It is the receiver characterized by the above.

  Here, in order to detect that another stronger radio signal (the radio signal of the subsequent packet) has arrived during reception of the radio signal of the previous packet, the current reception level is higher than the previous reception level. A method for detecting an increase beyond a predetermined threshold is conceivable. While receiving a wireless signal of a previous packet from a certain source, if a stronger other wireless signal from another source is received, naturally, the reception level will increase more than before, so that Such an increase may be detected.

However, the fluctuation of the amplitude of the radio signal may become very large, and even if the radio signal is from the same transmission source, the reception level may be reduced or increased.
For this reason, in order to accurately detect the arrival of other radio signals from different sources, reception levels that increase due to the arrival of other radio signals from different sources may occur in radio signals from the same source. It must be detected separately from level fluctuations.

  However, in order not to erroneously detect an increase in reception level that may occur in radio signals from the same transmission source as arrival of another radio signal, the threshold value related to the increase in reception level is set sufficiently large. It is necessary to keep it.

However, if the threshold is set too high, arrival can only be detected when the reception level of other radio signals from different sources is very high. That is, the arrival of another radio signal whose reception level is not so high cannot be detected, and the probability of detecting the arrival of another radio signal decreases.
On the other hand, when the threshold value is reduced, as described above, the probability that an increase in reception level that may occur in radio signals from the same transmission source is erroneously detected as arrival of another radio signal from a different transmission source increases. .

On the other hand, the reception level of the preamble part is stored as a reference level. When the arrival of another radio signal with a different source is detected, the arrival of another radio signal with a different source can be detected more accurately.
That is, large fluctuations in the reception level of radio signals from the same transmission source mainly occur in a portion (data portion) following the preamble portion. For example, in the case of a signal conforming to IEEE 802.11, the preamble portion has a smaller variation in reception level than the data portion. For this reason, by comparing the current reception level with a reference level based on the reception level of the preamble portion, compared with the previous reception level (reception level of the data portion), the radio from the same transmission source It is possible to reduce the probability of erroneously detecting reception level fluctuations that may occur in the signal as arrival of other radio signals of different sources.

(3) The radio signal is preferably a radio signal based on a communication scheme in which a modulation scheme of the preamble portion and a data portion provided after the preamble is different or different.

(4) More specifically, the modulation method of the preamble part is a phase modulation method, and the modulation method of the data part is an amplitude modulation method or selected from a plurality of modulation methods including an amplitude modulation method at the time of transmission. It is possible to use one modulation method. The phase modulation method is suitable as a preamble modulation method used for generating a reference level because level fluctuation is smaller than that of the amplitude modulation method.

(5) It is preferable that the amplitude modulation is a multi-level modulation scheme rather than the preamble modulation scheme. Since the level variation increases as the multi-level modulation method is used, there is an advantage of using the preamble for generating the reference level.

(6) In the above (1), when the detection unit detects arrival of another radio signal having a different transmission source, it abandons the demodulation of the packet received so far, It is preferably configured to start demodulation. In this case, it is possible to abandon the demodulation of the radio signal of the packet that has been received so far and to demodulate another radio signal having a different transmission source.

(7) In the above (2) to (5), when the detection unit detects arrival of another radio signal having a different transmission source, the demodulation of the radio signal received so far is abandoned and the transmission source is different. It can be configured to initiate demodulation of other radio signals. In this case, it is possible to abandon the demodulation of the radio signal received so far and to demodulate another radio signal having a different transmission source.

(8) The present invention viewed from another viewpoint is a receiver that receives a radio signal, and includes a gain control unit that performs gain adjustment of an amplifier circuit that amplifies the radio signal according to the reception level of the radio signal, When it is detected that the normal radio signal has arrived, the gain control unit enters a first state in which the gain follows the change in the reception level of the radio signal, and thereafter, the gain is fixed or the gain fluctuation is changed. The second state is set to be gentler than the first state, and is configured to maintain the second state during reception of the regular radio signal. Further, the gain control unit receives the radio signal during reception of the regular radio signal. When a rise in level is detected, the receiver releases the second state and returns to the first state.

According to the present invention, during reception of a regular radio signal, a gain state suitable for demodulation can be obtained by maintaining the second state in which the gain is fixed or the fluctuation of the gain is more gradual than in the first state. Can be secured.
However, in the present invention, when an increase in reception level is detected during reception of a regular radio signal, the second state is exceptionally canceled even during reception of a regular radio signal, The process returns to the first state in which the gain follows the change in the reception level of the radio signal.

This is because if the increase in reception level is caused by the arrival of another legitimate radio signal with a higher signal level, the gain for the legitimate radio signal received so far is This is because it is often a gain that is too large for the wireless signal.
In other words, if the gain is too large, demodulation of other radio signals having a higher signal level may fail, but in the present invention, an increase in the reception level is detected even during reception of a regular radio signal. Exceptionally, since the gain follows the change in the reception level of the radio signal, a gain appropriate for another radio signal having a higher signal level can be obtained.

(9) When a possibility that a regular radio signal has arrived is detected, the system further includes a determination unit that determines whether the radio signal is a regular radio signal, and the gain control unit includes: When an increase in reception level is detected during reception, the second state is canceled, the state returns to the first state, and then the second state is entered again. In the second state, it is preferable to determine whether or not the radio signal whose reception level has increased is a regular radio signal. In this case, the gain is adjusted according to the reception level increase amount, and the determination is performed in the second state in which the gain is stable, so that the determination accuracy can be improved.

(10) When an increase in the reception level is detected during reception of a regular radio signal and it is determined that the radio signal whose reception level has increased is a regular radio signal, the regular radio signal that has been received until then It is preferable that the demodulator is abandoned and the demodulation of the normal radio signal after the reception level rises is started. In this case, it is possible to abandon the demodulation of the regular radio signal that has been received so far and perform demodulation of another regular radio signal after arrival.
(11) When an increase in the reception level is detected during reception of a regular radio signal, the demodulation of the regular radio signal received up to that point is abandoned and the demodulation of the radio signal after the reception level is increased is started. It is preferable that it is comprised. In this case, it is possible to abandon the demodulation of the regular radio signal received so far and attempt to demodulate other radio signals after arrival.

(12) If an increase in reception level is detected during reception of a regular radio signal, but it is determined that the radio signal whose reception level has increased is not a regular radio signal, the gain is set to the gain before the increase in reception level. Returning, it is also possible to continue the demodulation of the regular radio signal received before the reception level rises. In this case, since the increase in the reception level is caused by noise other than the regular radio signal, it is preferable to continue the demodulation of the regular radio signal received before the increase in the reception level. Note that correction by error correction can be expected for erroneous demodulation due to an increase in reception level.

(13) The present invention from another viewpoint is a receiving method for receiving a radio signal of a packet, and based on an increase in reception level during reception of the radio signal of the packet, arrival of a radio signal of another packet is achieved. And a detection step of detecting.

(14) The present invention from another viewpoint is a reception processor for processing a reception signal of a packet radio signal, and based on an increase in reception level during reception of the packet radio signal, the radio of another packet A receiving processor comprising a detection unit for detecting arrival of a signal.

(15) A detection step of detecting arrival of a radio signal of another packet based on an increase in a reception level during reception of the packet radio signal in a computer provided in a receiver that receives the radio signal of the packet; A computer program for execution.

(16) The present invention viewed from another point of view is a reception method for receiving a radio signal of a packet having a preamble portion added to the head, and storing the reception level of the preamble portion as a reference level; A detection step of detecting arrival of another radio signal having a different transmission source when the reception level has risen beyond a reference level beyond a predetermined threshold during reception of the radio signal following the preamble portion. This is a receiving method.

(17) From another point of view, the present invention is a reception processor for processing a reception signal of a radio signal of a packet having a preamble portion added to the head, and stores the reception level of the preamble portion as a reference level. And a detection unit for detecting arrival of another radio signal having a different transmission source when the reception level rises above a predetermined threshold value above a reference level during reception of the radio signal following the preamble unit And a receiving processor.

(18) A storage step of storing a reception level of the preamble part as a reference level in a computer provided in a receiver that receives a radio signal of a packet with a preamble part added to the head, and a radio following the preamble part A computer program for executing a detection step of detecting arrival of another radio signal having a different transmission source when a reception level rises above a reference threshold level above a reference level during signal reception. is there.

(19) According to another aspect of the present invention, there is provided a receiving method for receiving a radio signal by a receiver including a gain control unit that performs gain adjustment of an amplifier circuit that amplifies the radio signal according to the reception level of the radio signal. When the possibility that the regular radio signal has arrived is detected, the first state is obtained in which the gain follows the change in the reception level of the radio signal. Thereafter, the gain is fixed or the gain variation is changed from the following state. The second state is also moderated, and the second state is maintained during reception of the regular radio signal. However, if an increase in reception level is detected during reception of the regular radio signal, The receiving method is characterized in that, even during reception, the second state is canceled and the state returns to the first state.

(20) The present invention from another viewpoint is a reception processor for processing a reception signal of a radio signal, and a gain for performing gain adjustment of an amplification circuit that amplifies the radio signal according to the reception level of the radio signal A control unit, and when the possibility that a regular radio signal has arrived is detected, the gain control unit enters a first state in which the gain follows a change in the reception level of the radio signal, and then the gain is fixed or gain Is in a second state where the fluctuation is more moderate than that in the first state, and is configured to maintain the second state during reception of the regular radio signal, and the gain control unit further comprises the regular radio signal. When the reception level is detected during reception, the second state is released, and the processor returns to the first state.

(21) A computer program that causes a computer provided in a receiver that receives a radio signal to function as a gain control unit that performs gain adjustment of an amplifier circuit that amplifies the radio signal in accordance with the reception level of the radio signal. When the possibility that the regular radio signal has arrived is detected, the gain control unit enters the first state in which the gain follows the change in the reception level of the radio signal, and thereafter, the gain is fixed or the gain fluctuation is changed. The second state, which is more gradual than the first state, is configured to maintain the second state during reception of the regular radio signal, and the gain control unit is configured to receive the regular radio signal during reception. When the increase in reception level is detected, the second state is canceled and the computer program returns to the first state.

  According to the present invention, when another stronger radio signal arrives during reception of the radio signal (regular radio signal) of the previous packet, it can be detected.

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 1st Embodiment mounted in the roadside communication apparatus. (A) is a road plan view when two vehicles at different positions transmit radio signals, and (b) shows the temporal change in RSSI when receiving duplicate packets from two vehicles. Show. It is a state transition diagram which shows the specific example of the processing content by the processor for reception. It is a chart which shows the change of the level of the processor for a reception at the time of receiving a radio signal as shown in FIG.3 (b). (a) shows RSSI of the radio signal of a packet, (b) is the enlarged view of smoothing RSSI which smoothed RSSI of (a). 10 is a state transition diagram of a receiving processor according to Modification 1. FIG. FIG. 10 is a state transition diagram of a receiving processor according to Modification 2.

[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, CSMA / CA is used for the vehicle-vehicle communication between the vehicle-mounted communication apparatuses 3 in this embodiment.

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.
Further, BPSK, QPSK, 16QAM, 64QAM, or the like is used as a subcarrier modulation scheme.

Furthermore, the in-vehicle communication device 3 according to the present embodiment transmits, for example, 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 packets transmitted by the in-vehicle communication devices 3 are theoretically transmitted in a time-series manner without overlapping each other, and there is a time gap of about 40 μs, for example, between the packets. .

The packet transmitted by each in-vehicle communication device 3 has a preamble part (preamble signal) at the head, and then has a data part in which information to be transmitted is stored. The preamble portion is a signal having a known pattern, and is used for synchronization processing.
The preamble portion includes a short preamble and a long preamble. QPSK (4-phase phase modulation) is used as the short preamble modulation scheme, and BPSK (two-phase phase modulation) is used as the long preamble modulation scheme. Both BPSK and QPSK are phase modulation schemes, and information is put on the phase, but the amplitude is not used to put information.

In the data part in this embodiment, subcarriers are modulated by a multi-level (high-speed) modulation scheme than the preamble part, for example, 16QAM (16-value quadrature amplitude modulation) or 64QAM (64-value quadrature amplitude modulation). It consists of an OFDM signal. In both 16QAM and 64QAM, information is added to the phase and amplitude.
The OFDM signal in the data portion has a large signal level fluctuation and may cause a very large power peak value, but the power may be reduced. That is, the PAPR (Peak to Average Power Ratio) of the data part is generally higher than the PAPR of the preamble part.

When multi-rate control is performed, an area for storing information indicating the transmission rate of the data part is secured next to the preamble, and the subsequent data part is modulated by a modulation scheme corresponding to the transmission rate specified in the area. Is modulated. The modulation method selected in the multi-rate control is, for example, any one of BPSK, QPSK, 16QAM, and 64QAM. In multi-rate control, the transmission rate can be different for each packet, and is selected by the transmission side (in-vehicle communication device 3).
In the present embodiment, an area for storing information indicating a transmission rate or the like is also regarded as a part of the data portion.

[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.
The present invention proposes a new measure for the roadside communication device 1 to appropriately receive the stronger transmission signal of the other in-vehicle communication device 3 that arrives after the previous radio signal from one in-vehicle communication device. 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 device 1 is configured by connecting the components shown in FIG. 2 as illustrated.
That is, the receiver 1R includes, in order from the left side, an antenna 101, a bandpass filter 102, a low noise amplifier 103, an attenuator 104, a low noise amplifier 105, a variable amplifier 106 including an AGC circuit, an orthogonal demodulator 107, an A / D converter 108, A detection circuit 109 and a reception processor 110 are provided.

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.
Thus, the circuit preceding the A / D converter 108 is an analog signal processing unit (analog receiving circuit) for (analog) radio signals. In this analog signal processing unit, the level of the radio signal can be adjusted by the attenuator 104 and / or the variable amplifier 106.
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.

  The receiving processor 110 according to the present embodiment includes, for example, an FPGA (Field Programmable Gate Array) that stores a control program, and as a functional unit realized by executing the control program, a detection unit 110A, a gain control unit 110B, 110C, a demodulation unit 110D, and a storage unit 110E.

  Among these, the detection unit 110A detects the arrival of the radio signal based on the reception level. The detection of the arrival of the radio signal includes the first detection for detecting the arrival of the radio signal in a no-signal state (only noise) and the second transmitter 3S during reception of the radio signal from the first transmitter 3S. There is a second detection for detecting the arrival of a stronger wireless signal from. Both the first and second detections are performed based on an increase in reception level.

On the other hand, the gain controller 110B can variably set the attenuation factor of the attenuator 104 and the amplification factor (gain) of the variable amplifier (amplifier circuit) 106 in accordance with the RSSI value.
In addition, when the detection unit 110A detects arrival of a radio signal due to an increase in RSSI, the determination unit 110C determines whether or not the packet is a regular packet (regular radio signal) with respect to the digitized I signal and Q signal. When the determination unit 110C determines that the determination unit 110C is normal, the demodulation unit 110D performs data demodulation on the I signal and the Q signal, and extracts information included in the normal packet.

  Note that since the IEEE802.11a / g / p short preamble is composed of 10 repetition signals, the determination processing by the determination unit 110C as to whether or not the packet is a regular packet is specifically performed at the beginning of the received packet. This is performed depending on whether or not the autocorrelation value for the preamble part exceeds a predetermined threshold value.

  The memory | storage part 110E memorize | stores the reference | standard level used for the detection (2nd detection) of a raise of RSSI. The storage unit 110E stores a value indicating an average reception level of the preamble part (an average value of RSSI in the whole preamble part or a partial range of the preamble part). The reference level of the storage unit 110 is updated every time the receiver receives the preamble part added to the head of the packet.

Further, the gain control unit 110B of the present embodiment changes the amplification factor of the variable amplifier 106 at a high speed when arrival of a radio signal is detected, but the amplification factor of the variable amplifier 106 is substantially changed during other periods. It is designed to keep it constant. Note that, in a period other than the period in which the gain of the variable amplifier 106 is changed at high speed, the gain of the variable amplifier 106 may be fixed, or the gain may be changed gradually.
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.

  FIG. 3A is a plan view of a road when two vehicles A and B at different positions transmit radio signals. An obstacle H such as a building is located between the vehicles A and B, and radio waves do not reach between the vehicles A and B. That is, the vehicles A and B (the in-vehicle communication device 3 mounted on them) are hidden terminals.

On the other hand, in Fig.3 (a), the roadside communication apparatus 1 installed in the intersection vicinity can receive the radio signal which vehicles A and B each transmit.
FIG. 3B shows a reception waveform (RSSI) when the roadside communication device 1 receives radio signals transmitted by the vehicles A and B. The roadside communication device 1 only receives noise until time t1, but receives a packet radio signal from the vehicle B at time t1. In FIG. 3 (b), the roadside communication device 1 receives the radio signal of the packet from the vehicle A redundantly at the time t <b> 2 in the middle of receiving the packet from the vehicle B. Since the vehicle A cannot detect the radio signal transmitted from the vehicle B, such a signal collision occurs even in the CSMA / CA system.
In FIG. 3, the vehicle A is closer to the roadside communication device 1 than the vehicle B, so that the radio signal of the vehicle A that has transmitted a packet later is the reception level (RSSI) than the radio signal of the vehicle B. Is getting bigger.

  The detection unit 110A performs detection (first detection) of arrival of the packet of the vehicle B at time t1, and also receives a packet of the vehicle A that is a stronger radio signal at time t2 during reception of the packet of the vehicle B. Detection of arrival (second detection) is also performed.

  FIG. 4 is a state transition diagram of the receiving processor 110 that performs the first detection and the second detection. As shown in FIG. 4, the receiving processor 110 has four operation states from level 0 to level 3. Among these, level 0 (initial state) is a default state where no increase in RSSI is detected (no signal state; noise is being received). In this case, the gain control unit 110B of the reception processor 110 has a level of The gain of the variable amplifier 106 is set to a higher default value (initial setting value) so that even a small wireless signal can be captured.

Level 1 is a high-speed tracking state (first state) in which the gain controller 110B of the receiving processor 110 rapidly follows the gain of the variable amplifier 106 in accordance with the RSSI value. Level 2 is the gain controller. 110B sets the variable amplifier 106 so that the gain of the variable amplifier 106 is fixed or the gain change is gradual (second state), and the determination unit 110C of the processor 110 determines whether or not the reached radio signal is a regular packet. This is a determination processing state for determination.
Level 3 is a state in which the gain of the variable amplifier 106 is fixed (second state), and the demodulation unit 110D of the reception processor 110 of the variable amplifier 106 performs demodulation of data with respect to the regular packet. is there.

As shown in FIG. 6, the reception processor 110, when the reception level (RSSI) exceeds the first threshold Th1 (S1; detection of possibility that a normal packet (normal radio signal) has arrived), When the operation state is changed from level 0 to level 1 and a predetermined follow-up time T1 unique to the variable amplifier 106 has elapsed (S2), the operation state is changed from level 1 to level 2.
Further, when the receiving processor 110 observes the normal packet within the predetermined determination time T2 as to whether or not it is a normal packet (S3), the receiving processor 110 performs a storage process (S4) described later and the like to set the operation state to level 3. Transition. When the data demodulation for the regular packet is completed (S5), the operation state is returned from level 3 to level 0. When level 3 is reached, in principle, the gain of the variable amplifier 106 is held in a fixed state (second state) until data demodulation for the regular packet is completed. When the demodulation is completed and the level returns to 0, the state where the gain of the variable amplifier 106 is fixed (second state) is released.

  Further, if the receiving processor 110 does not observe the regular packet within the predetermined determination time T2 as to whether or not it is a regular packet (S6), the received radio signal can be regarded as noise, so that the operation state is from level 2. Return to level 0. Also in this case, the state where the gain of the variable amplifier 106 is fixed or the gain change is gradual (second state) is canceled, and the gain returns to the default value (relatively large value).

  In addition, even in the case of level 3 (demodulation processing state), the reception processor 110 has a current RSSI (smoothed RSSI) that exceeds the second threshold Th2 than the reference level stored in the storage unit 110E. In other words, when {RSSI (smoothed RSSI) −reference level> Th2} (S7), the operating state is returned to level 1. That is, even when a regular packet is being received (during demodulation), the state where the gain of the variable amplifier 106 is fixed (second state) is released exceptionally. As a result, a high-speed tracking state (first state) in which the gain of the variable amplifier 106 rapidly follows in accordance with the RSSI value is set.

Thus, in this embodiment, even in the case of level 3, it is possible to return to level 1 due to the increase in RSSI.
Therefore, even if the demodulation process for the previous radio signal from the vehicle B is performed, the radio signal from the vehicle A (another source having a different transmission source) is generated by the further increase in the level (RSSI) of the input signal to the variable amplifier 106 When the possibility of arrival of the regular radio signal is detected, the demodulation process for the previous radio signal is canceled and abandoned. Then, the operation state shifts to the determination process and the demodulation process related to the subsequent radio signal from the vehicle A, and the determination target and the demodulation target are switched to the subsequent radio signal.
In addition, when the possibility of arrival of another regular radio signal with a different transmission source is detected and the demodulation process of the previous radio signal is abandoned, the demodulation process may be started immediately without performing the determination process. it can. In other words, if there is a large increase in the signal level exceeding the threshold Th2 during the demodulation process of the previous radio signal, the radio signal after the level increase is assumed to be a regular radio signal, and the received packet is immediately demodulated. It is preferable to transfer, adjust the gain, and demodulate the late arrival packet. Since the previous radio signal demodulation is abandoned, the radio signal after the reception level rise is estimated to be a normal radio signal, and the gain adjustment and the demodulation process are immediately performed, whereby the processing can be performed efficiently.
In the present embodiment, the event detected by the increase in the level of the input signal (RSSI) is “possibility of arrival of another normal radio signal with a different source”, but simply “different source”. It can also be understood as “arrival of another radio signal”.

  FIG. 5 shows a time chart when the signal having the waveform shown in FIG. 3B is received by the receiving processor 110 capable of processing shown in FIG. First, until time t1 when only noise is received, the receiving processor 110 is in the level 0 operation state, and the gain of the variable amplifier (AGC) 106 is relatively high.

  When the roadside communication device 1 receives a regular packet from the vehicle B at time t1, detection of arrival of the packet from the vehicle B (first detection) is performed when the RSSI exceeds the first threshold Th1. The operating state shifts to level 1. At level 1, the gain of the variable amplifier 106 decreases rapidly following the change in RSSI.

Next, when a predetermined follow-up time T1 elapses, the operation state shifts to level 2, and in the radio signal whose arrival is detected, a process for determining whether or not the packet is a regular packet is performed by confirming the presence of the preamble portion. Here, since the radio signal that has reached time t1 is a radio signal of a regular packet from vehicle B, the operating state shifts from level 2 to level 3.
At the time of transition to level 3, the receiving processor 110 uses the average RSSI level of the preamble portion of the packet from the vehicle B (the average RSSI value of the entire preamble portion or a part of the preamble portion) as a reference. As a level, a storage process (S4) stored in the storage unit 110E is performed.

  The reception processor 110 performs demodulation according to a predetermined internal parameter for demodulation during the level 3 demodulation processing. The internal parameters for demodulation are, for example, parameters for frequency and timing synchronization, and parameters for equalization processing according to transmission path characteristics. Since these parameters are generated using a preamble part prior to demodulation, different values are used for each packet.

  When the roadside communication device 1 receives a regular packet from the vehicle A at time t2 when the radio signal from the vehicle B is being demodulated (level 3), the current RSSI (RSSI temporal change is smoothed). Detection of the possibility of arrival of a packet from the vehicle A (second detection) by increasing the smoothed RSSI by exceeding the second threshold Th2 from the reference level stored in the storage unit 110E. ) Is performed. That is, at time t2, {RSSI (smoothed RSSI) −reference level> Th2} is satisfied, thereby detecting the possibility of arrival of a packet (regular radio signal) from the vehicle A (second detection). .

  When the possibility of arrival of a packet from the vehicle A is detected (second detection), the operation state returns to level 1. By returning to level 1, the gain of the variable amplifier 106 further decreases in accordance with the change in RSSI due to arrival of the packet from the vehicle A.

Then, the operating state shifts to level 2. In level 2, in the radio signal in which the possibility of arrival is newly detected, the presence / absence of the preamble part is confirmed, and the process for determining whether or not the packet is a regular packet is performed again. Here, since the radio signal that has reached time t2 is a radio signal of a regular packet from vehicle A, the operating state shifts from level 2 to level 3 (storage processing is also performed).
As described above, when the possibility of receiving another radio signal is detected, the operation state is quickly returned to level 1, the previous radio signal is discarded, and the gain of the variable amplifier 106 is adjusted in accordance with the subsequent radio signal. By making it follow at high speed, the subsequent radio signal determination process can be performed accurately.

When the reception processor 110 shifts to the level 3 demodulation process, the reception processor 110 generates an internal parameter for demodulation using the preamble portion of the packet from the vehicle A. At this time, the internal parameters for the packet from the vehicle B are discarded, and the demodulation of the packet from the vehicle B is abandoned.
Therefore, the radio signal from the vehicle A can be demodulated appropriately. When demodulation of the packet from the vehicle A is completed, the receiving processor 110 returns from level 3 to level 0.

  If the reception processor 110 determines that the radio signal that has reached time t2 is not a regular packet in the level 2 determination process, the reception processor 110 regards the radio signal that has reached time t2 as noise, not a regular packet, and the operating state From level 2 back to level 0. Also in this case, the state where the gain of the variable amplifier 106 is fixed or the gain change is gradual (second state) is canceled, and the gain returns to the default value (relatively large value).

In the present embodiment, the detection unit 110A compares the current reception level (smoothing RSSI) with the reference level stored in the storage unit 110E, so that the transmission source is different from the wireless signal that has been received so far. Detect the arrival of another radio signal. Here, the reference level stored in storage unit 110E is the reception level (average level) of the preamble of the packet (packet from vehicle B) that has been received so far.
In addition, since a preamble is added to the head of the packet, the reception level when another regular packet having a source different from that of the regular packet being received so far is reached is the level of the other regular packet. This is the preamble reception level.

  Therefore, when another packet arrives, the detection unit 110A determines the reception level (smoothed RSSI) of the other packet (subsequent packet) as the preamble of the packet (previous packet) that has been received so far. It is compared with the reception level of the part.

As shown in FIG. 6A, the radio signal (OFDM signal) in the data portion of the packet has a very large fluctuation, whereas the preamble portion has a predetermined symbol repetition pattern and has a small fluctuation. Therefore, as shown in FIG. 6B, in the smoothed RSSI obtained by smoothing the RSSI, the level of the preamble part is relatively stable compared to the data part.
Therefore, when the reception level of the preamble portion of the packet being received is used as a target to be compared with the current reception level (smoothed RSSI), arrival of another new radio signal can be accurately detected.

In other words, when receiving the arrival of a new other radio signal during reception of the data portion of the packet, the current reception level will be compared to the previous reception level if the detection is simply due to an increase in the reception level. Will detect that it has risen. However, in such detection, if the reception level greatly increases after the reception level greatly decreases due to the fluttering of the radio signal in the data part, it is easy to erroneously detect that a new other radio signal has arrived. Become.
In order to prevent such erroneous detection, a method using a moving average with a long reception level can be considered.However, as the time for performing the moving average is lengthened, detection of an increase in reception level is delayed, resulting in a new There is a concern that the synchronization determination of other radio signals cannot be performed. On the other hand, since the detection unit 110A of the present embodiment uses the reception level of the preamble portion of the packet being received as the reference level, the above-described erroneous detection can be prevented.
In the roadside communication device 1 of the present embodiment, when 11 dB is set as the threshold Th2 for detecting the arrival of other radio signals, 90% packet arrival can be detected in an environment where a hidden terminal can exist. Good results were obtained.

  Note that the reference level stored in the storage unit 110E does not need to be fixed to the reception level of the preamble part stored once, and may slightly vary during reception of the data part following the preamble part. For example, the reference level may be slightly changed from the stored reception level of the preamble part so as to slowly follow the fluctuation of the reception level of the data part.

[Variation 1 of the receiver of the roadside communication device]
FIG. 7 shows processing of Modification 1 of the receiver of the roadside communication device.
In the above embodiment, during reception of the data portion of the packet, the reference level used to detect the arrival of another new radio signal (late arrival packet) is used as the reference level of the previously received packet (previous packet). The reception level of the preamble part was used.

On the other hand, in the first modification, as shown in S7 of FIG. 7, the difference between the current reception level (RSSI) and the previous (previous) reception level (RSSI) exceeds the second threshold Th2. As the reception level increases, the operation state is returned from level 3 to level 1 when the reception level increases.
In other words, the reference level used to detect the arrival of another new radio signal (later arrival packet) is the data part (the part following the preamble part) of the packet (previous packet) received so far. A reception level may be used.
Note that the reception level of the data portion serving as the reference level may be a moving average of past reception levels in the same packet, or an instantaneous reception level at a specific time (typically just before an increase). Also good.

  The first modification is suitable for receiving a radio signal in which a signal such as a preamble defined in IEEE 802.11 is not added to the head. That is, the preamble defined in IEEE 802.11 is a signal with a stable level without amplitude modulation, but the first modification is suitable for receiving a radio signal that does not have a portion with a stable level.

Modification 1 can also be used in combination with the above embodiment. Here, “second threshold Th2” in the above embodiment is expressed as “threshold Th2-1”, and “second threshold Th2” in Modification 1 is expressed separately from “threshold Th2-2”.
When the modification 1 and the above-described embodiment are combined, the reception processor 110, during the packet demodulation processing at level 3, has a threshold Th2 that is higher than the reference level at which the current RSSI (smoothed RSSI) is stored in the storage unit 110E. In other words, when it exceeds 1, that is, {RSSI (smoothed RSSI) −reference level> Th2-1}, or “or”, the current reception level (RSSI) and the previous (past) reception level ( When the reception level increases as the difference from the RSSI increases beyond the threshold Th2-2, the possibility of arrival of another radio signal is detected. By doing so, it is assumed that the reception level of the preamble portion of the previous radio signal (packet) is the highest, and the reception level of the data portion following the preamble portion gradually decreases due to fading due to a change in the transmission path. Even if it is a case, it becomes possible to detect a later radio signal (packet).

Note that the return of the operating state to the level 1 due to the increase in the reception level (S7) may be performed not only from the level 3 but also from the level 2. That is, even when the reception level rises during the determination process, it can return to level 1.
In addition, about the point which abbreviate | omitted description in the modification 1, it is common in the said embodiment, and the same also about the modification 2 demonstrated next.

[Modification 2 of the receiver of the roadside communication device]
FIG. 8 shows processing of Modification 2 of the receiver of the roadside communication device.
This modification 2 is characterized in that processing returns to level 1 due to an increase in reception level during level 3 demodulation processing, and level 2 determination processing is subsequently performed. In the second modification, if it is determined that the radio signal whose reception level has increased as a result of the determination process is not a regular packet (regular radio signal), the gain is set to the gain before the reception level has increased (during the previous packet demodulation). And the previous packet parameters are used as internal parameters for demodulation.
Then, the demodulation of the previous packet received before the reception level rises is continued. If the cause of the increase in the reception level is not the arrival of the regular packet, the increase in the reception level is considered to be due to noise, so it does not shift to the demodulation process of noise that cannot be demodulated, but instead of demodulating the previous packet. By returning, demodulation of the previous packet can be continued.

In the previous packet, a portion that could not be demodulated due to noise can be expected to be corrected by error correction.
Further, when the level shifts from level 3 to levels 1 and 2 as the reception level increases during reception of the previous packet, the gain for the previous packet and the internal parameters for demodulation are stored in the storage unit 110E. In preparation for the return to demodulation (level 3) of the previous packet. Further, the radio signal received from the level 3 to the level 1 and 2 and demodulated again is stored in the buffer and prepared for the return to the demodulation (level 3) of the previous packet.
When the possibility of arrival of another normal radio signal with a different transmission source is detected due to an increase in reception level during the level 3 demodulation process, the level 1 gain high-speed tracking process is omitted and level 2 The determination process may be performed. In this case, the gain follow-up time T1 can be omitted. The level 1 gain high-speed tracking process is omitted, and the level 2 determination process is performed because the received signal level difference between the radio signal being demodulated (first arrival packet) and the second arrival radio signal (late arrival packet) Is preferable in a situation where it is assumed that is small. This is because if the level difference is small, determination processing can be performed without changing the gain.
If the gain follow-up time T1 can be omitted, when it is determined in the determination process that the radio signal after the reception level has risen is not a regular radio signal, demodulation of the previous packet received before the reception level has increased. It will be faster to return. Therefore, the reception probability of the previous packet is increased, which is advantageous.

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 this embodiment, the case where the road communication device receives the transmission signal of the vehicle-mounted communication device is described as an example. However, the vehicle-mounted communication device receives a radio signal from the road communication device, or other vehicle-mounted communication device. When receiving a radio signal from a communication apparatus, it is possible to receive more data by applying the same method.

DESCRIPTION OF SYMBOLS 1 Roadside communication apparatus 1R Receiver 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 Reception Processor 110A Detection Unit 110B Gain Control Unit 110C Determination Unit 110D Demodulation Unit 110E Storage Unit

Claims (21)

A receiver for receiving a radio signal,
A receiver comprising: a detection unit configured to detect arrival of another radio signal having a different transmission source based on an increase in reception level during packet reception. A receiver that receives a radio signal of a packet with a preamble added at the beginning,
A storage unit for storing the reception level of the preamble unit as a reference level;
During reception of a radio signal subsequent to the preamble part, when the reception level rises above a predetermined threshold with respect to a reference level, a detection unit that detects arrival of another radio signal having a different transmission source;
A receiver comprising: The receiver according to claim 2, wherein the radio signal is a radio signal based on a communication scheme in which a modulation scheme of the preamble portion and a data portion provided after the preamble is different or different. The modulation method of the preamble part is a phase modulation method,
The receiver according to claim 3, wherein the modulation method of the data part is an amplitude modulation method or one modulation method selected from a plurality of modulation methods including an amplitude modulation method at the time of transmission. The receiver according to claim 4, wherein the amplitude modulation is a multi-level modulation scheme than a modulation scheme of the preamble section. When the detection unit detects the arrival of another radio signal having a different transmission source, it abandons the demodulation of the packet received so far and starts demodulating another radio signal having a different transmission source. The receiver according to claim 1. When the detection unit detects the arrival of another radio signal with a different transmission source, it abandons the demodulation of the radio signal received so far and starts the demodulation of another radio signal with a different transmission source. The receiver according to any one of claims 2 to 5. A receiver for receiving a radio signal,
A gain control unit that adjusts the gain of an amplifier circuit that amplifies the radio signal according to the reception level of the radio signal,
When it is detected that the normal radio signal has arrived, the gain control unit enters a first state in which the gain follows the change in the reception level of the radio signal, and thereafter, the gain is fixed or the gain fluctuation is changed. The second state is made more gradual than the first state, and is configured to maintain the second state during reception of a regular radio signal,
Furthermore, the gain control unit cancels the second state and returns to the first state when an increase in reception level is detected during reception of a regular radio signal. When a possibility that a regular radio signal has arrived is detected, the apparatus further includes a determination unit that determines whether the radio signal is a regular radio signal,
When the gain control unit detects an increase in reception level during reception of a regular radio signal, the gain control unit cancels the second state, returns to the first state, and then enters the second state again.
The receiver according to claim 8, wherein the determination unit determines whether or not a radio signal whose reception level has increased is a regular radio signal when the gain control unit enters the second state again. When an increase in reception level is detected during reception of a regular radio signal, and it is determined that the radio signal whose reception level has increased is a regular radio signal, the received regular radio signal is demodulated. The receiver according to claim 9, wherein the receiver is configured to be abandoned and to start demodulating a normal radio signal after the reception level rises. When an increase in reception level is detected during reception of a normal radio signal, it is configured to abandon the demodulation of the normal radio signal that has been received and start demodulating the radio signal after the reception level has increased. The receiver according to claim 8. When an increase in reception level is detected during reception of a regular radio signal, but it is determined that the radio signal whose reception level has increased is not a regular radio signal, the gain is returned to the gain before the increase in reception level, The receiver according to claim 9, wherein the receiver is configured to continue demodulation of a normal radio signal received before the reception level increases. A reception method for receiving a radio signal of a packet,
A detection step of detecting arrival of a radio signal of another packet based on an increase in reception level during reception of the radio signal of the packet;
A receiving method comprising: A reception processor for processing a reception signal of a packet radio signal,
A receiving processor, comprising: a detection unit that detects arrival of a radio signal of another packet based on an increase in a reception level during reception of a packet radio signal. To the computer provided in the receiver that receives the wireless signal of the packet,
A detection step of detecting arrival of a radio signal of another packet based on an increase in reception level during reception of the radio signal of the packet;
A computer program for running. A reception method for receiving a radio signal of a packet with a preamble added at the beginning,
Storing a reception level of the preamble part as a reference level;
During the reception of the radio signal following the preamble part, when the reception level has risen beyond a predetermined threshold over a predetermined threshold, a detection step of detecting arrival of another radio signal with a different transmission source;
A receiving method comprising: A reception processor for processing a reception signal of a radio signal of a packet with a preamble portion added to the head,
A storage unit for storing the reception level of the preamble unit as a reference level;
During reception of a radio signal subsequent to the preamble part, when the reception level rises above a predetermined threshold with respect to a reference level, a detection unit that detects arrival of another radio signal having a different transmission source;
A receiving processor. In the computer provided in the receiver that receives the radio signal of the packet with the preamble portion added to the head,
Storing a reception level of the preamble part as a reference level;
During reception of a radio signal following the preamble part, a detection step of detecting arrival of another radio signal having a different transmission source when the reception level rises beyond a reference level beyond a predetermined threshold; and
A computer program for running. A reception method for receiving a radio signal by a receiver including a gain control unit that performs gain adjustment of an amplification circuit that amplifies the radio signal according to a reception level of the radio signal,
When the possibility that a regular radio signal has arrived is detected, the first state in which the gain follows the change in the reception level of the radio signal is entered. After that, the gain is fixed or the fluctuation of the gain is more gradual than in the first state. The second state is maintained during reception of the regular radio signal, but when the increase in the reception level is detected during reception of the regular radio signal, the regular radio signal is being received. Even if it exists, the said 2nd state is cancelled | released and it returns to the said 1st state. The receiving method characterized by the above-mentioned. A receiving processor for processing a received signal of a radio signal,
According to the reception level of the radio signal, a gain control unit that adjusts the gain of the amplifier circuit that amplifies the radio signal,
When it is detected that the normal radio signal has arrived, the gain control unit enters a first state in which the gain follows the change in the reception level of the radio signal, and thereafter, the gain is fixed or the gain fluctuation is changed. The second state is made more gradual than the first state, and is configured to maintain the second state during reception of a regular radio signal,
Furthermore, the gain control unit cancels the second state and returns to the first state when an increase in reception level is detected during reception of a regular radio signal. A computer program that causes a computer provided in a receiver that receives a radio signal to function as a gain control unit that performs gain adjustment of an amplifier circuit that amplifies the radio signal according to the reception level of the radio signal,
When it is detected that the normal radio signal has arrived, the gain control unit enters a first state in which the gain follows the change in the reception level of the radio signal, and thereafter, the gain is fixed or the gain fluctuation is changed. The second state is made more gradual than the first state, and is configured to maintain the second state during reception of a regular radio signal,
Furthermore, the gain control unit cancels the second state and returns to the first state when an increase in reception level is detected during reception of a regular radio signal.