JP2013153249A - Receiver, receiving method, receiving processor, and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver of a multi-antenna capable of precisely establishing synchronization with arriving radio signals.SOLUTION: A multi-antenna receiver 1R with plural receiving systems receiving radio signals having repetition signals for synchronization at a leading end comprises: a detection section 110A for acquiring a current value of a receiving level generated to plural receiving systems 1X, 1Y and a past value immediately before the current value; and a determination section 110C for selecting a receiving system out of the plural receiving systems 1X, 1Y on the basis of a difference of the current value and the past value of the receiving level for each of the acquired receiving systems 1X, 1Y, so that the radio signals received by the selected receiving system are used as an extraction object of a synchronization timing using the repetition signals.

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.

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 radio signals 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

For radio signals compliant with standards such as IEEE 802.11, the use of preamble signals and pilot signals included in the packet makes it possible to accurately select antennas in the case of multiple antennas and to optimally combine received signals. Can do.
However, the information that can be used when selecting one of a plurality of antennas at the stage of receiving the first part of each packet transmitted one after another from a large number of in-vehicle communication devices includes the reception level of the radio signal at each antenna. (RSSI) only.

In addition, a wireless signal compliant with IEEE 802.11 includes a synchronization short preamble at the beginning of the packet. However, if accurate synchronization processing is not performed on this, subsequent signal processing becomes impossible. It is not possible to make use of a simple synthesis diversity algorithm.
Accordingly, it is very important to select which antenna is used to perform the synchronization processing using the head portion of the packet when receiving a radio signal, based on the radio signal received by the antenna.

In the case of a multi-antenna receiver, it is conceivable to extract a synchronization timing using a short preamble for a combined signal of radio signals received by each antenna.
However, when the C / N ratio of the radio signal received by any antenna is small, the C / N ratio of the combined signal is often still small, so even if the synchronization timing is extracted using the combined signal, The extraction is not always accurate.

  In view of the above-described conventional problems, an object of the present invention is to provide a multi-antenna receiver capable of accurately establishing synchronization with an incoming radio signal.

  (1) The wireless device of the present invention is a multi-antenna receiver having a plurality of receiving systems that receives a wireless signal having a repeated signal for synchronization at the head, and a reception level generated in the plurality of receiving systems. Based on the difference between the current value and the past value of the reception level for each of the obtained reception systems, and an acquisition unit that acquires the current value of the current value and the past value close to the current value. And a selection unit that selects which radio signal received by the reception system is to be extracted from the synchronization timing using the repetitive signal.

  (2) According to the receiver of the present invention, the selection unit receives a radio signal received by any of the plurality of reception systems based on the difference between the current value and the past value of the reception level for each reception system. Is selected as a synchronization timing extraction target using a repetitive signal, for example, among radio signals received by a plurality of receiving systems, the difference between the current value of the reception level and the past value is the largest. By selecting a radio signal as a synchronization timing extraction target, a radio signal having a larger C / N ratio can be selected as the extraction target, and synchronization with an incoming radio signal can be accurately established.

(3) In the receiver of the present invention, for example, as the current value of the reception level, a moving average value within a first period from the current time to the first time point is adopted, and the past value of the reception level is It is preferable to adopt a moving average value in the second period from the first time point to the second time point.
The reason for this is that if an instantaneous value is adopted as the current value or past value of the reception level, even if the radio signal has a lot of noise components, it is easy to be selected as an extraction target when the reception level fluctuates instantaneously. This is to minimize the possibility that the selection will occur.

(4) However, if the time lengths of the first and second periods are made too long, synchronization timing extraction processing (processing such as calculation of autocorrelation values) performed on the radio signal selected as the extraction target will not be in time. .
Therefore, the first and second periods are set such that the remaining time obtained by subtracting the period from the second time point to the current time point from the duration of the repetitive signal is longer than the processing time required for the synchronization timing extraction process. It is preferable to set the time length.

  (5) In the receiver of the present invention, a detection unit that detects arrival of the radio signal based on a difference between a current value and a past value of the reception level; and a demodulation unit that demodulates the selected radio signal; The demodulation unit further stops the demodulation until then when the detection unit detects the arrival of the other radio signal during demodulation of the radio signal whose arrival has been detected earlier. It is preferable to start demodulation of the radio signal.

  The reason is that if the previous radio signal and the subsequent radio signal arrive in duplicate, if demodulation of the previous radio signal is continued, there is a high possibility that both radio signals will fail to be demodulated (coincidence). When a subsequent radio signal that causes a further increase in reception level is detected, if it is immediately switched to demodulation of the subsequent radio signal, the subsequent radio signal can be demodulated, and that one will fall together Because it is more rational.

(6) In the receiver according to the present invention, the selection unit may be configured such that a difference between a current value and a past value of the reception level for each reception system even when the demodulation unit starts demodulating another radio signal. Based on the above, it is preferable that it is possible to select which of the plurality of reception systems the reception signal received by the reception system is the synchronization timing extraction target.
By adopting such a selection unit, even when a third wireless signal arrives after another wireless signal, a wireless signal having a larger C / N ratio is selected as an object for extraction of synchronization timing. And synchronization with respect to incoming radio signals can be established accurately.

(7) Since the receiver of the present invention is a multi-antenna receiver, an “antenna selection method” for demodulating any one of the radio signals received by each reception system and the reception by each reception system Any of “signal combining methods” for demodulating a combined signal of radio signals can be employed.
For example, when the antenna selection method is employed, a demodulator that demodulates only the selected radio signal using the synchronization timing extracted from the selected radio signal may be provided.

  (8) Further, in the case of the receiver of the above-described signal synthesis method, demodulation that synthesizes and demodulates a plurality of the radio signals of the reception systems using the synchronization timing extracted from the selected radio signal. What is necessary is just to provide a part.

(9) The reception method of the present invention is the reception method performed by the receiver of the present invention described in the above (1) to (8), and is substantially the same invention that is different in category from the receiver of the present invention. .
Therefore, the receiving method of the present invention has the same effects as the receiver of the present invention described in the above (1) to (8).

(10) The reception processor of the present invention is a reception processor mounted on the receiver of the present invention described in the above (1) to (8), and performs substantially the same processing as the receiver of the present invention. .
Therefore, the receiving processor of the present invention has the same effects as the receiver of the present invention described in the above (1) to (8).

(11) The computer program of the present invention is a computer program for causing the receiving processor to execute substantially the same processing as that of the receiver of the present invention described in (1) to (8) above.
Therefore, the computer program of the present invention has the same operational effects as the receiver of the present invention described in the above (1) to (8).

  As described above, according to the present invention, a multi-antenna receiver capable of accurately establishing synchronization with an incoming radio signal can be obtained.

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 mounted in the roadside communication apparatus. (A) is a road plan view when two vehicles located between obstacles transmit radio signals, and (b) is a reception level when a roadside communication device receives packets from the two vehicles. It is a time chart which shows a time change. It is explanatory drawing of the present value and past value of a reception level. It is a state transition diagram which shows the specific example of the processing content of a receiving processor. It is a time chart which shows the time change of the reception level of two receiving systems. It is a functional block diagram of a receiving processor. It is a functional block diagram of the receiving processor which concerns on a 1st modification. It is a functional block diagram of the receiving processor which concerns on a 2nd modification.

[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 includes a roadside communication device 1 provided near an intersection and a plurality of in-vehicle communication devices 3 that can communicate with the roadside communication device 1. . The roadside communication device 1 is installed on a pillar of a traffic signal 2 at an intersection, for example.

An in-vehicle communication device 3 capable of communicating with the roadside communication device 1 is mounted on all or a part of each vehicle traveling on the road. The roadside communication device 1 can communicate with a large number (for example, about 200 vehicles) in-vehicle communication devices 3 existing in the communicable area.
The roadside communication device 1 is communicably 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).

In the system shown in FIG. 1, road-to-road communication between road-side communication devices 1 located at each intersection, road-vehicle and road-to-vehicle communication between the road-side communication device 1 and the vehicle-mounted communication device 3, and the vehicle-mounted communication device 3. Wireless communication is used for inter-vehicle communication. Among these, 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, there is an advantage that data can be arranged as densely as possible on the frequency axis.
Further, BPSK, QPSK, 16QAM, 64QAM, or the like is used as a subcarrier modulation scheme.

The in-vehicle communication device 3 of the present embodiment transmits, for example, a radio signal in a format compliant with IEEE802.11a / g / p according to an access control method based on CSMA / CA. For this reason, the packets wirelessly transmitted by the plurality of in-vehicle communication devices 3 are theoretically transmitted side by side in time series without overlapping each other, and a time gap of, for example, about 40 μsec is provided between the packets. There is.
Further, the packet transmitted by the in-vehicle communication device 3 includes 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 on the receiving side. This preamble section includes a “short preamble” and a “long preamble”, QPSK (4-phase phase modulation) is used as the short preamble modulation method, and BPSK (two-phase phase modulation) is used as the long preamble modulation method. ) Is used.
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 part has a large signal level fluctuation and may generate a very large power peak value, while the power may be small. 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, a storage area for information indicating the transmission rate of the data part is provided next to the preamble part, and the subsequent modulation scheme corresponding to the transmission rate specified in this storage area is used. The data part is modulated.
The modulation method selected in the multirate control is, for example, any one of BPSK, QPSK, 16QAM, or 64QAM. In multi-rate control, the transmission speed may be different for each packet, but is selected by the transmission side (the in-vehicle communication device 3). In the present embodiment, the storage area for information indicating the transmission rate and the like is also part of the data portion.

[Internal configuration of receiver of roadside communication device]
FIG. 2 is a block diagram showing an internal configuration of the receiver 1R in the roadside communication apparatus 1.
In the present embodiment, an object is to propose a measure for the roadside communication device 1 to appropriately receive the radio signal transmitted from the in-vehicle communication device 3. Therefore, in the following description, the roadside communication device 1 is described as “receiver 1R”, and the in-vehicle communication device 3 is described as “transmitter 3S”.

The receiver 1R of the roadside communication device 1 is a multi-antenna receiver, and includes two systems of reception systems 1X and 1Y and a reception processor 110 that performs information processing of radio signals received by these systems. .
The two reception systems 1X and 1Y are, in order from the left, the antenna 101, the bandpass filter 102, the low noise amplifier 103, the attenuator 104, the low noise amplifier 105, the variable amplifier 106 including the AGC circuit, the quadrature demodulator 107, and the A / A A D converter 108 and a detection circuit 109 are provided.

The antennas 101 of the receiving systems 1X and 1Y are omnidirectional antennas installed at intervals of half a wavelength or more, or directional antennas directed in the same direction.
Radio signals transmitted from the transmitter 3S are respectively received by the antennas 101 of the receiving systems 1X and 1Y, and a radio signal in a predetermined band among the received radio signals is extracted by the bandpass filter 102.

The radio signal with the narrowed band is entirely amplified 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 (AGC function).
The output signal of the variable amplifier 106 is demodulated by the quadrature demodulator 107 into an I signal that is an in-phase component and a Q signal that is a quadrature component, and the received signal of each component is digitally converted by an A / D converter 108 at the next stage. And input to the receiving processor 110.

As described above, the circuit preceding the A / D converter 108 is a signal processing unit (analog reception circuit) for an analog reception signal. In this circuit, the reception signal is received by the attenuator 104 and / or the variable amplifier 106. The amplification degree can be adjusted.
The output signal of the low noise amplifier 105 (the input signal of the variable amplifier 106) is envelope-detected by the detection circuit 109. A reception signal strength (RSSI: Received Signal Strength Indication) (hereinafter also referred to as “reception level”) that is the signal level of the envelope is also input to the reception processor 110.

[Each functional part of the receiving processor]
The receiving processor 110 of this embodiment is an FPGA (Field Programmable Gate Array) that stores a predetermined control program for gain adjustment for the two receiving systems 1X and 1Y, synchronization processing and demodulation processing of received radio signals, and the like. ). The functional units of the receiving processor 110 realized by executing the control program are a detection unit 110A, a gain control unit 110B, a determination unit 110C, a demodulation unit 110D, and a storage unit 110E.

Among these, the detection unit 110A detects the arrival of the radio signal from the transmitter 3S based on the increase in the reception level obtained from the reception systems 1X and 1Y.
This detection includes “first detection” for detecting arrival of a radio signal in a no-signal state (only noise), and another second during reception processing of a radio signal from a specific first transmitter 3S. And “second detection” for detecting arrival of a stronger wireless signal from the transmitter 3S. A specific method for detecting these arrivals will be described later.

The gain control unit 110B can variably set the attenuation factor of the attenuator 104 of each reception system 1X, 1Y and the amplification factor (gain) of the variable amplifier 106 in accordance with the RSSI value in each reception system 1X, 1Y. It is.
When the detection unit 110A detects the arrival of some radio signal due to an increase in RSSI in one or both of the reception systems 1X and 1Y, the determination unit 110C A process of determining whether or not the signal is a regular radio signal (regular packet) is performed.

The communication standard assumed in this embodiment is IEEE802.11a / g / p. In this communication standard, a short preamble is composed of 10 repeated signals.
Therefore, the determination process of whether or not the packet is a regular packet by the determination unit 110C is specifically performed depending on whether or not the autocorrelation value for the short preamble in the leading portion of the received packet exceeds a predetermined threshold value.

In addition, prior to the above determination process, the determination unit 110C determines, based on the difference between the current value and the past value of the reception level, the radio signal received by any of the reception systems 1X and 1Y as a symbol timing using a short preamble. Select whether to select (synchronization timing).
When the determination unit 110C determines that the regular packet has arrived, the demodulation unit 110D performs a predetermined demodulation process on the I signal and the Q signal of the normal packet, and restores transmission side information included in the normal packet. To do.

The storage unit 110E uses the current value of the reception level (RSSIc (c: current): see FIG. 6) and the current value to be used for detection (first and second detection) of RSSI increase in the detection unit 110A. And a past value (RSSIp (p: previous): refer to FIG. 6) of the reception level that is traced back by a predetermined time from the memory, respectively.
The RSSIc and RSSIp are stored in the memory for each of the reception systems 1X and 1Y, and are updated every time a predetermined sampling period (for example, 1/16 μsec) elapses.

The gain control unit 110B changes the amplification factor of the variable amplifier 106 at high speed when arrival of a radio signal is detected, but maintains the amplification factor substantially constant during other periods. Note that the amplification factor of the variable amplifier 106 may be maintained at a fixed value or may allow a gradual change.
As described above, in this embodiment, since the amplification factor of the variable amplifier 106 is maintained almost constant except when the arrival of the radio signal is detected, the autocorrelation value with respect to the short preamble is stable, and the normal value using the autocorrelation value is used. There is an advantage that packet determination processing can be performed accurately.

[Changes in reception level for hidden terminals]
FIG. 3A is a plan view of a road when two vehicles A and B at a position sandwiching an obstacle transmit radio signals.
As shown in FIG. 3A, an obstacle H such as a building is located between the two vehicles A and B, and no radio wave reaches between the two vehicles A and B. That is, the in-vehicle communication devices 3 mounted on the vehicles A and B are in a hidden terminal relationship with each other. However, since the roadside communication device 1 in the vicinity of the intersection has a clear line of sight with respect to both the vehicles A and B, the radio signals of the vehicles A and B can be received.

FIG. 3B is a time chart showing an example of a temporal change in the reception level (RSSI) when the roadside communication device 1 receives packets from two vehicles A and B.
In FIG. 3B, the roadside communication device 1 receives noise from the surroundings before time t1, but receives a radio signal from the farther vehicle B at time t1 and receives the radio signal from the vehicle B. It is assumed that the radio signal from the nearer vehicle A is received redundantly at time t2 in the middle of receiving the signal.

Vehicles A and B that are in a positional relationship of hidden terminals as shown in FIG. 3A cannot receive radio signals from the other party. For this reason, even when the CSMA / CA method is adopted, a superimposed radio signal collision may occur in the roadside communication device 1 as shown in FIG.
In the case of FIG. 3, since the vehicle A is closer to the roadside communication device 1 than the vehicle B, the wireless signal of the vehicle A that has transmitted the packet later is received level (RSSI) than the wireless signal of the vehicle B. ) Becomes larger.

  Therefore, the detection unit 110A of the reception program 110 not only performs “first detection” to detect that the packet of the vehicle B has arrived at the time t1, but is stronger at the time t2 during reception of the packet of the vehicle B. “Second detection” is also performed to detect that the packet of the vehicle A that is a radio signal has arrived.

[Current value and past value of reception level]
FIG. 4 is an explanatory diagram of the current value and the past value of the reception level (RSSI).
In FIG. 4, “T0” is a unit time (1.0 μsec in the example) of the moving average period, and “tc” is the current time.
The detection unit 110A of the reception processor 110 samples the input signal from the detection circuits 109 of the reception systems 1X and 1Y at a sampling period (for example, 1/16 of the period T0) that is sufficiently shorter than the unit time T0.

Here, the detection unit 110A calculates the next RSSIc and RSSIp using the RSSI data value at each sampling time included in the first period Tc immediately before the current time tc and the second period Tp before that. To do.
RSSIc: Moving average value of RSSI in the first period Tc from the current time point tc to the first time point tp1 RSSIp: Moving average value of RSSI in the second time period Tp from the first time point tp1 to the second time point tp2

The time length of the first period Tc and the second period Tp is the processing required for the symbol timing extraction process, which is the remaining time obtained by subtracting the time length from the second time point tp2 to the current time tc from the short preamble duration time (16 μs). In this embodiment, Tc = 3 × T0 (3 μsec) and Tp = 5 × T0 (5 μsec) are set.
In the example of FIG. 4, the first period Tc and the second period Tp are continuous. However, there may be a slight gap (for example, about 1 μsec) between these periods Tc and Tp.

The detection unit 110A records the calculated RSSIc and RSSIp values in the memory of the storage unit 110E for each of the reception systems 1X and 1Y, and updates the calculated values of RSSIc and RSSIp each time one sampling point elapses.
In addition, the detection unit 110A obtains the calculated values of RSSIc and RSSIp for each of the input signals (measured values of RSSI) from the detection circuits 109 of the two reception systems 1X and 1Y, and records them in the memory of the storage unit 110E.

  Hereinafter, the current value RSSIc and the past value RSSIp in the reception system 1X are described as “RSSIcx” and “RSSIpx”, and the RSSIc and RSSIp in the reception system 1Y are described as “RSSIcy” and “RSSIpy”.

[Process transitions in the receiving processor]
FIG. 5 is a state transition diagram showing a specific example of processing contents of the receiving processor 110.
As shown in FIG. 5, the receiving processor 110 has four operation states from level 0 to level 3.
Among these, level 0 (initial state) is a default state in which no increase in RSSI is detected (no signal state; receiving noise). In this case, the gain control unit 110B of the reception processor 110 sets the gain of the variable amplifier 106 to a higher default value (initial setting value) so that a radio signal with a low reception level 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 set so that the gain control unit 110B of the receiving processor 110 is in a state where 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 is set. Is a determination processing state for determining whether or not the reached radio signal is a regular packet.

Level 3 is a demodulation processing state in which the demodulation unit 110D of the reception processor 110 performs data demodulation on a regular packet in a state where the gain of the variable amplifier 106 is fixed (second state).
As illustrated in FIG. 5, the determination unit 110C of the receiving processor 110 determines whether the regular packet has reached when the condition S1 is satisfied at level 0, that is, when RSSIc−RSSIp> Th1 (first threshold). Assuming that there is a possibility, the operation state is shifted to level 1.

Here, if the reception level of either one of the two reception systems 1X and 1Y satisfies the condition S1, the determination unit 110C of the reception processor 110 determines whether the satisfied radio signal is a regular packet. As a determination target (symbol timing extraction target).
In addition, the determination unit 110C of the reception processor 110, when both reception levels of the two reception systems 1X and 1Y satisfy the condition S1, outputs a radio signal having a larger difference between the current value of the reception level and the past value. , It is selected as a determination target (symbol timing extraction target) whether or not it is a regular packet.

In other words, when only the following inequality (x) is established, the determination unit 110C extracts the symbol timing using the short preamble of the radio signal from the reception system 1X at level 2, and the following inequality (y) If only the above holds, at level 2, the symbol timing is extracted using the short preamble of the radio signal from the reception system 1Y.
RSSIcx-RSSIpx> Th1 (x)
RSSIcy-RSSIpy> Th1 (y)

  In addition, when both the inequalities (x) and (y) are satisfied, the determination unit 110C determines which of (RSSIcx−RSSIpx) and (RSSIcy−RSSIpy) is greater, and the value is Symbol timing is extracted using a short preamble of a radio signal from the larger receiving system 1X (or 1Y).

The gain adjustment unit 110B of the reception processor 110 causes the operating state to transition to level 2 when a predetermined follow-up time T1 unique to the variable amplifier 106 has passed at level 1 (condition S2).
Further, the determination unit 110C of the receiving processor 110 transitions the operation state to the level 3 when the normal packet is observed within the predetermined determination time T2 as to whether or not the packet is a normal packet at the level 2 (condition S3). The demodulator 110D returns the operation state to level 0 when the data demodulation for the regular packet is completed at level 3 (condition S5).

In level 3, as a general rule, the gain of the variable amplifier 106 is held in a fixed state (second state) until the data demodulation for the regular packet is completed.
On the other hand, when the demodulation is completed and the operation state returns to level 0, the state where the gain of the variable amplifier 106 is fixed (second state) is cancelled.

When the determination unit 110C of the receiving processor 110 does not observe the normal packet within the predetermined determination time T2 as to whether it is a normal packet or not at level 2 (condition S6), the arrived radio signal is regarded as noise, Return the operating state to level 0.
Also in this case, the state where the gain of the variable amplifier 106 is fixed or the change in gain is gradual (second state) is canceled and returned to the default value (relatively large value).

The demodulator 110D of the receiving processor 110 can reach another subsequent normal packet when the condition S7 is satisfied at level 3, that is, when RSSIc-RSSIp> Th2 (second threshold). Priority is given to the operation, and the operating state is returned to level 1.
That is, in the present embodiment, even when the regular packet is being demodulated at level 3, the state in which the gain of the variable amplifier 106 is fixed (second state) is canceled, and the gain of the variable amplifier 106 is adjusted according to the RSSI value. Becomes a high-speed follow-up state (first state) in which abruptly follows.

As in the case of the condition S1, the determination unit 110C of the reception processor 110 determines which one of the two reception systems 1X and 1Y satisfies the condition S7. A radio signal is selected as a determination target of whether or not it is a regular packet.
Similarly, if the reception levels of both of the two reception systems 1X and 1Y satisfy the condition S7, the reception processor 110 transmits the radio signal having the larger difference between the current value of the reception level and the past value as a normal packet. Is selected as a determination target.

As described above, in this embodiment, even in an operation state of level 3, it is possible to return to level 1 as RSSI increases due to a radio signal that arrives later.
Therefore, even if the demodulation process for the previous radio signal from the vehicle B shown in FIG. 3A is performed, the radio signal from the vehicle A is further increased by the further increase in the level (RSSI) of the input signal to the variable amplifier 106. When the possibility of reaching (another regular radio signal with a different transmission source) 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.
Also, in this case, when the possibility of arrival of another regular radio signal with a different source is detected and the demodulation process of the previous radio signal is abandoned, the demodulation process is started immediately without performing the determination process. You can also

In other words, if there is a significant increase in the signal level during the previous radio signal demodulation process, the radio signal after the level increase is assumed to be a normal radio signal, and the gain adjustment is made by switching to the demodulation of the late arrival packet immediately. It is preferable to perform demodulation of late arrival packets.
The reason for this is that, since abandoning demodulation of the previous radio signal, it is assumed that the radio signal after the reception level rises is a regular radio signal, and gain adjustment and demodulation processing are performed immediately, so that at least later This is because a reception process for a radio signal can be performed.

Note that, as indicated by the dashed arrow in FIG. 5, the operating state of the receiving processor 110 may be returned to level 1 even when the condition S7 is satisfied at level 2.
That is, even when there is a change in the reception level that satisfies the condition S7 during the determination process for the wireless signal that has arrived first, the operation state of the reception processor 110 may be returned to level 1.

[Time transition of processing in the receiving processor]
FIG. 6 is a time chart showing temporal changes in the reception levels of the two reception systems 1X and 1Y. Note that “RSSIx” in FIG. 6 means the reception level of the reception system 1X, and “RSSIy” means the reception level of the reception system 1Y.
Further, Δx1 in FIG. 6 indicates a reception level difference that occurs in the reception system 1X due to the radio signal that arrives first, and Δx2 indicates a reception level difference that occurs in the reception system 1X due to the radio signal that arrives during processing of the radio signal. Indicates.

Further, Δy1 in FIG. 6 indicates a reception level difference that occurs in the reception system 1Y due to the radio signal that arrives first, and Δy2 indicates a reception level difference that occurs in the reception system 1Y due to the radio signal that is reached during processing of the radio signal. Indicates.
In FIG. 6, it is assumed that Δx1>Δy1> Th1 and Δy2>Δx2> Th2. In FIG. 6, only the gain of the reception system 1Y is illustrated, but the gain of the reception system 1X varies according to the value of RSSIx.

As shown in FIG. 6, during reception of noise before time t1, the operating state of the receiving processor 110 is level 0, and the gain of the variable amplifier 106 is relatively high.
At time t1, when the roadside communication device 1 receives a regular packet from the vehicle B, the reception level difference Δx1, Δy1 between the reception systems 1X, 1Y exceeds the first threshold Th1, so that the packet arrives from the vehicle B. When detected (first detection), the operating state of the reception preamble 110 shifts to level 1. At this level 1, the gain of the variable amplifier 106 decreases rapidly following a change in the reception level (RSSIy).

Next, when a predetermined follow-up time T1 of the variable amplifier 106 elapses, the operation state shifts to level 2, and a process of determining whether or not the packet is a regular packet using the autocorrelation value of the short preamble of the radio signal that has detected arrival. Is done.
In the example of FIG. 6, since Δx1> Δy1, the radio signal received by the reception system 1X is selected as a synchronization timing extraction target, and the determination process is performed on the short preamble of the selected radio signal.

Since the radio signal that has reached time t1 is a normal packet from vehicle B shown in FIG. 3, the operating state of reception processor 110 shifts from level 2 to level 3.
The reception processor 110 performs demodulation according to a predetermined internal parameter for demodulation during the level 3 demodulation processing. This internal parameter for demodulation is, for example, a parameter for frequency and timing synchronization and a parameter for equalization processing according to transmission path characteristics. Since these parameters are generated using a preamble part prior to data demodulation, different values are used for each packet.

When the roadside communication device 1 receives the normal packet from the vehicle A at time t2 during demodulation of the normal packet from the vehicle B (level 3), the reception level difference Δx2, Δy2 between the reception systems 1X, 1Y is the second value. When the threshold Th2 is exceeded, arrival of a packet from the vehicle A is detected (second detection), and the operating state of the reception preamble 110 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.

Next, when a predetermined follow-up time T1 of the variable amplifier elapses, the operation state shifts to level 2, and it is determined whether or not the packet is a regular packet by using the autocorrelation value of the short preamble of the radio signal newly detected for arrival. Processing is performed.
In the example of FIG. 6, since Δy2> Δx2, the radio signal received by the reception system 1Y is selected as a symbol timing extraction target, and the determination process is performed on the short preamble of the selected radio signal.

Since the radio signal that has reached time t2 is a normal packet from vehicle A shown in FIG. 3, the operating state of reception processor 110 shifts from level 2 to level 3.
As described above, in the present embodiment, even when the previous wireless signal is being demodulated, when the arrival of another wireless signal is detected, the operation state is quickly returned to level 1, the previous wireless signal is discarded, Since the gain of the variable amplifier 106 follows at a high speed in accordance with the radio signal, the subsequent radio signal determination process can be performed accurately.

When the reception processor 110 shifts to the demodulation process (level 3) of the radio signal of the vehicle A, 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 appropriately demodulated. When the demodulation of the packet from the vehicle A is completed, the receiving processor 110 returns the operation state from the level 3 to the level 0.

Although not shown in FIG. 6, if the receiving processor 110 determines that the wireless signal that has reached the time t2 is not a regular packet during the level 2 determination process, the reception processor 110 regards the wireless signal as noise. The operating state is returned from level 2 to level 0 (see condition S6 in FIG. 5). 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 released, and the gain returns to the default value (relatively large value).
In the above-described embodiment, when a new wireless signal is detected, a channel different from the previously selected extraction target may be used as the synchronization timing extraction target. In that case, it is preferable to select a larger difference between the moving average value of the first period Tc and the moving average value of the second period Tp for each channel.

[Effect of receiver]
According to the receiver 1R of the present embodiment, the determination unit 110C of the reception processor 110 is based on the difference between the current values RSSIcx and RSSIpx and the past values RSSIcy and RSSIpy of the reception levels for the two reception systems 1X and 1Y. The radio signal received by any of the plurality of reception systems 1X and 1Y is selected as a symbol timing extraction target using a short preamble.

Therefore, as described above, of the radio signals received by the two receiving systems 1X and 1Y, the radio signal having the largest difference between the current values RSSIcx and RSSIpx and the past values RSSIcy and RSSIpy of the reception level is represented by the symbol timing. Therefore, a radio signal having a larger C / N ratio can be selected as the extraction target.
For this reason, regular packet determination processing using the autocorrelation value becomes accurate, and synchronization with an incoming radio signal can be accurately established.

[Variation of demodulator configuration]
7 to 9 are block diagrams showing variations of the configuration of the demodulation unit 110D in the reception processor 110. FIG.
As shown in FIGS. 7 to 9, the demodulation unit 110 </ b> D includes a synchronization processing unit 11, an FFT unit 12, and a subcarrier demodulation unit 13 as functional elements. Reference numeral 14 in the figure denotes a decoding unit that performs predetermined error correction decoding on the demodulated received data.

St in the figure is the symbol timing St obtained from the peak of the autocorrelation value of the short preamble by the determination unit 110C. The symbol timing St is input to the synchronization processing unit 11 (both when there are a plurality of symbol timings).
Based on the input symbol timing St, the synchronization processing unit 11 performs predetermined synchronization processing such as removal of a guard interval with respect to a regular packet made of an OFDM signal, and inputs it to the subsequent FFT unit 12.

The FFT unit 12 performs fast Fourier transform processing on the OFDM signal from which the guard interval has been removed, converts the signal into a signal for each subcarrier, and inputs the signal to the subcarrier demodulation unit 13 at the subsequent stage.
The subcarrier demodulator 13 compares the long preamble of the input signal with a reference signal stored in advance, estimates the phase and amplitude transmission path distortion for each subcarrier, removes the estimated distortion from the subcarrier, and transmits Equivalent to the data.

In the receiving processor 110 of FIG. 7, only one synchronization processing unit 11 and one FFT unit 12 are provided, and the reception data of each reception system 1X, 1Y is input to one synchronization processing unit 11 at the subsequent stage, respectively. .
Therefore, in the case of FIG. 7, the synchronization processing unit 11 receives the received signal (IQ signal) input from each of the receiving systems 1X and 1Y and selected by the determination unit 110C as the symbol timing extraction target. Is selected as an input signal to the FFT unit 12.

As described above, in the receiver 1R of FIG. 7, any one of the radio signals received by the receiving systems 1X and 1Y is selected, and the demodulation processing after the FFT unit 12 is performed using only the selected signal. The antenna selection method is performed.
On the other hand, in the reception processor 110 of FIG. 8, the demodulation unit 110D has two synchronization processing units 11X and 11Y corresponding to the reception systems 1X and 1Y, and reception signals input from these synchronization processing units 11X and 11Y ( IQ unit) is synthesized by a predetermined synthesis method (for example, maximum ratio synthesis method, selective synthesis method, etc.), and the synthesized signal is input to the FFT unit 12.

As described above, in the receiver 1R of FIG. 8, the demodulation unit 110D employs a signal combining method in which the radio signals received by the receiving systems 1X and 1Y are combined to improve sensitivity.
In the present embodiment, even in the case of such a combining method, the symbol timing St obtained from the peak of the autocorrelation value of the short preamble of the packet selected by the determination unit 110C as the symbol timing extraction target is obtained from both synchronization processing units. Input to 11X and 11Y, respectively.

  On the other hand, in the reception processor 110 of FIG. 9, the demodulation unit 110D is provided in two synchronization processing units 11X and 11Y corresponding to the reception systems 1X and 1Y and in the subsequent stage of these synchronization processing units 11X and 11Y, respectively. An FFT unit 12X, 12Y and a synthesizing unit 15 that synthesizes reception signals (IQ signals) input from the FFT units 12X, 12Y by a predetermined synthesizing method, and the synthesized signal is input to the subcarrier demodulation unit 13 Is done.

As described above, the receiver 1R of FIG. 9 also belongs to the signal synthesis method, similarly to the receiver 1R of FIG. 8, but the two FFT units 12 are provided corresponding to the reception systems 1X and 1Y. 8 is different from the receiver 1R.
As is well known, the FFT unit 12 is a circuit having a relatively large circuit scale among the receiving processors 110. Therefore, when the synthesis method is adopted, only one FFT unit 12 is used as shown in FIG. It is preferable to adopt a circuit configuration for synthesizing signals in the previous stage of the unit 12.

[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, the multi-antenna receiver 1R having the two reception systems 1X and 1Y is illustrated, but the present invention can be applied to a receiver having three or more reception systems.

  In the above-described embodiment, the case where the roadside communication device 1 receives the radio signal transmitted by the in-vehicle communication device 3 is exemplified. However, the radio signal transmitted by the roadside communication device 1 or another in-vehicle communication device 3 is specified. The present invention can also be applied when the in-vehicle communication device 3 receives. That is, the receiver 1 </ b> R of the present invention may be mounted on the in-vehicle communication device 3.

DESCRIPTION OF SYMBOLS 1 Roadside communication apparatus 1R receiver 3 In-vehicle communication apparatus 3S Transmitter 11 Synchronization processing part 12 FTT part 13 Subcarrier demodulation part 14 Decoding part 15 Synthesis | combination part 101 Antenna 110 Reception processor 110A Detection part (acquisition part)
110B Gain control unit 110C Determination unit (selection unit)
110D demodulation unit 110E storage unit

Claims (11)

A multi-antenna receiver having a plurality of reception systems for receiving a radio signal having a repeated signal for synchronization at the head,
An acquisition unit for acquiring a current value of a reception level generated in a plurality of the reception systems and a past value close to the current value;
Based on the difference between the current value and the previous value of the reception level for each of the acquired reception systems, the radio signal received by the reception system of the plurality of reception systems is used for the repetition signal. A selection unit for selecting whether to extract synchronization timing;
A receiver comprising:   The said selection part selects the said radio signal from which the difference of the present value and the past value of the said reception level becomes the largest among the said radio signals each received by the said several reception system as the extraction object of the said synchronization timing. Item 14. The receiver according to Item 1.   The current value of the reception level is a moving average value within a first period from a current time to a first time point, and the past value of the reception level is a second value from the first time point to a second time point. The receiver according to claim 1, wherein the receiver is a moving average value within a period.   The time of the first and second periods is such that the remaining time obtained by subtracting the period from the second time point to the current time point from the duration of the repetitive signal is longer than the processing time required for the synchronization timing extraction process. The receiver according to claim 3, wherein a length is set. A detection unit for detecting arrival of the radio signal based on a difference between a current value and a past value of the reception level, and a demodulation unit for demodulating the selected radio signal;
When the detection unit detects the arrival of another wireless signal during demodulation of the wireless signal whose arrival has been detected earlier, the demodulation unit stops the previous demodulation and demodulates the other wireless signal. The receiver of any one of Claims 1-4 which starts.   The selection unit is configured to select a plurality of reception systems based on a difference between a current value and a past value of the reception level for each reception system even when the demodulation unit starts demodulating another radio signal. 6. The receiver according to claim 5, wherein one of the receiving systems can select which radio signal received by the receiving system is to be extracted from the synchronization timing.   The receiver according to claim 1, further comprising a demodulator that demodulates only the selected radio signal by using the synchronization timing extracted from the selected radio signal.   7. The demodulator according to claim 1, further comprising: a demodulator configured to synthesize and demodulate the radio signals of the plurality of reception systems using the synchronization timing extracted from the selected radio signal. The listed receiver. Using a multi-antenna receiver equipped with a plurality of reception systems, a method for receiving a radio signal having a repeated signal for synchronization at the head,
Obtaining a current value of a reception level generated in a plurality of the reception systems and a past value close to the current value;
Based on the difference between the acquired reception level for each reception system acquired and the past value, the radio signal received by any of the plurality of reception systems is used as the repetitive signal. Selecting whether or not to extract the synchronization timing that has been
A receiving method comprising: A receiving processor that performs information processing on a wireless signal that is input from a plurality of receiving systems and that has a repeated signal for synchronization at the head,
An acquisition unit for acquiring a current value of a reception level generated in a plurality of the reception systems and a past value close to the current value;
Based on the obtained difference between the current value and the past value of the reception level for each reception system, the radio signal received by any of the plurality of reception systems is used as the repetitive signal. A selection unit for selecting whether to extract the synchronization timing that has been
A receiving processor. A computer program for causing a reception processor to perform information processing on a wireless signal having a repeated signal for synchronization input from a plurality of reception systems at the head,
Obtaining a current value of a reception level generated in a plurality of the reception systems and a past value close to the current value;
Based on the obtained difference between the current value and the past value of the reception level for each reception system, the radio signal received by any of the plurality of reception systems is used as the repetitive signal. Selecting whether or not to extract the synchronization timing that has been
A computer program comprising:

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