JP2016082554A - Frequency sharing method of wireless lan and narrow band communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for sharing the same frequency band between wireless LAN(LAN:Local Area Network) and a narrow band communication system (DSRC:Dedicated Short-Range Communication System).SOLUTION: A communication control unit 16 controls so that DSRC existence notification means 20 emits radio waves always continuously or periodically, notifies the existence of DSRC to the surrounding wireless LAN, a wireless LAN10 receives the radio waves by receiving means 11, RSSI means 13 detects the RSSI value of the radio waves, and when a detection value exceeds a predetermined threshold, waits for radio wave transmission from transmission means 14 via a modulation unit 15, for a certain time.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for a wireless LAN (LAN: Local Area Network) and a narrow area communication system (hereinafter referred to as DSRC: Dedicated Short-Range Communication System) to share the same frequency band.

  As a wireless LAN interference prevention technique, CS / CCA (CS / CCA: Carrier Sense / Clear Channel Assessment), NAV (NAV: Network Allocation Vector), and DFS (DFS: Dynamic Frequency Selection) are known.

  CS / CCA detects the preamble in the signal from the other wireless LAN inputted, makes the wireless communication line busy at that time, decodes the signal following the preamble, and reads the data of the length indicated in the telegram. Keep line busy for the period of reception. If the signal cannot be received normally, the function of returning the line to the idle state allows the own station to wait for transmission during the line busy period.

  The NAV is a virtual CCA function, and includes the scheduled time for using the line of the own station in a communication message, and transmits it to the communication partner station. The communication message is carried in an RTS (RTS: Request To Send) frame or a CTS (CTS: Clear To Send) frame.

  CS / CCA and NAV are technologies for preventing interference between wireless LANs, and when frequency sharing is attempted between wireless LANs and DSRCs, there is a problem that they cannot be applied to DSRCs with different modulation schemes and communication protocols. It was.

  DFS is a technology that prevents the wireless LAN from interfering with Doppler weather radar installed at the airport. Before the wireless LAN transmits radio waves on a certain channel, the presence or absence of a radar signal is detected on the channel. When detected, it shifts to another channel. However, the detection threshold is as high as −62 dBm EIRP (EIRP: Equivalent Isotropy Radiation Power), and the detection probability is said to be about 60% or more, and it is not specified to be 100%. For this reason, there is a problem that a weak DSRC signal cannot always be detected when frequency sharing is attempted between the wireless LAN and the DSRC.

  JP 2009-033628 A   JP 2011-004002 A   JP 2011-004003 A   JP2013-176015A

  IEEE Std 802.11, IEEE (IEEE: The Institute of Electrical and Electronics Engineers, Inc.), 2012.   Narrow-area communication (DSRC) system standard ARIB STD-T75, Japan Radio Industry Association 2001   DSRC System Base Station Installation Guidelines ITS FORUM RC-003, ITS Information and Communication Systems Promotion Conference 2003

  The problem to be solved is that when the wireless LAN and the DSRC are used in the same frequency band, the radio waves interfere with each other, so that frequency sharing cannot be performed.

In solving the problem, the basic conditions of wireless LAN and DSRC are taken into consideration. In other words, DSRC is a social infrastructure that has been put into practical use for non-stop toll collection systems (hereinafter referred to as ETC: Electronic Toll Collection System) such as expressways and services called ETC 2.0. This is a system that requires QoS (QoS: Quality of Service). Specifically, it is specified in Non-Patent Document 2 that the bit error rate (hereinafter referred to as BER: Bit Error Rate) in the communication zone is 1 × 10E-5 or less, and BER is degraded due to radio wave interference with the wireless LAN. It is not allowed to do.
On the other hand, the wireless LAN has the best ephoto system for line quality and should not seek interference protection from other licensed radio stations in the frequency allocation plan footnotes J174, J179, J183, etc. of the Ministry of Internal Affairs and Communications. It is stipulated.

  The present invention spatially separates the operation of the wireless LAN and the DSRC based on these basic conditions, limits a certain area centered on the roadside radio device of the DSRC to the DSRC operation, and other areas. Then, the wireless LAN can use the same frequency band as DSRC.

  For this purpose, the DSRC is installed in or near the DSRC roadside wireless device, and includes DSRC presence notification means for continuously and periodically transmitting radio waves therefrom, and the wireless LAN includes the DSRC presence notification. Receiving means for receiving radio waves transmitted from the means, and RSSI means for detecting the signal strength of the received signal (hereinafter referred to as RSSI: Received Signal Strength Indicator), and the RSSI value detected by the RSSI means is predetermined. When the threshold is exceeded, the wireless LAN waits for radio transmission from the wireless LAN for a certain time thereafter, and when the RSSI value exceeds the threshold again during the waiting time, the most important thing is to update the waiting time. Features.

  Since the present invention spatially separates the operable area of the wireless LAN and DSRC, the wireless LAN and DSRC can be operated in the same frequency band. That is, frequency sharing is possible.

  Further, according to the present invention, even if the DSRC is added to a new location, the DSRC operation notification area is automatically increased by adding the DSRC presence notification means in the added DSRC roadside wireless device or in the vicinity thereof. It is set, and a state where frequency sharing between the wireless LAN and the DSRC is possible can be maintained.

  It is a block diagram of the frequency sharing method of this invention. Example 1   It is explanatory drawing which shows the transmission sequence of a modulated wave and CW. Example 1   It is explanatory drawing of the procedure which sets the transmission EIRP of a DSRC presence notification means. (Example 2)   It is a block diagram of a DSRC presence notification means. (Example 2)   It is a block diagram of a DSRC presence notification means. (Example 3)   It is explanatory drawing of antenna switch control. (Example 3)   It is explanatory drawing of the frequency relationship between wireless LAN and DSRC.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram of the present invention. 10 is a wireless LAN, 11 is a wireless LAN receiving means, 12 is a demodulation means, 13 is an RSSI means, 14 is a transmission means, 15 is a modulation section, 16 is a wireless LAN communication control section, and 20 is a DSRC presence notification means. , 21 is a transmission unit of the DSRC presence notification unit, 22 is a modulation unit, 23 is a reception unit, 24 is a demodulation unit, and 25 is a communication control unit of the DSRC presence notification unit.

  The DSRC presence notification unit 20 also serves as a DSRC roadside wireless device. The DSRC presence notification unit 20 generates a modulation signal by the modulation unit 22 and transmits radio waves from the transmission unit 21 during DSRC communication. The reception system includes a reception unit 23 and a demodulation unit 24, and transmission / reception communication control is performed by the communication control unit 25.

  In the present invention, the communication control unit 25 instructs the modulation unit 22 to generate a CW (continuous wave) as shown in FIG. 2 in a time window in which the modulation unit 22 of the DSRC presence notification unit does not generate a modulation signal. To do. As a result, a modulated wave or CW is constantly transmitted from the transmission means 21. Here, the CW frequency is the same as the center frequency of the modulation signal.

  On the other hand, the wireless LAN 10 receives the radio wave by the receiving unit 11, demodulates it by the demodulation unit 12, and transmits the received data to the communication control unit 16 of the wireless LAN. The transmission data is generated by the communication control unit 16, modulated by the modulation unit 15, and then transmitted by radio waves from the transmission unit 14. The RSSI unit 13 detects the RSSI value of the received signal from the DSRC presence notification unit 20 and outputs it to the communication control unit 16 at least in the frequency sharing band with the DSRC. These components are the same as those of a normal wireless LAN.

  The RSSI value is detected by a wireless LAN channel including a DSRC downlink channel (5.775-5.805 GHz), that is, a 157 channel and a 161 channel when the channel width is 20 MHz / ch in the name of Non-Patent Document 1. Both channels are performed in a time division manner (see FIG. 7).

  The timing for detecting the RSSI value is a timing before the wireless LAN transmits a scan frame such as a beacon frame or a probe request frame, and is 10 seconds as an example. Further, the RSSI value is detected even within the DIFS (Distributed Interframe Space) + back-off time before the wireless LAN transmits individual data.

  In the present invention, the RSSI threshold of the wireless LAN is set to -82 dBm EIRP with a channel width of 20 MHz / ch as an example.

  If the RSSI value of the RSSI means 13 does not exceed the RSSI threshold in any of the two channels, the wireless LAN may transmit in the DSRC band (5.77-5.85 GHz).

  When the RSSI value of the RSSI means 13 exceeds the RSSI threshold in one of the two channels, the wireless LAN communication control unit 16 determines that the line is busy, and the wireless LAN channel that overlaps the DSRC band (the non-channel) The transmission standby state is entered at 157, 161, 165, and 169 channels under the name of Patent Document 1 (see FIG. 7). The waiting time is 3 seconds as an example. The wireless LAN performs RSSI detection even during the standby time, and when the RSSI value exceeds the threshold again, the wireless LAN controls data transmission to the modulation unit 15 so as to wait for 3 seconds from that point again.

This function on the wireless LAN side is an improvement of the CCA / ED (Clear Channel Assessment / Energy Detection) function described in Section 18.3.10.6 of Non-Patent Document 1.
The CCA / ED function refers to the ability to detect ambient energy, interference signals, undecodeable wireless LAN energy, etc. present in the reception channel.

  The improvement point is that CCA / ED is an option that is essential for frequency sharing with DSRC. Second, the threshold is -72 dBm. And -82 dBm, and third, the provision of the transmission standby time when the RSSI detection value exceeds the threshold.

  DSRC performs two-way communication between the roadside wireless device and the vehicle-mounted device. However, the vehicle-mounted device does not transmit radio waves by itself, and the roadside wireless device does not transmit a radio wave by itself in the DSRC communication zone generated by the roadside wireless device. Non-Patent Document 2 stipulates that radio waves be transmitted only when a signal in a predetermined modulation format is received from a device using a predetermined communication protocol. Therefore, even if the in-vehicle device receives the CW from the DSRC presence notification means shown in FIG. 2, it does not malfunction, and the on-vehicle device mounted on the vehicle has the same frequency band as the DSRC outside the DSRC communication zone. Note that even if a wireless LAN radio wave is received, no malfunction occurs in the vehicle-mounted device.

  In addition, there are operation modes such as an infrastructure mode, an ad hoc mode, and Wi-Fi tethering as the operation mode of the wireless LAN, but the present invention is applied to wireless LAN devices of all these operation modes.

Next, the procedure for setting the transmission EIRP of the transmission means 21 will be described with reference to FIG.
FIG. 3 is a vertical sectional view including both the wireless LAN and the DSRC presence notification means. In this case, the wireless LAN is an interfering station and the DSRC is an interfered station.

  In the DSRC circuit design, the minimum received power of the desired wave at the DSRC communication zone edge (point C in FIG. 3) differs depending on whether the vehicle-mounted device is a roadside device or the class of the roadside wireless device. Non-patent document 2 and non-patent document 3 specify −65 dBm, −65 dBm for class 1 of roadside wireless devices, and −75 dBm for class 2. This electric power is indicated by P3 in FIG.

  Furthermore, in order to ensure the required BER (1 × 10E-5) in the DSRC communication zone even in the presence of an interference wave, the desired wave-to-interference wave ratio C / I (C / I) is 21 dB as a carrier-to-interference ratio. Is ensured by the same Non-Patent Document 3. Therefore, the interference wave power allowable at the DSRC communication zone edge is P3-21 (dB).

  At the DSRC communication zone edge (point C in FIG. 3), when the received EIRP in front of the reception antenna that gives P3-21 (dB) as the DSRC receiver input power is written as P4, this is given by the following equation (1). The unit is dBm EIRP.

  Here, G represents the horizontal directivity gain of the DSRC reception antenna, and its unit is dB. G is determined by the absolute gain and directivity characteristics of the receiving antenna and the orientation of the boresight direction when the receiving antenna is installed in space. Since the interference wave from the wireless LAN to the DSRC is incident on the DSRC from almost the horizontal direction, the horizontal directionality gain of the DSRC is involved. This received EIRP is indicated by P4 in FIG.

  On the other hand, the maximum transmission EIRP of the wireless LAN is determined to be 17 dBm / MHz EIRP in the 5 GHz band OFDM (Orthogonal Frequency Division Multiplexing) system by law (Ministry of Internal Affairs and Communications ordinance of radio equipment). When the wireless LAN is positioned as an interference source for DSRC, since the DSRC receiver bandwidth is 4 MHz, the maximum transmission EIRP of the interference source is equivalent to 23 dBm EIRP. This is indicated by P2 in FIG.

  When transmitting from the wireless LAN at P2 of the maximum transmission EIRP, the propagation loss L1 for the reception EIRP to become P4 at the DSRC communication zone edge is given by the following Equation 2. The unit is dB.

Next, a propagation distance (D1 in FIG. 3) corresponding to the propagation loss is obtained from this propagation loss L1.
Next, a propagation loss corresponding to the propagation distance D1 + D2 is obtained, and this is set as L2. Here, D2 in FIG. 3 represents a DSRC communication zone radius and is defined as 30 m in Non-Patent Document 3.

  When the wireless LAN receives the radio wave transmitted from the DSRC presence notification means under the condition that the propagation distance is D1 + D2, the received EIRP at the front surface of the reception antenna of the wireless LAN is represented by the RSSI threshold power (this is indicated by P5 in FIG. 3). When the transmission EIRP of the DSRC presence notification means necessary for making P5 is −82 dBm EIRP is written as P1, this is given by the following Equation 3. The unit is dBm EIRP.

This transmission EIRP is indicated by P1 in FIG.
The above is the procedure for setting the transmission EIRP of the transmission means 21 in the DSRC presence notification means 20.

  FIG. 4 is a configuration diagram of another embodiment of the DSRC presence notification means 20. 31 is an antenna, 32 is a CW transmitter, and 33 is a CW generator.

  In the present embodiment, a DSRC presence notification means 20 is installed in the vicinity of the roadside wireless device separately from the roadside wireless device of DSRC, and a CW signal is constantly transmitted from there. The CW generator 33 generates a CW signal, and the generated CW signal is amplified by the transmitter 32 and transmitted from the antenna 31. The directivity of the antenna is omnidirectional in the horizontal plane.

The CW frequency generated by the CW generator 33 is set outside the DSRC band (5.77 to 5.85 GHz), and is 5.745 GHz as an example. This is the name of Non-Patent Document 1 and corresponds to the center frequency of 149 channels when the channel width is 20 MHz / ch (see FIG. 7). Correspondingly, the wireless LAN side performs RSSI detection on the channel of the CW frequency.
When a CW zone generated by one DSRC presence notification unit overlaps with a CW zone generated by another DSRC presence notification unit, the CW frequencies are set to be shifted from each other.
The rest is the same as in the first embodiment.

  The present embodiment is characterized in that the transmission EIRP from the DSRC presence notification means 20 in the first embodiment can be freely set as compared with the case where the transmission EIRP is restricted by the transmission power of the DSRC modulated wave. The first embodiment is effective when the minimum desired wave reception power of the roadside apparatus is −65 dBm (class 1) and the antenna directivity is narrow, that is, when the reception EIRP (P4) of Equation 1 is large, the desired wave minimum When the reception power is -75 dBm (class 2) and the antenna directivity is wide, that is, when the reception EIRP (P4) of Equation 1 is small, the transmission EIRP of the DSRC presence notification means 20 may be insufficient. In such a case, this embodiment is effective.

  In addition, a roadside radio apparatus is installed for each lane at the ETC toll booth. However, when this embodiment is applied, it is sufficient to provide one DSRC presence notification means 20 near the ETC toll booth.

  FIG. 5 is a configuration diagram of another embodiment of the DSRC presence notification means 20. 45a is a CW1 generator, 44a is a CW1 transmitter, 42a is a switch 1, 45b is a CW2 generator, 44b is a CW2 transmitter, 42b is a switch 2, 43 is a switch control unit, and 41 is an antenna group.

  This embodiment includes two CW generators 45a and 45b, and the generated CWs are amplified by the transmitters 44a and 44b, respectively, and then sent to one antenna in the antenna group 41 by the switches 42a and 42b. Connected and transmitted from the antenna. Here, the switch 1 (42 a) and the switch 2 (42 b) are controlled by the switch control unit 43.

  FIG. 6 illustrates the control relationship between the antenna group 41 and the switch 1 (42a) and the switch 2 (42b). Each antenna in the antenna group is connected to the terminals of the switch 1 (42a) and the switch 2 (42b) in a one-to-one correspondence. FIG. 6 shows only a part of the antenna a.

  Each aerial line (such as a in FIG. 6) of the aerial line group is arranged at equal intervals on the circumference in the horizontal plane. The bore sight direction of each antenna line is a direction radially outward from the center of the circle, and is directed in the horizontal direction. Each aerial line is given directivity, but as a group of aerial lines, it has a directivity close to omnidirectionality in a horizontal plane.

The switch control unit 43 sequentially connects the output of the CW1 transmitter 44a to each antenna of the antenna group 41 with the switch 1 (42a). Here, the connection time to each antenna is the same, and the period is 0.3 seconds as an example.
Similarly, the output of the CW2 transmitter 44b is switched by the switch 2 (42b), but the switch control unit 43 controls to connect to the antenna located on the substantially opposite side of the antenna to which the CW1 transmitter is connected. Therefore, when the CW1 radio wave is transmitted in a certain direction, control is performed so that the CW2 radio wave is transmitted from the antenna on the opposite side.

The frequencies of CW1 and CW2 are set to be different from each other.
Radio waves are constantly transmitted from the antenna group, but the radio waves are periodically transmitted in a specific direction in the horizontal plane.

In radio wave propagation in the actual environment, when the distance between the wireless LAN and DSRC presence notification means becomes a distance due to road surface reflection or building reflection, the direct wave and the reflected wave have the same amplitude locally at that point. May be out of phase. At that time, the radio wave from the DSRC presence notification means does not reach the wireless LAN. This is an event known as a two-wave model in radio wave propagation. Compared with the second embodiment, the present embodiment is characterized in that even in such a situation, it acts as a spatial diversity and a frequency diversity, and the radio waves from the DSRC presence notification means can be reliably delivered to the wireless LAN.
Other than this, the second embodiment is the same as the second embodiment.

    In this way, the DSRC presence notification means is provided, and a signal is transmitted continuously or periodically from there. On the other hand, on the wireless LAN side, the RSSI means detects the level of the signal, and the RSSI value is predetermined. When the threshold is exceeded, transmission is waited for a certain period of time, and when the RSSI value exceeds the threshold again during the waiting time, the waiting time is updated, so that the required BER of DSRC can be maintained. There is an effect that DSRC can be shared in the same frequency band.

  For other wireless communication systems other than the wireless LAN, by providing a long and short difference in the transmission standby time between the wireless LAN and the wireless communication system, frequency sharing is possible not only for the wireless LAN but also for other wireless communication systems. Is also applicable.

10 Wireless LAN
DESCRIPTION OF SYMBOLS 11 Wireless LAN receiving means 12 Wireless LAN demodulation part 13 RSSI means 14 Wireless LAN transmission means 15 Wireless LAN modulation part 16 Wireless LAN communication control part 20 DSRC presence notification means 21 DSRC transmission means 22 DSRC modulation part 23 DSRC reception part 24 DSRC demodulation part 25 DSRC communication control unit 31 antenna 32 CW transmitter 33 CW generator 41 antenna group 42a switch 1
42b Switch 2
43 Switch control unit 44a CW1 transmitter 44b CW2 transmitter 45a CW1 generator 45b CW2 generator

Claims (1)

  The narrow-area communication system (hereinafter referred to as DSRC) side includes a DSRC presence notification unit that is installed in or near the roadside wireless device and transmits a radio wave continuously or periodically. On the wireless LAN side, the DSRC presence notification unit A receiving means for receiving the transmitted radio wave and an RSSI means for detecting the signal strength (hereinafter RSSI) of the received signal, and the RSSI value detected by the RSSI means exceeds a predetermined threshold; The wireless LAN waits for radio transmission from its own station for a certain period of time thereafter, and updates the standby time when the RSSI value exceeds the threshold again during the standby time. Frequency sharing method with communication system.

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