JP5283356B2 - Beacon wireless communication device - Google Patents

Description

  The present invention relates to a beacon wireless communication apparatus that performs communication upon reception of a beacon.

  In recent years, wireless communication has been actively performed due to the spread of wireless LAN and the like. As a standardized wireless communication method, there is a wireless method for exchanging data when a beacon is received. One such wireless communication system is a beacon wireless communication system defined by IEEE 802.15.4. Refer to Non-Patent Document 1 for details of the IEEE 802.15.4 beacon wireless communication system.

FIG. 7 is a diagram for explaining the outline of the beacon wireless communication system.
Beacon wireless communication is performed between the coordinator 11 and a plurality of end devices 001 to 100 (ED). The coordinator 11 is a device such as a wireless LAN card and is used by being connected to the PC 10. Here, 100 end devices can communicate with one coordinator 11. As described above, the beacon wireless communication is characterized in that a large number of end devices can be connected to one coordinator 11. The end device is, for example, a device such as a temperature sensor installed in a factory site.

  Further, a 1-to-N star network is formed from one data distribution terminal (Coordinator, hereinafter referred to as CN) serving as a parent device and a receiving terminal (End Device, hereinafter referred to as ED) serving as a plurality of child devices. The CN broadcasts a synchronization signal (= beacon) at a fixed timing, and all EDs receive the beacon and analyze whether there is information addressed to themselves.

  Conventional beacon wireless communication systems are roughly classified into two systems. The method will be described below.

<Prior Art 1>
FIG. 8 is a diagram for explaining the first prior art.
All EDs receive a beacon, analyze whether there is information addressed to themselves, and start communication with the coordinator when information is addressed to themselves. For example, there are 100 EDs with identification numbers 1 to 100, and when sending data to EDs 10, 20, 30, 40, and 50 (5 units in total), the coordinator Inside, insert the identification numbers of these 5 EDs and send a beacon. When the ED receives a beacon and there is data addressed to itself, the ED performs data communication with other terminals in order from the earliest by avoiding a collision using the CSMA-CA method. Here, CSMA-CA (= Carrier Sense Multiple Access with Collision Avoidance) means that when ED detects external radio waves in reception mode and radio waves are transmitted from other terminals during transmission, This is a method of waiting for a minimum time + a random time and transmitting so as not to collide with other transmission radio waves.

  In the next beacon, different numbers such as 11, 21, 31, 41, 51 are clearly specified, and the corresponding ED performs data communication. However, there are cases where the collision cannot be avoided and fails. If the coordinator fails to acquire data from the ED, it will retry and communicate with the next beacon. FIG. 8 is an example in which transmission is made to Nos. 11, 21, 31, 41, 51 and No. 21 fails. In this case, for example, 21, 12, 22, 32, 42 is included in the next beacon signal. No. 21 and 21 that failed last time are sent again, and No. 52 is sent in the next beacon cycle instead.

<Conventional technology 2>
FIG. 9 is a diagram for explaining the second prior art.
There is also provided a communication method that does not cause collision between EDs using a timetable.
The first beacon describes that there is data for addresses 10, 20, 30, 40, and 50, and the CN sends a beacon. The ED receives the first beacon, and if there is its own number, the ED makes a reservation for a communication occupation time (request for securing slot) for inquiring a message to the CN with the next beacon. When 5 EDs make a reservation request, since the communication time is not guaranteed, the reservation is made by avoiding collision with other EDs by the CSMA-CA method.

In the second beacon, the CN transmits a beacon describing that the guaranteed slots for 10, 20, 30, 40, and 50 have been secured. The ED performs data communication using a designated security slot. In the third beacon, the CN sends the same beacon as in the second, and the ED makes a request to open a security slot. In the fourth beacon, the number requested to be released is deleted, and if there is any other ED to be distributed, a beacon describing that number (for example, 11, 21, 31, 41, 51) is transmitted. The ED receives the beacon, and the EDs of 10, 20, 30, 40, and 50 confirm that the security slot can be released because there is no number addressed to them. Also, since the EDs of 11, 21, 31, 41, 51 have their own numbers, processing for message reception is performed.
IEEE 802.15.4-2003, IEEE Standard for Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks (LR-WPANs)

In the prior art 1, radio wave collision occurs because the target EDs acquire data simultaneously at the same time in conjunction with the beacon. To avoid this, CSMA-CA avoids collisions.
If another ED is transmitting radio waves when the ED is transmitting radio waves, the ED waits for a certain period of time and checks the availability of the radio waves again. Here, the number of CSMA-CA standbys defined in IEEE802.15.4-2003 is defined by the macMaxCSMABackoff value. Since the maximum settable value of this value is 5, the maximum possible number of standby times is 6, and if the transmission fails after waiting 6 times, a retry is performed. The number of retries is specified by IEEE802.15.4-2003 as 3 times from the aMaxFrameRetries value. Even in the case of a total of four transmissions that are retried three times in addition to one transmission, the specific communication time is about 40 to 50 ms, which is 100 ms or less. Thus, for example, if the beacon period is about 500 ms, the ED tries to acquire data only during the first 0 to 100 ms, but does not perform any processing for the remaining 400 ms. If data cannot be acquired within the first 100ms, it will be treated as a failure.

  Here, rather than sending failed data in the next beacon cycle, it is more effective to send data using 400 ms (about 80% of the beacon cycle), which is the time to do nothing within one beacon cycle. Efficiency is by definition higher. Further, the occurrence of radio wave collision has a problem that wasteful data transmission is frequently performed and the utilization efficiency of radio resources is poor.

  In the prior art 2, ED requires at least 3 beacon periods to receive a message from CN (4 beacon periods are required when confirmation is made), so there is a problem that information transmission is delayed for 2 beacons. .

  The subject of this invention is providing the beacon radio | wireless communication apparatus which eliminates a collision factor and can perform information transmission efficiently by one beacon.

The beacon wireless communication apparatus of the present invention is a beacon wireless communication apparatus in a beacon wireless communication system in which a single base unit and a plurality of beacon wireless communication apparatuses communicate with each other wirelessly. An access time calculating means for calculating a time at which the own beacon wireless communication apparatus should access the parent device, and an access means for accessing the parent device at the calculated access time when the number is described It is characterized by that.

  According to the present invention, it is possible to provide a beacon wireless communication device with good information transmission efficiency while eliminating the cause of ED collision.

The embodiment of the present invention relates to a beacon communication method compliant with the IEEE 802.15.4 wireless communication standard.
Radio transmission collisions between EDs occur because a beacon signal is received, the ED interprets the signal, and the corresponding EDs attempt data acquisition (communication with the CN) all at once. In the beacon signal, a beacon period (T) (for example, 500 ms) and a transmission list (for example, 10, 20, 30, 40, 50) are specified. From the order listed in the transmission list, it is only necessary to acquire the third (N) data, and it can be seen that there are five (S) target EDs.

Since the transmission time B of the beacon signal (about 1 ms: the duration of the beacon signal) is determined in advance, the transmission interval α and the time AT to be transmitted are
α = (T−B) / S = (500-1) /5=99.8 ms
AT = B + (N−1) × α = 200.6 ms → ED 30 can be calculated as being used between 200.6 and 300.4 ms, and the target ED performs this calculation after receiving the beacon, and the calculated time Just go to If this method is used, it is possible to eliminate the cause of collision, and it is possible to efficiently transmit data in one beacon cycle.

FIG. 1 is a block diagram illustrating an internal configuration of a coordinator and an end device.
The end device 27 includes a radio frequency unit 16 for transmitting signals from the antenna 15 and demodulating radio waves received by the antenna 15, an MCU 17 for analyzing signals, and software 18 for operating the MCU 17. For example, one module. The software 18 includes application software and a communication protocol program in addition to basic software. The sensor 19 is provided when the end device 27 is a measuring device such as temperature, and acquires data to be transmitted to the coordinator 28. Further, the end device 27 is driven by the power from the battery 20. The above configuration other than the antenna 15 is mounted on the motherboard.

  The coordinator 28 is a device such as a wireless LAN card, and includes a radio frequency unit 22 that transmits and receives radio frequencies from the antenna 21, an MCU 23 that performs signal processing, and software 24 that operates the MCU 23, and is a module. . The battery 25 is also included in these and mounted on the motherboard. The coordinator 28 is connected to the PC 26 that is a data transmission / reception device.

FIG. 2 is a diagram for explaining the first embodiment of the present invention.
The ED that has received the beacon signal calculates the time it should access from the beacon signal. In the case of the 30th ED, it is only necessary to access during 200.6 to 300.4 ms, so sleep is performed for unnecessary 0 to 200.6 ms. In addition, after performing data communication, sleep until the next beacon.

The flowchart of FIG. 2 is a flowchart of a software ED side access time calculation method executed by the ED MCU. In step S10, beacon analysis is started. In this case, ED
The identification number is assumed to be 030 described third in the beacon signal. In step S11, the order written in the ED list in the beacon signal is calculated. In this case, N = 3 because it is the third. In step S12, the communication time interval α is calculated as (TB) / S. Here, T is the beacon period, B is the transmission time of the beacon signal, and S is the number of EDs listed in the ED list. In step S13, the access time is calculated by the calculation method described above.

FIG. 3 is a diagram for explaining the frame format of the beacon signal.
In FIG. 3, the ED list used in the embodiment of the present invention is described in the MAC layer payload in the MAC layer frame. Of the MAC layer payload, the super frame is a 2-byte field in which information defining the super frame and the beacon is described. GTS indicates the number of defined GTS (Guaranteed Time Slot). When the GTS is defined, definition information such as the data transmission direction of the GTS, the address of the assigned node, the start slot, and the number of slots used is included. Pending indicates the number of messages pending by the CN and its destination address. If data is pending, each address list is included. That is, in the embodiment of the present invention, ED identification numbers are sequentially described in the pending field as an ED list. In the case of the embodiment of the present invention, the order of description is also meaningful, and communication sections are calculated according to the order of description. The use of the beacon payload is not specified in IEEE 802.15.4.

FIG. 4 is a sequence diagram showing a state of communication between the coordinator and the end device.
When a beacon signal is sent from the coordinator (CN) and received by the end device, the end device checks whether its own identification number is in the ED list, and if the ED list has its own identification number The data request is made to the coordinator at the access time of the own end device. When the coordinator receives the data request, it sends an Ack to the end device, and then sends the requested data to the end device. When the end device receives the data, it sends an Ack to the coordinator. Here, the case where data is sent from the coordinator to the end device has been shown, but the same sequence also occurs when data is sent from the end device to the coordinator by issuing a data request from the coordinator to the end device.

FIG. 5 is a flowchart of processing executed by the MCU of the end device.
Before starting, it is in a sleep state and gets up at the same time as starting (step S15). Wake up is several ms (= δT) before the beacon arrives. In step S16, a timer is started. In step S17, a beacon signal is received, and this time is set as T1 as a reference time. This timer measures the time since the reception of the beacon signal. That is, the access time calculated by the ED itself is measured from the beacon reception time and specified. In step S18, it is determined whether or not the identification number of the own ED is included in the beacon signal. If the determination in step S18 is No, the sleep time is calculated in step S25. If the current time is T3, the elapsed time after receiving the beacon is T3-T1. Since the beacon period is T and the ED needs to wake up before ΔT when the beacon arrives, the sleep time can be calculated as T− (T3−T1) −ΔT. In step S26, the computer sleeps for the calculated time until the next beacon arrives.

  If the determination in step S18 is yes, in step S19, the number of all EDs in the ED list and the order of the identification numbers of the own ED in the ED list are acquired from the beacon signal. In step S20, the own ED access time is calculated by the method described above.

  In step S21, the sleep time is calculated. Assuming that the current time is T2, the elapsed time after receiving the beacon is T2-T1. When the access time is AT, the sleep time can be calculated as AT- (T2-T1). In step S22, the PC sleeps until its own ED access time, wakes up in step S23, and communicates with the coordinator in step S24. After the communication is completed, the sleep time is calculated in step S25, and in step S26, the process sleeps until the next beacon arrives and the process is completed.

FIG. 6 is a diagram for explaining a second embodiment of the present invention.
As a predetermined decision, an ED number that does not exist (dummy ED number), for example, 900 to 999 numbers is decided. The CN transmits the beacon signal including the dummy ED number. When the ED calculates its own access time, the access time is calculated with a total of 6 units (ED 10, 20, 30, 40, 50, 999), so the last one slot is left. This slot can be freely used by other EDs for communication to the upper CN.

  At this time, for example, the ED 89 and 99 are requested to communicate with the next beacon as a slot securing request to the CN. In the next beacon, CN adds ED 89 and 99 to the list, so that ED 89 and 99 can perform data communication.

  A plurality of dummy ED numbers may be set in the beacon signal. By doing so, the time for the ED to access the CN can be lengthened, and more EDs can communicate with the CN.

  In the prior art 1, a collision occurs. However, in the embodiment of the present invention, since the collision is suppressed, more reliable communication is possible. Further, in the prior art 2, if 3 beacon periods, for example, if the period is 500 ms, data transmission takes 1.5 seconds, but in the embodiment of the present invention, the transmission time can be shortened to 1/3, and 1 beacon period = Data transmission is possible in 0.5 seconds.

It is a block diagram explaining the internal structure of a coordinator and an end device. It is a figure explaining the 1st Embodiment of this invention. It is a figure explaining the frame format of a beacon signal. It is a sequence diagram which shows the mode of communication between a coordinator and an end device. It is a flowchart of the process which MCU of an end device performs. It is a figure explaining the 2nd Embodiment of this invention. It is a figure explaining the outline | summary of a beacon wireless communication system. It is a figure explaining 1st prior art. It is a figure explaining the 2nd prior art.

Explanation of symbols

15, 21 Antenna 16, 22 Wireless unit 17, 23 MCU
18, 24 Software 19 Sensor, etc. 20, 25 Battery 26 PC

Claims (3)

In a beacon wireless communication apparatus in a beacon wireless communication system in which a single base unit and a plurality of beacon wireless communication apparatuses communicate through wireless communication,
The received beacon signal, when the identification number of its own beacon the radio communication apparatus is described, the access time calculating means for self beacon radio communication device to calculate the relative time from the beacon to be accessed parent machine,
Access means for accessing the parent device at the calculated time;
Equipped with a,
The identification number of the dummy beacon wireless communication device is described in the beacon signal, and the beacon wireless communication device that wants to access the parent device accesses the parent device at an access time corresponding to the dummy identification number. Beacon wireless communication device. The beacon wireless communication apparatus according to claim 1 , wherein a plurality of dummy identification numbers can be set in a beacon signal. An access method to a parent device in a beacon wireless communication system in which a single parent device and a plurality of beacon wireless communication devices communicate via wireless,
The beacon wireless communication device
The received beacon signal, when the identification number of its own beacon wireless communication device is described, to calculate the relative time from the beacon itself beacon radio communication apparatus should access the parent machine,
Access the parent machine to the calculated time,
The identification number of the dummy beacon wireless communication device is described in the beacon signal, and the beacon wireless communication device that wants to access the parent device accesses the parent device at the access time corresponding to the dummy identification number. An access method characterized by that.

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