JP6630559B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system in which a plurality of wireless devices perform RIT communication.

  Gas companies arrange gas meters at demand locations in order to accumulate the amount of gas consumed by consumers. In recent years, smart meters have been in the spotlight, which are equipped with a wireless device in a gas meter, perform bidirectional data communication with a gas company, and can automatically and remotely measure gas consumption. . Such a smart meter can be used for a water meter, for example, and can also be used as an information source for improving the safety and use efficiency of an infrastructure network such as gas and water.

  In addition, various means have been proposed to realize data communication between the above-described smart meter and a gas company. For example, it has been considered to provide a smart meter with a short-range wireless device and construct a network for performing multi-hop communication between wireless devices. For such multi-hop communication, for example, a method using RIT (Receiver Initiated Transmission) has been studied (for example, Patent Document 1). This RIT method is a method in which a RIT Data Request Frame is intermittently transmitted from a receiving side to a transmitting side, and the transmitting side transmits data in synchronization with the Frame.

JP-A-2005-53593

  In the RIT method, by intermittently transmitting the RIT Data Request Frame from the receiving side to the transmitting side, it is possible to reduce power consumption compared to the conventional CSL method in which the transmitting side has to continuously transmit the Wakeup Sequence for a certain period of time. ing. There is a need for the development of a technology that further improves the advantage of the RIT method of low power consumption. In addition, it is necessary to develop a system that is highly resistant to interference from other systems using the same neighboring frequencies.

  The present invention has been made in view of the above-described problems, and has as its object to provide a wireless communication system that suppresses power consumption and is resistant to interference from other systems.

In order to solve the above problem, a wireless communication system according to the present invention is a wireless communication system that performs RIT communication in which a receiver periodically attempts to transmit a RIT Data Request Frame to a transmitter. Is provided with a receiving-side control unit that enters a reception standby state for a predetermined period after transmitting a RIT Data Request Frame to the transmitter, and the transmitter waits for reception if there is target data to be transmitted. The receiving state is established, and when the RIT Data Request Frame is received from the receiver in the receiving standby state, the transmitting side control unit that transmits the target data to the receiver is provided, and the receiving side control unit transmits the RIT Data Request Frame before transmitting the RIT Data Request Frame. By shifting to the reception standby state of the frequency band used for transmission, Carrier sense is performed, and if the received radio wave intensity of the frequency band exceeds the threshold, the reception standby state is released without continuing the reception standby state, and the transmission of the current RIT Data Request Frame is stopped, Until the transmission timing of the next RIT Data Request Frame, the carrier sense is suspended, and after transmitting the RIT Data Request Frame and before transmitting the target data, the transmitting-side control unit performs the process of the receiver indicated by the RIT Data Request Frame. The address information is transmitted to the receiver in a frame separate from the target data, and the receiving side control unit transmits the address of the own device only when the address information of the own device is received in the reception standby state. Receives target data stored in a frame separate from the frame in which the information is stored. Characterized in that it.

  The receiving side control unit may transmit a RIT Data Request Frame including only the address information of the receiver as the address information to the transmitter.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to suppress interference from another system in order to suppress power consumption and perform carrier sense.

FIG. 2 is an explanatory diagram illustrating a schematic configuration of a wireless communication system. FIG. 2 is a functional block diagram illustrating a schematic configuration of a wireless device. FIG. 9 is a first diagram for describing an RIT method of a comparative example. FIG. 9 is a second diagram for describing the RIT method of the comparative example. FIG. 3 is a first diagram for describing an F-RIT method. FIG. 11 is a third diagram for describing the RIT method of the comparative example. FIG. 14 is a fourth diagram for describing the RIT method of the comparative example. FIG. 2 is a second diagram illustrating the F-RIT method according to the embodiment. 5 is a theoretical model of power consumption by wireless communication. FIG. 3 is a diagram summarizing variables and constants related to power consumption calculation. 9 is a first graph illustrating a relationship between an intermittent operation interval and an evaluation index of power consumption performance. 9 is a second graph illustrating a relationship between an intermittent operation interval and an evaluation index of power consumption performance. An evaluation model in which a plurality of other wireless devices exist in a communication area of a pair of wireless devices is shown. FIG. 3 is a diagram illustrating a model sequence of a CSL-based method. FIG. 3 is a diagram illustrating a model sequence of the F-RIT method. 4 is a graph comparing and evaluating the success rate of establishing a communication link between the F-RIT method and the CSL-based method. It is a flowchart for demonstrating the flow of a process of a computer simulation. It is a figure showing the set value of each parameter of computer simulation. FIG. 9 is a first explanatory diagram for describing a computer simulation result of a success rate of establishing a communication link when Pre-CS is not introduced. FIG. 13 is a second explanatory diagram for describing a computer simulation result of a success rate of establishing a communication link when Pre-CS is not introduced. FIG. 9 is an explanatory diagram for explaining a data packet length of an upper layer assumed to be used; FIG. 9 is a first explanatory diagram for describing a computer simulation result of a success rate of establishing a communication link when Pre-CS is introduced. FIG. 13 is a second explanatory diagram for describing a computer simulation result of a success rate of establishing a communication link when Pre-CS is introduced.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, other specific numerical values, and the like shown in the embodiments are merely examples for facilitating the understanding of the present invention, and do not limit the present invention unless otherwise specified. In the specification and the drawings, elements having substantially the same function and configuration will be denoted by the same reference numerals, without redundant description, and elements not directly related to the present invention will be omitted. I do.

(Wireless communication system 100)
FIG. 1 is an explanatory diagram showing a schematic configuration of the wireless communication system 100. As shown in FIG. 1, the wireless communication system 100 includes a wireless device 110 and a gateway device 112. For example, the wireless communication system 100 is associated with a smart meter. The smart meter is used, for example, when gas is supplied from a gas company to a consumer, and is a device that automatically measures the amount of gas used.

  The wireless device 110 is provided in each smart meter, and transmits and receives at least data used by the smart meter. The gateway device 112 is installed in association with the smart meter, collects data of one or a plurality of wireless devices 110, and distributes data to one or a plurality of wireless devices 110. The center device 114 is composed of a computer or the like, and is a device belonging to a manager of the wireless communication system 100 such as a gas company or a power company. The center device 114 collects data of the gateway device 112 and transmits data to the gateway device 112. To deliver. Note that a plurality of gateway devices 112 and a plurality of groups G of the wireless devices 110 that communicate with the center device 114 via the gateway devices 112 are provided.

  Here, wireless communication is performed between the gateway device 112 and the center device 114 using a communication network such as a mobile phone network including the base station 116 or a PHS (Personal Handyphone System) network. Further, wireless communication is performed between the wireless devices 110 and between the wireless device 110 and the gateway device 112, for example, through an F-RIT (Feather-Receiver Initiated Transmission) method described later.

  In the present embodiment, a smart meter is arranged for each of a plurality of consumers. The smart meter is associated with a wireless device 110 or a gateway device 112, respectively, and the center device 114 collects information on the smart meter or controls the smart meter through the wireless device 110 or the gateway device 112. Therefore, the wireless device 110 and the gateway device 112 are arranged at a plurality of positions where the consumer exists.

  In the wireless communication system 100 for smart meters, multi-hop communication based on the RIT method is performed between a plurality of wireless devices 110. The RIT method is used for multi-hop communication in which data can be transmitted and received between terminals (nodes) by a relay method and the route of the terminal to be passed can be changed according to the radio wave condition, and conforms to the communication standard IEEE 802.15.4 / 4e. This is a communication method that realizes low power consumption. In the present embodiment, the F-RIT method in which the power consumption is further reduced from the RIT method is adopted. Hereinafter, after describing the configuration of the wireless device 110, the F-RIT method will be described in detail.

(Wireless device 110)
FIG. 2 is a functional block diagram illustrating a schematic configuration of the wireless device 110. The wireless device 110 includes a communication unit 150, a storage unit 152, and a central control unit 154. The communication unit 150 establishes wireless communication with the gateway device 112 and another wireless device 110. The storage unit 152 includes a ROM, a RAM, a flash memory, an HDD, and the like, and stores a program used for the wireless device 110 and various data.

  The central control unit 154 includes a CPU and a DSP, and controls the entire wireless device 110 by using a program stored in the storage unit 152. The central control unit 154 functions as the communication control unit 160 and the storage control unit 162.

  The communication control unit 160 controls the communication unit 150 to perform F-RIT multi-hop communication with the gateway device 112 and another wireless device 110.

  The storage control unit 162 acquires data such as the amount of gas used from the smart meter in which the storage device is provided, and causes the storage unit 152 to store the data. The storage control unit 162 causes the storage unit 152 to store data transmitted from the gateway device 112 or another wireless device 110.

  As described above, the wireless device 110 stores the data of the smart meter and the data received from the other wireless device 110 and the gateway device 112, and converts the data stored in the storage unit 152 into another wireless device as necessary. 110 and the gateway device 112. Hereinafter, such data to be transmitted is referred to as target data.

  FIG. 3 is a first diagram illustrating the RIT method of the comparative example. Here, regarding the wireless device 10 performing the multi-hop communication of the RIT method of the comparative example including the conventional method, when distinguishing between the transmitting side and the receiving side, the wireless device 10 on the transmitting side of the target data is set to the transmitter A ′ and the target data Is called a receiver B ′.

  As shown in FIG. 3, the receiver B 'transmits RIT Data Request Frame (indicated by a frame RFa' and a frame RFb 'in the figure) at intervals of a preset intermittent operation interval (MAC RIT Period). The RIT Data Request Frame has the same frame configuration as the MAC section of the communication standard IEEE 802.15.4.

  Specifically, in the RIT Data Request Frame (frame RFb ') transmitted by the receiver B', a network ID (PANID: Personal Area Network ID) of the receiver B 'and a PAN to which the wireless device 10 is added are identified. Information) and address information (identification information for identifying each wireless device 10 included in the wireless communication system 100). Further, the receiver B ′ stores the network ID and the address information of the transmitter A ′ that transmits the target data to the own device in the storage unit 152, and the RIT Data Request Frame (frame RFb ′) includes This network ID and address information are also included.

  Similarly, the RIT Data Request Frame (frame RFa ') transmitted by the transmitter A' includes, in addition to the network ID and address information of the transmitter A ', an unillustrated transmission of the target data to the transmitter A'. The network ID and address information of the wireless device 10 are included.

  Further, the radio device 10 performs carrier sense (CS) before transmitting the RIT Data Request Frame. The carrier sense (CS) measures a received radio wave intensity (a received power level, a received signal strength, an RSSI (Received Signal Strength Indication)) by shifting to a reception standby state for data in a frequency band used for transmission, and This is a process for checking whether the band is occupied by another device. As a result of the carrier sense CS, if the received radio wave intensity in the frequency band is equal to or less than the threshold, the wireless device 10 transmits a RIT Data Request Frame. As described above, in the RIT method, the receiver B 'periodically attempts to transmit the RIT Data Request Frame to the transmitter A'.

  Then, after transmitting the RIT Data Request Frame, the wireless device 10 enters a reception standby state for a predetermined period (RIT Data Wait Duration, which is indicated by a period WD in the drawing) set in advance. The central control unit 154 of the wireless device 10 controls the communication unit 150 so that functions necessary for reception are enabled during the reception standby state.

  FIG. 4 is a second diagram illustrating the RIT method of the comparative example. When the transmitter A 'obtains the target data TDF or generates the target data TDF internally, the transmitter A' enters a reception standby state as shown by hatching in FIG.

  Then, the transmitter A 'receives the RIT Data Request Frame transmitted by the receiver B'. If the network ID and the address information included in the RIT Data Request Frame indicate the own device, the transmitter A 'transmits the target data TDF to the receiver B'.

  Since the receiver B 'is in the reception standby state after transmitting the RIT Data Request Frame, the receiver B' can receive the target data TDF transmitted by the transmitter A '.

  As described above, the RIT method enables the receiver B 'to receive the target data TDF by intermittently transmitting the RIT Data Request Frame. Therefore, for example, the power consumption can be significantly reduced as compared with the CSL (Coordinated Sampled Listening) method in which the transmitter performs continuous transmission of Wakeup Frame called Wakeup Sequence to prompt the receiver to receive.

  FIG. 5 is a first diagram for describing the F-RIT method. Here, regarding the wireless device 110 performing the multi-hop communication of the F-RIT method, when distinguishing between the transmitting side and the receiving side, the wireless device 110 on the transmitting side of the target data TDF is referred to as the transmitter A, and the receiving side of the target data TDF. The wireless device 110 is called a receiver B.

  Similarly to the RIT method of the comparative example, the receiver B transmits an RIT Data Request Frame (indicated by a frame RFa and a frame RFb in the figure) at every preset intermittent operation interval.

  Here, in the F-RIT method, only the address information of the receiver B is included in the RIT Data Request Frame (frame RFb) transmitted by the receiver B, which is different from the RIT method. The network ID of B, the network ID of transmitter A, and the address information are not included. The same applies to the RIT Data Request Frame (frame RFa) transmitted by the transmitter A.

  When the transmitter A obtains the target data TDF or generates the target data TDF, the transmitter A enters a reception standby state as indicated by hatching in FIG. Then, upon receiving the RIT Data Request Frame transmitted by the receiver B, the communication control unit 160 (hereinafter, referred to as a transmission-side control unit) of the transmitter A receives the address information AD (of the receiver B) indicated in the RIT Data Request Frame. Regardless of the address information), the address information AD is transmitted to the receiver B. Here, for example, in the transmitter A, the address information AD of the receiver B that is appropriate as a transmission target is registered, and the transmission-side control unit indicates the registered address information AD and the received RIT Data Request Frame. If the address information AD is not registered, control may be performed such that the address information AD is not returned to the RIT Data Request Frame transmitted from the receiver B.

  After transmitting the RIT Data Request Frame, the communication control unit 160 of the receiver B (hereinafter, referred to as a reception-side control unit) receives the address information AD transmitted by the transmitter A because it is in the reception standby state. it can. Upon receiving the address information AD, the receiving side control unit confirms that the address information AD is the address information of the own device (receiver B).

  Then, after the address information AD, the transmission-side control unit transmits the target data TDF to the receiver B, and the reception-side control unit can receive the target data TDF because it is in the reception standby state. .

  Further, for example, when the address information AD transmitted by the transmitter A is not the address information of the own device, the receiving side control unit determines that the subsequently received data is not addressed to the own device and receives the data. No processing is performed, or even if received, it is not treated as valid data.

  As described above, in the F-RIT method, after the transmission-side control unit receives the RIT Data Request Frame and before transmitting the target data TDF, the address information AD of the receiver indicated in the RIT Data Request Frame is transmitted to the receiver B. Send to

  Then, when receiving the address information of its own device in the reception standby state, the receiving-side control unit receives the subsequently transmitted target data TDF. Therefore, it is possible to avoid a situation where the receiver B erroneously receives data transmitted from a device other than the transmitter A.

  Further, as described above, in the F-RIT method, only the address information of the receiver B is included in the RIT Data Request Frame, and the network ID of the receiver B, the network ID and the address information of the transmitter A are included in the RIT Data Request Frame. Not included. Since the RIT Data Request Frame is constantly intermittently transmitted, it is possible to greatly reduce power consumption by reducing the information amount of the RIT Data Request Frame and to improve radio wave use efficiency. It becomes possible.

  FIG. 6 is a third diagram illustrating the RIT method of the comparative example. FIG. 6 illustrates a case where the receiver C 'attempts to transmit the RIT Data Request Frame while the target data TDF is being transmitted from the transmitter A' to the receiver B 'in the RIT method.

  As described above, the carrier sense CS is performed before the transmission of the RIT Data Request Frame (frame RFc '). When the receiver C ′ determines that the frequency band is occupied by another wireless device 10 (transmitter A ′) as a result of the carrier sense CS and that transmission in the frequency band is impossible, the receiver C ′ waits for the postponement period and then again Perform carrier sense CS. At this time, if the transmission of the target data TDF has not been completed yet, the receiver C 'performs the carrier sense CS again after waiting for the postponement period.

  Then, in the carrier sense CS after the transmission of the target data TDF is completed, when the received radio wave intensity in the frequency band becomes equal to or less than the threshold, the receiver C 'transmits an RIT Data Request Frame.

  As described above, in the RIT method, CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) in which the carrier sense CS is repeated until the RIT Data Request Frame can be transmitted is applied. Here, the postponement period is set to be short each time the carrier sense CS is repeated at random.

  FIG. 7 is a fourth diagram illustrating the RIT method of the comparative example. As shown in FIG. 7, the CSMA / CA includes, for example, a process of continuing the carrier sense CS instead of repeating it.

  Specifically, as a result of the carrier sense CS, the receiver D ′ determines that the frequency band is occupied by another wireless device 10 (transmitter A ′) and that transmission in that frequency band is not possible. Continue carrier sense CS until is empty. That is, the receiver D 'maintains the reception standby state and continuously measures the received radio wave intensity until the received radio wave intensity becomes equal to or less than the threshold value.

  Then, when the transmission of the target data TDF is completed and the measured received radio wave intensity becomes equal to or less than the threshold, the receiver D 'transmits a RIT Data Request Frame.

  FIG. 8 is a second diagram for describing the F-RIT method according to the present embodiment. As shown in FIG. 8, in the F-RIT method, similarly to the RIT method, while the target data TDF is being transmitted from the transmitter A to the receiver B, the receiving side control unit of the receiver C detects the carrier sense CS. Do.

  However, if the frequency band is occupied by another wireless device 110 (transmitter A) and the received radio field intensity of the frequency band exceeds the threshold, the receiving side control unit of the receiver C continues the reception standby state. Instead, the reception standby state is immediately released and the carrier sense CS is terminated. Thereafter, the transmission of the current RIT Data Request Frame based on the carrier sense CS is stopped without performing the carrier sense CS again, and the carrier sense CS is suspended until the next transmission timing of the RIT Data Request Frame.

  As described above, in the F-RIT method, the repeated carrier sense CS is not performed. Such a processing method of the carrier sense CS is referred to as Pre-CS.

  The RIT Data Request Frame does not necessarily need to be transmitted periodically, and even if it is postponed until the next RIT Data Request Frame transmission timing, there is no significant effect on network performance. Rather, by increasing the priority of the target data TDF, the communication frequency can be suppressed, and even if the number of wireless devices 110 increases, a decrease in the communication success rate can be suppressed.

  Further, in the comparative example shown in FIG. 6, since the carrier sense CS is repeated, the power consumed for the carrier sense CS increases. Further, in the comparative example shown in FIG. 7, since the carrier sense CS is continuously executed, the reception standby state is lengthened, and the power consumption is further increased. In the Pre-CS, since the number of times of the carrier sense CS is small and the duration thereof is short, the power consumption can be significantly suppressed.

  In addition, here, the RIT Data Request Frame is Pre-CS, but the target data TDF may be Pre-CS before transmission. However, if CSMA / CA is performed before transmission, communication may be performed. The success rate can be further improved.

(1. Power consumption performance evaluation)
Next, regarding the performance of the above-described F-RIT method, among the CSL methods, the results of the power consumption performance evaluation comparing the MAC method based on the asynchronous CSL (hereinafter, the CSL-based method), which is the asynchronous method, will be described. It will be described in detail. In the CSL-based scheme, the same Pre-CS as in the F-RIT scheme is performed before transmitting the Wakeup Sequence.

(1-1. Modeling)
FIG. 9 is a theoretical model of power consumption by wireless communication. As shown in FIG. 9, an environment is assumed in which only a pair of radios exist in a communication area where radio waves of a pair of radios (Sender, Receiver) can reach. Further, it is assumed that no other wireless device exists outside the communication area, and the frequency at which a communication link establishment request is issued to the Sender is defined as the frequency λ _Link .

  FIG. 10 is a table summarizing variables and constants related to the power consumption calculation. FIG. 10A shows a table summarizing the variables of the power consumption calculation, and FIG. 10B shows the ID for each application. FIG. 10 (c) shows a table in which the values of the variables are summarized.

The intermittent operation intervals (MAC RIT Period, MAC CSL Period) in the F-RIT scheme and the CSL-based scheme are set to the same length T _CSL = T _RIT = T. In this modeling, the power consumption of the Pre-CS is not included in the calculation.

…（数式１）
ここで数式（１）の右辺はそれぞれ数式２となる。

…（数式２）
ただし、期間Ｔ_IDは単一ＩＤフレームの送信期間であり、Ｆ−ＲＩＴ方式ではＲＩＴ Ｄａｔａ Ｒｅｑｕｅｓｔ Ｆｒａｍｅの送信期間、比較手法ＣＳＬベース方式ではＷａｋｅｕｐ Ｓｅｑｕｅｎｃｅ Ｆｒａｍｅの送信期間に相当する。また、Ｐ_tおよびＰ_ｒはそれぞれ送信および受信動作に係る単位時間あたりの消費電力である。 The power consumption of the sender in the F-RIT method as the proposed method and the power consumption of the Sender in the CSL-based method as the comparison method are respectively set to _{PS: RIT} and _{PS : CSL} . The power consumption of the sender is power consumption P _{Int (RIT)} , P _{Int (CSL)} related to the intermittent transmission / reception operation, and power consumption P _{S: Link (RIT ) on} the sender side related to the link operation for capturing the intermittent transmission / reception operation of the communication partner. ₎ , _{PS: Link (CSL)} , and power consumption PS _{: Data} on the Sender side relating to the data transmission operation. Among them, a request for establishing a communication link occurs at a frequency λ _Link . The power consumption P _{S: RIT} and P _{S: CSL} can be expressed by Equation 1.

... (Formula 1)
Here, the right side of Expression (1) is Expression 2 respectively.

... (Formula 2)
However, the period T _ID is a transmission period of a single ID frame, and corresponds to a transmission period of a RIT Data Request Frame in the F-RIT system and a transmission period of a Wakeup Sequence Frame in the comparison method CSL-based system. _Pt and _Pr are the power consumption per unit time for the transmission and reception operations, respectively.

…（数式３）
ただしＰ _R:Link(RIT)およびＰ _R:Link(CSL)はそれぞれアクセス動作に係るＲｅｃｅｉｖｅｒ側の消費電力であり、Ｐ_R:Dataはデータ伝送動作に係るＲｅｃｅｉｖｅｒ側の消費電力であり、それぞれ数式４の様に表すことができる。

…（数式４） Next, Equation 3 is obtained by similarly modeling the power consumption _{PR: RIT} and _{PR : CSL} of the receiver.

... (Formula 3)
Where _{PR: Link (RIT)} and _{PR : Link (CSL)} are the receiver-side power consumption related to the access operation, and PR _{: Data} is the receiver-side power consumption related to the data transmission operation. 4 can be represented.

... (Formula 4)

…（数式５）
評価指標η_P<１であればＦ−ＲＩＴ方式に比べてＣＳＬベース方式の消費電力が大きく、評価指標η_P>１であればその逆となる。 An evaluation index η for comparing and evaluating the power consumption performance of the F-RIT method and the CSL-based method using these power consumptions _{PS: RIT} , _{PS : CSL} , _{PR: RIT} , and _{PR : CSL. P} is defined in Equation 5.

... (Equation 5)
If the evaluation index η _P <1, the power consumption of the CSL-based scheme is larger than that of the F-RIT scheme, and if the evaluation index η _P > 1, the opposite is true.

(1-2. Calculation result)
The power consumption performance of the F-RIT method is evaluated using the above evaluation index η _P. In the evaluation, on the assumption that the transmission speed is 100 kbps, which is standardized by the communication standard IEEE 802.15.4g and is adopted by U-Bus Air, various applications (upper layers) assumed for practical use as shown in FIG. Of the periods T _ID required for transmission of a single ID frame set in accordance with the ID length of 0.08 ms, 0.32 ms, and 1.28 ms. Other evaluation parameters are shown in FIG. Note that the Pre-CS operation period was set to T _CS = 0.01 ms with reference to the actual value of the current wireless device. In addition, the period T _Data required for data transmission, which has no difference in power consumption between the F-RIT and the CSL-based system, was set to 0 ms in both calculations.

FIGS. 11 and 12 are graphs showing the relationship between the intermittent operation interval T and the evaluation index ηP of the power consumption performance. FIG. 11A shows legends having different periods T _ID . If the period T _ID = 0.08ms in the intermittent operation interval T is equal to or greater than about 0.1s, when the period T _ID = 0.32ms in the intermittent operation interval T is equal to or greater than about 0.6 s, the direction of F-RIT method It can be seen that the power consumption performance is superior to the CSL-based method. Also, it can be seen that the power consumption performance of the F-RIT method improves as the period T _ID is set shorter. This is because when the period T _ID is shortened, the power consumption required for the dominant intermittent operation among the power consumption of the F-RIT method is reduced.

FIG. 11B shows a different legend of the frequency λ _Link . As shown in FIG. 11B, when the intermittent operation interval T is about 0.1 s or more at the frequency λ _Link = 0.1, the intermittent operation interval T is about 1.0 s or more at the frequency λ _Link = 0.001. In this case, it can be seen that the F-RIT method has better power consumption performance than the CSL-based method. Also, it can be seen that the power consumption performance of the F-RIT method improves as the frequency of access occurrence λ _Link increases. This is because the transmission power by the CSL-based wakeup sequence becomes dominant in the power consumption in an area where the frequency of access occurrence λ _Link is high.

FIG. 12 shows a P _t / P _r is different legends is the ratio between the power consumption P _r per unit according to the received operation and the power consumption P _t per unit according to transmission operation time period. It can be seen that towards the F-RIT scheme for all P _t / P _r when the intermittent operation interval T is equal to or greater than about 0.3s has excellent power performance in comparison with the CSL based method. Also in the region where T is about 0.3s or more, power performance of larger the F-RIT method P _t / _{P r} it can be seen that improved. This is because in the region where the intermittent operation interval T is wide, similarly to the region where the access frequency is high, the transmission power by the CSL-based wakeup sequence becomes dominant in the power consumption.

  As described above, under any of the conditions shown in FIGS. 11 and 12, when the intermittent operation interval T is about 1.0 s or more, the F-RIT method has better power consumption performance than the CSL-based method. It was shown that.

…（数式６） (1-3. Discussion)
The condition in which the F-RIT method is more advantageous than the CSL-based method is when ηP ≦ 1 as shown in Expression 6.

... (Formula 6)

…（数式７）

…（数式８） Therefore, by substituting Expressions 2 and 4 into Expression 6, and further substituting the power consumption ratio D _P related to the transmission / reception operation shown in Expression 7, Expression 8 can be calculated as a conditional expression.

... (Formula 7)

... (Equation 8)

That is, under the condition that satisfies Equation 8, the F-RIT scheme is always more advantageous in terms of power consumption performance than the CSL-based scheme. Equation 8 shows that the shorter the period T _ID , the more advantageous the power consumption performance of the F-RIT method. That is, the power consumption performance of the F-RIT scheme is improved as the ID length itself is shortened or the transmission speed is increased to shorten the period T _ID . Therefore, if a transmission band enabling higher-speed communication becomes available in the future, the power consumption performance of the F-RIT scheme will be further improved.

(2. Evaluation of success rate of communication link establishment in interference environment)
Subsequently, the success rate (transmission success rate) of establishing a communication link when a plurality of wireless devices are present in the communication area and causing interference is compared and evaluated between the F-RIT method and the CSL-based method.

(2-1. Modeling)
FIG. 13 shows an evaluation model in which a plurality of other wireless devices exist in a communication area of a pair of wireless devices. In the communication area of a pair of radios, it is assumed that N radios exist, and all radios have unique communication partners (that is, N / 2 communication pairs exist), and all radios It is assumed that a data transmission event occurs at a frequency λ _Link and becomes a Sender. In this modeling, the F-RIT method and the Pre-CS of the CSL-based method are omitted in order to avoid complication of theoretical calculation.

(2-2. Formulation of Success Rate of Communication Link Establishment)
FIG. 14 is a diagram showing a model sequence of the CSL-based system. FIG. 14A shows a case where the communication link establishment is successful, and FIG. 14B shows a case where the communication link establishment fails due to interference. Is shown.

…（数式９） First, the success rate S _(CSL) of establishing a communication link in the case of the CSL-based scheme is derived. In the section T _{Link (CSL)} that causes interference, the Wakeup Sequence intermittent operation interval T of the Sender (interference source Sender) in the communication pair that becomes the interference source and the ID return of the Receiver (interference source Receiver) in the communication pair that becomes the interference source T _{Link (CSL)} = T + T _ID + T _Data as the total value of the period T _ID required for the data transmission and the period T _Data required for the data transmission of the interference source Sender. Further, as shown in FIG. 14B, the interfered section in the desired communication pair is the maximum T _{Link (CSL)} . Assuming that a call is generated in each wireless device according to a Poisson distribution with a probability of frequency λ _Link , the probability that communication will not collide in the same way as the theoretical formula of the pure Aloha system, that is, the success rate S _{(CSL) of} establishing a communication link Can be expressed as Expression 9.

... (Formula 9)

Next, a success rate S _(RIT) of establishing a communication link in the case of the F-RIT method is derived. FIG. 15 is a diagram showing a model sequence of the F-RIT system. FIG. 15A shows a case where the communication link is successfully established, and FIG. 15B shows a case where the communication link is failed due to interference. Show the case.

…（数式１０） In the case of the F-RIT method, there are two types of causes of interference. The first one is intermittent transmission of a period T _ID by N-1 wireless devices serving as interference sources. Similarly to the case of the CSL-based system, the data transmission in the T _ID + T _Data section, which is the time length generated at the frequency λ _Link from each wireless device, is also an interference section. On the other hand, as shown in FIG. 15, the interfered section is a section T _{Link (RIT)} related to the establishment of a link between the sender and the receiver in the desired communication pair, and T _{Link (RIT)} = 2 · T _ID + T _Data . Become. As in the case of the CSL-based system, assuming that a call is generated in each wireless device according to the Poisson distribution with a probability of frequency λ _Link , the success rate S _{(RIT) of} establishing a communication link is calculated in the same way as the theoretical formula of the pure Aloha system. Is derived as Equation 10.

... (Formula 10)

(2-3. Calculation result and consideration)
FIG. 16 is a graph comparing and evaluating the success rates S _(RIT) and S _(CSL) of establishing a communication link between the F-RIT method and the CSL-based method. Note that FIG. 16 shows legends in which the period T _ID required for ID frame transmission is 0.32 ms, the frequency λ _{Link is} 0.001, and the number of Sender terminals N is 10, 100, and 1000. In FIG. 16, the vertical axis represents the success rates S _(RIT) and S _{(CSL) of} establishing a communication link, and the horizontal axis represents the intermittent operation interval T.

In this evaluation, attention was paid only to establishing a communication link, and the period T _Data = 0 required for data transmission was set. As shown in FIG. 16, when the intermittent operation interval T becomes 0.7 s or more, the F-RIT method becomes advantageous regardless of the number N of sender terminals. This is because, in the case of the CSL-based system, when the intermittent operation interval T increases, the wakeup sequence increases, and the radio wave occupation time per radio device that causes interference increases.

From these results, in an environment where the frequency λ _Link is high, when the intermittent operation interval T is set to be large in order to improve the power consumption performance, the success rate S ₍ F) of establishing the communication link of the F-RIT scheme compared to the CSL-based scheme is _RIT) is high, indicating that the radio wave efficiency of the protocol is excellent. Furthermore, it can be seen from Equations 9 and 10 that the higher the frequency λ _Link becomes, the more the superiority of the F-RIT scheme is improved. Therefore, it can be said that the F-RIT method is suitable for an ad hoc network protocol.

(3. Computer simulation of the effect of Pre-CS)
Subsequently, in order to quantitatively show the utility of the Pre-CS, the success rate of establishing a communication link of the F-RIT method and the CSL-based method when the data length (the period T _Data required for data transmission) is changed is calculated by a computer. Evaluate by simulation.

(3-1. Condition setting)
FIG. 17 is a flowchart for explaining the flow of the processing of the computer simulation, and FIG. 18 is a diagram showing the set values of the parameters of the computer simulation. Here, for the processing shown in FIG. 17, a simulation was performed by setting the setting values as shown in FIG. 18 for each parameter.

Next, the initial value of the intermittent transmission / reception operation timing of the wireless device and the transmission data generation timing are randomly assigned. After that, for each terminal, a collision between the section T _{Link (CSL)} and the section T _{Link (RIT)} for establishing a communication link in the sender of the desired communication pair and the interference section generated by the radio device serving as the interference source occurs. The detection rate is 10 μs, and the number of collisions is counted to calculate the success rate of establishing the communication link.

First, in order to show the validity of the present computer simulation, the relationship between the frequency λ _Link when Pre-CS is not performed and the success rate of establishing a communication link was evaluated by computer simulation, and a comparative evaluation with the above numerical calculation results was performed. Was done. The number of sender terminals N = 100, T = 5.0 s, and the period T _ID = 0.32 ms required for ID frame transmission. In addition, the number of trials in the computer simulation was set to 5,000.

(3-2. Computer simulation result)
FIGS. 19 and 20 are explanatory diagrams for explaining computer simulation results of the success rate of establishing a communication link when Pre-CS is not introduced. FIG. 19A shows a period T required for data transmission. _Data are shown a case where the 0ms, FIG. 19 (b), showing a case in which the period T _Data and 20 ms, in FIG. 20 (a), showing a case in which the period T _Data and 50 ms, 20 ( (b) shows a case where the period T _{Data is set} to 100 ms.

FIG. 21 is an explanatory diagram for explaining a data packet length of an upper layer assumed to be used, and shows a period T _Data required for transmitting one packet in each application at 100 kbps.

  19 and 20, the computer simulation results and the theoretical calculation results are almost the same. This shows the validity of the interference model and computer simulation used for the theoretical calculation.

Further, as shown in FIGS. 19 and 20, it can be seen that as the period T _Data required for data transmission becomes longer, the success rate of establishing a relative communication link of the F-RIT system is entirely deteriorated. This is because the frequency of collision between the F-RIT intermittent transmission / reception operation and the data transmission operation increases in proportion to the data length. On the other hand, when the frequency λ _Link is high, the above-mentioned increase in the collision frequency is suppressed because the intermittent operation interval T is long, and the superiority of the F-RIT scheme over the CSL-based scheme is maintained.

  In order to suppress the collision frequency between the intermittent transmission / reception operation and the data transmission operation, the above-mentioned Pre-CS is introduced. Under the same simulation conditions as in FIGS. 19 and 20, a computer simulation of the success rate of establishing a communication link when Pre-CS was introduced was performed.

FIGS. 22 and 23 are explanatory diagrams for explaining computer simulation results of the success rate of establishing a communication link when the Pre-CS is introduced. FIG. 22A shows a period T required for data transmission. _Data are shown a case where the 0ms, in FIG. 22 (b) showing a case in which the period T _Data and 20 ms, in FIG. 23 (a), showing a case in which the period T _Data and 50 ms, 23 ( (b) shows a case where the period T _{Data is set} to 100 ms.

22 and 23 show that the frequency of collision between the intermittent transmission / reception operation and the data transmission operation is suppressed by Pre-CS, and the success rate of establishing a communication link of the F-RIT scheme is not introduced by Pre-CS. It can be seen that it is greatly improved as compared with. As a result, under the conditions of λ _Link = 0.1 s ⁻¹ and T _Data = 100 ms, the success rate of establishing a communication link is improved by about 20 times at the maximum, and a success rate of establishing a communication link close to 100% can be achieved. .

  On the other hand, when Pre-CS is introduced into the CSL-based system, the success rate of establishing a communication link is slightly improved as compared with the case where Pre-CS is not introduced, but the effect is not so remarkable as in the F-RIT system. In order to further improve the success rate of establishing a CSL-based communication link, it is considered necessary to add a retransmission sequence, but the retransmission causes a problem that radio use efficiency is degraded.

  As described above, the F-RIT scheme is a highly mountable MAC protocol based on the RIT scheme. According to the wireless communication system 100 of the present embodiment, since the F-RIT scheme communication is used. Has the following advantages over systems using the CSL-based method.

That is, as shown in FIG. 11A, when the intermittent operation interval T is equal to or more than the predetermined value, the power consumption performance becomes superior as the period T _ID required for transmitting a single ID frame becomes shorter. In other words, the effect of reducing the power consumption by shortening the period T _ID is greater than that of the CSL-based method. In the wireless communication system 100, as described above, the RIT Data Request Frame includes only the address information of the receiver B, and includes the network ID of the receiver B, the network ID of the transmitter A, and the address information. Absent. Therefore, the period T _ID can be shortened, and the power consumption can be reduced more preferably than when this configuration is applied to a CSL-based system.

  Further, regarding the success rate of establishing a communication link when the Pre-CS is introduced, in the wireless communication system 100, as shown in FIGS. 22 and 23, the frequency of collision between the intermittent transmission / reception operation and the data transmission operation is suppressed, The success rate of establishing a communication link is greatly improved. On the other hand, in the system using the CSL-based method, the improvement rate of the success rate of establishing the communication link is small.

  This is for the following reason. That is, in the case of the CSL-based method, the success rate is improved by performing the carrier sense CS before transmitting the Wakeup Sequence. However, if the Wakeup Sequence cannot be transmitted in the Pre-CS, the communication link establishment fails. turn into. Therefore, in the CSL-based method, the improvement range by the Pre-CS is small, and the success rate is improved by adopting CSMA / CA that performs the carrier sense CS repeatedly.

  On the other hand, in the case of the F-RIT method, as shown in FIGS. 22 and 23, a success rate of almost 100% can be achieved without repeating the carrier sense CS for the RIT Data Request Frame. Rather, if CSMA / CA that repeatedly performs carrier sense CS on the RIT Data Request Frame is adopted, the RIT Data Request Frame is always transmitted and occupies the radio wave band, thereby lowering the success rate of establishing other communication links. It becomes a factor.

  That is, in the case of the conventional CSL-based system, the success rate is expected to be improved by adopting CSMA / CA rather than Pre-CS. However, the F-RIT system used in the wireless communication system 100 is different from the conventional one. Conversely, Pre-CS is more suitable for improving the success rate of establishing a communication link than CSMA / CA, and the radio wave use efficiency can be improved. Further, as a result of Pre-CS, the RIT Data Request Frame may not be transmitted, so that it is possible to further suppress power consumption.

  In addition, as shown in FIGS. 6 to 8, in the Pre-CS, the number and duration of the carrier sense CS can be suppressed as compared with the CSMA / CA, so that the number of transmissions of the RIT Data Request Frame can be reduced. In addition to the reduction, it is possible to further reduce power consumption.

In addition, as shown in FIGS. 11B and 12, when the intermittent operation interval T is equal to or larger than a predetermined value, the power consumption performance becomes superior as the frequency λ _{Link at} which the sender generates a communication link establishment request increases, the ratio between the power consumption P _t and the power consumption P _r per unit according to the received operation time becomes more and dominant large.

Regarding the success rate of establishing a communication link when Pre-CS is not introduced, as shown in FIG. 16, the superiority increases when the intermittent operation interval T is set to be large. Also, as can be seen from Equations 9 and 10, and FIGS. 19 and 20, the higher the frequency λ _Link , the higher the advantage.

As described above, when the frequency of data transmission λ _Link is high and the intermittent operation interval T is set large to improve power consumption performance, the transmission success rate of the F-RIT scheme is higher than that of the CSL-based scheme, It was shown that the radio use efficiency was excellent. Furthermore, the transmission success rate of the F-RIT method is evaluated by computer simulation, and by introducing the Pre-CS function, the communication link establishment success rate is improved up to about 20 times at the maximum, and the communication frequency λ _Link is 0.1s. ^Even under practical conditions of ^-1 and T _Data = 100 ms, a transmission success rate of nearly 100% can be achieved.

  In addition, the F-RIT method achieves excellent power consumption performance, high transmission success rate, and radio wave use efficiency by appropriately setting the ID time length and the intermittent operation interval even under conditions of high terminal density and high access frequency. An extremely practical MAC protocol that is compatible with the gas utility and water utility and is required for the realization of a Smart Utility Network (SUN). It is.

  Therefore, if the reception power of the wireless IC is reduced in the future and a high-efficiency transceiver having a large transmission / reception power ratio is realized, the effectiveness of the F-RIT scheme will become more remarkable. SUN can be deployed on an IP network by combining it with an IP upper layer optimized for the F-RIT method that realizes high radio use efficiency and low power consumption performance under high-density terminal environment, high access frequency conditions . For this reason, it is thought that it will be possible to realize a network of sensors where it is difficult to identify a communication partner on a regular basis, such as an unprecedented ultra-high-density sensor arrangement and energy harvesting sensor. It is considered that the F-RIT method can greatly contribute.

  As described above, the preferred embodiments of the present invention have been described with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such embodiments. It is obvious that those skilled in the art can conceive various changes or modifications within the scope of the claims, and these naturally belong to the technical scope of the present invention. I understand.

  For example, in the above-described embodiment, the case where the F-RIT method is applied to the multi-hop communication has been described. However, the present invention is not limited to the multi-hop communication. It can also be used in a communication mode for communicating to Specifically, there is an application example in which a plurality of sensors for home security are arranged in a house or the like, and a wireless device provided in each sensor individually communicates with a repeater.

  In addition, a program that causes a computer to function as the wireless device 110 and a computer-readable storage medium such as a flexible disk, a magneto-optical disk, a ROM, a CD, a DVD, and a BD that stores the program are also provided. Here, the program refers to data processing means described in an arbitrary language or description method.

  INDUSTRIAL APPLICABILITY The present invention can be used for a wireless communication system in which a plurality of wireless devices perform RIT communication.

A Transmitter B, C Receiver CS Carrier sense TDF Target data RFc frame (RIT Data Request Frame)
100 wireless communication system 160 communication control unit (transmission side control unit, reception side control unit)

Claims (2)

A wireless communication system for performing RIT communication in which a receiver periodically attempts to transmit a RIT Data Request Frame to a transmitter,
The receiver,
After transmitting the RIT Data Request Frame to the transmitter, a reception-side control unit that is in a reception standby state for a predetermined period,
The transmitter is
If there is target data that is data to be transmitted, it enters a reception standby state. When the RIT Data Request Frame is received from the receiver in the reception standby state, the transmission-side control unit transmits the target data to the receiver. With
The receiving side control unit,
Prior to the transmission of the RIT Data Request Frame, carrier sense for measuring the received radio wave intensity of the frequency band is performed by shifting to a reception standby state of the frequency band used for transmission, and the received radio wave intensity of the frequency band is set to a threshold. Is exceeded, the reception standby state is not continued, the reception standby state is released, the transmission of the current RIT Data Request Frame is stopped, and the carrier is not transmitted until the next transmission timing of the RIT Data Request Frame. Pause sense ,
The transmitting side control unit,
After receiving the RIT Data Request Frame, before transmitting the target data, the address information of the receiver indicated in the RIT Data Request Frame is transmitted to the receiver in a frame separate from the target data,
The receiving side control unit,
Only when the address information of the own device is received in the reception standby state, is the subsequent transmission of the target data stored in a frame different from the frame in which the address information of the own device is stored. A wireless communication system, characterized by: The receiving side control unit,
The wireless communication system according to claim 1, wherein the RIT Data Request Frame including only the address information of the receiver as address information is transmitted to the transmitter.

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