JP5142283B2 - Wireless packet communication method and system - Google Patents

Description

  The present invention relates to a wireless packet communication method and system for performing data packet communication between a wireless base station that performs wireless packet communication using a common wireless channel and a wireless terminal, and more particularly to a wireless personal area based on the IEEE 802.15.4 standard. The present invention relates to a radio packet communication method and system suitable for reducing the amount of discarded packets, especially for reducing power consumption in a radio terminal in the environment.

  A wireless LAN (Local Area Network) reduces the space for a cable as compared with a wired LAN, and portable terminals such as notebook personal computers (notebook PCs) impair portability. There are advantages such as being able to connect to a LAN without any problems. In addition, since the wireless LAN itself has become faster and cheaper, the practical use of the wireless LAN is further accelerated. Against this background, standardization of wireless LAN is being promoted by the Institute of Electrical and Electronics Engineering (IEEE).

  Particularly in a wireless packet communication system typified by a wireless LAN, contention of wireless resources among a plurality of terminals is regarded as a problem. In order to avoid the competition of radio resources, medium access control (MAC) is necessary. As a MAC protocol in this wireless LAN, a so-called carrier sense in which a terminal detects a carrier wave of another terminal before transmitting a packet, and when the carrier cannot be captured, a CSMA (Carrier Sense Multiple Access) is transmitted. ) Method has been proposed. Also, a CSMA / CA scheme (Carrier Sense Multiple Access with Collision Avoidance) is proposed in which a mechanism for avoiding packet collision is added to the CSMA scheme.

  In this CSMA / CA system, when communication is started and a response of an ACK (Acknowledge) signal is received from the wireless node of the communication partner, it is considered that communication is successful, and when an ACK signal is not received In this system, it is assumed that a communication collision with another wireless node has occurred, and the packet data is retransmitted again with a back-off time.

  In particular, in recent years, the CSMA / CA system is increasingly compliant with the IEEE 802.15.4 standard. The IEEE 802.15.4 standard is wireless communication using frequencies near 868 MHz, 915 MHz, and 2.45 GHz, and is particularly used for short-range communication for home appliances such as Zigbee (registered trademark). Zigbee (registered trademark) uses the PHY layer and the MAC layer defined in the IEEE 802.15.4 standard and standardizes the network layer and application layer above it. This Zigbee (registered trademark) makes it possible to realize ultra-low power consumption, downsizing, and low cost by making use of the features of the IEEE 802.15.4 standard.

  In this way, the IEEE 802.15.4 standard is not only for sensor networks, but also for realizing a ubiquitous network society in the future in addition to home networks, office networks, and communication networks with various medical devices attached to the human body. It is also attracting attention as a key technology.

  In wireless communication based on the IEEE 802.15.4 standard, short-range wireless communication is performed between an NC (Network-Coordinator) 71 that controls the network 7 and a plurality of EDs (End Devices) 72, as shown in FIG. Is common. Incidentally, as an example of the network 7, various network forms such as a star type, a tree type, and a mesh type can be selected.

  In wireless communication based on the IEEE 802.15.4 standard, a so-called superframe structure using a beacon is used. In this superframe structure, a CAP (Contention Access Period) in which all EDs 72 can access the beacon interval, a CFP (Contention Free Period) that can be accessed exclusively by a specific ED 72, and an inactive period in which all EDs 72 are prohibited from accessing. It is divided into. Further, the CFP is divided into seven equal parts by a GTS (Guaranty time Slot) mechanism, and can be assigned to the ED 72 to which communication is preferentially performed.

As conventional wireless packet communication systems based on the IEEE 802.15.4 standard, for example, Patent Documents 1 and 2 have been proposed. As techniques for minimizing packet collisions in the CSMA / CA scheme, for example, disclosed techniques of Patent Documents 3 and 4 have been proposed.
JP-A-2005-102218 JP 2008-026310 A JP 2004-242204 A JP 2006-197177 A G. Lu, B. Krishnamachari and CS Raghavendra, “Performance evaluation of the IEEE 802.15.4 MAC for low-rate low power wireless networks,” in Proceedings of the IEEE International Performance Computing and Communication Conference (IPCCC'04), Phoenix, AZ, Apr. 2004, pp. 701-706.

  By the way, in the network 7 shown in FIG. 10 according to the IEEE 802.15.4 standard, the slot of the CFP for incorporating the data flow sent from the ED 72 is predetermined for each ED 72 and fixed. Yes. When data is simultaneously transmitted from a plurality of EDs 72 to the NC 71, data is transmitted from another ED 72 at a very high rate even though there is no data transmitted from one ED 72. There is also. In such a case, in the conventional method described above, a slot that is not used for the one ED 72 has to be secured at all times, and such an empty slot is used for a large amount of data transmitted from another ED 72. Therefore, there is a problem that the slot cannot be used and the slot is wasted. In addition to this, regarding data to be transmitted from other EDs 72, there is a problem in that a CFP slot is not secured and the packet must be discarded.

  In the IEEE 802.15.4 standard, a scheme for reducing the packet discard rate has been proposed in the past (for example, see Non-Patent Document 1). However, each of these schemes has a problem in that it is necessary to make significant changes to the specifications of the ED 72 and thus the entire system, and it becomes difficult to apply to a system that is currently operating at present.

  Furthermore, the conventional super frame structure has a configuration in which the CAP, CFP, and Inactive periods follow the beacon, and thus there is a problem that power consumption cannot be reduced until the CFP ends in the frame. In particular, for the network 7, when the ED 72 is attached to a human body and information on internal organs is detected in real time, it is necessary to reduce the power consumption of the ED 72 as much as possible. For this reason, when applied as a medical communication system, there is a strong demand for lower power consumption particularly in the ED72.

  Therefore, the present invention has been devised in view of the above-described problems, and the object of the present invention is to reduce the packet discard rate by efficiently utilizing the CFP slot, thereby reducing the power consumption. It is an object of the present invention to provide a wireless packet communication method and system capable of performing the above.

  In order to solve the above-described problem, a wireless packet communication method according to the present invention is a wireless packet communication method in which wireless packet communication is performed between a plurality of wireless terminals and a wireless base station. A data information notification step for notifying the wireless base station of data information on data to be transmitted in advance, and a CFP (Contention Free Period) after a beacon on the wireless base station side based on the data information received in the data information notification step The number of slots in the CFP and the inactive period in a frame in which a CAP (Contention Access Period) and an inactive period continue is adjusted, and the slots constituting the CFP are adjusted for each data flow scheduled to be transmitted from each wireless terminal. Further allocation step, and the data flow in the allocation step The SRL update step for updating the slot constituting the CFP allocated for each time by writing it in an SRL (Slot Reservation List), the SRL updated by the SRL update step is referred to, and the CFP allocated for each radio terminal is referred to A slot notifying step for notifying a slot from the radio base station to each radio terminal by the beacon, and each radio terminal sending data to the radio base station for the slot of the CFP notified in the slot notifying step. And a data transmission step of transmitting.

  In order to solve the above-described problem, a wireless packet communication system according to the present invention provides data information on data to be transmitted in a wireless packet communication system that performs wireless packet communication between a plurality of wireless terminals and a wireless base station. In a frame in which a beacon is followed by a CFP (Contention Free Period), a CAP (Contention Access Period), and an Inactive period, based on the wireless terminal that notifies the wireless base station in advance, and the data information received from the wireless terminal. The number of slots in the CFP and the inactive period is adjusted, and an allocation unit that further allocates slots constituting the CFP for each data flow scheduled to be transmitted from each wireless terminal, and allocation for each data flow by the allocation unit In addition, the slots constituting the above CFP are written into the SRL (Slot Reservation List) SRL updating means for updating by means of, and referring to the SRL updated by the SRL updating means, and slot notification means for notifying each wireless terminal of the CFP slot assigned to each wireless terminal by the beacon. Each of the radio terminals transmits data to the radio base station in the CFP slot notified by the slot notifying unit in the radio base station.

  In the present invention having the above-described configuration, the packet discard rate can be kept low, and consequently the average power consumption can be kept low.

  Hereinafter, as a best mode for carrying out the present invention, a wireless packet communication method and system applied to a wireless personal area environment based on the IEEE 802.15.4 standard will be described in detail with reference to the drawings.

  A radio packet communication system 1 to which the present invention is applied includes, for example, as shown in FIG. 1, a plurality of radio terminals 2 and a radio base station 3 that controls the entire network. The wireless packet communication system 1 is a low-speed WPAN (Wireless Personal Area Network) based on the IEEE 802.15.4 standard. The wireless packet communication system 1 is not limited to the star type as shown in FIG. 1, and any network form such as a tree type or a mesh type may be applied.

  Further, in the wireless packet communication system 1, the wireless terminal 2 may be embedded (implanted) in the human body, or attached to the human body. And you may make it arrange | position the wireless base station 3 out of a human body. In such a case, the wireless terminal 2 images the inside of the human body or senses various information in the body, and transmits the acquired data to the wireless base station 3 outside the body. The radio base station 3 receives such data and analyzes it to detect a human body abnormality.

  The wireless terminal 2 can perform wireless packet communication with the wireless base station 3 at least in the WPAN, and further perform wireless packet communication with another wireless terminal 2 via the wireless base station 3. it can. Hereinafter, a case where packet data is wirelessly transmitted from the wireless terminal 2 to the wireless base station 3 will be described as an example. Incidentally, when the wireless terminal 2 is embedded in the human body, it is constituted by a very miniaturized chip.

  Similarly, the wireless base station 3 may have the same configuration as the above-described portable information terminal. The radio base station 3 plays a role as a coordinator. The wireless base station 3 acquires a beacon transmitted from the wireless terminal 2 and synchronizes them with each other in order to connect the wireless terminal 2 to the WPAN.

  The radio packet communication system 1 to which the present invention is applied uses a so-called superframe structure using a beacon 21 as shown in FIG. The superframe has a CFP (Contention Free Period) 22, a CAP (Contention Access Period) 23, and an Inactive period 24 after the beacon 21. Furthermore, the time between the two beacons 21 is divided into a predetermined number of slots regardless of the period of the superframe. In this superframe, the CAP 23 described above is followed by a CFP 22 that can be accessed exclusively by a specific wireless terminal 2 and an inactive period 24 in which all wireless terminals 2 are prohibited from accessing.

  Incidentally, in this superframe structure, the number of slots constituting the CFP 22 and the inactive period 24 is variable, and the number of slots constituting the CAP 23 is fixed. Since the number of slots constituting one frame is also fixed, when the number of CFP 22 slots is increased, the number of slots in the inactive period 24 is reduced accordingly, and the number of slots in the CFP 22 is reduced. In this case, the number of slots in the inactive period 24 is increased accordingly.

  Next, the operation of the wireless packet communication system 1 to which the present invention is applied will be described in detail with reference to FIG. In the example of FIG. 3, a case where data is transmitted from two wireless terminals 2 a and 2 b to one wireless base station 3 is taken as an example.

  First, in step S11, the wireless base station 3 is notified of data information from the wireless terminals 2a and 2b. The notification of the data information in step S11 is data information regarding data to be transmitted by each of the wireless terminals 2a and 2b. For example, when the wireless terminal 2a is going to send data to the wireless base station 3, the operation period, the data rate, etc. are notified as data information regarding the data to be sent. Similarly, the wireless terminal 2b also sends the operation period of the data to be sent, the data rate, etc. as data information. In many cases, the data rates and the like of data to be transmitted to each other are different between the wireless terminal 2a and the wireless terminal 2b. In step S11, the wireless base station 3 that has received the data information described above can acquire in advance various information including the data rate related to the data that the wireless terminal 2a and the wireless terminal 2b intend to send. Become. Note that. The timing of transmission of data information by these wireless terminals 2a and 2b is not limited to being simultaneous, and some intervals may occur.

  Next, the process proceeds to step S12, and the radio base station 3 performs slot allocation. The slot allocation in step S12 is performed based on the data information received by the radio base station 3 in step S11.

  In the allocation of slots in step S12, first, in this superframe structure, the number of slots constituting the CFP 22 and the inactive period 24 is adjusted. For example, when the amount of data to be inserted into the CFP 22 is large, the number of slots constituting the CFP 22 is increased as shown in FIG. Then, the number of slots in the inactive period 24 is decreased by the number of slots increased in the CPF 22. Conversely, when the amount of data to be inserted into the CFP 22 decreases, the number of slots constituting the CFP 22 is decreased. Then, the number of slots in the inactive period 24 is increased by the number of slots decreased in the CPF 22.

  Thus, in the present invention, when the amount of data to be inserted into the CFP 22 is large, the number of slots constituting the CFP 22 is increased so that processing is performed within one frame without straddling a plurality of frames. Thus, the slots constituting the frame can be used efficiently. Conversely, when the amount of data to be inserted into the CFP 22 is small, the number of slots constituting the CFP 22 can be reduced to turn off the power during the CAP 23 and the inactive period 24 after the CFP 22. It becomes possible to reduce electric power. That is, according to the present invention, when the amount of data received is likely to decrease, the power consumption can be reduced by increasing the proportion of slots constituting the CAP 23 and the inactive period 24.

  In this step S12, after adjusting the CFP 22 and the number of slots constituting the inactive period 24, the slots constituting the CFP 22 are further allocated for each data flow scheduled to be transmitted from each of the wireless terminals 2a and 2b. . For example, as shown in FIG. 4, it is possible to identify that the data flow from the wireless terminals 2a and 2b is scheduled to be transmitted over the flows F1 to F4 based on the received data information. To do. In such a case, the jth frame (jth frame) between the j-1th frame ((j-1) th frame) and the j + 1th frame ((j + 1) th frame) FIG. 4 shows an example in which the flows F1 to F4 are configured in the order of the flow F2, the flow F1, the flow F4, and the flow F3.

  In step S12, each slot of the CFP 22 is allocated in advance in order to insert these data flows into the frame. At this time, it is identified based on the above-described data information that 49 slots are required as a total of CFP 22 slots for the flows F1 to F4. First, the number of slots of the CFP 22 and the inactive period 24 is adjusted so as to secure 49 slots as slots of the CFP 22. Incidentally, in the figure, the number assigned to the lower side of the j-th frame is the slot number. It is. This slot No. 1 to 5 are assigned to the beacon 21. Therefore, the CFP 22 has a slot No. 6 to 53 will be assigned. Next, for the CFP 22, and for the flow F2, the slot No. 6 to 13 for slot F. 14 to 29 for slot F. 30 to 45 and a slot No. for the flow F3. 46 to 53 are assigned.

  In the data information transmitted in step S11 described above, information on the data amount in each of the flows F1 to F4 is also described. Therefore, by acquiring the data amount information from the data information for each of the flows F1 to F4, it is possible to determine how much the slots of the CFP 22 should be allocated for each of the flows F1 to F4. As a result, as described above, the slots of the CFP 22 as described above can be allocated to the flows F1 to F4 according to the size of the data amount.

  Next, the process proceeds to step S13, and the radio base station 3 writes information to an SRL (Slot Reservation List). This SRL is recorded on a recording medium such as a hard disk or a memory mounted on the radio base station 3, for example. If necessary, the SRL is accessed by accessing the recording medium on which the SRL is recorded. The written information can be read out.

  FIG. 5 shows an example in which slot assignments are actually written to the SRL in step S13. In the case of the j-th frame, the flow F2, the flow F1, the flow F4, and the flow F3 are described from the top in this order, and NS and NL are described for each of the flows F1 to F4.

  This NS is the slot number where data writing is started. NL indicates the number of slots necessary for data writing for each flow. The radio base station 3 updates this by writing information to this SRL as needed. This writing of information to the SRL means reservation of a slot for data transmitted from the wireless terminal 3 in the future.

Incidentally, this slot reservation is performed on a frame basis. For example, as shown in FIG. 6, the data packet from the wireless terminal 2 is transmitted at timing d _{k (i−1)} , timing d _ki , timing d _{k (i + 1)} , timing d _{k (i + 2)} . Suppose that the length of one frame is _TF . Also, for the current data transmission sent at timing d _ki , the jth frame specified by TD _ki , and the next data transmission sent at timing d _{k (i + 1)} Is assigned the j + 1-th frame specified by RD _ki .

In such a case, in the present invention, the adjustment of the number of slots of the CFP 22 and the allocation of the slots constituting the CFP 22 for each data flow transmitted from each wireless terminal 2 are added to the current data transmission, and the next data transmission Also run for minutes. That is, not only the j-th frame specified by TD _ki but also the reservation of the slot for the j + 1-th frame specified by the next RD _ki is reserved. Information about the reserved slot is written into the SRL described above.

Also, if the current data transmission is the data sent at timing d _{ki + 1} , the TD _{ki + 1} specifies the j + 1th frame, and it is specified by RD _{ki + 1.} Is the j + 2th frame. The j + 2th frame is a frame assigned at the next data transmission, and the slot is reserved in advance. In this way, while shifting sequentially TD _k and RD _k to the back of the frame, make a reservation for two times of the slot of the current data transmission and the next data transmission, to update the each time SRL.

  Next, the process proceeds to step S14, and the slot of the CFP 22 assigned to each of the radio terminals 2a and 2b in the previous step S13 is notified by the beacon 21 from the radio base station 3 to each radio terminal 2a and 2b. At this time, the radio base station 3 refers to the updated SRL, reads information regarding the slot written therein, and transmits this to the radio terminals 2a and 2b. The radio base station 3 does not transmit the information about all slots described in the SRL to the radio terminals 2a and 2b, but the slots related to the data flows scheduled to be transmitted by the radio terminals 2a and 2b. Can be notified. For example, among the flows F1 to F4 described above, when the flows F1 and F2 are scheduled to be transmitted by the wireless terminal 2a and the flows F3 and F4 are scheduled to be transmitted by the wireless terminal 2b, the wireless terminal 2a Is transmitted to the wireless terminal 2b is information related to the slots assigned to the flows F3 and F4.

  Next, the process proceeds to step S15, and each of the radio terminals 2a and 2b transmits data to the radio base station 3 to the slot of the CFP 22 notified in step S14. As a result, the radio base station 3 can insert data from the radio terminals 2a and 2b into the slots reserved in advance.

  According to the wireless packet communication method to which the present invention is applied, the following effects can be obtained.

  FIG. 7 shows a simulation result of the packet discard rate with respect to the number N of wireless terminals 2. In FIG. 7, DC indicates an operation cycle (= 1, 0.5). For comparison, the packet discard rate in the conventional IEEE 802.15.4 specification in addition to the packet discard rate in the present invention example is compared. Show.

  In either case, the packet discard rate increased as the number N of wireless terminals 2 increased. Further, the packet loss rate of the example of the present invention is lower than that of the conventional specification. In particular, when the number N of the wireless terminals 2 is large, there is a tendency that the difference in the packet discard rate compared with the conventional specification is further increased. In addition, as DC decreases, the packet discard rate tends to increase.

  As described above, in the present invention, since the slot allocation in step S12 described above is executed, it is possible to allocate a slot not to be used to the wireless terminal 2 desiring to transmit other data. It is possible to prevent the packet from being discarded due to being not secured.

  FIG. 8 shows a simulation result of the average delay time (ms) with respect to the number N of wireless terminals 2. In FIG. 8, the transmission of data information in step S11 is represented as “Request”, and the data transmission in step S15 is represented as “Data”. As a result, in any case, the average delay time increased as the number N of wireless terminals 2 increased. Incidentally, in the example of the present invention, the processing time increases as the above-described steps S11 to 14 are newly added as compared with the conventional example, and the packet transmission is slightly performed as compared with the conventional specification. The average delay time was increasing.

  FIG. 9 shows the relationship of average power consumption with respect to the number N of wireless terminals 2. Incidentally, this average power consumption was simulated for both the wireless terminal 2 and the wireless base station 3. As a result, in the example of the present invention, the power consumption of the wireless terminal 2 and the wireless base station 3 tends to decrease as compared with DC = 1 of the conventional example. In particular, it was found that the power consumption can be significantly reduced in the wireless terminal 2 as compared with the conventional example. The reason is that the CFP 22 is followed by the CAP 23 and the Inactive period, so that the power can be turned off as described above, and the power is also turned off during the period on the wireless terminal 2 side as well. This is because power consumption can be reduced. In particular, the present invention that can reduce the power consumption of the wireless terminal 2 is suitable particularly when the wireless terminal 2 is mounted in a human body and internal organ information is detected in real time.

It is a figure which shows the system configuration | structure in the radio | wireless packet communication system to which this invention is applied. It is a figure which shows a super-frame structure. It is a figure which shows the control flow of the radio | wireless packet communication system to which this invention is applied. It is a figure which shows the example which allocated the slot which comprises CFP for every data flow which is due to be transmitted from each wireless terminal. It is a figure which shows the example which wrote the allocation of the slot in SRL. It is a figure for demonstrating the slot reservation method by the radio | wireless packet communication system to which invention is applied. It is a figure which shows the simulation result of the packet discard rate with respect to the number N of wireless terminals. It is a figure which shows the simulation result of the average delay time (ms) with respect to the number N of radio | wireless terminals. It is a figure which shows the relationship of the average power consumption with respect to the number N of wireless terminals. 1 is a diagram illustrating a wireless communication network according to a general IEEE 802.15.4 standard. FIG.

1 wireless packet communication system 2 wireless terminal 3 wireless base station 21 beacon 22 CFP
23 CAP
24 Inactive period

Claims (8)

In a wireless packet communication method for performing wireless packet communication between a plurality of wireless terminals and a wireless base station,
A data information notification step of notifying the wireless base station in advance of data information related to data to be transmitted by each wireless terminal;
Based on the data information received in the data information notification step, on the radio base station side, the CFP and the Inactive in a frame in which a beacon is followed by a CFP (Contention Free Period), a CAP (Contention Access Period), and an Inactive period. An allocation step of adjusting the number of slots in the period and further allocating slots constituting the CFP for each data flow scheduled to be transmitted from each wireless terminal;
An SRL update step for updating the slot constituting the CFP assigned for each data flow in the assignment step by writing it in an SRL (Slot Reservation List);
A slot notification step of referring to the SRL updated in the SRL update step and notifying each wireless terminal of the CFP slot allocated to each wireless terminal from the wireless base station by the beacon;
A wireless packet communication method comprising: a data transmission step in which each of the wireless terminals transmits data to the wireless base station for the CFP slot notified in the slot notification step. In the assignment step, the adjustment of the number of slots of the CFP and the assignment of the slots constituting the CFP for each data flow transmitted from each wireless terminal are added to the current data transmission and the next data transmission Also run about
In the SRL update step, the number of slots of the CFP adjusted in the allocation step and the slots constituting the CFP allocated for each data flow are added to the current data transmission, and the next data transmission is stored in the SRL. The wireless packet communication method according to claim 1, wherein updating is performed by writing. The wireless packet communication method according to claim 1 or 2, wherein, in the data information notifying step, an operation cycle and a data rate are notified as the data information. The wireless packet communication method according to any one of claims 1 to 3, wherein the wireless packet communication protocol conforms to the IEEE 802.15.4 standard. In a wireless packet communication system that performs wireless packet communication between a plurality of wireless terminals and a wireless base station,
A wireless terminal that notifies the wireless base station in advance of data information related to data to be transmitted;
Based on the data information received from the wireless terminal, the number of slots in the CFP and the Inactive period in a frame in which a CFP (Contention Free Period), a CAP (Contention Access Period), and an Inactive period follow the beacon is adjusted. Allocation means for further assigning slots constituting the CFP for each data flow scheduled to be transmitted from each wireless terminal, and slots constituting the CFP assigned for each data flow by the assignment means are assigned to SRL (Slot Reservation List). SRL updating means for updating by writing to the SRL, and slot notifying means for referring to the SRL updated by the SRL updating means and notifying each wireless terminal of the CFP slot allocated for each wireless terminal by the beacon A wireless base station comprising
Each of the wireless terminals transmits data to the wireless base station to the CFP slot notified by the slot notification means in the wireless base station. The assigning means adjusts the number of CFP slots and assigns slots constituting the CFP for each data flow transmitted from each wireless terminal in addition to the current data transmission, Also run about
The SRL updating means adds the number of slots of the CFP adjusted in the assigning step and the slots constituting the CFP assigned for each data flow to the current data transmission, and stores the next data transmission in the SRL. The wireless packet communication system according to claim 5, wherein the wireless packet communication system is updated by writing. The wireless packet communication system according to claim 5 or 6, wherein the wireless terminal notifies an operation cycle and a data rate as the data information. The wireless packet communication system according to any one of claims 5 to 7, wherein the wireless packet communication protocol conforms to the IEEE 802.15.4 standard.

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