Terminal and communication method

Abstract

This terminal comprises: a schedule reception unit that receives a schedule that is broadcast and defines the transmission order of uplink transmission of the terminal and other terminals; a transmission order grasping unit that, on the basis of the schedule, grasps a preceding terminal that performs uplink transmission immediately before the terminal does; a notification reception unit that receives a transmission complete notification that is broadcast in a time unit in which uplink transmission is performed by the preceding terminal and indicates completion of uplink transmission; and a transmission determination unit that determines uplink transmission from the terminal when the transmission complete notification is a notification broadcast from the grasped preceding terminal.

Description

Terminal and communication method

[0001] The present disclosure relates to a terminal and a communication method.

[0002] Wireless LANs (IEEE802.11) use CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) for access control. In CSMA / CA, a terminal such as a station (STA) performs carrier sensing before transmitting a signal. If the terminal does not detect a carrier through carrier sensing, it transmits a signal. If the terminal detects a carrier through carrier sensing, it waits for a specified time and then performs carrier sensing again.

[0003] A known drawback of the CSMA / CA system is that throughput decreases when multiple terminals simultaneously attempt to transmit signals to a base station such as an AP (Access Point) (in the event of congestion). One of the causes of this is that carrier sense does not function effectively due to the hidden terminal problem, making signal collisions more likely to occur. When signals collide, data transmission and reception is not completed correctly, which prompts data retransmission, and in some cases leads to a vicious cycle of further bandwidth congestion.

[0004] Patent Document 1 proposes a CSMA wireless communication system that can save power.

[0005] Japanese Patent Application Laid-Open No. 2005-252692

[0006] As described above, the CSMA / CA system has a problem in that the throughput may decrease when signal congestion occurs.

[0007] Non-limiting examples of the present disclosure contribute to providing a terminal and a communication method that avoid signal congestion and suppress a decrease in throughput.

[0008] A terminal according to one embodiment of the present disclosure includes a schedule receiving unit that receives a broadcast schedule that determines the transmission order of upstream transmissions for the terminal and other terminals; a transmission order grasping unit that grasps the previous terminal that will perform upstream transmission one terminal before the terminal based on the schedule; a notification receiving unit that receives a transmission completion notification that is broadcast in the time unit in which the grasped previous terminal performs upstream transmission and indicates the completion of the upstream transmission; and a transmission determination unit that determines the upstream transmission from the terminal if the transmission completion notification is a notification broadcast from the grasped previous terminal.

[0009] In a communication method according to one embodiment of the present disclosure, a terminal receives a broadcast schedule that determines the order of upstream transmissions for the terminal and other terminals, identifies the previous terminal that will perform upstream transmission one terminal before the terminal based on the schedule, receives a transmission completion notification that is broadcast in the time unit in which the identified previous terminal performs upstream transmission and indicates the completion of the upstream transmission, and if the transmission completion notification is a notification broadcast from the identified previous terminal, determines to perform upstream transmission from the terminal.

[0010] In addition, these comprehensive or specific aspects may be realized by a system, an apparatus, a method, an integrated circuit, a computer program, or a recording medium, or may be realized by any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a recording medium. According to an embodiment of the present disclosure, signal congestion can be avoided and a decrease in throughput can be suppressed.

[0011] Further advantages and benefits of an embodiment of the present disclosure will become apparent from the specification and drawings. Such advantages and / or benefits may be provided by some of the embodiments and features described in the specification and drawings, respectively, but not necessarily all of them may be provided to obtain one or more identical features.

[0012] FIG. 1 is a diagram illustrating an example configuration of a communication system according to an embodiment of the present disclosure. FIG. 2 is a diagram illustrating an overview of the operation of the communication system. FIG. 3 is a diagram illustrating a processing layer. FIG. 4 is a diagram illustrating an example frame configuration. FIG. 5 is a diagram illustrating an example configuration of FCMS. FIG. 6 is a diagram illustrating an example configuration of MDS placement information. FIG. 7 is a diagram illustrating an example configuration of MDS. FIG. 8 is a diagram illustrating an example configuration of ACTS.

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings as appropriate. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or redundant explanation of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following explanation and to facilitate understanding by those skilled in the art.

[0014] The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0015] <System Configuration> Fig. 1 is a diagram showing an example configuration of a communication system according to an embodiment of the present disclosure. As shown in Fig. 1, the communication system includes terminals 1a to 1d, a base station 2, and an information processing device 3.

[0016] Terminals 1a to 1d are, for example, cameras installed in an office or store. Terminals 1a to 1d transmit data such as image data to base station 2. Hereinafter, when terminals 1a to 1d are not to be distinguished from one another, they may be simply referred to as terminal 1. Terminals 1a to 1d may also be referred to as STAs. Base station 2 wirelessly communicates with terminal 1 based on a wireless LAN (IEEE802.11) communication method. Base station 2 communicates with information processing device 3 via a network such as a LAN or the Internet. Base station 2 may also be referred to as AP.

[0017] The information processing device 3 is, for example, a server or a personal computer. The information processing device 3 schedules (instructs) upstream transmission of the terminal 1. The upstream transmission may mean transmission of an upstream signal.

[0018] 1, the terminals 1a to 1d are illustrated as cameras, but are not limited to this. The terminals 1a to 1d may also be IoT (Internet of Things) devices such as temperature sensors.

[0019] Furthermore, the information processing device 3 may process data transmitted from the terminal 1 in addition to scheduling upstream transmission in the terminal 1. For example, the information processing device 3 may perform image recognition processing on image data transmitted from the terminal 1.

[0020] Furthermore, the information processing device 3 may transmit data transmitted from the terminal 1 to a server such as a cloud server. The cloud server may process the data transmitted from the terminal 1.

[0021] Hereinafter, data may be referred to as a signal. Data and signals may be interpreted interchangeably.

[0022] <Overview of Operation of Communication System> Fig. 2 is a diagram illustrating an overview of operation of the communication system. Fig. 2 shows the terminal 1 and information processing device 3 shown in Fig. 1. Fig. 2 omits the illustration of the base station 2. The terminal 1 and the information processing device 3 exchange data (signals) via the base station 2.

[0023] "SC" shown in FIG. 2 indicates an uplink transmission schedule generated by the information processing device 3. The schedule determines, for example, the transmission order of uplink transmissions from terminal 1. "UL" shown in FIG. 2 indicates an uplink signal transmitted by terminal 1. "C" shown in FIG. 2 indicates a completion signal (transmission completion notification) indicating completion of transmission of the uplink signal. SL0, SL1, SL2, SL3, and SL4 shown in FIG. 2 indicate slots. Gaps are provided between each slot, which indicate inter-slot guard times. A slot may also be referred to as a time unit.

[0024] The information processing device 3 generates a schedule for upstream signals. In the following, the schedule indicates that upstream signals are transmitted in the order of terminal 1a, terminal 1b, terminal 1c, and terminal 1d.

[0025] The information processing device 3 broadcasts the generated schedule to the terminals 1 as indicated by arrow A2e in Fig. 2. Each of the terminals 1 determines (understands) the order in which to transmit an uplink signal based on the broadcast schedule.

[0026] For example, in the above example schedule, terminal 1b knows that it will transmit an uplink signal after terminal 1a. Terminal 1c knows that it will transmit an uplink signal after terminal 1b. Terminal 1d knows that it will transmit an uplink signal after terminal 1c.

[0027] After completing the transmission of the upstream signal, the terminal 1 broadcasts a completion signal indicating the completion of the transmission of the upstream signal.

[0028] For example, when terminal 1a completes transmission of an upstream signal, it broadcasts a completion signal as indicated by arrow A2a. When terminal 1b completes transmission of an upstream signal, it broadcasts a completion signal as indicated by arrow A2b. When terminal 1c completes transmission of an upstream signal, it broadcasts a completion signal as indicated by arrow A2c. When terminal 1d completes transmission of an upstream signal, it broadcasts a completion signal as indicated by arrow A2d.

[0029] The completion signal includes identification information of the terminal 1 that broadcast the completion signal. The terminal 1 decides to transmit an uplink signal based on the schedule and the identification information included in the completion signal. The terminal 1 that has decided to transmit an uplink signal transmits (unicasts) the uplink signal to the information processing device 3 and broadcasts the completion signal as described above.

[0030] For example, as described above, terminal 1b determines based on the schedule that it will transmit an uplink signal after terminal 1a. When terminal 1b receives a completion signal including the identification information of terminal 1a, it decides to transmit an uplink signal. Having decided to transmit an uplink signal, terminal 1b transmits (unicasts) the uplink signal to information processing device 3 as indicated by UL in SL2, and broadcasts the completion signal as indicated by arrow A2b. Note that terminals 1c and 1d are not terminals that will transmit an uplink signal after terminal 1a, and therefore do not decide to transmit an uplink signal even if they receive a completion signal including the identification information of terminal 1a.

[0031] For example, as described above, terminal 1c determines based on the schedule that it will transmit an uplink signal after terminal 1b. When terminal 1c receives a completion signal including the identification information of terminal 1b, it decides to transmit an uplink signal. Having decided to transmit an uplink signal, terminal 1c transmits (unicasts) the uplink signal to information processing device 3 as indicated by UL in SL3, and broadcasts the completion signal as indicated by arrow A2c. Note that terminals 1a and 1d are not the terminals that will transmit an uplink signal after terminal 1b, and therefore do not decide to transmit an uplink signal even if they receive a completion signal including the identification information of terminal 1b.

[0032] For example, as described above, terminal 1d knows that it will transmit an uplink signal after terminal 1c based on the schedule. When terminal 1d receives a completion signal including the identification information of terminal 1c, it decides to transmit an uplink signal. Having decided to transmit an uplink signal, terminal 1d transmits (unicasts) the uplink signal to information processing device 3 as indicated by UL in SL4, and broadcasts a completion signal as indicated by arrow A2d. Note that terminals 1a and 1b are not the terminals that will transmit an uplink signal after terminal 1c, and therefore do not decide to transmit an uplink signal even if they receive a completion signal including the identification information of terminal 1c.

[0033] As explained above, terminal 1 determines the transmission of an uplink signal based on the uplink signal schedule and the broadcast transmission completion signal. This operation causes the uplink signals transmitted by terminal 1 to be transmitted in a trickle pattern, as shown by "UL" in Figure 2. As a result, it is possible to prevent multiple terminals 1 from simultaneously attempting to transmit signals to base station 2 (suppressing congestion of uplink signals), and thus to suppress a decrease in throughput.

[0034] Although not described above, the present disclosure provides a technology that enables stable wireless communication even in an environment where interference waves are present in the surroundings (described in the <Operation Example> below).

[0035] <Processing Layer> When multiple terminals 1 transmit signals, particularly when multiple terminals 1 transmit signals with a uniformly determined amount of data, such as camera images, it is considered effective for the base station 2 to control communication using the TDMA (Time Division Multiple Access) method.

[0036] TDMA control is generally performed at the MAC (Medium Access Control) layer. However, because the MAC layer corresponds to the wireless LAN module and is usually implemented as a hardware chip, it is difficult to change the communication method from CSMA / CA to TDMA. Even if the communication method were to be changed from CSMA / CA to TDMA, it would be costly. Moreover, it is not practical because it would require changing the wireless LAN modules of both terminal 1 (STA) and base station 2 (AP).

[0037] Therefore, in this disclosure, a pseudo-TDMA system controlled by the application layer is proposed.

[0038] Fig. 3 is a diagram explaining layers. Fig. 3 shows layers in a terminal 1, a base station 2, and an information processing device 3. In Fig. 3, APP indicates the application layer. Network indicates the network layer. MAC / LLC indicates the MAC / LLC (Logical Link Control) layer. PHY indicates the physical layer.

[0039] The dotted arrow A3a in Fig. 3 indicates a path of conventional TDMA control, and the solid arrow A3b in Fig. 3 indicates a path of TDMA control according to the present disclosure.

[0040] As indicated by the dotted arrow A3a, conventional TDMA control is performed by the MAC / LLC layer between the terminal 1 and the base station 2.

[0041] In contrast, as indicated by solid arrow A3b, the TDMA control of the present disclosure is performed by the application layers of terminal 1 and information processing device 3. For example, the application layer of information processing device 3 schedules the uplink transmission of terminal 1. The application layer of terminal 1 determines the transmission of the uplink signal based on the schedule of the uplink signal and a transmission completion signal broadcast from terminal 1. This realizes a pseudo-TDMA method.

[0042] By performing TDMA control at the application layer, the TDMA method can be realized by developing software for the information processing device 3 and software (or firmware) for the terminal 1. This allows a pseudo-TDMA method to be realized easily and at low cost.

[0043] <Frame Structure> Fig. 4 is a diagram showing an example of a frame structure. The communication system shown in Fig. 1 performs transmission and reception using a frame made up of multiple slots as one unit. In the example of Fig. 4, a frame is made up of six slots.

[0044] Each slot has an inter-slot guard time after the data body (not shown in FIG. 4). The inter-slot guard time is used as a buffer when transmission is waiting or retransmission control occurs in the MAC layer.

[0045] One frame includes a frame control message slot (FCMS), one or more message data slots (MDS), and an activation slot (ACTS).

[0046] FCMS is a downlink slot (signal) located at the beginning of a frame.

[0047] The MDS and ACTS are uplink slots (signals). The MDS is placed after the FCMS. Figure 4 shows an example of a frame with four MDS1 to MDS4. The ACTS is placed after the MDS.

[0048] After each frame, an inter-frame guard time is provided as shown in Fig. 4. The inter-frame guard time is a grace period during which the information processing device 3 checks the data from the terminal 1 and determines the configuration of the next frame.

[0049] The inter-frame guard time is also used as a buffer to absorb packet delays due to waiting for the entire frame to be transmitted or retransmission at the MAC layer. For example, if data is collected every 15 minutes, the inter-frame guard time is the time until the next data collection starts. The frame is configured to ensure a sufficient inter-frame guard time.

[0050] The following explains FCMS, MDS, and ACTS.

[0051] FCMS Fig. 5 shows an example of the configuration of an FCMS. The FCMS is generated by the information processing device 3. The FCMS is a slot having schedule information for an uplink signal. The FCMS is broadcast to terminals 1, but may also be unicast by specifying one terminal 1, as will be explained in the following modification. The SC of SL0 shown in Fig. 2 may correspond to the FCMS shown in Fig. 5.

[0052] As shown in FIG. 5, the FCMS includes a service identifier, a system time, MDS configuration information, and ACTS configuration information.

[0053] The service identifier is an identifier that identifies the service of the frame. For example, in the case of FCMS, a word indicating pseudo-TDMA is stored as the service identifier.

[0054] The system time is the system time of the information processing device 3. The terminal 1 sets the system time of the information processing device 3, notified via the FCMS, to the clock (or timer) of the terminal 1. This synchronizes the times between the information processing device 3 and the terminal 1. Note that the information processing device 3 may set the system time of the FCMS, taking into consideration that the time of the terminal 1 may lag behind the system time of the information processing device 3 due to delays in the wireless section and delays in application processing.

[0055] The MDS allocation information is information (table) that indicates the schedule of the uplink signal in each terminal 1.

[0056] Fig. 6 is a diagram showing an example of the configuration of MDS arrangement information. As shown in Fig. 6, the MDS arrangement information includes a terminal identifier, a transmission time, retransmission request information, and a received data number.

[0057] The terminal identifier is an identifier assigned to terminal 1. For example, terminal identifier "0001" is an identifier assigned to terminal 1a. For example, terminal identifier "0002" is an identifier assigned to terminal 1b. For example, terminal identifier "0003" is an identifier assigned to terminal 1c. For example, terminal identifier "0004" is an identifier assigned to terminal 1d. The identifier may be the serial number of terminal 1.

[0058] The transmission time indicates the time when the terminal 1 transmits an uplink signal. The transmission time may be any information indicating the time when the uplink signal is transmitted. For example, the transmission time may be indicated by a slot number based on the FCMS shown in FIG. 4 (starting point).

[0059] Each terminal 1 determines the order in which to transmit an upstream signal based on the terminal identifier and transmission time included in the MDS configuration information. For example, assume that the transmission times shown in FIG. 6 are aaaa, bbbb, cccc, and dddd in descending order. In this case, terminal 1a with terminal identifier "0001" and transmission time "aaaa" determines that it will transmit an upstream signal first. Terminal 1b with terminal identifier "0002" and transmission time "bbbb" determines that it will transmit an upstream signal after terminal 1a with terminal identifier "0001" and transmission time "aaaa." Terminal 1c with terminal identifier "0003" and transmission time "cccc" determines that it will transmit an upstream signal after terminal 1b with terminal identifier "0002" and transmission time "bbbb." Terminal 1d with terminal identifier "0004" and transmission time "dddd" understands that it will transmit an upstream signal after terminal 1c with terminal identifier "0003" and transmission time "cccc." Terminal 1 determines the transmission of an upstream signal based on the transmission order of the upstream signals understood based on the MDS arrangement information and an upstream signal transmission completion notification, which will be described later.

[0060] The retransmission request information indicates a request for retransmission of an uplink signal. For example, retransmission request information "0" indicates that there is no request for retransmission of an uplink signal. Retransmission request information "1" indicates that there is a request for retransmission of an uplink signal.

[0061] If the retransmission request information is "0", the terminal 1 transmits the untransmitted data to the information processing device 3. If the retransmission request information is "1", the terminal 1 transmits the data with the next number of the received data number, which will be explained below, to the information processing device 3. When making a retransmission request to the terminal 1, the information processing device 3 may determine the transmission time of the uplink signal taking into consideration the data length of the retransmission request.

[0062] The received data number indicates the data number of data that has been completely received by the information processing device 3. The data number is cyclically assigned by the terminal 1.

[0063] Returning to the explanation of Fig. 5, the ACTS allocation information is information that notifies a new terminal 1 that wishes to join the communication system of Fig. 1 of the time unit (ACTS in Fig. 4) in which transmission of a join request is permitted. The new joining terminal 1 transmits a join request in the ACTS notified by the ACTS allocation information. The join request will be explained below in "ACTS".

[0064] MDS The MDS is a slot in which the terminal 1 transmits an uplink signal. As shown in Fig. 4, the MDS is placed after the FCMS. The number of MDSs can be equal to the number of terminals 1 accommodated in the communication system.

[0065] The MDS is assigned to terminal 1 according to the MDS configuration information of the FCMS. For example, in the example of Fig. 4, MDS1 may be assigned to terminal 1a, MDS2 may be assigned to terminal 1b, MDS3 may be assigned to terminal 1c, and MDS4 may be assigned to terminal 1d.

[0066] Note that UL and C of SL1 shown in Fig. 2 may correspond to MDS1 shown in Fig. 4. UL and C of SL2 shown in Fig. 2 may correspond to MDS2 shown in Fig. 4. UL and C of SL3 shown in Fig. 2 may correspond to MDS3 shown in Fig. 4. UL and C of SL4 shown in Fig. 2 may correspond to MDS4 shown in Fig. 4.

[0067] Fig. 7 shows an example of the configuration of an MDS. The MDS is generated by terminal 1. As shown in Fig. 7, the MDS includes configuration information, data, and a transmission completion notification. An inter-slot guard time is provided after the data body of the MDS.

[0068] The configuration information is information (table) such as file names and data numbers of data transmitted by the terminal 1. Data numbers are assigned cyclically.

[0069] The data is data transmitted by the terminal 1. For example, if the terminal 1 is a camera, the data may be image data from the camera. Hereinafter, the configuration information and data may be simply referred to as data.

[0070] The data is transmitted, for example, by TCP (Transmission Control Protocol) unicast to the information processing device 3. The local IP address of the information processing device 3 is acquired from the source IP address of the FCMS.

[0071] The transmission completion notice indicates the completion of data transmission. After the terminal 1 completes the data transmission, it broadcasts the transmission completion notice.

[0072] The transmission completion notification includes the terminal identifier of the terminal that has completed data transmission (the terminal identifier of the terminal that broadcasts the transmission completion notification). Other terminals that receive the transmission completion notification identify the terminal that has completed data transmission based on the terminal identifier included in the transmission completion notification. The terminal that identified the terminal decides to transmit data if it is the terminal that will transmit data next after the identified terminal (the terminal that has completed data transmission). The terminal that decided to transmit data transmits the data at, for example, the transmission time of the MDS placement information described in FIG. 6.

[0073] The slot length of the MDS may be variable. For example, when a retransmission request is made, the slot length of the MDS may be set to be long in consideration of the data that has not yet been transmitted and the data that will be retransmitted.

[0074] Furthermore, multiple MDSs may be assigned to one terminal 1. When a retransmission request is made, multiple MDSs may be assigned to one terminal, taking into consideration the data that has not yet been transmitted and the data that will be retransmitted.

[0075] ACTS ACTS is a slot for a terminal 1 newly joining the communication system to transmit a join request. ACTS is allocated after MDS (see FIG. 4) according to ACTS allocation information of FCMS (see FIG. 5). Note that the slot corresponding to ACTS is not shown in FIG. 2.

[0076] 8 is a diagram showing an example of the configuration of an ACTS. The ACTS is generated by the terminal 1. The ACTS may be transmitted by TCP unicast. The local IP address of the information processing device 3 is obtained from the source IP address of the FCMS.

[0077] As shown in Fig. 8, an ACTS contains a join request. The join request includes a terminal identifier such as the IP address and serial number of the terminal 1 sending the join request, and a request message. An inter-slot guard time is provided after the data body of the ACTS.

[0078] A new joining terminal 1 sends a join request within the ACTS period specified in the ACTS allocation information of the FCMS, but to avoid collisions when multiple terminals 1 send join requests, the terminal waits a random amount of time from the start of the ACTS before sending. If collisions still occur, they can be avoided by using CSMA / CA control in IEEE802.11.

[0079] When a terminal 1 newly joins the communication system, it first establishes a link with the base station 2. This link establishment is performed according to the IEEE802.11 procedure. For example, an authentication sequence is performed in which the base station 2 transmits a beacon frame and assigns an IP address using DHCP (Dynamic Host Configuration Protocol).

[0080] The information processing device 3 designs the slot timing taking into consideration that the transmission of the beacon frame and the authentication sequence are performed at timings that cannot be grasped by the information processing device 3. For example, the information processing device 3 may absorb jitter caused by the transmission of the beacon frame and the execution of the authentication sequence by using an inter-slot guard time.

[0081] <Operation Example> In the following, an operation example in which the terminal 1 goes to sleep will be described, but the terminal 1 does not have to go to sleep.

[0082] Operation Example 1 (No Delay) Fig. 9 is a diagram illustrating operation example 1 of the communication system. Arrow A9a in Fig. 9 indicates the schedule generated by the information processing device 3. In the example of Fig. 9, slots MDS0 to MDS11 are scheduled. In the following, the terminals transmitting data in MDS0, MDS1, ..., MDS10, and MDS11 are defined as terminals T0, T1, ..., T10, and T11, respectively.

[0083] Arrow A9b in Fig. 9 indicates the timing of actual UL transmission. In the example of Fig. 9, terminals T0 to T3 perform UL transmission according to the schedule. In other words, terminals T0 to T3 perform UL transmission according to the transmission time included in the MDS configuration information of the FCMS.

[0084] An arrow A9c in Fig. 9 indicates the operation of terminal T3 transmitting data in MDS 3. In other words, arrow A9c in Fig. 9 indicates the operation of terminal T3 to which MDS 3 is assigned.

[0085] Terminal T3 knows the terminal (previous terminal) that will transmit data immediately before terminal T3 based on the MDS arrangement information (schedule) of the FCMS. Since terminal T3 transmits data in MDS3, it knows terminal T2 that will transmit data in MDS2, which is immediately before MDS3.

[0086] Terminal T3 wakes up from sleep in the slot immediately before the slot in which terminal T3 transmits data. In the example of Fig. 9, terminal T3 transmits data in MDS3, so it wakes up in MDS2, which is immediately before MDS3. Terminal T3 determines the wake-up time based on the transmission time included in the MDS configuration information.

[0087] Terminal T3, which has woken up from sleep, receives a transmission completion notification broadcast by MDS2, which is immediately before MDS3, as indicated by arrow A9ca in Fig. 9. That is, terminal T3 receives a transmission completion notification from terminal T2 (the previous terminal that transmits data immediately before the data transmission of terminal T3) that it has grasped based on the schedule.

[0088] When terminal T3 receives the transmission completion notification from terminal T2 (the transmission completion notification including the terminal identifier of terminal T2), it decides to transmit data. Terminal T3 transmits data at the transmission time for terminal T3 included in the MDS arrangement information. For example, terminal T3 transmits data in MDS3 as shown by arrow A9cb in Figure 9. After transmitting the data, terminal T3 goes to sleep.

[0089] Operation Example 2 (When There is a Delay of 1 Slot) Fig. 10 is a diagram illustrating operation example 2 of the communication system. Arrow A10a in Fig. 10 indicates the schedule generated by the information processing device 3. In the example of Fig. 10, MDS0 to MDS11 are scheduled. As in Fig. 9, the terminals transmitting data in MDS0 to MDS11 are terminals T0 to T11.

[0090] Arrow A10b in Fig. 10 indicates the actual timing of UL transmission. In the example of Fig. 10, terminals T0 and T1 perform UL transmission in slot times according to the schedule. Terminal T2 is subjected to interference as indicated by arrow A10ba in Fig. 10, resulting in a one-slot delay in data transmission.

[0091] An arrow A10c in Fig. 10 indicates the operation of terminal T3 transmitting data in MDS 3. In other words, arrow A10c in Fig. 10 indicates the operation of terminal T3 to which MDS 3 is assigned.

[0092] Terminal T3 knows the terminal (previous terminal) that will transmit data immediately before terminal T3 based on the MDS arrangement information (schedule) of the FCMS. Since terminal T3 transmits data in MDS3, it knows terminal T2 that will transmit data in MDS2, which is immediately before MDS3.

[0093] Terminal T3 wakes up from sleep in the slot immediately before the slot in which terminal T3 transmits data. In the example of Fig. 10, terminal T3 transmits data in MDS3, and therefore wakes up in MDS2, which is immediately before MDS3, as shown by arrow A10ca in Fig. 10. Terminal T3 determines the time to wake up based on the transmission time included in the MDS configuration information.

[0094] Terminal T3, which has woken up from sleep, receives a transmission completion notification broadcast by MDS2, which is immediately before MDS3, as indicated by arrow A10ca in Fig. 10. That is, terminal T3 receives a transmission completion notification from terminal T2 (the previous terminal that transmits data immediately before the data transmission of terminal T3) that it has grasped based on the schedule.

[0095] 10, a data transmission delay of one slot occurs in MDS2 (terminal T2) as indicated by arrow A10ba. Therefore, in the operation of receiving the transmission completion notification as indicated by arrow A10ca, terminal T3 does not receive the transmission completion notification of terminal T2 (the previous terminal that transmits data immediately before the data transmission of terminal T3) that it has grasped based on the schedule.

[0096] If terminal T3 does not receive the transmission completion notification from terminal T2, it continues the operation of receiving the transmission completion notification. For example, terminal T3 performs the operation of receiving the transmission completion notification from terminal T2, as shown by arrow A10cb in Figure 10. That is, if terminal T3 does not receive the transmission completion notification from terminal T2 in the MDS immediately before the data transmission of terminal T3, it extends the operation of receiving the transmission completion notification.

[0097] In the extended operation for receiving the transmission completion notification, terminal T3 receives the transmission completion notification from terminal T2 and decides to transmit data. For example, when terminal T3 receives the transmission completion notification from terminal T2 as indicated by arrow A10cc in Fig. 10, it transmits data in MDS3 as indicated by arrow A10cd in Fig. 10. After transmitting the data, terminal T3 goes to sleep.

[0098] Operation Example 3 (When There is a Delay of 3 Slots) Fig. 11 is a diagram illustrating operation example 3 of the communication system. Arrow A11a in Fig. 11 indicates the schedule generated by information processing device 3. In the example of Fig. 11, MDS0 to MDS11 are scheduled. As in Fig. 9, the terminals transmitting data in MDS0 to MDS11 are terminals T0 to T11.

[0099] Arrow A11b in Fig. 11 indicates the timing of actual UL transmission. In the example of Fig. 11, terminal T0 (MDS0) receives interference as indicated by arrow A11ba in Fig. 11, causing a data transmission delay of three slots. Terminals T1 and T2 (MDS1 and MDS2) perform UL transmission without experiencing any data transmission delay.

[0100] An arrow A11c in Fig. 11 indicates the operation of terminal T3 transmitting data in MDS 3. In other words, arrow A11c in Fig. 11 indicates the operation of terminal T3 to which MDS 3 is assigned.

[0101] Terminal T3 knows the terminal (previous terminal) that will transmit data immediately before terminal T3 based on the MDS arrangement information (schedule) of the FCMS. Since terminal T3 transmits data in MDS3, it knows terminal T2 that will transmit data in MDS2, which is immediately before MDS3.

[0102] Terminal T3 wakes up from sleep in the slot immediately before the slot in which terminal T3 transmits data. In the example of Fig. 11, terminal T3 transmits data in MDS3, and therefore wakes up in MDS2, which is immediately before MDS3, as shown by arrow A11ca in Fig. 11. Terminal T3 determines the time to wake up based on the transmission time included in the MDS configuration information.

[0103] Terminal T3, which has woken up from sleep, receives a transmission completion notification broadcast by MDS2, which is immediately before MDS3, as indicated by arrow A11ca in Fig. 11. That is, terminal T3 receives a transmission completion notification from terminal T2 (the previous terminal that transmits data immediately before the data transmission of terminal T3) that it has grasped based on the schedule.

[0104] 11, a data transmission delay of three slots occurs in MDS0 (terminal T0) as indicated by arrow A11ba. Therefore, in the operation of receiving the transmission completion notification as indicated by arrow A11ca, terminal T3 does not receive the transmission completion notification of terminal T2 (the previous terminal that transmits data immediately before the data transmission of terminal T3) that it has grasped based on the schedule.

[0105] If terminal T3 does not receive the transmission completion notification from terminal T2, it continues the operation of receiving the transmission completion notification. For example, terminal T3 performs the operation of receiving the transmission completion notification from terminal T2, as shown by arrow A11cb in Figure 11. That is, if terminal T3 does not receive the transmission completion notification from terminal T2 in the MDS immediately before the data transmission of terminal T3, it extends the operation of receiving the transmission completion notification.

[0106] In the extended operation of receiving the transmission completion notification, when terminal T3 receives a transmission completion notification from a terminal other than terminal T2, it determines the amount of delay in data transmission. For example, as shown by arrow A11cc in Figure 11, when terminal T3 receives a transmission completion notification from terminal T0 (MDS0) instead of terminal T2, it determines that a data transmission delay of three slots has occurred. Terminal T3 determines the amount of delay in data transmission based on the terminal identification information included in the transmission completion notification and the terminal identification information and transmission time included in the MDS placement information.

[0107] Terminal T3 goes to sleep if a data transmission delay of three slots or more occurs. Before going to sleep, terminal T3 sets the timing to wake up based on the magnitude of the determined data transmission delay. For example, in the example of Figure 11, a transmission delay of three slots has occurred, so terminal T3 is set to wake up two slots later. In other words, terminal T3 is set to wake up one slot less than the data transmission delay (three slots) later (two slots later) in order to receive a transmission completion notification from terminal T2 (the terminal that transmits data before terminal T3).

[0108] Terminal T3 wakes up from the second sleep state based on the wake-up setting. In the example of Fig. 11, terminal T3 wakes up two slots after receiving the transmission completion notification from terminal T0, and therefore, as shown by arrow A11cd in Fig. 11, terminal T3 wakes up in the MDS immediately before the MDS in which terminal T3 performs the transmission operation.

[0109] Terminal T3, which has woken up from sleep, receives a transmission completion notification broadcast in MDS2, as indicated by arrow A11ce in Fig. 11. That is, terminal T3 receives a transmission completion notification from terminal T2 (the previous terminal that transmits data immediately before the data transmission of terminal T3) that it has grasped based on the schedule.

[0110] Upon receiving the transmission completion notification from terminal T2, terminal T3 decides to transmit data. Terminal T3 transmits data at a time (rescheduled time) based on the transmission time of terminal T3 included in the MDS placement information and the determined magnitude of data transmission delay. For example, terminal T3 transmits data in MDS3 as shown by arrow A11cf in Figure 11. After transmitting the data, terminal T3 goes to sleep.

[0111] <Block Diagram> Fig. 12 is a diagram showing an example of a block configuration of terminal 1. As shown in Fig. 12, terminal 1 has an application layer 11. The application layer 11 has a schedule receiving unit 21, a transmission order understanding unit 22, a notification receiving unit 23, a transmission determining unit 24, a delay amount determining unit 25, and a sleep unit 26. It may be considered that the functions of each unit in Fig. 12 are realized by the application layer 11.

[0112] The schedule receiving unit 21 receives the broadcast FCMS.

[0113] The transmission order ascertaining unit 22 ascertains, based on the FCMS, the terminal (previous terminal) that will transmit the MDS (previous MDS) immediately before the terminal 1 transmits the MDS.

[0114] The notification receiving unit 23 receives the transmission completion notification broadcast in the previous MDS.

[0115] Furthermore, if the notification receiving unit 23 does not receive a transmission completion notification in the previous MDS, it performs an operation to receive the transmission completion notification in the MDS after the previous MDS. That is, the notification receiving unit 23 extends the operation to receive the transmission completion notification. If the transmission completion notification is a notification broadcast from the recognized terminal, the transmission determining unit 24 determines uplink transmission. After the uplink transmission is completed, the transmission determining unit 24 broadcasts a transmission completion notification indicating the completion of the uplink transmission.

[0116] If the transmission completion notification is not a notification broadcast from the recognized terminal, the delay amount determination unit 25 determines the amount of delay in the upstream transmission.

[0117] The sleep unit 26 puts the terminal 1 to sleep based on the amount of delay. Furthermore, when the sleep unit 26 receives a transmission completion notification from a terminal other than the terminal (previous terminal) that previously transmitted an uplink signal, the sleep unit 26 puts the terminal 1 to sleep. Furthermore, before putting the terminal 1 to sleep, the sleep unit 26 sets the timing for waking up the terminal 1 based on the amount of delay.

[0118] <Hardware Configuration> Fig. 13 is a diagram showing an example of the hardware configuration of the terminal 1. As shown in Fig. 13, the terminal 1 has a control unit 31, a storage unit 32, and a communication unit 33. Note that if the terminal 1 is a camera, the terminal 1 has an imaging element.

[0119] The control unit 31 controls the entire terminal 1. The control unit 31 may be configured by a processor such as a CPU (Central Processing Unit). The functions of the application layer 11 (the schedule receiving unit 21, the transmission order understanding unit 22, the notification receiving unit 23, the transmission determining unit 24, the delay amount determining unit 25, and the sleep unit 26) shown in FIG. 12 may be realized by the control unit 31 executing a program stored in the storage unit 32.

[0120] The storage unit 32 stores a program for operating the control unit 31. The storage unit 32 also stores data for the control unit 31 to perform calculation processing, data for the control unit 31 to control each unit, etc. The storage unit 32 may be configured by a storage device such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, or an HDD (Hard Disk Drive).

[0121] The communication unit 33 communicates wirelessly with the base station 2. The communication unit 33 also communicates with the information processing device 3 via the base station 2.

[0122] <Summary of the embodiment> As described above, terminal 1 receives a broadcast FCMS. Based on the FCMS, terminal 1 identifies the terminal (previous terminal) that performs upstream transmission immediately before terminal 1. Terminal 1 receives a transmission completion notification broadcast in the MDS from which the identified previous terminal performs upstream transmission. If the transmission completion notification is a notification broadcast from the identified previous terminal, terminal 1 determines to perform upstream transmission. This operation avoids congestion in the MDS and suppresses a decrease in throughput.

[0123] <Modification 1> The information processing device 3 may specify one terminal and collect data from the specified terminal. In this case, the information processing device 3 may transmit the FCMS by unicast.

[0124] <Modification 2> If there is no response from a specific terminal 1 despite the information processing device 3 having issued an MDS transmission instruction a specified number of times, the information processing device 3 may transmit an FSMS by unicast to the specific terminal 1 to instruct it to transmit an MDS. When unicasting, retransmission control is performed, so that the MDS transmission can be executed appropriately.

[0125] If there is no response even after issuing an MDS transmission instruction by unicast a specified number of times, the information processing device 3 may delete the terminal 1 that did not respond from the management table. Then, the information processing device 3 may not assign an MDS to the terminal 1 deleted from the management table.

[0126] Although the embodiments have been described above with reference to the drawings, the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims. It is understood that such modifications or alterations also fall within the technical scope of the present disclosure. Furthermore, the components in the embodiments may be combined in any manner without departing from the spirit of the present disclosure.

[0127] In the above-described embodiments, the notation "... part" used for each component may be replaced with other notations such as "... circuit," "... assembly," "... device," "... unit," or "... module."

[0128] The present disclosure can be realized by software, hardware, or software in conjunction with hardware. Each functional block used in the description of the above embodiments may be partially or entirely realized as an LSI, which is an integrated circuit, and each process described in the above embodiments may be partially or entirely controlled by a single LSI or a combination of LSIs. The LSI may be composed of individual chips, or may be composed of a single chip that includes some or all of the functional blocks. The LSI may have data input and output. Depending on the degree of integration, the LSI may also be called an IC, system LSI, super LSI, or ultra LSI.

[0129] The integrated circuit method is not limited to LSI, and may be realized by a dedicated circuit, a general-purpose processor, or a dedicated processor. Also, a field programmable gate array (FPGA) that can be programmed after LSI manufacturing, or a reconfigurable processor that can reconfigure the connections and settings of circuit cells within the LSI, may be used. The present disclosure may be realized as digital processing or analog processing.

[0130] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derivative technologies, it is natural that such technology may be used to integrate functional blocks. The application of biotechnology, etc. is also a possibility.

[0131] The present disclosure is useful for wireless communication such as wireless LAN (IEEE802.11).

[0132] 1, 1a to 1d terminal 2 base station 3 information processing device 11 application layer 21 schedule receiving unit 22 transmission order grasping unit 23 notification receiving unit 24 transmission determining unit 25 delay amount determining unit 26 sleep unit

Claims

1. A terminal having: a schedule receiving unit that receives a broadcast schedule that determines the transmission order of uplink transmissions for the terminal and other terminals; a transmission order grasping unit that grasps the previous terminal that will perform uplink transmission immediately before the terminal based on the schedule; a notification receiving unit that receives a transmission completion notification that is broadcast in the time unit in which the grasped previous terminal performs uplink transmission and indicates the completion of uplink transmission; and a transmission determination unit that determines uplink transmission from the terminal when the transmission completion notification is a notification broadcast from the grasped previous terminal.

2. The terminal according to claim 1, wherein, if the transmission completion notification is not received in the time unit, the notification receiving unit performs an operation to receive the transmission completion notification in a time unit after the time unit.

3. The terminal according to claim 2, further comprising: a delay amount determination unit that determines the amount of delay in uplink transmission if the transmission completion notification is not a notification broadcast from the identified previous terminal; and a sleep unit that puts the terminal to sleep based on the amount of delay.

4. The terminal according to claim 3, wherein the sleep unit puts the terminal to sleep when the transmission completion notification is received from a terminal different from the identified previous terminal.

5. The terminal according to claim 3, wherein the sleep unit sets a timing for waking up the terminal based on the amount of delay before putting the terminal to sleep.

6. The terminal according to claim 1, wherein the transmission determination unit broadcasts a notification indicating completion of the upstream transmission after the upstream transmission is completed.

7. The terminal according to claim 1, wherein the application layer comprises the schedule receiving unit, the transmission order understanding unit, the notification receiving unit, and the transmission determining unit.

8. A communication method in which a terminal receives a broadcast schedule that determines the order of upstream transmissions for the terminal and other terminals, identifies the previous terminal that will perform upstream transmission immediately before the terminal based on the schedule, receives a transmission completion notification that is broadcast in the time unit in which the identified previous terminal performs upstream transmission and indicates the completion of the upstream transmission, and if the transmission completion notification is a notification broadcast from the identified previous terminal, determines to perform upstream transmission from the terminal.

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