JP6248434B2 - Wireless communication system, wireless base station, and wireless terminal - Google Patents

Description

  The present invention relates to a radio communication system, a radio base station, and a radio terminal.

  A wireless ad hoc network is known as an example of a wireless communication system. As a conventional technique related to a wireless ad hoc network, there are techniques described in Patent Documents 1 to 3 below.

  The technique described in Patent Document 1 aims to suppress competition of used time slots with so-called hidden terminals. Therefore, in the technology described in Patent Document 1, the time slot usage status of the wireless device existing within its own carrier sense range is transmitted and received between the wireless devices, and the time slot usage status table of itself and other wireless devices is created. To do. Then, the wireless terminal refers to the created time slot usage status table, and when all the time slots are in use, the wireless terminal uses any one of the time slots used by the wireless devices existing within its own carrier sense range. Is selected as a time slot for transmitting a periodic packet.

  The technique described in Patent Literature 2 aims to improve the success rate of frequency allocation to a frequency allocation where the hidden terminal problem does not occur even when the network scale increases. Therefore, in the technique described in Patent Document 2, when the set frequency arrangement becomes a hidden terminal problem link, if it is detected that the set frequency arrangement has not changed beyond the specified period, the process of changing the frequency setting To do.

  In the technology described in Patent Document 3, in a wireless sensor network, a node corresponding to a gateway (hereinafter, the gateway may be abbreviated as “GW”) receives a reception ready (CTS) packet as an example of a permission message. Broadcast. The node that has received the CTS packet recognizes that it is permitted to transmit data based on the CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) method. As a result, data transmission by the slot owner node is not performed, and as a result, the hidden terminal problem is solved.

JP 2010-171834 A JP 2007-235828 A Special table 2012-515487

  In a wireless ad hoc network, when a plurality of terminals in a positional relationship where carrier sense does not work according to the CSMA / CA method perform packet transmission at the same time, packet collision occurs. A terminal having such a positional relationship is called a hidden terminal.

  In a wireless ad hoc network, when the number of terminals increases, communication concentrates on a node corresponding to the GW from all directions, so that hidden terminals are likely to occur. For example, as schematically shown in FIG. 20, the terminals 200 and 300 that are in a positional relationship facing each other across the GW 100 correspond to hidden terminals. That is, the terminals 200 and 300 are both located within the communication range 100a of the GW 100, but are located outside the communication ranges 300a and 200a of the counterpart terminal. When packet collision occurs due to a hidden terminal, communication throughput decreases.

  Here, for example, when the number of terminals in a specific direction increases as viewed from the GW, the number of hidden terminals increases, and packet collision is likely to occur. Patent Documents 1 to 3 do not mention any countermeasures when the number of terminals in a specific direction is increased as viewed from the GW.

  One of the objects of the present invention is to suppress a decrease in communication throughput accompanying an increase in hidden terminals.

  One aspect of the present invention includes a plurality of wireless terminals and a wireless base station that changes assignment of time slots in which the wireless terminal can communicate depending on the direction in which the wireless terminal is located with respect to the local station.

  A decrease in communication throughput due to an increase in hidden terminals can be suppressed.

It is a figure which shows typically an example of the radio | wireless ad hoc network as a radio | wireless communications system which concerns on 1st Embodiment. It is a figure which shows an example of the time slot allocation according to direction by the gateway (GW) illustrated in FIG. It is a figure explaining the relationship of the time slot according to the direction illustrated in FIG. (A) is a figure which shows typically a mode that GW illustrated in FIG. 1 communicates, changing the directivity of a directional antenna, (B) typically shows a mode that the time slot according to a direction is allocated. FIG. It is a figure which shows the hardware structural example of GW illustrated in FIG. It is a functional block diagram of GW illustrated in FIG. It is a figure which shows the hardware structural example of the radio | wireless terminal illustrated in FIG. FIG. 2 is a functional block diagram of a wireless terminal illustrated in FIG. 1. It is a flowchart explaining operation | movement of GW illustrated in FIG.1, FIG5 and FIG.6. FIG. 9 is a flowchart for explaining the operation (when receiving time slot information) of the wireless terminal exemplified in FIG. 1, FIG. 7 and FIG. 8; 9 is a flowchart for explaining the operation (during communication) of the wireless terminal illustrated in FIGS. 1, 7, and 8. It is a figure explaining the effect of 1st Embodiment, (A) is a figure which illustrates the relationship between the number of terminals and the total communication successful packet number, (B) is a figure explaining the arrangement | positioning method of a radio | wireless terminal. . It is a flowchart explaining operation | movement of GW which concerns on the modification of 1st Embodiment. It is a functional block diagram of GW concerning a 2nd embodiment. It is a functional block diagram of the radio | wireless terminal which concerns on 2nd Embodiment. 16 is a flowchart for explaining the operation of the wireless terminal illustrated in FIG. 15 (at the time of transmitting position information). It is a flowchart explaining operation | movement of GW illustrated in FIG. 16 is a flowchart for explaining the operation of the wireless terminal illustrated in FIG. 15 (when receiving time slot information). It is a schematic diagram explaining the area | region which GW allocates a time slot in 2nd Embodiment. It is a figure which shows the example of terminal arrangement | positioning around GW.

  Embodiments of the present invention will be described below with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described below. Note that, in the drawings used in the following embodiments, portions denoted by the same reference numerals represent the same or similar portions unless otherwise specified.

(First embodiment)
FIG. 1 is a diagram schematically illustrating an example of a wireless ad hoc network as a wireless communication system according to the first embodiment. The wireless ad hoc network illustrated in FIG. 1 exemplarily includes a GW 10 corresponding to an example of a wireless base station, and a plurality of wireless terminals 20 located around the GW 10.

  A wireless terminal 20 (hereinafter also simply referred to as “terminal 20”) located within the communication range 10a of the GW 10 can communicate with the GW 10. The communication range 10a of the GW 10 is illustratively sectored by direction. In the example shown in FIG. 1, the communication range 10a is divided into eight sectors.

  Of the eight sectors, for example, time slots # 1 to # 4 are allocated to four sectors A to D, respectively. Therefore, terminal 20 located in sector A communicates with GW 10 using time slot # 1, and terminal 20 located in sector B communicates with GW 10 using time slot # 2. Similarly, terminal 20 located in sector C communicates with GW 10 using time slot # 3, and terminal 20 located in sector D communicates with GW 10 using time slot # 4.

  Here, since the sectors A and B are in a positional relationship facing each other across the GW 10, when the number of terminals 20 located in the sectors A and B increases, the number of hidden terminals increases. Therefore, the GW 10 assigns different time slots # 1 and # 2 to the sectors A and B that are in an opposing relationship, respectively. That is, for example, as shown in FIG. 2, time slots are allocated in synchronism so that time does not overlap with terminals located in the A direction and B direction, which are facing each other as viewed from the GW 10.

  Similarly, as shown in FIG. 1, since the sectors C and D are also in a positional relationship facing each other across the GW 10, the GW 10 has different time slots # 3 and # with respect to the sectors C and D in the opposing relationship. Assign 4 to each. That is, for example, as shown in FIG. 2, time slots are allocated in synchronism so that time does not overlap with a group of terminals located in the directions C and D, which are facing each other as viewed from the GW 10.

  Here, since the terminals located in sectors that are not in an opposing relationship across the GW 10 are not in a hidden terminal relationship, the time slots to be allocated may be asynchronous. For example, as shown in FIG. 3, time slots # 1 and / or # 2 may be asynchronous with time slots # 3 and / or # 4.

  Specifically, for example, as schematically illustrated in FIG. 4A, the GW 10 communicates with the terminal 20 while changing (rotating) the directivity of the directional antenna, thereby changing the direction in which the terminal 20 exists. Identify (determine). Then, the GW 10 classifies the communication range 10a into sectors, and implements the time slot allocation described above with reference to FIG. 2 and FIG. 3 when the number of terminals 20 located in the facing sector exceeds a predetermined threshold. (See FIG. 4B).

  Information on the allocated time slot is illustratively added to a beacon signal or the like and distributed (broadcast) from the GW 10 to the terminal 20. For example, the distribution can be performed using an omnidirectional omni antenna in the GW 10. The terminal 20 performs communication using the time slot instructed from the GW 10.

  Hereinafter, configuration examples of the GW 10 and the terminal 20 that realize such time slot allocation will be described with reference to FIGS. FIG. 5 is a diagram illustrating a hardware configuration example of the GW 10, and FIG. 6 is a block diagram illustrating a functional configuration example of the GW 10. FIG. 7 is a diagram illustrating a hardware configuration example of the terminal 20, and FIG. 8 is a block diagram illustrating a functional configuration example of the terminal 20.

  As illustrated in FIG. 5, the GW 10 includes, for example, an antenna unit 11, an antenna changeover switch (antenna command unit) 12, an RF chip 13, a CPU 14, and a memory 15.

  The antenna unit 11 illustratively has a function as a directional antenna and a function as an omnidirectional omni antenna, and both functions are switched according to control from the antenna changeover switch 12.

  The RF chip 13 is an example of a wireless circuit, and performs wireless signal transmission / reception processing.

  The CPU 14 is an example of an arithmetic processing unit that controls the overall operation of the GW 10, and controls the operation of the GW 10 by appropriately reading and operating a predetermined program and data stored in the memory 15. The control includes, for example, a process of giving an instruction to the antenna changeover switch 12 to switch the antenna unit 11 to a directional antenna or an omni antenna.

  The memory 15 stores the above programs and data, as well as information on the direction in which the terminal 20 exists, the number of terminals, and / or a threshold for communication volume, as will be described later.

  Next, focusing on the function of the GW 10 with reference to FIG. 6, the GW 10 illustratively shows the transmission / reception unit 131, the terminal presence direction determination unit 141, the count unit 142, the time slot allocation unit 143, and the terminal presence direction recording. Part 151. In FIG. 6, reference numerals 11 and 12 denote the antenna unit and the antenna command unit described above, respectively.

  The transmission / reception unit 131 is illustratively implemented by the RF chip 13 described above, and performs transmission / reception processing of a radio signal.

  The terminal presence direction determination unit 141 determines the direction in which the communicable terminal 20 is located by communicating with the terminal 20 while changing the directivity of the directional antenna.

  The terminal presence direction recording unit 151 is exemplarily implemented by the memory 15 described above, and the determination result by the terminal presence direction determination unit 141, that is, the information of the terminal 20 that can communicate for each direction in which the directional antenna faces. Record.

  The counting unit 142 counts the number of terminals 20 for each direction in which the directional antenna faces based on the information recorded in the terminal presence direction recording unit 151.

  The time slot allocating unit (time slot allocating control unit) 143 is based on the count result of the counting unit 142 when the number of terminals 20 located in the opposite direction across the GW 10 exceeds a predetermined threshold. 2 and FIG. 3, the above-described time slot allocation is performed. Information on the assigned time slot is notified to the terminal 20 through the transmission / reception unit 131 and the antenna unit 11 (omni antenna).

  Note that the terminal presence direction determination unit 141, the count unit 142, and the time slot allocation unit 143 are implemented by, for example, the CPU 14 described above operating by reading a predetermined program or data from the memory 15.

  On the other hand, as illustrated in FIG. 7, when focusing on hardware, the terminal 20 includes, for example, an antenna unit 21, an RF chip 22, a sensor 23, a CPU 24, and a memory 25.

  The antenna unit 21 transmits and receives radio signals.

  The RF chip 22 is an example of a wireless circuit, and performs wireless signal transmission / reception processing.

  The sensor 23 measures physical quantities (for example, temperature, humidity, acceleration, illuminance, wind direction, wind speed, earthquake motion, rainfall, volume of sound, water level, power usage, water usage, and gas usage). Measure (sense). A signal having physical quantity information representing the measured physical quantity is output to the CPU 24. In this case, the terminal 20 forms a sensor network as an example of a wireless ad hoc network.

  The CPU 24 is an example of an arithmetic processing device that controls the overall operation of the terminal 20. The CPU 24 controls the operation of the terminal 20 by appropriately reading and operating predetermined programs and data stored in the memory 25. .

  The memory 25 stores the above-described program and data, as well as time slot information allocated from the GW 10.

  Next, focusing on the function of the terminal 20 with reference to FIG. 8, the terminal 20 includes, for example, a transmission / reception unit 221, a time slot determination unit 241, an information generation unit 242, and a time slot information recording unit 251. . In FIG. 8, reference numeral 21 denotes the antenna unit described above.

  The transmission / reception unit 221 is illustratively implemented by the RF chip 22 described above, and performs transmission / reception processing of a radio signal.

  The time slot information recording unit 251 is exemplarily implemented by the memory 25 described above, and records time slot information received from the GW 10.

  The time slot determination unit 241 determines whether or not the current timing is a timing corresponding to the time slot allocated from the GW 10 based on the information on the time slot recorded in the time slot information recording unit 251.

  The information generation unit 242 generates information addressed to the communication partner GW 10 and other terminals 20. The information is transmitted through the transmission / reception unit 221 and the antenna unit 21 when the time slot determination unit 241 determines that the current timing corresponds to the time slot allocated from the GW 10.

  Hereinafter, operation examples of the GW 10 and the terminal 20 configured as described above will be described with reference to FIGS. 9 is a flowchart showing an example of the operation of the GW 10, and FIGS. 10 and 11 are flowcharts showing an example of the operation of the terminal 20.

  As illustrated in FIG. 9, the GW 10 controls the antenna unit 11 to be a directional antenna by the antenna command unit 12, and communicates with the terminal 20 while changing the directivity of the directional antenna (processing P11). Then, the GW 10 uses the terminal presence direction determination unit 141 to determine the direction in which the terminal 20 that has been able to communicate exists, and stores information on the terminal 20 that has been able to communicate in each direction in which the directional antenna is directed to the memory 15 (terminal presence direction recording). Part 151) (process P12).

  Next, the GW 10 counts the number of terminals that can communicate in each direction based on the information recorded in the terminal presence direction recording unit 151 by the counting unit 142 (process P13), and the number of terminals counted in each direction is a predetermined threshold value. Is determined (process P14). If the counted number of terminals does not exceed the threshold, the GW 10 ends the process (No route of process P14).

  On the other hand, if the counted number of terminals exceeds the threshold (Yes in process P14), the counting unit 142 further determines that the number of terminals counted in a facing relationship (face-to-face) across the GW 10 is a predetermined threshold. Is determined (process P15). Note that the threshold values in the processes P14 and P15 may be the same. As a result, if the threshold value is not exceeded, the GW 10 ends the process (No route of process P15).

  On the other hand, if the number of terminals counted in the facing direction exceeds the threshold (in the case of Yes in process P15), the GW 10 determines a time slot to be allocated for each facing direction by the time slot allocation unit 143. (Process P16). That is, as described above with reference to FIGS. 2 and 3, the time slot allocating unit 143 is synchronized so that the time does not overlap with a terminal group located in each direction in a facing relationship when viewed from the GW 10. Assign time slots.

  Information on the allocated time slot (time slot allocation information) is notified to the terminal 20 located in each direction by the antenna unit 11 (omni antenna) through the transmission / reception unit 131 (processing P17). For example, the time slot allocation information is broadcast by being added to a packet such as a beacon signal. The antenna unit 11 is illustratively switched to the omni antenna by the antenna command unit 12 at the timing after the above-described process P13.

  On the other hand, as illustrated in FIG. 10, the terminal 20 receives the packet with the time slot allocation information transmitted from the GW 10 through the antenna unit 21 and the transmission / reception unit 221 (processing P21). The transmission / reception unit 221 records the received time slot allocation information in the memory 25 (time slot information recording unit 251) (processing P22).

  Thereafter, as illustrated in FIG. 11, in the terminal 20, a communication request is generated by the information generation unit 242 (process P31). Then, the terminal 20 uses the time slot determination unit 241 to determine whether the current timing is a timing corresponding to the assigned time slot based on the time slot allocation information recorded in the time slot information recording unit 251. (Process P32).

  As a result of the determination, if the current timing is not a timing corresponding to the assigned time slot (No in process P32), the time slot determination unit 241 waits for a random time (process P34) and returns to process P32.

  On the other hand, if the current timing is a timing corresponding to the assigned time slot (Yes in process P32), the time slot determination unit 241 gives communication permission to the information generation unit 242, thereby the information generation unit Communication is started from 242 through the transmission / reception unit 221 (processing P33).

  As described above, according to the above-described embodiment, when the number of terminals within a certain range exceeds a predetermined number as viewed from the GW 10, and the phenomenon exists in two directions facing each other across the GW 10, the respective directions are present. A different time slot is assigned to each terminal in each direction. In other words, the GW 10 changes the allocation of time slots with which the terminal 20 can communicate depending on the position of the terminal 20 around the GW 10.

  Therefore, the frequency of occurrence of the hidden terminal problem for the GW 10 can be reduced, and the rate of occurrence of packet collision accompanying the increase of hidden terminals can be suppressed. As a result, the throughput of communication between the GW 10 and the terminal 20 can be improved, and the number of terminals 20 that can be accommodated by the GW 10 can be increased.

  FIG. 12 shows an example of the simulation calculation result. In the simulation calculation, as illustrated in FIG. 12B, the peripheral area of the GW 10 is divided sparsely and the number of terminals is increased while maintaining the ratio of the sparse and dense terminals. Each terminal 20 transmits to the GW 10. When the terminals 20 that are separated by more than the communicable distance try to make a call at the same time, if the received power difference in the GW 10 is less than the required SN ratio, it is determined that the packet has collided and communication has failed.

  A graph in which the number of successful communication packets is totaled while changing the total number of terminals is the graph shown in FIG. In FIG. 12A, a graph denoted by reference numeral 100 represents the graph according to the above-described embodiment, and a graph denoted by reference numeral 200 represents a graph according to the conventional method (Slotted ALOHA). As can be seen by comparing these graphs 100 and 200, according to the above-described embodiment, even if the number of terminals 20 increases, the throughput is improved because the deterioration of the throughput due to packet collision can be suppressed.

  Note that the threshold value for the number of terminals to which time slot allocation according to the above-described embodiment is applied is, for example, a case where the number of successful communication packets is improved by, for example, 5% or more. As a non-limiting example, the simulation environment may be applied when there are 200 or more terminals 20 around the GW 10. In FIG. 12B, when sparse: dense = 1: 9 is allocated, (200/4) × 0.9 = 45 terminals 20 exist in one dense area. . Therefore, the threshold value for the number of terminals can be set to 45.

(Modification)
In the embodiment described above, the time slot allocation for each direction is performed when the number of terminals exceeds a predetermined threshold. However, when the communication amount exceeds the predetermined threshold instead of the number of terminals, the same time slot allocation May be implemented.

  FIG. 13 shows an operation example of the GW 10 in that case. As illustrated in FIG. 13, the GW 10 controls the antenna unit 11 to be a directional antenna by the antenna command unit 12, and communicates with the terminal 20 while changing the directivity of the directional antenna (processing P11). Then, the GW 10 uses the terminal presence direction determination unit 141 to determine the direction in which the terminal 20 that has been able to communicate exists, and stores information on the terminal 20 that has been able to communicate in each direction in which the directional antenna is directed to the memory 15 (terminal presence direction recording). Part 151) (process P12).

  Next, the GW 10 measures, for example, the communication amount of the terminal 20 that can communicate with each direction based on the information recorded in the terminal presence direction recording unit 151 by the counting unit 142 (processing P13a), and the communication amount measured for each direction. Is determined to exceed a predetermined threshold (process P14a). If the measured communication amount does not exceed the threshold, the GW 10 ends the process (No route of process P14a).

  On the other hand, if the measured communication amount exceeds the threshold value (in the case of Yes in process P14a), the count unit 142 further determines that the communication amount measured in a direction facing (face-to-face) across the GW 10 is a predetermined threshold value. Is determined (process P15a). Note that the threshold values in the processes P14a and P15a may be the same. As a result, if the threshold is not exceeded, the GW 10 ends the process (No route of process P15a).

  On the other hand, if the traffic measured in the facing direction exceeds the threshold (Yes in process P15a), the GW 10 determines a time slot to be assigned for each facing direction by the time slot allocating unit 143. (Process P16). That is, as described above with reference to FIGS. 2 and 3, the time slot allocating unit 143 is synchronized so that the time does not overlap with a terminal group located in each direction in a facing relationship when viewed from the GW 10. Assign time slots.

  Information on the allocated time slot (time slot allocation information) is notified to the terminal 20 located in each direction by the antenna unit 11 (omni antenna) through the transmission / reception unit 131 (processing P17). For example, the time slot allocation information is broadcast by being added to a packet such as a beacon signal. The antenna unit 11 is illustratively switched to the omni antenna by the antenna command unit 12 at the timing after the above-described process P13a.

  In the simulation, each terminal 20 is set to transmit a packet with a probability of 1/360. When a time slot is allocated, the transmission timing is halved, so the terminal 20 is set to transmit with a probability of 1/180. Therefore, the space occupancy rate under the same conditions as the simulation in the above-described embodiment is 45 × (1/180) + 5 × (1/360) × 100 = 26.4%. Therefore, 26.4% of the maximum communication amount can be used for the above-described threshold.

  Note that the necessity for time slot allocation may be determined by combining the above-described threshold for the number of terminals and the threshold for the traffic. For example, even when the number of terminals in the two directions facing each other is equal to or less than the threshold value, the time slot allocation described above may be performed as long as the communication amount exceeds the threshold value in the two directions. On the other hand, even if the traffic volume is less than or equal to the threshold value in the two directions facing each other, the time slot allocation described above may be performed if the number of terminals exceeds the threshold value in the two directions.

(Second Embodiment)
In the first embodiment, the aspect in which the GW 10 determines the direction in which the terminal 20 exists by communicating with the terminal 20 while changing the directivity of the directional antenna has been described. However, even when the GW 10 does not have a directional antenna, time slot allocation similar to that of the first embodiment is possible. That is, in the second embodiment, the GW 10 can determine the direction in which the terminal 20 exists by acquiring the position information of the terminal 20 as GPS information, for example. Based on the determination result, the GW 10 can perform time slot allocation similar to that of the first embodiment.

  FIG. 14 shows a functional block diagram of the GW 10 according to the second embodiment, and FIG. 15 shows a functional block diagram of the terminal 20 according to the second embodiment. Note that the hardware configuration example of the GW 10 corresponds to a configuration in which the antenna changeover switch 12 is deleted in the first embodiment (FIG. 5). The hardware configuration example of the terminal 20 corresponds to a configuration additionally including the GPS sensor 26 (see FIG. 15) in the first embodiment (FIG. 7).

  As illustrated in FIG. 14, the GW 10 of the second embodiment is different from the configuration illustrated in FIG. 6 in that the antenna command unit 12 is deleted. Further, the GW 10 is different from the configuration illustrated in FIG. 6 in that a terminal presence direction determination unit 141a and a time slot allocation unit 143a are provided instead of the units 141 and 143. In FIG. 14, the parts denoted by the same reference numerals as those described above are the same as or similar to the parts described above unless otherwise specified.

  The terminal presence direction determination unit 141 a calculates the direction in which the terminal 20 exists based on GPS information transmitted from the terminal 20 and received through the antenna unit 11 and the transmission / reception unit 131. The GPS information is acquired by the GPS sensor 26 of the terminal 20 and notified to the GW 10. The GPS sensor 26 is an example of a position information acquisition unit that acquires position information of the terminal 20. The presence direction of each terminal 20 calculated by the terminal presence direction determination unit 141 a is recorded in the terminal presence direction recording unit 151.

  The time slot allocation unit (time slot allocation control unit) 143a determines, based on the count result of the count unit 142, when the number of terminals 20 located in the opposite direction across the GW 10 exceeds a predetermined threshold. 2 and FIG. 3, the above-described time slot allocation is performed. Further, based on the information recorded in the terminal presence direction recording unit 151, the time slot allocation unit 143a generates information (allocation area information) for specifying an area to which the time slot is allocated.

  The allocation area information may include, for example, the position information (coordinates) of the GW 10, the left end direction θ1 and the right end direction θ2 of the area to which time slots are allocated as illustrated in FIG. Information on the allocated time slot and allocated area information is notified to the terminal 20 through the transmission / reception unit 131 and the antenna unit 11 (omni antenna).

  Note that the functions of the terminal presence direction determination unit 141a and the time slot allocation unit 143a are implemented by, for example, the CPU 14 shown in FIG.

  On the other hand, as shown in FIG. 15, the terminal 20 of the second embodiment is different from the configuration illustrated in FIG. 8 in that a GPS sensor 26 is provided. The terminal 20 includes a time slot determination unit 241a, an information generation unit 242a, and a time slot / allocation area information recording unit 251a instead of the units 241, 242, and 251 as compared with the configuration illustrated in FIG. The point is different.

  The information generation unit 242a generates transmission information addressed to the GW 10, for example. The transmission information may include GPS information acquired by the GPS sensor 26.

  The time slot determination unit 241a determines whether or not the own terminal 20 is located in the allocation area based on the allocation area information among the time slot information and the allocation area information received from the GW 10 through the antenna unit 21 and the transmission / reception unit 221. Determine whether. Note that the location information of the terminal 20 can be acquired by the GPS sensor 26. As a result of the determination, if the own terminal 20 is located in the allocation area, the time slot determination unit 241a records the received time slot information in the time slot / allocation area information recording unit 251a.

  The time slot / allocation area information recording unit 251a records time slot information and allocation area information received from the GW 10.

  Note that the functions of the time slot determination unit 241a and the information generation unit 242a are implemented by, for example, the CPU 24 illustrated in FIG. Further, the time slot / allocation area information recording unit 251a is embodied by the memory 25 shown in FIG.

  Hereinafter, operation examples of the GW 10 and the terminal 20 according to the second embodiment configured as described above will be described with reference to FIGS. 16 to 18. 16 and 18 are flowcharts illustrating an operation example of the terminal 20, and FIG. 17 is a flowchart illustrating an operation example of the GW 10.

  First, as illustrated in FIG. 16, the terminal 20 acquires position information (GPS information) of the terminal 20 by the GPS sensor 26 (processing P41), and transmits the GPS information to the GW 10 through the transmission / reception unit 221 and the antenna unit 21. (Process P42).

  On the other hand, as illustrated in FIG. 17, when the GW 10 receives the GPS information transmitted from each terminal 20 through the antenna unit 11 and the transmission / reception unit 131 (processing P51), the terminal presence direction determination unit 141a causes each terminal 20 to receive the GPS information. The direction in which each exists is calculated (process P52). The calculated result is recorded in the terminal presence direction recording unit 151 (process P53).

  Thereafter, the GW 10 performs the processes P13 to P16 described above with reference to FIG. 9 by the count unit 142 and the time slot allocation unit 143a, and determines a time slot to be allocated for each direction in which the terminal 20 exists. Further, the time slot allocation unit 143a generates allocation area information.

  The allocated time slot information and allocated area information are broadcast through the transmitting / receiving unit 131 and the antenna unit 11 (omni antenna) (process P17a).

  As illustrated in FIG. 18, when the terminal 20 receives time slot information and allocation area information from the GW 10 through the antenna unit 21 and the transmission / reception unit 221 (processing P61), the terminal 20 receives the allocation received by the time slot determination unit 241a. Based on the area information and the position information of the own terminal 20, it is determined whether or not the own terminal 20 is located in the allocation area (processing P62 and P63).

  As a result of the determination, if the own terminal 20 is not located in the allocation area (No in process P63), the terminal 20 ends the process. On the other hand, if the terminal 20 is located in the allocation area (Yes in process P63), the GW 10 (time slot determination unit 241a) records the information on the time slot received from the GW 10 in the time slot / allocation area information recording. This is recorded in the part 251a (process P64).

  Thereafter, the terminal 20 performs transmission in the assigned time slot by performing the same processing (P31 to P34) as the operation at the time of communication illustrated in FIG.

  As described above, even when the GW 10 does not have a directional antenna, time slot allocation similar to that in the first embodiment can be performed. Therefore, the frequency of occurrence of the hidden terminal problem for the GW 10 can be reduced, and the rate of occurrence of packet collision accompanying the increase of hidden terminals can be suppressed. As a result, the throughput of communication between the GW 10 and the terminal 20 can be improved, and the number of terminals 20 that can be accommodated by the GW 10 can be increased.

  Note that, in the second embodiment described above, as in the modification of the first embodiment, whether or not time slot allocation is necessary may be determined in accordance with the traffic. Further, as described above, the necessity of time slot allocation may be determined according to both the number of terminals and the traffic.

  (Other)

  The number of divisions (number of sectors) in the peripheral area of the GW 10 is the ratio of the total number of terminals 20 located in the above-mentioned opposite sector to the number of terminals 20 located around the GW 10 as the division number increases. And the effect of reducing the frequency of occurrence of the hidden terminal problem is reduced. Therefore, it is desirable that the number of divisions is about 4 to 16 as a non-limiting example. Further, the angle of the area allocated from the GW 10 to the terminal 20 by the allocation area information may be allocated so that the number of terminals in the area or the angle of the sector fan becomes large. About the angle of a fan, when the said division | segmentation standard is 4-16, it is good to set it as 22.5 degree | times-90 degree | times illustratively.

10 Gateway (GW)
10a Communication range 11 Antenna section 12 Antenna selector switch (Antenna command section)
13 RF chip 14 CPU
141, 141a Terminal presence direction determination unit 142 Count unit 143, 143a Time slot allocation unit 15 Memory 151 Terminal presence direction recording unit 20 Wireless terminal 21 Antenna unit 22 RF chip 221 Transmission / reception unit 23 Sensor 24 CPU
241, 241a Time slot determination unit 242, 242a Information generation unit 25 Memory 251 Time slot information recording unit 251a Time slot / allocation area information recording unit 26 GPS sensor

Claims (12)

A radio base station;
A plurality of wireless terminals capable of communicating wirelessly with the wireless base station,
The radio base station is
A wireless communication system in which different time slots are assigned to a plurality of wireless terminals in a positional relationship that cannot receive wireless signals transmitted to the wireless base station in a communication area provided by the wireless base station . The positional relationship where the wireless signals cannot be received from each other is
The wireless communication system according to claim 1, wherein the wireless communication system has a relationship of being located in a direction facing each other across the wireless base station. The radio base station is
The wireless communication system according to claim 2, wherein the time slot assignment is performed when the number of wireless terminals located in the facing direction exceeds a predetermined number. The radio base station is
The wireless communication system according to claim 2, wherein the time slot assignment is performed when a communication amount of a wireless terminal located in the facing direction exceeds a predetermined amount. The radio base station is
A directional antenna,
A determination unit that determines the positional relationship by communicating with any of the wireless terminals while changing the directivity of the directional antenna;
The radio | wireless communications system of any one of Claims 1-4 provided with. The wireless terminal is
A location information acquisition unit that acquires location information of the wireless terminal;
A transmission unit that transmits the position information acquired by the position information acquisition unit to the radio base station,
The radio base station is
The radio | wireless communications system of any one of Claims 1-4 provided with the determination part which determines the said positional relationship based on the said positional information received from the said radio | wireless terminal. A wireless base station,
A determination unit for determining a positional relationship of a plurality of wireless terminals with respect to the wireless base station ;
Based on the determination result of the determination unit, different time slots are allocated to a plurality of wireless terminals in a positional relationship where wireless signals transmitted to the wireless base station cannot be received in the communication area provided by the wireless base station A radio base station comprising: a time slot allocation control unit; The positional relationship where the wireless signals cannot be received from each other is
The radio base station according to claim 7, wherein the radio base station has a relationship of being located in a direction facing each other across the radio base station. The time slot allocation control unit
The radio base station according to claim 8 , wherein when the number of radio terminals located in the facing direction exceeds a predetermined number, the time slot is assigned. The time slot allocation control unit
The radio base station according to claim 8 , wherein the time slot allocation is performed when a communication amount of a radio terminal located in the facing direction exceeds a predetermined amount. With a directional antenna,
The determination unit
The radio base station according to claim 7, wherein the positional relationship is determined by communicating with any of the radio terminals while changing the directivity of the directional antenna. The determination unit
Wherein the plurality of received from the wireless terminal, based on the position information of the plurality of wireless terminals, determines the positional relationship, the radio base station according to any one of claims 7-10.

Images