wireless communication system

Abstract

To provide a technique for accurately allocating time slots even when network delay may occur.SOLUTION: When a transmission activation request from a first mobile station 200a is received while a superior relay station 100 is suspending transmission, a first subordinate relay station 300a transmits the transmission activation request to the superior relay station 100 via a network. Upon receiving the transmission activation request, the superior relay station 100 transmits an idle frame indicating that slots other than one slot are in use. Upon receiving a signal from the first mobile station 200a in one slot, the first subordinate relay station 300a transmits the signal to the superior relay station 100 via the network. The superior relay station 100 receives the signal from the first subordinate relay station 300a and uses one slot for the first mobile station 200a.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to communication technology, and more particularly to a wireless communication system that communicates using time slots. [Background technology]

[0002] In a wireless communication system using TDMA (Time Division Multiple Access), a relay station is placed between a higher-level station and a lower-level station. The higher-level station generates usage status information for each time slot of the TDMA signal and transmits it to each relay station. Each relay station determines whether the time slot of the TDMA signal to be relayed is unused or in use from the received usage status information, and if it is unused, allows relay transmission in that time slot (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-298521 Summary of the Invention [Problem to be solved by the invention]

[0004] When relay stations include upper relay stations and lower relay stations and the upper relay stations and the lower relay stations are connected by a wired network, unstable network delays may occur in the wired network, which may result in inaccurate allocation of time slots to mobile stations.

[0005] The present invention has been made in view of the above circumstances, and its purpose is to provide a technique for accurately allocating time slots even when network delays may occur. [Means for solving the problem]

[0006] In order to solve the above problem, a wireless communication system according to one embodiment of the present invention defines a plurality of downlink time slots that are time-division multiplexed at a downlink frequency, and defines a plurality of uplink time slots that are time-division multiplexed at an uplink frequency that is different from the downlink frequency, and includes an upper relay station that is capable of transmitting signals at the downlink frequency and receiving signals at the uplink frequency, and a lower relay station that is connected to the upper relay station via a network, is capable of receiving signals at the uplink frequency, but is unable to transmit signals at the downlink frequency. The upper relay station suspends signal transmission when no signal is received, and when the upper relay station suspends transmission and receives a transmission start request on an uplink frequency from a mobile station wishing to start communication, the lower relay station transmits the transmission start request to the upper relay station via the network, and when the upper relay station receives the transmission start request from the lower relay station, it transmits an idle frame on the downlink frequency indicating that downlink time slots other than the first downlink time slot among the multiple downlink time slots are in use and that uplink time slots other than the first uplink time slot among the multiple uplink time slots are in use, and when the lower relay station receives a signal from the mobile station in the first uplink time slot on the uplink frequency, it transmits the signal to the upper relay station via the network, and the upper relay station receives the signal from the lower relay station and uses the first downlink time slot and the first uplink time slot for the mobile station.

[0007] Any combination of the above components, and any transformation of the present invention into a method, device, system, recording medium, computer program, etc., are also valid aspects of the present invention. [Effects of the Invention]

[0008] According to the present invention, time slots can be allocated accurately even when network delays may occur. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating a configuration of a wireless communication system according to an embodiment of the present invention. [Figure 2] 2(a) and 2(b) are diagrams showing the configuration of time slots defined in the wireless communication system according to FIG. [Figure 3] FIG. 2 is a diagram illustrating a configuration of an upper relay station in FIG. [Figure 4] FIG. 2 is a diagram illustrating a configuration of the mobile station of FIG. [Figure 5] FIG. 2 is a diagram illustrating a configuration of a lower relay station in FIG. [Figure 6] FIG. 10 is a diagram showing the data structure of slot information included in the idle frame up to now. [Figure 7] 7(a)-(f) are diagrams showing an overview of communication when the idle frame of FIG. 6 is used. [Figure 8] FIG. 2 is a diagram illustrating another configuration of the wireless communication system of FIG. [Figure 9] FIG. 10 is a diagram showing the data structure of slot information contained in a voice or data frame. [Figure 10] 10(a)-(h) are diagrams showing an outline of another communication when the idle frame of FIG. 6 is used. [Figure 11] 11(a)-(h) are diagrams showing an overview of communication in a situation where a problem occurs when using the idle frame of FIG. [Figure 12] 10 is a diagram illustrating a data structure of slot information included in an idle frame according to the present embodiment. FIG. [Figure 13] 13(a)-(h) are diagrams showing an overview of communication when the idle frame of FIG. 12 is used. [Figure 14] 2 is a sequence diagram showing a communication procedure in the wireless communication system of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] Before describing the present invention in detail, an overview will be provided first. An embodiment of the present invention relates to a wireless communication system including a relay station and a mobile station. The relay station may be classified into an upper relay station and a lower relay station. The wireless communication system uses the DMR (Digital Mobile Radio) standard, which is a TDMA wireless communication protocol defined by ETSI (European Telecommunications Institute). The ETSI DMR Tier 2 Standard is widely used in conventional systems that meet FB6, a station class defined by FCC (Federal Communications Commission). The following describes (1) the basic configuration, (2) the connection process so far, and (3) the connection process in this embodiment, in that order.

[0011] (1) Basic configuration 1 shows the configuration of a wireless communication system 1000. The wireless communication system 1000 includes an upper relay station 100, a first mobile station 200a and a second mobile station 200b collectively referred to as mobile stations 200, and a first lower relay station 300a to a fourth lower relay station 300d collectively referred to as lower relay stations 300. The number of mobile stations 200 included in the wireless communication system 1000 is not limited to "2", and the number of lower relay stations 300 is not limited to "4". The wireless communication system 1000 complies with, for example, the DMR standard.

[0012] In wireless communication system 1000, a downlink used for transmission from upper relay station 100 and an uplink used for reception at upper relay station 100 are defined. The frequency of the downlink (hereinafter referred to as the "downlink frequency") is different from the frequency of the uplink (hereinafter referred to as the "uplink frequency"). Furthermore, a plurality of downlink time slots that are time-division multiplexed are defined in the downlink frequency, and a plurality of uplink time slots that are time-division multiplexed are defined in the uplink frequency. The downlink time slots and the uplink time slots are collectively referred to as "time slots" or "slots."

[0013] 2(a)-(b) show the configuration of time slots defined in the wireless communication system 1000. FIG. 2(a) shows downlink time slots. A first downlink time slot designated "1" and a second downlink time slot designated "2" are repeated. FIG. 2(b) shows uplink time slots. A first uplink time slot designated "1" and a second uplink time slot designated "2" are repeated. The timing of the first downlink time slot and the first uplink time slot is different, and the timing of the second downlink time slot and the second uplink time slot is also different. In the following description, the first downlink time slot or the first uplink time slot may be referred to as "slot A," and the second downlink time slot or the second uplink time slot may be referred to as "slot B." Return to FIG. 1.

[0014] The upper relay station 100 is a wireless device that relays signals (voice frames, data frames) between multiple mobile stations 200. FIG. 3 shows the configuration of the upper relay station 100. The upper relay station 100 includes a transmitter 120, a receiver 130, a network communication unit 140, and a controller 150. The transmitter 120 is capable of transmitting signals using downlink frequencies, and the receiver 130 is capable of receiving signals using uplink frequencies. The area in which signals transmitted from the transmitter 120 can be received is shown as upper relay station transmission coverage 110 in FIG. 1. The network communication unit 140 is capable of communicating with multiple lower relay stations 300 via a wired network. The controller 150 controls the overall operation of the upper relay station 100. Returning to FIG. 1,

[0015] Mobile station 200 is a wireless device carried by a user and capable of performing voice communication or data communication. For example, a signal transmitted from first mobile station 200a for voice communication or data communication is received by upper relay station 100 and then transmitted from upper relay station 100 to second mobile station 200b. FIG. 4 shows the configuration of mobile station 200. Mobile station 200 includes a transmitter 220, a receiver 230, a controller 250, and an interface 260. Transmitter 220 is capable of transmitting signals using uplink frequencies, and receiver 230 is capable of receiving signals using downlink frequencies. The area in which signals transmitted from transmitter 220 can be received is indicated as mobile station transmission coverage 210 in FIG. 1. Controller 250 controls the overall operation of mobile station 200. Interface 260 is an interface with a user who uses mobile station 200 and includes, for example, an operating unit such as a PTT (Push To Talk) button, a microphone, a speaker, and a display. Return to Figure 1.

[0016] The mobile station transmission coverage 210 is smaller than the upper relay station transmission coverage 110. Therefore, depending on the location of the mobile station 200, a situation may occur in which the upper relay station transmission coverage 110 includes the mobile station 200, but the upper relay station 100 is not included in the mobile station transmission coverage 210. This can also be said to be a situation in which downlink communication is performed but uplink communication is not performed. To prevent such a situation from occurring, multiple lower relay stations 300 are installed within the upper relay station transmission coverage 110.

[0017] FIG. 5 shows the configuration of the lower relay station 300. The lower relay station 300 includes a receiving unit 330, a network communication unit 340, and a control unit 350. The receiving unit 330 is capable of receiving signals at uplink frequencies. On the other hand, the lower relay station 300 does not include a transmitting unit, and therefore cannot transmit signals at downlink frequencies. The network communication unit 340 is capable of communicating with the upper relay station 100 via a wired network. In this manner, each of the multiple lower relay stations 300 and the upper relay station 100 are connected via a wired network, for example, an Internet Protocol (IP) network. Returning to FIG. 1 , a signal transmitted from a mobile station 200 in a mobile station transmission coverage 210 that does not include the upper relay station 100, for example, the first mobile station 200a, is received by the first lower relay station 300a and transmitted from the first lower relay station 300a to the upper relay station 100.

[0018] (2) Connection process so far (2-1) Processing between the upper relay station 100 and the mobile station 200 In the conventional system, the upper relay station 100 is required to suspend signal transmission when it does not receive a signal from the mobile station 200. When the upper relay station 100 suspends signal transmission, the mobile station 200 (first mobile station 200a) that wishes to start communication transmits a transmission activation request on an uplink frequency. For clarity of explanation, unlike in FIG. 1, it is assumed here that the upper relay station 100 is included in the mobile station transmission coverage 210 of the first mobile station 200a.

[0019] Receiver 130 of upper relay station 100 receives a transmission activation request on the uplink frequency. When controller 150 accepts the transmission activation request, it generates an idle frame including information on currently available slots (hereinafter referred to as "slot information"), and transmitter 120 transmits the idle frame on the downlink frequency. FIG. 6 shows the data structure of the slot information included in the idle frame so far. The slot information indicates that slot A and slot B are unused. Slot A corresponds to the combination of the first downlink time slot and the first uplink time slot described above, and slot B corresponds to the combination of the second downlink time slot and the second uplink time slot described above. In this state, controller 150 defines two slots, but has not yet determined which is slot A or which is slot B. Return to FIG. 1.

[0020] The receiver 230 of the first mobile station 200a receives an idle frame. Since the relative timing of the idle frame is known, the controller 250 establishes synchronization with the upper relay station 100 based on the timing of receiving the idle frame. Since a known technique can be used to establish synchronization, a detailed description thereof will be omitted. Furthermore, once synchronization is established, the downlink time slot and the uplink time slot shown in FIGS. 2(a) and 2(b) are also formed in the first mobile station 200a. The controller 250 extracts slot information from the idle frame. If the controller 250 determines that both slot A and slot B are available in the slot information, it selects one of the slots, e.g., slot A. The controller 250 includes the selected slot number in a signal to be transmitted, e.g., a voice frame. The transmitter 220 transmits the voice frame to the upper relay station 100 in slot A, i.e., the first uplink time slot. The signal to be transmitted is not limited to a voice frame and may be a data frame.

[0021] The receiver 130 of the upper relay station 100 receives a voice frame from the first mobile station 200a in the first uplink time slot of the uplink frequency. The controller 150 permits the first mobile station 200a to use slot A based on the slot number included in the voice frame. The controller 150 also determines the uplink time slot in which the voice frame is received as the first uplink time slot. As a result, the controller 150 uses the first uplink time slot and the first downlink time slot, i.e., slot A, for the first mobile station 200a.

[0022] 7(a)-(f) show an overview of communications when the idle frame of FIG. 6 is used. FIG. 7(a) shows a signal transmitted from the upper relay station 100. Since transmission is paused, no signal is transmitted from the upper relay station 100, and only downlink time slots are specified. FIG. 7(b) shows a signal received at the first mobile station 200a. The first mobile station 200a selects one downlink time slot as slot A. FIG. 7(c) shows a signal transmitted from the first mobile station 200a. The first mobile station 200a transmits a signal in the first uplink time slot corresponding to the selected slot A. FIG. 7(d) shows a signal received at the upper relay station 100. The upper relay station 100 receives the signal from the first mobile station 200a.

[0023] FIG. 7(e) shows uplink time slots determined by the upper relay station 100. Since the slot number included in the signal from the first mobile station 200a includes slot A, the upper relay station 100 determines the uplink time slot in which the signal was received as the first uplink time slot. Here, the first uplink time slot is shown as "slot A." Furthermore, the upper relay station 100 arranges the first uplink time slot and the second uplink time slot alternately based on the determined first uplink time slot. FIG. 7(f) shows downlink time slots determined by the upper relay station 100. The upper relay station 100 determines the downlink time slot with the same timing as the first uplink time slot as the second downlink time slot. Furthermore, the upper relay station 100 determines the downlink time slot with the same timing as the second uplink time slot as the first downlink time slot.

[0024] FIG. 8 shows another configuration of the wireless communication system 1000. This shows a situation in which a second mobile station 200b is connected to the upper relay station 100 following a first mobile station 200a, and the first mobile station 200a and the second mobile station 200b communicate with each other via the upper relay station 100. The control unit 150 of the upper relay station 100 includes slot information in a voice frame received from the first mobile station 200a. FIG. 9 shows the data structure of the slot information included in the voice or data frame. The slot information is shown in the same manner as in FIG. 6, except that "Voice or Data" is stored in slot A, which corresponds to being in use. The slot information also indicates that slot B is unused. This slot information indicates that after communication with the first mobile station 200a is started, the first downlink time slot and the first uplink time slot are in use, and the second downlink time slot and the second uplink time slot are unused. Return to FIG. 8. The transmitter 120 of the upper relay station 100 transmits a voice frame at a downlink frequency in the second downlink time slot not assigned to the first mobile station 200a.

[0025] The receiver 230 of the second mobile station 200b receives the voice frame at the downlink frequency. The controller 250 extracts slot information from the voice frame. Based on the slot information, the controller 250 recognizes that slot B is available for use. The controller 250 reproduces the received voice frame. On the other hand, when transmitting a voice frame from the second mobile station 200b, the transmitter 220 transmits the voice frame to the upper relay station 100 at the uplink frequency in the second uplink time slot.

[0026] The receiver 130 of the upper relay station 100 receives the voice frame from the second mobile station 200b in the second uplink time slot of the uplink frequency. The controller 150 assigns the second downlink time slot and the second uplink time slot, i.e., slot B, to the second mobile station 200b. The first mobile station 200a uses slot A, and the second mobile station 200b uses slot B, whereby the first mobile station 200a and the second mobile station 200b communicate via the upper relay station 100.

[0027] (2-2) Processing when the lower relay station 300 is also included Next, assume that the mobile station transmission coverage 210 of the first mobile station 200a does not include the upper relay station 100 but includes the first lower relay station 300a, as shown in Fig. 1. As described above, when the upper relay station 100 pauses transmission, the mobile station 200, the first mobile station 200a, which wishes to start communication, transmits a transmission activation request on an uplink frequency.

[0028] When the upper relay station 100 pauses transmission, the receiver 330 of the first lower relay station 300a receives a transmission start request from the first mobile station 200a at the uplink frequency. The network communication unit 340 transmits the transmission start request to the upper relay station 100 via the wired network. The network communication unit 340 of the upper relay station 100 receives the transmission start request from the first lower relay station 300a. When the controller 150 receives the transmission start request, it generates an idle frame including slot information, and the transmitter 120 transmits the idle frame at the downlink frequency. The idle frame and slot information are the same as those described above, so a description thereof will be omitted here.

[0029] The receiver 230 of the first mobile station 200a receives the idle frame. The controller 250 establishes synchronization with the upper relay station 100 based on the timing of receiving the idle frame. The controller 250 selects one slot, for example, slot A, based on the slot information extracted from the idle frame. The controller 250 includes the selected slot number in a signal to be transmitted, for example, a voice frame. The transmitter 220 transmits the voice frame in slot A, i.e., the first uplink time slot. The signal to be transmitted is not limited to a voice frame and may be a data frame.

[0030] The receiver 330 of the first lower relay station 300a receives a voice frame from the first mobile station 200a in the first uplink time slot of the uplink frequency. The network communication unit 340 transmits the voice frame to the upper relay station 100 via the wired network. The network communication unit 340 of the upper relay station 100 receives the voice frame from the first lower relay station 300a. The controller 150 permits the first mobile station 200a to use slot A based on the slot number included in the voice frame. The controller 150 also determines the uplink time slot including the timing at which the network communication unit 340 received the voice frame as the first uplink time slot. As a result, the controller 150 assigns the first uplink time slot and the first downlink time slot to the first mobile station 200a.

[0031] 8 is the same as before, so a description thereof will be omitted here. As a result of this processing, the upper relay station 100 transmits a voice frame to the first mobile station 200a using the first downlink time slot in the downlink frequency. The first mobile station 200a transmits a voice frame to the first lower relay station 300a using the first uplink time slot in the uplink frequency, and the first lower relay station 300a transmits the voice frame received from the first mobile station 200a to the upper relay station 100.

[0032] Figures 10(a)-(h) show an overview of another communication when using the idle frame of Figure 6. Figures 10(a)-(c) are the same as Figures 7(a)-(c). Figure 10(d) shows a signal received at the first lower relay station 300a. The first lower relay station 300a receives a signal from the first mobile station 200a. Figure 10(e) shows a signal transmitted from the first lower relay station 300a via the communication network. The signal received from the first mobile station 200a is transmitted. Figure 10(f) shows a signal received at the upper relay station 100 via the communication network. The signal from the first lower relay station 300a is received.

[0033] FIG. 10(g) shows uplink time slots determined by upper relay station 100. Since the slot number included in the signal from first mobile station 200a includes slot A, the upper relay station 100 determines the uplink time slot that includes the timing at which the signal was received as the first uplink time slot. Here, the first uplink time slot is shown as "slot A." Furthermore, upper relay station 100 arranges the first uplink time slot and the second uplink time slot alternately based on the determined first uplink time slot. FIG. 10(h) shows downlink time slots determined by upper relay station 100. Upper relay station 100 determines the downlink time slot with the same timing as the first uplink time slot as the second downlink time slot. Furthermore, upper relay station 100 determines the downlink time slot with the same timing as the second uplink time slot as the first downlink time slot.

[0034] (2-3) Problems In (2-2), an indefinite network delay may occur between the first lower relay station 300a and the upper relay station 100. As described above, the upper relay station 100 determines the uplink time slot including the timing of receiving the voice frame as the first uplink time slot, so there is a risk that the first uplink time slot determined by the upper relay station 100 may differ from the first uplink time slot identified by the first mobile station 200a. This corresponds to the first downlink time slot determined by the upper relay station 100 differing from the first downlink time slot identified by the first mobile station 200a, and the slot A determined by the upper relay station 100 differing from the slot A identified by the first mobile station 200a.

[0035] Figures 11(a)-(h) show an overview of communication in a situation where a problem occurs when using the idle frame of Figure 6. Figures 11(a)-(e) are the same as Figures 10(a)-(e). Figure 11(f) shows a signal received by the upper relay station 100 via the communication network. The signal from the first lower relay station 300a is received due to network delay.

[0036] FIG. 11(g) shows uplink time slots determined by upper relay station 100. Since the slot number included in the signal from first mobile station 200a includes slot A, the upper relay station 100 determines the uplink time slot that includes the timing at which the signal was received as the first uplink time slot. Here, the first uplink time slot is shown as "slot A." Furthermore, upper relay station 100 arranges the first uplink time slot and the second uplink time slot alternately based on the determined first uplink time slot. FIG. 11(h) shows downlink time slots determined by upper relay station 100. Upper relay station 100 determines the downlink time slot with the same timing as the first uplink time slot as the second downlink time slot. Furthermore, upper relay station 100 determines the downlink time slot with the same timing as the second uplink time slot as the first downlink time slot.

[0037] The first mobile station 200a recognizes the downlink timeslot indicated as "Selection A" in Fig. 11(b) as the first downlink timeslot. Meanwhile, according to Fig. 11(h), the first downlink timeslot in the upper relay station 100 is different from the first downlink timeslot recognized by the first mobile station 200a. Also, the first mobile station 200a recognizes the uplink timeslot in which the signal was transmitted in Fig. 11(c) as the first uplink timeslot. Meanwhile, according to Fig. 11(g), the first uplink timeslot in the upper relay station 100 is different from the first uplink timeslot recognized by the first mobile station 200a.

[0038] As a result, slot A in the first mobile station 200a is different from slot A in the upper relay station 100. The upper relay station 100 uses slot B for communication with the second mobile station 200b. However, slot B that the upper relay station 100 causes the second mobile station 200b to use is slot A in the first mobile station 200a. As a result, transmission by the second mobile station 200b interferes with transmission by the first mobile station 200a.

[0039] (3) Connection process in this embodiment In order to allow upper relay station 100 and first mobile station 200a to recognize slots in the same way even in a situation where a network delay occurs, upper relay station 100 according to this embodiment executes the following process. Control unit 150 of upper relay station 100 sets slot A and slot B for multiple downlink time slots and multiple uplink time slots even when communication with mobile station 200 is not being executed.

[0040] Furthermore, upon receiving a transmission activation request from the lower-level relay station 300, the control unit 150 generates an idle frame including slot information indicating that either slot A or slot B is in use, even though both slots A and B are unused. FIG. 12 shows the data structure of slot information included in the idle frame according to this embodiment. Here, slot A is set to be unused, and slot B is set to be in use. In other words, although slot B is unused, the control unit 150 sets slot B to be in use. This corresponds to indicating that, among the multiple downlink time slots, downlink time slots other than the first downlink time slot are in use, and that, among the multiple uplink time slots, uplink time slots other than the first uplink time slot are in use. Based on this slot information, the upper-level relay station 100 instructs the first mobile station 200a to use slot A. Return to FIG. 8. The transmitter 120 transmits the idle frame at the downlink frequency.

[0041] The receiver 230 of the first mobile station 200a receives the idle frame. The controller 250 establishes synchronization with the upper relay station 100 based on the timing of receiving the idle frame. As a result, the slots A and B preset in the upper relay station 100 are the same as the slots A and B recognized by the first mobile station 200a. The controller 250 extracts slot information from the idle frame. As described above, the slot information indicates that slot B is in use, so the controller 250 selects the unused slot A. The transmitter 220 transmits a voice frame in slot A, i.e., the first uplink time slot. The signal to be transmitted is not limited to a voice frame and may be a data frame. The selected slot number does not have to be included in the voice frame or data frame.

[0042] The receiving unit 330 of the first lower relay station 300a receives a voice frame from the first mobile station 200a in the first uplink time slot of the uplink frequency. The network communication unit 340 transmits the voice frame to the upper relay station 100 via the wired network. The network communication unit 140 of the upper relay station 100 receives the voice frame from the first lower relay station 300a. The control unit 150 causes the first mobile station 200a to use slot A, which has been previously specified for the first mobile station 200a. Here, slot A is preset. Therefore, even if a network delay occurs, slot A used by the first mobile station 200a does not change. The upper relay station 100 uses the first downlink time slot and the first uplink time slot for the first mobile station 200a. The subsequent processing in FIG. 8 is the same as before, so a description thereof will be omitted here.

[0043] Figures 13(a)-(h) show an overview of communications when using the idle frames of Figure 12. Figure 13(a) shows uplink time slots determined by the upper relay station 100. The first uplink time slot and the second uplink time slot are alternately arranged. Figure 13(b) shows downlink time slots determined by the upper relay station 100. The first downlink time slot and the second downlink time slot are alternately arranged. Figures 13(c)-(h) are the same as Figures 11(a)-(f). In Figure 13(h), the upper relay station 100 causes the first mobile station 200a to use the preset slot A regardless of the timing of receiving a signal.

[0044] This configuration can be realized in hardware terms by the CPU, memory, and other LSIs of any computer, and in software terms by programs loaded into memory, but here we depict functional blocks realized by the cooperation of these. Therefore, it will be understood by those skilled in the art that these functional blocks can be realized in various forms using only hardware, only software, or a combination of both.

[0045] The operation of the wireless communication system 1000 configured as described above will be described. FIG. 14 is a sequence diagram showing a communication procedure in the wireless communication system 1000. The PTT button of the first mobile station 200a is pressed (S10). The first mobile station 200a confirms that it is not receiving a signal from the upper relay station 100 (S12). The first mobile station 200a transmits a transmission start request (S14, S16). The first lower relay station 300a transmits the transmission start request to the network (S18, S20). The upper relay station 100 receives the transmission start request (S22). The upper relay station 100 generates an idle frame by treating slot B as being in use (S24) and transmits the idle frame (S26, S28). The first mobile station 200a starts transmitting a signal in slot A (S30, S32). The first lower relay station 300a starts transmitting the signal to the network (S34, S36). The upper relay station 100 transmits a signal indicating that slot A is in use and slot B is unused (S38, S40, S42).

[0046] According to this embodiment, an idle frame including slot information indicating that all but one slot is in use is transmitted, so that it is possible to instruct the mobile station to use one slot. Furthermore, since the mobile station transmits a signal using the instructed slot, even if a network delay occurs, the upper mobile station can determine that the signal was received in the pre-instructed slot. Furthermore, since the slot-related authorization is common to the mobile station and the upper relay station, communication between the upper relay station and the mobile station can be accurately performed. Furthermore, since the slot-related authorization is common to the mobile station and the upper relay station, time slot allocation can be accurately performed even when a network delay may occur. Furthermore, since communication between the upper relay station and the mobile station is accurately performed, another mobile station can also communicate with the upper relay station using a different slot.

[0047] The present invention has been described above based on the embodiments. These embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of the components and treatment processes, and that such modifications are also within the scope of the present invention. [Explanation of symbols]

[0048] 100 upper relay station, 110 upper relay station transmission coverage, 120 transmission unit, 130 reception unit, 140 network communication unit, 150 control unit, 200 mobile station, 210 mobile station transmission coverage, 220 transmission unit, 230 reception unit, 250 control unit, 260 interface unit, 300 lower relay station, 330 reception unit, 340 network communication unit, 350 control unit, 1000 wireless communication system.

Claims

1. an upper relay station that defines a plurality of downlink time slots that are time-division multiplexed in a downlink frequency, and defines a plurality of uplink time slots that are time-division multiplexed in an uplink frequency different from the downlink frequency, and that is capable of transmitting signals using the downlink frequency and receiving signals using the uplink frequency; a lower relay station connected to the upper relay station via a network, capable of receiving signals at the uplink frequency but not capable of transmitting signals at the downlink frequency; the upper relay station suspends signal transmission when no signal is received; When the upper relay station is suspending transmission, the lower relay station receives a transmission start request from a mobile station that desires to start communication on the uplink frequency, and transmits the transmission start request to the upper relay station via the network; When the upper relay station receives the transmission start request from the lower relay station, the upper relay station transmits an idle frame on the downlink frequency indicating that downlink time slots other than a first downlink time slot among the plurality of downlink time slots are in use, and that uplink time slots other than the first uplink time slot among the plurality of uplink time slots are in use; When the lower relay station receives a signal from the mobile station in the first uplink time slot of the uplink frequency, the lower relay station transmits the signal to the upper relay station via the network; the upper relay station receives the signal from the lower relay station; A wireless communication system in which the upper relay station uses the first downlink time slot and the first uplink time slot for the mobile station.

2. the plurality of downlink time slots include the first downlink time slot and the second downlink time slot; the plurality of upstream time slots include the first upstream time slot and the second upstream time slot; the upper relay station, after starting communication with the mobile station, transmits information indicating that the first downlink time slot and the first uplink time slot are in use and that the second downlink time slot and the second uplink time slot are unused; 2. The wireless communication system according to claim 1, wherein, when the mobile station is referred to as a first mobile station, a second mobile station different from the first mobile station performs communication using the second downlink time slot and the second uplink time slot based on the information.

Images