JP5231925B2 - Wireless communication terminal, wireless base station, and communication method - Google Patents

Description

  The present invention relates to the technical field of mobile communication, and more particularly, to a wireless communication terminal, a wireless communication base station and a method used in a wireless communication system in which beacon signals are periodically transmitted.

  In recent years, various devices have been equipped with wireless local area network (LAN) interfaces. In particular, the spread of IEEE802.11 standard specifications to personal computers (PCs), home appliances, portable terminals, etc. is remarkable. When a portable terminal or the like becomes a communication terminal (STA) in IEEE802.11, it is important to save power.

  FIG. 1 is a conceptual diagram for explaining a method of saving power in a certain communication terminal STA. The horizontal axis is the time axis, “B” represents a beacon signal, “PS-Poll” represents a control signal described later, “ACK” represents an acknowledgment signal, “DATA” represents a data signal, and “SLEEP” represents a pause period. .

  The communication terminal STA operates in the power saving mode when there is no user data to be communicated. The power saving mode may be referred to as a battery saving mode, a power saving mode (PSM), or the like. In the power saving mode, a start-up period (Wake-Up period) and a sleep period (SLEEP period) are alternately visited, and the communication terminal receives a beacon signal during the start-up period and stops operating until the next start-up period comes. A period from the start period to the next start period is a sleep period. The period at which the communication terminal is activated is determined when the communication link is set up between the communication terminal and the radio base station (also referred to as access point AP) (may be uniquely determined by the system) .).

  When a certain communication terminal STA operates in the power saving mode, the downlink packet addressed to the communication terminal STA is once buffered by the radio base station AP. The radio base station AP describes the destination ID (association ID) of the buffered packet in the bitmap portion of the beacon frame, and transmits a beacon signal including the bitmap portion at a predetermined cycle. The beacon signal is periodically broadcast to all communication terminals in the cell. The information including the above association ID is particularly called a delivery traffic indication message (DTIM), and is included in a specific beacon signal among beacon signals periodically transmitted. In other words, DTIM is included in the beacon signal transmitted once in several times. Usually, the period of the activation period of the communication terminal (and the period of the sleep period) is determined according to the transmission period of the DTIM. Thereby, the transmission of the downlink packet can be started immediately after the DTIM.

  The communication terminal STA confirms the DTIM of the beacon signal and confirms whether or not the packet addressed to itself is buffered in the radio base station AP. If there is a packet addressed to the terminal itself, the communication terminal STA transmits a control signal for prompting transmission of the downlink packet to the radio base station AP. This control signal is called PS-Poll. When receiving the control signal (PS-Poll) from the communication terminal STA, the radio base station AP transmits a downlink packet in response to the operation mode of the communication terminal STA being changed from the power saving mode to the active mode. When the communication terminal STA completes reception of the downlink packet, the communication terminal STA enters the power saving mode again. Such a technique is described in Non-Patent Document 1, for example.

  On the other hand, the communication speed in the physical layer of the wireless LAN is increasing, and some old and new communication terminals may coexist in the same area. For example, IEEE802.11g of Non-Patent Document 2 defines the CTS-to-Self method in preparation for mixing with the conventional method using the 2.4 GHz band. FIG. 2 is a diagram for explaining the CTS-to-Self scheme. IEEE802.11b defines the operation of a DSSS communication terminal, which is a conventional method. IEEE802.11g defines the operation of a communication terminal that performs communication using an orthogonal frequency division multiplexing (OFDM) system, and also supports the conventional DSSS (Direct Sequence Spread Spectrum) system. If communication is possible only with the DSSS system and demodulation is not possible even after receiving an OFDM system packet, there is a concern that the communication terminal may transmit a packet without carrier sense as a result. In the above CTS-to-Self method, in order to solve this problem, it is defined that a transmission prohibition period (NAV: Network Allocation Vector) is set. Specifically, a communication terminal that is to start communication transmits a transmission permission signal (CTS-to-Self frame) addressed to itself by the DSSS method, and then transmits a packet by the OFDM method. Other communication terminals (which may be terminals conforming to IEEE802.11g or terminals conforming to IEEE802.11b) that have received the CTS-to-Self frame know that they should not be transmitted for a certain period thereafter. During the period indicated as “NAV” in the figure, transmission of terminals STA2 other than communication terminal STA1 is prohibited. By transmitting CTS-to-Self frames in DSSS format in this way, it becomes possible to transmit IEEE802.11g format packets while stopping communications even with terminals that support only IEEE802.11b format. IEEE802.11b / g system can be mixed.

  In the example shown in FIG. 1, a predetermined control signal (PS-Poll) is transmitted from the communication terminal STA to the radio base station AP, but Non-Patent Document 3 defines another method. Non-Patent Document 3 defines the standard specifications of IEEE802.11e, and defines the APSD (automatic power save delivery) method, which is a more efficient power-saving method than the power-saving method (IEEE802.11) of Non-Patent Document 1. doing.

FIG. 3 is a diagram for explaining the outline of the APSD method. In this scheme, an uplink packet is substituted for the control signal (PS-Poll) described in FIG. If there is no uplink packet, a null packet (NULL frame) is transmitted. For this reason, there is no need to prepare and transmit a special control signal PS-Poll after receiving a beacon signal periodically, reducing the signal processing burden, shortening the startup period, and thus achieving highly efficient power saving. Can do.
ANSI / IEEE std 802.11, Wireless LAN medium access control (MAC) and physical layer (PHY) specifications, 1999. ANSI / IEEE std 802.11, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications Amendment 4: Further Higher Data Rate Extension in the 2.4 GHz Band IEEE std 802.11e-2005, Amendment 8: Medium Access Control (MAC) Quality of Service Enhancements (IEEE802.11e standard), 11, Nov, 2005

  As described above, the wireless LAN defines various functions related to the IEEE802.11b / g mixed method and the power saving function. However, these systems do not guarantee that the communication terminal can communicate properly without collision in any situation.

  FIG. 4 shows one of the problems in the prior art. In the illustrated example, IEEE802.11b communication terminals STA1 and IEEE802.11g communication terminals STA2 and STA3 are mixed in the same region. Further, it is assumed that the communication terminal STA2 operates in the active mode, but the communication terminal STA3 operates in the power saving mode. As described above, prior to starting transmission, communication terminal STA1 transmits a transmission permission signal (CTS-to-Self) addressed to itself so as to reach surrounding communication terminals. Receiving this transmission permission signal, the communication terminal STA2 confirms that the terminal that starts transmission is STA1 (not its own terminal), and refrains from transmitting packets for a certain period (NAV). Thereafter, the communication terminal STA1 transmits data. In this case, in the illustrated example, the transmission permission signal (CTS-to-Self) from the communication terminal STA1 is transmitted during the sleep period of the communication terminal STA3. Accordingly, the communication terminal STA3 may not properly receive the transmission permission signal, and may transmit some packet (PS-Poll or data) after the sleep period ends. As a result, there is a possibility that communication by the communication terminal STA1 and communication by the communication terminal STA3 collide.

  FIG. 5 shows another problem in the prior art. In the illustrated example, it is assumed that the communication terminals STA1-3 are located in the cell of the common radio base station AP. It is assumed that the communication terminals STA1 and STA2 are close enough to communicate directly with each other, but the communication terminal STA3 is not close enough to directly communicate with the communication terminals STA1 and STA2. Each communication terminal is based on the IEEE802.11b or IEEE802.11g system. In this case, the communication terminals STA1 and STA2 and the communication terminal STA3 are hidden from each other. In such a positional relationship, one method for avoiding communication collision is the RTS / CTS method (the RTS / CTS method is described in Non-Patent Document 1, for example). According to this method, communication terminal STA1 desiring to start communication transmits a communication request signal (RTS: Request-to-Send) to base station apparatus AP. In response to this, the base station apparatus AP creates a transmission permission signal (CTS: Clear-to-Send) indicating that the communication terminal STA1 can start transmission, and notifies the communication terminals STA1-3 under its control. The communication terminal STA2 knows that the communication terminal STA1 will transmit thereafter, and refrains from transmitting a signal for a certain period thereafter (NAV). The communication terminal STA1 starts communication in response to the transmission permission signal CTS. In this way, even if the communication terminal is in the positional relationship of the hidden terminal, a device has been devised to prevent a communication collision.

  However, when the communication terminal STA3 that is in the positional relationship of the hidden terminal operates in the power saving mode and the transmission permission signal CTS is transmitted during the sleep period, the communication terminal STA3 cannot appropriately receive the transmission permission signal CTS. Also in this case, the communication terminal STA3 may transmit some packet after the sleep period ends. As a result, there is a possibility that communication by the communication terminal STA1 and communication by the communication terminal STA3 collide.

  The problem of the present invention is that when a predetermined control signal (RTS / CTS-to-Self) from the first terminal reaches other terminals including the second terminal, the communication of the other terminals is prohibited for a certain period. In the wireless communication system, when the predetermined control signal is transmitted within the sleep period of the second terminal operating in the power saving mode and the second terminal starts communication after the sleep period, the communication of the first terminal and the second terminal It is to avoid the problem of communication conflicts.

  In one form of the present invention, a wireless communication terminal that periodically receives a beacon signal from a wireless base station is used.

Wireless communication terminal
A buffering unit for accumulating data signals;
A control signal generating unit that generates a notice control signal for notifying that the data signal is transmitted;
A transmission unit for transmitting the data signal after transmission of the advance notice control signal;
So that the predetermined beacon signal and the notice control signal are received by the other wireless communication terminal during the activation period in which the other wireless communication terminal operating in the power saving mode is activated. The transmission unit is a wireless communication terminal configured to transmit the advance notice control signal in accordance with the predetermined beacon signal.

  In one form of the present invention, a radio base station that periodically transmits a beacon signal to at least the first and second radio communication terminals is used.

  A wireless communication terminal according to an embodiment of the present invention
  A radio base station periodically transmits a beacon signal to a radio communication terminal in a cell, and a radio communication terminal that is about to start transmitting a data signal transmits a notice control signal for notifying the transmission of the data signal, Transmission from another wireless communication terminal that has received the advance notice control signal is a wireless communication terminal that attempts to start transmission of the data signal in a mobile communication system that is prohibited for a certain period of time,
  The data so that a predetermined beacon signal and the advance notice control signal are received by the other wireless communication terminal during an activation period in which the other wireless communication terminal operating in the power saving mode is activated. A wireless communication terminal that transmits the notice control signal after waiting for the next transmission timing of the beacon signal after the signal is generated.

  According to the present invention, a transmission prohibition period can be appropriately set even for a communication terminal operating in the power saving mode, and as a result, the collision probability of wireless LAN packets can be reduced.

  According to one aspect of the present invention, the transmission permission signal (CTS or CTS-to-Self) or the transmission request signal (RTS) is delayed in accordance with the transmission period of the beacon signal. Even if a communication terminal is operating in the power saving mode, the communication terminal must periodically start in order to receive beacon signals periodically (at least there should be many communication terminals that start in that period. .) By allowing CTS or CTS-to-self to be received within the startup period, even a communication terminal in power saving mode can receive and analyze CTS, etc. Transmission can be effectively prohibited. Thereby, it is possible to effectively avoid the collision between the communication of the communication terminal in the active mode and the communication of the communication terminal in the power saving mode.

  Since DTIM includes destination information of downlink packets, there are a large number of communication terminals that are periodically activated to receive a beacon signal including DTIM. Therefore, it is preferable to match the period for delaying the transmission permission signal (CTS or the like) with the beacon signal including DTIM.

  The beacon signal including the DTIM and the transmission permission signal may be multiplexed not only by time multiplexing but by any appropriate method. For example, frequency multiplexing, code multiplexing, or a combination of one or more of them may be performed. However, from the viewpoint of easily separating the beacon signal and the transmission permission signal on the receiving side, it is preferable to time-multiplex them. For example, the transmission permission signal may be transmitted immediately after the beacon signal.

  Information indicating whether or not there is a communication terminal operating in the power saving mode may be managed by the radio base station AP, and the information may be included in the beacon signal. However, if there are no communication terminals operating in the power saving mode, even if they are relatively few, etc., delaying the transmission permission signal CTS etc. uniformly reduces the communication delay, etc. It is not preferable from the viewpoint. From such a point of view, it is preferable to determine whether or not to delay the transmission permission signal CTS or the like based on a situation determination such as the presence or absence of a communication terminal operating in the power saving mode. When the delay function of the transmission permission signal CTS is executed by the radio base station AP, whether or not to enable the function may be determined by the radio base station AP. When the delay function of the transmission permission signal (CTS-to-self) is executed in the communication terminal STA, whether or not to enable the function is information indicating whether or not there is a communication terminal operating in the power saving mode. Based on this, it may be determined by the communication terminal STA.

  When the transmission permission signal CTS is transmitted in response to the transmission request signal RTS, if the transmission permission signal CTS is delayed, the transmission side of the transmission request signal RTS has a longer period during which delivery confirmation cannot be obtained. . From the viewpoint of dealing with such concerns, the radio base station AP that has received the transmission request signal RTS may transmit a confirmation signal indicating that the transmission request signal RTS has been normally received to the communication terminal. Alternatively, when the beacon signal includes information indicating the presence / absence of a communication terminal operating in the power saving mode, the transmission timing of the transmission request signal RTS itself may be waited until the next beacon signal is transmitted. In this way, the confirmation signal can be omitted.

  The transmission period of DTIM may be changed according to the traffic in the cell. For example, the period may be adjusted based on the QoS or load of the packet. For example, when there are many delay-sensitive voice packets (VoIP), etc., by setting the DTIM interval short, even if this method is applied, the impact of delay is kept small while maintaining the impact on the voice quality. Can be avoided.

  Examples of the present invention will be described from the following viewpoints.

1. 1. First embodiment 1.1 System overview 1.2 Description of operation 1.3 Configuration of terminal STA Second Embodiment 2.1 System Overview 2.2 Operation Description 2.3 Configuration of Base Station AP Third embodiment

< 1.1 System overview >
FIG. 6 shows a wireless communication system assumed in the first embodiment of the present invention including the wireless base station AP and the communication terminals STA1-3. The first embodiment mainly attempts to solve the problems described in FIG. That is, in the first embodiment, when communication terminals conforming to IEEE802.11b and communication terminals conforming to IEEE802.11g are mixed, communication between the communication terminals does not collide. For convenience of explanation, it is assumed that the communication terminals STA1-3 are close enough to directly communicate with each other if operating in the active mode. The communication terminal STA1 is a communication terminal conforming to the IEEE802.11g system, and operates in the active mode. The communication terminal STA2 is a communication terminal conforming to the IEEE802.11b system, and operates in the active mode. The communication terminal STA3 is also a communication terminal conforming to the IEEE802.11b system, but operates in the power saving mode. The communication terminal STA3 operating in the power saving mode alternately operates in the start period and in the sleep period (pause), and the power saving method may be the IEEE802.11 method (method using PS-Poll). IEEE802.11e method (APSD method) may be used. For convenience of explanation, it is assumed that the power saving method is the APSD method.

< 1.2 Operation explanation >
As mentioned in the description of FIG. 4, while the communication terminal STA3 operating in the power saving mode (PSM) is operating (pause) in the sleep period, the communication terminal STA3 receives signals from other communication terminals. Cannot receive properly. Even if the communication terminal STA1 transmits a transmission permission signal (CTS-to-Self) -notice control signal-addressed to itself within this period, the communication terminal STA3 cannot properly receive it. Therefore, in the first embodiment of the present invention, the transmission timing is set so that the transmission permission signal (CTS-to-Self) is transmitted during the activation period in which the communication terminal operating in the power saving mode is activated. Is delayed. As a result, the transmission permission signal (CTS-to-Self) and the data signal of the communication terminal STA1 are maintained in the transmission buffer until the transmission timing comes.

  FIG. 7 shows an operation example according to the first embodiment. The horizontal axis is the time axis, “B” is a beacon signal, “DATA” is a data signal, “ACK” is an acknowledgment signal, “SLEEP” is a pause period, “CTS” is CTS-to-Self, and NAV is transmitted Represents each prohibited period. Radio communication terminals STA1-3 under the radio base station AP periodically receive beacon signals. As described above, a communication terminal that operates in the power saving mode periodically starts up and receives a beacon signal including DTIM. In the present embodiment, a transmission permission signal (CTS-to-Self) is transmitted from the communication terminal STA1 in synchronization with the transmission timing of the beacon signal including the DTIM. In other words, in addition to the beacon signal including DTIM, the transmission permission signal (CTS-to-Self) is received by the communication terminal STA3 that has visited the startup period in the power saving mode. The communication terminal STA2 in the active mode analyzes the received transmission permission signal (CTS-to-Self), confirms that STA1 will perform transmission thereafter, and refrains from transmitting its own terminal. Since the communication terminal STA3 is also in the activated state, it receives and analyzes not only the beacon signal but also the transmission permission signal (CTS-to-Self), confirms that STA1 will transmit thereafter, and refrains from transmitting its own terminal. it can. In this way, by delaying the timing at which the communication terminal STA1 transmits the transmission permission signal (CTS-to-Self) until the transmission timing of the beacon signal including the DTIM, not only the communication terminal STA2 in the active mode but also power saving Transmission of the communication terminal STA3 in the mode can also be prohibited. Thereby, it is possible to effectively avoid the possibility that the communication by the communication terminal STA1 immediately after transmitting the transmission permission signal (CTS-to-Self) and the communication by the communication terminal STA3 immediately after the sleep period collide. The illustrated example further shows that data transmitted by the communication terminal STA3 can be communicated without colliding in the period after the end of the sleep period of the communication terminal STA3 and before the transmission of the beacon signal.

< 1.3 Configuration of terminal STA >
FIG. 8 shows a configuration example of the communication terminal STA1 used in this embodiment. The communication terminal includes an information processing unit 801, a nonvolatile memory 802, a volatile memory 803, an operation unit 804, a wireless communication unit 805, and a display unit 806.

  The information processing unit 801 is a central processing unit CPU and controls the operation of each functional element in the communication terminal.

  The nonvolatile memory 802 permanently stores data and programs used in the communication terminal.

  Volatile memory 803 temporarily stores data and programs used in communication terminals.

  The operation unit 804 provides a user interface for inputting signals such as a numeric keypad, key buttons such as alphanumeric characters, a touch panel, and the like.

  The wireless communication unit 805 performs signal conversion for performing wireless communication using a carrier sense multiple access (CSMA) method, and performs wireless communication.

  The display unit 806 forms part of the user interface, displays data and options to the user, and receives selection contents as necessary.

  FIG. 9 shows a functional block diagram of the communication terminal STA in the present embodiment. FIG. 9 shows a radio reception unit 901, beacon processing unit 902, 11b terminal presence confirmation unit 903, power saving terminal presence confirmation unit 904, CTS delay control unit 905, DTIM period calculation unit 906, DTIM beacon processing unit 907, transmission permission A signal generation unit 908, a packet queuing unit 909, and a wireless transmission unit 910 are depicted. Although not limited to FIG. 9, as is clear from the context of this specification, the drawings are drawn from the viewpoint of explaining the present invention, and reproduce the actual circuit configuration, arrangement, dimensions, sequence, and the like. is not. In order to simplify the explanation, there are some elements that actually exist but are not drawn. For example, a data signal reception processing unit or the like is not drawn.

  The radio reception unit 901 receives a control signal and a data signal transmitted through the downlink radio link. The control signal includes the above-described beacon signal.

  Beacon processing section 902 periodically receives a beacon signal in the received signal. By periodically receiving the beacon signal, the communication terminal can synchronize with the radio base station.

  The 11b terminal existence confirmation unit 903 analyzes the beacon signal to confirm whether or not there is an IEEE802.11b communication terminal in the same cell. Note that the communication terminal shown in FIG. 9 is an IEEE802.11g communication terminal STA1. This confirmation may be made, for example, by confirming whether or not a predetermined bit in the beacon signal is 1. Thereby, it is possible to determine whether or not IEEE802.11g communication terminals and IEEE802.11b communication terminals are mixed in the cell. The 11b terminal existence confirmation unit 903 confirms the presence / absence of an IEEE802.11b terminal, and notifies the CTS delay control unit 905 of the result.

  The power saving terminal presence confirmation unit 904 analyzes the beacon signal to determine whether there is a communication terminal operating in the power saving mode. The function of the power saving terminal presence confirmation unit 904 is not essential to the present invention, but this function is preferable from the viewpoint of appropriately determining whether or not the transmission permission signal should be delayed. When the power saving terminal presence confirmation unit 904 functions, the beacon signal includes information indicating whether there is a communication terminal operating in the power saving mode. In this case, before entering the power saving mode, the communication terminal (communication terminal STA3 in the current example) notifies the radio base station AP that the power saving mode is entered. In response to this notification, the radio base station AP describes in the beacon signal transmitted thereafter that “there is a terminal operating in the power saving mode in the cell”. For example, some control bits may be prepared, and the presence or absence of a communication terminal operating in the power saving mode may be expressed according to the value of the bits. Note that this bit may represent whether or not a certain number of communication terminals in the cell are operating in the power saving operation mode. The power saving terminal existence confirmation unit 904 confirms the presence / absence of a communication terminal operating in the power saving mode and notifies the CTS delay control unit 905 of the result.

  The CTS delay control unit 905 provides a control signal to the packet queuing unit 909 according to the content notified from the 11b terminal presence confirmation unit 903 and / or the power saving terminal presence confirmation unit 904. As described with reference to FIG. 7, the first embodiment is a situation where IEEE802.11g communication terminals and IEEE802.11b communication terminals coexist, and one or more communication terminals save power. Most beneficial when operating in mode. However, when it is not a mixed situation, strictly speaking, it is not a situation where packet collision is a concern, or when all the communication terminals in the serving cell are operating in the active mode, etc. It is not always a good idea to delay the transmission permission signal (CTS-to-Self) uniformly as in the operation example 7 because it extends the delay of the system. Therefore, the CTS delay control unit 905 enables the delay function of the transmission permission signal (CTS-to-Self) as described in FIG. 7 according to the determination results of the 11b terminal and the power saving terminal existence confirmation units 903 and 904. The control signal corresponding to the determined content is given to the packet queuing unit 909.

  The DTIM period calculation unit 906 calculates when the next DTIM arrives based on the agreement with the radio base station AP (or matters determined in advance by the system) and the received beacon signal. Note that a transmission permission signal (CTS-to-Self), which will be described later, may be transmitted immediately after receiving a beacon signal including the DTIM without calculating the time when the next DTIM is transmitted.

  The DTIM beacon processing unit 907 confirms whether or not the packet addressed to itself is buffered in the radio base station AP by confirming the bitmap portion of the beacon signal. When the packet addressed to the terminal itself is buffered, the DTIM processing unit 907 instructs the packet queuing unit 909 so that the control signal (PS-Poll) or the data signal packet is transmitted at an appropriate timing.

  The transmission permission signal generation unit 908 creates a transmission permission signal (CTS-to-Self) addressed to the terminal (STA1). A data signal is transmitted after the transmission permission signal.

  The packet queuing unit 909 temporarily accumulates packets representing control signals or data signals transmitted from the communication terminal STA1, and transmits the packets to the wireless transmission 910 so that they are transmitted at an appropriate transmission timing and / or order. To do.

  The wireless transmission unit 910 converts a packet to be transmitted into a wireless signal and wirelessly transmits it to the wireless base station AP.

  Data signals arriving from the application layer are stored in the packet queuing unit 909. Prior to the transmission of the data signal, a transmission permission signal (CTS-to-Self) is transmitted. As described with reference to FIG. 7, in the first embodiment, the transmission timing of the transmission permission signal is delayed in accordance with the transmission timing of the next DTIM. The communication terminal STA3 operating in the power saving mode is activated at least in the cycle in which the DTIM is transmitted. Accordingly, the communication terminal STA1 transmits the transmission permission signal (CTS-to-Self) so that the communication terminal STA3 receives the beacon including DTIM and the transmission permission signal (CTS-to-Self). The transmission permission signal may be transmitted so that communication terminal STA3 receives the transmission permission signal (CTS-to-Self) immediately after the beacon signal including DTIM. Alternatively, the transmission permission signal may be transmitted so that the beacon signal including the DTIM and the transmission permission signal (CTS-to-Self) are frequency-multiplexed and / or code-multiplexed. In any case, the beacon signal including the DTIM and the transmission permission signal (CTS-to-Self) may be appropriately received by the communication terminal STA3.

  In the example shown in the figure, all the packets to be transmitted are temporarily stored in the packet queuing unit 909, and the transmission order and transmission timing may seem to be adjusted by the packet queuing unit 909. Is not essential to the present invention. It will be apparent to those skilled in the art that various device configurations are possible depending on the specific details of the communication terminal STA1.

< 2.1 System overview >
FIG. 10 shows a radio communication system assumed in the second embodiment of the present invention, including radio base stations AP and communication terminals STA1-3. The second embodiment mainly attempts to solve the problems described in FIG. That is, the second embodiment prevents the communication of communication terminals having a so-called hidden terminal positional relationship from colliding. Communication terminals STA1-3 are located in the same cell. If the communication terminals STA1, 2 operate in the active mode, they are close enough to communicate directly with each other. However, the communication terminal STA3 is not close enough to allow direct communication even in the active mode. The communication terminals STA1-3 may be either IEEE802.11b or IEEE802.11g. For convenience of explanation, it is assumed that the communication terminals STA1 and STA2 operate according to the IEEE802.11b system, and the communication terminal STA3 operates according to the IEEE802.11g system. The communication terminals STA1 and STA2 operate in the active mode, and the communication terminal STA3 operates in the power saving mode. The communication terminal STA3 operating in the power saving mode alternately operates in the start period and in the sleep period (pause), and the power saving method may be the IEEE802.11 method (method using PS-Poll). IEEE802.11e method (APSD method) may be used. For convenience of explanation, it is assumed that the power saving method is the APSD method.

< 2.2 Explanation of operation >
FIG. 11 shows an operation example according to the second embodiment. Radio communication terminals STA1-3 under the radio base station AP periodically receive beacon signals. As described above, a communication terminal that operates in the power saving mode periodically starts up and receives a beacon signal including DTIM. In this embodiment, communication control by the RTS / CTS method is performed. In the present embodiment, the transmission permission signal CTS from the radio base station AP is transmitted in accordance with the transmission timing of the beacon signal including the DTIM. This is different from the first embodiment.

  The communication terminal STA1 transmits a transmission request signal RTS to the radio base station AP in response to the generation of the uplink data signal. As described with reference to FIG. 10, since the communication terminals STA1 and STA2 are close enough to communicate directly and the communication terminal STA2 operates in the active mode, the communication terminal STA2 requests the transmission of the communication terminal STA1. The signal RTS can be received and analyzed. As a result of the analysis, the communication terminal STA2 refrains from transmitting for a certain period (sets a transmission prohibition period indicated by NAV).

  When the radio base station AP receives the transmission request signal RTS from the communication terminal STA1 and permits transmission of the communication terminal STA1, the radio base station AP creates a transmission permission signal CTS. The transmission request signal CTS is a control signal for notifying the communication terminal in the cell that the communication terminal STA1 is allowed to transmit. However, the transmission permission signal CTS is not transmitted immediately after receiving the transmission request signal RTS. This is different from the conventional RTS / CTS system.

  As described in the first embodiment, the communication terminal STA3 operating in the power saving mode is activated in the cycle of DTIM. In the second embodiment, the transmission permission signal CTS is transmitted from the radio base station AP to the communication terminals STA1-3 in the cell in accordance with the DTIM period. The communication terminal STA1 that has received the transmission permission signal CTS confirms that the transmission of its own terminal is permitted, and transmits a data signal. The communication terminal STA2 in the active mode confirms that a communication terminal other than its own terminal starts transmission, and refrains from transmission from the communication terminal STA2 for a certain period. Since the communication terminal STA3 is in the power saving mode but is in the start-up period, the communication terminal STA3 can receive and analyze the transmission permission signal CTS, confirm that the communication terminal other than its own terminal starts to transmit, and for a certain period, the communication terminal STA3 Refrain from sending from.

  In this way, by delaying the timing at which the radio base station AP transmits the transmission permission signal CTS to the transmission timing of the beacon signal including the DTIM, not only the communication terminal STA2 in the active mode but also the communication terminal STA3 in the power saving mode Can also be prohibited. Thereby, it is possible to effectively avoid the possibility that the communication by the communication terminal STA1 immediately after the transmission permission signal CTS is transmitted and the communication by the communication terminal STA3 immediately after the sleep period collide. The illustrated example further shows that data transmitted by the communication terminal STA3 can be communicated without colliding in the period after the end of the sleep period of the communication terminal STA3 and before the transmission of the beacon signal.

  In the case of the present embodiment, it may take a considerable amount of time after the transmission request signal RTS of the communication terminal STA1 is transmitted until the transmission permission signal CTS is received by the communication terminal STA1. In this case, the communication terminal STA1 cannot promptly confirm that the transmission permission signal RTS has been properly received. As a result, the communication terminal STA1 may retransmit the transmission permission signal CTS and increase wasteful signal processing. In order to deal with such a concern, it is preferable to return some confirmation signal to the communication terminal STA1 in response to the radio base station AP receiving the transmission permission signal RTS. This confirmation signal does not cause the transmission prohibition period to be set in another communication terminal, and may be a signal merely for confirming delivery of the transmission permission signal RTS.

< 2.3 Configuration of radio base station AP >
FIG. 12 shows a configuration example of the radio base station AP used in this embodiment. The wireless base station includes an information processing unit 1201, a nonvolatile memory 1202, a volatile memory 1203, an operation unit 1204, a wireless communication unit 1205, and a wired communication unit 1206.

  The information processing unit 1201 is a central processing unit CPU and controls the operation of each functional element in the radio base station.

  The nonvolatile memory 1202 permanently stores data and programs used in the radio base station.

  Volatile memory 1203 temporarily stores data and programs used in the radio base station.

  The operation unit 1204 provides a user interface for inputting signals such as a numeric keypad, key buttons such as alphanumeric characters, a touch panel, and the like.

  The wireless communication unit 1205 performs signal conversion for performing wireless communication with a communication terminal using a carrier sense multiple access (CSMA) method, and performs wireless communication.

  A wired communication unit 1206 performs signal conversion for connecting to a wired LAN and performs wired communication.

  FIG. 13 shows a functional block diagram of the radio base station AP in the present embodiment. FIG. 13 includes a wireless reception unit 1301, a reception packet processing unit 1302, a power saving terminal presence confirmation unit 1303, a CTS delay control unit 1304, an RTS packet processing unit 1305, a CTS packet generation unit 1306, an RTS reception confirmation packet generation unit 1307, A beacon generation unit 1308, a wired reception unit 1309, a packet queuing unit 1310, and a wireless transmission unit 1311 are depicted.

  Radio receiving section 1301 receives an uplink packet from a communication terminal.

  Received packet processing section 1302 extracts control packets and data packets in the received signal.

  The power saving terminal existence confirmation unit 1303 records that the communication terminal enters the power saving mode based on the notification signal transmitted from the communication terminal before entering the power saving mode. As mentioned in the description of the power saving terminal presence confirmation unit 904 in FIG. 9, the beacon signal may include information indicating whether or not there is a communication terminal operating in the power saving mode. In this case, before entering the power saving mode, the communication terminal (communication terminal STA3 in the current example) notifies the radio base station AP that the power saving mode is entered. In response to this notification, the radio base station AP describes in the beacon signal transmitted thereafter that “there is a terminal operating in the power saving mode in the cell”. For example, some control bits may be prepared, and the presence or absence of a communication terminal operating in the power saving mode may be expressed according to the value of the bits. Note that this bit may represent whether or not a certain number of communication terminals in the cell are operating in the power saving operation mode. The power saving terminal existence confirmation unit 1303 notifies the CTS delay control unit 1304 of the presence / absence of a communication terminal operating in the power saving mode.

  The CTS delay control unit 1304 gives a control signal to the packet queuing unit 909 according to the operation mode of the communication terminal located in the cell. As described with reference to FIG. 12, the second embodiment is most beneficial when the hidden terminal is operating in the power saving mode. If the communication terminal operating in the power saving mode is not in the service area, even if it is in the service area, the transmission permission signal CTS is uniformly delayed if the situation is such that packet collision is not a concern. On the contrary, it increases system delay and is not always a good idea. Therefore, the CTS delay control unit 1304 determines whether to enable the delay function of the transmission permission signal CTS as described in FIG. 12 according to the presence / absence of a communication terminal operating in the power saving mode. A control signal corresponding to the content is given to the packet queuing unit 1310. In the case of the APSD system, when shifting from the power saving mode to the active mode, some data packet (including a null packet) is transmitted from the communication terminal to the radio base station AP (FIG. 3 and the like). The CTS delay control unit 1304 can appropriately determine whether or not to enable the delay function of the transmission permission signal CTS by confirming the presence / absence of such a data packet and the notification from the power saving terminal presence confirmation unit.

  The RTS packet processing unit 1305 extracts the transmission permission signal RTS from the received signal, and determines whether or not to permit transmission to the transmission source communication terminal.

  The CTS packet generation unit 1306 creates a transmission permission signal CTS, and the transmission permission signal indicates that transmission of a data signal by a certain communication terminal is permitted.

  The RTS reception confirmation packet generation unit 1307 creates an acknowledgment packet indicating that the transmission request signal RTS has been properly received.

  The beacon generation unit 1308 generates a beacon signal that is periodically transmitted to the communication terminals in the cell. A beacon transmitted once at a time contains a DTIM. Information indicating whether or not an IEEE802.11b communication terminal and an IEEE802.11g communication terminal exist in the same cell may be included in the beacon signal. Further, information indicating whether or not there is a communication terminal operating in the power saving mode may be included in the beacon signal. The beacon signal is transmitted to the packet queuing unit 1310 and waits for transmission until a predetermined period comes.

  The wired receiving unit 1309 receives a downlink packet received from a higher-level station or the like in the wireless LAN system and supplies it to the packet queuing unit 1310.

  The packet queuing unit 1310 temporarily accumulates packets representing control signals or data signals transmitted to the communication terminal, and transmits the packets to the wireless transmission unit 1311 so as to be transmitted at an appropriate transmission timing and / or order. To do.

  The wireless transmission unit 1311 converts a packet to be transmitted into a wireless signal and wirelessly transmits it to the communication terminal.

  In response to the transmission request signal RTS arriving from the communication terminal, a transmission permission signal CTS addressed to the communication terminal is created and stored in the packet queuing unit 1310. The communication terminal transmits a data signal in response to receiving the transmission permission signal. As described with reference to FIG. 12, in the second embodiment, the transmission timing of the transmission permission signal CTS is delayed in accordance with the transmission timing of the next DTIM. The communication terminal STA3 operating in the power saving mode is activated at least in the cycle in which the DTIM is transmitted. Therefore, the radio base station AP transmits the transmission permission signal CTS so that the communication terminal STA3 receives the beacon including the DTIM and the transmission permission signal CTS. The transmission permission signal CTS may be transmitted so that the communication terminal STA3 receives the transmission permission signal CTS immediately after the beacon signal including the DTIM. Alternatively, the transmission permission signal may be transmitted so that the beacon signal including the DTIM and the transmission permission signal CTS are frequency-multiplexed and / or code-multiplexed. In any case, the beacon signal including the DTIM and the transmission permission signal CTS may be appropriately received by the communication terminal STA3.

  In the example shown in the figure, all packets to be transmitted are temporarily stored in the packet queuing unit 1310, and the transmission order and transmission timing may seem to be adjusted by the packet queuing unit 1310. Is not essential to the present invention. It will be apparent to those skilled in the art that various device configurations are possible depending on the specific details of the radio base station AP.

  Hereinafter, the modification regarding Example 1 and / or Example 2 of this invention is demonstrated. However, the division of the first and second embodiments and the modification examples is not essential to the present invention and is merely a convenience. The matter described in one example may apply as long as it does not contradict another example.

  (1) As described above, the beacon signal may include information indicating whether or not there is a communication terminal operating in the power saving mode. When such a beacon signal is received by the communication terminal, the communication terminal can know the presence / absence of the communication terminal operating in the power saving mode in the serving cell. For example, the communication terminal STA1 of the second embodiment can know the presence of a communication terminal operating in the power saving mode in the serving cell. As shown in FIG. 11, if the communication terminal STA1 transmits the transmission request signal RTS promptly after the occurrence of the uplink data, the communication terminal in the power saving mode is within the sleep period when the transmission request signal RTS is transmitted. might exist. As shown in FIG. 14, unlike the second embodiment, the communication terminal STA1 may delay the transmission timing of the transmission request signal RTS until the transmission timing of the beacon signal. In this case, transmission of the beacon signal, transmission / reception of the transmission request signal RTS, and transmission / reception of the transmission permission signal CTS by the radio base station AP are performed within the startup period of the communication terminal STA3 operating in the power saving mode. This method is preferable in that the period from when the communication terminal STA1 transmits the transmission request signal RTS until it receives the transmission permission signal CTS is extremely short. If this period is long, it is necessary to prepare a confirmation signal for the transmission request signal RTS as described above.

  (2) As described above, the transmission period of the DTIM substantially determines the activation period and the sleep period of the communication terminal. Then, the transmission permission signal (CTS-to-Self) of the first embodiment, the transmission permission signal (CTS) of the second embodiment, the transmission request signal (RTS) of the above modification, etc. are matched to the transmission cycle of the DTIM. Sent. Therefore, if the DTIM period is excessively long, the data signal is unnecessarily waited, which is not preferable from the viewpoint of improving the throughput. Conversely, if the DTIM period is excessively short, the communication terminal must be activated more than necessary, which is not preferable from the viewpoint of power saving. Therefore, it is preferable that the transmission cycle of DTIM is appropriately adjusted according to the communication status. For example, the cycle in which the beacon signal including the DTIM is transmitted may be changed according to the traffic in the cell. More specifically, the period includes the quality of service (QoS) of traffic in the cell, the number of times the radio base station AP has transmitted the transmission permission signal CTS, the number of times the radio base station AP has received the transmission request signal RTS, The number may be changed according to the number of wireless communication terminals operating in the power mode. Since QoS is an amount directly related to the allowable delay of the signal, it is preferable to use QoS based on the viewpoint of optimizing the DTIM transmission period according to the allowable delay.

  Although the present invention has been described with reference to particular embodiments, they are merely exemplary and those skilled in the art will appreciate various variations, modifications, alternatives, substitutions, and the like. Although specific numerical examples have been described in order to facilitate understanding of the invention, these numerical values are merely examples and any appropriate values may be used unless otherwise specified. The division of the embodiment or item is not essential to the present invention, and the matters described in two or more embodiments or items may be used in combination as necessary, or may be described in a certain embodiment or item. Matters may apply to matters described in other examples or items (unless they conflict). For convenience of explanation, an apparatus according to an embodiment of the present invention has been described using a functional block diagram. However, such an apparatus may be implemented by hardware, software, or a combination thereof. The present invention is not limited to the above embodiments, and various modifications, modifications, alternatives, substitutions, and the like are included in the present invention without departing from the spirit of the present invention.

The figure which shows an example of a power saving system. The figure which shows a CTS-to-Self system. The figure which shows another example of a power saving system. The figure which shows one of the problems. The figure which shows another problem. The figure which shows the radio | wireless communications system containing radio | wireless base station AP and communication terminal STA1-3. The figure which shows the operation example by 1st Example. The figure which shows the structure of a communication terminal. The functional block diagram of a communication terminal. The figure which shows the radio | wireless communications system containing radio | wireless base station AP and communication terminal STA1-3. The figure which shows the operation example by 2nd Example. The figure which shows the structure of a wireless base station. The functional block diagram of a radio base station. The figure which shows the operation example by a modification.

Explanation of symbols

801 Information processing unit 802 Non-volatile memory 803 Volatile memory 804 Operation unit 805 Wireless communication unit 806 Display unit 901 Wireless reception unit 902 Beacon processing unit 903 11b Terminal existence confirmation unit 904 Power saving terminal existence confirmation unit 905 CTS delay control unit 906 DTIM Period calculation unit 907 DTIM beacon processing unit 908 transmission permission signal generation unit 909 packet queuing unit 910 wireless transmission unit 1301 wireless reception unit 1302 reception packet processing unit 1303 power saving terminal existence confirmation unit 1304 CTS delay control unit 1305 RTS packet processing unit 1306 CTS packet generation unit 1307 RTS reception confirmation packet generation unit 1308 Beacon generation unit 1309 Wired reception unit 1310 Packet queuing unit 1311 Wireless transmission unit

Claims (14)

A radio base station periodically transmits a beacon signal to a radio communication terminal in a cell, and a radio communication terminal that is about to start transmitting a data signal transmits a notice control signal for notifying the transmission of the data signal , Transmission from another wireless communication terminal that has received the advance notice control signal is a wireless communication terminal that attempts to start transmission of the data signal in a mobile communication system that is prohibited for a certain period of time ,
During the startup period when the other radio communication terminals operating in the power saving mode is activated, so that a predetermined beacon signal and the warning control signal is received by the another wireless communication terminal, the data A wireless communication terminal that transmits the advance notice control signal after waiting for the next transmission timing of the beacon signal after the signal is generated . The warning control signal is represented by the transmission permission signal addressed to the wireless communication terminal, a radio communication terminal according to claim 1. Predetermined beacon signal transmitted at the transmission timing includes broadcast message indicating the destination information of the downlink data signal that are waiting to be sent, the wireless communication terminal according to claim 1 of the previous millet bacon signal. A wireless base station that periodically transmits a beacon signal to at least first and second wireless communication terminals,
A receiving unit for receiving a transmission request signal from the first wireless communication terminal;
In response to the transmission request signal, a permission signal generation unit that generates a transmission permission signal indicating that transmission of the data signal by the first wireless communication terminal is permitted;
A transmission unit for transmitting the transmission permission signal to at least the first and second wireless communication terminals;
During the activation period in which the second wireless communication terminal operating in the power saving mode is activated, the transmission unit transmits at least the first beacon signal and the transmission permission signal to the first and To the second wireless communication terminal ,
The beacon signal is a radio base station including information indicating which radio communication terminal is operating in a power saving mode .   The radio base station according to claim 4, wherein the transmission unit transmits the transmission permission signal immediately after the predetermined beacon signal. When the beacon signal indicates that no wireless communication terminal is operating in the power saving mode, the transmission permission signal is transmitted in response to the transmission request signal independently of the beacon signal. The radio base station according to claim 4 , further comprising a determination unit that controls the transmission unit. In the starting period, the transmission request signal is received, the radio base station according to claim 4, wherein. Before transmission of the transmission permission signal even after receiving the transmission request signal, the acknowledgment signal indicating that the transmission request signal has been received is transmitted to the first wireless communication terminal, according to claim 4 The radio base station described.   The radio base station according to claim 4, wherein the predetermined beacon signal includes a delivery message indicating destination information of a downlink data signal waiting for transmission. The radio base station according to claim 9 , wherein a cycle in which a beacon including the delivery message is transmitted is changed according to traffic in a cell. The cycle in which the beacon including the delivery message is transmitted is at least one of the service quality of traffic in the cell, the number of transmissions of the transmission permission signal, the number of receptions of the transmission request signal, and the number of wireless communication terminals operating in the power saving mode. altered radio base station according to claim 10, wherein in response to One. The operation in the power saving mode, the operation according to the standard specifications of IEEE802.11 or IEEE 802.11e, the radio base station according to claim 4. A radio base station periodically transmits a beacon signal to a radio communication terminal in a cell, and a radio communication terminal that is about to start transmitting a data signal transmits a notice control signal for notifying the transmission of the data signal , In a mobile communication system in which transmission from another wireless communication terminal that has received a notice control signal is prohibited for a certain period of time, a wireless communication terminal that attempts to start transmission of the data signal ,
During the startup period when the other radio communication terminals operating in the power saving mode is activated, so that a predetermined beacon signal and the warning control signal is received by the another wireless communication terminal, the data A communication method for transmitting the notice control signal after waiting for the next transmission timing of the beacon signal after the signal is generated . A communication method executed by a radio base station that periodically transmits beacon signals to at least first and second radio communication terminals,
Receiving a transmission request signal from the first wireless communication terminal;
Generating a transmission permission signal indicating that transmission of the data signal by the first wireless communication terminal is permitted in response to the transmission request signal;
Transmitting the transmission permission signal to at least the first and second wireless communication terminals;
It has, during the startup period of the second wireless communication terminals operating in the power saving mode is activated, in said transmitting step, at least the first predetermined beacon signal and the transmission permission signal And to the second wireless communication terminal ,
The communication method executed by a radio base station , wherein the beacon signal includes information indicating which radio communication terminal is operating in a power saving mode .

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