JP2004048539A - Radio communication system, radio base station, communication method and its program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a radio base station to be shared by different physical layers, and to efficiently execute retransmission processing in a radio LAN system. <P>SOLUTION: Terminal equipment corresponding to a frequency band A transmits a data packet D6<SB>1</SB>, and the reception of the D6<SB>1</SB>fails in an access point, and then when the terminal equipment retransmits a data packet D6<SB>2</SB>, the access point is switched to a frequency band B, and then the reception of the D6<SB>2</SB>fails. Afterwards, the terminal equipment continues to transmit an RTS each time a CTS stand-by timer expires. In this case, the fact that the CTS is transmitted and any response to this is not detected in the period of the frequency band A is stored, and when it is switched to the accessible period of the next frequency band A, the CTS is preferentially transmitted prior to a beacon signal. The terminal equipment receives the CTS, and executes carrier sense after the lapse of an already decided time, and retransmits a data packet D6<SB>3</SB>. When the access point normally receives the D6<SB>3</SB>, ACK is transmitted, and re-transmission processing is completed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wireless communication system, a wireless base station, a communication method, and a program applied to a wireless LAN system.
[0002]
[Prior art]
Recently, a wireless LAN (Wireless Local Area Network) has been widely used. Wireless LANs can be used indoors and outdoors. Indoors, a wireless LAN network is constructed by an access point (also called a wireless base station) and a plurality of personal computers each equipped with a wireless LAN card. Outdoors, access points are set up in fast food stores, stations, etc., and public wireless LAN services (so-called hot spots) using portable terminals such as notebook computers and PDAs (Personal Digital Assistants), and FWAs for homes and condominiums Fixed WirelessAccess (subscriber wireless access system) service becomes possible.
[0003]
Currently commercially available wireless LAN systems mainly use an ISM (Industrial Scientific & Medical) band (2.4 GHz band) and conform to IEEE802.11b with a transmission speed of 11 Mbps (bits / second). is there. Further, a 5 GHz band wireless LAN system has been institutionalized for indoor use, and a 5 GHz band wireless LAN system product conforming to IEEE 802.11a with a communication speed of 36 Mbps to 54 Mbps has been released.
[0004]
The IEEE (Institute of Electrical and Electronics Engineers) 802.11 system is one of wireless LAN protocols. This is a contention-free best-effort communication method of the CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) method. Of course, a wireless protocol other than the CSMA / CA scheme, for example, a protocol based on the ISMA (Idle Signal Multiple Access) scheme has been proposed. RS-ISMA (Reservation-based Slotted ISMA) has been proposed as an extension of the ISMA system.
[0005]
The 5 GHz band for indoor use is a frequency band of 5.15 to 5.25 GHz. Further, it is expected that the 5 GHz band will be opened to outdoor wireless LANs in the near future. As a result, the high-speed wireless LAN can be used not only indoors but also outdoors, and it is expected that public wireless LAN services will be rapidly expanded. Currently, it is scheduled to be open to the outdoors for the bands of 4.9-5 GHz and 5.03-5.09 GHz, and it is possible to arrange a total of 7 channels in both bands at 20 MHz per channel, with 54 Mbps. The above transmission speeds are possible. Also, a narrow band channel (10 MHz / 5 MHz) is possible, and in that case, the transmission speed is (27 Mbps / 13.5 Mbps).
[0006]
[Problems to be solved by the invention]
As described above, as the wireless LAN system, there are a plurality of systems (protocols or use frequency bands), and a new system may be developed in the future. Therefore, with the spread of wireless LANs, a situation in which a plurality of wireless LANs are mixed is assumed. For example, in the 5 GHz band wireless LAN system, the current system has a frequency band of 5.15-5.25 GHz, while the future new system has a frequency band of 4.9-5.0 GHz and 5.03. A frequency band of −5.09 GHz is being considered. It is expected that the existing system and the new system will coexist indoors, even if it is limited to a new system outdoors. In this case, if the access point does not support a plurality of systems, it is necessary to install access points corresponding to the plurality of systems, and various problems such as an increase in the installation cost of the access point occur.
[0007]
In the conventional wireless LAN system, even if one access point supports a plurality of systems, a plurality of systems are not simultaneously controlled by one access point, but the operation is set to any one of the systems and semi-fixed. Was used regularly. For this reason, there is no access point that can wait in a plurality of wireless LAN systems.
[0008]
Also, even in a method in which one access point supports a plurality of methods, if an existing wireless LAN terminal is forced to change, it is inconvenient for existing users, and in the worst case, the terminal of the existing method cannot be used. It is considered possible. In particular, in an IEEE 802.11 system device, it is possible to control an access time by providing a PCF (Point Coordinate Function) function (adjustment function), but generally, a wireless device without a PCF function is used. Since a large number of LAN devices are distributed, it is difficult to control an existing wireless LAN using a PCF. Here, the PCF function is a function for arbitrating the right of transmission by the access point as needed, and is defined as an optional function in the IEEE 802.11 system. More specifically, each terminal polls and inquires whether there is a transmission request, and issues a transmission right in response to the request.
[0009]
Furthermore, assuming that a wireless LAN system capable of waiting in a plurality of modes can be configured, if there is no measure for a lost packet (packet loss) caused by channel switching, it is necessary to transmit the packet again after a timeout. Since processing is required, there is a problem that transmission efficiency is reduced.
[0010]
Therefore, the object of the present invention is applied to a wireless communication system in which a plurality of wireless LAN systems are mixed, a wireless base station can be realized at low cost, a decrease in transmission efficiency can be prevented, and furthermore, an existing terminal can be used. An object of the present invention is to provide a wireless communication system, a wireless base station, a communication method, and a program that do not require a change in configuration.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problem, according to the invention of claim 1, a first broadcast signal of a first physical layer and a second broadcast signal of a second physical layer are alternately transmitted from a radio base station. A wireless communication system,
After receiving one of the first and second broadcast signals, a data packet is transmitted to the radio base station after a lapse of a predetermined time, and one of the first and second broadcast signals cannot be received. A first wireless terminal that prohibits transmission of a data packet to the wireless base station until one of the first and second broadcast signals can be received;
After receiving the other of the first and second broadcast signals, after a predetermined time elapses, transmits a data packet to the radio base station, receives an acknowledgment signal from the radio base station, or reaches a predetermined number of repetitions. This is a wireless communication system in which a second wireless terminal that repeatedly transmits a transmission permission request to a wireless base station until the wireless communication is performed is mixed.
[0012]
The invention according to claim 2 is a wireless base station in a wireless network including a plurality of wireless terminals and a common wireless base station,
At least two first and second physical layers below a common media access control layer;
Broadcast signal transmitting means for generating a first broadcast signal of the first physical layer and a second broadcast signal of the second physical layer alternately and transmitting the first and second broadcast signals to the wireless terminal With
The access of the wireless terminal of the first physical layer is enabled only within a first time from the transmission of the first broadcast signal, and the second physical signal is transmitted only within a second time from the transmission of the second broadcast signal. 2 wireless terminals of the physical layer can be accessed,
A data packet responding to the transmission permission despite giving the transmission permission in response to the transmission permission request from one of the wireless terminals of the first and second physical layers at one of the first and second times; Is a radio base station that stores a state in which the data packet is not received, and preferentially transmits a transmission permission for another type of data packet when one of the following first and second times is reached.
[0013]
The invention according to claim 6 is a communication method of a wireless base station in a wireless network including a plurality of wireless terminals and a common wireless base station,
Alternately generating a first notification signal of the first physical layer and a second notification signal of the second physical layer;
A broadcast signal transmitting step of transmitting the first and second broadcast signals to the wireless terminal,
The access of the wireless terminal of the first physical layer is enabled only within a first time from the transmission of the first broadcast signal, and the second physical signal is transmitted only within a second time from the transmission of the second broadcast signal. 2 wireless terminals of the physical layer can be accessed,
A data packet responding to the transmission permission despite giving the transmission permission in response to the transmission permission request from one of the wireless terminals of the first and second physical layers at one of the first and second times; This is a communication method for storing a state in which the data packet is not received, and when one of the following first and second times is reached, transmission permission is preferentially transmitted to another type of data packet.
[0014]
A communication method of a wireless base station in a wireless network including a plurality of wireless terminals and a common wireless base station,
Alternately generating a first notification signal of the first physical layer and a second notification signal of the second physical layer;
A broadcast signal transmitting step of transmitting the first and second broadcast signals to the wireless terminal,
The access of the wireless terminal of the first physical layer is enabled only within a first time from the transmission of the first broadcast signal, and the second physical signal is transmitted only within a second time from the transmission of the second broadcast signal. 2 wireless terminals of the physical layer can be accessed,
A data packet responding to the transmission permission despite giving the transmission permission in response to the transmission permission request from one of the wireless terminals of the first and second physical layers at one of the first and second times; A communication method for storing a state in which the data packet is not received, and sending a transmission permission to another type of data packet preferentially at one of the following first and second times to the computer. This is the program to be executed.
[0015]
According to the present invention, a wireless base station (access point) can be shared by wireless terminals in different physical layers. On the other hand, since no change in the configuration is required for the existing wireless terminal, the wireless base station can be easily introduced into a system in which the existing terminal device and the terminal device of the new system coexist. According to the present invention, it is possible to easily realize a wireless base station shared by two wireless LAN systems simply by adding a function to an existing wireless base station. A wireless base station that can be shared with the wireless LAN system can be realized. Furthermore, it remembers that it has not received a data packet responding to it even though it has given transmission permission, and when the next accessible time arrives, gives priority to other types of data packets to grant transmission permission. By transmitting, the efficiency of the retransmission process can be improved.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment in which the present invention is applied to a CSMA / CA wireless LAN will be described below. FIG. 1 shows an overall configuration of a system according to an embodiment. In FIG. 1, reference numeral 1 indicates a wireless LAN access point, reference numeral 2 indicates a wireless LAN terminal device (station), and reference numeral 3 indicates another wireless LAN terminal device (station).
[0017]
In one embodiment, it is assumed that the wireless LAN in the 5 GHz band can be used outdoors, and the terminal device 2 is connected to the existing 5.15 to 5.25 GHz frequency band (hereinafter referred to as the 5.2 GHz band as appropriate). The terminal device 3 is a newly developed 4.9-5 GHz frequency band (hereinafter, appropriately referred to as 4.9 GHz band) terminal device that can be used both outdoors and indoors. . The terminal devices 2 and 3 are both based on IEEE802.11a. The access point 1 and the terminal devices 2 and 3 are installed in a communicable area (called a service area, a cell, or the like). The access point 1 waits for an access from these two terminal devices 2 and 3.
[0018]
A network 4 is connected beyond the access point 1. The network 4 is, for example, a private or public Internet network. One or more user terminals 5 can be connected to the terminal device 2 on the user side. The user terminal 5 is a personal computer, a PDA, or the like. Similarly, one or more user terminals 6 can be connected to the terminal device 3.
[0019]
In computer networks, it is common to hierarchize functions that define physical techniques for transmitting information and logical techniques such as how to access remote resources. The layered structure of the IEEE802.11 system can be associated with the OSI reference model. The OSI reference model has a seven-layer hierarchical structure from the lowest physical layer to the highest application layer.
[0020]
In FIG. 1, an access point 1 and user terminal devices 2 and 3 include a physical layer (PHY: Physical Layer) 1a, 2a and 3a, a medium access control layer (MAC: Media Access Control) 1b, 2b and 3b, respectively. Upper layers 1c, 2c and 3c are provided. For example, the physical layer (PHY) includes a type of frequency band to be used, a band per channel, a modulation method (for example, a spread spectrum method), and encoding and decoding for error correction.
[0021]
The function of the medium access control layer (MAC) is to control and manage timing and multiple access related to packet communication in the wireless LAN system. For example, the CSMA / CA method is included in the medium access control layer (MAC). The medium access control layer (MAC) forms a sub-layer of the data link layer. Another sublayer is an LLC (Logical Link Control) layer. The upper layer collectively represents layers higher than the network layer above the LLC layer and the data link layer. Further, the access point 1 and the user terminal devices 2 and 3 have system controls 1d, 2d and 3d as hardware for controlling the operation of each device. The physical layers 1a, 2a, and 3a often have a relatively hardware configuration, and the medium access control layers 1b, 2b, and 3b and the upper layers 1c, 2c, and 3c perform software processing by a computer. It is often said.
[0022]
As a medium access control method in the wireless LAN method, several methods have been proposed. One of them is the CSMA / CA system which is an improvement on the CSMA system. In one embodiment, the access point 1, the user terminal devices 2 and 3 employ the CSMA / CA method as a medium access control method.
[0023]
In wireless communication, a function of detecting the presence or absence of a carrier is called a carrier sense function. The result of carrier sense indicates the presence or absence (busy / idle) of a packet (also called a frame) being transmitted from another station. In the CSMA system, when there is a packet to be transmitted by each terminal device, carrier sensing is performed before transmission, transmission of the packet is started when the terminal is idle, and transmission is stopped when the terminal is busy. In the CSMA system, a period in which carrier sense is not effective occurs due to a signal propagation delay time, and the problem of collision cannot be completely prevented. The CSMA / CA system has a collision avoidance mechanism in addition to carrier sense.
[0024]
In wireless communication, stations in which transmission signals do not reach each other because the distance between stations is too long or there is an obstacle that does not allow radio waves to pass are called hidden terminals. When a hidden terminal is present, the frequency of packet collisions increases between the hidden terminal and other stations because carrier sensing does not function effectively. The ISMA scheme is considered as one of the schemes for preventing the performance degradation of the CSMA scheme due to the presence of such hidden terminals.
[0025]
First, in order to facilitate understanding of the present invention, an example of the timing of an operation (retransmission control operation) at an existing CSMA type access point (denoted as AP in the figure) with reference to FIG. explain. The access point generates a beacon signal (denoted as B in the figure) at regular time intervals. The user terminal device (denoted as STA in the figure) receives the beacon signal (B), waits for DIFS (Distributed Inter-Frame Space), and then follows the random number generated by the device for collision avoidance. (Random Back-off) Carrier sensing is performed after waiting. After confirming that the channel is idle, transmission of the packet data D1 is started.
[0026]
The access point transmits ACK (Acknowledge: acknowledgment or acknowledgment signal) upon successful reception of the packet data D1. If the ACK reception fails, an RTS (Request to Send) is transmitted after an ACK waiting time (for example, 300 μsec) has elapsed from the transmission of the data to obtain a transmission opportunity.
[0027]
After receiving the RTS, the access point 1 waits for a SIFS (Short IFS) time, transmits a CTS (Clear to Send), and waits for transmission from the terminal device. When the terminal device receives the CTS, it transmits retransmission packet data D1 'after a DIFS and a random back-off time. Such a retransmission operation is defined in advance as being capable of retrying a specified number of times, for example, seven times, until a next beacon signal is received.
[0028]
FIG. 3 shows an operation of the embodiment of the present invention, and shows an operation example in a case where there is an access from the terminal device during the duplex switching reception. In the example of FIG. 3, the frequency band to be used is switched at intervals of the beacon signal (B) (also appropriately referred to as a beacon frame, for example, 100 msec) before transmitting the beacon signal (B). The diagrams showing the operation timing of the access point 1 are drawn above and below to show the frequency bands A and B, respectively. For example, frequency band A is a 5.2 GHz band of the existing system, and frequency band B is a 4.9 GHz band of the new system. If the two systems have different bandwidths per channel, different modulation systems, etc., the bandwidths, modulation systems, etc. are also switched at intervals of the beacon signal (B).
[0029]
In the example of FIG. 3, the first beacon signal is of frequency band A, and from the beacon signal (B) to the first frequency switching timing, access of the wireless LAN system of frequency band A is enabled, and the packet is received. It is possible. From the beacon signal (B) in the frequency band B after the first frequency switching timing to the second frequency switching timing, the wireless LAN system in the frequency band B can be accessed and packets can be received. After that, the frequency band A is used. Thus, the two frequency bands A and B are alternately switched in synchronization with the beacon signal (B).
[0030]
In the system configuration shown in FIG. 1, for example, the terminal device 2 uses the frequency band A of the existing system, and the terminal device 3 uses the frequency band B of the new system. Therefore, the terminal device 2 can receive the first frequency band A beacon signal (B), but the terminal device 3 cannot. The terminal device 2 that has received the beacon signal (B) performs carrier sense after a lapse of the DIFS and random back-off time, and sends out packet data D2. The access point 1 that has received the packet data D2 transmits an ACK. The terminal device 2 confirms that the transmission of the packet data D2 is successful by receiving the ACK.
[0031]
Next, the access point 1 switches the frequency band from A to B, and transmits a beacon signal (B). After receiving the beacon signal (B), the terminal device 3 performs carrier sense after a lapse of the DIFS and the random back-off time, and transmits the packet data D3. The access point 1 that has received the packet data D3 transmits an ACK. The terminal device 3 confirms that the transmission of the packet data D3 has been successful by receiving the ACK. Next, the access point 1 switches the frequency band from B to A, transmits a beacon signal (B) in the frequency band A, and waits for transmission from the terminal device 2 again.
[0032]
Note that the interval between the beacon signals (B) in each frequency band shown in FIG. 3 and the figures described below is set to a length that can be transmitted only once due to the limitation of the drawing space. The interval of the beacon signal (B) is set to a length that allows the above.
[0033]
Another operation example of the embodiment of the present invention will be described with reference to FIG. Another operation example is a case where the terminal device 3 cannot receive the beacon signal (B) in the frequency band B. In FIG. 4, when the terminal device 3 fails to receive the beacon signal (B) transmitted in the frequency band B, the terminal device 3 succeeds in receiving the beacon signal (B) in the frequency band B (below the beacon signal (B)). Within the interval) the sending of packets is prohibited. This function is provided in the terminal device 3 of the new wireless LAN system. With this function, the terminal device 3 does not transmit a packet to be transmitted even if there is a packet to be transmitted.
[0034]
Next, the access point 1 switches to the frequency band A and transmits the beacon signal (B), but the terminal device 3 cannot receive the signal because it is in another frequency band. Next, the access point 1 switches to the frequency band B and transmits the beacon signal (B). The terminal device 3 receives this. If the reception is successful, the carrier sense is performed and the packet data D4 is transmitted after a lapse of the predetermined DIFS and random back-off time. By such an operation, the terminal device 3 of the new wireless LAN system can stop useless transmission during the time when the terminal device is switched to another frequency band.
[0035]
FIG. 5 shows a retransmission control operation of a reference example for comparison with an operation example of one embodiment of the present invention in order to facilitate understanding of the present invention. This reference example is an operation in a case where an access is made from the terminal device 2 during a non-reception time zone during the switching operation. Since the terminal device 2 is compatible with the existing wireless LAN system, unlike the terminal device 3, the terminal device 2 does not have the function of prohibiting packet transmission as described above. The packet is transmitted even in the unreceivable time zone.
[0036]
In response to the access point 1 transmitting the beacon signal (B) in the frequency band A, the terminal device 2 performs carrier sensing after a predetermined DIFS and random backoff time has elapsed in order to prevent packet collision. Data D5 ₁ Is sent. At the access point 1, the packet data D5 ₁ Fails to receive ACK and does not send ACK.
[0037]
The terminal device 2 sends an RTS (transmission request) to the access point 1 to secure a transmission right in order to retransmit a transmission packet after waiting for a predetermined ACK waiting time (hereinafter referred to as an ACK waiting timer expiration). , The access point 1 receives the RTS and returns a CTS (transmission permission) after the SIFS. The terminal device 2 that has received the CTS performs carrier sense after a lapse of the predetermined DIFS and random backoff time, and performs packet data D5 ₂ Resend.
[0038]
Next, the access point 1 switches the frequency band A to the frequency band B and transmits a beacon signal (B). Since the frequency band B has been switched, the access point 1 is in a period during which packets in the waveband A cannot be received. From the viewpoint of the terminal device 2, this period is a period during which transmission is not possible. However, since the terminal device 2 has a configuration corresponding to the existing wireless LAN system, it does not know that the frequency band is switched. Therefore, the retransmitted packet data D5 ₂ Is not received by the access point 1 and does not send out ACK. For this reason, as shown in FIG. 5, the terminal device 2 continues to transmit the RTS every time the CTS waiting timer expires. In FIG. 5, the packet data D5 is output for the second time. ₂ This is an example in which the frequency band is switched when is transmitted. If the frequency band is switched later, a retry operation is performed until the specified number of times is reached.
[0039]
Then, when the RTS (transmission request) transmitted after switching to the frequency band A is received by the access point 1, the access point 1 receives the RTS and returns a CTS (transmission permission) after the SIFS. When the terminal device 2 having received this has passed the predetermined DIFS and random back-off time, it performs carrier sense and performs packet data D5. ₃ Resend. The access point 1 receives the retransmission data D5 ₃ Is normally received, an ACK is transmitted, and the retransmission processing is completed.
[0040]
FIG. 6 is a timing chart showing the operation of the retransmission processing according to the embodiment of the present invention. As in FIG. 5, the terminal device 2 transmits the data packet D6. ₁ And the data packet D6 ₁ Access point 1 fails to receive the ₂ Is transmitted from the terminal device 2, but since the frequency band on which the access point 1 waits has been switched to the frequency band B, D6 ₂ Receive fails. Thereafter, the terminal device 2 continues to transmit the RTS each time the CTS waiting timer expires.
[0041]
Then, the frequency band on which the access point 1 waits is switched to the frequency band A. The operation up to this point is the same as that of the reference example shown in the timing chart of FIG. In this embodiment, the medium access control layer of the access point 1 has a function of maintaining the previous state in the frequency band A and determining a transmission packet according to the held state (referred to as a priority control function). . That is, CTS (transmission permission) is transmitted during the period in which the frequency band A is accessible, and it is stored that there is no response to the CTS. After (B), the CTS is sent preferentially.
[0042]
Upon receiving the CTS, the terminal device 2 performs carrier sense after a lapse of the predetermined DIFS and random backoff time, and performs packet data D6. ₃ Resend. The access point 1 receives the retransmission data D6 ₃ Is normally received, an ACK is transmitted, and the retransmission processing is completed. A comparison between the reference example of FIG. 5 and the operation example of the embodiment shown in FIG. 6 is common in that exchange of data lost at the time of switching with respect to the existing wireless LAN terminal device 2 can be compensated. . In the operation example of FIG. 5, the CTS is transmitted in a period in which the access to the previous frequency band A is possible in comparison with the case where the RTS is received and the CTS is transmitted after waiting for a specified time SIFS, and then, in one embodiment. , The fact that no packet data responding to the CTS has been received is stored, and the CTS is preferentially transmitted when switching to the frequency band A. By this processing, the retransmission processing can be performed immediately after the frequency band is switched, and the transmission efficiency can be improved.
[0043]
FIG. 7 shows a flow of a transmission packet determination process controlled by the system control 1d and the medium access control layer 1b of the access point 1. First, in process ST1, it is determined whether the CTS was transmitted in the previous beacon frame but data reception has not been completed. If it is determined that the data reception has not been completed, in step ST2, the CTS is again determined as a transmission packet, and the process of determining a transmission packet at the access point ends. First, since the process ST1 is performed, the CTS is preferentially transmitted with respect to another transmission packet described below.
[0044]
If it is determined in the process ST1 that the data reception has been completed, it is determined in the process ST3 whether there is unconfirmed transmission data (retransmission data) that does not exceed the maximum number of retransmissions. If it is determined that there is, in process ST4, the retransmission data is determined to be a transmission packet, and the process of determining a transmission packet at the access point ends.
[0045]
If it is determined in the process ST3 that there is no unconfirmed transmission data that does not exceed the maximum number of retransmissions, it is determined in the process ST5 whether or not there is data to be newly transmitted. If it is determined that there is data to be newly transmitted, the new data is determined to be a transmission packet in process ST6, and the process of determining a transmission packet at the access point ends. If it is determined in the process ST5 that there is no data to be newly transmitted, it is determined in the process ST7 that there is no transmission packet other than the beacon signal, and the process of determining the transmission packet at the access point ends.
[0046]
Further, in one embodiment of the present invention, the system control of the access point 1 and the function of the PCF block appropriately set the interval (ie, accessible time) of the beacon signal (B) according to the load on each physical layer. Things can be controlled. With reference to FIGS. 8 and 9, a description will be given of how the interval of the beacon signal (B) is dynamically controlled.
[0047]
FIG. 8A shows an example of the interval of the beacon signal at the access point 1, and FIG. 8B shows another example of the interval of the beacon signal at the access point 1. In FIG. 8A, the time from when the beacon signal of frequency band A is transmitted to when the frequency is switched to frequency band B (the time during which data of frequency band B cannot be received) is T1, and the beacon signal of frequency band B is transmitted. The time from when the frequency is switched to the frequency band A (the time during which data in the frequency band A cannot be received) is T2. Then, the relationship of T1 time <T2 time is established. This is because the number of users in the frequency band B is larger than the number of users in the frequency band A, that is, the number of terminal devices belonging to the control of the access point. Desirably, the ratio between the T1 time and the T2 time is set according to the ratio of the number of users.
[0048]
On the other hand, in FIG. 8B, the relationship between the unreceivable time T3 of the data in the frequency band B and the unreceivable time T4 of the data in the frequency band A is T3> T4. This is because the number of users in frequency band B is smaller than the number of users in frequency band A. Preferably, the ratio between the T3 time and the T4 time is set according to the ratio of the number of users.
[0049]
FIG. 9 shows a flow of processing in which the interval between beacon signals is controlled by the medium access control layer 1b and the system control 1d of the access point 1. First, a beacon signal interval ratio increase / decrease determination process is performed. Therefore, in the process ST11, the traffic of the frequency band A is acquired by using, for example, the terminal device performing the authentication / registration work. The acquired traffic is denoted by Ta. Simultaneously (or sequentially), in process ST12, traffic in frequency band B is obtained. The acquired traffic is denoted by Tb. Traffic is acquired at appropriate time intervals so that the latest is acquired.
[0050]
In the process ST13, the previously obtained traffic Ta ′ of the frequency band A is compared with the currently obtained traffic Ta. In the process ST14, the previously obtained traffic Tb 'of the frequency band B is compared with the currently obtained traffic Tb. That is, it is detected whether the traffic of the frequency band A is unchanged, increased, or decreased. Similarly, whether the traffic in the frequency band B is unchanged, increased, or decreased is detected.
[0051]
In process ST15, a control method of the interval of the beacon signal is determined based on the comparison result. As a control method, for example, four types of methods are prepared as shown below.
[0052]
(1) If both frequency bands A and B increase, increase the interval with the larger difference (change amount)
(2) If the frequency band A increases or remains unchanged and the frequency band B decreases, the receivable time of the frequency band A increases.
(3) If the frequency band A decreases and the frequency band B increases or remains unchanged, the receivable time of the frequency band B increases.
(4) When both the frequency bands A and B are unchanged, the interval of the beacon signal is unchanged.
Thus, the interval ratio of the beacon signal is determined.
[0053]
Although the interval between beacon signals is controlled by traffic, the interval between beacon signals may be controlled according to a load other than traffic. For example, the interval between beacon signals may be controlled in response to a request from a terminal accommodated in the wireless system, for example, a request to increase the transmission capacity. Further, the beacon signal interval may be controlled depending on the type of data to be transmitted, for example, whether or not the data is transmitted in a stream. Further, the mode of transmitting the beacon signal may be controlled according to traffic or the like. For example, a mode in which a beacon signal in frequency band B is transmitted once when a beacon signal in frequency band A is transmitted twice consecutively is also possible.
[0054]
In FIG. 10, reference numeral 11 indicates an example of an access point. The configuration example of FIG. 10 is a case where the physical layer 11a can share the RF units of the two frequency bands. Antennas can be either shared or separated. For example, when switching between two wireless LAN systems in relatively close frequency bands, such as a 5.2 GHz band in the frequency band A and a 4.9 GHz band in the frequency band B, it is relatively easy to share the RF unit. it can.
[0055]
In the case of the wireless LAN system in the frequency band B, it is only necessary to additionally operate the function of the PCF block 11e in the medium access control layer 11b. That is, the PCF block 11e has a function of not transmitting when a beacon signal is not received and a function of dynamically controlling an interval between beacon signals. The priority control function 11f is a function for sending CTS preferentially when data for the CTS transmitted in the previous beacon frame has not been received.
[0056]
In FIG. 11, reference numeral 21 indicates another example of the access point. The configuration example of FIG. 11 is a case where the physical layer is divided into RF units 22a and 22b of two frequency bands. A switch unit 23 is provided between the RF units 22a and 22b and the medium access control layer 21b. By switching the switch unit 23, data from one RF unit is processed. The switching of the switch unit 23 and the ON / OFF of the function of the PCF block 21e are linked. That is, when the switch unit 23 selects the wireless LAN system of the frequency band B, the function of the PCF block 21e is turned on. Further, information on switching of the switch unit 23 is transmitted to the priority control function 21f added to the medium access control layer 21b.
[0057]
According to the above-described embodiment of the present invention, a wireless LAN compliant with IEEE 802.11a using an existing 5.2 MHz band and a new frequency band close to the frequency band, for example, a 4.9 MHz band compliant with IEEE 802.11a are used. One access point can cope with a wireless LAN. Therefore, the existing method enables the same indoor access as before, and when a new type of terminal device is brought into the home or office from the outside, or vice versa, the new type of terminal device is used outdoors. When the device is taken out, it can be seamlessly connected to the access point to which the present invention is applied, which is very convenient.
[0058]
The user of the terminal device can seamlessly connect to the network without being aware of the change of the communication medium, and does not need to make any changes to the existing wireless LAN terminal device indoors. The same access can be performed. In particular, the 5.2 GHz band is an unlicensed band for which outdoor use is prohibited, and thus the place of use is limited. According to the present invention, a service that expands the use place in combination with another communication system can be realized, and the inconvenience of the existing system can be eliminated.
[0059]
According to the embodiment of the present invention, an access point shared by two wireless LAN systems can be easily realized only by adding a function to an existing access point. Therefore, the number of steps for newly developing an access point is small, and an access point that can be shared by the two wireless LAN systems at a relatively low cost can be realized.
[0060]
Further, in one embodiment of the present invention, for example, when a CTS (transmission permission) is transmitted during the accessible period of the frequency band A, it is stored that no response packet to the CTS is received, and In the period, after the beacon signal (B), the CTS is preferentially transmitted for other types of data packets. This allows the wireless terminal to receive the CTS and retransmit the data packet immediately after the change of the accessible period, thereby improving the efficiency.
[0061]
The present invention is not limited to the above-described embodiment and other embodiments of the present invention, and various modifications and applications can be made without departing from the gist of the present invention. For example, the present invention can be applied not only to the CSMA-CA system but also to another wireless LAN system in which a transmission permission is transmitted in response to a transmission request and a terminal that has received the transmission permission transmits a data packet to a base station. Further, the present invention is applicable not only to the case where the number of physical layers is two, but also to the case where there are three or more types.
[0062]
【The invention's effect】
As is apparent from the above description, according to the present invention, a wireless base station (access point) can be shared by wireless terminal apparatuses in different physical layers, and a wireless base station is provided for each physical layer. The cost of installing a wireless base station can be greatly reduced as compared with the case of installing a wireless base station. On the other hand, since no change in the configuration is required for the existing terminal device, the wireless base station can be easily introduced into a system in which the existing terminal device and the terminal device of the new system coexist.
[0063]
According to the present invention, a wireless base station that is shared by two wireless LAN systems can be easily realized only by adding a function to an existing wireless base station. Specifically, since it can be dealt with only by making a minor change to the medium access control layer, the addition of the function does not increase the processing amount, memory capacity, power consumption, program size, and the like. Therefore, the number of steps for newly developing a wireless base station is reduced, and a wireless base station that can be shared by the two wireless LAN systems at a relatively low cost can be realized.
[0064]
Further, in the present invention, the existing system of the wireless LAN system is exclusively for indoor use, and when the new system can be used indoors and outdoors, by installing the wireless base station according to the present invention outdoors, In addition to being able to access indoors as before, when a new type of terminal device is brought from home to an office, office, or the like, or conversely, when a new type of terminal device is taken out, It is possible to seamlessly connect to the access point to which the present invention is applied, which is very convenient. Of course, by installing the wireless base station according to the present invention indoors, two wireless LAN systems can be used indoors.
[0065]
Further, according to the present invention, efficiency can be improved by making the procedure of packet retransmission processing generated by switching of communication channels efficient.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an overall configuration of a system according to an embodiment of the present invention.
FIG. 2 is a timing chart illustrating an example of operation (retransmission control operation) timing of an existing CSMA-based access point.
FIG. 3 is a timing chart showing an operation when there is an access from a terminal device in one embodiment of the present invention.
FIG. 4 is a timing chart showing an operation when the terminal device cannot receive a beacon signal of frequency band B in the embodiment of the present invention.
FIG. 5 is a timing chart showing an operation of transmitting data from a terminal device to an access point in a reference example compared with the present invention.
FIG. 6 is a timing chart for explaining an operation of transmitting data from a terminal device to an access point according to an embodiment of the present invention.
FIG. 7 is a schematic diagram illustrating a flow of a transmission packet determination process according to an embodiment of the present invention.
FIG. 8 is a timing chart for explaining control of a beacon signal interval according to an embodiment of the present invention.
FIG. 9 is a schematic diagram illustrating a flow of a control process of a beacon signal interval according to the embodiment of the present invention.
FIG. 10 is a block diagram showing a configuration example of an access point according to the present invention.
FIG. 11 is a block diagram showing another configuration example of the access point according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Access point (wireless base station), 2, 3 ... Terminal device, 1a, 2a, 3a ... Physical layer, 1b, 2b, 3b ... Medium access control layer, 1c, 2c, 3c ... Higher layers

Claims (7)

A wireless communication system in which a first broadcast signal of a first physical layer and a second broadcast signal of a second physical layer are alternately transmitted from a wireless base station,
When a data packet is transmitted to the radio base station after a lapse of a predetermined time after receiving one of the first and second broadcast signals, and one of the first and second broadcast signals cannot be received. A first wireless terminal that prohibits transmission of a data packet to a wireless base station until one of the first and second broadcast signals can be received;
After receiving the other of the first and second broadcast signals, a data packet is transmitted to the radio base station after a predetermined time has elapsed, and an acknowledgment signal from the radio base station is received or a predetermined number of repetitions are performed. A wireless communication system in which a second wireless terminal that repeatedly transmits a transmission permission request to the wireless base station until the wireless terminal arrives is mixed. In a wireless base station in a wireless network including a plurality of wireless terminals and a common wireless base station,
At least two first and second physical layers below a common media access control layer;
Broadcasting in which the first broadcast signal of the first physical layer and the second broadcast signal of the second physical layer are generated alternately and the first and second broadcast signals are transmitted to a wireless terminal. Signal transmission means,
The wireless terminal of the first physical layer can be accessed only within a first time from the transmission of the first broadcast signal, and within a second time from the transmission of the second broadcast signal. Only the access of the wireless terminal of the second physical layer is enabled,
In response to a transmission permission request in response to a transmission permission request from one of the first and second physical layers at one of the first and second times, a response to the transmission permission is given. A radio base station that stores a state in which a data packet to be transmitted is not received, and, when one of the following first and second times is reached, preferentially transmits a transmission permission for another type of data packet. . In claim 2,
A wireless base station configured to control a ratio between the first time and the second time. In claim 2,
The first and second physical layers are radio base stations using different frequency bands. In claim 2,
A radio base station in which one of the first and second physical layers can be used indoors only, and the other can be used indoors and outdoors. In a communication method of a wireless base station in a wireless network including a plurality of wireless terminals and a common wireless base station,
Alternately generating a first notification signal of the first physical layer and a second notification signal of the second physical layer;
A notification signal transmitting step of transmitting the first and second notification signals to the wireless terminal,
The wireless terminal of the first physical layer can be accessed only within a first time from the transmission of the first broadcast signal, and within a second time from the transmission of the second broadcast signal. Only the access of the wireless terminal of the second physical layer is enabled,
In response to a transmission permission request in response to a transmission permission request from one of the first and second physical layers at one of the first and second times, a response to the transmission permission is given. A communication method for storing a state in which a data packet to be received is not received, and sending a transmission permission to another type of data packet preferentially when one of the following first and second times comes. In a communication method of a wireless base station in a wireless network including a plurality of wireless terminals and a common wireless base station,
Alternately generating a first notification signal of the first physical layer and a second notification signal of the second physical layer;
A notification signal transmitting step of transmitting the first and second notification signals to the wireless terminal,
The wireless terminal of the first physical layer can be accessed only within a first time from the transmission of the first broadcast signal, and within a second time from the transmission of the second broadcast signal. Only the access of the wireless terminal of the second physical layer is enabled,
In response to a transmission permission request in response to a transmission permission request from one of the first and second physical layers at one of the first and second times, a response to the transmission permission is given. A communication method of storing a state in which a data packet to be transmitted is not received, and sending a transmission permission with priority to another type of data packet when one of the following first and second times comes. A program that runs on a computer.

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