Patent Application
20060286935
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2005-180745, filed Jun. 21, 2005, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a wireless communication system in which a plurality of users share a plurality of channels.
2. Description of the Related Art
Media access control (MAC) is control to decide on how a plurality of communication apparatuses, which communicate by sharing the same medium, should use the medium in transmitting communication data. Owing to media access control, even if two or more communication apparatuses transmit communication data by using the same medium at the same time, there is a lower possibility of a collision, in which a communication apparatus on the receiving side cannot separate communication data. Media access control also reduces the chance of a medium being left unused by any communication apparatuses, despite the presence of communication apparatuses having transmission requests.
In general, in wireless communication, since it is difficult for a communication apparatus to monitor transmission data while transmitting the data, media access control that does not rely on collision detection is used. IEEE 802.11, which is a typical technical standard for wireless local area networks (LANs), uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).
According to CSMA/CA in IEEE 802.11, in the header of a MAC frame, a period (called a duration) until the end of a sequence comprising one or more frame exchanges following the MAC frame is set. In the duration, a communication apparatus, which is irrelevant to the sequence and has no transmission right, waits for transmission upon determining a virtual reserved state of the medium. This prevents collision. On the other hand, a communication apparatus having a transmission right in this sequence recognizes that the medium is not used except for a period during which the medium is actually reserved.
IEEE 802.11 defines that the state of a medium is determined on the basis of a combination of virtual carrier sense on the MAC layer as in the former case and real carrier sense on the physical layer as in the latter case, and media access control is performed on the basis of the determination.
JP-A 2003-87856 (KOKAI) discloses a method of realizing wireless base stations which can be commonly used in a plurality of wireless LAN schemes in a wireless communication system in which a plurality of wireless LAN schemes with different physical layers are present. More specifically, a wireless base station is made to alternately generate the first notification signal on the first physical layer and the second notification signal on the second physical layer and transmit them to wireless terminals, and the first and second physical layers are switched in synchronism with the first and second notification signals. The wireless terminal corresponding to the first physical layer is allowed limited access for a predetermined period of time after the transmission time of the first notification signal, whereas the wireless terminal corresponding to the second physical layer is allowed limited access for a predetermined period of time after the transmission time of the second notification signal.
IEEE 802.11 using CSMA/CA has made attempts to increase the communication speed mainly by changing the protocol of the physical layer. With regard to the 2.4 GHz band, there have been changes from IEEE 802.11 (established in 1997, communication speed=2 Mbps) to IEEE 802.11b (established in 1999, communication speed=11 Mbps), and further to IEEE 802.11g (established in 2003, communication speed=54 Mbps). With regard to the 5 GHZ band, IEEE 802.11a (established in 1999, communication speed=54 Mbps) exists as a standard specifications.
As an approach for speeding up communication speed, there is a method for increasing the frequency bandwidth of a channel. To realize high speed communication due to extension communication bandwidth by bundling several channels, communication apparatus need to find and acquire several vacant channels. However, when securing a plurality of channels, there is a high possibility that a communication apparatus compete with some communication apparatus belonging to other system in the same frequency band. For example, in a case where a wireless LAN terminal using a 5 GHz band secures two 20 MHz channels for performing a 40 MHz communication, a frequency band for the two channels must be secured while circumventing radars that use the same communication band. Consequently, a scheme is required not to interfere with communication apparatus belonging to other system and to share the same frequency band.
Regarding communication using a single channel, it is suggested in IEEE 802.11h to circumvent radars which exist within the same communication band. For instance, in IEEE 802.11h, when a radar is detected on a channel that is currently used by a terminal, the terminal searches other channels. If the terminal finds another vacant channel, the terminal stops using the channel on which the radar is detected and switches the communication channel to another channel. Regarding communication using a plurality of channels in a bundle, in IEEE 802.11h, none of terminal operations are regulated, even when a radar is detected on any of the plurality of channels.
In a broadband communication, which is realized by simultaneously using a plurality of channels in a bundle, channel search is carried out to secure the plurality of channels. However, the terminal operation is not envisioned in the case where a substantial interference (for example, of a radar) appears irregularly or regularly in any of the multiple channels searched thereby.
The present invention is directed to provide a wireless communication apparatus, method, and system for performing high speed wireless communication using a wide frequency band, which can coexist with even when an interference source such as a radar use the same communication band.
A wireless communication apparatus according to one aspect of the present invention includes a wireless communication apparatus using any of a plurality of communication bands, comprising: a detection device configured to detect a cyclic interference with a first communication band of the plurality of communication bands; an assignment device configured to assign the first communication band to an extension channel and assign a second communication band of the plurality of communication bands to a control channel, when the cyclic interference has been detected by the detection device; and a communication device configured to perform wireless communication using the control channel and the extension channel.
A wireless communication system for searching frequency channels prior to communications includes a wireless LAN system on the basis of IEEE Std. 802.11-1999 [revision 2003 includes ISO/IEC 8802-11, 1999(E) ANSI/IEEE Std 802.11, 1999 edition, IEEE Std 802.11a-1999, IEEE Std 802.11b-1999, IEEE Std 802.11b-1999/Cor. 1-2001 and IEEE Std 802.11d-2001]. Hereinafter, the IEEE 802.11 wireless LAN system according to embodiments will be explained. The IEEE 802.11 standard is a standard related to a physical (hereinafter, referred to as PHY) layer and a medium access control (MAC) layer. The following will be described by drawing attention mainly to the process in the MAC layer. Further, the IEEE 802.11 standard described herein includes standards positioned as amendments and recommended practices of IEEE 802.11 standard.
A wireless communication apparatus shown in
The protocols processed by the first physical layer protocol processing device 11 include, for example, at least a physical layer protocol defined by IEEE 802.11a. Assume that the first communication bandwidth used by the first physical layer protocol processing device 11 has a bandwidth of, e.g., 20 MHz. The first physical layer protocol processing device 11 may use a so-called multiple-input multiple-output (MIMO) technique using a plurality of antennas 13A to 13C on each of the transmitting side and the receiving side. As the MIMO technique makes it possible to expect an increase in transmission capacity almost proportional to the number of antennas without changing the frequency band, it is therefore highly probable that this technique may be adopted for IEEE 802.11 Task Group n (TGn), which strives to further increase the throughput of IEEE 802.11.
Assume that the second physical layer protocol processing device 12 uses, for example, one or both of single-input single-output (SISO) and MIMO techniques. Assume that the second communication bandwidth used by the second physical layer protocol processing device 12 has a bandwidth of, e.g., 40 MHz. The first communication bandwidth exists within the second communication bandwidth.
The MAC layer 20 includes a channel access control device 21. The channel access control device 21 includes a carrier sense device 22, channel state management device 23, and channel reservation/release control device 24. The MAC layer 20 further includes a network system management device 25, which governs the generation of beacon frames, management of association and so forth and is extended as needed.
The carrier sense device 22 manages the idle/busy states of channels by managing carrier sense states on the basis of a combination of real carrier sense information obtained from the physical layer 10 and virtual carrier sense information obtained by a protocol at the MAC layer 20. That is to say, the carrier sense device 22 manages the idle/busy states of one or more first channels in the first communication bandwidth and one or more second channels in the second communication bandwidth instead of managing the idle/busy state of a single channel.
The channel reservation/release control device 24 generates a frame for controlling the virtual carrier sense state of the MAC layer 20, which is used to reserve a channel for a predetermined period of time or release the reserved channel. The frame generated by the channel reservation/release control device 24 is sent to the physical layer 10 and is transmitted by the first physical layer protocol processing device 11 and second physical layer protocol processing device 12.
The channel state management device 23 makes the carrier sense device 22, the channel reservation/release control device 24, and the first and second physical layer protocol processing devices 11 and 12 of the physical layer 10 operate in concert to perform desired channel access control.
Specific examples of the wireless communication apparatus shown in
Another wireless communication apparatus shown in
Note, however, that the wireless communication apparatus in
Examples of the wireless communication apparatus shown in
A network 100 shown in
The network 100 in
As stated above, 20M_ch_a and 20M_ch_b are not used simultaneously. In the network 100, the 40-MHz channel 40M_ch and one of the 20-MHz channels 20M_ch_a and 20M_ch-b which overlap 40M_ch in terms of frequency are used. In other words, a 40M/20M MIMO STA and a 40M/20M STA belonging to the network 100 do not simultaneously use 20M_ch_a and 20M_ch_b.
Referring now to
When AP or STA performs channel search prior to communication:
(1) Firstly, the communication bandwidth (such as a 20 MHz bandwidth or a 40 MHz bandwidth) in which the channel search should be carried out and a channel search sequence in which order the channel should be searched are determined in SME 40;
(2) Subsequently, a signal for channel search indication is transmitted from the SME 40 to the network system management device 25 in the MAC layer 20. With the channel search indication, the SME 40 notifies the network system management device 25 of the communication bandwidth in which the channel search should be carried out and the channel search sequence determined in (1). In this case, it is assumed that, for example, ch.1, ch.2 and ch.3 are searched in this order in a 40 MHz communication bandwidth;
(3) The network system management device 25, which receives the channel search indication, gives the indication to the carrier sense device 22 to perform carrier sense in accordance with the communication bandwidth (40 MHz) and the channel search sequence (ch.1 to ch.2 to ch.3) instructed by the SME 40 and demands to be informed of the idle/busy states of each channel (ch.1, ch.2 and ch.3);
(4) The carrier sense device 22 transmits a signal instructing the execution of a real carrier sense to the physical layer 10. At this time, the communication bandwidth (40 MHz) and channel number (ch.1, or ch.2, or ch.3) to be searched are informed to the physical layer 10 as a parameter. The channel number to be searched is given in the order according to the channel search sequence (ch.1 to ch.2 to ch.3) instructed in (3). In this example, the physical layer 10 is first instructed to carry out real carrier sense of ch.1. After receiving the carrier sense result of ch.1 from the physical layer 10, the carrier sense device 22 then instructs the physical layer 10 to carry out real carrier sense of ch.2. Further, on receiving the carrier sense result of ch.2 from the physical layer 10, the carrier sense device 22 instructs the physical layer 10 to carry out real carrier sense of ch.3. The following operations from (4) to (7) are carried out from ch.1, one at a time, in accordance with the instructed channel search sequence (ch.1 to ch.2 to ch.3). Upon terminating the sequence up to ch.3, the operation proceeds with (8);
(5) The physical layer 10 performs the real carrier sense of the instructed channel in the bandwidth instructed by the carrier sense device 22 of the MAC layer 20;
(6) It reports the result of the carrier sense to the carrier sense device 22 of the MAC layer 20;
(7) By combining the real carrier sense result obtained from the physical layer 10 in (6) and the virtual carrier sense information of the MAC layer 20, the carrier sense device 22 determines and stores the idle/busy state of the channel;
(8) The carrier sense device 22 reports the idle/busy state of each channel (ch.1, ch.2, ch.3) stored in (7) collectively to the network system management device 25;
(9) The network system management device 25 reports the idle/busy state of each channel received in (8) to SME 40; and
(10) Based on the idle/busy state of each channel reported in (9), SME 40 determines the channel (any one of ch.1, ch.2 and ch.3) to be used for data communication.
With regard to the series of terminal operation relevant to the above channel search, as shown in
Further, as shown in
The following explains an example of a channel search sequence and a terminal operation in which case a large interference power, such as radar, is detected on the identical channel during channel search or during communication using a channel selected in accordance with the channel search result.
In the explanations below, it is supposed that the terminal supports both a communication protocol using a 20 MHz communication bandwidth and a communication protocol using a 40 MHz communication bandwidth as explained in FIGS. 1 to 4, and a case of securing a total of two channels, of a 40 MHz channel and a 20 MHz channel is considered. The communication bandwidth of the channel search is assumed to be 20 MHz. Further, the wireless communication system assumes to occupy four channels each having a communication bandwidth of 20 MHz. When performing a 40 MHz communication by bundling two channels, one of the two channels is assumed to be a control channel and the other is an extension channel. The control channel is used for control information transmission, 20 MHz communication and 40 MHz communication. The extension channel is used with the control channel for the 40 MHz communication.
An example of a terminal operation when the terminal detects radar in the first embodiment is shown in
When performing the 40 MHz communication, it is necessary that the terminal secures two channels each having the 20 MHz communication bandwidth. In order to secure two unused channels the terminal searches ch.1 to ch.4 in order by using the 20 MHz communication band. As shown in
After terminating the search on all channels, based on the results of channel search, the two channels other than the channels in a BUSY state, i.e., ch.1 and ch.2, are determined to be used for the 40 MHz communication. In this time, the 40 MHz communication will be performed by using ch.1, which is in an IDLE state, as the control channel and ch.2, which is in a SUSPENSION state, as the extension channel.
As a result of channel search, if there are two or more unused channels recorded as IDLE, ch.2, which is recorded as SUSPENSION due to radar, will not be used, and the two channels from the unused channels will possibly be selected and used. In other words, the SUSPENSION channel is used for carrying out communication only when there is no unused channel or if there is only one unused channel. When both two channels, which are unused channels in an IDLE state, are secured, either channel can be the control channel or the extension channel.
Further, since the radar is generally a narrow beam revolving in a constant period, signal power transmitted by the radar is detected at the terminal at fixed time intervals (i.e., radar can be detected). Accordingly, when the radar is detected as in ch.2, the terminal can measure the cycle in which the signal power of the radar is detected and record the cycle and the duration of interference in a memory device and the like. By determining the cycle in which radar interference appears on the channel and performing radar avoidance operation in accordance with such cycle, the channel in a SUSPENSION state can be used as an extension channel for 40 MHz communication, coexisting with radar. The following explains an example of a radar avoidance operation based on the radar cycle.
Referring to
During the period in which the radar is not detected with the terminal due to the radar beam being directed to a different direction from the terminal in the present embodiment (time T in
Such channel search for searching for a substitute channel for ch.2 does not have to be carried out each time at every radar cycle. For example, the channel search can be carried out in every several radar cycles, or even be carried out irrespective of the radar cycle. As an example for carrying out channel search irrespective of the radar cycle, it may perform channel search at each communication in order to get hold of the IDLE channel to use as a substitute channel during the period in which the radar interference is detected, prior to the communication.
After ch.2 is switched to ch.3, the 40 MHz communication continues by using ch.1 and ch.3. Further, when ch.2 becomes IDLE again at time T+Δt2, ch.3 is switched to ch.2, and the 40 MHz communication is performed by using ch.1 and ch.2.
In the example of
As a method to realize the suspension of transmission in ch.2 during the radar period as in the operation of
According to the first embodiment explained above, even in the case of detecting a large cyclic interference (source), like radar, on any one of the plurality of channels when performing broadband communication by bundling a plurality of channels, communication can proceed without coming under the influence of such interference. Particularly, by setting the control channel to a channel where radar does not exist, without switching control channels or suspending communication on the control channel, communication using a communication band for one channel at minimum (only the control channel) can be performed at all times.
In addition, by setting a channel in which radar exists as an extension channel, frequency band of the extension channel can be switched smoothly while exchanging control information on the control channel at the time of radar detection. Alternatively, it is possible to switch to 20 MHz communication by suspending only the transmission on the extension channel without interrupting communication.
The first embodiment explains the example of operation in the case of detecting radar at the time of channel search, which is carried out before the terminal determines the channel to be used, whereas, the second embodiment explains the terminal operation in the case of being unable to detect radar at the time of channel search but eventually detecting radar after determining the channel to be used. As the radar appears periodically on the channel, the radar cannot be detected during the period in which the radar beam is directed to other directions. For this reason, there is a possibility of not being able to detect the radar at the time of channel search.
If ch.2 is used as an extension channel from the beginning, only the state of ch.2 is rewritten to SUSPENSION, and the role of ch.1 and ch.2 remain unchanged.
According to such second embodiment, as the control channel can be set to a channel in which radar does not exist as in the case with the first embodiment, communication using a communication band for at least one channel (only the control channel) can be carried out at all times without having to switch the control channel or suspending communication on the control channel.
In addition, by setting the channel in which radar exists as the extension channel, while exchanging control information on the control channel at the time of radar detection, the frequency band of the extension channel can be switched smoothly. Alternatively, it can be switched to a 20 MHz communication without interrupting the communication. The switching of these extension channels and the operation example of transmission suspension are similar to the first embodiment.
The third embodiment does not perform the measurement or recording of a radar cycle explained by the first embodiment. The third embodiment performs any one of the operation patterns described below at which time the radar is detected. Three operation patterns are described below.
In a first operation pattern, when radar is detected on a channel secured for 40 MHz communication, such channel is released. After releasing the relevant channel, 20 MHz communication is performed by continuing using only either one of the channels not undergone interference from the radar.
In the second operation pattern, when radar is detected on the channel, such channel is released, and another channel is secured anew. In other words, the channel to be used is switched to an unused channel from the channel in which the radar was detected, and the 40 MHz communication is continued. Thereafter switching the channel, there is no returning to the channel where the radar was detected, and the new channel to which the channel has been switched remains in use.
In such case, it is preferable that the channel to be newly switched to is a channel adjacent to the other channel in use.
However, when the adjacent channel is already BUSY, it is unable to secure two channels adjacently for 40 MHz communication; therefore, two distant channels will be used to perform 40 MHz communication. In such case, it is also possible to perform channel search anew in order to move to two channels secured adjacently. As a result of this channel search, when two adjacent unused channels are detected, both two channels are moved to these adjacent channels, and the 40 MHz communication continues. Further, when two adjacent unused channels cannot be detected, the channel in which radar is detected is released as described above, and a 20 MHz communication is to be performed with only one channel.
The third operation pattern is to continue using the channel in which radar is detected without releasing it, for 40 MHz communication.
However, in such case, the channel in which radar is detected remains in use by the use of a scheme in which interference caused to the radar is kept low, such as, by making the transmission power small or transmitting an electric wave to a direction different from the approaching direction of the radar.
Further, it is preferable to measure an interference occurrence rate (radar cycle) for all channels, in order to switch to channels with the least interference occurrence rate (i.e., a long radar cycle).
According to the first to third embodiments described above, even in the case where a radar is using the same communication band, a high-speed communication can be performed by using a wide frequency band, which is a bundle of a plurality of channels, without causing interference with the radar.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-180745 | Jun 2005 | JP | national |
