Source: https://patents.google.com/patent/JP2005051523A/en
Timestamp: 2019-12-06 07:51:10
Document Index: 420649884

Matched Legal Cases: ['art 11', 'art 1', 'art2', 'art 104', 'art 105', 'art 106', 'art 107', 'art 108', 'art 109']

JP2005051523A - Wireless communication system, wireless communication apparatus and wireless communication method, and computer program - Google Patents
JP2005051523A
JP2005051523A JP2003281587A JP2003281587A JP2005051523A JP 2005051523 A JP2005051523 A JP 2005051523A JP 2003281587 A JP2003281587 A JP 2003281587A JP 2003281587 A JP2003281587 A JP 2003281587A JP 2005051523 A JP2005051523 A JP 2005051523A
JP2003281587A
JP2005051523A5 (en
研三 西川
2003-07-29 Application filed by Sony Corp, ソニー株式会社 filed Critical Sony Corp
2005-02-24 Publication of JP2005051523A publication Critical patent/JP2005051523A/en
2005-02-24 Publication of JP2005051523A5 publication Critical patent/JP2005051523A5/ja
PROBLEM TO BE SOLVED: To form a self-distributed multi-channel wireless network by avoiding a deadlock state in which communication stations cannot recognize each other's existence.
Depending on an interference situation, a beacon transmission channel selected by one's own reference may not be a channel that can be received by all peripheral communication stations. A communication station that is receiving interference from other systems periodically transmits an interference notification signal (IAS) on all channels that are not receiving interference, informs neighboring stations of the channel that is receiving interference with its presence, and beacons. The beacon is refrained from being transmitted on the channel that is receiving interference so much that it cannot be heard.
The present invention relates to a wireless communication system, a wireless communication apparatus, a wireless communication method, and a computer program that communicate with each other between a plurality of wireless stations such as a wireless LAN (Local Area Network), and more particularly to a control station. The present invention relates to a wireless communication system, a wireless communication apparatus and a wireless communication method, and a computer program in which a wireless network is constructed by ad-hoc communication without any particular device.
More specifically, the present invention relates to wireless communication that forms an autonomous decentralized wireless network without the intervention of a specific control station without interference between neighboring wireless systems in a communication environment in which a plurality of channels are prepared. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system, a wireless communication apparatus, a wireless communication method, and a computer program, and in particular, a wireless communication system in which each communication station appropriately determines its own beacon transmission channel to form a multi-channel autonomous distributed wireless network. The present invention relates to a communication device, a wireless communication method, and a computer program.
One standard for wireless networks is IEEE (The Institute of Electrical and Electronics Engineers) 802.11 (for example, see Non-Patent Document 1), HiperLAN / 2 (for example, Non-Patent Document 2 or Non-Patent Document 2 or Non-Patent Document 2). (See Patent Document 3), IEEE 302.15.3, Bluetooth communication, and the like. As for the IEEE802.11 standard, there are various wireless communication systems such as the IEEE802.11a standard, the IEEE802.11b standard, etc., depending on the wireless communication system and the frequency band to be used.
In order to configure a local area network using wireless technology, a single device serving as a control station called an “access point” or “coordinator” is provided in the area, and is under the overall control of this control station. A method of forming a network is generally used.
However, when performing asynchronous communication between the communication device on the transmission side and the reception side in a wireless communication system in which an access point exists, wireless communication via the access point is always required. Has a problem of halving.
On the other hand, as another method of configuring a wireless network, “ad-hoc communication” in which terminals perform wireless communication directly and asynchronously has been devised. In particular, in a small-scale wireless network composed of a relatively small number of clients located in the vicinity, ad-hoc communication that allows any terminal to perform asynchronous wireless communication directly without using a specific access point is provided. It seems to be appropriate.
By the way, in the work environment in which information devices such as personal computers (PCs) are widespread and many devices are mixed in an office, it is assumed that communication stations are scattered and a plurality of networks are overlapped. The Under such circumstances, in the case of a wireless network using a single channel, there is no room for repairing the situation even if another system interrupts during communication or communication quality deteriorates due to interference or the like.
For this reason, in a conventional wireless network system, a plurality of frequency channels are prepared for coexistence with other networks, and one frequency channel used in a wireless communication device serving as an access point is selected and operated. The method of starting is generally adopted.
According to such a multi-channel communication method, when other systems can interrupt during communication or communication quality deteriorates due to interference or the like, the network operation is maintained by switching the frequency channel to be used, Coexistence with other networks can be realized.
For example, even in an IEEE 802.15.3 high-speed wireless PAN system, a plurality of frequency channels that can be used in the system are prepared, and a wireless communication device transmits a beacon signal as a piconet coordinator (PNC) to the surroundings after power-on In order to confirm the presence or absence of a device, an algorithm is adopted in which a frequency channel to be used is selected by performing a scanning operation over all available channels.
In an autonomous decentralized ad hoc network that does not have a control station, resource management for frequency channels is important in order to minimize interference with different wireless networks operating in the vicinity. However, in order to simultaneously switch the frequency channels used in the network, it is necessary for a representative station called a coordinator or an access point to instruct each terminal station about the channel to be used. In other words, it is difficult to switch frequency channels in an ad hoc network.
In order to use a plurality of frequency channels properly, taking HiperLAN / 2 as an example, a method of switching channels all at once has been considered. For example, an AP (base station) that is a central control station repeatedly notifies that the frequency channel is to be changed, and at a certain timing, the AP and an MT (mobile station) connected to the AP simultaneously switch channels. The decision as to whether or not to switch is determined by the AP. Information for determination is accumulated by following the processing procedure shown below. That is,
(1) In response to an instruction from the AP, the currently connected MT temporarily stops communication, scans another frequency channel, evaluates channel quality, and reports the result to the AP.
(2) In response to an instruction from the AP, the AP temporarily stops transmission of the broadcast channel, the connected MT scans the frequency channel currently in use and performs channel quality evaluation, and reports the result to the AP.
Further, in Bluetooth communication, a method is used in which each frequency channel is used fairly by performing frequency hopping randomly based on a central control station called a master. In order to configure a network, the existence of a central control station called a master is indispensable, which is a reference for frequency channel hopping patterns and synchronization in the time axis direction. When the master disappears, the network formed so far is temporarily disconnected, and a process for selecting a new master is required.
In addition, in an IEEE802.11 wireless LAN system, a network is formed by using a frequency channel initially set by an access point, so it is difficult to construct an ad hoc network without arranging a base station. It is. When communicating with a wireless communication device (terminal) accommodated in an AP operating on another frequency channel, the APs must be connected to each other by, for example, a wired LAN cable. That is, if the accommodated APs are not connected to each other, communication cannot be performed even if the wireless communication apparatuses (terminals) that are physically adjacent to each other are accommodated in different APs.
Also, in the IEEE 802.15.3 high-speed wireless PAN system, it is possible to scan all frequency channels first and search for coordinators existing in the vicinity. If this is started, it is impossible to grasp the usage status of other frequency channels. For this reason, even if there is a piconet with a different frequency channel used in the vicinity, communication with a wireless communication apparatus connected to the piconet cannot be performed.
As described above, in the conventional method, in order to determine the frequency channel switching timing, the setup process realized by message exchange or the like so that the participating terminals can start the frequency channel switching operation in synchronization with each other. A complicated mechanism such as mediation processing is required. In addition, the existence of a central control station such as an AP in IEEE802.11 or HiperLAN / 2 and a master in Bluetooth communication, which performs control mainly, is essential. If a central control station such as an AP or master disappears, some protocol processing or artificial setting change work is required to select a central control station to replace it, and communication is interrupted during that processing. There is a problem.
In addition to the measurement of the interference of the own channel, a radio communication system that determines the frequency channel by measuring the interference when an adjacent channel is used has been proposed (for example, see Patent Document 1). This is a system in which multi-channel is realized by intervening base stations.
For example, a method is conceivable in which a communication station designates a traffic reception channel by transmitting a beacon using a channel optimal for the local station. However, even a channel that is optimal for the local station may be a channel that is receiving interference for a communication station that receives the beacon. For example, if the beacon transmission channel of one station is an interference channel or an unusable channel because the communication quality deteriorates in the other station, these communication stations may communicate with each other on the other channel. Even if they can, they will fall into a deadlock state where they cannot recognize each other's existence forever.
JP-A-6-37762 International Standard ISO / IEC 8802-11: 1999 (E) ANSI / IEEE Std 802.11, 1999 Edition, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layers (PH) ETSI Standard ETSI TS 101 761-1 V1.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part 1: Basic Trunk Data Control ETSI TS 101 761-2 V1.3.1 Broadband Radio Access Networks (BRAN); HIPERLAN Type 2; Data Link Control (DLC) Layer; Part2: Radio Link Control (LC)
A further object of the present invention is to provide an excellent radio communication system, radio, which can suitably form an appropriate ad hoc network without interfering with each other in a communication environment in which a plurality of channels are prepared. To provide a communication device, a wireless communication method, and a computer program.
A further object of the present invention is to provide an excellent radio communication system, radio capable of performing channel access by effectively using a plurality of frequency channels in an autonomous distributed radio network that does not require a specific control station. To provide a communication device, a wireless communication method, and a computer program.
A further object of the present invention is to provide an excellent wireless communication system and wireless communication apparatus capable of avoiding a deadlock state in which each communication station cannot recognize each other's existence and forming an autonomous distributed multi-channel wireless network. And a wireless communication method, and a computer program.
The present invention has been made in consideration of the above-mentioned problems. The first aspect of the present invention is that ad hoc communication is performed by a plurality of wireless communication devices without a control station in a communication environment in which a plurality of channels are prepared. A wireless communication system forming a network based on communication,
Each communication station transmits a beacon at a predetermined beacon period on its own beacon transmission channel, and transmits an interference notification signal describing information on the interfered channel of the local station on another usable channel at a predetermined period. Send,
In an autonomous decentralized wireless communication system, each communication station broadcasts beacon information within a transmission frame period, and can recognize a network configuration by performing a scanning operation of beacon signals from other stations. However, in the case of an autonomous decentralized network that uses multi-channels, since the transmission frame is multiplexed on the frequency axis by the number of channels used, the communication station uses the same channel at the beacon transmission timing of other communications. If it is not shifted upward, it is impossible to receive a beacon, and it is difficult for a new entry station to determine its own beacon transmission timing and transmission channel.
Further, even if the communication station is the optimum channel for the own station, there is a possibility that the other station which is the communication partner is a channel receiving interference. For example, if the beacon transmission channel of one station is an interference channel or an unusable channel because the communication quality deteriorates in the other station, these communication stations may communicate with each other on the other channel. Even if they can, they will fall into a deadlock state where they cannot recognize each other's existence forever.
Therefore, in the present invention, each communication station periodically transmits a beacon signal using a channel having the least interference among the plurality of frequency channels. Consider that the beacon transmission channel is not necessarily a channel that all peripheral communication stations can receive. Specifically, a communication station that is receiving interference from another system periodically transmits a special signal called an interference notification signal on all channels that are not receiving interference, The peripheral channel is notified to the peripheral station.
Also, the peripheral communication station that has received the interference notification signal from the other station compares the beacon transmission channel with the interference information of the interference notification signal. When it is determined that a beacon is transmitted at a high interference level, the beacon transmission channel is changed. Similarly, when a beacon is received, the interference state is monitored as needed, and a channel where a beacon is easy to hear is selected for a communication station that wants to communicate frequently. That is, beacon transmission is refrained from a channel that is receiving interference such that the beacon cannot be heard.
Therefore, according to the present invention, each communication station can autonomously determine a communication channel and efficiently avoid interference, and can effectively improve communication capacity by effectively using multiple channels. it can.
Further, the communication station performs the channel scan operation of each channel at a period that is not synchronized with the transmission period of the interference notification signal.
The channel scan operation can detect the discovery or departure of a new beacon. Further, by performing the channel scan in a period that is not synchronized with the transmission period of the interference notification signal, the interference notification signal IAS from the peripheral station can be received at the frequency of once every several times. Therefore, even if the communication stations cannot receive each other's beacons due to interference, deadlock can be avoided by periodically receiving the interference notification signal.
Further, the communication station may not transmit the interference notification signal when there is no interfered channel. Thus, by omitting unnecessary transmission of the interference notification signal, it is possible to improve the utilization efficiency of the transmission line and reduce the power consumption of the apparatus.
The communication station transmits an interference notification signal with a period sufficiently longer than the beacon interval. Each communication station can detect the discovery or departure of a new beacon by performing a multi-channel scan operation at a period that is not synchronized with the transmission period of the interference notification signal. Further, by performing the channel scan in a period that is not synchronized with the transmission period of the interference notification signal, the interference notification signal IAS from the peripheral station can be received at the frequency of once every several times.
By the way, when it is difficult to communicate on a specific channel due to interference from a strong interference source, it is expected that adjacent terminals are likely to receive the same interference. As a result, under conditions where interference exists, it is conceivable that the number of packets reporting the interference increases more than necessary.
Further, unless there is a change such as a new terminal joining from another network, the packet for reporting the interference is not used. In other words, it is inefficient to transmit interference notification signals with high frequency even in a steady state. In addition, since the communication station cannot perform data transmission during the transmission period of the interference notification signal of the other station, it becomes a system overhead.
Therefore, if the communication station finds that there are other adjacent terminals having the same interference as a result of examining the adjacent terminals, the communication station changes the frequency so as to reduce the transmission frequency of the interference notification signal according to the number of the adjacent terminals. As a result, although the transmission range of the packet for reporting the interference of each communication station is slightly shifted, this packet is broadcast at the same frequency on average in the entire system.
In addition, when a new entry station appears in the wireless system, when a communication station newly entered from another network appears, there may be a phenomenon that the networks themselves overlap. In such a case, an existing communication station needs to transmit an interference notification signal at a frequency equal to or higher than a predetermined value in order to quickly notify a new entry station of the network configuration and interference channel information. Therefore, the communication station increases the transmission frequency of the interference notification signal for a predetermined time in response to the new entry of the communication station from another network (for example, by setting it to be the same as the beacon interval). Increase the possibility of finding interference notification signals. In addition, when the communication station detects a new entry station, the communication station notifies the peripheral station of the presence of the new entry station, and in response to receiving the notification, the transmission frequency of the interference notification signal is set for a predetermined time. Only to increase.
In addition, when a new entry station enters the wireless system, it is necessary to transmit an interference notification signal at a frequency equal to or higher than a predetermined value in order to quickly notify the network configuration and interference channel information. Therefore, the communication station gradually reduces the transmission frequency of the interference notification signal from the initial value according to the elapsed time since the new communication station entered. You may make it go.
According to a second aspect of the present invention, there is provided a computer program written in a computer-readable format so that wireless communication processing for operating autonomously and distributedly in a wireless communication environment is executed on a computer system. ,
An interference notification signal generating step for generating a beacon signal describing information on the interfered channel of the own station and an interference notification signal;
An interference notification signal analyzing step of analyzing the beacon signal received from the peripheral station and the interference notification signal;
A channel setting step for setting a channel for data transmission and reception;
A communication control step for controlling the beacon signal and the interference notification signal transmission operation of the own station, the beacon signal and the interference notification signal reception operation from the peripheral station,
According to the present invention, in a communication environment in which a plurality of channels are prepared, an excellent ad hoc network can be suitably formed without causing communication stations to interfere with each other. An apparatus, a wireless communication method, and a computer program can be provided.
In addition, according to the present invention, in an autonomous decentralized wireless network that does not require a specific control station (access point, base station, master station, etc.), channel access is achieved by effectively using a plurality of frequency channels. An excellent wireless communication system, wireless communication apparatus, wireless communication method, and computer program can be provided.
Further, according to the present invention, an excellent wireless communication system and wireless communication capable of forming an autonomous distributed multi-channel wireless network by avoiding a deadlock state in which each communication station cannot recognize each other's existence. An apparatus, a wireless communication method, and a computer program can be provided.
In addition, according to the present invention, in an autonomous distributed multi-channel wireless network, each communication station efficiently performs frequency allocation, thereby improving the overall system throughput and reducing the influence on other neighboring wireless systems. can do.
A. System Configuration The propagation path of communication assumed in the present invention is wireless, and a network is constructed among a plurality of communication stations using a transmission medium composed of a plurality of frequency channels. Further, the communication assumed in the present invention is a storage and exchange type traffic, and information is transferred in units of packets.
The wireless network system according to the present invention has an autonomous distributed system configuration in which no coordinator is arranged, and transmission control that effectively uses a plurality of channels by a transmission (MAC) frame having a gradual time division multiple access structure. Is done. Each communication station can also perform ad hoc communication in which information is directly and asynchronously transmitted according to an access procedure based on CSMA (Carrier Sense Multiple Access).
In a wireless communication system in which no control station is particularly arranged in this way, each communication station notifies beacon information so that other communication stations in the vicinity (that is, within the communication range) can know the existence of itself, and the network configuration can be changed. Notice. In addition, a communication station that newly enters the communication range of a certain communication station detects that it has entered the communication range by receiving a beacon signal, and decodes information described in the beacon to configure the network configuration Can know. Also, since the communication station transmits a beacon at the beginning of the transmission frame period, the transmission frame period in each channel used by each communication station is defined by the beacon interval.
Each wireless communication apparatus arbitrarily determines one of the available channels as a reference channel, and defines a predetermined transmission frame period on the reference channel. This reference channel is selected from among the multi-channels based on the own station such that the communication quality is good for the own station. In such a case, even if the channel is optimal for the own station, there is a possibility that the communication station receiving the beacon is a channel that is receiving interference. In this embodiment, by using a channel other than the reference channel, a mechanism for notifying the peripheral station of the presence of the user and information on the channel receiving the interference is prepared, thereby avoiding a deadlock state. is doing. Details of this mechanism will be described later.
The processing in each communication station described below is basically processing executed in all communication stations that enter the ad hoc network according to the present invention. However, depending on the case, not all communication stations configuring the network execute the processing described below.
FIG. 1 shows an arrangement example of communication devices constituting a wireless communication system according to an embodiment of the present invention. In this wireless communication system, a specific control station is not arranged, and each communication device operates in an autonomous and distributed manner to form an ad hoc network. In the figure, a state where communication devices # 0 to # 6 are distributed in the same space is shown.
In addition, the communication range of each communication device is indicated by a broken line in the same figure, and is defined as a range in which signals transmitted by itself can interfere with each other as well as communication with other communication devices within the range. That is, the communication device # 0 is in a range in which communication is possible with communication devices # 1, # 4 in the vicinity, and the communication device # 1 is in a range in which communication is possible with communication devices # 0, # 2, # 4 in the vicinity. The communication device # 2 is in a range in which communication with the communication devices # 1, # 3, and # 6 in the vicinity is possible, and the communication device # 3 is in a range in which communication is possible with the communication device # 2 in the vicinity. , Communication device # 4 is in a range where it can communicate with neighboring communication devices # 0, # 1, # 5, and communication device # 5 is within a range where it can communicate with neighboring communication device # 4. Device # 6 is in a range where it can communicate with communication device # 2 in the vicinity.
When communication is performed between specific communication devices, there is a communication device that can be heard from one communication device that is a communication partner but cannot be heard from the other communication device, that is, a “hidden terminal”.
FIG. 2 schematically shows a functional configuration of a wireless communication apparatus that operates as a communication station in a wireless network according to an embodiment of the present invention. The illustrated wireless communication apparatus performs appropriate channel access within the same wireless system in a communication environment in which a plurality of channels are prepared, so that appropriate ad hoc communication can be performed without interfering with other wireless systems. A network can be formed.
The wireless communication device 100 includes an interface 101, a data buffer 102, a central control unit 103, a beacon generation unit 104, an interference notification signal generation unit 105, a wireless transmission unit 106, a timing control unit 107, and a channel setting. Unit 108, antenna 109, radio reception unit 110, interference notification signal analysis unit 111, beacon analysis unit 112, and information storage unit 113.
The central control unit 103 centrally performs a series of information transmission and reception processing management and transmission path access control (multi-channel scan setting, channel setting, etc.) in the wireless communication apparatus 100.
The beacon generation unit 104 generates a beacon signal that is periodically exchanged with a nearby wireless communication device. In order for radio communication apparatus 100 to operate a radio network, its own beacon transmission slot position in each channel, its own reception slot position in each channel, beacon reception slot position from a neighboring communication apparatus in each channel, It defines its own scan operation cycle. These pieces of information are stored in the information storage unit 113, and are described in a beacon signal to notify surrounding wireless communication devices. The configuration of the beacon signal will be described later. Since the wireless communication device 100 transmits a beacon at the beginning of the transmission frame cycle, the transmission frame cycle in each channel used by the wireless communication device 100 is defined by the beacon interval.
The interference notification signal generation unit 105 generates an interference notification signal (Interference Annunciation Signal: IAS) for notifying a peripheral station of its presence and information on a channel receiving interference on channels other than the reference channel. To do.
The wireless transmission unit 106 performs predetermined modulation processing to wirelessly transmit the data temporarily stored in the data buffer 102, the beacon, and the interference notification signal IAS of the local station.
The antenna 109 wirelessly transmits a signal addressed to another wireless communication device on a selected frequency channel, or collects a signal transmitted from the other wireless communication device. In this embodiment, it is assumed that a single antenna is provided and that transmission and reception cannot be performed in parallel. Also, it is assumed that a plurality of frequency channels cannot be handled at the same time.
The wireless receiving unit 110 receives and processes signals such as information, beacons, and interference notification signals IAS transmitted from other wireless communication devices at a predetermined time. As a wireless transmission / reception method in the wireless transmission unit 106 and the wireless reception unit 110, various communication methods suitable for relatively short-distance communication applicable to a wireless LAN, for example, can be applied. Specifically, a UWB system, an OFDM system, a CDMA system, or the like can be employed.
The timing control unit 107 controls timing for transmitting and receiving radio signals. For example, own beacon transmission timing at the beginning of the transmission frame period in the beacon transmission channel, transmission timing of the interference notification signal IAS in other available channels, scan operation period in each channel, beacon from other communication devices in each channel Control reception timing.
The channel setting unit 108 selects a channel for actually transmitting and receiving a multi-channel radio signal. Specifically, among the plurality of prepared frequency channels, the best channel interference is set as the beacon transmission channel of the own station, and all the channels not receiving the interference are used for reporting the interference notification signal IAS. Set as channel.
The interference notification signal analysis unit 111 analyzes the interference notification signal IAS of another wireless communication apparatus that can be received on each channel, and information on the channel that the station uses as a reference channel or the channel that is receiving interference. Get etc.
The beacon analysis unit 112 analyzes beacon signals of other wireless communication devices that can be received, and analyzes the presence of nearby wireless communication devices. For example, information such as beacon reception timing in each channel, beacon transmission timing, interference information, and neighboring beacon reception timing described in received beacons from other communication devices is stored in the information storage unit 113 as neighboring device information. Is done.
The information storage unit 113 executes an execution procedure command (a program for performing scan setting, channel setting, etc.) such as a series of access control operations executed in the central control unit 103, beacon transmission timing of other communication stations, and interference notification information IAS. Transmission timing, multi-channel information, neighboring device information, interference information in each channel of the own station and peripheral stations, and the like are stored.
In the present embodiment, the wireless communication apparatus 100 operating as a communication station performs a gradual time division multiplexing in an ad hoc network environment without a specific control station in a communication environment in which a plurality of channels are prepared. Communication operation such as transmission control using a plurality of channels effectively or random access based on CSMA / CA is performed by a transmission (MAC) frame having an access structure.
Each communication station notifies the beacon information to notify other communication stations in the vicinity (that is, within the communication range) of its own existence and notifies the network configuration. In addition, a communication station that newly enters the communication range of a certain communication station detects that it has entered the communication range by receiving a beacon signal, and decodes information described in the beacon to configure the network configuration Can know.
A beacon transmission procedure of each communication station according to the present embodiment will be described with reference to FIG.
If the information transmitted by the beacon is 100 bytes, the time required for transmission is 18 microseconds. Since transmission is performed once every 40 milliseconds, the media occupation rate of the beacon for each communication station is as small as 1/22222.
Each communication station synchronizes gently while listening to beacons that oscillate in the vicinity. When a new communication station appears, the new communication station sets its own beacon transmission timing so that it does not collide with the beacon transmission timing of the existing communication station.
When there is no communication station in the vicinity, the communication station 01 can start transmitting a beacon at an appropriate timing. The beacon transmission interval is 40 milliseconds (described above). In the example shown at the top in FIG. 2, B01 indicates a beacon transmitted from the communication station 01.
Thereafter, the communication station that newly enters the communication range sets its own beacon transmission timing so as not to collide with the existing beacon arrangement. At this time, since each communication station acquires a preferential use area (TGP) immediately after beacon transmission, the beacon transmission timing of each communication station on one channel is more even within the transmission frame period than when it is dense. Dispersion is more preferable in terms of transmission efficiency. Therefore, in this embodiment, beacon transmission is started in the middle of the time zone in which the beacon interval is the longest in the range where the user can hear it.
For example, it is assumed that a new communication station 02 appears in a network state where only the communication station 01 exists, as shown in the uppermost stage in FIG. At this time, the communication station 02 receives the beacon from the communication station 01 and recognizes its existence and beacon position, and as shown in the second stage of FIG. 3, is approximately in the middle of the beacon interval of the communication station 01. Set own beacon transmission timing and start beacon transmission.
Furthermore, it is assumed that a new communication station 03 appears. At this time, the communication station 03 receives at least one of the beacons transmitted from each of the communication station 01 and the communication station 02 and recognizes the existence of these existing communication stations. Then, as shown in the third stage of FIG. 3, transmission is started at a timing almost in the middle of the beacon interval transmitted from the communication station 01 and the communication station 02.
Thereafter, the beacon interval is narrowed every time a communication station newly enters the neighborhood according to the same algorithm. For example, as shown at the bottom of FIG. 3, the communication station 04 that appears next sets the beacon transmission timing at a timing almost in the middle of the beacon interval set by each of the communication station 02 and the communication station 01, and then The appearing communication station 05 sets the beacon transmission timing at substantially the middle of the beacon interval set by the communication station 02 and the communication station 04.
However, a minimum beacon interval Bmin is specified so that the band (transmission frame period) does not overflow with beacons, and it is not allowed to place two or more beacon transmission timings within Bmin. For example, if the minimum beacon interval Bmin is defined as 2.5 milliseconds with a transmission frame period of 40 milliseconds, only a maximum of 16 communication stations can be accommodated within the reach of radio waves.
FIG. 4 shows an example of beacon transmission timing on one channel. However, in the example shown in the figure, the passage of time in a transmission frame period of 40 milliseconds is represented as a clock in which the hour hand moves clockwise on the ring.
In the example shown in FIG. 4, a total of 16 communication stations from the communication station 0 to the communication station F are configured as nodes of the network. As described with reference to FIG. 3, beacon placement is performed according to an algorithm in which beacon transmission timings of new entrant stations are sequentially set at almost the middle of the beacon interval set by an existing communication station. And When Bmin is defined as 2.5 milliseconds, no more communication stations can enter the network.
Similar to the case of the IEEE 802.11 system and the like, a plurality of packet intervals are also defined in this embodiment. The definition of the packet interval here will be described with reference to FIG. The packet interval here defines a Short Inter Frame Space (SIFS) and a Long Inter Frame Space (LIFS). Only packets with priorities are allowed to be transmitted at SIFS packet intervals, and other packets are allowed to be transmitted after LIFS + random backoff packet interval to obtain a value after confirming that the media is clear . As a calculation method of the random back-off value, a method known in the existing technology is applied.
Further, in the present embodiment, “LIFS” and “FIFS + backoff” (FIFS: Far Inter Frame Space) are defined in addition to the above-described packet intervals “SIFS” and “LIFS + backoff”. Normally, the “SIFS” and “LIFS + backoff” packet intervals are applied, but in the time zone in which a certain communication station is given priority for transmission, other stations use the “FIFS + backoff” packet interval. The station to which priority is given uses the packet interval in SIFS or LIFS.
Each communication station transmits a beacon at regular intervals, but for a while after transmitting the beacon, the station that transmitted the beacon is given transmission priority. FIG. 6 shows a state in which priority is given to the beacon transmitting station. This priority section is defined as Transmission Guaranteed Period (TGP). Further, a section other than TGP is defined as “Fairly Access Period (FAP)”. FIG. 7 shows the configuration of the transmission frame period. As shown in the figure, following the transmission of the beacon from each communication station, the TGP of the communication station that transmitted the beacon is allocated, and when the time has elapsed by the length of the TGP, it becomes FAP, and the next communication station FAP ends with the transmission of the beacon from. In addition, although the example where TGP starts immediately after the transmission of the beacon is shown here, the present invention is not limited to this. For example, the start time of the TGP is set by the relative position (time) from the transmission time of the beacon. Also good.
Here, the packet interval is considered again as follows. Each communication station performs transmission at an interval of LIFS + backoff in FAP. In addition, regarding the transmission of packets within the TGP of the local station of beacons, transmission at SIFS intervals is permitted. In addition, regarding the transmission of the packet within the TGP of the own station, the transmission at the LIFS interval is allowed. Furthermore, regarding the transmission of the packet within the TGP of the other station, the transmission is performed at the interval of FIFS + backoff. In the IEEE802.11 system, FIFS + backoff is always taken as a packet interval. However, according to the configuration according to the illustrated example, this interval can be reduced, and more effective packet transmission can be performed. .
In the above description, the priority transmission right is given only to the communication station in the TGP. However, the priority transmission right is also given to the communication station called by the communication station in the TGP. Basically, in TGP, priority is given to transmission, but there is nothing to be transmitted within the local communication station, but when it is known that other stations hold information to be transmitted to the local station, A paging message or a polling message may be sent to “other station”.
Conversely, if you have sent a beacon, but your station has nothing to send and you do not know that the other station has the information you want to send to your station, , The transmission priority given by TGP is abandoned and nothing is transmitted. Then, after the LIFS + back-off or FIFS + back-off has elapsed, another station starts transmission even in this time zone.
Considering the configuration in which TGP continues immediately after beacon transmission as shown in FIG. 7, the transmission efficiency is better when the beacon transmission timing of each communication station is evenly distributed within the transmission frame period than when it is dense. More preferred. Therefore, in this embodiment, beacon transmission is started in the middle of the time zone in which the beacon interval is the longest in the range where the user can hear it. However, there is also a utilization method in which the beacon transmission timing of each communication station is concentrated and the reception operation is stopped in the remaining transmission frame period to reduce the power consumption of the apparatus.
FIG. 8 shows a configuration example of the beacon signal format. As shown in the figure, the beacon signal has a preamble for notifying the presence of the signal followed by a heading and a payload part PSDU. In the heading area, information indicating that the packet is a beacon is posted. Further, the following information that is desired to be notified by a beacon is described in PSDU.
TX. ADDR: MAC address of transmitting station (TX) TOI: TBTT offset indicator (TBTT Offset Indicator)
NBOI: Neighbor Beacon Offset Information (Neighbor Beacon Offset Information)
TIM: Traffic Indication Map (Traffic Indication Map)
The TIM is broadcast information indicating to which communication station this communication station currently has information, and by referring to the TIM, the receiving station can recognize that it must receive it. it can. In addition, Paging is a field indicating that transmission is scheduled in the immediately following TGP among the receiving stations listed in the TIM, and the station specified in this field must be prepared for reception by TGP. . Other fields (ETC fields) are also prepared. The ETC field may include an Interfer Information field that describes the degree of interference in each prepared frequency channel, that is, the interference level (IntLCH).
The NBOI is information describing the beacon arrangement of neighboring communication stations. In the present embodiment, since a maximum of 16 beacons can be arranged in the transmission frame period in each channel, the NBOI is configured as a 16-bit length field corresponding to each beacon position, and the arrangement of received beacons is related. Describe information in bitmap format. Then, based on the beacon transmission timing of the local station, 1 is written in the bit corresponding to the relative position of the beacon reception timing from each communication station, and the bit position corresponding to the relative position of the timing not receiving the beacon remains 0. To do. In this embodiment, NBOI information is prepared for each available frequency channel.
FIG. 9 shows a description example of the NBOI. In the example shown in the figure, an NBOI field for indicating that the communication station 0 shown in FIG. 3 “can receive beacons from the communication stations 1 and 9” is shown. Regarding the bit corresponding to the relative position of the beacon that can be received, a mark is assigned if a beacon is received, and a space is assigned if it is not received. For other purposes, marking may be performed on a bit corresponding to a timing when a beacon is not received.
Each communication station receives each other's beacon signal and arranges its own beacon transmission timing while avoiding beacon collisions on each available frequency channel based on the description of the NBOI included in the communication station. Beacon reception timing can be detected.
FIG. 10 shows how a new entrant station arranges its own beacon transmission timing on a certain frequency channel while avoiding a collision with an existing beacon based on the description of NBOI. In each stage of the figure, the entry states of the communication stations STA0 to STA2 are shown. The left side of each stage shows the arrangement state of each communication station, and the right side shows the arrangement of beacons transmitted from each station.
The upper part of FIG. 10 shows a case where only the communication station STA0 exists. At this time, since STA0 tries to receive a beacon but is not received, STA0 can set an appropriate beacon transmission timing and can start beacon transmission in response to the arrival of this timing. The beacon is transmitted every 40 milliseconds (transmission frame). At this time, all bits in the NBOI field described in the beacon transmitted from STA0 are 0.
The middle part of FIG. 10 shows a state where STA1 has entered within the communication range of the communication station STA0. When STA1 attempts to receive a beacon, the beacon of STA0 is received. Further, since all the bits other than the bit indicating the transmission timing of the local station are 0 in the NBOI field of the beacon of STA0, the own beacon transmission timing is set approximately in the middle of the beacon interval of STA0 according to the above-described processing procedure.
In the NBOI field of the beacon transmitted by STA1, 1 is set in the bit indicating the transmission timing of the local station and the bit indicating the beacon reception timing from STA0, and all other bits are 0. Also, when STA0 recognizes the beacon from STA1, it sets 1 to the corresponding bit position in the NBOI field.
The lowermost part of FIG. 10 shows a state in which STA2 has entered the communication range of communication station STA1 after that. In the illustrated example, STA0 is a hidden terminal for STA2. For this reason, STA2 cannot recognize that STA1 has received a beacon from STA0, and as shown on the right side, there is a possibility that a beacon is transmitted at the same timing as STA0 and a collision occurs.
The NBOI field is used to avoid this phenomenon. First, the NBOI field of the beacon of STA1 is set to 1 in the bit indicating the timing at which STA0 is transmitting a beacon in addition to the bit indicating the transmission timing of the local station. Therefore, STA2 cannot directly receive the beacon transmitted by STA0, which is a hidden terminal, but recognizes the beacon transmission timing of STA0 based on the beacon received from STA1, and avoids beacon transmission at this timing.
Then, as shown in FIG. 11, at this time, the STA2 determines the beacon transmission timing substantially in the middle of the beacon interval between the STA0 and the STA1. Of course, in the NBOI in the transmission beacon of STA2, the bit indicating the beacon transmission timing of STA2 and STA1 is set to 1. With such a beacon collision avoidance function based on the description of the NBOI field, a beacon collision can be avoided by grasping the beacon position of a hidden terminal, that is, two adjacent stations.
B. Avoiding interference and deadlock in a multi-channel environment As described above, in an autonomous distributed wireless communication system, each communication station broadcasts beacon information within a transmission frame period and scans beacon signals from other stations. By performing the operation, the network configuration on one channel can be recognized. However, in the case of the multi-channel autonomous distributed network according to the present embodiment, the transmission frames as shown in FIG. 4 are arranged on the frequency axis by the number of used channels (see FIG. 12). ). For this reason, a communication station cannot receive a beacon unless it has shifted to the same channel at the beacon transmission timing of another communication, and it is difficult to grasp the network configuration on all channels.
As already described, in this embodiment, each communication station is provided with a single antenna, cannot transmit and receive in parallel, and cannot handle multiple frequency channels at the same time. Is assumed. Here, let us consider a state in which two communication stations are arranged in an interference environment as shown in FIG.
The communication station # 1 is arranged in a communication environment with a left slanted line indicating that it is receiving interference on the channel CH1 but not receiving interference on the channel CH2 (clear). It is set as a transmission channel. Further, the communication station # 2 is arranged in a communication environment with a right oblique line indicating that the channel CH2 receives interference but the channel CH1 does not receive interference (clear). Is set as the beacon transmission channel. In this situation, since the beacons are transmitted through the mutual interference channels, the existence of both parties cannot be noticed forever.
Therefore, each communication station periodically transmits a beacon signal using a channel having the least interference among the plurality of frequency channels, but depending on the interference situation, the beacon transmission channel selected by the standard of the local station is Consider that not all peripheral communication stations can receive channels. Specifically, a communication station that has received interference from another system periodically transmits an interference notification signal IAS on all channels that are not receiving interference, The peripheral stations are notified (see FIG. 14). In addition, in a channel that is subject to interference so that the beacon cannot be heard, the peripheral station refrains from transmitting beacons.
For example, the communication station transmits the interference notification signal IAS at a period sufficiently longer than the beacon interval. Further, the communication station performs a scanning operation of the interference notification signal IAS in a beacon period or a beacon number period on each channel that is not receiving interference.
FIG. 15 shows a format configuration example of the interference notification signal IAS. As shown in the figure, in the interference notification signal IAS, a preamble for notifying the presence of the signal is followed by a heading and a payload part PSDU. In the heading area, information indicating that the packet is the interference notification signal IAS is posted.
The PSDU has a structure that is simpler and requires a smaller total amount of data than the beacon signal in view of the purpose that the interference notification signal IAS notifies the interference status of the own station in each channel. In the illustrated example, in the PSDU, TX. An ADDR, an Interference Level field describing the degree of interference in each prepared frequency channel, that is, an interference level (IntLCH), and other fields (ETC field) are prepared.
The peripheral communication station that has received the interference notification signal IAS from another station compares the interference information of its own beacon transmission channel with the interference notification signal IAS. And when it turns out that the beacon is transmitted at a high interference level, the beacon transmission channel is changed to a channel where other stations can easily hear the beacon. Similarly, when a beacon is received, an interference state is monitored at any time, and a channel that is easy to hear a beacon is selected for a communication station that wants to communicate frequently.
By cooperative operation of each communication station through the exchange of such interference notification signal IAS, communication channels can be determined autonomously and distributed, and interference can be avoided efficiently, and by using multiple channels effectively The communication capacity can be greatly improved.
FIG. 16 shows a state where each station is performing a regular beacon transmission operation and an interference notification signal IAS scan operation on each channel when two communication stations are arranged. In the example shown in the figure, four channels # 1 to # 4 that can be used as a wireless communication system are prepared.
One communication station # 1 sets channel # 1 to its own beacon transmission channel, and transmits beacons at intervals of a predetermined transmission frame period. Also, on other channels # 2 and # 4 that do not transmit beacons, the local station's interference notification signal IAS is transmitted at an IAS transmission period (IAS Interval) that is sufficiently longer than the transmission frame period that is the beacon interval. . On channel # 3, the interference notification signal IAS is not transmitted because the interference state of the own station is poor or for other reasons. In the present embodiment, since the wireless communication apparatus cannot handle a plurality of frequency channels at the same time, the beacon transmission timing and the interference notification signal IAS transmission timing are arranged on each channel so that they do not overlap in time. Has been.
The other communication station # 2 sets channel # 3 as its own beacon transmission channel and transmits beacons at intervals of a predetermined transmission frame period. In addition, on the other channel # 2 and channel # 4 that do not transmit a beacon, the local station's interference notification signal IAS is transmitted at an IAS transmission period that is sufficiently longer than the transmission frame period that is the beacon interval. On channel # 3, the interference notification signal IAS is not transmitted because the interference state of the own station is poor or for other reasons. Since a plurality of frequency channels cannot be handled at the same time, the beacon transmission timing and the interference notification signal IAS transmission timing are arranged on each channel so that they do not overlap in time.
In the wireless communication system according to the present embodiment, all communication stations perform beacon transmission with a transmission frame period of the same length. In addition, since one communication station always transmits a beacon on the same channel, the peripheral station can grasp the expected beacon transmission time and channel periodically once receiving the beacon, and waits for reception at that timing. By doing so, beacons can be received.
Furthermore, each communication station performs a channel scan operation for each channel at a period that is not synchronized with the transmission period of the interference notification signal IAS. The channel scan operation can detect the discovery or departure of a new beacon. Further, by performing the channel scan at a period that is not synchronized with the transmission period of the interference notification signal IAS, as shown in FIG. 16, the interference notification signal IAS from the peripheral station is always transmitted to the channel. Can be received during scanning. Therefore, even if the communication stations cannot receive each other's beacons due to interference, the deadlock can be avoided by periodically receiving the interference notification signal IAS.
FIG. 17 shows, in the form of a flowchart, the transmission processing procedure of the interference notification signal performed by the communication station. Such processing operation is actually realized in a form in which the central control unit 103 of the wireless communication apparatus executes an execution command program stored in the information storage unit 113.
First, the communication station executes a scan operation for each channel, that is, a multi-channel scan operation at a predetermined timing (step S1).
Then, after the scanning operation, it is determined whether or not there is a channel in which the local station cannot receive a beacon due to a problem such as interference (step S2). When the interfered channel is detected, the channel is stored in the information storage unit 113 as a channel on which IAS transmission is not performed.
Here, it is determined whether or not the beacon transmission timing of the local station has arrived (step S3). When the beacon transmission timing arrives, a beacon transmission operation is performed on the beacon transmission channel of the local station (step S4).
Next, it is determined whether or not the local station's IAS transmission timing has arrived (step S5). When the IAS transmission timing of the local station arrives, the transmission operation of the interference notification signal IAS is sequentially performed on all the channels not receiving interference (step S6), and the process returns to step S3.
If the IAS transmission timing of the local station has not arrived, it is further determined whether or not the channel scan timing has arrived (step S7). If the channel scan timing has arrived, the process returns to step S1 to execute a multi-channel scan operation. On the other hand, if the channel scan timing has not arrived, the process returns to step S3.
If it is determined in step S2 that there is no channel through which the local station cannot receive a beacon, it is determined whether or not the beacon transmission timing of the local station has arrived (step S8). When the beacon transmission timing arrives, a beacon transmission operation is performed on the beacon transmission channel of the local station (step S9).
Next, it is further determined whether or not the channel scan timing has come (step S9). If the channel scan timing has arrived, the process returns to step S1 to execute a multi-channel scan operation. On the other hand, if the channel scan timing has not arrived, the process returns to step S8.
In the illustrated example, the communication station does not transmit the interference notification signal IAS when there is no interfered channel. By omitting unnecessary transmission of the interference notification signal IAS in this way, it is possible to improve the utilization efficiency of the transmission path and reduce the power consumption of the apparatus.
FIG. 18 shows a reception processing procedure of an interference notification signal performed by the communication station in the form of a flowchart. Such processing operation is actually realized in a form in which the central control unit 103 of the wireless communication apparatus executes an execution command program stored in the information storage unit 113.
The communication station first determines whether or not the scanning operation for each channel, that is, the timing of multi-channel scanning has arrived at a predetermined timing (step S11). When the multi-channel scan timing arrives, a scan operation for each channel, that is, a multi-channel scan operation is executed (step S12).
Here, it is determined whether or not the interference notification signal IAS from the peripheral station has been received on the channel on which the scanning operation has been performed (step S13). When the interference notification signal IAS is not received, the process returns to step S11 and the multi-channel scan operation is repeatedly executed.
When the interference notification signal IAS is received, the received packet is analyzed (step S14), and the channel interference information suffered by the transmission source is stored in the information storage unit 113.
Then, it is determined whether or not the current station is transmitting a beacon using a channel that is experiencing interference on the IAS transmitting station side (step S15). When beacon transmission is being performed on a channel other than the channel experiencing interference on the IAS transmitting station side, the process returns to step S12 and the multi-channel scanning operation is repeatedly executed.
On the other hand, if the own station is transmitting a beacon on a channel that is experiencing interference on the IAS transmitting station side, the channel that is not described as being interfered by the interference notification signal IAS from the peripheral station Among these, it is determined whether or not there is an available beacon transmission channel of the own station (step S16).
If it is determined that the beacon transmission channel of the local station can be changed (step S17), the beacon transmission channel is changed and the content is stored in the information storage unit 113.
When it is determined that the beacon transmission channel of the local station cannot be changed, a request for changing the beacon transmission channel is transmitted to the transmission source in the reception window (Listen Window) immediately after the interference notification signal IAS. (Step S18).
Thereafter, the process returns to step S12, and the multi-channel scan operation is repeatedly executed.
C. As mentioned above transmission period of the interference-report signal, the multi-channel autonomous decentralized wireless communication system according to the present invention, in a communicable channels each communication station, a packet informing the communication is difficult channel (beacon and the interference-report signal) It is equipped with a mechanism to send periodically. Therefore, even if there is a channel that is difficult to receive, by receiving a packet that reports interference on other receivable channels, it is possible to notice the presence of an adjacent terminal on that channel, and Interference channel can be known.
In addition, the communication station transmits the interference notification signal IAS at a period sufficiently longer than the beacon interval, for example. Each communication station performs a channel scan operation for each channel at a period that is not synchronized with the transmission period of the interference notification signal IAS. The channel scan operation can detect the discovery or departure of a new beacon. Further, by performing the channel scan at a period that is not synchronized with the transmission period of the interference notification signal IAS, as shown in FIG. 16, the interference notification signal IAS from the peripheral station is always transmitted to the channel. Can be received during scanning.
By the way, when it is difficult to communicate on a specific channel due to interference from a strong interference source, it is expected that there is a high possibility that adjacent stations are also receiving similar interference. Under the condition that interference exists, it is conceivable that the interference notification signal IAS increases more than necessary in the same system as a result of each station transmitting the interference notification signal IAS. Further, unless there is a change such as a new terminal joining from another network, the packet for reporting the interference is not used. In other words, it is inefficient to transmit the interference notification signal IAS with high frequency even in a steady state. In addition, since the communication station cannot perform data transmission during the transmission period of the interference notification signal IAS of other stations, it also becomes a system overhead.
Therefore, in this time mobile phone, the communication station transmits the interference notification signal IAS with an appropriate transmission frequency according to the communication status. Below, the optimal transmission frequency of the interference alerting | reporting signal IAS according to the structure and the condition of a communication system is demonstrated.
C-1. Transmission control of interference notification signal according to the number of terminals that receive interference on the same channel Autonomous distributed control that periodically reports that there is an interference channel on other channels when communication is difficult due to strong interference on a certain channel A wireless LAN is assumed. Assume that each communication station grasps the interference status of adjacent stations by using a beacon or a packet for reporting the interference.
When adjacent stations are receiving interference on the same channel, these adjacent communication stations transmit packets that report the same interference. As a result, the system as a whole invites a situation in which the interference notification signal IAS is transmitted more than necessary.
In view of this, when a neighboring station receives interference in the same channel, a mechanism is adopted in which the transmission frequency of the interference notification signal IAS is reduced according to the number of terminals.
Here, the transmission interval of each communication station beacon is T_SF, and the transmission frequency of the interference notification signal IAS in the initial state is also set to T_SF.
FIG. 19 shows a state when communication station A first enters a wireless system in which four channels # 1 to # 4 are prepared. In the example shown in the figure, the communication station A sets channel # 1 to its own beacon transmission channel, and arranges beacon transmission timing for each beacon interval T_SF on the channel. Further, the communication station A arranges the transmission timing of the interference notification signal IAS at the same transmission interval as the beacon interval T_SF in the other channels # 2 to # 4. However, since communication station channel # 3 is an interfered channel and communication is not possible, transmission of interference signal IAS is not performed on channel # 3.
After that, after transmitting a beacon for a while, it is assumed that there are two more communication stations in the vicinity having the same interference as a result of examining adjacent stations. In this case, the frequency of transmission is changed so that each peripheral station transmits the interference notification signal IAS at intervals of T_SF × 3, so that unnecessary interference notification is not performed. As a result, although the transmission range of the interference notification signal of each communication station slightly deviates, the interference notification signal IAS is notified with the same frequency on average in the entire system.
In FIG. 20, in the autonomous distributed communication system consisting of 4 channels shown in FIG. 19, when communication station B and communication station C newly join after communication station A, each communication station notifies each channel of interference notification. A state in which signals are arranged is shown.
In the illustrated example, the communication station A, after transmitting a beacon for a while, examines adjacent terminals and finds that communication stations B and C having the same interference exist in the vicinity. In this case, the transmission frequency is changed so that each communication station transmits the interference notification signal IAS at intervals of T_SF × 3, so that useless notification of interference is not performed.
In the above example, assuming that the number of adjacent terminals having interference on the same channel is n, the transmission frequency of the interference notification signal is set to T_SF × (n + 1). FIG. 21 shows the transmission operation of such an interference notification signal IAS in the form of a flowchart. Such an operation procedure is actually realized in a form in which the central control unit 103 in the wireless communication apparatus executes an execution command program stored in the information storage unit 113.
First, the interference notification signal transmission interval (IAS Interval) for transmitting the interference notification signal IAS for reporting the interference channel is set to be the same as the beacon period T_SF (step S21).
Next, the communication station periodically transmits an interference notification signal IAS at a predetermined interference notification signal transmission interval (step S22).
Here, for example, based on the interference notification signal IAS received from the adjacent station, it is determined whether or not there is an adjacent station that has interfered with the same channel as the own station (step S23).
If there is no adjacent station having the same interfered channel, the process directly returns to step S22, and the communication station periodically performs the operation of transmitting the interference notification signal IAS with the same interference notification signal transmission interval as before.
On the other hand, when there are n adjacent stations having the same interfered channel, the interference notification signal transmission interval is set to beacon period T_SF × (n + 1) (step S24). And it returns to step S22 and a communication station performs the transmission operation | movement of the interference alerting | reporting signal IAS periodically with a longer interval than before.
C-2. Consider a case where a terminal has newly entered from another network under the wireless communication environment described in the section C-1 of the transmission frequency C of the interference notification signal in response to the entry of a new communication station .
In this case, there are many terminals having the same interference, and even when the interference notification signal IAS is transmitted at an interval of T_SF × 3, for example, the transmission is temporarily performed at a relatively short T_SF interval for a while. Like that. At the same time, the communication station transmits a packet informing the adjacent station that a new entry terminal exists. Similarly, the adjacent station that receives this packet also sets the transmission interval of the interference notification signal IAS to T_SF for a while, and increases its transmission frequency.
When a communication station newly entered from another network appears, there may be a phenomenon in which the networks themselves overlap. In such a case, it is expected that other new communication stations will appear. Therefore, by adopting the mechanism as described above, the transmission frequency of the interference notification signal is temporarily increased, the possibility that the interference notification signal can be found from a new entry station is increased, and the discovery of a new terminal is accelerated.
FIG. 22 shows, in the form of a flowchart, the operation procedure of the communication station for temporarily increasing the transmission frequency of the interference notification signal IAS in response to finding a new entry station. Such an operation procedure is actually realized in a form in which the central control unit 103 in the wireless communication apparatus executes an execution command program stored in the information storage unit 113.
First, the communication station sets the transmission cycle of the interference notification signal IAS in consideration of the current communication environment (step S31).
Then, the communication station periodically transmits an interference notification signal IAS at a predetermined interference notification signal transmission interval (step S32).
Here, it is determined whether or not a new entry station has been found (step S33). When a new entry station is found, the neighboring station is notified of the presence of the new entry station (step S34).
When the own station finds a new entry station or recognizes the presence of a new entry station by notification from an adjacent station, the transmission frequency of the interference notification signal IAS is increased to increase the possibility that the new entry station will find it. Therefore, the interference notification signal transmission interval is set to be the same as the beacon period T_SF (step S35). Then, the communication station periodically transmits the interference notification signal IAS with the set interference notification signal transmission interval (step S36).
When a predetermined time elapses after the interference notification signal transmission interval is set to the beacon period (step S37), the process returns to step S31, and the transmission period of the interference notification signal IAS is set in consideration of the current communication environment. .
Further, even when a new entry station is not found in step S33, it is determined whether or not the presence of the new entry station is notified from the adjacent station (step S38). If neither the own station nor the adjacent station finds the presence of a new entry station, the process returns to step S32 as it is, and the communication station periodically performs interference notification signal IAS with the same interference notification signal transmission interval as before. The transmission operation is performed.
C-3. When a terminal newly enters from another network under the wireless communication environment described in the section C-1 of the transmission frequency of the interference notification signal according to the elapsed time from the new entry of the communication station, it is temporarily The frequency of transmission of the interference notification signal is increased to increase the possibility that the interference notification signal can be found from a new entry station, and the discovery of a new terminal is accelerated (described above). On the other hand, when a certain period of time has elapsed since the communication station newly entered, the possibility that the interference notification signal IAS has already been found increases, and therefore the necessity of setting the transmission frequency high gradually decreases. On the other hand, if the transmission frequency is kept high, it becomes a factor of reducing the channel utilization efficiency.
Therefore, in this embodiment, the time until a new terminal moves from another network is counted, and when the count value reaches a certain number, the transmission frequency of the interference notification signal IAS is decreased this time. . Here, when the count value reaches a certain number, it is determined that the transmission cycle is lengthened by T_SF.
When the transmission frequency of the interference notification signal IAS is controlled in this way, the transmission frequency of the interference notification signal IAS gradually decreases until a new entry station appears next time. As a result, the transmission frequency decreases according to the extent that the interference notification signal IAS is unnecessary, so that packets for notifying interference are not transmitted unnecessarily.
Thereafter, when a communication station that newly joins the network appears again, the transmission frequency of the interference notification signal IAS is returned to the initial value, and efforts are made for early detection.
FIG. 23 shows the operation procedure of the communication station in the form of a flowchart for controlling the transmission frequency of the interference notification signal IAS according to the elapsed time since the discovery of the new entry station. Such an operation procedure is actually realized in a form in which the central control unit 103 in the wireless communication apparatus executes an execution command program stored in the information storage unit 113.
First, the communication station sets the transmission cycle of the interference notification signal IAS to be the same as the beacon transmission cycle T_SF (step S41), and resets the counter value (step S42).
Then, the communication station periodically transmits an interference notification signal IAS at a predetermined interference notification signal transmission interval (step S43).
Here, it is determined whether or not a new entry station has been found (step S44). If no new entry station is found, the process returns to step S41 as it is, and the communication station periodically performs an operation of transmitting the interference notification signal IAS with an interference notification signal transmission interval in consideration of the current communication environment. .
On the other hand, when a new entry station is found, the counter value is incremented (step S45).
Note that the discovery of a new entry station may include notification from an adjacent station in the same manner as in the case shown in FIG.
Until the counter value reaches the predetermined value (step S46), the process returns to step S43, and the periodic transmission operation of the interference notification signal IAS is repeatedly executed.
When the counter value reaches a predetermined value, the transmission period of the interference notification signal IAS is increased by the beacon transmission period T_SF (step S47), and the process returns to step S42.
FIG. 1 is a diagram illustrating an arrangement example of communication apparatuses constituting a wireless communication system according to an embodiment of the present invention. FIG. 2 is a diagram schematically illustrating a functional configuration of a wireless communication apparatus according to an embodiment of the present invention. FIG. 3 is a diagram for explaining a beacon transmission procedure of each communication station according to the present embodiment. FIG. 4 is a diagram showing an example of beacon transmission timing on one channel. FIG. 5 is a diagram for explaining the definition of the packet interval. FIG. 6 is a diagram showing a state in which priority is given to the beacon transmitting station. FIG. 7 is a diagram showing the configuration of the transmission frame period. FIG. 8 is a diagram illustrating a configuration example of a beacon signal format. FIG. 9 is a diagram illustrating a description example of the NBOI. FIG. 10 is a diagram showing a state in which a new entry station arranges its own beacon transmission timing while avoiding a collision with an existing beacon based on the description of the NBOI on a certain frequency channel. FIG. 11 is a diagram illustrating a state in which the own beacon transmission timing is arranged while avoiding the beacon transmission timing of the hidden terminal based on the beacon information received by the new entry station. FIG. 12 is a diagram schematically showing a transmission frame configuration of an autonomous distributed multi-channel wireless communication system. FIG. 13 is a diagram showing a deadlock state when the beacon transmission channel of one station is an interference channel or a channel that cannot be used because the communication quality deteriorates in the other station. FIG. 14 is a diagram illustrating a state in which the communication station periodically transmits an interference notification signal IAS on all channels not receiving interference to notify the neighboring stations of the channel receiving interference. FIG. 15 is a diagram illustrating a format configuration example of the interference notification signal IAS. FIG. 16 is a diagram illustrating a state in which each station is performing a periodic beacon transmission operation and a scanning operation of the interference notification signal IAS on each channel when two communication stations are arranged. FIG. 17 is a flowchart illustrating a transmission processing procedure of an interference notification signal performed by a communication station. FIG. 18 is a flowchart showing a reception processing procedure of an interference notification signal performed by a communication station. FIG. 19 is a diagram illustrating a state in which the communication station arranges the beacon transmission position and the interference notification signal on each channel. FIG. 20 shows an interference notification signal for each channel when the communication station B and the communication station C newly join the communication station A after the communication station A in the 4-channel autonomous distributed communication system shown in FIG. It is the figure which showed a mode that it has arrange | positioned. FIG. 21 is a flowchart showing a processing procedure of the communication station for setting the transmission frequency of the interference notification signal to T_SF × (n + 1) (where n is the number of communication stations having the same interfered channel). FIG. 22 is a flowchart showing an operation procedure of the communication station for temporarily increasing the transmission frequency of the interference notification signal IAS in response to finding a new entry station. FIG. 23 is a flowchart showing an operation procedure of the communication station for controlling the transmission frequency of the interference notification signal IAS according to the elapsed time since the discovery of the new entry station.
DESCRIPTION OF SYMBOLS 100 ... Wireless communication apparatus 101 ... Interface 102 ... Data buffer 103 ... Central control part 104 ... Beacon generation part 105 ... Interference alert signal generation part 106 ... Radio transmission part 107 ... Timing control part 108 ... Channel setting part 109 ... Antenna 110 ... Radio reception unit 111 ... interference notification signal analysis unit 112 ... beacon analysis unit 113 ... information storage unit
In a communication environment in which a plurality of channels are prepared, a wireless communication system that forms a network based on ad hoc communication with a plurality of wireless communication devices without arranging a control station,
The communication station performs a channel scan operation for each channel at a period not synchronized with the transmission period of the interference notification signal.
The communication station compares the interference information of each channel of the peripheral station described in the interference notification signal received from the peripheral station with the beacon transmission channel of the local station, and transmits a beacon using a channel with a high interference level. If it turns out, the beacon transmission channel of its own station is changed to a channel where the peripheral station can easily hear the beacon.
A communication station without an interfered channel does not transmit an interference notification signal.
As a result of examining the adjacent terminal as a result of examining the adjacent terminal, the communication station, if it is found that there is an adjacent station having the same interfered channel, change the transmission frequency of the interference notification signal according to the number of the change, to change the transmission frequency,
The communication station increases the transmission frequency of the interference notification signal for a predetermined time according to the entry of a new communication station,
When the communication station discovers the entry of a new communication station, it notifies the peripheral station of this, and increases the transmission frequency of the interference notification signal for a predetermined time according to the notification that the new communication station has entered,
The wireless communication system according to claim 6.
The communication station gradually decreases the transmission frequency of the interference notification signal from the initial value according to the elapsed time since the new communication station entered,
A wireless communication device that operates autonomously and distributedly in a wireless communication environment,
Interference beacon signal generating means for generating a beacon signal and an interference notification signal describing information on the interfered channel of the own station;
Interference notification signal analysis means for analyzing the beacon signal and interference notification signal of the peripheral station received by the communication means;
Communication means for transmitting and receiving wireless data in each channel;
Channel setting means for setting a channel for data transmission and reception in the communication means;
Communication control means for controlling the beacon signal and interference notification signal transmission operation of the local station in the communication means, and the reception operation of the beacon signal and interference notification signal from the peripheral station;
The channel setting means determines its beacon transmission channel from the plurality of channels, and sets a channel other than the beacon transmission channel as a transmission channel of an interference notification signal.
The channel setting means removes the interfered channel of the local station from the beacon transmission channel and the transmission channel of the interference notification signal.
The wireless communication apparatus according to claim 10.
The communication control means controls the channel scan operation of each channel at a period not synchronized with the transmission period of the interference notification signal.
The interference notification signal analysis means compares the interference information of each channel of the peripheral station described in the interference notification signal received from the peripheral station and the beacon transmission channel of the own station,
If it is determined that the channel setting means transmits a beacon on a channel with a high interference level of the peripheral station based on the comparison result, the peripheral station listens to the beacon transmission channel of the local station. Change to easy channel,
When there is no interfered channel of the local station, the communication control unit does not transmit an interference notification signal, or the interference notification signal generation unit does not generate an interference notification signal.
If the communication control means determines that there is an adjacent station having the same interfered channel as a result of the analysis by the interference notification signal analysis means, the communication control means adjusts the transmission frequency of the interference notification signal according to the number of the adjacent stations and transmits ,
The communication control means increases the transmission frequency of the interference notification signal for a predetermined time according to the entry of a new communication station,
When the entry of a new communication station is found, it further comprises means for informing the peripheral station of this,
The communication control means increases the transmission frequency of the interference notification signal for a predetermined time in response to a notification that a new communication station has entered,
The wireless communication apparatus according to claim 16.
The communication control means gradually decreases the transmission frequency of the interference notification signal from the initial value according to the elapsed time since the new communication station entered,
A wireless communication method that operates autonomously and distributedly in a wireless communication environment,
In the channel setting step, a beacon transmission channel is determined from the plurality of channels, and a channel other than the beacon transmission channel is set as a transmission channel of an interference notification signal.
The wireless communication method according to claim 19.
In the channel setting step, remove the interfered channel of the own station from the beacon transmission channel and the transmission channel of the interference notification signal,
21. The wireless communication method according to claim 20, wherein:
The communication control step includes a step of controlling the channel scan operation of each channel at a period not synchronized with the transmission period of the interference notification signal.
In the interference notification signal analysis step, the interference information of each channel of the peripheral station described in the interference notification signal received from the peripheral station is compared with the beacon transmission channel of the own station,
In the channel setting step, if it is determined that a beacon is transmitted on a channel with a high interference level of the peripheral station based on the comparison result, the peripheral station listens to the beacon transmission channel of the local station. Change to easy channel,
When there is no interfered channel of the own station, the communication control step does not transmit an interference notification signal, or the interference notification signal generation step does not generate an interference notification signal.
In the communication control step, as a result of the analysis in the interference notification signal analysis step, if it is found that it exists in an adjacent station having the same interfered channel, the transmission frequency of the interference notification signal is adjusted according to the number and transmitted. ,
In the communication control step, according to the entry of a new communication station, the transmission frequency of the interference notification signal is increased by a predetermined time,
When the entry of a new communication station is found, it further comprises a step of notifying the peripheral station of this,
In the communication control step, the transmission frequency of the interference notification signal is increased by a predetermined time in response to a notification that a new communication station has entered,
27. The wireless communication method according to claim 26.
In the communication control step, according to the elapsed time since the new communication station entered, gradually reduce the transmission frequency of the interference notification signal from the initial value,
A computer program written in a computer-readable format to execute wireless communication processing for autonomously distributed operation in a wireless communication environment on a computer system,
Communication control step for controlling the beacon signal and the interference notification signal transmission operation of the own station, the beacon signal and the interference notification signal reception operation from the peripheral station,
JP2003281587A 2003-07-29 2003-07-29 Wireless communication system, wireless communication apparatus and wireless communication method, and computer program Pending JP2005051523A (en)
US10/898,227 US7565109B2 (en) 2003-07-29 2004-07-26 Wireless communication system, wireless communication apparatus, wireless communication method and computer program
JP2005051523A true JP2005051523A (en) 2005-02-24
JP2005051523A5 JP2005051523A5 (en) 2005-02-24
JP2003281587A Pending JP2005051523A (en) 2003-07-29 2003-07-29 Wireless communication system, wireless communication apparatus and wireless communication method, and computer program
JP2007267281A (en) * 2006-03-29 2007-10-11 Ntt Docomo Inc Wireless access point and control apparatus for management the same
JP2008545291A (en) * 2005-05-12 2008-12-11 コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ A method for multi-channel resource reservation in a wireless mesh network
JP2009514441A (en) * 2005-10-26 2009-04-02 クゥアルコム・インコーポレイテッドＱｕａｌｃｏｍｍ Ｉｎｃｏｒｐｏｒａｔｅｄ Flexible medium access control (MAC) for ad-hoc deployed wireless networks
JP2009152826A (en) * 2007-12-20 2009-07-09 Nec Corp Wireless communication controller, wireless communication control system, wireless communication control method, wireless communication control program and recording medium
WO2006025171A1 (en) * 2004-08-31 2006-03-09 Matsushita Electric Industrial Co., Ltd. Wireless communication method and wireless communication apparatus
EP2830388B1 (en) * 2012-03-23 2017-12-20 NEC Corporation Wireless communication terminal, mobile ad-hoc network, and network subscription method
JP2641441B2 (en) 1987-03-20 1997-08-13 株式会社日立製作所 Mobile radio communication method and a mobile radio communication system
US8270355B2 (en) 2007-12-20 2012-09-18 Nec Corporation Radio communication control device, radio communication control system, radio communication control method, radio communication control program and recording medium
US7565109B2 (en) 2009-07-21
JP3963700B2 (en) 2007-08-22 Method for changing 802.11 standard parameters in IEEE 802.11 standard WLAN
De Domenico et al. 2010 A survey on MAC strategies for cognitive radio networks