JPH0766805A - Wireless communication system - Google Patents

Abstract

(57) [Summary] [Purpose] To improve throughput by eliminating the influence of hidden terminals. [Configuration] Each wireless communication terminal Ma to Mg is provided with a previous reception information section 27, and when a packet is transmitted, the elapsed time from the last packet transmission / reception time to the current time and the transmission station address of the previously received packet are displayed. Each is included in the transmission. Also, when a packet is received, the elapsed time contained in this received packet is compared with the elapsed time measured by itself, and if both elapsed times do not match, there is a possibility of a hidden terminal. Self-recognizing that the wireless communication terminal is identified based on the previous transmission station address included in the received packet, and sends a control packet to this terminal to notify that there is a possibility of the hidden terminal. It is something that is done.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system for wirelessly transmitting packets between a plurality of wireless communication terminals such as a wireless LAN system, and more particularly to a system having a countermeasure function for hidden terminals.

[0002]

[Prior Art] In offices and office buildings,
LA using a coaxial cable as the information transmission system
N (Local Area Network) is often used. In such a wired LAN, when the layout is changed from the initial installation state, it takes time and cost to re-install it. Therefore, a wireless LAN is strongly desired. Particularly in Japan, CSMA / CD (Carrier Sense Multiple Access with 10 Mbps of IEEE802.3 standard widely used as a wired LAN is used.
Collision detection) is being standardized, while ensuring compatibility with the method.

By the way, as a communication form for realizing this wireless LAN system, a so-called equal distribution system in which both the access control system and the information transmission system communicate in a distributed system, and a centralized system in both the access control system and the information transmission system. There is a method that uses the centralized method in the access control system and a method that uses the distributed method in the information transmission system. Among them, the equal distribution method is (1) most compatible with the design concept of the LAN because terminals can directly communicate with each other in the control system / transmission system. (2) Since it is not necessary to prepare a central station, it is easy to introduce even if the number of terminals is small.

(3) Since there is no centralized station, the entire system does not go down and the reliability is high. (4) Since it is not necessary to turn back the signal at the central station,
The required bandwidth can be minimized. (5) No special work is required to install the central station. (6) There is no need to register between wired LANs. And many other advantages.

On the other hand, however, there is a problem in that all terminals must be provided with an access control function such as collision detection, and if there are hidden terminals, the throughput is greatly reduced. Here, the hidden terminal is a place where if there is a wireless communication terminal other than itself that is in communication, the carrier should be detected and the signal transmission thereof should be postponed. In addition, it is a terminal that sends a signal without being able to detect the carrier due to the fact that the terminal is behind the pillar. If such a terminal exists, the packet transmitted by the wireless communication terminal during communication is destroyed in the middle of the packet, and the throughput is significantly reduced.

Therefore, a wireless LA having high throughput
In order to construct the N system, measures against the hidden terminal are indispensable. However, in actual wireless communication, since it is difficult to clearly indicate the communication distance (service area) in the actual usage environment, the wireless communication terminal may try to access from outside the service area. In such a case, this wireless communication terminal becomes a hidden terminal.
In addition, the effect of frequency selective fading cannot be ignored.
That is, frequency selective fading is a phenomenon in which the received signal level of a certain radio frequency falls by several tens of dB, and the radio frequency that falls depends on the radio transmission environment.
For example, even if it is a radio frequency that was able to communicate normally until then, moving the wireless communication terminal or moving the antenna a little without moving the terminal changes the surrounding reflection condition. The level of the received signal may be extremely lowered, resulting in communication failure.

As described above, the hidden terminal is relatively easily generated due to the movement of the wireless communication terminal itself or the movement of the antenna, and it is difficult to reliably eliminate the influence of the hidden terminal.

On the other hand, one of the operational requirements of the wireless LAN system is the communication failure rate. IEEE 802.11 and R
The CR (Radio System Development Center) and others stipulate that the incommunicable rate is "0.1% / service area x day" or less. Therefore, even if a hidden terminal occurs, in order to satisfy the requirement of the communication failure rate, it is necessary to guarantee communication with the hidden terminal as much as possible, and an effective countermeasure is desired.

[0009]

As described above, the wireless communication system to which the equal distribution method is applied has many advantages, but on the other hand, there is a problem that throughput is greatly reduced when there are hidden terminals. Therefore, effective measures against this hidden terminal have been desired.

Therefore, a first object of the present invention is to provide a radio communication system capable of eliminating the influence of a hidden terminal and improving the throughput.
A second object of the present invention is to provide a wireless communication system capable of guaranteeing communication with a hidden terminal as much as possible and suppressing the communication failure rate.

[0011]

In order to achieve the first object, a wireless communication system according to the present invention is a wireless communication system for performing packet communication between a plurality of wireless communication terminals via a wireless channel. The wireless communication terminal is provided with a clocking means, a packet transmitting means, a comparing means, and a recognizing means. Then, the elapsed time from the transmission / reception time of the closest packet communication to the current time is measured by the time measuring means, and when transmitting the packet, information indicating the first elapsed time measured by the time measuring means is displayed. It is included in the above packet and transmitted. When a packet is received, the comparison means compares the first elapsed time included in the received packet with the second elapsed time at the current time measured by the time measuring means,
The presence of the hidden terminal is recognized based on the comparison result.

In the present invention, the comparing means determines whether the difference between the first elapsed time and the second elapsed time exceeds a predetermined range, and it is determined that the difference exceeds the predetermined range. If so, the control packet including the information to that effect is transmitted according to a predetermined procedure, while when the control packet is received, the presence of the hidden terminal is determined based on the information included in the control packet. It is characterized by recognizing.

Further, according to the present invention, when it is determined by the comparison means that the value obtained by subtracting the first elapsed time from the second elapsed time exceeds the predetermined value, the self-estimation based on this determination result. When the wireless communication terminal is recognized as a hidden terminal, and when the comparison means determines that the value obtained by subtracting the second elapsed time from the first elapsed time exceeds the predetermined value, The first control packet including the determination result is transmitted to the wireless communication terminal that has transmitted the packet including the first elapsed time, and the first control packet including the determination result is transmitted to the own wireless communication terminal.
When the control packet is received, the wireless communication terminal of its own is recognized as a hidden terminal based on the determination result included in the first control packet.

Furthermore, the present invention provides the recognition means according to the first aspect.
The determination result that the difference between the elapsed time and the second elapsed time exceeds the predetermined range is obtained in a predetermined number of times or more in its own wireless communication terminal or notified from another wireless communication terminal. If it is, the wireless communication terminal of its own is recognized as a hidden terminal.

Further, according to the present invention, when the recognition means recognizes its own wireless communication terminal as a hidden terminal, it voluntarily stops the subsequent packet transmission, and a warning indicating that it is a hidden terminal or an alarm accompanying it. It is also characterized in that at least one of control for notifying the user of information is performed.

Further, according to the present invention, the transmitting station address of the packet transmitted / received in the nearest past is stored as the previous transmitting station address, and when the packet is transmitted, the preceding transmitting station address is included and transmitted. When the second elapsed time measured by the own terminal is longer than the first elapsed time included in this packet when the packet is received, it is included in this received packet. It is also characterized in that the hidden terminal is recognized from the last transmitting station address, and the control packet for this hidden terminal is transferred via the wireless communication terminal that transmitted the packet.

On the other hand, in order to achieve the second object, another wireless communication system of the present invention determines to a wireless communication terminal whether or not the wireless communication terminal of the destination of the packet can receive the packet. Determination means, a detection means for detecting a relay wireless communication terminal capable of receiving the packet and capable of communicating with the destination wireless communication terminal, a relay request control means, and a packet And relay means. When the determination means determines that the destination wireless communication terminal cannot receive the packet, the relay request control means determines that the relay wireless communication terminal is detected by the detection means. When a packet including relay information is transmitted, and when a packet including the relay information is received, the packet relay means relays the packet to the corresponding wireless communication terminal of the destination. .

Further, according to the present invention, when the determination means does not return a response from the destination wireless communication terminal within a certain time after transmitting the packet, the wireless communication terminal cannot receive the packet. It is characterized by determining that

Further, the present invention is characterized in that the detecting means has various configurations as follows. One of them is to detect a relay wireless communication terminal based on identification information of a transmission source included in a packet received within a predetermined period in the past. The other one broadcasts a control packet containing identification information of its own wireless communication terminal, receives the control packet broadcast from another wireless communication terminal, and relays based on the received control packet. The wireless communication terminal for use is detected. Still another is to broadcast a control packet containing the history of packets received within a predetermined period in the past and identification information of its own wireless communication terminal, and to receive the control packet broadcast from another wireless communication terminal. Then, the relay wireless communication terminal is detected based on the history included in the received control packet. The control packet is broadcast at a predetermined time interval set according to the packet transmission traffic.

[0020]

As a result, according to the present invention, the following effects are exhibited. In other words, each wireless communication terminal always measures the elapsed time from the closest transmission / reception time of the packet communication performed in the past to the current time, and when transmitting the packet, this elapsed time is included in the packet for transmission. When a packet is received, the elapsed time of the transmitting terminal included in the received packet is compared with the elapsed time of its own terminal, and the existence of the hidden terminal is recognized based on the comparison result. For this reason, when a wireless communication terminal in the state of a hidden terminal appears in the system, the hidden terminal and other wireless communication terminals that have received the packet sent from this hidden terminal have the elapsed time included in the received packet. The terminal's own terminal does not match the elapsed time during timekeeping, which makes it possible to recognize that its own terminal or the wireless communication terminal that has transmitted the packet is a hidden terminal. Therefore, in response to this recognition result, it is possible to take measures such as voluntarily stopping packet transmission, and notifying the user of the recognition result to prompt the user to move the wireless communication terminal. The influence of the terminal is eliminated and the decrease in throughput is prevented.

Further, according to the present invention, when the elapsed time included in the received packet and the elapsed time being measured by the own terminal do not match, a control packet including information to that effect is transmitted to another wireless communication terminal. To be done. Therefore, not only the wireless communication terminal that has detected the mismatch of the elapsed times but also other wireless communication terminals can recognize the existence of the hidden terminal from the content of the control packet and the transmission / reception status of itself.

Further, according to the present invention, not only the difference between the elapsed time contained in the received packet and the elapsed time being measured at the own terminal, but which elapsed time is larger is determined, and the magnitude relationship is determined. Since the hidden terminal is recognized based on the result, more accurate recognition can be performed.

Further, in the present invention, when the result of the determination that the difference between the first elapsed time and the second elapsed time exceeds the predetermined range is a predetermined number of times or more within a predetermined period, The wireless communication terminal is recognized as a hidden terminal. Therefore, it is possible to prevent a packet from being temporarily received due to quality deterioration of the wireless transmission path, etc., from being erroneously recognized as a hidden terminal.
This makes it possible to make an accurate determination.

Further, according to the present invention, when the control packet cannot be directly sent to the hidden terminal, the control packet is sent via another wireless communication terminal capable of communication. Therefore, it is possible to promptly and surely notify the hidden terminal that it is the hidden terminal.

On the other hand, according to another aspect of the present invention, when the wireless communication terminal of the transmission destination becomes a hidden terminal and the packet transmitted from its own wireless communication terminal becomes unreceivable, its own wireless communication is performed. A relay wireless communication terminal capable of wireless communication with both the terminal and the destination wireless communication terminal is detected, and the packet is transmitted via this relay wireless communication terminal. For this reason, it becomes possible to transmit the packet even to the hidden terminal, which makes it possible to suppress the communication failure rate to a low level.

[0026]

(First Embodiment) FIG. 1 is a schematic configuration diagram of a wireless LAN system according to a first embodiment of the present invention.

In the figure, OL indicates a wired LAN system, and Ma to Mg indicate wireless communication terminals.
The wired LAN system comprises, for example, a loop network in which optical fibers are connected in a loop shape.
The system OL includes a plurality of wireless bridges BR1, BR2.
... is connected. These wireless bridges BR1 and B
R2, ... Have an interface function between the wired LAN system and the wireless LAN system, and these bridges BR1, BR2, ... Respectively include one of the wireless communication terminals Ma to Mg, Md, Me. Are connected.

In the wireless LAN system of this embodiment, the service area to be covered is divided into a plurality of wireless zones E1, E2, ... With a radius of about 20 m, and each of these wireless zones E1, E2 ,. Wireless bridge B
R1, BR2, ... Are arranged one by one. Further, in the system of the present embodiment, a plurality of radio frequencies owned is divided into a plurality of radio frequency groups, and these radio frequency groups are respectively assigned to the radio zones E1, E2 ,. At this time, different radio frequency groups are assigned to the radio zones adjacent to each other, and the same radio frequency group is repeatedly assigned to the radio zones sufficiently separated. This is to make effective use of radio frequencies.

Data terminals such as personal computers and workstations, voice terminals such as digital mobile phones, and various terminal devices such as image terminals such as facsimile machines are connected to the respective wireless communication terminals Ma to Mg via digital interfaces. Connected.
The wireless communication terminals Ma to Mg are located within the wireless zones E1, E2, ...
Using the radio frequency groups assigned to E2, ..., Radio communication is performed with other radio communication terminals located in the same radio zone E1, E2 ,. When communication is performed between wireless communication terminals located in different wireless zones, the wireless communication terminals Md and Me connected to the wireless bridges BR1, BR2, ... And the wired LAN system OL are used. In the wireless communication between the wireless communication terminals Ma to Mg, a plurality of wireless frequencies (for example, 4 frequencies) are simultaneously used in order to minimize deterioration of transmission quality due to frequency selective fading.

FIG. 2 shows the wireless communication terminal devices Ma to Mg.
3 is a circuit block diagram showing the configuration of FIG. In the figure, transmission data (user information) output from various terminal devices (not shown) is input to the transmission digital interface 11. In this transmission digital interface 11,
A transmission interface operation with the above various terminal devices is performed. Specifically, buffering, level conversion, speed conversion, timing adjustment, clock reproduction and clock synchronization of transmission data transferred from various terminal devices are performed. As the transmission digital interface 11, for example, an AUI of IEEE802.3 is adopted.
FIG. 3 (c) shows the frame structure of the transmission / reception data in this case, in which the preamble PRE is arranged at the head position, followed by the frame start delimiter SFD, the target station address DA, the transmission station address SA, and the user information length. LNG,
And the user information field UDF is arranged in order.
At the end, an error detection additional bit FCS is arranged.

The transmission data output from the transmission digital interface 11 is input to the packet construction unit 12. The packet composing unit 12 composes a packet to be transmitted in a wireless section, and the packet composed here includes a control packet and a user information packet. The control information packet is used in the hidden terminal self-recognition procedure. For example, as shown in FIG.
F, preamble PRE, frame start delimiter SF
D, elapsed time LT, previous transmitting station address LSA, packet identifier PD, destination station address DA, transmitting station address S
A and the additional bit ACS for address error are arranged,
Further, a control information field CDF, an error detection additional bit FCS, and an error correction additional bit ECS are arranged in order. On the other hand, the user information packet is used for wirelessly transmitting and receiving data transmitted and received by various terminal devices. For example, as shown in FIG. 3B, the random pulse transmission field RP is sequentially provided from the beginning.
F, preamble PRE, frame start delimiter SF
D, elapsed time LT, previous transmitting station address LSA, packet identifier PD, destination station address DA, transmitting station address S
A and the additional bit ACS for address error are arranged,
Further, user information length LNG, user information field UD
F, the additional bit for error detection FCS, and the additional bit for error correction ECS are arranged in this order.

Among the constituent elements of the packet, the random pulse transmission field RPF is a period for transmitting a random pulse for collision detection in order to realize the CSMA / CD system, and this random pulse for collision detection is used. Before sending data, it is determined whether a collision has occurred. The preamble PRE is a signal for the demodulation circuit of the wireless communication terminal on the receiving side to establish carrier synchronization and bit synchronization, and also the frame start delimiter SF.
D is a signal for the receiving wireless communication terminal to establish frame synchronization. Further, the transmission station address and the destination station address are addresses of various terminal devices connected to the wireless communication terminals on the transmitting side and the receiving side, and are each composed of 48 bits in AUI, for example.

The transmission packet output from the packet construction unit 12 is scrambled in order to randomize the data in the scramble unit 13 and then input to the encoding unit 14. In the coding unit 14, the transmission packet is divided into four series by serial / parallel conversion, and coding for error correction and error detection is performed. The reason for dividing into four sequences is that all sequences can be reproduced from the sequence received on the receiving side even if one of the four sequences is affected by frequency selective fading in the wireless transmission section. is there. For example, a (4, 3, 2) parity check code is used as the error detection code, and an error correction code is (2
1, 15, 4) Extended Hamming code is used.

The four series of transmission packet data output from the encoding unit 14 are respectively four modulation units 151 to 1
54 is input. In each of the modulators 151 to 154, first, the collision detector 26 is added to the random pulse transmission field RPF of the transmission packet data of 4 series.
The random pulses generated by are respectively inserted. Then, the intermediate frequency signal is digitally modulated by these transmission packet data. As the modulation method, for example, the π / 4 shift DQPSK method is used. The transmission intermediate frequency signals output from the modulators 151 to 154 are input to the high frequency unit (RF unit) 16. In the high frequency section 16, the transmission intermediate frequency signal is frequency-converted into four different carrier signals, amplified to a predetermined transmission power level, and then wirelessly transmitted from the transmission / reception antenna 17A to another wireless communication terminal. .

On the other hand, the four series of modulated wave signals transmitted from other wireless communication terminals are respectively received by the antennas 17A and 17B which are spaced apart from each other by a predetermined distance for space diversity reception. , To the high frequency section 16. The high-frequency unit 16 performs level compensation of the modulated wave signal received by each of the antennas 17A and 17B, frequency conversion into an intermediate frequency signal, band limiting processing, and the like. And this high frequency part 16
The reception intermediate frequency signal output from the antenna 17A is input to the demodulation units 181 to 184, and the reception intermediate frequency signal received from the antenna 17B is input to the demodulation units 191 to 194.

These demodulators 181-184, 191-
At 194, carrier synchronization, digital demodulation, clock synchronization (clock reproduction) and carrier detection are performed for each of the received intermediate frequency signals, among which the carrier detection signal, reproduced clock and demodulated data are supplied to the decoding unit 21. The carrier detection signal is also supplied to the collision detection unit 26. The carrier detection signal means the high frequency unit 1.
6 is "1" when the level in the designated frequency band of the received intermediate frequency signals supplied to the demodulation units 181 to 184 and 191 to 194 is equal to or higher than the specified level, and "0" when the level is lower than the specified level. Is the signal.

The collision detecting section 26 performs the following collision detection operation by using the random pulse transmission field RPF. That is, for example, the random pulse transmission field RPF is divided into 18 slots as shown in FIG. 4, of which one of the first slot (0th slot) and 17 slots from 1st to 17th are divided. A carrier signal is transmitted in a total of 9 slots including 8 randomly selected slots. And
During the other slot period, it is in the receiving state, and it is determined whether or not there is a carrier signal transmitted by another wireless communication terminal.

In the example of FIG. 4, the random patterns sent by the wireless communication terminal Ma and the wireless communication terminal Mb are the same up to the eighth slot, so collisions cannot be detected with each other. However, in the ninth slot, the wireless communication terminal Ma sends out a carrier signal, whereas the wireless communication terminal Mb does not send out a carrier signal. Therefore, the occurrence of collision is detected in the wireless communication terminal Mb. In the 13th slot, the wireless communication terminal Mb is transmitting a carrier signal, whereas the wireless communication terminal Ma is not transmitting a carrier signal. Therefore, the occurrence of collision is detected in the wireless communication terminal Ma. In this way, if the patterns of random pulses sent by the two wireless communication terminals are different even in part,
These wireless communication terminals can detect the occurrence of collision.

During the random pulse transmission, if the carrier signal is continuously transmitted from the slot next to the slot in which the collision has been detected to the end of the random pulse transmission field, until the other party detects the collision. The period can be shortened, and collision detection can be performed more reliably. For example, in the case of the random pulse pattern shown in FIG.
When a collision is detected in the ninth slot, the wireless communication terminal M
b continues to transmit the carrier signal from the 10th slot to the 17th slot as shown by the thick solid line in FIG. As a result, the wireless communication terminal Ma can detect the occurrence of a collision in the tenth slot, and the detection timing is earlier than in the case of FIG.

The demodulators 181 to 184 and 191 to 19
The demodulated data output from 4 is input to the decoding unit 21. The decoding unit 21 performs error detection processing and error correction decoding processing on the demodulated data, thereby reproducing one series of demodulated packet data. The demodulated packet data is descrambled by the descrambling unit 22 and then input to the packet decomposing unit 23. The packet disassembling unit 23 extracts the elapsed time LT and the last transmitting station address LSA from the demodulated packet data and supplies the same to the last receiving information unit 27. Also, the packet identifier PD in the demodulated packet data is extracted, and this packet identifier PD is input to the control unit 25. The control unit 25 identifies whether the packet received from the identifier PD is a user information packet or a control packet. Then, if it is a user information packet, it is directly transferred to various terminal devices (not shown) through the reception digital interface 24, while if it is a control packet, it is fetched and its contents are read.

By the way, the most characteristic part of the configuration of the wireless communication terminal of this embodiment is that the previously received information section 27 is provided. The previous reception information section 27 has a timer circuit, and always counts the elapsed time from the transmission / reception time of the closest packet transmission / reception performed by the timer circuit to the present time. Then, at the time of packet transmission, the elapsed time by the timer circuit at this point and the transmission station address of the packet transmitted / received in the nearest past are supplied to the packet composing unit 12 so as to be inserted into the transmission packet. .

On the other hand, when a packet is received, the elapsed time extracted from the received packet is compared with the current elapsed time by the timer circuit. When the elapsed time at the present time by the timer circuit is longer, it is determined that the packet transmitted last time from another wireless communication terminal could not be received, and the count value of the reception failure number counter is incremented. Also, if the elapsed time at the present time by the timer circuit is shorter and the previous sending station address is its own address, the control information packet is used immediately after the reception of the packet to send to the sending station address. The station sends information indicating that it could not receive the previously transmitted packet.

When the control information packet is received from another wireless communication terminal and the content of the notification is information indicating that the reception of the packet has failed, the control unit 25 uses its own previously received information unit 27. The count value of the reception failure counter is incremented.

Next, the operation of the system configured as described above will be described. Now, suppose that the wireless communication terminal Mc moves and goes out of the wireless zone E1 as shown in FIG. 6, for example. Then, the wireless communication terminal Mc becomes the wireless communication terminal M.
Although wireless communication is still possible between a and Mb, wireless communication with a wireless communication terminal Md far away cannot be performed. That is, the wireless communication terminals Mc and Md cannot detect the carrier signals transmitted by the terminals Md and Mc, and cannot detect packet collision. In other words, the wireless communication terminals Mc and Md are hidden terminals with respect to each other. In this state, both wireless communication terminals Mc and Md may simultaneously transmit packets to the other wireless communication terminals Ma and Mb. In this case, the wireless communication terminal M
Since a and Mb cannot correctly receive the packet from the wireless communication terminal Mc and the packet from the wireless communication terminal Md, the throughput is lowered.

However, in the system of this embodiment,
The throughput is prevented from decreasing due to the hidden terminal as follows. That is, as shown in FIG. 7, for example, at time t0, the wireless communication terminal Ma sends the packet Pa
And the wireless communication terminal Mc sends a packet Pc at time t1 after the end of sending the packet Pa. At this time, time t after the transmission of the packet Pc is completed.
In 2, the wireless communication terminals Ma, Mb, and Mc measure the elapsed time T21 from the transmission / reception disclosure time t1 of the previously transmitted / received packet Pc to the current time t2 by the timer circuit of the previous reception information unit 27. At the same time, the transmitting station address (address ADc of the wireless communication terminal Mc) included in the packet Pc transmitted / received last time is extracted by the packet disassembling unit 23 and stored in the memory in the previously received information unit 27.
On the other hand, the wireless communication terminal Md does not receive the packet Pc sent from the wireless communication terminal Mc as shown in FIG. For this reason, the reception disclosure time t0 of the packet Pa sent from the wireless communication terminal Ma two times before the present time to the current time t2.
The elapsed time T20 is counted by the timer circuit, and the transmission station address (wireless communication terminal Ma
Address ADa) is stored in the memory.

In this state, as shown in FIG. 7, for example, at time t2, the wireless communication terminal Mb sends the packet Pb.
Is sent. At this time, the packet Pb contains the current time t2 from the reception time t1 of the previously received packet Pc.
The elapsed time up to "T21" and the transmitting station address "ADc" (previous transmitting station address) of the received packet Pc are respectively inserted.

The above-mentioned wireless communication terminals Ma, Mc, Md are
When the packet Pb is received, the elapsed time T21 included in the packet Pb is compared with the elapsed time being measured by its own timer circuit. At this time, the wireless communication terminals Ma,
Of the Mc and Md, the elapsed time of the wireless communication terminals Ma and Mc is T21 as shown in FIG. Therefore, the elapsed time T21 included in the received packet Pb and the elapsed time T21 being measured by the own timer circuit match, and as a result, the wireless communication terminals Ma and Mc are brought into a state where their own terminals can normally communicate. It is determined that there is. On the other hand, the elapsed time by the timer circuit of the wireless communication terminal Md is T20 as shown in FIG. Therefore, the elapsed time T21 included in the received packet Pb does not match the elapsed time T20 being measured by the timer circuit of its own. Therefore, the wireless communication terminal Md recognizes that there is a packet that could not be received, and further, the previous transmission station address A included in the packet Pb received this time is detected.
Packets that could not be received from Dc are wireless communication terminals M
It can be recognized that it is the packet Pc sent by c.

Upon recognizing that the packet Pc could not be received, the wireless communication terminal Md causes the packet composing unit 12 to include a control packet P including notification information for notifying that the packet Pc could not be received.
d'is created and this control packet Pd 'is sent to the wireless communication terminal Mb capable of wireless communication with itself. The wireless communication terminal Mb receiving this control packet Pd ′
A control packet Pb 'in which information indicating that this control packet Pd' has been received is inserted is created, and the wireless communication terminal M
Send to c. That is, the wireless communication terminal Mb relays and transfers the control packet. The wireless communication terminal Mc that has received this control packet Pb 'recognizes from the content of the information inserted in this control packet Pb' that there is a wireless communication terminal that could not receive the packet Pc sent by itself. .

Each of the wireless communication terminals Ma to Mg counts the number of times, for example, the control unit 25 or the previous reception information unit 27 recognizes that the packet transmitted from another wireless communication terminal could not be received. A counter circuit and a second counter circuit for counting the number of times the terminal recognizes that there is a terminal that cannot receive the packet sent by itself are provided. Then, the number of times of recognition is counted by each of these counter circuits, and when these count values reach values satisfying a preset judgment condition, the wireless communication terminal of its own recognizes itself as a hidden terminal. Then, the subsequent transmission is stopped. With it,
An alarm signal is transferred to a terminal device connected to its own wireless communication terminal, an alarm LED is turned on in the terminal device, or a notification message for prompting a movement of the position is displayed on a display device such as an LCD. Further, the upper layer is notified of the information indicating that communication is not possible, thereby requesting a measure for making communication impossible.
Note that whether or not the number of times of recognition within a certain time exceeds a certain value is used as the above-mentioned determination condition for determining the hidden terminal.

On the other hand, as another example, as shown in FIG. 8, for example, at time t2, the wireless communication terminal Md transmits the packet Pd.
Is sent. At this time, the packet Pd contains the current time t2 from the reception time t0 of the previously received packet Pa.
The elapsed time up to "T20" and the transmission station address "ADa" (previous transmission station address) of the received packet Pa are inserted.

The radio communication terminals Ma and Mb which have received the packet Pd compare the result of the elapsed time "T20" contained in the packet Pd with the elapsed time T21 by their own timer circuit and the previous transmission contained in the packet Pd. From the station address “ADa”, it is determined that the wireless communication terminal Md could not receive the packet Pc sent by the wireless communication terminal Mc last time. Then, for example, the radio communication terminal Ma inserts the control packet Pa ′ into which the information indicating the determination result is inserted.
Is created and the control packet Pa ′ is transmitted to the wireless communication terminal Md.
And sent to Mc.

The wireless communication terminal Md that has received this packet Pa 'receives the packet P previously sent by the wireless communication terminal Mc.
Recognizing that c could not be received, the count value of the first counter circuit is incremented. Further, the wireless communication terminal Mc that has received the control packet Pa ′ recognizes from the content that there is a wireless communication terminal that cannot receive the packet Pc sent by itself, and the count value of the second counter circuit is Count up.

When transmitting a packet for the first time after the power is turned on, each of the wireless communication terminals Ma to Mg inserts the elapsed time from the time when the power is turned on to the current time into the packet as the elapsed time and uses the last transmitting station address as the last transmitting station address. Sends "not applicable" by inserting it in the packet. By doing so, it is possible to reduce the possibility that the wireless communication terminal receiving the packet makes an erroneous comparison judgment of the elapsed time.

As described above, in the system of this embodiment, the previously received information section 27 is provided in each of the wireless communication terminals Ma to Mg,
When a packet is transmitted, the elapsed time from the time of the last packet transmission / reception to the current time and the transmission station address of the previously received packet are included and transmitted. Also, when a packet is received, the elapsed time contained in this received packet is compared with the elapsed time measured by itself, and if both elapsed times do not match, there is a possibility of a hidden terminal. Self-recognizing that the wireless communication terminal is identified based on the previous transmission station address included in the received packet, and sends a control packet to this terminal to notify that there is a possibility of the hidden terminal. I am trying to do it.

Therefore, according to this embodiment, each wireless communication terminal can surely recognize whether or not it is a hidden terminal, and when it recognizes that it is a hidden terminal, it voluntarily stops transmission. Such measures can be taken. Therefore, there is no problem that the wireless communication terminal, which is a hidden terminal, continues to transmit packets without knowing it, and thus it is possible to prevent a decrease in throughput.

Further, since the wireless communication terminal recognized as a hidden terminal notifies the user by generating an alarm or displaying a notification message to that effect, the user hides his or her wireless communication terminal. It is possible to clearly know the state of being a terminal, and by doing so, the state of the hidden terminal can be quickly eliminated by itself, such as by moving the wireless communication terminal.

Further, in this embodiment, the number of times that it is recognized that the packet transmitted from another wireless communication terminal cannot be received and the number of times that it is recognized that there is a terminal that cannot receive the packet sent by itself is counted. However, when these numbers of times satisfy preset conditions, the terminal recognizes itself as a hidden terminal, so if, for example, a packet cannot be received temporarily due to quality deterioration of the wireless transmission path, etc. It is possible to prevent the terminal from being erroneously recognized as a hidden terminal as it is, and thereby to make an accurate determination.

Further, in the present embodiment, when the wireless communication with the wireless communication terminal which should notify the information indicating the possibility of the hidden terminal is impossible, the control packet including the above information can be communicated. The data is once transferred to another wireless communication terminal, and further transferred from this terminal to a target terminal. Therefore, the information indicating the possibility of the hidden terminal can be reliably notified to the corresponding terminal.

(Second Embodiment) FIG. 9 is a circuit block diagram showing the configuration of a wireless communication terminal device used in a wireless LAN system according to a second embodiment of the present invention.
Since the configuration of the wireless LAN system is the same as that shown in FIG. 1, detailed description thereof will be omitted.

Transmission data (user information) output from various terminal devices (not shown) is input to the digital interface 30. This digital interface 30
Then, the transmission interface operation with the above various terminal devices is performed. Specifically, buffering, level conversion, speed conversion, timing adjustment, clock reproduction and clock synchronization of transmission data transferred from various terminal devices are performed. As the digital interface 30, for example, an AUI of IEEE802.3 is adopted.

The transmission data output from the digital interface 30 is input to the address assigning section 31. The address assigning unit 31 assigns the transmission station address SA, the destination station address DA, and the relay station address RA to the transmission data when relay transmission is performed. Then, the transmission data to which these addresses are added is next input to the packet generation unit 32. In this packet generation unit 32, a unique field for wireless communication, for example, a wireless preamble PRE or a packet identifier PI is added. The transmission data output from the packet generator 32 is input to the encoder 33. Code part 33
In, the data is scrambled to randomize it, and then encoded for error correction and error detection.

FIG. 10 shows an example of the frame structure of the transmission packet data output from the encoding unit 33. FIG. 10A shows the frame structure in the normal case where relay transmission is not performed, and FIG. The respective frame configurations for relay transmission are shown. First, in the transmission packet data in the normal case, the preamble PRE is arranged at the head position, and then the frame start delimiter SFD, the packet identifier PI, the target station address DA, the transmission station address SA, the user information length LEN, and the user information field UDF.
, Then the error detection additional bit FC
S and an error correction additional bit ECS are arranged.
On the other hand, the transmission packet data for relay transmission is
The relay station address RA is inserted between the packet identifier PI of the transmission data and the target station address DA in the above normal case. The packet identifier PI is information for identifying the type of packet, and is "0" for an information packet, "1" for a relay packet, "2" for a relayed packet, and control. In the case of a packet, it is set to "3".

The transmission packet data output from the encoder 33 is input to the modulator 34. In the modulator 34, a collision detection random pulse generated from the carrier detector / collision detector 47 is added to the head position of the transmission packet data, that is, before the preamble PRE,
Further, the transmission intermediate frequency signal is digitally modulated by the transmission packet data. As a modulation method, for example, π
The / 4 shift DQPSK system is used.

The transmission intermediate frequency signal output from the modulator 34 is input to the high frequency section 35. This high frequency part 3
In 5, the transmission intermediate frequency signal is mixed with the local oscillation signal output from the local oscillator 37 composed of, for example, a frequency synthesizer by the mixer 36, and thereby converted into a modulated wave signal corresponding to the radio frequency. Then, the modulated wave signal is amplified to an output level by the transmission power amplifier 38, and then supplied to the transmission / reception shared antenna 40 via the antenna duplexer 39 and transmitted from this antenna 40 to another wireless communication terminal. It

On the other hand, the modulated wave signal transmitted from another wireless communication terminal is received by the antenna 40 and then input to the receiving amplifier 41 via the antenna duplexer 39, and the level is compensated. The modulated wave signal is mixed with the reception local oscillation signal output from the local oscillator 37 in the mixer 42, converted into a reception intermediate frequency signal, and then input to the demodulation unit 43. The demodulation unit 43 performs digital demodulation and clock synchronization (clock reproduction) on the received intermediate frequency signal, among which the reproduced clock and demodulated data are supplied to the decoding unit 44.
Further, the received intermediate frequency signal is input to the carrier detection unit / collision detection unit 47, where carrier detection is performed and a carrier detection signal is output. The carrier detection signal is "1" when the level of the received intermediate frequency signal supplied from the high frequency unit 35 to the demodulation unit 43 is within the specified frequency band, and is "0" when the level is below the specified level. Is the signal.

The decoding section 44 performs error detection processing, error correction decoding processing and descrambling processing on the demodulated data, thereby reproducing the demodulated packet data. This demodulated packet data is input to the packet disassembly unit 45. The packet disassembly unit 45 determines the packet identifier PI included in the demodulated packet data, and the determination result is input to the control unit 50. The address detecting unit 46 compares the target station address DA included in the demodulated packet data transferred from the packet decomposing unit 45 with the address of the self terminal, and the comparison result is input to the control unit 50. The digital interface 30 transfers a packet addressed to its own terminal to a terminal device (not shown) according to an instruction from the control unit 50.

By the way, the control unit 50 is provided with, for example, a microcomputer as a main control unit, and as its functions, the unreceivability judging means 51 and the relay terminal detecting means 52.
And a packet transmission control means 5 having a packet relay function.
3 and 3. Further, the control unit 50 is provided with a relay table 54 used for each of the above controls.
The relay table 54 includes a relay address table and a relay routing table.

The relay terminal detecting means 52 has a function of broadcasting a control packet to detect a relay terminal, and receives an information packet and a control packet transmitted from another wireless communication terminal and includes them in the received packet. The function of storing the transmitting station address or the reception history information stored in the relay address table of the relay table 54, and the relay terminal is specified based on the information stored in the relay address table, and the result is relay routing table. It has a function to store in.

Of these, the control packet broadcasting function is to send out control packets at a predetermined cycle T after the power is turned on. The CDMA / CD method is used as the access method for transmitting the control packet, as with the information packet. As the control packet, for example, FIG.
Or the one shown in FIG. 11 (b) is used. The broadcast cycle T of the control packet is set according to the packet transmission traffic.

In FIG. 11 (a), a frame start delimiter SFD, a packet identifier PI, a target station address DA and a transmitting station address SA are arranged in order following a preamble PRE, and an error detecting additional bit FCS is arranged at the end.
And an additional bit ECS for error correction is arranged. In addition, as shown in FIG. 11B, the transmitting station address S
A reception history field HIS is provided at the rear of A. When transmitting these control packets, the address of the self terminal is inserted into the transmitting station address SA, and the broadcast address common to all wireless communication terminals is inserted into the destination station address DA. Further, in the reception history field HIS, the transmission station address SA included in the information packet and the control packet received at a predetermined time in the past is inserted in the order of reception. These transmitting station addresses SA are stored as reception history information for each reception.
LEN is information indicating the data length of the reception history field HIS.

Next, the packet receiving / storing function, when the information packet and the control packet are received, when the transmitting station address SA included in the received information packet and the control packet and the reception history information are included, This reception history information is extracted and stored in the relay address table. The transmission station address SA and the reception history information stored in this relay address table are automatically erased after a lapse of a predetermined time Tout.

The relay address table is constructed as follows, for example. That is, when a control packet in which only the transmitting station address SA is inserted is used, a table for storing the transmitting station address SA in the order of reception is used as shown in FIG. 12, for example. The timer value has a predetermined time Tout when the transmitting station address SA is stored.
Is set and the corresponding transmitting station address SA is erased when this predetermined time has elapsed. Next, when the control station with the transmission station address SA and the reception history information inserted is used as a control packet, a table for storing the transmission station address SA and the reception history information is used as shown in FIG. To be done.

Further, the relay routing table is, for example, as shown in FIG.
When a hidden terminal is detected by 1, the hidden terminal is stored as a target station address, and the address of the wireless communication terminal to be relayed when transmitting a packet to the hidden terminal in association with the target station address is set. It is stored as a relay address.

The unreceivability judging means 51 recognizes the presence of a hidden terminal by the following two methods. The first method is to send an information packet to a target wireless communication terminal and then monitor whether or not a response is returned from this wireless communication terminal within a certain time, and then return the response even after a certain time has elapsed. If not, the wireless communication terminal for the above purpose is regarded as a hidden terminal. The second method is to recognize the presence of a hidden terminal based on the transmission station address and its reception history information stored in the relay address table.

The packet transmission control means 53 performs control for transmitting and receiving information packets, relay packets, relayed packets and control packets. The packet is identified by the packet identifier PI, and the transmission / reception control for each packet is executed according to the identification result.

For example, when the packet identifier PI of the received packet is "0", the received packet is recognized as an information packet. In this case, the address detector 4
In 6, the target station address DA included in the demodulated packet data is compared with the address of the self terminal, and if both addresses match, the target station address DA, the transmitting station address SA and the user data field included in the demodulated packet data. The UDF is transferred from the digital interface 30 to a terminal device (not shown). If the destination station address DA included in the demodulated packet data does not match the address of the self terminal, this information packet is discarded.

If the packet identifier PI of the received packet is "1", it is recognized as a relay packet. In this case, the address detecting unit 46 compares the relay station address RA included in the demodulated packet data with the address of the self terminal, and if both addresses match, the relay station address RA included in the demodulated packet data, The destination station address DA, the transmission station address SA, the data length LEN, and the user data field UDF are transferred to the packet generation unit 32 via the control unit 50. In the packet generator 32, the packet identifier PI of the transferred packet is rewritten to the relayed packet “2”. Then, this relayed packet is transmitted from the transmission system described above. If the destination station address DA included in the demodulated packet data does not match the address of the self terminal, this packet is discarded.

Further, when the packet identifier of the received packet is "2", it is recognized as a relayed packet. In this case, the address detecting unit 46 compares the target station address DA included in the demodulated packet data with the address of the self terminal, and if both addresses match, the target station address DA included in the demodulated packet data, The transmitting station address SA and the user data field UDF are transferred from the digital interface 30 to a terminal device (not shown). If the destination station address DA included in the demodulated packet data does not match the address of the self terminal, this packet is discarded.

If the packet identifier of the last received packet is "3", it is determined that the packet is a control packet. The target station address DA included in the control packet is a broadcast address common to all wireless communication terminals in the system. Therefore, the control unit 50 stores the transmission station address SA and the history information included in the received control packet in the relay address table.

Next, the operation of the system configured as described above will be described with reference to the timing chart shown in FIG. Here, among the wireless communication terminals Ma to Md, the wireless communication terminals Mb and Md are in a state capable of wireless communication with all terminals, but the wireless communication terminals Ma and Mc are between the wireless communication terminals Mb and Md. It is assumed that wireless communication is possible only by itself, and wireless communication is not possible between the wireless communication terminals Ma and Mc. That is, the wireless communication terminal M
a and Mc are in a state of being hidden terminals with respect to each other.

In the standby state, each wireless communication terminal Ma,
Mb, Mc, and Md are each a predetermined cycle T after the power is turned on.
The control packet is repeatedly broadcast with. For example, the wireless communication terminal Ma broadcasts control packets at timings to, to + T, ..., The wireless communication terminal Mb broadcasts at timings t2, t2 + T, ..., And the wireless communication terminal Mc sends timings t3, t3 + T ,. In addition, the wireless communication terminal Md
Respectively broadcast control packets at timings t4, .... At this time, the transmission timing of each control packet is arbitrarily set for each radio communication terminal Ma, Mb, Mc, Md, but the transmission operation is performed according to the CSMA / CD method so that a plurality of packets do not collide with each other. Further, in the control packet, the transmitting station address SA of the self terminal and the transmitting station address included in the packet received in the past fixed period, that is, the reception history information are inserted.

Further, each wireless communication terminal Ma, Mb, Mc, M
The d receives the control packet and the information packet broadcast from other wireless communication terminals. Then, every time these packets are received, the transmission station addresses included in these packets are extracted and stored in the relay address table 54 regardless of whether these packets are addressed to themselves. For example, the wireless communication terminal Ma is shown in FIG.
As shown in FIG. 7, assuming that control packets arrive from the wireless communication terminals Md and Mb, every time these control packets are received, the transmission station address #
FIG. 13A shows Md and reception history #Mb, #Mc, and transmission station address #Mb and reception history #Mc.
It is stored in the relay address table as shown in. Similarly, the wireless communication terminals Mb to Md are respectively shown in FIGS.
As shown in (a) and FIG. 16, the transmission station address of the received packet and the reception history information are stored in the relay address table.

By the way, looking at the transmission station address and the reception history information stored in the relay address table, the status of wireless communication between the wireless communication terminals Ma, Mb, Mc and Md, that is, the presence / absence of hidden terminals can be known. . For example, in the wireless communication terminal Ma, its own relay address table 5
From the transmission station address and the reception history stored in No. 4, although the wireless communication terminal Mc is transmitting the packet, its own terminal Ma cannot receive the transmission packet of the wireless communication terminal Mc. Therefore, it can be determined that the wireless communication terminal Mc is a hidden terminal for the wireless communication terminal Ma. On the contrary, in the wireless communication terminal Mc, the wireless communication terminal Ma becomes a hidden terminal. Control unit 5 of each wireless communication terminal Ma to Md
0 makes such a determination by software processing. When the presence of a hidden terminal such as the wireless communication terminals Ma and Mc is confirmed, the transmission station address of the hidden terminal and the wireless communication terminal Md capable of wireless communication with the hidden terminal, The address of Mb, that is, the relay address is associated with each other and stored in the relay routing table as shown in FIG.

Now, in this state, the wireless communication terminal M
It is assumed that a transmission request for the terminal device connected to the wireless communication terminal Mc is generated in the terminal device connected to a.
Then, the wireless communication terminal Ma determines from the stored content of the relay routing table that the destination wireless communication terminal Mc is a hidden terminal, and executes transmission control of the relay packet. That is, the radio communication terminal Ma selects a new one with a new reception timing from the relay station addresses stored in the relay routing table in the control unit 50,
A relay packet in which this relay station address #Md is inserted is generated. The configuration is shown in FIG. Then, the relay packet is transmitted.

On the other hand, the wireless communication terminal Md serving as a relay station
When the relay packet is received, it recognizes that it is a relay packet by its packet identifier RI, and then compares the relay address #Md included in this relay packet with the address #Md of its own terminal. When it is confirmed that the addresses match, the relay station address RA, the destination station address DA, the transmission station address SA, the data length LEN, and the user data field UDF in the received relay packet are passed through the control unit 50 to the packet generation unit. Three
2 and the packet generation unit 32 rewrites the packet identifier PI into the relayed packet “2”,
This relayed packet is transmitted.

Upon receiving the relayed packet, the wireless communication terminal Mc, which is the target station, recognizes that the packet is a relayed packet based on its packet identifier RI, and thereafter, the target station address #Mc included in this relayed packet. And the address #Mc of the self terminal. Then, when it is confirmed that the addresses match, the destination station address DA and the transmission station address SA included in the received relayed packet are received.
And the user data field UDF is transferred from the digital interface 30 to a terminal device (not shown). Thus, the relay wireless transmission of the information packet is performed from the wireless communication terminal Ma to the wireless communication terminal Mc which is in a hidden state for this terminal.

In each of the wireless communication terminals Ma to Md, the stored content of the relay address table is the initial value T of the timer.
It is deleted when out becomes 0. Further, even before this time-out, if a new control packet is received exceeding the table capacity, the address of this newly received control packet is stored instead of the stored old address.

As described above, in this embodiment, each wireless communication terminal periodically broadcasts a control packet to detect a relay terminal, and receives a control packet broadcast from another wireless communication terminal. The transmitting station address and the reception history information included in this control packet are stored in the relay address table, the presence of the hidden terminal is detected from the stored contents of the relay address table, and the packet is transmitted to this hidden terminal. The relay terminal is determined and these pieces of information are stored in the relay routing table. Then, when a transmission request to the hidden terminal occurs, the relay packet is transmitted by referring to the relay routing table, and when the relay packet transmitted from another wireless communication terminal is received, the relay packet is transmitted. Is converted into a relayed packet and transmitted to the intended hidden terminal.

Therefore, in this embodiment, the packet is transmitted to the hidden terminal via the relay terminal. For this reason, it becomes possible to transmit the packet even to the hidden terminal, which makes it possible to suppress the communication failure rate to a low level.

Further, since the control packet is sent out periodically and the relay terminal is determined based on the reception history information included in this control packet, each wireless communication terminal is updated periodically and is relatively new. The relay terminal can be determined based on the information, and thus the optimum relay terminal can be selected with high probability.

Further, in the present embodiment, when a relay packet is received and then this packet is retransmitted, the packet identifier is rewritten from "relay" to "relayed". As a child, even if the packet relay-transmitted by the relay station is reflected by the surrounding walls or pillars and received again by the relay station, the problem that the re-received packet is re-relayed disappears. It is possible to prevent a decrease in throughput due to invalid packets.

The present invention is not limited to the above embodiments. For example, in the first embodiment, if each wireless communication terminal has not received any packet from the power-on to the first packet transmission, the elapsed time from power-on to packet transmission is set as the elapsed time. Also, it is preferable to write "not applicable" as the last transmitting station address in each packet and transmit. By doing so, it is possible to prevent the wireless communication terminal receiving the packet from making an erroneous determination based on the elapsed time in the packet. Further, the packet transmission may be prohibited until the packet is received once or more after the power is turned on, or until the maximum value that can be written in the packet as the elapsed time is reached for a predetermined time. Even in this case, erroneous determination can be prevented.

In each of the above embodiments, the plurality of wireless zones E1, E2, ... Are connected by the wired LAN, but they may be connected by a wireless line.
Also, as the communication form, the system using the so-called equal distribution system to which the distributed system is applied to both the access control system and the information transmission system has been described, but both transmission systems may use the centralized system, and Can be applied to a system to which a centralized method is applied and a distributed method to an information transmission system.

In each of the above-mentioned embodiments, the system in which the random pulse method is applied as the collision detection method has been described as an example. However, as the collision detection method, another collision detection method such as a bit collation method may be applied. Furthermore, the present invention may be applied to a system to which the CSMA method, the ALOHA method, or the like that does not detect collision is applied.

As a modulation method, two-phase PSK, MSK,
Other modulation schemes such as 16QAM can also be applied. Also, as a measure against fading and delay dispersion, a system to which a multi-carrier transmission method is applied has been described, but other spread spectrum modulation methods such as a direct spread method may be applied, or an optical transmission method is applied. You may.

On the other hand, in the second embodiment, the control packet is transmitted by including the transmission station address of the packet received in the past as the reception history information. It may be transmitted including information indicating whether the packet was received two seconds ago.

In the second embodiment, a case has been described as an example where it is determined whether relay is necessary, that is, the presence of a hidden terminal is determined based on the stored contents of the relay address table. Alternatively, a normal information packet may be first transmitted to a wireless communication terminal of a transmission partner, and if a response is not returned from the partner terminal within a certain period, the partner terminal may be determined as a hidden terminal. In this way, the hidden terminal can be determined without increasing the system traffic. By the way, when the hidden terminal is determined based on the stored contents of the relay address table, the traffic of the system increases because the control packet is broadcast, but it is not necessary to monitor the response to the transmitted normal packet. The packet can be transmitted without causing a large transmission delay.

That is, when the system traffic is high, the method of judging the hidden terminal by monitoring the response to the normal packet is applied. On the other hand, when the system traffic is low and it is desired to reduce the packet transmission delay, A method for determining the presence of a hidden terminal based on the stored contents of the relay address table may be applied. Also,
The traffic may be monitored and the two determination methods may be switched depending on the traffic volume.

Traffic is detected by counting the number of information packets received at each wireless communication terminal, and when the traffic increases, the transmission cycle T of the control packet and the timer value Tout are changed to long values. May be. By doing so, it is possible to reduce the influence on the throughput of the entire system.

Furthermore, when a wireless communication terminal moves and enters an adjacent wireless zone with a different frequency, it becomes impossible to receive information packets and control packets from other wireless communication terminals. Therefore, if the transmission station address information stored in the relay address table falls below a certain threshold value due to timeout, it is switched to the next radio frequency and it is monitored whether packets can be received again. The radio frequency may be switched according to the result.

Furthermore, the functions similar to those of the wireless communication terminal may be provided in the wireless bridges BS1, BS2 ,. Further, in the frame structure of the control packet, the packet identifier can be omitted by distinguishing by using the frame start delimiter composed of a different bit pattern for each packet type.

In addition, the system configuration, the circuit configuration of the wireless communication terminal, various control procedures and control contents thereof can be variously modified and implemented without departing from the scope of the present invention.

[0103]

As described above in detail, the present invention is a wireless communication system for performing packet communication between a plurality of wireless communication terminals via a wireless channel, wherein each wireless communication terminal has a clocking means and a packet transmitting means. And a comparing means and a recognizing means. Then, the elapsed time from the transmission / reception time of the closest packet communication to the current time is measured by the time measuring means, and at the time of transmitting the packet, information indicating the first elapsed time measured by the time measuring means is displayed. It is included in the above packet and transmitted. Also,
When a packet is received, the comparison means compares the first elapsed time included in the received packet with the second elapsed time at the current time measured by the time measuring means, and based on the comparison result. It recognizes the existence of hidden terminals.

Therefore, according to the wireless communication system of the present embodiment, it is possible to provide a wireless communication system capable of eliminating the influence of a hidden terminal and improving the throughput.

In the wireless communication system of the present invention, the wireless communication terminal is provided with a judging means for judging whether or not the destination wireless communication terminal of the packet can receive the packet, and the wireless communication terminal can receive the packet. The wireless communication terminal includes a detection unit for detecting a relay wireless communication terminal capable of communicating with the transmission destination wireless communication terminal, a relay request control unit, and a packet relay unit. When the determination means determines that the destination wireless communication terminal cannot receive the packet, the relay request control means determines that the relay wireless communication terminal is detected by the detection means. When a packet including relay information is transmitted, and when a packet including the relay information is received, the packet relay means relays the packet to the corresponding wireless communication terminal of the destination. . Therefore, according to the present invention, it is possible to provide a wireless communication system capable of ensuring communication with a hidden terminal as much as possible and suppressing a communication failure rate to a low level.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a wireless LAN system according to a first embodiment of the present invention.

FIG. 2 is a wireless communication terminal device Ma of the system shown in FIG.
3 is a circuit block diagram showing the configuration of Mg.

FIG. 3 is a diagram showing configurations of a control packet, an information packet, and transmission / reception data.

FIG. 4 is a timing diagram used to describe a collision detection scheme using random pulses.

FIG. 5 is a timing diagram used to explain another example of the collision detection method using random pulses.

FIG. 6 is a diagram showing a system configuration when a hidden terminal exists.

7 is a timing chart for explaining the operation of the system shown in FIG.

8 is a timing diagram for explaining another operation of the system shown in FIG.

FIG. 9 is a circuit block diagram showing a configuration of a wireless communication terminal used in a wireless LAN system according to a second embodiment of the present invention.

10 is a diagram showing configurations of information packets and relay packets transmitted and received by the wireless communication terminal shown in FIG.

11 is a diagram showing a configuration of a control packet transmitted / received in the wireless communication terminal shown in FIG. 9.

FIG. 12 is a diagram showing an example of the configuration of a relay address table provided in the wireless communication terminal Ma.

FIG. 13 is a diagram showing another configuration example of a relay address table and a configuration example of a relay routing table provided in the wireless communication terminal Ma.

FIG. 14 is a diagram showing a configuration example of a relay address table provided in the wireless communication terminal Mb.

15 is a diagram showing a configuration example of a relay address table and a relay routing table provided in the wireless communication terminal Mc shown in FIG.

FIG. 16 is a diagram showing a configuration example of a relay address table provided in the wireless communication terminal Md.

FIG. 17 is a timing diagram using an operation description of the wireless LAN system according to the second embodiment.

[Explanation of symbols]

 Ma to Mg ... Wireless communication terminal OL ... Wired LAN system BR1, BR2 ... Wireless bridge E1, E2 ... Wireless zone 11 ... Transmission digital interface 12 ... Packet configuration unit 13 ... Scrambling unit 14, 33 ... Encoding unit 151-154 34 ... Modulation section 16, 35 ... High frequency section 17A ... Transmission / reception antenna 17B ... Reception only antenna 181 to 184, 191 to 194, 43 ... Demodulation section 21, 44 ... Decoding section 22 ... Descramble section 23 ... Packet decomposing section 24 ... Reception digital interface 25 ... Control unit 26 ... Collision detection unit 27 ... Previous reception information unit 30 ... Digital interface 31 ... Address assignment unit 32 ... Packet generation unit 36, 42 ... Mixer 37 ... Local oscillator 38 ... Transmission power amplifier 39 ... Antenna sharing Container 40 ... Transmitting / receiving antenna 41 ... Reception amplifier 45 ... Packet disassembling unit 46 ... Address detection unit 50 ... Control unit 51 ... Reception failure determination means 52 ... Relay terminal detection means 53 ... Packet transmission control means 54 ... Relay table

Claims (15)

[Claims] 1. A wireless communication system for performing packet communication between a plurality of wireless communication terminals via a wireless channel, wherein the wireless communication terminal has elapsed from a transmission / reception time of a packet communication most recently performed to a current time. A time measuring means for measuring time, a packet transmitting means for transmitting the packet by including the information representing the first elapsed time measured by the time measuring means in the packet, and receiving the packet And extracts the information indicating the first elapsed time contained in the received packet, and compares the extracted first elapsed time with the second elapsed time at the current time measured by the time measuring means. And a recognition means for recognizing the presence of the hidden terminal based on the comparison result of the comparison means. System. 2. The comparing means has means for judging whether or not a difference between the first elapsed time and the second elapsed time exceeds a predetermined range, and the recognizing means uses the comparing means for determining When it is determined that the difference between the elapsed time of 1 and the second elapsed time exceeds a predetermined range, control packet transmitting means for transmitting a control packet including information to that effect according to a predetermined procedure. The wireless communication system according to claim 1, further comprising: a means for recognizing the presence of a hidden terminal based on information included in the control packet when the control packet is received. . 3. The comparing means has means for judging whether or not a value obtained by subtracting the first elapsed time from the second elapsed time exceeds a predetermined value, and the recognizing means is provided by the comparing means. Means for recognizing its own wireless communication terminal as a hidden terminal based on the result of the determination when it is determined that the value obtained by subtracting the first elapsed time from the second elapsed time exceeds a predetermined value. The wireless communication system according to claim 2, further comprising: 4. The comparing means has means for judging whether or not a value obtained by subtracting the second elapsed time from the first elapsed time exceeds a predetermined value, and the recognizing means is provided by the comparing means. When it is determined that the value obtained by subtracting the second elapsed time from the first elapsed time exceeds a predetermined value, the determination is addressed to the wireless communication terminal that has transmitted the packet including the first elapsed time. A means for transmitting a first control packet including the result, and a determination result included in the first control packet when the first control packet addressed to its own wireless communication terminal is received. The wireless communication system according to claim 2, further comprising means for recognizing its own wireless communication terminal as a hidden terminal. 5. The recognizing means determines that the difference between the first elapsed time and the second elapsed time exceeds a predetermined range in a wireless communication terminal of a predetermined number of times within a predetermined period. The wireless communication system according to claim 2, further comprising means for recognizing its own wireless communication terminal as a hidden terminal when the wireless communication terminal is obtained or notified from another wireless communication terminal. 6. The recognizing means uses control to voluntarily stop the subsequent packet transmission when the wireless communication terminal of its own is recognized as a hidden terminal, and alarm information indicating that it is a hidden terminal or accompanying it. 6. The wireless communication system according to claim 1, further comprising means for performing at least one of control for notifying a person. 7. The wireless communication terminal stores time measuring means for measuring an elapsed time from a transmission / reception time of packet communication performed in the closest past to the current time, and a transmitting station address of a packet transmitted / received in the closest past. Storage means for storing the last transmission station address, information indicating the first elapsed time measured by the time measurement means when transmitting the packet, and the previous transmission station address stored in the storage means are included in the packet, respectively. And a packet transmitting means for transmitting the packet, and when the packet is received, information indicating the first elapsed time contained in the received packet is extracted, and the second information at the current time measured by the time measuring means is extracted. Determination means for determining whether a value obtained by subtracting the extracted first elapsed time from the elapsed time of exceeds a predetermined value, When it is determined that the value obtained by subtracting the first elapsed time from the second elapsed time exceeds a predetermined value, the determination result and the previous transmission included in the received packet Means for transmitting a second control packet including a station address to the wireless communication terminal that has transmitted the received packet; and a means for transmitting the second control packet addressed to the wireless communication terminal of its own. Means for sending a third control packet including information indicating that the second control packet has been received, to a wireless communication terminal corresponding to the last transmission station address included in the second control packet; When the third control packet addressed to the wireless communication terminal is received, the wireless communication terminal of its own is recognized as the hidden terminal based on the determination result included in the third control packet. And means for doing so.
The wireless communication system according to. 8. The wireless communication terminal has a storage means for storing a packet transmitted / received in the nearest past, and a value obtained by subtracting the second elapsed time from the first elapsed time by the comparing means exceeds a predetermined value. The wireless communication system according to claim 4, further comprising: a unit that transmits the packet stored in the storage unit when it is determined that the packet is stored. 9. The wireless communication terminal is stored in the storage means when storing the packet transmitted and received two times before last, and when the second control packet addressed to the wireless communication terminal of the wireless communication terminal is received. The wireless communication system according to claim 7, further comprising means for transmitting a packet. 10. A wireless communication system in which a packet is transmitted between a plurality of wireless communication terminals via a wireless channel, wherein the wireless communication terminal is capable of receiving the packet by a wireless communication terminal of a destination of the packet. Determination means for determining whether or not, a detection means for detecting a relay wireless communication terminal capable of receiving the packet and capable of communicating with the destination wireless communication terminal, and by the determination means A means for transmitting the packet including relay information to the relay wireless communication terminal detected by the detecting means when it is determined that the wireless communication terminal of the transmission destination cannot receive the packet; A packet relay means for relaying and transmitting the packet to the corresponding wireless communication terminal of the destination when the packet including the relay information is received. Wireless communication system according to claim. 11. The determining means determines that the wireless communication terminal cannot receive the packet when a response is not returned from the wireless communication terminal of the transmission destination even after a lapse of a certain time after transmitting the packet. The wireless communication system according to claim 10, wherein the determination is made. 12. The detection means detects a relay wireless communication terminal based on identification information of a transmission source included in a packet received within a predetermined period in the past. Wireless communication system. 13. The detecting means broadcasts a control packet including identification information of its own wireless communication terminal, and receives the control packet broadcast from another wireless communication terminal, and adds the control packet to the received control packet. 11. The wireless communication system according to claim 10, further comprising means for detecting a wireless communication terminal for relay based on the wireless communication terminal. 14. The detecting means broadcasts a control packet including a history of packets received within a predetermined period in the past and identification information of its own wireless communication terminal, and the detecting means broadcasted from another wireless communication terminal. The wireless communication system according to claim 10, further comprising: a unit that receives a control packet and detects a relay wireless communication terminal based on a history included in the received control packet. 15. The wireless communication system according to claim 13, wherein the detecting unit broadcasts the control packet at a predetermined time interval set according to the transmission traffic of the packet.