JP3198182B2 - Wireless LAN system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless LAN system for transferring a packet containing user information or control information between a plurality of wireless terminals.

[0002]

2. Description of the Related Art A LAN (Local Area Network) using a coaxial cable is often used for an information transmission system such as a campus. Such a wired LAN
In such a case, when a layout change or the like occurs from the initial installation state, it takes time and cost for re-installation, and thus a wireless LAN is strongly required. In particular, in Japan, IEEE 8 is widely used as a wired LAN.
02.3 standard 10Mbps CSMA / CD (Carrie
r Sense Multiple Access with Collision Detection)
Work is underway to standardize systems that ensure compatibility with the system.

In realizing this wireless LAN,
The following three communication modes are provided. First, a method in which both the access control system and the information transmission system are performed in a distributed system (hereinafter referred to as an equal distribution system), second, a method in which both are performed in a centralized system, and third, access control is performed in a centralized system, The system is a method performed in a distributed manner. Among them, the peer-to-peer distribution method uses the L
Most suitable for the design concept of AN, there is no need to prepare a central station, so it is easy to introduce even if the number of terminals is small, there is no central station, so the whole system does not go down, signal folding at the central station Since there is no need to perform this, there are many advantages such as the required bandwidth can be minimized, no special work such as installation of a centralized station is required, and registration of wired LANs is not required. On the other hand, there are drawbacks such as an access control function such as collision detection is required for all terminals, and if a hidden terminal is present, the throughput is greatly reduced.

[0004] Here, the hidden terminal means that when there is a wireless terminal other than the one that is currently communicating, the carrier must be detected and its own signal transmission must be forgotten. A terminal that sends out a signal. At this time, the packet transmitted by the wireless terminal that has already communicated is also destroyed from the middle, so that the throughput is greatly reduced.

In fact, in wireless communication, although there is a restriction on the communication distance (service area), it is difficult to clearly indicate this in an actual use environment, and there is a possibility of trying to access from outside the service area. Due to the fact that even if the antenna is slightly moved, the received signal level may be significantly reduced due to frequency selective fading caused by the reflected signal from the object,
When a new wireless terminal is added, or when the installation location is moved, the wireless terminal may become a hidden terminal.

[0006] Among the problems of the above-mentioned equal distribution method, several practical methods (such as a random pulse method) have been proposed in the past for access control such as collision detection. However, no effective method has been proposed for solving the problem of hidden terminals.

[0007]

As described above, the peer-to-peer system has many advantages as a wireless LAN, but has the disadvantage that the presence of a hidden terminal greatly reduces the throughput.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a wireless LAN system capable of detecting a hidden terminal and automatically removing the terminal, thereby improving the throughput.

[0009]

In order to achieve the above object, a wireless LAN system according to the present invention is a wireless LAN system for transferring a packet containing user information or control information between a plurality of wireless terminals. Wireless terminal transmits a response request packet, the second wireless terminal receiving the response request packet transmits a direct response packet addressed to the first wireless terminal, and the response request transmitted by the first wireless terminal. The third wireless terminal that has not received the packet, but has received the direct response packet addressed to the first wireless terminal,
Sending an indirect response request packet to the first wireless terminal addressed to the second wireless terminal that sent the direct response packet;
The second wireless terminal that has received the indirect response request packet to the first wireless terminal transmits an indirect response packet from the third wireless terminal addressed to the first wireless terminal, and the first wireless terminal A condition for the first wireless terminal to transmit a packet containing user information is determined based on the number of received direct response packets addressed to itself and the number of received indirect response packets addressed to itself. It is assumed that. For example, when the number of indirect response packets received by the first wireless terminal addressed to itself exceeds a certain value, or when the number of received indirect response packets addressed to self and the number of received direct response packets addressed to self are received. When the ratio exceeds a certain value, it is determined that the first wireless terminal is a hidden terminal, and transmission of a packet including user information is not performed.

[0010]

According to the present invention, each wireless terminal (first wireless terminal)
However, because it automatically determines whether or not it is a hidden terminal, and if it is a hidden terminal, it can automatically prohibit transmission of packets containing user information,
It is possible to prevent a decrease in throughput due to a hidden terminal. Therefore, it is possible to realize high throughput in a wireless LAN system such as an equal distribution system.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing a configuration example of a wireless LAN system of an equal distribution system according to an embodiment of the present invention. In the figure, 1a, 1b, 1c, 1d, 1e, 1f, 1
g is a wireless terminal, and various terminal devices such as a personal computer, a data terminal such as a workstation, a voice terminal, and an image terminal are connected to these wireless terminals 1a to 1g via a digital interface, so that they are mutually wireless. Communication is possible. However,
In order to reduce the power consumption of the wireless terminals 1a to 1g and effectively use the frequency, for example, to change the frequency used for each zone having a radius of about 20 m, wireless terminals in different zones, for example, 1a in the zone 2a Wireless terminal and 1f
Cannot communicate directly with wireless terminals. In such a case, communication is performed via the wireless terminals 1d and 1e connected to the bridges 3a and 3b and the wired LAN 4.

FIG. 3 is a diagram showing an example of frequency allocation in such a wireless LAN system. Since the frequency is changed for each zone as described above, for example, in the zone 2a, the bands of the frequencies f1-0, f1-1, f1-2, and f1-3 are set, and in the zone 2b, the frequencies f2-0, f2-1, and f2- are set.
2, the band of f2-3 is used. Here, the reason that a plurality of frequencies are used in one zone is to minimize the deterioration of transmission quality due to frequency selective fading which cannot be avoided in wireless communication.
This is because the data to be transmitted is divided into four streams, and four carrier signals having different frequencies are modulated and transmitted, as disclosed in Japanese Patent Application Laid-Open No. H11-218186 and Japanese Patent Application Laid-Open No. Hei 3-212886.

FIG. 4 is a diagram showing a configuration example of a frame employed in the wireless LAN system. For example, as an interface with various terminal devices, IEEE802.
When the AUI interface of No. 3 is adopted, the frame configuration on the interface is as shown in FIG.

On the other hand, there are two types of frame configurations for transmission on the wireless section, for example, as shown in FIGS. (1)
Shows the frame configuration of a control packet to be used in the hidden terminal self-recognition procedure in this embodiment. (2) is A
4 shows a frame configuration of a user information packet for transferring user information transferred between various terminal devices via a UI interface. These two types of packets are distinguished by a packet identifier (PD), and a control information field (CDF) is used in a control packet (FIG. 4A).
However, in the user information packet (FIG. 4B), the frame includes the user information length (LNG) and the user information field (UDF). Also, a random pulse transmission field (RPF), a preamble (PRE), a packet start delimiter (PSD), a destination station address (DA), a transmission station address (SA), an additional bit for error detection (ECS),
The error correction additional bit (FCS) is common to the two types of packets. In the user information packet (FIG. 4 (2)), the part from the target station address (DA) to the additional bit for error detection (ECS) is the same as the frame configuration on the AUI interface (FIG. 4 (3)). Hereinafter, each component of the frame will be described. The random pulse transmission field (RPF) is used in a wireless LAN of a peer-to-peer distribution system.
Japanese Patent Application No. 3-151876 for realizing SMA / CD
This is a period for transmitting a random pulse according to the “random pulse collision detection method” disclosed in the above publication, in which it is determined whether or not a collision has occurred before transmitting data. More specifically, as shown in FIG. 5, for example, the lantern pulse transmission field is divided into 18 slots, of which the first one slot (the 0th slot) and the first to first slots are set.
7. A carrier signal is transmitted to a total of nine slots of eight slots randomly selected from seventeen seventeen slots,
During the other slot period, the mobile station is in the reception state and determines whether there is a signal transmitted by another wireless terminal. If a signal transmitted by another wireless terminal is detected, it is determined that a collision has occurred.

In the example of FIG. 5, the wireless terminal 1a and the wireless terminal 1
Since the random pulse pattern transmitted by b is the same up to the eighth slot, no collision can be detected with each other. In the ninth slot, the wireless terminal 1a transmits a carrier signal, while the wireless terminal 2b does not transmit a carrier signal. Therefore, the wireless terminal 1a detects the carrier signal transmitted by the wireless terminal 1a and can determine that a collision has occurred. On the other hand, the wireless terminal 1a can detect a collision for the first time in the thirteenth slot in which the wireless terminal 1a does not transmit a carrier signal and the wireless terminal 1b transmits a carrier signal. In the sixteenth slot, the wireless terminal 1b detects the collision again in the seventeenth slot.

[0017] Theoretically, collision can be detected if the patterns of the random pulses transmitted by the two wireless terminals are partially different. Therefore, the collision miss rate is determined when the random pulse patterns transmitted by the two wireless terminals are the same, and when the carrier signal is transmitted to 9 of the 18 slots as shown in FIG. 1 /
₁₇ C ₈ (about 4.1 × 10 ^-5 ).

If a carrier signal is continuously transmitted from the next slot in which a collision is detected to the end of the random pulse transmission field during the transmission of a random pulse, the period until the other party detects a collision is shortened. Detection can be made more reliable. In the case of the random pulse pattern shown in FIG. 5, since the radio terminal 1b can detect the collision in the ninth slot, the carrier signal is continuously transmitted from the tenth slot to the seventeenth slot as shown by the thick line in FIG. . As a result, the wireless terminal 1a can detect a collision in the tenth slot, and continuously transmits a carrier signal from the eleventh slot to the seventeenth slot.

The preamble (PR) shown in FIGS.
E) is a signal for the demodulator of the wireless terminal on the receiving side to establish carrier synchronization and bit synchronization. The frame start delimiter (PSD) is used by the wireless terminal on the receiving side to perform packet synchronization. Sending station address (S
A), the target station address (DA) is the address (24) of various terminal devices connected to the transmitting and receiving wireless terminals.
4), the address of FIG. 4C passed over the AUI interface.

FIG. 7 is a diagram showing the configuration of the wireless terminal.
Transmission data (user information) input from various terminal devices to the wireless terminal via the digital interface is first subjected to level conversion, frame synchronization, speed conversion, and the like by the I / F unit 71. Subsequently, a packet identifier is added by the packet configuration unit 72, and scrambling is performed by the scramble unit 73 to randomize the data. Thereafter, the encoding unit 74 performs encoding for error correction and error detection, divides the sequence into four sequences, and adds a random pulse pattern generated by the collision detection unit 75 to the user information shown in FIG. As a frame configuration, the modulator 76,
The signals are input to 77, 78, and 79 for modulation, for example, four-phase PSK modulation. Next, in the RF unit 80, different R
In the case of the zone 2a in FIG. 2, for example, the F frequency is converted into f1-1, f1-2, f1-3, and f1-4 in FIG. This frequency is instructed from the control unit 81 to the RF unit 80.

Two antennas A and B are connected to the RF unit 80 for antenna diversity. The antenna A is used for both transmission and reception, and the antenna B is for reception only. The signal received by antenna A is sent to demodulators 82, 83, 84 and 85 via RF unit 80, and the signal received by antenna B is sent to demodulators 86, 87 and 8 via RF unit 80.
8, 89.

When transmitting a control packet, the control unit 81 writes a packet identifier, a transmitting station address, a destination station address, and control information into the packet forming unit 72, and the packet forming unit 72 writes these data in FIG. Output in the order shown in 1). Next, after these data are scrambled by the scrambler 73, the encoder 74 performs encoding for error correction and error detection, and
The sequence is divided into two sequences, and a random pulse pattern generated by the collision detection unit 75 is added to form a control frame configuration shown in FIG. 4A, and the modulators 76, 77, 78, and 7 respectively.
After the signal is input to the modulation section 9 and modulated, the RF section 80 converts the frequency into a different RF frequency and outputs the RF frequency from the antenna A.

The code part is disclosed in Japanese Patent Application No. 3-29258.
If the error correction method disclosed in No. 8 is applied, even if one of the four transmitted sequences becomes unavailable due to the influence of frequency selective fading or the like, the other three If all errors are corrected by the error correction code applied to each of the streams, communication can be performed correctly.

Of the signals input from the antennas A and B, the signal of the designated RF frequency, for example, in the case of the zone 2a in FIG. 2, f1-1, f1-2, f1- of FIG.
The signal of the frequency of f3-4 is subjected to level compensation, frequency conversion, band limitation, etc. in the RF unit 80, and the signal from the antenna A is sent to the demodulators 82, 83, 84, 85 and the antenna B
Are input to demodulators 86, 87, 88 and 89. The demodulators 82 to 89 perform carrier synchronization, demodulation (for example, four-phase PSK demodulation), clock synchronization (clock recovery), and carrier detection.
The demodulated data is sent to the decoding unit 90. The carrier detection signal is sent to the collision detection unit 75. Here, the carrier detection signal is 1 when the level of the signal input to the demodulators 82 to 89 from the RF unit 80 is higher than a specified value, and 0 when the level is smaller than the specified value. When a packet is normally received, during the reception of the random pulse transmission field, it is 1 only for the slot with carrier transmission, and continuously 1 from the preamble to the additional bit for error correction.

The data output from the demodulators 82 to 89 is subjected to error correction and error detection in the decoding section 90 and descrambling in the descrambling section 91, and then the packet identifier 92 is checked for a packet identifier. In the case of the user information packet, since the frame configuration from the destination station address to the additional bit for error detection is the same as the frame configuration on the AUI interface (FIG. 4 (3)), various Sent to terminal. In the case of a control packet, the control unit 81 reads the contents.
Next, a procedure for self-recognition of a hidden terminal in the wireless LAN system of the present embodiment will be described with reference to FIG.

FIG. 1A shows an example of the arrangement of wireless terminals on the premise of the example procedure. In the figure, 1a, 1b, 1c,
1d is a wireless terminal, between 1a-1b, 1a-1c,
It is assumed that direct communication is possible between 1a-1d, 1b-1c, and 1b-1d, but that communication is not possible directly between 1c-1d because the distance is too long.

For example, when only the three wireless terminals 1a, 1b, and 1c are communicating with the power on, there is no hidden terminal because they can communicate with each other, and it is difficult to reduce the throughput. Absent. However, if the wireless terminal 1d is powered on in this state, the wireless terminal 1d is a hidden terminal viewed from the wireless terminal 1c. For example, if both cannot send a packet to the wireless terminal 1a at the same time because they cannot be detected, they cannot send a packet to the end because they cannot detect a collision. However, the wireless terminal 1a cannot receive both packets correctly, and the throughput is greatly reduced. Resulting in.

Therefore, the wireless terminal 1d recognizes that it is a hidden terminal when the power is turned on by the following procedure, and prohibits transmission of a packet containing user information to prevent a decrease in throughput. it can.

First, when the wireless terminal 1d is powered on,
As shown in FIG. 1 (2), a response request packet is transmitted. The response request packet includes "01, 00, 00, 00" in the control information field in the control packet of FIG.
Is written. Specifically, as described above, a packet identifier,
After writing the transmitting station address, the target station address, and the control information, the control unit 81 sequentially sends them to the scramble unit 73 in accordance with the frame configuration of FIG. In this example, the response request packet sent by 1d is the wireless terminal 1a, 1
b, the signal can be received correctly, but the wireless terminal 1c cannot.

Wireless terminal 1a receiving the response request packet
Is, for example, after a waiting time randomly selected from a time of 0 to 110 ms, as shown in FIG.
A direct response packet addressed to d is sent. The direct response packet is obtained by writing “02,00,00,00” in the control time field in the control packet of FIG.

The direct response packet transmitted by the wireless terminal 1a is received by the wireless terminal 1a, and is transmitted to the wireless terminal 1c.
Even received. At this time, in the wireless terminal 1c, the wireless terminal 1a has transmitted to the wireless terminal 1d within a predetermined time in the past, in this case, for example, within 200 ms even though the response request packet from the wireless terminal 1d has not been received. To receive the direct response packet, it recognizes that it cannot currently communicate directly with the wireless terminal 1d, and sends an indirect response request packet to the wireless terminal 1d to the wireless terminal 1a as shown in FIG. Is sent. This packet is shown in FIG.
In the control packet of (1), "03,00,00,04" is written in the control information field.
However, here, the address of the wireless terminal 1d that is the indirect response destination is set to “00, 00, 04”.

The wireless terminal 1a having received the indirect response request packet sends an indirect response packet to the wireless terminal 1d as shown in FIG. 1 (5). This packet is obtained by writing “04,00,00,03” in the control information field in the control packet of FIG.
However, here, the address of the wireless terminal 1c to which the indirect response is made is set to “00, 00, 03”.

Further, in FIG. 1, thereafter, as shown in FIG. 1 (6), in response to the response request packet from the wireless terminal 1d, the wireless terminal 1b directly sends the response packet.

The wireless terminal 1d that has transmitted the response request packet
Counts the number of direct response packets and indirect response packets arriving within a fixed period of time, for example, within 400 ms from the transmission. When the relationship between the number of indirect response packets and the number of direct response packets satisfies a predetermined relationship, the wireless terminal 1d recognizes itself as a hidden terminal. Then, if the communication is started as it is, the wireless terminal 1d does not start the communication.
Actions such as turning on the alarm LED and notifying the upper layer of this to disable communication are performed. As an example of the specific relationship between the number of direct response packets and the number of indirect response packets,
It is conceivable that the number of indirect response packets exceeds a certain number, or that the ratio of the number of indirect response packets to the number of direct response packets exceeds a certain number.

In the example described above, between the wireless terminal 1d and the wireless terminal 1d between the wireless terminal from which the indirect response packet is returned.
Since communication cannot be performed directly between the wireless terminals, there is a high possibility that data will not correctly reach the other party even if a user information packet is transmitted and received between these wireless terminals. Sending such a packet that is unlikely to reach the other party correctly causes a decrease in throughput. Therefore, if the address of the wireless terminal that has sent the indirect response packet is stored as the communication-disabled party, the packet for user information addressed to the wireless terminal is not sent, and the failure of packet transmission is notified to the upper layer, It is possible to prevent a decrease in throughput.

The control packets such as the response request packet, the direct response packet, the indirect response request packet, and the indirect response packet are transmitted when the control unit 81 writes data in the packet configuration unit 72, and are transmitted when received. Is read from the packet decomposing unit 92 by the control unit 81.

The control unit 81 transmits and receives these control packets, and counts the number of direct response packets and the number of indirect response packets.
CPU peripheral circuits such as M and RAM are included. Also,
It is also conceivable that the processing is performed by a logic circuit without using the CPU.

Further, by adding zone information to these control packets, it is possible to make use of terminal control between zones. For example, when the number of indirect response packets exceeds a certain number, or when the ratio of the number of indirect response packets to the number of direct response packets exceeds a certain value, it is determined that the zone to which oneself belongs has changed, and the This can be a trigger for redoing the attribution change. Also, if a response packet is received directly from a wireless terminal belonging to a zone different from the zone to which you belong, the zone is recognized as possibly wrong. This can be a trigger for redoing the attribution change. In order to prevent the number of control packets from increasing unnecessarily, a direct response packet is returned for a response request packet from a different zone, but an indirect response packet is not returned.

The present invention is not limited to the above embodiment.

In the above-described embodiment, a plurality of zones are connected by a wired LAN, but a wireless connection is also conceivable.

The communication mode is based on the premise that the access control system and the information transmission system are both distributed in a distributed manner. However, both methods are performed in a centralized system, the access control is performed in a centralized system, and the information transmission system is performed in a distributed system. In the method to do with
The present invention can be applied. Specifically, a control device that performs access control transmits a response request packet proposed in the present invention, and another wireless terminal responds to this with a direct response packet and an indirect response packet. In this case, it corresponds to recognizing whether or not communication between the control device that performs access control and all terminals is possible.

In this embodiment, a random pulse method is applied as a collision detection method. However, another collision detection method such as a bit collation method may be applied, or a CS that does not perform collision detection.
It is also possible to apply the MA system, ALOHA system, and the like.

Further, four-phase PSK is applied as a modulation scheme, but other modulation schemes such as two-phase PSK, MSK, and 16QAM can be applied.

Although a multi-carrier transmission method is assumed as a measure against fading and delay dispersion, any transmission method such as a direct spread method or other SS (spread spectrum method) is used for a wireless section. It does not matter. The present invention is also applicable to a transmission system using light.

[0045]

As described above, the wireless LAN of the present invention
According to the system, each wireless terminal automatically determines whether or not itself is a hidden terminal, and if it is a hidden terminal, it can autonomously stop communication. It is possible to almost eliminate a decrease in throughput. Therefore, high throughput can be realized in a distributed wireless LAN system.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a self-recognition procedure of a hidden terminal in a wireless LAN system according to an embodiment of the present invention.

FIG. 2 is a wireless LAN of a peer-to-peer system according to an embodiment of the present invention;
FIG. 1 is a diagram illustrating a configuration of a system.

FIG. 3 is a diagram illustrating an example of frequency allocation in the wireless LAN system of FIG. 2;

FIG. 4 is a diagram showing a configuration of a frame employed in the wireless LAN system of FIG. 2;

FIG. 5 is a diagram illustrating an example of a random pulse pattern between wireless terminals.

FIG. 6 is a diagram showing another example of a random pulse pattern.

FIG. 7 is a block diagram illustrating a configuration of a wireless terminal in the wireless LAN system of FIG. 2;

[Explanation of symbols]

1a, 1b, 1c, 1d, 1e, 1f, 1g ... wireless terminal, 2a, 2b ... zone, 3a, 3b ... bridge, 4 ...
Wired LAN, 71: I / F unit, 72: Packet configuration unit,
73: scramble section, 74: code section, 75: collision detection section, 76, 77, 78, 79: modulator, 80: RF section,
81: control unit, 82, 83, 84, 85, 86, 87,
88, 89: demodulator, 90: decoding section, 91: descrambling section, 92: packet decomposing section, 93: I / F section.

Claims (5)

(57) [Claims] In a wireless LAN system for transferring a packet containing user information or control information between a plurality of wireless terminals, a first wireless terminal sends out a response request packet and a second wireless terminal receives the response request packet. Wireless terminal transmits a direct response packet addressed to the first wireless terminal, and does not receive the response request packet transmitted by the first wireless terminal, but transmits a direct response packet addressed to the first wireless terminal. The third wireless terminal that has received the packet sends an indirect response request packet to the first wireless terminal addressed to the second wireless terminal that sent the direct response packet, and sends the packet to the first wireless terminal. Receiving the indirect response request packet of the second wireless terminal sends an indirect response packet from the third wireless terminal addressed to the first wireless terminal, and the second wireless terminal transmits the indirect response packet addressed to the first wireless terminal. A condition for the first wireless terminal to transmit a packet containing the user information based on the number of received direct response packets and the number of received indirect response packets addressed to itself. L
AN system. 2. The wireless LAN system according to claim 1, wherein the first wireless terminal has a predetermined relationship between the number of received direct response packets addressed to the first wireless terminal and the number of indirect response packets received for the first wireless terminal. A wireless LAN system that does not transmit a packet containing the user information when the condition is satisfied. 3. The wireless LAN system according to claim 1, wherein the first wireless terminal stores an address of the third wireless terminal that transmitted the indirect response request packet, and stores the address as a target station address. A wireless LAN system which does not transmit a packet including user information. 4. The wireless L according to claim 1, wherein:
In the AN system, the first wireless terminal transmits a response request packet every time power is turned on. 5. The wireless L according to claim 1, wherein
In the AN system, the first wireless terminal transmits / receives a fixed number of packets every fixed time or
A wireless LA for transmitting a response request packet
N system.