JPH05260051A - Radio local area network system - Google Patents

Abstract

PURPOSE:To smooth transmission/reception at each terminal and to shorten time disabling communication as much as possible. CONSTITUTION:In a network composed of plural radio terminals and a central station enabling transmission/reception with all the terminals, all the frequency bands to be utilized are divided into three of a message channel, channel tone up and channel tone down or divided into four by adding channel tone jam as well. For terminal transmission, the up of a channel tone is transmitted after judging the idle of the message channel by sensing the up/down of the channel tone before transmitting a data packet, and packet transmission is started after no jamming is existent for prescribed time as the result of confirming the down. In this case, the central station plays the role of a repeater and recognizes the existence while including hidden terminals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a plurality of wireless terminals,
The present invention relates to a wireless local area network method for improving a network with one central station.

[0002]

2. Description of the Related Art C, which has hitherto been a representative of this type of communication,
SMA (Carrier Sense Multiplex)
The Access method performs the following operations when transmitting.

1. The terminal that has the data to send listens to the channel before sending. 2. If it is determined that the channel is idle, then transmission is started. 3. If the channel is determined to be busy, the transmission is abandoned. 4. If the transmission is abandoned, wait until an appropriate time, or wait until the communication currently using the channel is completed, and then repeat the steps 1 to 4 again.

[0004]

A maximum distance that can be transmitted and received by a wireless terminal is r, and a radius of a wireless LAN service zone is R.
Assuming that R = r / 2, as shown in FIG. 9A, all wireless terminals in the zone, including the central station, are within the receivable range of each other.

On the other hand, when R = r is set, as is apparent from FIG. 9B, some wireless terminals in the zone cannot directly transmit / receive. In this case, a terminal in a situation where it cannot receive the radio waves emitted by other wireless terminals is called a hidden terminal.

In the conventional CSMA system, the following 2
There is a street problem.

When there is no hidden terminal, as shown in FIG. 6, from the time when a certain communication is transmitted on the channel,
At least until after the maximum propagation delay τ, the channel does not seem to be used in the terminal to which the communication has not arrived, so when the communication is started, the communication collides with the above-mentioned communication and the communication fails. After that, all terminals can recognize the existence of communication. Therefore, the communication can be postponed to avoid the communication collision. In other words, in order for the communication to be successful, the condition is that no new communication is started within τ from the start time of a certain transmission. Further, in the case of communication collision, assuming that the packet length is T, at worst, the channel is wastefully used for 2τ + T.

When a hidden terminal exists, the hidden terminal may not recognize the existence of the communication even after the maximum propagation time τ has elapsed from the transmission start time as shown in FIG. Communication fails. In other words, in order for the first communication to succeed, including hidden terminals,
The condition is that new communication is not started from the transmission start time to the communication end time (τ + T). When a collision occurs, the channel is wasted for 2τ + 2T at worst.

Whether or not to allow hidden terminals depends on the wireless LAN.
It is considered that there is a big difference in the configuration. If you do not allow hidden terminals, all terminals must be within range of each other. In this case, since all terminals can grasp the channel status within the transmission delay, the wired access method (for example, CSMA method) can be used with a minimum change. Further, since the influence range (interference area) of communication in the zone is relatively wide with respect to the service zone radius, a large number of channels are required when the multi-zone is configured.

When a hidden terminal is allowed, the radius R of the service zone of the wireless LAN can be set to be the same as the maximum distance r that can be transmitted and received. Since the interference range is relatively narrow with respect to the service zone radius, the number of channels can be small even when a multi-zone configuration is adopted. In this case, since there are wireless terminals in the zone that have not been sent,
Sometimes it may be necessary to relay communications to those terminals. However, when such a zone configuration is adopted, it is considered that there is no problem because the central station can actively control communication. Above all, if hidden terminals are allowed, the biggest merit is that the end user can set up by only checking the two-way communication with the central office, which makes handling of the wireless LAN considerably easier.

The present invention is intended to facilitate the transmission / reception of each terminal in a network composed of a plurality of wireless terminals and a central station capable of transmitting / receiving all of them, and to shorten the time during which communication is not possible as much as possible. It has a basic purpose.

[0012]

SUMMARY OF THE INVENTION However, according to the present invention, before transmitting a data packet, the state of the message channel is judged from the state of the channel tone to avoid collision (hereinafter referred to as CTMA (Channel Tone Mul).
(hereinafter referred to as "tile access" method) or a method of preventing data packet collision by reserving a message channel with respect to the central station before transmitting the data packet (hereinafter referred to as CRMA (Channel R)).
servicing Multiple Acces
By adopting s) method), the above-mentioned conventional problems have been solved.

That is, according to the present invention, in a network composed of a plurality of wireless terminals and a central station capable of transmitting and receiving with all of them, all available frequency bands are message channel, channel tone up and channel tone down. In the terminal transmission, before transmitting the data packet, the channel tone upstream and downstream are sensed to determine the message channel idle, then the channel tone upstream is transmitted, and after confirming the downstream, packet transmission is started. It is a wireless local area network system characterized by being configured. Another aspect of the present invention is that in a network composed of a plurality of wireless terminals and a central station capable of transmitting and receiving all of them, all available frequency bands are used for message channels, channel tone up, channel tone down, and channel tone jam. It is divided into four, and the terminal transmission senses the up and down of the channel tone before transmitting the data packet to judge the idle of the message channel, then transmits the up of the channel tone, and confirms the down link returned by the central station. , A wireless local area network system characterized by being configured to start packet transmission. Further, it is characterized in that a hidden terminal is included in the plurality of wireless terminals. Next, another invention uses all available frequency bands for a message channel for data transmission and reservation of the channel in a network composed of a plurality of wireless terminals and a central station capable of transmitting and receiving with all of them. The control channel is divided into three, that is, uplink and downlink, and the terminal transmission sends a request packet to the control channel to the central station before data transmission,
This is a wireless local area network system characterized by being configured to receive a message channel usage right allocation from a central office. Further, the request packet is characterized by including its own station ID, destination ID, time when data to be transmitted is generated, and time required for data transmission.

[0014]

That is, in the case of starting the transmission after judging the state of the message channel from the state of the channel tone before transmitting the data packet of the present invention, the data packet is transmitted without fear of collision of transmission. can do.

Further, in the method of preventing the collision of data packets by reserving the message channel in the central office, the transmission of each terminal can be arranged and transmitted in a reasonable and minimum waiting time.

[0016]

Embodiment 1 An embodiment of the present invention will be described with reference to FIGS.

The present invention divides the total available frequency band into four parts: message channel, channel tone up, channel tone down, and channel tone jam (FIG. 1). The presence of channel tones indicates the presence or absence of communication depending on the presence of channel tones, and at the same time when there is a collision.

Before the terminal attempts to transmit a data packet, it first senses the channel tones (up, down). If the channel tones (both up and down) are not sensed, then it can be determined that the message channel is idle (empty). In this state, a signal is first sent out on the upstream channel tone. This signal is not received by all wireless terminals in the presence of hidden terminals, but at least at the central office. Upon receiving the channel tone upstream, the central office sends the same signal to the channel tone downstream.
That is, the central station
Has the same role as a repeater. Here, since all wireless terminals including hidden terminals are within the line of sight of the central station, it is possible to know that there is a terminal trying to transmit a packet due to the existence of the channel tone downlink. The wireless terminal, which has confirmed that the channel tone transmitted by itself has returned to the downlink channel tone via the central station, starts transmitting packets to the message channel for the first time (FIG. 2).

Channel tones may be transmitted from multiple wireless terminals during the exchange of channel tones. The central station transmits a channel tone jam signal (control frequency) when detecting a collision of channel tone upstream, that is, when receiving another channel tone upstream signal while receiving one channel tone upstream signal. Upon receiving the jam signal, the terminal learns that there is a signal collision, and stops the scheduled data packet transmission, and starts transmitting a channel tone signal again. The collision can be notified by modulating the channel tone downlink signal instead of the jam signal. In such a case, the entire frequency band
It is divided into a message channel and three, channel tone up and channel tone down.

The above will be further examined. First,
Consider the case when no collision occurs. Before the wireless terminal RT1 which is going to transmit the data,
The channel tone upstream signal is transmitted (Fig. 2). This signal is within the maximum propagation delay time (maximum time for the signal to propagate between the wireless terminal and the central station) τ and within the communication range (radius r) of RT1.
Is received by all wireless terminals within. That is, this signal allows the terminal seen from RT1 to refrain from the communication. Since the central station is also within this range, at worst it receives this signal after τ and sends the signal down the channel tone. Since all wireless terminals can further receive this signal by τ, transmission is suppressed by all wireless terminals including hidden terminals at this point. RT1
Listens to the channel tone down while transmitting the channel tone up signal. If the jam signal is not received for 2τ + z (constant where 0 <z <τ) after starting the transmission of the channel tone upstream, the transmission of the data packet is started on the message channel. When the data transmission time is T _f (frame time), the terminal continues to send the channel tone upstream for (2τ + Z) + T _f from the transmission start time.

During a period 2τ after RT1 starts transmitting a signal as a channel tone upstream signal, not all wireless terminals can know the existence of the signal, so that wireless terminals other than RT1 receive channel tone during this period. May emit a signal. Here, it is assumed that RT2 has started transmission. In this case, the central station detects the collision and sends a jam signal. There are two types of operations on the wireless terminal side depending on the timing. If the transmission of the RT2 channel tone signal occurs within Z after the start of the RT1 channel tone signal transmission, the RT1 can receive the jam signal before transmitting the packet to the message channel,
Both RT1 and RT2 forgo this transmission. If RT2 transmission occurs after Z after RT1 transmission starts,
Since RT1 has already started transmitting the data packet on the message channel, this jam signal is ignored and the transmission is performed until the transmission is completed. On the other hand, since RT2 receives this jam signal before transmitting a data packet to the message channel, it abandons the transmission to avoid collision on the message channel. When the transmission of the data packet is abandoned, the channel tone is stopped and the backoff is started according to the backoff algorithm. Then, the transmission is tried again by the above method.

From the above-described method of accessing the CTMA channel, the following can be considered.

As mentioned above, it is known that the performance of the CSMA system is considerably deteriorated by the presence of hidden terminals.
In the CTMA method, the central station mediates the channel tone upstream sent from the terminal, thereby making it possible to notify all terminals in the zone of the existence of a terminal (communication from a hidden terminal) trying to transmit a packet. For this reason,
It is considered that the performance degradation can be suppressed as much as possible by the hidden terminal as seen in the CSMA method. Also, CT
In the MA method, the collision on the channel tone is meaningful only when the communication occurs simultaneously within the time z (because in the other collisions, the data of the wireless terminal which has transmitted the channel tone first). (Because transmission is prioritized), and if there is no collision on the message channel so the propagation delay is negligible,
The throughput characteristic is considered to approach 1.

In a wireless LAN system, the central station is the center of control, and the load on it is rather heavy, which tends to be central station control. However, in this CTMA system, it mainly acts as a repeater of channel tones, and the central station's burden is high. Can be lightened.

Although the above embodiment has been described for one channel,
It can be multi-channel as shown in FIG.

[0026]

Second Embodiment Another embodiment of the present invention will be described with reference to FIGS.

In the CSMA method in the absence of hidden terminals, data packet transmission means holding the right to use the channel as it is. That is, if the transmission is successful from the start of the transmission of the data packet until after the maximum propagation delay τ, then the wireless terminal has been informed of the right to use the channel, and the collision can be prevented. However, in the presence of the hidden terminal, some terminals do not recognize the possession of the right to use the terminal, and the characteristics of the terminal rapidly deteriorate. When the communication from two wireless terminals, which are hidden terminals, collide with each other, assuming that the packet length is T, the maximum 2τ + 2T time channel is wastefully used. Meanwhile, other non-hidden wireless terminals determine that someone is using the channel (actually two terminals are occupying the channel in vain),
I will wait for the transmission.

Therefore, in the CRMA system of the present invention, it is decided to clearly separate the right to use the message channel from the actual use of the channel. In other words, the usage right is acquired by competition, but the bandwidth is effectively used by minimizing the amount of transmission wastefully used by the acquisition competition.

In the above-mentioned method, the entire available frequency band is divided into a message channel for data transmission and a control channel (uplink, downlink) used for reservation of the channel.
Divide into two (Fig. 3).

The operation of the above method will be described (FIG. 4). A wireless terminal that wants to send data first sends a request packet to the control channel in order to request the central station to assign a right to use the message channel. The control channel access method is based on the CSMA method. In this request packet, in addition to its own station ID and destination ID, the time (ini
t-data-time) and the time required to transmit the data (request-time) are also included. In response to this request, the central station examines the reservation status of the current channel, and adjusts the reservation so that the data waiting for transmission of each wireless terminal is started to be transmitted in the earliest time of generation. The time at which this terminal starts data transmission and the usage time are determined, and all wireless terminals are notified by using the broadcast function of the control channel downlink. Upon receiving this, the wireless terminal waiting for data communication compares the time when the data to be transmitted is generated with the time when the data in the packet is generated, and if the time at which the data of the own station is generated is delayed. In this case, the transmission time is delayed by the time required for data transmission. The wireless terminal sends the data packet to the message channel according to the designation of the central office.

The control channel access method is CSMA.
Since it is based on the scheme, it can be affected by hidden terminals in addition to the normal collision. However, by making the request packet length T _r sufficiently shorter than the data packet length T _f , useless transmission can be minimized even if a collision occurs. In the CSMA method, if the packet length is reduced with respect to the maximum propagation delay, the characteristics deteriorate, so the transmission efficiency of the control channel becomes a problem. However, since the influence of hidden terminals is greater than this, it will be discussed in the same way as the general CSMA method. It is not possible. Rather,
The solution is to reduce the request packet length drastically and shorten the request retransmission interval.

In the method of the present invention, it takes some time until the request is accepted. Therefore, for the accepted communication, the transmission delay is reduced as much as possible by organizing the data in the order of the time when the data was generated. This means that the communication for which the request has been accepted is fully scheduled, and collisions on the message channel will not occur.

Although the above embodiment has been described with respect to the operation with one channel, it is also possible to use multiple channels as shown in FIG.

[0034]

Comparative Example When the CTMA system and CRMA system of the present invention were compared with the conventional CSMA system, the following results were obtained.

A model common to all simulations (FIG. 9, (c)).

In this simulation, a single zone is targeted. There is one central station in the wireless zone,
As shown in (c), the radius is 50 around the central station.
It is assumed that the circle in [m] is the service zone. This service zone is quite large for a wireless LAN. For example, a square that fits within this circle is 70
[M] Squares. In the model, 200 terminals are randomly arranged in the circle. In an office with the highest terminal density, it is said that about one terminal exists in 10 m ² , so this is a state where the terminal density is considerably low. The radio waves emitted by each terminal are supposed to propagate in a circular shape centering on that terminal, and the propagation distance (distance that other terminals can reliably receive) is set to r [m] (r ≧ 50), and by changing this The ratio of hidden terminals in the wireless zone was changed for a certain terminal. Place the terminal by a computer,
The ratio of this hidden terminal was calculated (Table 1).

[0037]

[Table 1]

The detailed parameters are based on Ethernet. Some of them are too large for the wireless LAN, but since the results are normalized by the packet length and the like, they do not have much significance. Table 2 shows each simulation parameter.

[0039]

[Table 2]

It is assumed that data transfer is performed in bit serial at a speed of 10 Mbps. The packet length transmitted by each terminal is fixed. Also, in this simulation model, only communication from the terminal to the central office is considered.

(1) Comparison between CTMA method and CSMA method A comparison between CTMA method and CSMA method is shown in FIGS. The CTMA method is more sensitive to the normalized propagation delay a than the CSMA method without hidden terminals. However, a is represented by a = τ / T _f .

Traffic-throughput characteristics (Fig. 1
0), when the normalized propagation delay is small (a = 0.0
5) The CTMA method is superior in the maximum throughput, but as the normalized propagation delay becomes higher, the influence becomes larger in the CTMA method, so that the maximum throughput is CSMA.
The method will win. CSM at low traffic
It can be said that the A and CTMA methods are almost the same.

The throughput-average transmission delay characteristics show the same tendency, and when the normalized propagation delay is small, the CTMA method is superior to the CSMA method. However, although it cannot be read from FIG. 11, the area where the traffic is considerably small (S <
0.2), the CSMA method is superior. This is because the CTMA system takes more time to exchange channel tones than the CSMA system in a state where collisions hardly occur.

Packet average transmission delay (Delay)
D): If the average frame sending time is Td,

[0045]

[Equation 1]

It is represented by

However, Td is defined as the time it takes from the generation of a packet to the time when communication is successfully completed, and includes channel waiting time, collision recovery time, backoff time, and packet transmission time.

Whichever of the characteristics is taken, the CTMA method shows such a good characteristic that it cannot be compared with the CSMA method when there are hidden terminals. Since the channel tones cover the entire wireless zone and inform the hidden terminals of the state of the message channel, it can be said that all terminals that can sense the channel tones can communicate with each other without problems even if they are hidden terminals.

From the above, it can be said that the CTMA method is a method which is not affected by the hidden terminal problem at all. CS
Since the delay characteristic is more sensitive to the normalized propagation delay than the MA method, it can be said that it is suitable for an environment with a small propagation delay such as a wireless LAN.

(2) Comparison between CRMA method and CSMA method Since the CRMA method uses the CSMA method for communication reservation, it is affected by hidden terminals. The shorter the request packet length, the higher the probability of collision on the control channel. However, it exhibits rather good characteristics because of its fast recovery. This is possible because the acquisition of the right to use the channel is separated from the actual data transmission. Shortening the request packet length impairs the effect of carrier sense, which is an advantage of the CSMA method, but there is no problem if it keeps up with the tempo of data transmission on the message channel.

A comparison between the CRMA system characteristics and the CSMA system when there is a hidden terminal is shown in FIGS. When the request packet length is half the data packet length, C
The RMA method exhibits characteristics close to those of the CSMA method when there are no hidden terminals. When the length is shorter than that, the CRMA method shows quite good characteristics.

Traffic-throughput characteristics (Fig. 1
2) request length / data frame length (T _r
Since the maximum throughput exceeds 0.9 when / T _f ) = 0.3, it indicates that the CRMA method can sufficiently cope with the problem of hidden terminals if the request packet length can be sufficiently shortened.

Throughput-Average transmission delay characteristic (see FIG.
In 3), when traffic is low, CSM
It can be seen that the delay of method A is low. The CRMA method requires a reservation even when the message channel is idle, so it can be said that this is the effect of delay. When the traffic is high, the CRMA method schedules the message transmission according to the occurrence time of the data rather than the order in which the reservation was made, so that the delay is considerably suppressed.

It is said that a LAN is usually used in an area of about 30% of its capacity. The CRMA method exhibits throughput characteristics similar to those of the CSMA method when there are no hidden terminals in this area, and the delay can be suppressed low. Moreover, it can be seen that even if the request packet is sufficiently short, it can be a countermeasure against the influence of the hidden terminal.

(3) The CTM which has obtained the following result by the above
Regarding Method A: The CTMA method has a traffic-throughput characteristic when the normalized propagation delay is small, and CSM without hidden terminals.
The characteristics are almost the same as or better than those of the A method.

When the normalized propagation delay is small, the CTMA method shows a throughput-average transmission delay characteristic which is almost equal to or higher than the CSMA method without hidden terminals.

The CTMA method, when high traffic,
The effect of the normalized propagation delay is greater in the CTMA method. If the normalized propagation delay is large, it may be inferior to the CSMA method.

The CTMA method shows a characteristic that is incomparably better than the CSMA method when there are hidden terminals.

It can be said that The CTMA method is a method that is not affected by the hidden terminal problem at all, and its delay characteristic is more sensitive to the normalized propagation delay than the CSMA method. Therefore, the CTMA method is suitable for an environment with a small propagation delay such as a wireless LAN. Can be said to be.

Regarding the CRMA method, the CRMA method is basically affected by hidden terminals,
By sufficiently shortening the request packet length, this effect can be sufficiently reduced.

The CRMA method when there is a hidden terminal is
When the request packet length is half the data packet length,
It shows characteristics close to the CSMA method when there are no hidden terminals.

When the length is shorter than that, the CRMA method shows quite good characteristics, and the maximum throughput can reach 0.9 or more.

The CRMA method is inferior to the CSMA method in low traffic at throughput-average transmission delay characteristics, but the delay is considerably suppressed at high traffic.

It can be said that In the area of about 30% of the capacity which is the normal usage area of the LAN, the CRMA method shows the same throughput characteristics as the CSMA method when there is no hidden terminal and the delay is low even if there is a hidden terminal. It can be suppressed.

[0065]

According to the present invention, the condition of the message channel is judged from the condition of the channel tone before transmitting the data packet to avoid the collision. Therefore, the collision can be avoided with the minimum waiting time, and the communication can be smoothly performed. There is an effect that can be sent. This is especially effective when there are hidden terminals.

According to another aspect of the present invention, a data channel collision can be prevented by reserving a message channel for the central station before transmitting the data packet. Therefore, if there is a request for transmission from a plurality of terminals before and after, it is arranged in the order of acceptance, and there is an effect that it can be transmitted neatly without waste.

[Brief description of drawings]

FIG. 1 is a diagram showing a channel configuration in a CTMA system of the present invention.

FIG. 2 is an operation example diagram of the CTMA method.

FIG. 3 is a diagram showing a channel configuration in the same CRMA system.

FIG. 4 is an operation example diagram of the CRMA method.

FIG. 5 is a diagram showing an influence of a hidden terminal in a conventional method (CSMA method).

FIG. 6 is an operation schematic diagram of a conventional method (CSMA method).

FIG. 7 is a diagram showing a multi-channel configuration in the CTMA system of the present invention.

FIG. 8 is a diagram showing a multi-channel configuration in the same CRMA system.

FIG. 9A is a diagram showing a relationship between a transmitting station and a service zone. (B) is a figure of another example which shows the relationship between a transmission station and a service zone. (C) is a diagram of a simulation model of a wireless zone.

FIG. 10 is a comparison graph of the CSMA method and the CTMA method. (Traffic G-throughput S characteristic)

FIG. 11 is a comparison graph of the CSMA method and the CTMA method. (Throughput S-Average transmission delay D characteristic)

FIG. 12 is a comparison graph of the CSMA method and the CRMA method. (Traffic G-throughput S characteristic)

FIG. 13 is a comparison graph of the CSMA method and the CRMA method. (Throughput G-Average transmission delay D characteristic)

[Explanation of symbols]

 T Packet length τ Maximum propagation delay

Claims (7)

[Claims] 1. A network comprising a plurality of wireless terminals and a central station capable of transmitting and receiving with all of them,
The entire available frequency band is divided into three parts, a message channel, an upstream channel tone and a downstream channel tone, and terminal transmission senses the upstream and downstream channel tones before transmitting a data packet to judge the idle state of the message channel. After that, the wireless local area network system is characterized in that it is configured such that the upstream of the channel tone is transmitted, the downstream is confirmed, and then the packet transmission is started. 2. In a network composed of a plurality of wireless terminals and a central station capable of transmitting and receiving with all of them,
The entire available frequency band is divided into a message channel, channel tone up, channel tone down, and channel tone jam, and the terminal transmission senses the channel tone up and down before transmitting the data packet to detect the message channel A wireless local area network method characterized in that after determining idle, an upstream channel tone is transmitted, and after confirming the downstream channel, packet transmission is started. 3. The wireless local area network system according to claim 1, wherein a hidden terminal is included in the plurality of wireless terminals. 4. The wireless local area network system according to claim 1, wherein a plurality of channels are provided. 5. In a network composed of a plurality of wireless terminals and a central station capable of transmitting and receiving with all of them,
The entire available frequency band is divided into a message channel for data transmission, and a control channel used for reservation of the channel, etc. A wireless local area network system characterized in that a request packet is transmitted to a central station and a right of use of a message channel is allocated from a central office. 6. The request packet includes the terminal's own station I
6. The wireless local area network system according to claim 5, further comprising D, a destination ID, a time when data to be transmitted is generated, and a time required for data transmission. 7. The wireless local area network system according to claim 4, wherein a plurality of channels are provided.