JP2005012275A - Radio transmitter, radio packet transmitting method, and radio communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve transmission efficiency of a communication system while realizing collision avoidance of a radio packet by a CSMA/CA etc. <P>SOLUTION: The priority of the radio packet is set corresponding to the type of transmission data (ST1100), T<SB>CW</SB>being the maximum value of a collision avoidance time is calculated on the basis of this priority (ST1200), and a back-off time T<SB>B</SB>is randomly selected from a range of 0-T<SB>CW</SB>(ST1300). Collection of the usage state of a common channel is started (ST1400), and it is determined whether the radio packet can be transmitted by a carrier sense (ST1500, ST1600). If transmission is impossible, it is determined whether or not the common channel has much idle time at the time when T<SB>B</SB>has elapsed (ST2200), T<SB>CW</SB>is change or retained on the basis of the determination (ST2300, ST2400). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wireless transmission device, a wireless packet transmission method, and a wireless communication system using a CSMA / CA method or the like.
[0002]
[Prior art]
In a communication system in which each communication device is connected (accessed) to a wireless channel common to a plurality of communication devices (hereinafter simply referred to as a channel) and performs communication using wireless packets, contention access (wireless packet collision) is avoided. An access method is required. Each communication apparatus can prevent contention access due to transmission timing overlapping with other communication apparatuses by transmitting its own wireless packet in accordance with this access method.
[0003]
As a typical access method in a wireless LAN system, there is a CSMA / CA (Carrier Sense Multiple Access / Collision Aidance) method defined by the IEEE 802 Committee. In this method, when transmitting a wireless packet (carrier) of its own device using a common channel between each communication device, whether or not another communication device transmitted a wireless packet using this channel in advance. A process called carrier sense is detected. If a wireless packet is detected by carrier sense, transmission of the wireless packet of the own device at that timing is postponed, and carrier sensing is performed again after a predetermined time (collision avoidance time), and no wireless packet is detected. In this case, it transmits its own wireless packet. Here, the collision avoidance time is randomly selected by each communication device from the range of a predetermined time (maximum collision avoidance time), so the probability that the transmission timing overlaps with another communication device again at the next transmission timing is reduced. Can be made.
[0004]
However, in the above method, all wireless packets are treated evenly even with wireless packets carrying highly real-time information, and therefore there is a risk of transmission delay when communication is congested. . In order to improve this point, priorities are assigned to each wireless packet, and collision avoidance time is set according to the priorities, thereby avoiding wireless packet collision and sending data with high real-time priority. There is also a method that realizes priority control (see, for example, Patent Document 1).
[0005]
FIG. 4 is a flowchart showing the procedure of the above wireless packet transmission method.
[0006]
In S4 of this figure, depending on the type of data to be transmitted on the radio channel, the base station performs centralized control PCF (Point Coordination Function) to avoid collision of radio packets, or distributed control DCF (Distributed Coordination Function). Is used to determine whether to avoid collision of radio packets. When a wireless packet is transmitted by the centralized control PCF, this wireless packet is data to be transmitted with the highest priority. When collision avoidance is performed using the distributed control DCF, it is further determined in S7 whether the collision avoidance period is set shorter or longer depending on the type of data. In this way, priority transmission control of wireless packets is realized.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-237839 (FIG. 2)
[0008]
[Problems to be solved by the invention]
However, the conventional wireless packet transmission method has a problem that the transmission efficiency (frequency utilization efficiency) of the communication system is lowered because the collision avoidance time is randomly selected from a certain maximum collision avoidance time.
[0009]
That is, selecting a collision avoidance time randomly from a certain maximum collision avoidance time means that, on average, each wireless transmission device uses a certain collision avoidance time. Therefore, when each wireless transmission device detects a wireless packet of another device by carrier sense, it waits for a certain collision avoidance time to elapse and then tries to transmit the next wireless packet. However, it is not true that wireless packets are always transmitted by other devices during this collision avoidance time. Depending on the degree of congestion of the communication system, the wireless transmission device must wait for the wireless packet transmission of its own device even in a situation where the wireless packet transmission by another device has never occurred during the collision avoidance time. This is an inefficient method from the viewpoint of transmission efficiency of the communication system.
[0010]
The present invention has been made in view of the above points, and a wireless transmission device capable of improving the transmission efficiency of a communication system when collision avoidance of wireless packets is realized by a method such as CSMA / CA. An object is to provide a wireless packet transmission method and a wireless communication system.
[0011]
[Means for Solving the Problems]
The wireless transmission device of the present invention includes a detection unit that detects a wireless packet transmitted through a channel common to a plurality of wireless transmission devices at a predetermined time interval, and a wireless packet that is not detected by the detection unit. A state in which the wireless transmitting device other than the own device uses the channel within the time interval in which the wireless packet is not detected by the transmitting unit that transmits the wireless packet of the own device through the channel; A configuration is provided that includes a measuring unit that measures, and an adjusting unit that adjusts the time interval when the detection unit detects a wireless packet according to the measured use state of the channel.
[0012]
In the above configuration, the wireless transmission device of the present invention further includes selection means for randomly selecting the time interval when the detection means detects a wireless packet from a predetermined time range, and the adjustment means includes: Adjusting the predetermined time range in the selection unit according to the channel usage measured by the measurement unit, thereby indirectly adjusting the time interval when the detection unit detects the wireless packet. The structure to do is taken.
[0013]
According to these configurations, when collision avoidance of radio packets is realized by a method such as CSMA / CA, the collision avoidance time is set according to the degree of congestion of the communication system. Can be improved.
[0014]
In the wireless transmission device according to the aspect of the invention, in the configuration described above, the adjusting unit may be configured to transmit the wireless packet in the detecting unit based on the priority of the wireless packet to be transmitted, in addition to the usage status of the channel measured by the measuring unit. The structure which adjusts the said time interval at the time of detecting is taken.
[0015]
In the above-described configuration, the wireless transmission device according to the present invention is based on the priority assigned to the wireless transmission device that is the transmission destination of the wireless packet to be transmitted, or the type of data that the wireless packet to be transmitted has. Take the structure to be determined.
[0016]
According to these configurations, when collision avoidance of a radio packet is realized by a method such as CSMA / CA, the collision avoidance time is set in consideration of the priority of the radio packet. It is possible to realize priority transmission control of wireless packets in consideration. Thereby, for example, when the data placed on the wireless packet is data with strong real-time characteristics, it is possible to prevent the transmission delay by setting the collision avoidance time short.
[0017]
The base station apparatus of the present invention employs a configuration including any one of the radio transmission apparatuses described above.
[0018]
According to this configuration, it is possible to provide a base station apparatus having the same function and effect as described above.
[0019]
According to the radio packet transmission method of the present invention, a detection step of detecting radio packets transmitted via a channel common to a plurality of radio transmission devices at a predetermined time interval, and no radio packet was detected in the detection step A transmission step of transmitting a wireless packet through the channel; a measurement step of measuring a situation in which the wireless transmission device uses the channel within the time interval in which the detection of the wireless packet in the detection step is not performed; An adjusting step of adjusting the time interval used when detecting the wireless packet in the detecting step according to the measured use state of the channel.
[0020]
According to this method, when radio packet collision avoidance is realized by a method such as CSMA / CA, the collision avoidance time is set according to the congestion level of the communication system, so that the transmission efficiency of the communication system is improved. be able to.
[0021]
The wireless communication system of the present invention is a wireless communication system having a plurality of communication terminal devices and a base station device that controls communication of these communication terminal devices, and the communication terminal device is connected to the plurality of communication terminal devices. Detection means for detecting wireless packets transmitted through a common channel at a predetermined time interval, and transmission for transmitting a wireless packet of the own device through the channel when no wireless packet is detected by the detection means And the base station apparatus is configured to measure a situation where the plurality of communication terminal apparatuses use the channel, and according to the measured use situation of the channel, the communication terminal apparatus Determining means for determining the time interval for detecting a wireless packet; and notifying means for notifying the communication terminal apparatus of the determined time interval. Take the deposition.
[0022]
According to this configuration, when collision avoidance of radio packets is realized by a method such as CSMA / CA, the collision avoidance time is set according to the congestion level of the communication system, so that the transmission efficiency of the communication system is improved. Can be made.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The essence of the present invention is that each wireless transmission device grasps the usage status of a radio channel common to each wireless transmission device before transmission by carrier sense, and sets a collision avoidance time (Contention Window) according to the usage status. That is. Thereby, while avoiding the collision between radio packets, the utilization efficiency of the radio frequency band can be improved. Further, by setting the collision avoidance time in consideration of the priority of the wireless packet, the wireless packet priority transmission control considering the importance of the data can coexist.
[0024]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0025]
(Embodiment 1)
FIG. 1 is a block diagram showing the main configuration of a radio transmission apparatus according to Embodiment 1 of the present invention.
[0026]
The radio transmission device includes a buffer 101, a priority setting unit _{102, T CW} calculation unit 103, _{T B} selection unit 104, transmission control section 105, using status collecting unit 106, the carrier sense unit 107, radio transceiver unit 108, and transmission An antenna 109 is provided.
[0027]
The buffer 101 temporarily stores a wireless transmission packet generated from transmission data until the transmission timing arrives, and when a control signal instructing transmission is input from the transmission control unit 105, the buffer 101 outputs the wireless transmission packet to the wireless transmission / reception unit 108.
[0028]
The priority setting unit 102 sets the priority of the transmission data and outputs it to the _TCW calculation unit 103. T _CW calculation unit 103 calculates the _{T CW} below from the priority outputted from the priority setting unit 102, and outputs the _{T B} selection unit 104. T _B selection unit ₁₀₄ selects the _{T B} below on the basis of the _{T CW} output from the _{T CW} calculating unit 103, and outputs to the transmission control unit 105.
[0029]
On the other hand, the usage status collection unit 106 collects the usage status of radio channels (frequency bands) commonly used by each radio transmission apparatus for a certain period via the radio transmission / reception unit 108, and sends the information to the transmission control unit 105. Output. Further, the carrier sense unit 107 performs carrier sense of this frequency band (via the wireless transmission / reception unit 108) at a timing instructed by the transmission control unit 105, and notifies the transmission control unit 105 of the result.
[0030]
The transmission control unit 105 determines the transmission timing of the radio packet stored in the buffer 101 based on the information output from the usage status collection unit 106 and the carrier sense unit 107, and outputs a control signal to the buffer 101. . Also, the transmission control unit 105 outputs control signals to the _TCW calculation unit 103 and the carrier sense unit 107, and controls the _TCW update process and carrier sense timing described later. The radio transmission / reception unit 108 performs predetermined radio transmission processing such as up-conversion on the radio packet output from the buffer 101 and transmits the radio packet via the transmission antenna 109.
[0031]
Next, the procedure of the wireless packet transmission method of the wireless transmission apparatus having the above configuration will be described using the flowchart shown in FIG.
[0032]
When data to be transmitted occurs, priority setting section 102 sets the priority (priority value) of the radio packet according to the type of transmission data (ST1100). For example, the priority is set based on a QoS (Quality of Service) value of transmission data. Therefore, a high priority is set for data with high real-time characteristics such as voice and videophone video, and a low priority is set for best effort (BE) type data. Specifically, a user priority value included in a TCI (Tag Control Information) in a VLAN (Virtual LAN) -Tagged Frame defined in IEEE 802.1Q, or a TOS (Type of) defined in an IPv4 packet. Service) field values are compared between wireless buckets to set the priority of wireless packets. In addition, different values may be set for the priority for each wireless packet, or the same priority may be set for wireless packets composed of data of the same group.
[0033]
T _CW calculation unit 103, information regarding this priority _(the initial value of _{T CW)} wherein _T CW = below _{T CW} is the maximum value of the collision avoidance time on the basis of the (priority value) / Priority (Equation 1 )
(ST1200).
[0034]
T _B selection unit 104, a back-off time _{T B} is the latency in transmitting a radio packet is randomly selected from within the range of _{0~T CW} (ST1300). Specifically, since the T _CW corresponds to the number slot, selects the number of slots corresponding to T _B from this. For _example, if _{T CW} is 8 slots, _{T B} is selected from 1-8 slots.
[0035]
The usage status collection unit 106 collects information on the usage status of the above-mentioned common channel, that is, how much other radio transmission apparatuses have used this frequency band while the own device is waiting for transmission of the radio packet. Start (ST1400).
[0036]
Carrier sense section 107 performs carrier sense (ST1500), confirms whether the wireless channel to be used is being used by another wireless transmission device, and determines whether a wireless packet can be transmitted (ST1600). .
[0037]
In ST1600, when the radio packet is transmittable, to determine whether the next has elapsed backoff time _{T B} (ST1700), if the elapsed backoff time _{T B,} transmits a radio packet immediately (ST1800 ). If not elapsed backoff time _{T B,} returns to ST1400, the carrier sense unit 107 performs carrier sensing again.
[0038]
In ST1600, if the common channel is in use, i.e., when the radio packet is not transmitted, and then determines whether the elapsed backoff time _{T B} (ST2100), has passed the back-off time _{T B} In this case, the usage status of the collected common channel is checked to determine whether there is a lot of free time (ST2200). Then, the _TCW is changed or held as follows according to the collected usage status of the common channel.
[0039]
For example, the common channel is not used much in the use status collecting period, if such free time were _{many, T CW} holds the same value (ST2300), and returns to ST1300, the backoff time _{T B} Random selection is re-executed.
[0040]
Here, the value of _TCW is retained because the transmission timing coincided with other wireless packets this time, but as a result of collecting the usage status, it was found that the traffic of the communication system was free. This is because, in the next transmission period, even if the transmission frequency of the wireless packet is maintained as it is, it is determined that the possibility of overlapping transmission timings is low. Therefore, here, the case where the value of _TCW is held has been described as an example. However, the _TCW value may be updated more actively depending on the availability of usage conditions.
[0041]
On the other hand, the common channel is frequently used in the use status collecting period, if such free time was less, T _CW is changed by the following equation (ST2400),
T _CW = T _CW × 2 (Formula 2)
Random selection of _{T B} of ST1300 in the modified _{T CW} is re-executed.
[0042]
Here, the case where _TCW is updated to a double value has been described as an example. However, as a result of collecting usage conditions, it has been found that the traffic of the communication system is congested. This is performed in order to reduce the collision probability of the wireless packet in the transmission period, and is not particularly limited to twice. It is sufficient that _TCW is updated to a value larger than the previous value.
[0043]
In ST2100, if not passed the back-off time _{T B,} returns to ST1400, the carrier sense unit 107 performs carrier sensing again.
[0044]
FIG. 3 is a diagram showing an example of the transmission timing of the wireless packet transmitted by the above method on the time axis. Here, it is assumed that the processing up to ST1200 is completed in the above flow.
[0045]
At time _{T 1,} the collection of usage of the common channel is started with (ST1400), the carrier sense is performed (ST1500). This figure shows a case where transmission of a wireless packet is not possible (NG) as a result of carrier sense. Therefore, the process goes to ST2100 from ST1600, until after a back-off time _{T B,} the process of ST1400~ST1600 is repeated by the feedback loop of ST2100. It is assumed that all the carrier sense results during this period were NG.
[0046]
At time _{T 2,} since a lapse of _{T B,} usage of the oblique line portion in the figure is determined (ST2200). Here, when a vacant time there were many, in ST2300, T _CW is changed either held, or to a smaller value (in the figure shows the case where it is changed to a smaller value). When the backoff time T _B is reselected back to ST1300, T _CW is because it is changed to the previous values smaller value, T _B are also expected to be just less than the value of value T _{B '} The Then, if carrier sense is performed again (ST1500) and radio packets can be transmitted (ST1600), the processing of ST1400 to ST1700 is repeated until T _B ′ elapses.
[0047]
At time _{T 3,} the carrier sense is performed again (ST1500), the wireless packet transmission if (ST1600), because it passed the _{T B} ', the wireless packet is sent (ST1800).
[0048]
As described above, according to the present embodiment, when collision avoidance of radio packets is realized by the CSMA / CA method, the collision avoidance time _TCW is set according to the free state of the radio frequency band. Thus, for example, if the usage status of the common radio frequency band is free, the time interval until the next wireless packet is transmitted is maintained or shortened, so that the transmission efficiency of the communication system is improved. Can do. In addition, if the usage status of the common radio frequency band is congested, the time interval until the radio packet is transmitted next time becomes longer, so that collision of the radio packet is less likely to occur.
[0049]
In addition, since priority is given to wireless packets according to the type of transmission data, and the maximum value T _CW of collision avoidance time is set based on this, transmission control of wireless packets in consideration of data priority is realized. Can do. Thereby, for example, when the data placed on the wireless packet is data with strong real-time characteristics, it is possible to prevent the transmission delay by setting the collision avoidance time short.
[0050]
Here, the case where attention is paid to a large amount of free time has been described as an example of the common channel usage condition determination criterion. However, as the usage condition determination criterion, a wireless packet actually detected within a certain period of time is described. May be used.
[0051]
In addition, here, the case where the priority of a wireless packet is determined according to the type of data carried on the wireless packet has been described as an example. The priority of the wireless packet may be determined based on the order.
[0052]
Furthermore, although a communication system that transmits radio packets according to the CSMA / CA scheme has been described as an example here, the present invention is applicable to any communication system that avoids contention access of radio packets by a similar method. is there.
[0053]
Although the case where the present invention is configured by hardware has been described as an example here, it can also be realized by software.
[0054]
The wireless transmission device according to the present invention can be mounted on both a communication terminal device and a base station device in a mobile communication system such as a cellular or wireless LAN, and thereby has a function and effect similar to the above. An apparatus and a base station apparatus can be provided.
[0055]
Note that, here, an example has been described in which one wireless transmission device performs both carrier sense processing and collision avoidance time setting processing. However, in a mobile communication system, each communication terminal device performs carrier sense. Processing may be performed so that the base station apparatus sets the collision avoidance time and instructs each communication terminal apparatus.
[0056]
【The invention's effect】
As described above, according to the present invention, when radio packet collision avoidance is realized by a method such as CSMA / CA, the collision avoidance time is set according to the congestion degree of the communication system. The transmission efficiency of the system can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a main configuration of a radio transmission apparatus according to Embodiment 1 of the present invention. FIG. 2 is a flowchart showing a procedure of a radio packet transmission method according to Embodiment 1 of the present invention. FIG. 4 is a diagram showing an example of transmission timing of a wireless packet transmitted by the wireless packet transmission method according to the first embodiment of the present invention on the time axis. FIG. 4 is a flowchart showing a procedure of a conventional wireless packet transmission method. Figure [Explanation of symbols]
101 Buffer 102 priority setting unit 103 _{T CW} calculator 104 _{T B} selector 105 transmission controller 106 using status collecting unit 107 the carrier sense unit 108 wireless transceiver 109 transmitting antenna

Claims (7)

Detecting means for detecting radio packets transmitted through a channel common to a plurality of radio transmitting devices at predetermined time intervals;
When a wireless packet is not detected by the detecting means, a transmitting means for transmitting the wireless packet of its own device via the channel;
Measurement means for measuring a situation in which the wireless transmission device other than its own device uses the channel within the time interval in which detection of the wireless packet is not performed by the detection means;
Adjusting means for adjusting the time interval when detecting the wireless packet in the detecting means according to the measured use state of the channel;
A wireless transmission device comprising: The detection means further comprises a selection means for randomly selecting the time interval when detecting a wireless packet from a predetermined time range,
The adjusting means includes
By adjusting the predetermined time range in the selection unit according to the channel usage state measured by the measurement unit, the detection unit indirectly adjusts the time interval when the wireless packet is detected. ,
The wireless transmission device according to claim 1. The adjusting means includes
In addition to the use status of the channel measured by the measuring means, the time interval for detecting the wireless packet in the detecting means is adjusted based on the priority of the wireless packet to be transmitted.
The wireless transmission device according to claim 1. The priority is
It is determined based on the type of data of the wireless packet to be transmitted or the priority given to the wireless transmission device that is the transmission destination of the wireless packet to be transmitted.
The wireless transmission device according to claim 3. A base station apparatus comprising the radio transmission apparatus according to any one of claims 1 to 4. A detection step of detecting wireless packets transmitted through a channel common to a plurality of wireless transmission devices at a predetermined time interval;
If no wireless packet is detected in the detecting step, a transmitting step of transmitting the wireless packet through the channel;
A measurement step of measuring a situation in which the wireless transmission device uses the channel within the time interval in which the detection of the wireless packet is not performed in the detection step;
An adjusting step of adjusting the time interval used when detecting a wireless packet in the detecting step according to the measured use state of the channel;
A wireless packet transmission method comprising: A wireless communication system having a plurality of communication terminal devices and a base station device that controls communication of these communication terminal devices,
The communication terminal device
Detecting means for detecting radio packets transmitted via a channel common to the plurality of communication terminal devices at a predetermined time interval;
When a wireless packet is not detected by the detecting means, the transmitting means transmits the wireless packet of its own device through the channel, and
The base station device
Measuring means for measuring a situation in which the plurality of communication terminal devices use the channel;
Determining means for determining the time interval when the communication terminal apparatus detects a wireless packet according to the measured use state of the channel;
Notifying means for notifying the communication terminal device of the determined time interval,
A wireless communication system.

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