KR101332818B1 - Method and apparatus for communicating on multi-channel wireless network - Google Patents

Abstract

The present invention relates to a communication method and apparatus for a multi-channel wireless network, wherein a method of snooping a data channel using a data radio while not transmitting or receiving data and a result of the snooping when selecting a data channel A method of selecting an idle data channel using is provided. This prevents data channel collisions and prevents repeated channel selection processes, resulting in more efficient use of multiple data channels, resulting in higher network performance.

Multi Channel, Multi Hop, Wireless Network, Channel Selection, MAC, DCA

Description

Method and apparatus for multi-channel wireless network TECHNICAL FIELD

1 is a diagram illustrating a data channel selection process according to a general DCA media access control scheme;

2 is an example of configuration of a communication node according to the present invention;

3 is a reference diagram illustrating a snooping method and a data channel selection process of a data channel according to the present invention;

4 is an example of a multi-channel wireless network for explaining a snooping method of a data channel according to the present invention;

5 is an example of a data channel selection method according to a general DCA media access control scheme;

6 is an example of a snooping method and a data channel selection method of a data channel according to the present invention;

7 and 8 are graphs illustrating the effects of a snooping method and a data channel selection method of a data channel according to the present invention.

The present invention relates to a communication method and apparatus for a multi-channel wireless network, and more particularly, to a method of preventing collision between channels when transmitting data in multiple channels simultaneously in a multi-channel wireless network environment such as a multi-hop ad hoc network or a wireless network. And an apparatus.

In the conventional network environment, a single channel media access control (hereinafter, referred to as MAC) mainly provides one channel for communication between a plurality of nodes. In this case, since one data link uses one channel, there is no possibility of collision between channels.

Recently, in order to improve the transmission performance of a network in a multi-channel wireless network environment such as a multi-hop ad hoc network or a wireless mesh network, data is simultaneously transmitted through different channels. Multi-channel MAC technology has been studied. The IEEE 802.11b or 802.11g standard can transmit data on three channels at the same time, and the 802.11a standard can transmit data on 12 channels at the same time. Multi-channel MAC plays a role in adjusting the channel selection process so that multiple links use different channels when selecting a data channel for transmitting data.

However, there is a problem that a collision occurs in data transmission by selecting a channel that is used by a hidden node outside a communication distance in a multi-channel MAC. This is called the "hidden node problem." For example, if A and B nodes within a communication distance are communicating via data channel 1, a channel-to-channel collision occurs when a C node outside the communication distance selects data channel 1 to communicate with A node.

The reason for the collision in the data channel is as follows. When the data channel selected by the source node and the destination node is sent in a control frame such as CTS or RES, the node located within the communication distance of the two nodes can know the data channel selected by the two nodes.

However, because a node located between the communication distance and the carrier sensing distance (double the communication distance) can recognize the carrier but cannot interpret the control frame such as CTS or RES, what data channel is selected between the two nodes? I do not know. In other words, a "hidden node problem" occurs. Therefore, when selecting a data channel, there is a possibility to select a data channel currently in use, and data collision occurs if data is sent directly to the selected data channel. Then, data that has collided with the data being transmitted should be transmitted to another channel by repeating the process of selecting a data channel.

To solve this problem, a method of transmitting data only when the selected channel is idle by performing carrier sensing after switching the channel to the selected data channel by the source node can be used. However, this method has a problem of repeating the process of selecting the data channel again if the selected data channel is in use after carrier sensing. That is, it does not fundamentally solve the problem of reducing the transmission performance of the network by increasing traffic of a control channel and increasing data transmission delay.

In addition, even if the data channel is selected again, the probability of reselecting the data channel currently in use is high. As a result, even though a plurality of channels are used for data transmission, the transmission performance is not sufficiently improved because it is not effectively utilized. Simulation results show that in a multi-hop network, 14 links use only 2.13 channels simultaneously to transmit data using 5 data channels. That is, it can be seen that 2.87 channels out of five channels are not utilized at all and are wasted.

Accordingly, the present invention has been made to solve the problems of the prior art as described above, by effectively selecting a data channel in a multi-channel wireless network environment to prevent the collision of the data channel and to prevent repeated channel selection process as a result It is an object of the present invention to provide a communication method and apparatus that can increase the performance of a network by using the data channel more effectively.

In order to achieve the above object, the present invention provides a method of snooping a data channel using a data radio and a method of selecting an idle data channel using the result of the snooping when selecting a data channel. Suggest.

More specifically, according to an aspect of the present invention, in the communication node for transmitting and receiving data packets through a plurality of data channels shared between a plurality of communication nodes, a data radio (data radio) while not transmitting and receiving data packets It includes a snooping unit (snooping unit) for detecting the state of each data channel while circulating a plurality of data channels, using the idle data channel detected through the snooping unit as a data channel for transmitting and receiving data packets Selected by a communication node.

In this case, it is particularly preferable that the snooping unit detects a carrier by measuring an energy level of a specific data channel for a predetermined short time to determine whether the specific data channel is currently in use.

On the other hand, according to another aspect of the present invention the above object, a plurality of communication nodes; A control channel shared between the plurality of communication nodes and controlling transmission and reception of data packets between each communication node; And a plurality of data channels through which data packets are transmitted and received, wherein each communication node traverses the plurality of data channels using a data radio while not transmitting or receiving data packets. It provides a snooping (snooping) function for detecting, and is achieved by a wireless network characterized in that the idle data channel detected through the snooping function (selected) as a data channel for transmitting and receiving data packets.

On the other hand, according to another aspect of the present invention is a communication method for transmitting and receiving data packets through a plurality of data channels shared between a plurality of communication nodes, (a) each communication node does not transmit and receive data packets Sensing the state of each data channel while circulating a plurality of data channels using a data radio during the data radio; (b) selecting the detected idle data channel as a data channel for transmitting and receiving data packets; And (c) switching the data radio to the selected data channel.

According to another aspect of the present invention, another object of the present invention is to provide a method for preventing a collision between a plurality of data channels in a wireless network environment, wherein (a) each communication node constituting the wireless network environment does not transmit or receive data packets. Snooping the state of each data channel while traversing the plurality of data channels using a data radio while the device is not operating; And (b) selecting the detected idle data channel as a data channel for transmitting and receiving data packets using the snooping result.

On the other hand, according to another aspect of the present invention, the above object, in the media access control (Media Access Control) protocol module for a multi-channel wireless network environment, using a data radio (data radio) while not transmitting and receiving data packets And a snooping unit for sensing a state of each data channel while circulating a plurality of data channels, and selecting an idle data channel detected through the snooping unit as a data channel for transmitting and receiving data packets. Is achieved by a media access control protocol module.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In addition, the terms described below are defined in consideration of the functions of the present invention, which may vary depending on the intention of the user, the operator, or the custom. Therefore, the definition should be based on the contents throughout this specification.

The multi-channel MAC is largely divided into a synchronous multi-channel MAC that requires synchronization of the entire network and an asynchronous multi-channel MAC that does not require synchronization, and the present invention relates in particular to an asynchronous multi-channel MAC.

In particular, DCA is a representative asynchronous multi-channel MAC. The DCA uses a plurality of channels, one of which is designated as a control channel, and the other channels are used as a data channel for transmitting data packets. In addition, DCA uses two radios, one of which is used as a control radio and the other as a data radio.

The data radio may switch between a plurality of channels, and transmit data packets by switching to a selected data channel during data transmission. The control radio operates by being fixed to the control channel and is used as a path for transmitting and receiving control frames such as RTS, CTS, and RES to select a data channel. Since the control frame transmitted on the control channel can be received by all nodes located within the transmission range, other nodes located within the communication distance of each link can know the data channel selected by the link, thus selecting a data channel. You can choose to avoid the channel you are using.

On the other hand, when the data channel is selected, the DCA switches the data radio to the data channel and immediately transmits data. This approach is not a problem in a single hop network where all nodes are located within a communication distance of each other, but in a multi-channel network such as an ad hoc network or a wireless network network, many collisions occur between data channels. This severely degrades data transmission performance.

More specifically, FIG. 1 is a reference diagram illustrating a data channel selection process according to a general DCA media access control scheme.

Referring to FIG. 1, a process in which a source node S selects a data channel to send data to a destination node D is illustrated.

First, the source node S transmits a Request-To-Send (RTS) control frame through a control channel. At this time, the source node finds the currently available channel among the channel usage list, creates a free channel list, and sends it to the RTS control frame.

The destination node receiving the RTS sees its own channel usage list, finds the currently available channel, creates its own free channel list, and compares the free node list of the source node with both available channels. Select as the data channel. After the SIFS (Short InterFrame Space) time, the selected data channel is loaded into a clear-to-send control frame, and when the transmission is completed, the data radio is switched to the selected data channel.

The source node receiving the CTS control frame sends the selected data channel to the RES control frame to inform neighbor nodes of the source node of the selected data channel. At the same time, the data radio is switched to the selected data channel to exchange data with the destination node. Now, nodes around the source or destination nodes that receive the CTS and RES control frames do not use the selected data channel.

However, nodes located between the communication distance and the carrier sensing distance (twice the communication distance) can recognize the carrier but cannot interpret the control frame such as CTS or RES. I can not know. In other words, a "hidden node problem" occurs. Therefore, when selecting a data channel, there is a possibility to select a data channel currently in use, and data collision occurs if data is sent directly to the selected data channel. Then, the data that has collided with the data being transmitted has a problem that must be transmitted to another channel by repeating the process of selecting the data channel.

In order to solve this problem, the present invention provides a method of snooping a data channel using a data radio and a method of selecting an idle data channel using the result of the snooping when selecting a data channel. Suggest. In other words, the conventional DCA media access control method uses the data radio only while transmitting and receiving data and not at other times. With this in mind, the present invention is characterized by improving network performance by detecting the state of a plurality of data channels using data radio while not transmitting or receiving data.

More specifically, Figure 2 shows an example of the configuration of a communication node according to the present invention.

Referring to FIG. 2, the communication node 1 according to the present invention may detect a state of each data channel while circulating a plurality of data channels using a data radio while not transmitting or receiving data packets. (snooping unit) 10 and a control signal processing unit 20 for controlling the transmission and reception of data packets through a control channel (control channel) shared between a plurality of communication nodes. In addition, the communication node 1 according to the present invention is characterized by selecting the idle data channel detected through the snooping unit 10 as a data channel for transmitting and receiving data packets.

At this time, the snooping unit 10 detects a carrier by measuring the energy level of a specific data channel for a fairly short time of about 20 μs. If a carrier is detected, the data channel is determined to be in use.

In addition, the snooping unit 10 generates a channel usage list (hereinafter, referred to as a first list) which records the usage state of each data channel, and in addition, based on a result of detecting the state of each channel, A snooping channel list (hereinafter referred to as a second list) in which a snooping result of each channel is recorded is generated. Furthermore, a carrier free channel list (hereinafter referred to as a third list) in which data channel information that is not currently in use and no carrier is detected using the first list and the second list is recorded. .

More specifically, FIG. 3 is a reference diagram illustrating a snooping method and a data channel selection process of a data channel according to the present invention.

Referring to FIG. 3, the snooping unit 10 detects a state of each data channel while circulating a plurality of data channels using a data radio while not transmitting or receiving data packets. Further, a carrier free channel list (third list) is generated using the channel usage list (first list) and the snooping channel list (second list).

Meanwhile, the control signal processor 20 carries a carrier free channel list (third list) generated at the source node S when the source node sends a request to send (RTS) control signal to the destination node.

Also, the snooping unit 10 does not detect a carrier using its channel usage list (first list) and snooping channel list (second list) before the destination node receiving the RTS control signal selects a data channel. A carrier free channel list (third list) in which channel information is recorded is generated. The snooping unit 10 refers to a carrier free channel list (third list) generated at the destination node D and a carrier free channel list (third list) received from the source node S through an RTS control frame. A carrier free channel that can be used for both is selected as a data channel.

The control signal processor 20 carries the selected data channel information when the destination node D sends the CTS control signal to the source node S.

On the other hand, the snooping unit 10 finds a case in which the source node S receiving the CTS control signal selects and uses the data channel selected earlier by another link while switching the data radio to the selected data channel. To detect the usage of the selected channel for a predetermined time, for example SIFS time.

Meanwhile, as another embodiment of the present invention, only a channel recorded as an idle channel in the above-described channel use list (first list) is selectively selected in order to prevent the system load due to the large number of data channels to snoop. It is also possible to reduce the snooping time by modifying the circuit to

On the other hand, as another embodiment of the present invention, since the above-mentioned snooping consumes a certain amount of power, when the power state of the communication node falls below a predetermined reference value for the optimization of the system, the snooping unit 10 It can be implemented to turn off the operation.

Alternatively, in another embodiment of the present invention, when the communication node 1 has a fixed power source, the operation of the snooping unit 10 is turned on, and when the portable node has a portable power source, the operation of the snooping unit 10 is turned off. OFF).

Furthermore, in order to save power, the operation of the snooping unit 10 may be turned off when data is not normally transmitted or received, and the operation of the snooping unit may be turned on only when transmission of the data packet fails. .

The data channel snooping method and the data channel selection method using the same based on the configuration of the communication node 1 according to the present invention described above are as follows.

First, according to the present invention, when all communication nodes 1 sharing a plurality of channels do not transmit or receive data, as shown in FIG. 3, each data channel is traversed by a data radio. Snooping the status of each data channel. That is, the energy level of a data channel is measured for a very short time to find out whether the data channel is currently in use or not. At this time, if the number of data channels is large, the time spent by snooping only the channels recorded as idle channels in the channel usage list can be reduced.

Next, a snooping channel list (second list, see FIG. 6) is generated using the result of snooping each data channel. As shown in FIG. 6, '0' in the snooping channel list indicates that the channel is idle, and '1' indicates that the carrier is detected and the channel is busy. In addition, '-' indicates busy in the channel usage list and means no snooping.

When the data to be transmitted, the source node (S) sends an RTS control frame to the destination node (D). At this time, a carrier free channel list (third list) in which carriers are not detected while not being used by using the channel use list (first list) and the snooping channel list (second list) is generated and sent to the RTS control frame. As shown in FIG. 6, the carrier free channel list displays a data channel for which a carrier is not searched as '0' and the remaining channels as '1' without using a neighbor node within a communication distance.

Meanwhile, before receiving the RTS control frame, the destination node D separately generates a carrier free channel list using its channel usage list and snooping channel list before selecting a data channel. Now, the carrier free channel list generated by the carrier node is compared with the carrier free channel list received from the source node S, and both channels are idle as the data channel, and the CTS control frame is loaded into the source node S. Send to). When the transmission of the CTS control frame is completed, the data radio is switched to the selected data channel to complete the reception of the data.

On the other hand, upon receiving the CTS control frame, the source node S switches the data radio to the selected data channel to prepare for data transmission. At the same time, the selected data channel information is loaded in the RES control frame and transmitted through the control channel.

At this time, the source node (S) after switching the data radio to the selected data channel, in order to prevent the collision of the data channel of the selected data channel for a predetermined time, for example a slot time (20us) longer than SIFS. Detect the condition. As a result of carrier detection of the selected data channel, if the channel is idle, data is transmitted, and if the channel is in use, the aforementioned data channel selection process is repeated through the control channel.

Now, when the destination node (D) receives the data in the data channel, it sends an ACK control frame to indicate that the data is well received, and then resumes data channel snooping with the data radio. In addition, if there is data to be transmitted, RTS transmission is attempted through the control channel as described above.

When the source node S receives the ACK control frame, the source node S completes the data transmission process and resumes data channel snooping with the data radio. In addition, if there is data to be transmitted, RTS transmission is attempted through the control channel as described above.

4 is an example of a multi-channel wireless network for explaining the snooping method of the data channel according to the present invention, five data channels are shown.

Referring to FIG. 4, the Z angle link is displayed differently according to the current state. Here, the small circle 800 of the solid line represents the communication distance range of the source node S, the large circle 802 of the solid line represents the carrier sensing distance of the source node (double the communication distance), and the small circle of the dotted line (000 ) Denotes the communication distance range of the destination node D, and the large circle 902 of the dotted line indicates the carrier sensing distance (two times the communication distance) of the destination node. Nodes in the communication distance can interpret the control frame of the neighbor node to find out the data channel currently in use, but nodes placed between the communication distance and the carrier sensing distance cannot interpret the control frame of the neighbor node, but only the carrier of the neighbor node. Can only detect.

5 is an example of a data channel selection method according to a general DCA media access control scheme.

5, the channel usage list (first list) of the source node S and the destination node D is shown, respectively. Looking at the channel usage list on the left, the data channel 1 centered on the source node (S) is actually being used by another node outside the communication distance, but the control frame of the neighboring node cannot be interpreted, so it is idle. Is displayed. For the same reason, data channel 2 is only in use and is marked as idle (0). Data channels 3 and 4, on the other hand, are both in use by communication nodes within the communication distance and are marked as busy '1'. On the other hand, since data channel 5 is a link in which data channel is selected by a communication node within a communication distance, the data channel 5 is displayed as an idle state '0'.

Eventually, referring to the channel usage list of the source node S, channels 1, 2 and 5 are marked as available idle and can be selected as data channels, but in practice channels 1 and 2 are already used by other nodes outside the communication distance. In this case, if a channel 1 or channel 2 is selected as a data channel according to the "hidden node problem", a collision problem occurs.

6 is an example of a data channel snooping method and a data channel selection method according to the present invention proposed to solve the above-mentioned problem.

Referring to FIG. 6, the channel usage list (first list) of the source node S and the destination node D, the snooping channel list (second list), and the carrier free channel list (third list) using them are respectively. Shown.

Data channels 1 and 2 are actually being used by other nodes that are outside the communication distance, centering on the source node S, but the control frames of neighboring nodes cannot be interpreted, so each of the idle states' 0 in the channel usage list (first list). 'Is displayed. However, since channels 1 and 2 are used by nodes within the carrier sensing distance, carriers of channels 1 and 2 can be detected in the snooping channel list (second list), and are represented by the use state '1', respectively. As a result, according to the carrier free channel list (third list), channels 1 and 2 are not displayed as being used in the channel usage list, but carriers are detected and displayed as the use state '1', respectively. Accordingly, channels 1 and 2 cannot be selected as data channels. On the other hand, channel 5 is not displayed as being used in the channel usage list, and no carrier is detected so that it is displayed as '0' in the carrier free channel list. Therefore, according to the present invention, only channel 5 can be selected as a data channel in an idle state, thereby preventing data collision.

According to the present invention, when the destination node selects a data channel, the probability of selecting an idle channel is greatly improved, thereby increasing the number of data transmitted simultaneously and consequently improving the transmission performance of the network. 5 and 6, according to the present invention, it can be seen that the idle channel selection probability is greatly improved from 33.3% to 100%.

7 and 8 are graphs illustrating the effects of a snooping method and a data channel selection method of a data channel according to the present invention.

7 and 8 show simulation results when five channels are used in a multi-hop ad hoc network. As shown, when using the data channel snooping method according to the present invention it can be seen that the throughput (throughput) is increased by about 30% than the conventional carrier detection only.

As described above, according to the present invention, a data channel is effectively selected in a multi-channel wireless network environment to prevent collision of data channels and a repeated channel selection process, resulting in more efficient use of a plurality of data channels. Provided are a communication method and an apparatus capable of increasing.

That is, according to the present invention, a method of snooping a data channel using a data radio and a method of selecting an idle data channel using the result of the snooping when selecting a data channel, This can prevent data collisions and greatly improve the idle channel selection probability when selecting data channels.

In addition, the number of data transmitted simultaneously increases, and consequently, the transmission performance of the network is improved. According to the simulation results, the data channel snooping method according to the present invention shows that the throughput is increased by about 30% compared to the case of conventional carrier sensing only.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims (32)

A communication node for transmitting and receiving data packets through a plurality of data channels shared between a plurality of communication nodes, A snooping unit configured to sense a state of each data channel while circulating the plurality of data channels using a data radio while not transmitting or receiving data packets; And selecting an idle data channel detected through the snooping unit as a data channel for transmitting and receiving data packets. The method of claim 1, And the snooping unit detects a carrier by measuring an energy level of a specific data channel for a predetermined time to determine whether the specific data channel is currently in use. The method of claim 1, And the snooping unit reduces the snooping time by selectively traversing only channels recorded as idle channels in a first list of usage states of each channel when the number of data channels to be detected is greater than a predetermined criterion. The method of claim 1, The snooping unit generates a second list of recording snooping results of each channel based on a result of sensing a state of each channel. 5. The method of claim 4, Further comprising a control signal processing unit for controlling the transmission and reception of data packets through a control channel (control channel) shared between a plurality of communication nodes, The snooping unit generates a third list in which channel information in which carriers are not detected is recorded using a first list and a second list in which a state of use of each channel is recorded, And the control signal processor sends the generated third list when a source node sends a request to send (RTS) control signal to a destination node. The method of claim 5, The snooping unit generates a third list of channel information on which carriers are not detected using its first list and second list before the destination node receiving the RTS control signal selects a data channel. Communication node. The method according to claim 6, The snooping unit selects a carrier free channel that can be used both as a data channel by referring to the generated third list and the third list received from the source node, And the control signal processor sends the selected data channel information when the destination node sends a clear to send (CTS) control signal to the source node. The method of claim 7, wherein And the snooping unit senses a state of the selected data channel while the source node receiving the CTS control signal switches a data radio to the selected data channel. The method of claim 1, And turning off the snooping part when a power state drops below a predetermined reference value. The method of claim 1, And a stationary power supply to turn on the operation of the snooping unit, and a portable power source to turn off the operation of the snooping unit. The method of claim 1, And only operating the snooping unit when the data packet fails to be transmitted. delete delete delete delete delete delete delete delete A communication method for transmitting and receiving data packets through a plurality of data channels shared between a plurality of communication nodes, (a) sensing the state of each data channel while traversing the plurality of data channels using a data radio while each communication node is not transmitting or receiving data packets; (b) selecting the detected idle data channel as a data channel for transmitting and receiving data packets; And (c) switching the data lion to the selected data channel. 21. The method of claim 20, The step (a) is a communication method, characterized in that to determine whether the specific data channel is currently in use by detecting the carrier by measuring the energy level of the specific data channel for a predetermined time. The method of claim 20, wherein step (a) comprises: (a1) detecting a carrier by measuring an energy level of a specific data channel for a predetermined time; And (a2) detecting a data channel in which a carrier is not detected among the data channels that are not currently in use as an idle channel by using the usage state of each data channel and the carrier information detected in step (a1). Communication method. The method of claim 20, wherein step (a) comprises: And when the number of data channels to be detected is greater than a predetermined criterion, snooping time is reduced by selectively traversing only channels recorded as idle channels in a list of usage states of each channel. The method of claim 22, wherein step (b) (b1) when the source node sends a request to send (RTS) control signal to a destination node through a control channel shared between a plurality of communication nodes, carrying idle channel information detected by the source node; ; And (b2) The destination node receiving the RTS control signal compares the idle channel information detected by the source node with the source node idle channel information received through the RTS control signal from the source node and uses an idle channel that can be used both. And selecting the data channel and carrying the selected data channel information when transmitting a clear to send (CTS) control signal to the source node. The method of claim 24, wherein step (c) comprises: (c1) detecting a state of the selected data channel while the source node receiving the CTS control signal switches the data radio to the selected data channel. 21. The method of claim 20, And the step (a) is omitted if the power state of the communication node falls below a predetermined reference value. 21. The method of claim 20, And performing the step (a) if the communication node has a fixed power source, and omitting the step (a) if the communication node has a portable power source. 21. The method of claim 20, And the communication node performs step (a) only when transmission of the data packet fails. In the method for preventing a collision between a plurality of data channels in a wireless network environment, (a) snooping the state of each data channel while circulating the plurality of data channels using a data radio while each communication node constituting the wireless network environment does not transmit or receive data packets; ; And and selecting an idle data channel sensed using the snooping result as a data channel for transmitting and receiving data packets. The method of claim 29, wherein the step (a), And detecting a carrier by measuring an energy level of a specific data channel for a predetermined time to determine whether the specific data channel is currently in use. In the media access control protocol module for a multi-channel wireless network environment, A snooping unit configured to detect a state of each data channel while circulating a plurality of data channels using a data radio while not transmitting or receiving data packets, And selecting an idle data channel detected through the snooping unit as a data channel for transmitting and receiving data packets. The method of claim 31, wherein And the snooping unit detects a carrier by measuring an energy level of a specific data channel for a predetermined time to determine whether the specific data channel is currently in use.

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