JP4014950B2 - Wireless communication system and communication method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a communication system and a communication method for transmitting user data using a plurality of carriers, and more particularly to a communication system and a communication method capable of releasing or securing a carrier when necessary.
[0002]
[Prior art]
Hereinafter, a conventional wireless communication system will be described. FIG. 10 is a diagram illustrating a configuration of a communication device used in a conventional wireless communication system. In FIG. 10, 101 is a physical layer (PHY) unit, 102 is a medium access control (MAC) unit, 103 is a transmission / reception buffer (EC) unit, and 104 is a radio resource management unit.
[0003]
Here, the operation of the communication apparatus configured as described above will be described. The PHY unit 101 converts higher layer control information and user information into a format called burst, and controls transmission and reception between the access point and the wireless terminal. For example, when an orthogonal frequency division multiplexing (OFDM) modulation scheme is adopted, appropriate communication quality is provided according to the propagation environment such as the distance of the wireless terminal to the access point and interference conditions based on the provisions of the scheme. . That is, an appropriate transmission mode is selected.
[0004]
The MAC unit 102 determines a wireless terminal that performs communication, a transmission amount, and the like based on the status of the access point and the wireless terminal buffer, and controls the physical layer. For example, when a time division multiplexing method in which an access point performs centralized control is used as the MAC protocol, the MAC unit 102 of the access point determines how to use the carrier in the time axis direction based on a predetermined allocation request amount. To manage the transmission and reception. As the predetermined allocation request amount, for example, a predetermined allocation request amount, an allocation request amount calculated from the data amount of the transmission buffer addressed to each terminal, or data of the transmission buffer notified from each wireless terminal There is an allocation request amount calculated from the amount. The MAC unit 102 of the wireless terminal performs transmission / reception using the time allowed for the access point according to the determination of the access point.
[0005]
In addition, when using CSMA / CA (carrier sense multiple access with collision) as the MAC protocol, the MAC unit 102 of the access point synchronizes with each wireless terminal using a broadcast signal and a control signal that are periodically transmitted. Establish and notify the wireless terminal of the transmission time and transmission permission by the notification signal and the control signal. The MAC unit 102 of the wireless terminal performs transmission / reception based on a carrier sense result for a predetermined time in accordance with a notification signal and a control signal from an access point.
[0006]
The EC unit 103 accumulates data until transmission / reception is completed. When data management is performed for each user connection, the transmission buffer accumulates data for each user connection and reports the accumulated data amount to the MAC unit 102. Then, data is transmitted according to the transmission control. On the other hand, the reception buffer confirms the received data and requests retransmission if there is a transmission error.
[0007]
Next, transmission / reception management by the MAC unit 102 will be described. FIG. 11 is a diagram showing a frame configuration shown in the standard “ARIB STD-T70” of the radio industry, for example. In FIG. 11, the horizontal axis represents time, and the MAC unit 102 controls the line type, the wireless terminal that performs communication, the transmission amount, and the like in units of time called frames. BCH represents a line for transmitting broadcast information from the access point to each wireless terminal, and FCH represents a line for broadcasting the frame structure. The frame structure is indicated by the band allocation information, and the MAC scheduler on the wireless terminal side operates according to the broadcasted frame structure. “Down Link” is a period in which a downlink for transmitting user connection data from the access point to each wireless terminal is arranged. “Up Link” is a period in which an uplink for transmitting user connection data from each wireless terminal to the access point is arranged. The RCH is a random access line through which the wireless terminal transmits control information to the access point when no uplink is assigned to the wireless terminal. The ACH is a line for transmitting a response to the RCH of the previous MAC frame.
[0008]
FIG. 12 is a diagram illustrating a plurality of basic carriers managed by the access point. In FIG. 12, each trapezoid indicates a basic carrier, and a hatched portion indicates a plurality of basic carriers managed by a specific base station. In this example, three basic carriers are used. Normally, a wireless communication device performs transmission processing in a frequency band called a basic carrier. As can be seen in the report, a method for realizing a wider band transmission by using a band in which a plurality of basic carriers are bundled is being studied.
[0009]
[Problems to be solved by the invention]
However, in the above-described conventional wireless communication apparatus, when performing broadband communication using a plurality of carriers at the same time, it is considered that carriers are shared between access points and carriers are released or secured when necessary. It wasn't. Therefore, there is a problem in that there is a difference in communication quality between an access point with low communication traffic and an access point with high communication traffic.
[0010]
The present invention has been made in view of the above, and even when a wide band communication is performed using a plurality of carriers at the same time, the transmission efficiency of the entire system can be achieved by accommodating carriers between access points. An object of the present invention is to obtain a communication system and a communication method capable of improving the above.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, in the wireless communication system according to the present invention, when it is determined that an excessive number of carriers are secured for the current communication traffic, Send a “carrier release notification” to the access point to release the carrier, and after receiving the “carrier release notification”, determine that the number of carriers is insufficient for the current communication traffic, and An access point that performs communication by adding the open carrier when it is determined that the notified open carrier can be used.
[0012]
In the wireless communication system according to the next invention, a specific access point that has been determined to have a shortage of carriers due to an increase in communication traffic transmits an “carrier extension notification” specifying a requested carrier. And a peripheral access point that replies that when it is determined that the designated requested carrier can be released after receiving the “carrier extension notification”, and the access point that is the transmission source of the “carrier extension notification” Selects one of the peripheral access points that can release the requested carrier, requests the selected access point to release the carrier, and the selected access point releases the requested carrier, The access point of the carrier release request source performs communication by adding an open carrier. .
[0013]
In the wireless communication system according to the next invention, the peripheral access point that has received the “carrier extension notification” searches for an unused carrier to replace the designated requested carrier, and there is an available unused carrier. In this case, the unused carrier is acquired and the designated requested carrier is released.
[0014]
In the wireless communication system according to the next invention, each of the access points transmits a signal indicating that the carrier is used by including the IP address of the access point.
[0015]
In the communication method according to the next invention, the access point that has determined that an excessive number of carriers are secured for the current communication traffic transmits a “carrier release notification” to the peripheral access points. The carrier release step for releasing the carrier and the peripheral access point that has received the “carrier release notification” determines that the number of carriers is insufficient for the current communication traffic and uses the notified release carrier. A communication step of performing communication by adding the open carrier when it is determined to be possible.
[0016]
In the communication method according to the next invention, a specific access point that is determined to have a shortage of carriers due to an increase in communication traffic designates a “carrier extension notification” that designates a requested carrier to a peripheral access point. A carrier extension notification step, a response step of replying to that effect when the peripheral access point that has received the “carrier extension notification” determines that the designated request carrier can be released, and the specific The access point selects any one of the peripheral access points that can release the requested carrier, and requests the selected access point to release the carrier, and the selected access point requests A first opening step of releasing a carrier, and the specific access point is opened. Characterized in that it comprises a communication step of performing communication by adding carrier, a.
[0017]
In the communication method according to the next invention, the peripheral access point that has received the “carrier extension notification” searches for an unused carrier in place of the designated requested carrier, and there is an available unused carrier. A second release step of acquiring the unused carrier and releasing the designated requested carrier.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a communication system and a communication method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.
[0019]
Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a communication system according to the present invention. In FIG. 1, 1, 2, 3, 4 are access points (AP), 5 is a router (or hub) to which the access points are connected, and communication between access points is via this router (or hub). Done.
[0020]
FIG. 2 is a diagram showing a communication method according to the present embodiment, and more specifically, a diagram showing basic carriers managed by each access point shown in FIG. In FIG. 2, each trapezoid represents a basic carrier, and characters in the trapezoid indicate access points that manage the carrier. Also, the hatched portion represents a plurality of basic carriers managed by a specific base station. Here, for example, the access point 2 transmits a “carrier release notification” corresponding to the currently managed carrier, and the access point 3 that has received the “carrier release notification” searches for the released carrier. Use the detected carrier.
[0021]
Next, the communication method of the present embodiment in the communication system will be described in detail. FIG. 3 is a flowchart showing the operation of the access point that transmits the “carrier release notification”. FIG. 4 is a flowchart showing the operation of the peripheral access point that receives the “carrier release notification”. Each access point has a function of receiving a signal from a peripheral access point. Each access point transmits a signal (beacon) indicating that the carrier is used by including the access point's IP address. Then, by receiving this beacon, it is known which access point is using which carrier.
[0022]
Specifically, for example, the access point 2 shown in FIG. 2 transmits a “carrier release notification” to release the carrier, and the access point 3 receives the “carrier release notification” and uses the released carrier. The case will be described.
[0023]
First, the access point 2 determines whether the carrier usage rate is smaller than a predetermined threshold in the relationship between the current communication traffic and the number of used carriers (FIG. 3, step S1). And if it is larger than a predetermined threshold value (step S1, No), it will complete | finish without doing anything. On the other hand, if the usage rate is smaller than the predetermined threshold (step S1, Yes), it is determined that an excess carrier is secured for the current communication traffic.
[0024]
Next, the access point 2 uses the packet error rate, the number of retransmissions, and the like to determine the open carriers in the order of poor propagation environment (step S2). And the change of a carrier is notified with respect to the radio | wireless terminal which is communicating on the open carrier determined as mentioned above (step S3).
[0025]
Next, the access point 2 transmits a “carrier release notification” including its own IP address and carrier number using the connected wired network, and notifies the peripheral access point that the carrier is no longer used. (Step S4).
[0026]
Next, the peripheral access point (here, referred to as access point 3) that has received the “carrier release notification” performs carrier sense over a certain period of time in order to confirm whether or not the notified carrier is used ( FIG. 4, step S11). Then, the released carrier detection process (step S12), the process of determining whether the released carrier is an adjacent carrier from the carrier number included in the “carrier release notification” (step S13), the current communication traffic and the number of used carriers The process of determining whether the usage rate of the carrier currently managed in the relationship is larger than a predetermined threshold value (step S14) is sequentially performed.
[0027]
For example, when there is an access point that has already acquired a released carrier in step S12 (step S12, Yes), in step S13, the carrier number included in the “carrier release notification” is other than the adjacent carrier (step S13). No), or when the carrier usage rate is smaller than the predetermined threshold value (No in step S14), the operation ends as it is.
[0028]
On the other hand, in step S12, there is no access point that has acquired the released carrier (step S12, No), and in step S13, the carrier number included in the “carrier release notification” is an adjacent carrier (step S13, Yes). In step S14, if the carrier usage rate is greater than the predetermined threshold (Yes in step S14), the access point 3 that has received the “carrier release notification” receives a carrier for the current communication traffic. It is determined that there is a shortage, and an open carrier is acquired (step S15).
[0029]
After that, the access point 3 that has acquired the open carrier starts transmitting a beacon and starts using it as a communication carrier in the same manner as for an existing carrier.
[0030]
Thus, in this embodiment, the access point transmits user data using a plurality of carriers managed by itself. Then, the access point that has determined that an excess carrier has been secured for the current communication traffic transmits a carrier release notification to neighboring access points, and releases the carrier. After that, the neighboring access points that have received the carrier release notification by communication between access points judge whether the notified open carrier can be used when their communication traffic is not sufficient, and determined that it can be used. In this case, communication is performed by adding an open carrier. As a result, carriers can be accommodated according to communication traffic, so that the transmission efficiency of the entire system can be improved even when the communication traffic of a specific access point increases.
[0031]
In this embodiment, the IP address of the access point is included in the signal (beacon) indicating that the carrier is used, and each access point receives the beacon of the peripheral access point. Thereby, it can be easily known which access point is using which carrier.
[0032]
Embodiment 2. FIG.
FIG. 5 is a diagram illustrating a communication method according to the second embodiment. Since the configuration of the wireless communication system is the same as that of the first embodiment described above, the same reference numerals are given and description thereof is omitted. Here, only operations different from those of the first embodiment will be described. In the present embodiment, for example, the access point 3 transmits “carrier extension request”. Then, the access point 2 releases a carrier that can be used by the access point 3, and the access point 3 performs communication using the released carrier.
[0033]
Next, the communication method of the present embodiment will be described in detail. FIG. 6 is a flowchart showing the operation of the access point that transmits “carrier extension request”. FIG. 7 is a flowchart showing the operation of a peripheral access point that has received “carrier extension request”.
[0034]
More specifically, for example, the access point 3 requests to release a carrier using “carrier extension request”, and the peripheral access point 2 that has received “carrier extension request” indicates that the carrier can be released. A case will be described in which a carrier is released in response to a “carrier release request”, and then the access point 3 performs communication using the released carrier.
[0035]
First, the access point 3 determines whether the carrier usage rate is greater than a predetermined threshold in the relationship between the current communication traffic and the number of used carriers (FIG. 6, step S21). For example, when it is smaller than the predetermined threshold value (step S21, No), the process ends. On the other hand, when the usage rate is larger than the predetermined threshold (step S21, Yes), it is determined that only a small number of carriers can be secured for the current communication traffic.
[0036]
Thereafter, the access point 3 performs carrier sense on all carriers in order to select usable carriers. Then, by receiving beacons from neighboring access points, it investigates which access point manages which carrier, and is composed of the number of available carriers and the IP address of the corresponding access point. A required carrier is determined by creating a table (step S22).
[0037]
Next, the access point 3 transmits a “carrier extension request” including the number of the carrier (requested carrier) to be released to each access point using the wired network (step S23).
[0038]
Next, the access point 3 receives a “carrier extension request response” from each access point that has received “carrier extension request” (step S24). And when all the peripheral access points cannot release a carrier (step S25, No), it communicates with the present number of carriers. On the other hand, when it is notified from any of the peripheral access points that the carrier can be released (step S25, Yes), a “carrier release request” is transmitted to the access point (step S26). Here, it is assumed that a “carrier release request” is transmitted to the access point 2. When there is a response indicating that a carrier can be released from a plurality of access points, one of them is selected and a “carrier release request” is transmitted.
[0039]
Next, in the access point 3, in order to confirm whether or not the corresponding carrier is released, carrier sense is performed on the carrier (step S27). When detecting the release of the carrier, the access point 3 starts communication using the released carrier (step S28). If the access point 3 wishes to further expand the carrier, the carrier extension desired sequence is repeatedly executed.
[0040]
On the other hand, in the peripheral access point (access point 2) that has received the "carrier extension request", whether or not the usage rate of the designated carrier is greater than a predetermined threshold in the relationship between the current communication traffic and the number of carriers used Is determined (step S31 in FIG. 7). For example, when it is larger than a predetermined threshold value (step S31, No), the access point 2 determines that the designated carrier cannot be released and displays a “carrier extension desired response” indicating that fact. It transmits to the access point 3 (step S32). On the other hand, if it is smaller than the predetermined threshold (step S31, Yes), it is determined that the designated carrier can be released (step S33), and the “carrier extension desired response” indicating that is accessed. Transmit to point 3 (step S34).
[0041]
Next, the access point 2 enters a state of waiting for reception of a “carrier release request” (step S35). For example, when the “carrier release request” cannot be received from the access point 3 within a certain time (step S36, No), access is performed. It is determined that point 3 has acquired a carrier from another access point, and this sequence ends. On the other hand, when the “carrier release request” is received from the access point 3 within a certain time (step S36, Yes), the change of the carrier is notified to the wireless terminal that is communicating with the carrier to be released (step S37). Thereafter, the carrier is released (step S38).
[0042]
Thus, in this embodiment, the access point transmits user data using a plurality of carriers managed by the access point. At this time, the communication point increases, and the access point that has determined that only a small number of carriers can be secured with respect to the current communication traffic transmits a “carrier expansion request” to neighboring access points. Then, the access point that has received “carrier extension request” releases the carrier if the designated carrier can be released. As a result, carriers can be accommodated according to communication traffic, so that the transmission efficiency of the entire system can be improved even when the communication traffic of a specific access point increases.
[0043]
Embodiment 3 FIG.
FIG. 8 is a diagram illustrating a communication method according to the third embodiment. Since the configuration of the wireless communication system is the same as that of the first embodiment described above, the same reference numerals are given and description thereof is omitted. Here, only operations different from those in the first or second embodiment will be described. In the present embodiment, for example, the access point 3 transmits a carrier expansion request. Then, the access point 2 acquires a carrier that can be used by itself, and further releases the carrier desired by the access point 3. Thereafter, the access point 3 performs communication using the open carrier.
[0044]
Next, the communication method of the present embodiment will be described in detail. FIG. 9 is a flowchart showing the operation of the access point when changing the used carrier. The operation of the access point that transmits “carrier extension request” is the same as that in FIG. 6 of the second embodiment.
[0045]
First, the peripheral access point (access point 2) that has received “carrier extension request” performs carrier sense for all carriers. If there is no unused carrier, the same processing as in FIG. 7 is performed.
[0046]
On the other hand, when there is an unused and available carrier, the access point 2 transmits a “carrier extension desired response” indicating that the designated carrier can be released to the access point 3 (step S41). Step S42).
[0047]
Next, the access point 2 enters a reception waiting state for the “carrier release request” (step S43), and if it cannot receive the “carrier release request” from the access point 3 within a certain time (step S44, No), the access point 3 determines that a carrier has been acquired from another access point, and ends this sequence. On the other hand, when the “carrier release request” is received from the access point 3 within a certain time (step S44, Yes), the change of the carrier is notified to the wireless terminal that is communicating with the carrier to be released (step S44). S45). Then, the unused carrier is acquired and the used carrier is changed (step S46), and then the designated carrier is released (step S47). Thereafter, the access point 2 performs communication using the changed carrier.
[0048]
Thus, in this embodiment, the access point transmits user data using a plurality of carriers managed by itself. At this time, the access point that has received the “carrier extension request” searches for an unused carrier in place of the designated carrier, and if there is an unused and usable carrier, obtains this carrier, Free your career. As a result, carriers can be accommodated according to communication traffic, so that the transmission efficiency of the entire system can be improved even when the communication traffic of a specific access point increases.
[0049]
【The invention's effect】
As described above, according to the present invention, according to the present invention, an access point determined to have secured an excess carrier for the current communication traffic transmits a “carrier release notification” to neighboring access points, Free your career. After that, the access points in the vicinity that have received the “carrier release notification” by communication between access points determine whether or not the notified open carrier can be used when their communication traffic is not sufficient. If it is determined, communication is performed by adding an open carrier. As a result, carriers can be accommodated in accordance with communication traffic, and therefore a wireless communication system capable of improving transmission efficiency as a whole system even when communication traffic of a specific access point increases is obtained. There is an effect that it is possible.
[0050]
According to the next invention, an access point that has determined that communication traffic has increased and only a small number of carriers can be secured for the current communication traffic, transmits a “carrier extension notification” to neighboring access points. To do. Then, the access point that receives the “carrier extension notification” releases the carrier if the designated carrier can be released. As a result, carriers can be accommodated in accordance with communication traffic, and therefore a wireless communication system capable of improving transmission efficiency as a whole system even when communication traffic of a specific access point increases is obtained. There is an effect that it is possible.
[0051]
According to the next invention, the access point that has received the “carrier extension notification” searches for an unused carrier in place of the designated carrier, and if there is an unused and available carrier, acquires this carrier, Release the specified carrier. As a result, carriers can be accommodated in accordance with communication traffic, and therefore a wireless communication system capable of improving transmission efficiency as a whole system even when communication traffic of a specific access point increases is obtained. There is an effect that it is possible.
[0052]
According to the next invention, the IP address of the access point is included in the signal (beacon) indicating that the carrier is used, and each access point receives the beacon of the peripheral access point. As a result, it is possible to easily know which access point is using which carrier.
[0053]
According to the next invention, the access point transmits user data using a plurality of carriers managed by the access point. Then, the access point that has determined that an excess carrier has been secured for the current communication traffic transmits a carrier release notification to neighboring access points, and releases the carrier. After that, the neighboring access points that have received the carrier release notification by communication between access points judge whether the notified open carrier can be used when their communication traffic is not sufficient, and determined that it can be used. In this case, communication is performed by adding an open carrier. As a result, carriers can be accommodated according to communication traffic, so that the transmission efficiency of the entire system can be improved even when the communication traffic of a specific access point increases.
[0054]
According to the next invention, an access point that has determined that communication traffic has increased and a sufficient number of carriers can be secured with respect to the current communication traffic, transmits a “carrier extension request” to neighboring access points. To do. Then, the access point that has received “carrier extension request” releases the carrier if the designated carrier can be released. As a result, carriers can be accommodated according to communication traffic, so that the transmission efficiency of the entire system can be improved even when the communication traffic of a specific access point increases.
[0055]
According to the next invention, the access point that has received the “carrier extension request” searches for an unused carrier to replace the designated carrier, and if there is an unused and available carrier, acquires this carrier, Release the specified carrier. As a result, carriers can be accommodated according to communication traffic, so that the transmission efficiency of the entire system can be improved even when the communication traffic of a specific access point increases.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a communication system according to the present invention.
FIG. 2 is a diagram illustrating a communication method according to the first embodiment.
FIG. 3 is a flowchart showing an operation of an access point that transmits a “carrier release notification”.
FIG. 4 is a flowchart showing the operation of a peripheral access point that has received a “carrier release notification”.
FIG. 5 is a diagram illustrating a communication method according to a second embodiment.
FIG. 6 is a flowchart showing an operation of an access point that transmits “carrier extension request”.
FIG. 7 is a diagram illustrating an operation of a peripheral access point that has received a “carrier extension request”.
8 is a diagram illustrating a communication method according to Embodiment 3. FIG.
FIG. 9 is a flowchart showing the operation of the access point when changing the used carrier.
FIG. 10 is a diagram illustrating a configuration of a communication device used in a conventional wireless communication system.
FIG. 11 is a diagram showing a frame configuration shown in the standard “ARIB STD-T70” of the radio industry.
FIG. 12 is a diagram showing a plurality of basic carriers managed by an access point.
[Explanation of symbols]
1, 2, 3, 4 Access point (AP), 5 router (or hub).

Claims (7)

In a wireless communication system in which each access point transmits data using a single carrier or a plurality of carriers,
When it is determined that an excessive number of carriers are secured for the current communication traffic, a “carrier release notification” is sent to the peripheral access point to release the carrier. , The access point that performs communication by adding the open carrier when it is determined that the number of carriers is insufficient with respect to the current communication traffic and it is determined that the notified open carrier can be used,
A wireless communication system comprising: In a wireless communication system in which each access point transmits data using a single carrier or a plurality of carriers,
A specific access point that has determined that the carrier is insufficient due to an increase in communication traffic, and an access point that transmits a “carrier extension notification” specifying a requested carrier;
When it is determined that the specified requested carrier can be released after receiving the "carrier extension notification", a peripheral access point that replies to that effect,
With
The access point of the “carrier extension notification” transmission source selects any one of the peripheral access points that can release the requested carrier, and requests the selected access point to release the carrier.
The selected access point releases the requested carrier;
The wireless communication system, wherein an access point of the carrier release request source performs communication by adding an open carrier. The peripheral access point that has received the “carrier extension notification” searches for an unused carrier in place of the designated requested carrier, and when there is an available unused carrier, obtains the unused carrier and designates it. The wireless communication system according to claim 2, wherein the request carrier is released. 4. The wireless communication system according to claim 1, wherein each access point transmits a signal indicating that a carrier is used by including an IP address of the access point. 5. In a communication method executed in a wireless communication system in which each access point transmits data using a single carrier or a plurality of carriers,
A carrier release step in which an access point determined to have secured an excessive number of carriers for the current communication traffic sends a “carrier release notification” to the neighboring access points to release the carrier,
When the peripheral access point that has received the “carrier release notification” determines that the number of carriers is insufficient for the current communication traffic and determines that the notified open carrier can be used, In addition, a communication step for performing communication,
A communication method comprising: In a communication method executed in a wireless communication system in which each access point transmits data using a single carrier or a plurality of carriers,
A carrier access notifying step in which a specific access point that is determined to have a shortage of carriers due to an increase in communication traffic transmits a “carrier extension notification” that specifies a requested carrier to a peripheral access point;
When the peripheral access point that has received the "carrier extension notification" determines that the designated requested carrier can be released, a response step of returning that effect;
A request step in which the specific access point selects any one of the peripheral access points that can release the requested carrier, and requests the selected access point to release the carrier;
A first release step in which the selected access point releases a requested carrier;
A communication step in which the specific access point performs communication by adding an open carrier; and
A communication method comprising: The peripheral access point that has received the “carrier extension notification” searches for an unused carrier in place of the designated requested carrier, and when there is an available unused carrier, obtains the unused carrier and designates it. A second release step for releasing the requested carrier;
The communication method according to claim 6, further comprising:

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