JP4818208B2 - Communication system, base station, and communication method - Google Patents

Description

  The present invention relates to an OFDMA communication system, a base station, and a communication method.

The TDMA / TDD system that combines TDMA (Time Division Multiple Access) and TDD (Time Division Duplex) is adopted as a wireless access system for digital cellular phone systems and PHS systems. Yes. Furthermore, in addition to this, an OFDMA scheme that utilizes OFDMA (Orthogonal Frequency Division Multiplexing Access) has been proposed.
OFDM is a scheme in which a carrier wave that modulates data is divided into a plurality of “subcarriers” (subdivided carrier waves) orthogonal to each other, and a data signal is distributed and transmitted to each subcarrier.

Hereinafter, an outline of the OFDM scheme will be described.
FIG. 7 is a block diagram showing a configuration of an OFDM modulation apparatus used on the transmission side. Transmission data is input to the OFDM modulator. This transmission data is supplied to the serial / parallel converter 201 and converted into data consisting of a plurality of low-speed transmission symbols. That is, the transmission information is divided to generate a plurality of low-speed digital signals. This parallel data is supplied to an inverse fast Fourier transform (IFFT) unit 202.
Parallel data is assigned to each subcarrier constituting the OFDM and mapped in the frequency domain. Here, modulation such as BPSK, QPSK, 16QAM, and 64QAM is performed on each subcarrier. The mapping data is converted from transmission data in the frequency domain to transmission data in the time domain by performing an IFFT operation. As a result, a multicarrier modulation signal is generated in which a plurality of subcarriers that are orthogonal to each other are independently modulated. The output of the IFFT unit 202 is supplied to the guard interval adding unit 203.
As shown in FIG. 8, the guard interval adding unit 203 uses the rear part of the effective symbol of the transmission data as a guard interval and adds a copy to the front part of the effective symbol period for each transmission symbol. The baseband signal obtained by the guard interval adding unit is supplied to the quadrature modulation unit 204.
The quadrature modulation unit 204 performs quadrature modulation on the baseband OFDM signal supplied from the guard interval adding unit 203 by using the carrier signal supplied from the local oscillator 105 of the OFDM modulation device, and outputs an intermediate frequency (IF) Frequency conversion to signal or radio frequency (RF) signal. That is, the quadrature modulation unit frequency-converts the baseband signal into a desired transmission frequency band, and then outputs it to the transmission path.

FIG. 9 is a block diagram showing a configuration of an OFDM demodulator used on the receiving side. An OFDM signal generated by the OFDM modulation device of FIG. 7 is input to the OFDM demodulation device via a predetermined transmission path.
The OFDM received signal input to this OFDM demodulator is supplied to the orthogonal demodulator 211. The orthogonal demodulator 211 performs orthogonal demodulation on the OFDM received signal using the carrier signal supplied from the local oscillator 212 of the OFDM demodulator, converts the frequency from the RF signal or IF signal to the baseband signal, and converts the baseband signal. Obtain an OFDM signal. This OFDM signal is supplied to the guard interval removal unit 213.
The guard interval removing unit 213 is a guard interval adding unit 2 of the OFDM modulator.
The signal added in 03 is removed in accordance with a timing signal supplied from a symbol timing synchronization unit (not shown). The signal obtained by the guard interval removing unit 213 is supplied to the fast Fourier transform (FFT) unit 214.
The FFT unit 214 converts the input time domain received data into frequency domain received data by performing FFT. Further, demapping is performed in the frequency domain, and parallel data is generated for each subcarrier. Here, demodulation for modulation of BPSK, QPSK, 16QAM, 64QAM, etc. applied to each subcarrier has been performed. The parallel data obtained by the FFT unit 214 is supplied to the parallel / serial conversion unit 215 and output as reception data.

  As described above, OFDM is a scheme for dividing a carrier wave into a plurality of subcarriers. OFDMA is a scheme in which a plurality of subcarriers are collected from the subcarriers in the OFDM and grouped, and one or more of each group is assigned to each user to perform multiplex communication. Each of the above groups is called a subchannel. That is, each user communicates using one or more assigned subchannels. In addition, the subchannel is adaptively increased or decreased according to the amount of data to be communicated or the propagation environment.

Patent Document 1 discloses a method of assigning a pilot carrier by adaptively changing the pilot carrier according to the channel environment of each subchannel. In this allocation method, a small pilot carrier is allocated when the channel environment is good, and a large pilot carrier is allocated when the channel environment is bad. Thereby, the number of subchannels allocated to one user changes.
Special table 2005-520432

In the above prior art, when transmission data is temporarily reduced while communication of the user terminal is continued, the base station releases unnecessary subchannels for other user terminals.
When the transmission data amount of the user terminal increases again, in order to use the released subchannel again, it is necessary to wait for the subchannel allocated to the terminal of another user to be released. During this time, even if the communication data amount of the user's terminal increases again, the number of subchannels that can be used remains reduced, so the communication throughput at the user's terminal does not increase, and it takes time to complete data transmission. There is a problem that it takes.
Further, when subchannels are allocated, carrier sense for checking whether or not the subchannels can be used in advance is necessary. In order to allocate a new subchannel with an increased amount of data, carrier sense is performed for all subchannels, so that a long time is required for the processing. As a result, since it takes time to assign the subchannel, the throughput of communication in the user terminal decreases.
In the above case, communication throughput according to QoS cannot be provided to the user terminal.

  The present invention has been made in order to solve the above-described problem. In the communication system of the OFDMA communication system, the transmission data temporarily decreases while the communication of the user terminal is continued, and then increases again. Even so, it is possible to continue the communication without lowering the communication throughput of the user terminal, and to provide the user terminal with the throughput according to the QoS, the OFDMA communication system, the base The purpose is to obtain a station and a communication method.

In order to solve the above problems, a communication system according to the present invention provides:
Communication is performed between a base station and a plurality of terminals using a communication subchannel that performs data communication using one or a plurality of subchannels, and a notification subchannel that notifies the terminal of information related to the communication subchannels. In an OFDMA communication system,
Communication data amount acquisition means for acquiring a data amount of data communication performed by the communication subchannel, and channel assignment means for assigning the communication subchannel according to the communication data amount, wherein the channel assignment means includes the communication data When the amount decreases, the number of the allocated communication subchannels to be released is varied according to the priority (claim 1).
The channel allocating unit does not allocate the subchannel to the notification subchannel when the communication subchannel is released (claim 2).
In addition, when the communication subchannel is released, the channel allocation means allocates the subchannel again as a communication subchannel (claim 3).

Further, the priority is a QoS class (claim 4).

The base station according to the present invention includes a communication subchannel that performs data communication with a plurality of terminals using one or a plurality of subchannels, and a notification subchannel that notifies the terminal of information related to the communication subchannels Communication data amount acquisition means for acquiring the data amount of data communication performed by the communication subchannel, and channel assignment means for allocating the communication subchannel according to the communication data amount The channel allocating unit varies the number of the allocated communication subchannels to be released according to the priority when the communication data amount decreases (claim 5).
The channel allocating means does not allocate the subchannel to the notification subchannel when the communication subchannel is released (claim 6).
Further, when the communication subchannel is released, the channel allocation means allocates the subchannel again as a communication subchannel (claim 7).

Further, the priority is a QoS class (claim 8).

A communication method according to the present invention notifies a communication subchannel that performs data communication using one or a plurality of subchannels between a base station and a plurality of terminals, and information on the communication subchannels to the terminal. In the communication method in the OFDMA system in which communication is performed using a notification subchannel, a communication data amount acquisition step for acquiring a data amount of data communication performed by the communication subchannel, and a channel for allocating the communication subchannel according to the communication data amount An allocation step, wherein when the amount of communication data decreases, the channel allocation step varies the number of the allocated communication subchannels to be released according to priority. ).

  According to the present invention, when the amount of communication data decreases between a base station and a terminal with which communication has been established, at least one of a plurality of subchannels in which the data has become empty is not released. Since the allocation is maintained and is not allocated to other terminals, when the communication of the terminal increases again, throughput corresponding to the QoS can be provided to the user terminal without reducing the communication throughput. it can.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a communication system according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory diagram showing an OFDMA frame configuration used in a communication method according to an embodiment of the present invention.
This communication system is an OFDMA communication system in which communication is performed between a base station (CS: cell station) and a plurality of terminals (PS: personal station) using frames composed of a plurality of subchannels for each frequency band. System.

The frame configuration of FIG. 1 is, for example, a configuration in the case where there are four time slots (S1 to S4) used in the PHS system, the vertical axis is the frequency axis, and the horizontal axis is the time axis.
In FIG. 1, both the downlink period and the uplink period are divided into 28 frequency bands with respect to the frequency axis. The subchannel of the first frequency band is called a control subchannel and is used in the control channel (CCH).
Note that the first frequency band may be either the highest frequency band or the lowest frequency band. Also, the control subchannel indicates which subchannel of each time slot is used in each frequency band.
The example of FIG. 1 is an example of a PHS system, and the base stations that can be specified by the control subchannels C1 to C4 are four base stations. In the PHS system, the control channel is intermittently transmitted every 100 ms.
The remaining 27 frequency bands are composed of traffic subchannels T1 to T108 for transmitting and receiving data. There are 27 in the frequency direction and 4 in the time axis direction, for a total of 10
It consists of 8 subchannels.
This traffic subchannel includes an anchor subchannel and an extra subchannel.
An anchor subchannel is used to notify each terminal which subchannel is used by each terminal, and is used to negotiate between the base station and the terminal whether data has been exchanged correctly by retransmission control. It is a subchannel.

  The extra subchannel is a subchannel that transmits data to be actually used, and a plurality of extra subchannels can be assigned to one terminal. In this case, as the number of allocated extra subchannels increases, the band is expanded, and high-speed communication is possible.

Next, the configuration of the base station used in the communication system will be described. FIG. 2 is a block diagram of the base station of the communication system according to the embodiment of the present invention.
As shown in FIG. 2, the base station 1 is connected to an antenna and converts a signal from a signal processing unit 12 described later into an RF signal, or conversely converts the received RF signal so that the signal processing unit 12 can handle it. A wireless communication unit 11, a signal processing unit 12 for processing a received signal or a signal to be transmitted, a modulation / demodulation unit 13 for modulating or demodulating the signal, an external I / F unit 14 connected to a higher-level communication network, a signal processing unit 12, and It comprises a control unit 15 that controls the modem unit 13 and a storage unit 16 that stores QoS information and the like.

The control unit 15 acquires the communication data amount (communication data amount acquisition unit) and allocates subchannels according to the communication data amount (channel allocation unit). Then, when the communication data amount decreases, control is performed so as to maintain assignment of at least one subchannel among the assigned subchannels.
For this purpose, the control unit 15 maintains the allocation of an extra subchannel without transmission data, an ESCH (extra subchannel) setting unit 15-1 that sets an allocation for each terminal of an extra subchannel (ESCH) used in communication. ESCH instructing whether to start and instructing the ESCH (extra subchannel) setting unit 15-1 to release the extra subchannel and maintaining the extra subchannel allocation to the invalid signal (signal indicating non-permission) generating unit 15-3 The allocation maintenance control unit 15-2, the Invalid signal (signal indicating non-permission) generation unit 15-3 that generates an Invalid signal (signal indicating non-permission) in the V field of the PHY frame of the extra subchannel, and the storage unit 16 from the user QoS class acquisition unit 15-4 for acquiring information related to the QoS class of

In the communication system according to the embodiment of the present invention, whether to continue the subchannel connection is determined based on the QoS information of the terminal with a difference in the degree of occupation of the extra subchannel (ESCH). Make a decision.
Thereby, the throughput according to the QoS information can be provided to the user.

  Note that QoS (Quality of Service) is a function that reserves a band for a specific communication on a network and guarantees transmission quality so that data is not interrupted.

The QoS classes included in the QoS information are classified according to the communication priority, and can be classified into, for example, three types of streaming, file transfer, and best effort. Streaming is a class in which communication delay or stop is not allowed, such as real-time delivery of voice and moving images and videophones, and class 1 is the highest priority.
The file transfer is a class that requires a certain amount of bandwidth for an electronic file, and is a class 2 that has a lower priority than streaming.
The best effort is a class that does not guarantee QoS, and class 3 has the lowest priority.

  An extra subchannel allocation maintenance flow in the base station of the OFDMA communication system according to the embodiment of the present invention will be described.

FIG. 3 is a diagram showing an extra subchannel allocation maintenance flow in the base station of the communication system according to the embodiment of the present invention.
・ Start allocation maintenance flow.
The QoS class acquisition unit 15-4 of the base station 1 acquires information related to the user's QoS class from the storage unit 16 (step S1).
-The control part 15 sets a communication band according to the acquired QoS class (step S2). For example, when classified into the three types of classes (classes 1 to 3), the communication band assigned to class 1 having the highest priority is set to the widest band. Next, class 2 with the highest priority sets the communication band to be allocated to a medium band. The communication band assigned to class 3 having the lowest priority is set to the narrowest band.
The ESCH setting unit 15-1 sets the allocation for each terminal of the extra subchannel (ESCH) used in communication and establishes communication (step S3).
The ESCH allocation maintenance control unit 15-2 determines whether there is transmission data in each extra subchannel used in communication between the base station and the terminal (step S4), and determines that there is transmission data. In the case of the extra subchannel (Y in step S4), data transmission is continued as it is (step S5).
In the case of an extra subchannel with no transmission data (N in step S4), the ESCH allocation maintenance control unit 15-2 determines whether or not to start maintaining the allocation of the extra subchannel (step S6), and maintains the allocation. Is determined not to start, the ESCH setting unit 15-1 is instructed to release the extra subchannel (step S8), and the allocation maintenance flow ends.
If it is determined to start the allocation maintenance (Y in Step S6), the Invalid signal (signal indicating non-permission) is instructed to the generation unit 15-3, and the Invalid signal (represents non-permission) in the V field of the PHY frame. By transmitting the signal), transmission of the extra subchannel of empty data is continued (allocation is maintained). The control unit 15 determines whether or not a predetermined allocation maintenance time has elapsed (step S7), and when the allocation maintenance time has elapsed (Y in step S7), returns to the process of step S4.
Whether the extra subchannel with no transmission data is released or the allocation is maintained is determined according to the QoS class, the number of extra subchannels to be released and the number of extra subchannels to be allocated and maintained. For example, when classified into the above three classes (classes 1 to 3), class 1 does not release extra subchannels at all, class 2 releases half extra subchannels, and class 3 does 1/4 extra subchannels. For example, the channel is released.
Also, when maintaining the allocation of the extra subchannel, the allocation maintaining time is changed according to the QoS class. For example, when classifying into the above three types of classes (classes 1 to 3), t1> t2 where t1 is an assignment maintenance time of class 1, t2 is an assignment maintenance time of class 2, and t3 is an assignment maintenance time of class 3. It is assumed that a predetermined allocation maintenance time satisfying> t3 is allocated.
The released subchannel is preferably assigned to the extra subchannel without being assigned to the anchor subchannel of another terminal. This is because when assigned to the anchor subchannel of another terminal, even if the transmission data amount of the other terminal decreases, the anchor subchannel is not released until the communication connection is completed, but if it is an extra subchannel, This is because it may be released.

The communication method according to the embodiment of the present invention is a case where QoS is considered, and will be described in detail using a sequence of communication procedures between the terminal and the base station shown in FIG.
It is divided into the types of subchannels (control channel (CCH), anchor subchannel (ASCH) and extra subchannel (ESCH) constituting the communication channel (TCH)) that are communicated in the terminal (PS) and the base station (CS). It is a thing.

  This communication method keeps sending a signal from the base station to the terminal for a certain period of time even if the user data temporarily decreases, so that the base station does not allocate an extra subchannel (ESCH) to other terminals. As shown in FIG. 5, by continuing to transmit the downlink (link from the base station to the terminal), the terminal recognizes that the extra subchannel has already been allocated, and does not allocate it to other terminals.

FIG. 4 shows from communication start (terminal-base station connection) to communication end (terminal-base station release).
(1-1) Connection procedure
At the time of connection, the connection is made according to the same procedure as the existing PHS system.
A link channel (LCH) establishment (determined) is transmitted from the terminal to the base station through the control channel (CCH).
-Carry out carrier sense at the base station.
A link channel (LCH) assignment (allocation) is transmitted from the base station to the terminal through the control channel (CCH).
-Carry out carrier sense at the terminal.
As described above, prior to anchor subchannel (ASCH) connection, carrier sense is always executed by both the base station and the terminal. Thereby, it can be used for stable band control.

(1-2) Extra subchannel assignment and communication establishment
When an unused subchannel is assigned as an extra subchannel (ESCH) in the terminal, carrier sense is performed.
A ranging request (bandwidth setting request) is transmitted from the terminal to the base station using the anchor subchannel (ASCH) in the RCH field.
Such an extra subchannel (ESCH) request / assignment is transmitted via an anchor subchannel (ASCH).
-Carry out carrier sense at the base station.
A ranging response (band setting) is transmitted from the base station to the terminal using an anchor subchannel (ASCH) in the MAP field.
Start user data transmission / reception between the base station and the terminal.
A ranging request (bandwidth setting request) is transmitted from the terminal to the base station using the anchor subchannel (ASCH) in the RCH field.
-Carry out carrier sense at the base station.
When an extra subchannel (ESCH) is added, a subchannel that is not used by the terminal is assigned as an extra subchannel (ESCH), so carrier sense is performed.

(1-3) Extra subchannel (ESCH) allocation maintenance-A ranging response (band setting) is transmitted from the base station to the terminal through the anchor subchannel (ASCH) in the MAP field.
-User data is transmitted and received between the base station and the terminal.
When communication data decreases while transmitting / receiving user data, “Invalid”, which is a signal indicating non-permission, is placed in the V field of the anchor subchannel and is continuously transmitted from the terminal to the base station (communication continuation). ). At this time, the allocation is continuously maintained without releasing the extra subchannel (ESCH).
At this time, the number of extra subchannels to be released and the number of extra subchannels to be allocated are determined in accordance with the QoS class. Also, when maintaining the allocation of the extra subchannel, the allocation maintaining time is changed according to the QoS class.
When the data increases again, user data is transmitted using the extra subchannel (ESCH) that keeps maintaining the allocation without releasing the above-mentioned.

(1-4) Communication end
A communication channel (TCH) release request is made from the base station to the terminal through the control channel (CCH).
The call is disconnected and communication is terminated.

Next, as a comparative example, a sequence of an OFDMA communication method when QoS is not considered will be described.
FIG. 6 is an explanatory diagram showing a flow from communication start (terminal-base station connection) to communication end (terminal-base station release) when communication is performed without considering QoS.

(2-1) Connection procedure
At the time of connection, the connection is made according to the same procedure as the existing PHS system.
A link channel (LCH) establishment (determined) is transmitted from the terminal to the base station through the control channel (CCH).
-Carry out carrier sense at the base station.
A link channel (LCH) assignment (allocation) is transmitted from the base station to the terminal through the control channel (CCH).
-Carry out carrier sense at the terminal.

  As described above, prior to anchor subchannel (ASCH) connection, carrier sense is always executed by both the base station and the terminal. Thereby, it can be used for stable band control.

(2-2) Extra subchannel assignment and communication establishment
A ranging request (bandwidth setting request) is transmitted from the terminal to the base station using the anchor subchannel (ASCH) in the RCH field.
Band setting, that is, an extra subchannel (ESCH) request / allocation is transmitted through an anchor subchannel (ASCH).
-Carry out carrier sense of the anchor subchannel (ASCH) of the base station.
A ranging response (band setting) is transmitted from the base station to the terminal using an anchor subchannel (ASCH) in the MAP field.
-User data is transmitted and received between the base station and the terminal.
A ranging request (bandwidth setting request) is transmitted from the terminal to the base station using the anchor subchannel (ASCH) in the RCH field.
-Carry out carrier sense of the anchor subchannel (ASCH) of the base station.
A ranging response (band setting) is transmitted from the base station to the terminal using an anchor subchannel (ASCH) in the MAP field.
-User data is transmitted and received between the base station and the terminal.

(2-3) Extra subchannel (ESCH) release
The base station notifies the terminal that the extra subchannel (ESCH) has been released by the MAP of the anchor subchannel (ASCH). At this time, the terminal does not continue downlink transmission (from the base station to the terminal) on the opened extra subchannel (ESCH).
-User data is transmitted and received between the base station and the terminal.
A ranging request (bandwidth setting request) is transmitted from the terminal to the base station using the anchor subchannel (ASCH) in the RCH field.
Even when an extra subchannel (ESCH) once released is allocated based on a bandwidth extension request, an unused subchannel is allocated as an extra subchannel in the base station, so that the anchor subchannel (ASCH) of the base station Perform career sense.

As described above, when communication is performed without considering QoS, carrier sense is required when an extra subchannel (ESCH) is added.
A ranging response (band setting) is transmitted from the base station to the terminal using an anchor subchannel (ASCH) in the MAP field.
-User data is transmitted and received between the base station and the terminal.

(2-4) Communication end
A communication channel (TCH) release request is made from the base station to the terminal through the control channel (CCH).
・ Call is disconnected and communication is terminated.

  As described above, according to the present invention, when the amount of communication data decreases between a base station and a terminal with which communication is established, at least one of a plurality of subchannels is not released. Since the assignment is maintained and not assigned to other terminals, the communication throughput is not reduced when the communication of the terminal increases again. Further, the QoS service can be provided to the user terminal by changing the number of subchannels for which the allocation is maintained and the time for maintaining the subchannels according to the QoS class.

It is explanatory drawing which shows the frame structure of OFDMA used for the communication method which concerns on embodiment of this invention. It is a block diagram of the base station of the communication system which concerns on embodiment of this invention. It is a figure which shows the allocation maintenance flow of the extra subchannel in the base station of the communication system which concerns on embodiment of this invention. It is a sequence diagram in the communication system which concerns on embodiment of this invention. FIG. 5 is a diagram illustrating an allocation time for extra subchannel allocation in the sequence of FIG. 4. It is a sequence diagram of the communication method when not considering QoS. It is a block diagram which shows the structure of the OFDM modulation apparatus used for the conventional transmission side. It is explanatory drawing which shows a guard interval. It is a block diagram which shows the structure of the OFDM modulation apparatus used for the conventional receiving side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base station 11 Wireless communication part 12 Signal processing part 13 Modem / Demodulation part 14 External I / F part 15 Control part 15-1 ESCH (extra subchannel) setting part 15-2 ESCH (extra subchannel) allocation maintenance control part 15-3 Invalid signal (signal indicating non-permission) generation unit 15-4 QoS class acquisition unit 16 storage unit

Claims (9)

Communication between a base station and a plurality of terminals using a communication subchannel that performs data communication using one or a plurality of subchannels, and a notification subchannel that notifies the terminal of information related to the communication subchannels In an OFDMA communication system to perform,
Communication data amount acquisition means for acquiring a data amount of data communication performed by the communication subchannel; channel assignment means for assigning the communication subchannel according to the communication data amount;
With
The channel allocation means includes
A communication system, wherein when the amount of communication data decreases, the number of the allocated communication subchannels to be opened varies according to priority. The channel allocation means includes
The communication system according to claim 1, wherein when the communication subchannel is released, the subchannel is not assigned to the notification subchannel. The channel allocation means includes
The communication system according to claim 1 or 2, wherein, when the communication subchannel is released, the subchannel is assigned again as a communication subchannel. The communication system according to any one of claims 1 to 3, wherein the priority is a QoS class. An OFDMA scheme in which communication is performed using a communication subchannel that performs data communication with a plurality of terminals using one or a plurality of subchannels, and a notification subchannel that notifies the terminal of information related to the communication subchannels. In the base station
Communication data amount acquisition means for acquiring a data amount of data communication performed by the communication subchannel; channel assignment means for assigning the communication subchannel according to the communication data amount;
With
The channel allocation means includes
When the amount of communication data is reduced, in accordance with the priority, the base station characterized by varying the number of opening the communication sub-channel allocated. The base station according to claim 5, wherein, when the communication subchannel is released, the channel allocation means does not allocate the subchannel to the notification subchannel. The base station according to claim 5 or 6, wherein, when the communication subchannel is released, the channel allocation means allocates the subchannel again as a communication subchannel. The base station according to claim 5, wherein the priority is a QoS class. Communication is performed between a base station and a plurality of terminals using a communication subchannel that performs data communication using one or a plurality of subchannels, and a notification subchannel that notifies the terminal of information related to the communication subchannels. In the communication method in the OFDMA system,
A communication data amount acquisition step of acquiring a data amount of data communication performed by the communication subchannel;
A channel allocation step of allocating the communication subchannel according to the communication data amount;
Including
The channel allocation step includes:
Communication method the amount of communication data when reduced, in accordance with the priority, and wherein varying the number of opening the communication sub-channel allocated.

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