JP2009206551A - Base station device, and channel determination method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a base station device and a channel determination method which are capable of improving the communication quality of spatially multiplexed communication. <P>SOLUTION: A base station 12 employing a space division multiple access system includes: a carrier sense control part 38 which stops transmission of a communication signal to at least a part of mobile stations communicating with the base station 12, for a prescribed period and controls a radio part 22 and a disturbance wave level measurement part 30 so as to measure disturbance wave levels in communication channels assigned to the mobile stations for this transmission stop period; and a multiplexed channel determination part 40 which determines a communication channel for use in spatially multiplexed communication out of a plurality of communication channels on the basis of the measurement result. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a base station apparatus and a channel determination method, and more particularly to a mobile communication system employing a space division multiple access scheme.

  In a mobile communication system that employs a space division multiple access (SDMA) system, the number of users per base station can be obtained by sharing one communication channel with two or more mobile stations that can be spatially separated. Can be increased. On the other hand, this system has a problem that the communication quality tends to become unstable as compared with the case where one mobile station occupies one communication channel.

In a conventional mobile communication system, a mobile station requesting connection starts spatial multiplexing communication using the communication channel only when it is confirmed by carrier sense that no interference wave is detected on the communication channel notified from the base station. Like to do. Further, in Patent Document 1, in order to increase the success rate of the carrier sense executed by a mobile station requesting connection, a communication signal is transmitted to a mobile station already communicating on a communication channel for which spatial multiplexing communication is scheduled. A base station that transmits intermittently is disclosed.
JP 2007-180856 A

  Currently, it is desired to improve communication quality in a mobile communication system employing a space division multiple access method.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a base station apparatus and a channel determination method capable of improving the communication quality of spatial multiplexing communication.

  In order to solve the above problems, a base station apparatus according to the present invention is a base station apparatus that performs spatial multiplexing communication with two or more mobile station apparatuses using any one of a plurality of communication channels, A transmission stop means for stopping transmission of a communication signal to at least a part of mobile station apparatuses communicating with a base station apparatus for a predetermined period, and while transmission of the communication signal is stopped by the transmission stop means, Carrier sense means for measuring the interference wave level in communication channels assigned to some mobile station apparatuses, and used for the spatial multiplexing communication from among the plurality of communication channels based on the measurement result by the carrier sense means And multi-channel determining means for determining a communication channel to be performed.

  According to the present invention, the base station apparatus temporarily stops transmission of a communication signal to at least a part of the mobile station apparatus with which it is communicating, and in the meantime, the interference wave level in the communication channel assigned to the mobile station apparatus Is measured by carrier sense. And based on the measurement result, the communication channel used for spatial multiplexing communication is determined. That is, carrier sense is also performed in the communication channel used for communication. For this reason, it becomes possible to allocate a communication channel with few interference waves to the spatial multiplexing communication, and the communication quality of the spatial multiplexing communication can be improved.

  Also, in one aspect of the present invention, the transmission stop instruction means may at least partly communicate with the mobile station apparatus before starting the spatial multiplexing communication in response to a connection request from a new mobile station apparatus. The transmission of the communication signal is stopped for a predetermined period, and the multi-channel determining means determines a communication channel to be used for the spatial multiplexing communication from among the communication channels allocated to the at least some mobile station apparatuses.

  According to this aspect, the result of carrier sense in the communication channel used for communication can be acquired immediately before starting spatial multiplexing communication. For this reason, it is possible to accurately identify a communication channel with few interference waves and assign it to spatial multiplexing communication.

  Further, in this aspect, before starting the spatial multiplexing communication in response to a connection request from the new mobile station device, based on the quality of the signal received on the communication channel used for communication, It further includes a multiplex candidate channel selection means for selecting a communication channel candidate to be used for the spatial multiplex communication, and the transmission stop instruction means is communicating using the communication channel selected by the multiplex candidate channel selection means. The transmission of the communication signal to the station apparatus may be stopped for a predetermined period, and the multiple channel determination unit may determine a communication channel to be used for the spatial multiplexing communication from among the communication channels selected by the multiple candidate channel selection unit. .

  By doing so, the number of mobile station devices that the base station device stops transmitting communication signals for carrier sensing is reduced as compared to the case where carrier sensing is performed on all communication channels used for communication. Can be suppressed.

  In one aspect of the present invention, the transmission stopping unit stops transmission of a communication signal to at least a part of the communicating mobile station apparatus for a predetermined period at a predetermined cycle.

  According to this aspect, the result of carrier sense in the communication channel used for communication can be updated at a predetermined cycle.

  A channel determination method in a base station apparatus that performs spatial multiplexing communication with two or more mobile station apparatuses using any one of a plurality of communication channels according to the present invention, comprising: communicating with the base station apparatus; A step of stopping transmission of a communication signal to at least a part of the mobile station apparatuses being in a predetermined period, and a communication channel assigned to the at least some mobile station apparatuses while the transmission of the communication signal is stopped A step of measuring an interference wave level, and a step of determining a communication channel to be used for the spatial multiplexing communication from the plurality of communication channels based on a measurement result by the carrier sense.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an overall configuration diagram of a mobile communication system 10 according to an embodiment of the present invention. As shown in the figure, the mobile communication system 10 includes a base station 12 and a plurality of mobile stations 14 (here, three).

  The base station 12 performs multiplex radio communication with a plurality of mobile stations 14 by a TDMA / TDD (Time Division Multiple Access / Time Division Duplex) method. As shown in FIG. 2, each time frame (TDMA frame) according to the TDMA / TDD system includes four time slots and uplink (mobile station 14) for the downlink (radio transmission path from the base station 12 to the mobile station 14). 4 time slots for a radio transmission path from the base station 12 to the base station 12, that is, four time slots for transmission and reception (a total of 8 time slots). A communication channel used for communication between the base station 12 and each mobile station 14 is specified by a combination of a transmission / reception pair of time slots and one of a plurality of predetermined carrier frequencies.

  In addition, the base station 12 includes an adaptive array antenna. Using this adaptive array antenna, two or more mobile stations 14 for each communication channel and multiple radios based on a space division multiple access (SDMA) system. Communicate. That is, the base station 12 can perform radio communication simultaneously with each of the eight or more mobile stations 14 by using both the TDMA / TDD scheme and the SDMA scheme.

  The mobile station 14 is, for example, a portable mobile phone, a portable information terminal, or a communication card. When starting mobile communication with the base station 12, the mobile station 14 transmits a link channel establishment request (connection request) to the base station 12. Then, the mobile station 14 performs wireless communication with the base station 12 using the communication channel notified from the base station 12 in response to the link channel establishment request.

  When the base station 12 receives a link channel establishment request from the mobile station 14, if there is an empty slot in the base station 12 that is not used for communication among the four pairs of transmission and reception time slots, one of the empty slots is selected. A communication channel corresponding to is notified from the base station 12 to the mobile station 14. On the other hand, if there is no empty slot in the base station 12 (or if the empty slot cannot be used for some reason), a communication channel corresponding to one of the communication slots used for communication is transmitted from the base station 12 to the mobile station. 14 and the spatial multiplexing communication is started in the communication channel.

  In particular, in the mobile communication system 10, the base station 12 temporarily stops transmission of communication signals to the mobile station 14 with which it is communicating, and measures the interference wave level in the communication channel assigned to the mobile station 14 during that time. . Then, based on the measurement result, the base station 12 allocates a communication channel with less interference wave to the spatial multiplexing communication. Thereby, spatial multiplexing communication with stable communication quality is realized.

  Below, the structure and function with which the base station 12 is provided in order to implement | achieve the said process are demonstrated in detail.

  FIG. 3 is a functional block diagram of the base station 12. As shown in the figure, the base station 12 includes antenna elements 20-1 to 20-n, a radio unit 22, a signal processing unit 24 (a spatial multiplexing processing unit 26, a received signal quality acquisition unit 28, an interference wave level measurement unit 30). ), A baseband unit 32, a control unit 34 (multiplex candidate channel selection unit 36, carrier sense control unit 38, multiple channel determination unit 40), and a storage unit 42.

  The antenna elements 20-1 to 20-n constitute an adaptive array antenna. For each reception slot, each antenna element 20 receives a radio signal transmitted from each mobile station 14 to which a communication channel corresponding to the reception slot is assigned, and outputs the received radio signal to the radio unit 22. For each transmission slot, a radio signal supplied from the radio unit 22 is radiated to each mobile station 14 to which a communication channel corresponding to the transmission slot is assigned. Note that transmission / reception of radio signals is switched in a time-sharing manner in accordance with instructions from the radio unit 22.

  The radio unit 22 includes a low noise amplifier, a power amplifier, a band pass filter, and a mixer. The radio unit 22 down-converts the radio signal received by each antenna element 20 into an intermediate frequency signal, and outputs the intermediate frequency signal to the signal processing unit 24. Further, the signal input from the signal processing unit 24 is up-converted into a radio signal, and the radio signal is amplified to a transmission output level and supplied to each antenna element 20.

  The signal processing unit 24 includes, for example, a DSP (Digital Signal Processor) and a memory, and is realized by the DSP executing a program stored in the memory. The spatial multiplexing processing unit 26, the received signal quality acquisition unit 28, And an interference wave level measuring unit 30 functionally.

  The spatial multiplexing processing unit 26 controls the directivity pattern of the adaptive array antenna in order to realize multiplex communication using the SDMA scheme. That is, the spatial multiplexing processing unit 26, for each reception slot, a known signal (for example, a 16-bit unique word) notified to each mobile station 14 at the time of link channel establishment response and an intermediate frequency signal input from the radio unit 22 Known weights so as to minimize an error between the sum of values obtained by multiplying the head portion (portion including a known signal) by the weight of each antenna element 20 (weight coefficient including phase information and amplitude information). The optimum weight of each antenna element 20 is determined based on an arithmetic algorithm (for example, Minimum Mean Square Error (MMSE)). Then, the spatial multiplexing processing unit 26 separates and extracts the communication signal of each mobile station 14 spatially multiplexed from the intermediate frequency signal input from the radio unit 22, and the baseband unit extracts the extracted communication signal of each mobile station 14. 32. On the other hand, the spatial multiplexing processing unit 26 transmits to each mobile station 14 input from the baseband unit 32 based on the weight of each antenna element 20 determined in the immediately preceding reception slot corresponding to the transmission slot. Are weighted and output to the radio unit 22.

  The reception signal quality acquisition unit 28 acquires, for each reception slot, the quality of the communication signal of each mobile station 14 received in the reception slot (hereinafter referred to as “reception signal quality”). The reception signal quality is an index indicating the extraction accuracy when the communication signal of each mobile station 14 is extracted from the radio signal received in the reception slot. Here, the received signal quality acquisition unit 28, based on a known algorithm, the amount of change in weight between the communication signal received in the slot prior to the reception slot and the communication signal received in the reception slot. Is acquired as the received signal quality. It should be noted that the amount of fluctuation of the weight is affected by, for example, the amount of phase rotation of the symbol and the amount of fluctuation of power (see FIG. 4).

  The symbol phase rotation amount and the symbol power fluctuation amount change due to fading in the radio propagation path. For example, if fading is strong in a certain communication channel, the amount of symbol phase rotation and the amount of fluctuation in symbol power between the leading portion and trailing portion of the communication signal received on that communication channel increase. In this case, when the weight of each antenna element 20 determined based on the head part of the intermediate frequency signal input from the radio unit 22 is applied to the rear part, the communication signal of each mobile station 14 is received from the received radio signal. The extraction accuracy at the time of extracting is reduced. On the contrary, if fading is weak, the symbol phase rotation amount and the symbol power fluctuation amount become small, and the communication signal extraction accuracy is also improved.

  As a method by which the received signal quality acquisition unit 28 obtains the index, the value resulting from the fading frequency in the communication signal of each mobile station 14 is acquired as described above.

  In addition to the above-described values resulting from the fading frequency, the power difference between the mobile stations 14 having a spatial multiplexing relationship may be used as a value to obtain a certain degree of effect, and may be within a predetermined range.

  Alternatively, the spatial correlation value between the mobile stations 14 having a spatial multiplexing relationship may be used as an index, and may be within a predetermined range with 1 as the center.

  Alternatively, the signal from the mobile station 14 may be received continuously by a predetermined number using the predetermined number of frames as an index.

  In addition, the signal of the mobile station 14 may be received within the range using the fluctuation time range of a predetermined timing as an index.

  Further, it may be based on the fact that the absolute value of RSSI (Receive Signal Strength Indication) is sufficiently high.

  Further, the determination may be made by combining a plurality of these indexes.

  The interference wave level measurement unit 30 measures the intensity (interference wave level) of an interference wave signal detected by carrier sense described later, and stores the measurement result in the storage unit 42. For example, as shown in FIG. 5, the interference wave level measurement unit 30 stores the intensity of the interference wave signal detected in the communication channel in the storage unit 42 in association with the channel identification number for identifying the communication channel.

  The baseband unit 32 includes an A / D converter, a D / A converter, a local oscillation circuit, a demodulation circuit, and a modulation circuit. The baseband unit 32 demodulates the baseband signal (received data) from the communication signal of each mobile station 14 input from the signal processing unit 24, and transmits the obtained baseband signal to another base via a communication network (not shown). Transmit to station 12. Further, an intermediate frequency signal generated by the local oscillation circuit is modulated with a baseband signal (transmission data) received from another base station 12 via a communication network, and the obtained modulated signal is output to the signal processing unit 24. To do.

  The control unit 34 includes, for example, a CPU and a memory, and has a function of controlling each unit of the base station 12 when the CPU executes a program stored in the memory. In particular, the control unit 34 functionally includes a multiple candidate channel selection unit 36, a carrier sense control unit 38, and a multiple channel determination unit 40.

  In response to a link channel establishment request from a new mobile station 14, the multiplex candidate channel selection unit 36 receives the received signal quality (received signal quality acquired by the received signal quality acquisition unit 28 before starting spatial multiplexing communication with the mobile station 14). Based on the symbol phase rotation amount and symbol power fluctuation amount shown in FIG. 4, a communication channel candidate (hereinafter referred to as “multiplex candidate channel”) multiplexing to be used for spatial multiplexing communication is selected. Here, the multiplex candidate channel selection unit 36 may select a communication channel in which at least one of the symbol phase rotation amount and the symbol power fluctuation amount acquired by the received signal quality acquisition unit 28 is a predetermined amount or less as a multiplex candidate channel. Good. This is because a communication channel used for spatial multiplexing communication has a complicated directivity pattern control and inevitably deteriorates the received signal quality. Therefore, a communication channel with the best received signal quality is selected as a multiplex candidate channel. This is because it is desirable.

  In response to the link channel establishment request from the mobile station 14, the carrier sense control unit 38 and the radio unit 22 measure the interference wave level so as to perform carrier sense in the transmission slot of the multiple candidate channel selected by the multiple candidate channel selection unit 36. The unit 30 is controlled. That is, the carrier sense control unit 38 controls the radio unit 22 so as to stop transmission of a communication signal to the mobile station 14 that is communicating using multiple candidate channels for a predetermined period (for example, 1 to 3 frames). Then, while transmission of the communication signal is stopped, the carrier sense control unit 38 detects the interference wave signal in the multiplex candidate channel and wirelessly detects the intensity (interference wave level) of the detected interference wave signal. The unit 22 and the interference wave level measurement unit 30 are controlled.

  It should be noted that the carrier sense control unit 38 is a communication signal for at least a part of the mobile station 14 that is communicating at a predetermined period (for example, every few minutes) regardless of whether or not the link channel establishment request is received from the mobile station 14. The radio unit 22 and the jamming wave level measurement unit 30 may be controlled so as to measure the jamming wave levels in the communication channels assigned to the mobile stations 14 during the predetermined period (see FIG. 8). reference). In addition, the carrier sense control unit 38 may control the radio unit 22 and the interference wave level measurement unit 30 so as to measure the interference wave level in an empty slot that is not used for communication as needed.

  Based on the measurement result (see FIG. 5) by the interference wave level measurement unit 30, the multiplex channel determination unit 40 uses a communication channel (used for spatial multiplexing communication from among the multiplex candidate channels selected by the multiplex candidate channel selection unit 36). (Hereinafter referred to as “spatial multiplexed channel”). For example, the multiplex channel determination unit 40 may determine the communication channel having the lowest interference wave level among the multiplex candidate channels as the spatial multiplex channel. In this way, since the communication channel with the least interference wave is assigned to the spatial multiplexing communication, the communication quality of the spatial multiplexing communication can be improved.

  The storage unit 42 is composed of a memory element and stores the interference wave level of each communication channel as described above.

  Next, processing in which the base station 12 allocates a spatial multiplexing channel to the mobile station 14 will be described.

  FIG. 6 is a sequence diagram showing a first spatial multiplexing channel assignment process in the mobile communication system 10. Here, for the base station 12 that is communicating with each of four mobile stations 14 (mobile station 14-2 and mobile stations 14-3 to 14-5 not shown) using four communication channels, A case where the mobile station 14-1 requests a new connection will be described as an example.

  As shown in the figure, when the mobile station 14-1 transmits a link channel establishment request to the base station 12 (S100), the base station 12 receives received signal qualities in each of the four communication channels used for communication. (Symbol phase rotation amount, symbol power fluctuation amount) is acquired (S102). Then, the base station 12 selects a communication channel whose received signal quality is equal to or higher than a predetermined quality (at least one of the symbol phase rotation amount and the symbol power fluctuation amount is a predetermined amount or less) as a multiplex candidate channel (S104).

  Next, in order to perform carrier sense in the multiplex candidate channel selected in S104, the base station 12 communicates with the mobile station 14 (here, illustrated as the mobile station 14-2) using the multiplex candidate channel. Transmission of the communication signal to the mobile station 14-3 not to perform (S106), and carrier sense is performed in the multiplex candidate channel (S108). After the completion of the carrier sense, the base station 12 resumes the transmission of the communication signal stopped in S106 (S110).

  Then, based on the carrier sense result obtained in S108, the base station 12 determines the communication channel with the lowest interference wave level among the multiple candidate channels (here, the communication channel assigned to the mobile station 14-2) Is determined as a spatial multiplexing channel (S112). The spatial multiplexing channel determined in this manner is notified from the base station 12 to the mobile station 14-1 by a link channel establishment response together with a unique word which is a known signal (S114), and spatial multiplexing communication is started in the spatial multiplexing channel ( S116).

  FIG. 7 is a sequence diagram showing a second spatial multiplexing channel assignment process in the mobile communication system 10. Again, for base stations 12 communicating with four mobile stations 14 (mobile station 14-2 and mobile stations 14-3 to 14-5 not shown) using four communication channels, respectively. A case where the mobile station 14-1 requests a new connection will be described as an example.

  As shown in the figure, when the mobile station 14-1 transmits a link channel establishment request to the base station 12 (S200), the base station 12 receives received signal quality in each of the four communication channels used for communication. (Symbol phase rotation amount, symbol power fluctuation amount) is acquired (S202). Then, the base station 12 selects a communication channel whose received signal quality is equal to or higher than a predetermined quality (at least one of the symbol phase rotation amount and the symbol power fluctuation amount is a predetermined amount or less) as a multiplex candidate channel (S204).

  Next, a carrier sense result (described later) acquired in advance is referred to (S206). Based on the carrier sense result, a communication channel having the lowest interference wave level among the multiple candidate channels selected in S204 (here) Then, the communication channel assigned to the mobile station 14-2 is determined as a spatial multiplexing channel (S208). The spatial multiplexing channel determined in this manner is notified from the base station 12 to the mobile station 14-1 by a link channel establishment response together with a unique word that is a known signal (S210), and spatial multiplexing communication is started in the spatial multiplexing channel ( S212).

  FIG. 8 is a flowchart showing carrier sense processing executed at a predetermined cycle in the base station 12. Here, it is assumed that this process is executed when all four communication channels are used for communication.

  As shown in the figure, the base station 12 resets a timer for managing the execution timing of carrier sense (S300). Then, when a predetermined time (for example, 30 seconds) elapses after the timer reset in S300 (S302: Y), the base station 12 stops transmission of communication signals to all or a part of the mobile stations 14 in communication (S304). ), Carrier sense is performed in the communication channel in which transmission of the communication signal is stopped (S306). After the completion of the carrier sense, the base station 12 stores the carrier sense result in the storage unit 42 (S308), and resumes the transmission of the communication signal stopped in S304 (S310). Then, the base station 12 repeatedly executes the processes after S300 until an empty slot is formed (S312: N), and ends this process when an empty slot is formed (S312: Y).

  According to the mobile communication system 10 described above, the base station 12 temporarily stops transmission of communication signals to the mobile station 14 with which it is communicating, and in the meantime, the interference wave in the communication channel assigned to the mobile station 14 Measure the level. Then, based on the measurement result, the base station 12 allocates a communication channel with less interference wave to the spatial multiplexing communication. For this reason, the communication quality of spatial multiplexing communication can be improved.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the present invention is applied to a mobile communication system using both the TDMA / TDD scheme and the SDMA scheme, but the present invention is applicable to all mobile communication systems employing the SDMA scheme.

1 is an overall configuration diagram of a mobile communication system according to an embodiment of the present invention. It is a figure which shows the structure of the TDMA frame which concerns on embodiment of this invention. It is a functional block diagram of the base station which concerns on embodiment of this invention. It is a figure which shows an example of the received signal quality in each communication channel. It is a figure which shows an example of the jamming wave level of each communication channel memorize | stored in a memory | storage part. It is a sequence diagram which shows the 1st multiple channel allocation process which concerns on embodiment of this invention. It is a sequence diagram which shows the 2nd multiple channel allocation process which concerns on embodiment of this invention. It is a flowchart which shows the carrier sense process performed in the predetermined period in the base station which concerns on embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Mobile communication system, 12 Base station, 14 Mobile station, 20 Antenna element (adaptive array antenna), 22 Radio part, 24 Signal processing part, 26 Spatial multiplexing processing part, 28 Received signal quality acquisition part, 30 Interference wave level measurement part 32 baseband unit, 34 control unit, 36 multiplex candidate channel selection unit, 38 carrier sense control unit, 40 multiplex channel determination unit, 42 storage unit.

Claims (5)

A base station device that performs spatial multiplexing communication with two or more mobile station devices using any one of a plurality of communication channels,
Transmission stop means for stopping transmission of a communication signal for at least a part of the mobile station apparatus communicating with the base station apparatus for a predetermined period;
Carrier sensing means for measuring a jamming wave level in a communication channel assigned to at least some of the mobile station devices while transmission of the communication signal is stopped by the transmission stop means;
Multi-channel determining means for determining a communication channel to be used for the spatial multiplexing communication from the plurality of communication channels based on a measurement result by the carrier sense means;
A base station apparatus comprising: The base station apparatus according to claim 1,
The transmission stop instruction means stops a transmission of a communication signal for at least a part of the communicating mobile station apparatus for a predetermined period before starting the spatial multiplexing communication in response to a connection request from a new mobile station apparatus. And
The multi-channel determining means determines a communication channel to be used for the spatial multiplexing communication from among communication channels allocated to the at least some mobile station apparatuses.
A base station apparatus. The base station apparatus according to claim 2,
Before starting the spatial multiplexing communication in response to a connection request from the new mobile station apparatus, use it for the spatial multiplexing communication based on the quality of the signal received on the communication channel used for communication It further includes multiple candidate channel selection means for selecting communication channel candidates,
The transmission stop instruction means stops a transmission of a communication signal for a mobile station apparatus that is communicating using the communication channel selected by the multiple candidate channel selection means for a predetermined period,
The multiplex channel determination means determines a communication channel to be used for the spatial multiplex communication from among the communication channels selected by the multiplex candidate channel selection means.
A base station apparatus. The base station apparatus according to claim 1,
The transmission stop means stops transmission of a communication signal for at least a part of the communicating mobile station apparatus for a predetermined period in a predetermined cycle.
A base station apparatus. A channel determination method in a base station apparatus that performs spatial multiplexing communication with two or more mobile station apparatuses using any one of a plurality of communication channels,
Stopping transmission of communication signals for at least a part of mobile station apparatuses communicating with the base station apparatus for a predetermined period;
Measuring a jamming wave level in a communication channel assigned to the at least some mobile station devices while transmission of the communication signal is stopped;
Determining a communication channel to be used for the spatial multiplexing communication from the plurality of communication channels based on a measurement result by the carrier sense;
A channel determination method comprising:

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