JP2010226398A - Radio communication system, radio receiver and radio communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate complication due to the use of different systems in the system of selecting one optimum system from different radio systems, to reduce the influence of frequency selective fading and to perform selection and determination in a low layer without depending on a radio system as much as possible. <P>SOLUTION: The radio receiver applied to the radio communication system for selecting one of two or more kinds of OFDM communication systems and performing radio communication includes: OFDM demodulation parts 5-3(A-Z) for demodulating OFDM signals including a function (hereafter called a high autocorrelation function) highly autocorrelated to a predetermined frequency sub channel received from a radio transmitter; correlation ratio calculation parts 5-4(A-Z) for calculating the correlation value of a received high autocorrelation function and a known high autocorrelation function and calculating a correlation ratio indicating a ratio of the correlation value when there is no time difference and the correlation value when there is a time difference for each OFDM communication system; and a selection device 6-2 for selecting the OFDM communication system of the highest correlation ratio. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for performing wireless communication between a wireless transmission device and a wireless reception device by selecting one of a plurality of types of OFDM communication schemes.

  In recent years, it has been proposed to use different wireless systems such as cognitive radio and heterogeneous radio to supplement service areas, improve reliability, and effectively use frequency spectrum. Usually, in one radio system, transmission quality is measured unique to each system, and time and frequency slot switching in the system is performed to improve the utilization efficiency of the system. For example, an RSSI value in WI-LAN and a CINR value in WiMAX correspond to these transmission qualities.

  When one system is selected for a plurality of different systems, it is necessary to convert or replace these system-specific parameters into some uniform parameters and determine the selection. In order to perform this conversion (or replacement), it is necessary to determine the conversion method by performing mathematical formulas or experiments, but since it involves various parameters, it is generally not easy.

  In a broadband wireless communication system covering a wide service area, when the base station and the terminal are out of line of sight, the frequency characteristics of the propagation path are not flat due to interference of delayed waves due to reflection, diffraction, etc. Receive fading. For this reason, OFDM systems are applied to communication systems that are about to be put into practical use recently in consideration of resistance to fading. Also in this system, a radio system selection system that minimizes the influence of fading is desired.

  Patent Document 1 discloses a different system handoff method and a wireless communication terminal. In the technique described in Patent Document 1, in handoff of different wireless systems, the current throughput is compared with the estimated throughput of the handoff destination, and handoff processing is performed when improvement in throughput is expected.

  Patent Document 2 discloses a handoff control system between different types of wireless systems, an edge node used in the system, and a mobile communication terminal device. In the technique described in Patent Document 2, the same information is transmitted from the terminal, and so-called soft handoff is performed. However, there is no description of the criteria for determining switching (or handoff).

  Also, Non-Patent Document 1 discloses a technique for reducing the probability of erroneous detection of a signal, that is, the probability of determining that it does not exist when detecting a weak signal buried in noise. ing. In the method described in Non-Patent Document 1, a signal is detected by autocorrelation using a code sequence called a cyclic autocorrelation function (CAF).

  Non-Patent Document 2 discloses a technique for estimating a frequency characteristic of a propagation path using a preamble signal of an OFDM signal and achieving transmission line equivalence by an inverse function thereof.

JP 2008-270990 A JP 2004-274458 A

Muraoka et al., Spectrum Sensing Based on Maximum Period Autocorrelation Selection in Cognitive Radio (2008 IEICE Communication Society Conference, B-17-2) Takashi Fujimoto, Kanshiro Kashiwagi, Mitsuo Nohara, Kazunori Takeuchi, Takashi Matsumura, “Basic Characteristics of Propagation State Monitoring Device Using Software Defined Radio”, IEICE, IEICE Technical Report, vol. 107, no. 352, SR2007-60, pp. 93-98, November 2007

  Conventional attempts to replenish service areas, improve reliability, and effectively use frequency spectrum by selecting one of a plurality of different wireless systems (a combination of two or more systems is possible). In this case, one of the important consideration items is to speed up the selection and simplify the selection method. Selection methods include parameter monitoring at the physical layer (first layer), parameter monitoring at the MAC layer (second layer), parameter monitoring at the IP layer (third layer), and combinations thereof. . For example, in Patent Document 1, the determination is made based on the throughput. In this case, since the radio systems are different, the selected system is not necessarily optimal, and there is a possibility that it takes time to make a selection decision.

  A method using transmission delay as a criterion is also conceivable, but in that case, there is a possibility that the system or apparatus may be affected as it is. In addition, although a method of performing determination by RSSI or CINR is also conceivable, there is a possibility that the derivation method differs depending on the system. Therefore, it is necessary to perform conversion and replacement so as to unify system parameters and the like, and the examination is not easy, and a correct solution is not always obtained.

  In addition, when performing broadband communication in non-line-of-sight communication, so-called frequency selective fading is received, so that frequency characteristics may appear in transmission characteristics.

  The present invention has been made in view of such circumstances, eliminates the complexity of using different radio systems, further reduces the effects of frequency selective fading, and is a low layer that does not depend on the radio system as much as possible. An object of the present invention is to provide a wireless communication system, a wireless reception device, and a wireless communication method that can perform switching determination at the same time.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, the wireless communication system of the present invention is a wireless communication system that performs wireless communication by selecting any of a plurality of types of OFDM communication schemes between a wireless transmission device and a wireless reception device, and the wireless transmission device Transmits an OFDM signal including a high autocorrelation function (meaning a high autocorrelation function) to a specific frequency subchannel to the radio reception apparatus, and the radio reception apparatus transmits the radio signal for each OFDM communication scheme. OFDM communication with the highest correlation ratio, which shows the ratio between the correlation value when there is no time difference and the correlation value when there is a time difference, by calculating the correlation value between the high autocorrelation function received from the device and the known high autocorrelation function It is characterized by selecting a method.

  Thus, for each OFDM communication system, the correlation value between the high autocorrelation function received from the wireless transmission device and the known high autocorrelation function is calculated, and the correlation value when there is no time difference and the correlation value when there is a time difference Since the OFDM communication scheme having the largest correlation ratio indicating the ratio to the above is selected, parameters for selecting a plurality of different types of wireless systems can be obtained relatively easily, and the reliability of the selection can be improved.

  (2) Further, in the wireless communication system of the present invention, the wireless reception device measures a frequency characteristic in a propagation path of the entire system band, and a frequency characteristic in a propagation path of a specific frequency subchannel including the high autocorrelation function. And the difference between the average value of the frequency characteristics in the propagation path of the entire system band is corrected.

  In this way, the difference between the frequency characteristic in the propagation path of a specific frequency subchannel including a high autocorrelation function and the average value of the frequency characteristic in the propagation path of the entire system band is corrected, so that the frequency including the high autocorrelation function is corrected. It is possible to avoid underestimation or overestimation of the subchannel and reduce the error.

  (3) Further, the wireless reception device of the present invention is a wireless reception device applied to a wireless communication system that performs wireless communication by selecting one of a plurality of types of OFDM communication schemes, and received from the wireless transmission device An OFDM demodulator that demodulates an OFDM signal including a high autocorrelation function in a specific frequency subchannel, a storage unit that stores a known high autocorrelation function, and the received high autocorrelation function for each of the OFDM communication methods, Calculating a correlation value with the known high autocorrelation function, calculating a correlation ratio indicating a ratio between a correlation value when there is no time difference and a correlation value when there is a time difference, and the correlation ratio is And a selection unit that selects the largest OFDM communication system.

  Thus, for each OFDM communication system, the correlation value between the high autocorrelation function received from the wireless transmission device and the known high autocorrelation function is calculated, and the correlation value when there is no time difference and the correlation value when there is a time difference Since the OFDM communication scheme having the largest correlation ratio indicating the ratio to the above is selected, parameters for selecting a plurality of different types of wireless systems can be obtained relatively easily, and the reliability of the selection can be improved.

  (4) In addition, the wireless reception device of the present invention further includes a propagation path characteristic estimation unit that measures frequency characteristics in the propagation path of the entire system band, and the correlation ratio calculation unit includes a specific function including the high autocorrelation function. The correlation ratio is calculated by correcting the difference between the frequency characteristic in the propagation path of the frequency subchannel and the average value of the frequency characteristics in the propagation path of the entire system band, and the selection unit has the largest correlation ratio after the correction. It is characterized by selecting an OFDM communication system.

  In this way, the difference between the frequency characteristic in the propagation path of a specific frequency subchannel including a high autocorrelation function and the average value of the frequency characteristic in the propagation path of the entire system band is corrected, so that the frequency including the high autocorrelation function is corrected. It is possible to avoid underestimation or overestimation of the subchannel and reduce the error.

  (5) Moreover, the wireless communication method of the present invention is a wireless communication method for performing wireless communication by selecting one of a plurality of types of OFDM communication schemes between a wireless transmission device and a wireless reception device, In the wireless transmission device, a step of transmitting an OFDM signal including a high autocorrelation function in a specific frequency subchannel to the wireless reception device; and in the wireless reception device, for each OFDM communication scheme, the high signal received from the wireless transmission device Calculating a correlation value between an autocorrelation function and a known high autocorrelation function, calculating a correlation ratio indicating a ratio between a correlation value when there is no time difference and a correlation value when there is a time difference; and And selecting at least the largest OFDM communication system.

  Thus, for each OFDM communication system, the correlation value between the high autocorrelation function received from the wireless transmission device and the known high autocorrelation function is calculated, and the correlation value when there is no time difference and the correlation value when there is a time difference Since the OFDM communication scheme having the largest correlation ratio indicating the ratio to the above is selected, parameters for selecting a plurality of different types of wireless systems can be obtained relatively easily, and the reliability of the selection can be improved.

  (6) Further, in the wireless communication method of the present invention, in the wireless reception device, a step of measuring frequency characteristics in the propagation path of the entire system band, and a propagation path of a specific frequency subchannel including the high autocorrelation function And a step of correcting a difference between the frequency characteristic and an average value of the frequency characteristic in the propagation path of the entire system band.

  In this way, the difference between the frequency characteristic in the propagation path of a specific frequency subchannel including a high autocorrelation function and the average value of the frequency characteristic in the propagation path of the entire system band is corrected, so that the frequency including the high autocorrelation function is corrected. It is possible to avoid underestimation or overestimation of the subchannel and reduce the error.

  According to the present invention, for each OFDM communication system, a correlation value between a high autocorrelation function received from a wireless transmission device and a known high autocorrelation function is calculated, and when there is a time difference and a correlation value when there is no time difference, Since the OFDM communication method having the largest correlation ratio indicating the ratio to the correlation value is selected, parameters for selecting a plurality of different types of wireless systems can be obtained relatively easily, and the reliability of the selection can be improved. it can.

It is a figure which shows the autocorrelation function of a typical M series with high autocorrelation. It is a figure which shows the concept of the frame structure of OFDM system. It is a figure which shows the calculation part which calculates | requires the correlation value of the received signal of M series in the case of bit difference (tau) = 0 and a known signal on the receiving side. It is a figure which shows the calculation part which calculates | requires the correlation value of the received signal of M series in the case of bit difference (tau) = 1 symbol and a known signal on the receiving side. It is a figure which shows the basic composition of the radio | wireless communications system which concerns on 1st Embodiment. It is a figure which shows the structure of the radio | wireless communications system which concerns on 1st Embodiment. It is a figure which shows the structure of the apparatus which performs propagation path characteristic estimation. It is a figure which shows the concept of the characteristic obtained in the frequency characteristic estimation part of a propagation path. It is a figure which shows the apparatus structure in the case of correct | amending a correlation ratio in consideration of the influence of frequency selective fading. It is a figure which shows schematic structure of the radio | wireless communications system which concerns on 2nd Embodiment.

  The present embodiment is applied to a radio system using an OFDM system such as WiMAX or LTE. In particular, a plurality of existing radio systems are selected and switched to be used in order to effectively use frequencies and to perform highly reliable radio transmission. Provided is a method for making selection determination and selection execution relatively easily without changing the system parameters of an existing system. Embodiments of the present invention will be described below with reference to the drawings.

In the present embodiment, a data sequence having a good autocorrelation characteristic Ra (τ) such as an M sequence is used. The autocorrelation function of the M sequence can be expressed as in Equation (1). That is, in the M sequence m _i (m _i = 1 or −1) with a code length of L, a peak appears when the time difference τ is zero (no time difference) as shown in FIG. 1, and otherwise −1. / L.

信号復調時に相関をとると、式（１）のｍ_ｉのうちの１つは雑音ｎ（ここでは、平均値ゼロの白色ガウス雑音を仮定）を含んだ信号（＝ｍ＋ｎとする）、他の１つは、Ｍ系列に相当する信号で復調側では既知の信号である。従って、この場合、相関関数の符号長Ｌ内で平均値を求めると、τがゼロの場合は、Ｅ［・］をＬ内での時間平均と定義すると、
１＋Ｅ［ｎ］ ：τ＝０ ・・・（２）
また、τがゼロ以外では、
−１／Ｌ＋Ｅ［ｎ］ ：τ＝０以外 ・・・（３）
となる。本実施形態では、式（２）と式（３）との比（あるいは差）を検出し、その比が大きな無線方式を選択する。

Taking a correlation during signal demodulation, one of the m _i in the formula (1) is noise n (here, zero mean white Gaussian noise assumptions) (a = m + n) the signals containing, other One is a signal corresponding to the M sequence, which is a known signal on the demodulation side. Therefore, in this case, when the average value is obtained within the code length L of the correlation function, when τ is zero, if E [•] is defined as the time average within L,
1 + E [n]: τ = 0 (2)
If τ is not zero,
−1 / L + E [n]: other than τ = 0 (3)
It becomes. In the present embodiment, the ratio (or difference) between Expression (2) and Expression (3) is detected, and a radio system having a large ratio is selected.

  Normally, the average value E [n] of noise is zero, but since the average time is finite, it can take a value other than zero. A function such as an M sequence may be referred to as a cyclic autocorrelation function (CAF).

  As described above, in the present embodiment, the degree of the magnitude of the desired signal with respect to noise is calculated using the ratio (or difference, hereinafter referred to as “correlation ratio”) of the values of equations (2) and (3). Can be known about each wireless system. In other words, the average value of the autocorrelation function (τ = 0) obtained by synchronizing the demodulated signal of the M-sequence signal and, for example, when shifted by one symbol (other than τ = 0, it is not necessary to limit to one symbol) The average values of the autocorrelation functions are compared. This is considered to be almost equivalent to the comparison of the SN ratio of the received signal.

  Normally, in a wireless communication system using the OFDM system, adaptive modulation is applied, and the multi-value number of the modulation system (for example, 4 for QPSK, 16 for 16QAM, 64 for 64QAM, etc.) is changed. Since this method is a measurement of the reception performance of the wireless system, the two-phase PSK is preferable as the modulation method so that the discrimination error is reduced. The demodulated signal is preferably soft decision data.

  In the present embodiment, since a reference is provided that enables determination at a lower layer of the wireless system, this method can be applied to different wireless systems as long as the modulation method is the same. Therefore, it has the feature that selection judgment can be made based on the same standard.

  FIG. 2 is a diagram showing a frame structure of the OFDM scheme. As shown in FIG. 2, the OFDM frame includes a preamble section 2-1, a frequency subchannel 2-2, and a time subchannel 2-3. In the present embodiment, it is assumed that an M sequence is included in the frequency subchannel 2-2. The same effect can be obtained even if the M series is included in the time subchannel 2-3.

  The longer the code length of the M sequence is desirable, for example, 1023 bits can be considered. However, if the code length is too long, the number of information bits is reduced. In addition, when the frame length of the radio signal is shorter than the code length, it is desirable to continue to the subsequent frame length so that the characteristics of the high autocorrelation function do not deteriorate. For some reason, when the code length is limited by the frame length, a method using another code with a short code length L can be applied, but the characteristics may deteriorate.

  In addition, although the M sequence is represented here, for example, a Gold code may be used in which the correlation is small when there is a time shift in autocorrelation, even if the M sequence is not used.

  Further, when performing broadband communication in non-line-of-sight communication, so-called frequency selective fading is received, and therefore, when an M sequence is included in a frequency subchannel, frequency characteristics may appear and the characteristics may deteriorate. This patent also has a function of performing correction on the frequency axis assuming such fading.

[First Embodiment]
FIG. 3 is a diagram illustrating a configuration of an M-sequence autocorrelator on the reception side. FIG. 3 shows a case where there is no bit difference (τ = 0). The upper stage 3-1 is the received M series, and the lower stage 3-2 is the M series that is held in advance on the receiving side. The product of each corresponding data is taken by the multiplier 3-3, the sum is calculated by the adder 3-4, and after dividing by L in the divider 3-5, the correlation value is obtained. In this case, if the noise is ignored, the correlation value is “1” as shown in Expression (1).

  FIG. 4 is a diagram illustrating a data configuration in the case of shifting by 1 bit. In FIG. 4, the left end of the known data 3-2 on the receiving side does not contain data (indicated by “−”), but if the code length is sufficiently long (for example, 1023), there is no substantial effect even if ignored. It is not considered. When noise is ignored, the correlation value is “−1 / L” as shown in Equation (1).

  FIG. 5 is a diagram showing a basic configuration of the wireless communication system according to the present embodiment. The OFDM transmitter 5-1 creates an OFDM signal as shown in FIG. 2 and transmits it to the receiving side. The transmission signal is input to the OFDM demodulator 5-3 via the radio propagation path 5-2. The OFDM demodulator 5-3 demodulates the received signal to create soft decision data, and the correlation ratio calculator 5-4 obtains the correlation ratio using the data. The M sequence storage unit 5-5 has the same M sequence as that on the transmission side.

  FIG. 6 is a diagram illustrating a configuration of the wireless communication system according to the present embodiment. The received signal for system A is restored as soft decision data by (OFDM) demodulator 5-3 (AZ), and the correlation ratio is calculated by correlation ratio calculator 5-4 (AZ). The same operation is performed in the systems B, C, etc., and these correlation ratios are compared by the correlation ratio comparison unit 6-1, and the wireless system having the largest correlation ratio is selected. The selection device 6-2 switches to the wireless system selected by the correlation ratio comparison unit 6-1.

  FIG. 7 is a diagram illustrating a configuration of an apparatus that performs channel characteristic estimation. In this device, by extracting the preamble part 2-1 from the signal after passing through the RF part 7-1, the A / D converter 7-2, and the FFT part 7-3 and detecting its amplitude and phase, Estimate propagation path characteristics. The estimated characteristics are usually used to compensate for propagation path distortion in the equivalent section 7-4. In addition, the frequency characteristics (transfer function) of the propagation path can be acquired by reusing the conventional technique (Non-patent Document 1).

FIG. 8 is a diagram illustrating a concept of characteristics obtained by the frequency characteristic estimation unit of the propagation path. A signal transmitted from the transmission side becomes a delayed wave (multipath propagation wave) on the reception side due to reflection or diffraction, so that in the case of a wideband signal, the transmission signal itself becomes interference and causes frequency distortion. In the radio system selection method using the correlation value using the M sequence used in this embodiment, for example, when the frequency subchannel including the M sequence is in the position shown in FIG. May be a small measurement value). Therefore, the error can be reduced by calculating and correcting the average value of the frequency characteristics. That is, using the symbols in FIG.
(Corrected correlation ratio) = (Pave) / (Po) × (measured correlation ratio)
And it is sufficient. The same calculation may be performed in the case of overestimation.

  FIG. 9 is a diagram illustrating a device configuration in the case of correcting the correlation ratio in consideration of the influence of frequency selective fading. In the radio propagation path 5-2, when the transmission side and the reception side are out of line of sight, multipath propagation occurs and frequency selective fading due to delay occurs. For this reason, in this apparatus, it is the structure which added the propagation path characteristic estimation part 7-5 to the structure shown in FIG. The estimated value is input to the correlation ratio calculation unit 5-4, and correction is performed.

[Second Embodiment]
FIG. 10 is a diagram illustrating a schematic configuration of a wireless communication system according to the second embodiment. This radio communication system is based on the configuration shown in FIG. 6 and adopts a configuration in which the influence is reduced in consideration of the influence of frequency selective fading. (OFDM) demodulator 5-3 (AZ) demodulates the received signal, creates soft decision data, and the data and propagation path characteristic estimator / correction coefficient calculator 10-1 (AZ) The correlation ratio is obtained by the correlation ratio calculation unit 5-4 (A to Z) using the data obtained in the above. The same operation is performed in the systems B and C. These correlation ratios are compared by the correlation ratio comparison unit 6-1, and the selection system 6-2 selects the radio system having the largest correlation ratio.

  As described above, according to the radio communication system according to the present embodiment, parameters for selecting a plurality of different radio systems can be obtained relatively easily. Further, the reliability can be improved. In the above description, OFDM is targeted. However, if the modulation scheme is basically the same, it can be included in a plurality of wireless systems that also target FDM and TDM. In addition, this method is obtained by observing parameters in a lower layer, but a more desirable selection method can also be realized by using parameters in an upper layer together.

2-1 OFDM signal preamble section 2-2 OFDM signal frequency subchannel 2-3 OFDM signal time subchannel 3-1 M-sequence data (demodulated signal on receiving side)
3-2 M series data (known data on the receiving side)
3-3 Multiplier 3-4 Adder 3-5 Divider by L 5-1 OFDM Transmitter 5-2 Radio Propagation Channel 5-3 (AZ) (OFDM) Demodulator 5-4 (AZ) Correlation Ratio Calculation Unit 5-5 M Sequence Storage Unit 6-1 Correlation Ratio Comparison Unit 6-2 Selection Device 7-1 RF Unit 7-2 A / D Converter 7-3 FFT Unit 7-4 Equivalent Unit 7-5 Propagation Path Characteristic estimation unit (transfer function estimation)
10-1 (A to Z) Propagation path characteristic estimation unit / correction coefficient calculation unit

Claims (6)

A wireless communication system that performs wireless communication between a wireless transmission device and a wireless reception device by selecting one of a plurality of types of OFDM communication methods,
The wireless transmission device transmits an OFDM signal including a high autocorrelation function in a specific frequency subchannel to the wireless reception device,
The wireless reception device calculates a correlation value between a high autocorrelation function received from the wireless transmission device and a known high autocorrelation function for each OFDM communication method, and when there is a correlation value and a time difference when there is no time difference A wireless communication system, wherein an OFDM communication system having a largest correlation ratio indicating a ratio with a correlation value of the selected wireless communication system is selected.   The radio reception apparatus measures frequency characteristics in a propagation path of the entire system band, and determines a frequency characteristic in a propagation path of a specific frequency subchannel including the high autocorrelation function and a frequency characteristic in a propagation path of the entire system band. The wireless communication system according to claim 1, wherein a difference from the average value is corrected. A radio receiving apparatus applied to a radio communication system that performs radio communication by selecting one of a plurality of types of OFDM communication systems,
An OFDM demodulator that demodulates an OFDM signal including a high autocorrelation function in a specific frequency subchannel received from a wireless transmission device;
A storage unit for storing a known high autocorrelation function;
For each OFDM communication method, a correlation value between the received high autocorrelation function and the known high autocorrelation function is calculated, and a ratio between a correlation value when there is no time difference and a correlation value when there is a time difference is shown. A correlation ratio calculation unit for calculating a correlation ratio;
And a selection unit that selects the OFDM communication scheme having the largest correlation ratio. A propagation path characteristic estimation unit for measuring frequency characteristics in the propagation path of the entire system band;
The correlation ratio calculation unit corrects a difference between a frequency characteristic in a propagation path of a specific frequency subchannel including the high autocorrelation function and an average value of the frequency characteristics in a propagation path of the entire system band to obtain a correlation ratio. Calculate
The radio reception apparatus according to claim 3, wherein the selection unit selects an OFDM communication system having the largest corrected correlation ratio. A wireless communication method for performing wireless communication by selecting any of a plurality of types of OFDM communication methods between a wireless transmission device and a wireless reception device,
In the wireless transmission device, transmitting an OFDM signal including a high autocorrelation function in a specific frequency subchannel to the wireless reception device;
In the wireless receiver, for each OFDM communication system, a correlation value between a high autocorrelation function received from the wireless transmitter and a known high autocorrelation function is calculated, and there is a correlation value and a time difference when there is no time difference Calculating a correlation ratio indicating a ratio with a correlation value of
And selecting at least the OFDM communication method having the largest correlation ratio. In the wireless reception device, measuring the frequency characteristics in the propagation path of the entire system band,
The method further includes correcting a difference between a frequency characteristic in a propagation path of a specific frequency subchannel including the high autocorrelation function and an average value of the frequency characteristics in the propagation path of the entire system band. The wireless communication method according to claim 5.

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